TOXICOLOGY
■ Recently approved as an antidote for cyanide poisoning in the United
States
■ It reacts with CN to form cyanocobalamin (vitamin B 12 ), a nontoxic
compound which is readily excreted in urine.
■ It may replace the cyanide antidote package in the future due to its
ease of use and improved risk profile.Hydrogen SulfideHydrogen sulfide (H 2 S) is a gas formed as a byproduct of organic decomposi-
tion. It has a very strong, distinct “rotten egg” odor.Sources of H 2 S include:
■ Sewer or manure gas
■ Chemical or industrial processes, such as tanning, rubber vulcanizing,
mining, and manufacture of paper, silk, rayon, refrigerants, soap, and
petroleum products
■ Natural sources include hot springs and volcanic eruptions.MECHANISM/TOXICITY
■ H 2 S is a stronger inhibitor of cytochrome oxidase than CN →disruption
of oxidative phosphorylation →cellular hypoxia and lactic acidosis.
■ Spontaneously dissociatesfrom cytochrome oxidase
■ Direct mucous-membrane irritantSYMPTOMS/EXAM
■ Severity of symptoms depends on the concentration and duration of expo-
sure. Low concentration exposure may only produce mild mucous mem-
brane irritation. Brief exposures to very high concentrations can cause
immediate loss of consciousness.
■ Mucous membrane irritation: Conjunctivitis, rhinitis, bronchorrhea, pul-
monary edema
■ Headache, seizures, loss of consciousness, coma
■ Hypotension, bradycardia, dysrhythmias, cardiac arrest
■ N/VDIAGNOSIS
■ H 2 S poisoning should be considered in any patient presenting with rapid
onset of coma, shock, and marked lactic acidosis.
■ Clues to the diagnosis include:
■ Relevant occupational setting
■ Odor of rotten eggs at scene
■ Evidence of decreased tissue extraction of O 2 :
■ Arterial appearance of venous blood
■ Elevated measured venous O 2 saturation (>90%)
■ Marked lactic acidosis
■ Blood levels of sulfide and thiosulfate can serve as markers of H 2 S expo-
sure, but are not readily available in most clinical laboratories.TREATMENT
■ Acute stabilization as required
■ Administer 100% O 2.Sewer or manure gas
exposure? Rotten egg odor?
Think hydrogen sulfide
toxicity.Hydrogen sulfide toxicity:
Rapid coma, shock, and lactic
acidosis (as with CN);
spontaneous improvement
after exposure is ended