Study objectives: Transtracheal insufflation of oxygen-enriched air at a high flow rate has been proposed to support ventilation. The purpose of this study was to investigate the physiologic effects of high-flow insufflation unobtrusively with a respiratory inductive plethysmograph in patients with chronic respiratory failure. Using a respiratory inductive plethysmograph also permitted monitoring of end-expiratory lung volume, and respiratory variables could be quantified independently of the tracheal bias flow.
Design: Prospective randomized comparison of low-flow vs high-flow transtracheal insufflation.
Setting: Pulmonary division of a tertiary teaching hospital.
Patients: Fourteen spontaneously breathing outpatients with chronic hypoxemic respiratory failure carrying a transtracheal catheter for long-term oxygen therapy.
Interventions and measurements: Oxygen-enriched air (fraction of inspired oxygen, 0.37) at 15 L/min and oxygen at 1.5 L/min were transtracheally administered for 1 h each. The breathing pattern and the end-expiratory lung volume were monitored by inductive plethysmography along with pulse oximetry and transcutaneous Pco2. Arterial blood gases were also analyzed at the end of the hour of both low-flow and high-flow insufflation.
Results: High-flow insufflation decreased the mean (± SEM) minute ventilation (V̇e) by 20% from 8.37 ± 0.49 to 6.66 ± 0.57 L/min, the mean respiratory rate from 19.2 ± 0.9 to 15.7 ± 1.0 breaths/min, while mean expiratory time increased from 2.0 ± 0.1 to 2.8 ± 0.2 s, and end-expiratory lung volume decreased by 0.55 ± 0.15 L compared to low-flow oxygen insufflation (p < 0.05 for all comparisons). Mean arterial and transcutaneous Pco2 decreased from 45 ± 1 to 43 ± 1 mm Hg and from 54 ± 2 to 53 ± 2 mm Hg, respectively (p < 0.05 in both instances), while arterial Pao2 and oxygen saturation did not change.
Conclusions: High-flow transtracheal insufflation of oxygen-enriched air assists ventilation by reducing V̇e without compromising gas exchange and by reducing end-expiratory lung volume, possibly through the reversal of dynamic hyperinflation.