Use of near‐infrared spectroscopy to identify trends in regional cerebral oxygen saturation in horses

Summary Reasons for performing study Alterations in cerebral haemodynamics may contribute to perianaesthetic complications in horses. Near‐infrared spectroscopy ( NIRS ) is frequently used intraoperatively in man to provide information regarding cerebral perfusion. Objectives To determine whether NIRS can identify trends in regional cerebral oxygen saturation ( rSO 2 ) in horses and whether there is a correlation between rSO 2 and venous oxygen tensions. Methods A cerebral oximeter sensor recorded rSO 2 from the dorsal sagittal sinus of 6 healthy horses. Values for rSO 2 , arterial and venous oxygen and carbon dioxide tensions ( PaO 2 , PvO 2 , P a CO 2 and PvCO 2 respectively), along with arteriovenous oxygen saturations ( SavO 2 ) were recorded in unsedated (recording period [ RP ] 1), sedated ( RP 2) and anaesthetised horses ( RP 3–5) and during recovery ( RP 6–8). During anaesthesia, horses were ventilated to achieve states of normo‐ ( RP 3), hyper‐ ( RP 4) and hypocapnoea ( RP 5). Data were evaluated descriptively and analysed using linear mixed‐effects models and P earson's correlation coefficient. Results Overall mean ± s.d. values for rSO 2 , PaO 2 , PvO 2 , PaCO 2 , SavO 2 and mean arterial pressure varied significantly by RP (P<0.001). Significant decreases in rSO 2 were identified between RP 1 and the post anaesthetic periods (P<0.001). No significant differences in rSO 2 values were identified between RP 1 and the intra‐anaesthesia periods or between RP 3, RP 4 and RP 5. Significant correlations were identified between rSO 2 and PaO 2 (r = 0.448, P<0.001), rSO 2 and PvO 2 (r = 0.512, P<0.001) and rSO 2 and S av O 2 (r = 0.469, P<0.001). Conclusions This is the first study to identify trends in rSO 2 in horses using NIRS . A positive correlation was identified between rSO 2 and PvO 2 , suggesting that alterations in cerebral oxygenation may be reflected in PvO 2 . Potential relevance Near‐infrared spectroscopy may be used to monitor trends in rSO 2 during equine anaesthesia. Decreasing rSO 2 values may act as an early warning signal, alerting clinicians to potential cerebral desaturation events and indicating a need for intervention.