Differences in preductal and postductal arterial blood gas measurements in infants with severe congenital diaphragmatic hernia.

OBJECTIVE: To determine whether right-to-left shunting across the ductus arteriosus (DA) in patients with congenital diaphragmatic hernia (CDH) with suprasystemic pulmonary hypertension (PH) results in differences between preductal and postductal arterial blood gas (ABG) measurements.

DESIGN: Demographics, baseline echocardiographic parameters and differences in simultaneous right upper extremity (preductal) and umbilical artery (postductal) ABG samples were determined in newborns with PH and CDH.

SETTING: Newborn intensive care unit at Children's Hospital Colorado.

PATIENTS: 30 newborns with CDH and systemic or suprasystemic PH.

INTERVENTIONS: Simultaneous preductal and postductal ABGs were compared in 30 newborns with PH and CDH, and ventilator settings and fraction of inspired oxygen (FiO2) were adjusted based on preductal ABG samples. Differences in respiratory support before and after obtaining preductal ABG samples were compared.

RESULTS: All patients had severe PH by echocardiogram with right-to-left DA shunting. However, only two newborns (6.6%) had right-to-left shunting across the foramen ovale. When compared with postductal ABG samples, preductal arterial pH was 7.35±0.02 vs 7.30±0.02, PaCO2 40.8±1.9 vs 48.3±1.9, PaO2 99.3±7.8 vs 46±3, oxygen saturation 95.6±1.2 vs 85.2±1.7 and oxygenation index 14.1±2.3 vs 30.1±5.1 (p<0.05 for all comparisons). Targeting preductal ABG measurements allowed for significant weaning of FiO2.

CONCLUSIONS: Right-to-left DA shunting decreases postductal PaO2, oxygen saturation and pH, and increases PaCO2. Targeting preductal ABG measurements may allow for a more physiological approach to ventilator management, and potentially reduce lung injury.