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CO – “The Silent Killer”

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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CO – “The Silent Killer”

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  1. CO – “The Silent Killer”

  2. Carbon Monoxide (CO) vs.Carbon Dioxide (CO2)

  3. 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

  4. 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

  5. Pathophysiology

  6. Pathophysiology • 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

  7. O2 Dissociation Curve

  8. 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

  9. 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

  10. 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

  11. Diagnosis - Symptoms • Most common symptoms : headache 91% dizziness 77% weakness 53% nausea 47% confusion 43% shortness of breath 40%

  12. Cont… visual changes 25% chest pain 9% loss of consciousness 6% abdominal pain 5% muscle cramping 5%

  13. Cont… • 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.

  14. 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

  15. Cont… • 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.

  16. Diagnosis • 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

  17. Severity of CO intoxication • Inhaled CO concentration • Duration of exposure • Presence of systemic illnesses • cardiac and pulmonary diseases

  18. 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

  19. Pulse oximetry in CO poisoning • Unreliable with significant amount of abnormal Hb : MetHb, COHb • Pulse oximetry overestimates true fractional arterial oxygen saturation

  20. Neurologic evaluation • Neurologic examination • Neuroradiologic imaging : CT, MRI

  21. 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!

  22. 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

  23. 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 !

  24. Cont… • Oxygen 100 % • ABG • COHb • ECG • CXR • Cardiac enzymes • Cardiac monitoring

  25. Hyperbaric oxygen therapy • Enhanced elimination of COHb • Improved tissue oxygenation • Enhanced dissociation of CO from cytochrome oxidase

  26. Classic indications for HBO • Coma or loss of consciousness • Neurologic abnormalities • Cardiovascular dysfunction • Severe metabolic acidosis • COHb > 40 % • COHb > 15 %

  27. 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

  28. 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

  29. 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

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