Volume-Outcome Relationships in Extracorporeal Membrane Oxygénation: Is Bigger Really Better?* Graeme MacLaren, MBBS, FCCM Cardiothoracic ICU National University Health System Singapore; Department of Paediatrics University of Melbourne; and Paediatric ICU The Royal Children's Hospital Melbourne, Australia Sara K. Pasquali, MD, MHS Department of Pediatrics and Communicable Diseases University of Michigan Medical School C.S. Mott Children's Hospital Ann Arbor, Ml Heidi J. Dalton, MD, FCCM Division of Critical Care Phoenix Children's Hospital Phoenix, AZ
T
he association between larger volumes and improved performance has been accepted for years in various industries and has become an increasingly important topic in medicine. The notion that surgeons v^^ho more frequently perform a procedure achieve better outcomes than those with less experience has been grudgingly accepted for years (1), and several hundred publications clearly demonstrate a volume-outcome relationship for a host of medical procedures (2,3). However, although the relationship is consistent, its magnitude varies and the underlying associations differ between surgical disciplines (2, 4). The strongest associations between higher volume and improved outcome are observed when the procedure evaluated is high risk or high complexity (5). Extracorporeal membrane oxygénation (ECMO) is a good example of such a procedure. Patients placed on ECMO are desperately ill and unstable, often making the initiation process difficult and fraught with potential complications. As the majority of programs have several clinicians who perform
'See also p. 512. Key Words: extracorporeal life support; pediatrics; quality Dr. Pasquali consulted for Pfizer and Thallion Pharmaceuticals (Data Safety Monitoring Board member) and Ikaria (Scientific Advisory Board meeting attendee). Her institution received research grant support from Griese-Hutchinson-Woodson Award, Faith's Angels Congenital Heart Disease Research Award, and National Heart, Lung and Blood Institute (K08HL10363). The remaining authors have disclosed that they do not have any potential conflicts of interest. Copyright © 2013 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins DOI: 10.1097/CCM.0000000000000061
726
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ECMO cannulation, experience with access techniques in a variety of patient populations may be diluted. Furthermore, placement of access cannulas is not the only facet in the care of ECMO patients where volume and experience may play a role. How well the ICU team has been trained; the quality of ancillary clinical staff, radiological and laboratory support, and the effectiveness of teamwork between multiple medical and nursing disciplines all may play a more important role in determining patient outcomes (6). In other words, when applied to complex interventions such as ECMO, center volume may not be a good surrogate for quality. In this issue of Critical Care Medicine, Freeman et al (7) present an analysis of the volume-outcome relationship in 7,322 pédiatrie and neonatal ECMO patients from 40 hospitals participating in the Pédiatrie Health Information System. Centers were categorized as low, medium, or high volume based on the number of ECMO patients supported annually (< 20, 20-49, > 50 patients per year, respectively). After adjusting for possible confounders, they demonstrated that ECMO patients managed in low-volume centers had statistically higher mortality rates than in busier centers, with a cutoff for increased mortality noted at center volumes of less than 22 ECMO patients per year. This work complements the study by Karamlou et al (8), which noted a similar impact on survival for patients receiving ECMO for cardiac failure. Centers supporting less than 15 patients per year had reduced survival, despite risk adjustment. Higher volume centers have also been shown to use fewer resources. The randomized trial of ECMO for adult respiratory failure in the United Kingdom showed improved survival in patients treated at a single site, leading commentators to conclude that experience both with ECMO and conventional management provided superior care at high-volume centers (9). On the basis of this evidence, should smaller centers stop doing ECMO and refer all patients to institutions with higher case volumes? On the surface, this may seem to be logical. In some parts of the world, the impact of volume and outcome in cardiac surgical programs has resulted in concentration of such procedures in large-volume centers. This is not the case in the United States, however, where having a functioning cardiac program is considered an essential element of hospital care in many small, medium, and large centers. Although the data in the current report are compelling, there are several limitations. Freeman et al (7) used an administrative dataset based primarily on discharge coding and financial information to conduct their analysis; such datasets are limited by inherent difficulties with accurate case ascertainment and risk adjustment (10). Important variables that could not be assessed included patient complexity, severity of illness, pre-ECMO physiology, and institutional thresholds to initiate ECMO. There was also no attempt to assess outcome of patients with similar illnesses March 2014 • Volume 42 • Number 3
Editorials
who did not receive ECMO at the centers evaluated. This may be an important limitation, as a center may perform conventional care extremely well and choose to apply ECMO only in the most severely ill patients in whom survival may be low. Another center, however, may apply ECMO at a less critical time point where survival may be expected to be higher. Other relevant factors which were not accounted for included the model of care delivery (e.g., central ECMO teams providing oversight to multiple ICUs versus cohorting in single specialized units) and the robustness of quality initiatives, both of which might be more important than center volume (5). As has been demonstrated in other areas, center volume often explains only a portion of intercenter variation in performance, and this variation may persist even after adjustment for volume, suggesting that volume alone is not the only important factor in assessing quality of care (11). Furthermore, the author's findings may not be globally applicable. Some smaller centers may serve vital regional needs, and closing down their ECMO programs may compromise local healthcare provision. On the other hand, the study cannot be lightly dismissed. Although wholesale closure of smaller ECMO programs would be ill-advised, the study nonetheless demonstrates that variation in ECMO outcomes is attributable at least in part to center volume. Further investigation is necessary to determine which structures, processes, and outcome variables aside from volume are associated with achieving the highest quality care. Centers should collaborate to identify and disseminate best practices, reduce variation, and improve outcomes. This model has been successful in other areas of medicine (12, 13). A complementary approach to consider is regionalization of ECMO services. The advantages of centralizing general pédiatrie critical care services have been convincingly demonstrated (14, 15), and similar arguments could be made for pédiatrie ECMO services. This could have substantial ramifications in countries such as Japan, where there is no centralization of pédiatrie critical care services and almost every hospital offers ECMO. With centralization comes a need to establish retrieval capabilities and to demonstrate that referral center outcomes meet international standards. The study by Freeman et al (7) is an important addition to the growing body of literature aiming to address the difficult and controversial subject of center volume and outcome for patients receiving ECMO. It provides more evidence that there may indeed be a minimal caseload to meet an appropriate standard of care, and that this caseload may be significantly higher than previous recommendations ( 16). Although the key message of the study is aimed at government and healthcare
Critical Care Medicine
administrators, it should also spark discussion between clinicians in the critical care and ECMO communities, hopefully fostering regional collaboration to improve patient outcomes and contain healthcare costs, rather than continued competition.
REFERENCES 1. Luft HS, Bunker JP, Enthoven AC: Should operations be regionalized? The empirical relation between surgical volume and mortality. N EngI J Med 1 979; 301:1364-1369 2. Chowdhury MM, Dagash H, Pierro A: A systematic review of the impact of volume of surgery and specialization on patient outcome. Br J Surg 2007; 94•.^45-^6^ 3. Kizer KW: The volume-outcome conundrum. N EngI J Med 2003; 349;2159-2161 4. Pasquali SK, Li JS, Burstein DS, et al; Associafion of cenfer volume with mortality and complications in pédiatrie heart surgery. Pediatrics 2012; 129;e370-e376 5. Beca J: Regionalization and triage, in: ECMC Extracorporeal Cardiopulmonary Support in Critical Care. Fourth Edition. Annich GM, Lynch WR, MacLaren G, et al (Eds). Ann Arbor, Ml, ELSO, 2012, pp 439-450 6. Guerguerian AM, Ogino MT, Dalton HJ, ef al: Sefup and maintenance of extracorporeal life support programs. Pediatr Crit Care Med 2013; 14;S84-S93 7. Freeman CL, Benneft TD, Casper TC, ef al: Pediafric and Neonatal Extracorporeal Membrane Oxygénation: Does Center Volume Impact Mortality? Crit Care Med 2014; 42:51 2-519 8. Karamlou T, Vafaeezadeh M, Parrish AM, ef al; Increased exfracorporeal membrane oxygénation center case volume is associated with improved extracorporeal membrane oxygénation survival among pédiatrie patients. J Ttiorac Cardiovasc Surg 2013; 145:470-475 9. Peek GJ, Elbourne D, Mugford M, ef al: Randomised controlled trial and parallel economic evaluation of conventional ventilafory support versus extracorporeal membrane oxygénation for severe adult respiratory failure (CESAR). Heaitii Tectinol Assess 2010; 14;1-46 10. Pasquali SK, Peterson ED, Jacobs JP, ef al; Differential case ascertainment in clinical registry versus administrative data and impact on outcomes assessment for pediafric cardiac operations. Ann Thorac Surg 2013; 95:197-203 11. Pasquali SK, Jacobs JP, HeX,efal: The complex relationship between cenfer volume and outcome in patients undergoing the Norwood operation. Ann Thorac Surg 201 2; 93:1556-1562 12. Prager RL, Armenti FR, Bassett JS, et al; Michigan Society of Thoracic and Cardiovascular Surgeons; Cardiac surgeons and the qualify movement: The Michigan experience. Semin Thorac Cardiovasc Surg 2009;21;20-27 13. Share DA, Campbell DA, Birkmeyer N, ef al; How a regional collaborative of hospitals and physicians in Michigan cuf costs and improved the qualify of care. Health Aff (Millwood) 2011 ; 30:636-645 14. Pearson G, Shann F, Barry P, et al: Should paediafric intensive care be centralised? Trent versus Vicforia. Lancet 1997; 349:1 213-1217 15. Pearson G, Barry P, Timmins C, ef al: Changes in the profile of paediafric intensive care associated with centralisation. Intensive Care Med 2001; 27:1670-1673 16. Exfracorporeal Life Support Organization: ELSO Guidelines for ECMO Centers, 2010. Available af: hftp://www.elsonet.org/index. php/resources/guidelines.html Accessed September 3, 2013
wvvw.ccmjournal.org
727
Copyright of Critical Care Medicine is the property of Lippincott Williams & Wilkins and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
T
he association between larger volumes and improved performance has been accepted for years in various industries and has become an increasingly important topic in medicine. The notion that surgeons v^^ho more frequently perform a procedure achieve better outcomes than those with less experience has been grudgingly accepted for years (1), and several hundred publications clearly demonstrate a volume-outcome relationship for a host of medical procedures (2,3). However, although the relationship is consistent, its magnitude varies and the underlying associations differ between surgical disciplines (2, 4). The strongest associations between higher volume and improved outcome are observed when the procedure evaluated is high risk or high complexity (5). Extracorporeal membrane oxygénation (ECMO) is a good example of such a procedure. Patients placed on ECMO are desperately ill and unstable, often making the initiation process difficult and fraught with potential complications. As the majority of programs have several clinicians who perform
'See also p. 512. Key Words: extracorporeal life support; pediatrics; quality Dr. Pasquali consulted for Pfizer and Thallion Pharmaceuticals (Data Safety Monitoring Board member) and Ikaria (Scientific Advisory Board meeting attendee). Her institution received research grant support from Griese-Hutchinson-Woodson Award, Faith's Angels Congenital Heart Disease Research Award, and National Heart, Lung and Blood Institute (K08HL10363). The remaining authors have disclosed that they do not have any potential conflicts of interest. Copyright © 2013 by the Society of Critical Care Medicine and Lippincott Williams & Wilkins DOI: 10.1097/CCM.0000000000000061
726
www.ccmjournal.org
ECMO cannulation, experience with access techniques in a variety of patient populations may be diluted. Furthermore, placement of access cannulas is not the only facet in the care of ECMO patients where volume and experience may play a role. How well the ICU team has been trained; the quality of ancillary clinical staff, radiological and laboratory support, and the effectiveness of teamwork between multiple medical and nursing disciplines all may play a more important role in determining patient outcomes (6). In other words, when applied to complex interventions such as ECMO, center volume may not be a good surrogate for quality. In this issue of Critical Care Medicine, Freeman et al (7) present an analysis of the volume-outcome relationship in 7,322 pédiatrie and neonatal ECMO patients from 40 hospitals participating in the Pédiatrie Health Information System. Centers were categorized as low, medium, or high volume based on the number of ECMO patients supported annually (< 20, 20-49, > 50 patients per year, respectively). After adjusting for possible confounders, they demonstrated that ECMO patients managed in low-volume centers had statistically higher mortality rates than in busier centers, with a cutoff for increased mortality noted at center volumes of less than 22 ECMO patients per year. This work complements the study by Karamlou et al (8), which noted a similar impact on survival for patients receiving ECMO for cardiac failure. Centers supporting less than 15 patients per year had reduced survival, despite risk adjustment. Higher volume centers have also been shown to use fewer resources. The randomized trial of ECMO for adult respiratory failure in the United Kingdom showed improved survival in patients treated at a single site, leading commentators to conclude that experience both with ECMO and conventional management provided superior care at high-volume centers (9). On the basis of this evidence, should smaller centers stop doing ECMO and refer all patients to institutions with higher case volumes? On the surface, this may seem to be logical. In some parts of the world, the impact of volume and outcome in cardiac surgical programs has resulted in concentration of such procedures in large-volume centers. This is not the case in the United States, however, where having a functioning cardiac program is considered an essential element of hospital care in many small, medium, and large centers. Although the data in the current report are compelling, there are several limitations. Freeman et al (7) used an administrative dataset based primarily on discharge coding and financial information to conduct their analysis; such datasets are limited by inherent difficulties with accurate case ascertainment and risk adjustment (10). Important variables that could not be assessed included patient complexity, severity of illness, pre-ECMO physiology, and institutional thresholds to initiate ECMO. There was also no attempt to assess outcome of patients with similar illnesses March 2014 • Volume 42 • Number 3
Editorials
who did not receive ECMO at the centers evaluated. This may be an important limitation, as a center may perform conventional care extremely well and choose to apply ECMO only in the most severely ill patients in whom survival may be low. Another center, however, may apply ECMO at a less critical time point where survival may be expected to be higher. Other relevant factors which were not accounted for included the model of care delivery (e.g., central ECMO teams providing oversight to multiple ICUs versus cohorting in single specialized units) and the robustness of quality initiatives, both of which might be more important than center volume (5). As has been demonstrated in other areas, center volume often explains only a portion of intercenter variation in performance, and this variation may persist even after adjustment for volume, suggesting that volume alone is not the only important factor in assessing quality of care (11). Furthermore, the author's findings may not be globally applicable. Some smaller centers may serve vital regional needs, and closing down their ECMO programs may compromise local healthcare provision. On the other hand, the study cannot be lightly dismissed. Although wholesale closure of smaller ECMO programs would be ill-advised, the study nonetheless demonstrates that variation in ECMO outcomes is attributable at least in part to center volume. Further investigation is necessary to determine which structures, processes, and outcome variables aside from volume are associated with achieving the highest quality care. Centers should collaborate to identify and disseminate best practices, reduce variation, and improve outcomes. This model has been successful in other areas of medicine (12, 13). A complementary approach to consider is regionalization of ECMO services. The advantages of centralizing general pédiatrie critical care services have been convincingly demonstrated (14, 15), and similar arguments could be made for pédiatrie ECMO services. This could have substantial ramifications in countries such as Japan, where there is no centralization of pédiatrie critical care services and almost every hospital offers ECMO. With centralization comes a need to establish retrieval capabilities and to demonstrate that referral center outcomes meet international standards. The study by Freeman et al (7) is an important addition to the growing body of literature aiming to address the difficult and controversial subject of center volume and outcome for patients receiving ECMO. It provides more evidence that there may indeed be a minimal caseload to meet an appropriate standard of care, and that this caseload may be significantly higher than previous recommendations ( 16). Although the key message of the study is aimed at government and healthcare
Critical Care Medicine
administrators, it should also spark discussion between clinicians in the critical care and ECMO communities, hopefully fostering regional collaboration to improve patient outcomes and contain healthcare costs, rather than continued competition.
REFERENCES 1. Luft HS, Bunker JP, Enthoven AC: Should operations be regionalized? The empirical relation between surgical volume and mortality. N EngI J Med 1 979; 301:1364-1369 2. Chowdhury MM, Dagash H, Pierro A: A systematic review of the impact of volume of surgery and specialization on patient outcome. Br J Surg 2007; 94•.^45-^6^ 3. Kizer KW: The volume-outcome conundrum. N EngI J Med 2003; 349;2159-2161 4. Pasquali SK, Li JS, Burstein DS, et al; Associafion of cenfer volume with mortality and complications in pédiatrie heart surgery. Pediatrics 2012; 129;e370-e376 5. Beca J: Regionalization and triage, in: ECMC Extracorporeal Cardiopulmonary Support in Critical Care. Fourth Edition. Annich GM, Lynch WR, MacLaren G, et al (Eds). Ann Arbor, Ml, ELSO, 2012, pp 439-450 6. Guerguerian AM, Ogino MT, Dalton HJ, ef al: Sefup and maintenance of extracorporeal life support programs. Pediatr Crit Care Med 2013; 14;S84-S93 7. Freeman CL, Benneft TD, Casper TC, ef al: Pediafric and Neonatal Extracorporeal Membrane Oxygénation: Does Center Volume Impact Mortality? Crit Care Med 2014; 42:51 2-519 8. Karamlou T, Vafaeezadeh M, Parrish AM, ef al; Increased exfracorporeal membrane oxygénation center case volume is associated with improved extracorporeal membrane oxygénation survival among pédiatrie patients. J Ttiorac Cardiovasc Surg 2013; 145:470-475 9. Peek GJ, Elbourne D, Mugford M, ef al: Randomised controlled trial and parallel economic evaluation of conventional ventilafory support versus extracorporeal membrane oxygénation for severe adult respiratory failure (CESAR). Heaitii Tectinol Assess 2010; 14;1-46 10. Pasquali SK, Peterson ED, Jacobs JP, ef al; Differential case ascertainment in clinical registry versus administrative data and impact on outcomes assessment for pediafric cardiac operations. Ann Thorac Surg 2013; 95:197-203 11. Pasquali SK, Jacobs JP, HeX,efal: The complex relationship between cenfer volume and outcome in patients undergoing the Norwood operation. Ann Thorac Surg 201 2; 93:1556-1562 12. Prager RL, Armenti FR, Bassett JS, et al; Michigan Society of Thoracic and Cardiovascular Surgeons; Cardiac surgeons and the qualify movement: The Michigan experience. Semin Thorac Cardiovasc Surg 2009;21;20-27 13. Share DA, Campbell DA, Birkmeyer N, ef al; How a regional collaborative of hospitals and physicians in Michigan cuf costs and improved the qualify of care. Health Aff (Millwood) 2011 ; 30:636-645 14. Pearson G, Shann F, Barry P, et al: Should paediafric intensive care be centralised? Trent versus Vicforia. Lancet 1997; 349:1 213-1217 15. Pearson G, Barry P, Timmins C, ef al: Changes in the profile of paediafric intensive care associated with centralisation. Intensive Care Med 2001; 27:1670-1673 16. Exfracorporeal Life Support Organization: ELSO Guidelines for ECMO Centers, 2010. Available af: hftp://www.elsonet.org/index. php/resources/guidelines.html Accessed September 3, 2013
wvvw.ccmjournal.org
727
Copyright of Critical Care Medicine is the property of Lippincott Williams & Wilkins and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use.
