Methemoglobinemia is a condition characterized by elevated levels of methemoglobin in the blood. Methemoglobin is the oxidized form of hemoglobin, where the heme iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements has been converted from the usual ferrous (Fe2+) to the ferric (Fe3+) form. The Fe3+ form of iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements cannot bind BIND Hyperbilirubinemia of the Newborn O2, and, thus, leads to tissue hypoxia Hypoxia Sub-optimal oxygen levels in the ambient air of living organisms. Ischemic Cell Damage. Methemoglobinemia results from congenital Congenital Chorioretinitis defects or can occur after exposure Exposure ABCDE Assessment to oxidizing agents. Symptoms depend on methemoglobin levels and vary from simple cyanosis Cyanosis A bluish or purplish discoloration of the skin and mucous membranes due to an increase in the amount of deoxygenated hemoglobin in the blood or a structural defect in the hemoglobin molecule. Pulmonary Examination to neurologic and cardiac Cardiac Total Anomalous Pulmonary Venous Return (TAPVR) presentations. The condition can be fatal in the case of significant elevation of methemoglobin (> 70%). Diagnosis is established by measuring methemoglobin levels in blood using co-oximetry. Treatment of methemoglobinemia is with methylene blue or ascorbic acid, as they hasten the conversion of methemoglobin to hemoglobin.
Last updated: 27 Apr, 2021
Methemoglobinemia occurs when RBCs RBCs Erythrocytes, or red blood cells (RBCs), are the most abundant cells in the blood. While erythrocytes in the fetus are initially produced in the yolk sac then the liver, the bone marrow eventually becomes the main site of production. Erythrocytes: Histology contain elevated methemoglobin levels (normal range in adults is 0%–3%).
Methemoglobin is a form of hemoglobin in which ferrous (Fe2+) heme iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements is oxidized to the ferric (Fe3+) state, which is unable to bind BIND Hyperbilirubinemia of the Newborn O2.
Congenital Congenital Chorioretinitis:
Acquired due to exposure Exposure ABCDE Assessment to oxidizing agents:
Hemoglobin structure: 4 globin chains (β1, β2, ɑ1, and ɑ2) and 4 heme molecules (with iron Iron A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen. Trace Elements in the ferrous state) for binding with O2
Image by Lecturio.Methemoglobin levels are limited through different mechanisms:
Pathophysiology and management of methemoglobin (HbFe²⁺: hemoglobin, MetHbFe³⁺: methemoglobin,
NADPH
NADPH
Nicotinamide adenine dinucleotide phosphate. A coenzyme composed of ribosylnicotinamide 5′-phosphate (nmn) coupled by pyrophosphate linkage to the 5′-phosphate adenosine 2.
Pentose Phosphate Pathway:
nicotinamide adenine dinucleotide
Nicotinamide adenine dinucleotide
A coenzyme composed of ribosylnicotinamide 5′-diphosphate coupled to adenosine 5′-phosphate by pyrophosphate linkage. It is found widely in nature and is involved in numerous enzymatic reactions in which it serves as an electron carrier by being alternately oxidized (NAD+) and reduced (NADH).
Pentose Phosphate Pathway
phosphate
Phosphate
Inorganic salts of phosphoric acid.
Electrolytes, NADH:
nicotinamide adenine dinucleotide
Nicotinamide adenine dinucleotide
A coenzyme composed of ribosylnicotinamide 5′-diphosphate coupled to adenosine 5′-phosphate by pyrophosphate linkage. It is found widely in nature and is involved in numerous enzymatic reactions in which it serves as an electron carrier by being alternately oxidized (NAD+) and reduced (NADH).
Pentose Phosphate Pathway):
Oxidation of heme
iron
Iron
A metallic element with atomic symbol fe, atomic number 26, and atomic weight 55. 85. It is an essential constituent of hemoglobins; cytochromes; and iron-binding proteins. It plays a role in cellular redox reactions and in the transport of oxygen.
Trace Elements from ferrous state to ferric state produces MetHbFe³⁺. Cytochrome b5 reductase reduces MetHbFe³⁺ to HbFe²⁺. Methylene blue acts as an electron acceptor for
NADPH
NADPH
Nicotinamide adenine dinucleotide phosphate. A coenzyme composed of ribosylnicotinamide 5′-phosphate (nmn) coupled by pyrophosphate linkage to the 5′-phosphate adenosine 2.
Pentose Phosphate Pathway reductase and also facilitates the reduction of methemoglobin. Other compounds that can promote MetHbFe³⁺ reduction include glutathione and ascorbic acid.
Role of
nicotinamide adenine dinucleotide
Nicotinamide adenine dinucleotide
A coenzyme composed of ribosylnicotinamide 5′-diphosphate coupled to adenosine 5′-phosphate by pyrophosphate linkage. It is found widely in nature and is involved in numerous enzymatic reactions in which it serves as an electron carrier by being alternately oxidized (NAD+) and reduced (NADH).
Pentose Phosphate Pathway
phosphate
Phosphate
Inorganic salts of phosphoric acid.
Electrolytes (
NADPH
NADPH
Nicotinamide adenine dinucleotide phosphate. A coenzyme composed of ribosylnicotinamide 5′-phosphate (nmn) coupled by pyrophosphate linkage to the 5′-phosphate adenosine 2.
Pentose Phosphate Pathway) methemoglobin reductase:
NADPH
NADPH
Nicotinamide adenine dinucleotide phosphate. A coenzyme composed of ribosylnicotinamide 5′-phosphate (nmn) coupled by pyrophosphate linkage to the 5′-phosphate adenosine 2.
Pentose Phosphate Pathway is generated in the
glucose-6-phosphate dehydrogenase
Glucose-6-phosphate dehydrogenase
Pentose Phosphate Pathway reaction (2).
NADPH
NADPH
Nicotinamide adenine dinucleotide phosphate. A coenzyme composed of ribosylnicotinamide 5′-phosphate (nmn) coupled by pyrophosphate linkage to the 5′-phosphate adenosine 2.
Pentose Phosphate Pathway-methemoglobin reductase converts methylene blue (MB) to leukomethylene blue (the active form) using
NADPH
NADPH
Nicotinamide adenine dinucleotide phosphate. A coenzyme composed of ribosylnicotinamide 5′-phosphate (nmn) coupled by pyrophosphate linkage to the 5′-phosphate adenosine 2.
Pentose Phosphate Pathway as an electron donor (1). Leukomethylene blue, in turn, reduces methemoglobin to hemoglobin.
Symptoms depend on the etiology, chronicity, and level of methemoglobin.
Cyanosis
Cyanosis
A bluish or purplish discoloration of the skin and mucous membranes due to an increase in the amount of deoxygenated hemoglobin in the blood or a structural defect in the hemoglobin molecule.
Pulmonary Examination in methemoglobinemia:
A patient showing bluish discoloration on the right
foot
Foot
The foot is the terminal portion of the lower limb, whose primary function is to bear weight and facilitate locomotion. The foot comprises 26 bones, including the tarsal bones, metatarsal bones, and phalanges. The bones of the foot form longitudinal and transverse arches and are supported by various muscles, ligaments, and tendons.
Foot: Anatomy and left
hand
Hand
The hand constitutes the distal part of the upper limb and provides the fine, precise movements needed in activities of daily living. It consists of 5 metacarpal bones and 14 phalanges, as well as numerous muscles innervated by the median and ulnar nerves.
Hand: Anatomy (cyanotic nailbeds shown)
History:
Physical exam findings:
Color code suggestive of methemoglobin:
Blood with methemoglobin concentration > 15% of total hemoglobin levels appears brownish, as seen in the image (right side).
Methemoglobin measurement:
Use of co-oximetry (multiple-wavelength oximetry). Pictured above is a Rad-57 pulse oximeter applied to the finger of a child. Instead of just 2 wavelengths, co-oximetry utilizes 8 wavelengths.
Management of methemoglobinemia depends on the severity and chronicity.
Methemoglobin levels > 30% and associated with tissue hypoxia Hypoxia Sub-optimal oxygen levels in the ambient air of living organisms. Ischemic Cell Damage is a medical emergency:
In congenital Congenital Chorioretinitis methemoglobinemia: