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Newborn infants at high altitude can experience polycythemia (high hematocrit) and hyperviscosity (thick blood). Infants small for gestational age were at highest risk, impacting blood flow and oxygen delivery.
Area of Science:
- Neonatal Medicine
- Pediatric Hematology
- High-Altitude Physiology
Background:
- Neonatal polycythemia and hyperviscosity are concerns, particularly at high altitudes.
- Accurate hematocrit measurement in newborns is crucial for assessing these conditions.
Purpose of the Study:
- To determine the incidence of polycythemia and hyperviscosity in newborns at high altitude.
- To investigate the relationship between capillary and venous hematocrits.
- To explore the influence of birth weight and gestational age on these conditions.
Main Methods:
- Capillary hematocrits were measured in 790 infants within four hours of birth at 1,061 m altitude.
- Venous hematocrit and blood viscosity were determined when capillary hematocrit was ≥7%.
- Infants were categorized by gestational age, birth weight, and polycythemia/hyperviscosity status.
Main Results:
- Capillary hematocrits in the first hour were unreliable indicators of venous hematocrit.
- Venous polycythemia (hematocrit ≥65%) occurred in 4% of infants.
- Hyperviscosity occurred in 5% of infants; predictable at hematocrit ≥65%, but also seen between 60-64%.
- Infants small for gestational age had the highest risk, followed by those large for gestational age. Term infants appropriate for gestational age had the highest absolute number with hyperviscosity.
- Preterm infants <34 weeks gestation were unaffected.
Conclusions:
- High altitude may contribute to neonatal polycythemia and hyperviscosity.
- Capillary heel stick measurements require careful interpretation in the early neonatal period.
- Gestational age and birth weight are significant risk factors for neonatal hyperviscosity, with specific risks for SGA and LGA infants.
Abstract:
Capillary hematocrits were performed on 790 infants during the first four hours after birth. These infants were delivered between August 8 and December 7, 1974, at the University of Colorado Medical Center, which is at an altitude of 1,061 m above sea level. When the capillary hematocrit was 7% or greater, venous hematocrit and blood viscosity were determined. Capillary hematocrits obtained from warmed heels in the first hour after birth were spuriously high and not consistently related to venous hematocrit. Venous polycythemia, defined as a hematocrit of 65% or greater, occurred in 4% of the newborn population. Hyperviscosity (greater than 2 SD above the mean for newborns) occurred in 5% of the newborn infants. At a venous hematocrit of 65% or greater, hyperviscosity was predictable, but some infants with venous hematocrits between 60% and 64% also had hyperviscosity of the blood. The incidence of polycythemia and hyperviscosity was further related to birth weight and gestational age. The infants who were small for gestational age were at highest risk of polycythemia and hyperviscosity, followed by infants who were large for gestational age. However, the greatest number of infants with hyperviscosity were term appropriate for gestational age. Preterm infants with gestational ages of less than 34 weeks were not affected.