Hyperbaric Oxygen Therapy Module II CRC 432 Subacute Cardiorespiratory Care Problem-Based Learning

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 torr HBO general pressure range = 2 to 3 ata

Hyperbaric Oxygen Therapy Pressure: pressure = force/area Force: force = mass x acceleration

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 = barometric pressure

Hyperbaric Oxygen Therapy When surrounded by water: atmospheric pressure = water pressure = ambient 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) 3 atm (hyperbaric chamber)

Hyperbaric Oxygen Therapy ABSOLUTE PRESSURE vs. GAUGE PRESSURE 33 ft sea water = 1 atm Gauges set sea level pressure at 0 At 33 ft depth, gauge indicates 1 atm Absolute pressure = 2 atm

Hyperbaric Oxygen Therapy Standard atmospheric pressure: average sea level pressure 14.7 psi 1034 cm H 2 O kPa 760 mm Hg (torr) 33 ft H 2 O 29.9 in Hg

Hyperbaric Oxygen Therapy First sealed chamber called Domicilium built in 1662 Chamber held compressed air (21% O 2 ) 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 O 2 treated chronic conditions Father of English poet Thomas Lovell Beddoes

Hyperbaric Oxygen Therapy J. Priestly discovered O 2 in England 1776 Antoinne Lavoisier of France shares O 2 discovery

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 K = 2V x ½P K = ½V x 2 P If P increases, V decreases, & vice versa.

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. At 3 atm, V by ⅓, & D triples.

Hyperbaric Oxygen Therapy Boyle’s law During HBO, density in lungs increases. Deep scuba diving: density 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. P T = P 1 + P 2 + P 3 =... P n

Hyperbaric Oxygen Therapy Dalton’s law To calculate the partial pressure of a gas in a mixture of gases: P gas = F gas (P T – P H 2 O )

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 TRUE!!!

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 TRUE!!!

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 O 2 & N 2 molecules per volume compared to sea level. Summit at Mt. Everest (29,000 ft): 21% O 2, 78% N 2, 1% other # of O 2 & N 2 molecules per volume of air only 1/3 that at sea level. PO 2 & PN 2 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 O 2 & N 2 in the body fall, and fewer O 2 & N 2 molecules dissolve into the blood.

Hyperbaric Oxygen Therapy Henry’s & Dalton’s laws When ambient pressure increases (hyperbarism), the partial pressures of O 2 & N 2 in the body increase, and more O 2 & N 2 molecules dissolve into the blood.

Hyperbaric Oxygen Therapy Physiologic Effects Hyperoxygenation –Increases volume of O 2 in plasma –10 to 13 x greater than normal –Elevated O 2 levels purge toxins & CO from the body

Hyperbaric Oxygen Therapy Physiologic Effects Hyperoxygenation –At sea level while breathing room air plasma O 2 concentration is 0.3 vol% 100 torr x vol%/torr = 0.3 vol%

Hyperbaric Oxygen Therapy Physiologic Effects Hyperoxygenation –At sea level while breathing room air plasma O 2 concentration is 0.3 vol% 100 torr x vol%/torr = 0.3 vol%

Hyperbaric Oxygen Therapy Physiologic Effects Hyperoxygenation Alveolar Air Equation:

Hyperbaric Oxygen Therapy Physiologic Effects Hyperoxygenation HBO patient breathing F I O atm

Hyperbaric Oxygen Therapy Hyperoxygenation P A O 2 = 1,807 torr 1,807 torr x vol%/torr = 5.4 vol% PAO 2 = 0.4 (1,900 torr – 47 torr) – 40 torr(1.15)

Hyperbaric Oxygen Therapy Normal a-v difference = 5.0 vol% Arterial Blood PaO torr SaO % [Hb] 15 g% Mixed Venous Blood PvO 2 46 torr SvO 2 73% [Hb] 15 g%

Hyperbaric Oxygen Therapy CaO 2 = (1.34)(15) (0.975) + 100(0.003) = 19.6 vol% CvO 2 = (1.34)(15)(0.73) + 46(0.003 vol%.torr) = 14.6 vol% CaO 2 – CvO 2 = a-v diff = 5.0 vol%

Hyperbaric Oxygen Therapy PHYSIOLOGIC EFFECTS Hyperoxygenation –HBO increases dissolved oxygen in the plasma

Hyperbaric Oxygen Therapy Physiologic 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

Hyperbaric Oxygen Therapy Physiologic Effects Vasoconstriction –Reduces blood flow –No significant reduction in tissue O 2 nation –Benefits crushing type injuries –Benefits thermal burns –O 2 directly enters interstitial fluid promoting healing

Hyperbaric Oxygen Therapy Physiologic Effects Bactericidal/Bacteriostatic –Halts spread of toxins –Enhances killing of bacteria –Stimulates production of neutrophils

Hyperbaric Oxygen Therapy Physiologic 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 H 2 O = 2 atm, or 2 ata At 33 ft H 2 O, 2,112 lbs over each ft 2 of body (33 ft x 64 lbs/ft 3 = 2,112 lbs/ft 2 ) 66 ft H 2 O = 3 ata

Hyperbaric Oxygen Therapy Indications – CHRONIC –Nonhealing wounds –Refractory osteomyelitis –Radiation necrosis

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 pneumothorax

Hyperbaric Oxygen Therapy Hazards –O 2 Toxicity CNS toxicity (twitching, seizures, convulsions) Pulmonary toxicity (leaky A/C membrane) –Other Sudden decompression Reversible visual changes Claustrophobia

Hyperbaric Oxygen Therapy Hyperbaric Chambers –Monoplace transparent Plexiglas cylinder –One patient –No mask –No electric equipment inside –100% oxygen –Less expensive than multi-place

Hyperbaric Oxygen Therapy

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.

Hyperbaric Oxygen Therapy

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