The effects of high dose morphine and morphine plus nitrous oxide on urinary output in man

Renal effects of anaesthetic doses of morphine (2 mg/kg) were determined in 10 patients before and after the addition of 60 per cent nitrous oxide. While morphine had no effect on systemic arterial blood pressure, urinary osmolarity and output, or creatinine, osmolar or free water clearances the addition of nitrous oxide resulted in a reduction in all of these except urine osmolarity, which was significantly increased. These findings demonstrate that large doses of morphine are not antidiuretic in man, but suggest that morphine plus nitrous oxide markedly alters renal function.