Postural hypotension, hyponatremia, and salt and water intake: case reports

Postural hypotension (PH) and hyponatremia are common and often coexistent among patients with severe paralysis secondary to spinal cord injury. Volume depletion could account for these conditions. This study examined whether salt and water intake correlated with the severity of PH.

Participants were 4 patients with tetraplegia, motor and sensory complete, aged 68 to 83 years, who were paralyzed for 9 to 54 years, who had PH. These patients were ranked by the amount of ephedrine prescribed on a daily basis to treat PH over the preceding 2-year period.

The total urinary output of sodium and water and the effect of orthostasis on urine output rate, osmolality, sodium concentration, and creatinine secretion were determined over a 48-hour period of collection and compared with severity of PH.

The ephedrine requirements, in order of decreasing severity of PH, were 100 mg/d, 25 mg/d, 12.5 mg/d, and no ephedrine needed. The 24-hour sodium excretions in that order were 50, 92, 180, and 164 mEq. The urine volumes were 1.4, 3, 2.6, and 5.4 L, respectively. In the same order of decreasing PH severity, the sitting position relative to the recumbent position was characterized by increasing rates of creatinine secretion (ratios of 0.69, 0.74, 0.95, and 0.80), increasing rates of water excretion (ratios of 0.49, 0.28, 0.69, and 0.99), decreasing urine osmolality (ratios of 1.2, 1.8, 1.3, and 0.8), and increasing sodium concentrations (ratios of 0.9, 1.3, 1.2, and 2.6).

In these individuals with tetraplegia, severe PH was accompanied by avid conservation of water and impaired retention of sodium in the sitting position, as well as limited salt and water intake.