Inpatient Sodium Imbalances Linked to Adverse COVID-19 Outcomes

Miriam E. Tucker

March 10, 2021

Editor's note: Find the latest COVID-19 news and guidance in Medscape's Coronavirus Resource Center.

Both high and low serum sodium levels are associated with adverse outcomes for hospitalized patients with COVID-19, new research suggests.

In the retrospective study of 488 patients hospitalized with COVID-19 at one of two London hospitals between February and May 2020, hypernatremia (defined as serum sodium level >145 mmol/L) at any time point during hospital stay was associated with a threefold increase in inpatient mortality.

Hyponatremia (serum sodium level <135 mmol/L) was associated with twice the likelihood of requiring advanced ventilatory support. In-hospital mortality was also increased among patients with hypovolemic hyponatremia.

"Serum sodium values could be used in clinical practice to identify patients with COVID-19 at high risk of poor outcomes who would benefit from more intensive monitoring and judicious rehydration," say Ploutarchos Tzoulis, MD, PhD, and colleagues in their article, which was published online on February 24 in the Journal of Clinical Endocrinology and Metabolism.

The findings will also be presented at the virtual annual meeting of the Endocrine Society (ENDO 2021) March 20-24.

Should Sodium Be Included in a Risk Calculator for COVID-19?

Tzoulis, professor of endocrinology at the University College London Medical School, London, United Kingdom, told Medscape Medical News, "Sodium could be incorporated in risk calculators across other routine biomarkers, such as white cell count, lymphocytes, and CRP [C-reactive protein], in order to provide a tool for dynamic risk stratification throughout the clinical course of COVID-19 and assist clinical decision making."

Moreover, he said, "We should follow less conservative strategies in the rate and amount of fluid resuscitation in order to prevent hypernatremia, which is induced by negative fluid balance and can often be iatrogenic."

Asked to comment, Steven Q. Simpson, MD, professor of medicine, Division of Pulmonary, Critical Care, and Sleep Medicine, the University of Kansas, Kansas City, said that the article is missing key results that would assist in interpreting of the findings.

"Data regarding diuretic use and sparing of fluid administration are not in the paper.... It is simply not possible to tell whether serum sodium is a 'predictor'...or if it is a side effect of other issues or actions taken by physicians in patients who are progressing poorly.

"To say that sodium needs to be included in a risk calculator is to subtly suggest that there is some causal association with mortality, and that has quite clearly not been established," stressed Simpson, who is president of the American College of Chest Physicians but was not speaking for the organization.

He added: "The data are interesting, but not actionable. It is common practice in critical care medicine to adjust water and salt intake to maintain serum sodium within the normal range, so the paper really doesn't change any behavior."

Tzoulis told Medscape Medical News that, despite not having electronic medical record data on diuretic use or fluid input and output, "our acute physicians and intensivists at both study sites have been adamant that they've not routinely used diuretics in COVID-19 patients. Diuretics have been sparingly used in our cohort, and also the frequency of pulmonary edema was reported as below 5%."

Regarding volume of fluid intake, Tzoulis noted, "At our hospital sites, the strategy has been that of cautious fluid resuscitation. In fact, the amount of fluid given has been reported by our physicians and intensivists as 'on purpose much more conservative than the usual one adopted in patients with community-acquired pneumonia at risk of respiratory failure.' "

Hyper- and Hyponatremia Linked to Adverse COVID-19 Outcomes

In the study, 5.3% of the 488 patients had hypernatremia at hospital presentation, and 24.6% had hyponatremia. Of note, only 19% of those with hyponatremia underwent laboratory workup to determine the etiology. Of those, three quarters had hypovolemic hyponatremia, determined on the basis of a urinary sodium cutoff of 30 mmol/L.

The total in-hospital mortality rate was 31.1%. There was a strong, although nonsignificant, trend toward higher mortality in association with sodium status at admission. Death rates were 28.4%, 30.8%, and 46.1% for those who were normonatremic, hyponatremic, and hypernatremic, respectively (P = .07). Baseline serum sodium levels didn't differ between survivors (137 mmol/L) and nonsurvivors (138 mmol/L).

In multivariable analysis, the occurrence of hypernatremia at any point during the first 5 days in the hospital was among three independent risk factors for higher in-hospital mortality (adjusted hazard ratio, 2.74; P = .02). The other risk factors were older age and higher CRP level.

Overall, hyponatremia was not associated with death (P = .41).

During hospitalization, 37.9% of patients remained normonatremic; 36.9% experienced hyponatremia; 10.9% had hypernatremia; and 14.3% had both conditions at some point during their stay.

In-hospital mortality was 21% among those with normonatremia, compared to 56.6% for those with hypernatremia (odds ratio [OR], 3.05; P = .0038) and 45.7% for those with both (OR, 2.25; P < .0001).

The 28.3% mortality rate in the overall group that experienced hyponatremia didn't differ significantly from the 21.1% in the normonatremic group (OR, 1.34; P = .16). However, the death rate was 40.9% among the subgroup that developed hypovolemic hyponatremia, significantly higher than the normonatremic group (OR, 2.59; P = .0017).

The incidence of hyponatremia decreased from 24.6% at admission to 14.1% 5 days later, whereas the frequency of hypernatremia rose from 5.3% to 13.8%.

Key Finding: Link Between Hospital-Acquired Hypernatremia and Death

"The key novel finding of our study was that hospital-acquired hypernatremia, rather than hypernatremia at admission, was a predictor for in-hospital mortality, with the worst prognosis being reported in patients with the largest increase in serum sodium in the first 5 days of hospitalization," note Tzoulis and colleagues.

Hypernatremia was present in 29.6% of nonsurvivors, compared to 5.2% in survivors.

Among 120 patients with hyponatremia at admission, 31.7% received advanced respiratory support, compared to 17.5% and 7.7% of those with normonatremia or hypernatremia, respectively (OR, 2.18; P = .0011).

In contrast, there was no difference in the proportions needing ventilatory support between those with hypernatremia and those with normonatremia (16.7% vs 12.4%; OR, 1.44; P = .39).

Acute kidney injury occurred in 181 patients (37.1%). It was not related to serum sodium concentration at any time point.

Tzoulis and Simpson have disclosed no relevant financial relationships.

J Clin Endocrinol Metab. Published online February 24, 2021. Abstract

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