Acid-Base and Electrolyte Balance Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Acid-Base and Electrolyte Balance. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Acid-Base and Electrolyte Balance Indian Medical PG Question 1: All of the following statements about acid-base disorders are true, EXCEPT:
- A. Metabolic acidosis is compensated by increasing Pco2 (Correct Answer)
- B. Buffering may be intra & extra cellular
- C. pH determined by Pco2 and HCO3
- D. Respiratory acidosis is compensated by HCO3
Acid-Base and Electrolyte Balance Explanation: ***Metabolic acidosis is compensated by increasing Pco2***
- In **metabolic acidosis**, the primary problem is a decrease in **bicarbonate (HCO3-)**.
- The compensatory response is **respiratory**, involving an increase in **respiratory rate** and depth to **decrease Pco2**, thereby *raising* the pH back towards normal. Increasing Pco2 would worsen the acidosis.
*Buffering may be intra & extra cellular*
- **Buffering systems** operate both **intracellularly** (e.g., proteins, phosphates) and **extracellularly** (e.g., bicarbonate-carbonic acid system, hemoglobin).
- This dual buffering ensures a rapid and widespread response to changes in acid-base balance throughout the body.
*pH determined by Pco2 and HCO3*
- According to the **Henderson-Hasselbalch equation**, pH is directly proportional to the ratio of **bicarbonate (HCO3-)** to **Pco2**.
- This means that changes in either Pco2 (respiratory component) or HCO3- (metabolic component) will directly influence the overall pH of the blood.
*Respiratory acidosis is compensated by HCO3*
- In **respiratory acidosis**, the primary problem is an increase in **Pco2** due to hypoventilation.
- The compensatory response is **renal**, involving increased reabsorption of **bicarbonate (HCO3-)** and increased excretion of H+ ions to buffer the excess acid.
Acid-Base and Electrolyte Balance Indian Medical PG Question 2: HCO3/H2CO3 is the best buffer because it is:
- A. Its components can be increased or decreased in the body as needed (Correct Answer)
- B. Good acceptor and donor of H+ ions
- C. Combination of a weak acid and weak base
- D. pKa near physiological pH
Acid-Base and Electrolyte Balance Explanation: ***Its components can be increased or decreased in the body as needed***
- The **bicarbonate buffer system** is unique because its components, **bicarbonate (HCO3-)** and **carbon dioxide (CO2)**, are physiologically regulated by the kidneys and lungs, respectively.
- This allows for dynamic adjustment of buffer concentrations to maintain **pH homeostasis**, making it highly effective even when its pKa is not perfectly matched to physiological pH.
*Good acceptor and donor of H+ ions*
- While bicarbonate acts as an **acceptor of H+ ions** and carbonic acid can donate H+ ions, this characteristic is true for all effective buffer systems.
- This option does not highlight the unique advantage of the bicarbonate buffer over other physiological buffers.
*Combination of a weak acid and weak base*
- The bicarbonate buffer system indeed consists of **carbonic acid (H2CO3)**, a weak acid, and its conjugate base, **bicarbonate (HCO3-)**.
- However, this is the definition of any buffer system and doesn't explain why it's the *best* physiological buffer compared to others.
*pKa near physiological pH*
- The **pKa of the bicarbonate buffer system is 6.1**, which is not exactly at the physiological pH of 7.4.
- While buffers are generally most effective when their pKa is close to the pH they regulate, the **open nature and physiological regulation** of the bicarbonate system compensate for this difference.
Acid-Base and Electrolyte Balance Indian Medical PG Question 3: Increased anion gap metabolic acidosis is associated with all of the following conditions except:
- A. Starvation
- B. Diarrhoea (Correct Answer)
- C. Lactic acidosis
- D. Salicylate poisoning
Acid-Base and Electrolyte Balance Explanation: ***Diarrhoea***
- Diarrhoea causes **non-anion gap metabolic acidosis** due to the loss of **bicarbonate-rich fluids** from the gastrointestinal tract [3].
- The anion gap remains normal because **chloride levels increase** to compensate for the bicarbonate loss, maintaining electroneutrality.
*Starvation*
- Prolonged starvation leads to **ketoacidosis** as the body breaks down fats for energy, producing **ketone bodies** (acetoacetate, beta-hydroxybutyrate) [1].
- These unmeasured anions increase the **anion gap**.
*Salicylate poisoning*
- Salicylate poisoning causes an **increased anion gap metabolic acidosis** because salicylates are organic acids and interfere with cellular metabolism [2].
- It often presents as a **mixed acid-base disorder** with an initial respiratory alkalosis due to central respiratory stimulation [2].
*Lactic acidosis*
- Lactic acidosis results from the accumulation of **lactic acid**, an unmeasured anion, due to increased anaerobic metabolism (e.g., in shock or severe hypoxia) [2].
- This directly contributes to an **increased anion gap**.
Acid-Base and Electrolyte Balance Indian Medical PG Question 4: What is the most common cause of normal anion gap metabolic acidosis?
- A. Ingestion of ammonium chloride
- B. Lactic acidosis
- C. Ethylene glycol intoxication
- D. Renal tubular acidosis
- E. Salicylate intoxication
- F. External pancreatic drainage
- . Diarrhoea (Correct Answer)
- . Chronic renal failure
- . Methanol/Formaldehyde intoxication
- . Uterosigmoidostomy
- . Ketoacidosis
Acid-Base and Electrolyte Balance Explanation: ***Diarrhoea***
- Diarrhoea causes a **loss of bicarbonate** from the gastrointestinal tract, leading to a **normal anion gap metabolic acidosis** [2].
- The loss of bicarbonate is compensated by an **increase in chloride reabsorption** in the kidneys, maintaining a normal anion gap.
*Ingestion of ammonium chloride*
- Ingestion of ammonium chloride leads to **hyperchloremic metabolic acidosis** by contributing to a net gain of hydrogen ions.
- While it causes a normal anion gap metabolic acidosis, it is **not the most common cause** in clinical practice.
*Lactic acidosis*
- Lactic acidosis results from the accumulation of **lactic acid**, an unmeasured anion, leading to a **high anion gap metabolic acidosis** [1].
- This typically occurs in conditions of **tissue hypoxia** or impaired lactate metabolism [1].
*Ethylene glycol intoxication*
- Ethylene glycol metabolism produces various organic acids (e.g., **glycolic acid, oxalic acid**), which are unmeasured anions, causing a **high anion gap metabolic acidosis**.
- It is often associated with acute **kidney injury** and neurological symptoms.
*Renal tubular acidosis*
- Renal tubular acidosis (RTA) involves impaired acid excretion or bicarbonate reabsorption by the kidneys, resulting in a **normal anion gap metabolic acidosis** [1].
- While a significant cause, it is **less common globally** than diarrhoea as a cause of normal anion gap metabolic acidosis.
*Salicylate intoxication*
- Salicylate intoxication initially causes **respiratory alkalosis** due to central respiratory stimulation [1].
- At toxic levels, it can lead to **high anion gap metabolic acidosis** due to the accumulation of organic acids and uncoupling of oxidative phosphorylation.
*External pancreatic drainage*
- External pancreatic drainage can lead to significant **bicarbonate loss**, as pancreatic fluid is rich in bicarbonate.
- This loss causes a **normal anion gap metabolic acidosis**, similar to severe diarrhoea.
*Chronic renal failure*
- Chronic renal failure can cause metabolic acidosis, but it's typically a **high anion gap metabolic acidosis** due to the accumulation of unexcreted organic acids (e.g., phosphates, sulfates).
- In earlier stages, or when accompanied by specific renal tubular defects, it can sometimes present as normal anion gap acidosis.
*Methanol/Formaldehyde intoxication*
- Methanol and formaldehyde intoxication lead to **high anion gap metabolic acidosis** due to their metabolism into highly toxic substances like **formic acid**.
- These are characterized by severe systemic toxicity and visual disturbances.
*Uterosigmoidostomy*
- Uterosigmoidostomy involves diverting urine into the sigmoid colon, allowing for the reabsorption of **chloride** and the loss of **bicarbonate** from the body.
- This results in a **normal anion gap metabolic acidosis**, also known as **hyperchloremic metabolic acidosis**.
*Ketoacidosis*
- Ketoacidosis (e.g., diabetic ketoacidosis, alcoholic ketoacidosis) is characterized by the overproduction of **ketoacids** (beta-hydroxybutyrate, acetoacetate).
- These are unmeasured anions, leading to a prominent **high anion gap metabolic acidosis**.
Acid-Base and Electrolyte Balance Indian Medical PG Question 5: Patient with severe acidosis is treated with
- A. Dextrose
- B. Ringers lactate
- C. i.v. NaHCO3 (Correct Answer)
- D. None of the options
Acid-Base and Electrolyte Balance Explanation: ***i.v. NaHCO3***
- **Intravenous sodium bicarbonate (NaHCO3)** is the primary treatment for severe metabolic acidosis to directly correct the acid-base imbalance by providing bicarbonate ions [3].
- It works to **neutralize excess acid** in the bloodstream, raising the pH [4].
*Dextrose*
- **Dextrose** (glucose) is used to provide calories and prevent hypoglycemia, but it does not directly treat acidosis [1].
- While sometimes given in critically ill patients, it does not have an immediate or direct effect on **acid-base balance** [2].
*Ringers lactate*
- **Ringer's lactate solution** contains lactate, which is metabolized to bicarbonate in the liver; however, in severe acidosis, particularly **lactic acidosis**, the liver's ability to metabolize lactate might be impaired.
- Although it contains some electrolytes and can help with volume expansion, its bicarbonate-generating effect is slower and less reliable than direct bicarbonate administration in **severe acidosis**.
*None of the options*
- This option is incorrect because **i.v. NaHCO3** is a well-established and effective treatment for severe acidosis.
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