Effect of pressure support ventilation during weaning on ventilation and oxygenation indices in healthy horses recovering from general anesthesia

Abstract

Objective To determine if pressure support ventilation (PSV) weaning from general anesthesia affects ventilation or oxygenation in horses. Study design Prospective randomized clinical study. Animals Twenty client-owned healthy horses aged 5 +/- 2years, weighing 456 +/- 90kg. Methods In the control group (CG; n=10) weaning was performed by a gradual decrease in respiratory rate (fR) and in the PSV group (PSVG; n=10) by a gradual decrease in fR with PSV. The effect of weaning was considered suboptimal if PaCO2>50 mmHg, arterial pH<7.35 plus PaCO2>50mmHg or PaO2<60mmHg were observed at any time after disconnection from the ventilator until 30minutes after the horse stood. Threshold values for each index were established and the predictive power of these values was tested. Results Pressure support ventilation group (PSVG) had (mean +/- SD) pH 7.36 +/- 0.02 and PaCO2 41 +/- 3mmHg at weaning and the average lowest PaO2 69 +/- 6mmHg was observed 15minutes post weaning. The CG had pH 7.32 +/- 0.02 and PaCO2 57 +/- 6mmHg at weaning and the average lowest PaO2 48 +/- 5mmHg at 15minutes post weaning. No accuracy in predicting weaning effect was observed for fR (p=0.3474), minute volume (p=0.1153), SaO2 (p=0.1737) and PaO2/PAO2 (p=0.1529). A high accuracy in predicting an optimal effect of weaning was observed for VT>10L (p=0.0001), fR/VT ratio0.60 breaths minute-1L-1 (p=0.0001), VT/bodyweight>18.5mL kg-1 (p=0.0001) and PaO2/FiO2>298 (p=0.0002) at weaning. A high accuracy in predicting a suboptimal effect of weaning was observed for VT<10L (p=0.0001), fR/VT ratio0.60 breaths minute-1L-1 (p= 0.0001) and PeCO238mmHg (p=0.0001) at weaning. Conclusions and clinical relevance Pressure support ventilation (PSV) weaning had a better respiratory outcome. A higher VT, VT/body weight, PaO2/FiO2 ratio and a lower fR/VT ratio and PeCO2 were accurate in predicting the effect of weaning in healthy horses recovering from general anesthesia.