Lungs at altitude

Question 1

PiO2

Answer 1

PiO2 Pressure of inspired oxygen

PiGas = Patm x FiGas

Question 2

Normal Barometric Pressure

Answer 2

Barometric Pressure Altitude
KPa (mmHg)
101 (760) 0
57 (429) 4800
46 (347) 6300
37.5 (282) 8100
33.5 (252) 8848

Question 3

A-aDO2

Answer 3

Alveolar Arterial O2 difference
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 4

Normal blood gases

Answer 4

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

Question 5

Oxygen dissociation curve

Answer 5

Mediated by external parameters

Question 6

Normal response

Answer 6

Hyperventilation at 10000ft altitude
- Increases minute ventilation
- Lowers PaCO2
- Alkalosis initially
- Tachycardia
Adaptive changes
- Multiple
- Alkalosis compensated by renal
bicarbonate excretion

Question 7

Acute Mountain Sickness

Answer 7

Recent ascent to over 2500m.
Lake Louise score > 3.
Must have a headache and one other symptom.
Can only be reliably treated by descent - DON’T GO UP HIGHER.

Question 8

High Altitude Pulmonary Oedema

Answer 8

Unacclimatised individuals
Cough, shortness of breath
Rapid ascent above 8000ft (2438m)
2-5 days
Risk less if sleeping below 6000ft (1829m)
Incidence 2% at 4000m
Need O2, Gamow bag, steroids, sildenafil.

Question 9

High Altitude Cerebral Oedema

Answer 9

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