The role of ischaemia in the analgesia which follows Bier's block technique.
The effect of 30-min tourniquet ischaemia (Bier's block) on the antidromic homolateral left median nerve sensory potential (SP) and on the bilateral sympathetic skin response (SSR) was studied in 6 healthy volunteers. The SSR was provoked both acoustically and by electrical stimulation of the median nerve; the latter stimulus was also used to provoke the SP. After 28 min of tourniquet ischaemia, the electrical stimulus failed to provoke the SP and bilateral SSR, indicating blockade of the afferent limb of the reflex. The acoustic SSR was unaffected by ischaemia, and thus the efferent limb of the SSR was not blocked, indicating that ischaemia does not affect the post-ganglionic efferent C fibres. These findings confirm that 30 min of ischaemia blocks A beta afferent fibres but does not block efferent C fibres. Thus the analgesia following Bier's block alone, in some patients with sympathetically maintained pain, most likely results from the ischaemic blockade of sensory A beta fibres, confirmed both acoustically and by electrical stimulation of the median nerve.
Casale
Roberto
R
Service of Neurophysiology, Rehabilitation Center of Montescano, IRCCS, Fond. Clinica del Lavoro, PaviaItaly Oxford Regional Pain Relief Unit, Churchill Hospital, and The Nuffield Department of Anaesthetics, University of Oxford, Radcliffe Infirmary, Oxford OX3 7LJ UK.
Glynn
Chris
C
Buonocore
Michelangelo
M
D000161:Acoustic Stimulation; D000320:Adrenergic Fibers / Q000502:physiology; D000328:Adult; D004558:Electric Stimulation; D004562:Electrocardiography; D005073:Evoked Potentials, Somatosensory / Q000502:physiology; D005260:Female; D006339:Heart Rate / Q000502:physiology; D006801:Humans; D007511:Ischemia / Q000503:physiopathology*; D008297:Male; D008475:Median Nerve / Q000502:physiology*; D009407:Nerve Block; D010991:Plethysmography; D012684:Sensory Thresholds; D012867:Skin / Q000294:innervation*; D012879:Skin Physiological Phenomena; D013564:Sympathetic Nervous System / Q000502:physiology*