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Answers on 245.
A 45 year old housewife was admitted to hospital after a fall at home, after which she had had three fits. Although her eyes were open, she was not responding to questions and her husband gave the history. A month previously she had been admitted with haematemesis and had undergone emergency surgery, which entailed partial gastrectomy along with vagotomy and pyeloroplasty for a duodenal ulcer. For a week before this admission she had complained of abdominal discomfort, severe vomiting, and progressive weakness.
On examination she was drowsy, maintaining her airway but with slow breathing. She had generalised rigidity along with coarse twitches of facial and hand muscles. Her pupils were equal and reactive to light and her tendon reflexes were brisk. She had no neck stiffness and was apyrexial. Clinically she was dehydrated with a pulse rate of 104 beats/min and a blood pressure of 110/80 mm Hg.
Initial investigations revealed blood glucose of 9.6 mmol/l, sodium 136 mmol/l, potassium 4.0 mmol/l, calcium 2.59 mmol/l, creatinine 474 μmol/l, urea 22.9 mmol/l, haemoglobin 130 g/l, and serum albumin 38 g/l.
Computed tomography was performed followed by a lumbar puncture, both of which were normal.
Arterial blood gases were taken while breathing air (point A in fig 1) and showed a pH 7.57, carbon dioxide pressure (pCO2) 9.56 kPa (71.9 mm Hg), oxygen pressure (pO2) 6.25 kPa (47 mm Hg), bicarbonate 65.5 mmol/l, and a base excess of 37.7 mmol/l. At this point she was started on 35% oxygen.
Four hours later (point B) her pH was 7.6, pCO2 78.7 mm Hg (10.45 kPa), pO2 95 mm Hg (12.6 kPa), bicarbonate 76.8 mmol/l, and base excess 47.6 mmol/l. At this point she was started on intravenous saline with potassium, and her oxygen was increased to 60%.
Eight hours later (point C) her conscious level improved and arterial gas analysis showed a pH of 7.53, a pCO2 of 82 mm Hg (10.9 kPa), a pO2 of 78 mm Hg (10.4 kPa), a bicarbonate of 69.9 mmol/l, and base excess of 39.9 mmol/l. At this point acetazolamide was added and fluid replacement with saline and potassium continued.
Twenty four hours from admission her condition had improved considerably. Unfortunately she then experienced a sudden deterioration with respiratory distress. Blood gas analysis on 100% oxygen (point D) revealed a pO2 of 57.1 mm Hg (7.59 kPa), along with a pCO2 of 48 mm Hg (6.4 kPa), a pH of 7.51, a bicarbonate of 37 mmol/l, and a base excess of 12 mmol/l. A chest radiograph was taken (fig 2). She required tracheal intubation and ventilation at this point.
Thirty six hours after admission her oxygenation had improved and she was extubated.
During her admission she had large amounts of gastric aspirate through her nasogastric tube, which had a low pH despite her previous operation.
What is the diagnosis on admission? What other electrolyte result is essential in management of this condition?
Explain the effect of supplemental oxygen on the arterial blood gas result (point A to point B).
Explain the action of saline (point B to point C) and acetazolamide (point C onwards)?
What is the cause of her hypoxia at point D? How could this have occurred?