Air embolism secondary to suspected lymphatic tissue disruption with severe exercise‐induced pulmonary haemorrhage

Summary Air embolism is rare in horses and typically associated with complications following intravenous catheterisation or other medical procedures. Exercise‐induced pulmonary haemorrhage (EIPH) is common in racehorses but not usually associated with air embolism. This report describes a case of air embolism in a 4‐year‐old Thoroughbred with EIPH. The mare used for racing presented with recurrent mild epistaxis and severe neurological signs. Clinical examination revealed tachypnoea and tachycardia as well as a continuous systolic–diastolic heart murmur which varied in loudness (grade 4–6/6), with a right‐sided punctum maximum in the fourth intercostal space. Ultrasonography identified air bubbles in all four heart chambers. Laboratory findings included elevated muscle enzyme activities, a mildly increased serum amyloid A concentration, and decreased arterial oxygen partial pressure. Despite treatment with antibiotics, anti‐inflammatory drugs, and oxygen therapy, the mare's condition deteriorated, necessitating euthanasia. Post‐mortem examination revealed acute pulmonary emphysema, intra‐alveolar overload with haemosiderophages, cerebral haemorrhages and gas bubbles in tracheobronchial lymph nodes. Polymerase chain reaction analysis of the lung tissue detected equine herpesvirus‐5. Findings suggested pulmonary‐lymphatic air entry, potentially due to pulmonary parenchymal rupture from increased intravascular pressure associated with EIPH. This report describes rare air embolism unrelated to common iatrogenic causes, emphasising the need for further investigation into pulmonary‐lymphatic air entry in racehorses.