Cyanide toxicity

Background

Older cyanide kit with potential to cause metHgb which potentially problem as patient may have CO as well

Newer CyanoKit safer (but very expensive) without significant adverse rxn

PATHOPHYSIOLOGY

-glucose metabolized to pyruvate yields 2 ATP by anaerobic glycolysis. No O2 needed.

- pyruvate then enters Kreb cycle and with O2, yields 36 more ATP. Requires function of mitochondrial electron xport system, the last step of which transfers electrons to oxygen to form water.

- cyanide, hydrogen sulfide and carbon monoxide bind to and inhibit cytochrome part of electron xport chain.

- if pyruvate blocked from entering Krebs cycle, pyruvate metabolized to lactic acid- leads to lactic acidosis.

Diagnosis

-cn and h2s pts can’t extract o2 from blood. Po2 of venous blood similar to arterial blood. May diagnose cn poisoning by similar mixed venous o2 and arterial o2- get arterial and venous blood gases ana compare O2

- Venous PO2 = Arterial PO2

- lactic acidosis

- nl SaO2

Treatment

- goal is to remove cn from cytochrome enzyme and bind cn to something else

- give amyl nitrite inhaler followed by iv sodium nitrite to make MetHb- methb bind to cn and pulls cn out of tissue into blood to make cyanomethemoglobin.

- dose of sodium nitrite is 10cc of 3% soln over 2- 4 min. Ped dose is 0.2cc.kg. May cause hypotension if given too fast. Will generate methb level of 8%.

- if cn present, will rapidlly be converted to cnmethb. Lack of measurable methb levels p iv Na nitrite confirms cn presence.

- once cnmethb in blood, give sodium thiosulfate 12.5 gm (50 cc of 25% soln of 5X vol of na nitrite). Sulfur will bind with cn to make thiocyanate which is nontoxic and renally excreted.

-consider retreatment of incomplete response or oral cn poisoning with ongoing absorption.

- can also use vit b12 hydroxycobalamin to make cyanocobalamine

TREATMENT

- amyl nitrite inhaler

- then iv sodium nitrite

-> 10cc of 3% over 2- 4 min.(0.2cc/kg in peds)

- then sodium thiosulfate 12.5 gm (50 cc of 25% soln of 5X vol of na nitrite)

-follow methemoglobn levels

- also consider hydroxycobalamin

CO/CN Combined Poisoning

-if pt has co poisoning already and is given cn antidote and methb make, two dyshemoglobins cohb and methb will further inhibit o2 carriage.

- cn poisoning correlated with lactate level > 10mmol/L

- sodium thiosulfate given alone is safe without alteration of o2 carrying capacity of nitrites. Consider emperic tx c 12.5 mg to all smoke inhalation victims with hypotension, acidosis, or CV collapse.

CO/CN COMBINED POISONING

- sodium thiosulfate given alone (no alteration O2 carrying capacity)

-> consider emperic tx (12.5 mg) for smoke inhalation victims with

hypotension, acidosis, or CV collapse

-> See also Trauma: Burns (Severe)

See Also

Tox: Hydrogen Sulfide

Source

Pani

8/07 DONLDSON (adapted from Sandness, Mistry)