12: Metabolic Disturbances

Most common pH disturbance

Metabolic acidosis

Types of metabolic acidosis

• Titrational/anion gap: added acid

• Secretional: losing bicarb

Causes of anion gap acidosis

Added endogenous or exogenous acids

Endogenous acids that cause titrational/anion gap acidosis

• Ketoacids (ketones)

• Lactic acid

• Uremic acids

Exogenous acids that cause anion gap acidosis

Toxins: ethylene glycol, etc.

Causes of secretional acidosis

• GI loss

• Lack of renal reabsorption

Cations that keep the plasma electroneutral

K⁺ and Na⁺ and unmeasured cations

Anions that keep plasma electroneutral

HCO₃^- and Cl^- and unmeasured anions

Anion gap

(Na + K) - (HCO₃ + Cl) → essentially quantifies the unmeasured ions

Which type of metabolic acidosis results in an increased anion gap

Titrational → added acid!

How does a titrational acidosis increase the anion gap

Adding H⁺ eats up the HCO₃^-, and the unmeasured ions increase to maintain electroneutrality

Why doesn’t a secretional acidosis increase the anion gap

With a loss of HCO₃^-, there is a reflexive increase in Cl^- to maintain electroneutrality

Which type of acidosis commonly is accompanied by hyperchloremia (may not be above RI)

Secretional metabolic acidosis

What sample can’t be used to assess acidosis accurately

Venous sample

What ion moves in response to acidosis (and alkalosis)

K!!

Where does potassium move in acidosis

Out of the cell in exchange for H⁺

Where does potassium move in alkalosis

Into the cell in exchange for H⁺

Cause of metabolic alkalosis

Loss of chloride rich fluid

How does chloride loss drive alkalosis

The loss in Cl will cause a reflexive increase in HCO₃

Ways to loose chloride rich fluid

• GI loss: V/D

• GI sequestration (ruminants)

• Renal loss (diuretics)

• Administration of a base

Causes of chloride sequestration in ruminants

• Abomasal obstruction

• Functional obstruction: vagal indigestion or GIT atony

Conditions that cause paradoxical aciduria

• Severe metabolic alkalosis

• Hypochloremia (reflexive)

• Hypokalemia (reflexive)

• Dehydration

What happens in paradoxical aciduria

K is moving into the cells to push H⁺ out of the cells to try to reduce the metabolic alkalosis. But the patient is also dehydrated, so is trying to hold onto ions to keep water. Na is reabsorbed, but there isn’t enough Cl, so HCO₃^- is reabsorbed, and a cation needs to be excreted to maintain electroneutrality. But K is low, so H⁺ is excreted, even though the patient is alkalotic