Hyperbaric Oxygen Therapy Module II

1. Hyperbaric Oxygen TherapyModule II CRC 432 Subacute Cardiorespiratory Care Problem-Based Learning

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

3. 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

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

5. 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.

6. Hyperbaric Oxygen Therapy • Barometric pressure = measure of atmospheric pressure • Barometric pressure = atmospheric pressure • When surrounded by air: atmospheric pressure = ambient pressure = barometric pressure

7. Hyperbaric Oxygen Therapy • When surrounded by water: atmospheric pressure = water pressure = ambient pressure • CAUTION!!! Don’t confuse: atmospheric pressure & atmosphere as unit

8. Hyperbaric Oxygen Therapy • Atmospheric pressure can be ANY value: 1 atm (sea level) ½ atm (8,000 feet elevation) 3 atm (hyperbaric chamber)

9. 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

10. Hyperbaric Oxygen Therapy • Standard atmospheric pressure: average sea level pressure • 14.7 psi • 1034 cm H2O • 101.3 kPa • 760 mm Hg (torr) • 33 ft H2O • 29.9 in Hg

11. 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

12. 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 • Father of English poet Thomas Lovell Beddoes

13. Hyperbaric Oxygen Therapy • J. Priestly discovered O2 in England 1776 • Antoinne Lavoisier of France shares O2 discovery

14. 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)

15. 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.

16. 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.

17. Hyperbaric Oxygen Therapy Boyle’s law • During HBO, density in lungs increases. • Deep scuba diving: density of air increases, & breathing becomes more difficult.

18. Hyperbaric Oxygen Therapy Dalton’s law • PT = pressure exerted by gas equals the sum of all the Pgas of the constituent gases. PT = P1 + P2 + P3 = . . . Pn

19. Hyperbaric Oxygen Therapy Dalton’s law To calculate the partial pressure of a gas in a mixture of gases: Pgas = Fgas (PT – PH2O)

20. 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. ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? ?

21. Hyperbaric Oxygen Therapy Dalton’s law TRUE!!!

22. 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. ???????????????????????????????????????

23. Hyperbaric Oxygen Therapy Dalton’s law TRUE!!!

24. 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. ???????????????????????????????????????

25. Hyperbaric Oxygen Therapy Dalton’s law TRUE!!!

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

27. 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.

28. 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.

29. 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.

30. 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 blood.

31. Hyperbaric Oxygen Therapy Physiologic Effects • Hyperoxygenation • Increases volume of O2 in plasma • 10 to 13 x greater than normal • Elevated O2 levels purge toxins & CO from the body

32. Hyperbaric Oxygen Therapy Physiologic Effects • Hyperoxygenation • At sea level while breathing room air plasma O2 concentration is 0.3 vol% 100 torr x 0.003 vol%/torr = 0.3 vol%

33. Hyperbaric Oxygen Therapy Physiologic Effects • Hyperoxygenation • At sea level while breathing room air plasma O2 concentration is 0.3 vol% 100 torr x 0.003 vol%/torr = 0.3 vol%

34. Hyperbaric Oxygen Therapy Physiologic Effects • Hyperoxygenation Alveolar Air Equation:

35. Hyperbaric Oxygen Therapy Physiologic Effects • Hyperoxygenation HBO patient breathing FIO2 0.4@ 2.5 atm

36. Hyperbaric Oxygen Therapy Hyperoxygenation PAO2 = 1,807 torr 1,807 torr x 0.003 vol%/torr = 5.4 vol% PAO2 = 0.4 (1,900 torr – 47 torr) – 40 torr(1.15)

37. Arterial Blood PaO2 100 torr SaO2 97.5% [Hb] 15 g% Mixed Venous Blood PvO2 46 torr SvO2 73% [Hb] 15 g% Hyperbaric Oxygen TherapyNormal a-v difference = 5.0 vol%

38. Hyperbaric Oxygen Therapy CaO2 = (1.34)(15) (0.975) + 100(0.003) = 19.6 vol% CvO2 = (1.34)(15)(0.73) + 46(0.003 vol%.torr) = 14.6 vol% CaO2 – CvO2 = a-v diff = 5.0 vol%

39. Hyperbaric Oxygen Therapy PHYSIOLOGIC EFFECTS • Hyperoxygenation • HBO increases dissolved oxygen in the plasma

40. 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

41. Hyperbaric Oxygen Therapy Physiologic 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

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

43. Hyperbaric Oxygen Therapy Physiologic Effects • Angiogenesis/Neovascularization • Promote growth of new blood vessels • Promote collagen formation to support new blood vessels

44. 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

45. 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

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

47. 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

48. Hyperbaric Oxygen Therapy • Hazards • O2 Toxicity • CNS toxicity (twitching, seizures, convulsions) • Pulmonary toxicity (leaky A/C membrane) • Other • Sudden decompression • Reversible visual changes • Claustrophobia

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

50. Hyperbaric Oxygen Therapy