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Towards a Better Understanding of Body Mass Index and Patient Outcomes

O'Brien, James M. Jr., MD, MSc*; Needham, Dale M., MD, PhD

doi: 10.1213/ANE.0b013e3182025ca5
Editorials: Editorials
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From *Division of Pulmonary, Allergy, Critical Care, and Sleep Medicine and Center for Critical Care, The Ohio State University Medical Center, Columbus, Ohio; and Outcomes After Critical Illness and Surgery (OACIS) Group, Division of Pulmonary and Critical Care Medicine, and Department of Physical Medicine and Rehabilitation, Johns Hopkins University, Baltimore, Maryland.

Funding: No funding.

Conflicts of Interest: See Disclosures at the end of the article.

Address correspondence to James M. O'Brien, Jr., MD, MSc, Division of Pulmonary, Allergy, Critical Care, and Sleep Medicine and Center for Critical Care, The Ohio State University Medical Center, 201 Davis HLRI, Columbus, OH 43210. Address e-mail to james.obrien@osumc.edu.

Accepted October 1, 2010

Alongside the growing epidemic of obesity, there is a proliferation of observational studies examining excess body weight as a potential risk factor for poor outcomes from various procedures and diseases, including critical illness.1,2 Some studies bolster the evidence that increasing weight is associated with excess mortality and morbidity.35 However, in this issue of Anesthesia & Analgesia, Nafiu et al. suggest a lack of deleterious effects of obesity on short-term outcomes among elderly patients (>65 years) undergoing vascular surgery,6 consistent with some other studies of obesity and acute illness.710 These investigators examined the association between preoperative body mass index (BMI) and immediate postoperative morbidity and mortality using the National Surgical Quality Improvement Program database. After risk adjustment, the odds ratio for postoperative (up to 30 days) mortality was highest among underweight patients and lowest among overweight patients or those with class I obesity (BMI 30 to 34.9 kg/m2). Even severe obesity (BMI ≥ 40 kg/m2) did not appreciably increase the risk of mortality. Underweight patients also had greater morbidity and longer length of stay after surgery.

These results provide little support for the idea that excess weight increases the risk of surgical complications in elderly patients undergoing vascular procedures. However, because the majority of these procedures were not emergent (<15%), surgeons had some discretion in selecting patients for surgery. Hence, perhaps the lack of association between excess weight and patient outcomes is due to appropriate patient selection with exclusion of the higher BMI patients who may have been higher risk. If this were true, one might expect that such selection would result in similar risk-adjusted mortality between the normal and increased BMI patients. However, this was not the case. Instead, patients with overweight and obese BMIs appeared to have some degree of protection from negative outcomes. We speculate that this finding may arise, at least in part, because of discrimination against heavier patients.

While direct evidence of such discrimination is lacking from the current study, there is circumstantial evidence that supports our speculation. Bias against obese individuals by medical professionals is well documented1113 and may include disparities in care provided, including among ambulatory14,15 and critically ill patients.16 In the current study, obese patients were younger, more functionally independent, more commonly nonsmokers, and less likely to have disseminated cancer, recent weight loss, or a do-not-resuscitate order than did patients with normal BMIs. Some of these differences may be due to the interaction between vascular disease and excess weight (e.g., obese patients manifest symptoms of vascular disease at a younger age); however, it is also possible that heavier patients must be “healthier” than patients with normal BMIs for surgeons to consider them of equal risk and recommend and perform surgery. A prior study suggested that physicians attributed an increased risk of mortality to obesity in cases of septic shock, independent of APACHE II score or number of organ failures.17 This potential bias in selection for surgery could be explored by determining whether BMI is an independent predictor of referral for, and receipt of, a vascular surgical procedure. Thus, this study prompts us to ask whether surgeons are less likely to perform vascular surgical procedures (particularly nonemergent surgery) if a patient is obese.

This study also raises questions about potential differences in medical care provided, in both the pre- and perioperative periods. Considering that obesity is associated with greater health care resource utilization,18 it would be interesting to explore whether more intense medical management prior to surgery (e.g., blood pressure control, diabetes management) reduced obese patients' operative risk. Similarly, the presence of comorbidities prior to surgery may have led to greater attention to their management in the perioperative period. Future research should consider such questions.

The study's findings regarding underweight patients also deserve comment. Considering the higher rate of preoperative functional dependence (32.7% vs. 19.9% among normal BMI patients) and admission from a location other than home (12.9% vs. 8.7%, respectively), one could infer that this underweight group is not healthy and thin, but is underweight because of underlying disease, including frailty19 in these older patients. In addition to higher mortality, these underweight patients suffered higher rates of postoperative complications, including cardiac arrest, delayed weaning from mechanical ventilation, pneumonia, and reintubation. Their average hospital length of stay was almost 50% longer than for those with normal BMIs. Potentially confounding some of these associations was a higher rate of emergency surgery in underweight patients. Further investigation directed at underweight patients would be helpful to further explore these noteworthy findings. In particular, the effectiveness of preoperative efforts to mitigate complications via improving nutritional status and normalizing a patient's BMI before elective surgery is worthy of further study.

In most cases, vascular surgery procedures have a more profound effect on patients' morbidity than mortality. Even among this relatively high-risk group of elderly patients, operative mortality was <5%. As a result, patient-centered outcomes, such as quality of life and functional status, should be incorporated into decision-making regarding surgical intervention. Some patients may prefer accepting a small, but increased, risk of immediate postoperative mortality for a possible substantial improvement in longer-term functional status. For example, those who were functionally dependent preoperatively had almost 4 times the odds of death within 30 days. In isolation, this suggests that the operative risk among these patients might out-weigh the benefit. However, a patient might be willing to accept this risk if there is the potential for greater return to functional independence after the surgery. Future studies should consider patients' perspectives regarding balancing mortality and morbidity. Integral to informing this balance is a need for research that longitudinally evaluates long-term patient-centered outcomes after surgery. For example, although excess weight was not associated with increased complications in the immediate postoperative period, longer-term follow-up might identify complications occurring after hospital discharge, which would be important information for patients and surgeons.

The current study is a welcome addition to the literature examining BMI and patient outcomes. Although BMI is a readily available and apparent clinical variable, its true utility is realized when it is readily modifiable. Modification could include efforts to change a patient's BMI (e.g., through weight loss or weight gain) or to provide therapies aimed at mitigating increased risks associated with body weight. Although many questions remain, it is clear that excess weight should not be considered a risk factor for poor short-term outcomes among elderly vascular surgery patients, but further exploration of the worse outcomes experienced by underweight patients is clearly warranted.

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REFERENCES

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DISCLOSURES

Name: James M. O'Brien, Jr., MD, MSc.

Contribution: This author helped write the Editorial, but did no data analysis.

Attestation: This author approved the final manuscript.

Conflicts of Interest: James M. O'Brien, Jr. received research funding from NIH/NHLBI and reported a conflict of interest with Sepsis Alliance. University grant monies: Davis/Bremer Medical Research Award ($50K, 3/05–2/07); nonindustry grant monies: NHLBI HL075076 ($520,992, 4/05–3/09), NIH Clinical Research Loan Repayment Program ($163,371.28, 10/03–4/05, 10/06–7/07, 7/08–6/10); industry grant monies: Sub-I on studies of rhAPC, iseganan, PAF-ase, LY315920, Zemplar, ARDS Network ($1000/month, 6/02– 6/04), SubI on M01 RR0051 (NIH and Lilly, $0, 5/03–1/04). Principal investigator for aerosolized amikacin (Aerogen, $0, 8/05–6/06). Principal investigator for calfactant (Pneuma Pharmaceuticals, $0, 2009–2010). Consultant/Speakers' Bureau: Gave lecture on future perspectives on sepsis definitions. Honorarium donated to Sepsis Alliance. Received airfare and 2 night's hotel accommodations totaling approximately $1500 in value (2009). Gave lecture on ARDS to Lilly ($1500, 2003). Received honorarium from Lilly for talk on tidal volume ($1000, 2003). Unrestricted educational grant from Lilly to present talk at SCCM (approx. $2000 in travel expenses, 2005). Consultant to Medical Simulation Corporation ($4000, 2005–2006). Coauthor on manuscript with Lilly employees (2006). Consultant to Keimar, Inc. ($0, 2008–present). Board of Directors, Walk with a Doc ($0, 2007–2009). Board of Directors, Sepsis Alliance ($0, 2009–present).

Name: Dale M. Needham, MD, PhD.

Contribution: This author helped write the Editorial, but did no data analysis.

Attestation: This author approved the final manuscript.

Conflicts of Interest: This author reported no conflicts of Interest.

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