LOCALIZED HYPOTHERMIA INFLUENCES ASSESSMENT OF RECOVERY FROM VECURONIUM NEUROMUSCULAR BLOCKADE

The purpose of this study was to determine the extent to which localiz ed hypothermia of a monitored extremity alters the assessment of recov ery from vecuronium-induced neuromuscular blockade. Bilateral integrat ed evoked electromy ographic (IEMG) responses were measured in the uln ar distribution of 14 anaesthetized patients who had differing upper e xtremity temperatures as measured at the adductor pollicis to determin e whether localized hypothermia alters the clinical assessment of spon taneous recovery from vecuronium-induced neuromuscular blockade. All p atients received general anaesthesia with thiopentone, N2O/O-2 and opi oid 11/14 patients received isoflurane for blood pressure control. Bil ateral adductor pollicis oesophageal and ambient temperatures, and IEM G evoked response (t(1)) expressed as percent unparalyzed control were recorded during the anaesthetic. The difference in evoked response be tween the warmer and the colder upper extremity was calculated at 25%, 50% and 75% spontaneous recovery from neuromuscular blockade in the w arm extremity. Differences in temperature between extremities ranged f rom 0.2-11 degrees C. The difference in IEMG-evoked response between e xtremities war; proportional to the difference in temperature, and the re was a direct correlation (r = 0.78) between IEMG response and extre mity temperature; IEMG response was absent when extremity temperature was less than 25 degrees C. We concluded that localized hypothermia in the monitored extremity decreases the IEMG-evoked response to vecuron ium neuromuscular blockade; the greater the temperature decrease, the less the evoked response. Thus, the administration of nondepolarizing relaxants may be inappropriately influenced by monitoring neuromuscula r blockade in a cold extremity, especially if its temperature is <25 d egrees C.