VLD 421: Veterinary Clinical Biochemistry and Laboratory Diagnosis-II (0+1)

ALKALOSIS

Metabolic Alkalosis

• Metabolic Alkalosis may result from excessive loss of hydrogen ions,  excessive reabsorption of bicarbonate or ingestion of alkalis.
• Excess H⁺ loss
  • Loss of gastric secretions. eg. Vomition. ,
• Excessive Reabsorption of Bicarbonate
  • The bicarbonate and chloride concentrations are linked.
  • Only the loss of hydrogen ions is not occurs in the alkalosis but  chloride loss results bicarbonate reabsorption.
  • Chloride losse in the kidney usually occurs as a result of diuretic drugs.
  • The thiazide and loop diuretics are common cause for a metabolic alkalosis.
  • These drugs cause increased loss of chloride in the urine resulting in excessive bicarbonate reabsorption.
• Ingestion of Alkalis
  • Alkaline antacids 

Compensation

• • Respiratory Compensation
    • The respiratory centre in the brainstem responds rapidly to changes in CSF pH.
    • Thus, a change in plasma pH or PaCO2 results due to  change in ventilation within minutes.

Renal Compensation

• The kidneys respond to disturbances in acid base balance by altering the amount of bicarbonate reabsorbed and hydrogen ions excreted.
• However, it may take up to 2 days for bicarbonate concentration to reach a new equilibrium.
• These compensatory mechanisms are efficient and often makes the plasma pH to near normal.

Respiratory Alkalosis

• Respiratory Alkalosis is also called as primary H2CO3 deficit. This results when there is a decrease in [H2CO3] fraction with no corresponding change in HCO3- in plasma     .                                                 
• Excessive quantities of CO2 may be washed out of the blood by hyperventilation.

Mechanism

• Respiratory alkalosis is an abnormal physiological process in which there is a primary increase in the rate of alveolar ventilation relative to the rate of C02 production.
• Hypoxia
  Lung diseases: pneumonia, asthma, atelectasis, fibrosis. 
  Pulmonary edema.
  Cyanotic heart disease.
  Residence at high altitude.
  Central nervous system disorders
  Cerebral diseases: tumor, encephalitis, meningitis.
  Subarachnoid hemorrhage.
  Psychogenic hyperventilation, anxiety.
  Hypermetabolic states
  Fever.
  Thyrotoxicosis.
  Anemia
  Salicylate toxication.
  Septicemia.
  Cirrhosis of the liver.
  Pregnancy.
  Physical exercise.
  Renal compensation : Decrease in rate of excretion of hydrogen ions and decrease in HCo₃reabsorption.

Test to measure acid base balance :

• Anion gap : Difference between total plasma anions(HCo₃^-, cl^-) and cation (Na⁺ and K⁺)
• Measurement PCo₂
• _{Blood pH}