Preoperative and intraoperative risk factors for post-anaesthetic pulmonary oedema in horses

Background: Pulmonary oedema is an uncommon but life-threatening condition in horses. It is defined as an abnormal accumulation of liquid and solute in the extravascular tissues and spaces of the lungs, which causes oxygen diffusion impairment and a reduction in lung compliance. Diagnosis is determined by typical clinical signs, including frothy, haemorrhagic nasal discharge and respiratory distress, and can be supported by thoracic imaging and arterial blood gas analysis. In horses, post-anaesthetic pulmonary oedema (PAPOE) is poorly reported, and there is a lack of information regarding risk factors and prognosis. Objectives: The objective of the study was to determine risk factors and short-term outcome for PAPOE during the recovery period in horses. Study design: A retrospective case-control study including 17 cases and 53 controls. Methods: Medical records of clinical cases and controls over a period of four and a half years were reviewed. Short-term outcomes and risk factors for PAPOE were investigated using conditional multivariable logistic regression analysis. Results: Ascarid impaction prevalence in PAPOE cases was significantly higher than controls (p = 0.03). In a univariable analysis, the following variables were significantly associated with PAPOE (p ≤ 0.05): gastric reflux on admission, haemorrhage during surgery, intravenous crystalloid treatment prior to admission, fresh frozen plasma and hydroxyethyl starch administration during anaesthesia. On multivariable analysis, gastric reflux on admission (OR = 7.9, 95% CI 1.1, 57.2) and fresh frozen plasma treatment during anaesthesia (OR = 9.6, 95% CI 1.2, 79.1) were found as risk factors for PAPOE. There was no significant difference in outcome between cases and controls. Main limitations: The low number of cases, the lack of gross and histological post-mortem examinations of the horses that did not survive and the clinical definition of PAPOE. Conclusions: Gastric reflux and fresh frozen plasma administration during general anaesthesia are associated with PAPOE.