Increased rates of hypernatraemia during modest heatwaves in temperate climates.

Abstract

Hypernatraemia is associated with morbidity and mortality, particularly in the older person. Last summer, Ireland experienced prolonged periods of excessive heat. The Irish meteorological service defines a heatwave as temperatures exceeding 25°C for five consecutive days. This study sought to compare the frequency of hypernatraemia (sodium (Na+) >145 mmol/l) observed during a modest heatwave with that during average ambient temperature in the temperate Irish climate. Retrospective cross-sectional analysis with nested case-control study. The 10-day period from 24 June to 3 July in 2017 and 2018 were chosen as the control and heatwave periods, respectively. Patients aged >65 with at least one Na+ value recorded on the laboratory information system were included. Local meteorological data, age, gender and Na+ levels were evaluated. Maximum air temperatures were significantly higher during the heatwave period (mean 27°C vs. 16.8°C, P < 0.0001). Hypernatraemia was present in 3.6% (66/1840) of samples collected during the heatwave compared to 1.4% (23/1593) in the control period. The mean age of affected patients was similar in both groups, 75 years ±7 (P = 1.000). Almost half of participants (49.5%) were male. The frequency of hypernatraemia observed was not influenced by gender, P = 0.33. The median sodium concentrations were similar in both groups, P = 1.00. Hypernatraemia was 2.5 times more frequent in samples drawn during the heatwave compared to the control period. In this study, neither age nor gender impacted the profile of patients diagnosed with hypernatraemia. A modest rise in temperatures increases hypernatraemia rates in temperate climates.