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Hypochloraemic metabolic acidosis

Hypochloraemic metabolic alkalosis

Hyperchloraemic metabolic alkalosis

Explanation

0.9% N saline and Hartmann's solution are crystalloids that are recommended for fluid resuscitation. Unlike Hartmann's solution, 0.9% N. saline is not a physiological solution.

It is not physiological for a number of reasons:

The chloride concentration of the solution is high (154 mmol/L) compared with the normal range of 98-102 mmol/L

It lacks a number of key components including calcium, magnesium, glucose and potassium

It lacks bicarbonate or bicarbonate precursor buffer necessary to maintain plasma pH within normal limits

At a physiological pH there is a difference in the activity (concentration) of the so-called strong ions, these are positively and negatively charged. This imbalance is used to explain abnormalities of acid base balance. A normal strong ion difference (SID) is in the order of 40.

SID = ([Na+] + [K+] + [Ca2+] + [Mg2+]) - ([Cl-] + [lactate] + [SO42-])

To maintain electrical neutrality this imbalance is made up with the weaker anions (HCO3-, albumin and PO43-).

Aggressive volume resuscitation with 0.9% normal saline results in excessive chloride administration/accumulation and impairs renal bicarbonate reabsorption. The SID of 0.9% normal saline is 0 (Na+ = 154 mmol/L and Cl- = 154 mmol/L = 154 - 154 = 0). Therefore, aggressive administration of NS will decrease the plasma SID causing an acidosis.

Other causes of a hyperchloraemic acidosis include:

Gastrointestinal losses of bicarbonate (diarrhea, pancreatic fistula)

Renal causes (proximal renal tubular acidosis with failure of bicarbonate reabsorption)

TPN

Diabetic ketoacidosis

Overdose of ammonium chloride and hydrochloric acid

Answer Statistics

1

3%

2

91%

3

3%

4

5%

Times answered: 272