1272 RELATIONSHIP OF THE PULMONARY EXCRETION RATE OF CO (VeCO) AND THE BLOOD CARBOXYHEMOGLOBIN LEVEL (COHb) IN PREMATURES AND TERMS

Abstract

Using a flow-through collection system and a reduction gas detector (res.= 1 ppb CO/2.5 ml sample), we made paired measurements of VeCO and COHb in 32 terms (38-42 wks) and 24 prematures (28-36 wks) breathing room air in the first week of life. The terms included babies with a wide range of endogenous CO production rates (VCO). For an individual baby, VeCO was repeatable with an error of ± 8% of the mean VeCO over 3-4 hrs despite changes in room air CO (RACO). Based on the line (COHb=.16 RACO+.53; r=.59; n=56; p < .0005), we corrected COHb for each baby (COHbc=COHb-.16 RACO). Using COHbc, we found that COHbc=.021 VeCO+.19 (r=.71; n=56; p < .0005). When prematures were analyzed alone, the line (COHbc=.017 VeCO+.30) was less significant (r= .43; p < .05) compared to that (COHbc=.024 VeCO+.13; r=.75; p < .0005) of terms. A correction for terms alone (.17) did not alter their line; for prematures alone (.097), a 40% increase in the intercept resulted from babies with a high COHb and a low VeCO. These data suggest that in the steady state la) VeCO reflects VCO and is not affected by RACO, lb) COHb reflects both VCO and RACO and requires correction for RACO, 2) VeCO and COHbc are correlated over a wide range of VCO in prematures and terms, and 3) a paired high COHb and low VeCO may reflect problems of ventilation and perfusion or shunt which occur in prematures.