All EMS presentations
EnvironmentalClinical presentation

Carbon monoxide exposure

A streamlined, differential-led presentation for rapid clinical review.

Clinical snapshot

Twenty-second review

  • Carbon monoxide binds hemoglobin and impairs oxygen delivery and cellular respiration, causing headache, nausea, confusion, ischemia, and delayed neurologic injury.
  • Syncope, chest pain, neurologic deficit, pregnancy, severe headache, altered LOC, or multiple affected people requires high-flow oxygen and urgent assessment.
  • Keep viral illness or migraine in the differential; overlapping or concurrent illness remains possible.
  • For carbon monoxide exposure, trends and combinations of findings are more informative than one isolated vital sign.
Differentials

Compare the clinical patterns

The repeated material is grouped inside each possibility. Open only the condition you need.

Serious2 conditions
Severe poisoningTime-sensitive high-risk possibility

HPI

Clarify source and duration; others symptomatic; headache, nausea or confusion.

Signs & symptoms

Syncope, ischemia, neurologic change, acidosis, burns, or airway findings.

Focused exam

Expose appropriately, assess core temperature when available, inspect skin, and look for trauma or multisystem involvement; Reassess after decontamination, warming, cooling, or oxygen support.

Brief pathophysiology

Severe poisoning may cause carbon monoxide exposure through a time-sensitive process capable of rapid physiological deterioration.

Vital-sign pattern

What the trend may show

Possible pattern

Standard pulse oximetry can appear normal in carbon-monoxide poisoning. Exposure history, neurologic findings, ECG, and definitive co-oximetry matter more than the displayed SpO₂.

Oxygen saturation (SpO₂)

May appear normal

Standard SpO₂ cannot distinguish oxyhemoglobin from carboxyhemoglobin.

Heart rate (bpm)

May rise

Tachycardia can reflect tissue hypoxia or physiologic stress.

Respiratory rate (breaths/min)

May rise

Tachypnea may occur, but a normal rate does not exclude toxicity.

Blood pressure (mmHg)

Variable

Pressure may be preserved; hypotension suggests severe poisoning or another injury.

Front-load in the triage report

  • Severe poisoning: Syncope, ischemia, neurologic change, acidosis, burns, or airway findings.
  • Source and duration?
  • Others symptomatic?
Associated fire injuryTime-sensitive high-risk possibility

HPI

Clarify others symptomatic; headache, nausea or confusion; enclosed-space exposure.

Signs & symptoms

Syncope, ischemia, neurologic change, acidosis, burns, or airway findings.

Focused exam

Reassess after decontamination, warming, cooling, or oxygen support; Ensure scene safety; assess co-exposed persons, source, duration, neurologic and cardiac findings, pregnancy, burns, and inhalation injury.

Brief pathophysiology

Associated fire injury may cause carbon monoxide exposure through a time-sensitive process capable of rapid physiological deterioration.

Vital-sign pattern

What the trend may show

Possible pattern

Standard pulse oximetry can appear normal in carbon-monoxide poisoning. Exposure history, neurologic findings, ECG, and definitive co-oximetry matter more than the displayed SpO₂.

Oxygen saturation (SpO₂)

May appear normal

Standard SpO₂ cannot distinguish oxyhemoglobin from carboxyhemoglobin.

Heart rate (bpm)

May rise

Tachycardia can reflect tissue hypoxia or physiologic stress.

Respiratory rate (breaths/min)

May rise

Tachypnea may occur, but a normal rate does not exclude toxicity.

Blood pressure (mmHg)

Variable

Pressure may be preserved; hypotension suggests severe poisoning or another injury.

Front-load in the triage report

  • Associated fire injury: Syncope, ischemia, neurologic change, acidosis, burns, or airway findings.
  • Others symptomatic?
  • Headache, nausea or confusion?
Common1 condition
Mild CO poisoningCommon presentation pattern

HPI

Clarify source and duration; others symptomatic; headache, nausea or confusion.

Signs & symptoms

Headache, nausea, and dizziness shared by co-occupants may suggest exposure.

Focused exam

Expose appropriately, assess core temperature when available, inspect skin, and look for trauma or multisystem involvement; Reassess after decontamination, warming, cooling, or oxygen support.

Brief pathophysiology

Mild CO poisoning may explain the presenting symptoms through a common clinical mechanism, while serial assessment checks for complications or an alternate cause.

Vital-sign pattern

What the trend may show

Possible pattern

Standard pulse oximetry can appear normal in carbon-monoxide poisoning. Exposure history, neurologic findings, ECG, and definitive co-oximetry matter more than the displayed SpO₂.

Oxygen saturation (SpO₂)

May appear normal

Standard SpO₂ cannot distinguish oxyhemoglobin from carboxyhemoglobin.

Heart rate (bpm)

May rise

Tachycardia can reflect tissue hypoxia or physiologic stress.

Respiratory rate (breaths/min)

May rise

Tachypnea may occur, but a normal rate does not exclude toxicity.

Blood pressure (mmHg)

Variable

Pressure may be preserved; hypotension suggests severe poisoning or another injury.

Front-load in the triage report

  • Headache, nausea, and dizziness shared by co-occupants may suggest exposure.
  • Source and duration?
  • Others symptomatic?
Mimics2 conditions
Viral illnessImportant alternative presentation

HPI

Clarify source and duration; others symptomatic; headache, nausea or confusion.

Signs & symptoms

Similar symptoms may occur, but clustered location-based illness is a key clue.

Focused exam

Expose appropriately, assess core temperature when available, inspect skin, and look for trauma or multisystem involvement; Reassess after decontamination, warming, cooling, or oxygen support.

Brief pathophysiology

Viral illness can resemble carbon monoxide exposure through overlapping symptoms or referred physiology despite a different primary mechanism.

Vital-sign pattern

What the trend may show

Possible pattern

Standard pulse oximetry can appear normal in carbon-monoxide poisoning. Exposure history, neurologic findings, ECG, and definitive co-oximetry matter more than the displayed SpO₂.

Oxygen saturation (SpO₂)

May appear normal

Standard SpO₂ cannot distinguish oxyhemoglobin from carboxyhemoglobin.

Heart rate (bpm)

May rise

Tachycardia can reflect tissue hypoxia or physiologic stress.

Respiratory rate (breaths/min)

May rise

Tachypnea may occur, but a normal rate does not exclude toxicity.

Blood pressure (mmHg)

Variable

Pressure may be preserved; hypotension suggests severe poisoning or another injury.

Front-load in the triage report

  • Similar symptoms may occur, but clustered location-based illness is a key clue.
  • Source and duration?
  • Others symptomatic?
MigraineImportant alternative presentation

HPI

Clarify others symptomatic; headache, nausea or confusion; enclosed-space exposure.

Signs & symptoms

Similar symptoms may occur, but clustered location-based illness is a key clue.

Focused exam

Reassess after decontamination, warming, cooling, or oxygen support; Ensure scene safety; assess co-exposed persons, source, duration, neurologic and cardiac findings, pregnancy, burns, and inhalation injury.

Brief pathophysiology

Migraine can resemble carbon monoxide exposure through overlapping symptoms or referred physiology despite a different primary mechanism.

Vital-sign pattern

What the trend may show

Possible pattern

Standard pulse oximetry can appear normal in carbon-monoxide poisoning. Exposure history, neurologic findings, ECG, and definitive co-oximetry matter more than the displayed SpO₂.

Oxygen saturation (SpO₂)

May appear normal

Standard SpO₂ cannot distinguish oxyhemoglobin from carboxyhemoglobin.

Heart rate (bpm)

May rise

Tachycardia can reflect tissue hypoxia or physiologic stress.

Respiratory rate (breaths/min)

May rise

Tachypnea may occur, but a normal rate does not exclude toxicity.

Blood pressure (mmHg)

Variable

Pressure may be preserved; hypotension suggests severe poisoning or another injury.

Front-load in the triage report

  • Similar symptoms may occur, but clustered location-based illness is a key clue.
  • Others symptomatic?
  • Headache, nausea or confusion?
Red flags

Findings that should escalate concern

  • Syncope
  • Neurologic symptoms
  • Pregnancy
  • Cardiac symptoms
  • Syncope, chest pain, neurologic deficit, pregnancy, severe headache, altered LOC, or multiple affected people requires high-flow oxygen and urgent assessment.
  • Severe poisoning or associated fire injury: Syncope, ischemia, neurologic change, acidosis, burns, or airway findings.
Related EMS presentations

Continue the clinical pathway

NeurologicAltered LOC / confusionGeneral MedicalNausea / vomitingNeurologicHeadacheTraumaBurnsEnvironmentalChemical exposure
References

Clinical and academic sources

Curated clinical guidance and peer-reviewed evidence supporting this presentation. Current BCEHS guidance, medical direction, and local policy remain authoritative for practice.

BCEHS Handbook — specific CPGs

  1. J02: Carbon MonoxideBC Emergency Health Services Handbook

    Official BCEHS clinical practice guidance for carbon monoxide.

Supporting clinical and academic evidence

  1. CEDIS Presenting Complaint List updateCanadian Association of Emergency Physicians

    Presenting-complaint terminology and categorization context. It does not establish a prehospital “top 100” ranking.

  2. Clinical Guidance for Carbon Monoxide PoisoningUS Centers for Disease Control and Prevention

    Carbon monoxide exposure assessment and the limitation of conventional two-wavelength pulse oximetry.

  3. Clinical Practice Guideline SummariesWilderness Medical Society

    Evidence-based guidance for environmental and wilderness emergencies, including heat, cold, altitude, and drowning.

  4. S2k guideline diagnosis and treatment of carbon monoxide poisoningGerman Medical Science · 2021

    CO exposure recognition, co-oximetry, oxygen therapy, neurologic risk, and consultation for hyperbaric care.