What is the cause of hypotension in surgery?

Several things: Lots of things can cause low blood pressure. If it is related to surgery, the first thing i would consider would be bleeding (bad to miss and easy to correct). The anesthetic agents themselves can lower blood pressure. If the patietn had a heart attack during surgery the blood pressure could be low. So the anesthesiologist must figure out which problem it is, as the treatment depends on the cause.

Hypotension: Surgical hypotension may be from fluid or blood loss, anesthetic effect on vasculature, or from obstruction of venous return. Other less common causes also exist............