Airway Insufflation: Physiologic Effects on Acute and Chronic Gas Exchange in Humans

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Abstract
Reduction in dead space through conventional tracheostomy has been used to treat patients with chronic CO2 retention. The insufflation of air directly into the trachea by transtracheal catheter (airway insufflation, AI) provides reductions in dead space as great or greater than those of tracheostomy. The physiologic effects of AI on gas exchange have not been adequately studied because instillation of gases into the trachea contaminates minute ventilation (.ovrhdot.VL), dead space volume (VD), tidal volume (VT), and other indices of gas exchange, as measured by usual technics. We overcame this problem by devising special methods of measuring inspired and expired ventilation, alveolar and dead space ventilation, and VT and VD by using pneumotachographic timing of 5 patients with chronic CO2 retention from either COPD, scoliosis, or muscular dystrophy (annual average PaCO2 = 45 to 75 mm Hg) during 75 min of AI with serial gas exchange and arterial blood gas measurements. AI at about 5 L/min of room air through the trachea in 5 patients reduced .ovrhdot.VL by 18% (from 7.91 to 6.48 L/min), VT by 25% (from 450 to 338 ml), and VD by 37% (from 223 to 141 ml), while not affecting PaCO2 (from 51.8 to 48.2 mm Hg) or PaO2 (from 65.1 to 63.4 mm Hg). In 2 patients, AI administered continuously for 4 to 12 months (as 30 to 50% O2) maintained PaCO2 as well as or better than breathing enriched O2 from a tracheal collar via an open tracheostomy. Al also was considered more acceptable because of the availability of continuous speech and an effective cough. Thus, AI is a modality that (1) reduces VD, VT, and .ovrhdot.VL without affecting PaCO2 in the acute state, and (2) maintains or reduces PaCO2, presumably due to reductions in VD, in the chronic state. It may therefore be considered a relatively noninvasive alternative modality for the treatment of respiratory failure.