Low energy cooling strategies modulate biomarkers of kidney injury risk in older adults exposed to very hot and dry heat

Acute kidney injury (AKI) contributes to excess hospital admissions observed during heatwaves. We tested the hypothesis that water spray and fan use would modulate biomarkers of AKI risk in older adults exposed to 3 hours of very hot and dry heat. On each of three days (randomized), older adults (12-males/8-females; 66-84 years) were exposed to 3-hours of heating (47°C, 15% relative humidity) with no cooling intervention (control), water spray, or fan use. We assessed core temperature, fluid loss, biomarkers of AKI risk (AKIRISK™ Score), and kidney function (plasma creatinine and cystatin C). The increase in core temperature was 1.3±0.5°C (mean ± SD) in control, 1.0±0.2°C in water spray, and 1.9±0.7°C in the fan trial. Fluid loss was 0.9±0.2% in control, 0.4±0.2% in water spray, and 1.5±0.4% in fan. Compared to control, AKIRISK™ Score at end-heating was -0.18 [95% CI: -0.35, -0.02] lower in water spray (p=.047) and 0.26 [0.09, 0.44] higher in fan (p=.002). Repeated measures correlations demonstrated positive associations between end-heating core temperature (r=0.77; p<.001) and fluid loss (r=0.48; p=.001) both relative to end-heating AKIRISK™ Score. Compared to control, end-heating plasma creatinine was not different (p=.43) but plasma cystatin C was 0.07 [-0.13, -0.01] mg/L lower (p=.025) in water spray. Compared to control, end-heating creatinine was 0.08 [0.03, 0.12] mg/dL higher (p<.001) and cystatin C was 0.07 [0.01, 0.13] mg/L higher (p=.026) in the fan trial. These findings suggest that in very hot and dry conditions water spray can attenuate, while fans elevate, heat-related increases in AKI risk biomarkers.