Internal Medicine Practice Questions — USMLE Step 2 CK — Page 107

Question 2121Question →

Match each clinical presentation following a recent acute myocardial infarction (left) with its precise underlying pathophysiologic mechanism and anatomical basis (right).

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Answer

The mechanical complications of acute myocardial infarction each present with distinct timing, hemodynamic profiles, and physical exam findings that directly reflect their underlying anatomical disruption. Posteromedial papillary muscle rupture causes acute mitral regurgitation (giant v waves); ventricular septal rupture causes a left-to-right shunt (oxygen step-up); free wall rupture causes rapid tamponade (PEA arrest); and true aneurysms cause persistent ST elevations and stasis (mural thrombus/emboli).

Each clinical vignette provides highly specific hemodynamic and physical exam clues that uniquely identify a post-infarction mechanical complication. The matches correctly link the clinical presentation (e.g., giant v waves, O2 step-up, PEA, dyskinetic pouch) to the exact pathophysiologic mechanism and anatomical defect responsible for the syndrome.

Step-by-Step Solution

1

Analyze the first clinical presentation (cardiogenic shock post-inferior STEMI, soft murmur, giant v waves).

Identify acute mitral regurgitation due to papillary muscle rupture.

The inferior location predisposes the posteromedial papillary muscle to ischemic rupture. The giant v waves and soft murmur are classic for acute, severe mitral regurgitation.

2

Analyze the second clinical presentation (biventricular failure post-anterior STEMI, harsh murmur with thrill, oxygen step-up).

Identify a ventricular septal rupture.

The harsh murmur with a thrill and the diagnostic oxygen saturation step-up between the right atrium and right ventricle confirm a new left-to-right intracardiac shunt.

3

Analyze the third clinical presentation (sudden PEA arrest post-transmural STEMI, anechoic space with right ventricular diastolic bowing).

Identify a left ventricular free wall rupture.

Sudden PEA arrest accompanied by echocardiographic evidence of rapidly accumulating pericardial fluid causing tamponade physiology points directly to a full-thickness myocardial tear.

4

Analyze the fourth clinical presentation (late heart failure and TIA, persistent ST elevations, broad-based dyskinetic segment).

Identify a true ventricular aneurysm.

The late presentation (months later), persistent ST-segment elevations, and embolic event from a broad-based outward bulging area of fibrotic myocardium are pathognomonic for a true aneurysm.

Key Concept

Mechanical complications of acute myocardial infarction (AMI)

Question 2122Question →

A 28-year-old woman is brought to the emergency department by her roommate due to severe agitation, confusion, and palpitations. She has a history of Graves disease but stopped taking her medications three months ago. Temperature is 40.2°C (104.4°F), blood pressure is 160/90 mm Hg, pulse is 150/min and irregular, and respirations are 24/min. Physical examination reveals a diffuse goiter, bilateral exophthalmos, fine tremor, and diaphoresis. An electrocardiogram shows atrial fibrillation with rapid ventricular response. A clinical diagnosis of thyroid storm is made. Arrange the following therapeutic interventions in the most appropriate chronological order for the management of this patient, from the most immediate acute step to long-term definitive therapy.

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Answer

The correct chronological sequence is: administration of intravenous propranolol, followed by propylthiouracil, then potassium iodide, and finally radioactive iodine ablation.

The treatment of thyroid storm requires a careful, staged approach. First, life-threatening adrenergic symptoms must be controlled, typically with propranolol. Second, thyroid hormone synthesis must be halted using a thionamide like propylthiouracil (PTU). Third, the release of preformed hormone is blocked using iodine solutions (e.g., potassium iodide), which must be given at least an hour after the thionamide to prevent the iodine from being used to create more hormone. Finally, once the patient is completely stabilized and euthyroid (weeks to months later), definitive therapy such as radioactive iodine ablation can be performed.

Step-by-Step Solution

1

Administer intravenous propranolol

Controls adrenergic symptoms and lowers heart rate.

The most immediate life-threatening complications of thyroid storm are cardiovascular. Beta-blockade rapidly stabilizes the patient.

2

Administer propylthiouracil (PTU)

Halts the production of new thyroid hormones.

Blocking synthesis must occur before blocking release to ensure that subsequently administered iodine is not used to synthesize more hormone.

3

Administer potassium iodide

Inhibits the release of preformed thyroid hormones from the gland.

Must be given at least 1 hour after PTU. If given before PTU, the iodine will serve as a substrate and worsen the thyrotoxicosis (Jod-Basedow phenomenon).

4

Perform radioactive iodine ablation

Provides definitive, long-term cure of Graves disease.

Definitive therapy can only be safely pursued after the acute crisis has resolved and the patient has returned to a euthyroid state.

Key Concept

The management of thyroid storm follows a strict sequential protocol: beta-blockers for symptom control, thionamides to block hormone synthesis, iodine solutions (delayed by at least 1 hour) to block hormone release, and eventually definitive therapy once euthyroid.

Estimated Time:1m 0s

Question 2123Question →

A 58-year-old man is evaluated in the hospital for worsening abdominal distension and diffuse abdominal discomfort over the past 48 hours. He has a history of alcohol-associated cirrhosis. His temperature is $37.9^\circ\text{C}$ ( $100.2^\circ\text{F}$ ), blood pressure is $105/65\text{ mm Hg}$ , and pulse is $92/\text{min}$ . Physical examination shows a protuberant abdomen with shifting dullness and mild, diffuse tenderness to palpation without rebound or guarding. Neurologic examination shows a fully oriented patient with no asterixis.

Laboratory studies show the following:

Test	Result
Serum creatinine	$1.8\text{ mg/dL}$
Blood urea nitrogen	$34\text{ mg/dL}$
Total bilirubin	$4.5\text{ mg/dL}$

Diagnostic paracentesis yields ascitic fluid with a total leukocyte count of $800/\text{mm}^3$ and $85\%$ neutrophils. Intravenous cefotaxime is initiated. Which of the following is the most appropriate additional intervention for this patient?

Administration of intravenous albumin

Addition of intravenous metronidazole

Large-volume therapeutic paracentesis

Placement of a transjugular intrahepatic portosystemic shunt

Transfusion of fresh frozen plasma

Show answer & explanation

Answer: Administration of intravenous albumin

Answer

Administration of intravenous albumin

The correct intervention is the administration of intravenous albumin. This patient has spontaneous bacterial peritonitis (SBP), diagnosed by an ascitic fluid absolute neutrophil count (ANC) greater than

250/\text{mm}^3

(in this case,

800 \times 0.85 = 680/\text{mm}^3

). SBP can precipitate severe splanchnic arterial vasodilation, leading to decreased effective arterial blood volume, activation of the renin-angiotensin-aldosterone system, and subsequent severe renal vasoconstriction, a cascade known as hepatorenal syndrome (HRS). The administration of intravenous albumin expands the intravascular volume, binds vasodilatory molecules, and significantly reduces the incidence of HRS, thereby improving survival. It is specifically indicated for patients with SBP who have a serum creatinine

> 1.0\text{ mg/dL}

, BUN

> 30\text{ mg/dL}

, or total bilirubin

> 4.0\text{ mg/dL}

. This patient meets all three of these criteria.

Step-by-Step Solution

1

Calculate the absolute neutrophil count (ANC) in the ascitic fluid.

The ANC is

800 \times 0.85 = 680/\text{mm}^3

, which is greater than

250/\text{mm}^3

.

An ANC

\geq 250/\text{mm}^3

confirms the diagnosis of spontaneous bacterial peritonitis (SBP).

2

Evaluate the patient's laboratory values for high-risk features.

The patient has elevated serum creatinine (

1.8\text{ mg/dL}

), blood urea nitrogen (

34\text{ mg/dL}

), and total bilirubin (

4.5\text{ mg/dL}

).

These lab values meet the criteria for severe liver and renal impairment in the setting of SBP, indicating a high risk for hepatorenal syndrome.

3

Select the appropriate adjunctive therapy.

Intravenous albumin must be administered alongside antibiotics.

Current guidelines require IV albumin administration for SBP patients meeting specific renal or hepatic impairment thresholds to reduce mortality.

Key Concept

Management of spontaneous bacterial peritonitis and prevention of hepatorenal syndrome using intravenous albumin.

Question 2124Question →

Match each characteristic electrocardiogram (ECG) description with its corresponding cardiovascular diagnosis.

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Answer

The 'sawtooth' pattern matches atrial flutter, progressive PR lengthening matches Mobitz type I block, delta waves match Wolff-Parkinson-White syndrome, and diffuse ST elevations with PR depressions match acute pericarditis.

Each specific ECG description uniquely identifies the pathophysiology of its matched condition: atrial flutter involves a distinct macroreentrant atrial circuit; Mobitz type I involves reversible AV nodal fatigue; Wolff-Parkinson-White syndrome involves an accessory conduction pathway bypassing the AV node; and acute pericarditis involves diffuse epicardial and atrial inflammation.

Step-by-Step Solution

1

Analyze the baseline and P wave characteristics.

A 'sawtooth' baseline without normal P waves is identified as atrial flutter.

This pattern is uniquely produced by a rapid macroreentrant circuit in the atrium.

2

Evaluate the relationship between the P wave and the QRS complex.

A progressively lengthening PR interval followed by a dropped QRS represents Mobitz type I (Wenckebach) block.

This indicates reversible, progressive conduction delay and eventual failure at the AV node.

3

Examine the QRS complex morphology and PR interval duration.

A short PR interval with a slurred QRS upstroke (delta wave) identifies Wolff-Parkinson-White syndrome.

The accessory pathway bypasses the AV node, causing early, abnormal ventricular depolarization.

4

Assess ST segments and PR segments globally across the ECG.

Diffuse ST-segment elevations with PR-segment depressions confirm acute pericarditis.

Widespread inflammation affects the epicardium globally, distinguishing it from localized ischemia.

Key Concept

Characteristic electrocardiographic findings in common cardiovascular diseases

Estimated Time:1m 0s

Question 2125Question →

A 38-year-old woman is newly diagnosed with Raynaud phenomenon secondary to limited cutaneous systemic sclerosis. She is concerned about the progression of her condition and asks her physician about the treatment options available if her symptoms worsen over time. Arrange the following interventions in the correct sequential step-up escalation order for the management of Raynaud phenomenon, from the initial first-line approach to treatments reserved for severe, refractory disease with threatened digital ischemia.

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Answer

The correct sequence begins with conservative lifestyle modifications, followed by an oral dihydropyridine calcium channel blocker, then addition of a phosphodiesterase-5 inhibitor, and finally intravenous prostanoids for critical ischemia.

The management of Raynaud phenomenon follows a stepwise escalation based on symptom severity and response to previous treatments. All patients must start with conservative lifestyle modifications, primarily avoiding cold exposure, wearing warm clothing, and strictly discontinuing smoking. When symptoms persist despite these measures, pharmacologic therapy is initiated with an oral dihydropyridine calcium channel blocker (e.g., nifedipine, amlodipine). If symptoms remain inadequately controlled, additional vasodilatory agents, commonly phosphodiesterase-5 inhibitors (e.g., sildenafil) or angiotensin receptor blockers, are added to the regimen. Finally, in cases of severe refractory disease presenting with critical digital ischemia or non-healing digital ulcers, intravenous prostanoids (e.g., epoprostenol, iloprost) or endothelin receptor antagonists are indicated as advanced rescue therapy.

Step-by-Step Solution

1

Determine the initial, non-pharmacologic intervention.

Conservative measures such as cold avoidance and smoking cessation are universally recommended first.

Lifestyle modifications are required for all patients before initiating systemic medications.

2

Identify the first-line pharmacologic therapy.

An oral dihydropyridine calcium channel blocker is the initial medical treatment.

Calcium channel blockers are highly effective vasodilators with a well-established safety profile for treating Raynaud phenomenon.

3

Determine the appropriate add-on therapy for refractory symptoms.

A phosphodiesterase-5 inhibitor is added next.

PDE-5 inhibitors provide additional vasodilation through the nitric oxide pathway when monotherapy is insufficient.

4

Identify the rescue therapy for severe or tissue-threatening disease.

Intravenous prostanoids are used in severe cases.

Intravenous prostanoids are potent vasodilators and inhibitors of platelet aggregation reserved for critical ischemia or severe ulcers.

Key Concept

Stepwise pharmacological escalation for Raynaud phenomenon in systemic sclerosis

Question 2126Question →

A 28-year-old woman presents to the outpatient clinic reporting a painless swelling in her neck that has progressively enlarged over the past two months. She also describes experiencing drenching night sweats that require her to change her sleepwear, along with an unintended 5-kg (11-lb) weight loss during this time frame. Vital signs reveal a temperature of $37.9^\circ\text{C}$ ( $100.2^\circ\text{F}$ ). Physical examination identifies a 3.5-cm, firm, rubbery, mobile, and non-tender lymph node in the left supraclavicular fossa. The remainder of the examination shows no other palpable adenopathy or hepatosplenomegaly. Arrange the following steps in the most appropriate clinical sequence for the evaluation and management of this patient's condition.

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Answer

The correct sequence is: Initial laboratory tests (CBC, CMP, LDH), followed by an excisional lymph node biopsy, then whole-body PET-CT scan for staging, followed by a transthoracic echocardiogram for cardiac clearance, and finally the initiation of multi-agent systemic chemotherapy.

The standard sequence for a patient presenting with classic 'B symptoms' and a suspicious supraclavicular lymph node begins with non-invasive baseline laboratories to assess general health and tumor burden (LDH). The most critical next step is obtaining a definitive tissue diagnosis via an excisional lymph node biopsy, as maintaining tissue architecture is mandatory for lymphoma subtyping. Once the diagnosis is confirmed histologically, the disease must be staged using a PET-CT scan to determine its extent. Because the curative regimens for most lymphomas (like ABVD or CHOP) utilize cardiotoxic anthracyclines, a baseline echocardiogram is required before any drugs are infused. Finally, with the diagnosis, stage, and physiologic safety confirmed, systemic chemotherapy is initiated.

Step-by-Step Solution

1

Obtain initial laboratory tests.

Establishes baseline hematologic and metabolic function, and identifies prognostic markers like elevated LDH.

Provides a safe baseline and assesses tumor burden prior to pursuing invasive diagnostic testing.

2

Perform an excisional lymph node biopsy.

Yields a definitive histopathologic diagnosis and immunophenotype.

Intact lymph node architecture is necessary to distinguish between lymphoma subtypes (e.g., Hodgkin vs. non-Hodgkin); fine-needle aspiration (FNA) ruins this architecture and is inadequate.

3

Obtain a whole-body PET-CT scan.

Determines the full anatomic extent of the disease.

Accurate staging dictates the intensity, duration, and specific type of chemotherapy and/or radiation required.

4

Perform a transthoracic echocardiogram.

Measures the baseline left ventricular ejection fraction.

Anthracyclines (e.g., doxorubicin in ABVD or R-CHOP regimens) carry a risk of dose-dependent, irreversible cardiotoxicity. Baseline cardiac clearance is a strict prerequisite.

5

Initiate multi-agent systemic chemotherapy.

Targets and eradicates the malignant lymphoid cells.

Definitive treatment must be guided by the exact histology, stage, and physiologic baseline established in the preceding steps.

Key Concept

Sequential algorithm for the diagnosis, staging, and pre-treatment preparation of lymphomas.

Estimated Time:2m 0s

Question 2127Question →

Match each clinical and neuroimaging presentation of a central nervous system disorder in patients with advanced HIV infection to its most appropriate definitive or empiric management.

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Answer

The presentations map to the following treatments: Cryptococcal meningitis requires amphotericin B and flucytosine; Progressive multifocal leukoencephalopathy (PML) requires optimization of antiretroviral therapy; Toxoplasmosis requires sulfadiazine, pyrimethamine, and leucovorin; Cytomegalovirus encephalitis requires ganciclovir or foscarnet.

Each central nervous system infection in advanced HIV has a distinct clinical and radiographic profile that dictates its specific management. Cryptococcal meningitis is characterized by elevated intracranial pressure and is treated with amphotericin B and flucytosine. Toxoplasmosis presents with multiple ring-enhancing lesions and responds to sulfadiazine and pyrimethamine. JC virus causes progressive multifocal leukoencephalopathy (non-enhancing white matter lesions) and is managed solely by reversing immunosuppression with antiretroviral therapy. Cytomegalovirus causes ventriculitis and must be treated with targeted agents like ganciclovir or foscarnet.

Step-by-Step Solution

1

Analyze the first clinical vignette involving elevated opening pressure and a positive polysaccharide antigen test.

Identify the pathogen as Cryptococcus neoformans.

The polysaccharide capsule is characteristic of Cryptococcus, which typically presents with subacute meningitis and elevated intracranial pressure in patients with CD4 counts below

100

cells/mm

^3

.

2

Evaluate the second vignette detailing non-enhancing white matter lesions without edema.

Identify the condition as progressive multifocal leukoencephalopathy (PML) caused by the JC virus.

PML causes asymmetric demyelination without mass effect in severely immunocompromised hosts, distinguishing it from space-occupying lesions.

3

Examine the third vignette describing seizures and multiple ring-enhancing lesions in the basal ganglia.

Identify the etiology as Toxoplasma gondii.

Toxoplasmosis is the most common cause of ring-enhancing brain lesions in patients with advanced HIV and frequently presents with seizures and focal neurologic deficits.

4

Assess the fourth vignette featuring rapid neurologic decline and periventricular enhancement.

Identify the pathogen as Cytomegalovirus (CMV).

CMV encephalitis typically presents with ventriculitis and cranial nerve neuropathies in patients with CD4 counts typically less than

50

cells/mm

^3

.

5

Match each identified infectious etiology to its guideline-directed management.

Cryptococcus pairs with amphotericin B and flucytosine. PML pairs with antiretroviral therapy. Toxoplasmosis pairs with sulfadiazine and pyrimethamine. CMV pairs with ganciclovir or foscarnet.

Survival and recovery depend on utilizing the pathogen-specific antimicrobial or immune reconstitution strategy indicated for each distinct central nervous system infection.

Key Concept

Identifying opportunistic central nervous system infections in advanced HIV based on CD4 count, clinical presentation, and neuroimaging to determine the targeted pharmacotherapy.

Question 2128Question →

Evaluate the following clinical vignettes describing patients who developed acute kidney injury (AKI) in various clinical settings. Match each patient's clinical presentation to the most accurate pathophysiological diagnosis.

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Answer

The presentations map to distinct mechanisms: overdiuresis causes classic prerenal azotemia, cirrhosis with albumin-unresponsive AKI represents hepatorenal syndrome, post-contrast AKI is contrast-induced nephropathy (notable for FENa < 1%), and post-angiography AKI with livedo reticularis is atheroembolic renal disease.

The correct matches rely on synthesizing the patient history with specific diagnostic markers. Furosemide diuresis predictably shrinks the effective arterial blood volume, leading to a classic prerenal pattern characterized by a high BUN/Cr ratio and hyaline casts. Hepatorenal syndrome is distinguished from simple prerenal azotemia by its complete failure to improve after withdrawing diuretics and administering a dedicated volume expansion trial with intravenous albumin. Contrast-induced nephropathy represents a toxic injury to the tubules, but unlike classic ischemic acute tubular necrosis (which typically exhibits a FENa > 2%), the profound vasoconstrictive effect of the contrast media classically yields a FENa < 1%. Finally, atheroembolic renal disease is distinguished by its delayed onset (days to weeks post-procedure) alongside systemic signs of crystal embolization, such as livedo reticularis, blue toe syndrome, and eosinophilia.

Step-by-Step Solution

1

Evaluate the temporal context and inciting events for the acute kidney injury in each vignette.

Recent interventions include massive diuresis (first patient), progressive cirrhosis (second patient), iodinated contrast administration (third patient), and an invasive endovascular catheterization (fourth patient).

Establishing the precise clinical context acts as the primary branching logic in determining the etiology of acute kidney injury.

2

Analyze the accompanying physical examination signs and specific laboratory indices (urinalysis, FENa, urine sodium) for each presentation.

The first patient demonstrates a highly elevated BUN/Cr ratio with hyaline casts; the second shows fluid-unresponsiveness with severely depressed urine sodium; the third shows granular casts but a paradoxically low FENa (< 1%); the fourth displays cutaneous manifestations (livedo reticularis) and eosinophilia.

Urine indices and systemic signs separate etiologies that might otherwise present with similar temporal profiles, confirming the specific pathophysiologic mechanism.

Key Concept

Differentiating etiologies of acute kidney injury requires recognizing classic clinical contexts and appropriately interpreting urine indices, while maintaining high suspicion for exceptions such as contrast nephropathy, which typically presents with a FENa < 1%.

Estimated Time:2m 0s

Question 2129Question →

A 62-year-old woman is receiving care on the inpatient ward for a catheter-associated bloodstream infection. She was admitted 3 days ago with high fever, chills, and localized erythema around a peripheral intravenous catheter site. The catheter was promptly removed, and she was started on empiric intravenous vancomycin and piperacillin-tazobactam. Today, she reports feeling much better. Her temperature is 37.1°C (98.8°F), blood pressure is 128/82 mmHg, pulse is 76/min, and respirations are 14/min. The erythema at the prior catheter site has significantly improved. Blood cultures obtained on admission are now finalized and grow *Staphylococcus aureus*. Susceptibility testing demonstrates resistance to penicillin G and susceptibility to oxacillin, cefazolin, vancomycin, and daptomycin. Which of the following is the most appropriate next step in pharmacotherapy?

Transition to intravenous cefazolin monotherapy

Continue intravenous vancomycin monotherapy

Continue intravenous vancomycin and piperacillin-tazobactam

Continue intravenous piperacillin-tazobactam monotherapy

Transition to intravenous daptomycin monotherapy

Show answer & explanation

Answer: Transition to intravenous cefazolin monotherapy

Answer

Transition to intravenous cefazolin monotherapy

The patient has a bloodstream infection caused by methicillin-susceptible Staphylococcus aureus (MSSA), as indicated by the organism's susceptibility to oxacillin. For MSSA bacteremia, anti-staphylococcal beta-lactams (such as cefazolin, nafcillin, or oxacillin) are the drugs of choice. Clinical studies have consistently shown that beta-lactams provide superior bactericidal activity, leading to lower mortality rates, faster microbial clearance, and fewer relapses compared to vancomycin for MSSA infections. Therefore, the empiric broad-spectrum regimen should be de-escalated to targeted therapy with intravenous cefazolin.

Step-by-Step Solution

1

Interpret the blood culture susceptibility results.

The organism is Staphylococcus aureus that is susceptible to oxacillin, confirming a methicillin-susceptible S. aureus (MSSA) infection.

Oxacillin susceptibility is the laboratory surrogate marker used to differentiate MSSA from MRSA.

2

Identify the standard of care for MSSA bloodstream infections.

Anti-staphylococcal beta-lactams (e.g., cefazolin, nafcillin, oxacillin) are the first-line agents for MSSA.

Beta-lactams offer superior bactericidal activity, faster clearance of bacteremia, and lower mortality rates compared to vancomycin for MSSA infections.

3

Apply principles of antibiotic stewardship to modify the empiric regimen.

The empiric vancomycin and piperacillin-tazobactam should be discontinued and replaced with targeted cefazolin monotherapy.

De-escalating to the narrowest, most effective agent prevents antimicrobial resistance, limits collateral damage to normal flora, and reduces the risk of adverse drug events.

Key Concept

For methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia, empiric broad-spectrum antibiotics should be de-escalated to an anti-staphylococcal beta-lactam (e.g., cefazolin, nafcillin) because these agents have superior clinical outcomes compared to vancomycin.

Estimated Time:1m 15s

Question 2130Question →

Paramedics transport a 68-year-old male resident of a skilled nursing facility to the acute care clinic due to profound lethargy and weakness over the past 24 hours. According to the accompanying transfer paperwork, the patient has experienced large-volume, watery stools for five consecutive days following a treatment course of clindamycin for cellulitis. His daily medications include a transdermal fentanyl patch for severe osteoarthritis and oral acetaminophen. Initial triage vital signs show a temperature of 37.1 C (98.8 F), blood pressure of 88/58 mm Hg, heart rate of 114/min, and a respiratory rate of 9/min. Physical assessment is notable for somnolence, a delayed capillary refill of 4 seconds, and dry oral mucosa. Blood is drawn for an arterial blood gas and serum chemistry panels with the following results:

Lab Test	Value
Serum sodium	$135 \text{ mEq/L}$
Serum potassium	$2.9 \text{ mEq/L}$
Serum chloride	$112 \text{ mEq/L}$
Serum bicarbonate	$14 \text{ mEq/L}$
Blood urea nitrogen	$42 \text{ mg/dL}$
Serum creatinine	$1.9 \text{ mg/dL}$

Arterial blood gas (room air):

Parameter	Value
$pH$	$7.25$
$PaCO_2$	$35 \text{ mm Hg}$
$PaO_2$	$78 \text{ mm Hg}$

Which of the following is the most accurate interpretation of this patient's current acid-base status?

Normal anion gap metabolic acidosis with appropriate respiratory compensation

Normal anion gap metabolic acidosis and concurrent respiratory acidosis

Normal anion gap metabolic acidosis and concurrent respiratory alkalosis

High anion gap metabolic acidosis with appropriate respiratory compensation

High anion gap metabolic acidosis and concurrent respiratory acidosis

Show answer & explanation

Answer: Normal anion gap metabolic acidosis and concurrent respiratory acidosis

Answer

The most accurate interpretation is a normal anion gap metabolic acidosis with a concurrent respiratory acidosis.

The patient's lab results show a primary metabolic acidosis (

pH < 7.35

and low

[HCO_3^-]

). The anion gap is calculated as

135 - (112 + 14) = 9 \text{ mEq/L}

, which is normal. To determine if respiratory compensation is appropriate, Winter's formula must be applied:

Expected\ PaCO_2 = 1.5 \times 14 + 8 = 29 \pm 2 \text{ mm Hg}

. The patient's measured

PaCO_2

is

35 \text{ mm Hg}

. Since the measured

PaCO_2

is higher than the expected range of

27-31 \text{ mm Hg}

, the patient has a concurrent respiratory acidosis. This clinical picture is consistent with severe diarrhea causing bicarbonate loss (normal anion gap metabolic acidosis) alongside fentanyl-induced hypoventilation (respiratory acidosis).

Step-by-Step Solution

1

Analyze the pH and serum bicarbonate to identify the primary disorder.

The

pH

is

7.25

(acidemia) and

[HCO_3^-]

is

14 \text{ mEq/L}

(low). This indicates a primary metabolic acidosis.

Establishing the primary acid-base disturbance is the necessary first step before evaluating compensation.

2

Calculate the serum anion gap using the formula:

AG = [Na^+] - ([Cl^-] + [HCO_3^-])

.

AG = 135 - (112 + 14) = 135 - 126 = 9 \text{ mEq/L}

. This is a normal anion gap (normal range is typically

8-12 \text{ mEq/L}

).

Differentiating between normal and high anion gap metabolic acidosis helps narrow down the etiology. Here, bicarbonate loss from severe diarrhea causes a normal anion gap metabolic acidosis (NAGMA).

3

Calculate the expected respiratory compensation using Winter's formula:

Expected\ PaCO_2 = (1.5 \times [HCO_3^-]) + 8 \pm 2

.

Expected\ PaCO_2 = (1.5 \times 14) + 8 = 21 + 8 = 29 \pm 2

. The expected range is

27

to

31 \text{ mm Hg}

.

Winter's formula determines if the respiratory response (hyperventilation blowing off CO2) is adequate for the degree of metabolic acidosis.

4

Compare the expected

PaCO_2

to the patient's measured

PaCO_2

.

The measured

PaCO_2

(

35 \text{ mm Hg}

) is greater than the expected maximum of

31 \text{ mm Hg}

.

Because the actual

PaCO_2

is higher than the expected compensatory range, the patient is retaining CO2. This indicates an independent, superimposed primary respiratory acidosis, likely secondary to fentanyl-induced respiratory depression (evidenced by a respiratory rate of 9/min).

Key Concept

In patients with metabolic acidosis, Winter's formula must be used to calculate expected PaCO2 to rule out a mixed acid-base disorder; an actual PaCO2 higher than expected signifies a concurrent respiratory acidosis.

Question 2131Question →

An 81-year-old female resident of an assisted living facility is evaluated in the emergency department for severe, diffuse abdominal pain and intractable vomiting that began abruptly 5 hours ago. Her medical history includes hypertension and paroxysmal atrial fibrillation, for which she frequently misses her apixaban doses. On examination, the patient is agitated, diaphoretic, and writhing in pain. Abdominal examination reveals mild diffuse tenderness without guarding or rebound, which appears surprisingly benign given her reported level of pain.

Vitals:
* Temperature: $37.2^{\circ}\text{C} (99.0^{\circ}\text{F})$
* Pulse: $122/\text{min}$ , irregularly irregular
* Respirations: $32/\text{min}$
* Blood pressure: $148/85 \text{ mm Hg}$

Laboratory analysis reveals the following:

Serum Chemistry	Value
Sodium ( $\text{Na}^+$ )	$140 \text{ mEq/L}$
Potassium ( $\text{K}^+$ )	$3.2 \text{ mEq/L}$
Chloride ( $\text{Cl}^-$ )	$90 \text{ mEq/L}$
Bicarbonate ( $\text{HCO}_3^-$ )	$14 \text{ mEq/L}$
BUN	$28 \text{ mg/dL}$
Creatinine	$1.3 \text{ mg/dL}$

Arterial Blood Gas (Room Air)	Value
pH	$7.47$
$\text{pCO}_2$	$20 \text{ mm Hg}$
$\text{pO}_2$	$92 \text{ mm Hg}$

What is the most accurate interpretation of this patient's acid-base status?

High anion gap metabolic acidosis, metabolic alkalosis, and respiratory alkalosis

High anion gap metabolic acidosis and respiratory alkalosis

High anion gap metabolic acidosis and metabolic alkalosis with appropriate respiratory compensation

Respiratory alkalosis and metabolic alkalosis

Normal anion gap metabolic acidosis, metabolic alkalosis, and respiratory alkalosis

Show answer & explanation

Answer: High anion gap metabolic acidosis, metabolic alkalosis, and respiratory alkalosis

Answer

High anion gap metabolic acidosis, metabolic alkalosis, and respiratory alkalosis

The correct interpretation identifies a triple acid-base disorder. First, the anion gap is profoundly elevated at

36 \text{ mEq/L}

(

140 - (90 + 14)

), diagnosing a High Anion Gap Metabolic Acidosis (HAGMA), likely due to lactic acidosis from acute mesenteric ischemia. Second, applying Winter's formula (

1.5 \times 14 + 8 = 29

) shows the expected

\text{pCO}_2

should be

27-31 \text{ mm Hg}

. The actual

\text{pCO}_2

is

20 \text{ mm Hg}

, revealing an independent, concurrent Respiratory Alkalosis (driven by severe pain and hyperventilation). Finally, calculating the Delta Ratio (

\Delta\text{AG} / \Delta\text{HCO}_3^-

) yields

24 / 10 = 2.4

. A ratio

> 2.0

demonstrates that the bicarbonate level is inappropriately high for the degree of HAGMA, indicating a third, concurrent Metabolic Alkalosis (caused by intractable vomiting).

Step-by-Step Solution

1

Analyze the pH to determine the overall acid-base direction.

The pH is

7.47

, which indicates an overall alkalemia.

Establishing the net pH state is the first step, though significant hidden disorders can exist behind a misleading overall pH.

2

Calculate the serum Anion Gap (AG) to check for a hidden metabolic acidosis.

AG = \text{Na}^+ - (\text{Cl}^- + \text{HCO}_3^-) = 140 - (90 + 14) = 36

.

An

AG > 12 \text{ mEq/L}

confirms the presence of a primary High Anion Gap Metabolic Acidosis (HAGMA), regardless of the alkalemic pH.

3

Calculate the expected respiratory compensation using Winter's formula.

Expected

\text{pCO}_2 = 1.5 \times [\text{HCO}_3^-] + 8 \pm 2 = 1.5(14) + 8 = 29 \pm 2

(range

27-31 \text{ mm Hg}

). Actual

\text{pCO}_2

is

20 \text{ mm Hg}

.

Since the actual

\text{pCO}_2

(

20

) is lower than the expected range (

27-31

), there is a concurrent primary Respiratory Alkalosis.

4

Calculate the Delta Ratio (

\Delta\text{AG} / \Delta\text{HCO}_3^-

) to uncover additional metabolic disorders.

\Delta\text{AG} = 36 - 12 = 24

.

\Delta\text{HCO}_3^- = 24 - 14 = 10

. Delta Ratio

= 24 / 10 = 2.4

.

A Delta Ratio

> 2.0

indicates that the bicarbonate has not dropped as much as expected given the massive influx of unmeasured anions, proving the presence of a concurrent Metabolic Alkalosis.

Key Concept

Diagnosis of mixed (triple) acid-base disorders using Anion Gap, Winter's formula, and Delta Ratio.

Estimated Time:2m 0s

Question 2132Question →

A 64-year-old woman is brought to the emergency department due to a 2-day history of high fever, severe right upper quadrant abdominal pain, and confusion. She has a medical history of morbid obesity, for which she underwent a Roux-en-Y gastric bypass 5 years ago. She has not had a cholecystectomy. Her temperature is 39.5°C (103.1°F), blood pressure is 80/50 mmHg, pulse is 125/min, and respiratory rate is 24/min. Physical examination reveals profound scleral icterus and significant right upper quadrant tenderness with guarding.

Laboratory studies:

Parameter	Value
Leukocyte count	24,000/mm³ (15% bands)
Total bilirubin	7.2 mg/dL
Direct bilirubin	5.8 mg/dL
Alkaline phosphatase	580 U/L
Aspartate aminotransferase (AST)	190 U/L
Alanine aminotransferase (ALT)	210 U/L
Serum lactate	4.5 mmol/L

Intravenous fluids and broad-spectrum antibiotics (piperacillin-tazobactam) are immediately initiated. An abdominal ultrasound demonstrates a dilated common bile duct measuring 14 mm with echogenic material consistent with a stone, and a gallbladder containing multiple stones but without wall thickening. Despite aggressive fluid resuscitation, she requires vasopressor support.

Which of the following is the most appropriate next step in management?

Percutaneous transhepatic cholangiography with biliary drainage

Standard endoscopic retrograde cholangiopancreatography

Emergent open cholecystectomy with common bile duct exploration

Addition of intravenous vancomycin to the current regimen

Magnetic resonance cholangiopancreatography

Show answer & explanation

Answer: Percutaneous transhepatic cholangiography with biliary drainage

Answer

Percutaneous transhepatic cholangiography with biliary drainage

The correct answer is percutaneous transhepatic cholangiography (PTC) with biliary drainage. This patient's presentation of fever, right upper quadrant pain, jaundice, hypotension, and altered mental status represents Reynolds' pentad, indicative of severe acute ascending cholangitis complicated by septic shock. The immediate, life-saving intervention required is biliary decompression. Although standard endoscopic retrograde cholangiopancreatography (ERCP) is the first-line modality for biliary decompression, it is anatomically impossible in this patient. A previous Roux-en-Y gastric bypass divides the stomach and excludes the duodenum, preventing a standard endoscope from reaching the ampulla of Vater. Therefore, the most appropriate and rapidly available alternative to achieve source control in a hemodynamically unstable patient is a percutaneous transhepatic approach.

Step-by-Step Solution

1

Diagnose the acute condition based on clinical presentation and ultrasound findings.

The patient presents with fever, right upper quadrant pain, jaundice, hypotension, and confusion (Reynolds' pentad), alongside ultrasound evidence of a dilated common bile duct with a stone. This confirms the diagnosis of severe acute ascending cholangitis with septic shock.

Accurate diagnosis is required to recognize that this is a life-threatening emergency requiring immediate intervention beyond medical therapy.

2

Determine the standard first-line treatment for the diagnosed condition.

The standard of care for severe ascending cholangitis is emergent biliary decompression, typically achieved via transoral endoscopic retrograde cholangiopancreatography (ERCP).

Biliary decompression provides definitive source control for the infected, obstructed biliary tree.

3

Evaluate the patient's surgical history to assess anatomical feasibility of the standard treatment.

The patient had a Roux-en-Y gastric bypass. This procedure bypasses the duodenum (where the ampulla of Vater is located), making standard transoral ERCP anatomically impossible.

Failing to account for altered gastrointestinal anatomy can lead to dangerous delays and failed procedural attempts.

4

Select the most appropriate alternative intervention for the anatomically altered, hemodynamically unstable patient.

Percutaneous transhepatic cholangiography (PTC) with biliary drainage is selected.

PTC allows for rapid, minimally invasive biliary decompression through a transhepatic approach, bypassing the gastrointestinal tract anatomy entirely, which is essential for stabilizing a patient in septic shock.

Key Concept

Patients with severe acute ascending cholangitis require emergent biliary decompression. If a patient has a history of a Roux-en-Y gastric bypass, standard endoscopic access to the ampulla of Vater is impossible, rendering percutaneous transhepatic cholangiography (PTC) with drainage the preferred initial intervention for decompression.

Estimated Time:1m 40s

Question 2133Question →

A 65-year-old man comes to the clinic reporting a 3-month history of right calf cramping. The discomfort consistently begins after walking approximately three blocks and resolves completely within a few minutes of rest. He has a history of type 2 diabetes mellitus, hypertension, and a 40-pack-year smoking history. His current medications include metformin and lisinopril. Vital signs are within normal limits. On physical examination, the skin of the right lower extremity appears thin and shiny with decreased hair growth. The right dorsalis pedis pulse is diminished compared to the left. Which of the following is the most appropriate initial diagnostic test to evaluate this patient's condition?

Ankle-brachial index

Computed tomography angiography of the lower extremities

Venous duplex ultrasonography of the right lower extremity

Measurement of serum D-dimer

Exercise electrocardiography

Show answer & explanation

Answer: Ankle-brachial index

Answer

Ankle-brachial index

The patient's presentation of exertional calf pain relieved by rest, combined with thin, shiny skin and decreased distal pulses, is highly characteristic of intermittent claudication due to peripheral artery disease (PAD). The most appropriate initial diagnostic test for suspected PAD is the ankle-brachial index (ABI). The ABI compares the systolic blood pressure measured at the ankle to the systolic blood pressure measured at the brachial artery. An ABI of less than 0.90 is diagnostic for PAD. It is a highly sensitive, specific, and non-invasive first-line screening tool.

Step-by-Step Solution

1

Analyze the clinical presentation.

The patient has reproducible calf pain with exertion that is relieved by rest, alongside physical exam findings of diminished pulses and thin, shiny skin.

These findings represent intermittent claudication, which is the classic presentation of peripheral artery disease (PAD).

2

Determine the most appropriate initial diagnostic step for suspected PAD.

The ankle-brachial index (ABI) is the recommended first-line non-invasive test.

ABI provides a rapid, cost-effective, and highly sensitive method to confirm the diagnosis of PAD before considering any advanced imaging.

Key Concept

Diagnosis of Peripheral Artery Disease (PAD)

Question 2134Question →

A 64-year-old man presents to the emergency department with a 2-day history of progressive shortness of breath, orthopnea, and a dry cough. His medical history is significant for chronic obstructive pulmonary disease (COPD) and severe seropositive rheumatoid arthritis. Four months ago, his rheumatologist added infliximab to his regimen of methotrexate due to persistent joint erosions. Vital signs show a temperature of 37.1°C (98.8°F), blood pressure of 158/94 mmHg, pulse of 112/min, and respiratory rate of 26/min. Pulse oximetry is 88% on room air. Physical examination reveals elevated jugular venous pressure, a third heart sound (S3) gallop, and bilateral basilar crackles with mild expiratory wheezing. Chest radiography shows an enlarged cardiac silhouette, bilateral interstitial opacities, and blunting of the costophrenic angles. Which of the following is the most appropriate next step in management?

Intravenous furosemide

Inhaled albuterol and ipratropium

Intravenous piperacillin-tazobactam

Intravenous methylprednisolone

Immediate discontinuation of methotrexate and initiation of leucovorin

Show answer & explanation

Answer: Intravenous furosemide

Answer

Intravenous furosemide

This patient with severe rheumatoid arthritis recently started on infliximab presents with classic signs of acute decompensated heart failure (ADHF), including orthopnea, elevated jugular venous pressure, an S3 gallop, and pulmonary edema on chest radiograph. Tumor necrosis factor (TNF)-alpha inhibitors (e.g., infliximab, adalimumab, etanercept) are highly effective disease-modifying antirheumatic drugs (DMARDs); however, they are a well-documented cause of new-onset heart failure and can exacerbate existing left ventricular dysfunction. They are absolutely contraindicated in patients with moderate to severe (NYHA Class III/IV) heart failure. The most appropriate immediate management for his acute volume overload and resultant respiratory distress is diuresis using an intravenous loop diuretic such as furosemide.

Step-by-Step Solution

1

Analyze the physical examination and imaging findings.

The patient has elevated jugular venous pressure, an S3 gallop, cardiomegaly, and pulmonary edema.

These findings are classic for acute decompensated heart failure (ADHF).

2

Correlate the clinical syndrome with the patient's pharmacological history.

The patient recently started infliximab, a TNF-alpha inhibitor.

TNF-alpha inhibitors are known to precipitate new-onset heart failure or exacerbate underlying left ventricular dysfunction.

3

Determine the most appropriate immediate therapy.

Administer an intravenous loop diuretic such as furosemide.

Loop diuretics rapidly reduce volume overload and alleviate pulmonary edema in ADHF.

Key Concept

Tumor necrosis factor (TNF)-alpha inhibitors (e.g., infliximab, adalimumab, etanercept) can cause new-onset heart failure or worsen existing cardiac dysfunction. Patients presenting with signs of acute decompensated heart failure should be treated promptly with intravenous loop diuretics.

Estimated Time:1m 30s

Question 2135Question →

Match each patient's hepatitis B (HBV) serology profile with the most appropriate clinical diagnosis.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Profile 1 matches Resolved past HBV infection. Profile 2 matches Acute HBV infection. Profile 3 matches Immunity due to HBV vaccination. Profile 4 matches Inactive chronic HBV carrier.

Accurate interpretation of HBV serology relies on evaluating HBsAg (active infection vs. immunity), Anti-HBc (natural exposure vs. vaccination), and HBeAg/Anti-HBe status (infectivity and replication). The matched pairs correctly align these serological principles with their respective clinical phases.

Step-by-Step Solution

1

Analyze the HBsAg status for each profile.

Profiles 2 and 4 are HBsAg positive (active infection). Profiles 1 and 3 are HBsAg negative (no active infection).

HBsAg is the hallmark of active viral presence, distinguishing active disease from immunity or past infection.

2

Differentiate the HBsAg positive profiles (2 and 4).

Profile 2 has Anti-HBc IgM, indicating acute infection. Profile 4 has Anti-HBc IgG and Anti-HBe with normal ALT, indicating an inactive chronic carrier.

IgM antibodies represent acute or recent exposure, while IgG represents chronic or remote exposure.

3

Differentiate the HBsAg negative profiles (1 and 3).

Profile 1 has Anti-HBc (total) positive, indicating natural exposure and resolved infection. Profile 3 has Anti-HBc negative, indicating immunity from vaccination.

The HBV vaccine contains only HBsAg; therefore, vaccinated individuals will only develop Anti-HBs. Natural infection exposes the immune system to all viral proteins, leading to Anti-HBc production.

Key Concept

Interpretation of Hepatitis B virus (HBV) serological markers for disease staging

Estimated Time:1m 0s

Question 2136Question →

High-resolution manometry (HRM) is the gold standard for diagnosing esophageal motility disorders. According to the Chicago Classification v4.0, match the following esophageal motility disorders with their precise defining manometric criteria.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Type I Achalasia matches with elevated IRP, 100% failed peristalsis, and no pressurization. Type II Achalasia matches with elevated IRP, 100% failed peristalsis, and pan-esophageal pressurization. Type III Achalasia matches with elevated IRP and premature contractions. Distal Esophageal Spasm matches with normal IRP and premature contractions. Hypercontractile Esophagus matches with normal IRP and a DCI > 8,000 mmHg·s·cm.

The correct matches strictly follow the Chicago Classification algorithm for esophageal motility disorders. The first critical metric is the IRP. Achalasia requires an elevated IRP, while DES and Jackhammer require a normal IRP. Once IRP is established, the contractility pattern (failed, pressurized, premature, or hypercontractile) differentiates the specific subtype.

Step-by-Step Solution

1

Evaluate the Integrated Relaxation Pressure (IRP) to determine lower esophageal sphincter (LES) function.

An elevated IRP indicates impaired LES relaxation (defining achalasia), while a normal IRP rules out achalasia.

This primary branching point separates achalasia (Types I, II, and III) from other motility disorders (DES, Jackhammer).

2

Assess the contractility pattern in the esophageal body for cases with an elevated IRP.

100% failed peristalsis without pressurization is Type I. 100% failed peristalsis with pan-esophageal pressurization is Type II. Premature contractions indicate Type III.

The distinct contractility patterns dictate the achalasia subtype, which influences the choice of therapy (e.g., Type II responds best to pneumatic dilation or myotomy, while Type III often requires a longer myotomy).

3

Assess the contractility pattern in cases with a normal IRP.

Premature contractions with normal IRP define Distal Esophageal Spasm. Extremely high vigor contractions (DCI > 8,000) with normal IRP define Hypercontractile (Jackhammer) Esophagus.

Separating these prevents inappropriate achalasia treatments for patients with functioning LES relaxation.

Key Concept

Diagnosis and classification of esophageal motility disorders using high-resolution manometry criteria.

Estimated Time:2m 0s

Question 2137Question →

An independent, community-dwelling 71-year-old male schedules a clinic appointment due to persistent lumbar back pain that began spontaneously 6 weeks ago. The pain is described as a deep ache that does not improve with rest or ibuprofen. Over the past month, he has also experienced unusual fatigue and new-onset constipation. He has a history of mild essential hypertension controlled with amlodipine. Vital signs are within normal limits. Physical examination reveals point tenderness over the L4 spinous process.

Laboratory results are as follows:

Laboratory Test	Result	Reference Range
Hemoglobin	9.6 g/dL	13.5–17.5 g/dL
Mean corpuscular volume	89 fL	80–100 fL
Leukocytes	5,800/mm³	4,500–11,000/mm³
Platelets	142,000/mm³	150,000–400,000/mm³
Creatinine	2.1 mg/dL	0.6–1.2 mg/dL
Calcium	11.4 mg/dL	8.4–10.2 mg/dL
Alkaline phosphatase	95 U/L	40–120 U/L

Which of the following is the most appropriate initial diagnostic step to evaluate this patient's condition?

Serum protein electrophoresis

Radionuclide bone scan

Intact parathyroid hormone level

Bone marrow aspiration and biopsy

Prostate-specific antigen measurement

Show answer & explanation

Answer: Serum protein electrophoresis

Answer

Serum protein electrophoresis

This patient's presentation of hypercalcemia, acute renal insufficiency, normocytic anemia, and new-onset bone pain is classic for multiple myeloma. These hallmark clinical manifestations are frequently summarized by the acronym CRAB (Calcium elevation, Renal failure, Anemia, and Bone lesions). The hypercalcemia is responsible for his new-onset constipation. When multiple myeloma is suspected, the initial diagnostic approach focuses on identifying a monoclonal immunoglobulin (M-protein) or free light chains in the blood or urine. Therefore, the most appropriate initial, noninvasive diagnostic step is serum protein electrophoresis (SPEP), often performed concurrently with urine protein electrophoresis (UPEP) and a serum free light chain assay.

Step-by-Step Solution

1

Analyze the patient's clinical symptoms

An elderly male presents with severe bone pain, generalized fatigue, and new-onset constipation.

Identifying the clinical syndrome points toward a systemic illness rather than mechanical back pain.

2

Interpret the laboratory findings

The labs show normocytic anemia, acute kidney injury (elevated creatinine), hypercalcemia, and importantly, a normal alkaline phosphatase level.

These findings directly align with the CRAB criteria for multiple myeloma.

3

Synthesize symptoms and labs to form a diagnosis

The hypercalcemia explains the constipation; marrow infiltration explains the anemia; osteoclast activation explains the bone pain without corresponding osteoblast activity (keeping alkaline phosphatase normal).

Multiple myeloma is the most likely unifying diagnosis.

4

Determine the appropriate initial diagnostic step

Serum protein electrophoresis (along with urine protein electrophoresis and free light chains) is indicated.

Initial evaluation requires detecting a monoclonal paraprotein noninvasively before proceeding to definitive invasive testing like a bone marrow biopsy.

Key Concept

The initial evaluation of suspected multiple myeloma (presenting with the CRAB criteria: hyperCalcemia, Renal failure, Anemia, and Bone pain) relies on detecting a monoclonal paraprotein using serum and urine protein electrophoresis.

Estimated Time:1m 15s

Question 2138Question →

A 32-year-old man who recently emigrated from Southeast Asia presents to the emergency department with a 4-week history of productive cough, night sweats, unintentional weight loss, and low-grade fever. A chest radiograph reveals a cavitary lesion in the right upper lobe. You highly suspect active pulmonary tuberculosis. Arrange the following steps in the most appropriate chronological sequence for the management of this patient.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence is: 1) Institute airborne precautions, 2) Collect sputum specimens, 3) Initiate empiric four-drug therapy, and 4) Adjust the regimen based on susceptibility results.

The management of suspected active pulmonary tuberculosis follows a strict chronological protocol. Immediate airborne isolation is paramount to prevent transmission in the healthcare setting. Following isolation, diagnostic sputum samples must be collected prior to initiating treatment to avoid altering the mycobacterial burden and compromising diagnostic yield. Empiric multidrug therapy is then started to treat the active infection and reduce transmission risk. Finally, once cultures and susceptibility results return (which can take weeks), the regimen is adjusted appropriately to ensure targeted therapy and prevent drug resistance.

Step-by-Step Solution

1

Identify the need for immediate infection control.

Patient is placed in airborne isolation.

Prevents nosocomial spread of a highly contagious respiratory pathogen.

2

Obtain diagnostic samples.

Sputum is collected for AFB smear, culture, and NAAT.

Samples must be collected before therapy to ensure accurate culture and susceptibility testing.

3

Start empiric treatment.

RIPE therapy is initiated.

Reduces patient morbidity and further decreases infectivity while awaiting culture results.

4

Tailor therapy.

Regimen is modified if necessary.

Ensures effective treatment and prevents resistance once specific susceptibilities are known.

Key Concept

Chronological management of suspected active pulmonary tuberculosis requires prioritizing infection control, securing diagnostic samples prior to treatment, initiating empiric therapy, and later tailoring the regimen based on susceptibilities.

Question 2139Question →

A 19-year-old college student with a history of type 1 diabetes mellitus is brought to the emergency department by roommates after being found profoundly lethargic in his dorm room. Over the past three days, he has experienced progressive polyuria, polydipsia, nausea, and diffuse abdominal pain. He missed several doses of his basal insulin due to a recent upper respiratory tract infection. On examination, he appears acutely ill. Vital signs show a heart rate of 124/min, blood pressure of 88/54 mm Hg, and respiratory rate of 28/min with deep, labored breathing. Mucous membranes are extremely dry, and skin turgor is poor.

Laboratory studies reveal:
Serum chemistry:
Sodium: 131 mEq/L
Potassium: 3.1 mEq/L
Chloride: 95 mEq/L
Bicarbonate: 11 mEq/L
Blood urea nitrogen: 34 mg/dL
Creatinine: 1.5 mg/dL
Glucose: 685 mg/dL

Arterial blood gas analysis on room air demonstrates a pH of 7.12. Urinalysis shows 4+ ketones and 4+ glucose.

Arrange the following therapeutic interventions in the most appropriate chronological sequence for the optimal management of this patient's condition.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence is: Administer rapid intravenous normal saline, followed by intravenous potassium chloride, then initiate continuous intravenous regular insulin infusion, followed by changing intravenous fluids to include 5% dextrose when glucose drops, and finally administering subcutaneous long-acting insulin when the anion gap closes.

Optimal DKA management follows strict sequential priorities: volume expansion, electrolyte correction, acidosis resolution, and prevention of hypoglycemia. Intravenous isotonic saline is the universal first step to restore perfusion. Crucially, because this patient has severe hypokalemia (K+ = 3.1 mEq/L), potassium replacement must strictly precede insulin administration to prevent fatal arrhythmias from further intracellular potassium shifts. Once potassium is

\geq

3.3 mEq/L, continuous intravenous insulin is safely initiated to halt ketogenesis. As glucose levels predictably fall below 200-250 mg/dL during insulin therapy, 5% dextrose is added to the intravenous fluids to prevent hypoglycemia, allowing the continuation of insulin until the anion gap fully closes. Finally, a transition to subcutaneous long-acting insulin is performed once the ketoacidosis resolves and the patient can tolerate oral intake, ensuring sufficient overlap before discontinuing the intravenous insulin drip.

Step-by-Step Solution

1

Assess fluid status and administer 0.9% normal saline

Resolves severe hypovolemia, improves renal perfusion, and lowers counterregulatory hormones

Patients with DKA have profound osmotic diuresis leading to severe volume depletion, which must be addressed immediately as the first priority.

2

Evaluate serum electrolytes and administer intravenous potassium chloride

Restores total body potassium and safely raises serum potassium levels above 3.3 mEq/L

Insulin drives potassium intracellularly; giving insulin to a patient with a starting potassium < 3.3 mEq/L will trigger fatal arrhythmias. Potassium must be replenished first.

3

Initiate targeted therapy for ketoacidosis by starting a continuous intravenous regular insulin infusion

Halts ketogenesis and begins reversing the metabolic acidosis

Insulin is required to suppress lipolysis and ketone body production, effectively addressing the root cause of the high anion gap metabolic acidosis.

4

Monitor glucose response and add 5% dextrose to the intravenous fluids once glucose is < 250 mg/dL

Maintains normoglycemia while allowing continued insulin administration

The metabolic acidosis of DKA typically takes longer to resolve than the hyperglycemia. Adding dextrose prevents hypoglycemia while allowing the insulin drip to stay on until ketones are cleared.

5

Determine resolution of DKA and administer subcutaneous long-acting insulin

Provides basal insulin coverage before the intravenous insulin is stopped

A 1- to 2-hour overlap with subcutaneous insulin is mandatory before discontinuing the intravenous insulin drip to prevent immediate rebound ketoacidosis.

Key Concept

The sequential acute management algorithm for severe Diabetic Ketoacidosis (DKA) complicated by initial severe hypokalemia.

Question 2140Question →

Match the following patient presentations with the most likely underlying pathophysiologic mechanism of their hematologic abnormality.

Click a left item, then click its matching right item

Show answer & explanation

Answer

The correct matches are: the patient with the TTP pentad matches with ADAMTS13 deficiency; the patient with DIC matches with consumption of coagulation factors; the patient with ITP matches with anti-glycoprotein IIb/IIIa autoantibodies; and the patient with AIHA matches with IgG-coated red blood cell destruction.

Each vignette represents a distinct hematologic pathophysiology. TTP results from ADAMTS13 deficiency, allowing large von Willebrand factor multimers to shear red blood cells and consume platelets. DIC involves systemic activation of the coagulation cascade, depleting clotting factors and causing prolonged PT/PTT. ITP is an autoimmune destruction of platelets mediated by anti-glycoprotein IIb/IIIa antibodies without affecting the coagulation cascade. Warm AIHA is the antibody-mediated destruction of red blood cells, often producing spherocytes on a peripheral smear, and is frequently associated with lymphoid malignancies like CLL.

Step-by-Step Solution

1

Analyze the first clinical vignette for diagnostic clues.

Identified the presence of microangiopathic hemolytic anemia (MAHA), thrombocytopenia, renal impairment, and altered mental status with normal coagulation times.

These findings represent the classic pentad of Thrombotic Thrombocytopenic Purpura (TTP), which is caused by a deficiency in the ADAMTS13 protease.

2

Analyze the second clinical vignette for diagnostic clues.

Identified thrombocytopenia accompanied by prolonged PT and PTT, and low fibrinogen in the setting of severe infection (sepsis).

These laboratory derangements indicate consumption of coagulation factors, confirming the diagnosis of Disseminated Intravascular Coagulation (DIC).

3

Analyze the third clinical vignette for diagnostic clues.

Identified isolated thrombocytopenia without hemolysis and with normal coagulation studies in an otherwise healthy young adult.

This presentation is characteristic of Immune Thrombocytopenic Purpura (ITP), where autoantibodies target platelet surface antigens.

4

Analyze the fourth clinical vignette for diagnostic clues.

Identified extravascular hemolysis (jaundice, indirect hyperbilirubinemia, spherocytes) in a patient with underlying chronic lymphocytic leukemia.

These findings point to Warm Autoimmune Hemolytic Anemia (AIHA), caused by IgG autoantibodies binding to red blood cell surface antigens.

Key Concept

Differentiation of bleeding and hemolytic disorders based on peripheral smear findings and coagulation panels.

Internal Medicine

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