Aviation Medicine

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Blair Munford

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Aviation Medicine

  1. 1. AVIATION PHYSIOLOGYThe Scientific Foundation of Air Medical Transport Blair Munford, FANZCA NRMA CareFlight/New South Wales Medical Retrieval Service
  2. 2. Aviation Physiology and Critical Care Transport RELEVANT TO:q Mode of Transport – Road vs rotorwing vs fixed wingq Patient Selectionq Patient Treatmentq Aircrew Issues – Risks, precautions, fitness to fly. NRMA CareFlight 2
  3. 3. Aviation Medicine vs Aeromedicine vs Air Medicine A V IA T IO N P H Y S IO L O G Y A V IA T IO N A IR M E D IC IN E M E D IC IN E O c c u p a t io n a l C r itic a l C a r e & H e a lt h E m e r g e n c y M e d ic in e NRMA CareFlight 3
  4. 4. Stresses of Flightq Hypoxia q Immobilityq Dysbarism q Motion sicknessq Thermal stress q Spacial Disorientationq Dehydration q Third Spacingq Noise q Anxietyq Vibration q Dystemporismq G forces q Fatigue NRMA CareFlight 4
  5. 5. FOUR GAS LAWSq Boyles Law q Henry’s Law P1V1 = P2V2 Cdissolved = k.Pgaseous Trapped Gas Evolved Gas Disorders Disorders q Charles’ LawqDalton’s Law V1/V2 = T1/T2Ptot = P1 + P2 . . . + Pn (or Blair’s Hypoxia! modification) P.V = k.T NRMA CareFlight 5
  6. 6. THE ATMOSPHERE: Physicalq TROPOSPHERE: 0 (SL) -15,000m – Contains clouds. Temperature falls with altitude.q STRATOSPHERE: 15,000 - 50,000m – Includes ozone layerq MESOSPHERE: 50,000 - 80,000m (50-80km)q IONOSPHERE: 80 - 650 km – UV & gamma irradiation produces ionsq EXOSPHERE: 650 - 9,500 km. NRMA CareFlight 6
  7. 7. The Earth’s Atmosphere NRMA CareFlight 7
  8. 8. AVIATION PHYSIOLOGY EXAM? Q1. Identify the four components of the atmosphere. Air, Clouds, Birds, & Helicopters? NRMA CareFlight 8
  9. 9. THE ATMOSPHERE: ChemicalGAS % OF ATM P (SL) N2 78% 593mm Hg O2 20.95% 160mm Hg Ar 0.9% 7mm HgOther 0.05% 0.35mm Hg NRMA CareFlight 9
  10. 10. ALTITUDE TABLEAltitude Pressure pO2 Temp Volume (feet) (mm Hg) (mm Hg) (Celcius) Change SL 760 159 15.0 --- 1000 733 153 13.0 3.1% 2000 706 148 11.0 7.6% 4000 656 137 7.1 15.8% 7000 586 122 1.2 29.7%10,000 523 110 -4.8 45%20,000 349 73 -24.6 117% NRMA CareFlight 10
  11. 11. THE ATMOSPHERE: Physiologicalq Efficient (Physiological) zone – 0-12,000’ (0-4000m) Pb 760 - 480 mmHgq (Physiological) Deficiency zone – 12-45,000’ Pb 480 - 110 mmHgq Partial Space Equivalent Zone – 45-600,000’. Pressurisation mandatoryq Total Space Equivalent Zone – >600,000’ (200km). Weightlessness NRMA CareFlight 11
  12. 12. HYPOXIA“The Hidden Enemy of Air Medical Transport”q PATIENTS q AIRCREW NRMA CareFlight 12
  13. 13. CLASSIFICATION OF HYPOXIA q Hypoxic Hypoxia q Anaemic Hypoxia q Stagnant Hypoxia q Histotoxic Hypoxia NRMA CareFlight 13
  14. 14. EFFECTS OF HYPOXIAq CENTRAL NERVOUS SYSTEM – Progressive dysfunction starting with retina & higher centres.q RESPIRATORY SYSTEM – Increased MV with decreased PaCO2.q CARDIOVASCULAR SYSTEM – HR increases followed by peripheral vasoconstriction & cerebral vasodilatation NRMA CareFlight 14
  15. 15. STAGES OF HYPOXIAq INDIFFERENT q DISTURBANCE <10,000’, SaO2>90% 15-20,000’ SaO2 70-80% HR & RR increase Compensatory failure Effect on night vision Significant CNS changesq COMPENSATED q CRITICAL 10-15,000’ SaO2 80-90% 20,000’+ SaO2 <70% CO & sBP rise Rapid onset of coma & CNS symptoms seizures; death likely. NRMA CareFlight 15
  16. 16. OXYGEN THERAPYq ALVEOLAR GAS EQUATION PAO2 = PiO2 - PACO2 / R + Fq FiO2 CALCULATION FiO2(2) = FiO2(1) x P1 / P2 NRMA CareFlight 16
  17. 17. DYSBARISMq TRAPPED GAS DISORDERS (Boyles Law)q EVOLVED GAS DISORDERS (Henry’s Law) NRMA CareFlight 17
  18. 18. TRAPPED GAS DISORDERS q Physiological Air Spaces q Pathological Air Spaces q Technological Air Spaces (Equipment) NRMA CareFlight 18
  19. 19. Trapped Gas Disorders I: “Physiological”q Barotitis Media q Barodentalgia – Ascending squeeze – Ascending squeeze – Descending squeeze onlyq Barosinusitis q Baroenteralgia – Ascending squeeze – Ascending squeeze – Descending squeeze only NRMA CareFlight 19
  20. 20. Trapped Gas Disorders II: “Pathological” q Intracranial air q Open eye injury q Pneumothorax q Emphysema/bullae/ asthma q Bowel obstruction or rupture NRMA CareFlight 20
  21. 21. Trapped Gas Problems with Equipmentq Endotracheal/tracheostomy tube cuffsq Sengstarken-Blakemore tubesq Swann-Ganz balloonsq Pneumatic antishock garments (MAST)q Air splintsq Drainage bags – Nasogastric/intercostal/colostomy NRMA CareFlight 21
  22. 22. EVOLVED GAS DISORDERSq Remember Henry’s Lawq Problem is dissolved N2 (1.0 -1.5 L)q Requires decompression – Abrupt : Universal risk – Planned : At risk individuals only NRMA CareFlight 22
  23. 23. RISK FACTORS FOREVOLVED GAS DISORDERS q DIVING (& Hyperbaric training) q Prolonged altitude exposure q Obesity q Alcohol q Dehydration q Cold NRMA CareFlight 23
  24. 24. DECOMPRESSION SICKNESS Effects include: q Joints – “The Bends” q Skin - Bariobariatrauma q Central Nervous System q Arterial Gas Embolism !!! – “The chokes” - abrupt decompression NRMA CareFlight 24
  25. 25. CABIN PRESSURISATION I: PRINCIPLESq Applicable to fixed wing onlyq Partial defense against: – Hypoxia – Dysbarismq Creates artificial “Cabin Altitude”q Cabin altitude dependant on: – Actual altitude – Maximal pressure differential NRMA CareFlight 25
  26. 26. CABIN PRESSURISATION I: CALCULATIONSq Example I - Lear 35 Maximum cabin pressure differential 430mm Hg So @ 40,000’ (=141 mm Hg) can maintain cabin altitude of 570 mmHg = 8000’q Example II - King Air 200. Sea level cabin altitude requested. Max cabin pressure differential = 350 mm Hg. So can fly at 410 mm Hg = 16,000’ NRMA CareFlight 26
  27. 27. THERMAL STRESS I: PRINCIPLESq Remember mechanisms of heat loss: CONVECTION CONDUCTION EVAPORATION RADIATIONq Outside air temperature – drops 2 degrees C per 1000’ riseq Helo patients also at risk of temp rise NRMA CareFlight 27
  28. 28. THERMAL STRESS I: Special Risk Patientsq Paralysed/Sedatedq Intoxicatedq Polyinfused/transfusedq Immersion or other wetq Pre existing hypothermiaq Burns patientsq Prolonged transports NRMA CareFlight 28
  29. 29. HUMIDITY & DEHYDRATIONq Water vapour content falls with increasing altitude & decreasing temp.q Pressurised aircraft has WVP of outside pressure not cabin pressure EFFECTS ONq RESPIRATORY SYSTEMq Other mucus membranesq Endocrine/renal/CVS axis NRMA CareFlight 29
  30. 30. NOISEq Major hinderance to patient careq Level: Helo > Fixed wing > Roadq Noise interferes with – Communication – Patient assessment - e.g auscultationq Hearing protection & communications technology mandatory in helicopter. NRMA CareFlight 30
  31. 31. VIBRATIONq Interferes with: – Patient comfort – Metabolic Rate (increases) – Equipment: NIBP, SaO2, etc.q Vibration levels: Road(bad) > Helo > FW take off > Road (good) > FW cruiseq Vibration minimisation – Passive vs active NRMA CareFlight 31
  32. 32. GRAVITATIONAL FORCESq Levels of G force experienced: 1. Road vehicle (brake/swerve) 2. Fixed wing takeoff & landing 3. Road vehicle (normal driving) 4. Fixed wing climb/cruise/descent 5. Helicopter (all normal ops)q Positioning may minimise effects NRMA CareFlight 32
  33. 33. SPACIAL DISORIENTATION“INCORRECT PERCEPTION OF POSITION, MOTION OR ATTITUDE”Due to absent or incorrect input from one or more of:q Visual systemq Vestibular apparatusq Proprioceptive apparatus NRMA CareFlight 33
  34. 34. MOTION SICKNESSq Variable susceptibility Precipitating factors include:q Turbulenceq Spatial disorientationq Hot/stuffy environmentq Hunger or oversatiationq Fear or unpleasant stimuliq Medications NRMA CareFlight 34
  35. 35. “THIRD SPACING”q Fluid leakage into interstitiumq Increased during transportq Multifactorial – VIBRATION – G forces – Temperatureq Effects include: – Oedema/swelling under casts – Effective dehydration/hypovolaemia NRMA CareFlight 35
  36. 36. DYSTEMPORISMq Common name: “jet lag”q Occurs with transmeridian travelq Disturbance of circadian rhythmq Sun following (westward) versus sun shortening (eastward) travel.q Influenced by: activity/food/alcoholq Hypnotics for sleep restoration: – Temazepam vs oxazepam NRMA CareFlight 36
  37. 37. FATIGUE I: THE PROBLEMq Fatigue itself is a stressorq Fatigue is also the common point of other stressors.q Fatigue affects judgement & perception – INCLUDING OF FATIGUE ITSELFq Air medical crew fatigue is a potential killer: – OF PATIENTS – OF AIRCREW NRMA CareFlight 37
  38. 38. FATIGUE I: THE RISK FACTORSq Remember the avoidable: D*E*A*T*Hq Drugsq Exhaustionq Alcoholq Tobaccoq Hypoglycaemia NRMA CareFlight 38
  39. 39. SUMMARYq All medical transport including by air creates a sub optimal environment.q Many patients may be at risk from this exposure.q The challenge is to provide optimal care in spite of the environmentq Knowledge of the environment is the key to achieving this. NRMA CareFlight 39
  40. 40. THE ENDAny Questions?

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