Pathogenesis
- Oxidisation of the haem of haemoglobin by free radicals or things like hydrogen peroxide and nitric oxide.
- Shifts O2 dissociation curve to the left.
Causes
- Hereditary / Congenital: Hb and NADH-MetHb reductase deficiency
- Acquired:
* Medications eg. Amyl nitrite, Benzocaine, Dapsone, Lidocaine, Nitroglycerin, Nitroprusside, Phenacetin, Phenazopyridine, Prilocaine, Quinones, Sulfonamides (eg. sulfamethoxazole). Chloroquine.
* Chemical agents eg. Aniline dye derivatives (shoe dyes, inks) Butyl nitrite, Chlorobenzene, Nitrate-containing foods, Isobutyl nitrite, Naphthalene, Nitrophenol, Nitrous gases, Silver nitrate, and Trinitrotoluene. Sodium nitrite - used in food preservation.
Signs & Symptoms
- chocolate brown discoloration of the blood.
- SaO2 readings go crazy
0-10% - Features unlikely
10-30%- Mild effects
Blue-grey ‘apparent’ central cyanosis, fatigue, dizziness, headaches
30-50% - Moderate effects – weakness, tachypnoea, tachycardia
50-70% - Severe effects
stupor, coma, convulsions, respiratory depression, cardiac arrhythmias, acidosis
> 70% - Potentially fatal
Treatment
<20% - nothing
20 - 30% - oxygen therapy
>30% - methylene blue
1-2 mg/kg IV over 5 minutes - 1% (10mg/ml solution)
repeat up to 7 mg/kg
SpO2 normally dives as you give the methylene blue.
Recheck levels after an hour
Interesting Note
Hydrogen sulfide poisoning is similar to cyanide poisoning and can be treated by inducing metHb.
References
http://stemlynsblog.org/feeling-blue-at-st-emlyns/
http://www.rcemlearning.co.uk/modules/papa-smurf-has-a-seizure/
http://emergencymedicineireland.com/2011/07/why-methaemoglobinaemia-is-a-good-thing/
http://emergencymedicineireland.com/2011/07/why-methaemoglobinaemia-is-a-bad-thing/
- Oxidisation of the haem of haemoglobin by free radicals or things like hydrogen peroxide and nitric oxide.
- Shifts O2 dissociation curve to the left.
Causes
- Hereditary / Congenital: Hb and NADH-MetHb reductase deficiency
- Acquired:
* Medications eg. Amyl nitrite, Benzocaine, Dapsone, Lidocaine, Nitroglycerin, Nitroprusside, Phenacetin, Phenazopyridine, Prilocaine, Quinones, Sulfonamides (eg. sulfamethoxazole). Chloroquine.
* Chemical agents eg. Aniline dye derivatives (shoe dyes, inks) Butyl nitrite, Chlorobenzene, Nitrate-containing foods, Isobutyl nitrite, Naphthalene, Nitrophenol, Nitrous gases, Silver nitrate, and Trinitrotoluene. Sodium nitrite - used in food preservation.
Signs & Symptoms
- chocolate brown discoloration of the blood.
- SaO2 readings go crazy
0-10% - Features unlikely
10-30%- Mild effects
Blue-grey ‘apparent’ central cyanosis, fatigue, dizziness, headaches
30-50% - Moderate effects – weakness, tachypnoea, tachycardia
50-70% - Severe effects
stupor, coma, convulsions, respiratory depression, cardiac arrhythmias, acidosis
> 70% - Potentially fatal
Treatment
<20% - nothing
20 - 30% - oxygen therapy
>30% - methylene blue
1-2 mg/kg IV over 5 minutes - 1% (10mg/ml solution)
repeat up to 7 mg/kg
SpO2 normally dives as you give the methylene blue.
Recheck levels after an hour
Interesting Note
Hydrogen sulfide poisoning is similar to cyanide poisoning and can be treated by inducing metHb.
References
http://stemlynsblog.org/feeling-blue-at-st-emlyns/
http://www.rcemlearning.co.uk/modules/papa-smurf-has-a-seizure/
http://emergencymedicineireland.com/2011/07/why-methaemoglobinaemia-is-a-good-thing/
http://emergencymedicineireland.com/2011/07/why-methaemoglobinaemia-is-a-bad-thing/
