The Four Primary Disturbances of Acid-Base Balance

1. Primary Respiratory Acidosis
   • initiating event:  VþA (hypoventilation)
     • chronic obstructive pulmonary disease (COPD)
     • weak respiratory muscles (neuromuscular diseases)
     • barbiturate poisoning (central nervous system depression)
   • resultant effects:  CO2 retention
     •  PaCO2,  [H+] and  pH
   • compensations: 2ø metabolic alkalosis
     •  HCO3- retention via PaCO2 effect on renal proximal tubules

2. Primary Respiratory Alkalosis
   • initiating event:  VþA (hyperventilation)
     • salicylate intoxication (over-aggressive aspirin therapy)
     • CNS disorders
     • hyperexcitability
     • psychogenic paroxysmal hyperventilation ("brown paper bag" therapy)
     • artificial ventilation
   • resultant effects:  CO2 elimination
     •  PaCO2,  [H+] and  pH
   • compensations: 2ø metabolic acidosis
     •  HCO3- retention via reverse PaCO2 effect on renal proximal tubules

3. Primary Metabolic Acidosis
   • initiating events: renal and extrarenal
     • diabetes mellitus and ketoacidosis (larger than normal anion gap)
     • severe shock or heart failure and lactic acidosis (larger than normal anion gap)
     • diarrhea and loss of bicarbonate ions (normal anion gap)
     • renal tubular acidosis and retention of hydrogen ions (normal anion gap)
   • resultant effects:  [H+] and/or  [HCO3-],  pH
   • compensations: 2ø respiratory alkalosis
     (with renal participation if possible)
     •  CO2 elimination via  acid drive on ventilation
     • Kussmaul respiration (characteristic deep labored breathing)

4. Primary Metabolic Alkalosis
   • initiating events: renal and extrarenal
     • chronic potassium ion depletion (aggressive diuretic therapy, hyperaldosteronism)
     • protracted vomiting (pyloric obstruction, gastric ulcers) and loss of gastric acids
     • dehydration and depletion of extracellular fluid volume (contraction alkalosis)
   • resultant effects:  [H+] and/or  [HCO3-],  pH
     • urine pH will be paradoxically low (acidic) if there is chronic depletion of potassium ions
   • compensations: 2ø respiratory acidosis
     (with renal participation if possible)
     •  CO2 retention via  acid drive on ventilation
     • hypoventilation also  PaO2 which may limit compensation (hypoxic drive on breathing)