Arterial Blood Gas

Introduction

Arterial blood gas analysis is an essential part of diagnosing and managing a patient’s

oxygenation status and acid-base balance. The usefulness of this diagnostic tool is dependent

on being able to correctly interpret the results.

Acid-Base Balance

Overview

The pH is a measurement of the acidity or alkalinity of the blood. It is inversely proportional to

the number of hydrogen ions (H+) in the blood. The more H+ present, the lower the pH will be.

Likewise, the fewer H+ present, the higher the pH will be. The pH of a solution is measured on

a scale from 1 (very acidic) to 14 (very alkalotic). A liquid with a pH of 7, such as water, is

neutral (neither acidic nor alkalotic).

1 7 14

ACIDIC NEUTRAL ALKALOTIC

The normal blood pH range is 7.35 to 7.45. In order for normal metabolism to take place, the

body must maintain this narrow range at all times. When the pH is below 7.35, the blood is said

to be acidic. Changes in body system functions that occur in an acidic state include a decrease

in the force of cardiac contractions, a decrease in the vascular response to catecholamines, and

a diminished response to the effects and actions of certain medications. When the pH is above

7.45, the blood is said to be alkalotic. An alkalotic state interferes with tissue oxygenation and

normal neurological and muscular functioning. Significant changes in the blood pH above 7.8

or below 6.8 will interfere with cellular functioning, and if uncorrected, will lead to death.

So how is the body able to self-regulate acid-base balance in order to maintain pH within the

normal range? It is accomplished using delicate buffer mechanisms between the respiratory

and renal systems. Let’s examine each system separately.

The Respiratory Buffer Response...