Suspected venous air embolism during urinary tract endoscopy in a standing horse

During cystoscopy, performed with air insufflation in a standing Argentinian gelding, the horse showed ataxia and fell to the ground with generalised muscular twitching and horizontal nystagmus, tachypnoea and tachyarrhythmia. General anaesthesia was induced. Arterial blood gas-analysis before induction of anaesthesia revealed an increased pH, decreased partial pressure of carbon dioxide and decreased partial pressure of oxygen. Venous air embolism was suspected.