Endotracheal tolazoline for severe persistent pulmonary hypertension of the newborn

Pharmacotherapy for meconium aspiration

In this article we have attempted to review the current pharmacological treatment options for infants with meconium aspiration syndrome with or without persistent pulmonary hypertension. These treatments include ventilatory support, surfactant treatment and inhaled nitric oxide (INO), in addition to older and newer pharmacological treatments. These include sedatives, muscle relaxants, alkali infusion, antibiotics and the newer vasodilators. Many aspects of treatment, including ventilatory care, surfactant treatment and the use of INO, are reviewed in great detail in this issue. On the other hand, many newer pharmacological modalities of treatment described here have not been evaluated with randomized control trials. We have given an overview of these emerging therapies.

Magnesium sulfate for persistent pulmonary hypertension of the newborn

BACKGROUND

Persistent pulmonary hypertension of the newborn (PPHN) occurs in approximately 1.9 per 1000 newborns and may be more frequent in developing countries. There is strong evidence for the use of inhaled nitric oxide (iNO) and extra corporeal membrane oxygenation (ECMO) in the treatment of PPHN. However, many developing countries do not have access or the technical expertise required for these expensive therapies. Magnesium sulfate is a potent vasodilator and hence has the potential to reduce the high pulmonary arterial pressures associated with PPHN. If magnesium sulfate were found to be effective in the treatment of PPHN, this could be a cost effective and potentially life-saving therapy.

OBJECTIVES

To evaluate the use of magnesium sulfate compared with placebo or standard ventilator management alone, sildenafil infusion, adenosine infusion, or inhaled nitric oxide on mortality or the use of backup iNO or ECMO in term and near-term newborns (> 34 weeks gestational age) with PPHN.

SEARCH STRATEGY

The standard search strategy of the Cochrane Neonatal Review Group (CNRG) was used. No language restrictions was applied. The Cochrane Central Register of Controlled Trials (CENTRAL, The Cochrane Library, Issue 1, 2006) and MEDLINE (1966 to April 20, 2007) were searched for relevant randomized and quasi-randomized trials. In addition the reference lists of retrieved articles were reviewed and known experts were contacted to obtain unpublished data.

SELECTION CRITERIA

All randomised or quasi-random studies were eligible where one of the treatment groups received magnesium sulfate for PPHN.

DATA COLLECTION AND ANALYSIS

Standard methods of the Cochrane Collaboration and the CNRG were used, including independent assessment of trial quality and extraction of data by each author.

MAIN RESULTS

No eligible trials were found

AUTHORS' CONCLUSIONS

On the basis of the current lack of evidence, the use of magnesium sulphate cannot be recommended in the treatment of PPHN. Randomised controlled trials are recommended.

Pulmonary hypertension in the newborn

Pulmonary hypertension of the newborn occurs in 1.9 per 1000 live births and affected infants are hypoxaemic because of right-to-left shunts through the ductus arteriosus and foramen ovale. Pulmonary hypertension of the newborn may be primary, or secondary to a variety of conditions including intrapartum asphyxia, infection, pulmonary hypoplasia, congenital heart disease or drug therapy. It may occur in association with a normal number (maladaptation) or a decreased number of arteries (for example with pulmonary hypoplasia). Few strategies used in infants with pulmonary hypertension of the newborn have been subjected to rigorous evaluation. Inhaled nitric oxide has been shown to reduce the need for extracorporeal membrane oxygenation but not mortality, in term or near term born infants. Preliminary evidence suggests that other vasodilators given by the inhaled route may improve oxygenation and new vasodilators have become available; appropriately designed trials with long-term outcomes are required to test such therapies.

Recognition and management of pulmonary hypertension

Pulmonary hypertension (mean pulmonary arterial pressure > 20mm Hg at rest or > 30mm Hg during exercise) occurs (i) as primary pulmonary hypertension (no known underlying cause), (ii) as persistent pulmonary hypertension of the newborn or (iii) secondary to a variety of lung and cardiovascular diseases. In the last 10 to 15 years there have been significant advances in the medical management of this debilitating and life-threatening disorder. The main drugs in current use are anticoagulants (warfarin, heparin) and vasodilators, especially oral calcium antagonists, intravenous prostacyclin (prostaglandin I2; epoprostenol) and inhaled nitric oxide. Calcium antagonists, (e.g. nifedipine, diltiazem) are used chiefly in primary pulmonary hypertension. They are effective in patients who give a pulmonary vasodilator response to an acute challenge with a short acting vasodilator (e.g. prostacyclin, nitric oxide or adenosine), and are used in doses greater than are usual in the treatment of other cardiovascular disorders. Prostacyclin, given by continuous intravenous infusion, is effective in patients even if they do not respond to an acute vasodilator challenge. The long term benefit in these patients is thought to reflect the antiproliferative effects of the drug and/or its ability to inhibit platelet aggregation. It is used either as long term therapy or as a bridge to transplantation. Inhaled nitric oxide, which is used mainly in persistent pulmonary hypertension of the newborn, has the particular benefit of being pulmonary selective, due to its route of administration and rapid inactivation. Anticoagulants have a specific role in the treatment of pulmonary thromboembolic pulmonary hypertension and are also used routinely in patients with primary pulmonary hypertension. Nondrug treatments for pulmonary hypertension include (i) supplemental oxygen (> or = 15 h/day), which is the primary therapy in patients with pulmonary hypertension secondary to chronic obstructive pulmonary disease and (ii) heart-lung or lung transplantation, which nowadays is regarded as a last resort. Different types of pulmonary hypertension require different treatment strategies. Future advances in the treatment of pulmonary hypertension may come from the use of drug combinations, the development of new drugs, such as endothelin antagonists, nitric oxide donors and potassium channel openers, or the application of gene therapy.

Pulmonary versus systemic effects of vasodilator drugs: an in vitro study in isolated intrapulmonary and mesenteric arteries of neonatal piglets

The ability of several vasodilators to inhibit the responses to noradrenaline and U46619 (a thromboxane A2 analog) in isolated pulmonary and mesenteric arteries of neonatal piglets was compared. In pulmonary arteries, acetylcholine produced endothelium-dependent relaxations (pIC50 = about 6.8) while, in mesenteric arteries, a relaxant (< or = 10(-7) M) or a contractile response (> or = 10(-6) M) was observed. Sodium nitroprusside produced relaxant effects in pulmonary and mesenteric arteries contracted by noradrenaline (pIC50 = 6.6 and 6.0, respectively) and U46619 (pIC50 = 5.4 and 6.7, respectively). ATP induced an endothelium-independent relaxation in pulmonary arteries (pIC50 = about 4) but in mesenteric arteries it produced weak relaxant effects. In resting mesenteric arteries, ATP induced a concentration-dependent contraction which was not observed in pulmonary arteries. Prostaglandin E1 induced a contractile effect whereas, at higher concentrations, a relaxant response was observed. The alpha-adrenoceptor antagonist tolazoline had no effect on arteries contracted by U46619 but relaxed arteries contracted by noradrenaline being slightly more potent in mesenteric than in pulmonary arteries (pIC50 = 5.1 and 4.8, respectively). Nifedipine (> 10(-7) M) relaxed both arteries, mesenteric being more sensitive than pulmonary arteries and noradrenaline more sensitive than U46619-induced contractions. In conclusion, differences in the relaxant effects for all vasodilators were found depending on the artery, the vasoconstrictor used or both. However, ATP was the only drug which, regardless of the concentration or vasoconstrictor used, produced greater relaxant effects in pulmonary than in mesenteric arteries.