The Experts below are selected from a list of 81 Experts worldwide ranked by ideXlab platform
Alan H Morris - One of the best experts on this subject based on the ideXlab platform.
-
randomized clinical trial of pressure controlled Inverse Ratio Ventilation and extracorporeal co2 removal for adult respiratory distress syndrome
American Journal of Respiratory and Critical Care Medicine, 1994Co-Authors: Alan H Morris, C J Wallace, Ronald L Menlove, Terry P Clemmer, James F Orme, L K Weaver, Nathan C Dean, Frank Thomas, Thomas D East, Nathan L PaceAbstract:The impact of a new therapy that includes pressure-controlled Inverse Ratio Ventilation followed by extracorporeal CO2 removal on the survival of patients with severe ARDS was evaluated in a randomized controlled clinical trial. Computerized protocols generated around-the-clock instructions for management of arterial oxygenation to assure equivalent intensity of care for patients randomized to the new therapy limb and those randomized to the control, mechanical Ventilation limb. We randomized 40 patients with severe ARDS who met the ECMO entry criteria. The main outcome measure was survival at 30 days after randomization. Survival was not significantly different in the 19 mechanical Ventilation (42%) and 21 new therapy (extracorporeal) (33%) patients (p = 0.8). All deaths occurred within 30 days of randomization. Overall patient survival was 38% (15 of 40) and was about four times that expected from historical data (p = 0.0002). Extracorporeal treatment group survival was not significantly different from ...
-
randomized clinical trial of pressure controlled Inverse Ratio Ventilation and extracorporeal co2 removal for adult respiratory distress syndrome
American Journal of Respiratory and Critical Care Medicine, 1994Co-Authors: Alan H Morris, C J Wallace, Ronald L Menlove, Terry P Clemmer, James F Orme, Nathan C Dean, Frank Thomas, T D East, Lindell K Weaver, Nathan L PaceAbstract:The impact of a new therapy that includes pressure-controlled Inverse Ratio Ventilation followed by extracorporeal CO2 removal on the survival of patients with severe ARDS was evaluated in a randomized controlled clinical trial. Computerized protocols generated around-the-clock instructions for management of arterial oxygenation to assure equivalent intensity of care for patients randomized to the new therapy limb and those randomized to the control, mechanical Ventilation limb. We randomized 40 patients with severe ARDS who met the ECMO entry criteria. The main outcome measure was survival at 30 days after randomization. Survival was not significantly different in the 19 mechanical Ventilation (42%) and 21 new therapy (extracorporeal) (33%) patients (p = 0.8). All deaths occurred within 30 days of randomization. Overall patient survival was 38% (15 of 40) and was about four times that expected from historical data (p = 0.0002). Extracorporeal treatment group survival was not significantly different from other published survival rates after extracorporeal CO2 removal. Mechanical Ventilation patient group survival was significantly higher than the 12% derived from published data (p = 0.0001). Protocols controlled care 86% of the time. Average PaO2 was 59 mm Hg in both treatment groups. Intensity of care required to maintain arterial oxygenation was similar in both groups (2.6 and 2.6 PEEP changes/day; 4.3 and 5.0 FIO2 changes/day). We conclude that there was no significant difference in survival between the mechanical Ventilation and the extracorporeal CO2 removal groups. We do not recommend extracorporeal support as a therapy for ARDS. Extracorporeal support for ARDS should be restricted to controlled clinical trials.
-
a successful computerized protocol for clinical management of pressure control Inverse Ratio Ventilation in ards patients
Chest, 1992Co-Authors: T D East, Terry P Clemmer, James F Orme, Stephan H Bohm, Jane C Wallace, Lindell K Weaver, Alan H MorrisAbstract:We have developed a computerized protocol that provides a systematic approach for management of pressure control-Inverse Ratio Ventilation (PCIRV). The protocols were used for 1,466 h in ten around-the-clock PCIRV evaluations on seven patients with severe adult respiratory distress syndrome (ARDS). Patient therapy was controlled by protocol 95 percent of the time (1,396 of 1,466 h) and 90 percent of the protocol instructions (1,937 of 2,158) were followed by the clinical staff. Of the 221 protocol instructions, 88 (39 percent) not followed were due to invalid PEEPi measurements. Compared with preceding values during CPPV, the expired minute Ventilation was reduced by 27 percent during PCIRV while maintaining a pH that was not clinically different (mean difference in pH = 0.02). There was no difference in the PaO 2 , PEEPi, or the FIO 2 between PCIRV and CPPV. The PEEP setting was reduced by 33 percent from 9 ±0.05 to 6 ±0.6 and the I:E Ratio increased from 0.64 ± 0.04 to 2.3 ± 0.10. Peak airway pressure was reduced by 24 percent (from 59 ± 1.5 to 45 ±0.6) and mean airway pressure increased by 27 percent (from 22 ±0.8 to 28 ±0.6) in PCIRV. Right atrial and pulmonary artery pressures were higher and cardiac output lower in PCIRV but blood pressure was unchanged. The success of this protocol has demonstrated the feasibility of using PEEPi as a primary control variable for oxygenation. This computerized PCIRV protocol should make the future use of PCIRV less mystifying, simpler, and more systematic .
Nathan L Pace - One of the best experts on this subject based on the ideXlab platform.
-
randomized clinical trial of pressure controlled Inverse Ratio Ventilation and extracorporeal co2 removal for adult respiratory distress syndrome
American Journal of Respiratory and Critical Care Medicine, 1994Co-Authors: Alan H Morris, C J Wallace, Ronald L Menlove, Terry P Clemmer, James F Orme, L K Weaver, Nathan C Dean, Frank Thomas, Thomas D East, Nathan L PaceAbstract:The impact of a new therapy that includes pressure-controlled Inverse Ratio Ventilation followed by extracorporeal CO2 removal on the survival of patients with severe ARDS was evaluated in a randomized controlled clinical trial. Computerized protocols generated around-the-clock instructions for management of arterial oxygenation to assure equivalent intensity of care for patients randomized to the new therapy limb and those randomized to the control, mechanical Ventilation limb. We randomized 40 patients with severe ARDS who met the ECMO entry criteria. The main outcome measure was survival at 30 days after randomization. Survival was not significantly different in the 19 mechanical Ventilation (42%) and 21 new therapy (extracorporeal) (33%) patients (p = 0.8). All deaths occurred within 30 days of randomization. Overall patient survival was 38% (15 of 40) and was about four times that expected from historical data (p = 0.0002). Extracorporeal treatment group survival was not significantly different from ...
-
randomized clinical trial of pressure controlled Inverse Ratio Ventilation and extracorporeal co2 removal for adult respiratory distress syndrome
American Journal of Respiratory and Critical Care Medicine, 1994Co-Authors: Alan H Morris, C J Wallace, Ronald L Menlove, Terry P Clemmer, James F Orme, Nathan C Dean, Frank Thomas, T D East, Lindell K Weaver, Nathan L PaceAbstract:The impact of a new therapy that includes pressure-controlled Inverse Ratio Ventilation followed by extracorporeal CO2 removal on the survival of patients with severe ARDS was evaluated in a randomized controlled clinical trial. Computerized protocols generated around-the-clock instructions for management of arterial oxygenation to assure equivalent intensity of care for patients randomized to the new therapy limb and those randomized to the control, mechanical Ventilation limb. We randomized 40 patients with severe ARDS who met the ECMO entry criteria. The main outcome measure was survival at 30 days after randomization. Survival was not significantly different in the 19 mechanical Ventilation (42%) and 21 new therapy (extracorporeal) (33%) patients (p = 0.8). All deaths occurred within 30 days of randomization. Overall patient survival was 38% (15 of 40) and was about four times that expected from historical data (p = 0.0002). Extracorporeal treatment group survival was not significantly different from other published survival rates after extracorporeal CO2 removal. Mechanical Ventilation patient group survival was significantly higher than the 12% derived from published data (p = 0.0001). Protocols controlled care 86% of the time. Average PaO2 was 59 mm Hg in both treatment groups. Intensity of care required to maintain arterial oxygenation was similar in both groups (2.6 and 2.6 PEEP changes/day; 4.3 and 5.0 FIO2 changes/day). We conclude that there was no significant difference in survival between the mechanical Ventilation and the extracorporeal CO2 removal groups. We do not recommend extracorporeal support as a therapy for ARDS. Extracorporeal support for ARDS should be restricted to controlled clinical trials.
L. Gattinoni - One of the best experts on this subject based on the ideXlab platform.
-
ECMO or Removing CO2
2014Co-Authors: L. GattinoniAbstract:The enthusiasm risen by first successful Extra Corporeal Membrane Oxygenation (ECMO) at the beginning of the seventies by Hill and al. led to the first large randomized trial launched in 1974 to compare veno-arterial (VA) ECMO versus conventional therapy in adult acute respiratory distress syndrome (ARDS) patients. This trial, in 1975, although not completed, already showed discouraging negative results. Dr. Kolobow, at National Institute of Health (NIH), was studying a new membrane lung with greater surface exchange and thinner membrane to optimize the CO2 removal, later called CDML . The underlying hope was that in COPD patients an intermittent CO2 dialysis could potentially improve the clinical scenario. As a new fellow of Dr. Kolobow at NIH, between 1975 and 1977, I was responsible of testing the performances of the CDML, in awake sheep, by measuring the CO2 input and output across the membrane lung, as well as the CO2 removed as gas from the expiRation port of the membrane lung. As I was curious to see the respiratory response of the awake spontaneously breathing sheep during CO2 removal, through a closed respiratory circuit I measured the minute oxygen consumption and the CO2 exhaled from the animal. It was immediately evident the strong relationship between the CO2 removed by the artificial lung and the CO2 exhaled by the sheep. Being its metabolic CO2 production near constant, it became immediately evident that the CO2 exhaled by the sheep was decreased proportionally to the CO2 removed by the membrane lung, up to the complete apnea, when CO2 metabolicaly produced was completely cleared by the artificial lung. The oxygenation was provided by diffusion through the natural lung. The first set of experiments was published on Anesthesiology and the title of the paper focused on the capability of the membrane lung to control the spontaneous breathing. The idea of CO2 dialysis in chronic lungers was abandoned and the extracorporeal CO2 removal approach was extensively studied in experimental animals with the aim of applying it in ARDS patients to provide complete or partial lung rest. Therefore, between 1976 and 1980 a series of physiological studies explored the potential of CO2 removal, its physiology and the relationship between artificial and natural lungs. The best set we identified was the one providing complete CO2 clearance associated to 2-3 breath/minute to maintain lung volumes, while oxygenation was primarily performed by 200-300 mL/min at 100% oxygen insufflated into the trachea. The technique was called low frequency positive pressure Ventilation with extra corporeal CO2 removal (LFPPV-ECCO2R). The first patients were treated in Milan, and the first successful extracorporeal CO2 removal, presented in a poster session during an Intensive Care meeting in Paris in 1980. Curiously, this first successful CO2 removal, presented as poster, had as a neighbor poster the first report of Lackman on inverted Ratio Ventilation (both posters were completely neglected). The first experiences with LFPPV-ECCO2-R on 3 patients were published on Lancet in 1980. and 6 years later we reported on JAMA the results obtained in a group of 43 patients. We found that more than 70% of the patients improved lung function and 21 patients eventually survived without major technical accidents in more than 8000 hours of perfusion. Therefore we concluded that this technique could be a reliable alternative to conventional treatments. These results led to the investigations into the technological development of extracorporeal support devices. In 1984 we reported a strict association between the need of LFPPV-ECCO2R and total static lung compliance in a group of 36 ARDS patients meeting mortality rate criteria (90%) as defined in the Zapol ECMO trial. Total static lung compliance (TSLC) was the only predictive value of success or failure of the management of severe ARDS patients unresponsive to conventional treatment. We found that patients with TSLC lower than 25 ml/cmH2O did not tolerate PC-IRV or CPAP, patients with TSLC higher than 30 cmH2O were successfully treated with CPAP while the other patients (TSLC comprised between 25 and 30 cmH2O) had to be treated with PC-IRV for more than 48 h, or were then placed on LFPPV-ECCO2R if PaCO2 rose prohibitively. The results of the study became clear after the quantitative CT scan analysis was introduced in the evaluation of respiratory failure. It was shown, in fact, that the TSLC is strictly related to the size of the ventilatable ARDS lung, which, at TSLC around 25 cmH2O has the size of the normal lung of 2-3-year child ("baby lung"). Therefore we found that the ARDS lung is not stiff but just small. In the nineties ECMO was mainly diffused as the treatment for neonates affected by respiratory failure unresponsive to conventional treatment as reported by the ELSO registry. The results of the second randomized clinical trial on extracorporeal support were published in 1994 by Morris et al. The authors compared the effects of pressure-controlled Inverse Ratio Ventilation followed by LFPPV-ECCO2R to positive pressure Ventilation in 40 ARDS patients (21 ECCO2R patients and 19 mechanically ventilated). The study was stopped for futility and survival rates were not significantly different in the 2 groups (33%vs 42% in the control group, p=0.8), despite mortality was impressively improved sing the seventies. The study rose a lot of criticism for little experience with the technique in humans, the high pressure (PEEP and Peak) Ventilation and the elevate number of blood loss complications. The research in the field stopped until the new century when another prospective randomized trial on the efficacy and economic assessment of ECMO versus conventional mechanical Ventilation was conducted in the United Kingdom between 2001 and 2007 (CESAR trial). The results were published in 2009 on Lancet. The treatment arm of the study was treated at Glenfeld Hospital, a single high volume center capable of treating patients with ECMO. The control group was treated at the hospital of admission or at the nearest one participating to the study. The primary endpoint of the study, the survival at 6 months free of disabilities, was 63% in the ECMO-referred patients (75% of them actually received ECMO) vs 47% in control group. The study was criticized for the randomization of the patients and for the lack of information on the Ventilation settings in the control group, however the most important result is that the treatment of patients affected by respiratory failure unresponsive to conventional treatment in an high volume center with ECMO capabilities can significantly improve survival. The H1N1 flu pandemics of 2009 caused an impressive increase of the number of patients characterized by acute pneumonia with severe hypoxemia that were considered not safely ventilatable even with safe mechanical Ventilation criteria. The experience of australian and New Zealand investigators led to renewed interest for extracorporeal support and hundreds of ARDS patients worldwide received ECMO. The authors reported that the proper rescue therapy for life-threatening hypoxemia was high flow VV bypass and the overall mortality rate was 21%. After this report, and also due to political support, several countries in Europe, United States, South America, Canada, and Asia faced the pandemic using ECMO as buy time maneuver waiting the resolution of the underlying pathology. Obviously the use of ECMO without a scientific background was criticized as the only evidence for ECMO application was the presence of sever life-threatening hypoxemia in patients untreatable with conventional mechanical Ventilation. In Italy the Italian Health Authorities set up a national referral network (ECMOnet) of 14 selected intensive care units able to provide ECMO to face the H1N1 flu pandemic. Two clinical experts coordinated the communication between the authorities and the net and organized the opeRations. A call center service was set up to grant the communication between hospitals and the referral centers and a series of training courses were performed. A list of recommended national clinical criteria for early patient centralization and for ECMO eligibility was written up. Between August 2009 and March 2010, 153 patients were admitted to the 14 centers with suspected H1N1. Sixty patients were treated with ECMO; among them 49 patients had ARDS caused by H1N1, while 11 patients had ARDS because of other causes. Overall survival at hospital discharge was 41/60 (68.3%), while survival for confirmed H1N1 was 35/49 (72%) versus 6/11 (54%) for non confirmed H1N1. One patient died of cerebral hemorrhage, 16 patients had hemorrhagic complications and 10 of them had major bleeding events but none of them stopped the treatment. For what the ventilatory treatment concerned the setting was left to the referral center. In several centers in Italy ventilatory support was characterized by very low tidal volume and respiratory rate limited to 7-8 bpm with high mean airway pressure due to high PEEP. In Milan patients are initially treated with high PEEP (above 15 cmH2O) and low frequency Ventilation. In 2011 a study published on JAMA by Noah et al. compared the hospital mortality of patients affected by H1N1-related ARDS treated with ECMO in 1 of the 4 adult ECMO centers in the United Kingdom during the pandemic with matched patients who were not referred for ECMO from the Swine Flu Triage study. The hospital mortality rate was significantly lower in ECMO-referred patients compared to non-ECMO-referred patients. This study further reinforced the result that new geneRation devices and the promotion of support from experienced centers seems relevant for a successful ECMO treatment and to reduce hospital mortality. At the time we are writing the "Extracorporeal Membrane Oxygenation for Severe Acute Respiratory Distress Syndrome (EOLIA)" (NCT01470703) is currently recruiting participants. The goal of the study is to evaluate the impact on morbidity and mortality of VV ECMO instituted early after the diagnosis of ARDS not evolving favorably after 3-6 hours of optimal treatment. In conclusion it appears that , as Dr. Bartlett wrote to me, "the pigs did for ECMO more than whatever randomized trial". However, as the people start to use this technique they realized how powerful it is, and this explains the reason why, despite a lack of conventional "evidence" so many centers do apply this technique. To story continues..
-
Extracorporeal circulation in acute respiratory failure (Circulación extracorpórea en la Insuficiencia Respiratoria Aguda (IRA))
2011Co-Authors: L. GattinoniAbstract:INTRODUCTION ECMO (Extra Corporeal Membrane Oxygenation) provides extracorporeal temporary respiratory and/or cardiac support by the use of an artificial lung and/or heart in case of cardiopulmonary failure refractory to conventional treatment. It is important to note that ECMO does not treat the underlying pathology but it provides a life support system during the evaluation, diagnosis and resolution of the disease. ECMO is indicated in case of high mortality risk and if the underlying pathology is potentially reversible. In case of cardiac failure the initial etiology to treat the patients with ECMO are quite general. The ELSO registry in 1995 categorized 7 etiologies in the adult: cardiac arrest, post-cardiotomy cardiac arrest, cardiogenic shock, post cardiotomy cardiogenic shock, hypothermia, pulmonary insufficiency, other causes [1]. Indications in case of respiratory failure are Adult Respiratory Distress syndrome (ARDS), pneumonia, trauma, bridge or following lung transplantation but it has also been used, in combination with tracheal intubation and mechanical Ventilation to resolve acute asthma attacks and dynamic hyperinflation. In this paper we will primarily discuss the use of ECMO in respiratory failure where the common approach is the veno-venous (VV) bypass in contrast with the veno-arterial (VA) bypass which is used in presence of heart failure. ECMO HISTORY AND TECHNICAL EVOLUTION The first experience of oxygenating blood by an extracorporeal device was performed in 1885 during the perfusion of isolated organs by von Frey and Gruber [2]. After 2 decades, in 1916, MacLean isolated heparin, the primary anticoagulant used in the ECMO circuit. The first laboratory investigation into Extracorporeal Life Support (ECLS) were made in 1930 by John Gibbons, who developed an heart-lung machine in 1937 [3] to allow open heart surgery. In this system the anticoagulated blood was directly exposed to oxygen (“bubble” or “film” oxygenators), unfortunately with severe limitations as hemolysis, thrombocytopaenia, hemorrhage and organ failure. In 1944 Kolff and Berk performed blood oxygenation in cellophane chambers of artificial kidney [4]. From the fifties the technologies evolved and new techniques were introduced, as hypothermia and cross-circulation. In 1950 there was the early development of cardio-pulmonary bypass (CPB) and Gibbon performed the first intervention using CPB in 1953. In 1956 the oxygenators evolved due to the introduction by Clowes of membranes separating the gaseous and the liquid phase, reducing the negative effects of bubble oxygenators [5]. The next year Kammermeyer introduced silicone-membrane lung [6]. Kolobow introduced in the seventies a spiral coil membrane lung [7], widely used for over 30 years. In 1983 Larm [8] introduced a technique that allowed heparinization of all surfaces that come in contact with blood. A recent innovation has been the non-porous hollow fiber devices, characterized by low resistance to blood flow and by polymethylpentene fibers that combined with non-thrombogenic coatings decrease the need of platelets infusion and of continuous heparin infusion. Even the access devices have evolved through the time and the wire-reinforced walls now allow very thin cannula walls, reducing resistances to blood flow. Double lumen catheters reduced the risks of re-circulation and of the placement [9]. TECHNIQUE, CRITERIA and COMPLICATIONS During ECMO venous blood is drained from the venous system through catheters percutaneously inserted either peripherally, via cannulation of a femoral vein, or centrally, via cannulation of the right atrium. The blood is pumped through an artificial lung to oxygenate it and to extract carbon dioxide. The circuit is warmed and heparinized. Blood is then returned back to the patient either in an arterial (aorta, VA) or venous access (right atrium, VV). The VA mode substitutes both heart and lung function, and can be achieved by either peripheral or central cannulation, the VV configuRation provides respiratory support only and it is preferred in case of respiratory failure as it leaves normal hemodynamics, it is achieved by peripheral cannulation, usually of both femoral veins. The pumps inserted in the circuit may be of centrifugal or roller type. The centrifugal pump is gravity independent and the inflow is generated by negative pressure at the pump head. Negative pressure should not exceed -20 mmHg to avoid excessive hemolysis, cannula displacement, thrombus at the inflow and inadequate inflow pressures in the patient. The roller pump is gravity dependent, so it must be positioned below the patient level. The inflow is regulated by a bladder regulated by a servomechanism while the forward flow is generated by the compression of the tubing by the heads of the pump and the back plate of the housing. The flow depends on the rotations per minute of the pump, on the occlusion degree and on the tube diameter. Problems may be due to rupture at the tube/heads interface and blow out in the arterial line. New geneRation circuits are characterized by all surfaces coated with covalently bound heparin and the catheters are wire-reinforced. The system is primed first with a balanced crystalloid and protein coating then the blood is inserted into the circuit using with packed red blood cells and fresh frozen plasma. The support starts quite slowly to allow an adequate mixing of the prime with patient’s blood, the gas flow into the oxygenator is set at an appropriate rate and pressure to avoid apparatus rupture and it is set to maintain adequate CO2 tension. Oxygenation is obtained by the combination of minimal mechanically ventilating the patient natural lung. Several ventilator approaches have been described in association with ECMO. We believe that the most convenient are the ones which try to minimize the potential harm of mechanical Ventilation. Therefore, whatever approach is used, attention should be paid to minimize FiO2, plateau pressure and frequency. In our experience, immediately after starting ECMO we keep FiO2 and mean airway pressure as before the bypass. As we decrease the Ventilation down to 4-5 bpm this implies an increase of PEEP in order to maintain mean airway pressure. During the bypass, as soon as the patient improves, we first decrease the FiO2 down to 0.4, afterward we decrease PEEP at a rate not greater than 1 cmH2O every 2 hours. When reasonable ventilator set is reached, as an example FiO2 equal to 0.4 and PEEP between 10-15 cmH2O the formal weaning begins by decreasing the gas flow throughout the membrane lung. We decannulate the patient when he is able to tolerate mechanical Ventilation without any extracorporeal support (gas flow in the membrane lung equal to 0). Several aspects must be considered evaluating the institution of ECMO. The first one, as previously told, is the likelihood of organ recovery with therapy and during ECMO. Accepted exclusion criteria include contraindication to anticoagulation, (despite the use of surface heparinized apparatus requires reconsideRation of this criterion), multiple organ failure, advanced age or poor final prognosis of the underlying pathology, left ventricular failure, immunosuppression, unwitnessed cardiac arrest or cardiac arrest of prolonged duRation, aortic dissection or aortic incompetence, sever damage of the central nervous system [10]. The inclusion criteria depend on the centers that performs ECMO [10]. Patients should have been mechanically ventilated for less than 14 day, although some centers exceeded this limit, maximal medical management must have been failed, the disease must be reversible and the mortality risk must be high, although its definition is not easy. Centers usually apply a set of criteria that are modification of the criteria reported by Zapol et al. [11]. They include oxygenation, shunt, compliance and sometimes Murray score. Complications are related to technical aspects and to patient complications [10]. Technical aspects include tubing rupture, pump/heater malfunction, oxygenator failure, cannula related problems. Patient related problems are bleeding, neurological complications, additional organ failure due to non-pulsatile perfusion at end-organs, barotrauma, infection and metabolic disorders. The major complication is bleeding which occurs in 10-30% [12] of the patients and that can be reduced reducing heparinization o f the circuit. It must be noted that whatever maneuver, which is usually without risk, as an example the insertion of naso-gastric tube, may be, in these patients, a source of bleeding. Great attention, therefore, should be paid to all the maneuvers which potentially may damage the tissue surface. It worth to underline, however, that the real nightmare of this treatment is the occurrence of intracranial bleeding. ARDS Acute Respiratory Distress Syndrome (ARDS) has been first described in 1967 in the cornerstone paper published by Ashbaugh on Lancet [13]. ARDS may be caused by a noxious stimulus of either pulmonary or extra-pulmonary and it is characterized by acute pulmonary inflammatory states and acute hypoxemic respiratory failure arising from widespread diffuse injury to the alveolar-capillary membrane. The definition of ARDS evolved through the years and, to date, the routinely used definition is the one introduced by the American European Consensus Conference in 1994 [14]. This definition includes: • the sudden onset of acute hypoxemic respiratory failure • presence of diffuse pulmonary infiltrates that are not caused by hydrostatic pulmonary edema • absence of left atrial hypertension. According to this definition a cut-off value of the PaO2/FiO2 Ratio equal to 300 has been defined to indicate Acute Lung Injury (ALI)/ARDS patients: patients with a value comprised between 200 and 300 are define as ALI, while a Ratio lower than 300 indicates ARDS. Despite the great advantage of this definition of being a standard way to select patients it is affected by a series limitations (variability of chest X-rays interpretation [15], exclusion of the cardiogenic origin of pulmonary edema [16] and the alteRation of the oxygenation staus by PEEP use [17]). Moreover, it has been showed that over half of patients initially classified as ARDS did not met the criteria after 30 min of Ventilation with a standardized PEEP [17]. Accordingly the ARDS definition should be updated even considering the results provided by CT scan quantitative analysis, as the amount of lung tissue involved in the pathology, as indicated by the amount of pulmonary edema, and the potential for lung recruitment, defined as the percentage of tissue regaining aeRation from 5 cmH2O PEEP to 45 cmH2O end inspiratory plateau pressure [18]. Even the response to PEEP or pronation should be evaluated. ARDS has always been considered a rare pathology, however data on incidence are characterized by a great variability due to the criteria used to identify the patients and to logistic. Studies published in the eighties and nineties reported values between 1.5 and 8.3 case/100000 population, while the most recent studies reported an incidence of 17.9 case/100000 population in Scandinavia [19], 34 in Australia [20] and 78.9 in the King County (United States) [21]. Patients with ARDS are treated with different advanced methods of intensive care developed during the years, including mechanical Ventilation, permissive hypercapnia, prone position, fluid resuscitation, vasodilators. The primary treatment of ARDS used since the first description in the sixties is mechanical Ventilation. It is used as a buying time maneuver waiting the resolution of the underlying pathology. Through the years modalities and techniques have been sensibly modified to provide ventilatory support improving oxygenation while avoiding augmentation of the existing lung damage. In the seventies ALI/ARDS patients were ventilated with high tidal volumes and low PEEP levels [22-24]. Lung damages due to mechanical Ventilation were not known at that time and the only concerns were high inspiratory oxygen concentRation and hemodynamics. Clinical and experimental studies led to the development of the concept of Ventilator Induced Lung Injury (VILI) and the goal of mechanical Ventilation progressively shifted to the improvement of gas exchange to avoiding lung damages [25]. At the moment, in clinical practice it is widely accepted to ventilate ARDS patients with low tidal volumes normalized on patient ideal body weight (VT/IBW) to avoid excessive strain of the lung parenchyma and to limit plateau airway pressure [26]. The optimum PEEP level has not yet been established as 3 randomized trials on unselected ALI/ARDS population did not find mortality differences testing high versus low PEEP levels [27-29]. It is conceivable that these results are due to the variability of patients severity, the positive effects of high PEEP level on the most severe patients may be cancelled by the nil or negative effects on the less severe ones [30]. This suggest that a correct patients characterization is needed before tailoring mechanical Ventilation. There is a residual number of patients, however, in which mechanical Ventilation, even at very low volumes is not applicable and the goal of maintaining an adequate oxygenation is not compatible with a “lung protective strategy”. In these patients the use of Extracorporeal Membrane Oxygenation (ECMO) may be an additional treatment during the acute phase. ECMO in ARDS PATIENTS The first successful application of ECMO in a patient with respiratory failure was reported by Hill in 1972 [31] and Bartlett published in 1976 the experience of a newborn treated with ECMO who survived [32]. The enthusiasm risen by ECMO application led to the first large randomized trial launched in 1974 to compare VA ECMO versus conventional therapy in adult ARDS patients [11]. After 90 patients the trial was stopped for futility. The study revealed a 90% mortality both in the ECMO and in the conventional treatment group. This result discouraged the use of ECMO and further research in the field for years. However the idea of supporting the impaired lung by extracorporeal gas exchange was followed by Gattinoni and the group of Kolobow. They proposed to prevent further damage to the natural lung and “resting” it reducing respiratory rate, tidal volume and peak pressure (Low Frequency Positive Pressure Ventilation, LFPPV). Moreover they popularized the idea that the main function of breathing is CO2 removal and that it can be dissociated from oxygenation. Oxygenation was granted by apneic oxygenation while carbon dioxide was removed by the artificial lung. (ECCO2-R). In 1977 [33] the group published their results obtained on experimental animals spontaneously breathing, in which various amounts of CO2 were removed through an extracorporeal membrane lung. Ventilation was reduced proportionally to the amount of CO2 removed and it almost ceased when the extracorporeal CO2 removal approximated the CO2 production (VCO2). The technique was then used even for clinical application in ARDS patients. In 1980 Gattinoni et al published on Lancet their result on 3 patients in which terminal respiratory failure was reversed resting the lungs with diffusion oxygenation (3 bpm), avoiding possible pulmonary and extrapulmonary complications of conventional mechanical Ventilation and removed CO2 through a membrane lung by low flow VV bypass [34]. In 1986 Gattinoni et al reported the results of a study designed to evaluate the effects of LFPPV-ECCO2-R in a group of 43 patients with severe acute respiratory failure. Lung function improved in 31 (72.8%), and 21 patients (48.8%) eventually survived [35]. They did not report major technical accidents in more than 800 hours of perfusion, suggesting that this technique may be a reliable alternative to conventional treatments. These results led to many investigations into the technological development of extracorporeal support. Among these works Zwischenberger et al. refined the LFPPV-ECCO2-R technique developing a simplified arterio-venous extracorporeal CO2 removal, called AVCO2-R, with a low-resistance membrane gas exchanger [36]. In 1984 Gattinoni et al found that in a group of 36 ARDS patients meeting mortality rate criteria (90%) for LFPPV-ECCO2R total static lung compliance (TSLC) was the best predictive factor in deciding the management of severe ARDS patients unresponsive to conventional treatment [37]. Patients were ventilated for 48 hours with PEEP and pressure controlled inverted Ratio Ventilation (PC-IRV) before the connection to bypass, and, if possible they were allowed to spontaneously breathing or to were switched to CPAP. After 48 hours 19 patients still required LFPPV-ECCO2R, 5 were still on PC-IRV and 12 were on CPAP. The authors found that patients with TSLC lower than 25 ml/cmH2O did not tolerate PC-IRV or CPAP, patients with TSLC higher than 30 cmH2O were successfully treated with CPAP while the other patients (TSLC comprised between 25 and 30 cmH2O) had to be treated with PC-IRV for more than 48 h, or were then placed on LFPPV-ECCO2R if PaCO2 rose prohibitively. At that time it was not clear the meaning of the TSLC, which became clear after the quantitative CT scan was introduced in the assessment of respiratory failure. This technique clearly showed that the intrinsic lung characteristics of the ventilatable lung (specific lung compliance) are normal, therefore TSLC just reflects the size of the “baby lung” [38]. This concept fully accounted for the association between the need of ECMO and the low TSLC. ECMO was in the nineties the standard treatment for neonatal respiratory failure refractory to conventional treatments and it was extended even to premature, low birth weight infants, children and adults. The Extracorporeal Life Support Organization (ELSO) registry (introduced in the eighties) reported in July 1994, 9258 neonates (overall survival rate 81%), 754 pediatric (49%), and 130 adult patients (38%) with respiratory failure treated with ECMO. In 1994 [39] Morris published the results of a second randomized clinical trial in which pressure-controlled Inverse Ratio Ventilation followed by LFPPV-ECCO2-R (21 patients) was compared to positive pressure Ventilation (19 patients) in ARDS patients. Again they found that the survival rate was not significantly different between the two groups (42% in the control group versus 33% in the ECMO group), however the survival rate was significantly improved compared to the 1979 report. The results of the trial, however, rose a lot of criticism, mainly regarding the inhomogeneous Ventilation used in the ECMO group, the high peak pressure used and the methodology used that did not reach the modern standards as indicated by the elevate number of blood loss complications. The results of the trial stopped the research of ECMO application in ARDS. A retrospective case review of the ELSO registry from 1986-2006 published by Brogan et al. [40] showed a mortality rate of ARDS patients treated with ECMO of 50%. Between 2001 and 2007 another prospective randomized trial was conducted in the United Kingdom [41]. The trail compared conventional ventilatory support performed in various centers versus extracorporeal membrane oxygenation for severe adult respiratory failure performed at Glenfeld Hospital. The study included 180 patients from 68 centers, 90 patients in the ECMO group (68 effectively treated with ECMO) and 90 in the conventional treatment group. In the control group the intensivists could use any type of management they felt appropriate but the NIH ARDS strategy was recommended. The authors found that the primary endpoint, the survival at 6 months free of disabilities, was 63% in the ECMO group vs 47% in control group. It is important to note that the intervention in CESAR was referral to an ECMO center not treatment with ECMO (only 75% of ECMO-referred patients actually received ECMO). However it was impressive how the treatment of patients affected by respiratory failure in a center with ECMO capabilities can significantly increase survival rate. The study shows that ECMO referral is beneficial, however, as the Glenfeld Hospital is an expert high case volume center it is not certain that the result would be similar in smaller or less experienced centers. Even the non standard treatment of conventional treatment group rose some criticism. The recent H1N1 flu epidemics led to an increase of respiratory failure with patients considered not safely ventilable with current clinical criteria (i.e. tidal volume 6-8 ml/Kg and plateau pressure below 30-35 cmH2O) leading to renewed interest for extracorporeal support and hundreds of ARDS patients worldwide received ECMO, according to the ELSO registry. Typing “H1N1 and ECMO” in PubMed the displayed results are 93 from 2009 to January 2011. The most relevant report was the one performed by australian and New Zealand investigators [42]. The authors reported that, between June and August 2009, 68 patients with severe H1N1 influenza-associated ARDS were treated with ECMO. Before ECMO these patients, characterized by a median age of 34.4 years, had severe respiratory failure despite advanced mechanical ventilatory support. The authors reported a mortality rate of 21%. Freed et al. reported a mortality rate of 33% of 6 patients only 6 patients were treated with ECMO for influenza H1N1 related ARDS in Canada [43]. A prospective observational study of patients treated in Marseille South Hospital from October 2009 to January 2010 reported the data about 22 patients requiring mechanical Ventilation [44]. Eighteen were admitted to ICU for ARDS and 10 patients met the criteria fo
-
Extracorporeal circulation in acute respiratory failure (Circulación extracorpórea en la Insuficiencia Respiratoria Aguda (IRA))
2011Co-Authors: L. GattinoniAbstract:INTRODUCTION ECMO (Extra Corporeal Membrane Oxygenation) provides extracorporeal temporary respiratory and/or cardiac support by the use of an artificial lung and/or heart in case of cardiopulmonary failure refractory to conventional treatment. It is important to note that ECMO does not treat the underlying pathology but it provides a life support system during the evaluation, diagnosis and resolution of the disease. ECMO is indicated in case of high mortality risk and if the underlying pathology is potentially reversible. In case of cardiac failure the initial etiology to treat the patients with ECMO are quite general. The ELSO registry in 1995 categorized 7 etiologies in the adult: cardiac arrest, post-cardiotomy cardiac arrest, cardiogenic shock, post cardiotomy cardiogenic shock, hypothermia, pulmonary insufficiency, other causes [1]. Indications in case of respiratory failure are Adult Respiratory Distress syndrome (ARDS), pneumonia, trauma, bridge or following lung transplantation but it has also been used, in combination with tracheal intubation and mechanical Ventilation to resolve acute asthma attacks and dynamic hyperinflation. In this paper we will primarily discuss the use of ECMO in respiratory failure where the common approach is the veno-venous (VV) bypass in contrast with the veno-arterial (VA) bypass which is used in presence of heart failure. ECMO HISTORY AND TECHNICAL EVOLUTION The first experience of oxygenating blood by an extracorporeal device was performed in 1885 during the perfusion of isolated organs by von Frey and Gruber [2]. After 2 decades, in 1916, MacLean isolated heparin, the primary anticoagulant used in the ECMO circuit. The first laboratory investigation into Extracorporeal Life Support (ECLS) were made in 1930 by John Gibbons, who developed an heart-lung machine in 1937 [3] to allow open heart surgery. In this system the anticoagulated blood was directly exposed to oxygen (\u201cbubble\u201d or \u201cfilm\u201d oxygenators), unfortunately with severe limitations as hemolysis, thrombocytopaenia, hemorrhage and organ failure. In 1944 Kolff and Berk performed blood oxygenation in cellophane chambers of artificial kidney [4]. From the fifties the technologies evolved and new techniques were introduced, as hypothermia and cross-circulation. In 1950 there was the early development of cardio-pulmonary bypass (CPB) and Gibbon performed the first intervention using CPB in 1953. In 1956 the oxygenators evolved due to the introduction by Clowes of membranes separating the gaseous and the liquid phase, reducing the negative effects of bubble oxygenators [5]. The next year Kammermeyer introduced silicone-membrane lung [6]. Kolobow introduced in the seventies a spiral coil membrane lung [7], widely used for over 30 years. In 1983 Larm [8] introduced a technique that allowed heparinization of all surfaces that come in contact with blood. A recent innovation has been the non-porous hollow fiber devices, characterized by low resistance to blood flow and by polymethylpentene fibers that combined with non-thrombogenic coatings decrease the need of platelets infusion and of continuous heparin infusion. Even the access devices have evolved through the time and the wire-reinforced walls now allow very thin cannula walls, reducing resistances to blood flow. Double lumen catheters reduced the risks of re-circulation and of the placement [9]. TECHNIQUE, CRITERIA and COMPLICATIONS During ECMO venous blood is drained from the venous system through catheters percutaneously inserted either peripherally, via cannulation of a femoral vein, or centrally, via cannulation of the right atrium. The blood is pumped through an artificial lung to oxygenate it and to extract carbon dioxide. The circuit is warmed and heparinized. Blood is then returned back to the patient either in an arterial (aorta, VA) or venous access (right atrium, VV). The VA mode substitutes both heart and lung function, and can be achieved by either peripheral or central cannulation, the VV configuRation provides respiratory support only and it is preferred in case of respiratory failure as it leaves normal hemodynamics, it is achieved by peripheral cannulation, usually of both femoral veins. The pumps inserted in the circuit may be of centrifugal or roller type. The centrifugal pump is gravity independent and the inflow is generated by negative pressure at the pump head. Negative pressure should not exceed -20 mmHg to avoid excessive hemolysis, cannula displacement, thrombus at the inflow and inadequate inflow pressures in the patient. The roller pump is gravity dependent, so it must be positioned below the patient level. The inflow is regulated by a bladder regulated by a servomechanism while the forward flow is generated by the compression of the tubing by the heads of the pump and the back plate of the housing. The flow depends on the rotations per minute of the pump, on the occlusion degree and on the tube diameter. Problems may be due to rupture at the tube/heads interface and blow out in the arterial line. New geneRation circuits are characterized by all surfaces coated with covalently bound heparin and the catheters are wire-reinforced. The system is primed first with a balanced crystalloid and protein coating then the blood is inserted into the circuit using with packed red blood cells and fresh frozen plasma. The support starts quite slowly to allow an adequate mixing of the prime with patient\u2019s blood, the gas flow into the oxygenator is set at an appropriate rate and pressure to avoid apparatus rupture and it is set to maintain adequate CO2 tension. Oxygenation is obtained by the combination of minimal mechanically ventilating the patient natural lung. Several ventilator approaches have been described in association with ECMO. We believe that the most convenient are the ones which try to minimize the potential harm of mechanical Ventilation. Therefore, whatever approach is used, attention should be paid to minimize FiO2, plateau pressure and frequency. In our experience, immediately after starting ECMO we keep FiO2 and mean airway pressure as before the bypass. As we decrease the Ventilation down to 4-5 bpm this implies an increase of PEEP in order to maintain mean airway pressure. During the bypass, as soon as the patient improves, we first decrease the FiO2 down to 0.4, afterward we decrease PEEP at a rate not greater than 1 cmH2O every 2 hours. When reasonable ventilator set is reached, as an example FiO2 equal to 0.4 and PEEP between 10-15 cmH2O the formal weaning begins by decreasing the gas flow throughout the membrane lung. We decannulate the patient when he is able to tolerate mechanical Ventilation without any extracorporeal support (gas flow in the membrane lung equal to 0). Several aspects must be considered evaluating the institution of ECMO. The first one, as previously told, is the likelihood of organ recovery with therapy and during ECMO. Accepted exclusion criteria include contraindication to anticoagulation, (despite the use of surface heparinized apparatus requires reconsideRation of this criterion), multiple organ failure, advanced age or poor final prognosis of the underlying pathology, left ventricular failure, immunosuppression, unwitnessed cardiac arrest or cardiac arrest of prolonged duRation, aortic dissection or aortic incompetence, sever damage of the central nervous system [10]. The inclusion criteria depend on the centers that performs ECMO [10]. Patients should have been mechanically ventilated for less than 14 day, although some centers exceeded this limit, maximal medical management must have been failed, the disease must be reversible and the mortality risk must be high, although its definition is not easy. Centers usually apply a set of criteria that are modification of the criteria reported by Zapol et al. [11]. They include oxygenation, shunt, compliance and sometimes Murray score. Complications are related to technical aspects and to patient complications [10]. Technical aspects include tubing rupture, pump/heater malfunction, oxygenator failure, cannula related problems. Patient related problems are bleeding, neurological complications, additional organ failure due to non-pulsatile perfusion at end-organs, barotrauma, infection and metabolic disorders. The major complication is bleeding which occurs in 10-30% [12] of the patients and that can be reduced reducing heparinization o f the circuit. It must be noted that whatever maneuver, which is usually without risk, as an example the insertion of naso-gastric tube, may be, in these patients, a source of bleeding. Great attention, therefore, should be paid to all the maneuvers which potentially may damage the tissue surface. It worth to underline, however, that the real nightmare of this treatment is the occurrence of intracranial bleeding. ARDS Acute Respiratory Distress Syndrome (ARDS) has been first described in 1967 in the cornerstone paper published by Ashbaugh on Lancet [13]. ARDS may be caused by a noxious stimulus of either pulmonary or extra-pulmonary and it is characterized by acute pulmonary inflammatory states and acute hypoxemic respiratory failure arising from widespread diffuse injury to the alveolar-capillary membrane. The definition of ARDS evolved through the years and, to date, the routinely used definition is the one introduced by the American European Consensus Conference in 1994 [14]. This definition includes: \u2022 the sudden onset of acute hypoxemic respiratory failure \u2022 presence of diffuse pulmonary infiltrates that are not caused by hydrostatic pulmonary edema \u2022 absence of left atrial hypertension. According to this definition a cut-off value of the PaO2/FiO2 Ratio equal to 300 has been defined to indicate Acute Lung Injury (ALI)/ARDS patients: patients with a value comprised between 200 and 300 are define as ALI, while a Ratio lower than 300 indicates ARDS. Despite the great advantage of this definition of being a standard way to select patients it is affected by a series limitations (variability of chest X-rays interpretation [15], exclusion of the cardiogenic origin of pulmonary edema [16] and the alteRation of the oxygenation staus by PEEP use [17]). Moreover, it has been showed that over half of patients initially classified as ARDS did not met the criteria after 30 min of Ventilation with a standardized PEEP [17]. Accordingly the ARDS definition should be updated even considering the results provided by CT scan quantitative analysis, as the amount of lung tissue involved in the pathology, as indicated by the amount of pulmonary edema, and the potential for lung recruitment, defined as the percentage of tissue regaining aeRation from 5 cmH2O PEEP to 45 cmH2O end inspiratory plateau pressure [18]. Even the response to PEEP or pronation should be evaluated. ARDS has always been considered a rare pathology, however data on incidence are characterized by a great variability due to the criteria used to identify the patients and to logistic. Studies published in the eighties and nineties reported values between 1.5 and 8.3 case/100000 population, while the most recent studies reported an incidence of 17.9 case/100000 population in Scandinavia [19], 34 in Australia [20] and 78.9 in the King County (United States) [21]. Patients with ARDS are treated with different advanced methods of intensive care developed during the years, including mechanical Ventilation, permissive hypercapnia, prone position, fluid resuscitation, vasodilators. The primary treatment of ARDS used since the first description in the sixties is mechanical Ventilation. It is used as a buying time maneuver waiting the resolution of the underlying pathology. Through the years modalities and techniques have been sensibly modified to provide ventilatory support improving oxygenation while avoiding augmentation of the existing lung damage. In the seventies ALI/ARDS patients were ventilated with high tidal volumes and low PEEP levels [22-24]. Lung damages due to mechanical Ventilation were not known at that time and the only concerns were high inspiratory oxygen concentRation and hemodynamics. Clinical and experimental studies led to the development of the concept of Ventilator Induced Lung Injury (VILI) and the goal of mechanical Ventilation progressively shifted to the improvement of gas exchange to avoiding lung damages [25]. At the moment, in clinical practice it is widely accepted to ventilate ARDS patients with low tidal volumes normalized on patient ideal body weight (VT/IBW) to avoid excessive strain of the lung parenchyma and to limit plateau airway pressure [26]. The optimum PEEP level has not yet been established as 3 randomized trials on unselected ALI/ARDS population did not find mortality differences testing high versus low PEEP levels [27-29]. It is conceivable that these results are due to the variability of patients severity, the positive effects of high PEEP level on the most severe patients may be cancelled by the nil or negative effects on the less severe ones [30]. This suggest that a correct patients characterization is needed before tailoring mechanical Ventilation. There is a residual number of patients, however, in which mechanical Ventilation, even at very low volumes is not applicable and the goal of maintaining an adequate oxygenation is not compatible with a \u201clung protective strategy\u201d. In these patients the use of Extracorporeal Membrane Oxygenation (ECMO) may be an additional treatment during the acute phase. ECMO in ARDS PATIENTS The first successful application of ECMO in a patient with respiratory failure was reported by Hill in 1972 [31] and Bartlett published in 1976 the experience of a newborn treated with ECMO who survived [32]. The enthusiasm risen by ECMO application led to the first large randomized trial launched in 1974 to compare VA ECMO versus conventional therapy in adult ARDS patients [11]. After 90 patients the trial was stopped for futility. The study revealed a 90% mortality both in the ECMO and in the conventional treatment group. This result discouraged the use of ECMO and further research in the field for years. However the idea of supporting the impaired lung by extracorporeal gas exchange was followed by Gattinoni and the group of Kolobow. They proposed to prevent further damage to the natural lung and \u201cresting\u201d it reducing respiratory rate, tidal volume and peak pressure (Low Frequency Positive Pressure Ventilation, LFPPV). Moreover they popularized the idea that the main function of breathing is CO2 removal and that it can be dissociated from oxygenation. Oxygenation was granted by apneic oxygenation while carbon dioxide was removed by the artificial lung. (ECCO2-R). In 1977 [33] the group published their results obtained on experimental animals spontaneously breathing, in which various amounts of CO2 were removed through an extracorporeal membrane lung. Ventilation was reduced proportionally to the amount of CO2 removed and it almost ceased when the extracorporeal CO2 removal approximated the CO2 production (VCO2). The technique was then used even for clinical application in ARDS patients. In 1980 Gattinoni et al published on Lancet their result on 3 patients in which terminal respiratory failure was reversed resting the lungs with diffusion oxygenation (3 bpm), avoiding possible pulmonary and extrapulmonary complications of conventional mechanical Ventilation and removed CO2 through a membrane lung by low flow VV bypass [34]. In 1986 Gattinoni et al reported the results of a study designed to evaluate the effects of LFPPV-ECCO2-R in a group of 43 patients with severe acute respiratory failure. Lung function improved in 31 (72.8%), and 21 patients (48.8%) eventually survived [35]. They did not report major technical accidents in more than 800 hours of perfusion, suggesting that this technique may be a reliable alternative to conventional treatments. These results led to many investigations into the technological development of extracorporeal support. Among these works Zwischenberger et al. refined the LFPPV-ECCO2-R technique developing a simplified arterio-venous extracorporeal CO2 removal, called AVCO2-R, with a low-resistance membrane gas exchanger [36]. In 1984 Gattinoni et al found that in a group of 36 ARDS patients meeting mortality rate criteria (90%) for LFPPV-ECCO2R total static lung compliance (TSLC) was the best predictive factor in deciding the management of severe ARDS patients unresponsive to conventional treatment [37]. Patients were ventilated for 48 hours with PEEP and pressure controlled inverted Ratio Ventilation (PC-IRV) before the connection to bypass, and, if possible they were allowed to spontaneously breathing or to were switched to CPAP. After 48 hours 19 patients still required LFPPV-ECCO2R, 5 were still on PC-IRV and 12 were on CPAP. The authors found that patients with TSLC lower than 25 ml/cmH2O did not tolerate PC-IRV or CPAP, patients with TSLC higher than 30 cmH2O were successfully treated with CPAP while the other patients (TSLC comprised between 25 and 30 cmH2O) had to be treated with PC-IRV for more than 48 h, or were then placed on LFPPV-ECCO2R if PaCO2 rose prohibitively. At that time it was not clear the meaning of the TSLC, which became clear after the quantitative CT scan was introduced in the assessment of respiratory failure. This technique clearly showed that the intrinsic lung characteristics of the ventilatable lung (specific lung compliance) are normal, therefore TSLC just reflects the size of the \u201cbaby lung\u201d [38]. This concept fully accounted for the association between the need of ECMO and the low TSLC. ECMO was in the nineties the standard treatment for neonatal respiratory failure refractory to conventional treatments and it was extended even to premature, low birth weight infants, children and adults. The Extracorporeal Life Support Organization (ELSO) registry (introduced in the eighties) reported in July 1994, 9258 neonates (overall survival rate 81%), 754 pediatric (49%), and 130 adult patients (38%) with respiratory failure treated with ECMO. In 1994 [39] Morris published the results of a second randomized clinical trial in which pressure-controlled Inverse Ratio Ventilation followed by LFPPV-ECCO2-R (21 patients) was compared to positive pressure Ventilation (19 patients) in ARDS patients. Again they found that the survival rate was not significantly different between the two groups (42% in the control group versus 33% in the ECMO group), however the survival rate was significantly improved compared to the 1979 report. The results of the trial, however, rose a lot of criticism, mainly regarding the inhomogeneous Ventilation used in the ECMO group, the high peak pressure used and the methodology used that did not reach the modern standards as indicated by the elevate number of blood loss complications. The results of the trial stopped the research of ECMO application in ARDS. A retrospective case review of the ELSO registry from 1986-2006 published by Brogan et al. [40] showed a mortality rate of ARDS patients treated with ECMO of 50%. Between 2001 and 2007 another prospective randomized trial was conducted in the United Kingdom [41]. The trail compared conventional ventilatory support performed in various centers versus extracorporeal membrane oxygenation for severe adult respiratory failure performed at Glenfeld Hospital. The study included 180 patients from 68 centers, 90 patients in the ECMO group (68 effectively treated with ECMO) and 90 in the conventional treatment group. In the control group the intensivists could use any type of management they felt appropriate but the NIH ARDS strategy was recommended. The authors found that the primary endpoint, the survival at 6 months free of disabilities, was 63% in the ECMO group vs 47% in control group. It is important to note that the intervention in CESAR was referral to an ECMO center not treatment with ECMO (only 75% of ECMO-referred patients actually received ECMO). However it was impressive how the treatment of patients affected by respiratory failure in a center with ECMO capabilities can significantly increase survival rate. The study shows that ECMO referral is beneficial, however, as the Glenfeld Hospital is an expert high case volume center it is not certain that the result would be similar in smaller or less experienced centers. Even the non standard treatment of conventional treatment group rose some criticism. The recent H1N1 flu epidemics led to an increase of respiratory failure with patients considered not safely ventilable with current clinical criteria (i.e. tidal volume 6-8 ml/Kg and plateau pressure below 30-35 cmH2O) leading to renewed interest for extracorporeal support and hundreds of ARDS patients worldwide received ECMO, according to the ELSO registry. Typing \u201cH1N1 and ECMO\u201d in PubMed the displayed results are 93 from 2009 to January 2011. The most relevant report was the one performed by australian and New Zealand investigators [42]. The authors reported that, between June and August 2009, 68 patients with severe H1N1 influenza-associated ARDS were treated with ECMO. Before ECMO these patients, characterized by a median age of 34.4 years, had severe respiratory failure despite advanced mechanical ventilatory support. The authors reported a mortality rate of 21%. Freed et al. reported a mortality rate of 33% of 6 patients only 6 patients were treated with ECMO for influenza H1N1 related ARDS in Canada [43]. A prospective observational study of patients treated in Marseille South Hospital from October 2009 to January 2010 reported the data about 22 patients requiring mechanical Ventilation [44]. Eighteen were admitte
Thomas Changyao Tsao - One of the best experts on this subject based on the ideXlab platform.
-
effects of Inverse Ratio Ventilation versus positive end expiratory pressure on gas exchange and gastric intramucosal pco2 and ph under constant mean airway pressure in acute respiratory distress syndrome
Anesthesiology, 2001Co-Authors: Chungchi Huang, Meiju Shih, Yuchen Chang, Yinghuang Tsai, Thomas Changyao TsaoAbstract:Background: In patients with acute respiratory distress syndrome, whether Inverse Ratio Ventilation differs from high positive end-expiratory pressure (PEEP) for gas exchange under a similar mean airway pressure has not been adequately examined. The authors used arterial oxygenation, gastric intramucosal partial pressure of carbon dioxide (PiCO 2 ), and pH (pHi) to assess whether pressure-controlled Inverse Ratio Ventilation (PC-IRV) offers more benefits than pressure-controlled Ventilation (PCV) with PEEP. Methods: Seventeen acute respiratory distress syndrome patients were enrolled and underwent mechanical Ventilation with a PCV inspiratory-to-expiratory Ratio of 1:2, followed by PC-IRV 1:1 initially. Then, they were randomly assigned to receive PC-IRV 2:1, then 4:1 or 4:1, and then 2:1, alternately. The baseline setting of PCV 1:2 was repeated between the settings of PC-IRV 2:1 and 4:1. Mean airway pressure and tidal volume were kept constant by adjusting the levels of peak inspiratory pressure and applied PEEP. In each ventilatory mode, hemodynamics, pulmonary mechanics, arterial and mixed venous blood gas analysis, PiCO 2 , and pHi were measured after a 1-h period of stabilization. Results: With a constant mean airway pressure, PC-IRV 2:1 and 4:1 decreased arterial and mixed venous oxygenation as compared with baseline PCV 1:2. Neither the global oxygenation indices with oxygen delivery and uptake nor PiCO 2 and pHi were improved by PC-IRV. During PC-IRV, applied PEEP was lower, and auto-PEEP was higher. Conclusion: When substituting Inverse Ratio Ventilation for applied PEEP to keep mean airway pressure constant, PC-IRV does not contribute more to better gas exchange and gastric intramucosal PiCO 2 and pHi than does PCV 1:2 for acute respiratory distress syndrome patients, regardless of the inspiratory-to-expiratory Ratios.
James F Orme - One of the best experts on this subject based on the ideXlab platform.
-
randomized clinical trial of pressure controlled Inverse Ratio Ventilation and extracorporeal co2 removal for adult respiratory distress syndrome
American Journal of Respiratory and Critical Care Medicine, 1994Co-Authors: Alan H Morris, C J Wallace, Ronald L Menlove, Terry P Clemmer, James F Orme, L K Weaver, Nathan C Dean, Frank Thomas, Thomas D East, Nathan L PaceAbstract:The impact of a new therapy that includes pressure-controlled Inverse Ratio Ventilation followed by extracorporeal CO2 removal on the survival of patients with severe ARDS was evaluated in a randomized controlled clinical trial. Computerized protocols generated around-the-clock instructions for management of arterial oxygenation to assure equivalent intensity of care for patients randomized to the new therapy limb and those randomized to the control, mechanical Ventilation limb. We randomized 40 patients with severe ARDS who met the ECMO entry criteria. The main outcome measure was survival at 30 days after randomization. Survival was not significantly different in the 19 mechanical Ventilation (42%) and 21 new therapy (extracorporeal) (33%) patients (p = 0.8). All deaths occurred within 30 days of randomization. Overall patient survival was 38% (15 of 40) and was about four times that expected from historical data (p = 0.0002). Extracorporeal treatment group survival was not significantly different from ...
-
randomized clinical trial of pressure controlled Inverse Ratio Ventilation and extracorporeal co2 removal for adult respiratory distress syndrome
American Journal of Respiratory and Critical Care Medicine, 1994Co-Authors: Alan H Morris, C J Wallace, Ronald L Menlove, Terry P Clemmer, James F Orme, Nathan C Dean, Frank Thomas, T D East, Lindell K Weaver, Nathan L PaceAbstract:The impact of a new therapy that includes pressure-controlled Inverse Ratio Ventilation followed by extracorporeal CO2 removal on the survival of patients with severe ARDS was evaluated in a randomized controlled clinical trial. Computerized protocols generated around-the-clock instructions for management of arterial oxygenation to assure equivalent intensity of care for patients randomized to the new therapy limb and those randomized to the control, mechanical Ventilation limb. We randomized 40 patients with severe ARDS who met the ECMO entry criteria. The main outcome measure was survival at 30 days after randomization. Survival was not significantly different in the 19 mechanical Ventilation (42%) and 21 new therapy (extracorporeal) (33%) patients (p = 0.8). All deaths occurred within 30 days of randomization. Overall patient survival was 38% (15 of 40) and was about four times that expected from historical data (p = 0.0002). Extracorporeal treatment group survival was not significantly different from other published survival rates after extracorporeal CO2 removal. Mechanical Ventilation patient group survival was significantly higher than the 12% derived from published data (p = 0.0001). Protocols controlled care 86% of the time. Average PaO2 was 59 mm Hg in both treatment groups. Intensity of care required to maintain arterial oxygenation was similar in both groups (2.6 and 2.6 PEEP changes/day; 4.3 and 5.0 FIO2 changes/day). We conclude that there was no significant difference in survival between the mechanical Ventilation and the extracorporeal CO2 removal groups. We do not recommend extracorporeal support as a therapy for ARDS. Extracorporeal support for ARDS should be restricted to controlled clinical trials.
-
a successful computerized protocol for clinical management of pressure control Inverse Ratio Ventilation in ards patients
Chest, 1992Co-Authors: T D East, Terry P Clemmer, James F Orme, Stephan H Bohm, Jane C Wallace, Lindell K Weaver, Alan H MorrisAbstract:We have developed a computerized protocol that provides a systematic approach for management of pressure control-Inverse Ratio Ventilation (PCIRV). The protocols were used for 1,466 h in ten around-the-clock PCIRV evaluations on seven patients with severe adult respiratory distress syndrome (ARDS). Patient therapy was controlled by protocol 95 percent of the time (1,396 of 1,466 h) and 90 percent of the protocol instructions (1,937 of 2,158) were followed by the clinical staff. Of the 221 protocol instructions, 88 (39 percent) not followed were due to invalid PEEPi measurements. Compared with preceding values during CPPV, the expired minute Ventilation was reduced by 27 percent during PCIRV while maintaining a pH that was not clinically different (mean difference in pH = 0.02). There was no difference in the PaO 2 , PEEPi, or the FIO 2 between PCIRV and CPPV. The PEEP setting was reduced by 33 percent from 9 ±0.05 to 6 ±0.6 and the I:E Ratio increased from 0.64 ± 0.04 to 2.3 ± 0.10. Peak airway pressure was reduced by 24 percent (from 59 ± 1.5 to 45 ±0.6) and mean airway pressure increased by 27 percent (from 22 ±0.8 to 28 ±0.6) in PCIRV. Right atrial and pulmonary artery pressures were higher and cardiac output lower in PCIRV but blood pressure was unchanged. The success of this protocol has demonstrated the feasibility of using PEEPi as a primary control variable for oxygenation. This computerized PCIRV protocol should make the future use of PCIRV less mystifying, simpler, and more systematic .
