Determining the ventilatory volumes required to ventilate low birth weight infants with respiratory distress syndrome. Prediction of arterial carbon dioxide using minute volumes.

There are limited data on the volumes used to ventilate infants with respiratory distress syndrome (RDS). There are no data on the volumes to aim for to avoid hypocapnia or unacceptable levels of hypercapnia. In this pilot study we measured minute volumes (MV) in ventilated infants to determine whether MV can predict arterial carbon dioxide (PaCO(2)) within acceptable parameters. Low birth weight infants (n = 14) mechanically ventilated for RDS had lung function recorded (n = 53) as an arterial blood gas was taken. MVs were plotted against PaCO(2) giving the regression equation for prediction of PaCO(2) (mm Hg) with MV (ml/kg/min): PaCO(2) = 58.3 - 0.075 x MV, r = 0.62, r(2) = 0.38, p < 0.001, residual variance (s(2)) of 52.7 (s = 7.26). 95% CI give a predicted PaCO(2) +/- 15 mm Hg for a given MV. A MV of 200 ml/kg/min predicts a PaCO(2) of 43 mm Hg (95% Cl 29-58). PaCO(2) correlates reasonably well with MV. Setting appropriate MVs may allow closer targeting of PaCO(2), and prevent over- or under-ventilation.