Altitude

Question 1

Differentiate the altitude illnesses:
AMS
HAPE
HACE

Answer 1

ACUTE MOUNTAIN SICKNESS
>2.5km
Within half a day
Nonspecific:
Headache, nausea/vom, fatigue ++, insomnia, SOBOE
No findings OE

HIGH ALTITUDE PULMONARY OEDEMA
>3km
Within 2-3 days
10% mortality
Usual APO symptoms +- haemoptysis, sputum ++
Secondary to pulmonary HTN + capillary leak- not cardiac

HIGH ALTITUDE CEREBRAL OEDEMA
End-stage AMS
Blood-brain barrier leak —> oedema
Fatal within hours
Encephalopathy, ataxia, ALOC, papilloedema, sometimes focal

Question 2

Define ‘high altitude’:

Answer 2

> 2.4km

Modified by rapidity of ascent, sleeping altitude, preventative meds, underlying cardiopulmonary status.

Question 3

Treatment of the altitude illnesses:

Answer 3

ALL:
Descent
- 500m - 1km depending on severity
- Portable HBO bag still need to descend
- Supplemental O2 for sats >92% to limit pulmonary vasoconstriction
Fluid replacement
- Often hypovolaemic from altitude diuresis
Symptomatic:Ibuprofen, antiemetics
- Keep warm to limit sympathetic drive

HAPE
O2
Nifedipine
- 30mg SR BD
PPV PRN
Bronchodilators PRN

HACE:
Dexamethasone
- 8mg, then 4mg PO QID
Acetazolamide
- 250mg BD

Question 4

Mechanism of Acetazolamide in AMS:

Answer 4

Mimics/hastens acclimatisation biochemistry

HCO3 diuresis —> Metabolic acidosis
Counteracts the respiratory alkalosis that usually occurs
—> improves respiratory drive
—> improves oxygenation
—> reduces CSF production/ oedema

nausea, polyuria, tinnitus, frequency, peripheral paraesthesia

START DAY PRIOR TO ASCENT

Question 5

Physiological changes at altitude:

Answer 5

FiO2 is same- 21%. But barometric pressure less.

ACUTE
Hypoxia
Hypoxic vasoconstriction/ increased PVR —> cor pulmonale
Increased RR/ minute vol —> Resp alkalosis —> compensatory metabolic acidosis
Left shift of Hb/O2 curve
Increased hydrostatic pressure —> transudative APO

Pressure diuresis—> Hypovolaemia, increased HCT
Increased cerebral flow and CSF

CHRONIC
- EPO -> Polycythaemia
- RVH

Question 6

Risk factors for high altitude illness:

Answer 6

High altitude (>2.5km)
Rapid ascent
Not descending for sleep
Not preacclimatising
No prophylactic acetazolamide
Cardioresp comorbidity
Previous altitude illness
Exertion ++

Question 7

Altitude prophylaxis:

Answer 7

ACETAZOLAMIDE 125mg BD

or

DEXAMETHASONE 4mg BD

Question 8

What counts as ‘rapid ascent’?

Answer 8

> 625m per day (above 2.5km)