Hyperbaric Oxygen Therapy

# Hyperbaric Oxygen Therapy

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## Hyperbaric Oxygen Therapy

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1. Hyperbaric Oxygen Therapy Yan Wing Wa Intensive Care Unit Pamela Youde Nethersole Eastern Hospital 6 June 2005

2. Contents • Physics of hyperbaric therapy • Physiological changes in hyperbaric conditions • Indications / Contraindications of hyperbaric therapy • Hyperbaric therapy in Hong Kong • Protocol of hyperbaric therapy • +/- HBO therapy for carbon monoxide poisoning

3. Physics of hyperbaric therapy / diving One atmosphere (At) = 10.08 (10 metres sea water (msw) = 33.07 (33) feet sea water (fsw) = 33.9 (34) feet fresh water = 1.033 kg/cm2 = 14.696 (14.7) lbs/in2 (psi) = 1.013 (1) bars = 1013 millibars = 760 millimetres mercury (mmHg) = 760 torr

4. Absolute pressure (Pabs) Absolute pressure (Pabs) = Atmospheric pressure + Gauge pressure / Water pressure e.g. sea surface = 1 ATA 10 msw = 2 ATA 18 msw = 2.8 ATA

5. Pascal’s principle A pressure applied to a liquid will be transmitted “equally” throughout the liquid.

6. Ideal Gas Law P x V = N x R x T

7. Boyle’s Law P1 x V1 = P2 x V2 • At constant temperature the volume of a given mass of gas is inversely proportional to the absolute pressure • Volume changes are greatest near the water surface

8. Charles’ Law P P1 P2 = constant; = T T1 T2 P P2 = T T2 Vs: Adiabatic heating (Second Law of Thermodynamics)

9. Dalton’s Law Pabs = PgasA + PgasB + PgasC PgasA = Pabs x FgasA • The total pressure exerted by a mixture of gases is the sum of the partial pressures that would be exerted by each of the gases if it alone occupied the total volume • Atmospheric air (20% O2 and 80% N2) 1 ATA = 0.2 ATA O2 and 0.8 ATA N2 5 ATA = 1.0 ATA O2 and 4.0 ATA N2

10. Respiratory Gases Pabs – 47 273 + 0 VSTPD = VBTPS x ( ) x 760 273 + 37

11. Henry’s Law • Q = K x P gas • Q (volume of gas dissolved in liquid) = K x Pgas Q with Temp • At constant temperature, the amount of gas that will dissolve in a liquid is proportional to the partial pressure of that gas over the liquid • 1 ATA = x litres of gas in solution • 10 ATA = 10x litres of gas in solution • As pressure is reduced solubility falls • Most gas excreted by lung • Rapid ascent may lead to bubble formation

12. Nitrogen Narcosis

13. Inert Gas Narcosis • Effects are of rapid onset and recovery • Effects potentiated by • fatigue, narcotics, EtOH, CO2 retention • Adaptation possible, no true tolerance • Avoid making decision inside hyperbaric chamber Other inert gases • Helium – no narcotic effect, neon less narcotic • Argon, krypton, xenon more narcotic

14. Gas Diffusion • Net movement of gas molecules from an area of higher partial pressure to an area of lower partial pressure.  with  molecular weight of gas  viscosity of liquid temperature of liquid

15. Gas Flux = gases diffusion x Q • LaPlace’s Law P  = 2 x  / r

16. The Mechanism of Barotrauma • Barotrauma of Descent • Middle ear • Pulmonary • Sinus • Barotrauma of Ascent • Middle ear • Pulmonary

17. Physiological Changes in Hyperbaric Condition – Respiratory system • Changes in compliance • lung and chest wall • Changes in airway resistance • only in turbulent flow • Changes in work of breathing • Changes in V/Q match •  shunt • Changes in DO2 • Ca O2=19.5ml%(Hb bound) + 0.3ml%(dissolves) = 19.8ml% • CV O2=15.0ml% + 0.12ml% = 15.1ml% • Ca O2=19.5ml% + 6.7ml% = 26.2ml% (at 100% O2 3ATA) • Changes in CO2 transport • less efficient in HBO environment •   reduced Hb in venous blood •  •  carbamino compound with CO2 • Changes in control of respiration • ? slight depression of respiration drive in HBO

18. Cardiovascular System • Changes in blood volume distribution • Dive reflex:  heart rate • Blood pressure : same

19. Decompression Illness (DCI) • Uptake of inert gases (descent) • Elimination (ascent) • Bubbles formation • Biochemical damage (Inflammatory cascade) • DCI (within 24 hours) • Non-specific symptoms and signs • Brain (sensory > motor) • Spinal cord (retention of urine with overflow) • Vestibular disease • Musculoskeletal disease • Respiratory disease • (~ O2 toxicity, pulmonary barotrauma, asthma, salt water aspiration)

20. Oxygen Toxicity • Syperoxide anion [O2] generated as normal product of oxygen metbolism • O2 is highly reactive free radical • Sulphydryl group dependent enzymes • Unstaurated lipids • Membrance bound transport systems • O2 Controlled by antioxidant mechanisms • Superoxide dismutase, catalase, vitamins • O2 / antioxidant balance disturbed by increase pO2

21. CNS Oxygen Toxicity • Paul Bert effect • Major symptoms is convulsion • fibrillation of lip/cheek, pallor, palpitations, bradycardia, sweating, apprehension, nausea, vertigo, disturbed respiration, twitching, hallucinations • Contributory factors • Exercise, CO2 retention, previous hypoxia • Management • Off oxygen until symptoms resolved • Convulsions with diazepam IV

22. Pulmonary Oxygen Toxicity • Lorrain-Smith effect • Threshold pO2 0.5 – 0.75 ata • Symptoms • Irritation on deep inspiration, cough, burning on inspiration, paroxysms of cough, breathlessness • Signs • Reduced vital capacity, desaturation on exercise • Management • Reduce pO2 – recovery from all but most severe episodes • Control • Intermittent exposure (air or chamber gas breaks)

23. RN Table 60 - Hyperbaric Oxygen Therapy

24. Oxygen Toxicity • Dose may be calculated by UPTD • Unit Pulmonary Toxic Dose • Assumes pO2 0.5 no effect • UPTD little use because of variability in susceptibility • Main control is by use of intermittent exposure

25. Oxygen Toxicity • Toxicity dependent on pO2 and duration of exposure • pO2 > 3 ata – CNS symptoms dominant • pO2 > 2 ata – Pulmonary symptoms dominant • Considerable variability in susceptibility • Between individuals • From day to day • Symptoms may occur soon after reduction in pO2

26. Oxygen Toxicity •  fever •  work •  CO2 retention • steroid • anxious • adrenaline /noradrenaline • high dose penicillin • insulin infusion • thyrotoxicosis

27. Carbon Dioxide Retention • Direct result of alveolar hypoventilation, dense gas, breathing apparatus, poor scrubbing • Symptoms • Headache, sweating, palpitations, breathlessness, peripheral vasodilatation • Ultimately brain stem depression and cessation of breathing • Not specific • Interactions with O2 toxicity and decompression sickness

28. Indications for HBO –Undersea and Hyperbaric Medical Society (UHMS) • Related to diving and compressed air work • decompression illness • Air or gas embolism • Acute conditions • Carbon monoxide poisoning • Clostridial myonecrosis • soft tissue necrotising infections • Crush injury, compartment syndrome and other traumatic ischaemias • Exceptional blood loss anaemia

29. Mechanisms of action and effects of HBO • Increase of oxygenation of tissue fluids • Reduction in tissue oedema • Increased capillary proliferation • Increase in fibroblast growth • Increase in collagen formation • Decrease lipid peroxidation by PMN leucocytes

30. Side Effects of HBO Treatment • Cough, dyspnoea • Barotrauma • ear drums, sinuses • pulmonary • Oxygen toxicity • retrosternal discomfort, pulmonary oxygen toxicity, convulsion • Decompression Illness (Chamber attendants) • Fire Hazard!

31. Contraindications • Abnormal Eustachian Tube function • e.g. Upper respiratory tract infections or sinusitis • ENT assessment to ensure normal Eustachian tube function • prophylactic myringotomy if necessary • Drug therapy with • doxorubicin, disulfiram, bleomycin, cisplatin or mafenide acetate • Untreated pneumothorax

32. The Recompression Treatment Centre (RTC) • Up to 1994, recompression therapy was provided by UK Royal Navy • RTC opened in 1994 • Operated by HK Fire Services Department • Maintenance by EMSD • Medical supervision offered by Occupational Medicine Division, Labour Department • Intensive Care supported by ICU, PMH, ?now

33. Referral to Occupational Medicine Division, LD • Emergency • Notified Fire Service Department • Contact first call Occupational Health Officer and discuss the management plan • Transfer patients to RTC with referrals and medical records • Accompanied by medical staff of the relevant units

34. Control Panel with Fireman

35. Control Panel

36. Control Panel

37. Control Panel

38. Entrance to Chamber

39. Emergency Trolley

40. Medical equipments and consumables