Serum electrolyte profile.

Na⁺                  :135 – 145 mmol/l

K⁺                    :3.5 – 5.5 mmol/l

HCO₃^-              :22 – 30 mmol/l

Cl^-                    :95 – 106 mmol/l

Osmolar gap

Osmolar gap refers to the disparity between the measured serum osmolality and the calculated serum osmolality.

Osmolar Gap = Measured Posm – Calculated Posm

The normal osmolar gap is  10-15 mmol/L

Osmolar gap measurement provides a reasonably good screening procedure for toxins. Calculating intoxicants increase measured serum osmolality .

In a patient suspected of poisoning, a high osmolar gap (particularly if ≥ 25) with an otherwise unexplained high anion gap metabolic acidosis is suggestive of either methanol or ethylene glycol intoxication

What is the importance of anion gap

1.     It helps to determine the etiology of metabolic acidosis.

2.     It helps to detect acid base disorders in critically ill patients presented with classic acid base parameters within normal.

It helps to determine the nature of metabolic acidosis.

Conditions affecting anion gap.

A.     Anion gap increased in

a.      Diabetic ketoacidosis

b.      Lactic acidosis

c.       Acute renal failure

d.      Chronic renal failure

B.      Anion gap decreased in

a.      Increased unmeasured cations

b.      Severe hypermagnesaemia

c.       Severe hypercalcaemia

d.      Increased plasma lithium

Decreased plasma albumin.

Significance of anion gap.

•   Anion gap is the indicator of metabolic acidosis, it being use to categorize the metabolic acidosis.
• Anion gap helps in differentiation of simple acid base from mixed acid-base disorder.
• Anion gap detects the presence of ABD even in normal P^H.