Dose-response to inhaled nitric oxide in acute hypoxemic respiratory failure of newborn infants: a preliminary report

Effect of dexamethasone on endothelial nitric oxide synthase in experimental congenital diaphragmatic hernia

AIMS

To study the effect of prenatal glucocorticoid treatment on endothelial nitric oxide synthase (eNOS) expression in rats with congenital diaphragmatic hernia (CDH).

METHODS

CDH was induced in fetal rats by the maternal administration of nitrofen on day 9.5 of gestation. Dexamethasone was administered on days 18.5 and 19.5 before delivery of the fetuses on days 20.5 and 21.5. Pulmonary eNOS protein expression was studied by western immunoblotting and immunohistochemistry.

RESULTS

On day 20.5, eNOS expression was significantly reduced in CDH pups compared with normal control rats. Dexamethasone treated CDH pups had eNOS concentrations equivalent to those of normal animals. By day 21.5, however, there was no detectable difference in eNOS expression between the experimental groups.

CONCLUSIONS

eNOS is deficient in near term (day 20.5) CDH rats. Dexamethasone restores eNOS expression in these animals to that seen in normal rat lungs. At term, the precise role of eNOS in the pathophysiology of CDH remains uncertain.

Transient response to inhaled nitric oxide in meconium aspiration in newborn lambs

To compare the effects of the sustained exposure to inhaled nitric oxide (NO) on pulmonary gas exchange, cardiovascular function and lung mechanics in newborn lambs with pulmonary hypertension induced by tracheal instillation of meconium. Fifteen newborn lambs (<6 d old) were studied in three groups (n = 5): control, and pulmonary hypertension (5 mL x kg[-1] of a 20% meconium solution) with or without inhaled NO (20 ppm) exposure. Heart rate, systemic and pulmonary arterial pressures, arterial pH and blood gases, cardiac output, and pulmonary mechanics were measured. The exposure to inhaled NO in lambs with pulmonary hypertension, induced by experimental meconium aspiration, produced a transient response. There were a transient improvement in gas exchange, a decrease in pulmonary arterial pressure and airway resistance, without changes in cardiovascular profile. The transient and incomplete response to inhaled NO in experimental MAS might be related to the fact that hypoxemia is not only due to pulmonary vasoconstriction but also to parenchymal lung disease. We hypothesize that this poor and transient response could probably be avoided if strategies that increase lung recruitment, were applied before inhaled NO exposure.

Open randomised controlled trial of inhaled nitric oxide and early dexamethasone in high risk preterm infants

AIM

To determine whether treatment with inhaled nitric oxide (NO) and/or dexamethasone reduces the incidence of chronic lung disease (CLD) and/or death in high risk preterm infants.

METHODS

Infants below 32 weeks of gestation were recruited at 96 hours of age if they were deemed to be at high risk of developing CLD. Infants were randomly assigned to one of four treatment groups using a factorial design: (1) 5-20 parts per million inhaled NO for 72 hours; (2) 0.5-1 mg/kg/day intravenous dexamethasone for 6 days; (3) both drugs together; (4) continued conventional management.

RESULTS

Forty two infants were randomised: 10 infants received inhaled NO alone; 11 dexamethasone alone; 10 both treatments; and 11 neither treatment. There was no difference in the combined incidence of CLD and/or death before discharge from hospital between either infants treated with inhaled NO and controls (RR 1.05, 95% CI 0.84-1.25), or those treated with dexamethasone and controls (RR 0.95, 95% CI 0.79-1.18).

CONCLUSIONS

At 96 hours of age, neither treatment with inhaled NO nor dexamethasone prevented CLD or death.

Inhaled nitric oxide for severe acute respiratory distress syndrome: a blessing or a curse?

The effects of inhaled nitric oxide (NO) in two young adults who developed severe acute respiratory distress syndrome are presented. Modest improvements in gas exchange and reductions in pulmonary artery pressures occurred after the initiation of treatment with inhaled NO. However, both patients became "dependent" on the inhaled NO for stabilization of their cardiopulmonary function. Repeated attempts to discontinue the inhaled NO resulted in life-threatening deterioration in gas exchange and hemodynamic instability. Prolonged family discussions were held regarding the withdrawal of inhaled NO and other life-sustaining therapies, when the irreversible nature of the patients' lung disease became apparent. However, both families were strong in their desire to continue all therapies--due in large part to the single organ nature of the disease process. Both patients died while receiving inhaled NO and escalating doses of sedative and analgesics. Based on this experience, it is recommended that clearly defined goals or endpoints for the discontinuation of inhaled NO should be established before its initial administration. If these goals are not achieved, then the therapy should be considered a failure and withdrawn. A similar strategy should be applied to all life-sustaining therapies in the intensive care unit setting (e.g., mechanical ventilation, vasopressors, dialysis). This requires that critical care clinicians effectively communicate the difference between aggressive supportive care and definitive treatment of the underlying disease process to patients or their families, or both. Furthermore, until the results of ongoing clinical trials of inhaled NO become available, it is recommended that its administration be restricted to medical centers examining its use in clinical trials.