Treatment of severe persistent pulmonary hypertension of the newborn with magnesium sulphate

Magnesium Supplementation Attenuates Pulmonary Hypertension via Regulation of Magnesium Transporters

Pulmonary hypertension (PH) is characterized by profound vascular remodeling and altered Ca²⁺ homeostasis in pulmonary arterial smooth muscle cells (PASMCs). Magnesium ion (Mg²⁺), a natural Ca²⁺ antagonist and a cofactor for numerous enzymes, is crucial for regulating diverse cellular functions, but its roles in PH remains unclear. Here, we examined the roles of Mg²⁺ and its transporters in PH development. Chronic hypoxia and monocrotaline induced significant PH in adult male rats. It was associated with a reduction of [Mg²⁺]_i in PASMCs, a significant increase in gene expressions of Cnnm2, Hip14, Hip14l, Magt1, Mmgt1, Mrs2, Nipa1, Nipa2, Slc41a1, Slc41a2 and Trpm7; upregulation of SLC41A1, SLC41A2, CNNM2, and TRPM7 proteins; and downregulation of SLC41A3 mRNA and protein. Mg²⁺ supplement attenuated pulmonary arterial pressure, right heart hypertrophy, and medial wall thickening of pulmonary arteries, and reversed the changes in the expression of Mg²⁺ transporters. Incubation of PASMCs with a high concentration of Mg²⁺ markedly inhibited PASMC proliferation and migration, and increased apoptosis, whereas a low level of Mg²⁺ produced the opposite effects. siRNA targeting Slc41a1/2, Cnnm2, and Trpm7 attenuated PASMC proliferation and migration, but promoted apoptosis; and Slc41a3 overexpression also caused similar effects. Moreover, siRNA targeting Slc41a1 or high [Mg²⁺] incubation inhibited hypoxia-induced upregulation and nuclear translocation of NFATc3 in PASMCs. The results, for the first time, provide the supportive evidence that Mg²⁺ transporters participate in the development of PH by modulating PASMC proliferation, migration, and apoptosis; and Mg²⁺ supplementation attenuates PH through regulation of Mg²⁺ transporters involving the NFATc3 signaling pathway.

Oral sildenafil and inhaled iloprost in the treatment of pulmonary hypertension of the newborn

OBJECTIVE

This study was performed to examine the effectiveness and safety of oral sildenafil and inhaled iloprost in term newborns with persistent pulmonary hypertension of the newborn (PPHN).

PATIENTS AND METHODS

Oral sildenafil and inhaled iloprost were administered to 27 and 20 neonates, respectively, for treatment of persistent pulmonary hypertension. All patients were term infants at 37 gestational weeks or older. In the sildenafil group, 14 patients had meconium aspiration syndrome, 8 had asphyxia (hypoxic ischemic encephalopathy stages II and III), 3 had congenital pneumonia, 1 had transient tachypnea, and 1 had idiopathic PPHN. In the iloprost group, 9 patients had meconium aspiration syndrome, 7 had asphyxia (hypoxic ischemic encephalopathy stages II and III), 3 had congenital pneumonia, and 1 had transient tachypnea. Sildenafil citrate was administered via an oral feeding tube. Iloprost was administered endotracheally to patients on mechanical ventilation using a jet nebulizer.

RESULTS

Iloprost appeared to be more effective than sildenafil in the treatment of PPHN with regard to time to adequate clinical response, ventilatory parameters, duration of drug administration, duration of mechanical ventilation, duration of return to normal values of respiratory failure indices, use of MgSO4 as a second vasodilator and requirement for support with inotropic agents. We observed no side effects on blood pressure or homeostasis in any of the patients in the iloprost group. Systemic hypotension was significantly elevated in the sildenafil group. Four and three infants died of PPHN in the sildenafil and iloprost groups, respectively. Pulmonary systolic arterial pressure decreased to normal levels in the remaining 40 patients, and they were discharged from hospital.

CONCLUSION

We suggested that inhaled iloprost may be a safe and effective treatment choice in newborn infants with persistent pulmonary hypertension. In cases where treatment with inhaled iloprost, ECMO or INO is not possible, oral sildenafil can be an alternative therapy option in the treatment of PPHN.

Risk factors and outcomes of persistent pulmonary hypertension of the newborn in neonatal intensive care unit of Al-minya university hospital in egypt

Background:

Persistent pulmonary hypertension of the newborn (PPHN) result from the failure of the normal fetal-to-neonatal circulatory transition is associated with substantial infant mortality and morbidity.

Objective:

To estimate the possible risk factors and assess the outcome of these cases.

Materials and Methods:

Prospective study was performed enrolling all full-term and post-term newborn admitted to the NICU from January 2009 to April 2012, All neonates were subjected to complete history and physical examination, laboratory data including a complete blood count, arterial blood gases, blood glucose, serum electrolytes, and blood culture to exclude sepsis. Cases with PPHN had a continuous pulse oximeter, blood pressure and electrocardiography monitoring. Chest X-ray and echocardiogarphy were carried out to verify shunt and exclude structural congenital heart disease.

Results:

Out of the studied 640 infants, 32 infants (5%) developed PPHN, Meconium aspiration, birth asphyxia, hyaline membrane diseases, neonatal septicemia, post-term birth being large for gestational age, cesarean section, maternal overweight, and diabetes mellitus were associated with an elevated risk for PPHN. All neonates treated with O₂, 10 neonates with Mg sulphate, 16 with oral sildenafil and 12 with mechanical ventilation. After 6 months follow-up, 12 (37.54%) improved and followed-up without sequelae, 4 (12.5%) developed some neurodevelopmental impairment, 8 (25%) died, 3 (9.3%) developed chronic lungs diseases, 2 (6.2%) developed hearing defects and another 3 (9.3%) missed follow-up.

Conclusion:

PPHN was found in 5% of the studied population. Meconium aspiration, birth asphyxia, neonatal septicemia, post-term were associated with an elevated risk for PPHN. As this is a unit based study, a comprehensive countrywide survey on PPHN in Egypt is recommended to determine any regional differences in disease incidence.

Randomized controlled trial of magnesium sulfate in women at risk of preterm delivery-neonatal cardiovascular effects

OBJECTIVE

Use of antenatal magnesium sulfate (MgSO(4)) may reduce cerebral palsy in infants born very preterm. Low systemic blood flow in the first day in very preterm infants has been associated with cerebral injury and adverse motor outcome. The aim was to determine the effect of MgSO(4) on systemic blood flow in preterm infants.

STUDY DESIGN

Randomized trial of MgSO(4) versus saline placebo given to mothers at risk of delivery before 30 weeks gestation. Echocardiographic monitoring performed at 3 to 5, 10 to 12 and 24 h.

RESULT

A total of 48 infants were exposed to MgSO(4) and 39 to placebo. Infants exposed to MgSO(4) were significantly more likely to receive volume expansion (42% versus 21%). Inotrope use did not differ significantly (40% versus 26%). There was no significant difference in mean lowest superior vena cava (SVC) flow or right ventricular output (RVO), or incidence of low SVC flow or RVO in the first 24 h. Infants exposed to MgSO(4) had a significantly higher heart rate and were more likely to have low SVC flow at 10 to 12 h but not other times.

CONCLUSION

Antenatal MgSO(4) produced no consistent cardiovascular effects in the infant in the first 24 h. There is no evidence from this study to suggest the mechanism by which antenatal MgSO(4) prevents cerebral palsy is through a cardiovascular effect in the newborn.

Neurodevelopmental outcome of newborns with persistent pulmonary hypertension

BACKGROUND

Developmental disabilities have been reported in infants with persistent pulmonary hypertension of the newborn (PPHN) treated with inhaled nitric oxide (INO) or intravenous magnesium sulphate (MgSO(4)) and/or extracorporeal membrane oxygenation. This paper reports the rate of developmental disabilities at 2 years of age in a cohort of survivors of PPHN treated with INO, MgSO(4), or both during the neonatal period.

METHODS

Sixteen survivors of PPHN were prospectively followed up. These infants were treated with intravenous MgSO(4) and/or INO during the neonatal period. Neurodevelopmental assessment was carried out at 2 years of age using the Bayley Scales of Infant Development 2nd Edition by a developmental psychologist. Eleven (68.8%) infants completed the 2-year follow-up.

RESULTS

The median mental developmental index (MDI) and physical developmental index scores were 85 (interquartile range, IQR = 27) and 87 (IQR = 33), respectively. Two infants (18.2%) had developmental disability (MDI scores <70).

CONCLUSION

Survivors of PPHN are at risk of developmental disabilities. Early intervention programme and long-term follow-up should be integrated in the management of these infants.

A comparison of magnesium sulphate and sildenafil in the treatment of the newborns with persistent pulmonary hypertension: a randomized controlled trial

The aim of this prospective, randomized and controlled study was to compare the clinical efficacy of intravenous magnesium sulfate (MgSO₄) and oral sildenafil therapies with persistent pulmonary hypertension of the newborn. A total of 34 infants in the MgSO₄ group and 31 infants in the sildenafil group completed the study. The time to reach the adequate clinical response [defined as oxygen index (OI) level of <15, a pulmonary artery pressure of < 20 mmHg) was significantly shorter in the sildenafil group (p = 0.002). Duration of mechanical ventilation was longer and the number of the patients requiring inotropic support was higher in the MgSO₄ group (p = 0.001 and p = 0.002, respectively). Although among two groups the difference in OI > 5 as speculated in our hypothesis could only be found at 36 h of the treatment, sildenafil was more effective than MgSO₄ in the treatment of persistent pulmonary hypertension of the newborns with regard to time to adequate clinical response, duration of mechanical ventilation and support requirement with inotropic agents.

Current and future therapeutic options for persistent pulmonary hypertension in the newborn

Persistent pulmonary hypertension of the newborn (PPHN) is a potentially life-threatening condition that is characterized by supra-systemic pulmonary vascular resistance causing right-to-left shunting through the ductus arteriosus and/or foramen ovale, leading to a vicious cycle of hypoxemia, acidosis and further pulmonary vasoconstriction. Advances in neonatology including surfactant instillation, high-frequency ventilation, extracorporeal membrane oxygenation and, most importantly, inhaled nitric oxide (INO), have revolutionized the management of PPHN. However, given that INO does not improve oxygenation in a significant proportion (30-40%) of cases, there is an urgent need to consider other therapeutic options for PPHN. The issue is more important for developing nations with a higher PPHN-related health burden and limited resources. This article discusses the evidence about INO in term and preterm neonates in brief, and focuses mainly on the potential alternative drugs in the management of PPHN.

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.

Magnesium therapy in birth asphyxia

OBJECTIVE

Glutamate plays a critical role in the hypoxic ischaemic neuronal death. Two mechanisms of glutamate- induced neuronal death have been identified. One is rapid cell death that occurs in minutes and the second is delayed cell death that occurs over hours and is initiated principally by the activation of the N-methyl D-Aspactate (NMDA) receptor. Magnesium (Mg) is an NMDA receptor blocker. Systemic administration of Mg after a simulated hypoxic ischaemic insult has been shown to limit neuronal injury in several animal models. However, before embarking on to the use of Mg for neuronal protection in the human neonate it is important to study the safety and side effects of Mg administration.

METHODS

Forty terms, appropriate for gestational age babies with severe birth asphyxia (1 min Apgar score < 3 and 5 min Apgar score < 6), were randomly assigned to either the study group or the control group. Infants in both groups were treated as per unit protocol except that babies in the study group received intravenous injection of magnesium sulphate 250 mg/kg within half an hour of birth and subsequently 125 mg/kg at 24 and 48 hours of life.

RESULTS

The mean cord blood serum Mg levels were 0.78 (+/- 0.047) mmol/L in the control group and 0.779(+/-0.045) mmol/L in the study group. The serum Mg levels at 3, 6, 12, 24, 48 and 72 hours of life were 1.87(+/-0.6), 1.65(+/-0.059), 1.468 (+/-0.91), 1.881 (+/- 0.053), 1.916 (+/- 0.053) and 1.493 (+/- 0.084) mmol/L respectively in the study group. All these values were significantly higher than those obtained in the control group (p< 0.001). No significant alterations in heart rate, respiratory rate, oxygen saturation and mean arterial pressure were seen, following magnesium infusion with either 250 mg/kg or 125 mg/kg dose. The serum Mg levels in the study group ranged between 1.493 (+/- 0.084) and 1.916(+/-0.053) mmol/L, which are considered to be in the neuroprotective range.

CONCLUSION

Injection MgSO4 administered in a dose of 250 mg/kg and 125 mg/kg as an intravenous infusion is safe and the Mg levels obtained are in the range considered to be neuroprotective.

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.

Effect of increasing doses of magnesium in experimental pulmonary hypertension after acute pulmonary embolism

OBJECTIVE

To investigate the dose-related effects of magnesium on pulmonary vascular resistance and associated changes in cardiac output in porcine micro-embolic pulmonary hypertension.

DESIGN

Prospective, interventional animal study.

SETTING

University animal laboratory.

SUBJECTS

Forty anaesthetised and ventilated piglets.

INTERVENTIONS

Right heart catheterisation for the measurement of cardiac output, pulmonary artery pressure, central venous pressure and pulmonary capillary wedge pressure; arterial cannulation for measurement of arterial pressures and ionised magnesium levels; calculation of pulmonary and systemic vascular resistance before and after induction of acute pulmonary micro-embolism, and without or with the administration of magnesium (0.5, 1.0, 2.0 mmol/kg bolus and 1 mmol/kg bolus followed by 1 mmol/kg per h continuous infusion).

MEASUREMENTS AND MAIN RESULTS

The bolus administration of increasing doses of magnesium (0.5, 1.0, 2.0 mmol/kg) was associated with an increase in ionised serum magnesium levels and a dose-dependent decrease of mean pulmonary arterial pressure, an increase of cardiac output and a decrease of pulmonary vascular resistance. This effect was sustained after bolus administration (1 mmol/kg) followed by a continuous infusion of magnesium (1 mmol/kg per h).

CONCLUSIONS

Magnesium has a directly dose-dependent beneficial effect on the circulation in acute embolic pulmonary hypertension and improves cardiocirculatory impairment in massive pulmonary embolism (PE).

Update on extracorporeal membrane oxygenation

Extracorporeal membrane oxygenation (ECMO) consists of the application of intermediate-term cardiopulmonary bypass for the treatment of potentially reversible heart and/or lung failure in the neonate, child, and adult. Applications in the neonate include congenital diaphragmatic hernia, pulmonary hypertension, meconium aspiration syndrome, and pre- and post-operative congenital heart surgery support. In the older child, myocarditis, infections, and respiratory failure (RSV and ARDS) are the most frequent indications, in addition to peri-operative cardiac surgical support. A review of the institutional experiences at the University of Louisville spanning a 15-year period and comparison international data will be presented, along with a pertinent review of the literature. Technical considerations, complications, and long-term outcomes will be reviewed, and the potential interface between ECMO and other, less invasive technologies, i.e., high-frequency ventilation, replacement surfactant, and nitric oxide, will be discussed.

Nitric oxide inhalation and nitric oxide synthase inhibitor supplement for endotoxin-induced hypotension

BACKGROUND

This study was performed to determine whether a combined therapy of nitric oxide (NO) inhalation and nitric oxide synthase (NOS) inhibitor is effective in experimental animals with endotoxin-induced refractive hypotension accompanied by pulmonary hypertension.

METHODS

Escherichia coli lipopolysaccharide (1 mg/kg) was administered to 10 newborn piglets to induce endotoxemia. The experiment then began 60 min later, when the systemic arterial pressure dropped. The inhalation of 20 p.p.m. NO at 60 and 120 min of endotoxemia created a control group. Another group was also administered N w-nitro-L-arginine (L-NNA; 5 mg) after the first NO inhalation at 60 min of endotoxemia (the L-NNA group). Pulmonary arterial pressure, systemic arterial pressure and cardiac output were measured and compared among the groups.

RESULTS

Three of the 5 piglets in the control group died of hypotensive shock, while in the L-NNA group the systemic arterial pressure recovered to pre-endotoxin administration levels. The L-NNA group produced a further increase in pulmonary arterial pressure against which NO inhalation was effective.

CONCLUSION

Nitric oxide inhalation alone carries a potential risk of further lowering systemic arterial pressure in a piglet with hypotension induced by endotoxin, whereas the combined therapy resulted in the recovery of the blood pressure to pre-endotoxin levels. The combined therapy was simultaneously effective against pulmonary hypertension.

Neuronal protection with magnesium

Delayed neuronal death following hypoxic ischaemic insult is primarily mediated by the N-methyl D-aspartate (NMDA) receptor. The NMDA receptor antagonist MK 801, has been shown to limit neuronal death following hypoxic ischaemic injury but is too toxic to be used in the human neonate. Magnesium blocks the NMDA channel in a voltage dependent manner. Its administration after a simulated hypoxic ischaemic insult limits neurological damage in several animal models. The efficacy of magnesium in providing neuroprotection in the human neonate, however needs to be established in controlled clinical trials.

Developmental change in magnesium sulfate-induced relaxation of rabbit pulmonary arteries

Magnesium causes a variety of vascular smooth muscle to relax. The present study was designed to determine whether there is a developmental change in the magnesium-induced response of pulmonary vasculature. Isolated pulmonary arteries (PA) of newborn (1- to 3-day-old) and juvenile (4- to 6-wk-old) rabbits were suspended in organ chambers filled with modified Krebs-Ringer bicarbonate solution (95% O(2)-5% CO(2), 37.0 degrees C), and their isometric tension was recorded. In arteries preconstricted with endothelin-1 to a similar tension level, MgSO(4) caused greater relaxation of juvenile rabbit PA than that of the newborn rabbit PA. Verapamil, a voltage-dependent Ca(2+) channel blocker, attenuated magnesium-induced relaxation in juvenile rabbit PA but not in newborn PA. The uptake of Ca(2+) of juvenile rabbit PA was inhibited by MgSO(4), and the inhibition was attenuated by verapamil. The uptake of Ca(2+) of newborn rabbit PA was smaller than that of the juvenile PA and was not significantly affected by MgSO(4) and verapamil. These results demonstrate that there is a developmental increase in the dilator effect of MgSO(4) in rabbit PA. In newborn rabbit PA, an incomplete maturation of the voltage-dependent Ca(2+) channels may contribute to the smaller vasodilation induced by MgSO(4).

An international network for evaluating neuroprotective therapy after severe birth asphyxia

Animal studies have shown great promise in their applicability to potentially neuroprotective therapies for severe birth asphyxia in human babies. It is now necessary to consider a strategy to evaluate some or all of these techniques within the context of human neonatal randomized control trials (RCT). We have set up a pilot study for an international RCT of mature babies with severe asphyxia (defined by an Apgar score of 5 or less at 10 minutes) and have shown that we can recruit from 120 centers in 17 countries an average of three babies a week, which is the required number to undertake a study over a 2-year period with sufficient power to show a significant improvement in outcome. Particular attention must be given in future studies to the size of improvement in outcome required, generalizability of entry criteria, and the appropriate measure of functional outcome in treated babies.

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.

Serum levels of magnesium at birth related to complications of immaturity

Magnesium is a natural calcium channel blocker inhibiting vasoconstriction in numerous vascular beds. Magnesium sulphate given prior to birth to pre-eclamptic mothers and mothers in preterm labour has in retrospect been found to be associated with a decreased incidence of both intraventricular haemorrhage and cerebral palsy. Little is known about the effect of normal variations of serum magnesium in the very preterm baby, where morbidity is closely related to rapid vascular changes. We have analysed the absolute levels and normal variations of magnesium concentration in cord blood and during the first 3 weeks after birth for 69 infants born before 32 gestational weeks of age. The results show an inverse relation between serum magnesium at birth and gestational age. Higher levels of serum magnesium at birth within normal variations were associated with a delayed closure of the ductus arteriosus, and mild but not severe peri- and intraventricular haemorrhage.

Mortality among infants with high-risk congenital diaphragmatic hernia in Singapore

Several factors suggested to predict mortality in congenital diaphragmatic hernia (CDH) have not always been applicable in different centers. A retrospective review was conducted of 19 consecutive neonates in Singapore in whom CDH was diagnosed within 12 hours of birth to identify factors associated with mortality. Of the 19 cases, 15 (79%) were diagnosed using antenatal ultrasonography. Eight (42%) underwent primary repair at a median age of 23 hours (range, 12 to 50 hours). Of the 19 infants, 15 died (mortality rate, 79%). Survivors until hospital discharge were compared with nonsurvivors. Antenatal diagnosis and stomach position in left-sided defects had no effect on outcome, although polyhydramnios tended to be associated with nonsurvival. Significant postnatal factors associated with mortality included a low arterial pH level, low initial arterial-alveolar oxygen ratio, high initial alveolar-arterial oxygen gradient, as well as high oxygenation and ventilation indices. These results reflect difficulty in oxygenation because of pulmonary hypoplasia despite evidence of adequate ventilation. There was no difference between survivors and nonsurvivors in either their initial or best postductal blood gases. The "Bohn quadrants" did not aid in predicting survival of infants who underwent repair because all eight such infants had best postductal carbon dioxide values of less than 40 mm Hg and ventilation indices of less than 1,000. Yet only four (50%) survived until hospital discharge. Large-scale evaluation of these factors may be required in the future to demonstrate their validity and reliability because of changing management strategies for CDH.

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.

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.

Role of magnesium sulfate in seizure prevention in patients with eclampsia and pre-eclampsia

Eclampsia is a leading cause of maternal mortality. The prevention of seizure activity in pre-eclampsia and recurrent seizures in eclamptic patients is an essential aspect of management. Many drugs with anticonvulsant properties have been used to treat patients with pre-eclampsia and eclampsia. Magnesium sulfate is a significantly better drug than either diazepam or phenytoin for preventing recurrent seizures in eclamptic patients. Magnesium sulfate has diverse cardiovascular and neurological effects and also alters calcium metabolism. Although the drug crosses the placenta and may affect the fetus, these effects are clinically small and fetal morbidity has been shown to be reduced in randomised studies comparing magnesium sulfate to either phenytoin or benzodiazepines. Dosage regimens of magnesium sulfate are empirical. Because adverse effects of this agent are related to toxicity, the establishment of greater efficacy by using higher dosage regimens needs to be tested against a greater risk of adverse effects. The most serious toxicity related to magnesium sulfate use is magnesium sulfate use is neuromuscular blockade that may result in respiratory arrest. Magnesium sulfate is now the drug choice for treating eclamptic patients. However, further studies are required to establish the role of this agent as a prophylactic agent in the prevention of eclampsia.

In vitro effects of magnesium sulfate in isolated intrapulmonary and mesenteric arteries of piglets

Magnesium sulfate (MgSO4) has been proposed to be an efficient treatment in persistent pulmonary hypertension of the newborn. We compared the ability of MgSO4 to inhibit the responses to several vasoconstrictors in isolated intrapulmonary and mesenteric arteries from 10-17-d-old piglets. MgSO4 (3-100 mM) produced a slight vasodilator effect in pulmonary arteries precontracted with the thromboxane A2 mimetic U46619 (10(-6) M), noradrenaline (10(-5) M), and KCl (80 mM) (15.1 +/- 3.7%; 20 +/- 3.33%; 10.4 +/- 0.9% at 100 mM MgSO4 respectively). In contrast, in mesenteric arteries MgSO4, produced a marked vasodilation (80.4 +/- 4.0%, 93.1 +/- 3.46%, and 87.5 +/- 1.93% at 100 mM MgSO4, respectively, p < 0.01 versus pulmonary arteries). The vasodilator effect of MgSO4 was endothelium-independent and reversed by increasing the extracellular Ca2+ concentration. After incubation for 1 h of pulmonary arteries with three different MgSO4 concentrations (0, 1.2, and 4.8 mM) there were no differences in the contractile responses to U46619 nor in the vasodilator effects of acetylcholine or sodium nitroprusside. Rapid removal of Mg2+ from bath medium produced a transient vasodilation which was more marked in pulmonary than in mesenteric arteries and was greatly reduced by the removal of endothelium or by the nitric oxide synthase inhibitor L-NAME (10(-4) M). We conclude that MgSO4 is a poor vasodilator of pulmonary arteries in vitro and at physiologic concentrations appears to inhibit nitric oxide release from the pulmonary endothelium. Thus, the possible beneficial clinical effects of MgSO4 in persistent pulmonary hypertension of the newborn do not seem to be related to a direct effect on pulmonary vascular smooth muscle.

Acute effects of two different doses of magnesium sulphate in infants with birth asphyxia

The effects of two different doses of magnesium sulphate (MgSO4) were evaluated in a group of 15 full term infants with Apgar scores of < 6 at 10 minutes, studied within 12 hours of delivery. Seven infants received 400 mg/kg MgSO4 and eight received 250 mg/kg. After the larger dose, mean arterial pressure (MAP) fell by a mean of 6 mm Hg (13%) at one hour but was not significantly reduced thereafter. Respiratory depression lasted three to six hours. EEG readings and heart rate were not significantly different. Mean serum Mg2+ increased from 0.79 to 3.6 mmol/l at one hour. After 250 mg/kg MgSO4, MAP, EEG, tone and heart rate were unchanged. One infant developed transient respiratory depression. Mean serum Mg2+ rose from 0.71 to 2.42 mmol/l at one hour. MgSO4 (400 mg/kg) has an unacceptable risk of hypotension; 250 mg/kg MgSO4 was not associated with hypotension although respiratory depression can occur.

Magnesium sulphate as an alternative and safe treatment for severe persistent pulmonary hypertension of the newborn

Eleven newborns admitted consecutively to the neonatal unit with respiratory failure and severe persistent pulmonary hypertension (PPHN) were included in a clinical trial to assess the efficacy of magnesium sulphate (MgSO4) in the treatment of PPHN. A loading dose of 200 mg/kg MgSO4 was given over 20 minutes, followed by a continuous infusion of 20-150 mg/kg/hour to obtain a magnesium blood concentration between 3.5 and 5.5 mmol/l. Mean (SD) duration of treatment was 75.5 (19.8) hours. No other vasodilatory drug was administered before or during the treatment and patients were not hyperventilated. Mean (SEM) PaO2 values significantly increased from 42.6 (8.8) before treatment to 70.3 (24.1) mm Hg after 24 hours, with no change in pH or PCO2. Oxygen index and alveolar-arterial oxygen gradient (A-aDO2) were significantly lower after 24 hours; respectively, 46.8 (15.2) to 28.0 (9.0) and 624.3 (11.3) to 590 (58) mm Hg. Mean airway pressure could be significantly reduced from 19.5 (3.1) to 13.9 (3.9) cm H2O after 72 hours. Mean ventilatory time support was 131 hours and mean total oxygen dependency 10 days. No systemic hypotension nor any other adverse effect were noted. All infants survived and the neurodevelopmental assessment was normal at 6 and 12 months of age. It is concluded that magnesium sulphate is a non-aggressive and low-cost treatment of short duration which is easy to apply. It may have a role in the various treatment of PPHN.

Pulmonary hypertension in respiratory distress syndrome

Pulmonary hypertension was associated with nonresponse to surfactant in six premature infants with respiratory distress syndrome. The diagnosis was suspected on the basis of a discrepancy between the X-ray findings and the severity of the clinical status as reflected by hypoxia despite maximal ventilatory support. The diagnosis of pulmonary hypertension was made by pre- and postductal oxygen saturation differences or by echodoppler cardiography, showing suprasystemic right ventricular pressures or right to left shunts through a patent foramen ovale or the ductus arteriosus. The response to surfactant was quantified by the arterial/alveolar (a/A) ratio difference before and 1 hr after therapy ("delta a/A ratio"); the delta a/A ratio was 0 +/- 0.01, which indicates a nonresponse. A single dose of 1 mg/kg tolazoline was administrated and the response assessed by a/A difference. A delta a/A ratio of 0.11 +/- 0.11 (range 0.02-0.32) represented a dramatic response and enabled oxygenation in these severely ill infants. No significant side effects were observed. We conclude that pulmonary hypertension may be an important and reversible condition in certain cases of respiratory distress syndrome and has to be considered in infants who do not respond to surfactant.

[Indications for the use of magnesium in anesthesia and intensive care]

Magnesium (Mg), a cofactor in numerous enzymatic reactions, is often ignored by clinicians, as the symptomatology of Mg depletion is not specific and usually associated with that of the cause of the depletion. Furthermore, the plasma Mg concentration (0.8 to 1.1 mmol.L-1) is only equivalent to one percent of the total body content. A Mg deficit may exist while plasma Mg concentration is normal. Therefore other techniques for Mg assessment, such as the repletion test, as well as red blood cell and lymphocyte concentrations have been used. A renewed interest for Mg occurred as numerous studies have shown the therapeutic efficiency of Mg and as the mechanisms of its haemodynamic effects have been recognized. Mg regulates Na-K-ATPase activity, K channels activity and, most of all, it is a natural calcium channel blocking agent. These properties explain its important place in electrophysiology of myocardial cells and the effects on the tension of smooth muscles, resulting in a vasodilation and a bronchodilation respectively. The antagonistic effect of Mg on calcium decreases the presynaptic release of acetylcholine at the neuromuscular junction and the release of epinephrine at the peripheral sympathetic nerves and the adrenals. Mg potentiates the effect of non-depolarizing muscle relaxants. A Mg deficiency occurs often in ICU patients, in alcoholics and during use of diuretics. Simultaneous administration of Mg is often required for treatment of potassium deficiency. Mg has an anti-arrhythmic effect towards digoxin-mediated dysrhythmias and torsades de pointes, and can be efficient in other arrhythmias. Systematic use of Mg seems to decrease mortality of acute myocardial infarction and is justified during cardiac surgery, often associated with hypomagnesemia, because of vasodilation of coronary arteries and in order to prevent occurrence of arrhythmias. Mg, because of its calcium channel blocking properties and as it lowers the release of epinephrine, is indicated for surgery of pheochromocytoma. In eclamptic and pre-eclamptic patients, the use of Mg is valuable, but not as an anti-epileptic agent. Other clinical uses of Mg have been proposed, but they are either anecdotal or of uncertain efficiency.

Endotracheal tolazoline for severe persistent pulmonary hypertension of the newborn

The condition of a neonate with severe persistent pulmonary hypertension who became severely hypoxic and acidotic despite intensive conventional treatment improved dramatically after endotracheal administration of tolazoline. This logical mode of administration of vasodilator therapy for this condition has not been reported before. It seemed to be life saving in this case and it warrants further clinical trial.

Effects of magnesium sulphate and nitric oxide in pulmonary hypertension induced by hypoxia in newborn piglets

AIM

To examine the haemodynamic effects of intravenous magnesium sulphate on an animal model of neonatal pulmonary hypertension induced by hypoxia.

METHODS

The cardiac index (Q), pulmonary arterial pressure (PAP), systemic arterial pressure (SAP), and pulmonary (PVRI) and systemic (SVRI) vascular resistance indices were measured in nine newborn piglets (including three controls). Pulmonary hypertension was induced by lowering the FIO2 to 0.12-0.14, after which there was a significant increase in PAP and PVRI (37% and 142%, respectively; p < 0.01) and a significant fall in SAP and Q (30% and 33%, respectively; p < 0.01).

RESULTS

Magnesium sulphate was infused intravenously as four doses of 25 mg/kg, 15 minutes apart, which resulted in a significant mean (SD) increase in serum magnesium (0.83 (0.07) mmol/l to 1.82 (0.19) mmol/l; p < 0.01). After the initial dose SAP, SVRI, PAP and PVRI decreased, but not significantly. Each subsequent dose of (50, 75, 100 mg/kg) was accompanied by further significant reductions in these variables from control baseline (p < 0.05). The PVRI:SVRI ratio remained unchanged throughout. Inhaled nitric oxide (NO) 40 ppm was administered after the last dose of magnesium sulphate. The PVRI:SVRI significantly decreased (p < 0.05), indicating that reversible pulmonary hypertension remained after a maximum dose of magnesium sulphate.

CONCLUSIONS

Unlike NO, magnesium sulphate is not a selective pulmonary vasodilator and may lead to deleterious effects on systemic pressures in critically ill newborns.

Alternatives to ECMO

The past decade has witnessed technological advancements which are unparalleled in neonatology. ECMO has been demonstrated to be a powerful rescue treatment, but has perhaps been overutilised and is not universally available. Alternative treatments have been shown to be both safe and efficacious in the management of infants with respiratory failure. Direct head to head clinical trials will probably be necessary to establish appropriate criteria and indications for use, given the wide diversity of pathophysiology these unique patients present.

Nitric oxide

Although persistent pulmonary hypertension of the newborn (PPHN) has been considered to be a relatively rare condition, there is increasing evidence that pulmonary vasoconstriction is a common finding in moderate and severe respiratory distress syndrome. High pressure, high rate ventilation may overcome this problem but it is associated with an unacceptably high incidence of pneumothorax and chronic lung disease. Vasodilators including tolazoline, prostacyclin and nitroprusside have a nonspecific effect, often producing systemic as well as pulmonary hypotension. Nitric oxide (NO) offers an exciting alternative therapy. NO is produced by the conversion of arginine to citrulline by NO synthase in the vascular endothelial cells. The NO then diffuses through to the underlying smooth muscle leading to relaxation. It then combines with haemoglobin to form small quantities of methaemoglobin, preventing spread of its effect elsewhere. The main potential toxic effect is due to the rapid conversion of NO to nitrogen dioxide in the presence of oxygen. Animal studies have shown that concentrations of NO up to 100 ppm are safe and also effective in relieving vasoconstriction induced by hypoxia, thromboxane analogues and infusions of group B haemolytic streptococcus. Preliminary studies on adults with respiratory distress syndrome have been encouraging showing reductions in pulmonary artery pressure and improvements in oxygenation without any changes in systemic blood pressure. Two small studies indicate that NO therapy is both effective and safe when given to full term babies with PPHN. Further data are urgently needed to find optimal concentrations so that multicentre studies can be carried out.