Carbon monoxide toxicity

Background

• can co-occur with HCN (cyanide) toxicity in certain fires like industrial fires
  • treat HCN with Sodium thiosulfate 12.5grams
• multiple pts from same building/car
• winter months

=Half-Life

• decreases from 5 hrs to 1 hr with 100% FiO2,
  • to 20 min 2.5 atm HBO.

Workup

1. ECG
2. CXR
3. CT Head
4. Pregnancy test

Diagnosis

1. Symptoms generally depend on CO level (i.e. carboxyhemoglobin)
   1. 20-40%
      1. CNS SX first... Dizziness, Headache, weakness, n/v, disturbed judgment, confusion, decreased visual acuity (Often misdiagnosed as 'Flu', 'viral syndrome.)
   2. 40-60%:
      1. CP, DOE, Tachycardia, tachypnea, ataxia, syncope, seizures
   3. >60%
      1. arrhythmias, hypotension, coma, death
2. To get CO level, ABG with carboxyhemoglobin level (this needs to be specifically requested; done by co-oximetry)
   1. Pulse Ox usually NORMAL.
   2. Need co-oximetry. Oxygen Sat gap, SpO2-SaO2 increases as COHb increases.
   3. mortality usually due to ventricular arrhythmias.

Treatment

1. Treat with 100% oxygen by tight-fitting mask or endotracheal tube
2. Measure CO level q2-4 hours until <10%
   1. smokers... COHb level up to 10%
   2. <5% is normal
   3. levels not predictive of outcome
   4. lactate more useful for inferring tissue hypoxia

Hyperbaric Tx^

Indications

1. sz, coma, focal deficit
2. COHb > 25%
3. COHb > 15% in pregnancy (fetal Hb has greater affinity for CO, and nml intrauterine Mt Everest makes CO poisoning very toxic to fetus)
4. myocardial ischemia, arrhythmias

^Hyperbaric treatment is of contraversial utility (3 days of 100% FiO2 may be equivalent to hyperbaric)

Disposition

Admit

1. all symptomatic CO poisonings
2. all > 20%

Gas company and Fire Dept will test home/work environments.

Source

Tibbles, PM et al. NEJM. Hyperbaric oxygen Rx. 1996.

Scheinkestel, C. Med J Aust. 1999. 170: 2203-2210.