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A patient with complications from surgery was admitted to intensive care with sepsis, adult respiratory distress syndrome, and signs of impending renal failure. After 18 days of ventilation, further surgical intervention, and every trick in the microbiologist's book, he had recovered sufficiently for his sedation to be lightened. In addition, his persistent pyrexia gradually came under the control of paracetamol 1 g four times daily. Nutrition was supplied via a jejunostomy tube, and as his condition improved the paracetamol was administered in a soluble preparation by the same route.
By day ten he was much improved, with his sepsis resolving. Yet his sodium concentration was 159 mmol/L—13 mmol/L above our laboratory's upper limit. Changing jejunostomy feed to a low-sodium preparation, and swapping normal saline infusions to dextrose saline had no effect, and we assumed that a polyuric renal crisis was evolving.
Then one of the authors (MS), a senior staff nurse, remembered that soluble paracetamol contains sodium. Further investigation revealed that the preparation we were using contained 388 mg of sodium in each 500 mg tablet. In other words, the patient was receiving 3 g sodium a day, and had been doing so for 6 days. Back-of-envelope calculations then showed:
Over 6 days the excess sodium equals 13 mmol/L, which happens to be the exact amount over the upper limit of normal.