Which of the following is not usually a post-operative complication?

After surgery there is usually an increased adrenocoicoid activity and decreased sodium excretion. Hypokalaemia, glucose intolerance and nitrogen imbalance are seen after a surgery. If urine output is low and urine osmolality high, then both ADH secretion and the renal response to it are present. The cause here is most likely extrarenal water loss. If both urine output and urine osmolality are high, then osmotic diuresis is suspected. If urine osmolality is less than plasma osmolality, then the cause is attributable to reduced ADH secretion or abnormal renal response to ADH and in both cases, urine output is high.