Online Letters to the Editor
Association of Body Mass Index With Hospital Mortality in ICU Patients To the Editor:
I
n an observational cohort study including 154,308 ICU patients, Pickkers et al (1) showed that obese and seriously obese patients had the lowest risk of hospital death in a recent article in Critical Care Medicine. Strengths of this study include the large sample of patients and adjust for most of known risk factors that can affect mortality of ICU patients. Also, Pickkers et al (1) openly discuss the limitations of their work. However, the study employed observational designs, which are subject to uncontrolled confounding. In our view, several issues in the study design may confound interpretation of the results. First, illness severity is one of mostly important determinants for hospital death of ICU patients (2). Pickkers et al (1) have attempted to control illness severity differences among patients with different body mass index (BMI) by adjusting the Simplified Acute Physiology Score II (SAPS II), but a significant shortcoming of the SAPS II is inability to distinguish chronic disease from acute disease. This presents a potential problem in controlling for illness severity. It is generally believed that chronic diseases are more common in the obese patients. In our opinion, no matter how refined the adjustment is for differences in illness burden, it is never possible to ensure a complete adjustment for illness severity differences among ICU patients with various BMI and admission reasons. For example, an obese patient with chronic cardiac insufficiency and chronic obstructive pulmonary disease may qualify for a SAPS II score of 16 at baseline, but this patient would have a better short-term outcome than an underweight or normal patient with acute cardiac failure and acute respiratory insufficiency despite an equivalent SAPS II score. That is, a chronically higher SAPS II score in obese patients may manifest as a survival benefit. Thus, we argue that not taking impacts of acute versus chronic disease scoring on the study outcomes into account is injustice to conclude association between obesity and hospital mortality in the ICU patients. Second, transfusion and ethnicity were not included in adjusted potential confounders. It has been shown that transfusions independently contribute to increased risk for hospital death of ICU patients (3). Furthermore, available evidence shows the existence of important ethnic differences in therapies of ICU patients (4) and that black patients are almost three times more likely than white patients to die in-hospital following admission to the ICU (5). Additionally, lack of health insurance is associated with increased risk of hospital mortality in ICU patients. Thus, we cannot exclude possibility that these factors would have contributed to their results. Third, their study design did not include the detail about therapies of ICU patients. Consequently, it is difficult to estimate the degree to which interventions by ICU physicians might have influenced outcomes. From a clinical standpoint, obese patients have more physical care requirements. e80
www.ccmjournal.org
Furthermore, they may have an improved rate of chemical thromboprophylaxis, which is independently associated with survival (2). These bring to light the possibility that obese patients may be triaged to higher care standards. Thus, differences in care standards between obese and nonobese patients could account for subsequent differences in hospital death. The authors have disclosed that they do not have any potential conflicts of interest. Fu-Shan Xue, MD, Shi Yu Wang, MD, Rui Ping Li, MD Department of Anesthesiology, Plastic Surgery Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, People’s Republic of China
REFERENCES
1. Pickkers P, de Keizer N, Dusseljee J, et al: Body Mass Index Is Associated With Hospital Mortality in Critically Ill Patients: An Observational Cohort Study. Crit Care Med 2013; 41:1878–1883 2. Kiraly L, Hurt RT, Van Way CW 3rd: The outcomes of obese patients in critical care. J Parenter Enteral Nutr 2011; 35(5 Suppl):29S–35S 3. Zilberberg MD, Stern LS, Wiederkehr DP, et al: Anemia, transfusions and hospital outcomes among critically ill patients on prolonged acute mechanical ventilation: A retrospective cohort study. Crit Care 2008; 12:R60 4. Williams JF, Zimmerman JE, Wagner DP, et al: African-American and white patients admitted to the intensive care unit: Is there a difference in therapy and outcome? Crit Care Med 1995; 23:626–636 5. Horner RD, Lawler FH, Hainer BL: Relationship between patient race and survival following admission to intensive care among patients of primary care physicians. Health Serv Res 1991; 26:531–542 DOI: 10.1097/01.ccm.0000435673.83682.58
The “Obesity-Mortality Paradox” Phenomenon in Critically Ill Patients: One Size Does Not Fit All To the Editor:
I
n a recent issue of Critical Care Medicine, I read with great interest the article by Pickkers et al (1), which reported that a large observational database derived from the Dutch National Intensive Care Evaluation registry shows an inverse association between obesity and hospital mortality in critically ill patients that could not be explained by a variety of known confounders. Similarly, a short-term obesity-related survival benefit was also concluded in some previous meta-analyses for patients with or without surgical intervention in intensive care. Notably, these meta-analyses were statistically very heterogeneous, which indicates the need for caution in interpreting pooled estimates (1). As is known, types of specific diseases, severity of sickness, and management in critically ill patients may have diverse impacts of body mass index (BMI) on the hospital mortality. For instance, some meta-analyses conversely demonstrated that obesity is associated with higher risks of ICU death among severely traumatic patients and those with 2009 H1N1 infection (2, 3). In addition, we have identified the severity of Glasgow Coma Scale or Acute Physiology and Chronic Health Examination January 2014 • Volume 42 • Number 1
Association of Body Mass Index With Hospital Mortality in ICU Patients To the Editor:
I
n an observational cohort study including 154,308 ICU patients, Pickkers et al (1) showed that obese and seriously obese patients had the lowest risk of hospital death in a recent article in Critical Care Medicine. Strengths of this study include the large sample of patients and adjust for most of known risk factors that can affect mortality of ICU patients. Also, Pickkers et al (1) openly discuss the limitations of their work. However, the study employed observational designs, which are subject to uncontrolled confounding. In our view, several issues in the study design may confound interpretation of the results. First, illness severity is one of mostly important determinants for hospital death of ICU patients (2). Pickkers et al (1) have attempted to control illness severity differences among patients with different body mass index (BMI) by adjusting the Simplified Acute Physiology Score II (SAPS II), but a significant shortcoming of the SAPS II is inability to distinguish chronic disease from acute disease. This presents a potential problem in controlling for illness severity. It is generally believed that chronic diseases are more common in the obese patients. In our opinion, no matter how refined the adjustment is for differences in illness burden, it is never possible to ensure a complete adjustment for illness severity differences among ICU patients with various BMI and admission reasons. For example, an obese patient with chronic cardiac insufficiency and chronic obstructive pulmonary disease may qualify for a SAPS II score of 16 at baseline, but this patient would have a better short-term outcome than an underweight or normal patient with acute cardiac failure and acute respiratory insufficiency despite an equivalent SAPS II score. That is, a chronically higher SAPS II score in obese patients may manifest as a survival benefit. Thus, we argue that not taking impacts of acute versus chronic disease scoring on the study outcomes into account is injustice to conclude association between obesity and hospital mortality in the ICU patients. Second, transfusion and ethnicity were not included in adjusted potential confounders. It has been shown that transfusions independently contribute to increased risk for hospital death of ICU patients (3). Furthermore, available evidence shows the existence of important ethnic differences in therapies of ICU patients (4) and that black patients are almost three times more likely than white patients to die in-hospital following admission to the ICU (5). Additionally, lack of health insurance is associated with increased risk of hospital mortality in ICU patients. Thus, we cannot exclude possibility that these factors would have contributed to their results. Third, their study design did not include the detail about therapies of ICU patients. Consequently, it is difficult to estimate the degree to which interventions by ICU physicians might have influenced outcomes. From a clinical standpoint, obese patients have more physical care requirements. e80
www.ccmjournal.org
Furthermore, they may have an improved rate of chemical thromboprophylaxis, which is independently associated with survival (2). These bring to light the possibility that obese patients may be triaged to higher care standards. Thus, differences in care standards between obese and nonobese patients could account for subsequent differences in hospital death. The authors have disclosed that they do not have any potential conflicts of interest. Fu-Shan Xue, MD, Shi Yu Wang, MD, Rui Ping Li, MD Department of Anesthesiology, Plastic Surgery Hospital, Chinese Academy of Medical Sciences and Peking Union Medical College, Beijing, People’s Republic of China
REFERENCES
1. Pickkers P, de Keizer N, Dusseljee J, et al: Body Mass Index Is Associated With Hospital Mortality in Critically Ill Patients: An Observational Cohort Study. Crit Care Med 2013; 41:1878–1883 2. Kiraly L, Hurt RT, Van Way CW 3rd: The outcomes of obese patients in critical care. J Parenter Enteral Nutr 2011; 35(5 Suppl):29S–35S 3. Zilberberg MD, Stern LS, Wiederkehr DP, et al: Anemia, transfusions and hospital outcomes among critically ill patients on prolonged acute mechanical ventilation: A retrospective cohort study. Crit Care 2008; 12:R60 4. Williams JF, Zimmerman JE, Wagner DP, et al: African-American and white patients admitted to the intensive care unit: Is there a difference in therapy and outcome? Crit Care Med 1995; 23:626–636 5. Horner RD, Lawler FH, Hainer BL: Relationship between patient race and survival following admission to intensive care among patients of primary care physicians. Health Serv Res 1991; 26:531–542 DOI: 10.1097/01.ccm.0000435673.83682.58
The “Obesity-Mortality Paradox” Phenomenon in Critically Ill Patients: One Size Does Not Fit All To the Editor:
I
n a recent issue of Critical Care Medicine, I read with great interest the article by Pickkers et al (1), which reported that a large observational database derived from the Dutch National Intensive Care Evaluation registry shows an inverse association between obesity and hospital mortality in critically ill patients that could not be explained by a variety of known confounders. Similarly, a short-term obesity-related survival benefit was also concluded in some previous meta-analyses for patients with or without surgical intervention in intensive care. Notably, these meta-analyses were statistically very heterogeneous, which indicates the need for caution in interpreting pooled estimates (1). As is known, types of specific diseases, severity of sickness, and management in critically ill patients may have diverse impacts of body mass index (BMI) on the hospital mortality. For instance, some meta-analyses conversely demonstrated that obesity is associated with higher risks of ICU death among severely traumatic patients and those with 2009 H1N1 infection (2, 3). In addition, we have identified the severity of Glasgow Coma Scale or Acute Physiology and Chronic Health Examination January 2014 • Volume 42 • Number 1
