Non-invasive ventilation in acute respiratory failure: Effects of modes, obesity and body position

Abstract

Background: Non-invasive ventilation is safely used in the management of acute hypercapnic respiratory failure (AHRF). However, the factors associated with success are unclear. Objective: To compare the effects of BiPAP-S and AVAPS-S modes in patients with AHRF, as well as comparing the presence of obesity and body positioning during therapy on the outcomes. Methods: The prospective randomized study included 62 patients, (33 treated with BiPAP-S, 29 with AVAPS-S). The course of blood gas analysis and differences in measurements of ventilation were compared. Throughout the monitoring period, the patients treated in semi-recumbent and lateral positions at similar time periods, and the effect of changes in positioning was evaluated. Results: No difference was found in the course of PaCO2, pH, HCO3 levels, and length of hospital stay between both modes. There was a mean reduction of 5.7±4.1 mmHg in the PaCO2 levels with the AVAPS-S mode, and of 2.7±2.3 mmHg with the BiPAP-S mode per session (p<0.05). Presence of obesity didn9t make any change on the course of PaCO2 within both modes. No remarkable effect of body positioning was observed within both modes. Conclusion: Although the decrease in the PaCO2 levels with the AVAPS-S mode per session was remarkably high, the course was similar with both modes. Furthermore, obesity and body positioning had no prominent effect on the PaCO2 response and ventilator mechanics.