Continuous measurement of arterial oxygenation in mechanically ventilated horses.

Abstract

BACKGROUND: The possibility of accurately and continuously measuring arterial oxygen partial pressure (PaO) in horses may facilitate the management of hypoxaemia during general anaesthesia. OBJECTIVES: The aim of this study was to evaluate the ability of a novel fibreoptic sensor to measure PaO(PaO) continuously and in real time in horses undergoing ventilatory manoeuvres during general anaesthesia. STUDY DESIGN: In vivo experimental study. METHODS: Six adult healthy horses were anaesthetised and mechanically ventilated in dorsal recumbency. A fibreoptic sensor was placed in one of the facial arteries through a catheter to continuously measure and record PaO. After an alveolar recruitment manoeuvre, a decremental positive end-expiratory pressure (PEEP) titration using 20-minute steps of 5&#xa0;cm&#xa0;HO from 20 to 0&#xa0;cm&#xa0;HO was performed. An arterial blood sample was collected at 15&#xa0;minutes of ventilation at each PEEP level for PaOmeasurement using an automated blood gas machine (PaO). The agreement between PaOand PaOwas assessed by Pearson's correlation, Bland-Altman plot and four-quadrant plot analysis. In the last minute of ventilation at each PEEP level, a slow tidal inflation/deflation manoeuvre was performed. RESULTS: The mean relative bias between PaOand PaOwas 4% with limits of agreement between -17% and 29%. The correlation coefficient between PaOand PaOwas 0.98 (P&#xa0;<&#xa0;.001). The PaOand PaOconcordance rate for changes was 95%. Measurements of PaOduring the slow inflation/deflation manoeuvre at PEEP 15 and 10&#xa0;cm&#xa0;HO were not possible because of significant noise on the PaOsignal generated by a small blood clot. MAIN LIMITATIONS: Small sample size. CONCLUSION: The tested fibreoptic probe was able to accurately and continuously measure PaOin anaesthetised horses undergoing ventilatory manoeuvres. A heparinised system in the catheter used by the fibreoptic sensor should be used to avoid blood clots and artefacts in the PaOmeasurements.