9th February 2024

Introduction

Acid-base balance is the balance between the intake, production and elimination of hydrogen ions to maintain a pH between 7.35 and 7.45. Acidosis, a low pH under 7.35, refers to a raised hydrogen ion concentration and alkalosis, or a high pH over 7.45, refers to a low hydrogen ion concentration. pH is a negative logarithm of hydrogen ions; therefore, a slight change in pH results in a significant change in the concentration of hydrogen ions. To maintain this tight control, compensatory mechanisms occur within the kidneys and lungs.

Typical values on arterial blood gases are as follows:

pH 7.35 – 7.45

pO2 (on room air) >11.3 kPa

pCO2 4.7 – 6.0

HCO3- 22-28 mmol/l

It is essential to cite the percentage of inspired oxygen when documenting arterial blood gases.