The effect of ambient temperature on blood pressure of patients undergoing hemodialysis in the Pantanal-Brazil

Ambient temperature and the occurrence of intradialytic hypotension in patients receiving hemodialysis

Background

Intradialytic hypotension (IDH) is a common hemodialysis complication causing adverse outcomes. Despite the well-documented associations of ambient temperatures with fluid removal and pre-dialysis blood pressure (BP), the relationship between ambient temperature and IDH has not been adequately studied.

Methods

We conducted a cohort study at a tertiary hospital in southern Taiwan between 1 January 2016 and 31 October 2021. The 24-h pre-hemodialysis mean ambient temperature was determined using hourly readings from the weather station closest to each patient's residence. IDH was defined using Fall40 [systolic BP (SBP) drop of ≥40 mmHg] or Nadir90/100 (SBP <100 if pre-dialysis SBP was ≥160, or SBP <90 mmHg). Multivariate logistic regression with generalizing estimating equations and mediation analysis were utilized.

Results

The study examined 110 400 hemodialysis sessions from 182 patients, finding an IDH prevalence of 11.8% and 10.4% as per the Fall40 and Nadir90/100 criteria, respectively. It revealed a reverse J-shaped relationship between ambient temperature and IDH, with a turning point around 27°C. For temperatures under 27°C, a 4°C drop significantly increased the odds ratio of IDH to 1.292 [95% confidence interval (CI) 1.228 to 1.358] and 1.207 (95% CI 1.149 to 1.268) under the Fall40 and Nadir90/100 definitions, respectively. Lower ambient temperatures correlated with higher ultrafiltration, accounting for about 23% of the increased IDH risk. Stratified seasonal analysis indicated that this relationship was consistent in spring, autumn and winter.

Conclusion

Lower ambient temperature is significantly associated with an increased risk of IDH below the threshold of 27°C, irrespective of the IDH definition. This study provides further insight into environmental risk factors for IDH in patients undergoing hemodialysis.

Ambient temperature and ambulatory blood pressure: An hourly-level, longitudinal panel study

BACKGROUND

Variations of blood pressure (BP) related to air temperature have been reported previously; however, no evidence is available regarding the association of hourly ambient temperature with ambulatory blood pressure.

METHODS

We conducted a longitudinal panel study among 1895 patients from an outpatient department who received repeated ambulatory blood pressure monitoring in Urumqi, China between July 2020 and December 2021. We obtained hourly ambient temperature from the nearest monitoring station to the residential address, and measured 4 ambulatory blood pressure indicators. Linear mixed-effect model combined with distributed lag models were applied to investigate the cumulative associations of hourly temperature with BP.

RESULTS

A total of 97,466 valid blood pressure measurements were evaluated. We observed almost linear and monotonically decreasing relationships between temperature and blood pressure. The effects occurred in the same hour, attenuated thereafter and became insignificant approximately 36 h. A 10 °C decrease in temperature was significantly associated with increments of 0.84 mmHg in systolic blood pressure, 0.56 mmHg in diastolic blood pressure, 1.38 mmHg in mean arterial pressure, and 0.66 mmHg in pulse pressure over lag 0 to 36 h. Stronger associations were found among patients of female sex, age between 18 and 65 years, overweight or obesity, minority, less education or in the cold season, as well as those without hypertension or with coronary heart disease, or did not take anti-hypertension medication.

CONCLUSION

Our study provides robust evidence that hourly ambient temperature is inversely associated with ambulatory blood pressure. It also highlights a linear relationship between decreased ambient temperature and elevated BP, which may have implications for the prevention and management of hypertension in susceptible populations.

Correlation of NO and ET-1 Levels with Blood Pressure Changes in Hemodialysis Patients after Arteriovenous Fistula Surgery

Hemodialysis (HD) is the most common renal replacement therapy for patients with end-stage renal disease (ESRD) and can significantly reduce mortality and improve the quality of life of patients. The occurrence of intradialytic hypotension and intradialytic hypertension are important risk factors for death and disability during dialysis in patients with ESRD, yet their etiology remains unclear, and some studies suggest that nitric oxide (NO) and endothelin-1 (ET-1) may play an important role in these hemodynamic alterations. For this purpose we examined the changes in NO and ET-1 levels during hemodialysis in 30 patients on maintenance hemodialysis (MHD) after arteriovenous fistula surgery. Thirty dialysis patients were divided into group I (stable blood pressure during dialysis), group II (Intradialytic hypotension) and group III (Intradialytic hypertension) according to the change of blood pressure (BP) during hemodialysis, with 10 cases in each group. BP of MHD patients were measured Pre-dialysis (Pre-D), at 1 h of dialysis (1h-D), at 2 h of dialysis (Mid-D, 2h-D), at 3 h of dialysis (3h-D), and at the end of dialysis (Post-D); and blood samples were taken from the arterial end at Pre-D, Mid-D, and Post-D to measure NO and ET-1 levels. The results of the analysis showed that as dialysis proceeded and ended, the NO levels in the three groups gradually decreased, with significant differences compared with those before dialysis (p < 0.05); the ET-1 levels in group III gradually increased, with significant differences compared with those before dialysis (p < 0.05), while the increasing trend of ET-1 levels in group I and group II was not significant. The increasing trend of MAP in group I was not significant (p > 0.05); MAP in group II showed a gradual decrease and MAP in group III showed an increasing trend, and the difference between MAP after dialysis and before dialysis was significant (p < 0.05). Correlation analysis showed a significant positive correlation between ET-1 levels and MAP in Group III at Mid-D (r = 0.847, p = 0.002). This shows that serum ET-1 and NO levels are significantly higher than normal in MHD patients after arteriovenous endovascular fistula surgery, and both ET-1 and NO levels are changing during dialysis, and there may be a link between their changes and blood pressure changes. It is suggested that the blood pressure fluctuations that occur during dialysis in MHD patients may be related to endothelial cell dysfunction.