Effects of non-invasive mechanical ventilation on hemodynamic and gas exchanges parameters after cardiac surgery in patients with 300 >PaO₂/FiO₂ >150

Introduction

Non-invasive mechanical ventilation (NIV) has been used in hypoxic postoperative cardiac patients but more studies are necessary to clarify its respiratory and hemodynamic effects. Therefore, our objective was to study its effects in the oxygenation index (PaO₂/FiO₂) and in hemodynamic variables in this group of patients.

Methods

This is a randomized trial in which all postoperative cardiac patients having a pulmonary artery catheter and showing a PaO₂/FiO₂ between 150 and 300 (with FiO₂ 0.31), 1 hour after extubation, were included. The intervention group used NIV with a bilevel positive airway pressure (an inspiratory pressure to generate a tidal volume of 6 ml/kg and an expiratory pressure of 7 cmH₂O) with FiO₂ 0.4 during 3 hours. The control group used oxygen by Venturi mask in order to keep good oxygenation. In both groups, measurements were done in a basal situation (FiO₂ 0.31), in the first hour after beginning the treatment (FiO₂ 0.4) and 1 hour after the end of the intervention (FiO₂ 0.31). Variables studied included: pH, PaO₂, PaCO₂ and PaO₂/FiO₂ ratio, heart rate (HR), mean arterial pressure (MAP), pulmonary capillary wedge pressure (PCWP), central venous pressure (CVP), mean pulmonary arterial pressure (MPAP) and cardiac output (CO).

Results

Forty-two patients were included in the study period. The mean age was 65.7 ± 10 years. The basal variables were similar in the two groups. There was an increase in the PaO₂/FiO₂ ratio in the NIV group in the first hour (P < 0.05, 95% CI 74.8 to 6.6) and 1 hour after stopping the treatment (P < 0.05, 95% CI 90.7 to 10.8) compared with the control group. There were no significant changes in hemodynamic parameters, pH and PaCO₂ during NIV compared with the control group.

Conclusions

There were no changes in hemodynamic variables during the NIV period. However, these results suggest that NIV improved oxygenation even 1 hour after stopping the treatment.