Sympathetic neural blockade during regional analgesia : Clinical investigations in man

• Different opinions exist concerning the extent and intensi-ty of the concomitant sympathetic block during regional blockade, and how to test the completeness of the sympathetic blockade. Studies were performed on 21 volunteers and 162 patients scheduled for surgery of the urogenital area or surgery for varicose v-eins, and chronic pain patients. The regional blockades used were intrathecal, extradural or stellate ganglion blockade. The skin resistance response method (SRR) was used for recording sympathetic nervous activity in all studies. Laser Doppler flowmetry and skin temperature recordings were used during stellate ganglion blockade, to evaluate changes in skin blood flow and skin temperature. Changes in cardiac output were evaluated by the dye dilution method or thoracic impedance cardiography. Vagal activity was evaluated by recording changes in RR intervals from the electrocardiogram (ECG). Afferent blockade was assessed using the pin-prick method and also somatosensory evoked potentials (SEPs). A partial sympathetic blockade was seen during intrathecal, extradural and stellate ganglion blockade in most cases according to SRR-recordings. The haemodynamic parameters, cardiac output (CO), stroke volume (SV) and systemic vascular resistance (SVR) were well preserved, provided an i. v. pre-load infusion was given before and during onset of intrathecal blockade. There was no evidence of parasympathetic dominance causing hypotension during intrathecal blockade. The SEPs and SRRs were blocked in a similar way. For reliable assessment of sympathetic nerve block, it is necessary to evaluate the effect on both the sudomotor and vasoconstrictor fibres.

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MEDICIN

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