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Definition

One or more air bubbles get access to the circulatory system, causing blockade of one or multiple blood vessels.

Risk factors (attributed to presumptive venous air embolism)

 Dorsal location of the urinary tract relative to the right ventricle

 Presence of denuded epithelium

Pathogenesi

Urinary tract endoscopy was proposed to cause venous air embolism in two cases reported in the literature [5–7]. Please refer to the vascular air embolism section in Chapter 3: Complications of Intravascular Injection and Catheterization. Air was noted to be present within the renal pelvis during ultrasonographic examination performed 24 hours after the endoscopic procedure, which may suggest that air was absorbed through the renal vasculature [6]. The dorsal location of the urinary tract relative to the right ventricle is suggested to create a pressure gradient that favors the movement of air into the vasculature [7]. This may be additionally facilitated by the presence of denuded epithelium, which could increase the risk of air entering the bloodstream [5–7].

Prevention

Prevention of venous air embolism during urinary tract endoscopy would include use of alternative means to distend the urethra and bladder, such as saline solution or carbon dioxide gas, pre‐oxygenation with 100% oxygen, and anticoagulant therapy; however, the mucoid and crystalline nature of equine urine makes the use of saline to distend the bladder impractical [6, 7]. These precautions may be warranted in cases thought to be at higher risk for venous air embolism, such as cases presenting for hematuria or severe cystitis cases with denuded mucosa [7].

Diagnosis

Refer to Chapter 3: Complications of Intravascular Injection and Catheterization.

Treatment

The clinical signs and treatment of vascular air embolism are described in detail as a complication of intravenous catheterization and readers are directed to that chapter.

Expected outcome

In the cases described in the literature, and as described in Chapter 3, horses would be expected to recover and return to normal from this complication if recognized and insufflation was stopped. The horse described in Gordon et al. [5] was euthanized following recovery from two occurrences of presumptive vascular air embolism, due to a poor prognosis for a malignant lesion that prompted the cystoscopy.