Plasma cyclic guanosine monophosphate reflecting the severity of persistent pulmonary hypertension of the newborn.

The aim of the study was to examine the relationship between the plasma concentration of cyclic guanosine monophosphate (cGMP) and pulmonary pressure and hypoxia defined by oxygenation index (OI) in newborn infants with severe persistent pulmonary hypertension (PPHN) on inhaled nitric oxide (NO). In this prospective study, 18 newborn infants having Doppler ultrasound-diagnosed PPHN and treated with NO were investigated. The ratio of pulmonary artery to systemic artery pressure (PAP/SAP) and OI was assessed before treatment and at 0.5, 1, 12, and 24 h from the beginning of NO. At these time points, plasma concentrations of cGMP could be determined in 11 patients. The association of birth asphyxia as assessed by Apgar 1 min and 5 min and plasma cGMP before the NO treatment was examined. The initial median plasma concentration of cGMP was 37.3 pmol/ml (IQR 13.3-79.6). After the start of NO, cGMP increased significantly within 60 min (p = 0.003) and peaked at 12 h. Initial plasma cGMP was associated with Apgar score (1 and 5 min). OI decreased within 30 min of NO and PAP/SAP within 60 min. Persistent high PAP/SAP after 1 h of NO was associated with low cGMP concentration (r = 0.70, p = 0.02). We conclude that a significant increase in plasma cGMP is already evident after 60 min of NO therapy. This effect is accompanied by changes in oxygenation index and in pulmonary artery pressure. Initial plasma concentrations of cGMP were associated with hypoxia assessed as Apgar score.