Acid-Base Balance MCQ
The Henderson-Hasselbalch relationship, respiratory and metabolic acidosis and alkalosis, and the chair-side scenarios from enamel pH to diabetic ketoacidosis. 25 MCQs and 4 INBDE patient cases.
Concept summary and clinical relevance.
Quick-reference structure first, then detailed coverage. Mnemonics in amber, clinical pearls in blue.
Acid-base balance keeps blood pH near 7.4 using a fast lever (the lungs, adjusting CO2) and a slow lever (the kidneys, adjusting bicarbonate). For dentistry the payoff is recognizing the chair-side events: the anxious hyperventilating patient, the over-sedated patient retaining CO2, and the systemically ill patient in diabetic ketoacidosis. Learn the four basic disturbances and the body's compensations, and these become quick to read.
| Disturbance | Primary change | Common cause | Compensation |
|---|---|---|---|
| Respiratory acidosis | High CO2 | Hypoventilation (opioids, COPD) | Kidney retains bicarbonate |
| Respiratory alkalosis | Low CO2 | Hyperventilation (anxiety, pain) | Kidney excretes bicarbonate |
| Metabolic acidosis | Low bicarbonate | Added acid (DKA) or bicarbonate loss (diarrhea) | Lungs blow off CO2 (Kussmaul) |
| Metabolic alkalosis | High bicarbonate | Acid loss (vomiting) | Lungs retain CO2 (hypoventilation) |
Henderson-Hasselbalch & Buffers
- Normal arterial blood pH is tightly held between 7.35 and 7.45; below 7.35 is acidemia and above 7.45 is alkalemia.
- The bicarbonate buffer is the main one: CO2 plus water forms carbonic acid, which dissociates into hydrogen ion and bicarbonate (carbonic anhydrase speeds the first step).
- The Henderson-Hasselbalch relationship says pH tracks the ratio of bicarbonate to CO2; the lungs set CO2 (in minutes) and the kidneys set bicarbonate (over hours to days).
- Phosphate and proteins (including hemoglobin) also buffer, but bicarbonate is the dominant extracellular buffer.
Respiratory Acidosis & Alkalosis
- Respiratory acidosis is a high CO2 from hypoventilation: opioids and sedatives depressing the brainstem, COPD, or airway obstruction. The kidney compensates by retaining bicarbonate (slowly).
- Respiratory alkalosis is a low CO2 from hyperventilation: anxiety, pain, hypoxia, or high altitude.
- Hyperventilation lowers ionized calcium (more calcium binds albumin as pH rises), producing perioral and finger tingling and even carpopedal spasm.
- A patient with COPD who chronically retains CO2 shows a compensated picture with a high bicarbonate on labs.
Metabolic Acidosis & Alkalosis
- Metabolic acidosis is a low bicarbonate, from either added acid (diabetic ketoacidosis, lactic acidosis, salicylates, renal failure) or bicarbonate loss (diarrhea).
- The anion gap (sodium minus chloride and bicarbonate) separates high-gap acidosis (added acids) from normal-gap acidosis (bicarbonate loss, as in diarrhea).
- The lungs compensate for metabolic acidosis by deep, rapid Kussmaul breathing to blow off CO2.
- Metabolic alkalosis is a high bicarbonate, classically from vomiting (loss of gastric acid), producing a hypochloremic, hypokalemic alkalosis.
Clinical Scenarios
- Diabetic ketoacidosis: a high anion gap metabolic acidosis with fruity (acetone) breath and Kussmaul breathing, a medical emergency.
- Anxiety hyperventilation: respiratory alkalosis with tingling and lightheadedness, managed by slow breathing, not oxygen.
- Opioid over-sedation: respiratory acidosis with somnolence, slow breathing, and pinpoint pupils, reversed by naloxone with ventilatory support.
- Salicylate (aspirin) overdose: a mixed picture of respiratory alkalosis and high anion gap metabolic acidosis, with tinnitus, important when patients self-medicate dental pain.
25 board-style MCQs.
Active recall is the highest-yield study method. Pick an answer, check it, and read why every distractor is wrong.
- Question 1EasyNormal arterial blood pH is maintained in the range of:
- Question 2ModerateThe main buffer system of the blood is the:
- Question 3ModerateIn the bicarbonate buffer, carbonic anhydrase speeds the reaction between carbon dioxide and:
- Question 4ModerateBlood pH depends on the ratio of bicarbonate, controlled by the kidneys, to carbon dioxide, controlled by the:
- Question 5EasyA blood pH of 7.30 is best described as:
- Question 6ModerateThe lungs adjust blood pH faster than the kidneys because they regulate:
- Question 7ModerateRespiratory acidosis is caused by:
- Question 8ModerateRespiratory alkalosis in the dental chair is most often caused by:
- Question 9HardThe body compensates for a respiratory acid-base disturbance through the:
- Question 10HardThe perioral and finger tingling of acute hyperventilation is due to:
- Question 11HardA patient with COPD who chronically retains CO2 typically shows a compensatory:
- Question 12ModerateOpioids cause respiratory acidosis by:
- Question 13ModerateMetabolic acidosis is defined by a primary decrease in:
- Question 14HardWhich causes a HIGH anion gap metabolic acidosis?
- Question 15HardSevere diarrhea causes which acid-base disturbance?
- Question 16ModerateThe respiratory compensation for a metabolic acidosis is:
- Question 17ModerateProlonged vomiting characteristically causes:
- Question 18HardThe anion gap is calculated as sodium minus:
- Question 19ModerateMetabolic alkalosis is defined by a primary increase in:
- Question 20ModerateDiabetic ketoacidosis produces which acid-base picture?
- Question 21ModerateAn anxious patient who is hyperventilating, lightheaded, and tingling but not hypoxic should be managed by:
- Question 22ModerateAn over-sedated patient who is somnolent with slow, shallow breathing and pinpoint pupils most likely has:
- Question 23HardSalicylate (aspirin) overdose classically produces:
- Question 24ModerateAn early, characteristic symptom of salicylate toxicity is:
- Question 25EasyAt the enamel surface, demineralization begins once plaque pH falls below the critical level of about:
INBDE patient cases.
4 ADA INBDE-format patient cases on acid-base balance. Each case is a shared patient box plus linked questions with full distractor explanations.
4 patient cases · 20 linked questions
Founder, KYT Dental Services. These MCQs are reviewed by a practicing clinician and offered as an educational reference for dental students.
Other dental MCQ topics.
Same Learning Summary plus Core Recall MCQ format. Every topic includes practice questions with full distractor explanations.
Cranial nerves, bones and foramina, vasculature, mastication, and radiographic landmarks. The structural foundation every dental student returns to.
Brain regions, spinal pathways, autonomic nervous system, and clinical localization for dental patients.
Cardiac cycle, ECG, ventilation, gas exchange, and the vital-sign reasoning that informs safe dental care.