Is it true that urine output is expected to be high in the immediate postoperative period following surgery with CPB?

In the immediate postoperative period following surgery with cardiopulmonary bypass (CPB), it is indeed expected that urine output is high. This phenomenon is primarily attributed to several physiological responses that occur during and after the bypass procedure.

During CPB, there is a significant shift in blood volume and intravascular pressures, as well as changes to renal perfusion. When circulation is restored after the surgery, the kidneys typically respond with a diuretic phase, leading to increased urine output. This occurs as the body works to eliminate excess fluid and waste products accumulated during the procedure, commonly manifested as an elevated urine output.

Additionally, factors such as the administration of mannitol and changes in hormone levels, specifically atrial natriuretic peptide (ANP) which promotes diuresis, can also contribute to increased urine output in the postoperative phase. This increase can be an important indicator of renal perfusion and overall fluid balance in the patient after undergoing cardiac surgery.

In sum, the expectation of high urine output after surgery with CPB reflects a normal physiological response and is an important aspect for monitoring patient status in the immediate postoperative period.