Heatwaves and plasma sodium disturbances in patients with chronic kidney disease

Climate change and subsequent warmer temperatures may affect kidney and electrolyte-water balance, reflected by plasma sodium. Plasma sodium alterations are common among patients with chronic kidney disease (CKD).

We aimed to determine whether heatwaves were associated with plasma sodium levels in this population.

We obtained 38,740 plasma sodium measurements from 2964 patients with moderate or severe CKD, under nephrology care, in France, prospectively followed-up in the CKD-REIN study. Patients undergoing dialysis and patients with kidney transplant were not included. We estimated multinomial odds ratios (ORs) and 95 % confidence intervals (CIs) for abnormal plasma sodium levels associated with heatwave exposure in the past 3, 8 or 15 days. We used local temperature data to assess exposure to heatwaves.

Over a median follow-up of 5 years, 1730 (4.5 %) plasma sodium measurements were ≤ 135 mmol/L (hyponatremia) and 2797 (7.2 %) ≥ 145 mmol/L (hypernatremia). Thiazide diuretic use was associated with increased odds of hyponatremia, while loop diuretic use was associated with increased odds of both hyponatremia and hypernatremia. Summer season was associated with higher odds of hyponatremia. Exposure to at least 3 days of heatwave in the past 8 days was associated with increased odds of lower plasma sodium levels (OR [95 %CI]: 1.48 [1.10, 1.99]).

Heatwaves, particularly sustained ones, expose patients with CKD to hyponatremia. Generic recommendations to increase water intake during high temperatures may heighten this risk and are therefore inappropriate for this population. Plasma sodium monitoring should be considered for several weeks following a heatwave.