SUSCEPTIBILITY TO UPPER AIRWAY-OBSTRUCTION DURING PARTIAL NEUROMUSCULAR BLOCK

Background Airway obstruction after anesthesia may be caused or exagge rated by residual neuromuscular block, with loss of muscle support for collapsible upper airway structures. Methods: six male volunteers wer e studied before treatment, during stable partial neuromuscular block with vecuronium at a mean train-of-four (TOF) ratio of 50% (95% CI, 36 -61%), and after reversal by neostigmine. Catheter-mounted transducers were placed in the pharynx and esophagus to estimate, respectively, t he upper airway resistance, and the work of breathing (calculated as t he time integral of the inspiratory pressure developed by the respirat ory muscles, esophageal pressure time product) during quiet breathing, during breathing 5% carbon dioxide, and while breathing with an inspi ratory resistor. Breathing with pressure at the airway opening held at pressures from -5 to -40 cm H2O were also tested to assess airway col lapsibility. Results: Although breathing through a resistor increased upper airway resistance from 1.2 (0.67, 1.72) an H2O . 1(-1). s to 2.5 (1.32, 3.38) an H2O . 1(-1). s, and carbon dioxide stimulation reduce d resistance to 0.8 (0.46, 1.33) cm H2O . 1(-1). s, no effect of parti al neuromuscular block (mean TOF ratio, 52%) on upper airway propertie s could be shown. Conclusions Neuromuscular block with a TOF ratio of 50% can be present yet clinically difficult to detect in patients reco vering from anesthesia This degree of block has no effect on airway pa tency in volunteers, even during challenge. Airway obstruction during recovery from anesthesia thus is more likely to be caused by residual effects of general anesthetic agents or centrally acting analgesics, e ither alone or perhaps in concert with residual neuromuscular block.