[The effect of hypothermia and methoxyflurane-anaesthesia on sympatho-neuronal and sympatho-adrenal activity in the course of cardiac surgery (author's transl)].

The concentrations of adrenaline and noradrenaline, and dopamine-beta-hydroxylase in the plasma, and certain haemodynamic parameters, were determined in 14 children undergoing surgical correction of congenital cardiac defects under hypothermia at 30 degrees C and methoxyflurane anaesthesia. During the pre-operative phase of hypothermia at 30 degrees C, the adrenaline levels rose to about 300% of the inital levels, and the noradrenaline levels to about 200%. During the postoperative phase of re-warming at 34 degrees C, a further dysregulative release of catecholamines led to an increase in adrenaline levels to a critical concentration of about 800% of the norm, and in noradrenaline levels of about 400% of the norm. No change was seen in dopamine-beta-hydroxylase activity. Hypothermia thus results in a massive activation of the sympatho-neuronal and sympatho-adrenal systems, which is not prevented by methoxyflurane anaesthesia, and which may endanger the recently operated heart, particularly during the early post-operative period, because of the increased oxygen requirements imposed on the myocardium. In normothermia, on the other hand, methoxyflurane anaesthesia results in only a slight degree of activation of the sympathetic nervous system, which increased only slightly during the post-operative period. Under these conditions, the plasma dopamine-beta-hydroxylase activity remains unchanged. Unlike the changes in plasma catecholamine levels, dopamine-beta-hydroxylase activity cannot be regarded as an index of changes in sympatho-neuronal activity.