Ten observational studies were included in the review (196,978 patients). Study sample sizes varied from 518 to 112,616 patients. All results were risk-adjusted for age and gender and most were also adjusted for comorbidity and urgency of operation.
Hospital volume (seven studies): Compared with low-volume providers, there was a statistically significantly lower risk of postoperative mortality with high-volume hospitals (OR 0.55, 95% CI 0.44 to 0.69, I2=50%). Sensitivity analysis indicated no differences with any of the variables studied. Meta-regression did not find a relationship between volume cut-off point and the strength of the relationship. No publication bias was detected.
Surgeon volume (three studies): Compared with low-volume surgeons, there was a statistically significantly lower risk of postoperative mortality with high-volume surgeons in two studies (OR 0.58, 95% CI 0.46 to 0.73, I2=50%). Sensitivity analysis could not be performed due to data limitations.