Current and Future Burdens of Heat-Related Hyponatremia: A Nationwide Register-Based Study

Urban Heat and Burden of Hyponatremia

Importance

Hyponatremia (sodium level <135 mEq/L), the most prevalent electrolyte disorder in clinical practice, is associated with considerable clinical and economic burdens. Despite its recognized effect and indication of seasonal patterns, there is a research gap regarding heat-related hyponatremia. Addressing this issue is crucial, especially regarding projected increases in environmental temperature, particularly in urban areas.

Objective

To comprehensively analyze the association of heat in an urban setting with hyponatremia prevalence.

Design, Setting, and Participants

This cross-sectional study using retrospective time series analysis was conducted among all adult patients (age ≥18 years) presenting to the Charité-Universitätsmedizin Berlin between March 1, 2000, and August 31, 2023, with a blood sodium measurement.

Exposure

The daily heat index, which accounts for both outdoor air temperature and relative humidity.

Main Outcomes and Measures

The primary outcome measure was the daily number of hyponatremia cases, further categorized by severity. Differences in prevalence across age groups (adult patients, aged 18-65 years; and older patients, aged >65 years) and sexes were also examined.

Results

A total of 7 135 688 sodium measurements from 2 028 537 hospital visits were analyzed. The mean (SD) age at admission was 57.8 (17.8) years, and 51.7% of patients were male. A clear seasonal pattern of heat-related hyponatremia was evident among older patients, especially for moderate (sodium level, 125-129 mEq/L) and severe hyponatremia (sodium level, <125 mEq/L), where the cumulative risk over a lag period of 5 days reached a maximum relative risk (RR) of 1.26 (95% CI, 1.07-1.48) when the heat index reached 30 °C, compared with the temperature at which hyponatremia occurred least frequently. Older women were disproportionately more likely to experience hyponatremia compared with older men, with a cumulative RR of 1.10 (95% CI, 1.03-1.18) at a heat index of 26 °C. The highest RR was on lag day 0 for all subgroups (older patients: RR, 1.04 [95% CI, 1.00-1.08]; moderate and severe hyponatremia in older patients: RR, 1.05 [1.01-1.10]; and older women: RR, 1.07 [95% CI, 1.01-1.12]) and significantly increased when the heat index exceeded 15 °C (RR, 1.01 [95% CI, 1.00-1.02]).

Conclusions and Relevance

This cross-sectional study of patients with sodium measurements suggests that older people, especially women, were vulnerable to heat-related hyponatremia. Environmental heat was associated with an immediate exacerbation of hyponatremia. This finding highlights the importance of implementing prevention strategies to mitigate heat-related hyponatremia, as an increased burden in the future due to climate change is likely.

The Association of Outdoor Temperature with Severe Hyponatremia: A Study Based on the Stockholm Sodium Cohort

BACKGROUND

Hyponatremia is a common condition with unspecific symptoms and a complicated etiology. The impact of outdoor temperature on hyponatremia is not well-studied and varies depending on the climate and location. This study aimed to investigate the association between outdoor temperature and the prevalence of severe hyponatremia.

METHODS

This retrospective register-based cohort study based on the Stockholm Sodium Cohort investigated the association between ambient temperatures and severe hyponatremia (<125 mmol/L) in adults. Prevalence rates of severe hyponatremia were calculated as the number of days of severe hyponatremia divided by person-days at risk for the same temperature, using mean daily temperatures at the area of residence of each study participant to calculate exposure time. A prediction model incorporating changes in demographics and climate was used to estimate the burden of severe hyponatremia in Stockholm by 2050.

RESULTS

We identified 51,143 episodes of severe hyponatremia in 21,924 adults. A near linear modest increase in prevalence with rising temperatures was observed up to 20°C, followed by rapidly increasing rates at higher temperatures. The prevalence was higher with older age, reaching >100 days of hyponatremia per million person-days among +80-years-olds at temperatures over 22°C. Women experienced twice the rate observed in men. Temperature rises of 1°C or 2°C by the year 2050 are expected to be associated with higher prevalence rates by 66% and 73%, respectively.

CONCLUSIONS

There was a strong association between high temperatures and severe hyponatremia. The higher prevalence of severe hyponatremia was most pronounced among elderly.

Urea to Treat Hyponatremia Due to Syndrome of Inappropriate Antidiuretic Hormone Secretion: A Systematic Review and Meta-Analysis

RATIONALE & OBJECTIVE

The use of urea to treat hyponatremia related to the syndrome of inappropriate antidiuretic hormone secretion (SIADH) has not been universally adopted due to questions about effectiveness, safety, and tolerability. This systematic review and meta-analysis of observational studies addresses these questions.

STUDY DESIGN

This PRISMA-guided study examined published research across 4 electronic databases.

STUDY POPULATIONS

Patients with SIADH-related hyponatremia.

SELECTION CRITERIA

Clinical trials and observational studies reporting at least 1 outcome related to serum sodium concentration, symptom resolution, or adverse effects after oral or nasogastric urea administration.

DATA EXTRACTION

Data extraction was performed independently by 2 reviewers using a standardized form recording study characteristics, participant demographics, intervention details, and treatment outcomes.

ANALYTICAL APPROACH

A meta-analysis was conducted using the restricted maximum likelihood method for the random effects model to assess the effect of urea treatment on serum sodium and serum urea compared with other treatment modalities. Subgroup analyses were conducted based on treatment duration and SIADH severity.

RESULTS

Urea treatment significantly increased serum sodium (mean difference [MD], 9.08 [95% CI, 7.64-10.52], P<0.01) and urea (MD, 31.66 [95% CI, 16.05-47.26], P<0.01) in patients with SIADH, albeit with significantly high heterogeneity. Subgroup analysis based on the treatment duration showed a significant rise in the serum sodium level after 24 hours and 2, 5, 7, and 14 days, as well as after 1 year of treatment. Greater increases in serum sodium levels after treatment with urea occurred in patients with severe (<120 mEq/L) (MD, 18.04 [95% CI, 13.68-22.39]) than with moderate (120-129 mEq/L) (MD, 7.86 [95% CI, 6.78-8.94]) or mild (130-135 mEq/L) (MD, 8.00 [95% CI, 7.31-8.69]) SIADH-induced hyponatremia. Urea treatment was comparable to fluid restriction (MD, 0.81 [95% CI, -0.93 to 2.55], P = 0.4) and vaptans (MD, -1.96 [95% CI, -4.59 to 0.66], P=0.1) but superior to no treatment (MD, 7.99 [95% CI, 6.25-9.72], P<0.01). Urea was associated with minor adverse events, with poor palatability being the most common.

LIMITATIONS

As no randomized controlled trials investigating urea as a treatment for hyponatremia were identified for inclusion, these analyses were based on observational studies.

CONCLUSIONS

Urea is safe and effective for managing SIADH-induced hyponatremia. These finding suggest that urea may be a useful treatment modality in resource-limited settings or when other treatments are contraindicated or poorly tolerated.

TRIAL REGISTRATION

Registered at PROSPERO with study number CRD42024511685.

Dysnatremia in a changing climate: A global systematic review of the association between serum sodium and ambient temperature

OBJECTIVE

Both hyponatremia and hypernatremia have been reported to occur more frequently with higher ambient temperatures, although the underlying mechanisms are not well understood. Global temperatures are rising due to climate change, which may impact the incidence of dysnatremia worldwide. We aimed to identify, collate and critically appraise studies analyzing the relationship between climate measures (outdoor temperature, humidity) and serum sodium concentrations.

DESIGN

Systematic review, reported in accordance with PRISMA guidelines.

METHODS

MEDLINE and Embase were searched with relevant key terms. Studies assessing the effect on serum sodium measurement of elevated temperature or humidity versus a comparator were included.

RESULTS

Of 1466 potentially relevant studies, 34 met inclusion criteria, originating from 23 countries spanning all inhabited continents. The majority (30 of 34, 88%) reported a significant association between outdoor temperature and dysnatremia, predominantly lower serum sodium with increased ambient temperature. Humidity had a less consistent effect. Individuals aged above 65 years, children, those taking diuretics and antidepressants, those with chronic renal impairment or those undertaking physical exertion had increased vulnerability to heat-associated dysnatremia. The risk of bias was assessed to be high in all but four studies.

CONCLUSIONS

Higher ambient temperature is consistently associated with an increased incidence of hyponatremia. We infer that hyponatremia presentations are likely to rise with increasing global temperatures and the frequency of extreme heat events secondary to climate change. Evidence-based public health messages, clinician education and reduction in fossil fuel consumption are necessary to reduce the expected burden on healthcare services worldwide.

Assessment of 24 h Sodium and Potassium Urinary Excretion in Normotensive and Hypertensive Dominican Adults

Higher salt (sodium) intake has been associated with higher blood pressure (BP). The degree of association may be influenced by factors such as age, origin, and dietary components. This study aimed to evaluate the 24 h urinary sodium (Na) and potassium (K) excretion in normotensive and hypertensive Dominican adults and estimate their salt intake. 163 volunteers (18-80 years old) participated in a cross-sectional study. The 24 h Na and K urinary excretion were measured using an ion-selective electrode technique. Na and K urinary excretion (99.4 ± 46.5 and 35.0 ± 17.5 mmol/24 h) did not correlate with BP, except in the normotensive group, in which K correlated with SBP (0.249, p = 0.019). Na and K excretion were similar in normotensive and hypertensive subjects. When considering two age groups (18-45, 46-80 years), the Na-to-K molar ratio (3.1 ± 1.3) was higher in younger subjects (p = 0.040). Na-to-K ratio was associated with DBP in the total group (r = 0.153, p = 0.052), in the hypertensive group (r = 0.395, p < 0.001), and in the older group with SBP (0.350, p = 0.002) and DBP (0.373, p < 0.001). In the older group, Na-to-K ratio and DBP correlated after controlling for subjects with hypertension controlled by treatment (r = 0.236, p = 0.041). The Na-to-K ratio correlated, when salt intake was over 5 g/day (52.2%), with SBP (rho = 0.219, p = 0.044) and DBP (rho = 0.259, p = 0.017). Determinants of BP in the total sample were age (SBP, beta: 0.6 ± 0.1, p < 0.001; DBP, beta: 0.2 ± 0.1, p < 0.002), sex (SBP, beta: 11.2 ± 3.5, p = 0.001), body mass index (BMI) (SBP, beta: 1.0 ± 0.3, p < 0.001; DBP, beta: 0.4 ± 0.2, p = 0.01), and Na-to-K ratio (SBP, beta: 3.0 ± 1.1, p = 0.008; DBP, beta: -12.3 ± 4.0, p = 0.002). Sex and BMI were determinants in the younger group. Na-to-K molar ratio was determinant in the older group (SBP, beta: 6.7 ± 2.4, p = 0.005; DBP, beta: 3.8 ± 1.1, p < 0.001). The mean Na and salt intakes (2.3 and 5.8 g/day) were slightly higher and the K intake lower (1.4 g/day) than WHO recommendations.

[Climate change and (surgical) health in context]

BACKGROUND

The impacts of the climate crisis will result in a health crisis in addition to loss of habitats and increasing supply uncertainty. In this context, the health sector and especially surgery are relevant emitters of greenhouse gases, thus contributing to the magnitude of the climate crisis. Many reviews regarding the impacts on human health are available; however, a view from the surgical perspective has so far been underrepresented.

MATERIAL AND METHODS

This narrative review summarizes the relevance of climate-related changes for the surgical disciplines based on a literature search.

RESULTS

Immediate impacts are expected by the increasing number of extreme weather events, e.g., floods, droughts and wildfires. In these settings, surgery is a part of the disaster medicine chain but simultaneously the functionality of surgical departments can be impaired or even break down when they are themselves affected by extreme weather events. Heat waves cause an increase in surgical site infections, which may lead to postponement of elective surgery for patients at high risk. Collateral impacts are mirrored by an increase in the incidence of lung and skin cancers, which often need surgical treatment within a multidisciplinary setting. Additionally, there are indirect impacts that are of a very different nature, e.g., inadequate diet which leads to further deterioration of the greenhouse gas footprint of the health sector due to the necessity of bariatric surgical capacities.

CONCLUSION

The climate crisis represents a major challenge in surgery and all other medical disciplines. At the same time is it indispensable that the health sector and therefore surgery, take steps towards a zero emission pathway.