EFFECT OF NEOSTIGMINE AT DIFFERENT LEVELS OF MIVACURIUM-INDUCED NEUROMUSCULAR BLOCKADE

The effectiveness of neostigmine 40 mu g/kg for antagonism of two diff erent levels of neuromuscular blockade, induced by a bolus dose of miv acurium 0.15 mg/kg. was studied in 45 patients. The patients were anae sthetized with thiopentone, fentanyl, nitrous oxide in oxygen, and enf lurane. Neostigmine was administered at either 10% recovery of the twi tch height (TH10) at the adductor pollicis muscle (n=14) or upon reapp earance of the first response at the orbicularis oculi muscle (OO1) af ter train-of-four (TOF) stimulation (n=16), the latter representing a deeper degree of neuromuscular blockade. Fifteen of the 45 patients di d not receive neostigmine (control group). Neostigmine administration at OO1 rather than at TH10 at the adductor pollicis muscle caused reve rsal of neuromuscular blockade to occur 8 min earlier and shortened th e time to reach 25% recovery of the twitch height (TH25) at the adduct or pollicis muscle by about 5 min, compared with the control group. Ho wever, the time needed to reach a T4/T1 ratio greater than or equal to 0.8 was similar in both the early and late neostigmine administration groups, being 9 min faster than in the control group. It can be concl uded that there is no advantage in administering neostigmine al profou nd neuromuscular blockade to achieve clinically adequate recovery (T4/ T1 ratio greater than or equal to 0.8). However, the time between inje ction of mivacurium and TH25 may be shortened by using neostigmine at profound neuromuscular blockade, a procedure which may be useful in ca se of unpredictably difficult intubation, since diaphragmatic movement s usually reappear at TH25.