Oxygen Therapy Delivery and Body Position Effects Measured With Electrical Impedance Tomography.

Abstract

The aim of this prospective randomized crossover study was to compare the short-term effects of high-flow nasal cannula (HFNC) therapy and a 45° head-up tilt to the short-term effects of conventional oxygen (O2) therapy in post-abdominal surgery patients. A total of 18 subjects who were successfully weaned from ventilator support after abdominal surgery were included in the study. The subjects were randomly assigned to 2 groups: conventional O2 was applied in group A for 15 min, and HFNC (60 L/min) was applied in group B for 15 min. A 15-min washout period with conventional O2 was performed before the interventions were switched in both groups. Heart rate, blood pressure, breathing frequency, ratio of arterial partial pressure of oxygen to the fraction of inspired oxygen (PaO2 /FIO2 ), and subject-reported comfort scores were recorded. Changes in end-expiratory lung impedance (EELI) were calculated with electrical impedance tomography. Results are presented as the percent change in lung volume compared to baseline during volume-controlled continuous mandatory ventilation before extubation. HFNC improved EELI in both the ventral (conventional O2 vs HFNC, -48.2% ± 41.0 vs -30.0% ± 40.3, P < .001) and the dorsal (conventional O2 vs HFNC, -37.0% ± 75.9 vs -26.5% ± 68.4, P = .02) regions of the lungs. Subjective subject-reported scores indicated that HFNC was more comfortable than conventional O2 (conventional O2 vs HFNC, 5.8 ± 1.5 vs 6.9 ± 1.9, P = .02). No differences were found in the other examined parameters. A head-up tilt position with conventional O2 improved EELI in the dorsal regions (55.9% ± 100.1, P < .001) but not in the ventral regions (-37.9% ± 43.1%, P = .38) of the lungs compared to HFNC or conventional O2 alone. In post-abdominal surgery subjects who had been extubated, HFNC improved lung volume and patient comfort. A head-up tilt position introduced a heterogeneous increase in EELI in the dorsal regions of the lungs. HFNC therapy may be beneficial in this patient group. (ChiCTR1900020886, http://chictr.org.cn).