Late hyponatremia in very-low-birth-weight infants: incidence and associated risk factors

Higher versus lower sodium intake for preterm infants

BACKGROUND

Infants born preterm are at increased risk of early hypernatraemia (above-normal blood sodium levels) and late hyponatraemia (below-normal blood sodium levels). There are concerns that imbalances of sodium intake may impact neonatal morbidities, growth and developmental outcomes.

OBJECTIVES

To determine the effects of higher versus lower sodium supplementation in preterm infants.

SEARCH METHODS

We searched CENTRAL in February 2023; and MEDLINE, Embase and trials registries in March and April 2022. We checked reference lists of included studies and systematic reviews where subject matter related to the intervention or population examined in this review. We compared early (< 7 days following birth), late (≥ 7 days following birth), and early and late sodium supplementation, separately.

SELECTION CRITERIA

We included randomised, quasi-randomised or cluster-randomised controlled trials that compared nutritional supplementation that included higher versus lower sodium supplementation in parenteral or enteral intake, or both. Eligible participants were preterm infants born before 37 weeks' gestational age or with a birth weight less than 2500 grams, or both. We excluded studies that had prespecified differential water intakes between groups.

DATA COLLECTION AND ANALYSIS

Two review authors independently assessed eligibility and risk of bias, and extracted data. We used the GRADE approach to assess the certainty of evidence.

MAIN RESULTS

We included nine studies in total. However, we were unable to extract data from one study (20 infants); some studies contributed to more than one comparison. Eight studies (241 infants) were available for quantitative meta-analysis. Four studies (103 infants) compared early higher versus lower sodium intake, and four studies (138 infants) compared late higher versus lower sodium intake. Two studies (103 infants) compared intermediate sodium supplementation (≥ 3 mmol/kg/day to < 5 mmol/kg/day) versus no supplementation, and two studies (52 infants) compared higher sodium supplementation (≥ 5 mmol/kg/day) versus no supplementation. We assessed only two studies (63 infants) as low risk of bias. Early (less than seven days following birth) higher versus lower sodium intake Early higher versus lower sodium intake may not affect mortality (risk ratio (RR) 1.02, 95% confidence interval (CI) 0.38 to 2.72; I2 = 0%; 3 studies, 83 infants; low-certainty evidence). Neurodevelopmental follow-up was not reported. Early higher versus lower sodium intake may lead to a similar incidence of hyponatraemia < 130 mmol/L (RR 0.68, 95% CI 0.40 to 1.13; I2 = 0%; 3 studies, 83 infants; low-certainty evidence) but an increased incidence of hypernatraemia ≥ 150 mmol/L (RR 1.62, 95% CI 1.00 to 2.65; I2 = 0%; 4 studies, 103 infants; risk difference (RD) 0.17, 95% CI 0.01 to 0.34; number needed to treat for an additional harmful outcome 6, 95% CI 3 to 100; low-certainty evidence). Postnatal growth failure was not reported. The evidence is uncertain for an effect on necrotising enterocolitis (RR 4.60, 95% CI 0.23 to 90.84; 1 study, 46 infants; very low-certainty evidence). Chronic lung disease at 36 weeks was not reported. Late (seven days or more following birth) higher versus lower sodium intake Late higher versus lower sodium intake may not affect mortality (RR 0.13, 95% CI 0.01 to 2.20; 1 study, 49 infants; very low-certainty evidence). Neurodevelopmental follow-up was not reported. Late higher versus lower sodium intake may reduce the incidence of hyponatraemia < 130 mmol/L (RR 0.13, 95% CI 0.03 to 0.50; I2 = 0%; 2 studies, 69 infants; RD -0.42, 95% CI -0.59 to -0.24; number needed to treat for an additional beneficial outcome 2, 95% CI 2 to 4; low-certainty evidence). The evidence is uncertain for an effect on hypernatraemia ≥ 150 mmol/L (RR 7.88, 95% CI 0.43 to 144.81; I2 = 0%; 2 studies, 69 infants; very low-certainty evidence). A single small study reported that later higher versus lower sodium intake may reduce the incidence of postnatal growth failure (RR 0.25, 95% CI 0.09 to 0.69; 1 study; 29 infants; low-certainty evidence). The evidence is uncertain for an effect on necrotising enterocolitis (RR 0.07, 95% CI 0.00 to 1.25; 1 study, 49 infants; very low-certainty evidence) and chronic lung disease (RR 2.03, 95% CI 0.80 to 5.20; 1 study, 49 infants; very low-certainty evidence). Early and late (day 1 to 28 after birth) higher versus lower sodium intake for preterm infants Early and late higher versus lower sodium intake may not have an effect on hypernatraemia ≥ 150 mmol/L (RR 2.50, 95% CI 0.63 to 10.00; 1 study, 20 infants; very low-certainty evidence). No other outcomes were reported.

AUTHORS' CONCLUSIONS

Early (< 7 days following birth) higher sodium supplementation may result in an increased incidence of hypernatraemia and may result in a similar incidence of hyponatraemia compared to lower supplementation. We are uncertain if there are any effects on mortality or neonatal morbidity. Growth and longer-term development outcomes were largely unreported in trials of early sodium supplementation. Late (≥ 7 days following birth) higher sodium supplementation may reduce the incidence of hyponatraemia. We are uncertain if late higher intake affects the incidence of hypernatraemia compared to lower supplementation. Late higher sodium intake may reduce postnatal growth failure. We are uncertain if late higher sodium intake affects mortality, other neonatal morbidities or longer-term development. We are uncertain if early and late higher versus lower sodium supplementation affects outcomes.

Risk Factors and Effects of Severe Late-Onset Hyponatremia on Long-Term Growth of Prematurely Born Infants

PURPOSE

Sodium is an essential nutritional electrolyte that affects growth. A low serum sodium concentration in healthy premature infants beyond 2 weeks of life is called late-onset hyponatremia (LOH). Here, we investigated the association between LOH severity and growth outcomes in premature infants.

METHODS

Medical records of premature infants born at ≤32 weeks of gestation were reviewed. LOH was defined as a serum sodium level <135 mEq/L regardless of sodium replacement after 14 days of life. Cases were divided into two groups, <130 mEq/L (severe) and ≥130 mEq/L (mild). Characteristics and growth parameters were compared between the two groups.

RESULTS

A total of 102 premature infants with LOH were included. Gestational age ([GA] 27.7 vs. 29.5 weeks, p<0.001) and birth weight (1.04 vs. 1.34 kg, p<0.001) were significantly lower in the severe group. GA was a risk factor of severe LOH (odds ratio [OR], 1.328, p=0.022), and severe LOH affected the development of bronchopulmonary dysplasia (OR, 2.950, p=0.039) and led to a poor developmental outcome (OR, 9.339, p=0.049). Growth parameters at birth were lower in the severe group, and a lower GA and sepsis negatively affected changes in growth for 3 years after adjustment for time. However, severe LOH was not related to growth changes in premature infants.

CONCLUSION

Severe LOH influenced the development of bronchopulmonary dysplasia and developmental outcomes. However, LOH severity did not affect the growth of premature infants beyond the neonatal period.

Idiopathic SIADH in the premature newborn, a case report

BACKGROUND:

Hyponatremia is a common laboratory finding in premature and ill neonates. When the degree of hyponatremia is more severe, the likelihood of a pathologic entity increases. In this case report we describe a premature neonate with severe hyponatremia due to the idiopathic syndrome of inappropriate antidiuretic hormone secretion (SIADH).

CASE DESCRIPTION:

The patient is a male neonate, born prematurely. He was admitted to the neonatal intensive care unit and received non-invasive respiratory support. After 48 hours of life serum sodium (Na⁺) decreased to 115 mmol/l. Hyponatremia progressively worsened despite aggressive Na⁺ supplementation. The clinical and laboratory data were most consistent with severe SIADH. Fluid restriction was initiated which resulted in a gradual normalization of Na⁺. A causal factor for development of SIADH could not be identified.

CONCLUSION:

When a neonate presents with significant hyponatremia that is not responsive to conventional therapy, it is important to perform a diagnostic work-up for SIADH, even in the absence of overt triggering factors.

Late onset hyponatremia in preterm newborns: is the sodium content of human milk fortifier insufficient?

Introduction: In this study, we aimed to define the incidence and time to detection of late onset hyponatremia (LOH) as well as factors affecting its development in preterm newborns. We also aimed to determine the daily sodium requirement of these patients.Methods: We studied a total of 145 very low birth weight infants with a full or nearly full enteral diet and followed them up until discharge. We recorded demographic and clinic characteristics. We measured serum sodium (SNa) levels at least once a week after the second week. We compared infants with LOH with other infants to analyze possible risk factors.Results: Twenty-nine (20%) infants developed LOH in an average of 23.4 ± 7.8 days. The mean SNa level of these infants was 124.6 ± 5.6 mmol/L. Logistic regression analysis showed that a birth weight of less than 1000 g, preterm early membrane rupture, and nutrition with fortified human milk alone were risk factors for LOH. The mean daily amount of sodium added to the nutrition of hyponatremic preterm infants was 3.6 ± 2.1 mmol/L. Subgroup analysis showed that the incidence of LOH was two times higher (39.2%) in infants with a birth weight of less than 1000 g.Conclusion: We observed the development of LOH within three to four weeks in nearly half of preterm infants fed with fortified human milk, especially those with a birth weight of less than 1000 g. We believe that the sodium content of currently used human milk fortifiers should be increased.

Comparison of sodium ion levels between an arterial blood gas analyzer and an autoanalyzer in preterm infants admitted to the neonatal intensive care unit: a retrospective study

BACKGROUND

The difference in sodium ion levels determined with direct and indirect methods often exceeds the permissible limit clinically. Additionally, no previous study has assessed the difference in the sodium ion levels between direct and indirect methods in premature infants. Therefore, the present study aimed to compare sodium ion levels obtained using an arterial blood gas analyzer (ABGA; direct method) and an autoanalyzer (indirect method) to determine whether they are equivalent in premature infants.

METHODS

The present retrospective study included 450 preterm infants (weight, <2500 g) who were admitted to the neonatal intensive care unit (NICU) of our hospital between March 2012 and April 2014. We compared sodium ion levels in 1041 samples analyzed using an ABGA (Stat Profile® CCX Series, Nova Biomedical, Waltham, MA) and an autoanalyzer (ADVIA® 2400 Clinical Chemistry System, Siemens, Tarrytown, NY). The data were evaluated using Spearman's correlation coefficient analysis, Bland-Altman plot, Deming regression analysis, and multivariate logistic regression analysis.

RESULTS

The mean sodium ion levels were 134.6 ± 3.5 mmol/L using the ABGA and 138.8 ± 4.7 mmol/L using the autoanalyzer (P < 0.001). Among the 1041 samples, 957 (91.9 %) showed lower sodium ion levels with the ABGA than with the autoanalyzer and 74 (7.1 %) showed lower sodium ion levels with the autoanalyzer than with the ABGA. The incidence of hyponatremia identified using the ABGA was 51.9 % (541/1041), while the incidence of hyponatremia identified using the autoanalyzer was only 14.0 % (146/1041). The Deming regression analysis of the sodium ion levels between the ABGA and the autoanalyzer yielded the following formula: autoanalyzer Na (mmol/L) = 20.7 + (0.9 × ABGA Na [mmol/L]). In the multivariate logistic regression analysis, low plasma protein level (<4.3 g/dL) was found to be an independent risk factor for a sodium ion level difference of >4 mmol/L between the two methods (odds ratio = 2.870, P < 0.001).

CONCLUSION

The sodium ion levels determined using the ABGA and the autoanalyzer might not be equivalent in premature infants admitted to the NICU. Therefore, clinicians should be careful when diagnosing sodium ion imbalance in premature infants and providing treatment.

Impact of changes in serum sodium levels on 2-year neurologic outcomes for very preterm neonates

OBJECTIVE

The goal was to analyze the relationship between changes in serum sodium levels during the first month of life and impaired functional outcomes at 2 years of age for very preterm infants.

METHODS

All very preterm infants who were born at <33 weeks of gestation between January 1, 2003, and July 31, 2004, were hospitalized in the NICU, and survived to discharge were included in this study. Changes in serum sodium levels were measured, and infants were evaluated at corrected age of 2 years.

RESULTS

The analysis involved 237 patients, for whom 3927 serum sodium determinations were performed during the first month of life. We defined 3 tertiles of changes in serum sodium levels. A total of 84 infants demonstrated small changes in serum sodium levels (<8 mEq/ L), 86 demonstrated large changes (8 -13 mEq/L), and 67 demonstrated very large changes (13 mEq/L). The reference group was represented by the first tertile. At 2 years of age, large and very large changes in serum sodium levels were significantly associated with risk of impaired functional outcomes, after adjustment for gestational age and perinatal and neonatal hospitalization characteristics (large changes: odds ratio: 3.5 [95% confidence interval: 1.1-11.8]; P = .04; very large changes: odds ratio: 5.1 [95% confidence interval: 1.3-13.6]; P = .02).

CONCLUSIONS

Although large and very large changes in serum sodium levels may simply reflect the severity of illness and/or the quality of care, a causal relationship with outcomes cannot be excluded. Cautious fluid and electrolyte management is recommended for very premature infants.

Nutritional assessment and therapeutic interventions for the preterm infant

All components of assessment contribute to the final decision regarding nutritional status of the infant and the nutritional therapy indicated. One parameter by itself such as nutrient intake, weight change, or a laboratory value cannot clearly determine the total nutritional state of the infant. Achieving appropriate intakes and weight gains are two excellent parameters. Laboratory values can determine if nutrition is tolerated and manipulations are indicated.

SIADH: a case review

Because the syndrome of inappropriate secretion of antidiuretic hormone (SIADH) can cause neurologic sequelae with the potential to affect long-term outcomes, its prompt recognition and treatment are essential. Normally, antidiuretic hormone (ADH) is secreted when effective circulating blood volume is decreased. SIADH is marked by secretion of ADH in the presence of effective or normal circulating blood volume. This causes plasma hyponatremia simultaneously with plasma hypo-osmolality and inappropriate hyperosmolality of the urine. This article explains the pathophysiology of the syndrome; describes its diagnosis, clinical course, and treatment; and exemplifies the syndrome with a case study.