Often a patient will have a diminished urine output after a major operation. This may be the result of fluid and blood loss and the response of the adrenal cortex to stress - there is an increase in aldosterone release (adrenal cortex) and ADH release (posterior pituitary) in the first 24 hours after surgery. This results in both salt and water retention. Insufficient postoperative analgesia can precipitate acute urinary retention and anuria.
The oliguria should be temporary and not last more than 24h. If there is a urine output of less than 500 cubic centimetres in the first 24 hours then this warrants investigation.
There are various causes of postoperative oliguria/anuria that lasts more than 24h. These include:
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