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Charles Gomersall & Carolyne Chau
Mode
of poisoning
- inhalation
of hydrogen cyanide gas
- combustion product of cyanide containing products
- plastics
- glue removers
- wool, silk, nylon
- various seeds and plants
- chemical weapon
- sodium
nitroprusside infusion
- absorption
of cyanide-containing solutions or gas through skin
Mechanism
of toxicity
- binds
to cellular cytochrome oxidase and interferes with cellular respiration
Pharmacology
- metabolized
to less toxic metabolite thiocyanate (renally excreted)
- small
proportion chelated by hydroxycobalamin
Clinical
features
- onset of cell toxicity very rapid
- early
manifestations:
- anxiety,
confusion
- dyspnoea
- headache
- tachycardia
- hypertension
- rapidly
progresses to:
- stupor,
coma
- fits
- fixed,
dilated pupils
- hypoventilation
- hypotension,
cardiovascular collapse
- bradycardia,
heart block, ventricular arrhythmias
- odour of bitter almonds. However ability to detect this is genetically
determined and therefore sign is unreliable
- venous
blood looks the colour of arterial blood
- hallmarks of severe cyanide toxicity are persistent hypotension and
academia despite adequate arterial oxygenation
Investigations
- severe
lactic acidosis
- high
mixed venous saturation
Treatment
- 100% O2 but mainstay of treatment
is early use of antidotes
- amyl
nitrite
- induces
formation of methaemoglobin. Cyanide has high affinity for ferric
iron in methaemoglobin and as a result methaemoglobin is an
effective scavenger of unbound cyanide
- administration
by inhalation of crushable pearls: inhale for 15-30 sec with rest of
30 sec between inhalations. One pearl lasts ~2-3 mins. Aim for
methaemoglobin of ~5%
- sodium nitrite 300mg over 10 mins to provoke formation of
methaemoglobinaemia (scavenger for hydrogen cyanide )
- sodium thiosulphate 150 mg/kg IV followed by infusion of 30-60 mg/kg/h to
convert cyanide to thiocyanate. Risk of thiocyanate toxicity, particularly in
the presence of renal insufficiency. Thiocyanate readily dialyzable.
- cobalt ethylenediaminetetraacetic acid 600 mg IV over 1 min, accompanied
by glucose 50% 25 ml, followed by
another 300 mg if there is no response. Chelates cyanide.
- hydroxycobalamin
4-5 g IV. Not approved for use in cyanide toxicity in USA
- gastric
lavage followed by activated charcoal
- induced
emesis not recommended
- for cyanide poisoning due to smoke inhalation, most
authorities recommend use of thiosulfate, oxygen, and supportive measures and
recommend reserving nitrites for patients who are hypotensive, acidemic, or
comatose
- sodium bicarbonate for metabolic acidosis
- attendant staff must not undertake expired air resuscitation
Further
reading
Mokhlesi B. Adult toxicology in critical care. Part II:
specific poisonings. Chest 2003; 123:897-922
© Charles Gomersall & Carolyne Chau March 2005 |
