Dallas, TX - Increased body mass index (BMI) isn't a significant risk factor for in-hospital mortality after coronary artery bypass graft (CABG) surgery, but "underweight" patients seem to have the highest risk while somewhat "overweight" patients may fare the best, according to a multivariate analysis of a large CABG database [1].

"Thus, when [patients are] undergoing the physical insult of surgery, a little extra fat may be a protective factor," write Dr Ruyun Jin (Providence Health System, Portland, OR) and colleagues in a report published online June 20, 2005 in Circulation. "However, one must consider that in general, and especially after a CABG procedure, there is a negative effect on overall health, particularly coronary health, associated with being over one's ideal body weight." The report is scheduled to appear in the journal's June 28, 2005 issue.

In the group's analysis of 16 218 patients who had undergone isolated CABG at nine affiliated hospitals, those with BMIs ranging from about 23 kg/m² to 30 kg/m² had a lower mortality compared with other patients. "After adjustment for other risk factors, there appears to be some unexplained risk of mortality in the underweight and obese subgroups compared with the middle BMI subgroups," they write.

Parameter	Underweight	Normal	Overweight	Mild obesity	Moderate obesity	Extreme obesity
Defining BMI range (kg/m2)	<18.5	18.5-24.9	25-29.9	30-34.9	35-39.9	40
Proportion of group (%)	0.6	21.4	41.2	24.3	8.6	3.9
Mean BMI (kg/m2)	17.2	23.0	27.5	32.1	37.0	44.0
In-hospital mortality (%)	7.8	3.1	1.9	2.0	1.8	1.9
Unadjusted mortality OR (95% CI)	2.63 (1.19-5.82)	1.00	0.61 (0.47-0.80)	0.64 (0.47-0.85)	0.57 (0.37-0.88)	0.61 (0.33-1.11)
Adjusted* mortality OR (95% CI)	1.87 (0.79-4.42)	1.00	0.91 (0.73-1.28)	1.25 (0.90-1.72)	1.14 (0.73-1.87)	1.23 (0.69-2.55)

Risks typically associated with BMI "are based on longevity and health in general," coauthor Dr Gary L Grunkemeier (Providence Health System) told heartwire. But such risks might not relate to surgery in the same way. "You might not want to be overweight to live as long as you possibly can, but being a little overweight does not hurt, at all, your chances of surviving something as traumatic as cardiac surgery."

Because relationships between BMI groupings and in-hospital mortality ultimately weren't independently significant, one of the study's messages is that obesity probably shouldn't be—as it is sometimes viewed—a contraindication to CABG, Grunkemeier said.

Another message may be that clinicians should "pay more attention to underweight patients postoperatively," Jin said to heartwire, observing them more closely and, as needed, intervening more aggressively.

Although the report did not discuss biological mechanisms that might be behind any protective effect in patients who are moderately overweight, Jin and Grunkemeier proposed one possibility when interviewed. Surgery in such patients, they said, might induce a metabolic state of emergency, like a "starvation response," that promotes healing by boosting glucose production.