Respiratory Acidosis and Alkalosis Indian Medical PG Practice Questions and MCQs
Practice Indian Medical PG questions for Respiratory Acidosis and Alkalosis. These multiple choice questions (MCQs) cover important concepts and help you prepare for your exams.
Respiratory Acidosis and Alkalosis Indian Medical PG Question 1: Why does hyperventilation cause paresthesia?
- A. Increased O2
- B. Decreased CO2 (Correct Answer)
- C. Decreased pH
- D. Increased CO2
Respiratory Acidosis and Alkalosis Explanation: ***Decreased CO2***
- Hyperventilation leads to an excessive loss of **carbon dioxide (CO2)** from the body, causing **respiratory alkalosis**.
- The resulting alkalosis decreases the concentration of **ionized calcium** in the blood, leading to neuronal excitability and thus paresthesia.
*Increased O2*
- While hyperventilation increases the amount of **oxygen (O2)** breathed in, it is not the direct cause of paresthesia.
- The key physiological change leading to paresthesia is related to changes in **blood gas chemistry**, specifically CO2 and pH.
*Decreased pH*
- Hyperventilation causes a **decrease in CO2**, which subsequently leads to an **increase in pH** (respiratory alkalosis), not a decrease in pH.
- A decrease in pH (acidosis) generally leads to different symptoms, and is not the cause of paresthesia in this context.
*Increased CO2*
- Hyperventilation by definition involves **expelling more CO2** than normal, leading to a decrease in CO2 levels, not an increase.
- An underlying increase in CO2 would lead to **respiratory acidosis**, which has a different clinical presentation.
Respiratory Acidosis and Alkalosis Indian Medical PG Question 2: The interpretation of the following ABG value is: pH = 7.5, pCO2 = 50 mm Hg, HCO3 = 30 mEq/L
- A. Respiratory acidosis
- B. Metabolic acidosis
- C. Metabolic alkalosis (Correct Answer)
- D. Normal acid-base balance
Respiratory Acidosis and Alkalosis Explanation: ***Metabolic alkalosis (partially compensated)***
- The **pH of 7.5** indicates **alkalosis**, and the elevated **bicarbonate (HCO3) of 30 mEq/L** is the primary driver of this high pH.
- The elevated **pCO2 of 50 mm Hg** represents **partial respiratory compensation**, where the body retains CO2 to lower the pH toward normal.
- Since the pH remains elevated (not normalized to 7.35-7.45), this is **partially compensated** rather than fully compensated.
*Respiratory acidosis*
- This would be characterized by a **low pH** and an **elevated pCO2**, which is not seen here as the pH is high.
- Although pCO2 is elevated, the **high pH** and **high bicarbonate** rule out primary respiratory acidosis.
*Metabolic acidosis*
- This would present with a **low pH** and a **low bicarbonate** concentration.
- The given values show a **high pH** and **high bicarbonate**, which is the opposite of metabolic acidosis.
*Normal acid-base balance*
- A normal acid-base balance would have a **pH between 7.35-7.45**, a **pCO2 between 35-45 mm Hg**, and an **HCO3 between 22-26 mEq/L**.
- All three values are outside of their normal ranges, indicating an acid-base disturbance.
Respiratory Acidosis and Alkalosis Indian Medical PG Question 3: 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 Acidosis and Alkalosis 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 Acidosis and Alkalosis Indian Medical PG Question 4: A patient presents with the following arterial blood gas (ABG) and electrolyte values: pH: 7.34, Na: 135 mEq/L, Cl: 93 mEq/L, HCO3: 20 mEq/L, Random Blood Sugar (RBS): 420 mg/dl. What is the most likely acid-base disturbance?
- A. Normal Anion Gap Metabolic Acidosis (NAGMA)
- B. Respiratory Acidosis
- C. High Anion Gap Metabolic Acidosis (HAGMA) (Correct Answer)
- D. Metabolic Alkalosis
Respiratory Acidosis and Alkalosis Explanation: ### High Anion Gap Metabolic Acidosis (HAGMA)
- The **pH (7.34)** indicates **acidemia**, and the **low bicarbonate (20 mEq/L)** suggests a metabolic acidosis [1], [2].
- Calculation of the anion gap: Na - (Cl + HCO3) = 135 - (93 + 20) = 22 mEq/L. An anion gap > 12 mEq/L is considered high, confirming **High Anion Gap Metabolic Acidosis (HAGMA)** [4]. The **RBS of 420 mg/dl** also points towards a likely cause such as **diabetic ketoacidosis** [3].
*Normal Anion Gap Metabolic Acidosis (NAGMA)*
- This would be present if the calculated anion gap were within the normal range (typically 8-12 mEq/L).
- Causes of NAGMA (e.g., hyperchloremic acidosis) are typically associated with increased chloride levels to compensate for the bicarbonate loss, which is not the primary finding here [4].
*Respiratory Acidosis*
- This condition is characterized by a **low pH** and an **elevated PaCO2**, which is not provided but implied by the **low bicarbonate** not fitting a respiratory picture [2].
- While the pH is low, the primary disturbance given the other values (especially the low bicarbonate) is metabolic, not respiratory.
*Metabolic Alkalosis*
- Metabolic alkalosis is characterized by an **elevated pH** and an **elevated bicarbonate level**, which contradicts the presented values of low pH and low bicarbonate [2].
- This condition would involve a net gain of bicarbonate or a loss of acids, which is the opposite of the findings in this patient.
Respiratory Acidosis and Alkalosis Indian Medical PG Question 5: 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
Respiratory Acidosis and Alkalosis 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.
Respiratory Acidosis and Alkalosis Indian Medical PG Question 6: The primary respiratory compensation for metabolic acidosis is?
- A. HCO3 loss
- B. Cl- loss
- C. Hyperventilation (Correct Answer)
- D. Ammonia excretion in kidney
Respiratory Acidosis and Alkalosis 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.
Respiratory Acidosis and Alkalosis Indian Medical PG Question 7: 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 Acidosis and Alkalosis 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 Acidosis and Alkalosis Indian Medical PG Question 8: 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 Acidosis and Alkalosis 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 Acidosis and Alkalosis Indian Medical PG Question 9: 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
Respiratory Acidosis and Alkalosis 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.
Respiratory Acidosis and Alkalosis Indian Medical PG Question 10: In metabolic acidosis, what compensatory mechanism is activated first?
- A. Decreased CO2 excretion
- B. Increased respiratory rate (Correct Answer)
- C. Increased renal HCO3- excretion
- D. Increased renal H+ secretion
Respiratory Acidosis and Alkalosis Explanation: ***Increased respiratory rate***
- In metabolic acidosis, the body attempts to **decrease PCO2** through increasing ventilation, thus reducing the **acid load** by expelling more CO2.
- This **respiratory compensation** is rapid and begins within minutes to hours of the onset of acidosis.
*Decreased CO2 excretion*
- This option is incorrect because the body's compensatory mechanism for acidosis involves **increasing CO2 excretion** through hyperventilation, not decreasing it.
- Decreased CO2 excretion would lead to **respiratory acidosis**, further worsening the metabolic acidosis.
*Increased renal HCO3- excretion*
- In metabolic acidosis, the kidneys aim to **conserve bicarbonate**, not excrete it, to buffer the excess acid.
- Increased renal HCO3- excretion would exacerbate acidosis by reducing the body's primary **buffer system**.
*Increased renal H+ secretion*
- This is a renal compensatory mechanism that occurs in metabolic acidosis, but it is **slower to activate** (hours to days) compared to respiratory compensation.
- While important for long-term acid-base balance, it is **not the first mechanism** to be activated.
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