CO – “The Silent Killer”

Carbon Monoxide (CO) vs. Carbon Dioxide (CO 2 ) Carbon MonoxideCarbon 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 zLeading cause of poisoning mortality. zMost common cause of death in combustion related inhalation injury. z1000 to 2000 deaths / year ( USA ) zDifficult diagnosis : yincidence of unrecognized cases higher yestimated > visits / year

Sources of CO zMotor vehicle exhaust yrunning engine in closed space yfaulty exhaust systems zPropane gas -powered equipment ylift, water heater zCombustion for heating or cooking ycamping equipment, heating systems zSmoke inhalation in fires

Pathophysiology

zHemoglobin’s affinity for CO is 200 to 250 times its affinity for oxygen zCO binding to hemoglobin causes allosteric modifications increasing its affinity for oxygen zShift of O 2 dissociation curve to the left zDecreased tension at which O 2 is released from hemoglobin zLess O 2 delivery to the cells

O 2 Dissociation Curve

Pathophysiology - Cellular level z15 % of CO bound to extravascular heme- containing proteins zCytochrome oxidase yalteration in ATP production yintracellular acidosis ypersists after exposure zCardiac and skeletal myoglobin yoccuring at COHb 2 % yalteration in tissue O2 uptake

Pathophysiology - Cardiovascular zMyocardial depression consequence of yhypoxic stress yCO binding to cardiac myoglobin zArterial hypotension ymyocardial depression yNO-related peripheral vasodilatation zLOC with reduction of cerebral perfusion

Pathophysiology - Neurovascular zCO in circulation associated with massive increase in NO in perivascular tissues zNO released from vascular endothelial cells and platelets zProduction of oxygen radicals from impaired mitochondrial function zReaction NO with oxygen radicals to form peroxynitrite ( ONOO- ) zPeroxynitrite binds to perivascular tissue proteins causing injury zIncreased capillary permeability in CNS and pulmonary vascular beds

Diagnosis - Symptoms zMost common symptoms : headache91% dizziness77% weakness53% nausea47% confusion 43% shortness of breath40%

Cont… visual changes25% chest pain 9% loss of consciousness 6% abdominal pain 5% muscle cramping 5%

Cont… zThe Delayed Neuropsychiatric Syndrome ySubacute manifestation (days to months) yOccurs in spite of normal HbCO levels ysymptoms including : cognitive defects, personality changes, parkinsonism, amnesia, incontinence, gait disturbances, etc.

Diagnosis - Signs zPhysical exam signs ztachypnea, tachycardia, vestibular signs (Ataxia, motion sickness, Nystagmus, circling, head tilt, fall to one side) common zretinal hemorrhages uncommon but more specific

Cont… zSigns of smoke inhalation such as burn nasal hairs, injured mucous membranes, carbonaceous mucus discharge z“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 zHigh level of clinical suspicion zSerum COHb level zExhaled breath COHb level zPulse oximetry cannot distinguish between HbO2 and COHb zComprehensive neurological and neuropsychological assessment zCT brain to exclude other conditions

Severity of CO intoxication zInhaled CO concentration zDuration of exposure zPresence of systemic illnesses ycardiac and pulmonary diseases

Clinical evaluation zMaintain a high level of suspicion zHistory of exposure can be absent zCOHb y< 3 % non-smokers or < 10 % in smokers zABG : metabolic acidosis ( lactate ) zECG : ischemia, arrythmias

Pulse oximetry in CO poisoning zUnreliable with significant amount of abnormal Hb : MetHb, COHb zPulse oximetry overestimates true fractional arterial oxygen saturation

Neurologic evaluation zNeurologic examination zNeuroradiologic imaging : CT, MRI

Carbon Monoxide Alarm Your best protection! zInstall a carbon monoxide alarm close to sleeping areas. For more protection: yInstall one in every bedroom yInstall one on every level of your home zNever ignore a carbon monoxide alarm, IT COULD SAVE YOUR LIFE!

Emergency Alarm Sounds! zGet fresh air right away zCall local fire department zDo not re-enter an affected home until CO is gone yFire department can determine when it is safe to re-enter a building

Management of CO poisoning zIdentify the source to correct the problem zDomestic exposition yverification of heating or cooking appliances zOccupational exposition zCO poisoning : mandatory reporting to public health services zMaking the diagnosis can save lives !

Cont… zOxygen 100 % zABG zCOHb zECG zCXR zCardiac enzymes zCardiac monitoring

Hyperbaric oxygen therapy zEnhanced elimination of COHb zImproved tissue oxygenation zEnhanced dissociation of CO from cytochrome oxidase

Classic indications for HBO zComa or loss of consciousness zNeurologic abnormalities zCardiovascular dysfunction zSevere metabolic acidosis zCOHb > 40 % zCOHb > 15 %

CO poisoning in pregnancy zHigh incidence of neurologic abnormalities and stillbirth after CO poisoning zFetal Hb binds CO more avidly than Hb A zCO absorption and elimination slower in fetal circulation zHBO felt to be safe in pregnancy

Prevention of CO poisoning zPublic education about CO poisoning zIdentification of activities at risk zTraining of workers for proper use of propane- powered tools zAppropriate ventilation of confined places zIndustrial and domestic use of CO detectors

Problems in CO poisoning zAbsence of reliable method to estimate prospectively the severity of CO poisoning zDifficulty in comparing results of studies because no staging in severity of disease