Week 1: Acid-Base Homeostasis

The typical range (WNL) of arterial blood gases (ABGs) is:

• pH: 7.35-7.45.
• CO\(_2\): acidic; PaCO\(_2\) of 36-44 mmHg.
• HCO\(_3^-\): basic; 22-26 mEq/L.

Acid-base homeostasis is maintained via the Carbonic Acid-Bicarbonate Buffer System, among other buffer systems.

Acid-base imbalances are classified as either Acidosis (blood pH too low) or Alkalosis (blood pH too high), with a cause respiratory or metabolic in nature. Determining the cause requires interpreting the ABGs.

Interpreting ABGs

Step 1: measure blood pH.

• < 7.35 = acidosis.
• > 7.45 = alkalosis.

Step 2: measure PaCO\(_2\).

• Acidotic + increased PaCO\(_2\) = respiratory acidosis.
• Alkalotic + decreased PaCO\(_2\) = respiratory alkalosis.
• Otherwise = metabolic + compensation.

Step 3: measure HCO\(_3^-\).

• Acidotic + decreased HCO\(_3^-\) = metabolic acidosis.
• Alkalotic + increased HCO\(_3^-\) = metabolic alkalosis.
• Otherwise = no imbalance?

Step 4: determine compensation.

• If an imbalance exists, the other, non-associated value is partially or fully compensating.