Recovery of Airway Protection Compared with Ventilation in Humans after Paralysis with Curare

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Abstract
D-Tubocurarine (dTc) was administered intravenously to six healthy unanesthetized volunteers to assess the sensitivity to neuromuscular blockade of those muscles involved in protecting the airway against obstruction and/or aspiration relative to the muscles of inspiration. Each subject was given an intravenous bolus of dTc followed by an infusion to allow three different levels of inspiratory muscle weakness as measured by maximum inspiratory pressure (MIP). Levels of MIP were control (-90 cm H2O), -60, -40, and -20 cm H2O. Vital capacity (VC), hand grip strength (HGS), and end-tidal CO2 (PETCO2) were obtained at each level. At each level of weakness and at intermediate values during recovery, nuscles of airway protection were functionally assessed by noting the MIP at which the maneuver could be accomplished and the MIP at which they could not. The mean of these two values was calculated for each subject. The tests were: 1) ability to swallow, 2) ability to perform a valsalve maneuver, 3) prevent obstruction of the airway, and 4) ability to approximate teeth. These were compared with head lift and straight leg raising. At maximum neuromuscular blockade (MIP of -20 cm H2O), VC was 2.0 liters, HGs was 0, and PETCO2) was normal. Muscles of airway protection were still incapacitated. Swallowing returned above MIP of -43 cm H2O, approximation of teeth above -42 cm H2O, airway obstruction above -39 cm H2O, and valsalva above -33 cm H2O. Thus, although ventilation may be adequate at MIP = 25 mmHg, the muscles of airway protection are still nonfunctional. Further reversal of neuromuscular blockade must be accomplished before a patient whose trachea is estubated can protect the airway. All subjects who could accomplish a head lift could perform the airway protective maneuvers.

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