Methods

Subjects
Between October 1994 and June 1997, 24 consecutive neonates with 			 persistent pulmonary hypertension of the newborn (PPHN) who failed 			 high-frequency oscillatory ventilation were enrolled in this study. The 			 diagnosis of PPHN was made clinically and confirmed by echocardiogram (either 			 right-to-left or bidirectional flow at the ductal or arterial level, or 			 estimated pulmonary pressures from a tricuspid regurgitation jet, being greater 			 than two-thirds of the systemic arterial pressures). The studied neonates had 			 birthweights of 3125.5 ± 794 g (mean ± SD), and gestational ages of 			 39 ± 2.4 weeks (mean ± SD). There were 12 females and 12 males, and 22 			 were born outside the hospital. All neonates were ventilated for an average of 			 137.5 min (range 90–180 min) prior to INO therapy with 3100 A high-frequency 			 oscillatory ventilator (HFOV; Sensor Medics, Yorba Linda, California, USA). 			 Metabolic alkalosis was induced with a bicarbonate infusion. Sedation with 			 morphine and/or midazolam and neuromuscular blockade with pancuronium were 			 used. Synthetic surfactant (Exosurf Neonatal, The Wellcome Foundation Ltd, 			 London, UK) was administered to all neonates with respiratory distress syndrome 			 (RDS) and meconium aspiration syndrome (MAS). Dopamine and dobutamine were used 			 to maintain a mean arterial pressure between 45 and 55 mmHg.

Study protocol
Neonates were enrolled after informed consent was obtained from 			 parents. At enrollment, postductal arterial blood samples were drawn for 			 determination of pH, blood gas tensions, and methemoglobin saturation (270 			 Cooxime, Ciba-Corning, Diagnostics, Medfield, Massachusetts, USA) 10 min prior 			 to the treatment with INO and every 2–4 h thereafter. The mean oxygenation index 			 of all neonates [OI = mean airway pressure × fractional inspired 			 concentration of oxygen (FiO2)/post-ductal partial pressure of 			 arterial oxygen (PaO2)] during high-frequency ventilation and before 			 starting INO was 46.3 ± 5 (mean ± SEM). The NO gas (AHG, Jeddah, Saudi 			 Arabia) used in this study was certified at a concentration of 800 ppm NO with 			 < 1% contamination by other oxides of nitrogen. NO gas was introduced into 			 the ventilator circuit via an adaptor positioned on the inspiratory port of the 			 Fisher and Paykel humidification chamber. Thus, NO was mixed with the bias flow 			 gas of the oscillator and subsequently delivered to the neonate via the 			 inspiratory limb of the ventilator circuit. The resulting concentration of the 			 inhaled NO and NO2 was verified in-line by using an electrochemical 			 sensor (Pulmonox, Tofield, Alberta, Canada). Exhaled gas was scavenged; the 			 oxygen concentration was analyzed continuously before it reached the 			 neonate's endotracheal tube. Nitric oxide was initially administered at 			 20 ppm for at least 2 h. If there was no response while the neonate was on high 			 ventilatory support and FIO2 of 1.0, INO was increased gradually by 			 2 ppm to a maximum of 80 ppm. If there was a response, INO was maintained at 			 20 ppm and FIO2 was gradually decreased to 0.6, provided the 			 PaO2 was 80–120 mmHg. Nitric oxide then was weaned to 			 discontinuation. Ventilatory parameters thereafter were weaned and HFOV was 			 replaced by a conventional ventilator. An arterial/alveolar oxygen (a/A) ratio 			 less than 0.22 was used to define failure of HFOV and INO therapy, if INO 			 reached 80ppm on high ventilatory support.

Statistical analysis
Statistical analysis was performed with the assistance of the 			 Department of Biostatistics. Normally distributed continuous variables were 			 analyzed with the Student's t-test. Variables without a normal 			 distribution were analyzed with the Wilcoxon signed rank test. This study has 			 been approved by the Department of Pediatrics Research Committee and the King 			 Faisal Specialist Hospital and Research Centre's Research Advisory 			 Council.