Lungs At Altitude

Question 1

What is the death zone?

Answer 1

Over 8000m

Altitude above which difficult to sustain life without added O2

Question 2

What is the alveolar gas equation?

Answer 2

PAO2 = PiO2 – PaCO2/R**

• One version, not taking into account pH2O
  **R=respiratory quotient, = CO2 produced / O2 consumed

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 3

What is sea level?

Answer 3

Altitude = 0m
Atmospheric pressure = 100KPa
PiO2 = 0.20 x 100KPa = 20KPa

[PiGas = FiGas x Patm]

Question 4

What is the Alveolar Arterial O2 difference?

Answer 4

A-aDO2
Whilst normal pretty complete equilibration of O2, there normally is a small difference between Alveolar and arterial oxygen partial pressure

= PAO2 – PaO2 = (approx) 1KPa

Question 5

What is the normal response to lungs at altitude?

Answer 5

Normal response
Hypoxia leads to..
Hyperventilation at 10000ft altitude
- Increases minute ventilation
- Lowers PaCO2
- Alkalosis initially
- Tachycardia

Adaptive changes
- Multiple
- Alkalosis compensated by renal bicarbonate excretion

Question 6

What happens when things go wrong at altitude?

Answer 6

High Altitude Illness
- Acute Mountain Sickness
- High Altitude Pulmonary oEdema (HAPE)
- High Altitude Cerebral Oedema (HACE)

Question 7

What is acute mountain sickness?

Answer 7

Recent ascent to over 2500m
Lake Louise score  3
Must have a headache and one other symptom

Question 8

How can acute mountain sickness be treated?

Answer 8

Can only be reliably treated by descent

Question 9

What increases the risk of acute mountain sickness?

Answer 9

Recent travel to over 2500m, after a few hours
Sea level normal dwelling
Altitude, rate of ascent and previous history of AMS
Younger people

Question 10

What is High Altitude Pulmonary Oedema?

Answer 10

Unacclimatised individuals
Cough, shortness of breath
Rapid ascent above 8000ft (2438m)
2-5 days
Risk less if sleeping below 6000ft (1829m)
Speed of ascent slower (300-350m/day)
Individual susceptibility
Exercise
Respiratory Tract Infection
Incidence 2% at 4000m

Question 11

What is High Altitude Cerebral Oedema?

Answer 11

Serious
AMS not a pre requisite
Confusion
Behaviour change
Immediate descent
Symptoms may resolve relatively quickly
Gamow bag

Question 12

What is the normal barometric pressure at different altitudes?

Answer 12

Barometric Pressure Altitude in metres
KPa (mmHg)

101 (760) 0
57 (429) 4800
46 (347) 6300
37.5 (282) 8100
33.5 (252) 8848

Question 13

What is the normal blood gases at sea level?

Answer 13

Normal blood gases;

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