What is the clinical evidence from this study?

Study design: Cohort. Population: General surgery (n=4293). Intervention: Obesity (BMI > 30 kg/m2) vs. Normal weight (BMI 18.5-25 kg/m2). Primary outcome: Long-term mortality (HR 0.71, 95% CI 0.56-0.89).

July 30, 2015Open Access

Obesity – a risk factor for postoperative complications in general surgery?

Key Result

Obesity was associated with improved long-term survival (HR 0.71) compared to normal weight in patients undergoing general surgery, validating the obesity paradox.

Study Design

Type

Cohort (n=4,293)

Multicenter

PICO

Population

General surgery (n=4,293)

Intervention / Comparator

Obesity (BMI > 30 kg/m2) vs Normal weight (BMI 18.5-25 kg/m2)

Primary Outcome

Long-term mortality — HR 0.71 (0.56-0.89)

Main Result

Effect estimate: HR 0.71 (95% CI 0.56-0.89)

Absolute Event Rate: 14.8% vs 18.6%

Limitations

Recorded data on height and weight were partially self-reported
Potential bias in referral pattern as patients with major comorbidities are usually seen in a tertiary hospital
Analyses were restricted to the patient's first operation
No direct measurement of central or visceral adiposity, relying solely on BMI
Surgical procedures were performed 8-9 years prior to publication, and advances in clinical medicine may alter current practice
Observational character makes the study inherent to unmeasured confounding

Abstract

BACKGROUND: Obesity is generally believed to be a risk factor for the development of postoperative complications. Although being obese is associated with medical hazards, recent literature shows no convincing data to support this assumption. Moreover a paradox between body mass index and survival is described. This study was designed to determine influence of body mass index on postoperative complications and long-term survival after surgery. METHODS: A single-centre prospective analysis of postoperative complications in 4293 patients undergoing general surgery was conducted, with a median follow-up time of 6.3 years. We analyzed the impact of bodyweight on postoperative morbidity and mortality, using univariate and multivariate regression models. RESULTS: The obese had more concomitant diseases, increased risk of wound infection, greater intraoperative blood loss and a longer operation time. Being underweight was associated with a higher risk of complications, although not significant in adjusted analysis. Multivariate regression analysis demonstrated that underweight patients had worse outcome (HR 2.1; 95 % CI 1.4-3.0), whereas being overweight (HR 0.6; 95 % CI 0.5-0.8) or obese (HR 0.7; 95 % CI 0.6-0.9) was associated with improved survival. CONCLUSION: Obesity alone is a significant risk factor for wound infection, more surgical blood loss and a longer operation time. Being obese is associated with improved long-term survival, validating the obesity paradox. We also found that complication and mortality rates are significantly worse for underweight patients. Our findings suggest that a tendency to regard obesity as a major risk factor in general surgery is not justified. It is the underweight patient who is most at risk of major postoperative complications, including long-term mortality.

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