Lungs at altitude

Question 1

What is PiO2?

Answer 1

Pressure of inspired oxygen

Question 2

What is PiGas?

Answer 2

PiGas = Patm (atmospheric pressure) x FiGas

Question 3

What is the alveolar gas equation?

Answer 3

PAO2 = PiO2 - PaCO2/ R
A=Alveolar, a=arterial
R = 0.8 with a normal diet
R approx = 1 with primarily carbohydrate diet
R closer to 0.7 with fat rich diets

Question 4

What is the arterial carbon dioxide equation?

Answer 4

PaCO2 = kVCO2 / VA

Question 5

How is the death zone defined?

Answer 5

8000 metres
Altitude above which it is difficult to sustain life without added )2
All peaks over 8000m lie in Himalayas and Karakoram

Question 6

How does barometric pressure change with altitude?

Answer 6

As altitude increases in metres, the Barometric pressure decreases but not as much as going down in sea water

Question 7

What is the equation for Alveolar Arterial O2 difference?

Answer 7

PAO2 - PaO2 = (Approx) 1KPa
So if it is not 1, you know something is wrong

Question 8

what is the alveolar arterial O2 difference?

Answer 8

Whilst normal pretty complete equilibration of O2, there normally is a small difference between alveolar and arterial oxygen partial pressure

Question 9

What are the normal blood gases for O2, CO2 and pH

Answer 9

PaO2 = 10.5 - 13.5 KPa
PaCO2= 4.5 - 6.0 KPa
pH = 7.36 - 7.44

Question 10

What is the normal response to hypoxia?

Answer 10

• Hyperventilation at 10000ft altitude
• Lowers PaCO2
• Alkalosis initially (Alkalosis occurs when your body has too many bases
• Tachycardia
  Then over time you will adapt
• pH normalises and as we start to elevate off sea level

Question 11

Describe the oxygen dissociation curve

Answer 11

As we ascend…
- PiO2 falls (FiO2 remains constant)
- Decreased PAO2
- Decrease PaO2
- Peripheral chemoreceptors fire
- Activates increased ventilation, reducing PaCO2
- Increases PAO2 and PaO2

Question 12

What happens when things go wrong at high altitude?

Answer 12

Acute mountain sickness (recent ascent over 2500m, must have a headache and one other symptom)
Descend; the only reliable treatment [o2, recompress, acetazolamide

Question 13

What is High Altitude Pulmonary Oedema?

Answer 13

• Unacclimatised individuals
• Cough, shortness of breath
• Rapid ascent above 8000ft (2438m)
• 2-5 days
  Treatment:
• descend
• O2

Question 14

What is High Altitude Cerebral Oedema?

Answer 14

• Serious
• AMS not a pre requisite
• Confusion
• Behaviour change
• Immediate descent
• Symptoms may resolve relatively quickly
  Treatment: Descend or Gamow bag (last resort)

Question 15

What is the altitude and atmospheric pressure when flying?

Answer 15

Altitude = 10000m
Atmospheric pressure = 21KPa

Effective Cabin Atmosphere = 1890m
Cabin pressure 81KPa

If on long term oxygen flow rates, will need to give them additional oxygen when flying