Epinephrine lowers the serum potassium level through an effect on the β2-receptor. It is therefore difficult to evaluate whether depression of the ST level and the T wave on the electrocardiogram, during regional anaesthesia, is caused by a high plasma epinephrine level, a low serum potassium level, or both. For this purpose, we studied the relation between electrocardiogram and the plasma epinephrine and serum potassium concentrations during 20 intra-abdominal operations performed under combined epidural and general anaesthesia and in 18 subjects receiving intercostal nerve blockade. The results show that the hypokalaemic effect of epinephrine was reduced when the plasma epinephrine concentration exceeded 3 nmol L−1. A multiple regression analysis demonstrated that the ST level and the T-wave amplitude were most consistently affected by a low serum potassium level, while a high plasma epinephrine level correlated only to a depression in the T-wave amplitude. During surgery, only serum potassium correlated with these ECG variables.

Prolonged nerve conduction blockade has been proposed to result from the summed effects of charged and neutral local anaesthetics. Thirty-seven patients were randomly allocated to receive intravenous patient-controlled analgesia alone or combined with intercostal blockade (T7–T11) with a mixture of 0.45% bupivacaine and 0.6% phenol for post-cholecystectomy analgesia. Adequacy of pain relief was measured by patient scores on a 10-cm visual analogue scale and by dose–demand ratio, amounts of loading dose and total consumption of morphine and also the duration of patient-controlled analgesia in each group. No differences were found between groups in post-operative scores, dose–demand ratios and loading doses of morphine. However, in the combined treatment group, a significantly lower total consumption of morphine (P<0.05), associated with a shorter duration of patient-controlled analgesia (P<0.02) and a decreased mean number of unsuccessful demands (P<0.001) were recorded. Intercostal blockade with bupivacaine–phenol supplements intravenous patient-controlled analgesia for post-cholecystectomy pain relief.