METHEMOGLOBINEMIA DUE TO BIOLOGICAL POISONING – CASE REPORT

Geethika Sai Nutakki 1 , Indraja Siripurapu 1 , Ch. Manoj Kumar 2 and T V D Sasi Sekhar 3 . 1. Postgraduate,General Medicine, Dr.Pinnamaneni Siddhartha Institute of medical sciences and research foundation ,Chinaoutpalli, Krishna district, Andhra Pradesh. 2. AssociateProfessor, Dept. of General Medicine,Dr.Pinnamaneni Siddhartha Institute of medical sciences and research foundation, Chinaoutpalli, Krishna district, Andhra Pradesh, India. 3. Professor and HOD, Dept. of General Medicine, Dr.Pinnamaneni Siddhartha Institute of medical sciences and research foundation, Chinaoutpalli, Krishna district, Andhra Pradesh, India. ...................................................................................................................... Manuscript Info Abstract ......................... ........................................................................ Manuscript History


(1), 2079-2082
2080 Case 2:-A 25-year-old man was brought to emergency with alleged history of poisoning with about 100ml of pesticide within 90 minutes of ingestion. At presentation, he was conscious, coherent and cyanotic. His vital signs were as follows: pulse rate, 120/min;blood pressure,130/80mmHg and respiratory rate,26 breaths/min. SpO2 was 70% at ambient air and 86% with oxygen supplementation of 6L/min. Bilateral breath sounds were clear. Bilateral pin point pupils with sluggish reaction to light were noted. Within 30min. of hospitalization, he became unconscious for which he was intubated and mechanically ventilated.ABG analysis with CO-oximetryshowedpao 2 ,621mmHg,SaO2,99% and MetHb,80%. Patient had troponin I&T positive and urine for myoglobin was positive.
He was administered 1% methylene blue (1mg/kg). CO-oximetry after 1 hour showed MetHb of 50 %.A single volume of exchange transfusion was done. He gained consciousness and became oriented. Two doses of 1% methylene blue were repeated with an interval of 12 hours to prevent rebound methemoglobinemia and MetHb was 6.2% after 3 rd dose. In addition, he received inj.vitamin C 500mg in 5%dextrose once daily. He was extubated on 4 th day and discharged after 7days of admission, MetHb was 2% at the time of discharge without any neurological deficit.

Discussion:-
is an altered state of hemoglobin which results when there is an overwhelming oxidative stress exceeding the normal protective mechanisms. Acquired methemoglobinemia is induced by exposure to various oxidizing agents, most commonly due to nitrates and nitrites (1, 2).
The clinical manifestations (Table I) of methemoglobinemia are due to impaired oxygen delivery to the tissues and hence correlate with severity of methemoglobinemia. The onset of signs and symptoms in our cases was 30-60 minutes after pesticide ingestion.We observed bilateral pin point pupils in two cases and positive troponin and myoglobin in one case but this finding was not seen with similar poisoning described by George et al (4).
Common insecticides that induce methemoglobinemia include indoxacarb, aluminium phosphide, and paraquat.The pesticide consumed in our case reports contains biological extracts, stabilizers and fillers which was marketed to be safe and no mention of an antidote. We found only one case report (4) of toxicity with the similar pesticide in the literature. Biological extracts are rich in nitrogenous products and hence can potentially cause methemoglobinemia (4).

Figure 1:-
Methemoglobinemia should be suspected clinically by the presence of cyanosis in the presence of a normal PaO2 and chocolate-brown colored blood (Figure1). The presence of methemoglobinemia can be suspected when the SpO2 is significantly different from the SaO2 ("saturation gap").This saturation gap between SaO2 and SpO2 greater than 5% is a diagnostic clue to the presence of MetHb(5).To confirm methemoglobinemia, carbon monoxide (CO)-oximetry is required. Even CO-oximeters cannot distinguish between MetHb and sulfhemoglobin due to similar absorbance peaks at 630 nm (6).MetHb was detected by absorption spectrophometry after addition of sodium cyanide in the clinical biochemistry laboratory.  (7).The recommended dose of 1% methylene blue for adults is 1-2mg/kg diluted in 100ml of isotonic saline, infused intravenously over 5minutes.The response is usually rapid within 30minutes; the dose may be repeated in one hour if the level of methemoglobin is still high one hour after the initial infusion (8).Dextrose containing fluids should be co-administered in order to increase NADPH formation. Injection ascorbic acid (300 to 1000 mg/day) may be useful which activates alternate minor pathway. Serial measurements of methemoglobin levels should be performed following treatment with MB as rebound methemoglobinemia may occur up to 18 hours after MB administration. The dose can be repeated hourly up to a maximum of 7mg/kg over 24hours (9). As observed in one of our patients, symptoms of dyspnea and depressed mental status improved within 30 minutes of MB injection. Caution should be exercised to avoid over dosage (>7 mg/kg) because cumulative doses of MB can cause dyspnea, chest pain, hemolysis and paradoxical methemoglobinemia in some susceptible subjects.Methylene blue should not be administered to patients with known glucose 6-phosphate dehydrogenase (G6PD) deficiency.
Severe methemoglobinemia (MetHb>70%) is usually fatal, as evidenced in our first case though survival has been reported with a MetHb level of 80% in our case2 and previous reports (4,10).
In case of unresponsive methemoglobinemia with MB, exchange transfusion or hyperbaric oxygen may be beneficial (5).

Conclusion:-
We conclude that every physician should be cautious in cases of poisoning with unknown chemical composition which may potentially cause fatal complications like methemoglobinemia. A high index of clinical suspicion of methemoglobinemia is required in all cases of unexplained cyanosis.

Consent:-
Written informed consent was obtained from the patient's guardian/parent for the publication of this report.