Respiratory effects of pharingeal gas insufflation in patients with chronic obstructive pulmonary disease.

Objective: To evaluate the effects of pharyngeal gas insufflation (PGI) in clinically stable patients with chronic obstructive pulmonary disease (COPD).

Design: Prospective study in humans.

Setting: Department of Intensive Care Medicine at a University Hospital.

Patients: Seven clinically stable COPD patients.

Intervention: Pharyngeal dry fresh air insufflation (PGI) with a continuous flow rate of 4 L/min was given via a nasal catheter placed into the oropharynx. Baseline measurements with zero flow were made at the beginning and end of the test. After an equilibration period of 1 h at each stage, arterial blood samples were analyzed every 5 min until PaCO2 variation less than 5% confirmed the achievement of a steady state. Thereafter expiratory flow signal and expiratory gas were collected over a period of 3 min and arterial blood was sampled after 1'30" and 2'30" from the beginning of the test for the measurement of effective expiratory volume (VE eff), respiratory rate (RR), tidal volume (VT), dead space fraction (VD/VT), dead space (VD), alveolar ventilation (VA), total expiratory time (TE min), and PaCO2, respectively.

Results: During PGI VT, VD/VT, VD and VE eff fell significantly from baseline values, RR was slightly reduced and VA, TE min and PaCO2 remained unchanged throughout the study.

Conclusions: Although in our study the effect of PGI on VD could be overestimated since our device for expiratory gas flow measurement and collection significantly enlarged the anatomical dead space receiving the washout effect of the fresh gas insufflation, under the experimental conditions PGI produces a reduction in VD and VD/VT, and, as a consequence, a significative reduction in respiratory requirements in clinically stable COPD patients. If confirmed in clinical settings, potential advantages of PGI could include: a) reduction of the work of breathing in patients with intact neuro-respiratory coupling; b) minimizing hypercapnic side effects of oxygen therapy often seen in COPD patients.