Effects of high-frequency positive-pressure ventilation (HFPPV) and general anesthesia on intrapulmonary gas...

In nine patients undergoing diagnostic bronchoscopy, intrapulmonary gas distribution was evaluated by means of nitrogen 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 nitrogen washout delay improved during HFPPV as compared with spontaneous breathing. Compared with spontaneous breathing and also with apnea during general anesthesia, functional residual capacity was increased during HFPPV. During air breathing arterial PO2 (PaO2) and alveolararterial oxygen tension differences (D(A-a)O2) were the same during spontaneous breathing and HFPPV, but during oxygen 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 resulted in moderate hyperventilation. PaO2 could be controlled by adjustment of inspired oxygen concentration.