A simple quantitative bedside test to determine methemoglobin

Determination of time since deposition of bloodstains through NIR and UV-Vis spectroscopy - A critical comparison

Time elapsed since bloodstain deposition is a crucial aspect in forensic investigations, where non-destructive spectroscopic methods play a pivotal role. While extensive research has been conducted by UV-Vis spectroscopy, showcasing its utility in specific cases, there is still a paucity of studies based on NIR spectroscopy, which has the potential to overcome the limitations of the UV-Vis-based methods. To compensate for this disequilibrium, the present study aimed to evaluate the NIR applicability for estimating the age of forensic bloodstains and develop a performance comparison with UV-Vis spectroscopy methods. Capillary blood was sampled and subjected to a 16-day aging, during which it was repeatedly analyzed using both spectroscopic methods. Subsequently, chemometric analysis was applied to process the spectral data and independently assess the methods' performance. Classical preprocessing transforms (i.e., Savitzky-Golay derivatives and SNV transform) were used together with more targeted strategies, such as class centering, whose benefit was highlighted by PCA. Lastly, PLS regression models were computed to evaluate the effectiveness of both spectroscopic methods in estimating the time elapsed since blood trace deposition. Comparable root mean square errors in prediction (RMSEP) - 40 and 55 h for UV-Vis and NIR spectroscopy, respectively - were observed for both techniques, featuring an improvement with respect to the existing literature for NIR spectroscopy. Data fusion strategies for a multi-instrumental platform were also explored, evaluating advantages and disadvantages of low-level and mid-level approaches. The results indicated that NIR spectroscopy integrated with adequate chemometric strategies deserves increased appreciation in forensic bloodstain dating.

A Rare Case of Familial Methemoglobinemia with Congenital Heart Disease

Methemoglobinemia is a rare dyshemoglobin disorder which can either be congenital or acquired. Dyshemoglobin disorders can be asymptomatic or symptomatic. We narrate the case of a 12-year-old girl who presented with a fever, cough, and oxygen saturation of 85%. She was diagnosed with COVID-19, along with a large atrial septal defect and pulmonary arterial hypertension. Arterial blood gas analysis revealed normal partial pressure of oxygen and on 100% exposure to oxygen, blood color turned chocolate brown. After the resolution of COVID-19 in 10 days, the patient was treated with oral ascorbic acid and successful atrial septal defect repair. It is important to suspect dyshemoglobin disorder in a patient who presents with hypoxia/hypoxemia.

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.

Dapsone-Induced Methemoglobinemia Presenting Concomitantly With COVID-19 Pneumonia and Pulmonary Embolism: A Case Report

Acquired methemoglobinemia is a treatable condition that is often clinically subtle and can be missed on routine clinical assessment. We present a 73-year-old male who was evaluated in the emergency department with worsening respiratory symptoms requiring oxygen. He tested COVID-19 positive and had new pulmonary emboli evident on his CT chest. The patient was on dapsone therapy as a treatment for bullous pemphigoid. The discrepancy between his oxygen levels on the pulse oximeter and blood gas was noted and was treated with 3% methylene blue for dapsone-induced methemoglobinemia. The patient received treatment for COVID-19 pneumonia and pulmonary emboli. Our case demonstrates that dapsone-induced methemoglobinemia can present concomitantly with other more common causes of acute hypoxic respiratory failure. It is noteworthy for physicians to maintain a high index of suspicion for oxygen level discrepancy in hypoxic patients and consider the possibility of acquired methemoglobinemia. Hence, earlier detection and treatment of the etiology of tissue hypoxia.

Alternative methods for calculating percentage haemolysis of red cell concentrates in peripheral blood banks in Sri Lanka

Background

Haemolysis - one of the major limiting factors of red cell concentrate quality - must be measured as a quality-monitoring requirement. According to international quality standards, percentage haemolysis must be monitored in 1.0% of red cell concentrates produced monthly and maintained under 0.8%.

Objective

This study assessed three alternative methods for determining plasma haemoglobin concentration in peripheral blood banks that lack a plasma or low haemoglobin photometer - the gold-standard method - in Sri Lanka.

Methods

A standard haemolysate was prepared using an unexpired whole blood pack of normal haemoglobin concentration. A concentration series from 0.1 g/dL to 1.0 g/dL was prepared by diluting portions of standard haemolysate with saline. The alternative methods, namely visual haemoglobin colour scale, spectrophotometric calibration graph, and standard haemolysate capillary tube comparison, were designed using this concentration series and were used to test red cell concentrates received at the Quality Control Department of the National Blood Center, Sri Lanka, from February 2021 to May 2021.

Results

A strong correlation was observed between the haemoglobin photometer method and the alternative methods (R = ~0.9). Based on the linear regression model, the standard haemolysate capillary tube comparison method was the best of the three alternative methods (R ² = 0.974).

Conclusion

All three alternative methods are recommended for use in peripheral blood banks. The standard haemolysate capillary tube comparison method was the best model.

METHEMOGLOBINEMIA - A CASE REPORT AND LITERATURE REVIEW

The objective of this case report is to present a patient with acquired methemoglobinemia due to poisoning of an unknown cause. A 55-year-old man was brought to the Emergency Department, University Hospital Center Zagreb, with an unwell appearance, cyanotic, restless, and presented with a quantitative consciousness disorder. An initial assessment showed decreased oxygen saturation (SpO2 85 [%]), while point-of-care arterial blood gas (ABG) analysis assessed normal partial pressure of oxygen (pO2). Severe lactic acidosis with a compensatory drop in partial pressure of carbon dioxide (pCO2) and high rates of methemoglobin were found. Supportive oxygen therapy and crystalloid solutions were administered, which resulted in rapid clinical recovery within 40 minutes of the initial assessment. Clinical recovery was accompanied by normalized ABG test results taken serially. Typical antidotes, methylene blue and vitamin C, were not administered due to rapid clinical improvement. Methemoglobinemia can be congenital (hereditary) or acquired (toxic). Both conditions are rarely seen in emergency departments, nevertheless, they should be approached properly since methemoglobinemia can be a severe, and fatal, condition. Methemoglobinemia symptoms are the results of inadequate oxygen transport. The diagnosis was confirmed by co-oximetry, while three clinical entities suspected methemoglobinemia: refractory hypoxia, “cyanosis-saturation gap“ and dark brown blood. This paper reports our patient’s clinical presentation, discusses the causes and mechanisms of possible poisoning, and reviews recent guidelines for methemoglobinemia management.

Suspected Drinking Water Poisoning in a Domestic Kitten with Methemoglobinemia

A 4-month-old male indoor cat was referred for dyspnea, mental dullness and weakness, which appeared two days earlier. The cat had been adopted at 3 months of age. Physical exam showed cyanosis, dyspnea and mild hypothermia. The “spot test” was supportive of methemoglobinemia. Co-oximetry blood gas analysis revealed severe methemoglobinemia (81.40%), severe hyperchloremia and mild hyponatremia. CBC, biochemistry and urinalysis were within normal limits, blood smear showed the presence of Heinz bodies. Treatment was instituted with oxygen therapy, methylene blue 1% solution, ascorbic acid, intravenous fluid therapy. The clinical course was favorable with rapid improvement of cyanosis and methemoglobinemia (4.2%). Acquired methemoglobinemia was hypothesized. Two weeks after discharge the cat was asymptomatic but mild methemoglobinemia (15.60%) and hyperchloremia were evident. Exposure to oxidants contained in drinking water was suspected so the owners were instructed to use bottled water only. One month later the cat was asymptomatic, and methemoglobinemia and chloremia were within normal limits. Even if a congenital form due to cytochrome b5 reductase deficiency cannot be ruled out, drinking water intoxication is the most likely cause of methemoglobinemia in this cat.

CO-oximetry measurements and antioxidant effects of ascorbic acid and methylene blue in equine methemoglobinemic blood

OBJECTIVES

To determine the effects of time after sampling on CO-oximetry measurements of equine blood samples and the effects of adding ascorbic acid (AscAc) and methylene blue (MetBlue) to samples with methemoglobinemia.

DESIGN

Experimental study.

SETTING

University teaching hospital.

ANIMALS

Thirty healthy adult horses assigned to 5 groups.

INTERVENTIONS

Repeated CO-oximetry determinations were performed on venous (n = 6) and arterial blood samples (n = 7) stored at 0°C for 48 hours. Methemoglobinemia was induced in vitro in 17 additional blood samples. Six were used as untreated controls, 6 had AscAc added, and 5 had MetBlue added. Total hemoglobin, oxyhemoglobin, carboxyhemoglobin, methemoglobin (MetHb), and oxygen saturation of hemoglobin (SO₂ ) were measured.

MEASUREMENTS AND MAIN RESULTS

Oxyhemoglobin and SO₂ increased from 69.8% ± 10.2% and 90% ± 3% to 82.8% ± 7.9% and 99% ± 3%, respectively, after 8 hours in venous blood (mean ± SD, P < 0.001). There was an effect of treatment (P = 0.032) and of time (interaction P = 0.003) on MetHb% in methemoglobinemic samples. The difference in absolute MetHb% from time 0 was as follows: 7.0% (interquartile range [IQR] = 21.2), -0.2% (IQR = 3.5), and -4.4% (IQR = 5.2) at 48 hours in control, AscAc, and MetBlue groups, respectively (P < 0.05). There was no effect of time on MetHb% in the AscAc group (23% [IQR = 52.6] at time 0 to 23.2% [IQR = 56.9] after 48 h).

CONCLUSIONS

Storage of blood in ice water to determine O₂ Hb and SO₂ using a CO-oximeter should not exceed 4 hours. Measurement of MetHb% could be delayed by up to 48 hours if AscAc is added to the sample. MetBlue significantly decreased MetHb% over time. The limitations of this study include the fact that the antioxidant effects of AscAc and MetBlue were evaluated in vitro and not in vivo. Further studies are needed to evaluate different storage temperatures and syringe types.

A case report of acquired methemoglobinemia rescued by veno-venous extracorporeal membrane oxygenation

RATIONALE

Severe methemoglobinemia (Met-Hb) is rare. The delayed diagnosis and treatment often cause further damage. The management of cellular hypoxemia is challenging and the use of extra-corporeal membrane oxygenation (ECMO) has never been reported.

PATIENT CONCERNS

The young patient, healthy with unremarkable past medical history, was sent to emergency room with out-of-hospital circulatory arrest (OHCA) and severe generalized cyanosis. His family reported he ingested sodium nitrite accidentally.

DIAGNOSES

After successful resuscitation and return of spontaneous circulation (ROSC), the paradoxically normal arterial blood gas (ABG) with the unusual brownish blood led to the suspicion of Met-Hb. The lab test confirmed it and showed a very high level of 80%.

INTERVENTIONS

Because of recovered and normal cardiac function, we placed veno-venous extracorporeal membrane oxygenation (VV-ECMO) for tissue hypoxemia in addition to exchange transfusion, vitamin C, and methylene blue.

OUTCOMES

Met-Hb blood level dropped rapidly. After vigorous rehabilitation for weeks, the patient was able to be discharged home without major neurological sequela.

LESSONS

VV-ECMO can hyper-oxygenate the hypoxemic tissue regardless the etiology and minimize hypoxemia-reperfusion injury while awaiting the definite diagnosis and therapy.

Congenital methemoglobinemia: Rare presentation of cyanosis in newborns

Methemoglobin (MetHb) is an oxidized form on hemoglobin, which is unable to bind oxygen and consequently carry it to the tissues. Normally present in small quantities (<1%) without detrimental effects, its elevation produces hypoxemia which can be profound and even lethal. Methemoglobinemia is an abnormal increase of MetHb (>3%) of total hemoglobin. It can be classified in two types: hereditary and acquired. Acquired form is caused by exogenous oxidizing agents, such as nitrites or certain medications, while hereditary types of disease are the result of genetic deficiency in cytochrome B⁵ reductase, an enzyme responsible for MetHb reduction to hemoglobin. Little data is available on the epidemiology of methemoglobinemia. In general population only sporadic cases are described, while some isolated ethnic populations have increased incidence, possibly inherited from a common ancestor. We present a case of congenital methemoglobinemia in which detection of MetHb was hampered by faulty initial blood gas spectrometry results. A short literature review is also included.

Accuracy of detection of carboxyhemoglobin and methemoglobin in human and bovine blood with an inexpensive, pocket-size infrared scanner

Detecting life-threatening common dyshemoglobins such as carboxyhemoglobin (COHb, resulting from carbon monoxide poisoning) or methemoglobin (MetHb, caused by exposure to nitrates) typically requires a laboratory CO-oximeter. Because of cost, these spectrophotometer-based instrument are often inaccessible in resource-poor settings. The aim of this study was to determine if an inexpensive pocket infrared spectrometer and smartphone (SCiO®Pocket Molecular Sensor, Consumer Physics Ltd., Israel) accurately detects COHb and MetHb in single drops of blood. COHb was created by adding carbon monoxide gas to syringes of heparinized blood human or cow blood. In separate syringes, MetHb was produced by addition of sodium nitrite solution. After incubation and mixing, fractional concentrations of COHb or MetHb were measured using a Radiometer ABL-90 Flex® CO-oximeter. Fifty microliters of the sample were then placed on a microscope slide, a cover slip applied and scanned with the SCiO spectrometer. The spectrograms were used to create simple linear models predicting [COHb] or [MetHb] based on spectrogram maxima, minima and isobestic wavelengths. Our model predicted clinically significant carbon monoxide poisoning (COHb ≥15%) with a sensitivity of 93% and specificity of 88% (regression r2 = 0.63, slope P<0.0001), with a mean bias of 0.11% and an RMS error of 21%. Methemoglobinemia severe enough to cause symptoms (>20% MetHb) was detected with a sensitivity of 100% and specificity of 71% (regression r2 = 0.92, slope P<0.001) mean bias 2.7% and RMS error 21%. Although not as precise as a laboratory CO-oximeter, an inexpensive pocket-sized infrared scanner/smartphone detects >15% COHb or >20% MetHb on a single drop of blood with enough accuracy to be useful as an initial clinical screening. The SCiO and similar relatively low cost spectrometers could be developed as inexpensive diagnostic tools for developing countries.

Detecting Methemoglobinemia in Animals with a Drop of Blood

A major concern during pesticide development and use is the impact on non-target species, such as raptors or domestic cats and dogs. Sodium nitrite and para-aminopropiophenone (PAPP) are two toxicants currently being studied for the control of invasive species, such as starlings and feral swine. When given to an animal these compounds oxidize hemoglobin, which renders it unable to carry oxygen resulting in methemoglobinemia. This study developed a method to estimate methemoglobin levels in mammals and birds by examining the efficacy of sodium nitrite to induce the conversion of hemoglobin to methemoglobin. Varying concentrations of sodium nitrite were added to aliquots of coyote, vole, feral swine, starling, and duck blood, collected from captive animals. The blood samples were analyzed spectrophotometrically to determine percent methemoglobin and digitally to determine red color values (RCV) associated with different methemoglobin levels. The avian and mammalian blood reached 100% methemoglobin levels at 200 mM and 15 mM sodium nitrite, respectively. All animals had similar RCV for a given percent methemoglobin. In conclusion, this study developed a procedure to quickly determine methemoglobin levels in mammals and birds. Furthermore, percent methemoglobin can be estimated with one standard curve from any animal species and an image of a blood spot. The technique will be useful during field studies, in agricultural areas, or in a veterinarian’s office for the rapid diagnosis of methemoglobinemia in non-target animals that have eaten toxicants/baits or baited animals.

A bedside test for methemoglobinemia, Sri Lanka

Problem

Propanil is an aniline herbicide that is widely used for rice cultivation, but is also used for self-poisoning. Toxicity from propanil is largely due to methemoglobinemia. In resource-poor settings, the capacity to determine methemoglobin concentration is insufficient and prevents effective case management, which results in increased deaths from propanil poisoning.

Approach

Blood with a methemoglobin concentration greater than 15% of total haemoglobin levels appears brownish in colour. We introduced a colour reference chart that can be used to semiquantitatively determine methemoglobinemia. Each ward in three rural hospitals received a chart. Ward staff, medical officers and trainee doctors were given a presentation describing the test method and how it should be used with the relevant national treatment guidelines.

Local setting

In three rural hospitals in Sri Lanka, 401 patients were admitted with a diagnosis of propanil poisoning before the introduction of this test (2003–2007) and 262 patients after it was introduced (2008–2014), 46 of 663 patients died.

Relevant changes

The chart can be freely produced with any good-quality colour printer. In three rural hospitals, deaths from propanil poisoning fell from 10% of those admitted with this diagnosis in 2003–2007 (38/401) to 3% (8/262) in 2008–2014 and the use of methylene blue increased from 10% (13/136) to 55% (59/107) over this period.

Lessons learnt

This simple bedside test was associated with increased use of the first line treatment for propanil poisoning and improved survival. In 2011, the test was included in the national guidelines for the management of propanil poisoning.

Methemoglobinemia: Living with Dormant Devil

Methemoglobin is an oxidized form of hemoglobin. NADH methemoglobin reductase deficiency or inactivity is the cause of methemoglobin. Excessive production, resulting in accumulation, causes methemoglobinemia. It can be congenital or acquired. We present a case of dormant congenital methemoglobinemia detected accidentally on preoperative assessment, due to low oxygen saturation even at F1O₂-1.0 associated with central cyanosis. The patient had 27.7 % methemoglobin, living his life without any complications. The patient was operated upon successfully for tympanoplasty and mastoidectomy under local anesthesia by taking proper precautions.

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.

Diagnosis of snake envenomation using a simple phospholipase A2 assay

Diagnosis of snake envenomation is challenging but critical for deciding on antivenom use. Phospholipase A2 enzymes occur commonly in snake venoms and we hypothesized that phospholipase activity detected in human blood post-bite may be indicative of envenomation. Using a simple assay, potentially a bedside test, we detected high phospholipase activity in sera of patients with viper and elapid envenomation compared to minimal activity in non-envenomed patients.

Method of stabilizing blood for the determination of methemoglobin

Methemoglobin (MetHb) is a significant clinical problem for some poisonings. Its measurement is a problem as both formation and reduction of MetHb can occur even after sampling with time. The objective of this study was to discover a method to stabilize the blood samples for the determination of MetHb. First, hemolysates were prepared by diluting the MetHb blood samples with phosphate buffers under different pH values. The samples were stored at 4-8 °C and a day-to-day variability in the amount of MetHb was determined using the method described by Evelyn and Malloy. The results show that there is a significantchange in the amount of MetHbstored in both KH2PO4/Na2HPO4 and KH2PO4/Na2HPO4 .2H2O buffer solutions at pH of 6.7 and 6.9. Buffer solution containing phosphate composition of KH2PO4/Na2HPO4 ·2H2O (pH=7.0) gives relatively stable values for MetHb during the storage and the amount of MetHb samples in the buffer solution retain constant up to 9 days. Therefore, stabilized MetHb blood samples can be prepared using KH2PO4/Na2HPO4 ·2H2O buffer solution (pH=7) with non-ionic detergent and the samples can be stored for several days at 4-8 °C.

Toxicologists in public health--Following the path of Louis Roche (based on the Louis Roche lecture "An accidental toxicologist in public health", Bordeaux, 2010)

BACKGROUND

The global burden of clinical toxicology suggests a natural partnership with public health. This article reflects the content of a Louis Roche lecture given in 2010. HISTORICAL CONTEXT: Our practice and research in clinical toxicology has evolved from clinical cases to toxico-epidemiology to public health. This evolution in practice was initially unplanned but gained momentum and impact as we placed it more formally in a public health framework. This perspective is implicit in Louis Roche's call to "examine all aspects of the poisoning problem" and still provides a valuable starting point for any clinical toxicologist.

DISCUSSION

Clinical toxicology has always had a patient centered focus but its greatest successes have been related to public health interventions. Our early failures and later success in pubic health toxicology correlated with our understanding of the importance of partnerships outside our field. The most rapid dissemination and implementation of information derived from research occur through apriori partnerships with other agencies and international partners.

CONCLUSION

Addressing both local and global need has a number of bilateral synergies. Repositioning clinical toxicology into a public health framework increases access to strategic partnerships, research funds, and policy implementation while still addressing questions that are important to clinical practice.