Treatment of newborn infants with inhaled nitric oxide

Role of nitric oxide in hepatic ischemia-reperfusion injury

Hepatic ischemia-reperfusion injury (IRI) occurs upon restoration of hepatic blood flow after a period of ischemia. Decreased endogenous nitric oxide (NO) production resulting in capillary luminal narrowing is central in the pathogenesis of IRI. Exogenous NO has emerged as a potential therapy for IRI based on its role in decreasing oxidative stress, cytokine release, leukocyte endothelial-adhesion and hepatic apoptosis. This review will highlight the influence of endogenous NO on hepatic IRI, role of inhaled NO in ameliorating IRI, modes of delivery, donor drugs and potential side effects of exogenous NO.

Referral and transportation for neonatal extracorporeal membrane oxygenation

Data from 32 patients who were transported for neonatal extracorporeal membrane oxygenation (ECMO) over a 66-month period were reviewed. One ground ambulance transport had to be postponed because of poor weather conditions; the patient died. One patient was excluded for ECMO on arrival at the ECMO centre. Of the remaining 30 infants, 20 (67%) required ECMO treatment, of which four (20%) died. All 10 (33%) patients who were treated with conventional therapy survived. During transportation all children remained stable in terms of oxygenation. Early referral and transportation by an experienced and well-equipped transport team allows safe transport of these critically ill neonates.

Strategies for reduction of neonatal mortality

Infant mortality rates in developed countries have shown significant decreases in recent years. Two-thirds of infant mortality still occurs in the neonatal period and our aim in this study was to review the causes of these neonatal deaths and see where further improvements may be possible. A 6-yr review of all neonatal deaths of live-born infants over 500 g birthweight from 1991 to 1996 was made. The 1989 amended Wigglesworth classification was used to categorize cause of death and other perinatal variables were also recorded. Results show there were 34,375 births and 153 neonatal deaths. Classification of these deaths by Wigglesworth found 78 (51 per cent) due to congenital malformations, 58 (38 per cent) due to prematurity, 6 (4 per cent) due to asphyxia and 11 (7 per cent) due to specific other causes. The corrected neonatal mortality was 2.18. Neural tube defects alone accounted for 10 per cent of the total neonatal mortality. Fifty-five out of 58 infants who died due to prematurity had birthweight < 1000 g and survival rates in this group compared well to international standards. We conclude that a reduction in neonatal mortality is possible but is most likely to result from community focused measures such as increased use of pre- and peri-conceptional folate.

Inhaled nitric oxide therapy via nasopharyngeal tube in an infant with end-stage pulmonary hypertension

The delivery of nitric oxide (NO) via a nasopharyngeal tube is an alternative to endotracheal intubation. A male infant with end-stage pulmonary hypertension (PH) due to a severe hypoplastic lung developed a PH crisis on day 145 and received NO inhalation via a nasopharyngeal tube. Clinical improvement was maintained for 7 days with 18-22 ppm NO inhalation. The patient remained in close physical contact with his parents without the use of sedation. Blood methemoglobin levels remained below 1%. The environmental NO levels were less than 0.06 ppm and NO2 less than 0.3 ppm throughout the treatment, well within the safety margin. On day 152, the patient succumbed to hypoxemia and heart failure. The use of a nasopharyngeal NO delivery system without sedation, as an alternative to endotracheal intubation with sedation, was a practical method in treating a patient with PH while maintaining a certain quality of life for the patient and the family.

Management of severe pulmonary hypertension in an infant with obstructed total anomalous pulmonary venous return using magnesium sulfate

Severe hypoxemia and pulmonary hypertension occurred in an infant with total anomalous pulmonary venous return. Though under hyperventilation with high fractional inspired oxygen and prostaglandin E1, hypoxemia remained intractable. Magnesium sulfate was used in view of its vasodilating effect. Significant clinical improvement was observed without causing systemic hypotension and the mechanism is discussed.

Changes in alveolar-arterial oxygen difference and oxygenation index during low-dose nitric oxide inhalation in 15 newborns with severe respiratory insufficiency

We evaluated changes in alveolar-arterial oxygen differences (AaDO2) and oxygenation index (OI) during inhalation of low-dose nitric oxide (INO) in 15 newborns with severe respiratory insufficiency: congenital diaphragmatic hernia (CDH) -6, asphyxial lung disease -4, meconium aspiration syndrome (MAS) -2, respiratory distress syndrome -2, persistent pulmonary hypertension of newborn -1. Their mean birth weight was 2522 g (1030-3200 g, SD +/- 575), mean gestational age 36 weeks (29-39 weeks, SD +/- 3.2), mean initial AaDO2 = 607 mm Hg (574-628 mm Hg, SD +/- 14) and mean initial OI = 32 (6-57, SD +/- 12). INO was performed using the Pulmonox system (Messer Griesheim, Austria) at conventional regimens of mechanical ventilation. The initial value of 20 ppm nitric oxide (NO) was decreased 6 h later, first to 15 ppm and then, as quickly as possible, to 3 ppm. The mean inhalation period was 51 h (6-131 h, SD +/- 42). The initial value of AaDO2 and OI decreased significantly within the first 6 h of INO (P < 0.001). After the first 6 h, 4 patients died: 1 with MAS of an extrapulmonary cause and 3 CDH patients because of pulmonary hypoplasia. In the remaining 11 patients the decrease in AaDO2 and OI during the first 24 h of INO was highly significant (P < 0.0001).

CONCLUSION

In a heterogeneous group of 15 newborns with severe respiratory insufficiency, the initial AaDO2 and OI decreased significantly within the first 6 h of INO.

Nitric oxide and lung surfactant

Inhalation of nitric oxide (NO) is an experimental treatment for severe pulmonary hypertension. Being rapidly metabolized by hemoglobin, inhaled NO causes selective vasodilation in the pulmonary vascular bed. In addition to the vascular smooth muscle, other pulmonary structures are exposed to inhaled NO, resulting in suppression of NO synthesis in a variety of pulmonary cells and in potential toxicity. NO is a free radical that interacts with a number of proteins, particularly metalloproteins. Together with superoxide radical, it rapidly forms highly toxic peroxynitrite. Peroxynitrite is involved in the killing of microbes by activated phagocytosing macrophages. In severe inflammation, peroxynitrite may be responsible for damaging proteins, lipids, and DNA. Peroxynitrite added to surfactant in vitro is capable of decreasing the surface activity, inducing lipid peroxidation, decreasing the function of surfactant proteins, SP-A and SP-B, and inducing protein-associated nitro-tyrosine. Exposure of animals for prolonged periods (48 to 72 hours) to inhaled NO (80 to 120 ppm) has been associated with a decrease in surface activity. This is caused by binding of surfactant to iron-proteins that are modified by NO (particularly methemoglobin), or by peroxynitrite induced damage of surfactant. In contrast, exposure of isolated surfactant complex to NO during surface cycling strikingly decreases the inactivation of surfactant, preventing the conversion of surfactant to small vesicles that are no longer surface-active, and preventing lipid peroxidation. This finding is consistent with the function of NO as a lipid-soluble chain-braking antioxidant. It is possible that this lipophilic gas has as yet undefined roles in regulation of surfactant metabolism and maintenance of surface activity. Deficiency in pulmonary NO may be present during the early neonatal period in respiratory distress syndrome and in persistent fetal circulation. The premature lung is likely to be sensitive to NO toxicity that may include lung damage, abnormal alveolarization, and mutagenicity. Defining of the indications, the dosage, and the toxicity of inhaled NO therapy remains the challenge for experimental and clinical research.