ACIDOSIS AND ALKALOSIS MCQs

Question 1

What is the normal pH range of human blood?

Accepted Answer

7.35-7.45 — Blood pH is tightly regulated within a narrow range of 7.35 to 7.45. Even slight deviations from this range can have serious health consequences affecting various physiological processes. ---

Question 2

A patient with chronic obstructive pulmonary disease (COPD) has ABG results showing pH 7.28, PaCO2 58 mmHg, and HCO3- 26 mEq/L. What is the primary acid-base disorder?

Accepted Answer

Respiratory acidosis — The pH is low (acidosis), PaCO2 is elevated ( 45 mmHg), and HCO3- is normal. This indicates respiratory acidosis caused by inadequate ventilation and CO2 retention, typical in COPD. ---

Question 3

Which buffer system is the PRIMARY extracellular buffer system in the body?

Accepted Answer

Bicarbonate buffer system — The bicarbonate buffer system (H2CO3/HCO3-) is the primary extracellular buffer system, particularly in blood plasma, maintaining pH within the normal range of 7.35-7.45. ---

Question 4

A diabetic patient presents with rapid, deep breathing (Kussmaul respirations). Which acid-base disorder is this compensatory mechanism addressing?

Accepted Answer

Metabolic acidosis — Kussmaul respirations (rapid, deep breathing) represent respiratory compensation for metabolic acidosis. The body increases ventilation to eliminate CO2, reducing carbonic acid and helping raise blood pH. ---

Question 5

What is the normal range for arterial PaCO2?

Accepted Answer

35-45 mmHg — Normal arterial PaCO2 is 35-45 mmHg. Values above 45 mmHg indicate respiratory acidosis, while values below 35 mmHg indicate respiratory alkalosis. ---

Question 6

A patient with severe vomiting develops metabolic alkalosis. Which mechanism explains this?

Accepted Answer

Loss of gastric acid (HCl) — Vomiting causes loss of gastric acid (HCl), leading to metabolic alkalosis due to the loss of hydrogen ions and relative excess of bicarbonate in the blood. ---

Question 7

What is the normal range for serum bicarbonate (HCO3-)?

Accepted Answer

22-26 mEq/L — Normal serum bicarbonate is 22-26 mEq/L. Values above 26 mEq/L indicate metabolic alkalosis, while values below 22 mEq/L indicate metabolic acidosis. ---

Question 8

Which enzyme in renal tubular cells catalyzes the reaction between CO2 and water to form carbonic acid?

Accepted Answer

Carbonic anhydrase — Carbonic anhydrase catalyzes the reversible reaction between CO2 and water to form carbonic acid (H2CO3), which then dissociates into H+ and HCO3-, playing a crucial role in renal acid-base regulation. ---

Question 9

A patient has ABG results: pH 7.50, PaCO2 30 mmHg, HCO3- 23 mEq/L. What is the diagnosis?

Accepted Answer

Respiratory alkalosis — The pH is high (alkalosis), PaCO2 is low (<35 mmHg), and HCO3- is normal. This indicates respiratory alkalosis caused by hyperventilation and excessive CO2 elimination. ---

Question 10

What is the formula for calculating anion gap?

Accepted Answer

Na+ - (Cl- + HCO3-) — Anion gap is calculated as Na+ - (Cl- + HCO3-). The normal range is typically 8-12 mEq/L. An increased anion gap suggests metabolic acidosis with unmeasured anions. ---

Question 11

Which condition is characterized by an increased anion gap metabolic acidosis?

Accepted Answer

Diabetic ketoacidosis — Diabetic ketoacidosis causes increased anion gap metabolic acidosis due to accumulation of unmeasured ketone bodies (β-hydroxybutyrate and acetoacetate), which are acids not measured in routine electrolyte panels. ---

Question 12

A patient at high altitude develops dizziness and tingling in the extremities. Which acid-base disorder is most likely?

Accepted Answer

Respiratory alkalosis — High altitude causes hyperventilation (to compensate for low oxygen), leading to respiratory alkalosis. Symptoms include dizziness, tingling in extremities, and muscle cramps due to excessive CO2 elimination. ---

Question 13

In the proximal tubule, hydrogen ions are secreted into the tubular lumen primarily in exchange for which ion?

Accepted Answer

Sodium (Na+) — In the proximal tubule, hydrogen ions are secreted into the tubular lumen by specialized transporters primarily in exchange for sodium ions through Na+/H+ exchangers. ---

Question 14

Which pharmacological agent inhibits carbonic anhydrase and promotes bicarbonate excretion?

Accepted Answer

Acetazolamide — Acetazolamide inhibits carbonic anhydrase, preventing bicarbonate reabsorption in the kidneys and promoting its excretion, leading to metabolic acidosis correction in conditions like metabolic alkalosis. ---

Question 15

A patient with lactic acidosis due to septic shock would most likely present with which type of acid-base disorder?

Accepted Answer

Metabolic acidosis with increased anion gap — Lactic acidosis from tissue hypoperfusion in septic shock causes metabolic acidosis with increased anion gap due to accumulation of lactate, an unmeasured anion. ---

Question 16

What is the primary role of hemoglobin in acid-base balance?

Accepted Answer

Acts as intracellular protein buffer binding hydrogen ions — Hemoglobin acts as an intracellular protein buffer by binding with hydrogen ions, helping prevent large fluctuations in pH within red blood cells and contributing to overall buffering capacity. ---

Question 17

A patient with severe diarrhea develops metabolic acidosis. What is the mechanism?

Accepted Answer

Loss of bicarbonate-rich intestinal fluids — Severe diarrhea causes loss of bicarbonate-rich intestinal fluids, resulting in metabolic acidosis due to decreased bicarbonate levels in the blood without an increased anion gap. ---

Question 18

Which hormone promotes sodium reabsorption and can indirectly influence pH regulation?

Accepted Answer

Aldosterone — Aldosterone promotes reabsorption of sodium and bicarbonate ions in the kidneys, leading to increased blood pH and indirectly influencing acid-base regulation. ---

Question 19

A patient receives excessive intravenous bicarbonate. Which acid-base disorder will likely develop?

Accepted Answer

Metabolic alkalosis — Excessive bicarbonate intake causes metabolic alkalosis due to an excess of bicarbonate in the blood, increasing pH above the normal range. ---

Question 20

What compensatory mechanism does the body employ in metabolic alkalosis?

Accepted Answer

Decreased ventilation to retain CO2 — In metabolic alkalosis, the respiratory system compensates by decreasing ventilation rate to retain CO2, increasing carbonic acid levels and thereby lowering blood pH toward normal. ---

Question 21

Which buffer system is most important in regulating intracellular pH and urine pH?

Accepted Answer

Phosphate buffer system — The phosphate buffer system (HPO4²-/H2PO4-) plays a significant role in buffering intracellular fluids and urine, accepting or donating hydrogen ions depending on pH. ---

Question 22

A patient with anxiety disorder hyperventilates during a panic attack. What immediate acid-base change occurs?

Accepted Answer

Respiratory alkalosis — Hyperventilation during anxiety causes excessive elimination of CO2, leading to respiratory alkalosis characterized by decreased PaCO2 and increased pH. ---

Question 23

What is the normal range for the anion gap?

Accepted Answer

8-12 mEq/L — The normal anion gap is typically 8-12 mEq/L. Values greater than 12 mEq/L suggest metabolic acidosis due to unmeasured anions like lactate, ketones, or toxins. ---

Question 24

Which clinical finding is characteristic of severe metabolic acidosis?

Accepted Answer

Kussmaul respirations — Kussmaul respirations (rapid, deep breathing) are characteristic of severe metabolic acidosis, representing the body's attempt to compensate by eliminating CO2 and raising pH. ---

Question 25

A patient with chronic kidney disease cannot excrete hydrogen ions effectively. Which acid-base disorder develops?

Accepted Answer

Metabolic acidosis — Renal failure impairs the kidneys' ability to excrete hydrogen ions and generate bicarbonate, leading to metabolic acidosis due to accumulation of acids. ---

Question 26

What is the purpose of calculating the delta gap?

Accepted Answer

Assess coexistence of multiple acid-base disorders — Delta gap is calculated as (observed AG - 12) and assesses the coexistence of multiple acid-base disorders. A positive delta gap suggests metabolic alkalosis in addition to metabolic acidosis. ---

Question 27

Which medication is commonly used to treat severe metabolic acidosis by acting as a buffer?

Accepted Answer

Sodium bicarbonate — Sodium bicarbonate acts as a buffer by accepting hydrogen ions, thereby increasing blood pH in severe metabolic acidosis, though its use has potential complications. ---

Question 28

A patient with hyperaldosteronism develops which acid-base disorder?

Accepted Answer

Metabolic alkalosis — Hyperaldosteronism causes excessive sodium and bicarbonate reabsorption in the kidneys, leading to metabolic alkalosis due to increased bicarbonate levels in blood. ---

Question 29

What happens to potassium levels in metabolic acidosis?

Accepted Answer

Hyperkalemia due to K+ shift out of cells — In metabolic acidosis, hydrogen ions move into cells in exchange for potassium moving out, leading to hyperkalemia (increased serum potassium levels). ---

Question 30

Which condition causes respiratory acidosis due to respiratory depression?

Accepted Answer

Opioid overdose — Opioid overdose causes respiratory depression, leading to inadequate ventilation, CO2 retention, and respiratory acidosis due to decreased elimination of carbon dioxide. ---

Question 31

In the kidneys, hydrogen ions are excreted in urine buffered primarily by which substances?

Accepted Answer

Phosphate and ammonia — Hydrogen ions are excreted in urine buffered by phosphate and ammonia (NH3/NH4+), allowing the kidneys to eliminate acid while conserving bicarbonate for the extracellular fluid. ---

Question 32

A patient with salicylate (aspirin) toxicity initially develops which acid-base disorder?

Accepted Answer

Respiratory alkalosis initially — Salicylate toxicity initially causes respiratory alkalosis by directly stimulating the respiratory center, leading to hyperventilation and CO2 elimination, though metabolic acidosis may develop later. ---

Question 33

What is the primary advantage of using loop diuretics like furosemide in treating metabolic alkalosis?

Accepted Answer

They promote urinary excretion of bicarbonate — Loop diuretics like furosemide promote urinary excretion of bicarbonate ions, helping correct metabolic alkalosis by reducing blood bicarbonate concentration. ---

Question 34

A patient with methanol poisoning would present with which type of metabolic acidosis?

Accepted Answer

Increased anion gap — Methanol poisoning causes increased anion gap metabolic acidosis due to accumulation of formic acid and other toxic metabolites, which are unmeasured anions. ---

Question 35

What compensatory mechanism does the kidney employ in respiratory acidosis?

Accepted Answer

Increase H+ secretion and bicarbonate generation — In respiratory acidosis, kidneys compensate by increasing hydrogen ion secretion and generating additional bicarbonate ions, helping to raise blood pH toward normal over several days. ---

Question 36

Which symptom is characteristic of respiratory alkalosis?

Accepted Answer

Tingling in extremities and muscle cramps — Respiratory alkalosis causes tingling in the extremities, muscle cramps, and dizziness due to decreased CO2 levels and alkaline pH affecting nerve and muscle function. ---

Question 37

What is the relationship between serum osmolality and metabolic acidosis diagnosis?

Accepted Answer

Increased osmolal gap suggests toxic alcohols — An increased osmolal gap in metabolic acidosis suggests the presence of osmotically active substances like ethanol, methanol, or ethylene glycol, helping differentiate causes of acidosis. ---

Question 38

When would hemodialysis or continuous renal replacement therapy (CRRT) be indicated for acid-base disorders?

Accepted Answer

Severe metabolic acidosis when other treatments fail — Hemodialysis or CRRT may be necessary in severe cases of metabolic acidosis when other treatments fail, to directly remove accumulated acids and correct life-threatening acid-base imbalances. ---

Question 39

A patient has ABG results: pH 7.32, PaCO2 48 mmHg, HCO3- 18 mEq/L. What type of acid-base disorder is present?

Accepted Answer

Mixed respiratory and metabolic acidosis — The pH is low (acidosis), PaCO2 is elevated (respiratory acidosis), and HCO3- is decreased (metabolic acidosis). Both parameters are abnormal in the same direction, indicating a mixed disorder with both respiratory and metabolic acidosis.

ACIDOSIS AND ALKALOSIS MCQs

Questions, Answers & Explanations