Co the silent killer
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CO – “The Silent Killer”. Carbon Monoxide (CO) vs. Carbon Dioxide (CO 2 ). Incidence of CO poisoning. Leading cause of poisoning mortality. Most common cause of death in combustion related inhalation injury. 1000 to 2000 deaths / year ( USA ) Difficult diagnosis :

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Carbon monoxide co vs carbon dioxide co 2 l.jpg
Carbon Monoxide (CO) vs.Carbon Dioxide (CO2)

Incidence of co poisoning l.jpg
Incidence of CO poisoning

  • Leading cause of poisoning mortality.

  • Most common cause of death in combustion related inhalation injury.

  • 1000 to 2000 deaths / year ( USA )

  • Difficult diagnosis :

    • incidence of unrecognized cases higher

    • estimated > 42 000 visits / year

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Sources of CO

  • Motor vehicle exhaust

    • running engine in closed space

    • faulty exhaust systems

  • Propane gas -powered equipment

    • lift, water heater

  • Combustion for heating or cooking

    • camping equipment, heating systems

  • Smoke inhalation in fires

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  • Hemoglobin’s affinity for CO is 200 to 250 times its affinity for oxygen

  • CO binding to hemoglobin causes allosteric modifications increasing its affinity for oxygen

  • Shift of O2 dissociation curve to the left

  • Decreased tension at which O2 is released from hemoglobin

  • Less O2 delivery to the cells

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O2 Dissociation Curve

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Pathophysiology - Cellular level

  • 15 % of CO bound to extravascular heme-containing proteins

  • Cytochrome oxidase

    • alteration in ATP production

    • intracellular acidosis

    • persists after exposure

  • Cardiac and skeletal myoglobin

    • occuring at COHb 2 %

    • alteration in tissue O2 uptake

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Pathophysiology - Cardiovascular

  • Myocardial depression consequence of

    • hypoxic stress

    • CO binding to cardiac myoglobin

  • Arterial hypotension

    • myocardial depression

    • NO-related peripheral vasodilatation

  • LOC with reduction of cerebral perfusion

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Pathophysiology - Neurovascular

  • CO in circulation associated with massive increase in NO in perivascular tissues

  • NO released from vascular endothelial cells and platelets

  • Production of oxygen radicals from impaired mitochondrial function

  • Reaction NO with oxygen radicals to form peroxynitrite ( ONOO- )

  • Peroxynitrite binds to perivascular tissue proteins causing injury

  • Increased capillary permeability in CNS and pulmonary vascular beds

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Diagnosis - Symptoms

  • Most common symptoms :

    headache 91%

    dizziness 77%

    weakness 53%

    nausea 47%

    confusion 43%

    shortness of breath 40%

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visual changes 25%

chest pain 9%

loss of consciousness 6%

abdominal pain 5%

muscle cramping 5%

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  • The Delayed Neuropsychiatric Syndrome

    • Subacute manifestation (days to months)

    • Occurs in spite of normal HbCO levels

    • symptoms including : cognitive defects, personality changes, parkinsonism, amnesia, incontinence, gait disturbances, etc.

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Diagnosis - Signs

  • Physical exam signs

  • tachypnea, tachycardia, vestibular signs (Ataxia, motion sickness, Nystagmus, circling, head tilt, fall to one side) common

  • retinal hemorrhages uncommon but more specific

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  • Signs of smoke inhalation such as burn nasal hairs, injured mucous membranes, carbonaceous mucus discharge

  • “Classic” findings of cherry-red lips, skin, and mucus membranes are very rare.

    Note : - Young children (breath faster), elderly and household pets are usually effected first.

Diagnosis l.jpg

  • High level of clinical suspicion

  • Serum COHb level

  • Exhaled breath COHb level

  • Pulse oximetry cannot distinguish between HbO2 and COHb

  • Comprehensive neurological and neuropsychological assessment

  • CT brain to exclude other conditions

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Severity of CO intoxication

  • Inhaled CO concentration

  • Duration of exposure

  • Presence of systemic illnesses

    • cardiac and pulmonary diseases

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Clinical evaluation

  • Maintain a high level of suspicion

  • History of exposure can be absent

  • COHb

    • < 3 % non-smokers or < 10 % in smokers

  • ABG : metabolic acidosis ( lactate )

  • ECG : ischemia, arrythmias

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Pulse oximetry in CO poisoning

  • Unreliable with significant amount of abnormal Hb : MetHb, COHb

  • Pulse oximetry overestimates true fractional arterial oxygen saturation

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Neurologic evaluation

  • Neurologic examination

  • Neuroradiologic imaging : CT, MRI

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Carbon Monoxide AlarmYour best protection!

  • Install a carbon monoxide alarm close to sleeping areas. For more protection:

    • Install one in every bedroom

    • Install one on every level of your home

  • Never ignore a carbon monoxide alarm, IT COULD SAVE YOUR LIFE!

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EmergencyAlarm Sounds!

  • Get fresh air right away

  • Call local fire department

  • Do not re-enter an affected home until CO is gone

    • Fire department can determine when it is safe to re-enter a building

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Management of CO poisoning

  • Identify the source to correct the problem

  • Domestic exposition

    • verification of heating or cooking appliances

  • Occupational exposition

  • CO poisoning : mandatory reporting to public health services

  • Making the diagnosis can save lives !

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  • Oxygen 100 %

  • ABG

  • COHb

  • ECG

  • CXR

  • Cardiac enzymes

  • Cardiac monitoring

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Hyperbaric oxygen therapy

  • Enhanced elimination of COHb

  • Improved tissue oxygenation

  • Enhanced dissociation of CO from cytochrome oxidase

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Classic indications for HBO

  • Coma or loss of consciousness

  • Neurologic abnormalities

  • Cardiovascular dysfunction

  • Severe metabolic acidosis

  • COHb > 40 %

  • COHb > 15 %

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CO poisoning in pregnancy

  • High incidence of neurologic abnormalities and stillbirth after CO poisoning

  • Fetal Hb binds CO more avidly than Hb A

  • CO absorption and elimination slower in fetal circulation

  • HBO felt to be safe in pregnancy

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Prevention of CO poisoning

  • Public education about CO poisoning

  • Identification of activities at risk

  • Training of workers for proper use of propane-powered tools

  • Appropriate ventilation of confined places

  • Industrial and domestic use of CO detectors

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Problems in CO poisoning

  • Absence of reliable method to estimate prospectively the severity of CO poisoning

  • Difficulty in comparing results of studies because no staging in severity of disease