Assessment of Arterial-Alveolar Co₂ Gradient in Newborns: Implications for Metabolic and Nutritional Calculations

Background: VCO₂ measurement is unreliable if an arterial-alveolar gradient (aADC₂) exists We investigated the effect of several respiratory variables on aADCO₂ in ventilated newborns .Subjects: 24 ventilated newborns (gestational age 24-37 ws, birth weight 450-2940 g). Interventions: End tidal CO₂ was measured with a mainstream capnometer (CO₂ SMO 7100, Novametrix) Arterial pCO₂ was measured from indwelling catheters with Radiometer ABL610 gas analyzer. From these measures aADCO₂ was calculated Associations between respiratory severity indexes and aADCO₂ were assessed with regression analysis Results: aADCO₂ increased with increasing oxigenation index (OI, r=0.551), alveolar-arterial difference (AaDO₂, r=0.554) and mean airways preassure (MAP, r=0.324), and decreasing O₂ arterial-alveolar ratio (aApO₂, r=0.414). High aADCO₂ (≥5 torr) was observed for OI≥3, MAP≥4 cmH₂O, aApO₂≥0.6, AaDO₂≥50 torr. Conclusions: In ventilated newborns values of OI, MAP, and AaDO₂ above (below for aApO₂) the calculated cutoff values would make the estimates of VCO₂ unreliable.