co – “the silent killer”. carbon monoxide (co) vs. carbon dioxide (co 2 ) carbon...
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CO – “The Silent Killer”
Carbon Monoxide (CO) vs. Carbon Dioxide (CO2)
Carbon Monoxide
Carbon Dioxide
A byproduct of burning fuels
Gas exhaled with normal breathing
A poison even at low doses
An asphyxiant and poisonous at high doses
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
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
Pathophysiology
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
O2 Dissociation Curve
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
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
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
Diagnosis - Symptoms
Most common symptoms :headache 91%dizziness 77%weakness 53%nausea 47%confusion 43%shortness of breath 40%
Cont…
visual changes 25%chest pain 9%loss of consciousness 6%abdominal pain 5%muscle cramping 5%
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.
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
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.
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
Severity of CO intoxication
Inhaled CO concentrationDuration of exposurePresence of systemic illnesses
cardiac and pulmonary diseases
Clinical evaluation
Maintain a high level of suspicionHistory of exposure can be absentCOHb
< 3 % non-smokers or < 10 % in smokers
ABG : metabolic acidosis ( lactate )ECG : ischemia, arrythmias
Pulse oximetry in CO poisoning
Unreliable with significant amount of abnormal Hb : MetHb, COHb
Pulse oximetry overestimates true fractional arterial oxygen saturation
Neurologic evaluation
Neurologic examinationNeuroradiologic imaging : CT, MRI
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!
EmergencyAlarm Sounds!
Get fresh air right awayCall local fire departmentDo not re-enter an affected home
until CO is gone Fire department can determine when it is
safe to re-enter a building
Management of CO poisoning
Identify the source to correct the problemDomestic exposition
verification of heating or cooking appliances
Occupational expositionCO poisoning : mandatory reporting to public
health servicesMaking the diagnosis can save lives !
Cont…
Oxygen 100 %ABGCOHbECGCXRCardiac enzymesCardiac monitoring
Hyperbaric oxygen therapy
Enhanced elimination of COHbImproved tissue oxygenationEnhanced dissociation of CO from
cytochrome oxidase
Classic indications for HBO
Coma or loss of consciousnessNeurologic abnormalitiesCardiovascular dysfunctionSevere metabolic acidosisCOHb > 40 %COHb > 15 %
CO poisoning in pregnancy
High incidence of neurologic abnormalities and stillbirth after CO poisoning
Fetal Hb binds CO more avidly than Hb ACO absorption and elimination slower in fetal
circulationHBO felt to be safe in pregnancy
Prevention of CO poisoning
Public education about CO poisoningIdentification of activities at riskTraining of workers for proper use of propane-
powered toolsAppropriate ventilation of confined placesIndustrial and domestic use of CO detectors
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