Oliguria

You have received a telephone call from the nurse who is looking after your 68-year-old patient. He informs you that the patient has only voided 50 mL of urine in the 6 hours since he returned from the operating suite after a sigmoid colectomy for perforated diverticular disease. The nurse wants to give a bolus of frusemide to increase the urine output. What do you do?

While it is possible that this man's problem may be fluid retention and pump failure, it is more likely that he has received inadequate fluid replacement, either during or immediately after the operation and you are dealing with an under-filled patient.

There are many causes of oliguria in the postoperative period and a diuretic may be the worse way of managing the patient if appropriate assessment has not been made. You must go and see the patient. Given the scenario, this patient may have lost a considerable amount of fluid as a result of the peritonitis and may still be losing fluid into the peritoneal cavity. Remember that not all fluid lost by a patient may be readily evident. Patients with paralytic ileus and/or peritonitis can accumulate many litres of fluid within the peritoneal cavity - so-called ‘third space’ loses.

At the bedside you will look at the charts, note the details of the surgical procedure, calculate how much fluid was lost during the operation and how much was given. The amount of fluid given since the time of the operation should be noted. Any discharge from drains or a nasogastric tube should be measured.

The pre-operative state of health must be noted. A history of cardiac disease and heart failure will alert you to the possibility of pump failure.

In most instances it will be relatively safe to manage the problem at the bedside. Run in 500 mL of isotonic saline rapidly and observe the effect on urine output over the next few hours. Further boluses of fluid may be required and a diuretic should only be given once you are confident that the patient has had adequate fluid replacement. In more complex cases, the resources of an intensive care unit may be required to help determine the nature of the underlying problem.

In summary, the oliguria may be due to:

• inadequate filling

• inadequate output (pump failure)

• renal tract obstruction.

In other words, all the alternative explanations for oliguria must be considered; the problem may be something as simple as a blocked urinary catheter.

Wound discharge

Five days after undergoing a laparotomy for ischaemic small bowel (and bowel resection), your 73-year-old patient develops a pinkish discharge from the wound. What action do you take and why?

While there are a number of causes of discharge, the most urgent to consider is the possibility that this discharge is the harbinger of disruption of the deep layers of the wound, with the consequent risk of complete wound failure. Alert the nursing staff to provide some sterile dressings to cover the wound, should it suddenly burst.

Look to see if the patient has any risk factors for wound failure. What was his pre-operative nutritional status and have his serum proteins been measured? Find out what has happened to the patient since the operation. Has there been any process that could have led to an untoward increase in intra-abdominal pressure, such as a chest infection or paralytic ileus.

Explain to the patient what you fear and that he may need to be taken back to the operating theatre (for the wound to be resutured). The wound must be inspected. A non-inflamed wound with seepage of pink fluid is highly suggestive of acute failure of the wound. Extensive bruising around the wound might suggest discharge of a seroma, while a red, angry wound might make you think of infection.

If there is any doubt as to the nature of the problem, the wound should be gently probed (with sterile instruments). If you see the intestine, go no further. Be prepared to cover a dehisced wound with a sterile drape and call for help.

If the patient has suffered a deep wound dehiscence, why might it have happened?

The reasons for acute wound failure may be classified as follows:

• local factors: poor suturing techniques; poor tissue healing (infection, necrosis, malignancy, foreign bodies); increased intra-abdominal pressure

• general factors: malnutrition, diabetes mellitus. In most instances, acute wound failure is due to a local factor.