Internal Medicine

3151 questions

All types3,151 Multiple choice1,611 Multiple select73 Numeric81 Matching714 Ordering672

An $81$ -year-old woman arrives at the emergency room accompanied by her son due to worsening difficulty breathing and a persistent cough over the past $5$ days. She tells the physician that she needs to prop herself up on three pillows to sleep comfortably at night. Her medical history is significant for hypertension, coronary artery disease, and a $45$ -pack-year history of smoking. Her vital signs include a temperature of $36.8^\circ\text{C}$ ( $98.2^\circ\text{F}$ ), blood pressure of $160/92 \text{ mm Hg}$ , pulse of $102/\text{min}$ , and a respiratory rate of $24/\text{min}$ . Oxygen saturation is $90\%$ on ambient air. Physical examination shows engorged neck veins when she is sitting at a $45$ -degree angle. Auscultation of the lungs reveals bilateral crackles at the bases and scattered high-pitched expiratory wheezes. Cardiac auscultation reveals an extra diastolic heart sound heard shortly after S $2$ . Examination of the legs shows bilateral pitting edema up to the mid-calves. Which of the following is the most appropriate initial pharmacologic therapy for this patient?

Administration of inhaled albuterol and oral prednisone

Administration of inhaled tiotropium

Administration of intravenous furosemide

Measurement of arterial blood gas to calculate expected metabolic compensation

Administration of intravenous piperacillin-tazobactam

Show answer & explanation

Answer: Administration of intravenous furosemide

Answer

Administration of intravenous furosemide

This patient is presenting with acute decompensated heart failure (ADHF). Key identifying features include orthopnea (needing pillows to sleep), elevated jugular venous pressure, bilateral basilar crackles, a prominent S3 gallop (the extra diastolic heart sound), and peripheral pitting edema. The expiratory wheezing observed in this patient is often referred to as 'cardiac asthma,' which occurs because peribronchial edema causes physical compression and narrowing of the small airways. The most appropriate initial management for a patient in respiratory distress due to volume overload from ADHF is the administration of an intravenous loop diuretic, such as furosemide. This intervention rapidly decreases cardiac preload, reduces pulmonary congestion, and provides symptomatic relief.

Step-by-Step Solution

Identify the primary clinical syndrome based on the patient's history and physical examination.

The patient exhibits orthopnea, jugular venous distention, basilar crackles, an S3 gallop (extra diastolic sound after S2), and lower extremity edema.

These findings are the classic textbook signs of volume overload and elevated left ventricular filling pressures.

Determine the etiology of the expiratory wheezes in this specific context.

Although the patient has a heavy smoking history, the predominant signs indicate acute decompensated heart failure. The wheezing represents 'cardiac asthma' resulting from peribronchial airway edema.

Accurately diagnosing the root cause prevents the administration of therapies (like bronchodilators or steroids) that do not address the underlying fluid overload.

Select the most appropriate initial pharmacological intervention for the identified syndrome.

An intravenous loop diuretic, such as furosemide, is indicated.

Loop diuretics rapidly reduce cardiac preload and promote diuresis, directly mitigating the pulmonary congestion and relieving the patient's respiratory distress.

Key Concept

The clinical differentiation of acute decompensated heart failure from a COPD exacerbation relies on identifying distinct signs of volume overload (such as an S3 gallop, jugular venous distention, basilar crackles, and peripheral edema), which dictates immediate treatment with intravenous loop diuretics.

Estimated Time:1m 0s

Question 382Question →

Identify the classic autoantibody marker most strongly associated with each of the following clinical diagnoses.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Primary biliary cholangitis matches with Anti-mitochondrial antibodies, Autoimmune hepatitis with Anti-smooth muscle antibodies, Primary sclerosing cholangitis with p-ANCA, and Celiac disease with Anti-tissue transglutaminase IgA.

Each of the listed immune-mediated conditions has a distinct, high-yield serologic profile required for board examinations. Primary biliary cholangitis is famously associated with anti-mitochondrial antibodies. Autoimmune hepatitis (Type 1) features anti-smooth muscle antibodies. Primary sclerosing cholangitis, which has a strong link to inflammatory bowel disease, is associated with perinuclear anti-neutrophil cytoplasmic antibodies (p-ANCA). Finally, Celiac disease relies on anti-tissue transglutaminase IgA antibodies for initial serologic screening.

Step-by-Step Solution

Evaluate the underlying pathophysiology and known serologic markers for the listed gastrointestinal and hepatobiliary disorders.

Specific autoantibodies are identified for each condition based on classic clinical associations.

Identifying the correct serologic marker is essential for the diagnosis of these immune-mediated diseases.

Key Concept

Autoimmune and serologic markers in gastroenterology and hepatology

Question 383Question →

A 54-year-old man is admitted to the intensive care unit after being intubated for severe respiratory distress. He was witnessed aspirating gastric contents during a seizure 12 hours ago. Vital signs are blood pressure 90/60 mm Hg, pulse 112/min, and temperature 38.2°C (100.8°F). His height is 170 cm (5 ft 7 in) and weight is 75 kg (165 lb). A chest radiograph shows bilateral diffuse alveolar infiltrates without cardiomegaly. He is placed on mechanical ventilation. Current ventilator settings and arterial blood gas results are as follows:

Ventilator Parameter	Value
Mode	Volume-controlled
Tidal volume	650 mL
Respiratory rate	14/min
FiO2	0.70
PEEP	5 cm H2O

Blood Gas Parameter	Value
pH	7.25
PaCO2	60 mm Hg
PaO2	52 mm Hg
HCO3-	26 mEq/L

Which of the following interventions are indicated in the management of this patient's respiratory failure? (Select all that apply)

Select all that apply

Decrease the tidal volume to 400 mL

Increase the positive end-expiratory pressure (PEEP)

Increase the respiratory rate

Administer intravenous sodium bicarbonate

Administer intravenous furosemide

Show answer & explanation

Answer: Decrease the tidal volume to 400 mL; Increase the positive end-expiratory pressure (PEEP); Increase the respiratory rate

Answer

The indicated interventions are to decrease the tidal volume to 400 mL, increase the positive end-expiratory pressure (PEEP), and increase the respiratory rate.

This patient has severe acute respiratory distress syndrome (ARDS) following an aspiration event, defined by acute onset, bilateral infiltrates, a known clinical insult, and a

PaO_2/FiO_2

ratio less than 100 mm Hg (here,

52 / 0.70 = 74

). Standard management requires a lung-protective ventilation strategy. This involves decreasing the tidal volume to

6

mL/kg of predicted body weight (approximately 400 mL for a 66 kg male) to prevent alveolar overdistension and volutrauma. Because the patient is severely hypoxemic, increasing PEEP is necessary to recruit collapsed alveoli, decrease intrapulmonary shunting, and improve oxygenation. Finally, because decreasing the tidal volume will further lower minute ventilation and worsen the existing respiratory acidosis (

PaCO_2

60 mm Hg), the respiratory rate must be increased concurrently to facilitate

CO_2

clearance.

Step-by-Step Solution

Calculate the PaO2/FiO2 ratio and predicted body weight to confirm the diagnosis and determine target ventilator parameters.

The

PaO_2/FiO_2

ratio is

74

(severe ARDS), and the predicted body weight for a 170 cm male is roughly 66 kg.

Establishing the severity of ARDS and predicted body weight dictates the implementation of the lung-protective ventilation protocol.

Evaluate the current tidal volume against ARDS guidelines.

The current tidal volume is 650 mL (nearly

10

mL/kg), which is too high. It must be decreased to

6

mL/kg (approximately 400 mL).

High tidal volumes cause overdistension of functioning alveoli, leading to ventilator-induced lung injury (volutrauma) and increased mortality.

Evaluate the current oxygenation status (

PaO_2

and

FiO_2

) and the PEEP setting.

The patient remains severely hypoxemic despite a high

FiO_2

(0.70) while on a minimal PEEP of 5 cm

H_2O

. PEEP must be increased.

Increasing PEEP recruits collapsed alveoli, decreases intrapulmonary shunting, and improves oxygenation without risking further oxygen toxicity.

Address the respiratory acidosis (

pH

7.25,

PaCO_2

60 mm Hg) and the physiological effect of lowering the tidal volume.

The respiratory rate must be increased concurrently with the reduction in tidal volume.

Lowering the tidal volume directly decreases minute ventilation. The respiratory rate must be increased to compensate, maintain minute ventilation, and clear carbon dioxide.

Rule out inappropriate therapies based on hemodynamics and acid-base principles.

Furosemide and sodium bicarbonate are rejected as interventions.

Furosemide worsens hypotension in an already unstable patient. Bicarbonate paradoxically worsens intracellular acidosis when given for a primary respiratory acidosis.

Key Concept

The management of acute respiratory distress syndrome (ARDS) requires a lung-protective ventilation strategy involving low tidal volumes (

6

mL/kg of predicted body weight) to prevent volutrauma, increased PEEP to recruit alveoli and improve oxygenation, and an increased respiratory rate to maintain adequate minute ventilation for

CO_2

clearance.

Question 384Question →

A 45-year-old woman is evaluated in the outpatient clinic for a 6-month history of progressive shortness of breath on exertion and profound fatigue. She recently experienced an episode of lightheadedness that nearly resulted in syncope while climbing stairs. She has no significant past medical history, takes no medications, and has never smoked. Vital signs show a heart rate of $92/\text{min}$ , blood pressure of $118/74\text{ mmHg}$ , and oxygen saturation of $97\%$ on room air. Physical examination reveals a palpable right ventricular heave and a prominently accentuated $P_2$ component of the second heart sound. The lungs are clear to auscultation bilaterally. An electrocardiogram demonstrates right axis deviation and right ventricular hypertrophy. Chest radiography shows prominent central pulmonary arteries with rapid tapering of the peripheral vessels and clear lung fields.

Arrange the following diagnostic and management steps in the most appropriate chronological order according to guideline-directed evaluation of suspected pulmonary hypertension.

Drag items to arrange them in the correct order

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Answer

The correct sequential order for evaluating suspected pulmonary hypertension is: 1) Transthoracic echocardiography, 2) Radionuclide ventilation-perfusion (V/Q) scan, 3) Right heart catheterization, and 4) Acute pulmonary vasodilator challenge.

The diagnostic approach to unexplained pulmonary hypertension (PH) follows a strict algorithmic sequence. First, transthoracic echocardiography is performed to estimate pulmonary pressures and rule out left-sided heart disease (Group 2 PH). Second, a ventilation-perfusion (V/Q) scan is obtained to screen for chronic thromboembolic pulmonary hypertension (CTEPH, Group 4), as it is more sensitive than CT angiography for chronic disease. Third, if noninvasive workup points to Group 1 Pulmonary Arterial Hypertension (PAH), right heart catheterization is mandatory to definitively measure hemodynamics (mean pulmonary artery pressure

\geq 20\text{ mmHg}

, pulmonary capillary wedge pressure

\leq 15\text{ mmHg}

, and pulmonary vascular resistance

\geq 3

Wood units). Finally, during the right heart catheterization, an acute vasodilator challenge is conducted using a short-acting agent (e.g., inhaled nitric oxide) to identify patients who are candidates for calcium channel blocker therapy.

Step-by-Step Solution

Initial noninvasive screening with TTE.

Estimates pulmonary artery pressures and evaluates for left-sided heart disease.

TTE is the safest, most accessible initial test to confirm clinical suspicion of PH and rule out Group 2 PH (left heart disease).

Noninvasive etiologic evaluation with a V/Q scan.

Screens for chronic thromboembolic pulmonary hypertension (CTEPH).

A V/Q scan is the imaging modality of choice (more sensitive than CT pulmonary angiography) for ruling out Group 4 PH before proceeding to invasive testing.

Invasive hemodynamic confirmation via RHC.

Accurately measures mean pulmonary artery pressure (mPAP), pulmonary capillary wedge pressure (PCWP), and pulmonary vascular resistance (PVR).

RHC is the gold standard required to definitively diagnose pulmonary arterial hypertension (PAH) and differentiate pre-capillary from post-capillary etiologies.

Therapeutic triaging with an acute vasodilator challenge.

Determines pulmonary vasoreactivity.

Performed during the RHC in patients with confirmed Group 1 PAH to identify the minority of patients who will safely respond to long-term high-dose calcium channel blocker therapy.

Key Concept

The diagnostic algorithm for pulmonary hypertension requires sequential noninvasive screening (echocardiography), etiologic workup (V/Q scan for CTEPH), invasive confirmation (right heart catheterization), and therapeutic triaging (vasodilator testing).

Estimated Time:1m 30s

Question 385Question →

A 62-year-old man is evaluated in the intensive care unit for rapidly worsening oxygenation. Two days ago, he underwent an emergency exploratory laparotomy for a perforated duodenal ulcer. Blood cultures drawn at admission are currently growing *Escherichia coli* susceptible to ceftriaxone. He is receiving intravenous piperacillin-tazobactam, vancomycin, and a continuous norepinephrine infusion.

Current vital signs:
* Temperature: $38.5^\circ\text{C}$ ( $101.3^\circ\text{F}$ )
* Blood pressure: $90/55\text{ mmHg}$
* Heart rate: $120/\text{min}$

Physical examination reveals flat jugular veins. Lung auscultation demonstrates diffuse bilateral crackles. Echocardiography shows a hyperdynamic left ventricle with an estimated ejection fraction of $65\%$ and no valvular abnormalities. Chest radiography reveals new, dense bilateral alveolar infiltrates.

Prior to intubation, an arterial blood gas (ABG) on a $100\%$ non-rebreather mask showed:
* $\text{pH}$ : $7.28$
* $P_a\text{CO}_2$ : $30\text{ mmHg}$
* $P_a\text{O}_2$ : $55\text{ mmHg}$
* $\text{HCO}_3^-$ : $14\text{ mEq/L}$

The patient is immediately intubated. Initial ventilator settings on Assist-Control Volume Control mode are:
* Tidal volume: $450\text{ mL}$ ( $6\text{ mL/kg}$ of ideal body weight)
* Respiratory rate: $16/\text{min}$
* $\text{PEEP}$ : $8\text{ cm H}_2\text{O}$
* $\text{FiO}_2$ : $1.0$

Thirty minutes later, ventilator mechanics show a peak airway pressure of $32\text{ cm H}_2\text{O}$ and a plateau pressure of $22\text{ cm H}_2\text{O}$ . A repeat ABG is obtained:
* $\text{pH}$ : $7.14$
* $P_a\text{CO}_2$ : $48\text{ mmHg}$
* $P_a\text{O}_2$ : $58\text{ mmHg}$
* $\text{HCO}_3^-$ : $16\text{ mEq/L}$

Which of the following are the most appropriate immediate steps in management? (Select all that apply)

Select all that apply

Increase the ventilator respiratory rate

Increase the positive end-expiratory pressure

Administer intravenous furosemide

Maintain the current respiratory rate as the

P_a\text{CO}_2

reflects appropriate compensation

Escalate the antibiotic regimen to intravenous meropenem

Show answer & explanation

Answer: Increase the ventilator respiratory rate; Increase the positive end-expiratory pressure

Answer

Increase the ventilator respiratory rate AND Increase the positive end-expiratory pressure

The patient has developed Acute Respiratory Distress Syndrome (ARDS) secondary to intra-abdominal sepsis. The initial ABG demonstrated an appropriately compensated metabolic acidosis (

P_a\text{CO}_2

30\text{ mmHg}

). However, after intubation, the fixed respiratory rate of

16/\text{min}

failed to meet his physiologic minute ventilation needs, causing a severe iatrogenic respiratory acidosis (actual

P_a\text{CO}_2

48\text{ mmHg}

vs expected

30-34\text{ mmHg}

per Winter's formula). Because tidal volume is correctly restricted to

6\text{ mL/kg}

for lung protection, the ventilator respiratory rate must be increased to clear the excess

P_a\text{CO}_2

. Additionally, he exhibits a massive intrapulmonary shunt (

P_a\text{O}_2

58\text{ mmHg}

100\% \text{FiO}_2

). Because his plateau pressure is

22\text{ cm H}_2\text{O}

(safely below the

30\text{ cm H}_2\text{O}

limit for barotrauma), increasing the positive end-expiratory pressure (PEEP) is the most appropriate next step to recruit collapsed alveoli and improve oxygenation.

Step-by-Step Solution

Diagnose the primary pulmonary pathology based on clinical presentation.

The patient has Acute Respiratory Distress Syndrome (ARDS) secondary to intra-abdominal sepsis.

Characterized by acute onset of hypoxemia (P/F ratio < 100), bilateral infiltrates, and non-cardiogenic etiology (normal EF, flat neck veins).

Assess the post-intubation acid-base status using Winter's formula.

Expected

P_a\text{CO}_2 = 1.5 \times 16 + 8 \pm 2 = 30-34\text{ mmHg}

To determine if the measured

P_a\text{CO}_2

48\text{ mmHg}

is appropriate compensation for the metabolic acidosis or a secondary disorder.

Identify required ventilator adjustments for the uncompensated respiratory acidosis.

The respiratory rate must be increased.

Since tidal volume is locked at

6\text{ mL/kg}

for lung protection, minute ventilation must be augmented by raising the respiratory rate to clear the iatrogenic

P_a\text{CO}_2

accumulation.

Evaluate ventilator mechanics to address the refractory hypoxemia (

P_a\text{O}_2

58\text{ mmHg}

100\% \text{FiO}_2

Positive end-expiratory pressure (PEEP) should be increased.

The plateau pressure is

22\text{ cm H}_2\text{O}

, which is well below the dangerous threshold of

30\text{ cm H}_2\text{O}

, allowing safe upward titration of PEEP to recruit alveoli and improve oxygenation.

Key Concept

In severe ARDS complicated by metabolic acidosis, optimal mechanical ventilation requires balancing lung-protective tidal volumes (

6\text{ mL/kg}

) with appropriately high respiratory rates to prevent iatrogenic respiratory acidosis, while titrating PEEP to treat hypoxemia provided plateau pressures remain

< 30\text{ cm H}_2\text{O}

Question 386Question →

A 26-year-old pregnant woman at 28 weeks gestation is brought to the emergency department for severe shortness of breath that has worsened over the past 12 hours. She has a history of poorly controlled asthma. On arrival, she is lethargic, diaphoretic, and can only speak in single syllables. Her temperature is 37.0°C (98.6°F), blood pressure is 110/70 mmHg, pulse is 132/min, and respiratory rate is 36/min. Pulse oximetry shows an oxygen saturation of 86% on room air. Physical examination reveals a gravid uterus, profound accessory muscle use, and a "quiet chest" with minimal air movement bilaterally. An arterial blood gas analysis on room air demonstrates:

pH: 7.32
$PaCO_2$ : 48 mmHg
$PaO_2$ : 55 mmHg

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

Endotracheal intubation and mechanical ventilation

Administer intravenous furosemide

Administer broad-spectrum intravenous antibiotics

Administer intravenous sodium bicarbonate

Reassure the patient that her blood gas values are normal for pregnancy

Show answer & explanation

Answer: Endotracheal intubation and mechanical ventilation

Answer

Endotracheal intubation and mechanical ventilation

The correct answer is endotracheal intubation and mechanical ventilation. This patient is experiencing a severe asthma exacerbation leading to impending respiratory failure. Classic signs of impending respiratory arrest in asthma include an altered level of consciousness (lethargy), a 'quiet' or 'silent' chest on auscultation (indicating airflow is too poor to even generate wheezing), and a normalizing or elevated

PaCO_2

. During an acute asthma attack, patients typically hyperventilate, leading to a respiratory alkalosis (low

PaCO_2

). When the respiratory muscles fatigue, ventilation decreases, and the

PaCO_2

begins to rise. A

PaCO_2

of 48 mmHg in a severely dyspneic asthmatic patient is an absolute indication for immediate intubation and mechanical ventilation. Furthermore, because normal pregnancy is associated with a chronic respiratory alkalosis (

PaCO_2

normally 28-32 mmHg), a level of 48 mmHg is exceptionally dangerous in this context.

Step-by-Step Solution

Evaluate the patient's clinical presentation for signs of impending respiratory failure.

The patient exhibits lethargy, inability to speak in full sentences, and a 'quiet chest' indicating minimal air movement, all of which point to exhaustion and severe airflow obstruction.

Recognizing clinical signs of fatigue is critical in determining the urgency of airway intervention.

Interpret the arterial blood gas (ABG) in the context of an acute asthma exacerbation and pregnancy.

The ABG shows acidemia (pH 7.32) and hypercapnia (

PaCO_2

48 mmHg). In a normal asthma attack, hyperventilation causes respiratory alkalosis (low

PaCO_2

). A normal or elevated

PaCO_2

signifies respiratory muscle fatigue.

An elevated

PaCO_2

in an acute asthma exacerbation is a classic red flag for impending respiratory arrest.

Determine the appropriate intervention based on the clinical and objective findings.

The patient requires immediate endotracheal intubation and mechanical ventilation to secure the airway and ensure adequate gas exchange.

When a patient with severe asthma tires out and loses the ability to ventilate (hypercapnia, lethargy, quiet chest), definitive airway management is life-saving.

Key Concept

Impending respiratory failure in severe asthma exacerbation

Question 387Question →

A 73-year-old retired accountant is evaluated in the emergency department for severe, progressively worsening breathlessness over the past 48 hours. The patient has a 45-pack-year smoking history, essential hypertension, and hyperlipidemia. He reports needing to sleep propped up on three pillows to avoid suffocating and describes a non-productive cough. Temperature is $37.0^\circ \text{C}$ , blood pressure is $172/98 \text{ mmHg}$ , pulse is $105/\text{min}$ , and respirations are $26/\text{min}$ . Pulse oximetry shows $88\%$ on room air. The patient is sitting on the edge of the bed, using accessory muscles to breathe. Jugular venous pressure is measured at $11 \text{ cm H}_2\text{O}$ . Lung auscultation reveals a prolonged expiratory phase with diffuse bilateral wheezes and scattered crackles at the lung bases. Cardiac examination shows a laterally displaced apical impulse and an early diastolic sound heard best at the apex. Bilateral $1+$ pitting edema is present in the lower extremities. Arterial blood gas on room air shows a pH of 7.30, PaCO2 of $55 \text{ mmHg}$ , PaO2 of $58 \text{ mmHg}$ , and HCO3 of $26 \text{ mEq/L}$ . Chest radiograph demonstrates cephalization of the pulmonary vasculature, peribronchial cuffing, and a small right-sided pleural effusion without focal consolidation. Which of the following is the most appropriate initial pharmacological intervention for this patient's presentation?

Administration of an intravenous loop diuretic

Systemic administration of glucocorticoids

Administration of nebulized short-acting bronchodilators

Initiation of empiric oral azithromycin

Intravenous infusion of sodium bicarbonate

Show answer & explanation

Answer: Administration of an intravenous loop diuretic

Answer

Administration of an intravenous loop diuretic

The correct answer is Administration of an intravenous loop diuretic. This patient is presenting with acute decompensated heart failure (ADHF). Although his heavy smoking history, wheezing, and acute respiratory acidosis might initially suggest a chronic obstructive pulmonary disease (COPD) exacerbation, several critical findings point exclusively to cardiogenic pulmonary edema. The elevated jugular venous pressure, laterally displaced apical impulse (indicating cardiomegaly), and an S3 gallop are highly specific for left ventricular failure and volume overload. Furthermore, the chest radiograph shows cephalization of vessels and peribronchial cuffing, which are classic for pulmonary edema. The wheezing in this scenario represents 'cardiac asthma'—bronchospasm induced by peribronchial edema. The immediate cornerstone of therapy for ADHF with volume overload is preload reduction, achieved primarily through intravenous loop diuretics.

Step-by-Step Solution

Analyze the physical exam and imaging findings.

The patient has elevated JVP, an S3 gallop, a displaced apical impulse, orthopnea, and a chest radiograph showing cephalization and peribronchial cuffing.

These are hallmark signs of left ventricular fluid overload and cardiomegaly.

Evaluate the respiratory signs in context of the cardiovascular findings.

Despite the smoking history, wheezing, and hypercapnia (PaCO2 55 mmHg), the respiratory failure is driven by pulmonary edema ('cardiac asthma') rather than a primary COPD exacerbation.

The presence of structural and functional cardiac overload signs confirms the etiology of the respiratory distress.

Select the appropriate initial pharmacotherapy.

Intravenous loop diuretics (along with oxygen and potentially vasodilators given the severe hypertension) are indicated.

Loop diuretics provide rapid symptom relief in acute decompensated heart failure by reducing intravascular volume and decreasing ventricular preload.

Key Concept

Differentiating cardiac asthma (acute decompensated heart failure) from a COPD exacerbation is critical, as treatments for the latter can worsen heart failure.

Estimated Time:2m 0s

Question 388Question →

Match each distinct clinical presentation of chronic diarrhea to its corresponding fundamental pathophysiological mechanism or histological hallmark.

Click a left item, then click its matching right item

Show answer & explanation

Answer

The condition presenting with oculomasticatory myorhythmia matches the PAS-positive macrophage infiltration (Whipple disease). The diarrhea improving with nasogastric suction matches the peptide hormone-secreting neoplasm (Gastrinoma/Zollinger-Ellison). The malabsorption with uncorrectable low D-xylose matches the immune-mediated enteropathy (Celiac disease). The watery diarrhea with a macroscopically normal colonoscopy matches the subepithelial collagen layer/lymphocytosis (Microscopic colitis).

Each clinical presentation uniquely isolates a specific pathophysiological mechanism of chronic diarrhea: infectious infiltration (Whipple), acid-induced enzyme inactivation (ZES), structural mucosal loss (Celiac), and microscopic mucosal inflammation (Microscopic colitis).

Step-by-Step Solution

Analyze the first clinical presentation detailing oculomasticatory myorhythmia and polyarthritis alongside diarrhea.

Identify this as the classic systemic triad for Whipple disease.

Recognizing this pathognomonic neurological finding directly links to the histological hallmark of Tropheryma whipplei infection (PAS-positive, diastase-resistant macrophages).

Evaluate the second presentation involving diarrhea that ceases with nasogastric suction and severe duodenal ulcerations.

Identify this as Zollinger-Ellison syndrome.

Nasogastric suction removes the extreme gastric acid load produced by a gastrinoma; without the acid, intraluminal pancreatic enzymes are no longer inactivated, and the diarrhea resolves.

Interpret the diagnostic significance of a persistently low D-xylose excretion test despite pancreatic enzyme supplementation.

Localize the defect strictly to the small intestinal mucosa.

D-xylose is a monosaccharide absorbed directly by the intact mucosa without requiring pancreatic enzymes. Low absorption indicates primary mucosal destruction, such as in Celiac disease.

Assess the presentation of chronic watery diarrhea with a visually normal colonoscopy.

Identify this as microscopic colitis.

The defining feature of microscopic colitis is the absence of macroscopic (endoscopic) abnormalities despite significant histological inflammation (collagenous or lymphocytic).

Key Concept

Pathophysiological differentiation of chronic malabsorptive and secretory diarrheal syndromes

Question 389Question →

A $42$ -year-old woman is evaluated in the hospital on the second day of her admission for acute pancreatitis. She initially presented with severe epigastric pain, nausea, and vomiting. At the time of admission, laboratory studies showed a serum lipase of $2,400$ U/L, alanine aminotransferase (ALT) of $185$ U/L, and normal total bilirubin and alkaline phosphatase levels. Right upper quadrant ultrasound demonstrated gallstones in the gallbladder but no common bile duct dilation. She was treated with aggressive intravenous crystalloid resuscitation and opioid analgesics. Today, she reports that her abdominal pain has significantly improved and her nausea has completely resolved. She states she is feeling hungry and asks when she can eat. Her temperature is $37.4^\circ\text{C}$ ( $99.3^\circ\text{F}$ ), blood pressure is $125/78$ mmHg, pulse is $88$ /min, and respirations are $16$ /min. Abdominal examination reveals mild epigastric tenderness but no guarding or rebound. Bowel sounds are present. Which of the following is the most appropriate next step in management?

Initiate an oral low-fat diet

Administer prophylactic intravenous meropenem

Perform urgent endoscopic retrograde cholangiopancreatography

Obtain a contrast-enhanced computed tomography scan of the abdomen

Maintain strict nil per os status and initiate total parenteral nutrition

Show answer & explanation

Answer: Initiate an oral low-fat diet

Answer

The most appropriate next step is to initiate an oral low-fat diet.

The patient has mild acute gallstone pancreatitis that is improving rapidly with initial supportive care. For patients with mild acute pancreatitis who have experienced resolution of nausea and vomiting and report the return of hunger, early initiation of an oral diet (e.g., low-fat solid or liquid diet) is recommended. Early feeding has been shown to be safe, reduces the length of hospital stay, and lowers the risk of infectious complications by maintaining gut mucosal integrity and preventing bacterial translocation.

Step-by-Step Solution

Evaluate the clinical trajectory and laboratory findings.

The patient's pain and nausea have improved, hunger has returned, and initial labs showed no biliary obstruction.

To determine if the acute pancreatitis is mild and resolving or severe with complications.

Select the appropriate nutritional and management strategy.

An early oral low-fat diet should be initiated.

Early enteral nutrition prevents gut mucosal atrophy, decreases bacterial translocation, and reduces length of stay in mild pancreatitis.

Key Concept

Early oral feeding in mild acute pancreatitis

Estimated Time:1m 15s

Question 390Question →

A 56-year-old male patient is rushed to the emergency department following two episodes of voluminous vomiting of bright red blood at home. He has a past medical history significant for chronic hepatitis C infection and resultant portal hypertension. Upon arrival, he is lethargic but protecting his airway. His blood pressure is 82/48 mm Hg, and his pulse is 126/min. Physical examination reveals conjunctival pallor, prominent abdominal veins, and splenomegaly. Laboratory studies show a hemoglobin level of 6.8 g/dL and a platelet count of 65,000/mm³. Arrange the following steps in the management of this patient's acute bleeding episode in the most appropriate chronological order from first (most immediate) to last (salvage therapy).

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence prioritizes hemodynamic stability first, followed by pharmacologic portal pressure reduction and infection prophylaxis, then definitive endoscopic intervention, and finally TIPS as salvage therapy.

The management of acute variceal bleeding follows a strict, step-wise algorithm prioritizing patient stability. (1) Hemodynamic resuscitation with intravenous fluids (and blood products if indicated) is the absolute first step in any unstable patient with hemorrhagic shock. (2) Splanchnic vasoconstrictors (e.g., octreotide, terlipressin) and prophylactic antibiotics (e.g., ceftriaxone) are administered concurrently to halt the bleeding mechanism and prevent life-threatening infections. (3) Endoscopy (EGD) is then performed once the patient is adequately resuscitated to allow for definitive band ligation under safer conditions. (4) TIPS is reserved solely as a salvage procedure if the bleeding is refractory to both medical and endoscopic therapy.

Step-by-Step Solution

Assess hemodynamic status and prioritize immediate stabilization.

The patient is in hypovolemic shock (blood pressure 82/48 mm Hg, pulse 126/min).

Immediate placement of two large-bore intravenous catheters and fluid resuscitation is necessary to restore intravascular volume and prevent anoxic organ injury.

Initiate condition-specific pharmacotherapy for suspected variceal hemorrhage.

Intravenous octreotide and ceftriaxone are administered.

Octreotide causes splanchnic vasoconstriction to reduce portal venous pressure. Prophylactic antibiotics significantly reduce mortality and rebleeding rates in patients with cirrhosis presenting with gastrointestinal bleeds.

Achieve definitive hemostasis via direct visualization.

Esophagogastroduodenoscopy (EGD) is performed.

Endoscopy allows for the confirmation of bleeding esophageal or gastric varices and provides immediate therapeutic intervention such as endoscopic band ligation.

Determine the need for salvage therapy if bleeding continues.

TIPS placement is considered.

If standard medical and endoscopic therapies fail to control the acute hemorrhage, a transjugular intrahepatic portosystemic shunt is created to mechanically decompress the portal system.

Key Concept

Algorithm for the acute management of variceal hemorrhage in patients with portal hypertension.

Question 391Question →

During morning rounds, a 52-year-old woman reports feeling chilled and fatigued. She is currently hospitalized on day 10 of induction chemotherapy for acute promyelocytic leukemia. Her temperature is $38.7^\circ\text{C}$ ( $101.7^\circ\text{F}$ ), blood pressure is $122/76$ mmHg, heart rate is $94$ /min, and respiratory rate is $16$ /min. Pulse oximetry shows $98\%$ on room air. Physical examination reveals a right subclavian central venous port with a clean, dry, and intact dressing; there is no erythema, fluctuance, or tenderness around the site. The remainder of the examination, including thorough skin and mucosal evaluation, is unremarkable. Laboratory studies show a leukocyte count of $600/\text{mm}^3$ and an absolute neutrophil count of $120/\text{mm}^3$ . Blood cultures are drawn from the central port and a peripheral vein. Which of the following is the most appropriate next step in pharmacotherapy?

Intravenous cefepime

Intravenous cefepime and vancomycin

Intravenous ceftriaxone and azithromycin

Oral levofloxacin

Intravenous meropenem and caspofungin

Show answer & explanation

Answer: Intravenous cefepime

Answer

Intravenous cefepime

The correct answer is intravenous cefepime. This patient has febrile neutropenia (temperature

\ge 38.3^\circ\text{C}

and absolute neutrophil count

< 500/\text{mm}^3

), which is a life-threatening medical emergency. Because she is a high-risk patient (inpatient at the time of fever onset, undergoing intensive induction chemotherapy), she requires immediate empiric intravenous antibiotics. The initial regimen must have potent bactericidal activity against Pseudomonas aeruginosa and other serious Gram-negative pathogens. Monotherapy with an antipseudomonal beta-lactam (such as cefepime, meropenem, or piperacillin-tazobactam) is the standard of care. There are no specific indications to add Gram-positive or fungal coverage at this initial stage.

Step-by-Step Solution

Identify the clinical syndrome from the patient's presentation and laboratory results.

The patient has febrile neutropenia, defined as a single oral temperature of

\ge 38.3^\circ\text{C}

(

101.0^\circ\text{F}

) and an absolute neutrophil count

< 500/\text{mm}^3

Recognizing febrile neutropenia is critical as it is a medical emergency requiring prompt empiric antibiotics.

Stratify the patient's risk to determine the setting and route of therapy.

The patient is classified as high-risk because she is an inpatient undergoing induction chemotherapy with anticipated prolonged and profound neutropenia.

High-risk patients require admission (if not already hospitalized) and intravenous broad-spectrum antibiotics.

Evaluate the patient for specific indications that require targeted coverage beyond standard Gram-negative therapy.

The patient is hemodynamically stable, has a clean central venous port site, and has no signs of severe skin infection or pneumonia.

This confirms that additional Gram-positive coverage (like vancomycin) is not initially indicated.

Select the most appropriate empiric antimicrobial regimen.

Intravenous monotherapy with an antipseudomonal beta-lactam, such as cefepime, is the correct choice.

It provides necessary bactericidal activity against Pseudomonas aeruginosa and other serious pathogens without promoting unnecessary resistance.

Key Concept

High-risk febrile neutropenia is a medical emergency requiring immediate empiric intravenous monotherapy with an antipseudomonal beta-lactam (e.g., cefepime, meropenem, piperacillin-tazobactam); vancomycin is only added for specific clinical indications.

Question 392Question →

During a routine primary care visit, a $45$ -year-old man reports a $5$ -month history of worsening fatigue, generalized weakness, and decreased libido. He takes no daily medications and his past medical history is unremarkable. On physical examination, his heart rate is $54$ /min and blood pressure is $112/70$ mmHg. His skin is notably dry, and deep tendon reflexes exhibit a delayed relaxation phase. Visual field testing by confrontation reveals no deficits. Comprehensive metabolic panel is normal. Thyroid function testing reveals a free thyroxine (T4) concentration of $0.5$ ng/dL (Reference: $0.9-1.7$ ng/dL) and a thyroid-stimulating hormone (TSH) concentration of $2.4$ mIU/L (Reference: $0.4-4.0$ mIU/L). Which of the following is the most appropriate next step in the evaluation of this patient?

Measurement of 8 AM serum cortisol

Measurement of thyroid peroxidase antibodies

Initiation of levothyroxine therapy

Ultrasound of the thyroid gland

Measurement of serum reverse triiodothyronine

Show answer & explanation

Answer: Measurement of 8 AM serum cortisol

Answer

Measurement of 8 AM serum cortisol

The correct answer is to measure an 8 AM serum cortisol. This patient has clinical signs of hypothyroidism (fatigue, bradycardia, delayed deep tendon reflexes) confirmed by a low free T4 level. However, the TSH level is inappropriately normal. In a healthy pituitary gland, a low free T4 would result in significantly elevated TSH due to the loss of negative feedback. The combination of low free T4 and normal (or low) TSH strongly suggests central hypothyroidism. Whenever central hypothyroidism is suspected, it is critical to evaluate for other pituitary hormone deficiencies. Most importantly, the hypothalamic-pituitary-adrenal (HPA) axis must be assessed (usually starting with an 8 AM serum cortisol) before initiating levothyroxine. Thyroid hormone increases the hepatic clearance of cortisol; administering levothyroxine to a patient with undiagnosed concomitant central adrenal insufficiency can rapidly precipitate a life-threatening adrenal crisis.

Step-by-Step Solution

Interpret the laboratory findings.

The patient has a low free T4 with a TSH that is inappropriately within the normal range.

In primary hypothyroidism, a low T4 should stimulate the pituitary to produce high levels of TSH. A normal or low TSH indicates a central (pituitary or hypothalamic) etiology.

Identify the underlying diagnosis.

The laboratory pattern is diagnostic of central (secondary) hypothyroidism.

The pituitary gland is failing to mount an appropriate TSH response to low circulating thyroid hormone.

Determine the next best step in management.

Evaluate for other pituitary hormone deficiencies, specifically central adrenal insufficiency, by measuring an 8 AM serum cortisol.

Starting thyroid hormone replacement increases the metabolic clearance of cortisol. If a patient has undiagnosed concomitant central adrenal insufficiency, initiating levothyroxine can precipitate a fatal adrenal crisis.

Key Concept

Patients with central hypothyroidism (low free T4, inappropriately normal/low TSH) must be evaluated for central adrenal insufficiency prior to initiating levothyroxine to prevent an adrenal crisis.

Question 393Question →

A $68$ -year-old man presents to the clinic with a $3$ -month history of progressive fatigue, exertional shortness of breath, and a tingling sensation in both feet. He has a history of hypothyroidism and type $2$ diabetes mellitus. His medications include levothyroxine and metformin. Physical examination reveals pale conjunctivae, a smooth, red tongue, and decreased vibratory sensation in the lower extremities bilaterally.

Laboratory studies reveal the following:

Test	Result	Reference Range
Hemoglobin	$8.2 \text{ g/dL}$	$13.5 - 17.5 \text{ g/dL}$
Mean corpuscular volume (MCV)	$116 \text{ fL}$	$80 - 100 \text{ fL}$
Platelets	$140,000 \text{ /mm}^3$	$150,000 - 400,000 \text{ /mm}^3$
Leukocytes	$4,200 \text{ /mm}^3$	$4,500 - 11,000 \text{ /mm}^3$

A peripheral blood smear demonstrates macro-ovalocytes and multiple neutrophils with six or more nuclear lobes. Due to a misinterpretation of the preliminary results, the patient is exclusively prescribed high-dose oral folic acid.

Which of the following is the most likely outcome of this inappropriate monotherapy?

Partial or complete reversal of the megaloblastic anemia with progression of the neurologic deficits

Resolution of both the hematologic and neurologic abnormalities

Improvement of the neurologic symptoms with persistent macrocytic anemia

Development of new-onset severe, life-threatening hypokalemia

Precipitation of an acute intravascular hemolytic crisis

Show answer & explanation

Answer: Partial or complete reversal of the megaloblastic anemia with progression of the neurologic deficits

Answer

The correct answer is the option stating that there will be partial or complete reversal of the megaloblastic anemia with progression of the neurologic deficits.

The patient's presentation of fatigue, macrocytic anemia (MCV > 100 fL), hypersegmented neutrophils, and glossitis paired with neurologic deficits (decreased vibratory sensation, tingling) is the hallmark of Vitamin B12 (cobalamin) deficiency. The patient's long-term use of metformin is a known risk factor for B12 malabsorption. Vitamin B12 and folate are both required for DNA synthesis. In B12 deficiency, folate becomes trapped as 5-methyltetrahydrofolate, leading to impaired DNA synthesis and megaloblastic anemia. Administering high-dose folic acid bypasses this 'folate trap', providing the necessary substrates to resume DNA synthesis, thereby correcting the hematologic abnormalities. However, Vitamin B12 is independently required as a cofactor for the enzyme methylmalonyl-CoA mutase, which is critical for proper myelin synthesis in the nervous system. Folic acid has no effect on this pathway. Therefore, inappropriate folic acid monotherapy will correct the anemia (masking the most obvious sign of the disease) while allowing irreversible demyelination and neurologic deficits to progress unchecked.

Step-by-Step Solution

Diagnose the underlying condition based on the clinical presentation and laboratory findings.

The patient has macrocytic anemia (MCV 116 fL), hypersegmented neutrophils, glossitis, and peripheral neuropathy (decreased vibratory sensation). This classic constellation, combined with chronic metformin use, points to Vitamin B12 (cobalamin) deficiency.

Identifying the true deficiency is required to understand the consequences of the incorrect treatment.

Analyze the biochemical relationship between Vitamin B12 and folic acid in DNA synthesis.

Vitamin B12 is required to transfer a methyl group from 5-methyltetrahydrofolate (5-methyl THF) to homocysteine. Without B12, folate is trapped in the 5-methyl THF form (the 'folate trap'), halting DNA synthesis and causing megaloblastic anemia.

Understanding this pathway explains why high doses of folic acid can 'bypass' the trap and temporarily fix DNA synthesis.

Determine the impact of folic acid monotherapy on the neurologic symptoms of B12 deficiency.

Neurologic damage in B12 deficiency is due to impaired conversion of methylmalonyl-CoA to succinyl-CoA, leading to abnormal myelin accumulation. Folic acid plays no role in this pathway.

This confirms that while folate fixes the blood count, the spinal cord and peripheral nerve damage will quietly worsen.

Key Concept

Administration of high-dose folic acid to a patient with Vitamin B12 deficiency will correct the megaloblastic anemia but will mask the deficiency, allowing irreversible neurologic degeneration to progress.

Estimated Time:1m 15s

Question 394Question →

Match each patient's clinical presentation with its most likely characteristic cardiovascular pathology.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Chagas disease matches with left ventricular apical aneurysm. Ankylosing spondylitis matches with aortic root dilation. Systemic sclerosis matches with right ventricular hypertrophy. Hemochromatosis matches with dilated cardiomyopathy. Carcinoid syndrome matches with tricuspid valve thickening.

Each systemic condition presented has a highly specific predilection for certain cardiac structures due to distinct pathophysiological mechanisms, requiring integration of rheumatology, endocrinology, infectious disease, and cardiology.

Step-by-Step Solution

Identify the underlying systemic or infectious disease for each patient based on the clinical vignette.

Patient 1 has Chagas disease, Patient 2 has ankylosing spondylitis, Patient 3 has systemic sclerosis, Patient 4 has hemochromatosis, and Patient 5 has carcinoid syndrome.

Accurate diagnosis of the primary condition is required to anticipate its systemic and cardiac complications.

Determine the pathophysiological mechanism of cardiac involvement for each diagnosed condition.

T. cruzi destruction (apical aneurysm), HLA-B27 aortitis (aortic root dilation), pulmonary intimal fibrosis (cor pulmonale), myocardial iron deposition (dilated cardiomyopathy), and serotonin-mediated fibrosis (right-sided valvulopathy).

Linking the disease to its specific mechanism of cardiac injury reveals the structural pathology.

Match the specific cardiovascular pathology to the identified disease.

All items are successfully paired based on classic disease associations.

This completes the requirements of the matching question format.

Key Concept

Cardiovascular complications of systemic and infectious diseases

Estimated Time:2m 0s

Question 395Question →

Match each cardiovascular medication used in the management of arrhythmias and other cardiac conditions with its most characteristic adverse effect profile.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Amiodarone matches with pulmonary/thyroid/hepatic toxicity. Procainamide matches with drug-induced lupus. Adenosine matches with transient AV block/flushing. Sotalol matches with QT prolongation/torsades de pointes. Verapamil matches with constipation/gingival hyperplasia/negative inotropy.

Each cardiovascular medication has a unique, high-yield adverse effect profile that is heavily tested on the USMLE Step 2 CK. Amiodarone is famous for its wide-ranging tissue toxicities (lungs, liver, thyroid) due to its lipophilic nature and iodine content. Procainamide is a classic cause of drug-induced lupus. Adenosine administration is distinctly known for causing a brief period of asystole or AV block accompanied by severe flushing and chest discomfort. Sotalol carries a significant risk of QT prolongation leading to torsades de pointes. Verapamil's blockade of calcium channels commonly results in severe constipation and can depress cardiac contractility.

Step-by-Step Solution

Analyze Amiodarone

Identified as a Class III agent known for multi-organ tissue toxicity.

Recognizing the broad side effect profile (lungs, thyroid, liver) is essential for monitoring patients on chronic amiodarone therapy.

Analyze Procainamide

Matched with drug-induced lupus erythematosus.

Class IA agents (along with hydralazine and isoniazid) are the classic culprits for drug-induced lupus, confirmed by positive anti-histone antibodies.

Analyze Adenosine

Matched with transient AV block, flushing, and chest pain.

Its ultrashort half-life and mechanism of hyperpolarizing the AV node cause these brief, uncomfortable symptoms during administration for supraventricular tachycardia.

Analyze Sotalol

Matched with dose-dependent QT prolongation and torsades de pointes.

As a Class III agent, it delays repolarization (prolonged QT), which increases the risk of early afterdepolarizations and polymorphic ventricular tachycardia.

Analyze Verapamil

Matched with constipation, gingival hyperplasia, and negative inotropy.

Calcium channel blockade affects gastrointestinal smooth muscle motility and myocardial contractility, making it contraindicated in decompensated heart failure.

Key Concept

Adverse effect profiles of cardiovascular medications (antiarrhythmics and calcium channel blockers).

Question 396Question →

A $45$ -year-old hospitalized patient is being evaluated for derangements in sodium and water balance. Evaluate the following four clinical laboratory profiles. Match each laboratory profile and dynamic test result with the most likely underlying pathophysiologic diagnosis.

Click a left item, then click its matching right item

Show answer & explanation

Answer

Profile 1 maps to SIADH, Profile 2 maps to Central diabetes insipidus, Profile 3 maps to Nephrogenic diabetes insipidus, and Profile 4 maps to Primary polydipsia.

Each laboratory profile distinctly maps to a water balance disorder. SIADH and primary polydipsia present with hyponatremia and low serum osmolality, but are differentiated by urine osmolality (inappropriately high in SIADH, appropriately low in primary polydipsia). Central and nephrogenic diabetes insipidus present with hypernatremia and dilute urine, and are differentiated by their ability to concentrate urine in response to exogenous desmopressin.

Step-by-Step Solution

Evaluate the serum sodium and serum osmolality for each laboratory profile.

Profiles 1 and 4 indicate hypotonic hyponatremia (water excess); Profiles 2 and 3 indicate hypertonic hypernatremia (water deficit).

This fundamentally divides the differential diagnosis into states of water retention versus water loss.

For the hyponatremic profiles, evaluate the urine osmolality.

Profile 1 has inappropriately concentrated urine (

>100

mOsm/kg) pointing to SIADH. Profile 4 has appropriately maximally dilute urine (

<100

mOsm/kg) pointing to primary polydipsia.

To determine if the kidneys are appropriately excreting the excess free water in response to the hyponatremia.

For the hypernatremic profiles, evaluate the response to exogenous desmopressin (ADH).

Profile 2 shows a massive increase in urine osmolality, indicating central diabetes insipidus. Profile 3 shows no significant change, indicating nephrogenic diabetes insipidus.

To differentiate between central lack of ADH production and peripheral renal resistance to ADH.

Key Concept

Diagnosis of water balance disorders (diabetes insipidus, SIADH, primary polydipsia) through interpretation of serum and urine osmolality, and response to desmopressin.

Question 397Question →

An emergency medicine physician is managing a 26-year-old female patient who presents with acute respiratory distress, diffuse polyphonic expiratory wheezing, and prominent accessory muscle use. Supplemental oxygen is applied via nasal cannula. To prevent impending respiratory failure, the physician must escalate her treatment in a stepwise fashion based on her clinical response. Arrange the following therapeutic interventions in the standard sequential order of escalation for a severe asthma exacerbation, from the initial first-line step to the final intervention of last resort.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence for escalating treatment in a severe acute asthma exacerbation is: nebulized albuterol and ipratropium first, followed by systemic corticosteroids, then intravenous magnesium sulfate, and finally rapid sequence intubation for refractory failure.

Acute severe asthma exacerbations require a strict algorithmic approach to minimize the need for invasive ventilation. The universal first step is continuous or frequent inhaled bronchodilators (albuterol/ipratropium). Systemic corticosteroids must be given concurrently to halt inflammation. If the patient remains in severe distress with poor air movement, IV magnesium sulfate is added as a smooth muscle relaxant. Endotracheal intubation is delayed as long as safely possible and acts as the definitive final step if the patient tires out and develops respiratory failure.

Step-by-Step Solution

Identify the need for immediate, rapid-onset bronchodilation.

Nebulized albuterol and ipratropium are administered.

Short-acting beta-agonists (SABA) provide the fastest relief of acute bronchospasm and are the universal first step.

Address the underlying inflammatory cascade of the asthma attack.

Systemic corticosteroids are administered.

Steroids decrease airway inflammation and prevent late-phase responses but take 4-6 hours to reach peak efficacy, so they must be given early.

Reassess the patient's work of breathing and escalate medical therapy if unimproved.

Intravenous magnesium sulfate is infused.

Magnesium is a bronchodilator adjunct used specifically for severe, life-threatening exacerbations that do not respond adequately to initial treatments.

Recognize the signs of impending respiratory muscle fatigue and failure.

Rapid sequence intubation is performed.

Mechanical ventilation is the absolute last resort for asthmatic patients due to high risks of barotrauma and dynamic hyperinflation; it is only used when medical therapies fail.

Key Concept

Stepwise escalation of medical therapy in acute severe asthma exacerbation.

Question 398Question →

A 54-year-old man with a history of end-stage renal disease on hemodialysis is currently hospitalized for management of suspected endocarditis. He presented three days ago with a two-week history of fatigue, severe night sweats, and intermittent fevers. His hemodialysis is accessed via a right internal jugular tunneled catheter. Vital signs today show a temperature of $39.4^\circ\text{C}$ ( $102.9^\circ\text{F}$ ), blood pressure of $108/64\text{ mm Hg}$ , pulse of $115/\text{min}$ , and respiratory rate of $16/\text{min}$ . Cardiac auscultation reveals a new high-pitched, blowing early diastolic murmur heard best at the left sternal border. Transesophageal echocardiography reveals a $1.5\text{-cm}$ oscillating vegetation on the aortic valve with severe aortic regurgitation. At the time of admission, empiric intravenous vancomycin and cefepime were initiated. Blood cultures drawn before the first antibiotic dose are now growing *Staphylococcus aureus*. The isolate is sensitive to oxacillin, cefazolin, and vancomycin, but resistant to penicillin. Which of the following is the most appropriate next step in the pharmacologic management of this patient?

Discontinue vancomycin and cefepime, and begin intravenous cefazolin

Continue intravenous vancomycin and discontinue cefepime

Discontinue vancomycin and cefepime, and begin oral clindamycin

Continue the current regimen and add intravenous gentamicin

Discontinue vancomycin and cefepime, and begin intravenous daptomycin

Show answer & explanation

Answer: Discontinue vancomycin and cefepime, and begin intravenous cefazolin

Answer

Discontinue vancomycin and cefepime, and begin intravenous cefazolin

For methicillin-susceptible Staphylococcus aureus (MSSA) infective endocarditis, anti-staphylococcal beta-lactams (such as cefazolin, nafcillin, or oxacillin) are the treatment of choice. They have been shown to be more rapidly bactericidal and are associated with significantly lower rates of treatment failure and mortality compared to vancomycin. Therefore, the empiric regimen should be de-escalated to a targeted, narrow-spectrum beta-lactam agent once susceptibility results confirm the presence of MSSA.

Step-by-Step Solution

Identify the primary diagnosis based on clinical and diagnostic findings.

The patient has native valve infective endocarditis, complicated by severe aortic regurgitation.

Establishes the severity of the infection and dictates the need for aggressive, bactericidal intravenous therapy.

Analyze the microbiological culture and susceptibility data.

Blood cultures are growing methicillin-susceptible Staphylococcus aureus (MSSA).

Guides the transition from empiric therapy to targeted antimicrobial therapy.

Select the optimal pharmacotherapy for the identified pathogen.

Intravenous cefazolin (or another anti-staphylococcal beta-lactam like nafcillin) is selected.

Anti-staphylococcal beta-lactams are superior to vancomycin for MSSA infections, providing better clinical outcomes and faster bacterial clearance.

Key Concept

For methicillin-susceptible Staphylococcus aureus (MSSA) bacteremia and infective endocarditis, anti-staphylococcal beta-lactams (e.g., cefazolin, nafcillin) are the treatment of choice and are superior to vancomycin.

Question 399Question →

A 45-year-old woman is evaluated in the urgent care clinic for a three-day history of chills, malaise, and a cough productive of rust-colored sputum. She takes no daily medications and has no chronic medical conditions. Vital signs show a temperature of $38.4^\circ\text{C}$ ( $101.1^\circ\text{F}$ ), blood pressure of $118/76\text{ mmHg}$ , heart rate of $92/\text{min}$ , and respiratory rate of $18/\text{min}$ . Oxygen saturation is $96\%$ on room air. Auscultation of the chest reveals focal crackles and egophony at the left lung base. A point-of-care chest radiograph demonstrates a left lower lobe consolidation without pleural effusion. Which of the following is the most appropriate next step in management?

Prescribe oral amoxicillin

Prescribe oral levofloxacin

Prescribe oral amoxicillin-clavulanate and azithromycin

Administer intravenous ceftriaxone and admit to the hospital

Prescribe oral furosemide

Show answer & explanation

Answer: Prescribe oral amoxicillin

Answer

Prescribe oral amoxicillin

The correct intervention is to prescribe oral amoxicillin. This patient presents with classic signs and symptoms of community-acquired pneumonia (CAP), including fever, productive cough, focal crackles, and a lobar consolidation on chest radiography. Her stable vital signs and CURB-65 score of 0 indicate she is perfectly suited for outpatient management. According to the American Thoracic Society (ATS) and Infectious Diseases Society of America (IDSA) guidelines, empiric treatment for outpatient CAP in previously healthy adults without major comorbidities should consist of high-dose oral amoxicillin, oral doxycycline, or an oral macrolide (in areas with low pneumococcal macrolide resistance). Amoxicillin provides excellent targeted coverage against Streptococcus pneumoniae, the most common typical bacterial pathogen causing CAP.

Step-by-Step Solution

Evaluate the clinical presentation and diagnostic findings.

The patient has symptoms (fever, productive cough), physical exam findings (focal crackles, egophony), and imaging (lobar consolidation) diagnostic of community-acquired pneumonia (CAP).

Establishing the correct diagnosis prevents misapplication of therapies intended for other conditions like heart failure.

Determine the appropriate setting of care.

The patient is hemodynamically stable, has no hypoxemia, is not confused, and is under 65 years old (CURB-65 score = 0). She can be treated as an outpatient.

Severity of illness dictates whether outpatient oral therapy or inpatient intravenous therapy is required.

Identify comorbidities to guide empiric antibiotic selection.

The patient has no chronic medical conditions and no reported recent antibiotic use.

Current infectious disease guidelines stratify empiric CAP treatment based strictly on the presence or absence of comorbidities.

Select the guideline-concordant antibiotic.

High-dose oral amoxicillin (or alternatively, doxycycline or a macrolide if local resistance is low) is the correct monotherapy.

Using narrow-spectrum agents in healthy individuals ensures good antibiotic stewardship and prevents resistance.

Key Concept

Outpatient empiric management of community-acquired pneumonia in healthy adults

Question 400Question →

A 32-year-old woman is evaluated in the outpatient clinic for progressive fatigue and severe muscle weakness that has worsened over the last month. She reports that her weakness is most pronounced in her thighs and shoulders, making it difficult to climb stairs or comb her hair. She has no chronic medical conditions and does not take any prescription or over-the-counter medications. Her blood pressure is 112/74 mm Hg, pulse is 84/min, and respiratory rate is 16/min. Physical examination reveals normal muscle bulk but 3/5 motor strength in the proximal upper and lower extremities bilaterally. Sensation is intact.

Laboratory analysis reveals the following:

Serum chemistry:
$Na^+$ : 140 mEq/L
$K^+$ : 2.6 mEq/L
$Cl^-$ : 114 mEq/L
$HCO_3^-$ : 14 mEq/L
Blood urea nitrogen: 14 mg/dL
Creatinine: 0.8 mg/dL

Arterial blood gas (room air):
$pH$ : 7.29
$pCO_2$ : 29 mm Hg
$pO_2$ : 96 mm Hg

Urinalysis:
$pH$ : 6.5
Specific gravity: 1.012
Ketones: Negative
Protein: Negative

Urine electrolytes:
$Na^+$ : 45 mEq/L
$K^+$ : 15 mEq/L
$Cl^-$ : 25 mEq/L

Which of the following best describes this patient's acid-base disturbance and underlying etiology?

Normal anion gap metabolic acidosis with adequate respiratory compensation due to impaired distal tubular hydrogen secretion

Normal anion gap metabolic acidosis with concurrent respiratory acidosis due to impaired proximal tubular bicarbonate reabsorption

Normal anion gap metabolic acidosis with concurrent respiratory alkalosis due to gastrointestinal bicarbonate loss

High anion gap metabolic acidosis with adequate respiratory compensation due to accumulation of unmeasured organic acids

Normal anion gap metabolic acidosis with adequate respiratory compensation due to renal resistance to aldosterone

Show answer & explanation

Answer: Normal anion gap metabolic acidosis with adequate respiratory compensation due to impaired distal tubular hydrogen secretion

Answer

The patient has a normal anion gap metabolic acidosis with adequate respiratory compensation caused by Type 1 (distal) renal tubular acidosis, characterized by impaired distal tubular hydrogen secretion.

This patient's serum anion gap is

140 - (114 + 14) = 12 \text{ mEq/L}

, indicating a normal anion gap metabolic acidosis (NAGMA). To assess if this is a simple or mixed disorder, Winter's formula must be applied to predict the expected respiratory compensation: expected

pCO_2 = 1.5 \times [HCO_3^-] + 8 \pm 2

. For this patient,

(1.5 \times 14) + 8 = 29 \text{ mm Hg}

. Because the actual

pCO_2

is exactly 29 mm Hg, the respiratory compensation is fully adequate, and there is no concurrent respiratory disorder. To determine the etiology of the NAGMA, the urine anion gap (

U_{Na} + U_{K} - U_{Cl}

) is calculated. A positive UAG (

45 + 15 - 25 = +35 \text{ mEq/L}

) indicates impaired renal ammonium excretion, identifying Renal Tubular Acidosis (RTA) rather than gastrointestinal bicarbonate loss (which typically produces a negative UAG). The combination of hypokalemia and an inappropriately basic urine pH (6.5) in the face of systemic acidosis is diagnostic of Type 1 (distal) RTA, which occurs due to impaired distal tubular hydrogen ion secretion.

Step-by-Step Solution

Calculate the serum Anion Gap (AG) to classify the primary acid-base disorder.

AG = Na^+ - (Cl^- + HCO_3^-) = 140 - (114 + 14) = 12 \text{ mEq/L}

An AG of 12 mEq/L is normal. Combined with the low pH (7.29) and low serum bicarbonate (14 mEq/L), this confirms a Normal Anion Gap Metabolic Acidosis (NAGMA).

Calculate the expected respiratory compensation using Winter's formula.

Expected

pCO_2 = (1.5 \times [HCO_3^-]) + 8 \pm 2 = (1.5 \times 14) + 8 \pm 2 = 29 \pm 2 \text{ mm Hg}

Because the actual

pCO_2

is exactly 29 mm Hg, the patient has adequate respiratory compensation without a superimposed secondary respiratory disorder.

Calculate the Urine Anion Gap (UAG) to distinguish between renal and gastrointestinal etiologies of NAGMA.

UAG = U_{Na} + U_{K} - U_{Cl} = 45 + 15 - 25 = +35 \text{ mEq/L}

A positive UAG indicates that the kidneys are failing to properly excrete ammonium (

NH_4^+

). This points to a renal etiology (Renal Tubular Acidosis) rather than gastrointestinal bicarbonate loss (which would present with a negative UAG).

Evaluate serum potassium and urine pH to determine the specific subtype of Renal Tubular Acidosis.

The patient has severe hypokalemia (

2.6 \text{ mEq/L}

) and an inappropriately high urine

pH

(

6.5

Type 1 (distal) RTA is caused by impaired distal

H^+

secretion, leading to an inability to acidify urine (urine

pH > 5.5

) and resultant potassium wasting. Type 4 RTA would present with hyperkalemia, and Type 2 RTA typically has a urine

pH < 5.5

once systemic acidosis is established.

Key Concept

The evaluation of a normal anion gap metabolic acidosis requires calculating the expected respiratory compensation (Winter's formula) to rule out mixed disorders, followed by the urine anion gap (UAG) to differentiate renal tubular acidosis (positive UAG) from gastrointestinal losses (negative UAG).

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