Acid Base

The interpretation of acid base is best learnt by some examples.

pH = 7.09                (7.35-7.45)
CO2 = 2.3               (4.5-6.1 kPa)
HCO3 = 6               (22-33 mmol/l)


pH = 7.09    (7.35-7.45)    a low pH = ACIDOSIS   

What is giving rise to this?        HCO3 = 6      (22-33 mmol/l)  low bicarbonate.   Hence METABOLIC.

CO2 = 2.3   (4.5-6.1 kPa)  low CO2. Therefore RESPIRATORY ALKALOSIS = compensation

The biochemical interpretation of these results is that the patient is acidotic. The cause of this is metabolic. The body is attempting to compensate for this by removing carbon dioxide. The compensation is only partial though as the pH is not back to normal. Hence the acid base status is

Partially compensated metabolic acidosis                 eg Diabetic Ketoacidosis

Example 1

Example 2

pH = 7.57                (7.35-7.45)
CO2 = 6.5               (4.5-6.1 kPa)
HCO3 = 40              (22-33 mmol/l)


pH = 7.57    (7.35-7.45)    a high pH = ALKALOSIS   

What is giving rise to this?        HCO3 = 40      (22-33 mmol/l)  high bicabonate.   Hence METABOLIC.

CO2 = 6.5   (4.5-6.1 kPa)  high CO2. Therefore RESPIRATORY ACIDOSIS = compensation

The biochemical interpretation of these results is that the patient is alkalotic. The cause of this is metabolic. The body is attempting to compensate for this by retaining carbon dioxide. The compensation is only partial though as the pH is not back to normal. Hence the acid base status is

Partially compensated metabolic alkalosis                 eg after several days of diarrhoea