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.

1/2 life of COHb:

decreases from 5 hrs to 1 hr with 100% FiO2,

to 20 min 2.5 atm HBO.

1. Symptoms generally depend on CO level (i.e. carboxyhemoglobin)

20-40%:

CNS SX first... Dizziness, Headache, weakness, n/v, disturbed judgment, confusion, decreased visual acuity.

Often misdiagnosed as 'Flu', 'viral syndrome.'

40-60%: CP, DOE, Tachycardia, tachypnea, ataxia, syncope, seizures

>60%: arrhythmias, hypotension, coma, death

2. To get CO level, ABG with carboxyhemoglobin level (this needs to be specifically requested; done by co-oximetry)

Pulse Ox usually NORMAL.

Need co-oximetry. Oxygen Sat gap, SpO2-SaO2 increases as COHb increases.

mortality usually due to ventricular arrhythmias.

1. Treat with 100% oxygen by tight-fitting mask or endotracheal tube

2. Measure CO level q2-4 hours until <10%.

smokers... COHb level up to 10%.

<5% is normal.

levels not predictive of outcome.

lactate more useful for inferring tissue hypoxia.

indications for HBO...

sz, coma, focal deficit

COHb > 25%

COHb > 15% in pregnancy (fetal Hb has greater affinity for CO, and nml intrauterine Mt Everest makes CO poisoning very toxic to fetus)

myocardial ischemia, arrhythmias

recently...double-blind sham controlled study by...

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

Questions the HBO benefit\risk for CO. 3 days of 100% FiO2 (NBO) is equivalent to hyperbaric (2-3 atmospheres); severe poisoning.

admit

all symptomatic CO poisonings.

all > 20%.

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

ECG, CXR, CT Head in all pts.

ICON.

4 randomized HBO trials. two showed benefit, two showed no benefit. however, only at mild cases.

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