Hyperbaric Medicine

1. Hyperbaric Medicine Rosen’s Chapter 200 March 1, 2007 Michael Savino, PGY-2

2. Hyperbaric Oxygen Therapy(HBO) • Involves intermittently breathing pure oxygen at greater than ambient pressure • Think of oxygen as a drug and the hyperbaric chamber as a dosing device • Elevating tissue oxygen tension is the primary effect

3. Hyperbaric Oxygen Therapy(HBO) • Primary therapy for: • Decompression sickness • Air embolism • Carbon monoxide poisoning • Adjunct therapy for: • Surgical intervention • Antibiotics

4. Accepted Indications • Air or gas embolism • Carbon monoxide poisoning • Clostridial myositis and myonecrosis • Crush injury, compartment syndrome, acute traumatic ischemias • Decompression sickness • Enhance healing of wounds • Necrotizing fasciitis • Chronic osteomyelitis • Radiation necrosis, brown recluse spider bites • Thermal burns

5. History of Hyperbaric Therapy • British physician, Henshaw, in 1662 used a chamber fitted with a large pair of organ bellows, so that air could either be compressed into the chamber or extracted from it. • In this ‘domicilium' increased pressures were used for the treatment of acute disease, and reduced pressures for the treatment of chronic diseases. • Oxygen discovered in 1775

6. 1889 – Moir used hyperbaric therapy to treat workers building railroad tunnels underneath the Hudson River. Reduced mortality rate of decompression sickness from 25% to only 1.6% per year. • 1926 - Six-story “steel ball hospital” in Cleveland, Ohio. The facility was capable of treating patients in 72 rooms over 12 floors at pressures of 3 atm absolute.

7. Basic Mechanisms • Boyle’s Law – pressure and volume inversely proportional under constant temperature • By increasing ambient pressure to 2 atm, decreases the volume by ½ • Therapeutic for bubble forming diseases such as decompression sickness or arterial gas embolism • Henry’s Law – at a given temperature, the amount of gas dissolved in solute is directly proportional to the partial pressure of the gas. • By increasing ambient pressure, more oxygen can be dissolved in the plasma

8. Mechanism of action • Angiogenesis in ischemic tissues • Bacteriostatic/bactericidal actions • Carboxyhemoglobin dissociation hastened • Clostridium perfringens alpha toxin synthesis inhibited • Vasoconstriction • Temporary inhibition of neutrophil Beta 2 integrin adhesion

9. Monoplace (1 person) or multiplace (2-14 patients) chamber • Pressures applied inside the chamber are usually 2-3 x atm pressure, plus may have an additional hydrostatic pressure equivalent of 1-2 atm. • Treatments last from 2-8 hours

10. Complications • Middle ear barotrauma • Middle ear barotrauma is the most common adverse effect of HBO treatment • As ambient pressure within the chamber increases, patient must be able to equalize the pressure in his/her middle ear • If not, pressure gradient develops across the tympanic membrane. Pain followed by hemorrhage or serous effusion develops • Prevention: teaching patient auto-insufflation technique or use of decongestants • If auto-insufflation fails, tympanostomy tubes are placed.

11. Complications • Pulmonary barotrauma • Rare • Suspect if pulmonary or hemodynamic changes occur during or shortly after decompression • Place chest tube if pneumothorax develops

12. Complications • Oxygen Toxicity - Manifested by injuries to lungs, CNS, and eyes: • Lungs – • Can impair elasticity, vital capacity, and gas exchange. Rare. But may occur when duration and pressures exceed normal therapeutic protocols • CNS toxicity – • Manifests as a grand mal seizure. (1-4/10,000 patients). • Risk is higher in hypercapnic, acidotic, or septic patients • Eyes – • Progressive myopia has been reported in patients undergoing repetitive daily therapy • Reversible within 6 weeks of discontinuing treatment

13. CLINICAL APPLICATIONS • Arterial gas embolism occurs when vascular wall is disrupted, as in: • Trauma • Iatrogenic (surgical) – cardiovascular, Ob/gyn, neurosurgical and orthopedic procedures, opening of central venous catheters • Iatrogenic (nonsurgical) - Pulmonary overexpansion during mechanical ventilation

14. Scuba Divers • Arterial gas embolism can occur due to pulmonary expansion on decompression • Decompression sickness (caisson disease or “the bends”) is attributed to formation of nitrogen bubbles in the body on decompression • Also occurs in miners and astronauts

15. Emergency treatment of gas bubble disorders • ABC’s plus hyperbaric oxygen therapy • Transfer to hyperbaric chamber ASAP • Gas bubbles may persist in tissues for days • Animal studies have shown efficacy of HBO therapy, but randomized clinical trials on humans have not been done

16. Mechanism of action of HBO in arterial gas embolism and decompression sickness – reduction of gas volume (Boyle’s Law), which can reduce vascular compromise acutely • Hyperoxygenation hastens inert gas diffusion and there is theoretical effect associated with leukocyte adherence to vascular endothelium damaged by bubbles

17. Carbon Monoxide Poisoning • Carbon monoxide poisoning is the leading cause of injury and death by poisoning in the world • Affinity of CO for hemoglobin (forming carboxyhemoglobin) is 200 times that of oxygen. • Risk of developing neurologic sequelae including: cognitive effects, memory loss, dementia, parkinsonism, paralysis, chorea, cortical blindness, personality changes and peripheral neuropathy. • Delayed sequelae occur 2-40 days after poisoning. • Incidence of sequelae is 25-50% after severe poisoning

18. Carbon Monoxide Poisoning • Supplemental oxygen is first line therapy • HBO causes carboxyhemoglobin dissociation to occur faster than pure oxygen at sea level pressure. • Animal studies show: improvement in • mitochondrial oxidative processes • Inhibition of lipid peroxidation • Impairment of leukocyte adhesion to injured vessels

19. Clostridial Myonecrosis(gas gangrene) • Prompt recognition is important • Mortality rates of 11-52% • Most authors agree on the clinical benefit of HBO treatment, but in retrospective studies, comparison among patient groups, evaluation of efficacy based on “tissue salvage” is difficult to obtain. • Diffused oxygen which raises capillary p02 levels at the wound site, stimulates capillary budding and granulation of new, healthy tissue.

20. Necrotizing Fasciitis andFournier’s gangrene • Riseman and colleagues reported that addition of HBO to surgical and antibiotic treatment reduced mortality versus surgery and antibiotics alone. • May suppress growth of anaerobic organisms • May increase leukocyte function and suppress bacterial growth

21. Blood loss anemia • Intermittent hyperbaric therapy exposures have been used to relieve temporary physiologic stress from acute anemia • Rarely used for this purpose • May be useful when crossmatching incompatibilities and religious beliefs prevent blood transfusions

22. Crush injury • HBO is used in limited degree for acute traumatic peripheral ischemia and suturing of severed limbs. • Reduces infection and wound dehiscence and improves healing • Improves oxygenation to hypoperfused tissue • Causes arterial hyperoxia causing vasoconstriction and decreased edema formation. • Also, intermittent pressure stimulates circulation and reduces edema. • Early use of HBO may reduce compartment pressures enough to avoid fasciotomy.

23. Gamow Bags, a rescue product for high-altitude climbers and trekkers, is used for the treatment of moderate to extreme altitude sickness. By increasing air pressure around the patient, the Bag simulates descents as much as 7,000 feet

24. Emerging concepts • Increasing interest and research regarding HBO therapy as adjunct treatment in wound healing • Use of HBO in multiple sclerosis, cerebral palsy, and vegetative coma is also being explored

25. OMM Considerations • None