Discussion: 

The main differential diagnoses for her intraoperative cardiovascular collapse included amniotic fluid embolism (AFE), pulmonary embolism (PE) and VAE. The presence of air in the right atrium on scan suggested VAE as the most likely cause with a large volume of air entering the uterine sinuses, travelling to the heart via the inferior vena cava.  From numerous reported fatalities after vaginal insufflation, it is recognised that the uterine sinuses are particularly vulnerable to air entry and this is especially so during pregnancy.2-5  Furthermore delivery in the presence of placenta previa in particular is known to allow enough air into the systemic circulation to result in serious embolic manifestations.6 The resultant right ventricular dysfunction results from the  acute increase in right ventricular afterload due to significant air emboli blocking the right ventricular outflow tract.

While amniotic fluid embolism (AFE), which is often associated with instantaneous DIC and massive postpartum haemorrhage, not seen here, typically presents with on-table collapse, the presence of air bubbles rather than amniotic fluid particles via bedside echocardiography helped distinguish VAE from AFE.7

Prior to surgery, the patient had a history of recurrent exertional presyncope/syncope. This was investigated as an inpatient after the surgery for which a CT pulmonary angiogram was performed on POD 8.  While PE was a possible differential for her collapse and might explain the non-specific CTPA findings, preoperatively, the patient was comfortable on room air without oxygen supplementation and as VAE could also manifest with similar CTPA findings, PE was considered less likely to be the cause for her intra-operative collapse.