Arterial Blood Gases [ABG] : Emergency Learning

Part 1 ABG Learning

Definitions

pH

Negative log of Hydrogen ion activity
pH = -log [H+]

PaO2

The partial pressure of Oxygen in the gas phase in equilibrium with the arterial blood

PaCO2

The partial pressure of Carbon Dioxide in the gas phase in equilibrium with the arterial blood

HCO3

Concentration of bicarbonate in the plasma calculated from the pH and PCO2 using the Henderson-Hasselbach equation

Standard bicarbonate

Plasma [HCO3-] present in a blood sample, fully oxygenated at 38oC and equilibrated in vitro with PCO2 40 mmHg.
It is the plasma [HCO3-] after elimination of respiratory component and is an index of degree of metabolic alkalosis or acidosis

Buffer Base
Total amount of all the conjugate bases in 1L of arterial blood which can accept H+ in the blood.
Hb-/HbO2- = 9 mmol/L
HCO3- = 24 mmol/L
Protein = 15 mmol/L
TOTAL = 48 mmol/L

A mixed disorder
Two or more primary acid-base abnormalities coexist

Compensation
Refers to normal body processes tending to return arterial pH back to normal (Respiratory or Renal)

Video Take ABG