The impact of different rates of sodium reduction on the central nervous system in acute hypernatremia in rabbits

Abstract

Acute hypernatremia is a prevalent electrolyte imbalance in the intensive care unit (ICU), closely associated with the severity of patients’ conditions. This study employs animal experimentation to investigate the effects of varying sodium reduction rates on the central nervous system in acute hypernatremia, aiming to identify the optimal rate of sodium reduction. A stepwise sodium titration approach was used to establish an acute hypernatremia model, targeting a sodium increase of 0.5 mEq/L per hour (target serum sodium: a rise of 15 mEq/L within 48 h from baseline). Subsequently, a stepwise sodium decrement method was applied to reduce sodium levels to baseline. The study included four groups with different target sodium reduction rates: 1 mEq/L/h (Slow group), 2 mEq/L/h (Middle group), 3 mEq/L/h (Fast group), and Sham surgery group. Blood sodium and potassium levels, as well as urine sodium and potassium, were measured at various time points; central venous pressure (CVP) and intracranial pressure (ICP) were monitored; fluid intake and output were recorded to calculate fluid balance. After sodium reduction, brain tissue was extracted for pathological examination. Twenty adult, healthy male rabbits were randomly assigned to four groups (five rabbits per group). Before and after sodium reduction, the ICP significantly increased in the Fast group from 7.00 ± 0.71 to 13.20 ± 2.95 and in the Middle group from 6.80 ± 0.45 to 11.40 ± 0.89 (p = 0.015 and p = 0.000, respectively); the Slow group showed no significant change in ICP. Pathological findings revealed edema and disorganized brain tissue in the cerebral cortex and brainstem in the Fast and Middle groups, with statistically significant differences compared to the sham-operated group in semi-quantitative analysis. For acute hypernatremia that develops within 48 h, sodium reduction rates exceeding 1 mEq/L/h are associated with greater increases in ICP and more severe brain edema. Therefore, for managing acute hypernatremia,our result prompted that sodium reduction rates might not exceed 1 mEq/L/h.