Health status and the preoperative change in serum potassium concentration

When evaluating preanaesthetic abnormal serum potassium (S-K) levels, the anaesthetist often relies upon blood tests performed on admission to hospital 1 or more days prior to surgery. However, the S-K is often altered between admission to hospital and the induction of anaesthesia. In this study, we examined the effects of health status and medication on the preoperative change in S-K concentration in 150 unselected elderly men awaiting urological operations. Oral daily medication was not given preoperatively on the day of surgery. One third of the patients showed a change of 0.4 mmol/l or more (range -1.1 to +1.2), with an increase as common as a decrease. Those on treatment with calcium-channel blockers or diuretics showed an increase in the S-K concentration in the preoperative period, while patients using oral antidiabetics showed a decrease. The use of beta-adrenoceptor antagonists was not a significant predictor of the change in S-K concentration. In conclusion, we found that alterations in serum potassium were common prior to surgery, but only a small fraction of this variance could be accounted for by health status and medication.