'Alveolar recruitment strategy' improves arterial oxygenation after cardiopulmonary bypass

Introduction

Atelectasis occurs during general anaesthesia [1]. During cardiopulmonary bypass, this atelectasis is exacerbated by the physical collapse of the lungs. As a result, poor arterial oxygenation is often seen post-operatively. Studies using an alveolar recruitment strategy have improved oxygenation after non-cardiac surgery [2].

Methods

We tested the effect of an 'alveolar recruitment strategy' on arterial oxygenation in a prospective, randomised, controlled study of 78 patients undergoing cardiopulmonary bypass. Divided equally into three groups of 26, Group 'No PEEP' received standard post bypass manual lung inflation, and no PEEP applied until on ICU. Group '5 PEEP' received standard post bypass manual inflation, and then 5 cmH₂O PEEP applied and maintained until extubation on ICU. The third group 'treatment group', received a pressure controlled stepwise increase in PEEP up to 15 cmH₂O and tidal volumes of 18 ml/kg or a peak inspiratory pressure of 40 cmH₂O was reached. This was maintained for 10 cycles, and the PEEP of 5 cmH₂O was maintained until extubation on ICU. Arterial blood samples were analysed at 30 min post induction of anaesthesia, and then at 30 min, 1, 2 and 6 hours post bypass. The length of ICU stay, hospital stay and incidence of chest infections was recorded.

Results

In both the zero PEEP and 5 PEEP groups there was a decrease in arterial oxygenation at 30 min post bypass (mean decrease of 15.5 and 15.0 respectively), however in the treatment group there was an increase in oxygenation compared to baseline at 30 min (mean increase of 1.9). The difference between the treatment group and the other two control groups was very significant at 30 min with P < 0.001. At 1 h post bypass the difference was significant at P = 0.002 for the no PEEP group and P = 0.04 for the 5 PEEP group (Fig. 1). No significant difference was found between the two control groups. At 2 and 6 hours post bypass there was not a significant difference between the three groups. There was no significant difference in ICU stay, hospital stay or incidence postoperative chest infections. No complications due to the alveolar manoeuvre occurred.

Figure 1

Conclusions

We conclude that the application of an alveolar recruitment strategy improves arterial oxygenation up to one hour after cardiopulmonary bypass surgery. We hypothesize that this improvement is lost after one hour due to routine ICU nursing care which includes open circuit suctioning and disconnections from the ventilator thus removing the PEEP. This would allow atelectasis to reoccur. The results of this study suggest that the early impairment of gas exchange that occurs postoperatively in cardiac surgery can be reversed, thus allowing for earlier extubation.