Decrease in serum potassium concentration during epidural anaesthesia

A mean decrease in the arterial serum potassium concentration (S-K) of 0.40 mmol/l (range 0-1.0) was found in 45 elderly men who were studied before and after induction of epidural anaesthesia (using mepivacaine 2% with adrenaline). The decrease was similar in patients who received acetated Ringer solution or dextran 40 in normal saline as intravenous fluid supplementation. No difference in S-K change was found between patients with a normal (less than 115 mumol/l) or elevated serum creatinine concentration. The decrease in S-K prevailed at the end of surgery except in patients with an elevated serum creatinine. Corrections of S-K for changes in arterial blood pH and rectal temperature during induction of anaesthesia did not explain the decrease in S-K. Correlations of clinical parameters such as the extension of anaesthesia, amount of intravenous fluid given and blood pressure changes gave conflicting results. A smaller decrease or no change in S-K was usually seen in arterial (n = 7) and venous (n = 7) samples when no intravenous fluid was given, as well as in venous samples when acetated Ringer solution was given (n = 6).