TRACHEAL GAS INSUFFLATION IMPROVES VENTILATORY EFFICIENCY DURING METHACHOLINE-INDUCED BRONCHOSPASM

Introduction: Barotrauma and cardiovascular insufficiency are frequent ly encountered problems in patients with acute bronchospastic disease who require mechanical ventilation. Permissive hypercapnia is a recogn ized strategy for minimizing these adverse effects; however, it has po tential risks. Tracheal gas insufflation (TGI) has been shown to incre ase carbon dioxide elimination efficiency and thus could permit mechan ical ventilation at lower peak airway pressures without inducing hyper capnia. However, caution exists as to the impact of TGI on lung volume s, given that expiratory flow limitation is a hallmark of bronchospast ic disease. Purpose: To examine these issues, we studied ventilatory a nd hemodynamic effects of continuous TGI as an adjunct to mechanical v entilation before and after methacholine-induced bronchospasm. Materia ls and Methods: Ten anesthetized, paralyzed dogs were ventilated on vo lume-controlled mechanical ventilation during administration of contin uous TGI (0, 2, 6, and 10 L/min) while total inspired minute ventilati on (ventilator-derived minute ventilation plus TGI) was kept constant. In an additional step, with TGI flow of 10 L/min, total inspired minu te ventilation was decreased by 30%. Results: PaCO2 decreased (44 +/- 7 mm Hg at zero flow to 34 +/- 7 mm Hg at 6 L/min and 31 +/- 6 mm Hg a t 10 L/min, respectively, P < .05), as did the dead space to tidal vol ume ratio at TGI of 6 and 10 L/min compared with zero flow. There were no significant changes in end-expiratory transpulmonary pressure, mea n arterial pressure, or cardiac output. During the highest TGI flow (1 0 L/min), with a 30% reduction of total inspired minute ventilation, b oth PaCO2 and peak airway pressure remained less than during zero flow conditions. Conclusion: We conclude that TGI increases carbon dioxide elimination efficiency during constant and decreased minute ventilati on conditions without any evidence of hyperinflation or hemodynamic in stability during methacholine-induced bronchospasm. Copyright (C) 1997 by W.B. Saunders Company.