Hospital Volume and Outcomes of Mechanical Ventilation
http://www.100md.com
《新英格兰医药杂志》
To the Editor: In the article by Kahn et al. (July 6 issue),1 the number of patients receiving mechanical ventilation per hospital bed was about 0.7 per year in hospitals in the lowest quartile of hospital volume (150 patients per year), as compared with 1.6 per year in hospitals in the highest quartile of volume (>400 patients per year). The decision to initiate mechanical ventilation in a given patient rests on the course of the disease, the quality of nursing, and the availability of ventilators. Thus, among patients with identical Acute Physiology and Chronic Health Evaluation (APACHE) scores, the proportion admitted to an intensive care unit (ICU) may vary among hospitals. In equally good units, the number of deaths will be the same, given a low threshold and good clinical judgment. However, mortality will fall as the number of patients who undergo mechanical ventilation rises, as suggested by Figure 2 in the article.
Tom Hughes-Davies, F.R.C.P.
Breamore Marsh
Fordingbridge SP6 2EJ, United Kingdom
thhd@thhd.fsnet.co.uk
References
Kahn JM, Goss CH, Heagerty PJ, Kramer AA, O'Brien CR, Rubenfeld GD. Hospital volume and the outcomes of mechanical ventilation. N Engl J Med 2006;355:41-50.
To the Editor: The article by Kahn et al. can be used to illustrate a few additional points relevant to policy. First, on the basis of crude estimates (Table 1), the 356 total or 25 annual deaths avoided in the ICU owing to the use of regionalization policies1 (in which patients are transported to the highest-volume hospitals) are less than the 501 total and 36 annual deaths prevented by a 10% improvement in outcomes across all hospitals. The same applies to in-hospital mortality. To attain across-the-board improvement in outcomes, we need to figure out how to optimize recent advances in mechanical ventilation.2 Second, although regionalization may benefit patients undergoing some procedures,3 it is not yet clear how regionalization could be made more cost-effective. Third, the policies based on volume–outcome relationships must involve strong causal assumptions.4 One causal assumption is that whatever it is about high-volume hospitals that makes them have better outcomes must always be preserved and incentivized by policies such as regionalization and local quality initiatives.
Table 1. Deaths Potentially Avoided Owing to the Regionalization of Mechanical Ventilation.
Onyebuchi A. Arah, M.D., Ph.D.
Academic Medical Center
1100 DE Amsterdam, the Netherlands
o.a.arah@amc.uva.nl
References
Epstein AM. Volume and outcomes -- it is time to move ahead. N Engl J Med 2002;346:1161-1164.
Tobin MJ. Advances in mechanical ventilation. N Engl J Med 2001;344:1986-1996.
Dudley RA, Johansen KL, Brand R, Rennie DJ, Milstein A. Selective referral to high-volume hospitals: estimating potentially avoidable deaths. JAMA 2000;283:1159-1166.
Urbach DR, Baxter NN. Does it matter what a hospital is "high volume" for? Specificity of volume-outcome associations for surgical procedures: analysis of administrative data. BMJ 2004;328:737-740.
The authors reply: Hughes-Davies suggests that the lower mortality rate observed at high-volume hospitals may be due to variation in the use of mechanical ventilation, with higher-volume hospitals using ventilation in a broader group of patients who may be less likely to die. Our data show that the reverse is true: the APACHE III score and unadjusted mortality rate were higher in the hospitals in the higher quartiles according to volume. In addition, our multivariate model controlled for APACHE score. Thus, the odds ratios for mortality can be interpreted as the relative odds of death for patients with equally severe illness, regardless of how many such patients are in each quartile.
Arah succinctly summarizes our results and notes some of the important policy implications of our study. Although these data support the need for an investigation of regionalization of critical care, it is unknown how regionalization will ultimately affect patient outcomes. Regional care centers may not be able to maintain high-quality care practices if faced with even greater numbers of patients, and the act of transferring patients to high-volume hospitals may itself cause harm. As we noted in our Discussion, the improvement of the quality of care at all hospitals is the best approach to reducing critical care mortality.
Research on knowledge transfer, the science of implementing effective practice, is in its infancy in critical care. An important part of this research agenda is the identification of the processes of care at high-volume hospitals that account for improved performance. These processes might include the implementation of protocolized weaning and lung-protective ventilation, optimal staffing ratios for nurses and respiratory therapists, and a culture of collaboration between representative disciplines in the ICU, among others. Regionalization is just one, and perhaps not the most efficient, method to ensure that every patient requiring mechanical ventilation has access to the best available care.
Jeremy M. Kahn, M.D.
Gordon D. Rubenfeld, M.D.
University of Washington
Seattle, WA 98104
nodrog@u.washington.edu
Tom Hughes-Davies, F.R.C.P.
Breamore Marsh
Fordingbridge SP6 2EJ, United Kingdom
thhd@thhd.fsnet.co.uk
References
Kahn JM, Goss CH, Heagerty PJ, Kramer AA, O'Brien CR, Rubenfeld GD. Hospital volume and the outcomes of mechanical ventilation. N Engl J Med 2006;355:41-50.
To the Editor: The article by Kahn et al. can be used to illustrate a few additional points relevant to policy. First, on the basis of crude estimates (Table 1), the 356 total or 25 annual deaths avoided in the ICU owing to the use of regionalization policies1 (in which patients are transported to the highest-volume hospitals) are less than the 501 total and 36 annual deaths prevented by a 10% improvement in outcomes across all hospitals. The same applies to in-hospital mortality. To attain across-the-board improvement in outcomes, we need to figure out how to optimize recent advances in mechanical ventilation.2 Second, although regionalization may benefit patients undergoing some procedures,3 it is not yet clear how regionalization could be made more cost-effective. Third, the policies based on volume–outcome relationships must involve strong causal assumptions.4 One causal assumption is that whatever it is about high-volume hospitals that makes them have better outcomes must always be preserved and incentivized by policies such as regionalization and local quality initiatives.
Table 1. Deaths Potentially Avoided Owing to the Regionalization of Mechanical Ventilation.
Onyebuchi A. Arah, M.D., Ph.D.
Academic Medical Center
1100 DE Amsterdam, the Netherlands
o.a.arah@amc.uva.nl
References
Epstein AM. Volume and outcomes -- it is time to move ahead. N Engl J Med 2002;346:1161-1164.
Tobin MJ. Advances in mechanical ventilation. N Engl J Med 2001;344:1986-1996.
Dudley RA, Johansen KL, Brand R, Rennie DJ, Milstein A. Selective referral to high-volume hospitals: estimating potentially avoidable deaths. JAMA 2000;283:1159-1166.
Urbach DR, Baxter NN. Does it matter what a hospital is "high volume" for? Specificity of volume-outcome associations for surgical procedures: analysis of administrative data. BMJ 2004;328:737-740.
The authors reply: Hughes-Davies suggests that the lower mortality rate observed at high-volume hospitals may be due to variation in the use of mechanical ventilation, with higher-volume hospitals using ventilation in a broader group of patients who may be less likely to die. Our data show that the reverse is true: the APACHE III score and unadjusted mortality rate were higher in the hospitals in the higher quartiles according to volume. In addition, our multivariate model controlled for APACHE score. Thus, the odds ratios for mortality can be interpreted as the relative odds of death for patients with equally severe illness, regardless of how many such patients are in each quartile.
Arah succinctly summarizes our results and notes some of the important policy implications of our study. Although these data support the need for an investigation of regionalization of critical care, it is unknown how regionalization will ultimately affect patient outcomes. Regional care centers may not be able to maintain high-quality care practices if faced with even greater numbers of patients, and the act of transferring patients to high-volume hospitals may itself cause harm. As we noted in our Discussion, the improvement of the quality of care at all hospitals is the best approach to reducing critical care mortality.
Research on knowledge transfer, the science of implementing effective practice, is in its infancy in critical care. An important part of this research agenda is the identification of the processes of care at high-volume hospitals that account for improved performance. These processes might include the implementation of protocolized weaning and lung-protective ventilation, optimal staffing ratios for nurses and respiratory therapists, and a culture of collaboration between representative disciplines in the ICU, among others. Regionalization is just one, and perhaps not the most efficient, method to ensure that every patient requiring mechanical ventilation has access to the best available care.
Jeremy M. Kahn, M.D.
Gordon D. Rubenfeld, M.D.
University of Washington
Seattle, WA 98104
nodrog@u.washington.edu