High Altitude Pulmonary Edema - Symptoms

Symptoms

Physiological and symptomatic changes often vary according to the altitude involved.

The Lake Louise Consensus Definition for High Altitude Pulmonary Edema has set widely-used criteria for defining HAPE symptoms:

Symptoms: at least two of:

• Difficulty in breathing (dyspnea) at rest
• Cough
• Weakness or decreased exercise performance
• Chest tightness or congestion

Signs: at least two of:

• Crackles or wheezing (while breathing) in at least one lung field
• Central cyanosis (blue skin color)
• Tachypnea (rapid shallow breathing)
• Tachycardia (rapid heart rate)

Intermediate Altitudes (1500-2500 m or 4900-8200 feet)

Clinical symptoms are unlikely. Blood oxygen levels remain >90%.

High Altitude (2500-3500 m or 8200-11500 feet)

Clinical symptoms are common and may develop after 2-3 days. Blood oxygen levels may drop below 90% or lower during exercise. Prior acclimation will decrease the severity of the symptoms.

Extreme Altitude (>5800 m or 19000 feet)

Blood oxygen levels are <90%, even at rest. Progressive deterioration may occur despite acclimation.

The initial cause of HAPE is a shortage of oxygen which is caused by the lower air pressure at high altitudes. The mechanisms by which this shortage of oxygen causes HAPE are poorly understood, but two processes are believed to be important:

1. Increased pulmonary arterial and capillary pressures (pulmonary hypertension) secondary to hypoxic pulmonary vasoconstriction.
2. An idiopathic non-inflammatory increase in the permeability of the vascular endothelium.

Although higher pulmonary arterial pressures are associated with the development of HAPE, the presence of pulmonary hypertension may not in itself be sufficient to explain the development of edema: severe pulmonary hypertension can exist in the absence of clinical HAPE in subjects at high altitude.