|LETTER TO EDITOR
|Year : 2017 | Volume
| Issue : 3 | Page : 414-415
Anesthetic management of congenital methemoglobinemia in an emergency cesarean section
Sanjivini Gupta, Gaurav Chauhan, Chandni Chauhan
Department of Anaesthesiology and Intensive Care, Aruna Asif Ali Government Hospital, Delhi, India
|Date of Web Publication||11-Sep-2017|
Department of Anaesthesiology and Intensive Care, Aruna Asif Ali Government Hospital, Delhi
Source of Support: None, Conflict of Interest: None
|How to cite this article:|
Gupta S, Chauhan G, Chauhan C. Anesthetic management of congenital methemoglobinemia in an emergency cesarean section. J Anaesthesiol Clin Pharmacol 2017;33:414-5
|How to cite this URL:|
Gupta S, Chauhan G, Chauhan C. Anesthetic management of congenital methemoglobinemia in an emergency cesarean section. J Anaesthesiol Clin Pharmacol [serial online] 2017 [cited 2018 May 22];33:414-5. Available from: http://www.joacp.org/text.asp?2017/33/3/414/173330
A 26-year-old female presented for emergency cesarean section for fetal distress. On preanesthetic evaluation, she gave a history of bluish tinge of lips and nails and dark colored blood since childhood. She had two uneventful surgeries in the past. Echocardiography was done 1 year back which was reported normal. There was no history of drug intake, exposure to dyes or chemicals. On examination, the patient had greyish skin and mild cyanosis on the tongue, nails, and lips. Her cardiovascular and respiratory systems were found to be normal. Pulse oximetry showed saturation of 75% on room air. On giving 100% oxygen the saturation remained the same. The hematological investigations showed hemoglobin (Hb %) 10 g/dl, hematocrit 30%, and other routine investigations, were within normal limits. Arterial blood gas (ABG) analysis reported the pH-7.44, PaO2-93 mm Hg and SaO2-96%. Due to emergency indication and history of uneventful caesarean section, spinal anesthesia was planned. An 18 gauge intravenous line was secured and monitoring was done as per standard protocol of the institution. Subarachnoid block was given at L3-4 level with 25 G spinal needle with 2 ml bupivacaine (0.5%, heavy), in left lateral position. The surgery lasted for 60 min. Vitals remained within normal limits and blood loss was about 400 ml. However, SpO2 values remained between 75% and 78% throughout the surgery. Dark color of blood was noted at surgical site. On the completion of surgery, the patient was shifted to postanesthesia care unit and monitored for 24 h. Chest X-ray, 12 lead electrocardiogram and echocardiography were normal. Methemoglobin (MetHb) levels were 26% and congenital methemoglobinemia was suspected because the patient had history of cyanosis and dark blood since childhood. The autosomal dominant condition of congenital hemoglobinopathy was ruled out by negative history of similar condition in parents and negative laboratory test on Hb electrophoresis. Patient was discharged uneventfully on 4th postoperative day.
Methemoglobinemia, can be postulated to be related to redox imbalance. Congenital methemoglobinemia can arise from globin mutation that stabilizes iron in the ferric state (e.g., HbM, Iwata) making them amenable to reduction despite intact enzyme systems and from mutation that impairs the enzymes which reduce MetHb to Hb mainly NADPH MetHb reductase. It is further subdivided into, type 1 congenital methemoglobinemia (erythrocyte reductase deficiency) and type 2 congenital methemoglobinemia (generalized reductase deficiency) occurs when the enzyme does not work anywhere in the body., Methemoglobinemia can also arise in patients with pyruvate kinase deficiency due to impaired production of nicotinamide adenine dinucleotide — the essential cofactor for diaphorase I. Similarly, patients with glucose-6-phosphate dehydrogenase deficiency may have impaired production of cofactor, nicotinamide adenine dinucleotide phosphate.,
Pulse oximetry displays value around 85% corresponding to MetHb equal to or below 35%. Above these levels of MetHb, pulse oximetry overestimates the true saturation of Hb and tissue hypoxia might go unnoticed, leading to misdiagnosis by unsuspecting physician., Even ABG falls short of providing an accurate estimation of MetHb as, PaO2 derived from ABG is not a true reflection of oxygen carrying capacity of Hb. Saturation gap is usually >5% in methemoglobinemia.
Co-oximetry is considered to be a gold standard in monitoring of MetHb. It uses light of four wavelengths (535, 585, 594, and 626 nm), to detect HbO2, HbCO2, Hb, and MetHb, respectively. It should be used ideally in all the cases. Even the co-oximeter cannot be considered a perfect method to measure MetHb. It is postulated that the absorbance spectrum of the fully oxidized form of MetHb is slightly different from the partially oxidized forms. It is still not certain whether the co-oximeters discriminate these molecules, so it is conceivable that total MetHb (sum of complete and partially oxidized forms) is still underdetected. There is a general consensus that, therapeutic decisions should be guided by the severity of the clinical parameters, rather than the value of MetHb shown by co-oximeter.,
Treatment protocol of methemoglobinemia consists of removal of the inducing agents, administration of high-flow O2 and co-oximetric analysis. In cases of significant clinical symptoms (dizziness, headache, anxiety, dyspnea, somnolence, and seizures), methylene blue is used as specific antidote. Many authors suggest the use of methylene blue at MetHb >30%, regardless of the presence of symptoms. It can be a source of error in the measurement of MetHb by co-oximeter, as its light absorbance spectrum (620 nm) is similar to that of MetHb, which overestimates the concentration of MetHb after treatment. Urine, skin and mucous membranes assumes bluish tinge during treatment, which interferes with the interpretation of cyanosis after treatment., So, it is recommended that analysis of the sample by co-oximetery should precede institution of methylene blue.
Methemoglobinemia is a syndrome with multiple etiologies and its diagnosis should be considered in the cases not responding to oxygen therapy. The artifacts and inaccuracies arising from conventional pulse oximetry and blood gases may either suggest the diagnosis or hinder the establishment and monitoring of treatment protocol. With the knowledge of these pathophysiological entities and limitations of conventional monitoring equipments, the anestheiologist can be sensitized to diagnose and conduct appropriate treatment.
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