Hypoxia Dr Simon Brown

The Prevalence

The Problem

The Physiology

The Prevention

Decompression & Hypoxia

The Prevalence of Decompression

UK [1990-99]: 77

Decompression Occurrence

Canada [1985-99]:

164

USA [1974-83]: 355

Australia [1990-99]:

5

GREECE [2005]: At least 1

UK [1990-99]: 77

Decompression Occurrence

Canada [1985-99]:

164

USA [1974-83]: 355

Australia [1990-99]:

5

Your Company ?

Selected Incidents

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

not seen on flight deck

121 Fatalities

Selected Incidents

USA 1996 - Boeing 727 33,000 ft (cabin altitude horn warning sounded) Cabin altitude climbed to 14,000 ft, masks deployed Flt Eng inadvertently opened outflow valve - cabin

alt increased Captain, Flt Eng and No1 unconscious First Officer donned mask at first warning Captain, Flt Eng and No1 regained consciousness

in descent

Selected Incidents

UK 1998 - Boeing 737 35,000 ft (cabin altitude 20,000 ft) Captain couldn’t don oxygen mask quickly enough Senior cabin crew took off her mask to help Captain Captain and cabin crew member unconscious

F/O Had Donned Mask & Descended Aircraft Captain unaware he had been unconscious

Made various incorrect switch selections

“ . . .it is possible that neither fully appreciated the

nature of hypoxia.”

[UK AAIB, referring to the unconscious Captain and No1]

Cabin Decompression

How Cabin Pressurisation Works

[Picture of aircraft outflow valve]

[Animation of aircraft pressurisation system]

Not As Uncommon As You Think

Cabin Decompression

Causes Include: A/C Pack or Bleed Failures Outflow Valve Failures Door Seal/Latching Failures Structural Failures

“ . . .it is possible that neither fully appreciated the

nature of hypoxia.”

The Problem

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

Lack of InsightLoss of Judgement

Loss of Self-criticismEuphoria

Feelings of UnrealityMental Incoordination

Loss of Memory

Unconscious DEATH

Physical Signs

Muscular IncoordinationIncreased Heart RateCyanosis (Blue Lips)

Hyperventilation+

Susceptibility to hypoxia increased by:Susceptibility to hypoxia increased by:

- final altitude- final altitude- time taken to climb- time taken to climb- exercise- exercise- cold- cold- illness- illness- fatigue- fatigue- drugs/alcohol- drugs/alcohol- smoking- smoking

HYPOXIAHYPOXIA

Signs & Symptoms of Hypoxia

Above 20,000 ft Exaggeration of all signs and

symptoms Comprehension and mental

performance decline rapidly Unconsciousness occurs with

little or no warning

Cabin Decompression

May be Slow or Fast

Cabin

Noise

Fogging/Dust

Temperature

Masks

Body

Ears/Sinuses

Hyperventilate

Faintness

Unconsciousness

Physiology of Hypoxia

How does oxygen get from the lungs into the bloodstream?

Respiration Respiration Physiology of Hypoxia

Capillaries

Alveolus

Respiration

Capillary

Physiology of Hypoxia

Alveolus

O2CO2

Respiration

Gas Exchange Takes Place

by Diffusion Only

Physiology of Hypoxia

Capillary

Alveolus

O2CO2

Respiration

This Requires

Pressure

Physiology of Hypoxia

Capillary

Alveolus

O2CO2

PressurePressure

[Film clip demonstrating pressure.]

The Atmosphere

Sea Level

14 psi (760 mm Hg or 1 bar)

18,000 feet

1/2 sea level pressure

34,000 feet

1/4 sea level pressure

40,000 feet

1/5 sea level pressure

Pressure

8,000 ft

1.5x

SL

1x

The Volume of a Gas Increases

as the Pressure Drops

Gas Expansion

Respiration

This Requires

Pressure

Physiology of Hypoxia

Capillary

Alveolus

O2CO2

RespirationRespiration

This Requires

Pressure

Capillary

Alveolus

OO22CO2

Physiology of Hypoxia

Sea Level

14 psi(760 mm Hg or 1 bar)

18,000 feet

1/2 sea level pressure

34,000 feet

1/4 sea level pressure

40,000 feet

1/5 sea level pressure

Holding your breath works down here . . .

. . . but not up here

Oxygen Saturation

Breathing RateSubject stops breathing

10 secs

100 %

50 %

Cabin Altitude 8,000 ft

25,000 ft

Physiology of Hypoxia

Nitrogen

78%

Other

Gases

1%

Oxygen

21%

Only 1/5 of the pressure is

Oxygen

A Bit More on Pressure- The Atmosphere

Nitrogen

78%

Other

Gases

1%

Oxygen

21%

Nitrogen

78%

Other

Gases

1%

Oxygen

21%

Now ALL of the pressure is

Oxygen

More Oxygen

A Bit More on Pressure- The Atmosphere

A Bit More on PressureA Bit More on Pressure

++ ++ ++ ++

++==

4040°°

==

88°°

Nitrogen

78%

Other

Gases

1%

Oxygen

21%

Nitrogen

78%

Other

Gases

1%

Oxygen

21%

Now ALL of the pressure is

Oxygen

More Oxygen

A Bit More on Pressure- The Atmosphere

Time of Useful Consciousness(TUC)

ALTITUDESITTING QUIETLY

MODERATE ACTIVITY

RAPID DECOMPRESSION

35,000 FT45

SECONDS30

SECONDS 20 SECONDS

Hypoxia Video

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

Time of Useful Consciousness(TUC)

ALTITUDESITTING QUIETLY

MODERATE ACTIVITY

RAPID DECOMPRESSION

35,000 FT45

SECONDS30

SECONDS 20 SECONDS

Prevention

Stay Below 10,000 ft!

Cabin Decompression . . .

. .or if you suspect hypoxia ? . . .

CARRY OUT THE ACTIONS IN THE SAFETY MANUAL

Prevention

GET ON OXYGEN GET ON OXYGEN AND AND STAYSTAY ON IT ON IT

DON’TDON’T HOLD YOUR BREATH HOLD YOUR BREATH

Holding your breath works down here . . .

. . . but not up here

Questions?