Spinal anesthesia and functional sympathetic nerve block

Abstract

By measuring pulse rate (PR), blood pressure (BP), electrical integral skin resistance (SR), and skin surface temperature in different areas, the activity of the sympathetic nerves in spinal anaesthetics of different levels was evaluated. It was found that the sympathetic subsystems for vasomotor and sudomotor activity have their own innervation and that the functionally different effectors also manifest different deficiency reactions in low- and medium-level spinal anaesthesia. Functional sympathetic innervation, however, is unimportant after high sensory spread of spinal anaesthesia. The sympathetic nerves show similar signs of deficiency during administration of centrally acting general anaesthetics. In contrast to these, however, high spinal anaesthesia does not block the vagal component of the autonomic nervous system. The unopposed parasympathetic nerves directly affect the heart and other effectors, which may result in life-threatening cardiovascular reactions with decreases in BP and bradycardia. If high sympathetic blockade is recognized early, such life-threatening situations can be managed successfully. Suitable means of measuring sympathetic activity are the observation of BP, HR, temperature, and particularly SR at the hand. Sympathetic nerve blockade due to spinal anaesthesia first causes a reduction of SR in the lower extremity. In high spinal anaesthesia there is also a loss of sympathetic activity at the hands. Subsequently, hand temperature increases, and finally bradycardia and hypotension occur. The functional reaction of sympathetic activity is indicated by correlation of the vasomotor and sudomotor activities in high and low spinal anaesthesia. Failure of sudomotor activity can be observed on average at least 3 min prior to an increase in acral temperature and 9 min at the hands in cases of high spinal anaesthesia.(ABSTRACT TRUNCATED AT 250 WORDS)