Respiratory and Metabolic Alkalosis — MCQs
In a patient with a pH of 7.2 and a bicarbonate level of 15 mEq/L, what does this imply about the acid-base status?
All of the following statements about acid-base disorders are true, EXCEPT:
A 75-year-old man develops acute confusion and drowsiness after a dental procedure. He has a history of severe chronic lung disease due to smoking. Earlier in the day, he had a tooth extraction and afterwards was given acetaminophen with codeine (Tylenol 3) for pain relief.For the above patient with new symptoms, select the most likely acid base disorder.
A young patient presents with muscle spasms, numbness in the hands and feet, seizures, and difficulty in breathing due to laryngospasm. His blood work reveals an electrolyte imbalance. What is the most likely cause of these manifestations?
20 mEq (mmol) of potassium chloride in 500 ml of 5% dextrose solution is given intravenously to treat-
A patient has hyperaldosteronism. Which lab finding is expected?
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?
Hyperkalemia is due to all of the following except:
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?
Which one of the following biochemical abnormalities can be produced by repeated vomiting?
Respiratory and Metabolic Alkalosis Indian Medical PG Practice Questions and MCQs
Question 1: In a patient with a pH of 7.2 and a bicarbonate level of 15 mEq/L, what does this imply about the acid-base status?
- A. Normal acid-base status
- B. Respiratory acidosis with partial metabolic compensation
- C. Respiratory acidosis
- D. Metabolic acidosis (Correct Answer)
Explanation: ***Metabolic acidosis*** - A **low pH (7.2)** indicates **acidosis**, and a **low bicarbonate level (15 mEq/L)** is the primary disturbance suggesting a metabolic origin. - This combination points to an excess of acid or a loss of bicarbonate, leading to **metabolic acidosis**. *Normal acid-base status* - A **normal pH** would typically range from 7.35 to 7.45, and **bicarbonate** levels would be between 22-26 mEq/L. - The given values (pH 7.2, HCO3 15 mEq/L) are significantly outside of these normal ranges. *Respiratory acidosis with partial metabolic compensation* - Respiratory acidosis is characterized by a **low pH** and an **elevated pCO2**, not primarily a low bicarbonate. - Metabolic compensation would involve an increase in bicarbonate to buffer the acidosis, but the primary disturbance here is low bicarbonate, indicating a metabolic rather than respiratory etiology. *Respiratory acidosis* - Respiratory acidosis is primarily caused by **hypoventilation**, leading to an **increase in pCO2** and a decrease in pH. - In this case, the primary abnormality is the **low bicarbonate**, not an elevated pCO2, which characterizes metabolic acidosis.
Question 2: 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
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.
Question 3: A 75-year-old man develops acute confusion and drowsiness after a dental procedure. He has a history of severe chronic lung disease due to smoking. Earlier in the day, he had a tooth extraction and afterwards was given acetaminophen with codeine (Tylenol 3) for pain relief.For the above patient with new symptoms, select the most likely acid base disorder.
- A. respiratory acidosis (Correct Answer)
- B. metabolic alkalosis
- C. metabolic acidosis
- D. respiratory alkalosis
Explanation: ***Respiratory acidosis*** - The patient has **severe chronic lung disease** and was given **codeine**, an opioid, which can cause significant **respiratory depression**. - This combination leads to **hypoventilation**, resulting in **CO2 retention** and thus, respiratory acidosis, often manifesting as acute confusion and drowsiness. *Metabolic alkalosis* - This condition is characterized by an increase in **bicarbonate** levels, often due to vomiting, diuretic use, or hyperaldosteronism, none of which are suggested by the clinical scenario. - While patients with chronic lung disease can sometimes develop compensatory metabolic alkalosis, the acute presentation of confusion and drowsiness after opioid administration points away from this as the primary, acute problem. *Metabolic acidosis* - This typically results from an accumulation of **lactic acid** (e.g., shock), **ketoacids** (e.g., DKA), or renal failure, or loss of bicarbonate (e.g., severe diarrhea). - There is no clinical information provided that suggests these etiologies; rather, the acute symptoms point towards a respiratory cause. *Respiratory alkalosis* - This occurs due to **hyperventilation**, leading to excessive CO2 excretion and decreased PCO2. - The patient's acute confusion and drowsiness, combined with his history and recent medication, suggest **hypoventilation** rather than hyperventilation.
Question 4: A young patient presents with muscle spasms, numbness in the hands and feet, seizures, and difficulty in breathing due to laryngospasm. His blood work reveals an electrolyte imbalance. What is the most likely cause of these manifestations?
- A. Respiratory Alkalosis (Correct Answer)
- B. Metabolic Alkalosis
- C. Respiratory Acidosis
- D. Metabolic Acidosis
Explanation: ***Respiratory Alkalosis*** - **Hyperventilation** (the likely underlying cause) leads to decreased partial pressure of carbon dioxide (**PCO2**), causing an increase in pH and **respiratory alkalosis**. - This **alkalosis** decreases **ionized calcium** levels by increasing calcium binding to albumin, leading to **hypocalcemia**. - **Hypocalcemia** causes increased neuromuscular excitability, resulting in **muscle spasms, numbness** (paresthesias), **seizures**, and **laryngospasm** (difficulty breathing). - This is the classic presentation of **hypocalcemic tetany** secondary to respiratory alkalosis. *Metabolic Alkalosis* - This imbalance is primarily characterized by an increase in **bicarbonate (HCO3-)** concentration, often due to **vomiting** or diuretic use. - While it can also cause alkalosis leading to **hypocalcemia** and similar neurological symptoms, the acute and severe presentation with prominent tetany and laryngospasm is more characteristic of **respiratory alkalosis**. - Metabolic alkalosis typically has a more gradual onset. *Respiratory Acidosis* - Caused by **hypoventilation**, leading to an increase in **PCO2** and a decrease in pH (acidosis). - **Acidosis increases ionized calcium**, so this would not cause hypocalcemic symptoms. - This condition typically manifests as **somnolence, confusion**, or CNS depression, not the neuromuscular excitability seen in this patient. *Metabolic Acidosis* - Characterized by a decrease in **bicarbonate (HCO3-)** and a decrease in pH, often due to conditions like **diabetic ketoacidosis** or **renal failure**. - **Acidosis increases ionized calcium**, making hypocalcemic tetany unlikely. - Symptoms usually include **Kussmaul breathing** (compensatory hyperventilation) and potential cardiac arrhythmias, which do not match this patient's presentation of tetany and laryngospasm.
Question 5: 20 mEq (mmol) of potassium chloride in 500 ml of 5% dextrose solution is given intravenously to treat-
- A. Hypokalemia (Correct Answer)
- B. Hyperkalemia
- C. Hypernatremia
- D. Hyponatremia
Explanation: ***Hypokalemia*** - The administration of **potassium chloride (KCl)** is a direct method to **replenish potassium stores** in the body, effectively treating low serum potassium levels. - Adding KCl to an intravenous solution, such as **5% dextrose**, ensures systemic distribution to correct this electrolyte imbalance. *Hyperkalemia* - **Hyperkalemia** refers to dangerously high levels of potassium in the blood, so administering more potassium chloride would worsen this condition, not treat it. - Treatment for hyperkalemia typically involves measures to **shift potassium into cells** or **increase its excretion**, not supplementation. *Hypernatremia* - **Hypernatremia** is an elevated sodium level, usually caused by dehydration or excessive sodium intake. Giving potassium chloride would not directly address sodium balance. - Treatment primarily involves administering **hypotonic fluids** to dilute the excessive sodium. *Hyponatremia* - **Hyponatremia** is a low sodium level in the blood. While fluid management is crucial for hyponatremia, potassium chloride specifically targets potassium levels, not sodium. - For hyponatremia, treatment varies based on severity and acuity and often includes **sodium replacement** or fluid restriction.
Question 6: A patient has hyperaldosteronism. Which lab finding is expected?
- A. Metabolic acidosis
- B. Hyperkalemia
- C. Hypokalemia (Correct Answer)
- D. Hyponatremia
Explanation: ***Hypokalemia*** - **Aldosterone** increases the excretion of **potassium** in the kidneys, leading to decreased serum potassium levels [1]. - This effect is mediated by aldosterone's action on the principal cells of the collecting duct, promoting potassium secretion into the urine [1]. *Metabolic acidosis* - **Hyperaldosteronism** typically causes **metabolic alkalosis** due to increased hydrogen ion excretion by the kidneys [1]. - Aldosterone promotes the reabsorption of sodium and water, and the excretion of potassium and hydrogen ions, leading to alkalosis [2]. *Hyperkalemia* - **Aldosterone's primary role** is to promote **potassium excretion** in the kidneys [1]. - Therefore, **excessive aldosterone** production would lead to **hypokalemia**, not hyperkalemia. *Hyponatremia* - **Aldosterone** promotes **sodium reabsorption** in the kidneys, which usually leads to normal or even slightly elevated serum sodium levels [1]. - **Hyponatremia** would be an unexpected finding in hyperaldosteronism [3].
Question 7: 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
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.
Question 8: Hyperkalemia is due to all of the following except:
- A. Addison's disease
- B. Excess hemolysis
- C. Alkalosis (Correct Answer)
- D. Acute renal failure
Explanation: ***Alkalosis*** - **Alkalosis** causes an **intracellular shift of potassium** in exchange for hydrogen ions [1], typically leading to **hypokalemia**, not hyperkalemia [1]. - This shift helps to buffer the alkaline state by moving hydrogen ions out of cells. *Acute renal failure* - In **acute renal failure**, the kidneys lose their ability to excrete potassium, leading to its accumulation in the blood. - This impaired **potassium excretion** is a common cause of **hyperkalemia** in these patients. *Addison's disease* - **Addison's disease** (primary adrenal insufficiency) results in decreased production of **aldosterone**, a hormone that promotes potassium excretion [1]. - Reduced **aldosterone** activity leads to reduced potassium secretion in the renal tubules, causing **hyperkalemia** [1]. *Excess hemolysis* - **Hemolysis** refers to the breakdown of red blood cells, which contain a high concentration of **intracellular potassium** [1]. - When red blood cells lyse, they release their intracellular potassium into the bloodstream, directly causing **hyperkalemia**.
Question 9: 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)
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.
Question 10: 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
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.
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