The Effect of Regional Hypothermia of Neuromuscular Transmission

Hwang, Kyung Ho; Kim, Sung Yell; Bae, Sang Chul; Shin, Hyung Chul; Park, Wook

Abstract

To determine the influence of hypothermia on the neuromuscular transmission, 25 patients were studied during O2-N2O(50%)-enflurane(1-2%) anesthesia without any muscle relaxants. Ventilation was controlled to maintain normocapnia and neuromuscular transmission was monitored by delivering train-of-four(TOF) stimuli to the ulnar nerve at wrist(Accelograph, Biometer) while the circulation to the ipsilateral forearm was occluded by tourniquet for 20 minutes. Regional hypothermia was induced to the isolated arm by intravenous injecton of 20ml normal saline cooled by 10degrees C and by surface cooling with ice pack in 15 patients (hypothermia group). To compare the neuromuscular transmission in hypothermia with 10 patients in normothermia whose temperature were maintained at normothermia by intravenous injection of 20ml normal saline of 36degrees C(normothermia group), TOF response was measured following temperature gone down. The results obtained were as follows. First twitch height of TOF response(T1) was not changed, significantly in normothermia group for 20 minutes. In hypothermia group, T1 was decreased insignificantly until the temperature fell to 32degrees C, but it began to decrease significantly from below 31degrees C as compared to normothermia group, e. g., 82.4+/-31.2/o(p<0.05), 73.1+/-29.6%(p<0.0l), 53.2+/-14.4%(p<0.01), 38.7+/-18.7% (p<0.01), and 35.9+/-16.3%(p<0.01) at 31, 30, 29, 28 and 27C respectively. T4 ratio was not affected in both normothermia and hypothermia groups. In 5 eases of 15 hypothermia patients, we observed transient increase of T, under the moderate hypothermia(35~32degrees C) before markedly diminution of T, under the profound hypothermia(< or =31degrees C)