Hypoxia Flashcards
What is the partial pressure of the oxygen both inside and outside the lungs at sea level?
- Partial pressure of oxygen at sea level = 159mmHg
- In the lungs = 102mmHg
Reduction is due to presence of water vapour and carbon dioxide.
Above what height is an oxygen mask required?
10,000ft
At 34,000ft on 100% oxygen what is the pressure equal to?
That at MSL
At 42,000ft on 100% oxygen, what is the pressure equal to?
10,000ft AMSL
What is required above 42,000ft?
Pressure breathing equipment
What is the mechanical effect of the partial pressure of oxygen on oxygen transfer in the lungs.
- As altitude increases there is a drop in oxygen this will mean less oxygen is in the lungs, therefore less oxygen in the blood flow
What are the causes of hypoxia?
- Reduced atmospheric temperature (lack of oxygen) = hypoxic hypoxia
- Inhalation of carbon monoxide = hypemic hypoxia
- Restricted movement of oxygen enriched blood as a result of sustained high ‘G’ = stagnant hypoxia
- Body cells are impaired and accept or use the oxygen = histoxic hypoxia
What are the primary physiological and behavioural consequence of hypoxia for flight crew and passengers?
- First symptoms = personality changes, euphoric, lose some inhibitions, may appear to be intoxicated.
What are some common symptoms of hypoxia?
- Increased breathing rate
- Light-headedness or dizziness
- Tingling or warm sensations
- Sweating
- Reduced vision
- Sleepiness
- Blue colour on skin, fingernail and lips
- Behaviour changes
- Failing concentration
- Impaired reasoning
- Attention and memory failure
Reasons why Hypoxia symptoms are hard to detect.
- Victims cannot tell that they are hypoxic
- Unpleasant sensations experienced in suffocation are absent in hypoxia - they may be absent or so slight as to go unnoticed.
What is the relationship between hypoxia onset and both vision and cognitive performance?
- Reduces both vision and performance
- Night vision is susceptible to hypoxia especially above 4000ft, a smoker has a blood stream equating to partial hypoxia and so has reduced night vision.
What are some way to prevent hypoxia?
- Pressurisation system in an aircraft.
What are the main factors influencing variation in hypoxia onset (tolerance) between individuals?
People are more susceptible if:
- Over weight
- A smoker
- After drinking alcohol
- A seated person is less likely to suffer than a person doing physical activity.
- After an explosive decompression over a progressive decompression in a pressurised aircraft
What are the factors that affect the likelihood of suffering from hypoxia?
- In cold conditions
- During high activity
- If a person is sick with a cold or flu
- If a person is under the influence of drugs or alcohol
How can hypoxia be treated?
- By giving pure oxygen
- Descending to a lower altitude where more oxygen is present
What is the time of useful consciousness?
The time available to recognise that one is hypoxic and to do something about it.
What are the approximate times of useful consciousness?
- 18,000ft = 15-30 minutes
- 25,000ft = 3-5 minutes
- 35,000ft = 30-45 seconds
- 45,000ft = 12 seconds
What is the oxygen paradox?
When someone suffers from hypoxia, they will get worse before they get better. This lasts about 15 seconds - DO NOT REMOVE OXYGEN MASK.
What are the effects of cabin pressurisation loss at 25,000ft and above due to rapid/explosive - sudden loss in cabin pressure due to damage to the aircraft?
- Loud bang/thump/clap as internal air meets external air
- Cloud/fog/mist in the cabin due to drop in temperature
- Rush of air
- Decrease in temperature
- Flying debris
- Oxygen masks drop
What are the effects of cabin pressurisation loss at 25,000ft and above due to slow decompression?
- May not be obvious
- Oxygen masks dropping
- Unusual noise e.g. whistling or hissing sound around door area
- Occupants may have ear discomfort or ‘popping’, joint pain or stomach pain due to gas expansion.
What are the actions flight crew must take with high altitude cabin pressurisation failure?
- IMMEDIATELY don Oxygen masks
- Rapid descent to reduce the aircraft altitude to 10000’ or less
- If not structural damage, the aircraft should be flown at VMO/MMO
- A descending 90 degree turn to vacate the airway
- MAYDAY call
What are the principle features of supplemental oxygen systems to assist with in-flight pressurisation emergency?
- Most large aircraft are fitted with two oxygen systems (crew and pax), additional portable bottles are located throughout the aircraft.
- Passenger Oxygen System - masks fall automatically if cabin altitude is approximately 14000ft - oxygen flows for 12 minutes and cannot be shut off.
- Flight Crew Oxygen System - the mask can supply 100% on the regulator or a moisture (NORMAL). An EMERGENCY switch supplies 100% under pressure to purge smoke or fumes
