Mixed Acid-Base Disorders Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Mixed Acid-Base Disorders. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Mixed Acid-Base Disorders Indian Medical PG Question 1: A patient of CKD has presented with protracted vomiting. ABG shows pH = 7.40, pCO2 = 40 mm Hg, HCO3 = 24 mEq/L, Na = 145 mEq/L, Chloride = 100 mEq/L. What is the observation?
- A. Normal anion gap metabolic acidosis
- B. No acid base abnormality
- C. High anion gap metabolic acidosis and metabolic alkalosis (Correct Answer)
- D. High anion gap metabolic acidosis
Mixed Acid-Base Disorders Explanation: ***High anion gap metabolic acidosis and metabolic alkalosis***
- The **calculated anion gap** is 145 - (100 + 24) = 21, which is elevated (normal 8-12), indicating a **high anion gap metabolic acidosis**. [1]
- The **ΔΔ ratio (ΔAG / ΔHCO3)** is (21-12) / (24-24) = 9/0, which is indeterminate but given the **normal pH and Bicarbonate**, a co-existing metabolic alkalosis that is compensating for the acidosis is likely. [1]
*Normal anion gap metabolic acidosis*
- This would be characterized by a **normal anion gap** (8-12 mEq/L), which is not the case here (elevated to 21 mEq/L). [1]
- Normal anion gap acidosis usually involves **loss of bicarbonate** or **addition of chloride**, leading to hyperchloremia.
*No acid base abnormality*
- While the **pH and HCO3** are within the normal range, the elevated anion gap indicates an underlying acid-base disturbance. [1]
- A comprehensive assessment, including anion gap calculation, reveals an abnormality **despite normal pH**. [1]
*High anion gap metabolic acidosis*
- Although there is a **high anion gap metabolic acidosis**, the **normal pH and bicarbonate** suggest a second primary acid-base disorder. [1]
- In an isolated high anion gap metabolic acidosis, the pH and bicarbonate would typically be **lower than normal**.
Mixed Acid-Base Disorders Indian Medical PG Question 2: A male patient presents to the emergency department. The arterial blood gas report is as follows: pH, 7.2; pCO2, 81 mmHg; and HCO3, 40 meq/L. Which of the following is the most likely diagnosis?
- A. Respiratory alkalosis
- B. Metabolic acidosis
- C. Respiratory acidosis (Correct Answer)
- D. Metabolic alkalosis
Mixed Acid-Base Disorders Explanation: ***Respiratory acidosis***
- The **pH of 7.2** indicates **acidemia**, while the **elevated pCO2 (81 mmHg)** points to a primary respiratory problem [2].
- The elevated **HCO3 (40 meq/L)** suggests **renal compensation** attempting to buffer the increased carbonic acid [1].
*Respiratory alkalosis*
- This condition presents with an **elevated pH (alkalemia)** and a **decreased pCO2**, which is opposite to the given ABG values [2].
- While there might be metabolic compensation with a decreased HCO3, the primary disturbance is an increase in respiratory rate leading to excessive CO2 exhalation.
*Metabolic acidosis*
- Metabolic acidosis is characterized by a **low pH** and a **low HCO3**, with a compensatory decrease in pCO2 [1].
- The given ABG shows a high HCO3, which rules out primary metabolic acidosis.
*Metabolic alkalosis*
- This condition would typically show an **elevated pH** and an **elevated HCO3**, with a compensatory increase in pCO2.
- While both HCO3 and pCO2 are high in the given ABG, the low pH points to a primary acidosis, not alkalosis.
Mixed Acid-Base Disorders Indian Medical PG Question 3: The primary respiratory compensation for metabolic acidosis is?
- A. HCO3 loss
- B. Cl- loss
- C. Hyperventilation (Correct Answer)
- D. Ammonia excretion in kidney
Mixed Acid-Base Disorders Explanation: ***Hyperventilation***
- In **metabolic acidosis**, the body attempts to raise the pH by decreasing the **partial pressure of carbon dioxide (PCO2)**.
- **Hyperventilation** increases the excretion of CO2, a volatile acid, which directly reduces the amount of carbonic acid in the blood and helps to buffer the excess acid.
*HCO3 loss*
- **Bicarbonate (HCO3-) loss** is a cause or consequence of metabolic acidosis, not a compensatory mechanism.
- The kidneys generally try to *retain* or regenerate bicarbonate during acidosis, rather than losing it.
*Cl- loss*
- **Chloride ion (Cl-) loss** is not a primary respiratory compensatory mechanism for metabolic acidosis.
- While shifts in chloride can occur in acid-base imbalances, they are typically related to renal handling or fluid shifts, not direct respiratory compensation.
*Ammonia excretion in kidney*
- **Ammonia excretion** by the kidneys is a renal (kidney) compensatory mechanism, not a respiratory one.
- The kidneys excrete ammonia to excrete hydrogen ions (H+), thereby regenerating bicarbonate and helping to correct the acidosis over a longer period.
Mixed Acid-Base Disorders Indian Medical PG Question 4: The lab reports of a patient given below: pH = 7.2, HCO3 = 10 mEq/L, PCO2 = 30 mmHg. This exemplifies which of the following disorders?
- A. Metabolic alkalosis
- B. Respiratory acidosis
- C. Metabolic acidosis (Correct Answer)
- D. Respiratory alkalosis
Mixed Acid-Base Disorders Explanation: ***Metabolic acidosis***
- The pH of 7.2 is acidic, and the **bicarbonate (HCO3) of 10 mEq/L** is significantly low (normal: 22-28 mEq/L), indicating a primary metabolic disturbance causing acidosis.
- The **PCO2 of 30 mmHg** is also low (normal: 35-45 mmHg), which represents **partial respiratory compensation** through hyperventilation to blow off CO2 and raise pH.
- This is a classic example of **metabolic acidosis with respiratory compensation**.
*Metabolic alkalosis*
- This condition would be characterized by a **high pH** and a **high bicarbonate (HCO3)** level, which is the opposite of the given values.
- The body would attempt to compensate by increasing PCO2 through hypoventilation.
*Respiratory acidosis*
- This would present with a **low pH** and a **high PCO2** (>45 mmHg), indicating a primary respiratory problem leading to CO2 retention and acid accumulation.
- Metabolic compensation would show elevated HCO3, not the low HCO3 (10 mEq/L) seen here.
*Respiratory alkalosis*
- This condition is characterized by a **high pH** (>7.45) and a **low PCO2**, due to excessive ventilation causing CO2 elimination.
- While PCO2 is low in the given scenario, the pH is acidic (7.2), not alkalotic, ruling out this diagnosis.
Mixed Acid-Base Disorders Indian Medical PG Question 5: A person with type 1 diabetes ran out of her prescription insulin and has not been able to inject insulin for the past 3 days. The patient is hyperventilating to compensate for her metabolic acidosis. Which of the following reactions explains this respiratory compensation for metabolic acidosis?
- A. H2O ⇌ H+ + OH-
- B. H+ + NH3 ⇌ NH4+
- C. CH3CHOHCH2COOH ⇌ CH3CHOHCH2COO- + H+
- D. CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3- (Correct Answer)
Mixed Acid-Base Disorders Explanation: ***CO2 + H2O ⇌ H2CO3 ⇌ H+ + HCO3-***
- This reaction represents the **bicarbonate buffer system**, which is central to maintaining **pH balance** in the body.
- In response to **metabolic acidosis**, the body hyperventilates to **decrease CO2** levels, shifting the equilibrium to the left and reducing H+ which compensates for the increased acidity.
*H2O ⇌ H+ + OH-*
- This reaction describes the **autoionization of water**, which is fundamental but does not directly explain the body's respiratory compensation mechanism for metabolic acidosis.
- While it shows the presence of H+ ions, it doesn't illustrate how the respiratory system manipulates CO2 to influence pH.
*H+ + NH3 ⇌ NH4+*
- This reaction represents the **ammonia buffer system** primarily active in the **kidneys** for acid excretion.
- It plays a role in renal compensation for pH imbalances, but it is not the mechanism for respiratory compensation.
*CH3CHOHCH2COOH ⇌ CH3CHOHCH2COO- + H+*
- This represents the **dissociation of beta-hydroxybutyric acid**, a **ketone body** produced in diabetic ketoacidosis (DKA).
- While DKA is the cause of the metabolic acidosis in this patient, this specific reaction describes the *production* of H+ ions, not the *respiratory compensatory mechanism* to address it.
Mixed Acid-Base Disorders Indian Medical PG Question 6: 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
Mixed Acid-Base Disorders 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.
Mixed Acid-Base Disorders Indian Medical PG Question 7: When resuscitating a patient in shock which of the following is not an adequate parameter to predict end point of resuscitation?
- A. Mixed venous oxygen saturation
- B. Base deficit
- C. Lactate
- D. Blood pressure (Correct Answer)
Mixed Acid-Base Disorders Explanation: ***Blood pressure***
- While essential for initial assessment and guiding treatment, **blood pressure** can be maintained within normal limits even in significant shock states due to compensatory mechanisms [1].
- Blood pressure alone does not reflect **tissue perfusion** or cellular oxygenation, which are the true endpoints of resuscitation [1].
*Mixed venous oxygen saturation*
- **Mixed venous oxygen saturation (SvO2)** reflects the balance between oxygen delivery and consumption, providing insight into global tissue oxygenation.
- A low SvO2 indicates inadequate oxygen delivery relative to demand, making it a valuable target for guiding resuscitation.
*Base deficit*
- **Base deficit** is a measure of metabolic acidosis and reflects the severity of tissue hypoperfusion and anaerobic metabolism.
- Normalization of base deficit indicates correction of metabolic derangements and improved tissue perfusion.
*Lactate*
- **Lactate** is a product of anaerobic metabolism, which occurs when tissues are not adequately perfused or oxygenated.
- Elevated lactate levels indicate tissue hypoperfusion, and serial measurements are crucial for monitoring the effectiveness of resuscitation and predicting outcomes.
Mixed Acid-Base Disorders Indian Medical PG Question 8: What is the most common underlying cause of hypoxemia in patients with pneumonia?
- A. Shunting
- B. Reduced lung volume
- C. Impaired gas exchange
- D. Ventilation-perfusion mismatch (Correct Answer)
Mixed Acid-Base Disorders Explanation: ***Ventilation-perfusion mismatch***
- This occurs when areas of the lung are either **well-perfused but poorly ventilated** (e.g., due to alveolar filling or collapse in pneumonia), or **well-ventilated but poorly perfused**.
- In pneumonia, inflammatory exudates and consolidation fill alveoli, impairing ventilation while perfusion to these areas continues, creating a **low V/Q ratio** and leading to hypoxemia.
*Shunting*
- **True shunting** (blood bypassing ventilated lung entirely) is a severe form of V/Q mismatch where the V/Q ratio is zero.
- While shunting can occur in severe pneumonia, it represents an extreme, non-correctable form of V/Q mismatch and is not the *most common* or primary mechanism for hypoxemia in the broader spectrum of pneumonia.
*Reduced lung volume*
- **Reduced lung volume** can contribute to hypoxemia by limiting the overall surface area for gas exchange, but it is not the primary or most direct mechanism caused by the pathological changes in pneumonia.
- It often results from conditions like atelectasis or pleural effusions, which may coexist with pneumonia but are distinct from the primary parenchymal inflammation.
*Impaired gas exchange*
- **Impaired gas exchange** is a general term describing the inability to adequately oxygenate blood and/or remove carbon dioxide.
- While V/Q mismatch is a specific mechanism of impaired gas exchange, "impaired gas exchange" itself is too broad and does not pinpoint the underlying physiological process most commonly responsible in pneumonia.
Mixed Acid-Base Disorders Indian Medical PG Question 9: When VA/Q is infinity, it means
- A. Dead space (Correct Answer)
- B. Unrelated to VA/Q ratio
- C. The PO2 of alveolar air is 159 mmHg and PCO2 is 0 mmHg
- D. Atelectasis
Mixed Acid-Base Disorders Explanation: ***Dead space***
- An infinite V/Q ratio implies that **ventilation (V)** is occurring, but **perfusion (Q)** is zero.
- This scenario defines **dead space**, where air enters the alveoli but no blood flow is available for gas exchange.
- This is the **most accurate and complete answer** to describe the physiological meaning of VA/Q = ∞.
*Unrelated to VA/Q ratio*
- This statement is incorrect because VA/Q being infinity is a specific and highly significant state within the **ventilation-perfusion relationship**.
- An infinite ratio directly indicates a complete decoupling of ventilation and perfusion, with profound physiological consequences.
*The PO2 of alveolar air is 159 mmHg and PCO2 is 0 mmHg*
- While this describes the **gas composition** in dead space (VA/Q = ∞), it is not the **physiological term** for the condition.
- With no perfusion, alveolar air remains essentially **unchanged from inspired air**: PO2 ≈ 150-159 mmHg (atmospheric level) and PCO2 ≈ 0 mmHg.
- No oxygen is extracted and no CO2 is added because there is **no blood flow**.
- However, "dead space" is the more precise physiological answer.
*Atelectasis*
- **Atelectasis** refers to the collapse of lung tissue, which typically leads to an absence of **ventilation (V)** in that region.
- This condition would result in a **VA/Q ratio of zero** (V=0, Q present), the opposite of infinity.
Mixed Acid-Base Disorders Indian Medical PG Question 10: A 60-year-old man with type 2 diabetes on metformin and insulin presents with 3 days of nausea, vomiting, and diffuse abdominal pain. He appears ill and confused. Vital signs: BP 95/60 mmHg, HR 115/min, RR 28/min, T 37.2°C. Labs show glucose 380 mg/dL, pH 7.28, HCO3 18 mEq/L, anion gap 24, serum osmolality 310 mOsm/kg, negative urine ketones, creatinine 2.8 mg/dL (baseline 1.1), lactate 8.2 mmol/L. Apply physiological principles to determine the primary acid-base and metabolic disturbance.
- A. Hyperosmolar hyperglycemic state complicated by lactic acidosis from metformin (Correct Answer)
- B. Diabetic ketoacidosis with renal failure from volume depletion
- C. Sepsis-induced lactic acidosis with stress hyperglycemia
- D. Alcoholic ketoacidosis with concurrent diabetic emergency
- E. Mixed metabolic acidosis from uremia and starvation ketosis
Mixed Acid-Base Disorders Explanation: ***Hyperosmolar hyperglycemic state complicated by lactic acidosis from metformin***
- The patient exhibits severe hyperglycemia and high serum osmolality without significant ketonemia, typical of **Hyperosmolar Hyperglycemic State (HHS)** in Type 2 Diabetes.
- The high **anion gap metabolic acidosis** is primarily explained by a markedly elevated **serum lactate (8.2 mmol/L)**, likely due to **Metformin-Associated Lactic Acidosis (MALA)** precipitated by acute kidney injury.
*Diabetic ketoacidosis with renal failure from volume depletion*
- **Negative urine ketones** and a relative lack of severe metabolic acidosis solely from ketones rule out classic Diabetic Ketoacidosis (DKA).
- While volume depletion and renal failure are present, the absence of **ketonemia/ketonuria** points away from DKA toward an HHS-dominant pattern.
*Sepsis-induced lactic acidosis with stress hyperglycemia*
- Although sepsis can cause lactic acidosis, the glucose of 380 mg/dL and signs of severe dehydration are more characteristic of a **primary diabetic emergency** rather than simple stress hyperglycemia.
- The patient lacks definitive localized infection signs or a classic **febrile response**, making MALA secondary to renal failure a more specific explanation for the high lactate.
*Alcoholic ketoacidosis with concurrent diabetic emergency*
- **Alcoholic ketoacidosis** typically presents with positive ketones and a history of chronic alcohol abuse followed by starvation, which is not indicated here.
- The serum glucose in alcoholic ketoacidosis is often low or normal, unlike the **hyperglycemia** seen in this patient.
*Mixed metabolic acidosis from uremia and starvation ketosis*
- While the creatinine is elevated (2.8 mg/dL), the **anion gap of 24** and lactate of 8.2 suggest lactic acidosis is the dominant driver rather than **uremic toxins** alone.
- **Starvation ketosis** would result in positive ketones, which are explicitly documented as negative in this case.
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