Retrospective study of the changes in dynamic compliance and ventilation/perfusion mismatch following salbutamol inhalation in hypoxaemic mechanically ventilated anaesthetized horses.

To study the changes in dynamic compliance (C dyn), ventilation/perfusion (V ˙ / Q ˙) mismatch and haemodynamic variables in hypoxaemic anaesthetized horses whose PaO 2 increased following salbutamol inhalation. Retrospective, clinical, cohort study. A group of 73 client-owned horses treated with salbutamol when PaO 2 <100 mmHg (13.3 kPa) during anaesthesia. Horses were divided into two groups: responders (R), where PaO 2 after salbutamol ≥1.2 PaO 2 before treatment (i.e. ≥20% increase), and non-responders (NR), where PaO 2 after salbutamol <1.2 PaO 2 before treatment. Demographic data and intraoperative variables before treatment were compared between R and NR. C dyn , arterial to end-tidal carbon dioxide difference [P(a-E´)CO 2 ], estimated ratio of dead space to tidal volume (est.V D /V T), estimated shunt fraction (F-shunt), heart rate, systolic, mean and diastolic arterial pressure and dobutamine requirements were compared before and after treatment within R and NR. For each variable, the difference (Δ) between values pre- and posttreatment was calculated and compared between groups R and NR. Numerical data were compared using univariate or bivariate analysis and categorical data were compared using chi-square test; p < 0.05. Of the 73 horses 50 were classified as R while 23 horses were classified as NR. There was no statistical difference between R and NR for demographic data or initial intraoperative variables except for body weight [R: 531 (170–715) kg, NR: 540 (420–914) kg]. While salbutamol did not alter C dyn in either group, it significantly decreased P(a-E´)CO 2 , est.V D /V T and F-shunt in R only. ΔP(a-E´)CO 2 , Δest.V D /V T and ΔF-shunt were significantly greater in R (−17.8%, −19.0% and −24.1%, respectively) than in NR (11.5%, 6.6% and −0.3%, respectively). In hypoxaemic anaesthetized horses responding to inhaled salbutamol by a ≥1.2 increase in PaO 2 no change in C dyn was detected, but indicators of V ˙ / Q ˙ mismatch improved. [ABSTRACT FROM AUTHOR]