Toxic gases

How do toxic gas poisonings commonly present?

As acute toxicities.

How is carbon monoxide produced?

By incomplete combustion of carbon-containing fuels.

What fuels can produce carbon monoxide?

Natural gas, methane, propane, petroleum gas, gasoline, and diesel.

What household appliances can be sources of carbon monoxide?

Malfunctioning furnaces, water heaters, gas stoves, portable heaters, grills, and fireplaces.

What engine-powered equipment can cause carbon monoxide exposure?

Automobiles and portable generators.

Carbon monoxide sources

• malfunctioning fuel-burning appliances

• equipment powered by internal combustion engines

• fireplaces, charcoal burned in homes

What conditions promote carbon monoxide formation?

blocked flues, malfunctioning/unvented fuel equipment, poor ventilation (prevention of oxygen to source)

what is complete combustion?

there is enough oxygen for the carbon atoms in the carbon containing fuel to bind with 2 oxygen atoms to form carbon dioxide

what is incomplete combustion?

not enough oxygen for the carbon atoms in the carbon containing fuel to bind with 2 oxygen atoms → only can bind with 1 oxygen forming CO

What are the odor and color of carbon monoxide?

It is odorless and colorless.

CO mech of toxicity

• readily absorbed into the blood and combines with hemoglobin

  • competes with oxygen for the same iron binding site on heme

• turns Hgb into carboxyhemoglobin

• Hgb binds to CO in preference to oxygen

How strongly does carbon monoxide bind hemoglobin compared with oxygen?

Its affinity is up to approximately 250 times greater.

t/f: some binding sites on hemoglobin can have CO and O₂

true

How does carbon monoxide cause tissue hypoxia?

-causes a leftward shift of the oxygen-hgb dissociation (OHD)

-left shift makes it hard for oxygen to be released from hgb in presence of low PaO₂

Hgb binds tightly to and has a higher affinity for oxygen when…

• it is a relaxed conformational state

• the PaO₂ is decreased or low

Hemoglobin has a lower affinity for oxygen and delivers (unloads) oxygen when…

• it is a tense conformational state

• the PaO₂ is increased or high

What does PaO2 measure?

The partial pressure of oxygen dissolved in arterial blood plasma.

which gas causes cherry red-colored blood?

carbon monoxide

Why does PaO2 alone not describe hemoglobin's oxygen delivery?

PaO2 measures dissolved oxygen, rather than how much oxygen hemoglobin carries or releases.

Which organs are especially vulnerable to carbon monoxide poisoning?

The brain and heart.

CO clinical signs

• resp distress

• lethargy

• behavioral changes

• tachycardia, arrhythmias

• vomiting, diarrhea

• convulsions, seizures, ataxia

• cherry red skin color

  • ingestion of cyanide causes this

• death

CO treatment

• remove animals and people from source. goal is to restore normal O₂ to brain and heart

• use either a combo of CO₂ and O₂ or 100% O₂

• oxygen chamber

What are common sources of ammonia exposure?

Decomposing animal waste, anhydrous ammonia fertilizer, and poorly ventilated confinement operations.

Ammonia mech of toxicity

• very strong odor

• reacts with water forming ammonium hydroxide, which is a strong base

• reacts with water in lungs and MM causing severe irritation and thermal injury

What is a characteristic property of ammonia?

A very strong, pungent odor.

Which tissues are primary targets of ammonia?

The lungs, eyes, and mucous membranes of the nose and airways.

ammonia exposure clinical signs

• conjunctivitis

• tearing

• nasal discharge

• coughing, shallow breath

• corneal edema and loss of sight

• death

What treatment measures are listed for ammonia exposure?

Remove the patient from exposure, provide adequate ventilation, and flush affected eyes.

Why is filling an empty anhydrous ammonia tank with livestock drinking water dangerous?

Residual ammonia can contaminate the water and cause rumen alkalosis and hyperammonemia.

What neurologic consequence can result from hyperammonemia?

Encephalopathy.

What are sources of hydrogen sulfide?

• Natural gas deposits

• sulfur springs and lakes

• manure pits

  • hog manure pits- under floor or liquid storage systems that hold swine waste as an active anaerobic environment

    • gas released from pits when manure slurry is stirred or agitated

    • H₂S is heavier than air, sinks and pools inside empty or agitated manure pits

What are the characteristic physical properties of hydrogen sulfide?

It is a colorless, flammable gas with a rotten-egg odor.

hydrogen sulfide mech of toxicity

• H2S forms a caustic alkaline substance when it reacts with moisture
  on ocular and respiratory mucous membranes

  • severe chemical conjunctivitis

  • pulmonary edema and upper resp irritation

• irritant causing local inflammation of MM

• gas binds to Cytochrome C Oxidase in mitochondria → similar to CO and cyanide

• blocks oxygen from receiving electrons → aerobic ATP production stops b/c cells cannot receive oxygen even tho blood is oxygenated = tissue hypoxia

• called “knock-down” gas

Which organs are major targets of hydrogen sulfide?

The brain, lungs, heart, and eyes.

-high concentrations “paralyze” the resp center

How can high hydrogen sulfide concentrations cause respiratory arrest?

They can paralyze the respiratory center.

Why is smell an unreliable warning of hydrogen sulfide exposure?

High concentrations impair the sense of smell, creating a false sense of safety.

What ocular signs occur with hydrogen sulfide exposure?

Severe conjunctivitis and lacrimation.

hydrogen sulfide clinical signs

• Dyspnea, pulmonary irritation, inflammation, and edema

• unconsciousness

• V+

• death

What signs can pigs show at low hydrogen sulfide concentrations?

Anorexia and agitation at approximately 20 ppm.

What signs are listed for humans exposed to 50-100 ppm hydrogen sulfide?

Vomiting, diarrhea, and anorexia.

What treatment is emphasized for severe hydrogen sulfide poisoning?

Artificial respiration or assisted ventilation to reestablish breathing.

What is the main agricultural source of nitrogen dioxide?

Rapid bacterial decomposition of high-nitrate plant material stored in silos.

When do nitrogen dioxide gas levels peak after a silo is filled?

Within approximately 1-5 days.

-majority cases occur in September and October after harvest

What are the characteristic color and odor of nitrogen dioxide?

Yellow to yellow-brown gas with a bleach-like odor.

-collects and concentrates in silo bin, heavier than air

What disease is associated with nitrogen dioxide exposure?

Silo-filler's disease.

-delayed inflammatory disease resulting in cough, hypoxia and nodular lung patterns

nitrogen dioxide mech of toxicity

• reacts w/ water in resp tract to form nitric acid

• chemical irritation of bronchioles and alveoli leading to cell death

  • pulmonary edema due to fluid accumulation

• can cause systemic tissue damage - those exposed may not show clin signs for hours to few days

What are the primary target organs of nitrogen dioxide?

-pulmonary: resp tract and lungs

-ocular irritant, irritates nasopharyngeal cavity

clin signs for low concentrations of NO₂

• can occur within 3 weeks post-exposure

• dyspnea

• tachypnea

• coughing

• weakness

• cyanosis

What treatments are for nitrogen dioxide exposure?

• steroids and O₂ to treat pulmonary edema

• antibiotics for bronchopneumon