Capillary blood gases in the neonate. A reassessment and review of the literature
S. E. Courtney, K. R. Weber, L. A. Breakie, S. W. Malin, C. V. Bender, S. M. Guo and R. M. Siervogel
Division of Newborn Medicine, Children's Medical Center, Dayton, OH 45404.
Heel puncture capillary blood gas (CBG) measurements continue to be used in
neonates for estimating arterial blood gas values. Review of the literature
reveals general agreement that CBG PO2 values are of little use in
predicting arterial PO2 and that CBG pH values are reliable predictors of
arterial pH; opinion varies regarding CBG PCO2. We conducted a two-part
study comparing postductal arterial and CBG values. First, 50 infants were
studied, each only once. All infants had umbilical arterial catheters in
place. Blood was obtained simultaneously from the umbilical artery catheter
and the warmed heels. Results demonstrated poor predictability of arterial
values from CBG pH and PCO2 as well as for PO2. Second, to determine if
variation both within and among individuals was similar, repeated
measurements were made in 27 additional infants comparable to the first
group. We obtained 3 to 28 simultaneous postductal arterial and CBG samples
from each infant. A random-effects nested analysis of variance indicated
that for pH, variation was largely the result of between-subject or
within-subject replicates effects, while for PO2 and PCO2, most variation
was explained by differences between the two techniques (umbilical artery
catheter vs CBG). The results indicate that CBG measurements do not
accurately predict arterial values in neonates. Extreme caution should be
used when management decisions are based on CBG values.
