Can Phase Angle in Newborns at Neonatal Intensive Care Units Be an Indicator of Mortality and Prognosis?

Background: The bioelectrical impedance (BI) phase angle (PA), analyzed directly through BI analysis (BIA), is determined by tissue cellularity, representing a direct measure of cellular stability and, for this reason, has been studied and considered as an indicator of prognosis and nutrition status in adults and children.

Objective: We aimed to determine if PA can be an indicator of mortality and prognosis in newborns admitted to the neonatal intensive care unit (NICU).

Methods: Transversal study conducted at a public NICU in Curitiba, Paraná, Brazil. All newborns, preterm and term, were considered eligible for the study if admission to the NICU occurred by the first hour of life. The Score for Neonatal Acute Physiology II, as well as the Perinatal Extension version, were developed to assess the risk of mortality for all newborns, measured within 12 hours of admission. BIA measurements were conducted using the tetrapolar BioScan Maltron 916, with single-frequency (50 kHz) tetrapolar BI. PA was calculated as the arc tangent: (Xc/R) x 180°/π.

Results: BIA was measured during the first 24 hours of admission for all newborns (n = 93), repeated between 24 and 48 hours (n = 79) and again after 7 days (n = 55), always when possible. PA measurements decreased in the first 48 hours in premature newborns, particularly among those who died. The premature newborns also showed a significant decrease from the first to the last PA measurement (P = .001). In addition, whereas full-term newborns showed an increase of PA at 1 week of life, preterm infants continued to have a decrease in values. For preterm newborns, PA measurements decreased and more sharply so for those who died. This result should be viewed with caution given the small number of deaths, but it should be investigated to understand the role of PA in the prognosis of NICU newborns.

Conclusions: The absolute value of PA during the first 24 hours of life was not a good marker for severity or mortality. However, the decrease of PA between different moments of evaluation was a good marker of severity. The decrease of PA in the first 48 hours in premature newborns, and that when the decrease is more pronounced, may be indicative of mortality. The difference in PA values between these newborns is probably a significant variable for mortality and prognosis and not a cutoff value.