Adrenaline, cyclic AMP and potassium during general anaesthesia with and without epidural analgesia

Twenty patients undergoing abdominal surgery under general anaesthesia were studied to determine whether beta 2-adrenergic receptor sensitivity and adrenaline-induced hypokalaemia are related to preceding adrenergic stress. Half of the patients were given epidural analgesia with bupivacaine-adrenaline before starting surgery and then a booster dose after 60 min of surgery. The others were given only the epidural dose of bupivacaine-adrenaline at 60 min. Despite marked increases in the plasma adrenaline concentration after the intra-operative epidural dose, there was no decrease in the serum potassium concentration in either group. In the patients who received only the 60 min dose, the plasma adrenaline concentrations increased more, but the plasma level of cyclic AMP (a marker for beta 2-stimulation) increased similarly, which suggests that beta 2-adrenoceptor responsiveness was somewhat reduced. After the intraoperative bupivacaine-adrenaline, the T wave amplitude decreased, but neither U waves nor tachycardia developed. In conclusion, adrenergic stimulation during surgery does not decrease the serum potassium concentration, regardless of whether the surgical stress response has been modified by epidural analgesia. This lack of a hypokalaemic effect might be partly due to reduced responsiveness of beta 2-adrenoceptors to adrenaline.