Hyperbaric Medicine for Exploration Class Missions Gregory Stewart MD Friday January 18 th , 2013

2. Hyperbaric Medicine for Exploration Class Missions Gregory Stewart MD Friday January 18th, 2013 Western University CPSX

3. Objectives • Discuss Exploration Medicine and its importance to Life on Earth • Discuss the Space Environment & the Physiology of Decompression Stress • Discuss the Clinical Manifestations & Treatment of Decompression Sickness • Discuss the Medical Training for Management of Decompression Sickness on Exploration Class Missions

4. Disclosures None

5. Why Explore? • “The greatest danger for most of us is not that our aim is too high and we miss it, but that it is too low and we reach it.” • Michelangelo

6. William Munkhouse • Ship Surgeon on HMS Endeavour in 1768 with Captain James Cook • He discovered that “Antiscorbatics” prevent ‘Scurvy’ and reduce crew mortality from ~50% to 0% • This enabled longer missions at sea

7. John Stapp MD • Pioneer of the modern restraint system (pictured) • “The most reliable instrument for measuring the varied effects of dynamic force on man is man”

8. Joseph Kerwin MD • First Physician in Space & Skylab (pictured) • Spaceflight Data Era • “Exploration of the heavens still has a value independent of the commercial and military arguments we use in its defense. The hunger to know and to see is one of our defining characteristics as human beings”

10. Leonard Butson WAG

11. George Stewart ERA

12. Student Pilot

13. Instrument & Commercial Pilot

14. Research at KSC • Topic: Medical Education for Exploration Class Missions • Stewart & Drudi. McGill Journal of Medicine. 2011.

19. Training at JSC • University of Texas Medical Branch Introduction to Aerospace Medicine

25. Hyperbaric Training • Divers Alert Network (DAN) & Emergency Room Physician • Aerospace Medical Association (ASMA) & Undersea Hyperbaric Medical Society (UHMS) • Professional Association of Diving Instructors (PADI) Scuba Instructor

30. Divisions of the Atmosphere • Physiological Zone: 0 - 10,000 feet • No Supplemental Oxygen Required • Deficient Zone: 10,000 – 50,000 feet • Supplemental Oxygen Required • Space Zone: >50,000 feet • Full Pressure Suit (U2, SR71) or Spacecraft

31. Space Environment • International Space Station – 21% O2 • 101 kPa = 14.7 psi = 760 mmHg • Space Shuttle EVA “Campout” – 23% O2 • 70.3 kPa = 10.2 psi = 530 mmHg • EMU Space Suit – 100% O2 (Prebreathe) • 29.7 kPa = 4.3 psi = 220 mmHg (EVA)

32. Space Environment • Cabin atmospheric pressure in all current spacecraft is sea level pressure • Space suit pressure represents a compromise between engineering concerns (suit flexbility) and physiological risks (decompression stress)

33. Decompression • Decompression is a serious concern in space and is 1 of 3 Class One emergency alarms on ISS • Fire & Toxic are others • Decompression can be sudden (orbital debris) or gradual (leak) in either the ISS cabin or EMU space suit

34. Decompression Sickness (DCS) • DCS (Henry’s Law): a disease caused when the total gas tension dissolved in an astronauts body tissues exceeds ambient hydrostatic pressure and gas bubble formation occurs • Two Environments: • Altitude/Hypobaric DCS (Aviation, Space) • Hyperbaric DCS (Diving)

35. Physiology of DCS • Bubble Formation vs Bubble Growth ? • The presence of bubbles in body tissues serves as a nuclei for the initiation of biochemical and cellular processes that once begun, can lead to morbidity and mortality (even after the bubbles are gone)

36. Physiology of DCS • Our current understanding of hypobaric DCS has been derived by extrapolation from experience with hyperbaric DCS • While analogous, they are fundamentally different in terms of: • Pressure profile: gradual in EVAs • Bubble formation: slower in EVAs • Symptom onset: during EVAs!!! • Natural History: less serious in EVAs

37. Decompression Sickness • Diagnostic Criteria for DCS • Certain: exposure with symptom onset <48 hours and verified with physician exam • Possible: exposure with symptom onset <24 hours and typical complaints (no exam) OR resolution with O2 (before exam) • Type I DCS (typical): itching, rash, joint pain, muscle aches or numbness/tingling • Type 2 DCS (serious): paralysis, respiratory distress, audiovestibular dysfunction, shock

38. Differential Diagnosis for DCS • Diving Related • Pulmonary Barotrauma • Near-Drowning • Immersion Pulmonary Edema • Marine Animal Envonemation • Gas Toxicity • Hyercapnia • Hyperventilation • Inner Ear Barotrauma • Not Diving Related • Sprains/Strains • Viral/Bacterial Illness • Cerebrovascular Accident (Stroke) • Migraine • Toxic Ingestion • Spinal Cord Compression • Drug Side Effects • Psychiatric Conditions

39. Hypobaric DCS Symptoms • Joint and Limb Pain: 70.7% • Extremity Paresthesia: 32.9% • Numbness: 23.5% • Muscular Weakness: 17.1% • Dizziness: 15.7% • Headache: 8.6% • Nausea and Vomiting: 7.8% • Visual Disturbances: 7.9% • Fatigue and Malaise: 5.7%

40. Hypobaric DCS Joint Pain • Elbows: 34% • Shoulders: 30% • Knees: 29% • Arms: 10% • Wrists: 9% • Hips: 5% • Legs: 4% • Ankles: 4% • Hands: 2% • Feet: 2%

41. Microgravity DCS • No reported cases of DCS in Microgravity • The microgravity environment may blend decompression stress of both flying and diving operations (fluids shifts in diving with pressure changes in aviation)

42. Cabin Decompression • NASA uses BUMPER to determine risks of meteoroid and orbital debris impact damage and critical penetration of spacecraft • Over 15 year lifespan of ISS there is a 48% risk of penetration and a 15% chance of station evacuation

43. Mir 24 1997 • Cabin depressurization occurred with the collision of a Progress cargo vessel with the Mir station • Astronaut Mike Foale roughly determined initial depressurization rate by monitoring his own sensation of Eustachian tube popping while performing module isolation

44. Soyuz 11 1971 • Decompression of the capsule on re-entry due to a procedural error resulting in the death of three cosmonauts • Management of the issue required closure of a cabin vent that was out of reach of the restrained crew during sudden capsule decompression

45. EVA Decompression • EMU space suit pressure readings below 3.9 psi activates the secondary oxygen pack switch to purge mode • This maintains a survivable internal pressure for up to 30 minutes • Typical micrometeoroid hole (<4mm) • A hole >4mm is considered critical • The risk of EVA decompression is 1 in 8 over the lifetime of ISS

46. Exploration DCS • Diagnostic dilemmas become even more intense in the setting of severe DCS during an exploration class mission • Since the nature of DCS symptoms at onset does NOT predict eventual severity, an onsite hyperbaric facility would be ideal with a high tempo EVA exploration mission

47. Treatment of DCS • Four Principles • Increase the ambient pressure • Increase the partial pressure of O2 inspired • Fluids through the intravascular route • Supportive care including airway management

48. Treatment of DCS • 1) “Wait and See” Approach • Allows operations to continue • 2) Return to Cabin Ambient Pressure • Acceptable for mild Type 1 DCS • 3) Ground Level Oxygen “Post-breathe” • Acceptable if Type 2 DCS ruled out • 4) Hyperbaric Oxygen Therapy (HBOT) • US Navy Treatment Table 6

49. US Navy Treatment Table 6

50. Physiology of HBOT • Decrease bubble size and volume • Increases gas off-loading (100% O2 Window) & increases O2 delivery to tissues • Decreases tissue edema & inflammation • HBOT has been observed to be effective long after tissue bubbles have been removed