Increased body condition score has a detrimental effect on arterial oxygen tension and increases the risk of hypoxaemia in anaesthetised horses

Abstract

SummaryBackgroundImpaired oxygenation during anaesthesia can be detrimental. Bodyweight and body shape influence arterial oxygen tension (PaO2) but the effect of body condition score (BCS) has not been investigated.ObjectivesTo examine the effect of BCS on respiratory indices.Study designRetrospective.MethodsIn total, 524 anaesthetic records were reviewed. Records from healthy adult horses under isoflurane anaesthesia in dorsal recumbency, receiving controlled mechanical ventilation, with complete ventilation and arterial blood gas data and BCS assessment by one person (KL) were included in data analysis. Data were analysed using student's t‐test, Mann–Whitney U test, chi‐squared analysis and logistic regression.ResultsIn total, 135 records for 85 horses with BCS <6/9 (Group N) and 50 horses with BCS ≥6/9 (Group O) met the inclusion criteria. Overall, there was a strong negative correlation between BCS and PaO2 (Spearman's r = 0.72, p < 0.001). Group O had significantly lower PaO2 (112 [50–546 mmHg]) compared to Group N (380 [65–658 mmHg], p < 0.001) which remained when horses were further categorised by bodyweight >500 kg (118 mmHg vs. 390 mmHg, p < 0.001) and <500 kg (160 mmHg vs. 451 mmHg, p < 0.04). Group O were 34 times more likely to be hypoxaemic (PaO2 < 100 mmHg) compared to Group N (χ2 = 34.39, p = 0.03). Alveolar dead space fraction was greater in Group O (0.27 [0.10–0.41]) versus Group N (0.24 [0.12–0.35]), p < 0.001. Multivariate logistic regression analysis identified a significant association between PaO2 and bodyweight (p = 0.01), alveolar dead space fraction (p = 0.005) and BCS (p < 0.001).Main limitationsRetrospective design.ConclusionsBody condition score ≥6/9 has a detrimental effect on PaO2, alveolar dead space fraction and is a risk factor for hypoxaemia in healthy anaesthetised horses in dorsal recumbency.