The woman and her family have symptoms consistent with carbon monoxide poisoning, as their symptoms began when it started getting cold and they likely had increased use of gas appliances. A COHb level would be the most appropriate test to confirm this suspicion. The man was exposed to paint remover fumes in an enclosed space and is presenting with symptoms of CO poisoning. A COHb level would be helpful in this case to diagnose CO poisoning and guide management. Treatment for exposures from paint removers may need to continue longer than other sources due to longer half-life of carboxyhemoglobin formation. Severe metabolic acidosis is a potential complication of CO poisoning.

1. • A 43 y/o woman presents with a 3-week history of
intermittent headache, nausea, and fatigue. Her
husband and children also have similar symptoms.
They all were diagnosed with a viral syndrome by a
private doctor. The symptoms began when it started
to get cold. The symptoms are worse in the morning
and improve while she is at work. Her V/S: 123/75,
83, 37.0, O2 98%. PE – unremarkable. What is the
most appropriate next step to confirm your
suspicion?
a) A mono spot test
b) Nasal pharyngeal swab for influenza test
c) COHb level
d) Lead level

2. • A 35-year-old man presents complaining of
headache, weakness, nausea, and vomiting after
working with paint remover in an enclosed space.
Which of the following statements regarding
management of this patient’s problem is TRUE?
a) A special antidote kit is required
b) Carboxyhemoglobin level is not helpful in this case
c) Treatment must continue longer in patients with this
exposure than from other sources
d) The patient’s oxygen–hemoglobin dissociation curve is
shifted to the right
e) Severe metabolic acidosis may be present

3. Carbon Monoxide

4. Carbon Monoxide (CO)
• an odorless, colorless, tasteless gas
• produced by incomplete combustion of carbon
materials
• normally present in air at < 10 parts per million (ppm)
or less; toxicity begins at 100 ppm
• also an endogenous substance (normal breakdown of
heme)
• 200-250 times greater affinity for hemoglobin than O2
• reversible binding at the iron-porphyrin center of
hemoglobin, producing carboxyhemoglobin (COHb)

5. Sources of Carbon Monoxide
Automotive exhaust
Motorboat exhaust
Propane-fueled heaters
Wood- or coal-burning stoves or heaters
Structure fires
Gasoline-powered generators or motors
Natural gas–powered heaters/furnaces/generators
Methylene chloride
Forklifts

6. Pathophysiology
• Half-lives of COHb
– room air: 249 - 320 minutes
– 100% oxygen: 74 - 80 minutes
– methylene chloride exposure: up to 13 hours
• COHb level increase  relative anemia &
hypoxia
• There is a separate toxicity to carbon
monoxide irrespective of the level of COHb.

8. Pathophysiology
• 10-15% of CO is dissolved unbound into
plasma >>move>> intracellular
• CO inhibits cytochrome oxidase, interfering
with cellular respiration and ATP generation
 a relative uncoupling of oxidative
phosphorylation
 lactic acidosis

9. Pathophysiology
• Release of guanylate cyclase & nitric oxide 
endothelial dysfunction & vasodilatation 
hypotension
• Relative hypoxia + hypotension  ischemia-
reperfusion injury in cardiac myocytes, neuronal
tissue
• Rhabdomyolysis, acute myocardial infarction,
neuronal cell death
• Cells in the basal ganglia are particularly sensitive

10. Clinical Features
• Clinical presentation is highly variable
• Clinical scenarios:
– unconscious patient pulled from a house fire, or
from a running car in a closed garage
– the patient with "flu-like" symptoms
– the elderly person presenting with syncope and
ischemic ECG changes

11. Shannon: Haddad and Winchester's Clinical Management of Poisoning and Drug
Overdose, 4th ed.

12. Shannon: Haddad and Winchester's Clinical Management of Poisoning and Drug
Overdose, 4th ed.

13. • CO poisoning should always be in the dDx for
1. comatose patients
2. patients with mental status changes
3. patients with an elevated anion gap
metabolic acidosis or otherwise
unexplained lactic acidosis
• A comatose pt removed from a fire scene
should be assumed to have CO poisoning
until proven otherwise, even in the absence
of cutaneous or airway burns.

14. Diagnosis
• blood COHb levels (using co-oximetry )
• COHb serves as a marker of severity and helps
to stratify pts at risk for delayed sequelae
• SaO2 appear artificially high in routine ABG
• Correlation between arterial and venous
COHb levels is excellent  VBG sample
analyzed with co-oximetry is usually sufficient

15. Diagnostic Study Findings Associated with CO Poisoning
↑ COHb level (normal 0-5%; not correlate well w/
symptoms)
Artificially elevated oxyhemoglobin saturation using pulse
oximetry (higher than the saturation on the ABG, pulse
oximetry gap)
↑ lactate
↑ anion gap metabolic acidosis
↑ CPK (rhabdomyolysis > cardiac source)
↑ troponin (diffuse cardiac myonecrosis > focal CAD)
Variable ECG findings—ranges from normal to injury pattern
Bilateral globus pallidus lesions on MRI
Not recommend to rely solely on pulse co-oximeters to detect
CO poisoning

16. Neuroimaging
• CT brain: change in 12 h of CO exposure + LOC
• Symmetric low-density areas at globus
pallidus, putamen, caudate nuclei
• CT changes in 24 h  poor outcome
• Not influence patient management
• Reserved for patients who show poor
response or have an equivocal diagnosis
• MRI appears to be superior

17. www.learningradiology.com

18. Bilateral hypodensity in the globus pallidus and hippocampal regions on admission CT.
Coric V et al. J Neurol Neurosurg Psychiatry 1998;65:245-
247
©1998 by BMJ Publishing Group Ltd

19. Other Tests
• Neuron-specific enolase or S100B and CSF
myelin basic protein are markers for CO
neurotoxicity
• More useful to determine prognosis than
diagnosis

20. Treatment
• Immediate removal from the contaminated
environment
• Initial resuscitation steps
• Supplemental oxygen (conc. ≈ FiO2 1.0)
immediately …and for at least 4 hours
• Severely poisoned pts >> continuous cardiac
monitoring, an IV line established, and an ECG
performed.

21. Hyperbaric Oxygen (HBO) Therapy
• Enhance elimination of COHb (reduces the half-
life to ≈ 30 min)
• Increases amount of dissolved O2 in plasma
• Reduces CO binding to other heme-containing
proteins
• Questionable benefit over normobaric oxygen
• May reduce incidence of neurologic sequelae
• The question of who will benefit most, and when
to refer, remains controversial.

22. Commonly Utilized Indications for Referral for
Hyperbaric Oxygen Treatment
Syncope
Confusion/altered mental status
Seizure
Coma
Focal neurologic deficit
Pregnancy with COHb level >15%
Blood level >25%
Evidence of acute myocardial ischemia
Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 7th ed.

23. HBO Therapy
• The patient needs to be clinically stable (+
secure airway, stable hemodynamic) before
referral or transport for HBO.
• Complications:
– Pneumothorax
– Barotrauma to the ears
– Seizures from oxygen toxicity (usually with
prolonged or multiple treatments)
– Gas embolism

25. Disposition Considerations
Symptom Severity Disposition Comments
Minimal or no Home Assess safety issues
symptoms
Headache Home after Administer 100% O2 in ED
Vomiting symptom Observe 4 h
Elevated CO level resolution Assess safety issues
Ataxia, seizure, Hospitalize Administer 100% O2 in ED
syncope, chest Consult with CO level, comorbid
pain, focal hyperbaric conditions—including
neurologic deficit, specialist pregnancy—and age; stability
dyspnea, ECG of the patient must be
changes considered if considering
transfer for hyperbaric
oxygen
Tintinalli's Emergency Medicine: A Comprehensive Study Guide, 7th ed.

26. Special Populations
• Children:
– more susceptible (↑fetal hemoglobin,
↑metabolic rate)
– HBO - good safety profile
• Elderly:
– higher risk from poisoning (esp. serious comorbid)
– CAD – low COHb (4-6%) can cause ECG changes &
myocardial ischemia

27. Special Populations
• Pregnant pts:
– HBO therapy if they meet criteria or if there are
signs of fetal distress
– Normobaric oxygen therapy should be prolonged
(slower elimination of CO from the fetus)

28. Thank You

29. • A 43 y/o woman presents with a 3-week history of
intermittent headache, nausea, and fatigue. Her
husband and children also have similar symptoms.
They all were diagnosed with a viral syndrome by a
private doctor. The symptoms began when it started
to get cold. The symptoms are worse in the morning
and improve while she is at work. Her V/S: 123/75,
83, 37.0, O2 98%. PE – unremarkable. What is the
most appropriate next step to confirm your
suspicion?
a) A mono spot test
b) Nasal pharyngeal swab for influenza test
c) COHb level
d) Lead level

30. • A 35-year-old man presents complaining of
headache, weakness, nausea, and vomiting after
working with paint remover in an enclosed space.
Which of the following statements regarding
management of this patient’s problem is TRUE?
a) A special antidote kit is required
b) Carboxyhemoglobin level is not helpful in this case
c) Treatment must continue longer in patients with this
exposure than from other sources
d) The patient’s oxygen–hemoglobin dissociation curve is
shifted to the right
e) Severe metabolic acidosis may be present