REVIEW URRENT C OPINION
Extracorporeal life support for severe acute respiratory distress syndrome Aleksandra Leligdowicz a,b and Eddy Fan a,b
Purpose of review To provide a summary of the recent literature on extracorporeal membrane oxygenation (ECMO) in adults with severe acute respiratory distress syndrome (ARDS), focusing on advances in equipment, current conventional and unconventional indications, complications, and future applications. Recent findings ECMO use has increased during the past 5 years. Advances in cannulation, circuit design, and patient selection have made it a safer therapeutic option in severe ARDS, and its use has become more widespread for nonconventional indications. Summary High-quality evidence for the routine use of ECMO for management of adult patients with severe ARDS is still lacking. An ongoing randomized controlled trial (ECMO to rescue lung injury in severe ARDS) will contribute valuable data to guide clinical decisions to opt for this supportive therapy. Keywords acute respiratory distress syndrome, critical care, extracorporeal life support, ICU, mechanical ventilation
INTRODUCTION Severe acute respiratory distress syndrome (ARDS) continues to be associated with a greater than 40% mortality [1,2], despite significant advances in its management since its first description [3]. In patients who have severe ARDS, extracorporeal life support (ECLS) can support heart and lung function, allowing for lung recovery and resolution of underlying disease [4]. Extracorporeal membrane oxygenation (ECMO), a form of ECLS, enables oxygenation and carbon dioxide elimination in one of two main configurations: venoarterial or venovenous. Venoarterial ECMO provides cardiopulmonary support by draining blood from major venous structures and returning oxygenated blood to the arterial system. Venovenous ECMO provides gas exchange to venous blood and subsequently returns that blood to the right atrium before entry to pulmonary circulation, without providing direct cardiac support [5]. Venovenous ECMO predominates in adult patients, representing 78% of ECLS usage in this population [5]. The use of venovenous ECMO for acute respiratory failure in adults was first described over 40 years ago [6,7]. Since its introduction (Fig. 1 [1,3,5–17, 18 ,19,20]), ECMO has been widely accepted as supportive therapy in neonatal and pediatric ICUs [13,21]. However, early trials in adults who had severe &
acute respiratory failure and were treated with ECMO did not show improved hospital or long-term survival [10]. In 1989, to promote research, develop guidelines, and most importantly to maintain a registry of ECLS cases used for analysis of risk factors, outcomes, and epidemiologic trends, the extracorporeal life support organization (ELSO, www.elsonet.org) [5] was formed. A resurgence in global enthusiasm for the use of this potentially life-saving therapy occurred following the encouraging results from the conventional ventilatory support versus extracorporeal membrane oxygenation for severe adult respiratory failure multicenter randomized controlled trial [5,19]. The 2009 H1N1 epidemic further provided evidence for its potential use; however, the benefit of ECMO is not clearly established because of the heterogeneous results in different centers [15–17,18 ,22,23 ]. Improvement in outcomes may merely be due to &
&&
a
Interdepartmental Division of Critical Care Medicine, University of Toronto and bThe University Health Network, Toronto, Ontario, Canada Correspondence to Eddy Fan, MD, PhD, Toronto General Hospital, 585 University Avenue, PMB 11-123, Toronto, ON M5G 2N2, Canada. Tel: +1 416 340 4800x5061; fax: +1 647 776 3148; e-mail: [email protected] Curr Opin Crit Care 2015, 21:13–19 DOI:10.1097/MCC.0000000000000170
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www.co-criticalcare.com
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
Respiratory system
KEY POINTS There is a lack of definitive evidence for the benefit of venovenous ECMO in adult patients with ARDS. In the past 5 years, application of ECMO has rapidly increased and the patient population considered for this supportive therapy has broadened. Continued evolution in ECMO technology, smaller systems, introduction of telemedicine, and cannulation in peripheral hospital sites by mobile ECMO teams for transfer to experienced centers offer a promise for improved outcomes in appropriately selected adult patients with severe ARDS. Adverse events on venovenous ECMO should be analyzed over time to understand how novel advances contribute to changes in complication and mortality rates. Future studies into optimal timing of initiation of venovenous ECMO, selection of patients who will benefit most, and ideal mechanical ventilation strategies during ECMO will help determine whether its use can improve survival and long-term outcomes in patients with severe ARDS.
early referrals of patients with severe ARDS to an ECMO specialist center [24 ,25], where these complex patients may benefit from more homogeneous care by experienced physician and nursing management [26 ,27], along with greater use of evidencebased therapies (i.e., low tidal volume ventilation) [28]. &
&&
1970
1960s: Development advances in artificial heart and lung extracorporeal blood circuit8 1967: First description of adult acute 3 respiratory distress syndrome 1965-9: First reports of early experience with the Bramson 6,9 Membrane Lung
ADVANCES IN CANNULATION TECHNIQUES AND EQUIPMENT For the past three decades, increased simplicity and decreased size of ECMO circuits and ongoing optimization of cannula, oxygenator, and pump technology are contributing to improved outcomes in
2011: Start of EOLIA RCT (ClinicalTrials.gov Identifier NCT01470703) 2012: Berlin definition of ARDS1 2012: Introduction of portable ECMO system20 2010s: Five-fold increase in annual 5 ECMO use for severe ARDS
1994: First randomized clinical trial in use of ECCO2R in ARDS12 1990s: Increased use of ECMO in neonatal population13
1972: Hill et al., describe first use of 7 ECMO 1979: Zapol et al., present first RCT of ECMO use in ARDS10, a negative study
1960
Overall, the survival of patients treated with ECLS for adult respiratory failure depends on its cause and in most recent large studies ranges between 51 and 79% [5,15]. However, as this therapy is currently often used as a last resort in severe ARDS when standard therapies fail, presumably the fatality rate would likely be higher without ECMO (i.e., clinicians believe that death would be near certain without ECMO). Nevertheless, ECMO use as a bridge to recovery has increased during the past 5 years [29], managing sicker patients at higher costs [30]. Since 2009, the annual number of adult respiratory ECLS cases around the world has drastically increased from 100 to more than 500 cases per year [5]. A similar trend is present in the pediatric population, in which despite ECMO application for increasingly complex patients, consistent survival benefit is noted [5,13]. In this review, we focus on the literature published during the last 2 years to provide an overview of recent advances in equipment, current conventional and unconventional indications, complications, and to consider future applications of venovenous ECMO in severe ARDS.
1980
1986: Observational data on successful extracorporeal CO2 removal (ECOO2R) in severe 11 ARDS 1989: ELSO society formed (www.elsonet.org5)
1990
2000
2010
2008: Introduction of Avalon dual lumen catheter14 15-18 2009: H1N1 pandemic 2009: Peek et al. present CESAR19, transfer to ECMO referral center confers survival benefit in ARDS
FIGURE 1. Timeline of extracorporeal membrane oxygenation application in management of severe acute respiratory distress syndrome. 14
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Volume 21 Number 1 February 2015
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
Extracorporeal life support for severe ARDS Leligdowicz and Fan
patients treated with ECMO [31]. The introduction of percutaneous single-site cannulation with the Avalon elite bicaval dual lumen catheter (Maquet Cardiovascular AG, Rastatt, Germany) [14] has allowed patient mobilization by avoiding femoral cannulation [32] and decreased the rate of complications [33]. An increase in the use of centrifugal pumps over a roller-head pump has allowed for faster pump assembly and cannulation time as well as a lower priming volume [29]. Novel rotational pumps with diagonally streamed impellers (Deltastream DP3; Medos Medizintechnik AG, Stolberg, Germany) can increase the pump speed, further minimize the pump size and priming volume as well as reduce blood contact with foreign surfaces, thereby resulting in less hemolysis and a lower inflammatory response [34]. Modern polymethylpentene hollow fiber oxygenators can also decrease inflammation, result in superior gas exchange, lower resistance to flow, and less shear of red blood cells as well as have a longer lifespan requiring less frequent changes, thereby lowering the potential for complications [31]. Finally, the introduction of miniaturized, portable ECMO available as a self-contained system with an oxygenator, a pump, and all components to provide ECMO support (CardioHelp; Maquet Cardiovascular AG, Rastatt, Germany) facilitates location-independent stabilization and interhospital transfer, making initiation of ECMO possible even in hospitals without critical care resources [20,35 ]. &
CONVENTIONAL INDICATIONS FOR VENOVENOUS EXTRACORPOREAL MEMBRANE OXYGENATION IN ACUTE RESPIRATORY FAILURE Although severe ARDS is the most common reason for initiating ECMO, there are no absolute criteria for appropriate patient selection. Suggested indications include severe hypoxemia (PaO2/FiO2 < 80), uncompensated hypercapnia with concomitant acidemia (pH < 7.15), or significantly elevated end-inspiratory plateau pressures (>35–45 cm of H2O) in patients with ARDS from a potentially reversible condition (i.e., pneumonia) [36]. In addition, given the lack of definitive evidence for ECMO and promising favorable trials of prone ventilation [37], an additional criterion of failed prone ventilation (or presence of a contraindication to prone ventilation) should be considered [38]. PreECMO simplified acute physiology score II and sequential organ failure assessment scores may predict ICU discharge [22,39], and possibly influence the decision to initiate ECMO. Similarly, there are no absolute contraindications to initiating ECMO. Most contraindications
are relative and include first, conditions incompatible with normal life if the patient recovers; second, preexisting conditions that affect the quality of life (CNS status, end-stage malignancy, risk of lifethreatening bleeding with limited anticoagulation); third, age and size of patient; and fourth, futility: patients who are too sick, have been on conventional therapy too long (e.g., mechanical ventilation for >7 days), or have a fatal diagnosis [40]. Overall, success of ECMO continues to depend on individualized patient selection and reversibility of the underlying disease process [29]. Young patients with severe ARDS who fail lung-protective ventilation and who have single organ failure and no comorbid conditions may be the most likely candidates to benefit [18 ,38]. Interestingly, during the H1N1 pandemic in New Zealand, morbidly obese patients (BMI 30 kg/m2) were more likely to develop viral pneumonia requiring ECMO support; however, their mortality was the same as that in nonobese patients requiring ECMO support [41], suggesting morbid obesity is not a contraindication. &
UNCONVENTIONAL AND FUTURE USES OF EXTRACORPOREAL MEMBRANE OXYGENATION IN ACUTE RESPIRATORY FAILURE The recent increase in the use of ECMO resulted in application of this technology in patients with less severe forms of ARDS [32,42]. The benefit from early ECMO in milder forms of hypoxemic respiratory failure may be due to lung-protective ventilation with exceedingly low tidal volumes (approximately 3 ml/kg) [43,44], which may further reduce ventilator-induced lung injury (VILI) [45] and mortality [46] in patients mechanically ventilated for ARDS. Additionally, by reducing hypoxic pulmonary vasoconstriction and unloading the right ventricle, venovenous ECMO may reduce the effect that acute lung injury has on right ventricular dysfunction [47]. The use of ECMO as bridge to lung transplantation is a growing indication in many centers [48]. For instance, patients with idiopathic pulmonary fibrosis are well known to have a high mortality, but recent advances in mechanical ventilation settings and the possibility of lung transplant eligibility during admission may allow a subset of these patients to benefit from ECMO as a new strategy to bridge critical candidates to definitive therapy [49]. Additionally, patients bridged to lung transplantation with ECMO can be awake, facilitating rehabilitation pretransplant, decreasing weakness and deconditioning [29,49], especially as active participation in physical therapy, including
1070-5295 Copyright ß 2015 Wolters Kluwer Health, Inc. All rights reserved.
www.co-criticalcare.com
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
15
Respiratory system
ambulation, may hasten posttransplantation recovery in these patients [50]. Patients with ARDS or refractory shock caused by an intoxication may also benefit from ECMO [51]. Data to support this originate from case reports and retrospective observational cohort studies [52], with no randomized control trials to support its benefit. In instances of hemodynamic instability due to calcium channel antagonist, beta blocker, antiarrhythmic, tricyclic antidepressant, or chloroquine intoxication that is refractory to vasopressor and inotropic support, venovenous ECMO can be considered as a salvage therapy and a bridge to recovery. The use of venovenous ECMO may also be advantageous in patients with inhalational injuries, such as aspiration of organic hydrocarbons found in paint removers and paint thinners or smoke inhalation. ARDS after cardiac surgery is diagnosed in 20% of patients, with a mortality rate approaching 80% [53]. In postoperative hemodynamically stable patients with refractory hypoxemia, venovenous ECMO can be lifesaving and may prevent left ventricular distension, persistent left atrial hypertension, and pulmonary edema associated with the use of venoarterial ECMO. The use of venovenous ECMO in patients at a very high risk of bleeding has been described in the context of respiratory failure after massive atonic uterine bleeding [54] and ARDS due to pulmonary contusions after polytrauma [55,56]. Although these patients are at a high risk of hemorrhage due to coagulopathies and preexisting bleeding, delaying anticoagulation for 48–72 h can avert bleeding and the use of centrifugal pumps and oxygenators can decrease platelet consumption and reduce hemolysis. Furthermore, percutaneous insertion of a double-lumen cannula allows for a singlepuncture site in emergency settings. Particularly in polytrauma patients who have a blood lactate less than 14.4 mmol/l, pH more than 7.01, and an injury severity score less than 63, the use of ECMO can facilitate survival and the possibility of organ recovery for donation [56].
COMPLICATIONS The ELSO registry collects data on 46 different complications in patients treated with ECMO for respiratory failure. These can be classified into those directly related to the ECMO circuit and those due to patient-related factors [5,36]. Most frequently encountered mechanical problems include oxygenator failure, cannula problems, pump malfunction (16, 8, and 2%, respectively) [5]. Tubing or circuit rupture is rare (
Extracorporeal life support for severe acute respiratory distress syndrome Aleksandra Leligdowicz a,b and Eddy Fan a,b
Purpose of review To provide a summary of the recent literature on extracorporeal membrane oxygenation (ECMO) in adults with severe acute respiratory distress syndrome (ARDS), focusing on advances in equipment, current conventional and unconventional indications, complications, and future applications. Recent findings ECMO use has increased during the past 5 years. Advances in cannulation, circuit design, and patient selection have made it a safer therapeutic option in severe ARDS, and its use has become more widespread for nonconventional indications. Summary High-quality evidence for the routine use of ECMO for management of adult patients with severe ARDS is still lacking. An ongoing randomized controlled trial (ECMO to rescue lung injury in severe ARDS) will contribute valuable data to guide clinical decisions to opt for this supportive therapy. Keywords acute respiratory distress syndrome, critical care, extracorporeal life support, ICU, mechanical ventilation
INTRODUCTION Severe acute respiratory distress syndrome (ARDS) continues to be associated with a greater than 40% mortality [1,2], despite significant advances in its management since its first description [3]. In patients who have severe ARDS, extracorporeal life support (ECLS) can support heart and lung function, allowing for lung recovery and resolution of underlying disease [4]. Extracorporeal membrane oxygenation (ECMO), a form of ECLS, enables oxygenation and carbon dioxide elimination in one of two main configurations: venoarterial or venovenous. Venoarterial ECMO provides cardiopulmonary support by draining blood from major venous structures and returning oxygenated blood to the arterial system. Venovenous ECMO provides gas exchange to venous blood and subsequently returns that blood to the right atrium before entry to pulmonary circulation, without providing direct cardiac support [5]. Venovenous ECMO predominates in adult patients, representing 78% of ECLS usage in this population [5]. The use of venovenous ECMO for acute respiratory failure in adults was first described over 40 years ago [6,7]. Since its introduction (Fig. 1 [1,3,5–17, 18 ,19,20]), ECMO has been widely accepted as supportive therapy in neonatal and pediatric ICUs [13,21]. However, early trials in adults who had severe &
acute respiratory failure and were treated with ECMO did not show improved hospital or long-term survival [10]. In 1989, to promote research, develop guidelines, and most importantly to maintain a registry of ECLS cases used for analysis of risk factors, outcomes, and epidemiologic trends, the extracorporeal life support organization (ELSO, www.elsonet.org) [5] was formed. A resurgence in global enthusiasm for the use of this potentially life-saving therapy occurred following the encouraging results from the conventional ventilatory support versus extracorporeal membrane oxygenation for severe adult respiratory failure multicenter randomized controlled trial [5,19]. The 2009 H1N1 epidemic further provided evidence for its potential use; however, the benefit of ECMO is not clearly established because of the heterogeneous results in different centers [15–17,18 ,22,23 ]. Improvement in outcomes may merely be due to &
&&
a
Interdepartmental Division of Critical Care Medicine, University of Toronto and bThe University Health Network, Toronto, Ontario, Canada Correspondence to Eddy Fan, MD, PhD, Toronto General Hospital, 585 University Avenue, PMB 11-123, Toronto, ON M5G 2N2, Canada. Tel: +1 416 340 4800x5061; fax: +1 647 776 3148; e-mail: [email protected] Curr Opin Crit Care 2015, 21:13–19 DOI:10.1097/MCC.0000000000000170
1070-5295 Copyright ß 2015 Wolters Kluwer Health, Inc. All rights reserved.
www.co-criticalcare.com
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
Respiratory system
KEY POINTS There is a lack of definitive evidence for the benefit of venovenous ECMO in adult patients with ARDS. In the past 5 years, application of ECMO has rapidly increased and the patient population considered for this supportive therapy has broadened. Continued evolution in ECMO technology, smaller systems, introduction of telemedicine, and cannulation in peripheral hospital sites by mobile ECMO teams for transfer to experienced centers offer a promise for improved outcomes in appropriately selected adult patients with severe ARDS. Adverse events on venovenous ECMO should be analyzed over time to understand how novel advances contribute to changes in complication and mortality rates. Future studies into optimal timing of initiation of venovenous ECMO, selection of patients who will benefit most, and ideal mechanical ventilation strategies during ECMO will help determine whether its use can improve survival and long-term outcomes in patients with severe ARDS.
early referrals of patients with severe ARDS to an ECMO specialist center [24 ,25], where these complex patients may benefit from more homogeneous care by experienced physician and nursing management [26 ,27], along with greater use of evidencebased therapies (i.e., low tidal volume ventilation) [28]. &
&&
1970
1960s: Development advances in artificial heart and lung extracorporeal blood circuit8 1967: First description of adult acute 3 respiratory distress syndrome 1965-9: First reports of early experience with the Bramson 6,9 Membrane Lung
ADVANCES IN CANNULATION TECHNIQUES AND EQUIPMENT For the past three decades, increased simplicity and decreased size of ECMO circuits and ongoing optimization of cannula, oxygenator, and pump technology are contributing to improved outcomes in
2011: Start of EOLIA RCT (ClinicalTrials.gov Identifier NCT01470703) 2012: Berlin definition of ARDS1 2012: Introduction of portable ECMO system20 2010s: Five-fold increase in annual 5 ECMO use for severe ARDS
1994: First randomized clinical trial in use of ECCO2R in ARDS12 1990s: Increased use of ECMO in neonatal population13
1972: Hill et al., describe first use of 7 ECMO 1979: Zapol et al., present first RCT of ECMO use in ARDS10, a negative study
1960
Overall, the survival of patients treated with ECLS for adult respiratory failure depends on its cause and in most recent large studies ranges between 51 and 79% [5,15]. However, as this therapy is currently often used as a last resort in severe ARDS when standard therapies fail, presumably the fatality rate would likely be higher without ECMO (i.e., clinicians believe that death would be near certain without ECMO). Nevertheless, ECMO use as a bridge to recovery has increased during the past 5 years [29], managing sicker patients at higher costs [30]. Since 2009, the annual number of adult respiratory ECLS cases around the world has drastically increased from 100 to more than 500 cases per year [5]. A similar trend is present in the pediatric population, in which despite ECMO application for increasingly complex patients, consistent survival benefit is noted [5,13]. In this review, we focus on the literature published during the last 2 years to provide an overview of recent advances in equipment, current conventional and unconventional indications, complications, and to consider future applications of venovenous ECMO in severe ARDS.
1980
1986: Observational data on successful extracorporeal CO2 removal (ECOO2R) in severe 11 ARDS 1989: ELSO society formed (www.elsonet.org5)
1990
2000
2010
2008: Introduction of Avalon dual lumen catheter14 15-18 2009: H1N1 pandemic 2009: Peek et al. present CESAR19, transfer to ECMO referral center confers survival benefit in ARDS
FIGURE 1. Timeline of extracorporeal membrane oxygenation application in management of severe acute respiratory distress syndrome. 14
www.co-criticalcare.com
Volume 21 Number 1 February 2015
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
Extracorporeal life support for severe ARDS Leligdowicz and Fan
patients treated with ECMO [31]. The introduction of percutaneous single-site cannulation with the Avalon elite bicaval dual lumen catheter (Maquet Cardiovascular AG, Rastatt, Germany) [14] has allowed patient mobilization by avoiding femoral cannulation [32] and decreased the rate of complications [33]. An increase in the use of centrifugal pumps over a roller-head pump has allowed for faster pump assembly and cannulation time as well as a lower priming volume [29]. Novel rotational pumps with diagonally streamed impellers (Deltastream DP3; Medos Medizintechnik AG, Stolberg, Germany) can increase the pump speed, further minimize the pump size and priming volume as well as reduce blood contact with foreign surfaces, thereby resulting in less hemolysis and a lower inflammatory response [34]. Modern polymethylpentene hollow fiber oxygenators can also decrease inflammation, result in superior gas exchange, lower resistance to flow, and less shear of red blood cells as well as have a longer lifespan requiring less frequent changes, thereby lowering the potential for complications [31]. Finally, the introduction of miniaturized, portable ECMO available as a self-contained system with an oxygenator, a pump, and all components to provide ECMO support (CardioHelp; Maquet Cardiovascular AG, Rastatt, Germany) facilitates location-independent stabilization and interhospital transfer, making initiation of ECMO possible even in hospitals without critical care resources [20,35 ]. &
CONVENTIONAL INDICATIONS FOR VENOVENOUS EXTRACORPOREAL MEMBRANE OXYGENATION IN ACUTE RESPIRATORY FAILURE Although severe ARDS is the most common reason for initiating ECMO, there are no absolute criteria for appropriate patient selection. Suggested indications include severe hypoxemia (PaO2/FiO2 < 80), uncompensated hypercapnia with concomitant acidemia (pH < 7.15), or significantly elevated end-inspiratory plateau pressures (>35–45 cm of H2O) in patients with ARDS from a potentially reversible condition (i.e., pneumonia) [36]. In addition, given the lack of definitive evidence for ECMO and promising favorable trials of prone ventilation [37], an additional criterion of failed prone ventilation (or presence of a contraindication to prone ventilation) should be considered [38]. PreECMO simplified acute physiology score II and sequential organ failure assessment scores may predict ICU discharge [22,39], and possibly influence the decision to initiate ECMO. Similarly, there are no absolute contraindications to initiating ECMO. Most contraindications
are relative and include first, conditions incompatible with normal life if the patient recovers; second, preexisting conditions that affect the quality of life (CNS status, end-stage malignancy, risk of lifethreatening bleeding with limited anticoagulation); third, age and size of patient; and fourth, futility: patients who are too sick, have been on conventional therapy too long (e.g., mechanical ventilation for >7 days), or have a fatal diagnosis [40]. Overall, success of ECMO continues to depend on individualized patient selection and reversibility of the underlying disease process [29]. Young patients with severe ARDS who fail lung-protective ventilation and who have single organ failure and no comorbid conditions may be the most likely candidates to benefit [18 ,38]. Interestingly, during the H1N1 pandemic in New Zealand, morbidly obese patients (BMI 30 kg/m2) were more likely to develop viral pneumonia requiring ECMO support; however, their mortality was the same as that in nonobese patients requiring ECMO support [41], suggesting morbid obesity is not a contraindication. &
UNCONVENTIONAL AND FUTURE USES OF EXTRACORPOREAL MEMBRANE OXYGENATION IN ACUTE RESPIRATORY FAILURE The recent increase in the use of ECMO resulted in application of this technology in patients with less severe forms of ARDS [32,42]. The benefit from early ECMO in milder forms of hypoxemic respiratory failure may be due to lung-protective ventilation with exceedingly low tidal volumes (approximately 3 ml/kg) [43,44], which may further reduce ventilator-induced lung injury (VILI) [45] and mortality [46] in patients mechanically ventilated for ARDS. Additionally, by reducing hypoxic pulmonary vasoconstriction and unloading the right ventricle, venovenous ECMO may reduce the effect that acute lung injury has on right ventricular dysfunction [47]. The use of ECMO as bridge to lung transplantation is a growing indication in many centers [48]. For instance, patients with idiopathic pulmonary fibrosis are well known to have a high mortality, but recent advances in mechanical ventilation settings and the possibility of lung transplant eligibility during admission may allow a subset of these patients to benefit from ECMO as a new strategy to bridge critical candidates to definitive therapy [49]. Additionally, patients bridged to lung transplantation with ECMO can be awake, facilitating rehabilitation pretransplant, decreasing weakness and deconditioning [29,49], especially as active participation in physical therapy, including
1070-5295 Copyright ß 2015 Wolters Kluwer Health, Inc. All rights reserved.
www.co-criticalcare.com
Copyright © 2015 Wolters Kluwer Health, Inc. All rights reserved.
15
Respiratory system
ambulation, may hasten posttransplantation recovery in these patients [50]. Patients with ARDS or refractory shock caused by an intoxication may also benefit from ECMO [51]. Data to support this originate from case reports and retrospective observational cohort studies [52], with no randomized control trials to support its benefit. In instances of hemodynamic instability due to calcium channel antagonist, beta blocker, antiarrhythmic, tricyclic antidepressant, or chloroquine intoxication that is refractory to vasopressor and inotropic support, venovenous ECMO can be considered as a salvage therapy and a bridge to recovery. The use of venovenous ECMO may also be advantageous in patients with inhalational injuries, such as aspiration of organic hydrocarbons found in paint removers and paint thinners or smoke inhalation. ARDS after cardiac surgery is diagnosed in 20% of patients, with a mortality rate approaching 80% [53]. In postoperative hemodynamically stable patients with refractory hypoxemia, venovenous ECMO can be lifesaving and may prevent left ventricular distension, persistent left atrial hypertension, and pulmonary edema associated with the use of venoarterial ECMO. The use of venovenous ECMO in patients at a very high risk of bleeding has been described in the context of respiratory failure after massive atonic uterine bleeding [54] and ARDS due to pulmonary contusions after polytrauma [55,56]. Although these patients are at a high risk of hemorrhage due to coagulopathies and preexisting bleeding, delaying anticoagulation for 48–72 h can avert bleeding and the use of centrifugal pumps and oxygenators can decrease platelet consumption and reduce hemolysis. Furthermore, percutaneous insertion of a double-lumen cannula allows for a singlepuncture site in emergency settings. Particularly in polytrauma patients who have a blood lactate less than 14.4 mmol/l, pH more than 7.01, and an injury severity score less than 63, the use of ECMO can facilitate survival and the possibility of organ recovery for donation [56].
COMPLICATIONS The ELSO registry collects data on 46 different complications in patients treated with ECMO for respiratory failure. These can be classified into those directly related to the ECMO circuit and those due to patient-related factors [5,36]. Most frequently encountered mechanical problems include oxygenator failure, cannula problems, pump malfunction (16, 8, and 2%, respectively) [5]. Tubing or circuit rupture is rare (
