Underestimation of gas embolism during hysteroscopic surgery? 
How to recognise symptoms and reduce fatalities. Presentation of three cases

Background: Subclinical venous air embolism (VAE) may be present during many surgical procedures including uterine surgery. Air is by far the most frequent and most dangerous gas, due to insoluble nitrogen. VAE may cause a brief and transient drop in EtCO2; a decrease in SpO2; and even severe organ dysfunction and death. Vague symptoms may be overlooked. Severe symptoms mimic other conditions, e.g. severe anaphylaxis, fat or tissue embolization or acute coronary syndrome. 
Case report: Over a one-month period, we experienced episodes of suspected VAE in three women undergoing hysteroscopic surgery, of whom two had cardiac arrest. All patients were in lithotomy position, had their cervix dilated before insertion of a resectoscope. All women had a drop in EtCO2 and SpO2and two also had cyanosis of upper body, shock and cardiac arrest (figure 1). One patient survived with no sequelae, one did not survive resuscitation and one survived after ECMO therapy, but with severe neurological damage. Peri-arrest trans thoracic echo dopler (TEE) in patient 3 confirmed wast amounts of air in the central circulation (cineloop 1-3)
Discussion: The mechanism behind VAE is complex and multifactorial; Air can be sucked into incised or open veins above heart level due to subatmospheric pressure; Pressurised distension media with air can be absorbed in all positions. Repeated instrumentation of the cervix can act like a piston and air can be pumped into the uterine cavity. Small amounts of air are mostly asymptomatic. Larger amounts of bubbles may cause a physical obstruction of the pulmonary artery leading to right heart failure. Acute reduction of left heart preload can cause PEA. Bubbles may overwhelm the filtering capacity of the lung capillary bed, and pass through to the systemic circulation - even in patients without a persistent foramen ovale. Gas can trigger an inflammatory response, causing bronchoconstriction, pulmonary capillary leakage and systemic hemoconcentration. 
Gas entering the right heart can be detected peri-operatively by continuous echocardiography or by monitoring EtCO2 meticulously. Even minor obstructions of the blood flow to the lungs cause a reduction of EtCO2. 
Learning points: VAE is probably a common perioperative complication. EtCO2 decrease is the first symptom. Positioning the patient with surgical field below heart level, changing surgical technique and termination of surgery if EtCO2 occurs may reduce morbidity and mortality.

Underestimation of gas embolism during hysteroscopic surgery? How to recognise symptoms and reduce fatalities. Presentation of three cases