carbon monoxide poisoning

CO Poisoning

Cause

Carbon monoxide, a colorless and odorless gas, can be potentially fatal after exposure if not properly diagnosed and treated. Carbon monoxide poisoning is associated with:

  • Automobile exhaust
  • Inadequately ventilated heaters (hence most commonly occurring in the winter)
  • Methylene chloride ingestion (converts to CO hepatically)

Pathophysiology

Carbon monoxide has several pathophysiological consequences on oxygen transport and utilization:

  • Carbon monoxide binds to heme with 240x the affinity of oxygen forming carboxyhemoglobinemia
  • Allosteric changes of the heme moiety prevent oxygen unloading peripherally
  • CO binds to various proteins affecting oxidative phosphorylation

Symptoms

In addition to a history consistent with CO exposure, patients with mild CO poisoning present with:

  • Headache (most common symptom)
  • Viral-like symptoms (e.g. dizziness, nausea, vomiting, malaise)
  • Altered mental status

Patients severely exposed to carbon monoxide typically present with:

  • Neuropsych symptoms: seizures, delirium
  • Cardiology symptoms: myocardial ischemia, arrhythmias
  • **Mortality **

Physical exam signs of carbon monoxide toxicity may include:

  • Tachycardia
  • Pallor or Cherry-red skin
  • Memory disturbance
  • Neuropsychiatric: emotional lability, impaired judgment
  • Pulmonary edema

Diagnosis

The diagnosis of carbon monoxide poisoning is dependent upon:

  • History
  • Physical exam
  • Arterial blood gases demonstrating elevated carboxyhemoglobin levels

Following the diagnosis of carbon monoxide poisoning, an electrocardiogram is recommended to detect for ischemia as myocardial infarction is a common complication.

Carboxyhemoglobin shifts the oxygen dissociation curve to the left, impairing the ability of heme to unload oxygen at the tissue level. This results in tissue hypoxia. The kidney responds to tissue hypoxia by producing more erythropoietin (EPO). EPO stimulates the bone marrow to differentiate more red blood cells. Chronic CO toxicity is a cause of secondary polycythemia.

Chronic tobacco smokers may have up to 15% carboxyhemoglobin at baseline.

Carbon monoxide saturation levels above 40% is considered to be severe exposure, whereas levels above 55% can potentially be fatal.

Management

The management of carbon monoxide poisoning includes:

  • Removal from the carbon monoxide source
  • 100% high-flow oxygen or a hyperbaric oxygen chamber (decreases the half life of CO)
  • Intubate if necessary