High-Frequency Oscillatory Ventilation in Adults: HFOV Weaning and Transition to CV
Thirty-two patients (20.5%) had a pulmonary artery catheter during HFOV. At baseline, patients with a pulmonary artery catheter did not differ from those without a PA catheter with regard to age, acute physiology and chronic health evaluation (APACHE) II score, LIS, Fio2, Pao2/Fio2 ratio, OI, Paco2, ventilator pressures, or ventilator days prior to HFOV. Central venous pressure (CVP) increased immediately after starting therapy with HFOV and remained higher than the value during CV throughout the 72 h (p = 0.01) [Fig 2, bottom, B]. Pulmonary artery occlusion pressure (PAOP) was significantly greater than the baseline value at 3 h after initiation of HFOV (p = 0.03) and 6 h after initiation of HFOV (p = 0.03), but the difference did not persist beyond 6 h. Cardiac output (CO) decreased significantly immediately after starting therapy with HFOV and remained lower than the baseline value throughout the study (p = 0.0043), but it was within the normal range.
Seventy-seven patients (48.7%) improved with HFOV and were successfully weaned to CV after 6.1 ± 5.5 days. Only 33% of these patients died, but they averaged 23.3 ± 21.2 days of therapy with HFOV and CV. From HFOV initiation until transition to CV, there were small changes in the mean pressure amplitude of oscillation (ie, 71 ± 17 to 65 ± 16 cm H2O; p = 0.002) and frequency (4.7 ± 1.0 to 5.2 ± 1.8 Hz; p = 0.048). mPaw declined from 30.8 ± 5.7 cm H2O on HFOV initiation to 23.9 ± 5.3 prior to transition to CV (p < 0.0001), to 21.0 ± 4.6 immediately following the transition to CV (p < 0.0001 [compared with pretransition mPaw]). There were no significant changes in gas exchange or hemodynamics with the transition to CV.
Fourty-one patients (26%) had therapy with HFOV discontinued due to difficulties with oxygenation, ventilation, or hemodynamics. Their median duration of HFOV was 18.6 h (range, 0 to 668 h), Nineteen of these patients (12%) had therapy with HFOV discontinued within 4 h. Compared with other patients, these 19 had lower baseline pH values (7.19}± 0.13 vs 7.29 ± 0.11, respectively; p =.001), higher baseline OI (37.8 ± 15.8 vs 30.3 ± 0.13, respectively; p = 0.03), and higher mortality rate (90% vs 57%, respectively; p = 0.11).