High Altitude Illness - Revision Notes

Going along with the environmental theme, another topic that confused me coming up to the boards was the different types of altitude illness. I have attempted a simplified summary below.

High altitude illnesses are a spectrum involving the same pathophysiological mechanisms. 

• Acute Mountain Sickness

• High Altitude Pulmonary Edema (HAPE)

• High Altitude Cerebral Edema (HACE)

 Behaviour is important in aetiology

• Rapid ascent

• Sleeping altitude

Susceptibility of individuals depends on

• Hypoxic ventilatory response

• Vital Capacity

Pathophysiology

• Hypobaric hypoxia is the main issue

• Atmospheric pressure decreases with altitude, as does PO2
  

• Relative hypoxia stimulates carotid bodies, which triggers hyperventilation

• PaO2  rises, PaCO2  falls, leading to respiratory alkalosis

• Renal compensation by increased loss of bicarbonate

• Hypoxia stimulates constriction of pulmonary blood vessels (hypoxic vasoconstriction)

• Hypoxia leads to cerebral vasodilation (causing oedema)

• Hypoxia stimulates renin angiotensin system leading to fluid retention

Acute Mountain Sickness

• Common
• Over 2000m

Clinical features

• Headache

• Fatigue

• Nausea & vomiting

• Anorexia

• Fluid retention

• Starts within hours, lasts for days

Management

• Oxygen

• NSAID

• Acetazolamide

• Dexamethasone

• Cease ascent

High Altitude Pulmonary Oedema (HAPE)

• Over 3000m usually

• No need for prior AMS

• Non cardiac - associated with sevre pulmonary hypertension

Clinical Features

• Dyspnoea on exertion

• Dry cough 

• Fever

• Dyspnoea at rest

• Progressive hypoxia

• Can be confused with pneumonia

High Altitude Cerebral Edema (HACE)

• Most severe for of altitude sickness

• Over 4500m

• Often associated with high altitude pulmonary oedema

Clinical Features

• Ataxia

• Altered mental state - > coma

• Focal findings are rare

Management

High Altitude Pulmonary Edema (HAPE)

• Descend at least 500m (or hyperbaric oxygen)
• Minimize exertion
• Oxygen is life saving
• Nifedipine may have a role in pulmonary hypertension
• Salbutamol?

High Altitude Cerebral Edema (HACE)

• Descend/ Hyperbaric

• Oxygen

• Dexamethsaone

• Acetazolamide

Comments

[family tree maker free]

Hello, everybody! This summer I am planning to climb the mountains of my native region. I will do it for the first time and I thought that I was well prepared for this mission - I bought all necessary equipment and drawn a route. But I was unaware that such altitude illnesses may occur. Now I will take this fact into consideration and take proper measures of protection.