Each of the simple disorders produces predictable changes in [HCO3] & pCO2.
Guidelines:
    * IF Both [HCO3] & pCO2 are low THEN Suggests presence of either a Metabolic Acidosis or a Respiratory Alkalosis (but a mixed disorder cannot be excluded)
    * IF Both [HC)3 & pCO2 are high THEN Suggests presence of either a Metabolic Alkalosis or a Respiratory Acidosis (but a mixed disorder cannot be excluded)
    * IF [HCO3] & pCO2 move in opposite directions THEN a mixed disorder MUST be present

 

 

 

 

COMPENSATION: Assess the Compensatory Response
Principle: The 6 Bedside Rules are used to assess the appropriateness of the compensatory response.
Guidelines:
    * If the expected & actual values match => no evidence of mixed disorder
    * If the expected & actual values differ => a mixed disorder is present

 

 

Some Aids to Interpretation of Acid-Base Disorders
"Clue"  Significance

High anion gap
Always strongly suggests a metabolic acidosis.

Hyperglycaemia
If ketones present also diabetic ketoacidosis

Hypokalaemia and/or hypochloraemia
Suggests metabolic alkalosis

Hyperchloraemia 
Common with normal anion gap acidosis

Elevated creatinine and urea
Suggests uraemic acidosis or hypovolaemia (prerenal renal failure)

Elevated creatinine
Consider ketoacidosis: ketones interfere in the laboratory method (Jaffe reaction) used for creatinine measurement & give a falsely elevated result; typically urea will be normal.

Elevated glucose
Consider ketoacidosis or hyperosmolar non-ketotic syndrome

Urine dipstick tests for glucose and ketones
Glucose detected if hyperglycaemia; ketones detected if ketoacidosis

 

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