55 year old female a known case of thryotoxicosis in control posted for abdomino perineal resection during surgery there was sudden drop in B.P., and end tidal CO2 decreased from 40 to 10 mmHg. On auscultation there was a mill wheel murmur, what is the diagnosis –

Presence of Mill wheel murmur and decrease in End tidal CO2 during surgery suggests Air embolism:- "If air enters the vein in sufficient amount, it will go to the right heart and lung causing an air-lock obstruction in the pulmonary artery. This may result in a loud continuous precordial murmur, the so called "Mill wheel murmur".