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
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