Hyperoxia in mechanically ventilated patients

Introduction

Supplemental oxygen is part of the supportive treatment of hypoxaemic respiratory failure. Prolonged exposure to high fractions of inspired oxygen (FiO₂) has been shown to be injurious to the lung in vitro [1]. The optimal paO₂ in critical illness has not been established but the clinical impression is that patients are frequently exposed to a higher FiO₂ than is necessary. The aim of this study was to investigate current oxygen treatment in patients undergoing prolonged mechanical ventilation and determine whether this resulted in exposure to a higher FiO₂ than that required to adequately oxygenate haemoglobin (SaO₂ >95%).

Methods

Indices of oxygenation were collected for 30 patients requiring mechanical ventilation >2 days. Data were collected 4-hourly for 48 hours. The PaO₂:FiO₂ ratio was determined for each data point and used to model the theoretical FiO₂ required to maintain an SaO₂ of 95% (paO₂ = 10.7 kPa).

Results

The results are shown in Figure 1. Data are expressed as medians (IQR). The median observed FiO₂ was 0.4 throughout the study whereas the median FiO₂, calculated to maintain an SaO₂ of 95%, was 0.3.

Figure 1

abstract

Conclusion

Our data demonstrate that critically ill patients may be exposed to a higher FiO₂ than that required to maintain adequate oxygenation. Further, these results highlight an area of ICU care that has received little study, with no published clinical trials examining the effect of FiO₂ on outcome.