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Resistance to Breathing in Healthy Subjects following Endotracheal Intubation under Topical Anesthesia

Thomas J. Gal, MD^*, and Paul M. Suratt, MD

*Assistant Professor, Anesthesiology. Department of Anesthesiology and the Pulmonary Division, Department of Internal Medicine, University of Virginia Medical Center, Charlottesville, Virginia 22908. Assistant Professor, Internal Medicine. Department of Anesthesiology and the Pulmonary Division, Department of Internal Medicine, University of Virginia Medical Center, Charlottesville, Virginia 22908.

Abstract

To identify possible airway constriction following endotracheal intubation under topical anesthesia, airway resistance (Raw) and specific conductance (sGaw) were measured with a body plethysmograph in six awake, healthy, nonsmoking men aged 23 to 29. Subjects were studied while breathing under four conditions: (1) through a large bore mouthpiece (control); (2) through an 8.0-mm internal diameter 25-cm long endotracheal tube held externally (external resistance); (3) while intubated with an identical endotracheal tube; and (4) following extubation as they again breathed through the mouthpiece. To determine the effect of the lidocaine aerosol used for topical anesthesia prior to intubation, Raw was measured in six additional subjects before and after the upper airway had been topically anesthetized. Topical anesthesia produced no significant change in Raw or sGaw in these subjects. In subjects whose tracheas were intubated the mean values of Raw (in cm H₂O/L/sec) and sGaw (in L/sec/cm H₂O/L) in each of the four above conditions were: control, 0.99, 0.30; external resistance, 2.34, 0.13; intubation, 2.75, 0.11; and following extubation, 1.00 and 0.30. The increase in Raw and decrease in sGaw during tracheal intubation were significantly greater than the changes noted with subjects breathing through the tube as an external resistance (p < 0.01). Tracheal intubation increased residual volume and decreased vital capacity but did not alter functional residual capacity or total lung capacity. We conclude that tracheal intubation under topical anesthesia increases airway resistance more than the resistance produced by the addition of the tube to the control airway. This additional resistance reflects reflex narrowing of airways distal to the tube, which may be more severe in patients whose airways are not anesthetized.

Key Words: AIRWAY • Resistance; INTUBATION • Endotracheal: airway resistance.

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