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AVMO > Hypoxia and hyperventilation and protection system > Flashcards

Hypoxia and hyperventilation and protection system Flashcards

1
Q

Describe how oxygen can be stored or generated on-board aircraft

A 
Stored 
- Solid - oxygen candle - exothermic reaction give O2 600:1
Gaseous
Liquid oxygen - LDBO or LOX
On board oxygen generation
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2
Q

Describe how oxygen can be delivered to aircrew

A 
Constant flow system
- direct flow 
- reservoir
Demand regulators
- diluted demand
- pressure demand
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3
Q

Explain how a pressure demand oxygen regulator works

A

Has a safety pressure
When inspiration occurs, creates pressure drop in the mask which opens the inlet value allowing the air in. The outlet value doesn’t open as a compensation tube delivers the pressure to the outside of the outlet value to stop it opening with the inflow pressure. When expiration occurs pressure increase to open the outlet value and closes the inlet value allowing 1 direction flow.

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4
Q

Types of aircraft pressurisation

A

Unpressurised - Cabin = ambient
High differential. Cabin&raquo_space; ambient
Low differential. Cabin > ambient

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5
Q

Explain how cabin pressurisation works

A

Air intake from engine, circulates in the cabin and filtrate.
Air conditions
Exception is Dreamliner with using compressers

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6
Q

Advantages and disadvantages of high differential systems and how they protect from hypoxia protection

A 
Advantages
- Comfortable temp
- reduced pressure changes
- no O2 requirement
- no DCI risk
Disadvantages
- Performance penalty
- Large decompression risk 
- dry Ari
Hypoxia protection
- routine - breath cabin air
- Emergency - supplementary oxygen
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7
Q

Low differential systems, advantages, disadvantages and hypoxia protection

A 
Advantages
- optimum endurance - reduced fuel
- reduced decompression risk
- military population
Disadvantages
- risk of hypoxia
- risk of DCI
- temperature/environment
- breathing air system required
Hypoxia protection
- routine: supplemental oxygen supply, delivery system, continuous use
- emergency - backup systems
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8
Q

Causes of loss of cabin pressure

A 
Engine failure
Control system failure
Leaks
Loss of canopy
Loss of doors or windows
Structural failure
Weapons
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9
Q

Altitude associated with risk of DCI

A

18000ft

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10
Q

Factors impacting rate and time of decompression

A

Size of defect
Volume of cabin
Pressure differential - absolute cabin pressure pre-decompression, absolute aircraft pressure
Descent profile
Pressurisation system
Aerodynamic effects - aerodynamic suction

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11
Q

EXAM

What are the effects of rapid decompression

A 
Trauma
Air last/flail
Pressure changes - ears, sinuses, gut and lungs
Hypoxia
DCI
Cold
Noise
Psych
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12
Q

Aircrew actions in the event of a decompression

A 
Don Oxygen immediately
Select 100% oxygen
Select emergency pressure
Check connections-push
Breathe at normal rate and depth
Initiate emergency descent <10000ft CABALT
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13
Q

Aircrew O2 requirements for altitude levels

A

0-10000ft - Air
10000 - 33700ft. Increase % O2
33700 - 40000ft. 100% O2
>40000ft - 100% O2 pressurised breathing

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14
Q

Define hypoxia

A

A lack of oxygen to the tissues sufficient to cause impairment of function

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15
Q

Causes of in-flight hypoxia

A

Failure of oxygen systems
Decompression event
Ascent to altitude without supplement O2
Toxic fumes

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16
Q

Body oxygen stores?

A

Blood
Muscle - not useful as too tightly bound
Lung (FRC) is the only store that can be increase. Oxygen is continuously absorbed

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17
Q

Why is oxygen consumption rate

A

~3-5 mls/kg/min at rest

~250-400 mls/min

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18
Q

What is VO2 Max and what effects it

A

VO2 max - maximal oxygen uptake
= CO x (CaO2-CvO2)

Affected by

  • age
  • sex
  • genes
  • training
  • Drugs eg EPO
  • Disease
  • Altitude - 3% decline per 1000ft. O2 cost is the same butt perception of effort is greater
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19
Q

4 types of hypoxic

A

Hypoxic hypoxia
Hypaemic hypoxia
Stagnant hypoxia
Histotoxic hypoxia

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20
Q

Define Hypoxic hypoxia, aviation causes and medical cause

A 
Reduced oxygen in the alveoli
Aviation causes
- altitude - hypobaric hypoxia
- oxygen system failure
Medical cause
- hypoventilation
- respiratory pathology: acute and chronic
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21
Q

Define Hypaemic hypoxia, aviation causes and medical causes

A 
Reduced oxygen content
Aviation causes
- carbon monoxide: binds to the same sight as O2. Binds to cytochrome C oxidase 
Medical causes
- anaemia
- haemorrhage
- Hb abnormalities
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22
Q

Define stagnant hypoxia, aviation causes and medical causes

A 
Reduced oxygen delivery
Aviation causes
- pulling G
- Cold
Medical cause
- shock
- arterial disease
- cardiac failure
- emboli
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23
Q

Define histotoxic hypoxia, aviation causes and medical causes

A

Reduced oxygen metabolism
Aviation causes
- toxic smoke and fumes: hydrogen cyanide, carbon monoxide
Medical cause
- alcohol (neurology and tissue), poisoning

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24
Q

Alveolar gas level at the following

  • MSL on RA
  • 10000ft on RA
  • 18000ft on RA
  • 18000ft on O2
  • 33700ft on O2
  • 40000ft on O2
  • 45000ft on O2
  • 45000ft on O2 and Pressure 30mmHg
A

MSL on RA - O2 103, N 570, CO2 40, H2O 47.
10000ft - O2 55, N 381, CO2 40, H2O 47
18000ft - O2 39, N 264, CO2 30, H2O 47
18000Ft on O2 - O2 103, N 190, CO2 40, H2O 47
33700ft on O2 - O2 103, CO2 40, H2O 47
40,000ft on O2 - O2 55, CO2 40, H2O 47
45000ft on O2 - O2 35, CO2 30, H2O 47
45000ft on O2 + Pressure - O2 55, CO2 40, H2O 47

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25
Q

Summary of physiological oxygen requirements

A

PAO2 55mmHg. >Air at 10000ft >100% O2 at 40000ft

PAO2 103mmHg >Air MSL. >100% O2 33700ft

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26
Q

Summarise aircrew O2 requirements at different levels of altitude

A

0-10000ft. Air
10000 - 33700ft. Increasing % O2
33700-40000ft 100% O2
>40000ft - 100% O2 + pressure breathing

27
Q

Summary of PAX O2 requirement at different levels of altitude

A

0-10000ft - air
10000-13000ft - air for 30mins max. 15mins emergency O2 available all pax
>13000ft Supplementary O2

28
Q

Responses to hypoxia

A

Early responses (compensation)

  • increase ventilation - hyperventilation will alway occur with hypoxia
  • cardiovascular response

Late responses (adaptation) eg climbing a mountain

  • Metabolic > increase production of 2,- BPG
  • Haematological >increased EPO > increase HB
29
Q

Explain the cardiovascular response to hypoxia in the early response

A

SNS response

  • increase HR and CO
  • Increase SVR > increase venous return and BP, Pulmonary vasoconstriction

Alteration of regional perfusion

  • Increase coronary blood flow, cerebral blood flow
  • Decrease renal blood flow, splanchnic blood flow, all other.
30
Q

Symptoms and signs of hypoxia

A

Physical effects

  • muscular in coordination
  • sensory deficits - touch and vision
  • hot flushes
  • Cyanosis
  • hyperventilation

Performance effects

  • personality change
  • loss of judgement
  • loss of self-criticism
  • Euphoria
  • loss of short term memory
  • mental in coordination

Late effects

  • decrease consciousness
  • Air Hunger
  • Loss of consciousness
  • muscle spasms
  • death
31
Q

Effects of low level hypoxia eg rotary wing

A 
< 10000ft - mild or no symptoms (unless of exertion)
10000-15000ft
- skilled task impaired
- headache pronounced
- reduced work capacity
32
Q

Define time of useful consciousness

A

The period of time between onset of exposure to reduce oxygen in inspired air and the point when performance is impaired such that effective action is impossible

Eg at 25000ft TUC is 3-5min

33
Q

What determines TUC

A

Altitude
Time of exposure
Breathing gas
Rate of ascent

34
Q

Factors affecting tolerance to hypoxia

A 
Drugs
Alcohol and hangover
Smoking
Other illnesses
Physical fitness
Rate of ascent
Exercise at altitude
Stress and workload
Cold - increase metabolic rate and O2 consumption
Fatigue - ? Unsure why
35
Q

Inflight corrective actions for PE eg suspected hypoxia

A

Oxygenate
Aviate
Navigate
Communicate

Don oxygen mask immediately
Select 100% Oxygen
Select emergency pressure
Toggle down/tighten bayonet fittings
Check connections - push only
Breathe at normal rates and depth
Check on others
36
Q

Post flight actions for hypoxia

A

If possible medical personnel to meet aircraft
Aircrew to report to medical immediately
Comprehensive medical examination by AVMO
PM220

37
Q

What are problems with oxygen

A 
Oxygen toxicity
Oxygen paradox
Oxygen trapping - oxygen ear, atelectasis
Mission endurance
Fire hazard
38
Q

Define oxygen paradox

A

A temporary worsening of hypoxia symptoms with the re-introduction of oxygen

Usually mild with flushing and poor performance
Occasionally severe with potential for spasm
Or rarerly LOC

Only transient

MOA: hypocapnic cerebral vasoconstriction which takes time to normalise and relief of hypoxic vasoconstriction with O2 resulting in reduced arterial BP

39
Q

Explain Oxygen ear

A

After having 100% oxygen the middle ear is filled with 100% oxygen. The middle ear absorbs with oxygen and due too the lack of nitrogen this reduces the pressure causing a negative pressure. This causes suction of TM and Eusachian tube = pain

40
Q

Explain oxygen lung

A

Occurs with breathing O2 and using G suit going > +3Gz
Type of absorption atelectasis
Can cause physiologically significant shunt

Symptoms: retrosternal discomfort, cough/ inspiration snatch. Can persist for 24 hours after flight

Improves with cough as it increases PEEP to open airway.

41
Q

Describe Aircrew controlled breathing cycle (ACBC)

A 
Rule of 5s
Breath in for 5 seconds
Hold for 5 seconds
Breath out for 5 seconds
Rest for 5 normal breaths
Repeat up to 5 times
A few deep coughs
42
Q

Describe pressure breathing for altitude

A

It is an emergency get me down capability
Safety pressure is always on
Minor over pressure starts at 26000ft
Full pressure by 40000ft
Breathing technique: in for 2, hold for 2, out for 4
ACBC

43
Q

Problems with pressure breathing

A

Need increased mask tension
Distant airways, middle ear, lungs and chest
Communication difficulty
Irritation of eyes
Increase WOB > hyperventilation
Circulatory effects - pressure breathing syncope

44
Q

Define hyperventilation and result

A

As breathing faster and/or deeper than needed for the removal of CO2

Results

  • reduction of CO2 = respiratory alkalosis
  • increase pH decreases plasma Ca2+ = nerve and muscle function, paraesthesiae in lips and fingers, Carlo-pedal spasm.
  • cerebral vasoconstriction
45
Q

Symptoms of hyperventilation

A 
Tachycardia
Reduced BP
Hypokalaemia
Numbness and tingling of extremities
Paraesthesia - unlikely if due to hypoxia
Hyperreflexes and muscle cramping
Seizures
Increase anxiety
Increase irritability
46
Q

Aviation related causes of hyperventilation

A 
Hypoxia - hypoxic ventilatory response
Emotion - pain, stress, anxiety
Vibration
Motion sickness
Anti-G straining
Pressure breathing
47
Q

Corrective actions for hyperventilation

A 
Assume hypoxia
Oxygenate
Aviation
Navigate
Communicate
Don oxygen mask immediately
Select 100% oxygen
Select emergency pressure
Toggle down/tighten bayonet fitting
Check connections- push only
Control rate and depth of breathing ACBC
Descend
Smoke and fumes
Declare emergency
Control rate and depth of breathing - ACBC
DASM hypoxia check list
48
Q

Fick’s law can be used to explain the occurrence of hypoxic hypoxia at high altitude because
A. The density of air is less
B. The diffusion constant of O2 is less
C. Diffusion distance for O2 increase
D. The pressure gradient (change P) for O2 is reduced.

A

D? A?

49
Q

Oxygen paradox may occur
a. When pressure breathing above 40,000ft
B. When recovering on oxygen from profound hypoxia
C. When PaO2 drops below 55mmHg
D. When an oxygen regulator fails

A

B. When recovering on oxygen from profound hypoxia

50
Q

State the safety rules relating to oxygen

A

? Ask lecturer’s as unclear in lecture notes and textbook

51
Q

Describe the effects of pressure breathing

A

Need increased mask tension
Distension of airways: upper airways, middle ear, lungs and chest
Communication difficulty
Irritation of eyes
Increase WOB - tendency to hyperventilation
Circulatory effects - pressure-breathing syncope.

52
Q

What hypoxia protection system are in place in aircraft

A

Ambient pressure eg altitude limitation and cabin pressurisation

Supplemental oxygen system
- enrichment and pressure breathing

53
Q

Process post event of decompression

A

AVMO

  • PAN/Mayday response
  • immediate cares
  • consider causes and consequences
  • PM220 - physiological incident form
  • call SAVMO

Aircrew

  • ASR
  • Sentinel
  • USN forms if PE in F19 F/G
54
Q

What would make an ideal oxygen system

A 
Oxygen purity
Minimal dead space
Acceptable temperature
Dispersion of expirate
Reliable
Automatic
Matches high peak inspiration flow rates
Comfortable 
Minimal resistance to breathing 
Copes with RD
Pressure breathing
Leakage and safety pressure
Want % of oxygen to adjust with altitude
55
Q

Explain Solid oxygen and its advantages and problems

A 
Oxygen candle
Used in Dixie cup oxygen 
Exothermic reaction releases oxygen
Advantages
- small and light
- cheap and long shelf life
- reliable and intuitive 
- low risk

Problems

  • finite storage
  • continuous supply
  • runs until exhausted
  • Exothermic production
56
Q

Advantages and disadantages to Gaseous oxygen systems

A

Advantage

  • common, simple, cheap and available
  • no ongoing losses with unused
  • usually 1800 psi - 10 L Cylinder = ~2210 L

Disdvantages

  • Bulky, heavy.
  • poses an explosive hazard
  • finite
  • needs to be dry as moisture will freeze at altitude
57
Q

Advantages and disadvantages of liquid oxygen

A

Advantages

  • 1L of LOX = 840 L of O2 = saves on space and weight
  • low risk of explosive hazard
  • limited use

Disadvantage

  • logistics are troublesome
  • inefficient with ongoing losses
  • expensive to refil
  • Contamination
58
Q

Explain how OBOGS works and advantages and disadvantages

A

It is a molecular sieve using Zeolite
- filter out Nitrogen
Requires bleed air to enter and drive the filtering process

Types

  • Cobham - F/A-18F, E/A-18G - product gas is always high FiO2 - no dilute. 2 sieve beds
  • Honeywell - Hawk, PC-21, F-35. Product gas is regulator gas mix. Deliver cleaner and drier product
59
Q

When is emergency oxygen is used

A

Will improve
- hypoxia, DCI, contamination per se
Will not improve - Hyperventilation, anxiety, atelectasis

60
Q

Explain the features of constant flow system

A

Structurally: oxygen store, mass flow regulating device, simple hose and mask
- 100% oxygen all the time
Inefficient and wasteful

Used reservoirs systems in Dixie cups

61
Q

Features of demand regulators

A 
Automatic air dilution
- economical, 100% oxygen possible
Barostatic control
safety pressure
Inspiration demand
62
Q

Be able to label and demonstration the components of a oronasal mask

A 
Inlet port
Non return inspiration valve
Compensation tube
Ice guard
Face piece of mask
Valve seat
Valve plate
Springs
Compensation chamber
Diaphragm 
Piston
Outlet snout

Anti-suffocation valve
PB toggle
Reflected seal

63
Q

Dixie cups. Function

A 
100% O2 constant flow
One size fits all
Duration 10mins
Tethered, no mobility
Maintain PO2 at Tracha 83mmHg
64
Q

PRICE check

A

Pressure - ensure enough oxygen pressure and quantity
Regulator
Indicator - check flow indicator eg Doll’s eye
Connections - push in to ensure secure
Emergency - ensure emergency oxygen is ready, Brief passengers on location and proper use.

AVMO (49 decks)

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