Hyperventilation Syndrome

Expansion

Acute hyperventilation lowers carbon dioxide and produces a respiratory alkalosis, with three groups of consequences:

Neuromuscular, from a fall in ionised calcium

• Alkalosis exposes negative charges on albumin, so more calcium binds to it
• Total calcium is unchanged, but ionised calcium falls
• Perioral and peripheral paraesthesiae, carpopedal spasm, positive Trousseau and Chvostek signs, and in severe cases tetany

Cerebral

• Carbon dioxide is a potent cerebral vasodilator, so hypocapnia causes cerebral vasoconstriction and reduced blood flow
• Light-headedness, visual disturbance, and eventually syncope

Cardiovascular and other

• Chest tightness, palpitations
• Left shift of the oxygen dissociation curve, impairing tissue unloading

Crucially, hyperventilation syndrome is a diagnosis of exclusion. Pulmonary embolism, asthma, metabolic acidosis such as diabetic ketoacidosis or salicylate poisoning, sepsis and pain all cause hyperventilation and must be excluded before it is attributed to anxiety.