Cough threshold after upper abdominal surgery.

The effect of upper abdominal surgery under general anaesthesia on the cough threshold was studied in 26 patients, on the basis of the concentrations of capsaicin and citric acid causing cough. Cough threshold was determined after administering doubling doses of nebulised aerosols of capsaicin and citric acid before operation and on the first and fourth postoperative days. There was an increase in cough threshold (decrease in cough sensitivity) in response to both inhaled irritants on the first postoperative day from the preoperative day and a return towards preoperative values by the fourth day after surgery. The increase in cough threshold on the first postoperative day correlated with the time since opiate administration (r = 0.7 for capsaicin, 0.52 for citric acid). These results show that the threshold concentration of chemical irritants causing cough is increased on the first postoperative day after upper abdominal surgery.