Hyperbaric Oxygen Therapy & Oxygen Toxicity. Module III. CRC 431 Special Procedures

Hyperbaric Oxygen Therapy

&

Oxygen Toxicity

Module III

CRC 431 Special Procedures

HBO OUTLINE

• Definitions

• History

• Altitude/descent

• Gas laws

Hyperbaric Oxygen Therapy

• Therapeutic oxygen at pressures greater than 1 atm

• Unit expressing HBO pressure = ata

• Ata = atmospheric pressure absolute

• 1 ata = 1 atmosphere (atm), or 760 torr

• HBO general pressure range = 2 to 3 ata

Hyperbaric Oxygen Therapy

• Pressure:

Pressure = Force/Area

• Force:

Hyperbaric Oxygen Therapy

• Ambient pressure = surrounding pressure on land, or under water.

• Atmospheric pressure = surrounding pressure caused by the weight of air.

• Water pressure = surrounding pressure caused by weight of water.

Hyperbaric Oxygen Therapy

• Barometric pressure = measure of atmospheric pressure

• Barometric pressure = atmospheric pressure

• When surrounded by air:

atmospheric pressure =

ambient pressure =

Hyperbaric Oxygen Therapy

• When surrounded by water:

ambient pressure = water

pressure

• CAUTION!!! Don’t confuse:

atmospheric pressure & atmosphere as unit.

Hyperbaric Oxygen Therapy

• Atmospheric pressure can be ANY value:

1 atm (sea level)

½ atm (8,000 feet elevation)

Hyperbaric Oxygen Therapy

ABSOLUTE PRESSURE vs. GAUGE PRESSURE

• 33 ft sea water = 1 atm

• Gauges set sea level pressure at 0 torr

• At 33 ft depth, gauge indicates 1 atm

Hyperbaric Oxygen Therapy

• First sealed chamber called Domicilium built in 1662

• Chamber held compressed air (21% O₂)

• Treated various ailments: scurvy, arthritis, inflammation, rickets

• Likely too little compression to benefit patients

Hyperbaric Oxygen Therapy

• Beddoes is known as the “Father of Respiratory Therapy”

• Thomas Beddoes founded the “Pneumatic Institute in Bristol,” England 1780

• Patients inhaled different gases to treat their diseases

• Pneumatic laboratory enriched with O₂ treated chronic conditions

Hyperbaric Oxygen Therapy

• J. Priestly discovered O₂ in England 1776

• Antoinne Lavoisier of France shares O₂ discovery

• Father of English poet Thomas Lovell Beddoes

Hyperbaric Oxygen Therapy

GAS LAWS

Air under hyperbaric conditions obeys the same gas laws as air in the atmosphere. Boyle’s law (1627 – 1691)

Dalton’s law (1766 – 1844) Henry’s law (1774 – 1790)

Hyperbaric Oxygen Therapy

Boyles’s law

• When mass & T are

K

, V & P inverse

K

= V x P

Hyperbaric Oxygen Therapy

Boyle’s law

• When mass & T are

K

, D & P direct

K

= D/P

• Consider container open at one end holding 1 L at 1 atm.

• At 2 atm, V by ½, & D doubles.

Hyperbaric Oxygen Therapy

Boyle’s law

• During HBO, D in lungs increases.

• Deep scuba diving: D of air increases, & breathing becomes more difficult.

Hyperbaric Oxygen Therapy

Dalton’s law

• P_T = pressure exerted by gas equals the sum of all the P_gas of the constituent

gases.

Hyperbaric Oxygen Therapy

Dalton’s law

To calculate the partial pressure of a gas in a mixture of gases:

Hyperbaric Oxygen Therapy

Dalton’s law

TRUE or FALSE

The sum of the partial pressures of all the gases in a gas mixture can never exceed the total pressure of the gas mixture.

? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

Hyperbaric Oxygen Therapy

Dalton’s law

Hyperbaric Oxygen Therapy

Dalton’s law

TRUE or FALSE

As air pressure increases (hyperbarism) or decreases (altitude), the partial

pressures exerted by the constituent gases increases or decreases, as well. ???????????????????????????????????????

Hyperbaric Oxygen Therapy

Dalton’s law

Hyperbaric Oxygen Therapy

Dalton’s law

TRUE or FALSE

When room air is compressed in a

hyperbaric chamber, the percentage of the individual gases in the mixture is the same.

Dalton’s law

TRUE!!!

Hyperbaric Oxygen Therapy

Dalton’s law

• Lower partial pressures at altitude reflect presence of less O₂ & N₂ molecules per volume compared to sea level.

• Summit at Mt. Everest (29,000 ft): 21% O₂, 78% N₂, 1% other

• # of O₂ & N₂ molecules per volume of air only 1/3 that at sea level.

Hyperbaric Oxygen Therapy

Henry’s law

Amount of gas that dissolves in a liquid at a given temperature is a function of the partial pressure of the gas in

contact with the liquid, and the

solubility of the gas in that particular liquid.

Hyperbaric Oxygen Therapy

Henry’s law

SIMPLIFIED: As the partial pressure of a gas above the surface of a liquid

increases, more of that gas will dissolve into that liquid.

Hyperbaric Oxygen Therapy

Henry’s & Dalton’s laws

When ambient pressure decreases

(altitude), the partial pressures of O₂ & N₂ in the body fall, and fewer O₂ & N₂ molecules dissolve into the blood.

Hyperbaric Oxygen Therapy

Henry’s & Dalton’s laws

When ambient pressure increases

(hyperbarism), the partial pressures of O₂ & N₂ in the body increase, and more O₂ & N₂ molecules dissolve into the

Hyperbaric Oxygen Therapy

Physiological Effects

• Hyperoxygenation

– Increases volume of O₂ in plasma

– 10 to 13 x greater than normal

– Elevated O₂ levels purge toxins & CO from the body

Hyperbaric Oxygen Therapy

Physiological Effects

• Hyperoxygenation

– At sea level while breathing room air plasma O₂ concentration is 0.3 vol%

Hyperbaric Oxygen Therapy

Physiological Effects

• Hyperoxygenation Alveolar Air Equation:

Hyperbaric Oxygen Therapy

Physiological Effects

• Hyperoxygenation

HBO patient breathing FIO₂ 0.40 @ 2.5 atm

PAO₂ = 0.40(1,900 mm Hg – 47 mm Hg) –

Hyperbaric Oxygen Therapy

Hyperoxygenation

PAO₂ = 0.40 (1,900 torr – 47 torr) – 40 torr(1.15)

PAO₂ = 1,807 torr

• 1,807 torr × 0.003 vol%/torr = 5.4 vol% • 5.4 ml O₂/100 ml plasma

Hyperbaric Oxygen Therapy

Normal a-v difference = 5.0 vol%

Arterial Blood

PaO₂ 100 mm Hg SaO₂ 97.5%

[Hb] 15 g%

Mixed Venous Blood

PvO₂ 46 mm Hg SvO₂ 73%

Hyperbaric Oxygen Therapy

CaO₂ = (1.34)(15)(0.975) + 100(0.003) = 19.6 vol%

CvO₂ = (1.34)(15)(0.73) + 46(0.003) = 14.6 vol%

Hyperbaric Oxygen Therapy

PHYSIOLOGICAL EFFECTS

• Hyperoxygenation

– HBO increases dissolved oxygen in the plasma

Hyperbaric Oxygen Therapy

Physiological Effects • Direct Pressure

– Shrinks gas bubbles (Boyle’s law) to expedite reabsorption of gases

– Good for decompression sickness (DCS – aka: “the bends”)

Hyperbaric Oxygen Therapy

Physiological Effects • Vasoconstriction

– Reduces blood flow

– No significant reduction in tissue O₂nation

– Benefits crushing type injuries

– Benefits thermal burns

– O₂ directly enters interstitial fluid promoting healing

Hyperbaric Oxygen Therapy

Physiological Effects

• Bactericidal/Bacteriostatic

– Halts spread of toxins

– Enhances killing of bacteria

Hyperbaric Oxygen Therapy

Physiological Effects

• Angiogenesis/Neovascularization

– Promote growth of new blood vessels

– Promote collagen formation to support new blood vessels

Hyperbaric Oxygen Therapy

• Atmospheric pressure caused by weight of gas molecules in contact with earth’s surface

• Atmospheric pressure exerted on a surface of water

• Pressure decreases with altitude

• Denver, CO at 5,280 ft elevation; 1 atm = 630 torr

Hyperbaric Oxygen Therapy

• Water more dense than air

• 33 ft sea water = 1 atm (760 torr)

• Pressure at any depth = hydrostatic pressures + atm pressure

• Depth of 33 ft of H₂O = 2 atm, or 2 ata

• At 33 ft H₂O, 2,112 lbs over each ft2 _of body (33 ft x 64 lbs/ft3 _{= 2,112 lbs/ft}2₎

Hyperbaric Oxygen Therapy

• Indications – CHRONIC – Nonhealing wounds – Refractory osteomyelitis – Radiation necrosis www.uhms.org/indications/indications.htm

Hyperbaric Oxygen Therapy

• Hazards

– Fire: 50 deaths worldwide in 20 years (1997)

• Most common FATAL complication

• Only 100% cotton fabrics in chambers

• No alcohol/petroleum products

• No sprays, makeup, deodorant

– Barotrauma

• Ear/sinus trauma

• Tympanic membrane rupture

Hyperbaric Oxygen Therapy

• Hazards

– O₂ Toxicity

• CNS toxicity (twitching, seizures, convulsions)

• Pulmonary toxicity (leaky A/C membrane)

– Other

• Sudden decompression

• Reversible visual changes

Hyperbaric Oxygen Therapy

• Hyperbaric Chambers

– Monoplace transparent Plexiglas cylinder

– One patient

– No mask

– No electric equipment inside

– 100% oxygen

Hyperbaric Oxygen Therapy

multiplacehyperchamber.jpg • Multi-place chambers

– large tanks able to accommodate 2 – 14 people

– achieve pressures up to 6 atm

– have a chamber lock entry system that allows

medical personnel to pass through without altering the pressure of the inner chamber

– allows patients to be directly cared for by staff

– filled with compressed air; patients breathe 100% oxygen through facemask, head hood, or

Hyperbaric Oxygen Therapy

multiplacehyperchamber.jpg

COHb% SYMPTOMS

≤ 10% Usually none

10-20% Mild headache, dyspnea

20-30% Throbbing headache, impaired concentration

30-40% Severe headache, impaired thinking

40-50% Confusion, lethargy , syncope 50-60% Respiratory failure, seizures 60-70% Coma, convulsions, depressed

cardiac & respiratory function ≥ 70% Coma, rapidly fatal

Oxygen Toxicity

Joseph Priestly said in 1775,

“. . . it [oxygen] might be peculiarly

salutary to the lungs in certain morbid cases . . .” and “. . . oxygen might burn the candle of life too quickly, and too

soon exhaust the animal powers within. . . .”

Oxygen Toxicity

• Present overview biochemical processes involved in normal cellular utilization of oxygen .

• Discuss implications in the context of hyperoxia.

• Explain biochemical role of antioxidants.

• Describe the pathophysiological aspects of pulmonary oxygen toxicity.

Oxygen Toxicity

• Oxidation: loss of electrons

• Reduction: gain of electrons

• Dismutation: same molecular species is oxidized and reduced, and two different entities are formed.

Oxidation

e–, e–, e–

e–, e–, e–, e–,

e–, e– Reduction e–, e–, e–

Dismutation

Oxidation

e–, e–, e– _{e–, e–, e–, e–,} e–, e–

e–, e–, e–

Reduction

Oxygen Toxicity

• Atmosphere

• Lungs

• A/C membrane

• Dissolved in plasma as PaO₂ (Henry’s law od Solubility)

• Chemically & reversibly bound to Hb

Atmosphere

Alveolar & End-Pulmonary Capillary

Diffusion Gradient Arterial Tissues 150 mm Hg 100 mm Hg 50 mm Hg 0 mm Hg

Oxygen Toxicity

• Oxygen atom – 8 electrons (e-₎ – 2 e- _{in 1s orbital} – 2 e- _{in 2s orbital} – 4 e- _{in 2p orbitals (p} x, py, pz) • 2 e- _{are paired}

• 2 e- _{are unpaired spin in same direction causing} paramagnetism

Electron Transport Chain • http://www.science.smith.edu/departme nts/Biology/Bio231/etc.html • http://www.youtube.com/watch?v=xbJ0 nbzt5Kw&feature=related • http://www.youtube.com/watch?v=ajZaj FrCjtA&feature=related • http://www.youtube.com/watch?v=RvqR 4pExHX8&feature=related • http://www.youtube.com/watch?v=eizHV QfeMwo&feature=related

• Single electron transfers

• O₂ undergoes 4 univalent reductions • 1 e- _{at a time to O}

2

• O₂ gains 1 e- at a time

• Reduction of each O₂ atom produces 1 H₂O

• Reduction of O₂ molecule = 2 H₂O Mitochondrion: Electron Transport

Mitochondrion: Electron Transport Chain

• e- _{brought to ETC from Kreb’s Cycle}

by electron carriers – NADH – FADH₂ – http://bcs.whfreeman.com/thelifewir e/content/chp07/0702001.html • Overall reaction: O₂ + 4H+ _{+ 4e}- _{2 H} 2O

Cytotoxic Metabolites of Oxygen • O

-2• (superoxide anion)

• H₂O₂ (hydrogen peroxide)

Cytotoxic Metabolites of Oxygen

• 1st Electron Transfer : O₂ + e- _{→ O} -2• • 2nd Electron Transfer : O -2• + e- + 2H+ → H₂O₂ • 3rd Electron Transfer: H₂O₂ + e- _{+ H}+ → H₂O + OH•

• 4th Electron Transfer: OH• + e- _{+ H}+ _→ H₂O

Overall Reaction

O₂ + 4H+ _{+ 4e}- _{→ 2 H}

2O

O

₂

Metabolism

Summary Univalent Reduction of O₂

O₂ O1₂• _{H2O2 OH• H2O}

e– _e– _{+ 2H}+ _e– _{+ H}+ _e– _{+ H}+

Free Radicals

• form during chemical RXN between atoms when one product contains unpaired electron in outermost shell

• extremely unstable state

• highly reactive with other molecules to achieve stable state

Free Radicals

• During oxygen metabolism, natural by-products often possess unpaired

valence shell electrons

• O1₂• and OH• contain unpaired

electrons in their outermost shells

Endogenous A

ntioxidant

Defense

M

echanisms

• ROS & free radicals can compromise the integrity of cell membranes

• cytotoxic effects of ROS & free radicals can occur

• Normally, they do not

Endogenous A

ntioxidant

Defense

M

echanisms

• Counteract potentially harmful effects of the oxygen metabolites generated

during aerobic respiration

• ROS & free radicals cytotoxic

– Large quantities

Endogenous Antioxidant

Defense Mechanisms

• Oxidative stress

• Double-edged sword

– Essential for life: PMNs

– Potentially lethal & damaging: amount

• PMNs release O1

2• & proteolytic enzymes to wage war with invading microbes

• Destroy cell wall of microbes

• Antioxidant defense mechanisms protective

Oxidative Damage

Destruction of Normal Tissue • Immunocompromised (e.g., AIDS)

• Frequent pulmonary infections (e.g., CF)

Animations & Information

• http://plantandsoil.unl.edu/croptechnol ogy2005/pages/animationOut.cgi?anim_ name=lipid_peroxidation.swf • http://www.medmotion.com/html/hydro xyl.html • http://www.cyberlipid.org/perox/oxid00 02.htm#3