Metabolic Acidosis

Question 1

Define metabolic acidosis.

Answer 1

A decrease in pH and bicarbonate concentration in tissues caused by either accumulation of excess acids stronger than carbonic acid or by abnormal losses of fixed base from the body; blood pH is < 7.35 and HCO3 < 21 mEq/L.

Question 2

What HCO3 levels are associated with a metabolic acidosis?

Answer 2

HCO3 < 21 mEq/L

Question 3

What are the clinical features of metabolic acidosis?

Answer 3

1. Hyperventilation
2. Dysrhythmias
3. Decreased cardiovascular response to catecholamines
4. Decreased myocardial contractility and cardiac output
5. Hypotension, shock

Question 4

What is the differential diagnosis of metabolic acidosis?

Answer 4

1. Body is producing too much acid
2. Body has been poisoned with acids
3. Body is losing HCO3 or cannot exrete H+
4. Body has received too much normal saline

Question 5

What are etiologies of metabolic acidosis in which the body is producing too much acid?

Answer 5

1. Chronic renal failure
2. Lactic acidosis
3. Malignant hyperthermia
4. Diabetic ketoacidosis

Question 6

What are etiologies of metabolic acidosis in which the body has been poisoned with acids?

Answer 6

1. Methanol ingestion (formic acid)
2. Ethylene glycol ingestion (glycolic and oxalic acids)
3. Aspirin

Question 7

What are etiologies of metabolic acidosis in which the body is losing HCO3 or cannot excrete H+?

Answer 7

1. Renal tubular acidosis
2. Pancreatic, biliary, or intestinal fistulas
3. Diarrhea
4. Acute renal failure

Question 8

What is a common perioperative cause of hyperchloremic metabolic acidosis?

Answer 8

Overadministration of normal saline

Question 9

What is the management of metabolic acidosis?

Answer 9

1. Ensure adequate oxygenation and ventilation
2. Ensure adequate oxygen delivery to tissues
3. Treat cause of acidosis
4. Consider hemodialysis
5. Consider bicarbonate therapy (only if pH < 7.1)

Question 10

When should hemodialysis be considered for treatment of metabolic acidosis?

Answer 10

When metabolic acidosis is severe, not responsive to other treatments (fluids, inotropes/pressors, transfusions) and is not otherwise contraindicated.

Question 11

What might be the cause of a metabolic acidosis in a patient recently treated with sodium nitroprusside?

Answer 11

Cyanide poisoning.

Question 12

What can be used to treat cyanide poisoning?

Answer 12

Sodium nitrite and sodium thiosulfate.

Question 13

How does sodium nitrite treat cyanide poisoning?

Answer 13

Sodium nitrite produces methemoglobin which combines with CN- to produce cyanomethemoglobin.

Question 14

How does sodium thiosulfate treat cyanide poisoning?

Answer 14

Sodium thiosulfate catalyzes the conversion of CN- to thiocyanate.

Question 15

When should bicarbonate therapy be used in the treatment of metabolic acidosis?

Answer 15

Only if pH < 7.1 (level associated with dysrhythmias and decreased response to catecholamines).

Question 16

What acidic pH is associated with dysrhythmias and decreased response to catecholamines?

Answer 16

pH < 7.1

Question 17

Why is bicarbonate therapy for metabolic acidosis controversial?

Answer 17

Possible complications of bicarbonate therapy for metabolic acidosis include:

• CNS acidosis
• hypercapnia
• tissue hypoxia due to left shift of oxy-Hb dissociation curve
• volume overload
• hypokalemia
• alkali stimultion of organic acidosis
• high sodium content (especially in neonates/children)

Question 18

What is the formula for oxygen delivery?

Answer 18

DO2 = CO x (Hb x SaO2 x 1.34) + (PaO2 x 0.003)

Question 19

What blood sample values can be used to provide an indication of tissue perfusion?

Answer 19

Lactate

SvO2