Effects of arterial carbon dioxide on recovery from rocuronium-induced neuromuscular blockade in anesthetized patients

Background: Respiratory function can be impaired during general anesthesia involving neuromuscular blockers such as rocuronium. However, the magnitude of the problems and the efficacy of their reversal with antagonistic drugs are not known.

Objective: To investigate the effects of arterial carbon dioxide (PaCO₂) on recovery from rocuronium-induced neuromusuclar blockade with or without antagonism by neostigmine.

Methods: Ninety patients were randomly divided into six groups; group I and A, normal PaCO₂ (35-45mmHg), group II and B, low PaCO₂ (30-35mmHg), group III and C, high PaCO₂ (45-50mmHg). The extent of neuromuscular blockade was evaluated by train-of-four (TOF) -watch accelerograph. Anesthesia was induced with intravenous propofol, fentanyl, and rocuronium 0.6mg/kg. Additional injection of rocuronium 0.15mg/kg per time was given whenever the first twitch of TOF (T1) recovered to 25%. The residual neuromuscular blockade was antagonized with neostigmine 0.02mg/kg in the groups I, II and III, when T1 reached 25%. The duration from T1 25% to 75% was recorded and defined as the recovery index and that from T1 25% to TOFR 0.9 was the recovery time.

Results: Both the recovery index and recovery time in group II were much shorter than in group I (p <0.05), while much longer in group III than in group I (p <0.05). No significant differences were found for the comparisons of those of values between groups B and A, or between groups C and A, although they were longer in group C than in group B. A linear relationship was found between the recovery index or recovery time and PaCO₂.

Conclusion: Elevated PaCO₂ prolongs the spontaneous recovery of neuromuscular blockade induced by rocuronium, as well as recovery after small doses of neostigmine, with a linear relationship.