Respiratory Alkalosis DDx

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 acclimatization
  • 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

References and Links


CCC 700 6

Critical Care

Compendium

Emergency physician MA (Oxon) MBChB (Edin) FACEM FFSEM with a passion for rugby; medical history; medical education; and informatics. Asynchronous learning #FOAMed evangelist. Co-founder and CTO of Life in the Fast lane | Eponyms | Books | vocortex |

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