U of U PA School Acid/Base Disorders Nephrology

What is the process of evaluating an acid/base disorder? (6)

Evaluate clinical context

Determine pH

Determine primary disorder

Assess compensation

Evaluate anion gap

Compose differential

What are the normal values for an ABG?

pH - 7.35-7.45

PaCO2 - 35-45 mmHg

PaO2 - 75-100 mmHg

HCO3- - 22-26 mEq/L

What is the range for a normal anion gap?

Anion gap 3-11

How are alkalosis and alkalemia different?

Alkalosis - process that increases serum HCO3

Alkalemia - blood pH >7.45

How are acidosis and acidemia different?

Acidosis - process that decreases serum HCO3

Acidema - blood pH <7.35

Whta causes metabolic acidosis?

Gain of acid

-Increased internal production

-External ingestion

-Decreased acid excretion

Loss of a base

-Excess diarrhea

-Renal bicarb loss in renal tubular acidosis

How is winters formula used?

If CO2 is lower than predicted - secondary respiratory alkalosis exists

If CO2 is within predicted range - appropriate compensation

If CO2 is higher than predicted - secondary respiratory acidosis exists

What is the equation for anion gap?

Na+ - (Cl- + HCO3-)

What causes high anion gap metabolic acidosis? (11)

M - methanol

U - uremia

D - DKA, drunk/dietary ketoacidosis

P - paraldehyde

I - iron, isopropanol, isoniazid

L - lactic acidosis

E - ethylene glycol

S - salicylates - aspirin, pepto bismal

Why does methanol cause high anion gap acidosis? What is the treatment?

Creates formic acid

Treatment - fomepizole (ADH inhibitor) OR IV ethanol+hemodialysis

Why does uremia cause high anion gap acidosis?

Excess uric and sulfate acid

Why is ethylene glycol extra dangerous? How is it treated?

Tastes sweet, kids more likely to ingeest

Treated same as methanol

What causes normal anion gap metabolic acidosis?

H - Hyperalimentation

A - Addisons disease

R - Renal tubular acidosis

D - Diarrhea

A - Acetazolamide

S - Spironolactone

S - Saline infusion

What causes hyperalimentation?

Total parenteral nutrition (TPN) done incorrectly

How do Addisons disease and spironolactone cause normal anion gap metabolic acidosis?

Decreased aldosterone causes increased potassium and H+ retention

Normally aldosterone increases sodium reabsorption and excretion of potassium and H+

What causes rental tubular acidosis?

Inability to excrete H+

Inability to reabsorb Cl-

Inability to reabsorb bicarb

What is the most common cause of normal anion gap metabolic acidosis?

Diarrhea

Can be normal and high anion gap metabolic acidosis

How does acetazolamide cause normal anion gap metabolic acidosis?

Block carbonic anhydrase, decreasing reabsorption of sodium and bicarb

How does a saline infusion cause normal anion gap metabolic acidosis?

When NS is the only thing given for multiple days or >2L given for a non hemorrhage cause

pH of 5

What is the treatment for metabolic acidosis?

Correct underlying problem

If severe and pH <7.1 IV sodium bicarb

If severe and pH <7.2 AND AKI/CKD - sodium bicarb

What causes low (<25 mEq/L) urine chloride metabolic alkalosis? (5)

Vomiting

NG suctioning

Factitious diarrhea

CF

Diuretics - late effect

What causes high (>40 mEq/L) urine chloride metabolic alkalosis?

Hypokalemia - severe

Diuretics - early effect

Primary mineralocorticoid excess - excess aldosterone

What are the symptoms of metabolic alkalosis? (4)

AMS

Nausea and vomiting

Numbness

Tetany/spasms

How does hypokalemia cause metabolic alkalosis?

Low serum potassium causes intracellular potassium to move out of cell in exchange with H+ ions

How does vomiting cause metabolic alkalosis?

Loss of H+ in stomach acid due to vomiting or chronic NG suctioning

How does excess aldosterone cause metabolic alkalosis?

Excretion of potassium and hydrogen

What type of alkalosis do diuretics cause?

Contraction alkalosis

How do diuretics cause metabolic alkalosis?

Diuretics can increase RAAS, increasing aldosterone, causing excretion of potassium and hydrogen

Causes alkalosis with low chloride

What is the treatment for diuretics metabolic alkalosis?

Discontinue diuretics

Potassium replacement

Slow IV NS

What is the treatment for metabolic alkalosis?

Potassium replacement and IV NS

If severe - Diamox/acetazolamide

H2 receptor blockers or PPIs if chronic NG suctioning to prevent hydrogen loss