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


Correspondence: Keila Kazue Ida, Departamento de Cirurgia, Faculdade de Medicina Veterinária e Zootecnia, Universidade de São Paulo, Avenida Professor Doutor Orlando Marques de Paiva 87 – Cidade Universitária, São Paulo, SP CEP 05508-270, Brazil. E-mail:



To determine if pressure support ventilation (PSV) weaning from general anesthesia affects ventilation or oxygenation in horses.

Study design

Prospective randomized clinical study.


Twenty client-owned healthy horses aged 5 ± 2 years, weighing 456 ± 90 kg.


In the control group (CG; = 10) weaning was performed by a gradual decrease in respiratory rate (fR) and in the PSV group (PSVG;= 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 > 50 mmHg or PaO2 < 60 mmHg were observed at any time after disconnection from the ventilator until 30 minutes after the horse stood. Threshold values for each index were established and the predictive power of these values was tested.


Pressure support ventilation group (PSVG) had (mean ± SD) pH 7.36 ± 0.02 and PaCO2 41 ± 3 mmHg at weaning and the average lowest PaO2 69 ± 6 mmHg was observed 15 minutes post weaning. The CG had pH 7.32 ± 0.02 and PaCO2 57 ± 6 mmHg at weaning and the average lowest PaO2 48 ± 5 mmHg at 15 minutes post weaning. No accuracy in predicting weaning effect was observed for fR (= 0.3474), minute volume (= 0.1153), SaO2 (= 0.1737) and PaO2/PAO2 (= 0.1529). A high accuracy in predicting an optimal effect of weaning was observed for VT > 10 L (= 0.0001), fR/VT ratio ≤ 0.60 breaths minute−1 L−1 (= 0.0001), VT/bodyweight > 18.5 mL kg−1 (= 0.0001) and PaO2/FiO2 > 298 (= 0.0002) at weaning. A high accuracy in predicting a suboptimal effect of weaning was observed for VT < 10 L (= 0.0001), fR/VT ratio ≥ 0.60 breaths minute−1 L−1 (= 0.0001) and Pe′CO2 ≥ 38 mmHg (= 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 Pe′CO2 were accurate in predicting the effect of weaning in healthy horses recovering from general anesthesia.