PULMONARY MECHANICS OF DOGS DURING TRANSTRACHEAL JET VENTILATION

Study objective: To quantify the delivered tidal volume and other sele cted measurements of pulmonary mechanics in an animal model during tra nstracheal jet ventilation (TTJV), with comparison to positive-pressur e mechanical ventilation (PPMV) and spontaneous breathing. Design: Pro spective, nonblinded laboratory animal study. Interventions: Seven mon grel dogs weighing 24.5+/-3.7 kg were anesthetized, paralyzed, and pla ced within a specially designed volume plethysmograph with the head an d neck externalized. Ventilation was performed using TTJV under variab le inspiratory time:expiratory time ratios (T(I):T(E))(1:1, 1:2, 1:3, 1:4, 1.5:2.5, 2:1, 2:2, 3:1, and 4:1) and variable driving air pressur es (40, 45, and 50 psi). The dogs then were ventilated with PPMV. Tida l volume, tracheal pressure, transpulmonary pressure, air flow, arteri al pressure, central venous pressure, and arterial blood gases were me asured during spontaneous ventilation, TTJV, and PPMV. Quasistatic com pliance of the lungs was measured after all methods of ventilation. St atistical signficance was accepted at P < .05. Results: There was no s ignificant difference between delivered tidal volume during TTJV (446/-69 mL at a T(I):T(E) of 1:3 and 45 psi) and spontaneous breathing (5 06+/-72 mL). TTJV delivered a tidal volume significantly higher than t he standard 15 mL/kg volume used for mechanical ventilation in dogs. T racheal pressure and transpulmonary pressure were not significantly di fferent between TTJV and PPMV. Variations in T(I):T(E) had no signific ant effect on most of the measured variables, specifically tidal volum e or transpulmonary pressure. Minute ventilation increased significant ly and Pco2 decreased signficantly as frequency increased during T(I): T(E) settings of 1:1, 1:2, and 2:1. Increases in the driving air press ure during TTJV significantly increased the tidal volume as it was rai sed from 40 psi to 50 psi. There was no change in quasistatic lung com pliance during any method of ventilation. Conclusion: TTJV delivers an effective tidal volume comparable to both spontaneous breathing and P PMV in a dog model. In the absence of upper-airway obstruction, there was no significant difference in the pulmonary pressures, resistance, and compliance during TTJV, as compared to mechanical ventilation. Var iation in T(I):T(E) during TTJV had no major effect on pulmonary mecha nics, except to increase minute ventilation and decrease Pco2 as the f requency was increased significantly. Increasing the driving air press ure to the TTJV apparatus significantly augmented delivered tidal volu me due to increased air flow.