Respiratory Regulation of Acid-Base Balance Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Respiratory Regulation of Acid-Base Balance. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Respiratory Regulation of Acid-Base Balance Indian Medical PG Question 1: What is the best immediate management strategy for a patient experiencing respiratory alkalosis due to anxiety-induced hyperventilation?
- A. Rebreathing in paper bag (Correct Answer)
- B. IPPV
- C. Normal saline
- D. Acetazolamide
Respiratory Regulation of Acid-Base Balance Explanation: ***Rebreathing in paper bag***
- This helps to **increase the inspired CO2 concentration**, thereby correcting the hypocapnia (low CO2) caused by hyperventilation.
- It's a simple, non-invasive method to raise arterial PCO2 and normalize blood pH in acute respiratory alkalosis.
*IPPV*
- **Intermittent positive pressure ventilation (IPPV)** would further reduce CO2 by assisting ventilation and is typically used for respiratory *acidosis* or failure [1].
- This intervention would worsen the patient's respiratory alkalosis rather than alleviating it.
*Normal saline*
- **Normal saline** administration is primarily used for volume expansion or to correct electrolyte imbalances; it does not directly address respiratory alkalosis.
- It would not correct the underlying issue of excessive CO2 exhalation.
*Acetazolamide*
- **Acetazolamide** is a carbonic anhydrase inhibitor that reduces bicarbonate reabsorption and is used to treat metabolic alkalosis or as a diuretic.
- It would not be an immediate or appropriate solution for acute respiratory alkalosis and might even worsen the acid-base balance if used improperly.
Respiratory Regulation of Acid-Base Balance Indian Medical PG Question 2: A patient with pH of 7, pCO2 of 30 mmHg and Bicarbonate levels of 10 meq. What is the acid base abnormality?
- A. Respiratory alkalosis
- B. Metabolic alkalosis
- C. Respiratory Acidosis
- D. Metabolic Acidosis (Correct Answer)
Respiratory Regulation of Acid-Base Balance Explanation: ***Metabolic Acidosis***
- The pH is 7, which is severely **acidotic** (normal range 7.35-7.45). This indicates an acid-base disorder where the body is too acidic.
- The **bicarbonate level is 10 mEq/L** (normal range 22-26 mEq/L), which is significantly low, directly contributing to the acidosis and pointing towards a metabolic origin.
*Respiratory alkalosis*
- This condition involves an **elevated pH** (alkalosis) due to a primary decrease in pCO2.
- In this case, the pH is acidic, not alkaline.
*Metabolic alkalosis*
- This condition involves an **elevated pH** (alkalosis) due to a primary increase in bicarbonate levels.
- Here, the pH is acidic and bicarbonate is low, directly contradicting metabolic alkalosis.
*Respiratory Acidosis*
- This condition involves a **decreased pH** (acidosis) due to a primary increase in pCO2.
- Although the pH is acidotic, the pCO2 is 30 mmHg (normal range 35-45 mmHg), which is low, indicating a respiratory compensation rather than the primary cause.
Respiratory Regulation of Acid-Base Balance Indian Medical PG Question 3: Which of the following is the common cause of respiratory failure type 2 ?
- A. Chronic bronchitis exacerbation (Correct Answer)
- B. Acute attack asthma
- C. ARDS
- D. Pneumonia
Respiratory Regulation of Acid-Base Balance Explanation: ***Chronic bronchitis exacerbation***
- **Chronic bronchitis** is a common cause of **Type 2 respiratory failure**, characterized by **hypercapnia** (elevated CO2) due to impaired alveolar ventilation [1].
- An exacerbation worsens **airflow obstruction** and leads to increased work of breathing and CO2 retention [1].
*Acute attack asthma*
- While severe asthma can cause respiratory failure, it typically presents initially as **Type 1 (hypoxemic)**, with severe bronchospasm and V/Q mismatch [2].
- **Hypercapnia** in asthma is a sign of **severe, impending respiratory collapse** rather than the primary cause of respiratory failure.
*ARDS*
- **Acute Respiratory Distress Syndrome (ARDS)** is a classic cause of **Type 1 (hypoxemic) respiratory failure**, characterized by widespread inflammation and fluid accumulation in the lungs [2].
- ARDS primarily involves impaired oxygenation rather than CO2 elimination issues, unless it progresses to severe stages with significant muscle fatigue.
*Pneumonia*
- **Pneumonia** predominantly causes **Type 1 (hypoxemic) respiratory failure** due to consolidation and V/Q mismatch in affected lung areas, leading to impaired oxygen diffusion [2].
- While severe, widespread pneumonia can eventually lead to ventilatory failure, its initial and primary impact is on oxygenation.
Respiratory Regulation of Acid-Base Balance Indian Medical PG Question 4: Renal tubular acidosis with ABG value pH = 7.24 PO2=80; PaCO2= 36 Na = 131; HCO3 = 14 Cl= 90; BE = -13 Glucose = 135 the above ABG picture suggests –
- A. Metabolic acidosis (Correct Answer)
- B. Respiratory alkalosis
- C. Metabolic alkalosis
- D. Respiratory acidosis
Respiratory Regulation of Acid-Base Balance Explanation: The ABG shows a pH of 7.24, indicating **acidemia** [1]. The HCO3 is 14 mEq/L, which is significantly **low**, and the base excess (BE) is -13 [1]. The PaCO2 of 36 mmHg is within the normal range, indicating no significant primary respiratory derangement [2]. The overall picture is consistent with an uncompensated or partially compensated **metabolic acidosis** [1][2].
***Metabolic acidosis***
- The **low pH (acidemia)**, **low bicarbonate (HCO3)**, and **negative base excess (BE)** are direct indicators of metabolic acidosis [1].
- The **PaCO2 within normal limits** or slightly decreased suggests either no respiratory compensation or insufficient compensation for the metabolic derangement [1][2].
*Respiratory acidosis*
- This would present with a **low pH** and an **elevated PaCO2** as the primary defect, which is not seen here (PaCO2 is normal) [1].
- Bicarbonate would typically be normal or elevated if compensated, not significantly decreased.
*Respiratory alkalosis*
- This would be characterized by an **elevated pH** and a **low PaCO2**, which is the opposite of the findings in this ABG [1].
- HCO3 would be normal or low if compensated.
*Metabolic alkalosis*
- This would present with an **elevated pH** and an **elevated HCO3**, which contradicts the given ABG values (low pH and low HCO3) [2].
Respiratory Regulation of Acid-Base Balance Indian Medical PG Question 5: A hyperventilating patient has the following ABG values: pH=7.53, pCO2=20 mmHg, HCO3= 26 mEq/L. What is the most likely diagnosis?
- A. Metabolic alkalosis
- B. Metabolic acidosis
- C. Respiratory alkalosis (Correct Answer)
- D. Respiratory acidosis
Respiratory Regulation of Acid-Base Balance Explanation: ***Respiratory alkalosis***
- The pH of 7.53 indicates **alkalemia**, and the low pCO2 (20 mmHg) is the primary driver, signifying **respiratory alkalosis**
- A hyperventilating patient exhales more CO2, leading to a decrease in its partial pressure in the blood and a subsequent rise in pH
- The HCO3 is within normal range (26 mEq/L), indicating **uncompensated respiratory alkalosis**
*Metabolic alkalosis*
- This would be characterized by a high pH and an elevated **HCO3**, but the HCO3 is within the normal range (26 mEq/L)
- While it causes alkalemia, the primary disturbance here is respiratory, not metabolic
*Metabolic acidosis*
- This would present with a **low pH** and a low **HCO3**, which is contrary to the given ABG values
- The patient's pH is elevated, indicating an alkalotic state, not acidotic
*Respiratory acidosis*
- This would be defined by a **low pH** and an elevated **pCO2**, which is the exact opposite of the provided ABG results
- The patient's high pH and low pCO2 rule out respiratory acidosis
Respiratory Regulation of Acid-Base Balance Indian Medical PG Question 6: 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)
Respiratory Regulation of Acid-Base Balance 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.
Respiratory Regulation of Acid-Base Balance Indian Medical PG Question 7: In plasma, if pH is 5, what is the fraction of base to acid?
- A. 0.01
- B. 0.1 (Correct Answer)
- C. 1
- D. 10
Respiratory Regulation of Acid-Base Balance Explanation: ***0.1***
- This question applies the **Henderson-Hasselbalch equation**: pH = pKa + log([base]/[acid]). For the **bicarbonate buffer system** (the primary plasma buffer), pKa ≈ 6.1.
- Substituting the given values: $5 = 6.1 + \log([HCO_3^-] / [H_2CO_3])$
- Rearranging: $\log([HCO_3^-] / [H_2CO_3]) = 5 - 6.1 = -1.1$
- Therefore: $[HCO_3^-] / [H_2CO_3] = 10^{-1.1} ≈ 0.079$
- Among the given options, **0.079 is closest to 0.1**, making this the correct answer.
- Note: pH 5 in plasma is physiologically impossible (incompatible with life), but this tests theoretical understanding of the buffer equation.
*0.01*
- This ratio would correspond to an even **more acidic** condition with $\log([base]/[acid]) = -2$.
- Using Henderson-Hasselbalch: pH = 6.1 + (-2) = 4.1, which is lower than the given pH of 5.
- The calculated ratio of 0.079 is much closer to 0.1 than to 0.01.
*1*
- A ratio of 1 means **equal concentrations** of base and acid, which occurs when pH = pKa.
- This would give pH = 6.1, not the given pH of 5.
- This represents a **neutral buffer condition**, not the acidic state described.
*10*
- This ratio indicates an **alkaline** solution with 10 times more base than acid.
- Using Henderson-Hasselbalch: pH = 6.1 + log(10) = 6.1 + 1 = 7.1 (physiological alkalosis).
- This contradicts the given acidic pH of 5.
Respiratory Regulation of Acid-Base Balance Indian Medical PG Question 8: Which one of the following biochemical abnormalities can be produced by repeated vomiting?
- A. Metabolic acidosis
- B. Metabolic alkalosis (Correct Answer)
- C. Ketosis
- D. Uraemia
Respiratory Regulation of Acid-Base Balance Explanation: ***Metabolic alkalosis***
- Repeated vomiting leads to the loss of **hydrochloric acid (HCl)** from the stomach, causing **hypochloremic metabolic alkalosis** with an increase in serum **bicarbonate (HCO3-)** and a rise in blood pH.
- The loss of H+ and Cl- ions results in **compensatory hypokalemia** as the kidneys exchange K+ for H+ to maintain electroneutrality.
- **Volume depletion** from vomiting triggers aldosterone secretion, which further promotes K+ loss and H+ excretion, perpetuating the alkalosis (contraction alkalosis).
- This is one of the most common causes of metabolic alkalosis in clinical practice.
*Metabolic acidosis*
- This condition is characterized by a decrease in **serum pH** and **bicarbonate levels**, typically due to excess acid production or bicarbonate loss from diarrhea or renal tubular acidosis.
- Vomiting does not directly cause metabolic acidosis; rather, it leads to the opposite effect by removing acidic gastric contents.
*Ketosis*
- **Ketosis** occurs when the body metabolizes fat for energy, producing **ketone bodies**, common in conditions like uncontrolled diabetes or prolonged starvation.
- While severe, prolonged vomiting with reduced oral intake can indirectly lead to starvation ketosis, the primary and most characteristic biochemical abnormality of repeated vomiting is metabolic alkalosis, not ketosis.
*Uraemia*
- **Uraemia** is a syndrome caused by the accumulation of **nitrogenous waste products** (urea, creatinine) in the blood, primarily due to kidney failure.
- Vomiting may be a *symptom* of uraemia, but it does not *cause* uraemia. Kidney function is the primary determinant of urea levels.
Respiratory Regulation of Acid-Base Balance Indian Medical PG Question 9: Which drug is given to prevent acute mountain sickness?
- A. Acetazolamide (Correct Answer)
- B. Dexamethasone
- C. Digoxin
- D. Diltiazem
Respiratory Regulation of Acid-Base Balance Explanation: ***Acetazolamide***
- **Acetazolamide** is a **carbonic anhydrase inhibitor** that acidifies the blood and increases respiratory drive, thereby aiding acclimatization to high altitude.
- It is the **drug of choice** for the prevention and treatment of acute mountain sickness (AMS) and high altitude cerebral edema (HACE).
*Dexamethasone*
- **Dexamethasone**, a corticosteroid, is primarily used for the **treatment** of severe AMS and HACE, rather than prevention.
- It works by reducing swelling and inflammation in the brain but does not facilitate physiological acclimatization.
*Digoxin*
- **Digoxin** is a cardiac glycoside used to treat **heart failure** and **atrial fibrillation**.
- It has no role in the prevention or treatment of acute mountain sickness.
*Diltiazem*
- **Diltiazem** is a **calcium channel blocker** used to treat hypertension, angina, and certain arrhythmias.
- It is not indicated for the prevention or treatment of acute mountain sickness.
Respiratory Regulation of Acid-Base Balance Indian Medical PG Question 10: Carbonic anhydrase activity is found in all of the following except?
- A. Brain
- B. Kidney
- C. RBC
- D. Plasma (Correct Answer)
Respiratory Regulation of Acid-Base Balance Explanation: ***Plasma***
- **Carbonic anhydrase** is an intracellular enzyme that catalyzes the rapid interconversion of carbon dioxide and water to carbonic acid, **bicarbonate**, and protons.
- It is notably **absent in plasma** in healthy individuals, as it is primarily found within cells where its function is crucial for pH regulation and CO2 transport.
*Brain*
- Carbonic anhydrase is found in various brain cells, including **neurons**, **oligodendrocytes**, and **astrocytes**.
- It plays a vital role in pH regulation, fluid balance, and the production of cerebrospinal fluid (CSF) within the **central nervous system**.
*Kidney*
- The kidney is rich in carbonic anhydrase, particularly in the **proximal tubules** and collecting ducts.
- It is critical for **bicarbonate reabsorption** and proton excretion, essential processes for maintaining acid-base balance.
*RBC*
- **Red blood cells (RBCs)** contain a high concentration of carbonic anhydrase (specifically CA-I and CA-II isoforms).
- This enzyme facilitates the rapid conversion of CO2 to bicarbonate for transport to the lungs and the reverse reaction for **CO2 exhalation**.
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