Hindawi Publishing Corporation Pulmonary Medicine Volume 2011, Article ID 189205, 6 pages doi:10.1155/2011/189205 Research Article The Effect of Arterial pH on Oxygenation Persists Even in Infants Treated with Inhaled Nitric Oxide Aimee M. Barton, 1 M. Kabir Abubakar, 1 Jennifer Berg, 1 and Martin Keszler 2 1 Department of Pediatrics, Georgetown University Hospital, 3800 Reservoir Road NW, M3400, Washington, DC 20007, USA 2 Department of Pediatrics, Women and Infants Hospital, 101 Dudley Street, Providence, RI 02905, USA Correspondence should be addressed to Aimee M. Barton, amg57@georgetown.edu Received 22 January 2011; Accepted 6 May 2011 Academic Editor: Irwin Reiss Copyright © 2011 Aimee M. Barton et al. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Objective. To validate the empiric observation that pH has an important effect on oxygenation in infants receiving iNO. Study Design. Demographics, ventilator settings, arterial blood gases (ABG), and interventions for up to 96 hours of life were extracted from the charts of 51 infants receiving iNO. Need for ECMO and survival to discharge were noted. Mean blood pressure (MBP) and mean airway pressure (MAP) were recorded. The arterial/alveolar (a/A) ratio was used as the primary outcome. Analysis was by simple linear regression and multiple linear regression analyses and Fisher’s exact test. pH responsiveness was arbitrarily defined as a correlation coefficient (CC) of >0.40 with P< 0.05. Results. Mean gestational age was 38.8 weeks and mean birth weight was 3300 g. All patients had clinical diagnosis of PPHN. Clear responsiveness to pH was found in 31/51 infants. MAP and MBP did not correlate with a/A ratio. Three responders had a critical pH > 7.55. Of 11 patients requiring ECMO, only 3 exhibited responsiveness at any time in their course. Three responders required ECMO. Conclusion. This small study suggests that failure or inability to optimize pH may account for observed unresponsiveness to iNO. Maintaining a pH > 7.5 using hyperventilation is not recommended. 1. Introduction Hypoxemic respiratory failure continues to be a significant source of morbidity and mortality for term and near-term infants and is the most common reason for neonatal extra- corporeal membrane oxygenation (ECMO) referral. Hypox- emic respiratory failure is commonly associated with per- sistent pulmonary hypertension of the newborn (PPHN), a syndrome characterized by failure to achieve or maintain the normal decrease in pulmonary vascular resistance (PVR) that occurs after birth [1]. Increased PVR leads to pul- monary hypertension, right ventricular dilatation, tricuspid insufficiency, myocardial dysfunction, and extrapulmonary right-to-left shunting, which leads to severe hypoxemia that is often unresponsive to conventional therapy [2]. ECMO remains a treatment of last resort, reserved for infants who fail to respond to such therapies. In the last decade and a half, multiple randomized cont- rolled trials have shown that iNO improves oxygenation and decreases the need for ECMO in term and near-term infants with hypoxemic respiratory failure [3–8]. However, up to 40% of infants treated with iNO in these pivotal trials required ECMO. Response rate to iNO is inversely related to the severity of pulmonary disease and is facilitated by optimizing lung aeration by employing interventions such as exogenous surfactant and high-frequency ventilation. Despite these measures, a significant proportion of infants do not respond to iNO. In our NICU at Georgetown University Hospital, iNO has been in routine use for infants with hypoxic respiratory failure who do not improve with high-frequency ventilation, oxygen, inotropic support, and surfactant (when appropri- ate, as in cases of RDS in late preterm infants or meconium aspiration syndrome) since the late 1990s. We have made the empirical observation that infants receiving iNO are more likely to respond if their arterial pH is within high normal range of 7.40–7.45 than if it is in the low normal or acidotic range (< 7.35). Infants who had initially failed to respond to iNO often demonstrated responsiveness when we subsequently achieved a higher arterial pH.