Hypophosphatemia in Critically Ill Children: Risk Factors, Outcome and Mechanism

Fluid and electrolyte pathophysiology in common febrile illness in children and the implications for clinical management

Achieving fluid homeostasis and the management of fluid and electrolyte complications are constants in the treatment of seriously ill children worldwide. Consensus on the most appropriate fluid strategy for unwell children has been difficult to achieve and has evolved over the last two decades, most notably in high-income countries where adverse events relating to poor fluid management were identified more readily, and official robust inquiries were possible. However, this has not been the situation in many low-income settings where fluids that are prohibited from use in high-income countries may be all that are available, local guidelines and processes to recognise adverse events are not developed, and there has been limited training on safe fluid management for front-line healthcare workers. This narrative review outlines the fluid and electrolyte pathophysiology of common febrile illnesses in children, describes the evolution of this field and concludes with implications and principles of a fluid management strategy for seriously ill children. This review was prepared as a physiological background paper to support evidence presented to the WHO Guideline Development Group for Fluid Guidelines in Children, Geneva, March 2024.

Differential Serum Phosphate Levels in Pediatric Febrile Syndromes and Their Clinical Significance

BACKGROUND

The potential of hypophosphatemia (HP) to differentiate between febrile syndromes and its clinical significance in children without sepsis were not previously described.

METHODS

Data were retrospectively collected of febrile children aged 3 months to 18 years, hospitalized at general pediatric wards during 2010-2019. Phosphate levels were compared between bacterial infection (BI), viral infection (VI), and Kawasaki disease (KD). Regression analyses were used to evaluate the relationship between HP and outcome.

RESULTS

Of 3963 febrile children, 559 had BI, 3271 had VI, and 133 had KD. In BI compared to VI and KD, HP was more prevalent (49.2%, 19.7%, and 31.6%, respectively; P<0.001) and more severe [median (interquartile range) phosphate standard deviation score: -1.85 (2.08), -0.56 (2.08), and -1.20 (2.28), respectively; P<0.001]. In the BI group, Pi-SDS level was lower among patients with than without bacteremia (-2.33 ± 1.8 vs. -0.79 ± 1.68; P<0.001). Phosphate levels displayed discriminatory potential between bacterial and viral etiologies, with an area under the curve of 0.719 (95% CI, 0.697-0.742). Minimal phosphate standard deviation score values had a negative weak correlation with the maximal C-reactive protein levels and white blood cell count. Univariate and multivariate analyses showed an association of HP with a more severe disease course, manifested by longer hospital stay [+2.10 (95% CI, 0.75-3.46) days; P=0.003] and a higher rate of intensive care unit admission [odds ratio, 2.63 (95% CI, 1.94-3.56); P<0.001).

CONCLUSIONS

Hypophosphatemia rates were highest in bacterial etiology, intermediate in KD, and lowest in viral etiology and were associated with poorer outcomes. Phosphate level may serve as a marker for ruling out a bacterial etiology.

The impact of tubular dysfunction and its relationship with acute kidney injury in children

BACKGROUND

Tubular dysfunction can cause electrolyte disturbances with potentially serious consequences. We studied the epidemiology and outcomes of electrolyte disturbances and tubular dysfunction among critically ill children and evaluated their relationships with acute kidney injury (AKI).

METHODS

We conducted a prospective cohort study recruiting children aged 1 month to ≤ 18 years old admitted to the pediatric intensive care unit (PICU) from 6/2020 to 6/2021. The serum levels of sodium, potassium, calcium, phosphate, and magnesium were reviewed and simultaneous urinary investigations for tubular function were performed among children with electrolyte disturbances.

RESULTS

Altogether there were 253 episodes of admission. The median (interquartile) age was 4.9 (1.3-11.0) years and 58.1% were male. The median number of electrolyte disorders was 3 (2-4) types. Hypophosphatemia (74.2%), hypocalcemia (70.3%) and hypermagnesemia (52.9%) were the three commonest types of disturbances. Urinary electrolyte wasting was commonly observed among children with hypomagnesemia (70.6%), hypophosphatemia (67.4%) and hypokalemia (28.6%). Tubular dysfunction was detected in 82.6% of patients and urinary β2-microglobulin level significantly correlated with the severity of tubular dysfunction (p < 0.001). The development of tubular dysfunction was independent of AKI status. Tubular dysfunction was associated with mortality (p < 0.001) and was an independent predictor of PICU length of stay (LOS) (p < 0.001). The incorporation of the tubular dysfunction severity into the AKI staging system improved the prediction of PICU LOS.

CONCLUSIONS

Tubular dysfunction was associated with both morbidity and mortality in critically ill children and its assessment may help to capture a more comprehensive picture of acute kidney insult.

Calcium, Phosphate, and Vitamin D in Children and Adolescents with Chronic Diseases: A Cross-Sectional Study

Chronic diseases may affect the nutritional status of children and adolescents. Calcium (Ca), phosphorus (P), and vitamin D (Vit-D) are crucial nutrients for their growth and development. Proper diagnosis and treatment are critical components of personalized and precision medicine. Hence, we conducted a cross-sectional and comparative study to evaluate Ca, P, and Vit-D levels in their non-skeletal functions and their association with health and nutritional biomarkers in children and adolescents with diverse chronic conditions. We performed anthropometric, body composition, clinical evaluation, biochemical analysis, and dietary survey methods. A total of 78 patients (1-19 years, 43 females, 42 children) took part in this study. Overall, 24, 30, and 24 participants were obese, undernourished, and eutrophic, respectively. Results found that 74% and 35% of individuals had deficient Vit-D and Ca intake, respectively. Most cases were normocalcemic. Results also found that 47% of the subjects had Vit-D deficiency (VDD), 37% were insufficient, and 37% had hypophosphatemia. Of the 46% and 31% of patients with VDD and insufficient levels, 19% and 11% were hypophosphatemic, respectively. Calcium, P, and Vit-D levels were associated with anthropometric parameters, body mass index, body composition, physical activity, diet, growth hormones, and the immune, liver, and kidney systems. These results show the coincident risk of altered Ca, P, and Vit-D metabolism in children and adolescents with chronic diseases.

Renal Involvement in Multisystem Inflammatory Syndrome in Children: Not Only Acute Kidney Injury

Kidney involvement has been poorly investigated in SARS-CoV-2 Multisystem Inflammatory Syndrome in Children (MIS-C). To analyze the spectrum of renal involvement in MIS-C, we performed a single-center retrospective observational study including all MIS-C patients diagnosed at our Pediatric Department between April 2020 and May 2022. Demographic, clinical, pediatric intensive care unit (PICU) admission's need and laboratory data were collected at onset and after 6 months. Among 55 MIS-C patients enrolled in the study, kidney involvement was present in 20 (36.4%): 13 with acute kidney injury (AKI) and 7 with isolated tubular dysfunction (TD). In eight patients, concomitant AKI and TD was present (AKI-TD). AKI patients needed higher levels of intensive care (PICU: 61.5%, p < 0.001; inotropes: 46.2%, p = 0.002; second-line immuno-therapy: 53.8%, p < 0.001) and showed lower levels of HCO3- (p = 0.012), higher inflammatory markers [neutrophils (p = 0.092), PCT (p = 0.04), IL-6 (p = 0.007)] as compared to no-AKI. TD markers showed that isolated TD presented higher levels of HCO3- and lower inflammatory markers than AKI-TD. Our results indicate a combination of both pre-renal and inflammatory damage in the pathogenesis of kidney injury in MIS-C syndrome. We highlight, for the first time, the presence of tubular involvement in MIS-C, providing new insights in the evaluation of kidney involvement and its management in this condition.

Hypophosphataemia definitions, incidence and associated outcomes in paediatric intensive care: A retrospective cohort study in post-cardiac surgical patients <2 years of age

AIM

Hypophosphataemia has been linked to higher morbidity and mortality in intensive care but there is inconsistency in the definition of hypophosphataemia for infants and children. We aimed to determine the incidence of hypophosphataemia in a group of at-risk children in paediatric intensive care unit (PICU) and associations with patient characteristics and clinical outcomes using three different hypophosphataemia thresholds.

METHODS

Retrospective cohort study of 205 post-cardiac surgical patients <2 years of age admitted to Starship Child Health PICU, Auckland, New Zealand. Patient demographics and routine daily biochemistry for 14 days after PICU admission were collected. Rates of sepsis, mortality and length of mechanical ventilation were compared between groups with different serum phosphate concentrations.

RESULTS

Out of 205 children, 6 (3%), 50 (24%) and 159 (78%) had hypophosphataemia at thresholds of <0.7, <1.0 and <1.4 mmol/L, respectively. There were no differences in gestational age at birth, sex, ethnicity or mortality in those with and without hypophosphataemia at any threshold. Children with a serum phosphate <1.4 mmol/L had more mean (SD) total hours of mechanical ventilation (85.2 (79.6) vs. 54.9 (36.2) h, P = 0.02) and those with mean serum phosphate <1.0 mmol/L had more mean hours of mechanical ventilation (119.4 (102.8) vs. 65.2 (54.8) h, P < 0.0001), episodes of sepsis (14% vs. 5%, P = 0.03) and longer length of stay (6.4 (4.8-20.7) vs. 4.9 (3.9-6.8) days, P = 0.02).

CONCLUSIONS

Hypophosphataemia is common in this PICU cohort and serum phosphate <1.0 mmol/L is associated with increased morbidity and length of stay.

Hypophosphatemia in infants with severe bronchiolitis and association with length of mechanical ventilation

OBJECTIVES

Electrolyte disorders occurs frequently in children with bronchiolitis. The aim of the present study was to describe the frequency of hypophosphatemia and to evaluate its association with length of mechanical ventilation in infants admitted to a pediatric intensive care unit (PICU) with bronchiolitis.

METHODS

This retrospective cohort study included infants aged between 7 days and 3 months admitted to a PICU between September 2018 and March 2020 and diagnosed with severe acute bronchiolitis requiring respiratory support. Infants with a chronic condition that could potentially be a confounding factor were excluded. The primary outcome was the frequency of hypophosphatemia (<1.55 mmol/L); the secondary outcomes were the frequency of hypophosphatemia during the PICU stay, and the association with length of mechanical ventilation (LOMV).

RESULTS

Among the 319 infants admitted 178 had at least one phosphatemia value and were included in the study. The frequency of hypophosphatemia was 41% at PICU admission (61/148) and 46% during the PICU stay (80/172). The median [IQR] LOMV was significantly longer in children with hypophosphatemia at admission (109 [65-195] h vs. 67 [43-128] h, p = 0.007), and in multivariable linear regression lower phosphatemia at admission was associated with longer LOMV (p < 0.001) after controlling for severity (PELOD2 score) and weight.

CONCLUSION

Hypophosphatemia was frequent in infants with severe bronchiolitis admitted to a PICU and was associated with a longer LOMV.

Mild Hypophosphatemia-Associated Conditions in Children: The Need for a Comprehensive Approach

To better understand the causes of hypophosphatemia in children, we evaluated all serum phosphate tests performed in a tertiary hospital with unexpected but persistent temporary or isolated hypophosphatemia over an 18 year period. We collected 29,279 phosphate tests from 21,398 patients, of which 268 (1.2%) had at least one result showing hypophosphatemia. We found that endocrinopathies (n = 60), tumors (n = 10), and vitamin D deficiency (n = 3) were the medical conditions most commonly associated with mild hypophosphatemia, but in many patients the cause was unclear. Among patients with endocrinopathies, those with diabetes mellitus were found to have lower mean serum phosphate levels (mean 3.4 mg/dL) than those with short stature (3.7 mg/dL) or thyroid disorders (3.7 mg/dL). In addition, we found a correlation between glycemia and phosphatemia in patients with diabetes. However, despite the potential relevance of monitoring phosphate homeostasis and the underlying etiologic mechanisms, renal phosphate losses were estimated in less than 5% of patients with hypophosphatemia. In the pediatric age group, malignancies, hypovitaminosis D, and endocrine disorders, mostly diabetes, were the most common causes of hypophosphatemia. This real-world study also shows that hypophosphatemia is frequently neglected and inadequately evaluated by pediatricians, which emphasizes the need for more education and awareness about this condition to prevent its potentially deleterious consequences.

Early hypophosphatemia in critically ill children and the effect of parenteral nutrition: A secondary analysis of the PEPaNIC RCT

BACKGROUND & AIMS

Hypophosphatemia during critical illness has been associated with adverse outcome. The reintroduction of enteral or parenteral nutrition, leading to refeeding hypophosphatemia (RFH), has been presented as potential risk factor. We investigated the occurrence of early RFH, its association with clinical outcome, and the impact of early parenteral nutrition (PN) on the development of early RFH in pediatric critical illness.

METHODS

This is a secondary analysis of the PEPaNIC randomized controlled trial (N = 1440), which showed that withholding supplemental parenteral nutrition (PN) for 1 week (late-PN) in the pediatric intensive care unit (PICU) accelerated recovery and reduced new infections compared to early-PN (<24 h). Patients with renal replacement therapy or unavailable phosphate concentrations were excluded from this analysis. Early RFH was defined as serum/plasma phosphate <0.65 mmol/L and a drop of >0.16 mmol/L within 3 days of admission to the PICU. The association between baseline characteristics and early RFH, and the association of early RFH with clinical outcome were investigated using logistic and linear regression models, both uncorrected and corrected for possible confounders. To examine the impact of nutritional intake on phosphate concentrations, structural nested mean models with propensity score and censoring models were used.

RESULTS

A total of 1247 patients were eligible (618 early-PN, 629 late-PN). Early RFH occurred in 40 patients (3%) in total, significantly more in the early-PN group (n = 31, within-group occurrence 5%) than in the late-PN-group (n = 9, within-group occurrence 1%, p < 0.001). Patients who were older (OR 1.14 (95% CI 1.08; 1.21) per year added, p < 0.001) and who had a higher Pediatric Risk of Mortality (PIM3) score had a higher risk of developing early RFH (OR 1.36 (95% CI 1.15; 1.59) per unit added, p < 0.001), whereas patients in the late-PN group had a lower risk of early RFH (OR 0.24 (95% CI 0.10; 0.49), p < 0.001). Early RFH was significantly associated with a 56% longer PICU stay (p = 0.003) and 42% longer hospital stay (p = 0.007), but not with new infections (OR 2.01 (95% CI 0.90; 4.30), p = 0.08) or length of mechanical ventilatory support (OR 1.05 (95% CI -3.92; 6.03), p = 0.68), when adjusted for possible confounders. Increase of parenteral nutrition intake (in % kcal of predicted resting energy expenditure) decreased phosphate concentrations (c = -0.002 (95% CI -0.002; -0.001).

CONCLUSIONS

Early RFH occurred in 3% of critically ill children. Patients randomized to late-PN had a lower chance of developing early RFH, which may be explained by the more gradual build-up of nutrition. As early RFH might impact recovery, it is important to closely monitor phosphate concentrations in patients, especially of those at risk for early RFH.

Associations between Phosphate Concentrations and Hospital Mortality in Critically Ill Patients Receiving Mechanical Ventilation

Phosphate concentrations change continuously throughout hospitalization; however, it is unclear which available phosphate measures are most clinically important for predicting hospital mortality. Therefore, we investigated phosphate concentrations in association with hospital mortality following admission to the intensive care unit. We retrospectively enrolled all adult patients receiving mechanical ventilation. Phosphate concentrations were divided into three categories: initially measured phosphate (iP); maximum−minimum phosphate values (ΔP); and phosphate arithmetic average (Pmean). In total, 175 patients were enrolled. The hospital mortality rate was 32.6%, and the most common primary diagnosis was respiratory failure. In multivariable logistic regression analyses, the odds ratios for hospital mortality in association with ΔP and Pmean values were 1.56 and 2.13, respectively (p < 0.0001). According to the obtained receiver operating characteristic curve, ΔP (0.75) and Pmean (0.72) each showed a fair predictive power for hospital mortality. In evaluating relative risks, we found that higher concentrations of Pmean and ΔP were each associated with a higher hospital mortality. ΔP and Pmean values were significantly associated with hospital mortality in critically ill patients, compared to iP. These findings showed that throughout hospitalization, it is important to reduce phosphate level fluctuations and maintain appropriate phosphate concentrations through consistent monitoring and corrections.

Hypophosphatemia at Admission is Associated with Increased Mortality in COVID-19 Patients

Background

Electrolyte disturbances are commonly observed in patients with coronavirus disease 2019 (COVID-19) and associated with outcome in these patients. Our study was designed to examine whether hypophosphatemia is associated with mortality in COVID-19 patients.

Methods

Patients diagnosed with COVID-19 and hospitalized in Renmin Hospital of Wuhan University between January 30 and February 24, 2020 were included in this study. Patients were divided into two groups, a hypophosphatemia group and a non-hypophosphatemia group, based on a serum phosphate level of 0.8 mmol/L. Logistic regression was performed to analyze the relationship between hypophosphatemia and mortality. A locally weighted scatterplot smoothing (LOWESS) curve was plotted to show the detailed association between mortality rate and serum phosphate level. A Kaplan–Meier survival curve was drawn to compare the difference in cumulative survival between the two groups.

Results

Hypophosphatemia at admission occurred in 33 patients, with an incidence of 7.6%. The hypophosphatemia group had a significantly higher incidence of respiratory failure (54.5% vs 32.6%, p=0.013) and mortality (57.6% vs 15.2%, p<0.001). Multivariate logistic regression indicated that age (OR=1.059, p<0.001), oxygen saturation (OR=0.733, p<0.001), white blood cells (OR=1.428, p<0.001), lymphocytes (OR=0.075, p<0.001) and hypophosphatemia (OR=3.636, p=0.015) were independently associated with mortality in the included patients. The hypophosphatemia group had significantly shorter survival than the non-hypophosphatemia group (p<0.001).

Conclusion

Hypophosphatemia at admission is associated with increased mortality in COVID-19 patients. More attention and medical care should be given to COVID-19 patients with hypophosphatemia at admission.

Hypophosphatemia in critically ill pediatric patients receiving enteral and oral nutrition

BACKGROUND

Hypophosphatemia(HP) is related to several comorbidities in pediatric intensive care units (PICUs). This study aimed to evaluate the incidence of HP in severely ill pediatric patients receiving oral and/or enteral nutrition. The secondary objectives were to investigate the association between HP and the inflammatory state, PICU length of stay, severity, mortality, nutrition status, and protein, energy, calcium, vitamin D, and phosphate intake.

METHODS

A prospective, observational cohort study was conducted in a PICU of a quaternary hospital. Participants aged between 28 days and 14 years were included. Anthropometric and laboratory assessments were performed ≤72 h after PICU admission and repeated after 7 days for three consecutive times. Energy, protein, calcium, phosphate, and vitamin D intake per day of hospitalization were recorded individually. The Pediatric Index of Mortality 2 (PIM2) was used to determine each patient's severity score.

RESULTS

A total of 103 participants were included in the study. Hypophosphatemic events ranged from 27.2% to 37.5% among the assessments. HP was associated with high C-reactive protein levels (P = .012) and lower energy adequacy (P = .037). Serum phosphorus was inversely correlated (weak correlation) with PIM2 (P = .017).

CONCLUSION

HP is common in critically ill pediatric patients, even when they are not receiving parenteral nutrition. It is necessary to monitor serum phosphorus levels and consider the possibility of early replacement, especially in patients showing high levels of inflammation. In addition to inflammation itself, low energy intake and illness severity were related to HP.

Hypophosphatemia in critically ill adults and children - A systematic review

BACKGROUND & AIMS

Phosphate is the main intracellular anion essential for numerous biological processes. Symptoms of hypophosphatemia are non-specific, yet potentially life-threatening. This systematic review process was initiated to gain a global insight into hypophosphatemia, associated morbidity and treatments.

METHODS

A systematic review was conducted (PROSPERO CRD42020163191). Nine clinically relevant questions were generated, seven for adult and two for pediatric critically ill patients, and prevalence of hypophosphatemia was assessed in both groups. We identified trials through systematic searches of Medline, EMBASE, Scopus, Cochrane Central Register of Controlled Trials, CINAHL, and Web of Science. Quality assessment was performed using the Cochrane risk of bias tool for randomized controlled trials and the Newcastle-Ottawa Scale for observational studies.

RESULTS

For all research questions, we identified 2727 titles in total, assessed 399 full texts, and retained 82 full texts for evidence synthesis, with 20 of them identified for several research questions. Only 3 randomized controlled trials were identified with two of them published only in abstract form, as well as 28 prospective and 31 retrospective studies, and 20 case reports. Relevant risk of bias regarding selection and comparability was identified for most of the studies. No meta-analysis could be performed. The prevalence of hypophosphatemia varied substantially in critically ill adults and children, but no study assessed consecutive admissions to intensive care. In both critically ill adults and children, several studies report that hypophosphatemia is associated with worse outcome (prolonged length of stay and the need for respiratory support, and higher mortality). However, there was insufficient evidence regarding the optimal threshold upon which hypophosphatemia becomes critical and requires treatment. We found no studies regarding the optimal frequency of phosphate measurements, and regarding the time window to correct hypophosphatemia. In adults, nutrient restriction on top of phosphate repletion in patients with refeeding syndrome may improve survival, although evidence is weak.

CONCLUSIONS

Evidence on the definition, outcome and treatment of clinically relevant hypophosphatemia in critically ill adults and children is scarce and does not allow answering clinically relevant questions. High quality clinical research is crucial for the development of respective guidelines.

Phosphate disturbance in critically ill children: Incidence, associated risk factors and clinical outcomes

Background

Hypophosphatemia is one of the common disorders that develop in critically ill patients. It has potential complications and is often unrecognized in those patients.

Objective

Determining the incidence of hypophosphatemia in critically ill children, its association with clinical outcomes and the possible risk factors.

Methods

50 patients were enrolled in the study. Levels of serum phosphate were measured on day 1 and day 7 of PICU (Pediatric intensive care unit) stay. The following variables were analyzed: age, gender, diagnosis on admission, malnutrition, phosphorus intake, clinical severity score on admission OFI (Organ Failure Index) and daily scores PELOD (Pediatric Logistic Organ Dysfunction), sepsis, use of dopamine, furosemide and steroids and assessment of nutrition by z scores.

Results

The incidence of hypophosphatemia on admission was 42%. On seventh day of admission incidence of hypophosphatemia was 62%. Malnutrition was present in 24% of patients, serum phosphorus level was significantly lower in malnourished than in well-nourished children (p value = 0.018). Hypophosphatemia was associated with prolonged PICU length of stay (p < 0.001) but was not associated with increased mortality (p = 0.13). Cases on parenteral nutrition and insufficient oral intake while on mechanical ventilator significantly showed hypophosphatemia (p = 0.017). Hypophosphatemia was associated with the use of furosemide, dopamine, steroids and β2 agonist.

Conclusion

Hypophosphatemia was common in the first 7 days of PICU hospitalization and was associated with prolonged PICU stay, Significant association between hypophosphatemia and duration of use of mechanical ventilation, use of furosemide, dopamine, steroids and β2 agonist.

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Hypophosphatemia was common in the first 7 days of pediatric intensive care unit hospitalization.

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Significant association between hypophosphatemia and duration of use of mechanical ventilation.

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Hypophosphatemia was associated with prolonged pediatric intensive care unit length of stay.

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Hypophosphatemia was associated with use of furosemide, dopamine, steroid and β2 agonist.

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Good nutrition of critically ill children has an important role in improving their clinical condition.