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Aeromedical Retrieval > Module Three > Flashcards

Module Three Flashcards

1
Q

Describe atmospheric pressure.

A

1 x column of air/atmosphere. 1 atm = 14.7 psi / 1.03 kg/cm2 / 760 mmHg.

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2
Q

Where is the densest air?

A

At sea level.

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3
Q

What happens to barometric pressure as you ascend?

A

It decreases.

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4
Q

Describe Boyle’s Law.

A

Volume varies inversely with pressure if temperature is unchanged. With ascent, volume of gases increase, and pressures decrease proportionately.

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5
Q

What is the maximum elevation that an unpressurised aircraft will reach?

A

10,000 feet / 523 mmHG, volume 1.3-1.5 x at sea level.

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6
Q

Described Charles’ Law.

A

If the pressure of a gas is constant, the volume of that gas is proportional to its absolute temperature. If heated - gas expands, if cooled - gas contracts.

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7
Q

Describe the make-up of the atmosphere.

A

Mixed gases of uniform percent up to around 70,000 ft. Consists of 20.95% O2, 78.08% nitrogen, and less than 1% CO2, hydrogen, argon, neon, and helium.

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8
Q

Describe Dalton’s Law.

A

The total pressure of a gas is the sum of its partial pressures.

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9
Q

What is the relevance of Dalton’s Law to altitude?

A

As altitude increases, the partial pressure of O2 decreases but its percentage of the atmosphere remains the same. This may cause/exacerbate hypoxia.

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10
Q

Describe Henry’s Law.

A

The solubility of a gas in liquid is directly proportional to the partial pressure of the gas in contact with the liquid. With more pressure, more gas is dissolved, with less pressure, less is dissolved (or liberated from the solution, e.g. opening fizzy drink).

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11
Q

What are the four atmospheric physiologic zones?

A

Physiological/efficient zone
Physiological deficient zone
Partial space equivalent zone
Total space equivalent zone

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12
Q

Describe the physiological/efficient zone (5).

A

Sea level - 10,000 ft.
Barometric pressure: 760-523 mmHg.
Temperature drops 2C / 1000 ft gained.
Most acceptable zone for normal physiological function.
Mandated supplemental O2 > 10,000 ft.

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13
Q

Describe the physiological deficient zone (7).

A

10,000 - 50,000 ft.
Barometric pressure: 523mmHg - 87mmHg.
Normal phys. function progressively impaired above this.
Period of useful consciousness about 20 mins at 18,000 ft and 1-2 mins at 30,000 ft.
100% O2 required at 33,700 ft.
Pressure breathing required at 40,000 ft.
Pressure garment required at 50,000 ft.

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14
Q

Describe the partial space equivalent zone.

A

50,000 ft - 120 miles.
Pressurised environment mandatory.

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15
Q

Define hypoxia.

A

Oxygen deficiency in body tissues sufficient to cause impairment of physiological functioning.

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16
Q

Describe the four types of hypoxia.

A

Hypobaric - pressure issue
Hypaemic - RBC issue (anaemia)
Stagnant - pipe/pump failure (circulatory)
Histotoxic - tissues can’t use O2

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17
Q

What are the factors that influence hypoxia in AME? (3)

A

Altitude/rate of ascent/duration at alt.
Fitness/phys activity/metabolic rate/ETOH/meds/acclimatisation
Any medical condition that can interfere with gas exchange, O2 carriage in blood, blood circulation, and cellular O2 utilisation.

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18
Q

How is O2 transferred in the body?

A

It flows via a pressure gradient, there is no active transport so natural impediments to diffusion must be overcome.

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19
Q

Describe oxygen carriage in the blood.

A

It is bound to Hb at 1.39ml of O2/g of Hb
It is dissolved in plasma at 0.03ml/mmHg.

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20
Q

Describe oxygen transport in anaemia.

A

Some might have 100% oxygen saturation, but there content is much lower, which causes hypoxia at the tissue level.

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21
Q

What might an anaemic patient require in AME?

A

A sea level cabin.

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22
Q

PaO2

A

Partial pressure of oxygen in arterial blood.

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23
Q

PAO2

A

Partial pressure of oxygen in the alveoli.

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24
Q

Describe the relationship between SpO2 and PAO2.

A

It is curved, not linear.

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25
Q

What is the formula for barometric pressure?

A

The partial pressure of the atmosphere multiplied by 0.21.

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26
Q

What does the oxygen cascade rely on?

A

The pressure differences to perfuse from the gas in the alveoli to the capillaries, to the arteries, to the tissues. If not enough pressure, shunting occurs between the capillaries and the arteries.

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27
Q

What are the initial signs of hypoxia?

A

Large individual variation, often insidious and unrecognised.
Disinhibition - loquacity, euphoria, hyperactivity, restlessness.

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28
Q

What are the secondary signs of hypoxia? (6)

A

Decreased attention span, impaired memory, deterioration in visual field and/or depth and colour perception, depression, impaired judgment, impaired psychomotor performance.

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29
Q

What are the late signs of hypoxia?

A

Progressive psychomotor impairment leading to unconsciousness and death.

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30
Q

What are the practical implications of altitude? (5)

A

Put O2 on your patients.
O2 needs will increase with higher altitude.
Pneumothoraces will expand.
Pt factors.
Equipment factors.

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31
Q

If 100% O2 were delivered at 10,000, 9,000, 8,000, 7,000, 6,000, 5,000, 4,000, 3,000, 2,000, and 1,000 feet, what would be the sea level equivalent?

A

1000 - 100%
2000 - 95%
3000 - 90%
4000 - 90%
5000 - 85%
6000 - 80%
7000 - 80%
8000 - 75%
9000 - 75%
10,000 - 70%

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32
Q

What patient spaces will be affected by changes in pressure?

A

Head (barodentalgia), eye, chest, abdomen (barogastralgia).

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33
Q

What equipment spaces will be affected by changes in pressure?

A

ETT cuff, pressure bags, OGT bag, VAC mat.

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34
Q

Name specific challenges of the transport environment. (9).

A

Pressure changes, acceleration, vibration, turbulence, noise, confined spaces, poor ambient light, poor temperature control, psychological effects of flight.

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35
Q

Define acceleration.

A

The rate at which velocity changes with time, in terms of speed and direction.
Linear - from change in speed in a straight line
Radial/centripetal - from change in direction
Angular - from simultaneous change in both speed and direction.
Directly related to force applied to it and inversely proportional to the mass of the object.
Can be positive or negative (deceleration).

36
Q

What is acceleration usually referenced to in-flight?

A

The long axis of the body.

37
Q

When is acceleration a problem in-flight?

A

Take-off and landing, during turns, fixed-wing (usually well-controlled in heli).

38
Q

Define G force.

A

Unit of acceleration - the force per unit mass due to gravity - causes a perception of weight. The reactive force felt during acceleration.

39
Q

What is the G force of a commercial aircraft on take-off?

A

Up to 1.5g.

40
Q

What patients are most at risk with acceleration?

A

Those with cardiovascular decompensation and head injuries.

41
Q

What is the optimal patient positioning to mitigate acceleration?

A

Transversely across cabin - often not practical. Need to predict and prepare. Beware of inclines as well.

42
Q

Define vibration.

A

Any movement which is repeatedly alternating in direction.

43
Q

Which aircraft is vibration greatest in?

A

Heli (as well as engine and turbulence, added vibration from main and tail rotors and gearbox)

44
Q

What are the effects of low frequency vibration? (10)

A

Fatigue, SOB, motion sickness, chest and abdo discomfort, blurred vision, impaired thermoregulation, increased metabolic rate, increased heart rate and BP, peripheral vasoconstriction, disrupted clot formation.

45
Q

What are the patient care issues with vibration?

A

Clinical evaluation is difficult/impossible - pulse palpation, chest wall excursions, abdo palpation, auscultation.

46
Q

What are the equipment issues with vibration? (6)

A

Can’t read small calibrations, can’t use stethoscope/sphygmo, monitoring equipment may misread/fail, no glass containers, interference with PPM function, need to secure equipment.

47
Q

Discuss turbulence in AME.

A

Similar clinical implications to vibration.
Can cause motion sickness and fear.
Secure everything and everyone.
Helis handle turbulence better than planes.

48
Q

Discuss motion sickness in AME.

A

Difficult to manage.
Non-drug measures: direction facing
Prophylactic maxalon and ondansetron useless.
Hyoscine/cyclizine/promethazine best but might not be practical.

49
Q

What is ultrasonic noise and what can it cause?

A

Frequencies over 20,000 Hz (common from jet engines).
Fatigue, dizziness, headache, nausea, tinnitus, motion sickness.
Interferes with concentration and communication, especially with tasks needing constant vigilance.

50
Q

What can be done to reduce noise in AME?

A

Wear hearing protection - decreases fatigue and minimises long term hearing loss.

51
Q

Describe the psychological factors of flight.

A

Fear of flying, agitation, nausea and vomiting, abdo pain, diaphoresis, tachycardia, tachypnoea, HTN, exacerbation of underlying conditions like angina.

52
Q

How can the environmental effects of flight be minimised?

A

Prophylactic patient care interventions.

53
Q

What patients are at particular risk of poor temperature control in AME?

A

Sepsis, severe trauma, paralysed from drugs, children, neonates.

54
Q

What are other critical physiological and environmental factors?

A

Vestibular dysfunction and spatial disorientation; and visual and central disorientation.

55
Q

What are the aviation transport considerations for decompression illness?

A

High flow O2 to enhance nitrogen elimination and reduce bubble size.
Sea level or lowest possible safe altitude.
Fluid therapy.
Supine position.
Henry’s law and Boyle’s law.

56
Q

What are the aviation transport considerations for small bowel obstruction?

A

Restrict cabin altitude to decrease effects of Boyle’s law.
NGT on free drainage to decompress stomach.

57
Q

What are the aviation transport considerations for hypoxia?

A

The percentage of O2 remains constant, but the partial pressure of available oxygen decreases.
Aim: decrease effects of hypoxic hypoxia.
Pressurise cabin to near sea level.
Calculate O2 requirements for flight to ensure you have enough supply.
Dalton’s law.

58
Q

What are the aviation transport considerations for pneumothorax?

A

Cabin restriction.
Decompress chest prior to flying.

59
Q

What are the aviation transport considerations for penetrating eye injury? (3)

A

Antiemetics to prevent vomiting - which would increase intraocular pressure
Consider cabin restriction to prevent possible air expansion in the globe
Supplemental oxygen - high O2 requirement from the retina - any hypoxia will aggravate injury.
Boyle’s law and Dalton’s law.

60
Q

What are the environmental considerations for all AME? (9)

A

Gas laws, plus:
Altitude
G-forces
Vibration
Turbulence
Motion sickness
Noise
Confined space
Poor lighting

61
Q

What is air travel measured in?

A

Nautical miles/hr (knots)

62
Q

Define speed.

A

The distance travelled in a given unit of time.

63
Q

Define velocity.

A

Speed applied to a given direction.

64
Q

What is the standard international unit for measuring force?

A

Newton - acceleration of a mass of 1kg x 1m/s squared.

65
Q

How many newtons is 1G?

A

9.81N.

66
Q

Define weight.

A

The force we sense when gravity is applied to a mass.

67
Q

Describe long accelerations.

A

Lasting longer than 2 seconds in excess of 1G.

68
Q

Describe how acceleration is referenced to the body.

A

Gz - vertical axis of body (head to toe)
Gx - anteroposterior axis (through chest)
Gy - force applied laterally.

69
Q

What effect does acceleration have on a supine patient?

A

Gz forces cause greater displacement of organs and fluid than if patient was seated (Gx) in fixed-wing.
In heli - seated patient feels acceleration on Gz and supine patient on Gx.

70
Q

Which axis is acceleration tolerated the least?

A

Gz - more space for organs to shift, and greater hydrostatic pressures produced as G forces applied to a longer column. Physiological effects depend on whether it is positive or negative.

71
Q

What factors influence tolerance of acceleration? (8)

A

Hypoxia, hypoglycaemia, hypovolaemia, acidosis.
Rate of onset, magnitude, duration, direction.

72
Q

What are the effects of sustained high positive vertical G force (+Gz)? (3)

A

BP falls in head and increases in feet - blood pools and reduces venous return. At +5Gz, blood flow to brain ceases leading to unconsciousness.
After six seconds of +Gz, baroreceptors in carotid artery initiate compensation, but not robust hypovolaemic and septic patients.
Abdo viscera and diaphragm pulled down, leading to incr in residual lung capacity, distended apical alveoli and compressed basal alveoli - resulting in preferential ventilation of lung apices at the same time that perfusion to the apical alveoli is reduced. This causes V/Q (ventilation/perfusion) mismatch.

73
Q

What are the effects of sustained high negative vertical G force (-Gz)? (4)

A

Hydrostatic pressures will increase venous return, causing reflex bradycardia.
Peripheral vessels in lower body dilate and reduce BP.
Pooling of blood in brain will raise ICP and reduce cerebral perfusion pressure.
Abdo organs and diaphragm will be pushed up reducing residual capacity and cause V/Q mismatch equal and opposite to +Gz.

74
Q

How can the effects of acceleration on the patient be limited? (3)

A

Hypovolaemic - if supine feet first on take-off in fixed-wing/road ambo to incr venous return.
Fluid overload/high vent pressures/HI/penetrating eye injury - head first in fixed-wing/road on take-off
Can’t change position during retrieval so best strategy is to request a smooth transit. Use full length of runway, shallow gradient to reduce tilt, secure equipment.

75
Q

How can the effects of vibration be limited?

A

Avoid direct contact between pt and airframe, padding, secure everything and everyone, avoid turbulence and excessive turning.

76
Q

What are common equipment challenges during retrieval? (3)

A

Faulty/inadequate/missing/unfamiliar equipment
Oxygen depletion
Power failure

77
Q

What characteristics should equipment in the retrieval setting have? (5)

A

Ease of use, compatibility, robustness, small size, light weight.

78
Q

What is the most dangerous hazard in decompression?

A

Hypobaric hypoxia - oxygen diffuses out of venous system into alveoli leading to deoxygenated blood.

79
Q

What patient care considerations are required due to reduced pressure at altitude?

A

Sinus/middle ear/teeth - pockets expand causing pain
ETT cuffs - risk of tracheal mucosa pressure necrosis. If above 2-3000 ft let some air out of cuff and monitor pressure with monometer.
Lung damage - rare. Gas stretches lung tissue against closed airway. Arterial gas emboli.
Abdo/GI - if over 25,000 ft gas expansion can cause pain.

80
Q

What is decompression sickness?

A

A group of effects produced by exposure to altitude that are not due to expansion of trapped gas/hypoxia. Likely supersaturation of body tissues with nitrogen, which upon decompression produces bubbles.

81
Q

What are the symptoms of decompression sickness? (6)

A

Limb and joint pain
Resp disturbances
Skin irritation
CNS disturbances
Visual disturbances
CVS collapse
Usually improve with descent (air travel).

82
Q

At what altitude does the drop in the partial pressure of oxygen usually start causing physiological effects?

A

3000 metres/8000 ft

83
Q

What are the main strategies to prevent hypoxia at altitude?

A

Low altitude flying
Increasing inspired oxygen %
Pressurisation of cabin

84
Q

What are commercial cabin pressures kept at?

A

5000 - 8000 ft

85
Q

What are the disadvantages of pressurising the cabin? (3)

A

Additional weight, fuel consumption, structural safety hazard of large pressure difference across aircraft.

86
Q

What are the disadvantages of flying at low altitude? (3)

A

Less safe, more expensive, longer flight.

87
Q

What are the clinical reasons for low altitude transfer? (6)

A

DCS - rotary wing under 500 feet and fixed wing sea level cabin
Lung/chest injuries - expansion of gas can be deadly
Post lung surgery - suture rupture
Eye surgery/penetrating eye injury - gas expansion in orbit
Facial/base of skull fractures - secondary intracranial injury
Abdo - large unreduced hernias/volvulus/intussusception - air can be trapped in bowel - could cause ischaemia/perf

Aeromedical Retrieval (16 decks)

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