Effects of methemoglobinemia on pulse oximetry and mixed venous oximetry

Seizures and severe methaemoglobinaemia following accidental ingestion of amyl nitrite

We present a case of a man in his late 40s presenting with generalised tonic-clonic seizures and profound methaemoglobinaemia shortly after inadvertent ingestion of amyl nitrite. Arterial blood gas analysis demonstrated methaemoglobin levels exceeding the upper detection threshold of our analyser, accompanied with profound cyanosis despite apparent oxygen saturations of 94%. Prompt administration of intravenous methylene blue led to a rapid and complete recovery. This case highlights the importance of swift recognition and treatment of methaemoglobinaemia particularly when the precipitating factor may be unknown at the time of presentation. This case also demonstrates the potential limitations of bedside blood gas analysers in diagnosis.

[Methemoglobinemia]

Methemoglobinemia (MetHb) refers to the state of oxidation of the iron ion "ferrous" (Fe2+) to iron "ferric" (Fe3+) within the heme molecule that makes up hemoglobin (Hb). This state is physiological if its level remains controlled. The ferrous state of the heme molecule occurs in the event of significant oxidative stress. The pathophysiology of MetHb involves NADH, NADPH and glucose cycle enzymes such as cytochrome-b5-reductase. MetHb can be acquired or more rarely, congenital. Acquired causes include drug-induced effects such as topical anesthetics, or toxic effects such as nitrites. Primary causes are linked to enzyme deficiencies or constitutional Hb abnormalities. Excessively high MetHb causes symptoms of varying intensity, depending on the level of MetHb and associated comorbidities. Clinical signs are dominated by cyanosis, indicative of tissue hypoxia, which can be complicated by severe metabolic disorders leading to death. Diagnosis can be complex, as the resulting biological abnormalities may go undetected. Treatment is mainly based on identifying the etiology and restoring the heme molecule to its physiological state. Methylene blue is the main antidote in cases of elevated MetHb, but precautions must be taken in its use, and its physico-chemical effects must be understood. We provide an update on methemoglobinemia, summarizing its pathophysiology and clinical presentations, complementary tests and therapeutic principles.

Shades of Blue: A Case Series of Acquired Methemoglobinemia

Acquired methemoglobinemia (MetHb) is a rare but potentially life-threatening condition that has varied etiology, usually toxin- or drug-induced. We had five cases of acquired methemoglobinemia during six months. Their presentation varied from an asymptomatic state to respiratory distress. The presence of cyanosis and low oxygen saturation (SpO2), despite normal partial pressure of oxygen (PaO2) and chocolate brown-colored blood, were diagnostic clues present in all cases. A high level of methemoglobinemia was detected on arterial blood gas (ABG), confirming the diagnosis. Methylene blue was used as an antidote along with supportive care in symptomatic cases. All these cases of methemoglobinemia recovered completely. A high index of suspicion for methemoglobinemia should be maintained in cases presenting with persistent hypoxia or cyanosis despite normal PaO2.

Treatment of a life-threatening dapsone intoxication

The case report describes a case of a severe dapsone (more than 200 tablets dapsone 100 mg) and mild methotrexate intoxication (10 tablets methotrexate 10 mg) as an attempt to commit suicide, resulting in severe cyanosis with elevation in methemoglobin concentration, treated with methylene blue, ascorbic acid, folinic acid, multidose activated charcoal and hemodialysis. Measurements of blood gases, dapsone and methotrexate levels were performed. Furthermore a hepatitis, pulmonary artery thrombus and a strange taste sensation were diagnosed, probably related to dapsone. The patient recovered and was discharged from hospital after five days. Acute intoxication from excessive dapsone intake is uncommon and clear treatment guidelines are lacking. We here report the treatment modalities as a result of a dapsone intoxication, including the effects on the overall condition of the patient.

A Case of Severe Hypoxia Caused by Phenazopyridine-Induced Methemoglobinemia: A near Fatal Event from Over-the-Counter Medication Use

Methemoglobinemia is a rare blood disorder characterized by the oxidation of heme iron from ferrous (Fe²⁺) to ferric (Fe³⁺) state, which increases oxygen affinity and impairs oxygen release to the tissue causing hypoxia. It can be congenital or acquired; however, most cases are acquired and caused by exogenous substances such as medications, chemicals, and environmental substances. Phenazopyridine is an over-the-counter urinary analgesic medication commonly used for symptomatic relief of dysuria and has been reported to cause methemoglobinemia. However, only a handful of cases of phenazopyridine-induced methemoglobinemia have been reported. We present a case of an 89-year-old female who presented with severe hypoxia, shortness of breath, headache, nausea, and dizziness caused by phenazopyridine-induced methemoglobinemia. She was found to have a methemoglobin level of 21.5% and was treated with methylene blue, leading to a rapid improvement of her symptoms. She was taking one over-the-counter phenazopyridine 200 mg tablet three times daily for two weeks for her chronic dysuria. This case highlights the need to have a high index of suspicion of phenazopyridine-induced methemoglobinemia in a patient presenting with unexplained shortness of breath with a history of phenazopyridine use as it could lead to severe methemoglobinemia with hypoxia that could potentially be fatal if not promptly diagnosed.

Detection of hypoxia by near-infrared spectroscopy and pulse oximetry: a comparative study

SIGNIFICANCE

Pulse oximetry is widely used in clinical practice to monitor changes in arterial oxygen saturation (SpO2). However, decreases in SpO2 can be delayed relative to the actual clinical event, and near-infrared spectroscopy (NIRS) may detect alterations in oxygenation earlier than pulse oximetry, as shown in previous cerebral oxygenation monitoring studies.

AIM

We aim to compare the response of transcutaneous muscle NIRS measures of the tissue saturation index with pulse oximetry SpO2 during hypoxia.

APPROACH

Episodes of acute hypoxia were induced in nine anesthetized Yucatan miniature pigs. A standard pulse oximeter was attached to the ear of the animal, and a transcutaneous NIRS sensor was placed on the hind limb muscle. Hypoxia was induced by detaching the ventilator from the animal and reattaching it once the pulse oximeter reported 70% SpO2.

RESULTS

Twenty-four episodes of acute hypoxia were analyzed. Upon the start of hypoxia, the transcutaneous NIRS measures changed in 5.3 ± 0.4 s, whereas the pulse oximetry measures changed in 14.9 ± 1.0 s (p < 0.0001).

CONCLUSIONS

Transcutaneous muscle NIRS can detect the effects of hypoxia significantly sooner than pulse oximetry in the Yucatan miniature pig. A transcutaneous NIRS sensor may be used as an earlier detector of oxygen saturation changes in the clinical setting than the standard pulse oximeter.

[A Case of Methemoglobinemia Caused by Toluidine Revelation with Dyspnea and Cyanosis]

Toluidine is a known cause of bladder cancer, but it is less widely recognized as a cause of methemoglobinemia because methemoglobinemia is rare. We herein report a case of methemoglobinemia caused by toluidine in a 50-year-old man. A solution of toluidine overflowed from its container during transportation and adhered to the man's clothes, but he drove to his workplace 100 km away without changing his clothes or undergoing decontamination. Before arriving at his workplace, he developed dyspnea and called emergency services, and he was then transported to a local hospital. He had significant cyanosis upon arrival, and arterial blood gas analysis revealed a high methemoglobin level of 44%. He was diagnosed with toluidine-induced methemoglobinemia and was transported to our hospital, where he was admitted to the intensive care unit. Treatment for methemoglobinemia was started immediately after hospitalization, and the patient's symptoms and methemoglobin level improved. Methemoglobinemia should be considered in workers who handle toluidine and develop cyanosis and dyspnea.

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.

Impact of ethnicity on the accuracy of measurements of oxygen saturations: A retrospective observational cohort study

Background

Pulse oximeters are routinely used in community and hospital settings worldwide as a rapid, non-invasive, and readily available bedside tool to approximate blood oxygenation. Potential racial biases in peripheral oxygen saturation (SpO2) measurements may influence the accuracy of pulse oximetry readings and impact clinical decision making. We aimed to assess whether the accuracy of oxygen saturation measured by SpO2, relative to arterial blood gas (SaO2), varies by ethnicity.

Methods

In this large retrospective observational cohort study covering four NHS Hospitals serving a large urban population in Birmingham, United Kingdom, consecutive pairs of SpO2 and SaO2 measurements taken on the same patient within an interval of less than 20 min were identified from electronic patient records. Where multiple pairs of measurements were recorded in a spell, only the first was included in the analysis. The differences between SpO2 and SaO2 measurements were compared across groups of self-identified ethnicity. These differences were subsequently adjusted for age, sex, bilirubin, systolic blood pressure, carboxyhaemaglobin saturations and the time interval between SpO2 and SaO2 measurements.

Findings

Paired O2 saturation measurements from 16,818 inpatient spells between 1st January 2017 and 18th February 2021 were analysed. The cohort self-identified as being of White (81.2%), Asian (11.7%), Black (4.0%), or Other (3.2%) ethnicities. Across the cohort, SpO2 was statistically significantly higher than SaO2 (p < 0.0001), with medians of 98% (interquartile range [IQR]: 95-100%) vs. 97% (IQR: 96-99%), and a median difference of 0.5% points (pps; 95% confidence interval [CI]: 0.5-0.6). However, the size of this difference varied considerably with the magnitude of SaO2, with SpO2 overestimating by a median by 3.8pp (IQR: 0.4, 8.8) for SaO2 values <90% but underestimating by a median of 0.4pp (IQR: -2.0, 1.4) for an SaO2 of 95%. The differences between SpO2 and SaO2 were also found to vary by ethnicity, with this difference being 0.8pp (95% CI: 0.6-1.0, p < 0.0001) greater in those of Black vs. White ethnicity. These differences resulted in 8.7% vs. 6.1% of Black vs. White patients who were classified as normoxic on SpO2 actually being hypoxic on the gold standard SaO2 (odds ratio: 1.47, 95% CI: 1.09-1.98, p = 0.012).

Interpretation

Pulse oximetry may overestimate O2 saturation, and this is possibly more pronounced in patients of Black ethnicity. Prospective studies are urgently warranted to assess the impact of ethnicity on the accuracy of pulse oximetry, to ensure care is optimised for all.

Funding

PIONEER, the Health Data Research UK (HDR-UK) Health Data Research Hub in acute care.

Acquired methemoglobinemia in children presenting to Italian pediatric emergency departments: a multicenter report

INTRODUCTION

Methemoglobinemia (MetHb) is a rare inherited or acquired cause of cyanosis in children. Owing to its rarity, case reports and case series are mostly available in the current literature. This study reports data on a large sample of children with acquired MetHb.

METHODS

Data on patients admitted for acquired MetHb between January 2007 to December 2020 was extracted from the databases of five Italian pediatric emergency departments (EDs). Demographical and clinical characteristics was reported and discussed.

RESULTS

Nineteen cases of acquired MetHb were evaluated. Ten patients (52.6%) were male and 9 (47.4%) were female. The median age was 8.23 months. The median time from trigger to symptom onset was 6 hours. Mostly, the intoxication presumptively occurred by home ingestion of contaminated food, mainly badly preserved vegetable broth. All patients were cyanotic at admission, most patients also presented tachycardia and/or tachypnea, and two patients were comatose. Antidotal therapy with methylene blue was given in 14 patients (73.7%). The median hospital stay was 2 days. All patients survived.

DISCUSSION

As MetHb leads to the pathognomonic brown blood discoloration, blood gas analysis is mandatory immediately upon hospital arrival of a cyanotic patient. A correct medical history is crucial to identify the trigger and remove it. In our sample, the age onset was much lower than in the previous literature, and MetHb mainly due to ingestion of contaminated vegetable broth. Methylene blue led to a rapid recovery in all patients. Oxygen therapy may well lead to complete recovery when methemoglobin levels do not exceed 30% in asymptomatic and 20% in mildly symptomatic patients.

CONCLUSIONS

The diagnosis and management of acquired MetHb in the emergency setting requires acknowledgment of this condition as a cause of cyanosis in the weaning child. Indeed, when promptly recognized and treated, this severe condition rapidly resolves with no significant acute sequelae.

Survival after self‐poisoning with sodium nitrite: A case report

Sodium nitrite ingestion poses a considerable public health threat. The incidence of sodium nitrite self‐poisoning in the United States has been trending upward since 2017. Our case report describes an intentional sodium nitrite ingestion with favorable outcomes. We highlight the proper treatment of this ingestion with intravenous methylene blue. Sodium nitrite is an oxidizing agent that is commonly found in processed meats, fish, and cheeses as a preservative, antimicrobial, and food coloring agent. It is an odorless, white crystalline powder that has been confused for table salt or granulated sugar. It has become more readily available in large quantities online. Unfortunately, online forums exist that detail how to dose sodium nitrite for suicide. Furthermore, it has been recently discussed in popular news streams after a celebrity died of an overdose. Sodium nitrite toxicity is capable of causing severe methemoglobinemia with high mortality. Prompt identification is crucial. We discuss the important implications in regard to media coverage, imitative suicide, and accessibility of sodium nitrite.

Pulse Oximetry: The Working Principle, Signal Formation, and Applications

Pulse oximeters are routinely used in various medical-grade and consumer-grade applications. They can be used to estimate, for example, blood oxygen saturation, autonomic nervous system activity and cardiac function, blood pressure, sleep quality, and recovery through the recording of photoplethysmography signal. Medical-grade devices often record red and infra-red light-based photoplethysmography signals while smartwatches and other consumer-grade devices usually rely on a green light. At its simplest, a pulse oximeter can consist of one or two photodiodes and a photodetector attached, for example, a fingertip or earlobe. These sensors are used to record light absorption in a medium as a function of time. This time-varying absorption information is used to form a photoplethysmography signal. In this chapter, we discuss the working principles of pulse oximeters and the formation of the photoplethysmography signal. We will further discuss the advantages and disadvantages of pulse oximeters, which kind of applications exist in the medical field, and how pulse oximeters are utilized in daily health monitoring.

Once in a blue moon: Primaquine-induced methemoglobinemia - A case report

Methemoglobinemia is a rare blood disorder that should be suspected in patients with cyanosis and low oxygen saturation of around 85%, especially when both do not improve despite supplemental oxygen. We describe the case of a 67-year-old lung transplant patient who was treated with primaquine and clindamycin because of a positive Pneumocystis jirovecii polymerase chain reaction on bronchoalveolar lavage fluid. Soon thereafter the patient developed increasing shortness of breath, central cyanosis and hypoxia, with an oxygen saturation of 86% on pulse oximetry despite supplemental oxygen. Arterial blood gas analysis showed a peculiar dark brown color and a significantly increased methemoglobin percentage. A diagnosis of methemoglobinemia due to primaquine was made. As treatment option, we preferred ascorbic acid over methylene blue because of concerns of possibly eliciting a serotonin syndrome. Our patient recovered rapidly after initiation of appropriate treatment. A high index of suspicion is crucial since this condition is potentially fatal.

Recommendations for diagnosis and treatment of methemoglobinemia

Methemoglobinemia is a rare disorder associated with oxidization of divalent ferro‐iron of hemoglobin (Hb) to ferri‐iron of methemoglobin (MetHb). Methemoglobinemia can result from either inherited or acquired processes. Acquired forms are the most common, mainly due to the exposure to substances that cause oxidation of the Hb both directly or indirectly. Inherited forms are due either to autosomal recessive variants in the CYB5R3 gene or to autosomal dominant variants in the globin genes, collectively known as HbM disease. Our recommendations are based on a systematic literature search. A series of questions regarding the key signs and symptoms, the methods for diagnosis, the clinical management in neonatal/childhood/adulthood period, and the therapeutic approach of methemoglobinemia were formulated and the relative recommendations were produced. An agreement was obtained using a Delphi‐like approach and the experts panel reached a final consensus >75% of agreement for all the questions.

Methylene Blue Infusion to Treat Severe Dapsone-Induced Methemoglobinemia in a Pediatric Patient

Dapsone overdose is a well-known potent cause of methemoglobinemia and hemolytic anemia. We discuss a case of a two-year-old male who developed severe persistent methemoglobinemia treated with multiple doses of methylene blue (MB), multidose activated charcoal, and vitamin C. Methylene blue infusion (rather than bolus dosing) aided in controlling this patient's methemoglobin (MetHb) levels and symptoms and may reduce the total needed dose.

Methemoglobinemia Unmasked by Use of Sodium Nitroprusside and Hypothermia in a Case of Chronic Thromboembolic Pulmonary Hypertension During Pulmonary Endarterectomy: A Case Report

In performing pulmonary endarterectomy (PEA) for a patient with chronic thromboembolic pulmonary hypertension (CTEPH), we encountered methemoglobinemia that was unmasked by hypothermia while on cardiopulmonary bypass (CPB). The patient on dapsone therapy for antiphospholipid antibody syndrome had developed acquired methemoglobinemia that went undiagnosed because her cyanosis was believed to be due to CTEPH and the resulting ventilation-perfusion (V/Q) mismatch. Although pharmacological triggers for methemoglobin are well known, causation by hypothermia is not described. Monitoring saturation while on CPB was challenging because of nonpulsatile blood flow but was overcome using cerebral oximetry.

Dapsone-induced methemoglobinemia in pediatrics post-renal transplant

Dapsone has been utilized for the prevention of Pneumocystis jirovecii pneumonia in immunosuppressed patients including pediatric kidney transplant recipients, in whom trimethoprim-sulfamethoxazole (TMP-SMX) is contraindicated. Dapsone adverse effects include methemoglobinemia, but there are no reports of the burden and impact of methemoglobinemia in pediatric kidney recipients that are taking dapsone for PJP prophylaxis. We conducted a retrospective chart review of all pediatric kidney recipients who had received dapsone at any time posttransplant. The indication, duration, and adverse effects of dapsone therapy were assessed. In addition, methemoglobin levels were assessed, and summary statistics performed. Data demonstrated that more than half of the patients on dapsone were not screened for methemoglobinemia. Of those screened, there was a significantly higher acquired-methemoglobinemia (77%) than previously reported in the literature. We also demonstrate significantly more anemia in patients on dapsone. Methemoglobinemia did not affect patient or graft survival and resolved with cessation of dapsone. We conclude that pediatric kidney recipients often develop methemoglobinemia and / or anemia on dapsone. We recommend if pediatric transplant recipients are prescribed dapsone, routine testing for methemoglobinemia and anemia should be done.

Multi-analyte calibration and verification of a multi-parameter laser-based pulse oximeter

Almost since its introduction pulse oximetry was known to overestimate oxygen saturation in cases of carbon monoxide poisoning or elevated methemoglobin (metHb) levels. To eliminate this dangerous behavior some manufacturers have added additional LED emitters to try to increase the number of measured hemoglobin species and to improve measurement accuracy, but have not been very successful. We hypothesized that the use of narrow-band laser light sources would make accurate and precise measurement of the four primary species of hemoglobin possible, even in cases of elevated levels of carboxyhemoglobin (COHb). Calibration and verification studies were performed on a tissue simulator that employed an artificial finger pulsating with whole human blood. This simulator allowed safe generation of 165 different combinations of the levels of oxyhemoglobin (O₂Hb), COHb, metHb, and reduced hemoglobin (RHb) for calibration of the laser-based pulse oximeter. A follow-on study used 56 mixed hemoglobin levels for verification and statistical analysis of the performance of this device. This laser-based pulse oximeter measured all four species of hemoglobin accurately and precisely (A_RMS ≤ 1.8%) for metHb levels in the clinically normal range. At elevated metHb levels the device continued to provide accurate and precise measurements of metHb and RHb (A_RMS ≤ 1.7%). The use of monochromatic laser light sources can create a new generation of highly accurate, multi-parameter, pulse oximeters.

Transcutaneous monitoring of hemoglobin derivatives during methemoglobinemia in rats using spectral diffuse reflectance

SIGNIFICANCE

Untreated methemoglobinemia may cause severe hypoxemia and even death when methemoglobin levels in the blood stream exceed 70%. Although CO-oximetry can be used to monitor the response to treatment for methemoglobinemia, it is costly and requires an invasive procedure for collecting blood samples from patients. A pulse CO-oximeter with a contact probe can be used to continuously and non-invasively measure the percentage of methemoglobin, as well as the percutaneous oxygen saturation. In terms of the prevention of infectious diseases, however, it is desirable to monitor methemoglobin and oxygen saturation levels in a non-contact manner. Diffuse reflectance spectral imaging is promising as a non-contact, non-invasive, and cost-effective clinical diagnostic tool for methemoglobinemia.

AIM

To demonstrate the feasibility of visible spectral diffuse reflectance for in vivo monitoring of hemoglobin derivatives and evaluating methemoglobin production and reduction as well as hypoxemia during methemoglobinemia in rats.

APPROACH

A new imaging approach based on the multiple regression analysis aided by Monte Carlo simulations for light transport was developed to quantify methemoglobin, oxygenated hemoglobin, and deoxygenated hemoglobin using a hyperspectral imaging system. An in vivo experiment with rats exposed to sodium nitrite (NaNO2) at different doses was performed to confirm the feasibility of the method for evaluating the dynamics of methemoglobin, oxygenated hemoglobin, and deoxygenated hemoglobin during methemoglobinemia. Systemic physiological parameters, including the percutaneous arterial oxygen saturation, heart rate (HR), and pulse distention, were measured by a commercially available pulse oximeter, and the results were compared to those obtained by the proposed method.

RESULTS

Both the methemoglobin concentration and methemoglobin saturation rapidly increased with a half-maximum time of <20  min. They reached their maximal values nearly 60 min after the administration of NaNO2. Tissue oxygen saturation dramatically dropped to a minimum of 33.7  %    ±  0.4  %  , 23.1  %    ±  5.6  %  , 8.8  %    ±  1.7  %  , and 9.7  %    ±  5.1  %   on average for NaNO2 doses of 25, 37.5, 50, and 75 mg/kg, respectively. Changes in methemoglobin concentration and tissue oxygen saturation are indicative of the temporary production of methemoglobin and severe hypoxemia during methemoglobinemia. Profound increases in the HR and pulse distention implied an elevated cardiac output caused by tachycardia and the resultant increase in peripheral blood volume to compensate for the hypoxia and hypoxemia during methemoglobinemia. This was in agreement with the time course of the peripheral hemoglobin volume concentration obtained by the proposed method.

CONCLUSIONS

The proposed method is capable of the in vivo non-contact simultaneous evaluation of methemoglobin levels and hypoxemia during methemoglobinemia, and that it has potential as a tool for the diagnosis and management of methemoglobinemia.

The Role of Methemoglobin and Carboxyhemoglobin in COVID-19: A Review

Following the outbreak of a novel coronavirus (SARS-CoV-2) associated with pneumonia in China (Corona Virus Disease 2019, COVID-19) at the end of 2019, the world is currently facing a global pandemic of infections with SARS-CoV-2 and cases of COVID-19. Since severely ill patients often show elevated methemoglobin (MetHb) and carboxyhemoglobin (COHb) concentrations in their blood as a marker of disease severity, we aimed to summarize the currently available published study results (case reports and cross-sectional studies) on MetHb and COHb concentrations in the blood of COVID-19 patients. To this end, a systematic literature research was performed. For the case of MetHb, seven publications were identified (five case reports and two cross-sectional studies), and for the case of COHb, three studies were found (two cross-sectional studies and one case report). The findings reported in the publications show that an increase in MetHb and COHb can happen in COVID-19 patients, especially in critically ill ones, and that MetHb and COHb can increase to dangerously high levels during the course of the disease in some patients. The medications given to the patient and the patient’s glucose-6-phospate dehydrogenase (G6PD) status seem to be important factors determining the severity of the methemoglobinemia and carboxyhemoglobinemia. Therefore, G6PD status should be determined before medications such as hydroxychloroquine are administered. In conclusion, MetHb and COHb can be elevated in COVID-19 patients and should be checked routinely in order to provide adequate medical treatment as well as to avoid misinterpretation of fingertip pulse oximetry readings, which can be inaccurate and unreliable in case of elevated MetHb and COHb levels in the blood.

COULD COVID-19 BE A HEMOGLOBINOPATHY?

The world is struggling to deal with the corona pandemic. Effective therapies are still awaited due to the lack of understanding of the pathophysiological mechanism of the disease. Bearing recent research and clinical observations in mind, the authors propose a novel physiological mechanism of COVID-19 and explain development of COVID-19 related acute respiratory distress syndrome (ARDS) secondary to COVID-19 related hemoglobinopathy. It is a consistent observation that the radiological picture of COVID-19 related ARDS bears more resemblance to high altitude pulmonary edema (HAPE) than typical ARDS. There has been great controversy regarding this proposed similarity. The main argument from those objecting to this comparison is that the etiology is hypoxia in case of HAPE and inflammation in COVID-19 related ARDS. We propose that considering the recent bioinformatics prediction models, COVID-19 might first infect red blood cells via CD147 and cause hemoglobin damage. The resulting hypoxemia may cause pulmonary hypoxic vasoconstriction leading to HAPE-like lung lesions. The now introduced alveolar hypoxia further exaggerates hemoglobinopathy hypoxemia leading to a vicious cycle. In this review, the authors recommend laboratory experiments to prove these hypotheses. The proposed physiological mechanism has significant therapeutic implications. If proven, the authors suggest the use of exchange transfusion as adjunct therapy and development of anti-CD147 drugs.

Acquired methemoglobinemia presenting to the pediatric emergency department: a clinical challenge

OBJECTIVES

Acquired methemoglobinemia (MetHb) is an uncommon presentation of cyanosis in the pediatric emergency department (ED), making its diagnosis and management a clinical challenge. Through this case series we hope to improve clinician ability to recognize the potential for MetHb in pediatric ED patients and to avoid overlooking this important cause of cyanosis.

METHODS

This was a case series using a health records review, investigating patients diagnosed with MetHb at our pediatric ED during 2007-2018. We included only cases with methemoglobin saturation ≥5%.

RESULTS

Ten patients were diagnosed with MetHb in our pediatric ED during the study period. Five had an underlying hematologic disease who received a pharmacologic trigger known to induce MetHb as well (four dapsone, one rasburicase). The other five patients were previously healthy, who presented with a clinical picture of hemolytic anemia, all of whom were diagnosed with previously unknown glucose-6-phosphate dehydrogenase (G6PD) deficiency. Two of the patients received methylene blue, and five patients needed packed red blood cells. All of the patients survived the acute MetHb episode.

CONCLUSION

Acquired MetHb in the pediatric ED is a rare but important cause of cyanosis. Diagnosis and management of acute, acquired MetHb in the ED requires a high level of suspicion, and a background knowledge of the common precipitants and underlying conditions associated with this condition. We hope this case series will help ED physicians to consider MetHb in pediatric patients presenting with cyanosis and persistent hypoxia. Exposure to known precipitants (e.g., medications and foods), particularly in the setting of active treatment for malignancy or with symptoms of hemolytic anemia should further increase suspicion.

Convolutional Neural Networks for Spectroscopic Analysis in Retinal Oximetry

Retinal oximetry is a non-invasive technique to investigate the hemodynamics, vasculature and health of the eye. Current techniques for retinal oximetry have been plagued by quantitatively inconsistent measurements and this has greatly limited their adoption in clinical environments. To become clinically relevant oximetry measurements must become reliable and reproducible across studies and locations. To this end, we have developed a convolutional neural network algorithm for multi-wavelength oximetry, showing a greatly improved calculation performance in comparison to previously reported techniques. The algorithm is calibration free, performs sensing of the four main hemoglobin conformations with no prior knowledge of their characteristic absorption spectra and, due to the convolution-based calculation, is invariable to spectral shifting. We show, herein, the dramatic performance improvements in using this algorithm to deduce effective oxygenation (SO₂), as well as the added functionality to accurately measure fractional oxygenation (\documentclass[12pt]{minimal} \usepackage{amsmath} \usepackage{wasysym} \usepackage{amsfonts} \usepackage{amssymb} \usepackage{amsbsy} \usepackage{mathrsfs} \usepackage{upgreek} \setlength{\oddsidemargin}{-69pt} \begin{document}$${{\bf{SO}}}_{{\bf{2}}}^{{\boldsymbol{f}}{\boldsymbol{r}}}$$\end{document}SO2fr). Furthermore, this report compares, for the first time, the relative performance of several previously reported multi-wavelength oximetry algorithms in the face of controlled spectral variations. The improved ability of the algorithm to accurately and independently measure hemoglobin concentrations offers a high potential tool for disease diagnosis and monitoring when applied to retinal spectroscopy.

Cerebral oximetry performance testing with a 3D-printed vascular array phantom

Cerebral oximetry based on near-infrared spectroscopy represents a unique noninvasive tool for real-time surgical monitoring, yet studies have shown a significant discrepancy in accuracy among commercial systems. Towards the establishment of a standardized method for performance testing, we have studied a solid phantom approach - based on a 3D-printed cerebrovascular module (CVM) incorporating an array of 148 cylindrical channels - that has several advantages over liquid phantoms. Development and characterization of a CVM prototype are described, including high-resolution imaging and spectrophotometry measurements. The CVM was filled with whole bovine blood tuned over an oxygen saturation range of 30-90% and molded-silicone layers simulating extracerebral tissues were used to evaluate penetration depth. Saturation measurement accuracy was assessed in two commercially-available clinical cerebral oximeters. For one oximeter, both neonatal and pediatric sensors showed a high degree of precision, whereas accuracy was strongly dependent on saturation level and extracerebral geometry. The second oximeter showed worse precision, yet greater robustness to variations in extracerebral layers. These results indicate that 3D-printed channel array phantoms represent a promising new approach for standardized testing of clinical oximeters.

"On Vivo" and Wearable Clinical Laboratory Testing Devices for Emergency and Critical Care Laboratory Testing

BACKGROUND

Point-of-care testing (POCT) devices are designed for clinical laboratory testing at the bedside or near the patient and can significantly reduce the turnaround time for laboratory test results. The next generation for clinical laboratory testing may be devices that are worn or attached to the patient.

CONTENT

POCT devices that are designed where samples are tested directly on the patient include bilirubinometers, pulse oximeters, breathalyzers (for alcohol and, more recently, cannabinoid detection), transcutaneous blood gas analyses, and novel testing applications such as glucose and tumor signatures following surgical excision. The utility of these devices with special reference for use within the intensive care unit and the emergency department is reviewed.

SUMMARY

It is likely that wearable POCT devices will be developed in the future that can meet current and emerging clinical needs. Advancements in biomedical engineering and information technology will be needed in the creation of next-generation devices.

Congenital methaemoglobinaemia diagnosed in an adolescent boy

A 14-year-old boy of Asian origin presented with a history of bluish discolouration of the finger and toenail bed with associated mild fatiguability on exertion since early childhood. Clinical examination revealed bilaterally symmetric uniform central cyanosis with no associated clubbing. Cardiovascular and respiratory system examination was normal. Pulse oximetry revealed an oxygen saturation of 87% in all four limbs. Transthoracic and transoesophageal echocardiography showed no evidence of shunt lesions. In view of the past diagnosis of pulmonary arteriovenous fistulae made at 4 years of age, a repeat cardiac catheterisation study was done, which revealed no shunt at any level. Interestingly, arterial oxygen tension of the chocolate-brown blood was normal in all the samples, suggesting the possibility of methaemoglobinaemia. Co-oximetry revealed methaemoglobin levels of 36%, confirming the diagnosis. Secondary causes were ruled out. The family was counselled about the hereditary nature of the condition.

Methemoglobinemia should be suspected when oxygen saturation apparently decreases after prilocaine infiltration during intravenous sedation

During intravenous sedation, a decrease in SpO2 is usually the result of respiratory failure. However, we experienced a case with SpO2 decrease that was caused by methemoglobinemia in prilocaine infiltration anesthesia during sedation. This indicates that methemoglobinemia should be considered if low SpO2 is sustained unrelated to sedation level.

Congenital methemoglobinemia misdiagnosed as polycythemia vera: Case report and review of literature

Methemoglobinemia is a rare overlooked differential diagnosis in patients presented with cyanosis and dyspnea unrelated to cardiopulmonary causes. Our patient is 29 year old Indian non-smoker male, his story started 6 months prior to presentation to our center when he had generalized fatigue and discoloration of hands. He presented with persistent polycythemia with elevated hemoglobin level. The patient was misdiagnosed in another center as polycythemia and treated with Imatinib. The diagnosis of PV was revisited and ruled out in view of negative JAK2, normal erythropoietin level and absence of features of panmyelosis. Clinical cyanosis and lowoxygen saturation in the presence of normal arterial oxygen tension was highly suggestive of methemoglobinemia. Arterial blood gas revealed a methemoglobin level of 38% (normal: 0-1.5%). Cytochrome B5 reductase (Methemoglobin reductase B) was deficient at level of <2.6 U/g Hb) (normal: 6.6-13.3), consistent with methemoglobin reductase (cytochrome b5) deficiency and hence the diagnosis of congenital methemoglobinemia was established. The role of Imatinib in provoking methemoglobinemia is questionable and association between Imatinib and methemoglobinemia never described before. In our case, there were no other offending drugs in aggravating the patients’ symptoms and cyanosis. The patient started on Vitamin C 500 mg once daily for which he responded well with less cyanosis and significant reduction of methemoglobin level. Congenital methemoglobinemia is a rare underreported hemoglobin disease and often clinically missed. Upon extensive review of English literature for cases of congenital methemoglobinemia due to deficiency of cytochrome b5 reductase, we found 23 cases diagnosed as type I (including the case reported here). 17 cases (~74%) of type I and 6 cases (27%) of type II. There is male predominance 73% versus 26% in females. Almost half of reported cases 12 cases (52%) are Indian, 2 Japanese, 3 English, 2 Arabic, one case Spanish and one case Italian. For type I, the median calculated age is 31 years with cyanosis and shortness of breath being the most common sign and symptoms. For type II: Six cases were reported in English literature, all in pediatric age group with median calculated age at presentation is 6 years with neurologic manifestations and mental retardation are the most common type II associated symptoms. Due to lack of systematic epidemiological studies, congenital methemoglobinemia is under diagnosed as it is under investigated and usually overlooked especially when presenting in adulthood and in absence of obvious acquired agents.

In vivo photoacoustic imaging of chorioretinal oxygen gradients

Chorioretinal imaging has a crucial role for the patients with chorioretinal vascular diseases, such as neovascular age-related macular degeneration. Imaging oxygen gradients in the eye could better diagnose and treat ocular diseases. Here, we describe the use of photoacoustic ocular imaging (PAOI) in measuring chorioretinal oxygen saturation (CR  -  sO2) gradients in New Zealand white rabbits (n  =  5) with ocular ischemia. We observed good correlation (R2  =  0.98) between pulse oximetry and PAOI as a function of different oxygen percentages in inhaled air. We then used an established ocular ischemia model in which intraocular pressure is elevated to constrict ocular blood flow, and notice a positive correlation (R2  =  0.92) between the injected volume of phosphate buffered saline (PBS) and intraocular pressure (IOP) as well as a negative correlation (R2  =  0.98) between CR  -  sO2 and injected volume of PBS. The CR  -  sO2 was measured before (baseline), during (ischemia), and after the infusion (600-μL PBS). The ischemia-reperfusion model did not affect the measurement of the sO2 using a pulse oximeter on the animal's paw, but the chorioretinal PAOI signal showed a nearly sixfold decrease in CR  -  sO2 (n  =  5, p  =  0.00001). We also observe a sixfold decrease in CR  -  sO2 after significant elevation of IOP during ischemia, with an increase close to baseline during reperfusion. These data suggest that PAOI can detect changes in chorioretinal oxygenation and may be useful for application to imaging oxygen gradients in ocular disease.

Camera-based pulse-oximetry - validated risks and opportunities from theoretical analysis

Camera-based pulse-oximetry has recently shown to be feasible, even when the signal is corrupted by noise and motion artifacts. Earlier work showed that using three instead of the common two wavelengths improves robustness of the measurement, however without a thorough investigation on the optimal wavelength selection. We therefore performed a search to identify these wavelengths to further improve the robustness of the measurement. Besides motion, it is empirically known that there are several other factors that influence the measurement leading to falsely-low or falsely-high SpO₂ readings. These factors include the presence of dyshemoglobins or other species. In this paper, we use a theoretical skin-model to study how these factors influence the measurement, and how a proper wavelength selection can reduce the impact on the measurement. Additionally, we show that adding a third wavelength does not only improve robustness, but can also be exploited to create a reliability index for the measurement. Finally, we show that the presence of dyshemoglobins in arterial blood can not only be detected but also quantified. We illustrate this by comparing the estimated COHb levels of a small group of smokers and non-smokers, which typically have different CO-levels.

Detection of Hb Rothschild HBB: c.[112T>A or 112T>C], Through High Index of Suspicion on Abnormal Pulse Oximetry

We describe a case with a low oxygen affinity hemoglobin (Hb) variant who presented with cyanosis in the absence of cardiopulmonary disease. The patient, a 27-year-old pregnant female (P1G2), complained of a productive cough and bluish discoloration of the lips that started 3 days prior to seeking attention. She had no previous episodes and has generally been in good health. A positive family history of cyanosis was obtained in one sibling. Systematic examination, notably the cardiorespiratory system, revealed no abnormalities. The arterial Hb oxygen saturation (SpO₂) on pulse oximetry was 81.0% and Hb separation studies revealed an Hb variant identified as Hb Rothschild [β37(C3)Trp→Arg] (HBB: c.[112 T>A or 112 T>C]) by gene sequencing. The amino acid substitution (Trp→Arg) is an important contact point at the α1β2 interface and favors a T-quaternary state of the Hb tetramer. This leads to a low oxygen affinity state, which results in premature release of oxygen and drop in oxygen saturation. In the absence of cardiopulmonary disease, a decreased oxygen saturation reading, with or without cyanosis, should arouse suspicion for a possible dysHb.

Diagnostic dilemma: Low oxygen saturation during cardiac surgery

We report a case of rheumatic heart disease with severe mitral stenosis having cyanosis and low oxygen saturation on pulse oximetry. The findings of clinical examination and low values on pulse oximetry were inconsistent with the findings of normal partial pressure of oxygen and oxygen saturation on arterial blood gas analysis, leading to diagnostic dilemma. In such clinical scenario, the anesthesiologist should be aware and vigilant about the differential diagnosis of low oxygen saturation on pulse oximetry.

Diagnosis, Treatment, and Prevention of Hemodialysis Emergencies

Given the high comorbidity in patients on hemodialysis and the complexity of the dialysis treatment, it is remarkable how rarely a life-threatening complication occurs during dialysis. The low rate of dialysis emergencies can be attributed to numerous safety features in modern dialysis machines; meticulous treatment and testing of the dialysate solution to prevent exposure to trace elements, toxins, and pathogens; adherence to detailed treatment protocols; and extensive training of dialysis staff to handle medical emergencies. Most hemodialysis emergencies can be attributed to human error. A smaller number are due to rare idiosyncratic reactions. In this review, we highlight major emergencies that may occur during hemodialysis treatments, describe their pathogenesis, offer measures to minimize them, and provide specific interventions to prevent catastrophic consequences on the rare occasions when such emergencies arise. These emergencies include dialysis disequilibrium syndrome, venous air embolism, hemolysis, venous needle dislodgement, vascular access hemorrhage, major allergic reactions to the dialyzer or treatment medications, and disruption or contamination of the dialysis water system. Finally, we describe root cause analysis after a dialysis emergency has occurred to prevent a future recurrence.

Case Report of Methemoglobinemia in a Toddler Secondary to Topical Dapsone Exposure

Aczone gel 5% contains dapsone and is a commonly used topical dermatologic therapy for acne in adolescents and adults. We describe the first reported pediatric case of a previously healthy girl presenting with acute onset of methemoglobinemia after exposure to her sibling's Aczone gel. The patient was successfully treated with methylene blue initially and subsequently needed an additional dose for rebound methemoglobinemia. This case demonstrates the complications of systemic absorption of dapsone in the pediatric population resulting in clinically significant methemoglobinemia from a single topical application.

Conscious Intravenous Sedation in Dentistry: A Review of Current Therapy

Several sedation options are used to minimize pain, anxiety, and discomfort during oral surgery procedures. Minimizing or eliminating pain and anxiety for dental care is the primary goal for conscious sedation. Intravenous conscious sedation is a drug-induced depression of consciousness during which patients respond purposefully to verbal commands. No interventions are required to maintain a patent airway, and spontaneous ventilation is adequate as well as cardiovascular function. Patients must retain their protective airway reflexes, and respond to and understand verbal communication. The drugs and techniques used must therefore carry a broad margin of safety.

Adjustment of oxygen use by means of pulse oximetry: an important tool for patient safety

OBJECTIVE

To assess patient's level of oxygenation by means of pulse oximetry, avoiding hypoxia (that causes rapid and severe damage), hyperoxia, and waste.

METHODS

Calculations were made with a 7% margin of error and a 95% confidence interval. Physical therapists were instructed to check pulse oximetry of all patients with prescriptions for physical therapy, observing the scheduled number of procedures.

RESULTS

A total of 129 patients were evaluated. Hyperoxia predominated in the sectors in which the patient was constantly monitored and hypoxia in the sectors in which monitoring was not continuous.

CONCLUSIONS

Professionals involved in patient care must be made aware of the importance of adjusting oxygen use and the risk that non-adjustment represents in terms of quality of care and patient safety.

Global methaemoglobinaemia research output (1940-2013): a bibliometric analysis

Bibliometric studies, which involve the use of statistical methods, are increasingly being used for research assessment. A bibliometric analysis was conducted to evaluate the publication pattern of methaemoglobinaemia research output at the global level based on the Scopus database. We analysed selected documents with "methemoglobinemia", or "methaemoglobinaemia" as a part of the title and reported the following parameters: trends of publication output, country of publication, journal pattern, collaborative measures, citations pattern, and institute productivity. A total of 1770 articles were published worldwide. The time trend for the number of articles showed an increase after 2000. The highest number of articles related to methaemoglobinaemia was from the USA (24.8 %), followed distantly by the UK (4.5 %), India (3.7 %), and France (3.7 %). No data related to methaemoglobinaemia were published from 152 countries. The total number of citations at the date of data collection was 10,080, with an average of 5.7 citations per document. The USA and UK had the highest h-index of 31 and 14, respectively, and six countries had an h-index of 9-14. It is notable that Canada was ranked eighth in the number of publications but fourth in h-index and India was ranked third in the number of publications but eighth in h-index. Furthermore, Canada produced the most internationally collaborated papers out of the total number of publications for each country (16.1 %), followed by the UK (13.9 %). This bibliometric analysis provides data contributing to a better understanding of the methaemoglobinaemia research field. The number of publications on methaemoglobinaemia increased significantly after 2000. The USA was the most productive country as measured by total publications. The USA and UK achieved the highest h-index in the field of methaemoglobinaemia research, signifying a higher quality of research than other countries.

Comparison of Cerebral Oximeter and Pulse Oximeter Values in the First 72 Hours in Premature, Asphyctic and Healthy Newborns

AIM

The monitoring of oxygenation is essential for providing patient safety and optimal results. We aimed to determine brain oxygen saturation values in healthy, asphyctic and premature newborns and to compare cerebral oximeter and pulse oximeter values in the first 72 hours of life in neonatal intensive care units.

METHODS

This study was conducted at the neonatal intensive care unit (NICU) of Van Yüzüncü Yil University Research and Administration Hospital. Seventy-five neonatal infants were included in the study (28 asphyxia, 24 premature and 23 mature healthy infants for control group). All infants were studied within the first 72 hours of life. We used a Somanetics 5100C cerebral oximeter (INVOS cerebral/somatic oximeter, Troy, MI, USA). The oxygen saturation information was collected by a Nellcor N-560 pulse oximeter (Nellcor-Puriton Bennet Inc, Pleasanton, CA, USA).

RESULTS

In the asphyxia group, the cerebral oximeter average was 76.85 ± 14.1, the pulse oximeter average was 91.86 ± 5.9 and the heart rate average was 139.91 ± 22.3. Among the premature group, the cerebral oximeter average was 79.08 ± 9.04, the pulse oximeter average was 92.01 ± 5.3 and the heart rate average was 135.35 ± 17.03. In the control group, the cerebral oximeter average was 77.56 ± 7.6, the pulse oximeter average was 92.82 ± 3.8 and the heart rate average was 127.04 ± 19.7.

CONCLUSION

Cerebral oximeter is a promising modality in bedside monitoring in neonatal intensive care units. It is complementary to pulse oximeter. It may be used routinely in neonatal intensive care units.

P-chloroaniline poisoning causing methemoglobinemia: a case report and review of the literature

Background. Methemoglobin (MetHb) most commonly results from exposure to an oxidizing chemical but may also arise from genetic, dietary, or even idiopathic etiologies. P-chloroaniline (PCA) was one of the first substances described in the context of acquired methemoglobinemia. Case Report. We report the case of a cyanotic chemistry worker who presented to our emergency department (ED) after working with PCA. His peripheral oxygen saturation (SpO₂) measured by pulse oximetry was at 81% and remained on that level despite oxygen administration (100% oxygenation via nonrebreather mask). His MetHb level was measured at 42.8% in arterial blood gas analysis. After treatment with intravenous methylene blue cyanosis resolved and the patient was discharged after 36 hours of observation. Conclusion. Acquired methemoglobinemia is a treatable condition, which may cause significant morbidity and mortality. The knowledge about the most common causes, fast diagnostic, and proper treatment is crucial.

Comparison of two new generation pulse oximeters with arterial oxygen saturation in critically ill children

OBJECTIVES

To compare the performance of two new generation pulse oximeters, one with enhanced signal extraction technology (SET) and other without enhanced SET in detecting hypoxemia and to correlate it with arterial blood gas analysis.

METHODS

Forty-eight patients, admitted to pediatric intensive care unit (PICU) of a teritiary care teaching hospital in India for critical care and support during the study period, who had an arterial catheter in situ were included. Children with those disease conditions known to interfere with pulse oximetry and blood gas analysis were excluded.184 set of observations were made during the study period. Each set had oxygen saturation (SpO2) measured from both the pulse oximeters and the corresponding arterial oxygen saturation (SaO2). The values were compared for occurrence of true and false alarms during periods of normal BP, hypotension and varying degrees of hypoxia.

RESULTS

The mean arterial SaO2 in the study was 94.4 % ± 4.9. The mean SpO2 recorded in conventional and enhanced signal extraction technology (SET) pulse oximeters were 94.9 % ± 4.5 and 97.2 % ± 4.7 respectively. Enhanced signal extraction technology pulse oximeter detected 4/27 (15 %) of true hypoxemic events and 1 event was a false alarm. Conventional pulse oximeter detected 11/27 (41 %) true hypoxemic events but recorded 6 false alarms.

CONCLUSIONS

Both pulse oximeters were not found to be performing satisfactorily in picking up hypoxemia in the study. There was good correlation with mean SpO2 from pulse oximeters and arterial SaO2. The reliability of pulse oximetry decreases with worsening hypoxemia and hypotension, and the sensitivity for picking up hypoxemia can be as low as 15 %.