Sympathetic activity and haemodynamic variables during spinal analgesia in man

Abstract

At present there is a lack of information concerning haemodynamic changes related to the degree of sympathetic blockade during spinal analgesia. In this investigation, involving 36 patients, changes in haemodynamic parameters were studied in 30 patients receiving spinal analgesia and in six patients having "sham spinal" analgesia. Three local anaesthetic solutions were used: bupivacaine without and with glucose and tetracaine with glucose. Skin conductance responses were used to evaluate changes in provoked sympathetic activity. It was found, as in previous studies, that a complete block of sympathetic activity in the foot was seen in only 60% of patients with an average analgesic level of T4. A partial sympathetic blockade was registered up to and above the level of analgesia. In 25/30 cases only minor alterations in cardiac output, heart rate, stroke volume, mean arterial pressure and systemic vascular resistance were seen in spinal analgesia whose level reached on average T4-5. In five cases in whom analgesia reached T4-3, mean arterial pressure fell greater than or equal to 30% with a well-preserved cardiac output, but with complete sympathetic blockade up to T5 and in two cases also in the hand. Only minor differences were observed between the different anaesthetic solutions.

Vagal and sympathetic activity during spinal analgesia

“…Sympathetic blockade during spinal analgesia, as measured by these, is frequently partial. Our present results confirm those of previous work (2,5). In more caudad dermatomes, skin conductance responses tend to be more depressed.…”

“…The height of pinprick analgesia, especially if above T,, was significantly correlated with hypotension. The association of the T, level with increasing degrees of hypotension has been noted both for pinprick and temperature analgesic levels (5), and during ascent of skin thermal fronts ( 14). In summary, the precise mechanism of severe hypotension occurring during the onset of spinal analgesia remains to be fully explained.…”

“…Recent work has shown that sympathetic blockade induced by spinal analgesia may not be as extensive as previously thought (1)(2)(3)(4). Haemodynamic studies during spinal analgesia, with patients fluid-loaded intravenously before the block, have shown only minor falls in blood pressure, corresponding to a reduction in peripheral vascular resistance with preservation of cardiac output (5). Some patients undergoing spinal analgesia experience more severe hypotension.…”

Bupivacaine spinal anaesthesia

“…Only with complete sympathetic blockade, with an analgesia level of T3-4, were decreases in mean arterial pressure of more than 30% recorded in 5/36 patients. Differences in this respect between plain and hypcrbaric bupivacaine and tetracaine are small (82). However, there are also reports of a greater degree of hypotension associated with hyperbaric than with plain bupivacaine, indicating that the density of the local anaesthetic solution may play a role in blocking sympathetic fibres (8,56).…”

Effects of vagal nerves or vagosympathetic trunks stimulation on the hemodynamics during spinal anesthesia in cats

“…Greene [10] reported that sympathetic nerve block was two segments higher than that of sensory analgesia level, while Chamberlain and Chamberlain [11] reported that the level of sympathetic block is six segments higher than the sensory block. In cases with a higher-level block of pain sensation in normotensive patients, considered complete block of sympathetic nerve resulted in a mean arterial pressure decrease of 30% or 40% [12,13] during spinal anesthesia. Though we could not measure the sensation level, we recorded CSNA directly and compared it with systolic and diastolic blood pressures and heart rate.…”