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Influence of Overweight on ICU Mortality: A Prospective Study

Posted on: Wednesday, 23 February 2005, 03:00 CST

To the Editor:

We read with interest the prospective study of the influence of overweight on ICU mortality by Goulenok and colleagues1 in CHEST (April 2004), and noted the provocative findings and conclusions that obesity is an independent prognostic variable in ICU mortality. Despite the fact that the perception of obesity as a mere overfed state with excess energy storage in the form of fat is no longer sustainable in modem medicine, the insidious ramifications of the overfed model continue to permeate the management and epidemiologic research on obesity. The shortcomings of the body mass index as a measure of obesity are emphasized by the fact that the individual metabolic and physiologic aberrations that are common in obesity, such as impaired glucose metabolism2 and cardiopulmonary dysfunction, are by themselves significant independent variables in ICU mortality. Thus, unifying the term overweight under the rubric of body mass index grossly deflects our observations from the pathologic components of the obesity syndrome, which have an independent impact on mortality.

Jeevanandam et al3 observed that protein-energy malnutrition rapidly ensues among obese trauma patients, which is strongly suggestive of the fact that hypoproteinemia may be a regular feature among physiologically stressed obese individuals. An extrapolation of this observation includes the postulation that the stressed obese patient is in a malnourished state with the possibility of coexisting derangements in the utilization of or overt deficiencies of vitamins, metabolic cofactors, and minerals that may lead to suboptimal function under the high metabolic demands of critical illness. Yet, documentation of the nutritional status of the obese subject is distinctly sparse in the medical literature on the subject.

Perhaps significantly, the study did not report on the distribution of comorbid conditions such as hypertension, diabetes, depression, psychoneurotic illnesses, and sleep-disordered breathing that are encountered with increased frequency among obese subjects. If present, the multiple comorbid factors by themselves may be independent confounders of the observed mortality, besides being associated with the use of multiple medications, the potential of which toxicity in patients with critical illnesses is high due to a diminished drug clearance capacity.

While analyzing the mortality data for obese patients in the ICU, we should not neglect the fact that obesity is predominantly a disease of persons in the lower socioeconomic classes,4,5 whose utilization of health resources prior to hospitalization is marginal, and who are also known to have higher hospital mortality from cancer, cardiac disease, and major surgery owing to poorly explained factors.6,7

To the skeptic, a multifactorial condition such as obesity that has poorly characterized nutritional derangements, and a tendency for glucose impairment and complex cardiopulmonary disturbance, and is frequently associated with multiple medical problems does not measure up well as an independent determinant of mortality in the ICU without controlling for the associated factors.

REFERENCES

1 Goulenok C, Monchi M, Chiche JD, et al. Influence of overweight on ICU mortality: a prospective study. Chest 2004; 125:1441-1445

2 Lind L, Lithell H. Impaired glucose and lipid metabolism seen in intensive care patients is related to severity of illness and survival. Clin Intensive Care 1994; 5:100-105

3 Jeevanandam M, Young DH, Schiller WR. Obesity and the metabolic response to severe multiple trauma in man. J Clin Invest 1991; 87:262-269

4 Dekkers JC, Podolsky RH, Treiber FA, et al. Development of general and central obesity from childhood into early adulthood in African American and European American males and females with a family history of cardiovascular disease. Am J Clin Nutr 2004; 79:661-668

5 Drewnowski A, Specter SE. Poverty and obesity: the role of energy density and energy costs. Am J Clin Nutr 2004; 79:6-16

6 Taylor FC, Ascione R, Rees K, et al. Socioeconomic deprivation is a predictor of poor postoperative cardiovascular outcomes in patients undergoing coronary artery bypass grafting. Heart 2003; 89:1062-1066

7 Hole DJ, McArdle CS. Impact of socioeconomic deprivation on outcome after surgery for colorectal cancer. Gr J Surg 2002; 89:586- 590

Daniel S. Dube, MD

Stanford University Medical Center

Stanford, CA

Reproduction of this article is prohibited without written permission from the American College of Chest Physicians (e-mail: permissions@chestnet.org).

Correspondence to: Daniel S. Dube, MD, Postdoctoral Fellow in Pulmonary and Critical Care Medicine, Stanford University Medical Center, 300 Pasteur Dr, H3143, Stanford, CA 94305-5236; e-mail: danieldube@stanford.edu

Copyright American College of Chest Physicians Feb 2005

Source: Chest

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