AVIATION PHYSIOLOGYAVIATION PHYSIOLOGYThe Scientific Foundation The Scientific Foundation

ofofAir Medical TransportAir Medical Transport

Blair Munford, FANZCABlair Munford, FANZCA

NRMA CareFlight/New South NRMA CareFlight/New South Wales Medical Retrieval Wales Medical Retrieval

Service Service

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Aviation Physiology and Aviation Physiology and Critical Care TransportCritical Care Transport

RELEVANT TO:RELEVANT TO: Mode of TransportMode of Transport

– Road vs rotorwing vs fixed wingRoad vs rotorwing vs fixed wing Patient SelectionPatient Selection Patient TreatmentPatient Treatment Aircrew IssuesAircrew Issues

– Risks, precautions, fitness to fly.Risks, precautions, fitness to fly.

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Aviation Medicine vs Aviation Medicine vs AeromedicineAeromedicine

vs Air Medicinevs Air Medicine

AV IA TIO NMED IC INE

O ccu p ation a lH ea lth

Critical Care &Em ergency M edicine

AIRM EDICINE

AVIAT ION PHYSIOLOGY

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Stresses of FlightStresses of Flight

HypoxiaHypoxia DysbarismDysbarism Thermal stressThermal stress DehydrationDehydration NoiseNoise VibrationVibration G forcesG forces

ImmobilityImmobility Motion sicknessMotion sickness Spacial Spacial

DisorientationDisorientation Third SpacingThird Spacing AnxietyAnxiety DystemporismDystemporism FatigueFatigue

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FOUR GAS LAWSFOUR GAS LAWS

Boyles LawBoyles Law

P1V1 = P2V2P1V1 = P2V2

Trapped Gas Trapped Gas DisordersDisorders

Dalton’s LawDalton’s Law

PPtottot = = P1 + P2 . . . P1 + P2 . . . + P+ Pnn

Hypoxia!Hypoxia!

Henry’s LawHenry’s Law

CCdissolveddissolved = k.P = k.Pgaseousgaseous

Evolved Gas Evolved Gas DisordersDisorders

Charles’ LawCharles’ Law

V1/V2 = T1/T2V1/V2 = T1/T2(or Blair’s modification)(or Blair’s modification)

P.V = k.TP.V = k.T

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THE ATMOSPHERE: PhysicalTHE ATMOSPHERE: Physical TROPOSPHERE: TROPOSPHERE: 0 (SL) -15,000m0 (SL) -15,000m

– Contains clouds. Temperature falls with Contains clouds. Temperature falls with altitude.altitude.

STRATOSPHERE: STRATOSPHERE: 15,000 - 50,000m15,000 - 50,000m– Includes ozone layerIncludes ozone layer

MESOSPHERE: MESOSPHERE: 50,000 - 80,000m (50-80km)50,000 - 80,000m (50-80km) IONOSPHERE: IONOSPHERE: 80 - 650 km80 - 650 km

– UV & gamma irradiation produces ionsUV & gamma irradiation produces ions EXOSPHERE: EXOSPHERE: 650 - 9,500 km.650 - 9,500 km.

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The Earth’s AtmosphereThe Earth’s Atmosphere

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AVIATION PHYSIOLOGY AVIATION PHYSIOLOGY EXAM?EXAM?

Q1. Identify the four components of the atmosphere.

Air, Clouds,Birds, &Helicopters?

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THE ATMOSPHERE:THE ATMOSPHERE:ChemicalChemical

GAS % OF ATM P (SL)

N2 78% 593mm Hg

O2 20.95% 160mm Hg

Ar 0.9% 7mm Hg

Other 0.05% 0.35mm Hg

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ALTITUDE TABLEALTITUDE TABLE

Altitude(feet)

Pressure(mm Hg)

pO2(mm Hg)

Temp(Celcius)

VolumeChange

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%

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THE ATMOSPHERE:THE ATMOSPHERE:PhysiologicalPhysiological

Efficient (Physiological) zoneEfficient (Physiological) zone– 0-12,000’ (0-4000m) P0-12,000’ (0-4000m) Pbb 760 - 480 mmHg 760 - 480 mmHg

(Physiological) Deficiency zone(Physiological) Deficiency zone– 12-45,000’ P12-45,000’ Pbb 480 - 110 mmHg 480 - 110 mmHg

Partial Space Equivalent ZonePartial Space Equivalent Zone– 45-600,000’. Pressurisation mandatory45-600,000’. Pressurisation mandatory

Total Space Equivalent ZoneTotal Space Equivalent Zone– >600,000’ (200km). Weightlessness>600,000’ (200km). Weightlessness

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HYPOXIAHYPOXIA“The Hidden Enemy of Air Medical “The Hidden Enemy of Air Medical

Transport”Transport”

PATIENTSPATIENTS AIRCREWAIRCREW

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CLASSIFICATION OF HYPOXIACLASSIFICATION OF HYPOXIA

Hypoxic HypoxiaHypoxic Hypoxia

Anaemic HypoxiaAnaemic Hypoxia

Stagnant HypoxiaStagnant Hypoxia

Histotoxic HypoxiaHistotoxic Hypoxia

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EFFECTS OF HYPOXIAEFFECTS OF HYPOXIA

CENTRAL NERVOUS SYSTEMCENTRAL NERVOUS SYSTEM– Progressive dysfunction starting with Progressive dysfunction starting with

retina & higher centres.retina & higher centres. RESPIRATORY SYSTEMRESPIRATORY SYSTEM

– Increased MV with decreased PaCO2.Increased MV with decreased PaCO2. CARDIOVASCULAR SYSTEMCARDIOVASCULAR SYSTEM

– HR increases followed by peripheral HR increases followed by peripheral vasoconstriction & cerebral vasoconstriction & cerebral vasodilatationvasodilatation

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STAGES OF HYPOXIASTAGES OF HYPOXIA

INDIFFERENTINDIFFERENT<10,000’, SaO2>90%<10,000’, SaO2>90%

HR & RR increaseHR & RR increase

Effect on night visionEffect on night vision

COMPENSATEDCOMPENSATED10-15,000’ SaO2 80-10-15,000’ SaO2 80-

90%90%

CO & sBP riseCO & sBP rise

CNS symptomsCNS symptoms

DISTURBANCEDISTURBANCE15-20,000’ SaO2 70-15-20,000’ SaO2 70-

80%80%

Compensatory failureCompensatory failure

Significant CNS changesSignificant CNS changes

CRITICALCRITICAL20,000’+ SaO2 <70%20,000’+ SaO2 <70%

Rapid onset of coma & Rapid onset of coma & seizures; death likely.seizures; death likely.

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OXYGEN THERAPYOXYGEN THERAPY

ALVEOLAR GAS EQUATIONALVEOLAR GAS EQUATION

PPAAO2 = PiO2 - PO2 = PiO2 - PAACO2 / R + FCO2 / R + F

FiO2 CALCULATIONFiO2 CALCULATION

FiO2FiO2(2) (2) = FiO2 = FiO2(1) (1) x P1 / P2 x P1 / P2

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DYSBARISMDYSBARISM

TRAPPED GAS DISORDERSTRAPPED GAS DISORDERS

(Boyles Law)(Boyles Law)

EVOLVED GAS DISORDERSEVOLVED GAS DISORDERS

(Henry’s Law)(Henry’s Law)

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TRAPPED GAS DISORDERSTRAPPED GAS DISORDERS

Physiological Air Physiological Air SpacesSpaces

Pathological Air SpacesPathological Air Spaces

Technological Air Technological Air SpacesSpaces

(Equipment)(Equipment)

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Trapped Gas Disorders I: Trapped Gas Disorders I: “Physiological”“Physiological”

Barotitis MediaBarotitis Media– Ascending squeezeAscending squeeze– Descending Descending

squeezesqueeze

BarosinusitisBarosinusitis– Ascending squeezeAscending squeeze– Descending Descending

squeezesqueeze

BarodentalgiaBarodentalgia– Ascending Ascending

squeeze onlysqueeze only

BaroenteralgiaBaroenteralgia– Ascending Ascending

squeeze onlysqueeze only

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Trapped Gas Disorders II: Trapped Gas Disorders II: “Pathological”“Pathological”

Intracranial airIntracranial air Open eye injuryOpen eye injury PneumothoraxPneumothorax Emphysema/Emphysema/

bullae/ asthmabullae/ asthma Bowel obstruction Bowel obstruction

or ruptureor rupture

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Trapped Gas Problems with Trapped Gas Problems with EquipmentEquipment

Endotracheal/tracheostomy tube cuffsEndotracheal/tracheostomy tube cuffs Sengstarken-Blakemore tubesSengstarken-Blakemore tubes Swann-Ganz balloonsSwann-Ganz balloons Pneumatic antishock garments (MAST)Pneumatic antishock garments (MAST) Air splintsAir splints Drainage bagsDrainage bags

– Nasogastric/intercostal/colostomyNasogastric/intercostal/colostomy

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EVOLVED GAS DISORDERSEVOLVED GAS DISORDERS

Remember Henry’s LawRemember Henry’s Law

Problem is dissolved N2Problem is dissolved N2(1.0 -1.5 L)(1.0 -1.5 L)

Requires decompressionRequires decompression– Abrupt : Universal riskAbrupt : Universal risk– Planned : At risk individuals Planned : At risk individuals

onlyonly

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RISK FACTORS FORRISK FACTORS FOREVOLVED GAS DISORDERSEVOLVED GAS DISORDERS

DIVING (& Hyperbaric DIVING (& Hyperbaric training)training)

Prolonged altitude Prolonged altitude exposureexposure

ObesityObesity AlcoholAlcohol DehydrationDehydration ColdCold

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DECOMPRESSION SICKNESSDECOMPRESSION SICKNESS

Effects include:Effects include: JointsJoints

– ““The Bends”The Bends” Skin - BariobariatraumaSkin - Bariobariatrauma Central Nervous SystemCentral Nervous System Arterial Gas Embolism !!!Arterial Gas Embolism !!!

– ““The chokes” - abrupt The chokes” - abrupt decompressiondecompression

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CABIN PRESSURISATION I:CABIN PRESSURISATION I:PRINCIPLESPRINCIPLES

Applicable to fixed wing onlyApplicable to fixed wing only Partial defense against:Partial defense against:

– HypoxiaHypoxia– DysbarismDysbarism

Creates artificial “Cabin Altitude”Creates artificial “Cabin Altitude” Cabin altitude dependant on:Cabin altitude dependant on:

– Actual altitudeActual altitude– Maximal pressure differentialMaximal pressure differential

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CABIN PRESSURISATION I:CABIN PRESSURISATION I:CALCULATIONSCALCULATIONS

Example I - Lear 35Example I - Lear 35Maximum cabin pressure differential 430mm Maximum cabin pressure differential 430mm

Hg So @ 40,000’ (=141 mm Hg) can maintain Hg So @ 40,000’ (=141 mm Hg) can maintain cabin altitude of 570 mmHg = 8000’cabin altitude of 570 mmHg = 8000’

Example II - King Air 200.Example II - King Air 200.Sea level cabin altitude requested. Max cabin Sea level cabin altitude requested. Max cabin

pressure differential = 350 mm Hg. So can pressure differential = 350 mm Hg. So can fly at 410 mm Hg = 16,000’fly at 410 mm Hg = 16,000’

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THERMAL STRESS I: THERMAL STRESS I: PRINCIPLESPRINCIPLES

Remember mechanisms of heat loss:Remember mechanisms of heat loss:

CONVECTIONCONVECTION

CONDUCTIONCONDUCTION

EVAPORATIONEVAPORATION

RADIATIONRADIATION Outside air temperatureOutside air temperature

– drops 2 degrees C per 1000’ risedrops 2 degrees C per 1000’ rise Helo patients also at risk of temp riseHelo patients also at risk of temp rise

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THERMAL STRESS I: THERMAL STRESS I: Special Risk Patients Special Risk Patients Paralysed/SedatedParalysed/Sedated IntoxicatedIntoxicated Polyinfused/transfusedPolyinfused/transfused Immersion or other wetImmersion or other wet Pre existing Pre existing

hypothermiahypothermia Burns patientsBurns patients Prolonged transportsProlonged transports

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HUMIDITY & DEHYDRATIONHUMIDITY & DEHYDRATION Water vapour content falls with Water vapour content falls with

increasing altitude & decreasing temp.increasing altitude & decreasing temp. Pressurised aircraft has WVP of Pressurised aircraft has WVP of

outsideoutside pressure pressure notnot cabin pressure cabin pressure

EFFECTS ONEFFECTS ON RESPIRATORY SYSTEMRESPIRATORY SYSTEM Other mucus membranesOther mucus membranes Endocrine/renal/CVS axisEndocrine/renal/CVS axis

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NOISENOISE

Major hinderance to patient careMajor hinderance to patient care Level: Helo > Fixed wing > RoadLevel: Helo > Fixed wing > Road Noise interferes withNoise interferes with

– CommunicationCommunication– Patient assessment - e.g auscultationPatient assessment - e.g auscultation

Hearing protection & Hearing protection & communications technology communications technology mandatory in helicopter.mandatory in helicopter.

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VIBRATIONVIBRATION Interferes with:Interferes with:

– Patient comfortPatient comfort– Metabolic Rate (increases)Metabolic Rate (increases)– Equipment: NIBP, SaO2, etc.Equipment: NIBP, SaO2, etc.

Vibration levels:Vibration levels:Road(bad) > Helo > FW take off > Road (good)Road(bad) > Helo > FW take off > Road (good)

> FW cruise > FW cruise Vibration minimisationVibration minimisation

– Passive vs activePassive vs active

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GRAVITATIONAL FORCESGRAVITATIONAL FORCES

Levels of G force experienced:Levels of G force experienced:

1. Road vehicle (brake/swerve) 1. Road vehicle (brake/swerve)

2. Fixed wing takeoff & landing2. Fixed wing takeoff & landing

3. Road vehicle (normal driving)3. Road vehicle (normal driving)

4. Fixed wing 4. Fixed wing climb/cruise/descentclimb/cruise/descent

5. Helicopter (all normal ops)5. Helicopter (all normal ops) Positioning may minimise effectsPositioning may minimise effects

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SPACIAL DISORIENTATIONSPACIAL DISORIENTATION

““INCORRECT PERCEPTION OF INCORRECT PERCEPTION OF POSITION, MOTION OR ATTITUDE”POSITION, MOTION OR ATTITUDE”

Due to absent or incorrect input from Due to absent or incorrect input from one or more of:one or more of:

Visual systemVisual system Vestibular apparatusVestibular apparatus Proprioceptive apparatusProprioceptive apparatus

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MOTION SICKNESSMOTION SICKNESS Variable susceptibilityVariable susceptibility

Precipitating factors include:Precipitating factors include: TurbulenceTurbulence Spatial disorientationSpatial disorientation Hot/stuffy environmentHot/stuffy environment Hunger or oversatiationHunger or oversatiation Fear or unpleasant stimuliFear or unpleasant stimuli MedicationsMedications

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““THIRD SPACING”THIRD SPACING” Fluid leakage into interstitiumFluid leakage into interstitium Increased during transportIncreased during transport MultifactorialMultifactorial

– VIBRATIONVIBRATION– G forcesG forces– TemperatureTemperature

Effects include:Effects include:– Oedema/swelling under castsOedema/swelling under casts– Effective dehydration/hypovolaemiaEffective dehydration/hypovolaemia

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DYSTEMPORISMDYSTEMPORISM Common name: “jet lag”Common name: “jet lag” Occurs with transmeridian travelOccurs with transmeridian travel Disturbance of circadian rhythmDisturbance of circadian rhythm Sun following (westward) versus sun Sun following (westward) versus sun

shortening (eastward) travel.shortening (eastward) travel. Influenced by: activity/food/alcoholInfluenced by: activity/food/alcohol Hypnotics for sleep restoration:Hypnotics for sleep restoration:

– Temazepam vs oxazepamTemazepam vs oxazepam

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FATIGUE I: THE PROBLEMFATIGUE I: THE PROBLEM

Fatigue itself is a stressorFatigue itself is a stressor Fatigue is also the common point of Fatigue is also the common point of

other stressors.other stressors. Fatigue affects judgement & Fatigue affects judgement &

perceptionperception– INCLUDING OF FATIGUE ITSELFINCLUDING OF FATIGUE ITSELF

Air medical crew fatigue is a Air medical crew fatigue is a potential killer:potential killer:– OF PATIENTSOF PATIENTS– OF AIRCREWOF AIRCREW

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FATIGUE I: FATIGUE I: THE RISK FACTORSTHE RISK FACTORS

Remember the Remember the avoidable:avoidable:

D*E*A*T*HD*E*A*T*H DDrugsrugs EExhaustionxhaustion AAlcohollcohol TTobaccoobacco HHypoglycaemiaypoglycaemia

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SUMMARYSUMMARY

All medical transport including by air All medical transport including by air creates a sub optimal environment.creates a sub optimal environment.

Many patients may be at risk from Many patients may be at risk from this exposure.this exposure.

The challenge is to provide optimal The challenge is to provide optimal care in spite of the environmentcare in spite of the environment

Knowledge of the environment Knowledge of the environment is the key to achieving this.is the key to achieving this.

THE ENDTHE END

Any Questions?Any Questions?