Effect of hypocarbia and hypercarbia on the antagonism of pancuronium-induced neuromuscular blockade with neostigmine in man.

The effects of variations in carbon dioxide concentration on the antagonism of pancuronium-induced neuromuscular block by neostigmine were studied in 21 patients: normocarbia (PE'CO2 5.4%, PaCO2 4.93 kPa, n = 7), hypocarbia (PE'CO2 3.6%, PaCO2 3.30 kPa, n = 7) and hypercarbia (PE'CO2 7.5%, PaCO2 7.13 kPa, n = 7). Mechanical and electromyographic responses to ulnar nerve stimulation (0.1 Hz and 2 Hz) were recorded. A 90% block during nitrous oxide in oxygen anaesthesia was maintained by incremental single injections of pancuronium and reversed with neostigmine 0.35 mg kg-1 with atropine 0.0175 mg kg-1. The recovery of twitch tension up to 50% was similar in all groups but thereafter slower in the hypercarbia group. The recovery times from 25% to 75% twitch tension correlated with PaCO2 (r = 0.55, P less than 0.05). A residual block of about 10% was seen in hypercarbic patients. However, the recovery of e.m.g. amplitude and train-of-four ratios was similar in all groups. Thus, the impaired recovery of twitch tension seems to be the result of depressed contractility rather than failure of neuromuscular transmission.