Methemoglobin formation in children with congenital heart disease treated with inhaled nitric oxide after cardiac surgery

Inhaled NO at a crossroads in cardiac surgery: current need to improve mechanistic understanding, clinical trial design and scientific evidence

Inhaled nitric oxide (NO) has been used in pediatric and adult perioperative cardiac intensive care for over three decades. NO is a cellular signaling molecule that induces smooth muscle relaxation in the mammalian vasculature. Inhaled NO has the unique ability to exert its vasodilatory effects in the pulmonary vasculature without any hypotensive side-effects in the systemic circulation. In patients undergoing cardiac surgery, NO has been reported in numerous studies to exert beneficial effects on acutely lowering pulmonary artery pressure and reversing right ventricular dysfunction and/or failure. Yet, various investigations failed to demonstrate significant differences in long-term clinical outcomes. The authors, serving as an advisory board of international experts in the field of inhaled NO within pediatric and adult cardiac surgery, will discuss how the existing scientific evidence can be further improved. We will summarize the basic mechanisms underlying the clinical applications of inhaled NO and how this translates into the mandate for inhaled NO in cardiac surgery. We will move on to the popular use of inhaled NO and will talk about the evidence base of the use of this selective pulmonary vasodilator. This review will elucidate what kind of clinical and biological barriers and gaps in knowledge need to be solved and how this has impacted in the development of clinical trials. The authors will elaborate on how the optimization of inhaled NO therapy, the development of biomarkers to identify the target population and the definition of response can improve the design of future large clinical trials. We will explain why it is mandatory to gain an international consensus for the state of the art of NO therapy far beyond this expert advisory board by including the different major players in the field, such as the different medical societies and the pharma industry to improve our understanding of the real-life effects of inhaled NO in large scale observational studies. The design for future innovative randomized controlled trials on inhaled NO therapy in cardiac surgery, adequately powered and based on enhanced biological phenotyping, will be crucial to eventually provide scientific evidence of its clinical efficacy beyond its beneficial hemodynamic properties.

Killer hiding under normal oxygen saturation: a case report about methemoglobinemia

BACKGROUND

Inhaled nitric oxide (iNO) is a choice for the treatment of pulmonary hypertension (PH), especially in cases after cardiac surgery. Potential side effects include the formation of higher oxides of nitrogen and methemoglobin (MetHb). Methemoglobinemia is the oxidation of ferrous iron to iron within hemoglobin, impairing its ability to transport oxygen and resulting in tissue hypoxemia. A level of MetHb >10% will induce clinical hypoxia manifestations, and MetHb >70% may be fatal.

CASE DESCRIPTION

Herein we report a rare case of methemoglobinemia due to iNO therapy in a child after cardiac surgery. We found that as MetHb concentrations increased, pulse oximetry overestimated oxygen supplementation without warning clinicians that dangerous hypoxia was developing. Finally, MetHb and oxyhemoglobin (O₂Hb) in arterial blood gas (ABG) provide diagnostic clues. Methylene blue and low dose vitamin C (VC) were used to successfully save the life of the child.

CONCLUSIONS

iNO administration in the intensive care unit should be managed with close monitoring of MetHb levels during treatment. We emphasize the limitations of traditional methods used to assess oxygenation status, especially in the context of methemoglobinemia. In addition, treatment for methemoglobinemia in acute settings should be initiated as soon as possible.

Met-Hemoglobin Is a Biomarker for Poor Oxygen Delivery in Infants Following Surgical Palliation

BACKGROUND

Infants with cyanotic congenital heart disease demonstrate wide fluctuations in hemoglobin (Hb), oxygen saturation, and cardiac output following palliation. Methemoglobin (Met-Hb), the product of Hb oxidation, may represent a compensatory mechanism during hypoxia and may be utilized as a biomarker.

METHODS

Arterial and venous Met-Hb levels were obtained from infants requiring palliation. The primary outcome was to describe the relationship between Met-Hb and other indices of tissue oxygenation (venous saturation, estimated arteriovenous oxygen difference [Est AV-Diff], and lactate). Secondary outcomes were to determine the impact of elevated Met-Hb levels ≥1.0% and the effect of red blood cell (RBC) transfusion on Met-Hb levels.

RESULTS

Fifty infants and 465 Met-Hb values were studied. Venous Met-Hb levels were significantly higher than arterial levels (venous: 0.84% ± 0.36% vs arterial: 0.45% ± 0.18%; P < .001). Venous Met-Hb demonstrated a significant inverse relationship with venous oxygen saturation (R = -0.6; P < .001) and Hb (R = -0.3, P < .001) and a direct relationship with the Est AV-Diff (R = 0.3, P < .001). A total of 129 (29.6%) venous Met-Hb values were elevated (≥1.0%) and were associated with significantly lower Hb and venous saturation levels and higher Est AV-Diff and lactate levels. Methemoglobin levels decreased significantly following 65 RBC transfusions (0.94 ± 0.40 vs 0.77 ± 0.34; P < .001). Linear mixed models demonstrated that higher venous Met-Hb levels were associated with lower measures of tissue oxygenation and not related to any preoperative clinical differences.

CONCLUSION

Methemoglobin may be a clinically useful marker of tissue oxygenation in infants following surgical palliation.

New Modalities for the Administration of Inhaled Nitric Oxide in Intensive Care Units After Cardiac Surgery or for Neonatal Indications: A Prospective Observational Study

BACKGROUND

Nitric oxide (NO) has a well-known efficacy in pulmonary hypertension (PH), with wide use for 20 years in many countries. The objective of this study was to describe the current use of NO in real life and the gap with the guidelines.

METHODS

This is a multicenter, prospective, observational study on inhaled NO administered through an integrated delivery and monitoring device and indicated for PH according to the market authorizations. The characteristics of NO therapy and ventilation modes were observed. Concomitant pulmonary vasodilator treatments, safety data, and outcome were also collected. Quantitative data are expressed as median (25th, 75th percentile).

RESULTS

Over 1 year, 236 patients were included from 14 equipped and trained centers: 117 adults and 81 children with PH associated with cardiac surgery and 38 neonates with persistent PH of the newborn. Inhaled NO was initiated before intensive care unit (ICU) admission in 57%, 12.7%, and 38.9% with an initial dose of 10 (10, 15) ppm, 20 (18, 20) ppm, and 17 (11, 20) ppm, and a median duration of administration of 3.9 (1.9, 6.1) days, 3.8 (1.8, 6.8) days, and 3.1 (1.0, 5.7) days, respectively, for the adult population, pediatric cardiac group, and newborns. The treatment was performed using administration synchronized to the mechanical ventilation. The dose was gradually decreased before withdrawal in 86% of the cases according to the usual procedure of each center. Adverse events included rebound effect for 3.4% (95% confidence interval [CI], 0.9%-8.5%) of adults, 1.2% (95% CI, 0.0%-6.7%) of children, and 2.6% (95% CI, 0.1%-13.8%) of neonates and methemoglobinemia exceeded 2.5% for 5 of 62 monitored patients. Other pulmonary vasodilators were associated with NO in 23% of adults, 95% of children, and 23.7% of neonates. ICU stay was respectively 10 (6, 22) days, 7.5 (5.5, 15) days, and 9 (8, 15) days and ICU mortality was 22.2%, 6.2%, and 7.9% for adults, children, and neonates, respectively.

CONCLUSIONS

This study confirms the safety of NO therapy in the 3 populations with a low rate of rebound effect. Gradual withdrawal of NO combined with pulmonary vasodilators are current practices in this population. The use of last-generation NO devices allowed good compliance with recommendations.

Utility of routine methemoglobin laboratory assays in critically ill pediatric subjects receiving inhaled nitric oxide

PURPOSE

Inhaled nitric oxide (iNO) has been associated with safety risks including reports of methemoglobinemia. While standard of care recommends routine monitoring of methemoglobin in subjects on iNO therapy, the utility of this practice remains unknown.

MATERIALS AND METHODS

This retrospective chart review aimed to determine the frequency of methemoglobinemia in pediatric patients receiving iNO. Included subjects were under 18 years of age receiving iNO therapy with at least one methemoglobin concentration measured from 10/18/2014 to 11/18/2016.

RESULTS

In total, 1809 methemoglobin concentrations were collected in 247 subjects during the study period. Median age was 0.33 (0.04-0.83) years. The mean methemoglobin concentration was 1.33% (±0.42) while receiving a mean iNO dose of 11.71 ppm (±7.97). Twenty-nine subjects had a total of 131 methemoglobin concentrations analyzed while receiving iNO doses above 20 ppm which were similar to the entire cohort at 1.33% (±0.42); (p = .95).

CONCLUSIONS

Pediatric patients receiving iNO at doses below 40 ppm have minimal risk of developing clinically significant methemoglobinemia. Routine, ongoing monitoring of metHb levels in all pediatric subjects receiving iNO therapy at doses <40 ppm without the presence of risk factors predisposing the subject to increased risk of methemoglobinemia is unnecessary and should be avoided.

Review of inhaled nitric oxide in the pediatric cardiac surgery setting

Surgical intervention for congenital heart disease (CHD) can be complicated by pulmonary hypertension (PH), which increases morbidity, mortality, and medical burden. Consequently, postoperative management of PH is an important clinical consideration to improve outcomes. Inhaled nitric oxide (iNO) is a widely accepted standard of care for PH and has been studied in the context of cardiac surgery for CHD. However, large randomized, double-blind, placebo-controlled, multicenter clinical trials in pediatric patients are limited. This review will provide an overview of the clinical studies in this setting and will discuss general treatment considerations to facilitate a better understanding of the clinical use of iNO for PH after pediatric cardiac surgery.

Case files of the medical toxicology fellowship at Banner Good Samaritan Medical Center in Phoenix, AZ: methemoglobinemia following dapsone exposure

Acquired methemoglobinemia is a common, potentially fatal syndrome that can occur as a result of exposure to numerous xenobiotics. A case report of a 14-month-old female who developed methemoglobinemia following a dapsone ingestion. The child was treated with numerous boluses of methylene blue and ultimately required a continuous infusion of methylene blue. The common causes of methemoglobinemia, as well as the underlying pathophysiology, diagnosis, and treatment strategies are discussed.

Methaemoglobinaemia risk factors with inhaled nitric oxide therapy in newborn infants

BACKGROUND

Inhaled nitric oxide (iNO), commonly used for hypoxic neonates, may react with haemoglobin to form methaemoglobin (MetHb). MetHb monitoring during iNO therapy has been questioned since low doses of iNO are used.

AIM

To evaluate the incidence of and identify risk factors associated with elevated MetHb in neonates treated with iNO.

METHODS

Neonates who were treated with iNO and had at least one MetHb measurement were included. Demographic characteristics and methods of iNO administration (dosage, duration) at the time of each MetHb measurement were analysed.

RESULTS

Four hundred and fifty-two MetHb measurements from 81 premature and 82 term and near-term infants were analysed. MetHb was above 5% in one-term infant, and between 2.5-5% in 16 infants. A higher maximum dose of iNO (22.7 vs 17.7 p.p.m.), but not gestational age, was a significant risk factor for elevated MetHb. Significantly higher oxygen levels (75.5% vs 51.7%) were associated with higher MetHb in term infants. Preterm infants had no risk for high MetHb when iNO was kept below 8 p.p.m. These data suggest the possibility of limiting blood withdrawal when low doses iNO are used.

CONCLUSION

High MetHb is exceptional in neonates treated with low dose iNO. Associated risk factors are related to high iNO dose and the simultaneous use of high concentrations of oxygen.

Carboxyhemoglobin formation as an unexpected side effect of inhaled nitric oxide therapy in severe acute respiratory distress syndrome

OBJECTIVE

To report an unexpected cause of carboxyhemoglobinemia associated with inhaled nitric oxide therapy in severe acute respiratory distress syndrome.

DESIGN

Case report.

SETTING

Medical critical care unit at Lausanne University Hospital.

PATIENT

One female patient with acute respiratory distress syndrome treated with inhaled nitric oxide, who developed a simultaneous increase in blood methemoglobin and carboxyhemoglobin.

CONCLUSIONS

Potential pathophysiologic mechanisms linking acute respiratory distress syndrome, inhaled nitric oxide, methemoglobin, and carboxyhemoglobin are discussed. Since carboxyhemoglobin has a negative influence on oxygen-carrying capacity, this effect may potentially offset the beneficial influence (if any) of inhaled nitric oxide on arterial PO2. This observation does not support the use of inhaled nitric oxide in the treatment of acute respiratory distress syndrome.