Ventilation and neuromuscular blocking drugs

Ventilatory failure after administration of neuromuscular blocking agents is an important factor in anaesthesia-related perioperative morbidity and mortality. Improved knowledge and new monitoring methods may avoid ventilatory failure caused by incomplete recovery of neuromuscular function in the postoperative period. Central respiratory muscles are less sensitive than, and their time course of neuromuscular block is different from those of, pharyngeal muscles and those of the upper airway. Differences in potency and time course of neuromuscular block may lead to incorrect assessment of ventilatory function during onset and recovery. Even if recovery of the mechanical adductor pollicis train-of-four (TOF) response to a ratio of 0.70 has previously been associated with adequate ventilatory capacity, it is now shown that hypoxic ventilatory responses may be markedly reduced despite adequate respiratory force at a TOF ratio of 0.70. Hence, partial paralysis may interfere with ventilatory regulation in hypoxaemia. Consequently, monitoring neuromuscular function by peripheral nerve stimulation in one muscle yields limited information about total ventilatory capacity, especially the function of the upper airway and ventilatory regulation. Therefore, neuromuscular monitoring should be used with caution during recovery and should always be combined with bedside clinical tests if possible.