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

Hyperbaric Oxygen Therapy &

Oxygen Toxicity

Module IIICRC 431

Special Procedures

HBO OUTLINE

• Definitions• History• Altitude/descent• Gas laws• Physiological effects of HBO

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

mm Hg• HBO general pressure range = 2 to 3

ata


• Pressure:Pressure = Force/Area

• Force:Force = mass x

acceleration

Remember: MIP, not NIF!!!


• 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.


• Barometric pressure = measure of atmospheric pressure

• Barometric pressure = atmospheric pressure

• When one is surrounded by air: atmospheric pressure = ambient pressure = barometric pressure


• Absolute pressure: referenced against a perfect vacuum:

gauge pressure + atmospheric pressure.• Gauge pressure: referenced against

ambient air pressure: absolute pressure - atmospheric

pressure


• When surrounded by water: ambient pressure = water

pressure

• CAUTION!!! Don’t confuse: atmospheric pressure & “atmosphere” (atm) used as a unit.


• Atmospheric pressure can be ANY value:1 atm (sea level); 760 mm Hg½ atm (8,000 ft elevation); 380 mm Hg3 atm (hyperbaric chamber); 2,280 mm Hg


ABSOLUTE PRESSURE vs. GAUGE PRESSURE

• 33 ft sea water = 1 atm• Gauges set sea level pressure at 0 mm

Hg• At 33 ft depth, gauge indicates 1 atm• Absolute pressure = 2 atm


• 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


• 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


• J. Priestly discovered O2 in England 1776; called “dephlogisticated air.”

• Antoinne Lavoisier of France shares O2 discovery; named oxygen

• Father of English poet Thomas Lovell Beddoes


GAS LAWSAir under hyperbaric conditions obeys

the same gas laws as air at sea level.

Boyle’s law (1627 – 1691)Dalton’s law (1766 – 1844)Henry’s law (1774 – 1790)


Boyle’s law

• When mass & T are K, V & P inverse

K = V x P• If P increases, V decreases, & vice

versa



Boyle’s law

• During HBO, D in lungs increases.• Deep scuba diving: D of air

increases, & breathing becomes more difficult.


Dalton’s law

• PT = pressure exerted by gas equals the sum of all the Pgas of the constituent gases.

PT = P1 + P2 + P3 + . . . Pn


Dalton’s law To calculate the partial pressure of a gas in

a mixture of gases:Pgas = Fgas (PT – PH2O)

EXAMPLES:150 mm Hg = 0.21(760 mm Hg – 47 mm Hg)160 mm Hg = 0.21(760 mm Hg – 0 mm Hg)

Hyperbaric Oxygen TherapyDalton’s law

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

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


Dalton’s law

TRUE!!!

Hyperbaric Oxygen TherapyDalton’s law

TRUE or FALSEAs air pressure increases (hyperbarism) or decreases (altitude), the partial pressures exerted by the constituent gases increases or decreases, as well.

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Dalton’s law

TRUE!!!


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.

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Dalton’s law

TRUE!!!


Hyperbaric Oxygen TherapyDalton’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.

• PO2 & PN2 only 1/3 that at sea level


Henry’s lawAmount 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.


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.


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.


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 plasma.


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



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

100 mm Hg x 0.003 vol%/mm Hg = 0.3 vol%


Physiological Effects• HyperoxygenationAlveolar Air Equation:

PAO2 = FIO2(PB – PH2O) – PaCO2 (FIO2 + [1.00 – FIO2 ÷ R])



HBO patient breathing FIO2 0.40 @ 2.5 atm

PAO2 = 0.40(1,900 mm Hg – 47 mm Hg) –

40 mm Hg(0.40+ [1.00 + 0.40/0.8])

Hyperbaric Oxygen TherapyHyperoxygenation


Normal a-v difference = 5.0 vol%

Arterial Blood

PaO2 100 mm Hg SaO2 97.5%

[Hb] 15 g%




– HBO increases dissolved oxygen in the plasma


Physiological Effects• Direct Pressure

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

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

– Good for air/gas embolism


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


Physiological Effects• Bactericidal/Bacteriostatic

– Halts spread of toxins– Enhances killing of bacteria– Stimulates production of neutrophils


Physiological Effects• Angiogenesis/Neovascularization

– Promote growth of new blood vessels– Promote collagen formation to

support new blood vessels


• 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 mm Hg

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/ft2)• 66 ft H2O = 3 ata


• Indications – CHRONIC– Nonhealing wounds– Refractory osteomyelitis– Radiation necrosis

www.uhms.org/indications/indications.htm


• 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• pneumothorax


• Hazards– O2 Toxicity

•CNS toxicity (twitching, seizures, convulsions)

•Pulmonary toxicity (leaky A/C membrane)

– Other•Sudden decompression•Reversible visual changes•Claustrophobia


• Hyperbaric Chambers– Monoplace transparent Plexiglas

cylinder– One patient– No mask– No electric equipment inside– 100% oxygen– Less expensive than multi-place




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 endotracheal tube.


img_header.jpg

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

Oxygen Toxicity

Joseph Priestley 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 of biochemical processes involved in normal cellular utilization of oxygen.

• Discuss implications of the processes 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 products (species) are formed.

Oxidatione–, e–, e–

e–, e–, e–, e–, e–, e–

Reductione–, e–, e–

Dismutation

Oxidatione–, e–, e–

e–, e–, e–, e–, e–, e–

e–, e–, e–

Reduction

Loss of electrons Gain of electrons

Leo the lion goes gerrr!

Oxygen Toxicity

• Atmosphere• Lungs• A-C membrane

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

• Chemically & reversibly bound to Hb• Mitochondria & electron transport

chain

Atmosphere

Alveolar & End-Pulmonary Capillary Diffusion Gradient Arterial

Tissues

150 mm Hg

100 mm Hg

50 mm Hg

0 mm Hg

PO2 Levels: Atmosphere to Mitochondria

Oxygen Toxicity

• Oxygen atom– 8 electrons (e-)– 2 e- in 1s orbital– 2 e- in 2s orbital

– 4 e- in 2p orbitals (px, py, pz)• 2 e- are paired • 2 e- are unpaired spin in same direction

causing paramagnetism

e

Mitochondrion

MitochondrionElectron micrograph

Electron Transport Chain• http://www.youtube.com/watch?

v=xbJ0nbzt5Kw&feature=related• http://www.youtube.com/watch?

v=ajZajFrCjtA&feature=related• http://www.youtube.com/watch?

v=RvqR4pExHX8&feature=related• http://www.youtube.com/watch?

v=eizHVQfeMwo&feature=related• http://www.youtube.com/watch?

v=XI8m6o0gXDY

• Single electron transfers occurs 4 times/O2 molecule)

• O2 undergoes 4 separate univalent reductions

• 1 e- at a time added to O2

• O2 gains 1 e- at a time

• Reduction of O2 molecule = 2 H2O

Mitochondrion: Electron Transport Chain

bc1c oxidase

Q • ubiquinone, or co-enzyme Q

dehydrogenase

Mitochondrion: Electron Transport Chain

• e- brought to ETC from Kreb’s Cycleby electron carriers– NADH

– FADH2

– http://bcs.whfreeman.com/thelifewire/content/chp07/0702001.html

• Overall reaction:O2 + 4H+ + 4e- 2 H2O

Cytotoxic Metabolites of Oxygen

• O-2• (superoxide anion)

• H2O2 (hydrogen peroxide)

• OH• (hydroxyl radical)

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 H2O

O2 Metabolism

Summary Univalent Reduction of O2

O2 O-2• H2O2 OH• H2O

e– e– + 2H+e– + H+ e– + H+

H2O

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• ROS includes free radicals

Free Radicals

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

• O12• (singlet O2) and OH• contain

unpaired electrons in their outermost shells

• highly unstable, reactive, & can be cytotoxic

Endogenous Antioxidant Defense Mechanisms • ROS & free radicals can

compromise the integrity of cell membranes

• cytotoxic effects of ROS & free radicals can occur

• Normally, they do not • Aging?

Endogenous Antioxidant Defense Mechanisms • Counteract potentially harmful

effects of the oxygen metabolites generated during aerobic respiration

• ROS & free radicals cytotoxic– Large quantities– Defense mechanisms

lacking/compromised

Endogenous Antioxidant Defense Mechanisms

• Oxidative stress• Double-edged sword

– Essential for life: PMNs– Potentially lethal & damaging: amount

• PMNs release O-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, COPD)• Granulomatous disease (e.g., CGD)

Enyzymatic Antioxidant Defense Mechanisms

• Superoxide dismutase (SOD): breaks down 2 O-

2• species to H2O2 & O2

• Catalase: breaks down H2O2 to H2O & O2

• Glutathione peroxidase: breaks down H2O2 to H2O & R-OHs

Non-Enyzymatic Antioxidant Defense Mechanisms

• Vitamin E (alpha tocopherol): membrane-bound & stops free radical reactions

• Vitamin C (ascorbic acid): membrane-bound & stops free radical reactions

Pulmonary O2 Toxicity

• Disruption of A/C membrane: unsaturated fatty acids along phospholipid bilayer are targets

• Exudation of fluid• Alveolar fibrosis

Animations & Information• http://plantandsoil.unl.edu/

croptechnology2005/pages/animationOut.cgi?anim_name=lipid_peroxidation.swf

• http://www.medmotion.com/html/hydroxyl.html

• http://www.cyberlipid.org/perox/oxid0002.htm#3

• http://www.youtube.com/watch?v=GItnvCzV618

Documents

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