Internal Medicine Practice Questions — USMLE Step 2 CK — Page 23

Question 441Question →

A 56-year-old man is brought to the emergency department by paramedics after being found unresponsive in an alley. The paramedics administered intravenous naloxone en route, which resulted in a transient increase in his respiratory rate, but he remains obtunded upon arrival. The patient is unhoused and has a history of severe alcohol use disorder. His temperature is 36.1°C (97.0°F), blood pressure is 105/65 mm Hg, pulse is 92/min, and respirations are 8/min and shallow. Pulse oximetry shows 88% on room air.

Laboratory studies show the following:
Serum sodium: 142 mEq/L
Serum potassium: 4.8 mEq/L
Serum chloride: 100 mEq/L
Serum bicarbonate: 12 mEq/L
Blood urea nitrogen: 32 mg/dL
Serum creatinine: 1.7 mg/dL

Arterial blood gas analysis on room air:
pH: 7.18
$pCO_2$ : 50 mm Hg
$pO_2$ : 60 mm Hg

Based on these findings, which of the following best describes this patient's acid-base disturbance?

High anion gap metabolic acidosis and concurrent respiratory acidosis

High anion gap metabolic acidosis with appropriate respiratory compensation

High anion gap metabolic acidosis and concurrent respiratory alkalosis

Normal anion gap metabolic acidosis and concurrent respiratory acidosis

Primary respiratory acidosis with appropriate metabolic compensation

Show answer & explanation

Answer: High anion gap metabolic acidosis and concurrent respiratory acidosis

Answer

High anion gap metabolic acidosis and concurrent respiratory acidosis

The patient's laboratory results reveal an elevated anion gap of 30 mEq/L (142 - [100 + 12]), which establishes a primary high anion gap metabolic acidosis (HAGMA), likely due to a toxic alcohol ingestion or lactic acidosis. To determine if there is a secondary acid-base disorder, Winter's formula must be applied to calculate the expected respiratory compensation: expected

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

. For this patient, the expected

pCO_2

is

(1.5 \times 12) + 8 = 26 \pm 2

mm Hg. The actual

pCO_2

of 50 mm Hg is significantly higher than the expected range (24-28 mm Hg). This indicates inadequate alveolar ventilation resulting in CO2 retention, thereby diagnosing a concurrent primary respiratory acidosis. This is clinically consistent with the patient's shallow respirations and low respiratory rate, likely due to central nervous system depression from an unknown intoxicant.

Step-by-Step Solution

1

Calculate the anion gap to identify the primary metabolic disturbance.

Anion gap =

142 - (100 + 12) = 30

mEq/L.

An anion gap > 12 mEq/L establishes the presence of a primary high anion gap metabolic acidosis (HAGMA).

2

Apply Winter's formula to determine the expected respiratory compensation for the metabolic acidosis.

Expected

pCO_2 = 1.5 \times [HCO_3^-] + 8 \pm 2 = 1.5 \times 12 + 8 \pm 2 = 26 \pm 2

mm Hg.

This establishes the target range of

pCO_2

(24 to 28 mm Hg) that would be expected if the patient's respiratory system were appropriately compensating.

3

Compare the actual measured

pCO_2

to the expected

pCO_2

to identify any secondary acid-base disorder.

The actual

pCO_2

is 50 mm Hg, which is significantly higher than the expected maximum of 28 mm Hg.

A

pCO_2

higher than the expected compensated range indicates inadequate alveolar ventilation, signifying a concurrent primary respiratory acidosis. This aligns clinically with the patient's hypoventilation due to suspected intoxication.

Key Concept

Diagnosis of mixed acid-base disorders requires calculating the anion gap to identify a primary metabolic acidosis, followed by applying Winter's formula (

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

) to determine if the respiratory compensation is appropriate, insufficient (indicating concurrent respiratory acidosis), or excessive (indicating concurrent respiratory alkalosis).

Estimated Time:1m 30s

Question 442Question →

A $28$ -year-old man comes to the clinic for a routine wellness examination. He has no significant past medical history and takes no medications. He has no symptoms of fatigue, bone pain, abdominal pain, or polyuria. Family history is notable for mild hypercalcemia in his father, who has never required medical or surgical intervention. Vital signs are within normal limits. Physical examination is unremarkable. Laboratory testing reveals the following:

Serum calcium: $11.3\ \text{mg/dL}$ (normal: $8.4\text{--}10.2\ \text{mg/dL}$ )
Serum phosphorus: $2.8\ \text{mg/dL}$ (normal: $2.7\text{--}4.5\ \text{mg/dL}$ )
Serum creatinine: $0.9\ \text{mg/dL}$
Serum intact parathyroid hormone: $58\ \text{pg/mL}$ (normal: $10\text{--}65\ \text{pg/mL}$ )
Serum 25-hydroxyvitamin D: $34\ \text{ng/mL}$ (normal: $20\text{--}50\ \text{ng/mL}$ )

Based on the information provided, which of the following is the most appropriate next step in the evaluation of this patient?

Technetium-99m sestamibi parathyroid scan

Measurement of serum parathyroid hormone-related peptide

Measurement of 24-hour urinary calcium excretion

Initiation of oral bisphosphonate therapy

Surgical exploration of the neck

Show answer & explanation

Answer: Measurement of 24-hour urinary calcium excretion

Answer

Measurement of 24-hour urinary calcium excretion

This patient presents with mild, asymptomatic hypercalcemia and an inappropriately normal intact parathyroid hormone (PTH) level. In the presence of hypercalcemia, a normal PTH level is not truly normal; it indicates a failure of the parathyroid glands to adequately suppress hormone secretion. This presentation (PTH-dependent hypercalcemia) is characteristic of primary hyperparathyroidism and familial hypocalciuric hypercalcemia (FHH). The patient's family history of untreated hypercalcemia strongly suggests FHH, an autosomal dominant disorder caused by an inactivating mutation in the calcium-sensing receptor (CaSR) in the parathyroid glands and kidneys. To distinguish between primary hyperparathyroidism and FHH, the most appropriate next step is measurement of 24-hour urinary calcium excretion. Patients with FHH typically have hypocalciuria (urine calcium-to-creatinine clearance ratio

< 0.01

), whereas those with primary hyperparathyroidism usually have normal or elevated urinary calcium.

Step-by-Step Solution

1

Analyze the patient's laboratory findings.

The patient has hypercalcemia with an inappropriately normal intact PTH level.

This establishes the diagnosis of PTH-dependent hypercalcemia, which is primarily caused by either primary hyperparathyroidism or familial hypocalciuric hypercalcemia (FHH).

2

Incorporate the clinical and family history into the diagnostic reasoning.

The patient is completely asymptomatic, and his father has a history of untreated mild hypercalcemia.

This highly suggestive family history points toward FHH, an autosomal dominant benign disorder of the calcium-sensing receptor.

3

Identify the definitive test to differentiate the remaining diagnostic possibilities.

A 24-hour urine calcium collection must be ordered.

FHH causes increased renal calcium reabsorption, resulting in a low urine calcium level (urine calcium-to-creatinine clearance ratio < 0.01). Primary hyperparathyroidism generally presents with normal or elevated urinary calcium.

Key Concept

Patients with PTH-dependent hypercalcemia (elevated or inappropriately normal PTH) must undergo 24-hour urinary calcium measurement to differentiate primary hyperparathyroidism from familial hypocalciuric hypercalcemia (FHH) before any imaging or surgical interventions are considered.

Question 443Question →

A 32-year-old woman presents to the ambulatory care clinic reporting four days of frequent, large-volume, watery stools after returning from an international trip. During the interview, she is noticeably distressed and pacing the room. She states she is terrified of acquiring a severe parasitic infection and has been breathing rapidly for the past hour. Physical examination reveals dry mucous membranes and hyperactive bowel sounds. Vital signs include a heart rate of $112/\text{min}$ , blood pressure of $105/65\ \text{mm Hg}$ , and respiratory rate of $30/\text{min}$ . Laboratory results are as follows:

Serum sodium: $138\ \text{mEq/L}$
Serum potassium: $3.4\ \text{mEq/L}$
Serum chloride: $116\ \text{mEq/L}$
Serum bicarbonate: $12\ \text{mEq/L}$

Arterial blood gas (room air):
pH: $7.38$
$pCO_2$ : $21\ \text{mm Hg}$

Which of the following best characterizes this patient's current acid-base status?

Mixed normal anion gap metabolic acidosis and primary respiratory alkalosis

Appropriately compensated normal anion gap metabolic acidosis

Mixed high anion gap metabolic acidosis and primary respiratory alkalosis

Mixed normal anion gap metabolic acidosis and primary respiratory acidosis

Primary respiratory alkalosis with appropriate metabolic compensation

Show answer & explanation

Answer: Mixed normal anion gap metabolic acidosis and primary respiratory alkalosis

Answer

Mixed normal anion gap metabolic acidosis and primary respiratory alkalosis

The correct answer accurately synthesizes all steps of the acid-base algorithm. The pH is 7.38 (primary acidosis). The low bicarbonate (12 mEq/L) identifies the acidosis as metabolic. The anion gap is 10 mEq/L, defining it as a normal anion gap (hyperchloremic) metabolic acidosis, consistent with bicarbonate loss from diarrhea. Finally, applying Winter's formula yields an expected pCO2 of 24 to 28 mm Hg. The patient's actual pCO2 of 21 mm Hg is significantly lower than this range, indicating she is hyperventilating beyond what is required for compensation. This confirms a superimposed primary respiratory alkalosis, clinically correlating with her acute distress and tachypnea.

Step-by-Step Solution

1

Determine the primary acid-base disorder by evaluating the pH.

The pH is

7.38

, which is less than

7.40

(acidemia).

The direction of the pH deviation from normal (7.40) always indicates the primary disorder. Therefore, the primary process is an acidosis.

2

Examine the serum bicarbonate and

pCO_2

to identify the source of the acidosis.

Serum bicarbonate is low (

12\ \text{mEq/L}

) and

pCO_2

is low (

21\ \text{mm Hg}

).

A primary metabolic acidosis is characterized by a low bicarbonate level. The decreased

pCO_2

indicates a respiratory response.

3

Calculate the serum anion gap.

\text{Anion Gap} = \text{Na} - (\text{Cl} + \text{HCO}_3) = 138 - (116 + 12) = 10\ \text{mEq/L}

.

Determining whether the metabolic acidosis is an anion gap or non-anion gap process narrows the differential. An AG of

10

is normal (reference range

8-12\ \text{mEq/L}

). Severe diarrhea typically causes a normal anion gap metabolic acidosis due to direct bicarbonate loss.

4

Determine if the respiratory compensation is appropriate using Winter's formula.

\text{Expected } pCO_2 = (1.5 \times 12) + 8 \pm 2 = 18 + 8 \pm 2 = 26 \pm 2

(range

24-28\ \text{mm Hg}

).

Winter's formula calculates the expected respiratory compensation for a given degree of metabolic acidosis to identify superimposed respiratory disorders.

5

Compare the actual

pCO_2

to the expected

pCO_2

.

The actual

pCO_2

(

21\ \text{mm Hg}

) is lower than the expected range (

24-28\ \text{mm Hg}

).

Because the patient is blowing off more

CO_2

than expected for simple compensation, there is a coexisting primary respiratory alkalosis, likely driven by her acute anxiety and hyperventilation.

Key Concept

Diagnosis of mixed acid-base disorders requires sequential analysis: determining the primary disorder via pH, calculating the anion gap, and verifying respiratory compensation using Winter's formula.

Question 444Question →

A 64-year-old woman is brought to the emergency department by emergency medical services due to severe, worsening shortness of breath that began 24 hours ago. The patient has a history of ischemic cardiomyopathy with a left ventricular ejection fraction of $30\%$ , hypertension, type 2 diabetes mellitus, and chronic obstructive pulmonary disease (GOLD stage III). Her temperature is $37.2^\circ\text{C}$ ( $99.0^\circ\text{F}$ ), blood pressure is $170/95\text{ mm Hg}$ , pulse is $118/\text{min}$ , and respirations are $28/\text{min}$ . Pulse oximetry shows $86\%$ on room air. She appears in moderate respiratory distress and is using accessory muscles of respiration. Lung auscultation reveals prolonged expiration, diffuse expiratory wheezing, and bilateral crackles at the lung bases. Cardiovascular examination shows distant heart sounds, a normal S1 and S2, and a prominent S3 gallop. The jugular venous pressure is estimated at $13\text{ cm H}_2\text{O}$ . There is $2+$ bilateral lower extremity pitting edema.

Laboratory studies show:

Lab Test	Result	Reference Range
pH	$7.27$	$7.35 - 7.45$
pCO $_2$	$56\text{ mm Hg}$	$35 - 45\text{ mm Hg}$
pO $_2$	$55\text{ mm Hg}$	$75 - 105\text{ mm Hg}$
HCO $_3^-$	$25\text{ mEq/L}$	$22 - 28\text{ mEq/L}$
TSH	$1.2\text{ \mu U/mL}$	$0.4 - 4.0\text{ \mu U/mL}$
Free T4	$0.6\text{ ng/dL}$	$0.9 - 1.7\text{ ng/dL}$

Chest radiograph reveals cardiomegaly, bilateral pleural effusions, and cephalization of the pulmonary vasculature. Which of the following is the most appropriate next step in management?

Intravenous furosemide and noninvasive positive pressure ventilation

Systemic corticosteroids and nebulized albuterol

Intravenous metoprolol

Intravenous sodium bicarbonate

Oral levothyroxine

Show answer & explanation

Answer: Intravenous furosemide and noninvasive positive pressure ventilation

Answer

The most appropriate next step in management is to administer intravenous furosemide and noninvasive positive pressure ventilation.

The correct answer properly targets both the underlying volume overload and the acute respiratory distress. The patient's presentation of wheezing, an S3 gallop, elevated jugular venous pressure, and radiographic evidence of pulmonary edema is diagnostic of acute decompensated heart failure (ADHF). Intravenous loop diuretics are first-line for volume removal. Concurrently, noninvasive positive pressure ventilation (NPPV) is indicated for patients with ADHF who have severe dyspnea, hypoxia, or respiratory acidosis, as it decreases the work of breathing and favorably alters cardiopulmonary hemodynamics by reducing both preload and afterload.

Step-by-Step Solution

1

Analyze the clinical presentation to differentiate between a chronic obstructive pulmonary disease exacerbation and acute decompensated heart failure.

The presence of a prominent S3 gallop, elevated jugular venous pressure, and cardiomegaly strongly points to acute decompensated heart failure rather than a primary pulmonary etiology.

Patients with a history of both heart failure and lung disease frequently present with overlapping symptoms like dyspnea and wheezing (cardiac asthma).

2

Evaluate the patient's hemodynamic and respiratory status using vital signs, physical exam, and laboratory data.

The patient is hypertensive, hypoxic, and has an acute respiratory acidosis (

pH\ 7.27

,

pCO_2\ 56\text{ mm Hg}

), indicating severe respiratory distress secondary to pulmonary edema.

Identifying the severity of the respiratory failure determines the urgency and modality of respiratory support needed.

3

Select the optimal initial therapeutic interventions for acute decompensated heart failure presenting with respiratory distress.

Intravenous loop diuretics (furosemide) and noninvasive positive pressure ventilation are selected.

Furosemide rapidly reduces volume overload, while noninvasive positive pressure ventilation decreases both right ventricular preload and left ventricular afterload, rapidly improving oxygenation without the need for immediate intubation.

Key Concept

Differentiating 'cardiac asthma' (acute decompensated heart failure) from a chronic obstructive pulmonary disease exacerbation is critical; management of acute heart failure with respiratory distress requires prompt administration of intravenous diuretics and noninvasive positive pressure ventilation.

Estimated Time:2m 0s

Question 445Question →

During an evening shift in the emergency department, a $71$ -year-old woman is evaluated for a three-day history of progressively worsening dyspnea and increased production of thick, yellowish-green sputum. She has a history of severe chronic obstructive pulmonary disease (COPD), essential hypertension, and osteoarthritis. Her current maintenance medications include a long-acting muscarinic antagonist, a long-acting beta-agonist, and as-needed albuterol.

Vital signs reveal a temperature of $37.6^\circ C$ ( $99.7^\circ F$ ), heart rate of $118/min$ , respiratory rate of $28/min$ , and blood pressure of $142/85 \text{ mm Hg}$ . Oxygen saturation is $86\%$ on room air.

On physical examination, she is in acute respiratory distress and is utilizing accessory muscles of respiration. Jugular venous pressure is visibly elevated at $10 \text{ cm H}_2\text{O}$ . Lung auscultation demonstrates prolonged expiration, diffuse expiratory wheezing, and faint bibasilar crackles. She has $2+$ pitting edema in both lower extremities.

Laboratory studies are notable for:
Leukocyte count: $12,500/\mu L$
Brain natriuretic peptide (BNP): $210 \text{ pg/mL}$ (normal $<100 \text{ pg/mL}$ )
Thyroid-stimulating hormone (TSH): $1.4 \mu\text{U/mL}$ (normal $0.5-5.0 \mu\text{U/mL}$ )
Free T4: $0.5 \text{ ng/dL}$ (normal $0.9-1.7 \text{ ng/dL}$ )

Arterial blood gas on room air:
pH: $7.27$
PaO2: $56 \text{ mm Hg}$
PaCO2: $66 \text{ mm Hg}$
HCO3: $29 \text{ mEq/L}$

A chest radiograph shows hyperinflation with flattened diaphragms and enlarged central pulmonary arteries, without focal consolidation.

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

Trial of noninvasive positive pressure ventilation

Intravenous administration of furosemide

Intravenous administration of piperacillin-tazobactam

Intravenous administration of sodium bicarbonate

Initiation of oral levothyroxine

Show answer & explanation

Answer: Trial of noninvasive positive pressure ventilation

Answer

Trial of noninvasive positive pressure ventilation

The correct answer provides ventilatory support. This patient is experiencing a severe acute exacerbation of COPD complicated by acute-on-chronic hypercapnic respiratory failure, as evidenced by her significant acidemia (pH 7.27) and elevated PaCO2 (66 mm Hg). In patients with a COPD exacerbation, a pH <= 7.35 and/or PaCO2 >= 45 mm Hg is a strong indication for a trial of noninvasive positive pressure ventilation (NPPV). NPPV improves alveolar ventilation, reduces the work of the fatigued respiratory muscles, and significantly decreases both mortality and the need for endotracheal intubation.

Step-by-Step Solution

1

Analyze the clinical presentation.

The patient has cardinal symptoms of a COPD exacerbation (dyspnea, increased sputum volume, sputum purulence).

Identifying the primary clinical syndrome guides the diagnostic and therapeutic pathway.

2

Interpret the acid-base status.

The arterial blood gas reveals an acute-on-chronic respiratory acidosis with a pH of 7.27 and PaCO2 of 66 mm Hg.

The degree of acidemia dictates whether supportive care alone is sufficient or if ventilatory assistance is required.

3

Evaluate the cardiac and endocrine findings.

Elevated JVP, lower extremity edema, and mildly elevated BNP in a COPD patient indicate cor pulmonale. The low Free T4 with normal TSH indicates euthyroid sick syndrome.

These secondary findings serve as distractors and must be correctly identified as consequences of chronic lung disease and acute severe illness rather than primary pathologies requiring immediate targeted intervention.

4

Determine the priority management step.

A trial of noninvasive positive pressure ventilation (NPPV) is selected.

In an awake, cooperative patient with a COPD exacerbation and respiratory acidosis (pH <= 7.35), NPPV is the most appropriate immediate intervention to reduce the work of breathing, reverse respiratory acidosis, and decrease the need for endotracheal intubation.

Key Concept

Noninvasive positive pressure ventilation (NPPV) is the first-line intervention for patients with acute exacerbations of COPD who develop acute-on-chronic respiratory acidosis (pH <= 7.35) or clinical signs of respiratory muscle fatigue.

Question 446Question →

A 32-year-old woman with a history of systemic lupus erythematosus presents to the clinic with new-onset bilateral lower extremity edema, worsening fatigue, and newly elevated blood pressure of 150/95 mmHg. Recent laboratory studies show worsening normocytic anemia, hypocomplementemia (decreased C3 and C4), and an increasing serum creatinine level from 0.8 mg/dL to 1.6 mg/dL. Arrange the following clinical steps in the most appropriate sequential order for the standard diagnosis and management of this patient's suspected complication.

Drag items to arrange them in the correct order

Show answer & explanation

Answer

The correct sequence begins with non-invasive confirmation using urinalysis and protein quantification, followed by a renal biopsy for histologic classification, then intensive induction immunosuppression, and finally transitioning to long-term maintenance therapy.

Lupus nephritis is a major organ-threatening complication of systemic lupus erythematosus. The standard of care demands a stepwise approach: initially confirming the presence of renal injury with non-invasive tests (urinalysis, spot protein-to-creatinine ratio), followed by an invasive renal biopsy to precisely classify the histologic severity (Classes I-VI). Because treatments for severe proliferative classes (III and IV) involve highly toxic agents, biopsy confirmation is mandatory before exposing the patient to these risks. Once confirmed, induction therapy (high-dose steroids plus an agent like mycophenolate or cyclophosphamide) is started to rapidly induce remission. After 3 to 6 months of successful induction, therapy is de-escalated to a maintenance regimen (e.g., lower-dose mycophenolate or azathioprine) to sustain remission while reducing long-term adverse effects.

Step-by-Step Solution

1

Confirm and quantify renal involvement non-invasively.

Urinalysis and urine protein-to-creatinine ratio demonstrate active urine sediment and significant proteinuria.

Before performing invasive procedures, clinical suspicion of lupus nephritis must be corroborated by non-invasive functional markers of renal injury.

2

Obtain tissue for histologic classification via renal biopsy.

Biopsy results classify the disease severity (e.g., Class IV diffuse proliferative lupus nephritis).

Because treatment regimens range from observation to highly toxic immunosuppressants, tissue diagnosis is required to guide appropriate therapy without exposing patients to unnecessary risks.

3

Administer induction immunosuppressive therapy.

Active renal inflammation is halted, and renal function begins to stabilize or improve.

Severe classes of lupus nephritis require immediate, aggressive treatment (e.g., mycophenolate mofetil or cyclophosphamide with high-dose steroids) to prevent permanent end-stage renal disease.

4

De-escalate to maintenance immunosuppressive therapy.

The patient maintains disease remission on a less toxic medication regimen.

Prolonged use of induction agents carries high risks of toxicity (e.g., infection, malignancy, infertility); thus, transitioning to a safer maintenance regimen is necessary once initial remission is achieved.

Key Concept

Diagnosis and step-wise management of lupus nephritis

Question 447Question →

A 74-year-old man residing in a skilled nursing facility is evaluated on hospital day $3$ for a complicated urinary tract infection. He was initially brought to the emergency department for altered mental status and a new fever. On admission, his temperature was $38.9^\circ\text{C}$ ( $102.0^\circ\text{F}$ ), and his long-term indwelling urinary catheter was found to be obstructed with purulent sediment. The catheter was promptly removed, and he was started empirically on intravenous vancomycin and piperacillin-tazobactam. Today, the patient is afebrile, his mental status has returned to baseline, and he is tolerating an oral diet. Blood cultures obtained on admission show no growth. A urine culture obtained via straight catheterization prior to antibiotic initiation grows $>100,000\text{ CFU/mL}$ of Escherichia coli. Susceptibility testing reveals the organism is susceptible to ceftriaxone, ciprofloxacin, and trimethoprim-sulfamethoxazole, but resistant to ampicillin. Which of the following is the most appropriate next step in management?

Discontinue vancomycin and continue intravenous piperacillin-tazobactam.

Discontinue vancomycin and piperacillin-tazobactam, and begin oral nitrofurantoin.

Discontinue vancomycin and piperacillin-tazobactam, and begin oral trimethoprim-sulfamethoxazole.

Continue both intravenous vancomycin and piperacillin-tazobactam to complete a 7-day course.

Discontinue all antimicrobial therapy as the patient is now asymptomatic following catheter removal.

Show answer & explanation

Answer: Discontinue vancomycin and piperacillin-tazobactam, and begin oral trimethoprim-sulfamethoxazole.

Answer

Discontinue vancomycin and piperacillin-tazobactam, and begin oral trimethoprim-sulfamethoxazole.

The correct action demonstrates the core principles of antimicrobial stewardship: narrowing the antibiotic spectrum based on culture data and transitioning from intravenous to oral therapy when clinically appropriate. The patient presented with a complicated, catheter-associated urinary tract infection accompanied by systemic symptoms, necessitating empiric broad-spectrum coverage (vancomycin and piperacillin-tazobactam). Now, with source control achieved (catheter removal) and clinical stability established (afebrile, tolerating oral intake), the empiric regimen must be adjusted. The culture shows E. coli susceptible to trimethoprim-sulfamethoxazole, a highly bioavailable oral agent with excellent penetration into the urinary tract and renal parenchyma. Discontinuing the broad intravenous agents and starting oral trimethoprim-sulfamethoxazole provides optimal targeted therapy.

Step-by-Step Solution

1

Evaluate the patient's clinical response to initial empiric therapy.

The patient is clinically stable, afebrile, has returned to his baseline mental status, and is tolerating oral intake.

Determines if the patient has achieved source control and is physiologically eligible for transition from intravenous to oral antibiotics.

2

Analyze the microbiological data and susceptibility results.

Urine culture confirms a single pathogen, Escherichia coli, which is susceptible to trimethoprim-sulfamethoxazole, ceftriaxone, and ciprofloxacin.

Identifies the specific pathogen to allow for de-escalation from empiric broad-spectrum therapy to targeted, narrow-spectrum therapy.

3

Select the most appropriate targeted therapy for a complicated urinary tract infection.

Oral trimethoprim-sulfamethoxazole is chosen.

It provides excellent systemic and renal tissue penetration (unlike nitrofurantoin), strictly targets the isolated pathogen without overly broad coverage, and utilizes the oral route.

Key Concept

Antibiotic de-escalation involves transitioning clinically stable patients from broad-spectrum intravenous empiric antibiotics to narrow-spectrum targeted oral therapy once culture and susceptibility data are available.

Question 448Question →

Match each patient's clinical presentation with its corresponding primary structural or hemodynamic finding.

Click a left item, then click its matching right item

Show answer & explanation

Answer

The presentations match as follows: Mitral stenosis with elevated transmitral gradient; Aortic stenosis with fixed LV outflow obstruction; HCM with dynamic LV outflow obstruction; and Tricuspid regurgitation with RV volume overload.

Each clinical vignette highlights classic physical exam findings that indicate a specific structural cardiac defect. Recognizing these defects (mitral stenosis, aortic stenosis, hypertrophic cardiomyopathy, and tricuspid regurgitation) allows for direct correlation with the underlying pathophysiologic and hemodynamic disturbances.

Step-by-Step Solution

1

Identify the valvular or structural pathology in the first presentation.

The first patient has mitral stenosis.

An opening snap followed by a low-pitched diastolic murmur at the apex is the classic physical exam finding for mitral stenosis.

2

Identify the valvular or structural pathology in the second presentation.

The second patient has aortic stenosis.

Exertional syncope, a harsh systolic murmur radiating to the carotids, and pulsus parvus et tardus are hallmark signs of severe aortic stenosis.

3

Identify the valvular or structural pathology in the third presentation.

The third patient has hypertrophic cardiomyopathy (HCM).

Syncope in a young patient accompanied by a systolic murmur that intensifies with the Valsalva maneuver (which decreases preload) indicates dynamic left ventricular outflow obstruction typical of HCM.

4

Identify the valvular or structural pathology in the fourth presentation.

The fourth patient has tricuspid regurgitation.

Injection drug use strongly predisposes to right-sided endocarditis. A holosystolic murmur at the left lower sternal border that increases with inspiration signifies tricuspid regurgitation.

5

Correlate each identified pathology with its primary hemodynamic consequence.

The pairs are logically connected based on pathophysiology.

Matching the clinical diagnosis to the underlying mechanism of disease verifies the correct pairs.

Key Concept

Correlation of physical exam findings (heart murmurs and peripheral pulse variations) with underlying structural cardiac pathologies and their specific hemodynamic alterations.

Estimated Time:1m 30s

Question 449Question →

A 68-year-old man is brought to the emergency department by his family due to confusion, a severe headache, and high fever that began 24 hours ago. He has a history of type 2 diabetes mellitus and hypertension. His temperature is 39.2°C (102.6°F), blood pressure is 112/74 mm Hg, heart rate is 115/min, and respiratory rate is 22/min. Physical examination shows marked nuchal rigidity. Neurologic examination reveals lethargy and a mild left-sided hemiparesis. The physician suspects bacterial meningitis. Arrange the following management steps in the most appropriate chronological order for this patient.

Drag items to arrange them in the correct order

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Answer

The correct sequence of management is: 1) Draw blood for cultures, 2) Administer empiric dexamethasone and broad-spectrum intravenous antibiotics, 3) Obtain a non-contrast CT scan of the head, and 4) Perform a lumbar puncture.

In cases of suspected bacterial meningitis, the general rule is to obtain a lumbar puncture (LP) before initiating empiric antibiotics to maximize the diagnostic yield of cerebrospinal fluid cultures. However, if the patient has 'red flag' indications for a head CT before the LP (such as age > 60, immunocompromise, history of CNS disease, altered mental status, new-onset seizure, or focal neurologic deficits), this standard sequence must be altered. Because obtaining a CT scan delays the LP, empiric antibiotics (and dexamethasone) must be given immediately to prevent poor outcomes from delayed treatment. Blood cultures should always be drawn before giving antibiotics, as this takes only minutes and does not significantly delay therapy. Once cultures are drawn and antibiotics are administered, the patient undergoes the head CT to rule out a mass lesion, followed by the LP if the CT is clear of mass effect.

Step-by-Step Solution

1

Identify the suspected diagnosis and the presence of indications for neuroimaging prior to lumbar puncture.

The patient has suspected bacterial meningitis with indications for a head CT before LP (age > 60, altered mental status, and focal neurologic deficit).

Recognizing these red flags is critical to prevent cerebral herniation from an LP in the setting of increased intracranial pressure.

2

Determine the first step in suspected meningitis when antibiotics are planned.

Blood cultures should be drawn immediately.

Blood cultures take only minutes to obtain and must be collected prior to antibiotic administration to maximize pathogen yield without delaying therapy.

3

Determine the timing of antimicrobial therapy.

Empiric antibiotics and dexamethasone must be administered immediately after blood cultures.

Because the required CT scan and subsequent LP will delay definitive cerebrospinal fluid (CSF) analysis, life-saving empiric therapy must not be delayed.

4

Determine the sequence of the remaining diagnostic procedures.

A head CT is performed, followed by a lumbar puncture if the CT is clear.

The CT rules out mass effect, making the LP safe to perform to obtain CSF for definitive diagnosis.

Key Concept

In patients with suspected bacterial meningitis who have indications for a head CT before lumbar puncture (e.g., age >60, immunocompromise, altered mental status, focal neurologic deficits), blood cultures should be drawn and empiric antibiotics administered immediately, prior to imaging and LP.

Question 450Question →

During physical examination of the cardiovascular system, palpation of the arterial pulse can provide critical clues regarding underlying hemodynamics. Match the following characteristic arterial pulse abnormalities with the cardiovascular condition they most classically represent.

Click a left item, then click its matching right item

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Answer

Pulsus parvus et tardus matches with Severe aortic stenosis; Pulsus paradoxus matches with Cardiac tamponade; Water-hammer pulse matches with Chronic aortic regurgitation; Pulsus alternans matches with Severe left ventricular systolic dysfunction.

Each arterial pulse abnormality has a specific hemodynamic mechanism that maps reliably to one underlying pathology: aortic stenosis causes fixed outflow obstruction (parvus et tardus); tamponade restricts filling and causes ventricular interdependence (paradoxus); aortic regurgitation causes a widened pulse pressure (water-hammer); and severe heart failure causes alternating myocardial contractility (alternans).

Step-by-Step Solution

1

Analyze the description of Pulsus parvus et tardus.

Identify it as a weak and delayed pulse upstroke.

This physical finding directly reflects a mechanical, fixed outflow tract obstruction, typical of severe aortic stenosis.

2

Analyze the description of Pulsus paradoxus.

Identify it as an exaggerated drop (>10 mm Hg) in systolic blood pressure upon inspiration.

This finding reflects exaggerated ventricular interdependence in a fixed pericardial space, the classic hallmark of cardiac tamponade.

3

Analyze the description of a Water-hammer (Corrigan) pulse.

Identify it as a bounding, rapid-rising, and rapid-falling pulse.

This relates to a markedly widened pulse pressure with rapid diastolic runoff of blood back into the ventricle, characteristic of chronic severe aortic regurgitation.

4

Analyze the description of Pulsus alternans.

Identify it as alternating strong and weak pulse amplitudes in the setting of a regular heart rate.

This indicates severely depressed left ventricular contractility, reflecting altering end-diastolic volumes or stroke volumes on a beat-to-beat basis.

Key Concept

Physical examination findings in cardiovascular disease frequently involve characteristic arterial pulse abnormalities that correlate directly with the underlying anatomical and hemodynamic derangement.

Question 451Question →

A 68-year-old man with a history of severe chronic obstructive pulmonary disease (COPD) is brought to the emergency department by his wife due to worsening shortness of breath, profound fatigue, and confusion. According to the wife, the patient has had severe, large-volume, watery diarrhea for the past four days. His temperature is $37.2^\circ\text{C}$ ( $99.0^\circ\text{F}$ ), blood pressure is $100/60$ mm Hg, pulse is $112$ /min, and respiratory rate is $24$ /min. Physical examination reveals dry mucous membranes, decreased skin turgor, and diminished breath sounds bilaterally with a prolonged expiratory phase.

Laboratory results are as follows:

Test	Result
Sodium	$136$ mEq/L
Potassium	$3.1$ mEq/L
Chloride	$112$ mEq/L
Bicarbonate	$14$ mEq/L
Blood urea nitrogen	$42$ mg/dL
Creatinine	$1.6$ mg/dL
Albumin	$4.0$ g/dL

Arterial blood gas analysis on room air:

Test	Result
pH	$7.14$
pCO $_2$	$43$ mm Hg
pO $_2$	$62$ mm Hg

Which of the following best describes this patient's primary acid-base disturbance?

Mixed normal anion-gap metabolic acidosis and respiratory acidosis

Uncompensated normal anion-gap metabolic acidosis

Mixed high anion-gap metabolic acidosis and respiratory acidosis

Normal anion-gap metabolic acidosis with appropriate respiratory compensation

Mixed high anion-gap metabolic acidosis and respiratory alkalosis

Show answer & explanation

Answer: Mixed normal anion-gap metabolic acidosis and respiratory acidosis

Answer

Mixed normal anion-gap metabolic acidosis and respiratory acidosis

The correct interpretation involves a multi-step analysis. First, the patient has severe acidemia (pH 7.14). The low bicarbonate (14 mEq/L) identifies a primary metabolic acidosis, which is clinically consistent with his history of severe diarrhea (intestinal loss of bicarbonate). Calculating the anion gap [136 - (112 + 14) = 10 mEq/L] confirms a normal anion-gap metabolic acidosis (NAGMA). To determine if respiratory compensation is appropriate, Winter's formula must be applied: Expected pCO2 = (1.5 × HCO3-) + 8 ± 2. In this patient, Expected pCO2 = (1.5 × 14) + 8 ± 2 = 29 ± 2 mm Hg. The patient's actual pCO2 is 43 mm Hg, which is significantly higher than the expected target of 27-31 mm Hg. Because the patient is retaining more CO2 than expected (due to his severe underlying COPD), he has a superimposed, concomitant respiratory acidosis.

Step-by-Step Solution

1

Evaluate the pH to determine the primary acid-base direction.

The pH is 7.14, which indicates significant acidemia.

Establishing acidemia or alkalemia is the mandatory first step in acid-base interpretation.

2

Examine the serum bicarbonate (HCO3-) and pCO2 to identify the primary disorder.

The serum bicarbonate is markedly low at 14 mEq/L, confirming a primary metabolic acidosis. This is clinically consistent with massive bicarbonate loss from severe diarrhea.

A low pH driven by a low bicarbonate defines metabolic acidosis.

3

Calculate the serum anion gap (AG).

AG = Na+ - (Cl- + HCO3-) = 136 - (112 + 14) = 136 - 126 = 10 mEq/L.

Determining the anion gap (normal 8-12 mEq/L) is required to categorize the metabolic acidosis. An AG of 10 mEq/L indicates a normal anion-gap (hyperchloremic) metabolic acidosis.

4

Apply Winter's formula to determine the expected respiratory compensation (expected pCO2).

Expected pCO2 = (1.5 × 14) + 8 ± 2 = 21 + 8 ± 2 = 29 ± 2 mm Hg (Range: 27 to 31 mm Hg).

Winter's formula determines if the lungs are adequately blowing off CO2 to compensate for the metabolic acidosis.

5

Compare the expected pCO2 to the measured pCO2.

The measured pCO2 is 43 mm Hg. Because the measured pCO2 (43) is significantly higher than the expected pCO2 (27-31), there is an additional primary respiratory acidosis.

When actual pCO2 exceeds expected pCO2 in a metabolic acidosis, a superimposed respiratory acidosis is present. The patient's severe COPD prevents adequate hyperventilation.

Key Concept

Acid-base interpretation using Winter's formula to identify mixed acid-base disorders in patients with underlying lung disease.

Question 452Question →

Match each classic clinical presentation to the most likely acute gastrointestinal diagnosis.

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Answer

The correct pairings successfully match Cullen sign to acute hemorrhagic pancreatitis, Rovsing sign to acute appendicitis, pain out of proportion to exam to acute mesenteric ischemia, Reynolds pentad to acute ascending cholangitis, and the classic obstructive triad with surgical history to mechanical small bowel obstruction.

Each classic physical examination finding or historical clue uniquely identifies a specific acute abdominal pathology. Cullen sign indicates retroperitoneal tracking of blood from severe hemorrhagic pancreatitis. Rovsing sign relies on referred peritoneal irritation typical of appendicitis. Pain out of proportion to exam is the classic descriptor for bowel ischemia before transmural infarction occurs. Reynolds pentad expands upon the biliary obstruction of cholangitis to include systemic septic shock. Finally, the obstructive triad of pain, vomiting, and obstipation is driven by physical blockage, most often from post-surgical adhesions.

Step-by-Step Solution

1

Analyze the finding of periumbilical ecchymosis in a patient with severe, radiating epigastric pain.

Identified as Cullen sign, which correlates with acute hemorrhagic pancreatitis.

Blood from retroperitoneal hemorrhage tracks along fascial planes to the umbilicus.

2

Evaluate the clinical sign where left lower quadrant palpation causes right lower quadrant pain.

Identified as Rovsing sign, which correlates with acute appendicitis.

Palpation increases pressure in the colon, referring pain to the inflamed parietal peritoneum surrounding the appendix.

3

Assess the presentation of sudden, severe pain with a benign physical exam in a patient with atrial fibrillation.

Identified as acute mesenteric ischemia.

Atrial fibrillation strongly predisposes the patient to a superior mesenteric artery embolism, causing early ischemic pain before transmural infarction and peritonitis develop.

4

Identify the combination of fever, jaundice, right upper quadrant pain, hypotension, and altered mental status.

Identified as Reynolds pentad, which correlates with acute ascending cholangitis.

This pentad reflects a severe infection of the biliary tract that has progressed to systemic shock and central nervous system dysfunction.

5

Analyze the presentation of crampy pain, intractable vomiting, obstipation, and a history of multiple laparotomies.

Identified as mechanical small bowel obstruction.

Prior abdominal surgeries frequently cause intra-abdominal adhesions, which are the most common etiology of mechanical small bowel obstruction.

Key Concept

Diagnosis of acute abdominal pathologies based on classic physical examination signs and patient history.

Question 453Question →

Paramedics bring a distressed gentleman in his late sixties to the emergency department. He reports severe, unremitting abdominal pain that began $48$ hours ago as intermittent cramps but has now become constant and sharply localized. His last bowel movement was three days ago, and he has vomited dark, foul-smelling fluid multiple times since yesterday. His surgical history is notable for a ruptured appendix requiring an open appendectomy in his twenties.

On evaluation, his temperature is $38.8^\circ\text{C}$ ( $101.8^\circ\text{F}$ ), heart rate is $122/\text{min}$ , blood pressure is $88/54\text{ mmHg}$ , and respiratory rate is $22/\text{min}$ . The abdomen is tense, visibly distended, and exquisitely tender to light palpation across all quadrants, with involuntary guarding. Auscultation reveals a silent abdomen. Laboratory analysis demonstrates a leukocyte count of $19,500/\text{mm}^3$ and a serum lactate of $4.5\text{ mmol/L}$ . Upright abdominal radiography displays multiple dilated loops of small bowel with air-fluid levels and a complete absence of gas in the rectum.

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

Nasogastric tube placement and serial abdominal examinations

Transfer to radiology for an abdominal computed tomography scan

Initiation of intravenous broad-spectrum antibiotics and close observation

Urgent surgical exploration

Administration of intravenous sodium bicarbonate

Show answer & explanation

Answer: Urgent surgical exploration

Answer

Urgent surgical exploration

The clinical presentation is highly indicative of a strangulated small bowel obstruction (SBO). The patient has a history of abdominal surgery (open appendectomy), which strongly predisposes him to adhesive disease. While uncomplicated SBO can initially be managed conservatively with nasogastric decompression and intravenous fluids, the presence of fever, tachycardia, hypotension, severe localized pain, peritoneal signs (guarding), marked leukocytosis, and lactic acidosis signifies intestinal ischemia or infarction. When these warning signs of strangulation are present, conservative management and additional imaging must be abandoned in favor of immediate operative intervention to resect necrotic bowel and prevent further clinical deterioration.

Step-by-Step Solution

1

Identify the primary clinical syndrome from the presentation and imaging.

The patient's history of prior abdominal surgery, obstipation, bilious/feculent vomiting, and radiographic evidence of dilated small bowel loops with absent rectal gas confirm a mechanical small bowel obstruction (SBO).

Establishing the baseline diagnosis is necessary before evaluating for complications.

2

Assess the patient for signs of complicated disease, such as ischemia or strangulation.

The patient exhibits fever (

38.8^\circ\text{C}

), tachycardia (

122/\text{min}

), hypotension (

88/54\text{ mmHg}

), peritonitis (involuntary guarding), marked leukocytosis (

19,500/\text{mm}^3

), and lactic acidosis (

4.5\text{ mmol/L}

).

Differentiating between simple and complicated (strangulated) SBO dictates the entire management pathway.

3

Select the most appropriate management pathway based on the presence of complications.

Because clear signs of bowel ischemia and hemodynamic instability are present, the patient must bypass conservative measures and proceed directly to the operating room.

Strangulated SBO involves compromised blood flow leading to necrosis and perforation; it requires emergent surgical exploration to resect non-viable bowel and prevent death.

Key Concept

Management of complicated (strangulated) small bowel obstruction

Question 454Question →

A 59-year-old woman suddenly collapses while walking in the hospital corridor. A rapid response team arrives immediately. The patient is completely unresponsive, apneic, and has no palpable carotid pulse. The team brings a crash cart with a manual defibrillator, and cardiac monitoring reveals coarse ventricular fibrillation. Arrange the following resuscitative interventions in the correct chronological sequence according to current Advanced Cardiac Life Support (ACLS) guidelines for this rhythm.

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Answer

The correct chronological sequence is: 1) Initiate high-quality chest compressions, 2) Deliver the initial unsynchronized biphasic shock, 3) Administer 1 mg of intravenous epinephrine, 4) Deliver the third unsynchronized biphasic shock, 5) Administer 300 mg of intravenous amiodarone.

The Advanced Cardiac Life Support (ACLS) guidelines for a shockable rhythm (ventricular fibrillation or pulseless ventricular tachycardia) dictate a highly specific, cyclical sequence of events. First, high-quality CPR must be initiated instantly upon recognition of cardiac arrest. Second, as soon as the rhythm is identified as shockable, the initial defibrillation (shock 1) is delivered, followed immediately by 2 minutes of CPR. If the rhythm remains shockable, a second shock is delivered, followed by another 2 minutes of CPR. It is during this specific CPR cycle (after the 2nd shock) that the first dose of epinephrine (1 mg) is administered. If the rhythm is still shockable at the next check, a third shock is delivered. During the CPR cycle following this third shock, antiarrhythmic therapy (such as 300 mg of amiodarone) is administered to treat refractory ventricular fibrillation. This rigid sequence optimizes myocardial perfusion while systematically escalating interventions.

Step-by-Step Solution

1

Identify the cardiac arrest rhythm and establish the foundational initial action.

High-quality chest compressions are initiated immediately.

CPR maintains vital organ perfusion and is the very first step in the chain of survival while the defibrillator is being prepared.

2

Determine the priority intervention for a shockable rhythm.

The initial unsynchronized biphasic shock is delivered.

For ventricular fibrillation, early defibrillation is the most definitive treatment and must be performed as soon as the device is attached and charged.

3

Sequence the administration of vasopressors in the algorithm.

Intravenous epinephrine is administered.

ACLS guidelines state that epinephrine is given every 3-5 minutes, starting during the CPR cycle that follows the second shock, if the rhythm remains shockable.

4

Sequence the progression to refractory interventions.

The third unsynchronized biphasic shock is delivered.

After the CPR cycle containing epinephrine, if the rhythm check still shows ventricular fibrillation, a third shock is mandated.

5

Sequence the administration of antiarrhythmics.

Intravenous amiodarone is administered.

Antiarrhythmic therapy (amiodarone or lidocaine) is reserved for truly refractory ventricular fibrillation and is given during the CPR cycle following the third shock.

Key Concept

Advanced Cardiac Life Support (ACLS) Pulseless Arrest Algorithm for Shockable Rhythms

Question 455Question →

Match each clinical presentation of chronic liver disease to the most appropriate next step in management or definitive therapy.

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Answer

Primary biliary cholangitis is treated with ursodeoxycholic acid; Primary sclerosing cholangitis strictures are managed with ERCP and dilation; Autoimmune hepatitis is treated with prednisone and azathioprine; Hemochromatosis requires therapeutic phlebotomy; Wilson disease requires D-penicillamine or trientine.

The correct matches align distinct clinical and serologic presentations of chronic hepatobiliary disorders to their specific, mechanism-directed therapies. Primary biliary cholangitis is managed with ursodeoxycholic acid to alter the bile acid pool and delay disease progression. Primary sclerosing cholangitis requires ERCP for dominant strictures to relieve obstruction. Autoimmune hepatitis necessitates immunosuppression to halt immune-mediated hepatocyte destruction. Hemochromatosis requires physical removal of excess total body iron through phlebotomy. Wilson disease requires copper chelation.

Step-by-Step Solution

1

Analyze the first vignette to identify the underlying disease mechanism.

Identified Primary Biliary Cholangitis (PBC) based on middle age, female sex, pruritus, positive AMA, and isolated elevated alkaline phosphatase.

Accurate diagnosis is required before selecting the specific pharmacologic or procedural intervention.

2

Analyze the remaining clinical vignettes for key diagnostic markers.

Identified PSC (ulcerative colitis history, MRCP showing beaded ducts), Autoimmune Hepatitis (ASMA positive, elevated IgG), Hemochromatosis (transferrin saturation > 45%, high ferritin, bronze diabetes), and Wilson disease (Kayser-Fleischer rings, low ceruloplasmin).

Each hepatobiliary pathology has a distinct serologic and demographic profile.

3

Select the definitive therapy or next best step for each identified pathology.

Matched PBC to ursodeoxycholic acid, PSC to ERCP stricture dilation, AIH to immunosuppression, Hemochromatosis to phlebotomy, and Wilson disease to copper chelation.

Therapies are highly specific to the pathophysiologic mechanism (e.g., removing excess iron, chelating copper, suppressing autoimmunity, altering bile acid composition).

Key Concept

Clinical presentation and specific therapeutic interventions for chronic hepatic and biliary diseases.

Question 456Question →

A 62-year-old man with a history of ischemic cardiomyopathy suddenly collapses while walking in the hospital corridor. A rapid response team arrives immediately. The patient is unresponsive, apneic, and has no palpable carotid pulse. High-quality chest compressions are initiated, and a defibrillator is attached. The monitor displays coarse ventricular fibrillation.

Assuming the patient remains in refractory ventricular fibrillation throughout the resuscitation, arrange the following advanced cardiac life support (ACLS) interventions in the correct chronological sequence.

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Answer

The correct chronological sequence is: deliver the initial shock, immediately resume chest compressions, perform a rhythm check after 2 minutes of CPR and deliver a second shock, administer epinephrine, and finally administer amiodarone.

According to the Adult Cardiac Arrest Algorithm, the management of pulseless ventricular fibrillation (VF) begins with immediate high-quality CPR and rapid defibrillation. Once the defibrillator is attached and VF is recognized, the very first step is to deliver an unsynchronized shock. Crucially, immediately after the shock is delivered, chest compressions must be resumed for a full 2-minute cycle without stopping to check the rhythm or pulse. After 2 minutes, a rhythm check is performed, and if VF persists, a second shock is delivered. During the CPR cycle following the second shock, epinephrine 1 mg IV is administered. If VF continues after a third shock, an antiarrhythmic such as amiodarone (300 mg IV) is administered. This strict sequence maximizes coronary and cerebral perfusion while allowing appropriate intervals for electrical and pharmacological therapy.

Step-by-Step Solution

1

Identify the shockable rhythm and deliver the first shock.

The initial shock attempts to depolarize the myocardium and terminate the ventricular fibrillation.

Early defibrillation is the most critical intervention for survival in shockable cardiac arrest.

2

Immediately resume cardiopulmonary resuscitation (CPR) starting with chest compressions.

Blood flow to the heart and brain is temporarily restored.

Prolonged pauses in compressions severely decrease survival rates. A pulse or rhythm check should never immediately follow a shock delivery.

3

Re-evaluate the rhythm after 2 minutes of CPR and deliver a second shock.

A second defibrillation attempt is made for refractory ventricular fibrillation.

ACLS guidelines mandate a rhythm check only after complete 2-minute cycles of CPR to minimize hands-off time.

4

Administer the first dose of epinephrine.

Epinephrine 1 mg is given intravenously while CPR is ongoing.

Epinephrine is administered after the second shock (during the subsequent CPR cycle) and every 3-5 minutes thereafter to improve coronary and cerebral perfusion pressure.

5

Deliver a third shock (after another 2 minutes of CPR) followed by amiodarone.

Amiodarone 300 mg is administered intravenously.

Antiarrhythmic medications are indicated for ventricular fibrillation that persists after high-quality CPR, multiple shocks, and vasopressor administration.

Key Concept

Advanced Cardiac Life Support (ACLS) management sequence for pulseless ventricular fibrillation and pulseless ventricular tachycardia.

Estimated Time:1m 30s

Question 457Question →

Match each clinical presentation or hemodynamic profile in a patient with advanced liver cirrhosis to the most appropriate systemic complication.

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Answer

The correct pairings identify hepatopulmonary syndrome by orthodeoxia, hepatorenal syndrome by volume-refractory acute kidney injury, portopulmonary hypertension by elevated pulmonary pressures with normal wedge pressure, and hepatic hydrothorax by a right-sided transudative effusion.

Each clinical presentation perfectly aligns with the established diagnostic criteria for systemic complications of cirrhosis. The key to differentiating them lies in recognizing specific defining features: orthodeoxia for hepatopulmonary syndrome, albumin-refractory kidney injury for hepatorenal syndrome, precapillary hypertension hemodynamics for portopulmonary hypertension, and a right-sided transudate for hepatic hydrothorax.

Step-by-Step Solution

1

Evaluate the pulmonary presentation involving positional hypoxemia.

Matches Hepatopulmonary syndrome.

Platypnea and orthodeoxia are the classic hallmarks of intrapulmonary vascular dilations found in hepatopulmonary syndrome, as gravity redirects blood to the dilated basilar vessels when the patient stands.

2

Assess the renal presentation of volume-unresponsive kidney injury.

Matches Hepatorenal syndrome.

The strict diagnostic criteria for hepatorenal syndrome require lack of improvement in renal function after 48 hours of holding diuretics and administering intravenous albumin, with no other identifiable cause of renal disease.

3

Analyze the right heart catheterization hemodynamics (mPAP 35 mmHg, PCWP 10 mmHg).

Matches Portopulmonary hypertension.

These findings indicate precapillary pulmonary hypertension (elevated pulmonary pressures with normal left-sided filling pressures), which in the setting of liver disease is diagnostic of portopulmonary hypertension.

4

Identify the cause of an isolated right-sided transudative pleural effusion in a cirrhotic patient.

Matches Hepatic hydrothorax.

Without primary cardiopulmonary disease, a transudative right pleural effusion in cirrhosis is driven by the transfer of ascites through small diaphragmatic defects.

Key Concept

Differentiating the major systemic complications of advanced liver cirrhosis based on specific clinical criteria and distinct pathophysiological mechanisms.

Question 458Question →

Match each characteristic arterial pulse finding on physical examination with its most likely underlying cardiovascular pathology.

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Answer

Pulsus parvus et tardus matches with Severe aortic stenosis; Pulsus paradoxus matches with Cardiac tamponade; Pulsus bisferiens matches with Hypertrophic cardiomyopathy; Pulsus alternans matches with Severe left ventricular failure; Water-hammer pulse matches with Severe aortic regurgitation.

Each arterial pulse contour directly reflects the underlying hemodynamic derangement: fixed mechanical obstruction (parvus et tardus), ventricular interdependence within a constrained space (paradoxus), dynamic outflow obstruction (bisferiens), struggling myocardial contractility (alternans), or rapid diastolic aortic runoff (water-hammer).

Step-by-Step Solution

1

Analyze 'Pulsus parvus et tardus'

Matched with Severe aortic stenosis.

The stenotic valve mechanically limits outflow, leading to a weak and late-peaking pulse.

2

Analyze 'Pulsus paradoxus'

Matched with Cardiac tamponade.

Increased right heart filling during inspiration bows the septum into the left ventricle in a fixed pericardial space, dropping left-sided stroke volume.

3

Analyze 'Pulsus bisferiens'

Matched with Hypertrophic cardiomyopathy.

A double-peaking pulse occurs due to brisk initial ejection followed by dynamic outflow tract obstruction.

4

Analyze 'Pulsus alternans'

Matched with Severe left ventricular failure.

Alternating weak and strong beats reflect the struggling myocardium's beat-to-beat variation in contractility.

5

Analyze 'Water-hammer (Corrigan) pulse'

Matched with Severe aortic regurgitation.

A bounding, rapid-rising and rapidly collapsing pulse results from wide pulse pressure and rapid diastolic runoff.

Key Concept

Correlation of abnormal arterial pulse waveforms with structural and hemodynamic cardiovascular pathologies.

Question 459Question →

Match each of the following serum laboratory profiles with the most likely underlying clinical diagnosis. (Reference ranges: Calcium $8.4-10.2\text{ mg/dL}$ , Phosphorus $2.7-4.5\text{ mg/dL}$ , Intact PTH $15-65\text{ pg/mL}$ )

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Answer

The laboratory profiles correctly map to their underlying pathophysiological states by analyzing whether the parathyroid response is the primary driver (adenoma, surgical absence) or a secondary compensatory mechanism (CKD, vitamin D deficiency, malignancy).

Each profile distinctively tests the feedback loops of the parathyroid axis. Primary abnormalities of the parathyroid gland present with PTH levels that drive the calcium levels, whereas secondary conditions present with PTH levels responding appropriately to the primary calcium or phosphate derangement, or being suppressed by a tumor-derived PTH analog.

Step-by-Step Solution

1

Evaluate the serum calcium level.

Classify the patient's state as hypercalcemic (profiles 1 and 4) or hypocalcemic (profiles 2, 3, and 5).

Establishing the initial calcium derangement directs the diagnostic algorithm toward primary versus secondary parathyroid disorders.

2

Analyze the intact PTH level in the context of the calcium level.

Identify if the PTH is mediating the calcium abnormality (e.g., high PTH causing high calcium) or appropriately responding to it (e.g., high PTH attempting to correct low calcium).

This differentiates primary hyperparathyroidism (high Ca, high PTH) from PTH-independent hypercalcemia (high Ca, low PTH), and primary hypoparathyroidism (low Ca, low PTH) from secondary hyperparathyroidism (low Ca, high PTH).

3

Assess the serum phosphorus level.

Distinguish between the different causes of secondary hyperparathyroidism.

In hypocalcemia with high PTH, a low phosphorus indicates impaired gut absorption (vitamin D deficiency), whereas a high phosphorus indicates impaired renal excretion (chronic kidney disease).

Key Concept

Interpretation of the calcium, phosphorus, and PTH axes to diagnose bone and mineral metabolism disorders.

Question 460Question →

Match the following cardiac arrhythmias and conduction disorders with their characteristic electrocardiogram (ECG) findings.

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Answer

Multifocal atrial tachycardia corresponds to multiple distinct P waves. Wolff-Parkinson-White syndrome corresponds to a short PR interval and delta wave. Mobitz type I corresponds to progressive PR lengthening before a dropped beat. Third-degree block corresponds to independent but regular P-P and R-R intervals.

Each rhythm disorder has a highly specific electrocardiographic signature based on its underlying electrophysiological mechanism, as detailed in the correct pairings.

Step-by-Step Solution

1

Identify the distinguishing ECG feature for multifocal atrial tachycardia (MAT).

MAT requires the presence of three or more distinct P-wave morphologies in the same lead.

The rhythm originates from multiple competing ectopic foci in the atria, causing variations in atrial depolarization pathways.

2

Identify the distinguishing ECG feature for Wolff-Parkinson-White (WPW) syndrome.

WPW is characterized by a short PR interval, a wide QRS complex, and a delta wave (slurred upstroke).

An accessory pathway bypasses the AV node's natural delay, causing premature ventricular depolarization.

3

Identify the distinguishing ECG feature for Mobitz type I second-degree AV block.

Mobitz type I exhibits progressive lengthening of the PR interval until a QRS complex is dropped.

This occurs due to progressive fatigue and delayed conduction through the AV node.

4

Identify the distinguishing ECG feature for third-degree (complete) AV block.

Third-degree AV block shows completely dissociated P waves and QRS complexes.

There is a complete failure of conduction, forcing the atria and ventricles to rely on separate, independent pacemakers.

Key Concept

Identifying characteristic electrocardiogram (ECG) patterns for arrhythmias and conduction blocks is essential for accurate diagnosis and management.

Internal Medicine

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