what is the diagnosis?

[ismailalamin]

A 75-year-old man with type 2 diabetes and hypothyroidism underwent bilateral total knee replacement at our hospital. His functional capacity had been moderately limited by knee pain, but he could easily climb one flight of stairs without symptoms.
His medications at that time included levothyroxine (Synthroid) and metformin (Glucophage). He had no known cardiac or pulmonary disease.
The preoperative evaluation, including laboratory tests and electrocardiography, was within normal limits. Spinal anesthesia was used for surgery, and he was given 2 mg of midazolam (Versed) intravenously for sedation. No additional sedation was given. He was given oxygen via nasal cannula at 2 L/min.
All vital signs were stable at the start of the procedure. However, about halfway through, when the thigh tourniquet was released, his oxygen saturation dropped abruptly from 100% to 92%. All other vital signs remained stable, and he was asymptomatic, was oriented to person, time, and place, was conversing freely, and was in no distress. The oxygen flow was increased to 6 L/min, his oxygen saturation improved, and the procedure was then completed as planned.
At the conclusion of the surgery, before the patient was transported to the postanesthesia care unit (PACU) and while his oxygen
flow rate was still 6 L/min, his oxygen saturation again dropped to 92%. A simple face mask was placed, and the oxygen flow rate was increased to 10 L/min. His oxygen saturation stayed low, near 90%.
Bleeding during surgery had been nominal. He had received 2 L of lactated Ringer’s solution and 500 mL of hetastarch (Hextend)
during surgery. He continued to be asymptomatic in the PACU.

What is the most likely cause of oxygen desaturation during bilateral total knee arthroplasty?

[Mohammed x.man]

i think its fat embolism because the mode of onset is rapid plus the fact that knee joint rich in fat ..so after release the tourniquet vasodilated material release from the site of the tourniquet which could cause vasodilatation and hypotension plus hypoxia ... MI is far away although it could be possible because he is diabetic and dose not complain of chest pain... thromboembolism is far diagnosis ...it always take some time to happen ... excessive sedation is not fit ...its low dose of medazolam and as far as i know its short acting drug !!!! could u plz replay my explanation?!?!?