Morbid Obesity and ICU Outcomes
Morbid Obesity and ICU Outcomes
Abstract & Commentary
Synopsis: In this retrospective study of complications and outcomes in 117 morbidly obese patients (BMI 40 kg/m2 or more) admitted to a medical ICU, morbidity and mortality were substantially higher than in a group of matched nonobese controls with comparable diagnoses and severity of illness according to APACHE II score.
Source: El-Solh A, et al. Morbid obesity in the medical ICU. Chest. 2001;120:1989-1997.
In this study from the university of buffalo, the medical records of patients admitted to the medical ICUs of 2 large teaching hospitals who were morbidly obese (defined as a body mass index [BMI] of 40 kg/m2 or more) were reviewed and compared with data from patients with similar diagnoses and severity of illness who had BMI values less than 30 kg/m2. The study sample consisted of 117 morbidly obese patients admitted between 1994 and 2000, and 132 randomly selected nonobese patients from the same time period. Data collected included demographic information, comorbid conditions, admission APACHE II score, invasive procedures, organ failure, and in-hospital mortality. Only patients remaining in the ICU for more than 24 hours were included.
The ages of the obese and nonobese patients were comparable, as were the reasons for ICU admission. There were no age or gender differences between the 2 groups, although the obese patients had significantly higher prevalence of cardiac, pulmonary, and endocrine comorbidities. APACHE II scores on ICU admission were not different in the 2 groups. However, significantly more of the obese patients were intubated and ventilated (61% vs 46%; P = 0.02), and the obese patients were ventilated longer than their nonobese counterparts (7.7 days vs 4.6 days; P < 0.001). When gender, comorbidities, and APACHE II score were controlled for in multiple linear regression analyses, only BMI was a significant determinant of the time difference in mechanical ventilation between the obese and nonobese patients. Length of ICU stay was also longer in the obese patients (9.3 vs 5.8 days; P < 0.001). Overall mortality was 30% in the morbidly obese patients and 17% in the nonobese patients (P = 0.02).
El Solh and associates conclude that critically ill, morbidly obese patients are at increased risk of morbidity and mortality compared to nonobese patients. They also suggest that the APACHE II severity of illness score may underestimate the true severity of illness in such patients, and that another way of assessing illness severity in morbidly obese patients is needed.
Comment by David J. Pierson, MD
This study confirms, apparently for the first time with actual data, what experienced clinicians have always known: that obese patients do not fare as well as their nonobese fellow patients when they become critically ill, other things being equal. They require longer periods of mechanical ventilation, are harder to wean, get multiple organ failure more frequently, and have increased overall mortality. There are a number of serious limitations to this study, but I strongly suspect that a well-designed, prospective cohort study would yield similar findings.
The potential reasons for increased complications and worse outcomes among morbidly obese patients are numerous. Obtaining and maintaining vascular access may be difficult, and routine care such as turning, bathing, and dressing changes are harder to do well. Bedside patient assessment may be more difficult, so that worsening of the primary problem or the appearance of complications may not be detected as readily as in nonobese patients. Given the importance of early mobilization after surgery or acute medical illness in preventing deep venous thrombosis and other complications, the threat of these things increases with the degree of obesity in patients whose BMI markedly exceeds the norm. Drug tissue disposition and pharmacokinetics may differ substantially in the very obese from what is expected, increasing the likelihood of adverse effects, under- or overdosing, and prolonged clearance and their consequences.
Although BMI was not assessed as a continuous variable in this study, these predispositions to adverse outcomes probably become more and more problematic as BMI increases, regardless of what prompts admission to the ICU. This study does not help us deal better with the problems of managing morbidly obese patients in the ICU, but it may help to raise awareness and facilitate the special efforts that are needed in bringing such patients through critical illness successfully.
Dr. Pierson is Professor of Medicine, University of Washington, Medical Director, Respitory Care, Harborview Medical Center, Seattle, WA.
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