EFFECTS OF HIGH-FREQUENCY POSITIVE-PRESSURE VENTILATION (HFPPV) AND GENERAL-ANESTHESIA ON INTRA-PULMONARY GAS-DISTRIBUTION IN PATIENTS UNDERGOING DIAGNOSTIC BRONCHOSCOPY

Abstract

In 9 patients undergoing diagnostic bronchoscopy, intrapulmonary gas distribution was evaluted using N2 washout. The investigations were performed with the patients in the supine position, first awake during spontaneous breathing and then during general anesthesia with high-frequency positive-pressure ventilation (HFPPV) via a pneumatic valve connector. With HFPPV a ventilatory frequency (f) of 60/min and a relative insufflation time (t%) of 22% of the ventilatory cycle were used. Gas distribution in terms of lung clearance index and N2 washout delay improved during HFPPV as compared with spontaneous breathing. Compared with spontaneous breathing and with apnea during general anesthesia, functional residual capacity was increased during HFPPV. During air breathing arterial Po2 (Pao2) and alveolararterial O2 tension differences (D(A-a)o2) were the same during spontaneous breathing and HEPPV, but during O2 breathing Pao2 was lower and D(A-a)o2 higher with HFPPV. Ventilatory volumes set according to a nomogram for the pneumatic valve connector and HFPPV caused moderate hyperventilation. Pao2 could be controlled by adjustment of inspired O2 concentration.