Hypoxia Dr Simon Brown Decompression Hypoxia The Prevalence

Hypoxia Dr Simon Brown

Decompression & Hypoxia The Prevalence The Problem The Physiology The Prevention

The Prevalence of Decompression

Decompression Occurrence UK [1990 -99]: Canada [1985 -99]: 77 164 5 Australia [1990 -99]: USA [1974 -83]: GREECE [2005]: 355 At least 1

Decompression Occurrence UK [1990 -99]: Canada [1985 -99]: Australia [1990 -99]: USA [1974 -83]: Your Company 77 164 5 355 ?

Selected Incidents Greece 2005 - Boeing 737 Cabin probably did not pressurise in climb Q F/D crew did not don masks Q Cabin Crew and pax did don drop-down masks Q Autopilot levelled aircraft at 34, 000 ft Q Interceptor saw FO “slumped” over controls Captain not seen on flight deck Q 121 Fatalities

Selected Incidents USA 1996 - Boeing 727 33, 000 ft (cabin altitude horn warning sounded) Q Cabin altitude climbed to 14, 000 ft, masks deployed Q Flt Eng inadvertently opened outflow valve - cabin alt increased Q Captain, Flt Eng and No 1 unconscious Q First Officer donned mask at first warning Q Captain, Flt Eng and No 1 regained consciousness in descent Q

Selected Incidents UK 1998 - Boeing 737 35, 000 ft (cabin altitude 20, 000 ft) Q Captain couldn’t don oxygen mask quickly enough Q Senior cabin crew took off her mask to help Captain Q Captain and cabin crew member unconscious Q F/O Had Donned Mask & Descended Aircraft Captain unaware he had been unconscious Q Made various incorrect switch selections

“. . . it is possible that neither fully appreciated the nature of hypoxia. ” [UK AAIB, referring to the unconscious Captain and No 1]

Cabin Decompression How Cabin Pressurisation Works [Picture of aircraft outflow valve] [Animation of aircraft pressurisation system]

Cabin Decompression Causes Include: Q A/C Pack or Bleed Failures Q Outflow Valve Failures Q Door Seal/Latching Failures Q Structural Failures Not As Uncommon As You Think

The Problem “. . . it is possible that neither fully appreciated the nature of hypoxia. ”

What is Hypoxia?

Definition: Hypoxia is a condition when oxygen available to tissues is insufficient to meet their needs Hypoxia is recognised to be the most serious single physiological hazard during flight at altitude

What Is Hypoxia • Insufficient Oxygen for the Tissues • Brain tissues most sensitive to lack of oxygen • Therefore, first symptoms of hypoxia are related to higher mental function

HYPOXIA Higher Functions Physical Signs Lack of Insight Loss of Judgement Loss of Self-criticism Euphoria Feelings of Unreality Mental Incoordination Loss of Memory Muscular Incoordination Increased Heart Rate Cyanosis (Blue Lips) Hyperventilation Unconscious + DEATH

HYPOXIA Susceptibility to hypoxia increased by: - final altitude - time taken to climb - exercise - cold - illness - fatigue - drugs/alcohol - smoking

Signs & Symptoms of Hypoxia Above 20, 000 ft Q Exaggeration of all signs and symptoms Q Comprehension and mental performance decline rapidly Q Unconsciousness occurs with little or no warning

Cabin Decompression Cabin Body Noise Fogging/Dust Temperature Masks Ears/Sinuses Hyperventilate Faintness Unconsciousness May be Slow or Fast

Physiology of Hypoxia How does oxygen get from the lungs into the bloodstream?

Physiology of Hypoxia Respiration Alveolus Capillaries

Physiology of Hypoxia Respiration Alveolus O 2 Capillary

Physiology of Hypoxia Respiration Gas Exchange Takes Place by Diffusion Only Alveolus O 2 Capillary

Physiology of Hypoxia Respiration This Requires Pressure Alveolus O 2 Capillary

Pressure [Film clip demonstrating pressure. ]

The Atmosphere 40, 000 feet 1/5 sea level pressure 34, 000 feet 1/4 sea level pressure 18, 000 feet 1/2 sea level pressure Sea Level 14 psi (760 mm Hg or 1 bar)

Pressure Gas Expansion 1 x The Volume of a Gas Increases as the Pressure Drops SL 1. 5 x 8, 000 ft

Physiology of Hypoxia Respiration This Requires Pressure Alveolus O 2 Capillary

Physiology of Hypoxia Respiration This Requires Pressure Alveolus 40, 000 feet 1/5 sea level pressure 34, 000 feet 1/4 sea level pressure 18, 000 feet O 2 CO 2 1/2 sea level pressure Sea Level 14 psi(760 mm Hg or 1 bar) Capillary

Holding your breath works down here. . . but not up here

Physiology of Hypoxia Subject stops breathing Breathing Rate 10 secs Oxygen Saturation 100 % 50 % Cabin Altitude 8, 000 ft 25, 000 ft

A Bit More on Pressure - The Atmosphere Nitrogen 78% Oxygen 21% Other Gases 1% Only 1/5 of the pressure is Oxygen

A Bit More on Pressure - The Atmosphere Nitrogen More Oxygen 78% Oxygen 21% Other Gases 1% Now ALL of the pressure is Oxygen

A Bit More on Pressure 40° = + 8° = + +

A Bit More on Pressure - The Atmosphere Nitrogen More Oxygen 78% Oxygen 21% Other Gases 1% Now ALL of the pressure is Oxygen

Time of Useful Consciousness (TUC) ALTITUDE SITTING QUIETLY 35, 000 FT 45 SECONDS MODERATE RAPID ACTIVITY DECOMPRESSION 30 SECONDS 20 SECONDS

Hypoxia Video [Video clip of rapid decompression and hypoxia at 25, 000 ft in Qineti. Q’s hypobaric chamber. ]

Time of Useful Consciousness (TUC) ALTITUDE SITTING QUIETLY 35, 000 FT 45 SECONDS MODERATE RAPID ACTIVITY DECOMPRESSION 30 SECONDS 20 SECONDS

Prevention Stay Below 10, 000 ft!

Prevention Cabin Decompression. . . or if you suspect hypoxia ? . . . CARRY OUT THE ACTIONS IN THE SAFETY MANUAL

GET ON OXYGEN AND STAY ON IT DON’T HOLD YOUR BREATH

Holding your breath works down here. . . but not up here

Questions?