139 Prevalence of Hypernatraemia in the West of Ireland during 2018 Heatwave: A Retrospective Cross-sectional Study

Background Hypernatraemia is a surrogate marker of morbidity and mortality, particularly in the older person.(1) Met Eireann defines a heatwave as 5 consecutive days >25°C. HSE guidelines outline preventative strategies for community-dwelling adults and inpatients during heatwaves.(2) Our objective was to compare the prevalence of hypernatraemia (Na>145mmol/l), in biochemical samples during the heatwave of 2018 to the same period in 2017 Methods A retrospective cross-sectional study using patient demographics, biochemical data from Laboratory Information System and meteorological data from Met Éireann was performed. A ten-day period from 24thJune to 3rdJuly was assessed in 2017 and 2018. Patients aged >65 with at least one biochemical sample were included. Only the first sample from each patient was included. Predictor variables of age, gender and source of sample were measured. Results Maximum air temperatures were higher in 2018 than 2017 (mean 27 v 16.8°C, p<0.0001). Hypernatraemia had 3.6% prevalence (66/1840 samples) during the heatwave of 2018 in comparison to 1.4% prevalence (23/1593 samples) in 2017. This corresponds to a prevalence ratio of 2.5 in heatwave 2018 compared with 2017. In 2018 hypernatraemic samples: 56%(n=37) were male, mean age was 75 with 71(n=47) General Practitioner(GP) samples,12%(n=8) inpatients and 17%(n=11) from outpatient department(OPD). In 2017 hypernatraemic samples: 30%(n=7) were male, mean age was 75 and 74%(n=17) were GP samples,17%(n=4) were inpatients, 9%(n=2) from OPD. The sources of total samples (regardless of Na level) were 63% GP, 7% inpatients and 30% outpatients. Conclusion Hypernatraemia was 2.5 times more prevalent during the heatwave in 2018 than the previous year in patients aged over 65. Hypernatraemia is more prevalent in GP and inpatients taking into account the usual distribution of samples by source. Current guidelines are either not being adhered to or ineffective, a matter which merits further evaluation.