0071643192.pdf

TOXICOLOGY

Carbon Monoxide

Carbon monoxide (CO) is an odorless and colorless gas produced by incom-
plete combustion of fuels or organic material.

Common sources of CO include vehicle exhaust, ovens, house fires, fur-
naces, and portable generators.

Methylene chloride, a solvent found in paint removers, degreasers, and other
similar products, is metabolized in vivo to CO following absorption.

MECHANISM/TOXICITY

■ Binds to hemoglobin →carboxyhemoglobin (COHb), which is incapable
of carrying O 2 →impaired O 2 delivery, cellular hypoxia, lactic acidosis
■ Shifts the oxyhemoglobin dissociation curve to left →↓release of O 2 to
tissues from normal hemoglobin
■ Binds to heme groups in mitochondira and triggers oxidative injury
■ CO has even greater affinity for fetal hemoglobin →higher fetal levels
and toxicity for any given maternal exposure.

SYMPTOMS/EXAM

The symptoms and signs of CO toxicity are vague and nonspecific, and, if not
severe, will resolve shortly after removal from CO source.

■ Headache, dizziness, weakness
■ Tachycardia, chest pain
■ Dyspnea
■ Nausea/vomiting (no diarrhea)
■ Confusion, memory impairment (delayed)
■ In severe cases: Myocardial ischemia, seizures, syncope, coma, cardiac
arrest

DIAGNOSIS

■ Direct measurement of COHb in either arterial or venous blood via co-
oximetry
■ Normal nonsmoker = 2–3%
■ Smokers = <10%.
■ Pulse oximetry cannotdistinguish COHb from oxyhemoglobin.
■ Expected ABG findings:
■ Normal PaO 2 (measuring dissolved O 2 )
■ Metabolic acidosis (from lactateaccumulation)
■ NormalcalculatedO 2 saturation (calculated from PaO 2 )

TREATMENT

■ Removal of the patient from CO source
■ Acute stabilization as required
■ Administration of 100%O 2 :
■ Reduces the elimination half-life of CO from approximately 4–5 hours
(room air) to 1 hour
■ Continue until COHb level is ≤5%.
■ Hyperbaric O 2 (HBO)
■ Further reduces the elimination half-life of CO to 20–30 minutes
■ Indications are listed in Table 6.20.

The solvent methylene

chloride is metabolized to

carbon monoxide after

absorption.

CO poisoning:

Normal pulse oximetry

ABG with metabolic acidosis

and normal PaO 2

Elimination half life of CO

Room air: 4–5 hours

100% O 2 : 1 hour

Hyperbaric O 2 :

20–30 minutes