Lungs At Altitude Flashcards
How is the death zone defined
Over 8000 m
Sea level
Altitude = 0m
Atmospheric pressure = 100KPa
PiO2 = 0.20 x 100KPa = 20KPa
[PiGas = FiGas x Patm]
Sea level normal blood gases
PaO2 10.5 - 13.5 KPa
PaCO2 4.5 - 6.0 KPa
pH 7.36 - 7.44
Sea level normal PaO2
10.5-13.5 KPa
Sea level normal PaCO2
4.5-6.0 KPa
Sea level normal pH
7.36-7.44
Right shift oxygen dissociation curve due to
Acidity
2,3 DPG*
Increased temperature
Increased PCO2
[*2,3 biphosphoglycerate]
FiO2 does what with altitude
Remains constant at approx 0.21
PiO2 does what with altitude
Falls
Lungs at altitude- 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
Barometric pressure at an altitude of 0m
101 KPa
Barometric pressure at an altitude of 4800m
57 KPa
Barometric pressure at an altitude of 6300m
46 KPa
Barometric pressure at an altitude of 8100m
37.5 KPa
Barometric pressure at an altitude of 8848m
33.5 KPa
A-aDO2- 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
PAO2 =
PiO2 - PaCO2/R
PaO2 =
PAO2 - (A-aDO2)
Adaptive changes of lungs at altitude
Multiple
Alkalosis compensated by renal bicarbonate excretion
Hyperventilation at 10000ft altitude
Increases minute ventilation
Lowers PaCO2
Alkalosis initially
Tachycardia
High altitude illness examples
Acute mountain sickness
High altitude pulmonary oedema (HAPE)
High altitude cerebral oedema (HACE)
Why does oxygen dissociation curve shift to the right
Shifts to right to give off more oxygen because areas which are more metabolically active have a higher CO2 concentration and lower pH
Acute mountain sickness
Recent ascent to over 2500m
Lake Louise score >/= 3
Must have a headache and one other symptom
Ascending…
PiO2 falls
Decreased PAO2
decreased PaO2
Peripheral chemoreceptors fire (eg carotid)
Activates increased ventilation (Va), reducing PaCO2
Increased PAO2
increase PaO2
Hyperventilation
PaCO2 DROPS
PaO2 REMAINS HIGHER
Alveolar oxygen tension as you go higher
Linear drop in PaO2
Treatment of acute mountain sickness
Can only be reliably treated by descent
[o2, recompress, acetazolamide]
Blood gases at height
Lower PaO2
Lower PaCO2
Higher end of pH (alkalosis)
At risk of acute mountain sickness if
Recent travel to over 2500m, after a few hours
Sea level normal dwelling
Altitude, rate of ascent and previous history of AMS
Younger people
Respiratory quotient
0.8
High altitude pulmonary oedema
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
Treatment of high altitude pulmonary oedema
O2
Decent urgent
Gamow bag
Steroids
Ca2+ blockers?
Sildenafil
High altitude cerebral oedema
Serious
AMS not a pre requisite
Confusion
Behaviour change
Immediate descent
Symptoms may resolve relatively quickly
Treatment of high altitude cerebral oedema
Immediate descent
Gamow bag
Who should avoid flying
Pneumothorax
-Not with a closed pneumothorax
Infectious TB
Major haemoptysis
Very high oxygen requirements at sea level
-> 4L/minute
High altitude pulmonary oedema cause
Pulmonary capillaries become leaky
Effective cabin atmosphere
1890m
Cabin pressure
81 KPa
Atmospheric pressure at altitude of 10000m
21 KPa
If SpO2 is low, what must happen before flying
<95%
Physiological test eg hypoxic test
Hypoxic hypoxia
Low PaO2 due to high altitude
Above 10000ft
Symptoms of HAPE
Cough
Frothy sputum
Breathlessness
Chest pain
Symptoms of HACE
Confusion
Ataxia
