Asphyxiants are gases that reduce or displace oxygen in the air, leading to suffocation. The main asphyxiants are carbon monoxide, carbon dioxide, and hydrogen sulfide. Carbon monoxide binds strongly to hemoglobin, preventing oxygen transport. Carbon dioxide buildup leads to lack of oxygen in tissues. Hydrogen sulfide paralyzes the respiratory center. Diagnosis of carbon monoxide poisoning involves analyzing blood samples for carboxyhemoglobin levels above 10%. Exposure to high concentrations of any of these gases can rapidly lead to loss of consciousness, respiratory failure, and death.

1. Asphyxiants (Irrespirable Gases)
Toxicology & Forensic
Serology
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Dr. Aamir Ali Khan
Biochemistry

2. Asphyxiants
•An Asphyxiants gas, also known as a simple Asphyxiants, is a nontoxic
or minimally toxic gas which reduces or displaces the normal oxygen
concentration in breathing air.
•Breathing of oxygen-depleted air can lead to death by asphyxiation
(suffocation).
•Because Asphyxiants gases are relatively inert and odorless, their
presence in high concentration may not be noticed, except in the case of
carbon dioxide (hypercapnia).

3. Asphyxiants
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• Asphyxiantsmainlyproducerespiratory embarrassment;
importantasphyxiantsinclude
– Carbon Monoxide (CO)
• Reduceoxygencarrying capacity
– Carbon dioxide(CO2)
• Lackofoxygenin tissue
– Hydrogen Sulphide(H2S)
• Paralysesrespiratory center

4. Carbon Monoxide(CO)
Toxicology & Forensic
Serology
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• Colorless, odorless, non irritant gas
• Cant perceivedby senses
• Incompletecombustion ofcarbon &organic
matter = Carbon monoxide
• Sources; illuminating gas,oil heater,gasheater,
vehicleengine etc

5. Carbon Monoxide (CO) cont..
• CO has200-300 timehigheraffinityto Oxygen
• Displace oxygen form carboxy hemoglobin and is
more stable
• Ultimatelyresultin anoxia(severedepletionofoxygen).

6. Sign& Symptoms
Toxicology & Forensic
Serology
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Carbon Monoxide Poisoning: Here’s What You Need To Know | Just Boilers

7. Sign& Symptoms
CO H b
% Saturation Symptoms
No appreciableSymptoms
Breath shortness, mildheadache,flushedskin
Throbbing headache,buzzinginear,dullingofsenses,muscle
weakness
Severe headache,nausea,vomiting,breathlessness,incoordination,
muscleweakness,dimvision,impairedjudgment
Symptoms intensified,maybemistakenwithdrunk, mental confusion,
memory loss, palpitationanddyspnea(Shortness of breath)
Intermittentasphyxiaconvulsion, coma,Cheyne-Stokesrespiration(a rare
abnormal breathing pattern),respiratory paralysis& death
0-10
10-20
20-30
30-40
40-50
50-70
>70 Rapidlyfataldueto respiratory arrest
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8. Diagnosis ofC O
https://www.verywellhealth.com/carbon-monoxide-poisoning-diagnosis
Toxicology & Forensic
Serology
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9. BloodTest
Collection of Blood Sample for
Chemical Analysis
Collect the blood from peripheral veins. Add sodium fluoride as a
preservative and preferably seal the bottle with a layer of liquid paraffin
on the top.
Method 1:asuspected sample diluted with four times its volume of water &add few
drops of3 % aqueoustannicacidto solution andshaken well
If>10 % C O present,itformpinkishwhite
precipitate
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10. BloodTest
Method 2:A suspectedblood samplediluted with
20 timesitsvolumeofwater&10 drops of10 %
causticsoda addedto it.
Normal blood becomes greenishbrown but
Blood containing >10 % CO retainsits
brightred color asno methemoglobinis formed
Toxicology & Forensic
Serology
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11. Carbon Dioxide Poisoning
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Toxicology & Forensic
Serology
• This is heavy,colorless, odorless &Poison gas
• Result fromcompletecombustion ofcarbon
containing compounds
• Formed dueto fermentation&decomposition of
organic matter
• Sources;refrigeratingplants,manholes,wells,re-
breathingclose spaces

12. CO2 Poisoning cont…
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Toxicology & Forensic
Serology
• Pure CO2 inhalation may cause vagal inhibitory
response (Stopping the heart by stimulation of
the vagus nerve in the neck. This can be
caused by pressure on the neck) , spasm of glottis,
instant death
• > 50%CO2 may result immediate unconsciousness &
deathfrom deficiencyofoxygen supplyto brain& tissues
• Unexpected deathfrom CO2 under anesthesia

13. Hydrogen SulphidePoisoning
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Toxicology & Forensic
Serology
• Sulphuratedgas;acolorless gaswithrotten eggsmell
• Found ifSulphur containing compound underdecay
• Such assewers,formed during artificialsilk manufacturingetc
• Formed inhumanintestineduring lifeanddueto
putrefactionafter death
• Converts oxyhemoglobin to methemoglobin &
sulphmethemoglobin after death

14. H2S Poisoning Cont..
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Toxicology & Forensic
Serology
• Ifpure H2S inhaleddeathoccur at once
• Result inparalysisoftherespiratory Centre
• A 0.2% concentrationinairprovedfatalinfew
minutes

17. Reference
Toxicology & Forensic
Serology
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• Textbook ofMedical Jurisprudence, Forensic medicineandToxicology, BV Subrahmanym Seventhedition