The purpose of this study was to test whether gastric acid suppressants are associated with an increased risk of postoperative pneumonia in patients undergoing elective surgery.

The design used was a population-wide retrospective cohort analysis, and the setting was Canadian acute care hospitals between 1 April 1992 and 31 March 2008. Consecutive patients aged >65 years admitted for an elective operation. Postoperative pneumonia recorded in inpatient postoperative notes.

A total of 593,265 patients were included, of whom about 21% were taking an acid suppressant (most commonly omeprazole or ranitidine). Overall, 6,389 patients developed postoperative pneumonia, with a rate significantly higher for those taking acid suppressants (13 per 1000) than controls (10 per 1000), equivalent to a 30% increase in frequency (odds ratio 1.30 (95% confidence interval 1.23 to 1.38), P<0.001). However, no increase in risk was observed after adjustment for duration of surgery, site of surgery, and other confounders (odds ratio 1.02 (0.96 to 1.09), P=0.48). The general safety of acid suppressants extended to those patients prescribed proton pump inhibitors, experiencing long term treatment, receiving high doses, and undergoing high risk procedures.

After adjustment for patient and surgical characteristics, acid suppressants are not associated with an increased risk of postoperative pneumonia among elderly patients admitted for elective surgery.