Exhalation time effects on arterial and venous blood oxygen content and arterial PCO2 during high frequency jet ventilation of surfactant-depleted cats.

Abstract

Since high frequency jet ventilation (HFJV) relies on lung mechanics for the passive removal of expiratory gas, one would predict that the time allowed for exhalation would have serious effects on cardiopulmonary function. To document these effects we lavaged the lungs of ten cats with 30 ml/kg of saline six times, then sampled arterial and venous blood while the animals were ventilated conventionally at 30 BPM and then with HFJV at 600 BPM, varying inspiratory/expiratory ratios (I/E) from 1:1 to 1:5. The animals breathed 100% O2 throughout the study, and the mean airway pressure was held constant for each animal when the I/E was varied during HFJV. Decreasing the I/E from 1:1 to 1:5 during HFJV resulted in an increase of arterial oxygen content (Cao2) from 11.3 +/- 1.2S E to 13.6 +/- 1.2 ml O2/100 ml blood (P less than 0.01), a decrease of PaCO2 from 43 +/- 6 to 27 +/- 4 mm Hg, and an increase of alveolar to arterial oxygen gradient from 351 +/- 49 to 377 +/- 49 mm Hg. The ratio of systemic blood flow to oxygen consumption (Q/VO2) was similar during conventional ventilation and with HFJV at I/E of 1:1 (18.9 +/- 3.7 vs 18.0 +/- 2.9) but decreased when I/E was reduced to 1:5 during HFJV (13.9 +/- 2.1). The ratio of the product of CaO2 and Q (systemic oxygen availability) to VO2 (SO2 T/VO2) remained unchanged during all modes of ventilation (1.75 +/- 0.15). The increase in CaO2 observed when I/E was reduced from 1:1 to 1:5 during HFJV was counterbalanced by a decrease in Q/VO2 such that SO2 T/VO2 remained relatively constant.