Translaryngeal jet ventilation and end-tidal PCO2 monitoring during varying degrees of upper airway obstruction.

STUDY OBJECTIVES

To explore the ventilatory adequacy of translaryngeal jet ventilation (TLJV) during partial upper airway obstruction and the usefulness of monitoring end-tidal CO2 (PETCO2) during this condition.

DESIGN

Prospective, nonrandomized, sequential crossover design.

SETTING AND PARTICIPANTS

Apneic dog model (five dogs; mean weight, 23 kg).

INTERVENTIONS

Animals were intubated with a 9.0-mm endotracheal tube with the tip positioned above the cricothyroid membrane. Upper airway obstructions of 40%, 69%, and 80% were created. TLJV was performed through the cricothyroid membrane using a 13-gauge catheter with 100% oxygen, 45 psi, 15 breaths per minute, and 30% inspiratory time for 15 minutes at each upper airway obstruction. Data collected at baseline (no upper airway obstruction) and one-minute intervals included arterial blood pressures, continuous PaCO2 measurements, and PETCO2 at the TLJV catheter tip and above the level of obstruction. Arterial blood gases were obtained at 0 and 15 minutes. Data were analyzed using Pearson's correlation, analysis of variance, and Turkey's multiple comparisons (significance, P less than .05).

MEASUREMENTS AND RESULTS

Baseline values for all variables did not significantly differ at the onset of each testing phase. Mean pH increased significantly from baseline during 69% upper airway obstruction (7.36 to 7.54, P less than .05) and 80% upper airway obstruction (7.39 to 7.61, P less than .01). Mean PaCO2 decreased significantly from baseline during all upper airway obstructions: 40% upper airway obstruction (39.9 to 33.6 mm Hg, P less than .01), 69% upper airway obstruction (38.3 to 25.6 mm Hg, P less than .001), and 80% upper airway obstruction (36.2 to 18.2 mm Hg, P less than .001). PaCO2, PETCO2, and pH differed significantly between each level of upper airway obstruction (P less than .01). PETCO2 was significantly correlated with PaCO2 (r = .84, P less than .001) and did not significantly differ from PaCO2. No signs of barotrauma were observed in any animal at any degree of upper airway obstruction.

CONCLUSION

TLJV during partial upper airway obstruction in our model provided safe and adequate-to-supranormal minute ventilation. In fact, marked hypocapnia and alkalemia occurred at levels of 69% and 80% upper airway obstruction, thus dispelling concepts that TLJV may cause hypercapnia during partial upper airway obstruction. PETCO2 correlates well with PaCO2 and may be valuable for monitoring ventilation when using TLJV in the nonobstructed or partially obstructed upper airway.