Original Article

Journal of Perinatology (2009) 29, 698–701; doi:10.1038/jp.2009.69; published online 25 June 2009

Methemoglobin to cumulative nitric oxide ratio and response to inhaled nitric oxide in PPHN

M J Pabalan1, S P Nayak1, R M Ryan1, V H Kumar1 and S Lakshminrusimha1

1Department of Pediatrics, Division of Neonatology, University at Buffalo, Women and Children's Hospital of Buffalo, Buffalo, NY, USA

Correspondence: Dr S Lakshminrusimha, Department of Pediatrics, Division of Neonatology, University of Buffalo, Women and Children's Hospital of Buffalo, 219 Bryant Street, Buffalo, NY 14222, USA. E-mail: slakshmi@buffalo.edu

Received 24 August 2008; Revised 21 January 2009; Accepted 25 February 2009; Published online 25 June 2009.

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Abstract

Background:

 

One-third of infants with persistent pulmonary hypertension of the newborn (PPHN) do not respond to inhaled nitric oxide (iNO). If iNO is not delivered to the pulmonary vasculature because of parenchymal lung disease, it cannot interact with hemoglobin to form methemoglobin (MHb).

Objective:

 

To study the correlation between oxygenation response to iNO in infants with PPHN secondary to parenchymal lung disease and initial MHb% to cumulative NO exposure (ppm times hours) ratio (MHb/SigmaNO).

Study Design:

 

Retrospective chart review of neonates with PPHN secondary to parenchymal lung disease treated with iNO comparing non-responders (PaO2/FiO2 ratio<10 change with iNO) with responders (greater than or equal to10 change).

Result:

 

Non-responders (n=16) had a PaO2/FiO2 of 83plusminus48 (meanplusminuss.d.) and decreased to 74plusminus44 after iNO. PaO2/FiO2 increased from 70plusminus48 to 151plusminus63 with iNO among responders (n=36). The MHb/SigmaNO ratio was low (0.024plusminus0.012) among non-responders compared with responders (0.07plusminus0.053, P<0.005).

Conclusion:

 

Inadequate oxygenation response to iNO is associated with lower MHb/SigmaNO, suggesting suboptimal delivery of iNO to the pulmonary vasculature.

Keywords:

lung recruitment, oxygenation, pulmonary hypertension, hypoxia

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