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

Abstract

OBJECTIVE: To study the changes in dynamic compliance (C), ventilation/perfusion (V&#x2d9;/ Q&#x2d9;) mismatch and haemodynamic variables in hypoxaemic anaesthetized horses whose PaOincreased following salbutamol inhalation. STUDY DESIGN: Retrospective, clinical, cohort study. ANIMALS: A group of 73 client-owned horses treated with salbutamol when PaO<100 mmHg (13.3 kPa) during anaesthesia. METHODS: Horses were divided into two groups: responders (R), where PaOafter salbutamol &#x2265;1.2 PaObefore treatment (i.e. &#x2265;20% increase), and non-responders (NR), where PaOafter salbutamol <1.2 PaObefore treatment. Demographic data and intraoperative variables before treatment were compared between R and NR. C, arterial to end-tidal carbon dioxide difference [P(a-E&#xb4;)CO], estimated ratio of dead space to tidal volume (est.V/V), 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 (&#x394;) 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. RESULTS: 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 Cin either group, it significantly decreased P(a-E&#xb4;)CO, est.V/Vand F-shunt in R only. &#x394;P(a-E&#xb4;)CO, &#x394;est.V/Vand &#x394;F-shunt were significantly greater in R (-17.8%,&#xa0;-19.0% and&#xa0;-24.1%, respectively) than in NR (11.5%, 6.6% and&#xa0;-0.3%, respectively). CONCLUSIONS AND CLINICAL RELEVANCE: In hypoxaemic anaesthetized horses responding to inhaled salbutamol by a &#x2265;1.2 increase in PaOno change in Cwas detected, but indicators of V&#x2d9;/ Q&#x2d9; mismatch improved.