Cerebral blood flow velocity acutely decreases in newborns who respond to inhaled nitric oxide

Regional cerebral blood flow is directly proportional to the Doppler velocity time integral of flow in corresponding cerebral arteries. This study was performed to determine whether an acute change in the velocity time integral of cerebral blood flow occurs in newborns with pulmonary hypertension who experience an acute improvement in pulmonary hemodynamics and gas exchange at the onset of inhaled nitric oxide therapy. Twenty-two newborns with lung disease and an oxygenation index >25 were treated with 10 to 20 parts per million inhaled nitric oxide. Measurements of heart rate, blood pressure, arterial blood gases, right and left ventricular planimetry, and Doppler ultrasonography were performed before and after 30 to 60 minutes of therapy. Nitric oxide inhalation was associated with a significant acute change in arterial blood pressure, pH, arterial carbon dioxide tension, arterial oxygen tension, proportion of right-to-left ductal shunt, estimated systolic pulmonary arterial pressure, and right ventricular diastolic and systolic areas. In the middle cerebral artery, peak systolic flow velocity (49+/-5 vs. 41+/-4, cm/sec), diastolic flow velocity (21+/-3 vs. 14+/-3, cm/sec), and the velocity time integral (10.3+/-1.1 vs. 7.9+/-1.1, cm) all decreased (p<0.05). These changes only occurred in a subgroup of 17 patients who experienced an improvement in arterial oxygen tension > or =10 mm Hg. The velocity time integral of flow in the middle cerebral artery is acutely decreased in newborns with pulmonary hypertension who experience an acute increase in oxygenation after the onset of inhaled nitric oxide.

Persistent pulmonary hypertension of the newborn: experience in a single institution

Persistent pulmonary hypertension of the newborn (PPHN) remains one of the most challenging situations in the neonatal intensive care unit, and it is associated with high mortality and morbidity. The optimal treatment for PPHN is controversial. We report our 9-year experience in the management of PPHN through a retrospective review of 29 neonates with persistent pulmonary hypertension. The diagnosis of PPHN is made by echocardiography and/or preductal and postductal oxygen tension difference. The treatment modalities include supportive medical care, vasodilator therapy, mechanical ventilation and correction of underlying conditions. The wide diversity of etiologies of PPHN, the complications of vasodilator therapy, the management of assisted ventilation, the mortality and the morbidity are evaluated. There are 29 patients enrolled in this study, including 18 male and 11 female babies. Twenty-two patients (72%) are referred from other hospitals. The mean birth body weight is 2707 +/- 693 grams (range: 1450-4100 grams) and the mean gestational age is 37.1 +/- 3.1 weeks (range: 31-41 weeks). The underlying clinical conditions include meconium aspiration syndrome (n = 8), perinatal asphyxia (n = 7), respiratory distress syndrome (n = 5), sepsis and/or pneumonia (n = 4), congenital diaphragmatic hernia (n = 3) and idiopathic persistent fetal circulation (n = 2). In addition to supportive medical care and correction of underlying clinical conditions, most of the patients receive vasodilator therapy (Tolazoline) and nonhyperventilation respirator management. The overall mortality rate is 27.6% (8/29). The duration on ventilator therapy in the survival group (9.3 +/- 8.6 days) is not significantly different from in the mortality group (6.0 +/- 7.1 days) (p = 0.13). There is also no statistically significant difference between these two groups both in the maximal alveolar-arterial oxygen tension difference (594 +/- 53 mmHg and 613 +/- 37 mmHg, p = 0.145) and in the maximal oxygenation index (49.7 +/- 29.6 and 61.1 +/- 36.9, p = 0.172) before vasodilator therapy. However, twenty-four hours after treatment, these two parameters change significantly with the former changes to 426 +/- 198 mmHg and 643 +/- 7 mmHg, respectively (p < 0.001), and the latter changes to 21.6 +/- 15.8 and 82.3 +/- 54.8, respectively (p < 0.001). Skin rash, gastrointestinal hemorrhage, hypotension and hyponatremia are the most common complications of Tolazoline therapy. Eight patients have pulmonary complications including pneumothorax (n = 5) and pulmonary interstitial emphysema (n = 3). Two patients develop chronic lung disease. Three patients have neurodevelopmental handicap. In conclusion, we achieve a survival rate of nearly 75% in PPHN mainly with the administration of Tolazoline therapy and the nonhyperventilation respirator approach. Further well-controlled and multicenter studies with newer treatment modalities are crucial for the improvement of survival of PPHN in Taiwan.

Analysis of nonsteroidal antiinflammatory drugs in meconium and its relation to persistent pulmonary hypertension of the newborn

OBJECTIVE

The objective of this study was to detect fetal exposure to nonsteroidal antiinflammatory drugs (NSAIDs) by meconium analysis and to determine the relationship between fetal exposure to NSAIDs and the development of persistent pulmonary hypertension of the newborn (PPHN).

METHODS

In a case-control study of the inborn and outborn nurseries of a large urban medical center, meconium was collected from 101 newborn infants (40 with the diagnosis of PPHN based on clinical or echocardiographic criteria and 61 randomly selected, healthy, term infants [control]) and analyzed for NSAIDs (ibuprofen, naproxen, indomethacin, and aspirin) by gas chromatography/mass spectrometry. The risk of developing PPHN was determined in infants who were exposed antenatally to NSAID.

RESULTS

Infants with PPHN (n = 40) had a mean gestation of 38.9 weeks and birth weight of 3524 g, which were similar to the those of the control group (n = 61). However, the incidence of low Apgar scores (</=6) at 1 minute and 5 minutes was significantly higher in the PPHN group than in the control group. The diagnoses associated with PPHN were primary PPHN (25%), meconium aspiration syndrome (35%), respiratory distress syndrome (20%), low Apgar score/asphyxia (12.5%), and pneumonia/sepsis (8%). Mean duration of ventilator support for the PPHN group was 11 days. Nitric oxide (NO) was given to 19 infants (47.5%) for a mean duration of 25.4 hours. Fourteen of the 19 infants who were treated with NO (74%) required extracorporeal membrane oxygenation, and 2 died. The overall incidence of positive NSAID in meconium in the study population (n = 101) was 49.5%: 22.8% were positive for ibuprofen, 18.8% for naproxen, 7.9% for indomethacin, and 43.6% for aspirin. There was poor agreement (Cohen's kappa = 0.09) between maternal history of NSAID use and NSAID detection in meconium. PPHN was significantly associated with 1) the presence of at least 1 NSAID in meconium (odds ratio [OR] = 21.47; 95% confidence interval [CI] = 7.12-64.71) or 2) the presence in meconium of aspirin (OR = 8.09; 95% CI = 3.27-20.10), ibuprofen (OR = 12.89; 95% CI 3.93-42.32), or naproxen (OR = 3.31; 95% CI = 1.17-9.33). By logistic regression analysis, low Apgar scores at 1 and 5 minutes and the antenatal exposure to aspirin, naproxen, and ibuprofen were significantly associated with PPHN and treatment with inhaled NO or extracorporeal membrane oxygenation.

CONCLUSION

We confirm by meconium analysis the results of previous studies that demonstrated that the use of NSAIDs during pregnancy, particularly aspirin, ibuprofen, and naproxen, is high; is grossly underestimated by maternal history; and is significantly associated with PPHN. Thus, the easy access to over-the-counter NSAIDs of pregnant women should be reevaluated, and the potential dangers of these drugs to the newborn infant should be more effectively promoted.

Extremely thickened media of small pulmonary arteries in fatal pulmonary hypertension with congenital heart disease--a morphometric and clinicopathological study

There are patients with congenital heart disease and fatal pulmonary hypertension in whom the medial hypertrophy of the small pulmonary arteries is quite beyond the extent of ordinary cases of hypertension, a condition described as pulmonary hypertension with extremely thickened media of small pulmonary arteries (PH/ETM). Lungs from 6 infants, all younger than 2 years of age, who had congenital heart disease and fatal pulmonary hypertension, were analyzed by accurately measuring the media using Suwa's method. In PH/ETM, the media of the small pulmonary arteries was shown to be not only unusually thick, but extending toward the periphery, whereas the intimal changes were unexpectedly mild. In the PH/ETM group, the % wall thickness at a diameter of 50 microm (%Tw(50)), determined from regression analysis, was 23.2+/-1.3%, which was significantly higher than in either the control (10.3+/-1.2%) or ventricular septal defect group (18.9+/-1.6%). In persistent pulmonary hypertension of the newborn (PPHN), it was 22.3+/-1.8%, not significantly different from PH/ETM. The striking medial hypertrophy in PH/ETM and PPHN was apparently confined to small pulmonary arteries and in both conditions is likely to be the result of maldevelopment of these arteries. Surgical intervention may trigger a critical elevation of the pulmonary arterial resistance.

Growth of the vascular tree

Major changes occur in the pulmonary circulation at birth. Failure of normal adaptation leads to pulmonary hypertension of the newborn. The basis for this may be abnormal growth of the lung in utero or a failure of the mechanisms which lead to vasodilatation in the newborn period. This article describes normal development of the pulmonary arteries and veins, their branching pattern and structure and discusses the factors which may control this growth. Endothelial function and dysfunction are crucial in adaptation, and new experimental studies are aiding our understanding of the control and action of factors produced by the endothelium, e.g. nitric oxide, prostacyclin and endothelin. The study of infants with pulmonary hypertension, together with the experimental studies, will aid in producing effective methods of controlling increased pulmonary artery pressure in the newborn period.

During neonatal mechanical ventilatory support, the delivered nitric oxide concentration is affected by the ventilatory setting

OBJECTIVE

To assess whether the delivered nitric oxide (NO) concentration is affected by a change in the ventilatory setting during neonatal mechanical ventilatory support.

DESIGN

Prospective, experimental study.

SETTING

Laboratory at Nagoya City University Medical School.

INTERVENTIONS

This study was performed by using a pressure-limited, time-cycled, ventilatory support with a neonatal circuit and a 50-mL silicone test lung. NO in N2 gas was administrated into the inspiratory limb at a distance of 4 cm, 80 cm, or 160 cm from the Y piece connected to the adapter of an endotracheal tube. The NO concentration was measured every 0.5 sec by a chemiluminescence analyzer at the Y piece.

MEASUREMENT AND MAIN RESULTS

NO concentrations were compared with each of the ventilatory settings of peak inspiratory pressure (PIP) (10-30 cm H2O), positive end-expiratory pressure (0-10 cm H2O), ventilatory flow (10, 20, 30 L/min), and ventilatory rate (30, 40, 50, 60, 70 breaths/min), respectively. The NO concentration was significantly lower when NO was added at 4 cm than at 80 cm or 160 cm from Y piece at the same ventilatory setting of PIP, positive end-expiratory pressure and ventilatory flow, respectively, (p < .01). Although the NO concentration was increased as the settled PIP level was increased (p < .01 or p < .05), it was not changed when the settled positive end-expiratory pressure level was increased. A decrease was seen in the NO concentration as the settled ventilatory flow was increased (p < .01). Lastly, the NO concentration fluctuated greatly in association with the settled ventilatory rate.

CONCLUSION

The NO concentration delivered to patients is influenced by the ventilatory setting during neonatal mechanical ventilatory support.

Congenital pulmonary venous stenosis presenting as persistent pulmonary hypertension of the newborn

Congenital pulmonary venous stenosis (CPVS) has been previously described in older infants and children, typically manifesting as failure to thrive with congestive heart failure and subsequent respiratory deterioration. We report on 2 cases of CPVS which presented during the immediate newborn period as severe persistent pulmonary hypertension of the newborn.

The cGMP-specific phosphodiesterase inhibitor E4021 dilates the pulmonary circulation

We investigated the pulmonary vascular effects of E4021, a potent inhibitor of cGMP-specific phosphodiesterase, in control late-gestation fetal lambs, and in newborn lambs with persistent pulmonary hypertension (PPHN) after prenatal ligation of the ductus arteriosus. E4021 alone significantly relaxed fifth-generation pulmonary arteries isolated from control fetal lambs, an effect completely blocked after inhibition of nitric oxide synthase (NOS). In contrast, E4021 did not relax pulmonary arteries isolated from hypertensive lambs. Pretreatment with E4021 (10(-7) M) significantly enhanced relaxations to the NO donor S-nitrosyl-acetyl-penicilamine (SNAP) in arteries from both control and hypertensive lambs. In control, fully instrumented fetal lambs, infusions of E4021 (31 microgram/min) selectively dilated the pulmonary circulation, an effect again blocked after inhibition of NO synthase. Further studies were performed in newborn lambs with PPHN to study the vascular effects of E4021 alone, and in combination with inhaled NO. E4021 alone (1 to 100 microgram/kg/min) decreased pulmonary artery pressure (Ppa) in a dose-dependent fashion, and had minimal effect on systemic pressure. At the highest dose (100 microgram/kg/min), the dilation was selective for the pulmonary circulation. In subsequent protocols, E4021 (10 microgram/kg/min) significantly decreased Ppa and pulmonary vascular resistance (PVR), but these pulmonary vascular effects were not enhanced after NO inhalation at 0.5 or 5 ppm. We speculate that the lack of enhancement was due to the dramatic effects of E4021 alone. Potent, specific phosphodiesterase inhibitors such as E4021 may prove to be useful in the treatment of PPHN.

Alveolar capillary dysplasia: diagnostic potential for cardiac catheterization

OBJECTIVE

Alveolar capillary dysplasia is a rare cause of persistent pulmonary hypertension of the newborn. Infants with this condition die despite maximal medical intervention including inhaled nitric oxide therapy and extracorporeal membrane oxygenation. To date, diagnosis of this lethal condition was made by open lung biopsy or during postmortem examination. We examined the possibility that distinct cardiac catheterization findings could be used in the diagnosis of this lethal disorder.

STUDY DESIGN

We present three infants with fatal persistent pulmonary hypertension of the newborn refractory to extracorporeal membrane oxygenation and inhaled nitric oxide therapy, two with postmortem autopsy confirmation of alveolar capillary dysplasia. Each infant underwent cardiac catheterization to complete the diagnostic evaluations.

RESULTS

Significant right ventricular hypertension and normal pulmonary venous return were demonstrated, but a markedly diminished or absent capillary blush phase was noted in each infant. This finding is distinct from the normal capillary blush seen in infants with persistent pulmonary hypertension of the newborn of other etiologies.

CONCLUSION

Cardiac catheterization may provide a useful alternative to tissue examination in the diagnosis of alveolar capillary dysplasia.

Postnatal pulmonary hypertension after repair of congenital diaphragmatic hernia: predicting risk and outcome

BACKGROUND

Pulmonary hypertension (PH) after congenital diaphragmatic hernia (CDH) repair remains a significant cause of morbidity and mortality. Although treatment advances have improved overall survival, a new cohort of patients is surviving with PH beyond the postnatal period. Because the clinical entity of postnatal persistent pulmonary hypertension (PPHTN) in CDH patients has not been published, the authors undertook a retrospective study of our neonatal CDH experience to characterize this group of infants.

METHODS

Charts of all infants with CDH treated at this institution from January 1991 to June 1997 were reviewed (n = 51). Persistent pulmonary hypertension by echocardiographic (Echo) measurements at the time of discharge identified PPHTN patients. Control survivors had normal pulmonary artery pressures at discharge. Physiological parameters and the results of therapeutic interventions were analyzed to predict PPHTN.

RESULTS

Seven infants (four boys, three girls) had PPHTN at discharge. Significant differences with the control group were noted in length of stay, duration of intubation, and duration of nitric oxide therapy. Extracorporeal membrane oxygenation (ECMO) duration was not significantly different between the groups. By 12 months of age, PPHTN resolved in six patients (87%), and one died at 13 months. Regardless of therapy, two parameters showed 100% positive predictive value for identifying patients with PPHTN (P < .001): an Echo demonstrating PH at 2 months of age or continued oxygen requirement at 3 months. Oxygen requirement at 2 months had a 67% predictive value of PPHTN.

CONCLUSIONS

With current treatment strategies for CDH, infants can survive with persistent pulmonary hypertension beyond the newborn period. The long-term survival rate is excellent, and normalization of pulmonary artery pressures can be expected. PPHTN can be predicted in those infants with Echo-defined pulmonary hypertension at 2 months.

Cerebral blood flow during treatment for pulmonary hypertension

AIM

To determine if the haemodynamics of systemic and cerebral circulation are changed during treatment for persistent pulmonary hypertension of the newborn (PPHN).

METHODS

Fifteen term newborn piglets with hypoxia induced pulmonary hypertension were randomly assigned either tolazoline infusion (Tz), hyperventilation alkalosis(HAT), and inhaled nitric oxide (iNO). Mean pulmonary arterial pressure (PAP), mean systemic arterial pressure (SAP), and cerebral blood flow volume (CBF) were measured.

RESULTS

During hypoxic breathing, PAP increased significantly in all groups. After treatment PAP decreased significantly in all groups, but no significant difference was observed between groups. SAP decreased significantly only in the Tz group, and CBF reduced significantly only in the HAT group. On the other hand, iNO did not change SAP or CBF.

CONCLUSION

Inhaled NO might be ideal for the resolution of pulmonary hypertension.

Inhaled nitric oxide does not affect adenosine 5'-diphosphate-dependent platelet activation in infants with persistent pulmonary hypertension of the newborn

OBJECTIVE

To investigate the effect of inhaled nitric oxide (NO) treatment in newborns with persistent pulmonary hypertension on adenosine 5'-diphosphate (ADP)-dependent platelet activation.

METHODS

After parental informed consent, infants with persistent pulmonary hypertension of the newborn were randomly assigned to receive conventional treatment (control group) or treatment with 40 parts per million of inhaled NO. Platelet activation was measured at time of entry and 30 minutes later by surface expression of P-selectin in response to increasing concentrations of the agonist ADP (0, 2, 5, 10, and 20 microM) using fluorescence-activated flow cytometry.

RESULTS

We examined 11 infants in the inhaled NO group and 13 in the control group. P-selectin expression, quantified as mean fluorescence, was not significantly different in the two groups of patients at baseline. Median percent change from baseline fluorescence was assessed using the Wilcoxon matched-pairs signed-rank test. At 30 minutes after enrollment there were no statistically significant changes from baseline fluorescence in either group of patients and at all ADP concentrations.

CONCLUSION

Thirty minutes of exposure to 40 ppm of inhaled NO does not inhibit ADP-dependent platelet activation as measured by surface expression of P-selectin in infants with persistent pulmonary hypertension of the newborn.

Pulmonary and systemic effects of the phosphodiesterase inhibitor dipyridamole in newborn lambs with persistent pulmonary hypertension

Nitric oxide (NO) relaxes vascular smooth muscle by increasing the intracellular concentration of cGMP. In the pulmonary circulation, cGMP is inactivated by specific phosphodiesterases (PDE5). Dipyridamole, a clinically approved drug, has inhibitory activity against PDE5 and has been reported to augment the response to inhaled NO in persistent pulmonary hypertension of the newborn (PPHN). We wished to determine whether dipyridamole alone, or in combination with NO, can be used to treat a newborn lamb model of PPHN. In newborn lambs with PPHN, dipyridamole infused at 0.02 mg/kg/min for 45 min alone, or in combination with 5 ppm of inhaled NO for the final 15 min, significantly decreased pulmonary and systemic blood pressure, decreased pulmonary vascular resistance, and increased pulmonary blood flow. There was no significant difference between the pulmonary vascular effects of 5 ppm NO alone compared with the effects of NO combined with dipyridamole. In control lambs, the 45-min infusion of dipyridamole did not change pulmonary pressure whereas systemic pressure decreased by 28 +/- 3%. These systemic effects in control lambs persisted 90 min after discontinuing the dipyridamole infusion. Systemic arteries isolated from both control and PPHN lambs were significantly more sensitive to dipyridamole than pulmonary arteries. We conclude that dipyridamole has significant hemodynamic effects in both the pulmonary and systemic circulations of newborn lambs with pulmonary hypertension as well as in the systemic circulation of newborn control lambs. The pronounced effects of dipyridamole on the systemic circulation limits its utility as an adjunct to inhaled NO in the treatment of PPHN.

Involvement of thromboxane A2 and prostacyclin in the early pulmonary hypertension after porcine meconium aspiration

Severe perinatal aspiration of meconium is frequently complicated by unsuccessful neonatal adaptation with associated pulmonary hypertension. This vascular complication is supposedly related to pulmonary release of vasoconstrictory agents, including metabolites of arachidonic acid. Thus, to investigate the role of prostanoids on these meconium-induced circulatory changes in the lungs, the hemodynamic response to meconium instillation was studied in acetylsalicylic acid-pretreated juvenile pigs. Twelve 10-wk-old pigs with adapted lung circulation received 3 mL/kg of 65 mg/mL human meconium via the endotracheal tube. Six of them were medicated with 10 mg/kg acetylsalicylic acid 30 min before meconium insufflation. Hemodynamic parameters and urinary excretion of stable metabolites of thromboxane A2 and prostacyclin were measured serially for 6 h after the insult. Meconium administration induced a biphasic increase in mean pulmonary artery pressure and pulmonary vascular resistance, and a rapid rise in urinary levels of prostanoid metabolites. Acetylsalicylic acid pretreatment prevented the initial (0-1 h) pulmonary hypertensive response and increase in prostanoid excretion. During the second phase (1-6 h), acetylsalicylic acid did not attenuate the progressive increase in mean pulmonary artery pressure and pulmonary vascular resistance nor did it affect the longitudinal distribution of the pulmonary resistances. Our results thus show that in adapted porcine lungs, arachidonic acid metabolites contribute to the early hypertensive response, but have only minor effects during the second phase vascular hypertension.

Coordinated regulation of genes of the nitric oxide and endothelin pathways during the development of pulmonary hypertension in fetal lambs

Ligation of the ductus arteriosus in utero produces fetal and neonatal pulmonary hypertension and alterations in the hemodynamic responses to nitric oxide and endothelin-1 in fetal and newborn lambs. To determine whether fetal pulmonary hypertension alters the expression of the genes of the nitric oxide and endothelin-1 pathways, seven fetal lambs (123-126-d gestation) underwent ligation of the ductus arteriosus. Near-term (138-139-d gestation), total lung RNA, and protein were prepared from control and ductal ligation fetal lambs for RNase protection assays and Western blotting. Ligation of the ductus arteriosus was associated with decreased expression of endothelial nitric oxide synthase mRNA and protein, and the alpha1 and the beta1 subunits of soluble guanylate cyclase protein; and with increased expression of phosphodiesterase V mRNA. Ligation of the ductus arteriosus was also associated with increased expression of preproendothelin-1 mRNA and with decreased expression of endothelin B receptor (ET(B)) mRNA. These results suggest that there is coordinated regulation of genes of the nitric oxide pathway, which would decrease nitric oxide and cGMP concentration, thereby decreasing pulmonary vasodilator activity. There is also coordinated regulation of genes of the endothelin-1 pathway, which would increase endothelin-1 concentration and limit ET(B) receptor activation, thereby increasing pulmonary vasoconstrictor activity. These alterations in gene expression would increase fetal pulmonary vascular resistance, contributing to the development of pulmonary hypertension after birth.

Nitric oxide: biological role and clinical uses

Nitric oxide is a product of the conversion of L-arginine by the enzyme nitric oxide synthase. Nitric oxide is involved in a variety of physiological situations and is produced by many different cell types. It is involved in neurotransmission, maintenance of vascular smooth muscle tone, and cytotoxicity. Nitric oxide has been suggested to play an anti-inflammatory role by inhibiting the expression of the genes for inflammatory cytokines. The pathophysiological role of nitric oxide is also evident in a variety of diseases, including septic shock, asthma, reperfusion injury, etc. Nitric oxide, by stimulating the production of cyclic GMP, relaxes smooth muscles of the cardiovascular, respiratory, gastrointestinal, and genito-urinary systems. Recent studies have provided important information on the use of inhaled nitric oxide for the management of several diseases characterized by the presence of abnormal pulmonary vascular tone, such as persistent pulmonary hypertension of the newborn. This review addresses the biology and clinical uses of inhaled nitric oxide.

Models of persistent pulmonary hypertension of the newborn (PPHN) and the role of cyclic guanosine monophosphate (GMP) in pulmonary vasorelaxation

At birth, a marked decrease in pulmonary vascular resistance allows the lung to establish gas exchange. Persistent pulmonary hypertension of the newborn (PPHN) occurs when this normal adaptation of gas exchange does not occur. We review animal models used to study the pathogenesis and treatment of PPHN. Both acute models, such as acute hypoxia and infusion of vasoconstrictors, and chronic models of PPHN created both before and immediately after birth are described. Inhaled nitric oxide is an important emerging therapy for PPHN. We review nitric oxide receptor mechanisms, including soluble guanylate cyclase, which produces cGMP when stimulated by nitric oxide, and phosphodiesterases, which control the intensity and duration of cGMP signal transduction. A better understanding of these mechanisms of regulation of vascular tone may lead to safer use of nitric oxide and improved clinical outcomes.

[Inhaled nitric oxide: a physiologic treatment of persistent pulmonary arterial hypertension in the newborn]

Fetal pulmonary circulation is characterized by high resistance and low pulmonary blood flow. Right-to-left shunting through the foramen ovale and/or patent ductus arteriosus is necessary to perfuse the placenta and insure fetal life. At birth, pulmonary arterial blood flow increases immediately by 8- to 10-fold, and allows pulmonary gas exchange and postnatal life. In some circumstances, this adaptation to extra-uterine life is inadequate, because of persistent high pulmonary resistance (PPHN). Due to the lack of a selective pulmonary vasodilator, the treatment of this syndrome remained purely symptomatic using high oxygen levels and barotraumatic mechanical hyperventilation. When this medical treatment failed, the only alternative was extracorporeal membrane oxygenation (ECMO). The discovery of the major role of various endothelium-derived factors including nitric oxide (NO) in the control of vascular reactivity led to dramatic switches in the concepts of severe neonatal respiratory failure and the therapeutic approach of PPHN. It was shown, first in experimental animals then in a few infants with hypoxemic respiratory failure, that NO inhalation selectively vasodilated the vasoconstricted pulmonary vessels, and reversed right-to-left shunting and refractory hypoxemia. Whether inhaled NO also reduces mortality and/or morbidity in hypoxic infants remains to be proven by appropriate randomized clinical trials. However, not only PPHN is associated with pulmonary diseases of various etiologies and underlying pathophysiologic mechanisms, but also inhaled NO is used in conjunction with other validated therapeutic strategies including ante- or postnatal steroids, exogenous surfactants, and high-frequency oscillatory ventilation. Thus, the relevant primary endpoint might be not only crude survival but the most physiological and economical way of obtaining it.

[Persistent pulmonary hypertension in newborn infants]

On the basis of a review of the literature, a survey is presented concerning persistent pulmonary hypertension of the newborn. In this article the authors focus on the pathophysiology, diagnostic criteria and treatment, including mechanical ventilation, pharmacological vasodilation and extracorporal membrane oxygenation. Particular emphasis is placed on the treatment of the condition with inhaled nitric oxide. Nitric oxide is a selective pulmonary vasodilator and able to improve ventilation/ perfusion mismatching in cases where there is an affection of the pulmonary parenchyma. Data from randomized trials with close long-term follow-up is necessary before routine nitrogen oxide treatment can be recommended.