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1. General Principles & Basic Science MCQs

Practice Set 522 of 789

This practice set contains high-yield board review questions covering key concepts in 1. General Principles & Basic Science. Each clinical scenario is designed to test your diagnostic and management skills relevant to this subspecialty.

Question 10421

Topic: 1. General Principles & Basic Science

A patient develops a pressure ulcer in the heel after prolonged immobilization. What type of bed surface would be most effective in preventing and managing further pressure ulcers by optimally distributing pressure?

. Standard hospital mattress.
. Foam mattress overlay.
. Egg-crate mattress.
. Low-air-loss mattress.
. Water mattress.

Correct Answer & Explanation

. Low-air-loss mattress.

Explanation

Low-air-loss (LAL) mattresses are highly effective for pressure ulcer prevention and management. They consist of multiple air-filled cells that are individually controlled to continuously adjust and redistribute pressure, minimizing prolonged high-pressure points and optimizing blood flow to the skin. While foam and egg-crate mattresses offer some improvement over standard mattresses, LAL systems provide superior pressure redistribution, making them the most effective choice for high-risk patients or those with existing ulcers.

Question 10422

Topic: 1. General Principles & Basic Science

When setting the suction pressure for surgical drains in orthopedic surgery (e.g., Hemovac or JP drain), what is the main goal in relation to pressure, considering wound healing and bleeding?

. Maximum continuous high negative pressure to ensure complete drainage.
. Intermittent high negative pressure to prevent clot formation.
. Lowest effective negative pressure to evacuate fluid without damaging tissues or promoting bleeding.
. Positive pressure to push fluid out of the wound.
. Maintaining atmospheric pressure within the drain.

Correct Answer & Explanation

. Lowest effective negative pressure to evacuate fluid without damaging tissues or promoting bleeding.

Explanation

The goal for surgical drain suction pressure should be the lowest effective negative pressure. While drains are designed to evacuate fluid (seroma, hematoma), excessive negative pressure can damage surrounding tissues, promote bleeding by sucking small vessels, or increase the risk of drain occlusion by sucking in tissue. Therefore, maintaining sufficient, but not excessive, negative pressure is key to achieve drainage without adverse effects. Maximum continuous high negative pressure is detrimental. Intermittent high negative pressure is less common, and positive or atmospheric pressure wouldn't provide effective drainage.

Question 10423

Topic: 1. General Principles & Basic Science

What is the approximate maximum safe external pressure that can be applied to the skin over a prolonged period (e.g., in a cast or splint) without significantly risking compromise to capillary blood flow and tissue viability?

. 10 mmHg
. 20 mmHg
. 30 mmHg
. 40 mmHg
. 50 mmHg

Correct Answer & Explanation

. 30 mmHg

Explanation

The capillary closing pressure, or the pressure at which capillary blood flow is significantly compromised, is generally estimated to be around 25-32 mmHg. Therefore, any prolonged external pressure exceeding this threshold (i.e., above 30 mmHg) over the skin can lead to tissue ischemia, ulceration, and necrosis. Casts and splints should be applied carefully to avoid exceeding this critical pressure, especially over bony prominences.

Question 10424

Topic: Infection, Pharmacology & VTE

An 80-year-old female with a non-displaced wrist fracture is prescribed NSAIDs for pain. She has a history of hypertension controlled with Lisinopril and a baseline creatinine of 1.2 mg/dL. What is the most significant concern regarding NSAID use in this patient related to her blood pressure and renal function?

. Increased risk of hyperkalemia
. Decreased efficacy of Lisinopril and potential for worsening hypertension
. Increased risk of hyponatremia
. Development of nephrogenic diabetes insipidus
. Acute liver injury

Correct Answer & Explanation

. Decreased efficacy of Lisinopril and potential for worsening hypertension

Explanation

NSAIDs can antagonize the antihypertensive effects of ACE inhibitors like Lisinopril by inhibiting prostaglandin synthesis, which otherwise mediates renal vasodilation and contributes to blood pressure control. This can lead to worsening hypertension. Furthermore, NSAIDs can cause acute kidney injury, particularly in elderly patients with pre-existing renal compromise or those on ACE inhibitors, by reducing renal blood flow. They also increase the risk of hyperkalemia when combined with ACE inhibitors. While hyperkalemia is a concern, the question specifically asks about blood pressure and renal function, where the blunting of antihypertensive effect and risk of AKI are prominent. Hyponatremia, diabetes insipidus, and liver injury are less direct or common concerns in this context.

Question 10425

Topic: 1. General Principles & Basic Science

During closed reduction and percutaneous pinning of a distal radius fracture under Bier block, a 40-year-old male develops sudden hypotension (BP 80/50 mmHg), bradycardia (HR 45 bpm), and lightheadedness immediately after tourniquet deflation. What is the most likely explanation for these findings?

. Systemic toxicity of local anesthetic
. Vasovagal reaction
. Acute hypovolemia
. Pulmonary embolism
. Allergic reaction to the local anesthetic

Correct Answer & Explanation

. Vasovagal reaction

Explanation

A vasovagal reaction is a common cause of sudden hypotension and bradycardia, often triggered by pain, anxiety, or in this case, potentially by the sudden release of local anesthetic into the systemic circulation after tourniquet deflation, or even just the stress of the procedure. Local anesthetic toxicity typically presents with CNS symptoms (e.g., seizures, perioral numbness) followed by cardiovascular collapse, often with arrhythmias, but a bradycardic presentation can occur; however, a simple vasovagal response is more common and less severe acutely. Acute hypovolemia is unlikely if the patient was well-hydrated. Pulmonary embolism and allergic reactions would present differently.

Question 10426

Topic: Infection, Pharmacology & VTE

A 30-year-old male with an open calcaneus fracture develops fever (39°C), rash, and eosinophilia post-operatively. He has been receiving IV antibiotics (e.g., cefazolin) and NSAIDs for pain. His serum creatinine rises from 1.0 to 3.0 mg/dL and his urine studies show white blood cells and eosinophils. What is the most likely cause of his acute kidney injury?

. Acute tubular necrosis (ATN)
. Pre-renal azotemia
. Acute interstitial nephritis (AIN)
. Post-renal obstruction
. Hepatorenal syndrome

Correct Answer & Explanation

. Acute interstitial nephritis (AIN)

Explanation

The clinical picture of fever, rash, eosinophilia, and acute kidney injury with eosinophiluria is highly suggestive of Acute Interstitial Nephritis (AIN), a hypersensitivity reaction often triggered by medications like antibiotics (beta-lactams, sulfonamides), NSAIDs, or proton pump inhibitors. While ATN and pre-renal azotemia are common causes of AKI, the systemic allergic features point away from them. Post-renal obstruction would have different signs and symptoms. Hepatorenal syndrome is seen in advanced liver disease. AIN requires withdrawal of the offending agent and sometimes corticosteroids.

Question 10427

Topic: 1. General Principles & Basic Science

During a total knee arthroplasty, the patient's blood pressure drops acutely from 130/80 mmHg to 80/45 mmHg. The surgical field becomes suddenly obscured by dark venous blood. What is the most appropriate immediate action by the surgeon?

. Administer 1 gram of Tranexamic Acid (TXA)
. Ask anesthesia to administer a vasopressor
. Check the tourniquet pressure
. Apply direct pressure to the surgical field and identify the bleeding source
. Order cross-matched blood immediately

Correct Answer & Explanation

. Apply direct pressure to the surgical field and identify the bleeding source

Explanation

A sudden drop in blood pressure and obscured surgical field with dark venous blood strongly suggests a large venous hemorrhage. The most immediate and critical action for the surgeon is to apply direct pressure to the bleeding site to achieve hemostasis and identify the source. While anesthesia should be alerted and will manage systemic circulation (fluids, vasopressors if needed), and blood ordering is important, controlling the surgical bleeding is paramount. TXA is for antifibrinolytic support but not immediate mechanical hemostasis. Checking tourniquet pressure is relevant only if the tourniquet was inflated and is malfunctioning, but in this scenario, the issue is active bleeding. Direct pressure is the key.

Question 10428

Topic: 1. General Principles & Basic Science

A 58-year-old male with chronic back pain takes a daily opioid (e.g., oxycodone). He undergoes a lumbar microdiscectomy. Post-operatively, he is confused, has diminished bowel sounds, and complains of nausea. His serum sodium is 126 mEq/L. He is euvolemic. What is the most likely cause of his hyponatremia?

. Addison's disease
. Cerebral salt wasting
. SIADH due to opioid use
. Hypothyroidism
. Diuretic-induced hyponatremia

Correct Answer & Explanation

. SIADH due to opioid use

Explanation

Opioids are known to stimulate ADH release, leading to free water retention and dilutional hyponatremia consistent with SIADH. In the post-operative setting, other factors like pain and stress also contribute to ADH release. The patient is euvolemic and confused, which fits the picture of SIADH. Addison's disease (adrenal insufficiency) can cause hyponatremia but is usually associated with hyperkalemia, hypovolemia, and specific symptoms. Cerebral salt wasting leads to hypovolemia. Hypothyroidism can cause hyponatremia, but opioids are a more direct and acute cause in this scenario. Diuretic-induced hyponatremia would be pertinent if he were on diuretics.

Question 10429

Topic: Infection, Pharmacology & VTE

A 70-year-old male with a history of long-standing diabetes presents with a non-healing foot ulcer requiring debridement and partial amputation. His baseline creatinine is 1.5 mg/dL. He is started on vancomycin and piperacillin/tazobactam. On post-operative day 3, his creatinine rises to 2.8 mg/dL. His urine output is adequate. What is the most likely cause of his acute kidney injury?

. Pre-renal azotemia due to dehydration
. Acute tubular necrosis (ATN) from nephrotoxic antibiotics
. Acute interstitial nephritis (AIN) from antibiotics
. Rhabdomyolysis
. Cholesterol emboli

Correct Answer & Explanation

. Acute tubular necrosis (ATN) from nephrotoxic antibiotics

Explanation

This patient has multiple risk factors for acute kidney injury: advanced age, diabetes, pre-existing renal insufficiency, and exposure to nephrotoxic antibiotics (vancomycin and piperacillin/tazobactam, particularly the combination). While AIN is possible with antibiotics, ATN is a more common form of drug-induced AKI, especially with direct nephrotoxins like vancomycin. Pre-renal azotemia is less likely given adequate urine output. Rhabdomyolysis and cholesterol emboli would have other clinical features not mentioned. The combination of nephrotoxic drugs and risk factors points strongly to ATN.

Question 10430

Topic: Biology, Genetics & Bone Healing

A 50-year-old female with a history of hypertension and obesity is scheduled for a prolonged posterior spinal fusion. Her pre-operative labs are unremarkable. During surgery, she loses 1500 mL of blood and receives 4 units of packed red blood cells and 3 liters of crystalloid. Her post-operative sodium is 135 mEq/L, potassium 4.5 mEq/L, and ionized calcium is 0.8 mmol/L (normal 1.1-1.3 mmol/L). What is the most likely cause of her hypocalcemia?

. Hypoparathyroidism
. Acute pancreatitis
. Citrate toxicity from massive transfusion
. Vitamin D deficiency
. Tumor lysis syndrome

Correct Answer & Explanation

. Citrate toxicity from massive transfusion

Explanation

Massive blood transfusions, particularly with packed red blood cells, can lead to hypocalcemia due to citrate toxicity. Citrate is an anticoagulant added to blood products; it chelates calcium, and if infused rapidly or in large volumes, the liver's ability to metabolize citrate can be overwhelmed, leading to a decrease in ionized calcium. This is a common and important complication in major orthopedic surgeries with significant blood loss. Hypoparathyroidism, acute pancreatitis, vitamin D deficiency, and tumor lysis syndrome are less likely acute causes in this context, though some may contribute to baseline risks.

Question 10431

Topic: 1. General Principles & Basic Science

A 60-year-old male with a known history of severe peripheral vascular disease and diabetes is scheduled for a below-knee amputation due to critical limb ischemia. His baseline blood pressure is 160/90 mmHg. What is the most appropriate perioperative blood pressure target to minimize surgical and cardiac risk?

. Maintain systolic BP <100 mmHg
. Maintain mean arterial pressure (MAP) >90 mmHg
. Maintain BP within 20% of his baseline values
. Maintain systolic BP >180 mmHg to ensure limb perfusion
. Target a MAP of 60-65 mmHg

Correct Answer & Explanation

. Maintain BP within 20% of his baseline values

Explanation

For patients with chronic hypertension, the optimal perioperative blood pressure target is usually to maintain it within 20% of their baseline values. This approach prevents both hypotension, which can lead to organ hypoperfusion (especially in patients with vascular disease, heart disease, or renal insufficiency where autoregulation curves are shifted), and severe hypertension, which increases the risk of stroke and myocardial events. A systolic BP <100 mmHg or MAP of 60-65 mmHg might be too low and cause hypoperfusion. Maintaining MAP >90 mmHg might be too high. A systolic BP >180 mmHg is dangerous. The goal is individualized based on their usual physiology.

Question 10432

Topic: Biology, Genetics & Bone Healing

A 55-year-old female with a recent history of a pathological femur fracture due to metastatic breast cancer undergoes intramedullary nailing. She is receiving zoledronic acid infusions. On post-operative day 2, she complains of paresthesias and muscle cramps. Her serum calcium is 7.2 mg/dL (corrected), phosphate 4.0 mg/dL. What is the most likely cause of her hypocalcemia?

. Hypoparathyroidism
. Vitamin D deficiency
. Acute pancreatitis
. Zoledronic acid-induced hypocalcemia
. Renal failure

Correct Answer & Explanation

. Zoledronic acid-induced hypocalcemia

Explanation

Zoledronic acid (a potent bisphosphonate) is used to treat hypercalcemia of malignancy and reduce skeletal-related events in metastatic bone disease. A known side effect is hypocalcemia, particularly in patients with pre-existing vitamin D deficiency or renal impairment. The symptoms of paresthesias and muscle cramps are classic for hypocalcemia. Hypoparathyroidism would also cause hypocalcemia but is less likely in this context without parathyroid surgery. Vitamin D deficiency often contributes but zoledronic acid is the direct trigger. Acute pancreatitis would have other symptoms. Renal failure could contribute but is not the primary cause of acute symptomatic hypocalcemia here.

Question 10433

Topic: 1. General Principles & Basic Science

A 70-year-old female with a history of osteoporosis and chronic NSAID use for osteoarthritis undergoes a distal radius fracture repair. On post-operative day 3, her serum creatinine has increased from 1.0 mg/dL to 1.8 mg/dL, and her urine output is stable. Her serum potassium is 5.8 mEq/L. What is the most likely cause of her hyperkalemia?

. Adrenal insufficiency
. Excessive potassium intake
. Acute kidney injury from NSAID use
. Tumor lysis syndrome
. Diabetic ketoacidosis

Correct Answer & Explanation

. Acute kidney injury from NSAID use

Explanation

NSAIDs can cause acute kidney injury, particularly in elderly patients, and in this setting, a rise in creatinine from 1.0 to 1.8 mg/dL is indicative of AKI. One of the consequences of AKI is impaired potassium excretion, leading to hyperkalemia. NSAIDs can also directly inhibit prostaglandin-mediated renin release and aldosterone production, contributing to hyperkalemia. Adrenal insufficiency would present with other symptoms and is less likely. Excessive potassium intake is not mentioned. Tumor lysis syndrome and DKA are unrelated in this context.

Question 10434

Topic: Infection, Pharmacology & VTE

A 68-year-old female with a femoral neck fracture is undergoing hemiarthroplasty. She has a history of atrial fibrillation on warfarin. Her INR is 2.5 pre-operatively. What is the most appropriate management of her anticoagulation?

. Proceed with surgery as INR 2.5 is acceptable for orthopedic surgery
. Administer 10 mg Vitamin K intravenously
. Administer Fresh Frozen Plasma (FFP) to normalize INR
. Delay surgery and continue warfarin for 3-5 days
. Administer Protamine Sulfate

Correct Answer & Explanation

. Administer Fresh Frozen Plasma (FFP) to normalize INR

Explanation

For emergent orthopedic surgery like a hip fracture repair in a patient on warfarin, an INR of 2.5 is too high and increases the risk of significant perioperative bleeding. The most rapid and effective way to reverse warfarin is to administer Fresh Frozen Plasma (FFP), which contains all clotting factors. Vitamin K works more slowly (6-24 hours). Delaying surgery is associated with increased morbidity and mortality for hip fractures. Protamine sulfate reverses heparin, not warfarin. An INR of 2.5 is generally not acceptable for major orthopedic surgery.

Question 10435

Topic: Infection, Pharmacology & VTE

A 60-year-old male undergoing a posterior spinal fusion is placed in the prone position. During the procedure, the anesthesiologist notes a sudden drop in blood pressure and a gradual increase in central venous pressure (CVP). The surgical field appears venous and engorged. What is the most likely cause of these hemodynamic changes?

. Cardiac tamponade
. Pulmonary embolism
. Inferior vena cava (IVC) compression
. Anaphylaxis
. Massive hemorrhage

Correct Answer & Explanation

. Inferior vena cava (IVC) compression

Explanation

In the prone position, especially on an inadequately padded or positioned frame, compression of the inferior vena cava (IVC) by the abdominal contents can occur. This leads to reduced venous return to the heart, causing hypotension. The increased CVP reflects the back-pressure from the obstructed venous flow. A venous, engorged surgical field is also consistent with impaired venous drainage. Cardiac tamponade and pulmonary embolism would also cause hypotension and increased CVP but are less directly related to prone positioning itself. Anaphylaxis would have other systemic signs. Massive hemorrhage would typically cause a decrease in CVP unless the hemorrhage was into a confined space or a massive compensatory fluid load was given.

Question 10436

Topic: 1. General Principles & Basic Science

A 55-year-old female undergoes a lumbar laminectomy. Post-operatively, she is receiving D5 0.45% Normal Saline at 100 mL/hr. Her urine output is 120 mL/hr. On post-operative day 1, her serum sodium is 128 mEq/L. She is asymptomatic. What is the most appropriate modification to her intravenous fluids?

. Change to 3% hypertonic saline at 30 mL/hr
. Change to 0.9% Normal Saline at 100 mL/hr
. Change to D5W at 100 mL/hr
. Discontinue intravenous fluids and allow oral intake if tolerated
. Increase D5 0.45% Normal Saline to 150 mL/hr

Correct Answer & Explanation

. Discontinue intravenous fluids and allow oral intake if tolerated

Explanation

The patient is asymptomatic with mild hyponatremia (128 mEq/L) on post-operative day 1. The D5 0.45% Normal Saline she is receiving is a hypotonic solution, which can contribute to hyponatremia, especially in the post-operative period when ADH levels may be elevated due to stress, pain, or opioids. Since she is asymptomatic and has good urine output, the most appropriate and safest step is to discontinue hypotonic IV fluids and encourage oral intake, provided she tolerates it. This allows her kidneys to excrete free water and correct the sodium imbalance physiologically. Changing to 3% hypertonic saline is too aggressive for asymptomatic mild hyponatremia. Changing to 0.9% Normal Saline would prevent further dilution but is not as effective as stopping hypotonic fluids. D5W is even more hypotonic. Increasing the current fluid would worsen hyponatremia.

Question 10437

Topic: Biology, Genetics & Bone Healing

A 60-year-old female with a history of osteoporosis and multiple fragility fractures is admitted for a hip fracture. She has a serum calcium of 8.0 mg/dL (normal 8.5-10.2 mg/dL) and elevated PTH. What is the most likely cause of her hypocalcemia?

. Hypoparathyroidism
. Vitamin D deficiency
. Pseudohypoparathyroidism
. Primary hyperparathyroidism with 'hungry bone syndrome'
. Chronic kidney disease

Correct Answer & Explanation

. Primary hyperparathyroidism with 'hungry bone syndrome'

Explanation

This patient's presentation of osteoporosis, multiple fractures, hypocalcemia (8.0 mg/dL), and elevated PTH is classic for 'hungry bone syndrome' occurring after the surgical removal of a parathyroid adenoma (for primary hyperparathyroidism) or, in this context, possibly a rebound effect. While the question doesn't explicitly state parathyroidectomy, 'primary hyperparathyroidism with 'hungry bone syndrome' can occur in states of high bone turnover. Given the elevated PTH, it's not hypoparathyroidism. Vitamin D deficiency often causes hypocalcemia and elevated PTH but less commonly with such profound bone disease. Pseudohypoparathyroidism would have elevated PTH but end-organ resistance. Chronic kidney disease can cause secondary hyperparathyroidism and hypocalcemia but with a different clinical picture of kidney failure.

Question 10438

Topic: Biology, Genetics & Bone Healing

Regarding the management of non-unions, which of the following statements is TRUE?

. Hypertrophic non-unions typically require bone grafting.
. Atrophic non-unions usually heal with rigid fixation alone.
. Infection is a contraindication to surgical intervention for non-union.
. The diamond concept for non-union treatment includes stability, biology, growth factors, and mechanical environment.
. Electrical stimulation is the first-line treatment for all types of non-unions.

Correct Answer & Explanation

. The diamond concept for non-union treatment includes stability, biology, growth factors, and mechanical environment.

Explanation

The 'diamond concept' for non-union treatment emphasizes four key factors: adequate stability (mechanical environment), healthy biology (vascularity, tissue viability), growth factors (e.g., bone morphogenetic proteins), and local bone graft. This holistic approach is crucial for successful healing. Hypertrophic non-unions demonstrate sufficient biology but lack stability; therefore, they primarily require stable fixation without the need for additional bone graft. Atrophic non-unions lack both stability and biology, thus requiring rigid fixation AND bone grafting. Infection is a common cause and significant complication of non-unions, and it must be addressed (debridement, antibiotics) before or concurrently with definitive non-union surgery, not a contraindication to intervention. Electrical stimulation is an adjunctive treatment, usually considered after surgical attempts, not a first-line for all non-unions, especially atrophic types.

Question 10439

Topic: 1. General Principles & Basic Science

Which of the following is the most effective method for preventing heterotopic ossification (HO) after total hip arthroplasty (THA), particularly in high-risk patients?

. Administration of systemic corticosteroids.
. Pre-operative calcium and vitamin D supplementation.
. Indomethacin or other NSAIDs administered post-operatively.
. Targeted intraoperative radiation therapy.
. Early and aggressive mobilization.

Correct Answer & Explanation

. Indomethacin or other NSAIDs administered post-operatively.

Explanation

Indomethacin or other non-steroidal anti-inflammatory drugs (NSAIDs), administered post-operatively for 7-14 days, are highly effective in preventing heterotopic ossification (HO) after THA, especially in high-risk patients (e.g., history of HO, ankylosing spondylitis, hypertrophic osteoarthritis). The mechanism involves inhibiting prostaglandin synthesis, which plays a role in osteoblast differentiation. Radiation therapy (either single dose pre- or post-op) is also highly effective but generally reserved for patients who cannot tolerate NSAIDs or have an extremely high risk. Systemic corticosteroids are not standard for HO prevention. Calcium and vitamin D are for bone health, not HO. Early mobilization is generally beneficial but not a primary preventative measure for HO itself.

Question 10440

Topic: 1. General Principles & Basic Science

Which complication is most characteristic of a posterior hip dislocation?

. Femoral head avascular necrosis.
. Sciatic nerve injury.
. Deep vein thrombosis.
. Trochanteric non-union.
. Vascular injury to the femoral artery.

Correct Answer & Explanation

. Sciatic nerve injury.

Explanation

Sciatic nerve injury is the most common and characteristic neurological complication of a posterior hip dislocation, occurring in 10-20% of cases. The sciatic nerve is anatomically vulnerable as it passes posterior to the hip joint. Femoral head avascular necrosis is also a significant complication, especially with delayed reduction, but sciatic nerve injury is more immediately characteristic. DVT is a general complication of trauma/immobility. Trochanteric non-union is relevant to hip fractures, not dislocations. Femoral artery injury is rare in posterior dislocation and more common in anterior dislocations.

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