Methaemoglobinaemia after inhalation of nitric oxide in infant with pulmonary hypertension

When to say no to inhaled nitric oxide in neonates?

Inhaled nitric oxide (iNO) was approved for use in critically ill term and near-term neonates (>34 weeks gestational age) in 1999 for hypoxic respiratory failure (HRF) with evidence of pulmonary hypertension. In 2011 and 2014, the National Institutes of Health and American Academy of Pediatrics respectively recommended against the use of iNO in preterm infants <34 weeks. However, these guidelines were based on trials conducted with varying inclusion criteria and outcomes. Recent guidelines from the American Thoracic Society/American Heart Association, the Pediatric Pulmonary Hypertension Network (PPHNet) and European Pediatric Pulmonary Vascular Disease Network recommend the use of iNO in preterm neonates with HRF with confirmed pulmonary hypertension. This review discusses the available evidence for off-label use of iNO. Preterm infants with prolonged rupture of membranes and pulmonary hypoplasia appear to respond to iNO. Similarly, preterm infants with physiology of pulmonary hypertension with extrapulmonary right-to-left shunts may potentially have an oxygenation response to iNO. An overview of relative and absolute contraindications for iNO use in neonates is provided. Absolute contraindications to iNO use include a ductal dependent congenital heart disease where systemic circulation is supported by a right-to-left ductal shunt, severe left ventricular dysfunction and severe congenital methemoglobinemia. In preterm infants, we do not recommend the routine use of iNO in HRF due to parenchymal lung disease without pulmonary hypertension and prophylactic use to prevent bronchopulmonary dysplasia. Future randomized trials evaluating iNO in preterm infants with pulmonary hypertension and/or pulmonary hypoplasia are warranted. (233/250 words).

Life-Threatening Extreme Methemoglobinemia during Standard Dose Nitric Oxide Therapy

We report the first case of life-threatening extreme neonatal-acquired methemoglobinemia that occurred during inhaled nitric oxide (iNO) at the standard 20 ppm dose in a neonate with early onset sepsis and suprasystemic pulmonary hypertension. Life-threatening methemoglobinemia has been efficaciously treated with methylene blue and ascorbic acid, while stopping iNO and starting iloprost and sildenafil. The patient was subjected to various tests (including gene sequencing and hemoglobin electrophoresis) and did not have any known genetic cause or predisposition for methemoglobinemia. Neuroimaging and the 2-year clinical follow-up were completely normal.

Undiagnosed intraoperative methaemoglobinaemia

Methaemoglobinaemia is a rare but potentially dangerous haemoglobinopathy that is often underdiagnosed. It is one of the causes for unexplained cyanosis with dark-coloured blood, especially in the absence of cardiac or pulmonary pathology. Not uncommonly so, it is an incidental perioperative finding in cases of dark-coloured blood not improving with oxygen in apparently acyanotic patients. The present case report is of a child with deaf-mutism posted for cochlear implant surgery who presented with 'chocolate-coloured blood' in the surgical field, despite blood gas analysis showing a normal partial pressure of oxygen.

The novel nitric oxide donor PDNO attenuates ovine ischemia-reperfusion induced renal failure

Background

Renal ischemia-reperfusion injury is a common cause of acute kidney injury in intensive care and surgery. Recently, novel organic mononitrites of 1,2-propanediol (PDNO) were synthesized and shown to rapidly and controllably deploy nitric oxide in the circulation when administered intravenously. We hypothesized that intravenous infusion of PDNO during renal ischemia reperfusion would improve post-ischemic renal function and microcirculation.

Methods

Sixteen sheep were anesthetized, mechanically ventilated, and surgically instrumented. The left renal artery was clamped for 90 min, and the effects of ischemia were studied for a total of 8 h. Fifteen minutes prior to the release of the clamp, intravenous infusions of PDNO (n = 8) or vehicle (1,2 propanediol + inorganic nitrite, n = 8) were initiated (180 nmol/kg/min for 30 min, thereafter 60 nmol/kg/min for the remainder of the experiment).

Results

Renal artery blood flow, cortical and medullary perfusion, and diuresis and creatinine clearance decreased in the left kidney post ischemia. However, in the sheep treated with PDNO, diuresis and creatinine clearance in the left kidney were significantly higher post ischemia compared to vehicle-treated animals (1.7 ± 0.5 vs 0.7 ± 0.3 ml/kg/h, p = 0.04 and 7.5 ± 2.1 vs 1.7 ± 0.6 ml/min, p = 0.02, respectively). Left renal medullary perfusion and oxygen uptake were higher in the PDNO group (73 ± 9 vs 37 ± 5% of baseline, p = 0.004 and 2.6 ± 0.4 vs 1.6 ± 0.3 ml/min, p = 0.02, respectively). PDNO significantly increased renal oxygen consumption and reduced the oxygen utilization for sodium reabsorption (p = 0.03 for both). Mean arterial blood pressure was significantly reduced by PDNO (83 ± 3 vs 94 ± 3 mmHg, p = 0.02) but was still within normal limits. Total renal blood flow was not affected, and there were no signs of increased blood methemoglobin concentrations or tachyphylaxis.

Conclusions

The novel nitric oxide donor PDNO improved renal function after ischemia. PDNO also prevented the persistent reduction in medullary perfusion during reperfusion and improved renal oxygen utilization without severe side effects.

Role of nitric oxide in liver transplantation: Should it be routinely used?

Ischemia-reperfusion injury (IRI) continues to be a major contributor to graft dysfunction, thus supporting the need for therapeutic strategies focused on minimizing organ damage especially with growing numbers of extended criteria grafts being utilized which are more vulnerable to cold and warm ischemia. Nitric oxide (NO·) is highly reactive gaseous molecule found in air and regarded as a pollutant. Not surprising, it is extremely bioactive, and has been demonstrated to play major roles in vascular homeostasis, neurotransmission, and host defense inflammatory reactions. Under conditions of ischemia, NO· has consistently been demonstrated to enhance microcirculatory vasorelaxation and mitigate pro-inflammatory responses, making it an excellent strategy for patients undergoing organ transplantation. Clinical studies designed to test this hypothesis have yielded very promising results that includes reduced hepatocellular injury and enhanced graft recovery without any identifiable complications. By what means NO· facilitates extra-pulmonary actions is up for debate and speculation. The general premise is that they are NO· containing intermediates in the circulation, that ultimately mediate either direct or indirect effects. A plethora of data exists explaining how NO·-containing intermediate molecules form in the plasma as S-nitrosothiols (e.g., S-nitrosoalbumin), whereas other compelling data suggest nitrite to be a protective mediator. In this article, we discuss the use of inhaled NO· as a way to protect the donor liver graft against IRI in patients undergoing liver transplantation.

Inhaled nitric oxide therapy for pulmonary disorders of the term and preterm infant

The 21st century began with the FDA approval of inhaled nitric oxide therapy for the treatment of neonatal hypoxic respiratory failure associated with pulmonary hypertension in recognition of the 2 randomized clinical trials demostrating a significant reduction in the need for extracorporeal support in the term and near-term infant. Inhaled nitric oxide is one of only a few therapeutic agents approved for use through clinical investigations primarily in the neonate. This article provides an overview of the pertinent biology and chemistry of nitric oxide, discusses potential toxicities, and reviews the results of pertinent clinical investigations and large randomized clinical trials including neurodevelopmental follow-up in term and preterm neonates. The clinical investigations conducted by the Eunice Kennedy Shriver NICHD Neonatal Research Network will be discussed and placed in context with other pertinent clinical investigations exploring the efficacy of inhaled nitric oxide therapy in neonatal hypoxic respiratory failure.

Sildenafil Prevents Rebound Pulmonary Hypertension after Withdrawal of Nitric Oxide in Children

RATIONALE

Rebound pulmonary hypertension (PHT) can complicate the weaning of nitric oxide (NO), and is in part related to transient depletion of intrinsic cyclic guanosine monophosphate. Rebound is characterized by increased pulmonary arterial (PA) pressure, cardiopulmonary instability, and in some cases, the need to continue NO beyond the intended period of use. There is anecdotal evidence that sildenafil, a phosphodiesterase-5 inhibitor, may prevent recurrence of rebound.

OBJECTIVES

We investigated the role of sildenafil in preventing rebound (an increase in PA pressure of 20% or greater, or failure to discontinue NO) in patients in whom previous attempts had not been made to wean from NO.

METHODS

Thirty ventilated infants and children, receiving 10 ppm or greater inhaled NO, were randomized to receive 0.4 mg/kg of sildenafil, or placebo, 1 h before discontinuing NO. Twenty-nine patients completed the study.

MEASUREMENTS

PA pressures and blood gases were measured before the study drug, and 1 and 4 h after stopping NO.

MAIN RESULTS

Rebound occurred in 10 of 14 placebo patients, and 0 of 15 sildenafil patients (p < 0.001). PA pressure increased by 25% (14-67) in placebo patients, and by 1%(-9-5) in sildenafil patients (p < 0.001). Four placebo patients could not be weaned from NO due to severe cardiovascular instability, whereas all sildenafil patients were weaned (p = 0.042). Duration of ventilation after study was 98.0 (47.0-223.5) h for placebo patients and 28.2 (15.7-54.6) h for sildenafil patients (p = 0.024).

CONCLUSION

A single dose of sildenafil prevented rebound after withdrawal of NO, and reduced the duration of mechanical ventilation. Prophylaxis with sildenafil should be considered when weaning patients from inhaled NO.

Cardiovascular drugs for the newborn

This article reviews the various cardiovascular drugs for newborns, including antiarrhythmics, antihypertensives, inotropes, and pulmonary vasodilators. Antiarrhythmic drugs are classified according to their mechanisms of action, such as effects on ion channels, duration of repolarization, and receptor interaction, which help with understanding the effects of individual antiarrhythmic drugs and selection of drugs for specific arrhythmias. Drug treatment for hypertension should start with a single drug from one of the following classes: ACE inhibitors, angiotensin-receptor antagonists, beta-receptor antagonists, calcium channel blockers, or diuretics. The inotropic drug should be selected according to its specific pharmacologic properties and the specific cardiovascular abnormality to be corrected. An effective pulmonary vasodilator must dilate the pulmonary vasculature more than the systemic vasculature.

Phosphodiesterase inhibitors for persistent pulmonary hypertension of the newborn: a review

Persistent pulmonary hypertension of the newborn (PPHN) is a complex syndrome with multiple causes, with an incidence of 0.43-6.8/1,000 live births and a mortality of 10-20%. Survivors have high morbidity in the forms of neurodevelopmental and audiological impairment, cognitive delays, hearing loss, and a high rate of rehospitalization. The optimal approach to the management of PPHN remains controversial. Inhaled nitric oxide (iNO) is currently regarded as the gold standard therapy, but with as many as 30% of cases failing to respond, has not proven to be the single magic bullet. Given the complex pathophysiology of the disease, any such magic bullet is unlikely. A number of recent studies have suggested a role for specific phosphodiesterase (PDE) inhibitors in the management of PPHN. Sildenafil, a specific PDE5 inhibitor, appears the most promising of such agents. We aim to review the current status and limitations of iNO and the potential of PDE inhibitors in the management of PPHN. The reasons why caution is warranted before specific PDE5 inhibitors like sildenafil are labelled as potential magic bullets for PPHN will be discussed. The need for randomized-controlled trials to determine the safety, efficacy, and long-term outcome following treatment with sildenafil in PPHN is emphasized.

Inhaled nitric oxide and methemoglobin in full-term infants with persistent pulmonary hypertension of the newborn

Inhaled nitric oxide (iNO), a potent pulmonary vasodilator, has become a mainstay therapy for neonates with persistent pulmonary hypertension of the newborn (PPHN). However, it also oxidizes hemoglobin to methemoglobin (metHgb), thereby reducing the delivery of oxygen to tissues. Studies have suggested that elevated levels of metHgb may be avoided by limiting iNO concentration to less than 40 parts per million (ppm). However, the relationship between iNO exposure and elevated levels of metHgb (greater than 4%) has not been examined. Therefore, we studied this relationship in full term newborns with PPHN. We reviewed the charts of twenty-eight neonates with a diagnosis of PPHN admitted to our Intensive Care Nursery between 1/92 and 10/97. Our retrospective analysis demonstrated that: (1) high metHgb levels can occur with exposure to low iNO concentration (three of eight newborns with maximum metHgb levels >4% had been exposed to no more than 40 ppm of iNO concentration); and (2) cumulative iNO ( summation operatoriNO) exposure was the best predictor of elevated metHgb levels (seven of nine newborns receiving summation operatoriNO>2000 ppm x hour had maximum metHgb levels >4%).

Methemoglobinemia: Toxicity of inhaled nitric oxide therapy

Elevation in methemoglobin is a known toxicity of inhaled nitric oxide (NO) therapy. This article describes two significant episodes of methemoglobinemia. These cases illustrate the probable cause and the treatment strategies for the potential for delivery of high concentrations of NO, resulting in methemoglobinemia with moderate and even low-dose delivered NO. We propose mechanisms for this occurrence and means of prevention.