Carbon monoxide poisoning

Question 1

3 mechanisms of CO toxicity

Answer 1

1. formation of carboxyhemoglobin (no O2 carrying capacity)
2. shifts oxyhemoglobin curve to the left (impairs offloading)
3. interferes with cellular respiration by binding to mitochondrial cytochrome oxidase (increased binding during hypotension and hypoxia)

Question 2

What are sources of carbon monoxide (5)

Answer 2

Incomplete combustion of all carbon-containing products:
Car, boat, pickup truck beds
Propane powered equipment in enclosed space
Indoor burning stoves: wood, charcoal, natural gas for cooking and heating
Use of kitchen stoves as extra source of heat
Indoor use of charcoal burning grills, generators
Fires

Question 3

What is the comparative affinity of CO for hemoglobin?

Answer 3

250 x that of oxygen

Question 4

What are symptoms of acute CO toxicity

Answer 4

CNS: headache, dizziness, confusion, depressed LOC, coma, seizures, hallucinations
CVS: hypotension, tachycardiac, cardiac arrest, palpatations, SOB, hyperthermia
GI: N/V, abdominal pain
Metabolic: WAGMA, lactate incr

Question 5

What are delayed symptoms of CO toxicity:

Answer 5

focal neurologica deficits
seizures
psychiatric or cognitive changes
“Executive functioning” dementia, amnestic syndromes, psychosis, parkinsonism, paralysis, chorea
-	Adults >> peds

Question 6

What are normal levels of CO?

Answer 6

0-5%, smokers 6-10%

higher in neonates, patients with hemolytic anemia

Question 7

What are necessary investigations

Answer 7

CO level, ECG, pregnancy test

Question 8

Management?

Answer 8

100% FiO2

+/- hyperbaric oxygen

Question 9

What are indications for hyperbaric O2 in carbon monoxide toxicity?
(talk to hyperbaric O2 specialist, can vary by centre)

Answer 9

Evidence of end-organ damage
o	Neuro: LOC, coma, sz, confusion or altered mental status, ataxia
o	Abnormal cellular function: Cardiac ischemia, arrythmias
o	Prolonged CO exposure > 24 hours
o	Fetal distress in pregnancy
COHb levels
o	>25% in adult
o	>15% in pregnant or peds
Possible indications:
o	Inability to oxygenate
o	Metabolic acidosis
o	Abnormal neuropsych exam

Question 10

What are complications of hyperbaric oxygen

Answer 10

oxygen induced seizures (1/1000)

barotrauma

Question 11

What is the half life of COHb at

1. room air
2. 100% FiO2
3. hyperbaric O2

Answer 11

Room air: 5 hours
100% FiO2: 90 minutes
HBOT: 30 minutes

Question 12

How to determine CO level?

Answer 12

ABG

Question 13

What are associated findings on imaging of CO toxicity?

Answer 13

CT head: bilateral hypodensities in globus pallidus, internal capsule

Question 14

Non CNS/CVS CO toxicity? (4)

Answer 14

Pulmonary edema
Rhabdo, compartment syndrome
Retinal hemorrhages
Cutaneous bullae

Question 15

What 2 systems does CO toxicity affect most and why?

Answer 15

Brain and Cardiac
high O2 consumption
worst outcomes with decreased O2 delivery and utilization

Question 16

Why does CO toxicity cause cardiac dysfunction?

Answer 16

high affinity for cardiac myoglobin