High water evaporation rate is associated with low blood pressure in chronic peritoneal dialysis patients

The relationship between water evaporation rate (WER) and blood pressure (BP) in continuous ambulatory peritoneal dialysis (CAPD) patients has not been addressed before. This study was undertaken to evaluate the effects of WER on the BP and body weight (BW) of end-stage renal disease patients treated with CAPD.

Based on mean WER of each month, the year 2005 was divided into "high WER" and "low WER" stages. This study enrolled 66 CAPD patients at our center during 2005. The BP and BW of each patient were collected monthly. WER was measured with a class A evaporation pan.

Compared to the high WER stage, CAPD patients had higher BP (systolic: 142 ± 29 vs 134 ± 27 mmHg, p < 0.001; diastolic: 86 ± 17 vs 84 ± 16 mmHg, p < 0.001) and BW (56.8 ± 10.2 vs 56.1 ± 10.2 kg, p < 0.001) in the low WER stage. Ambient temperature was significantly higher in the high WER stage (p = 0.004) and it was also positively correlated with WER (r = 0.82, p = 0.0012). Both mean BP (r = -0.72, p = 0.0089) and BW (r = -0.79, p = 0.002) showed inverse relationships to the WER. Moreover, both mean BP (r = -0.95, p < 0.001) and BW (r = -0.90, p < 0.001) also showed negative linear regressions to ambient temperature. There was a positive linear regression between mean BP and BW (r = 0.85, p = 0.0004). Multiple linear regression analysis found that WER (β = -0.672, p = 0.026) was an independent factor correlated to patients' mean BP.

CAPD patients had lower BP and BW in the high WER stage. These decreases were associated with higher ambient temperature and WER. We hypothesize that increased insensible salt and fluid loss secondary to high WER during hot seasons, especially in subtropical areas, ameliorates the hypervolemia and hypertension in CAPD patients.