Bioimpedance spectroscopy measurements of phase angle and height for age are predictive of outcome in children following surgery for congenital heart disease

Abstract

Objective: Children with congenital heart disease (CHD) are often growth restricted (low weight- and/or height-for-age) which may increase risk of poor post operative resilience. Bioelectrical impedance spectroscopy (BIS) has been used to determine body composition in different clinical settings and has been shown to mark differences in nutritional state and clinical outcome. In disease conditions were fluid is not normally distributed it is proposed that raw impedance values and BIS derived phase-angle may serve as prognostic indicators of clinical outcome. We sought to describe the relationship between nutritional status, phase-angle and post-operative outcomes in children with congenital heart disease.

Design: Single centre prospective cohort study.

Setting: Paediatric Intensive Care Unit (PICU), Southampton Children's Hospital.

Patients: 122 children with CHD following cardiac surgery (March 2015-April 2016). Outcome variables included growth, mechanical-ventilation, PICU length of stay (PICU-LOS) and phase-angle at 50 Hz.

Measurements and main results: BIS measurements were taken before and on the day of surgery (day 0), day 2 post-operatively and on discharge from hospital. Pre-operative moderate malnutrition defined as height-for-age-z-score (HAZ) ≤-2 was observed in 28.5% of infants and 20.6% of children. Regression analysis was used to investigate the relationship between phase-angle, HAZ and clinical outcomes. Moderate-malnutrition (HAZ ≤-2) was associated with an increased PICU-LOS (odds ratios (OR) with 95% confidence interval: 1.8; 1.1-2.7, p = 0.008) whilst a low phase-angle (≤2.7° on day 2 was associated with longer PICU-LOS (OR 7.8; 2.7-22.45, p < 0.001)); When the model was adjusted for age, known risk factors and length of surgery, HAZ ≤-2 and phase-angle ≤2.7° on day 2 were associated with longer PICU-LOS (p = 0.001 and p = 0.04 respectively) and together explained 81.7% of the variability in PICU-LOS.

Conclusions: Moderate malnutrition (HAZ ≤-2) in infants and children undergoing cardiac surgery is associated with longer PICU-LOS. Post-operative measures of BIS phase angle may further improve our ability to identifying hose children with an increased risk of prolonged PICU-LOS compared to using pre-operative anthropometry alone.

Keywords: Bioelectrical impendence; Congenital heart disease; Nutrition; Phase angle.