Sun28November0628PM 10

A 75-year-old man has a laparotomy for the correction of a small bowel obstruction. He has a past history of orthotopic bladder reconstruction for carcinoma of the bladder. Forty-eight hours postoperatively on HDU he becomes confused and is unable and unwilling to accept oral fluids. His pulse rate, blood pressure and urine output are within normal limits.

Serum biochemistry reveals:

Na+ 147 mmol/L

K+ 3.1 mmol/L

Chloride 134 mmol/L

Urea 14.3 mmol/L

Creatinine 82 µmol/L

Glucose 14 mmol/L

He is breathing air.

Blood gas analysis shows:

pH 7.26

PaCO2 2.57 kPa

PaO2 9.92 kPa

HCO3 16.3 mmol/L

Base excess -14.6 mmol/L

Lactate 1.6 mmol/L

Which is the most appropriate initial intervention?

(Please select 1 option)

Potassium supplementation via a central venous catheter

Intravenous sliding scale insulin infusion

Rehydration with 0.9% sodium chloride and correction of blood glucose Incorrect answer selected

Encourage patient to breathe into a paper bag

Intravenous infusion of 1.26% sodium bicarbonate and potassium replacement This is the correct answer

Explanation

The patient has a hyperchoraemic metabolic acidosis with respiratory compensation.

There is also a mild hypernatraemia and hypokalaemia. Lactate concentrations are normal which suggests that the acidosis is not secondary to organ hypoperfusion.

Hyperchloraemic metabolic acidosis is a documented complication of neobladder formation. However, it usually improves with time and is mild. Severe and persistent metabolic acidosis may manifest when patients undergo further surgery for other reasons, as is the case in this patient. Neobladder formation following radical cystectomy or cystoprostatectomy is becoming increasingly more common, and medical staff treating patients with neobladders should recognise and treat metabolic acidosis with intravenous fluids and bicarbonate. Associated electrolyte abnormalities may include hypokalemia, hypocalcaemia, and hypomagnesaemia. Hypokalemia is caused by both intestinal (secretion) and renal losses. This depletion of potassium can be exacerbated by the correction of acidosis.

Rehydrating the patient with 0.9% N. saline is likely to exacerbate the hyperchloraemic state. Potassium supplementation alone via a central venous catheter will not be sufficient treatment. Encouraging the patient to breathe into a paper bag might be a treatment of an acute respiratory alkalosis but inappropriate in this patient. The patient has hyperglycaemia secondary to the metabolic stress response and not ketoacidosis.

Answer Statistics

1

7%

2

6%

3

21%

4

2%

5

66%

Times answered: 321