Edema Formation Mechanisms — MCQs
A patient with heart failure presents with worsening peripheral edema. Which of the following mechanisms contributes most directly to this finding?
A 65M presents with worsening dyspnea and leg swelling. Physical examination reveals an elevated jugular venous pressure and bilateral lower extremity pitting edema. Most likely cause of his symptoms?
Interstitial fluid volume can be measured by:
Calculate net filtration pressure with the following data: PGC = 42 mm Hg, πGC = 12 mm Hg, PBC = 16 mm Hg. Assume that no proteins were filtered.
The image shows a Negative Pressure Wound Therapy (NPWT) dressing applied to a patient's wound. What is the ideal negative pressure range commonly used for NPWT to promote wound healing?
In uveitis, site of keratic precipitate is:
A 50-year-old female with a 50 kg body weight suffered burns after a pressure cooker blast, involving 45% of her total body surface area. How much fluid should be given in the first 8 hours?
A woman who weighs 50 kg is brought to you with severe burns over the body. You estimate that the non superficial burns cover 60% of body surface area. What is the rate of fluid to be given in the first 8 hours for this patient?
Which of the following best describes the mechanism of action of Lubiprostone?
GFR is increased by all except?
Edema Formation Mechanisms Indian Medical PG Practice Questions and MCQs
Question 1: A patient with heart failure presents with worsening peripheral edema. Which of the following mechanisms contributes most directly to this finding?
- A. Lymphatic obstruction
- B. Decreased plasma oncotic pressure
- C. Increased capillary hydrostatic pressure (Correct Answer)
- D. Increased vascular permeability
Explanation: ***Increased capillary hydrostatic pressure*** - In **heart failure**, the heart's inability to effectively pump blood forward leads to a **backup of blood** in the venous system. [1] - This elevated venous pressure is transmitted backward to the capillaries, increasing **capillary hydrostatic pressure**, which significantly promotes the filtration of fluid from the capillaries into the interstitial space, causing edema. [1] *Lymphatic obstruction* - **Lymphatic obstruction** typically results in **lymphedema**, which is initially non-pitting and affects specific areas due to localized lymphatic damage. - While it can cause edema, it is not the primary or most direct mechanism for generalized peripheral edema in typical **heart failure**. *Decreased plasma oncotic pressure* - **Decreased plasma oncotic pressure**, often due to conditions like **liver disease** or **nephrotic syndrome**, reduces the osmotic pull of fluid back into the capillaries. - While it can contribute to edema, this is not the most direct or primary mechanism in heart failure, where fluid retention is predominantly driven by pressure changes. *Increased vascular permeability* - **Increased vascular permeability**, often seen in **inflammation** or **allergic reactions**, allows proteins and fluid to leak out of capillaries, forming exudative edema. - This is rarely the main cause of the widespread, **pitting edema** seen in heart failure, which is transudative and primarily pressure-driven.
Question 2: A 65M presents with worsening dyspnea and leg swelling. Physical examination reveals an elevated jugular venous pressure and bilateral lower extremity pitting edema. Most likely cause of his symptoms?
- A. Hypothyroidism
- B. Right-sided heart failure (Correct Answer)
- C. Chronic kidney disease
- D. Liver cirrhosis
Explanation: Right-sided heart failure - **Elevated jugular venous pressure (JVP)** and **bilateral lower extremity pitting edema** are classic signs of fluid overload due to the inability of the right ventricle to effectively pump blood [2], [4]. - **Dyspnea** can occur due to congestion in the lungs (if left-sided failure is also present) or due to increased effort of breathing with significant fluid retention [1], [3]. *Hypothyroidism* - While **hypothyroidism** can cause **non-pitting edema** (myxedema), it does not typically lead to elevated JVP. - The dyspnea in hypothyroidism is often related to respiratory muscle weakness or pleural effusions, not primarily venous congestion. *Chronic kidney disease* - **Chronic kidney disease** can cause **fluid overload** and **edema**, but it typically presents with **pitting edema** and elevated JVP. - However, the primary cause of the fluid retention in CKD is impaired renal excretion, not cardiac pump dysfunction, as in this case. *Liver cirrhosis* - **Liver cirrhosis** can lead to **ascites** and **peripheral edema** due to low albumin and portal hypertension. - Elevate JVP is not a typical feature of cirrhosis unless there is a co-existing cardiac condition.
Question 3: Interstitial fluid volume can be measured by:
- A. Tritium oxide - Sodium thiosulfate
- B. Inulin - Serum albumin labelled with radioactive Iodine (Correct Answer)
- C. Inulin - Radioactive sodium
- D. Aminopyrine - Sucrose
Explanation: ***Inulin - Serum albumin labelled with radioactive Iodine*** - The **interstitial fluid volume** is calculated by subtracting the plasma volume from the extracellular fluid volume. - **Inulin** is used to measure **extracellular fluid volume** because it freely distributes throughout the extracellular space but does not enter cells. - **Serum albumin labeled with radioactive iodine** measures **plasma volume** as it stays primarily within the bloodstream due to its large size. *Tritium oxide - Sodium thiosulfate* - **Tritium oxide** (or D2O) is used to measure **total body water (TBW)**, as it distributes throughout all fluid compartments. - **Sodium thiosulfate** is used to measure **extracellular fluid volume**, similar to inulin. *Inulin - Radioactive sodium* - While **inulin** measures **extracellular fluid volume**, **radioactive sodium** (typically 24Na) also measures extracellular fluid volume but can slightly overestimate it due to slow intracellular penetration. - This combination doesn't directly provide a method for exclusively calculating interstitial fluid by subtraction from plasma volume. *Aminopyrine - Sucrose* - **Aminopyrine** is primarily used to measure the **volume of distribution of specific drugs** or gastric acid secretion, not fluid compartments. - **Sucrose** can be used to measure **extracellular fluid volume** as it does not readily cross cell membranes, similar to inulin, but it's not the primary combination for measuring interstitial fluid from the given options.
Question 4: Calculate net filtration pressure with the following data: PGC = 42 mm Hg, πGC = 12 mm Hg, PBC = 16 mm Hg. Assume that no proteins were filtered.
- A. 14 mm Hg (Correct Answer)
- B. 28 mm Hg
- C. Data not sufficient
- D. 34 mm Hg
Explanation: ***14 mm Hg*** - The **net filtration pressure (NFP)** is calculated using the formula: **NFP = (PGC - PBC) - πGC**. - Plugging in the given values: (42 mmHg - 16 mmHg) - 12 mmHg = 26 mmHg - 12 mmHg = **14 mmHg**. *28 mm Hg* - This answer likely results from an incorrect application of the NFP formula, such as adding the oncotic pressure instead of subtracting it, or miscalculating the difference between hydrostatic pressures. - For example, if both hydrostatic and oncotic pressures were added (42 + 12 + 16), it would yield a much higher number, or if the subtraction was done incorrectly. *Data not sufficient* - All necessary variables for calculating the NFP are provided: **glomerular hydrostatic pressure (PGC)**, **glomerular oncotic pressure (πGC)**, and **Bowman's capsule hydrostatic pressure (PBC)**. - The assumption that "no proteins were filtered" simplifies the calculation, confirming that sufficient data is available. *34 mm Hg* - This result would occur if the oncotic pressure in Bowman's capsule (πBC) was incorrectly considered, or if a different formulation of the NFP calculation was used. - Given that **πBC is assumed to be zero** (as no proteins are filtered into Bowman's capsule), any calculation that leads to 34 mmHg is likely based on an error in applying the formula, such as adding **πGC** instead of subtracting it from the hydrostatic pressure difference.
Question 5: The image shows a Negative Pressure Wound Therapy (NPWT) dressing applied to a patient's wound. What is the ideal negative pressure range commonly used for NPWT to promote wound healing?
- A. -125 mm Hg (Correct Answer)
- B. 60-80 mm Hg
- C. 130 mm Hg
- D. 80-100 mm Hg
Explanation: ***-125 mm Hg*** - **Negative Pressure Wound Therapy (NPWT)** uses controlled subatmospheric (negative) pressure to promote wound healing. - The most commonly used pressure setting is **-125 mm Hg**, which has been extensively validated in clinical studies. - This pressure level effectively promotes granulation tissue formation, reduces edema, removes exudate, and increases blood flow to the wound bed. - **-75 to -125 mm Hg** is the typical therapeutic range, with -125 mm Hg being the standard setting for most wound types. *60-80 mm Hg* - This represents **positive pressure**, not negative pressure used in NPWT. - NPWT requires subatmospheric (below atmospheric) pressure, denoted by the negative sign. - Positive pressures in this range would be used in compression therapy for venous insufficiency, not vacuum-assisted wound closure. *130 mm Hg* - This is a **positive pressure** value and does not apply to NPWT. - NPWT uses negative (suction) pressure, not positive compression. - If interpreted as -130 mm Hg, this would be at the higher end and might increase patient discomfort without additional benefit over -125 mm Hg. *80-100 mm Hg* - These are **positive pressure** values not used in NPWT. - NPWT specifically requires negative pressure (vacuum/suction) to work effectively. - This range would be excessively high even for compression therapy and inappropriate for NPWT.
Question 6: In uveitis, site of keratic precipitate is:
- A. Lens anterior capsule
- B. Corneal endothelium (Correct Answer)
- C. Lens posterior capsule
- D. Corneal stroma
Explanation: ***Corneal endothelium*** - **Keratic precipitates (KPs)** are inflammatory cellular deposits that adhere to the **posterior surface of the cornea**, specifically the endothelial layer, in uveitis. - They represent aggregates of inflammatory cells, such as macrophages and lymphocytes, that have migrated from the inflamed anterior chamber. *Lens anterior capsule* - The **anterior capsule of the lens** is a smooth, acellular membrane and does not typically accumulate inflammatory deposits like **keratic precipitates**. - While inflammatory cells can be observed in the **anterior chamber**, they do not specifically adhere to the lens capsule in this manner. *Lens posterior capsule* - Similar to the anterior capsule, the **posterior capsule of the lens** is not the site for deposition of **keratic precipitates**. - Inflammation affecting the lens would typically present as cataract formation or direct lens inflammation, not KPs. *Corneal stroma* - The **corneal stroma** is the thickest layer of the cornea and is primarily composed of collagen fibrils and keratocytes. - While inflammation can affect the stroma (e.g., in stromal keratitis), **keratic precipitates** specifically form on the **innermost layer**, the endothelium, facing the anterior chamber.
Question 7: A 50-year-old female with a 50 kg body weight suffered burns after a pressure cooker blast, involving 45% of her total body surface area. How much fluid should be given in the first 8 hours?
- A. 4.5 litres (Correct Answer)
- B. 4 litres
- C. 5 litres
- D. 6 litres
Explanation: ***4.5 litres*** - The **Parkland formula** for fluid resuscitation in burn patients is **4 mL x body weight (kg) x % TBSA burned**. - For this patient: 4 mL x 50 kg x 45% = 9000 mL. Half of this volume (4500 mL or **4.5 litres**) is given in the first **8 hours**. *4 litres* - This volume would be insufficient for a patient with a 45% TBSA burn and 50 kg body weight according to the **Parkland formula**. - Undersupplying fluid in severe burns can lead to **hypovolemic shock** and organ dysfunction. *5 litres* - This volume is slightly more than the calculated amount for the first 8 hours based on the **Parkland formula**. - Over-resuscitation can lead to complications such as **pulmonary edema** and **abdominal compartment syndrome**. *6 litres* - This volume is significantly higher than the recommended amount for the first 8 hours, indicating **over-resuscitation**. - Excessive fluid administration can worsen burn edema, leading to **compartment syndromes** and potentially impacting organ function negatively.
Question 8: A woman who weighs 50 kg is brought to you with severe burns over the body. You estimate that the non superficial burns cover 60% of body surface area. What is the rate of fluid to be given in the first 8 hours for this patient?
- A. 1000 ml/hr
- B. 500 ml/hr
- C. 1250 ml/hr
- D. 750 ml/hr (Correct Answer)
Explanation: ***750 ml/hr*** - The Parkland formula is used for fluid resuscitation in burn patients: **4 mL x kg x %TBSA burn**. For this patient: 4 mL x 50 kg x 60% = **12,000 mL** over 24 hours. - Half of this total fluid (6,000 mL) is given in the **first 8 hours**: 6,000 mL / 8 hours = **750 mL/hr**. *1000 ml/hr* - This rate would deliver 8,000 mL in the first 8 hours, which is **over-resuscitation** for this patient according to the Parkland formula. - Excessive fluid administration can lead to complications such as **compartment syndrome** and **pulmonary edema**. *500 ml/hr* - This rate would deliver 4,000 mL in the first 8 hours, which is **under-resuscitation** for this patient according to the Parkland formula. - Inadequate fluid resuscitation can lead to **burn shock**, **renal failure**, and increased mortality. *1250 ml/hr* - This rate would deliver 10,000 mL in the first 8 hours, which represents significant **over-resuscitation** and is not indicated. - Such a high rate is well beyond the calculated needs and could result in severe fluid overload and its associated complications.
Question 9: Which of the following best describes the mechanism of action of Lubiprostone?
- A. Chloride channel activator (Correct Answer)
- B. Chloride channel inhibitor
- C. Sodium channel activator
- D. Sodium channel inhibitor
Explanation: ***Chloride channel activator*** - Lubiprostone is a **prostaglandin E1 derivative** that specifically activates **chloride channels (ClC-2)** on the apical membrane of intestinal epithelial cells. - This activation leads to an increase in **fluid secretion into the intestinal lumen**, softening stool and promoting bowel movements. *Chloride channel inhibitor* - Medications that inhibit chloride channels would likely **reduce fluid secretion** in the intestines, potentially worsening constipation. - This mechanism is **opposite** to the therapeutic effect of lubiprostone, which aims to increase fluid content in the stool. *Sodium channel activator* - Activating sodium channels in the intestine could lead to increased fluid absorption or altered electrolyte balance, but this is **not the primary mechanism** of action for lubiprostone. - Lubiprostone's effect is centered around **anion (chloride) secretion**, not direct sodium channel activation. *Sodium channel inhibitor* - Inhibiting sodium channels might reduce sodium absorption, potentially increasing luminal water, but this is **not how lubiprostone works**. - Lubiprostone specifically targets **chloride channels** to achieve its cathartic effect.
Question 10: GFR is increased by all except?
- A. Renal stone in ureter (Correct Answer)
- B. Efferent arteriole constriction
- C. Decreased oncotic pressure
- D. Increased renal blood flow
Explanation: ***Renal stone in ureter*** - A **renal stone in the ureter** would obstruct urine flow, leading to a buildup of pressure in **Bowman's capsule**. - This increased capsular hydrostatic pressure would **decrease the net filtration pressure**, thereby reducing GFR, not increasing it. *Efferent arteriole constriction* - **Constriction of the efferent arteriole** increases resistance to blood flow out of the glomerulus. - This elevates the **glomerular hydrostatic pressure (P_GC)**, which in turn increases the net filtration pressure and thus GFR. *Decreased oncotic pressure* - **Decreased plasma oncotic pressure (π_GC)** means there is less protein in the blood to pull fluid back into the glomerulus. - This reduction in the opposing force to filtration increases the net filtration pressure, leading to a higher GFR. *Increased renal blood flow* - **Increased renal blood flow** directly enhances the delivery of blood to the glomerulus. - This generally leads to a higher **glomerular hydrostatic pressure** and thus an increased GFR, assuming autoregulation mechanisms are not overwhelmed.
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