Hypoxia and hyperventilation and protection system Flashcards
Describe how oxygen can be stored or generated on-board aircraft
Stored - Solid - oxygen candle - exothermic reaction give O2 600:1 Gaseous Liquid oxygen - LDBO or LOX On board oxygen generation
Describe how oxygen can be delivered to aircrew
Constant flow system - direct flow - reservoir Demand regulators - diluted demand - pressure demand
Explain how a pressure demand oxygen regulator works
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.
Types of aircraft pressurisation
Unpressurised - Cabin = ambient
High differential. Cabin»_space; ambient
Low differential. Cabin > ambient
Explain how cabin pressurisation works
Air intake from engine, circulates in the cabin and filtrate.
Air conditions
Exception is Dreamliner with using compressers
Advantages and disadvantages of high differential systems and how they protect from hypoxia protection
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
Low differential systems, advantages, disadvantages and hypoxia protection
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
Causes of loss of cabin pressure
Engine failure Control system failure Leaks Loss of canopy Loss of doors or windows Structural failure Weapons
Altitude associated with risk of DCI
18000ft
Factors impacting rate and time of decompression
Size of defect
Volume of cabin
Pressure differential - absolute cabin pressure pre-decompression, absolute aircraft pressure
Descent profile
Pressurisation system
Aerodynamic effects - aerodynamic suction
EXAM
What are the effects of rapid decompression
Trauma Air last/flail Pressure changes - ears, sinuses, gut and lungs Hypoxia DCI Cold Noise Psych
Aircrew actions in the event of a decompression
Don Oxygen immediately Select 100% oxygen Select emergency pressure Check connections-push Breathe at normal rate and depth Initiate emergency descent <10000ft CABALT
Aircrew O2 requirements for altitude levels
0-10000ft - Air
10000 - 33700ft. Increase % O2
33700 - 40000ft. 100% O2
>40000ft - 100% O2 pressurised breathing
Define hypoxia
A lack of oxygen to the tissues sufficient to cause impairment of function
Causes of in-flight hypoxia
Failure of oxygen systems
Decompression event
Ascent to altitude without supplement O2
Toxic fumes
Body oxygen stores?
Blood
Muscle - not useful as too tightly bound
Lung (FRC) is the only store that can be increase. Oxygen is continuously absorbed
Why is oxygen consumption rate
~3-5 mls/kg/min at rest
~250-400 mls/min
What is VO2 Max and what effects it
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
4 types of hypoxic
Hypoxic hypoxia
Hypaemic hypoxia
Stagnant hypoxia
Histotoxic hypoxia
Define Hypoxic hypoxia, aviation causes and medical cause
Reduced oxygen in the alveoli Aviation causes - altitude - hypobaric hypoxia - oxygen system failure Medical cause - hypoventilation - respiratory pathology: acute and chronic
Define Hypaemic hypoxia, aviation causes and medical causes
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
Define stagnant hypoxia, aviation causes and medical causes
Reduced oxygen delivery Aviation causes - pulling G - Cold Medical cause - shock - arterial disease - cardiac failure - emboli
Define histotoxic hypoxia, aviation causes and medical causes
Reduced oxygen metabolism
Aviation causes
- toxic smoke and fumes: hydrogen cyanide, carbon monoxide
Medical cause
- alcohol (neurology and tissue), poisoning
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
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
Summary of physiological oxygen requirements
PAO2 55mmHg. >Air at 10000ft >100% O2 at 40000ft
PAO2 103mmHg >Air MSL. >100% O2 33700ft
Summarise aircrew O2 requirements at different levels of altitude
0-10000ft. Air
10000 - 33700ft. Increasing % O2
33700-40000ft 100% O2
>40000ft - 100% O2 + pressure breathing
Summary of PAX O2 requirement at different levels of altitude
0-10000ft - air
10000-13000ft - air for 30mins max. 15mins emergency O2 available all pax
>13000ft Supplementary O2
Responses to hypoxia
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
Explain the cardiovascular response to hypoxia in the early response
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.
Symptoms and signs of hypoxia
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
Effects of low level hypoxia eg rotary wing
< 10000ft - mild or no symptoms (unless of exertion) 10000-15000ft - skilled task impaired - headache pronounced - reduced work capacity
Define time of useful consciousness
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
What determines TUC
Altitude
Time of exposure
Breathing gas
Rate of ascent
Factors affecting tolerance to hypoxia
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
Inflight corrective actions for PE eg suspected hypoxia
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
Post flight actions for hypoxia
If possible medical personnel to meet aircraft
Aircrew to report to medical immediately
Comprehensive medical examination by AVMO
PM220
What are problems with oxygen
Oxygen toxicity Oxygen paradox Oxygen trapping - oxygen ear, atelectasis Mission endurance Fire hazard
Define oxygen paradox
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
Explain Oxygen ear
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
Explain oxygen lung
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.
Describe Aircrew controlled breathing cycle (ACBC)
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
Describe pressure breathing for altitude
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
Problems with pressure breathing
Need increased mask tension
Distant airways, middle ear, lungs and chest
Communication difficulty
Irritation of eyes
Increase WOB > hyperventilation
Circulatory effects - pressure breathing syncope
Define hyperventilation and result
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
Symptoms of hyperventilation
Tachycardia Reduced BP Hypokalaemia Numbness and tingling of extremities Paraesthesia - unlikely if due to hypoxia Hyperreflexes and muscle cramping Seizures Increase anxiety Increase irritability
Aviation related causes of hyperventilation
Hypoxia - hypoxic ventilatory response Emotion - pain, stress, anxiety Vibration Motion sickness Anti-G straining Pressure breathing
Corrective actions for hyperventilation
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
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.
D? A?
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
B. When recovering on oxygen from profound hypoxia
State the safety rules relating to oxygen
? Ask lecturer’s as unclear in lecture notes and textbook
Describe the effects of pressure breathing
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.
What hypoxia protection system are in place in aircraft
Ambient pressure eg altitude limitation and cabin pressurisation
Supplemental oxygen system
- enrichment and pressure breathing
Process post event of decompression
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
What would make an ideal oxygen system
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
Explain Solid oxygen and its advantages and problems
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
Advantages and disadantages to Gaseous oxygen systems
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
Advantages and disadvantages of liquid oxygen
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
Explain how OBOGS works and advantages and disadvantages
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
When is emergency oxygen is used
Will improve
- hypoxia, DCI, contamination per se
Will not improve - Hyperventilation, anxiety, atelectasis
Explain the features of constant flow system
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
Features of demand regulators
Automatic air dilution - economical, 100% oxygen possible Barostatic control safety pressure Inspiration demand
Be able to label and demonstration the components of a oronasal mask
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
Dixie cups. Function
100% O2 constant flow One size fits all Duration 10mins Tethered, no mobility Maintain PO2 at Tracha 83mmHg
PRICE check
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.
