The purpose of this chapter is to teach a structured method for the assessment of acid-base disorders. The
three stages involved are outlined
in the table below.
Structured Approach to Diagnosis of Patients with Acid-Base Disorders
First: Initial Clinical Assessment
A clinical assessment based on clinical
details is an essential first step
From the history, examination and initial investigations, make a clinical decision as to what is the most likely
acid-base disorder(s).
This is very important but be aware that in some situations, the history may be inadequate, misleading or the range of
possible diagnoses large.
Mixed disorders are often difficult: the history and examination alone are usually insufficient in sorting these out.
Second: Acid-Base Diagnosis
Perform a systematic evaluation of the blood
gas and other results and make an acid-base diagnosis
Synthesise the information to make an overall
clinical diagnosis
Attempt to produce an overall diagnosis of the patient’s condition to guide therapy. Do not view the acid-base
disorder in isolation. The history, examination and results often allow very early diagnosis but it is very useful
to systematically check the whole picture.
The essential first step is to assess the available clinical information (history, examination, investigations)
and use this to make a clinical decision as to the possible and most likely acid-base diagnosis. A knowledge
of the pathophysiology of conditions which cause acid-base disorders is extremely useful in making these initial
assessments.
Sometimes these initial assessments are easy but sometimes they are misleading but in all cases they provide
an initial clinical hypothesis used to guide the next step. Consider the following clinical scenario as a practical
example.