Increasing drowsiness and respiratory depression in an older patient with renal impairment

Mr A, a 78-year-old man, was admitted electively for a hip fracture repair. His medical history included hypertension and mild chronic kidney disease (baseline creatinine 90 μmol/L). On the day of admission, he was started on oral morphine sulfate solution 10 mg every four hours when required for pain. His usual antihypertensive, amlodipine 5 mg once daily, was continued. On day 2, because of significant postoperative anxiety, oral lorazepam 1 mg at night was added. On day 5, the nursing staff noted he was increasingly drowsy and difficult to rouse. His respiratory rate was recorded at 8 breaths per minute, with an oxygen saturation of 89% on room air. Arterial blood gas analysis showed a respiratory acidosis: pH 7.25, PaCO2 8.6 kPa. His serum creatinine on day 6 had risen to 180 μmol/L, a doubling from baseline. Examination revealed pinpoint pupils, no focal neurological deficit, and no evidence of infection. The morphine was withheld, and lorazepam was also withheld. Within 12 hours, his respiratory rate returned to 14 breaths per minute and he became more alert. Over the next 24 hours, his renal function remained impaired but stable. No rechallenge with morphine was performed. Alternative explanations, such as acute kidney injury from dehydration or the effects of his other medications, were considered.