Monitoring persistent pulmonary hypertension of the newborn using the arterial to end tidal carbon dioxide gradient.

Persistent pulmonary hypertension of the newborn (PPHN) can be monitored theoretically by the difference of the partial pressure of arterial (PaCO 2 ) to end-tidal CO 2 (EtCO 2 ). We aimed to test the hypothesis that the PaCO 2 -EtCO 2 gradient in infants with PPHN would be higher compared to infants without PPHN. Prospective, observational study of term-born ventilated infants with echocardiographically-confirmed PPHN with right-to-left shunting and term-born control infants without respiratory disease. The PaCO 2 -EtCO 2 gradient was calculated as the difference between the PaCO 2 measured from indwelling arterial sample lines and EtCO 2 measured by continuous Microstream sidestream capnography. Twenty infants (9 with PPHN and 11 controls) were studied with a median (IQR) gestational age of 39.5 (38.7-40.4) weeks, a birthweight of 3.56 (3.15-3.93) kg and a birthweight z-score of 0.03 (- 0.91 to 1.08). The PaCO 2 -EtCO 2 gradient was larger in the infants with PPHN compared to those without PPHN after adjusting for differences in the mean airway pressure and fraction of inspired oxygen (adjusted p = 0.037). In the infants with PPHN the median PaCO 2 -EtCO 2 gradient decreased from 10.7 mmHg during the acute illness to 3.3 mmHg pre-extubation. The median difference in the gradient was significantly higher in infants with PPHN (6.2 mmHg) compared to infants without PPHN (-3.2 mmHg, p = 0.022). The PaCO 2 -EtCO 2 gradient was higher in infants with PPHN compared to term born infants without PPHN and decreased over the first week of life in infants with PPHN. The gradient might be utilised to monitor the evolution and resolution of PPHN.