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