Primary Acid-Base Disorders

There are four primary disorders; if you count the acute and chronic phases of the respiratory disorders.

1. Metabolic acidosis
2. Metabolic alkalosis
3. Respiratory Acidosis (Acute and Chronic)
4. Respiratory Alkalosis (Acute and Chronic)

From the Henderson Hasselbach equation, we can see the following compensations.

Determine the primary disorder/process by looking at the pH and the PCO2

Primary Acid-Base Disorders & their Compensation
Primary Disorder		Problem	pH	HCO3–	PaCO2	Comment
Metabolic acidosis		Loss of HCO3– or gain of H+	↓	⇓	↓ (comp)
Metabolic alkalosis		Gain of HCO3– or loss of H+	↑	⇑	↑ (comp)
Respiratory acidosis	Acute	Hypoventilation	↓		⇑	Buffers in the blood raise bicarb a little bit. Kidneys not yet involved. pH not as normal here.
	Chronic		↓	↑(comp)	⇑	full renal compensation has kicked. pH more normalized here.
Respiratory alkalosis	Acute	Hyperventilation	↑		⇓	Buffers in the blood decrease bicarb a little bit. Kidneys not yet involved. pH not as normal here.
	Chronic		↑	↓(comp)	⇓	full renal compensation has kicked. pH more normalized here.

The initial change is in red and the compensation is in green. The dotted line shows small bicarb compensation with whole body buffering without renal involvement yet.

The lungs can respond to raise pCO2 rapidly. The kidneys can take 3-5 days to fully compensate. As such, the initial bicarb response in acute respiratory disorders comes from whole-body buffering without renal involvement as of yet.

Notice that for each primary disorder, the bicarb and PaCO2 all point in the same direction. For the metabolic process, the pH always matches in the same direction as the bicarb and pCO2. For respiratory disorders, the pH always goes in a reverse direction to the bicarb and pCO2.