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 h of very hot and dry heat. On each of 3 days (randomized), older adults (12 males/8 females; 66-84 yr) were exposed to 3 h 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 (means ± 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 with control, the AKIRISK score at end-heating was -0.18 [95% CI: -0.35, -0.02] lower in water spray (<i>P</i> = 0.047) and 0.26 [0.09, 0.44] higher in fan (<i>P</i> = 0.002). Repeated-measures correlations demonstrated positive associations between end-heating core temperature (<i>r</i> = 0.77; <i>P</i> < 0.001) and fluid loss (<i>r</i> = 0.48; <i>P</i> = 0.001), both relative to the end-heating AKIRISK score. Compared with control, end-heating plasma creatinine was not different (<i>P</i> = 0.43), but plasma cystatin C was 0.07 [-0.13, -0.01] mg/L lower (<i>P</i> = 0.025) in water spray. Compared with control, end-heating creatinine was 0.08 [0.03, 0.12] mg/dL higher (<i>P</i> < 0.001), and cystatin C was 0.07 [0.01, 0.13] mg/L higher (<i>P</i> = 0.026) in the fan trial. These findings suggest that in very hot and dry conditions, water spray can attenuate, whereas fans elevate heat-related increases in AKI risk biomarkers.<b>NEW & NOTEWORTHY</b> Acute kidney injury contributes to the increased mobility and mortality reported during heatwaves. Air conditioning is protective but may not be available to all; thus, there is a need to identify non-air-conditioning-dependent cooling strategies. We show that water spray mitigates, but fans elevate heat-related increases in biomarkers of acute kidney injury in older adults exposed to 3 h of very hot and dry conditions.