Body Mass Index is a Promising Predictor of Response to Oral Rehydration Saline in Children with Vasovagal Syncope

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Body Mass Index is a Promising Predictor of Response to Oral Rehydration Saline in Children with Vasovagal Syncope

Vasovagal syncope (VVS), characterized by transient loss of consciousness due to cerebral hypoperfusion, is the most prevalent form of syncope in pediatric populations. Despite its generally benign prognosis, recurrent episodes significantly impair quality of life and pose risks of injury, necessitating effective therapeutic strategies. Oral rehydration saline (ORS), aimed at expanding blood volume, is widely recommended for pediatric VVS. However, its efficacy remains inconsistent, with a substantial proportion of patients failing to respond. This variability is attributed to the heterogeneous pathophysiology of VVS, which includes hypovolemia, autonomic dysfunction, and vasomotor instability. Identifying predictors of ORS responsiveness could enable personalized treatment, optimizing outcomes while avoiding unnecessary interventions.

Body mass index (BMI), a simple anthropometric measure, has emerged as a potential biomarker for blood volume status. Lower BMI correlates with reduced blood volume and increased susceptibility to syncope, suggesting its utility in stratifying patients likely to benefit from volume expansion therapies like ORS. This study investigated the predictive value of baseline BMI for ORS response in children with VVS, hypothesizing that lower BMI would predict favorable therapeutic outcomes.

Study Design and Patient Population

The retrospective case-control analysis included 74 children (aged 5–17 years) diagnosed with VVS at Peking University First Hospital between November 2010 and June 2019. Diagnosis followed established guidelines, requiring:

  1. Recurrent syncope triggered by upright posture, prolonged standing, or environmental stressors.
  2. Exclusion of cardiac, neurological, or metabolic etiologies via electrocardiography, echocardiography, and neuroimaging.
  3. Positive head-up tilt test (HUTT) demonstrating vasovagal response (cardioinhibitory, vasoinhibitory, or mixed subtypes).

Patients with comorbidities such as hypertension, renal dysfunction, or heart failure were excluded. All participants received ORS III (Anjian Pharma), containing 3.375 g anhydrous glucose, 0.725 g sodium citrate, 0.65 g sodium chloride, and 0.375 g potassium chloride dissolved in 250 mL water, administered daily for three months.

Clinical and Hemodynamic Assessments

Baseline evaluations included detailed medical history, physical examination, and anthropometric measurements. BMI was calculated as weight (kg) divided by height squared (m²). HUTT protocols involved supine rest for 10 minutes followed by 60° upright tilt for 45 minutes or until syncope occurred. Hemodynamic parameters (heart rate, blood pressure) were monitored continuously. Positive HUTT responses were classified as:

  • Cardioinhibitory: Heart rate decline >40% or <40 beats/minute without significant blood pressure drop.
  • Vasoinhibitory: Systolic blood pressure (SBP) drop >50% or <80 mmHg without marked bradycardia.
  • Mixed: Concurrent heart rate and blood pressure reductions.

Symptom severity was quantified using a validated scoring system:

  • 0: No syncope/presyncope.
  • 1: 1 episode/month.
  • 2: 2–4 episodes/month.
  • 3: 2–7 episodes/week.
  • 4: >1 episode/day.

Treatment Response Criteria

Patients were categorized as responders if symptom scores decreased by ≥1 point after three months of ORS therapy. Non-responders showed no improvement. Follow-up assessments utilized structured questionnaires administered via clinic visits or telephone interviews.

Statistical Analysis

Data analysis employed SPSS 22.0. Continuous variables were expressed as mean ± standard deviation or median (interquartile range). Group comparisons used Student’s t-test, Mann-Whitney U test, or chi-square tests. Spearman’s correlation assessed relationships between BMI and HUTT response time. Logistic regression identified predictors of ORS response. Receiver operating characteristic (ROC) curves determined BMI’s predictive performance, with optimal cutoff values selected via Youden’s index.

Key Findings

Baseline Characteristics and Treatment Response

Of 74 patients (38 females, 36 males; median age 10 years), 52 (70.3%) responded to ORS, while 22 (29.7%) did not. Groups showed no significant differences in sex, age at first syncope, HUTT hemodynamic subtype, or pretreatment symptom scores. However, responders exhibited:

  • Shorter symptom duration: Median 9.5 months vs. 34.3 months in non-responders (P = 0.001).
  • Lower baseline BMI: Median 16.4 kg/m² (IQR 15.5–17.8) vs. 20.7 ± 3.6 kg/m² (P < 0.001).

BMI and Hemodynamic Correlations

Baseline BMI positively correlated with HUTT response time (time to syncope/presyncope onset) after adjusting for sex (r = 0.256, 95% CI 0.067–0.439, P = 0.029). Lower BMI predicted earlier symptom provocation during orthostatic stress, suggesting hypovolemia as a key mechanism in these patients.

Predictive Performance of BMI

ROC analysis demonstrated strong predictive accuracy for baseline BMI (AUC 0.818, 95% CI 0.704–0.932, P < 0.001). A cutoff of 18.9 kg/m² yielded 83% sensitivity and 73% specificity. Patients below this threshold were significantly more likely to benefit from ORS.

Discussion

This study establishes baseline BMI as a practical, noninvasive predictor of ORS efficacy in pediatric VVS. The strong association between lower BMI and therapeutic response aligns with the hypothesis that hypovolemia underlies syncope in these patients. By expanding plasma volume, ORS mitigates orthostatic intolerance caused by inadequate venous return, particularly in leaner individuals with reduced blood volume reserves.

The correlation between BMI and HUTT response time further supports its role in reflecting hypovolemia severity. Earlier syncope during tilt testing in low-BMI patients indicates diminished compensatory mechanisms to orthostatic stress, which ORS ameliorates through volume expansion.

Notably, the optimal BMI cutoff (18.9 kg/m²) provides a clear clinical threshold for treatment stratification. This value aligns with pediatric BMI percentiles, corresponding to approximately the 25th percentile for children aged 10–12 years, distinguishing underweight/normal-weight patients from overweight counterparts.

Clinical Implications

Current guidelines advocate ORS as first-line therapy for pediatric VVS, yet up to 30% derive no benefit. Unnecessary treatment prolongs symptom duration, increases healthcare costs, and delays alternative therapies. BMI measurement offers a rapid, cost-effective tool to identify ideal ORS candidates, enhancing personalized care.

Limitations and Future Directions

The retrospective design and single-center recruitment limit generalizability. Although BMI correlates with blood volume, direct measurements (e.g., isotope dilution) could strengthen mechanistic insights. Prospective multicenter studies validating the 18.9 kg/m² cutoff across diverse populations are warranted.

Conclusion

Baseline BMI ≤18.9 kg/m² effectively predicts ORS responsiveness in children with VVS, enabling targeted therapy for those most likely to benefit. Integrating BMI into clinical decision-making optimizes resource utilization and improves outcomes in this common pediatric condition.

doi.org/10.1097/CM9.0000000000001168

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