Nitrite‐induced methaemoglobinaemia – aetiology, diagnosis and treatment

Abstract

SummaryA 41-year-old woman presented with the clinical features of methaemoglobinaemia after drinking Chinese herbal medicine. A life threatening methaemoglobin level of 68% was measured. Both clinical and laboratory diagnostic difficulties were encountered. The pitfalls of pulse oximeter, blood gas analysis and co-oximeter interpretation during diagnosis and after methylene blue administration are discussed. Methaemoglobinaemia is an unusual and potentially fatal condition in which haemoglobin is oxidised to methaemoglobin and loses its ability to bind and transport oxygen. We present a case of accidental ingestion of sodium nitrite to illustrate the pitfalls of management. Case historyA 41-year-old woman with a history of hypertension presented to the Accident and Emergency Department with dizziness and a bluish skin colour. These symptoms occurred 5 min after taking some Chinese herbal medicine. Her treatment for hypertension included metoprolol (daily dose of 100 mg) and sustained release nifedipine (daily dose of 20 mg). The Chinese herbal medicine included 6 g Natrii Sulfa, which was prescribed by a herbalist for weight loss. On admission, she was disorientated as to time and place. Physical examination showed brownish blue cyanotic discoloration of the skin and tachycardia. The rest of the physical examination was unremarkable. Her blood pressure was 126 ⁄ 49 mmHg with a heart rate of 110 beats.min . The pulse oximeter showed an S p O 2 of 77-80% on 100% oxygen. An arterial blood sample was drawn which was chocolate brown and did not change in colour after agitation in air. The arterial blood gas analysis showed pH 7.398, P a CO 2 4.49 kPa, P a O 2 42 kPa and BE ) 4 mmol.l )1 . Chest X-ray was normal. With no identifiable cardiopulmonary pathology and normal alveolar-arterial oxygen gradient, methaemogloblinaemia was suspected. The patient was transferred to the intensive care unit (ICU). After ICU admission, the patient's conscious level improved. Arterial blood was sent for analysis by cooximetry and variable wavelength spectrophotometer; blood samples were also taken for full blood count, renal function and toxicology screening. These showed the methaemoglobin concentration was 68% and the haemoglobin concentration 12.5 g.dl )1 . The spectrophotometer found a small absorption peak at 628 nm, which disappeared after addition of potassium cynanide. The diagnosis of methaemoglobinaemia was confirmed. Methylene blue (100 mg) was given intravenously. The serial oxygen saturation changes in the pulse oximeter, arterial blood gases as well as the methaemoglobin concentrations are shown in Figs 1 and 2. The skin and arterial blood colour became pink 30 min after methylene blue injection. The S p O 2 increased from 88% to 98% and the P a O 2 25 kPa. The methaemoglobin concentration dropped to 10.8% after 30 min of methylene blue treatment. On the second day of admission, the patient remained well. The methaemoglobin concentration dropped to 0.6% and haemoglobin concentration to 11.4 g.dl )1

Blood Levels of Methemoglobin in Patients with Aluminum Phosphide Poisoning and its Correlation with Patient’s Outcome

“…Although methemoglobinemia due to AlP intoxication has been reported only in one case [7], the present study showed that there is a significant association between blood level of Met-Hb and mortality in AlP intoxication cases. Clinical manifestations of methemoglobinemia are due to decreased O 2 -carrying capacity of hemoglobin and consequent tissue hypoxia [13]. We believe that in patients suffering from AlP intoxication, death occurs mainly due to other more serious complications such as hypotension and shock rather than methemoglobinemia.…”

Linkage Isomerization in Heme−NOx Compounds: Understanding NO, Nitrite, and Hyponitrite Interactions with Iron Porphyrins

“…61 However, nitrite can also be harmful to mammals, as it can oxidize ferrous hemoglobin (Hb) and increase the in vivo levels of ferric Hb to result in the blood disorder methemoglobinemia. 62,63 …”

Acute oral dose of sodium nitrite induces redox imbalance, DNA damage, metabolic and histological changes in rat intestine

“…Accidental or intentional acute exposure to high levels of nitrite has been reported to cause death, mainly due to methemoglobinemia [8,9]. Chronic exposure to lower doses of nitrite causes adverse health effects, which includes birth defects, respiratory tract ailments, damage to the nervous system and paralysis [10].…”