Fluid and Electrolyte Disorders — MCQs
Which of the following is a manifestation of magnesium deficiency?
Which of the following is a cause of metabolic acidosis with a normal anion gap?
Hypocalcemia in a child may be associated with
All of the following are features of hyperkalemia on ECG, EXCEPT:
A breast fed child presents with hypernatremia (Serum sodium > 170m Eq/L). His urine sodium is 70 mEq/L. Which of the following is the most likely cause –
Interstitial fluid volume can be determined by:
Which of the following conditions is a direct indication for initiating dialysis?
Treatment of choice in severe dehydration is:
"Active core rewarming" refers to
Which fluid is ideally given for a patient experiencing dehydration?
Fluid and Electrolyte Disorders Indian Medical PG Practice Questions and MCQs
Question 1: Which of the following is a manifestation of magnesium deficiency?
- A. Tetany (Correct Answer)
- B. Hyperreflexia
- C. Hyporeflexia
- D. All of the options
Explanation: ***Tetany*** - Magnesium deficiency can lead to increased neuronal excitability and **neuromuscular irritability**, manifesting as **tetany**. - This is often seen in conjunction with **hypocalcemia** because magnesium is essential for normal parathyroid hormone function and calcium homeostasis. *Hyperreflexia* - While magnesium deficiency can cause increased neuromuscular excitability, **hyperreflexia** is not the primary or most characteristic manifestation. - Instead, tetany, which involves more generalized muscle spasms and cramps, is a more specific sign of severe deficiency. *Hyporeflexia* - **Hyporeflexia** is more commonly associated with **hypermagnesemia**, where high magnesium levels depress neuromuscular transmission. - Magnesium deficiency, in contrast, tends to enhance muscle and nerve activity, leading to symptoms like tetany. *All of the options* - While some forms of increased neuromuscular excitability like hyperreflexia might be present, **tetany** is the most direct and classic manifestation of significant magnesium deficiency due to its critical role in regulating muscle and nerve function. - Hyporeflexia is characteristic of excess magnesium, not deficiency.
Question 2: Which of the following is a cause of metabolic acidosis with a normal anion gap?
- A. Diabetic ketoacidosis
- B. Aspirin poisoning
- C. Renal tubular acidosis (Correct Answer)
- D. Lactic acidosis
Explanation: ***Renal tubular acidosis*** - **Renal tubular acidosis (RTA)** is characterized by a defect in renal acid excretion or bicarbonate reabsorption, leading to **metabolic acidosis** with a **normal anion gap** [1]. - The deficiency in net acid excretion results in the retention of chloride ions to maintain electroneutrality, hence it's also known as **hyperchloremic metabolic acidosis** [1]. *Diabetic ketoacidosis* - **Diabetic ketoacidosis (DKA)** is a high anion gap metabolic acidosis caused by the accumulation of **ketoacids** (beta-hydroxybutyrate, acetoacetate). - These unmeasured anions increase the anion gap, distinguishing it from normal anion gap acidosis. *Aspirin poisoning* - **Aspirin (salicylate) poisoning** typically causes a **mixed acid-base disorder** with both metabolic acidosis and respiratory alkalosis [1]. - The metabolic acidosis component is a **high anion gap acidosis** due to the accumulation of salicylates and their metabolites. *Lactic acidosis* - **Lactic acidosis** is a common cause of **high anion gap metabolic acidosis**, resulting from the overproduction or decreased clearance of **lactate** [1]. - The increased concentration of lactate, an unmeasured anion, leads to the widening of the anion gap.
Question 3: Hypocalcemia in a child may be associated with
- A. DiGeorge syndrome
- B. Magnesium deficiency
- C. Hypoparathyroidism
- D. All of the options (Correct Answer)
Explanation: ***All of the options*** - **Hypocalcemia** can stem from various causes, and all the listed conditions (DiGeorge syndrome, magnesium deficiency, and hypoparathyroidism) are known to cause it. - A comprehensive understanding of potential etiologies is crucial for accurate diagnosis and treatment of hypocalcemia in children. *Digeorge syndrome* - **DiGeorge syndrome** is a genetic disorder associated with abnormal development of the **thymus** and **parathyroid glands**, leading to **hypoparathyroidism** and subsequent hypocalcemia. - This condition is characterized by a deletion on **chromosome 22q11.2**, resulting in various clinical manifestations including **cardiac defects** and **immune deficiencies**. *Magnesium deficiency* - **Magnesium deficiency (hypomagnesemia)** can impair the release of **parathyroid hormone (PTH)** and reduce target organ responsiveness to PTH, leading to **hypocalcemia**. - Adequate magnesium levels are essential for the proper functioning of the **parathyroid glands** and calcium homeostasis. *Hypoparathyroidism* - **Hypoparathyroidism** is a condition where the **parathyroid glands** produce insufficient amounts of **parathyroid hormone (PTH)**, which is crucial for regulating calcium levels. - Insufficient PTH leads to decreased reabsorption of calcium in the kidneys and reduced calcium release from bones, resulting in **hypocalcemia**.
Question 4: All of the following are features of hyperkalemia on ECG, EXCEPT:
- A. Shortened QT interval
- B. Peaked T waves
- C. Wide QRS complex
- D. U waves (Correct Answer)
Explanation: ***U waves*** - **U waves** are typically associated with **hypokalemia**, not hyperkalemia. They are small deflections immediately following the T wave. - Their presence suggests an abnormality in myocardial repolarization due to low potassium levels. *Shortened QT interval* - A **shortened QT interval** is *not* a typical finding in hyperkalemia; hyperkalemia usually causes a **prolonged PR interval** and QRS widening, which can make QT measurement difficult but does not inherently shorten it. - A shortened QT interval is more commonly seen in conditions like **hypercalcemia** or inherited short QT syndrome. *Peaked T waves* - **Peaked T waves** (also known as "tenting" of the T waves) are one of the earliest and most classic ECG signs of hyperkalemia [1]. - This occurs due to abnormally rapid repolarization of the ventricles. *Wide QRS complex* - As hyperkalemia progresses, the **QRS complex widens** due to a slowing of intraventricular conduction [1]. - This widening can eventually lead to a **sine wave pattern** if not treated, indicating severe hyperkalemia and impending cardiac arrest.
Question 5: A breast fed child presents with hypernatremia (Serum sodium > 170m Eq/L). His urine sodium is 70 mEq/L. Which of the following is the most likely cause –
- A. Acute tubular necrosis
- B. Severe dehydration
- C. Excessive intake of sodium (Correct Answer)
- D. Diabetes insipidus
Explanation: ***Excessive intake of sodium*** - A critically elevated **serum sodium (>170 mEq/L)** coupled with a high **urine sodium (70 mEq/L)** in a breastfed infant indicates that the kidneys are actively trying to excrete excess sodium. This pattern is consistent with an exogenous sodium overload. - This scenario suggests the ingestion of a **hypertonic solution** or food, likely by mistake, leading to significant sodium toxicity requiring rapid renal excretion. *Acute tubular necrosis* - In ATN, there's impaired renal concentration and reabsorption, but acute kidney injury often leads to **normonatremia or hyponatremia**, not severe hypernatremia. - While urine sodium can be high in ATN due to tubular damage, the primary cause of such extreme hypernatremia would typically be external sodium load. *Severe dehydration* - Severe dehydration usually causes **pre-renal acute kidney injury**, characterized by **high serum sodium** due to water loss, but the kidneys would **conserve sodium**, resulting in a very **low urine sodium** (<20 mEq/L). - The high urine sodium of 70 mEq/L in this case **argues against dehydration** as the primary cause of hypernatremia. *Diabetes insipidus* - Diabetes insipidus (DI) causes **hypernatremia due to free water loss** from the kidneys, resulting in a **dilute urine** with a **low urine osmolality** and typically **low urine sodium**. - The elevated urine sodium of 70 mEq/L is inconsistent with the renal handling of sodium seen in diabetes insipidus.
Question 6: Interstitial fluid volume can be determined by:
- A. Radioactive iodine and radiolabelled water
- B. Radioactive sodium and radioactive water
- C. Radioactive sodium and radioactive labelled albumin (Correct Answer)
- D. Radioactive water and radiolabelled albumin
Explanation: ***Radioactive sodium and radioactive labelled albumin*** - **Interstitial fluid volume** (ISF) is the difference between **extracellular fluid** (ECF) and **plasma volume**. - **Radioactive sodium** can be used to estimate ECF, and **radioactive labelled albumin** can be used to estimate plasma volume. *Radioactive iodine and radiolabelled water* - **Radioactive iodine** (often as iodide) is used for **extracellular fluid** (ECF) measurement, not directly for ISF alone. - **Radiolabelled water** (e.g., tritiated water) is used to measure **total body water** (TBW), which includes intracellular and extracellular components. *Radioactive sodium and radioactive water* - **Radioactive sodium** is used to measure **extracellular fluid** (ECF) due to its limited entry into cells. - **Radioactive water** (e.g., tritiated water) measures **total body water** (TBW), not specifically interstitial fluid. *Radioactive water and radiolabelled albumin* - **Radioactive water** measures **total body water** (TBW), which encompasses all fluid compartments. - **Radiolabelled albumin** measures **plasma volume** because albumin remains within the vascular space.
Question 7: Which of the following conditions is a direct indication for initiating dialysis?
- A. Severe metabolic acidosis
- B. Fluid overload
- C. Severe hyperkalemia (Correct Answer)
- D. Acute kidney injury
Explanation: ### Severe hyperkalemia - **Severe hyperkalemia** (potassium levels typically >6.5 mEq/L or rapidly rising, especially with ECG changes) is an immediate life-threatening indication for dialysis when conservative measures fail or are insufficient [1]. - Dialysis effectively removes **excess potassium** from the blood, preventing fatal cardiac arrhythmias. *Severe metabolic acidosis* - While **severe metabolic acidosis** (pH <7.1-7.2) can be an indication, it is often managed first with bicarbonate administration and is typically not a stand-alone **direct** *emergency* indication for dialysis unless accompanied by other severe features or resistance to medical therapy. - The decision to dialyze for acidosis often depends on the underlying cause, degree of renal failure, and response to initial management [2]. *Fluid overload* - **Fluid overload** is a common complication of kidney failure, but it becomes a *direct* indication for dialysis when it is **refractory to diuretic therapy** and causes life-threatening symptoms such as **pulmonary edema** [2]. - Without such refractory state and immediate danger, fluid overload itself is not always an *immediate* trigger for dialysis compared to severe hyperkalemia. *Acute kidney injury* - **Acute kidney injury** (AKI) is the underlying *condition* that can lead to indications for dialysis, but AKI itself is not a *direct indication* for dialysis. - Dialysis is initiated for the *complications* of AKI, such as refractory hyperkalemia, severe metabolic acidosis, or fluid overload, rather than the diagnosis of AKI alone [2].
Question 8: Treatment of choice in severe dehydration is:
- A. Plasma
- B. Isolyte P
- C. Ringer lactate
- D. Normal saline (Correct Answer)
Explanation: ***Normal saline*** - **Normal saline (0.9% sodium chloride)** is an isotonic solution, making it the preferred initial intravenous fluid for rapidly correcting severe dehydration and restoring intravascular volume [1]. - Its **electrolyte composition** closely mimics the body's extracellular fluid, minimizing osmotic shifts and providing effective volume expansion [1]. *Plasma* - **Plasma** is primarily used for expanding blood volume in cases of **hemorrhage** or severe **protein deficiency**, not for simple dehydration. - It carries risks of allergic reactions and disease transmission, making it inappropriate for routine dehydration treatment. *Isolyte P* - **Isolyte P** is a hypotonic solution, typically used for maintenance fluid therapy in children, especially in situations where **sodium restriction** is desirable. - It is not suitable for rapid volume expansion in severe dehydration due to its low sodium content, which could worsen hypotonicity in an already depleted patient. *Ringer lactate* - **Ringer's lactate** is an isotonic crystalloid solution often used for fluid resuscitation, but it contains **lactate**, which is metabolized in the liver to bicarbonate. - While generally safe, in severe shock situations with impaired liver function or lactic acidosis, the metabolism of lactate can be compromised, potentially exacerbating acidosis. **Normal saline** avoids this concern as a first-line agent [2].
Question 9: "Active core rewarming" refers to
- A. Heated crystalloids (Correct Answer)
- B. Heated humidified O2
- C. Peritoneal dialysis
- D. All of the options
Explanation: ***Heated crystalloids*** - **Heated crystalloids** administered intravenously contribute to active core rewarming by directly introducing warm fluids into the circulatory system, raising the internal body temperature. - This method is particularly effective for **moderate to severe hypothermia** as it rapidly delivers heat to the body's core. *Heated humidified O2* - Administering **heated and humidified oxygen** helps prevent further heat loss from the respiratory tract and contributes to rewarming. - While beneficial, it is generally considered a less aggressive or primary method of **active core rewarming** compared to direct intravenous fluid administration because it does not directly warm the bloodstream. *Peritoneal dialysis* - **Peritoneal dialysis** involves introducing warm dialysate into the peritoneal cavity, allowing for heat exchange. - This is an invasive procedure primarily used when other rewarming methods are insufficient, and it is a specific type of active core rewarming, but not the only one or most common representation of the term itself. *All of the options* - While **heated humidified O2** and **peritoneal dialysis** are methods of active rewarming, the question asks for what "active core rewarming" refers to. - Each of these options represents a specific technique, and while all contribute to rewarming the core, **heated crystalloids** are a more general and common representation encompassed by the term "active core rewarming."
Question 10: Which fluid is ideally given for a patient experiencing dehydration?
- A. Plasma
- B. Normal Saline (Correct Answer)
- C. Blood
- D. 5% dextrose
Explanation: ***Normal Saline*** - **Normal saline (0.9% sodium chloride)** is an **isotonic solution** that effectively increases **extracellular fluid volume**, making it ideal for treating **dehydration** and hypovolemia [1]. - It closely mimics the **osmolality of plasma** and stays predominantly in the intravascular space, helping to restore circulating volume [1]. *Plasma* - **Plasma** is primarily used for **coagulation factor deficiencies** or volume expansion in cases of severe **hypoproteinemia**, not routine dehydration. - It contains **proteins and clotting factors** that are not typically needed for simple dehydration and carries risks of **allergic reactions and transfusion-related acute lung injury (TRALI)**. *Blood* - **Blood transfusions** are indicated for patients with **significant anemia** or **acute blood loss**, not for generalized dehydration. - Using blood for dehydration would be inappropriate due to risks such as **transfusion reactions**, **infections**, and **iron overload**. *5% dextrose* - **5% dextrose in water (D5W)** is an **isotonic solution initially**, but once the dextrose is metabolized, it becomes **hypotonic**, causing free water to shift into the cells [1]. - While it provides some free water, it is not ideal for primary rehydration in cases of significant volume depletion due to its lack of electrolytes and potential for causing **hyponatremia** if given in large quantities [1].
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