Respiratory Alkalosis

Causes

• Stimulated respiratory drive
  • CNS
    • CVA, ICH, psychogenic
  • Hypermetabolic
    • Thyrotoxicosis
    • Pregnancy (Progesterone)(Secondary to reduced FRC)
    • Sepsis (fever) (often before metabolic acidosis)
    • DT, anxiety, pain
    • DKA and aspirin OD
  • Environmental
    • HYPERthermia (Heat tetany)
  • Drugs
    • Aspirin OD
    • Progesterone
  • Liver failure (encephalopathy) with hyperammonaemia (ammonia)
• Iatrogenic mechanical ventilation

Hypoxemia induced

• Pneumonia, PE, asthma
• Congenital heart disease
• Chronic altitude compensation
• Early in altitude acclimatisation

Compensation for metabolic acidosis

NOTE:

• Self-perpetuating process: Hyperventilation removes CO2 which causes cerebral acidosis and stimulates further increase in ventilation
• Chronic respiratory alkalosis is unique in that it CAN have full metabolic compensation (Only acid-base disorder that allows this)

Clinical

• Associated changes
  • HYPOcalcaemia, HYPOkalaemia, HYPOphosphatemia
  • Decreased Co2 reduces H+ binding, increases negative charge of proteins and increases binding of calcium to proteins
    • Thus reducing ionised calcium
  • Hypocalcaemia with tetany and carpopedal spasm
• Shift 02 dissociation curve to the left (Alkalosis) (Increased affinity of Hb for O2)

Correction

• Treat underlying cause
• Re-breather mask