Acid-Base Balance and Imbalance - Module 3

A set of practice questions to review acid-base balance concepts, ABG interpretation, compensation, and clinical implications for respiratory and metabolic disturbances.

What is the Goldilocks pH range for arterial blood?

7.35 to 7.45; values below indicate acidosis and above indicate alkalosis.

What do PaCO2 and bicarbonate (HCO3-) represent in ABGs?

PaCO2 reflects respiratory acid content (CO2 in blood); HCO3- reflects metabolic base. The balance of these two determines the pH.

Which organ systems regulate acid-base balance and how quickly do they act?

Lungs regulate CO2 within minutes; kidneys regulate bicarbonate (HCO3-) over hours to days.

If the blood pH is below normal, what general acid-base disorder is present?

Acidosis.

If the blood pH is above normal, what general acid-base disorder is present?

Alkalosis.

Which ABG pattern indicates a primary respiratory disturbance?

A pH change accompanied by a PaCO2 change in the same direction (e.g., low pH with high PaCO2 = respiratory acidosis; high pH with low PaCO2 = respiratory alkalosis).

What is the ABG pattern for acute respiratory acidosis?

Low pH, high PaCO2, normal HCO3- (no renal compensation yet).

What is the ABG pattern for chronic respiratory acidosis?

Low pH, high PaCO2, elevated HCO3- due to renal compensation.

What is the ABG pattern for respiratory alkalosis?

High pH, low PaCO2; HCO3- may be normal or decreased depending on metabolic compensation.

What is the ABG pattern for metabolic acidosis?

Low pH, low HCO3-; PaCO2 may be low due to respiratory compensation (hyperventilation).

What is the ABG pattern for metabolic alkalosis?

High pH, high HCO3-; PaCO2 may be high due to respiratory compensation.

What are the common causes of metabolic acidosis?

DKA (diabetic ketoacidosis), severe diarrhea leading to bicarbonate loss, renal failure, lactic acidosis.

What are the common causes of metabolic alkalosis?

Vomiting or suctioning (loss of gastric acid), diuretic use causing hydrogen loss, ingestion of bicarbonate.

What are the typical signs of respiratory acidosis?

Early: restlessness, confusion, headache; Late: lethargy, stupor, coma.

What are the typical signs of respiratory alkalosis?

Lightheadedness, dizziness, tingling around mouth and fingers, tetany; can progress to confusion, seizures.

What are the typical signs of metabolic acidosis?

Kussmaul respirations; headache, confusion, lethargy; nausea/vomiting; potential arrhythmias and hypotension.

What are the typical signs of metabolic alkalosis?

Confusion, dizziness, agitation; muscle cramps, tremors, tingling; often hypokalemia.

What is meant by metabolic and respiratory compensation in ABGs?

Compensation is the body's attempt to restore pH toward normal by the non-primary system: renal compensation for respiratory disturbances and respiratory compensation for metabolic disturbances; response times differ (fast vs slow).

What is the stepwise approach to ABG interpretation?

Step 1: determine if pH is acidemic or alkalemic; Step 2: identify whether PaCO2 or HCO3- matches the direction of the pH (primary driver); Step 3: assess compensation by the other parameter; Step 4: classify as uncompensated, partially compensated, or fully compensated; then determine immediate cause (respiratory vs metabolic).