Perfusion Index in Very Low Birth Weight Premature Infants During Their First 2 Weeks of Life

Abstract

Background: Our program of research focuses on thermal and circulatory stability in extremely premature infants. In prior studies, we found that infants have long periods of time in which foot temperature (FT) is higher than central temperature. We thus wanted to determine whether blood flow in the foot is increased when FT is elevated. Perfusion index (PI) can be used as a clinical indicator of peripheral perfusion, but reports on use of PI in premature infants are lacking. We employed exploratory methodology to examine foot perfusion and temperature in very low birth weight infants.

Aims: For premature infants after birth: (1) describe foot PI values for the first 2 weeks of life and (2) describe the relationship of longitudinal FT and PI.

Study design: Case study design with longitudinal FT and PI in 17 infants born at <29 weeks' gestation with birth weight < 1,200 g for 2 weeks after birth.

Results: Infants averaged 851 g at birth and were 24-29 weeks' gestational age. The mean PI across all infants for 14 days was 1.04, SD = 0.79. Using a repeated measures multilevel model approach confirmed that FT and PI were positively related in these infants.

Conclusions: These findings demonstrate that perfusion is increased in the periphery in extremely premature infants when FT is increased. PI measures can be used as a trend for peripheral perfusion, and these values increase over the first 2 weeks of life in infants weighing more than 750 g.

Keywords: body temperature; hypothermia; neonatal; perfusion index; preterm; thermoregulation.

Figure 1.

Conceptual framework for the Knobel-Dail program of research. IVH = intraventricular hemorrhage; NEC = necrotizing enterocolitis; VLBW = very low birth weight.

Figure 2.

Boxplot of perfusion index (PI) means for all infants in the study by birth weight group in grams for their first and second weeks of life. The top of each box is the 75th percentile and bottom is the 25th percentile, middle line is the median with a diamond showing the skew when the mean is different than the median. Top tail is the 95th percentile and bottom tail is the 5th percentile.

Figure 3.

Exemplar plots of foot temperature and foot perfusion index measures over the first 2 weeks of life in one infant. GA = gestational age.

Figure 4.

Regression lines of average perfusion index values by infant birth weight group over the first 2 weeks of life. Time = Each point on the x-axis represents a 4-hr block of time.