Pediatric Review - International Journal of Pediatric Research

Methaemoglobinemia is an uncommon but potentially fatal haemoglobinopathy. It leads to rapid oxygen saturation and therefore requires prompt recognition and treatment [1,2]. It can be induced by congenital mutations or it can be acquired. One of the ways to acquire it is by using topical anaesthetics such as nitrates, benzocaine, and lidocaine [3]. The first case of benzocaine-induced Methaemoglobinemia was reported in 1977 [4]. It occurs in approximately 3.5 out of 10,000 cases of reported Methaemoglobinemia[5,6]. Those who are unknowingly susceptible to developing Methaemoglobinemia and receive anaesthetics during hospital procedures are at risk of serious adverse effects and clinical deterioration if not treated correctly.[5]

A 20-day-old male baby weighing 1.7 kgs born out of a non-consanguineous relationship to a primi mother was brought to the emergency room with complaints of seizure-like activity in the past 1 hour, bluish discolouration of the skin for the past 1 day and loose watery stools since 3 days. He was delivered by LSCS at 34 weeks (Indication: Premature rupture of membranes) with a birth weight of 1.6 kgs and required positive pressure ventilation for 30 seconds to initiate breathing at the referral hospital. After a NICU stay for 1 week, the baby was discharged with a weight of 1.57 kg. No other significant history was noted.

Within a few minutes of arrival, the baby had 2 episodes of seizures in the form of cyclical movements involving all 4 limbs, each episode lasting for 2-3 minutes. On examination, the baby was irritable, crying with central cyanosis. He was tachypnoeic (RR: 70/min), with bilateral equal air entry on auscultation. Saturations were 85% in all 4 limbs on room air. He had tachycardia (HR: 180/min), no audible murmur, with bilaterally well-felt femoral pulses and no radio femoral delay.

Central cyanosis was present, with cool peripheries and mottled skin. Capillary filling time was prolonged (> 3 seconds). Blood pressures in all 4 limbs were within the normal range. Perianal rash with excoriation of overlying skin was present. The rest of the systemic and general examination was unremarkable.

Methemoglobinemia is a form of haemoglobin that has been oxidized, changing its heme iron configuration from Fe2+ to Fe3+ (ferric state) [3]. Congenital causes of Methaemoglobinemia include being deficit in the enzyme cytochrome b5 reductase (Cyb5R) [7].

Mechanism of Methaemoglobinemia

Drugs like benzocaine cause an oxidative stress converting Fe2+ to Fe3+ increasing the levels of methaemoglobin. Absence of or low levels of Cyb5R lead to congenital Methaemoglobinemia.

Figure 2: Mechanism ofMethaemoglobinemia

Patients with Methaemoglobinemia can be asymptomatic.[3] Once, levels exceed 20%, they can develop hypoxia, cyanosis, shock, seizures and altered mental status such as in this patient. Levels>70% are typically fatal.[7]

Methaemoglobinemia can be treated with methylene blue or ascorbic acid [3].⁾.Methylene blue is a reducing agent through the nicotinamide adenine dinucleotide phosphate (NADPH) methaemoglobin reductase pathway and in low concentrations, it is reduced to leucomethylene blue, which reacts with methemoglobin in the blood, reducing to haemoglobin [3]. A low dose of methylene blue is given, 1-2 mg/kg of 1% solution IV over five minutes, and the dose can be repeated within one hour if hypoxia symptoms aren’t resolved [7]. This patient was given 1 mg/kg of 1% methylene blue, which resolved his symptoms and normalized his methemoglobin levels to 1.1%.