All practice questions

Question 7301Question →

Evaluate the following unique presentations of thermal and chemical injuries. Match each distinct clinical presentation with the most appropriate immediate next step in management.

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Answer

The clinical presentations match their corresponding interventions based on the primary limb- or life-threatening mechanism of each specific injury: compartment syndrome requires escharotomy, impending airway edema requires intubation, rhabdomyolysis requires high-volume hydration, and alkaline liquefactive necrosis requires immediate massive irrigation.

Each specific burn type carries a predictable and uniquely dangerous complication. Recognizing the hallmark signs (leathery circumferential burn, soot in airway, myoglobinuria, and chemical exposure) allows the clinician to preemptively intervene before irreversible tissue loss, airway obstruction, or renal failure occurs.

Step-by-Step Solution

1

Analyze the circumferential extremity burn presentation.

Identified signs of vascular compromise (diminished pulses, paresthesia) secondary to an inelastic eschar.

This confirms impending burn-induced compartment syndrome, dictating immediate surgical decompression via escharotomy.

2

Analyze the closed-space structural fire presentation.

Identified hard signs of inhalation injury (hoarseness, singed hairs) despite currently stable oxygenation.

Thermal injury to the upper airway causes progressive, unpredictable edema. Securing the airway early prevents catastrophic loss of the airway.

3

Analyze the high-voltage electrical shock presentation.

Identified severe muscle injury and myoglobinuria (reddish-brown urine).

Myoglobin is nephrotoxic. The specific management goal for rhabdomyolysis in electrical burns is a higher-than-normal urine output (75-100 mL/hr) to flush the renal tubules.

4

Analyze the alkaline chemical burn presentation.

Identified a highly corrosive tissue exposure causing liquefactive necrosis.

Unlike thermal burns, chemical burns continue to destroy tissue as long as the agent is present. Immediate, high-volume irrigation is the definitive first step.

Key Concept

Pathophysiology and targeted acute management of specialized burn injuries (circumferential thermal, inhalational, high-voltage electrical, and alkaline chemical).

Question 7302Question →

For each of the described victims of thoracic injury, select the most critical diagnostic or therapeutic intervention to optimize their survival or establish a definitive diagnosis.

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Answer

The clinical presentations map to their respective optimal interventions based on hemodynamic status and specific injury patterns: rapid deceleration with widened mediastinum requires CT angiography; penetrating chest trauma with witnessed arrest requires emergency department thoracotomy; penetrating chest trauma in severe shock with confirmed tamponade requires urgent operative sternotomy; and a continuous air leak despite chest tube placement requires bronchoscopy.

Each matching pair accurately applies Advanced Trauma Life Support (ATLS) algorithms for thoracic trauma. Hemodynamically stable patients with signs of blunt aortic injury need CT angiography. Witnessed arrest in penetrating chest trauma is the classic indication for an ED resuscitative thoracotomy. Unstable patients with tamponade who still have a pulse need to bypass ED thoracotomy for controlled exploration in the operating room. Tracheobronchial tears, marked by persistent air leaks, are definitively diagnosed via bronchoscopy.

Step-by-Step Solution

1

Analyze hemodynamic stability and arrest status.

Identified that the blunt trauma patient and the patient with the air leak are stable; the stab wound patient is in severe shock; the gunshot wound patient has suffered witnessed cardiac arrest.

Hemodynamic status dictates whether the patient can undergo advanced imaging (stable) or requires immediate operative/resuscitative intervention (unstable/arrest).

2

Differentiate penetrating thoracic trauma management based on pulse status.

Determined that witnessed arrest mandates emergency department resuscitative thoracotomy, whereas presence of a pulse despite profound hypotension mandates immediate transfer to the operating room.

Emergency department thoracotomy carries high morbidity and is strictly reserved for those in extremis (arrest), as controlled operative exploration yields better outcomes for those who still have a pulse.

3

Correlate specific blunt thoracic findings with diagnostic modalities.

Matched widened mediastinum with CT angiography to rule out blunt aortic injury, and massive continuous air leak with bronchoscopy to rule out tracheobronchial tearing.

Specific radiographic and clinical signs of blunt chest trauma dictate targeted definitive diagnostics to prevent catastrophic complications.

Key Concept

Advanced management algorithms for severe blunt and penetrating thoracic trauma, specifically distinguishing indications for emergency department thoracotomy versus operative intervention.

Question 7303Question →

Match each patient's clinical presentation of an acute abdomen with the most appropriate next step in diagnosis or management.

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Answer

The patient with atrial fibrillation and pain out of proportion matches with CT angiography. The patient with Reynold's pentad matches with ERCP. The patient with diffuse peritonitis matches with emergent exploratory laparotomy. The patient with uncomplicated small bowel obstruction matches with nasogastric tube decompression.

The correct matches align classic acute abdominal syndromes with their gold-standard initial management steps. Mesenteric ischemia requires CT angiography to evaluate the mesenteric vessels. Severe cholangitis with shock requires emergent biliary decompression via ERCP. A rigid abdomen with peritonitis requires immediate surgical exploration. An uncomplicated small bowel obstruction requires conservative management with NGT decompression and IV fluids.

Step-by-Step Solution

1

Analyze the first patient's presentation.

The combination of atrial fibrillation and severe pain out of proportion to a benign exam suggests acute mesenteric ischemia.

Atrial fibrillation predisposes patients to arterial emboli, and the lack of peritoneal signs early in the disease process is a hallmark of mesenteric ischemia.

2

Analyze the second patient's presentation.

The constellation of fever, right upper quadrant pain, jaundice, hypotension, and confusion diagnoses severe acute ascending cholangitis.

This is a life-threatening biliary infection that rapidly progresses to sepsis if not decompressed.

3

Analyze the third patient's presentation.

Diffuse rigidity, involuntary guarding, and rebound tenderness indicate a surgical abdomen with generalized peritonitis.

Peritonitis from a presumed perforated viscus is a surgical emergency.

4

Analyze the fourth patient's presentation.

Prior surgery, colicky pain, bilious vomiting, and distension without peritonitis suggest an uncomplicated small bowel obstruction (SBO).

Postoperative adhesions are the most common cause of SBO, and the absence of peritonitis indicates it is uncomplicated.

5

Determine the next appropriate step for each condition based on standard surgical guidelines.

Mesenteric ischemia requires CT angiography; severe cholangitis requires ERCP; generalized peritonitis requires exploratory laparotomy; uncomplicated SBO requires NGT decompression.

These steps represent the gold-standard initial triage and management for these specific surgical and gastrointestinal emergencies.

Key Concept

Triage and initial management of acute surgical abdomen presentations.

Question 7304Question →

A clinician is evaluating four non-diabetic adult patients who presented with recurrent episodes of neuroglycopenia. A 72-hour fasting test was performed for each patient. Match each patient's laboratory profile obtained during the symptomatic hypoglycemic episode (glucose $<55\text{ mg/dL}$ ) to the most likely underlying etiology.

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Answer

Profile 1 matches Insulinoma; Profile 2 matches Exogenous insulin; Profile 3 matches Secretagogue ingestion; Profile 4 matches Non-islet cell tumor hypoglycemia.

Each patient's hypoglycemia etiology is systematically determined by evaluating the presence of endogenous insulin production (C-peptide), precursor processing (proinsulin), and exogenous secretagogues.

Step-by-Step Solution

1

Evaluate serum insulin levels during the hypoglycemic episode.

Profiles 1, 2, and 3 show high insulin (insulin-mediated). Profile 4 shows low insulin (non-insulin-mediated).

This differentiates hyperinsulinemic states from causes like severe liver failure, adrenal insufficiency, or NICTH where insulin is appropriately suppressed.

2

Analyze C-peptide levels in the hyperinsulinemic profiles.

Profile 1 and 3 have high C-peptide. Profile 2 has low C-peptide.

C-peptide is co-secreted with endogenous insulin. High insulin with low C-peptide proves the insulin came from an exogenous source.

3

Check the secretagogue screen and proinsulin levels for profiles with high C-peptide.

Profile 1 has a negative screen and high proinsulin. Profile 3 has a positive screen.

This step distinguishes between autonomous tumoral secretion of insulin (insulinoma) and pharmacologically stimulated endogenous secretion (sulfonylureas/meglitinides).

Key Concept

Diagnostic evaluation of fasting hypoglycemia using the insulin, C-peptide, and oral hypoglycemic agent screen axis.

Question 7305Question →

Emergency medical services bring a $32$ -year-old gravid patient (estimated $32$ weeks gestation) to the trauma bay following a high-speed motor vehicle collision. Paramedics report she was a restrained passenger wearing a lap belt without a shoulder strap. Upon arrival, the patient is immobilized on a backboard with a left lateral tilt. She is pale, diaphoretic, and confused. Vital signs are temperature $36.5^\circ\text{C}$ ( $97.7^\circ\text{F}$ ), pulse $138/\text{min}$ , respirations $28/\text{min}$ , and blood pressure $78/42\text{ mm Hg}$ . Physical examination reveals a protuberant abdomen that is rigid, with diffuse rebound tenderness and a transverse ecchymosis across the lower abdomen. Fetal heart rate monitoring demonstrates a baseline of $105/\text{min}$ with absent variability and recurrent late decelerations. Despite the rapid intravenous infusion of $2\text{ L}$ of warmed crystalloids and $2\text{ units}$ of uncrossmatched type O-negative blood, her blood pressure remains $82/45\text{ mm Hg}$ . A bedside focused assessment with sonography for trauma (FAST) shows a large volume of anechoic fluid in the hepatorenal and splenorenal recesses. Which of the following is the most appropriate next step in management?

Urgent exploratory laparotomy

Multiphase computed tomography imaging of the torso

Bedside perimortem cesarean delivery

Administration of intravenous tocolytics

Observation with continuous electronic fetal monitoring

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Answer: Urgent exploratory laparotomy

Answer

Urgent exploratory laparotomy

The correct intervention is urgent exploratory laparotomy. This patient is presenting with hemorrhagic shock secondary to blunt abdominal trauma, as evidenced by persistent hypotension despite aggressive fluid and blood product resuscitation. The bedside FAST examination is positive, indicating massive intraperitoneal hemorrhage. In any trauma patient, hemodynamic instability coupled with a positive FAST dictates immediate surgical source control. Although this patient is pregnant and the fetus is exhibiting signs of distress (recurrent late decelerations, absent variability), maternal survival is the absolute priority. The most effective way to resuscitate the fetus is to rapidly stabilize the mother by controlling the hemorrhage via laparotomy. A concurrent cesarean delivery may be performed in the operating room once maternal hemorrhage is addressed, but transferring the patient for an exploratory laparotomy is the critical next step.

Step-by-Step Solution

1

Identify the patient's hemodynamic status and trauma mechanism.

The patient is in severe hemorrhagic shock (blood pressure

82/45\text{ mm Hg}

, pulse

138/\text{min}

) following blunt abdominal trauma (seatbelt injury), unresponsive to initial fluid and blood resuscitation.

Determining hemodynamic stability is the primary decision point in the Advanced Trauma Life Support (ATLS) algorithm.

2

Interpret the diagnostic imaging.

The FAST examination reveals free anechoic fluid in the abdomen.

A positive FAST in the setting of blunt trauma confirms massive intraperitoneal hemorrhage as the source of shock.

3

Integrate the obstetric findings with maternal trauma priorities.

Although there is fetal distress (bradycardia, late decelerations), maternal stabilization via laparotomy takes absolute precedence.

Fetal survival is entirely dependent on maternal perfusion. The most effective fetal resuscitation is aggressive maternal resuscitation and surgical hemorrhage control.

Key Concept

Hemodynamically unstable trauma patients with a positive FAST examination require immediate exploratory laparotomy, and maternal stabilization always takes precedence over fetal interventions in gravid trauma patients.

Estimated Time:1m 30s

Question 7306Question →

A 68-year-old man is brought to the emergency department for worsening shortness of breath, increased sputum production, and confusion over the past 24 hours. He has very severe chronic obstructive pulmonary disease (COPD) and uses home oxygen therapy. The patient's wife reports that for the past 3 days, he has also had multiple episodes of large-volume, watery diarrhea.

Vital signs are temperature 37.6°C (99.7°F), blood pressure 110/70 mm Hg, pulse 115/min, and respirations 26/min. Physical examination shows a barrel chest, diffuse bilateral wheezing, and a prolonged expiratory phase. The mucous membranes are dry.

Laboratory results from today are as follows:

Serum chemistries:

Test	Result
Sodium	135 mEq/L
Potassium	3.5 mEq/L
Chloride	102 mEq/L
Bicarbonate	23 mEq/L
Blood urea nitrogen	28 mg/dL
Creatinine	1.2 mg/dL

Arterial blood gas:

Test	Result
pH	7.17
PaCO2	66 mm Hg
PaO2	50 mm Hg
HCO3-	23 mEq/L

A review of the patient's electronic medical record reveals an arterial blood gas obtained during a routine clinic visit 2 months ago when he was feeling well:

Baseline Arterial blood gas:

Test	Result
pH	7.36
PaCO2	56 mm Hg
PaO2	62 mm Hg
HCO3-	31 mEq/L

Which of the following combinations of acid-base disorders best describes this patient's current condition?

Acute-on-chronic respiratory acidosis and normal anion gap metabolic acidosis

Acute-on-chronic respiratory acidosis and high anion gap metabolic acidosis

Acute respiratory acidosis and normal anion gap metabolic acidosis

Chronic respiratory acidosis and normal anion gap metabolic acidosis

Uncompensated acute respiratory acidosis

Show answer & explanation

Answer: Acute-on-chronic respiratory acidosis and normal anion gap metabolic acidosis

Answer

Acute-on-chronic respiratory acidosis and normal anion gap metabolic acidosis

The correct answer is acute-on-chronic respiratory acidosis and normal anion gap metabolic acidosis. The patient's baseline ABG shows a compensated chronic respiratory acidosis (PaCO2

56 \text{ mm Hg}

, HCO3-

31 \text{ mEq/L}

). Today, his PaCO2 has acutely increased to

66 \text{ mm Hg}

(an acute increase of

10 \text{ mm Hg}

). For an acute rise in PaCO2, the HCO3- should increase by

1 \text{ mEq/L}

per

10 \text{ mm Hg}

rise in PaCO2. Therefore, his expected HCO3- is

32 \text{ mEq/L}

(

31 + 1

). His actual HCO3- is

23 \text{ mEq/L}

, which is significantly lower than expected, indicating a concurrent metabolic acidosis. The anion gap is calculated as

135 - (102 + 23) = 10 \text{ mEq/L}

, which is normal. This normal anion gap metabolic acidosis is clinically supported by his 3-day history of severe diarrhea, which causes profound gastrointestinal bicarbonate loss.

Step-by-Step Solution

1

Analyze the baseline arterial blood gas.

The baseline ABG shows a PaCO2 of 56 mm Hg and HCO3- of 31 mEq/L, consistent with a compensated chronic respiratory acidosis.

Establishing the patient's baseline is necessary to correctly interpret the current acute changes in patients with severe COPD.

2

Evaluate the current PaCO2 and calculate the expected compensation.

The PaCO2 has acutely increased by 10 mm Hg (from 56 to 66 mm Hg). The expected acute increase in HCO3- is 1 mEq/L, making the new expected HCO3- 32 mEq/L (31 + 1).

In acute respiratory acidosis, the HCO3- increases by 1 mEq/L for every 10 mm Hg increase in PaCO2.

3

Compare actual HCO3- to expected HCO3-.

The actual HCO3- is 23 mEq/L, which is significantly lower than the expected 32 mEq/L. This indicates a superimposed metabolic acidosis.

A lower-than-expected bicarbonate level in the setting of respiratory acidosis confirms a concurrent metabolic acidosis.

4

Calculate the anion gap.

Anion Gap = Na+ - (Cl- + HCO3-) = 135 - (102 + 23) = 10 mEq/L. This is within the normal range.

The anion gap differentiates between a normal anion gap and a high anion gap metabolic acidosis. The normal gap points to GI bicarbonate loss from diarrhea.

Key Concept

Patients with chronic respiratory acidosis who develop an acute exacerbation require step-wise acid-base analysis utilizing their baseline ABG values to accurately calculate expected compensation and identify superimposed metabolic disorders.

Estimated Time:2m 0s

Question 7307Question →

Match each patient's acquired acid-base and electrolyte derangement profile with the pharmacological agent most likely responsible for these findings.

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Answer

The correct answer links the hypocalciuric alkalosis to thiazide diuretics, the hyperchloremic acidosis with alkaline urine to carbonic anhydrase inhibitors, the hypercalciuric alkalosis to loop diuretics, and the hyperkalemic acidosis to aldosterone antagonists.

Each pharmacological agent acts on a specific segment of the nephron, creating a unique signature of electrolyte and acid-base changes based on the localized transport mechanisms disrupted.

Step-by-Step Solution

1

Analyze the primary acid-base disturbance described in each presentation.

Two profiles exhibit metabolic alkalosis (patients 1 and 3), and two exhibit a normal anion gap metabolic acidosis (patients 2 and 4).

Categorizing the primary acid-base derangement immediately narrows down the physiological mechanism of action.

2

Differentiate the causes of metabolic alkalosis based on the urinary calcium handling.

Patient 1 presents with hypocalciuria (characteristic of thiazides), while Patient 3 presents with hypercalciuria (characteristic of loop diuretics).

Thiazides and loop diuretics both cause hypokalemic contraction alkalosis, but they have profoundly opposite effects on renal calcium handling.

3

Differentiate the causes of metabolic acidosis based on potassium levels and urine pH.

Patient 2 shows an alkaline urine pH due to bicarbonate wasting, identifying a carbonic anhydrase inhibitor. Patient 4 shows hyperkalemia, identifying an aldosterone antagonist.

Acetazolamide causes a proximal RTA-like picture with hypokalemia, whereas spironolactone causes a Type 4 RTA-like picture defined by hyperkalemia.

Key Concept

Diuretic-induced acid-base and electrolyte derangements can be precisely distinguished by their unique downstream effects on serum potassium, acid-base balance, and urinary calcium handling.

Estimated Time:1m 30s

Question 7308Question →

An occupational health physician refers a 41-year-old male to an internist after discovering a resting heart rate of $112\text{/min}$ during an annual workplace screening. The patient reports experiencing intermittent palpitations, profound heat intolerance, and a 5-kg (11-lb) weight loss over the past three months despite a significantly increased appetite. He has no significant past medical history and takes no medications. His blood pressure is $150/85\text{ mmHg}$ . Physical examination demonstrates warm and moist skin, a fine resting tremor in both hands, and a diffusely enlarged, non-tender thyroid gland. No proptosis or periorbital edema is observed.

Laboratory studies yield the following results:

Laboratory Test	Result	Reference Range
Thyroid-stimulating hormone (TSH)	$6.8\text{ }\mu\text{U/mL}$	$0.4 - 4.0\text{ }\mu\text{U/mL}$
Free thyroxine (T4)	$3.2\text{ ng/dL}$	$0.9 - 1.7\text{ ng/dL}$
Free triiodothyronine (T3)	$7.1\text{ pg/mL}$	$2.0 - 4.4\text{ pg/mL}$

Which of the following is the most appropriate next step in diagnosing the underlying cause of this patient's condition?

Magnetic resonance imaging of the brain

Radioactive iodine uptake scan

Measurement of thyroid-stimulating immunoglobulins

Measurement of serum thyroglobulin levels

Ultrasonography of the thyroid gland

Show answer & explanation

Answer: Magnetic resonance imaging of the brain

Answer

Magnetic resonance imaging of the brain

This patient presents with classic clinical features of thyrotoxicosis, confirmed by elevated serum free T4 and free T3 levels. In primary hyperthyroidism (such as Graves disease or toxic nodular goiter), the elevated circulating thyroid hormones exert negative feedback on the pituitary gland, leading to a profoundly suppressed TSH level. However, this patient's TSH is inappropriately elevated. The combination of high thyroid hormone levels and an elevated or normal TSH indicates a central (secondary) cause of hyperthyroidism, which is most commonly due to a TSH-secreting pituitary adenoma. The most appropriate next diagnostic step is a magnetic resonance imaging (MRI) scan of the brain to visualize the expected pituitary macroadenoma.

Step-by-Step Solution

1

Analyze the patient's symptoms and vital signs.

The patient exhibits classic signs of thyrotoxicosis, including resting tachycardia, heat intolerance, weight loss, and a fine tremor.

To establish the primary clinical syndrome before interpreting laboratory values.

2

Evaluate the provided laboratory values.

Free T4 and Free T3 are elevated, confirming thyrotoxicosis. However, the TSH is also inappropriately elevated rather than suppressed.

To determine whether the hyperthyroidism is primary (thyroid origin) or secondary (central origin).

3

Interpret the combination of elevated thyroid hormones and elevated TSH.

This pattern indicates secondary (central) hyperthyroidism, as a normal pituitary gland would completely suppress TSH production in the presence of high circulating T4 and T3.

To identify the pathophysiologic mechanism of the disease.

4

Determine the next best step in diagnostic management based on the central etiology.

Imaging of the brain is indicated to visualize a suspected TSH-secreting pituitary adenoma.

Definitive diagnosis and subsequent surgical planning for a pituitary tumor require direct visualization via MRI.

Key Concept

Secondary (central) hyperthyroidism is characterized by elevated circulating thyroid hormones (Free T4 and T3) alongside an inappropriately normal or elevated TSH. The most appropriate next step in evaluation is a pituitary MRI to identify a TSH-secreting pituitary adenoma.

Question 7309Question →

A 22-year-old man with a history of type 1 diabetes mellitus is brought to the emergency department due to progressive lethargy, nausea, vomiting, and diffuse abdominal pain over the past 24 hours. He reports having a severe sore throat and fever for the last three days. His temperature is 37.5°C (99.5°F), blood pressure is 92/58 mm Hg, pulse is 128/min, and respirations are 28/min and deep. Physical examination reveals dry mucous membranes, delayed capillary refill, and a fruity breath odor. Laboratory evaluation reveals:

Laboratory Test	Result
Serum glucose	580 mg/dL
Serum sodium	132 mEq/L
Serum potassium	3.1 mEq/L
Serum chloride	98 mEq/L
Serum bicarbonate	10 mEq/L
Blood urea nitrogen	35 mg/dL
Serum creatinine	1.6 mg/dL
Arterial pH	7.15
Urinalysis	Large ketones, large glucose

Arrange the following management steps in the most appropriate chronological sequence for this patient.

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Answer

The correct sequence is: Intravenous 0.9% sodium chloride bolus → Intravenous potassium chloride → Continuous intravenous regular insulin infusion → Add 5% dextrose to intravenous fluids → Subcutaneous long-acting insulin.

The correct sequence prioritizes immediate life-saving interventions while preventing iatrogenic complications. Intravenous fluids (0.9% NaCl) are universally the first step in DKA to restore volume and renal perfusion. Next, because the patient's potassium is critically low (< 3.3 mEq/L), potassium chloride must be given before insulin to prevent life-threatening hypokalemia. Once potassium is confirmed to be ≥ 3.3 mEq/L, an intravenous insulin infusion is started to halt ketogenesis. As glucose levels fall below 250 mg/dL, dextrose is added to the fluids to prevent hypoglycemia while allowing continued insulin administration to close the anion gap. Finally, once the anion gap resolves and the patient can eat, they are transitioned to subcutaneous insulin.

Step-by-Step Solution

1

Assess volume status and initiate fluid resuscitation.

Intravenous 0.9% normal saline is given immediately.

The patient is hypotensive, tachycardic, and severely dehydrated due to osmotic diuresis; volume expansion is always the first priority.

2

Evaluate initial serum potassium level before administering insulin.

Intravenous potassium chloride is administered next.

The patient's potassium is 3.1 mEq/L (below the critical 3.3 mEq/L threshold). Insulin causes an intracellular shift of potassium, so giving insulin now would cause life-threatening hypokalemia.

3

Initiate insulin therapy once potassium is safe.

Continuous intravenous regular insulin infusion is started.

Insulin is required to stop ketogenesis and close the anion gap. It is safe to start only after potassium is ≥ 3.3 mEq/L.

4

Monitor glucose and adjust intravenous fluids.

Dextrose 5% is added to the intravenous fluids.

When serum glucose reaches 200-250 mg/dL, dextrose must be added to prevent hypoglycemia while the insulin infusion continues to clear ketones.

5

Transition to maintenance diabetes therapy.

Subcutaneous long-acting insulin is administered.

This is done when the anion gap is closed (usually ≤ 12 mEq/L) and the patient can eat, allowing for the eventual discontinuation of the IV insulin drip (1-2 hours later).

Key Concept

In the management of diabetic ketoacidosis, if the initial serum potassium is < 3.3 mEq/L, potassium repletion must precede insulin therapy to prevent severe, potentially fatal insulin-induced hypokalemia.

Question 7310Question →

Emergency medical services bring a 72-year-old woman to the hospital after her daughter found her profoundly lethargic at home. According to the daughter, the patient has had severe, watery, non-bloody diarrhea for the past five days. Her past medical history is significant for severe chronic obstructive pulmonary disease requiring home oxygen therapy, hypertension, and osteoarthritis. Upon arrival, the patient is difficult to arouse.

Temperature is $37.2^\circ\text{C}$ ( $99.0^\circ\text{F}$ ), blood pressure is $88/54$ mmHg, pulse is $114$ /min, and respiratory rate is $26$ /min. Physical examination reveals dry mucous membranes, delayed capillary refill, and decreased breath sounds bilaterally with a prolonged expiratory phase.

Arterial blood gas (room air) and serum chemistries are obtained:

Laboratory Parameter	Result
Arterial pH	$7.21$
$\text{PaCO}_2$	$42$ mmHg
$\text{PaO}_2$	$56$ mmHg
Sodium	$139$ mEq/L
Potassium	$3.1$ mEq/L
Chloride	$114$ mEq/L
Bicarbonate	$15$ mEq/L
Blood urea nitrogen (BUN)	$48$ mg/dL
Creatinine	$2.1$ mg/dL

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

Mixed non-anion gap metabolic acidosis and respiratory acidosis

Mixed high anion gap metabolic acidosis and respiratory acidosis

Non-anion gap metabolic acidosis with appropriate respiratory compensation

High anion gap metabolic acidosis with appropriate respiratory compensation

Mixed non-anion gap metabolic acidosis and respiratory alkalosis

Show answer & explanation

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

Answer

Mixed non-anion gap metabolic acidosis and respiratory acidosis

The correct answer is a mixed non-anion gap metabolic acidosis and respiratory acidosis. The first step in evaluating this patient's acid-base status is identifying the primary disorder: the

pH

is

7.21

(acidemia) and the serum bicarbonate is

15

mEq/L (decreased), signifying a primary metabolic acidosis. Next, the anion gap must be calculated:

\text{Na}^+ - (\text{Cl}^- + \text{HCO}_3^-) = 139 - (114 + 15) = 10

mEq/L. Because this falls within the normal physiologic range (

8-12

mEq/L), the patient has a normal anion gap (hyperchloremic) metabolic acidosis, which directly corresponds to her history of profound watery diarrhea causing massive gastrointestinal bicarbonate loss. The final step is assessing the adequacy of respiratory compensation using Winter's formula: Expected

\text{PaCO}_2 = (1.5 \times 15) + 8 \pm 2 = 30.5 \pm 2

mmHg. For appropriate respiratory compensation, her

\text{PaCO}_2

should fall between

28.5

and

32.5

mmHg. However, her measured

\text{PaCO}_2

is

42

mmHg. Because her measured

\text{PaCO}_2

is substantially higher than expected, she is retaining

\text{CO}_2

, representing a superimposed, concurrent primary respiratory acidosis. This occurs because her severe underlying chronic obstructive pulmonary disease and lethargy prevent her from achieving the necessary compensatory hyperventilation.

Step-by-Step Solution

1

Analyze the primary acid-base disorder by looking at pH and bicarbonate.

The arterial pH is

7.21

(acidemia) and serum bicarbonate (

\text{HCO}_3^-

) is

15

mEq/L (low). This indicates a primary metabolic acidosis.

Establishing the direction of the primary disorder dictates which compensatory formula must be applied.

2

Calculate the anion gap (AG) to determine the etiology of the metabolic acidosis.

AG = \text{Na}^+ - (\text{Cl}^- + \text{HCO}_3^-) = 139 - (114 + 15) = 139 - 129 = 10

mEq/L.

A normal AG (

8-12

mEq/L) confirms a non-anion gap metabolic acidosis, which in this patient is due to profound gastrointestinal bicarbonate loss from diarrhea.

3

Determine expected respiratory compensation using Winter's formula.

Expected

\text{PaCO}_2 = (1.5 \times \text{HCO}_3^-) + 8 \pm 2

. Here,

(1.5 \times 15) + 8 = 22.5 + 8 = 30.5 \pm 2

(range

28.5

to

32.5

mmHg).

Winter's formula determines the physiologic

\text{CO}_2

elimination expected in response to a specific degree of metabolic acidosis.

4

Compare the measured

\text{PaCO}_2

to the expected

\text{PaCO}_2

.

The measured

\text{PaCO}_2

is

42

mmHg, which is significantly higher than the maximum expected value of

32.5

mmHg.

An inappropriately elevated

\text{PaCO}_2

indicates a concurrent primary respiratory acidosis, secondary to hypoventilation from her underlying chronic obstructive pulmonary disease and severe fatigue.

Key Concept

Identifying mixed acid-base disorders using the anion gap and Winter's formula

Question 7311Question →

Match each Hepatitis B virus (HBV) serologic profile to its most accurate clinical interpretation.

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Answer

Profile 1 matches Acute Hepatitis B; Profile 2 matches Resolved past infection; Profile 3 matches Vaccine-induced immunity; Profile 4 matches Chronic Hepatitis B.

Hepatitis B serology requires sequential interpretation. HBsAg determines active versus absent infection. Core antibodies (Anti-HBc IgM vs IgG) distinguish acute from chronic/past exposure. Surface antibodies (Anti-HBs) determine immunity. HBeAg correlates with infectivity.

Step-by-Step Solution

1

Evaluate the presence of HBsAg.

Profiles 1 and 4 have positive HBsAg, indicating active infection (acute or chronic). Profiles 2 and 3 have negative HBsAg, indicating absence of active infection.

HBsAg is the primary marker of active HBV infection.

2

Differentiate the active infections (Profiles 1 and 4) using Anti-HBc.

Profile 1 has Anti-HBc IgM (acute). Profile 4 has Anti-HBc IgG (chronic).

IgM antibodies against the core antigen indicate recent, acute exposure, whereas IgG indicates past or ongoing chronic exposure.

3

Differentiate the non-active/immune profiles (Profiles 2 and 3) using Anti-HBc.

Profile 2 has Anti-HBc IgG, meaning the patient was exposed to the actual virus (resolved natural infection). Profile 3 is negative for all core antibodies.

The HBV vaccine only contains surface antigen. Therefore, vaccinated individuals will only develop Anti-HBs, never Anti-HBc.

Key Concept

Interpretation of Hepatitis B Serologic Panels

Question 7312Question →

Match each diagnostic laboratory profile with the most likely etiology of thyrotoxicosis.

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Answer

Exogenous levothyroxine intake matches the profile of low RAIU and undetectable thyroglobulin. Subacute granulomatous thyroiditis matches low RAIU and elevated thyroglobulin. Graves disease matches diffusely increased RAIU. A TSH-secreting pituitary adenoma matches central hyperthyroidism with an increased alpha-subunit.

The diagnosis of thyrotoxicosis relies on a structured laboratory algorithm. Primary hyperthyroidism presents with a suppressed TSH and elevated Free T4. Within this category, high radioactive iodine uptake (RAIU) indicates new hormone synthesis (e.g., Graves disease with a diffuse pattern). Low RAIU indicates release of preformed hormone or an exogenous source. These are distinguished by serum thyroglobulin, which is released from damaged follicles in destructive thyroiditis (elevated) but suppressed in exogenous hormone ingestion (undetectable). Conversely, central hyperthyroidism presents with a normal or elevated TSH despite high Free T4; TSH-secreting adenomas typically also hypersecrete the alpha-subunit.

Step-by-Step Solution

1

Evaluate the TSH and Free T4 relationship to determine the origin.

Low TSH with high Free T4 indicates primary hyperthyroidism. Normal or high TSH with high Free T4 indicates central hyperthyroidism (TSH-secreting adenoma).

This establishes whether the source of thyrotoxicosis is driven by the pituitary or is independent of it.

2

Assess the radioactive iodine uptake (RAIU) in patients with primary hyperthyroidism.

High RAIU suggests active de novo hormone synthesis (e.g., Graves disease). Low RAIU suggests release of preformed hormone or exogenous intake.

RAIU distinguishes hyperactive glandular synthesis from thyroid destruction or factitious thyrotoxicosis.

3

Use serum thyroglobulin to differentiate the specific causes of low RAIU thyrotoxicosis.

Elevated thyroglobulin indicates thyroid follicular destruction (subacute thyroiditis). Undetectable thyroglobulin indicates an exogenous hormone source (exogenous levothyroxine intake).

Thyroglobulin is released during follicular damage but is suppressed when taking exogenous pure levothyroxine.

Key Concept

Diagnostic evaluation of thyrotoxicosis using thyroid function tests, radioactive iodine uptake, and serum markers.

Question 7313Question →

A 29-year-old man is evaluated in the hospital for ongoing fever. He was admitted 4 days ago with high fevers, chills, and pleuritic chest pain. His medical history is significant for opioid use disorder with active intravenous heroin use. On admission, his temperature was 39.2°C (102.6°F). Physical examination revealed a new holosystolic murmur at the lower left sternal border. Computed tomography of the chest showed multiple peripheral cavitary lesions. Two sets of blood cultures were drawn, and he was started on empiric intravenous vancomycin and ceftriaxone. A transthoracic echocardiogram demonstrated a 1.5-cm mobile vegetation on the anterior leaflet of the tricuspid valve. Today, the patient's temperature is 38.4°C (101.1°F). The admission blood cultures are now growing methicillin-susceptible *Staphylococcus aureus* (MSSA). Which of the following is the most appropriate next step in pharmacotherapy?

Discontinue current antibiotics and start intravenous cefazolin

Continue intravenous vancomycin and discontinue intravenous ceftriaxone

Continue intravenous vancomycin, discontinue intravenous ceftriaxone, and add intravenous gentamicin

Discontinue current antibiotics and start oral linezolid

Discontinue current antibiotics and start intravenous daptomycin

Show answer & explanation

Answer: Discontinue current antibiotics and start intravenous cefazolin

Answer

Discontinue current antibiotics and start intravenous cefazolin

The correct answer requires recognizing that for severe, invasive infections caused by methicillin-susceptible Staphylococcus aureus (MSSA), antistaphylococcal beta-lactams (such as cefazolin, nafcillin, or oxacillin) are the superior treatment choice. Although vancomycin is an appropriate initial empiric choice to cover potential MRSA, it has slower bactericidal activity against MSSA compared to beta-lactams. Continuing vancomycin once MSSA is confirmed is associated with prolonged bacteremia, higher rates of treatment failure, and increased mortality. Therefore, the most appropriate next step in antibiotic stewardship and patient management is to discontinue both the vancomycin and the ceftriaxone (which was covering gram-negatives) and initiate targeted therapy with intravenous cefazolin.

Step-by-Step Solution

1

Identify the primary diagnosis based on the clinical presentation

The patient has native valve right-sided infective endocarditis complicated by septic pulmonary emboli.

The combination of intravenous drug use, a new tricuspid regurgitation murmur, cavitary lung lesions, a large tricuspid vegetation, and positive blood cultures confirms the diagnosis.

2

Evaluate the current empiric antibiotic regimen against the culture results

The patient is receiving empiric vancomycin and ceftriaxone, but the pathogen is identified as methicillin-susceptible Staphylococcus aureus (MSSA).

Broad-spectrum empiric therapy must be narrowed and optimized once the exact pathogen and its susceptibilities are identified.

3

Determine the optimal targeted pharmacotherapy for the identified pathogen

Therapy should be de-escalated to an intravenous antistaphylococcal beta-lactam, such as cefazolin, nafcillin, or oxacillin.

Beta-lactams provide superior bactericidal activity, faster clearance of bacteremia, and significantly improved survival rates compared to vancomycin for MSSA endovascular infections.

Key Concept

De-escalation of empiric therapy to an antistaphylococcal beta-lactam (e.g., cefazolin, nafcillin) is the standard of care for methicillin-susceptible Staphylococcus aureus (MSSA) endocarditis, as beta-lactams are clinically superior to vancomycin for MSSA.

Question 7314Question →

A 21-year-old man is brought to the emergency department after sustaining a direct blow to the left side of his abdomen during a rugby match. On presentation, he complains of severe left upper quadrant pain that radiates to his left shoulder. Initial vital signs show a blood pressure of 118/76 mmHg, heart rate of 92/min, and respiratory rate of 18/min. Bedside focused assessment with sonography for trauma (FAST) reveals a moderate amount of free fluid in the splenorenal recess. Two large-bore peripheral intravenous lines are established, and blood is drawn for laboratory studies. Ten minutes later, the patient becomes agitated, pale, and diaphoretic. Repeat vital signs show a blood pressure of 72/38 mmHg and a heart rate of 144/min. Which of the following is the most appropriate next step in management?

Exploratory laparotomy

Computed tomography of the abdomen and pelvis with intravenous contrast

Splenic artery angiography and embolization

Diagnostic peritoneal lavage

Administration of intravenous vasopressors

Show answer & explanation

Answer: Exploratory laparotomy

Answer

Exploratory laparotomy is the most appropriate next step for a hemodynamically unstable patient with a positive FAST exam.

The correct response is exploratory laparotomy. This patient sustained blunt abdominal trauma and presents with a positive FAST exam and subsequent hemodynamic collapse. The combination of shock (blood pressure 72/38 mmHg, heart rate 144/min) and confirmed intra-abdominal fluid (hemoperitoneum) dictates immediate transport to the operating room for surgical exploration to arrest the bleeding. Any delay for further diagnostics is contraindicated.

Step-by-Step Solution

1

Assess the patient's initial mechanism of injury and clinical presentation.

The patient experienced blunt abdominal trauma and initially presented hemodynamically stable with a positive FAST exam showing intra-abdominal fluid (likely blood from a splenic injury).

Establishing the initial baseline is crucial for trauma evaluation.

2

Evaluate the patient's sudden change in clinical status.

The patient rapidly developed severe hypotension (72/38 mmHg) and tachycardia (144/min), indicating acute hemorrhagic shock and hemodynamic instability.

Dynamic changes in vital signs dictate the immediate treatment pathway in the Advanced Trauma Life Support (ATLS) algorithm.

3

Apply the blunt abdominal trauma algorithm for an unstable patient.

A hemodynamically unstable patient with blunt abdominal trauma and a positive FAST exam requires immediate exploratory laparotomy.

Definitive surgical hemostasis must be achieved without delay; further diagnostic imaging is contraindicated.

Key Concept

Hemodynamically unstable patients with blunt abdominal trauma and a positive FAST exam must be taken immediately for exploratory laparotomy.

Question 7315Question →

A 41-year-old female warehouse employee is brought to the emergency department after being struck by a reversing forklift and pinned against a concrete wall. She complains of diffuse abdominal pain and dizziness.

Vital signs upon arrival are temperature $36.4^\circ\text{C}$ ( $97.5^\circ\text{F}$ ), blood pressure $78/45\text{ mmHg}$ , heart rate $132/\text{min}$ , and respiratory rate $22/\text{min}$ .

Primary survey reveals a patent airway, and breath sounds are equal bilaterally. Her neck veins are flat. The pelvis demonstrates no mechanical instability to gentle compression. A focused assessment with sonography for trauma (FAST) demonstrates a substantial anechoic stripe in Morison's pouch.

She immediately receives a transfusion of uncrossmatched type O-negative packed red blood cells. Following this initial resuscitation, her blood pressure rises to $92/55\text{ mmHg}$ and her heart rate slows to $115/\text{min}$ . The physician notes that her peripheral pulses remain weak and her capillary refill time is delayed.

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

Immediate transfer to the operating room for celiotomy

Cross-sectional imaging of the abdomen with intravenous contrast

Endovascular evaluation and targeted arterial embolization

Diagnostic peritoneal lavage

Focused observation in the intensive care unit with serial hemoglobin monitoring

Show answer & explanation

Answer: Immediate transfer to the operating room for celiotomy

Answer

Immediate transfer to the operating room for celiotomy

The correct answer is immediate transfer to the operating room for celiotomy. This patient has sustained blunt abdominal trauma and presents with severe hemorrhagic shock. Although her blood pressure slightly improved following an initial blood transfusion, she remains tachycardic with weak peripheral pulses and delayed capillary refill. This clinical picture characterizes her as a 'transient responder.' According to Advanced Trauma Life Support (ATLS) protocols, a hemodynamically unstable patient or a transient responder with a positive Focused Assessment with Sonography for Trauma (FAST) exam requires emergent exploratory laparotomy (celiotomy) to identify and control the source of intra-abdominal hemorrhage. Any delay for further imaging or diagnostic procedures is contraindicated and severely increases the risk of mortality.

Step-by-Step Solution

1

Identify the patient's hemodynamic status.

The patient initially presented with profound hypotension and tachycardia. After a blood transfusion, her vital signs improved only marginally, with persistent signs of hypoperfusion (weak pulses, delayed capillary refill).

Determining precise hemodynamic stability, including identifying 'transient responders', is the most critical branching point in the trauma evaluation algorithm.

2

Interpret the adjunct primary survey findings.

The FAST examination is positive for free fluid in Morison's pouch (the hepatorenal recess).

A positive FAST in the context of blunt abdominal trauma indicates hemoperitoneum as the likely source of shock.

3

Determine the definitive management step.

A hemodynamically unstable patient, or a transient responder, with a positive FAST requires immediate surgical exploration.

Diagnostic delays in unstable patients increase mortality; immediate source control via celiotomy is absolutely mandated.

Key Concept

Hemodynamically unstable patients (including transient responders) with blunt abdominal trauma and a positive FAST require immediate exploratory laparotomy (celiotomy).

Estimated Time:1m 15s

Question 7316Question →

Select the most appropriate first-line antimicrobial therapy for each of the following patients presenting with a characteristic infectious syndrome.

Click a left item, then click its matching right item

Show answer & explanation

Answer

The correct matches pair early localized Lyme disease with oral doxycycline, uncomplicated cystitis with oral nitrofurantoin, non-purulent cellulitis with oral cephalexin, and primary syphilis with intramuscular benzathine penicillin G.

Each specific clinical vignette describes a hallmark presentation of a common outpatient infection, each with a highly standardized first-line treatment pathway. Recognizing erythema migrans directs the clinician to doxycycline; uncomplicated dysuria directs to nitrofurantoin; non-purulent skin erythema directs to a first-generation cephalosporin like cephalexin; and a painless genital chancre strictly mandates benzathine penicillin G.

Step-by-Step Solution

1

Evaluate the first presentation.

Diagnose early localized Lyme disease based on the classic erythema migrans rash.

Identifying the disease allows for the selection of the correct first-line therapy, which is oral doxycycline.

2

Evaluate the second presentation.

Diagnose uncomplicated acute cystitis due to the presence of lower urinary tract symptoms without systemic signs.

Nitrofurantoin is first-line because it concentrates effectively in the urine and avoids unnecessarily broad systemic coverage.

3

Evaluate the third presentation.

Diagnose non-purulent cellulitis based on the rapidly spreading erythema without an abscess or purulence.

Oral cephalexin is selected as it provides optimal coverage against beta-hemolytic streptococci and methicillin-susceptible Staphylococcus aureus (MSSA).

4

Evaluate the fourth presentation.

Diagnose primary syphilis based on the single painless genital chancre.

Intramuscular benzathine penicillin G is the definitive treatment for all stages of syphilis (unless neurosyphilis is present).

Key Concept

First-line empiric and targeted antimicrobial selection for classic outpatient infectious syndromes.

Question 7317Question →

An emergency medical services team brings a 58-year-old man to the hospital due to severe, continuous substernal chest pain, shortness of breath, and profound diaphoresis that began 45 minutes ago. His medical history is significant for hyperlipidemia and a 35-pack-year smoking habit. Initial vital signs demonstrate a blood pressure of $85/50\text{ mmHg}$ , a heart rate of $55/\text{min}$ , and a respiratory rate of $20/\text{min}$ . Physical examination reveals significantly elevated jugular venous pressure, but the lung fields are completely clear to auscultation bilaterally. A 12-lead electrocardiogram demonstrates $3\text{ mm}$ ST-segment elevations in leads II, III, and aVF. Which of the following is the most appropriate next step in the management of this patient's hypotension?

Immediate transport for a computed tomography angiography of the chest

Administration of nebulized albuterol and intravenous corticosteroids

Administration of an intravenous normal saline bolus

Administration of intravenous vancomycin and piperacillin-tazobactam

Withhold interventions until quantitative serum troponin levels are resulted

Show answer & explanation

Answer: Administration of an intravenous normal saline bolus

Answer

Administration of an intravenous normal saline bolus

The correct answer addresses the specific pathophysiology of a right ventricular (RV) infarction. This patient's electrocardiogram shows an inferior myocardial infarction (ST elevations in II, III, aVF), and the physical examination reveals elevated jugular venous pressure with clear lung fields. This triad is the classic presentation of an RV infarction. In this state, the right ventricle loses its contractility and becomes a passive conduit, making it highly dependent on adequate right-sided filling pressures (preload) to push blood into the left side of the heart. Consequently, the first-line therapy to correct the resulting hypotension is volume resuscitation with an intravenous normal saline bolus to maximize preload. Standard angina medications that reduce preload, such as nitroglycerin, must be strictly avoided as they can precipitate profound cardiovascular collapse.

Step-by-Step Solution

1

Analyze the electrocardiogram findings and initial vital signs.

ST-segment elevations in leads II, III, and aVF indicate an acute inferior myocardial infarction. The blood pressure is profoundly low (

85/50\text{ mmHg}

) accompanied by relative bradycardia.

Identifying the anatomical location of the infarction is critical to predicting and treating specific hemodynamic complications.

2

Correlate the physical examination findings with the type of infarction.

The combination of elevated jugular venous pressure and completely clear lungs in the setting of an inferior myocardial infarction points directly to right ventricular involvement.

Right ventricular infarction leads to poor forward flow to the left ventricle, causing systemic hypotension while keeping the pulmonary circulation free of edema.

3

Determine the optimal physiological intervention for the hypotension.

The infarcted right ventricle acts as a passive conduit and becomes highly dependent on elevated preload to maintain cardiac output, making intravenous fluids the necessary initial treatment.

Preload must be artificially supported with a normal saline bolus to push blood through the impaired right heart; conversely, preload-reducing agents must be strictly avoided.

Key Concept

The classic triad of an acute right ventricular infarction includes hypotension, elevated jugular venous pressure, and clear lung fields; the initial treatment of choice is optimizing preload with an intravenous normal saline bolus.

Question 7318Question →

A 22-year-old woman with a history of bulimia nervosa and type 1 diabetes mellitus is brought to the emergency department by her roommate due to severe lethargy and confusion. The roommate reports that the patient has been intentionally restricting her insulin doses and has been vomiting frequently over the past 3 days. Temperature is 37.0°C (98.6°F), blood pressure is 100/60 mmHg, pulse is 118/min, and respirations are 24/min.

Laboratory studies show:

Parameter	Value
Serum sodium	142 mEq/L
Serum potassium	3.4 mEq/L
Serum chloride	94 mEq/L
Serum bicarbonate	16 mEq/L
Blood glucose	480 mg/dL

Arterial blood gas on room air:

Parameter	Value
pH	7.32
$pCO_2$	32 mmHg
$pO_2$	95 mmHg

Assuming a baseline normal serum anion gap of 12 mEq/L and a normal serum bicarbonate of 24 mEq/L, what is the calculated delta ratio ( $\frac{\Delta AG}{\Delta HCO_3^-}$ ) for this patient?

Show answer & explanation

Answer: 2.5

Answer

The calculated delta ratio is 2.5.

The delta ratio is calculated by dividing the change in anion gap (

\Delta AG

) by the change in serum bicarbonate (

\Delta HCO_3^-

). For this patient, the measured anion gap is

142 - (94 + 16) = 32

. The

\Delta AG

is

32 - 12 = 20

. The

\Delta HCO_3^-

is

24 - 16 = 8

. Therefore, the delta ratio is

\frac{20}{8} = 2.5

. In an uncomplicated high anion gap metabolic acidosis (like pure diabetic ketoacidosis), the ratio is typically between 1.0 and 2.0. A ratio greater than 2.0 indicates that the bicarbonate level is higher than expected for the degree of anion gap elevation, which signifies a concurrent metabolic alkalosis. In this clinical scenario, the metabolic alkalosis is driven by the patient's frequent vomiting, leading to a loss of

H^+

and

Cl^-

.

Step-by-Step Solution

1

Calculate the patient's measured serum anion gap.

AG = 142 - (94 + 16) = 32

mEq/L.

The first step in evaluating a metabolic acidosis is determining the presence and size of an anion gap.

2

Calculate the change in anion gap (

\Delta AG

).

\Delta AG = 32 - 12 = 20

mEq/L.

This value represents the excess unmeasured anions contributing to the acidosis.

3

Calculate the change in serum bicarbonate (

\Delta HCO_3^-

).

\Delta HCO_3^- = 24 - 16 = 8

mEq/L.

This determines how much the bicarbonate has dropped from the normal baseline.

4

Calculate the delta ratio.

Ratio = \frac{20}{8} = 2.5

.

The delta ratio helps identify mixed acid-base disorders, such as a concurrent metabolic alkalosis.

Key Concept

The delta ratio (

\frac{\Delta AG}{\Delta HCO_3^-}

) is used in high anion gap metabolic acidosis to identify concurrent mixed acid-base disorders, with a ratio > 2.0 indicating an additional metabolic alkalosis.

Alternative Method

The delta gap (expected bicarbonate) can also be calculated as: Measured

HCO_3^-

+

\Delta AG

. Here,

16 + 20 = 36

mEq/L. Since the expected normal bicarbonate (36) is significantly higher than the normal baseline of 24, a concurrent metabolic alkalosis is confirmed.

Estimated Time:1m 30s

Question 7319Question →

A $29$ -year-old man is evaluated in the hospital for worsening bloody diarrhea and abdominal pain. He was admitted $5$ days ago for a severe exacerbation of ulcerative pancolitis, presenting at that time with $12$ bloody bowel movements daily, severe cramps, and a weight loss of $4.5\text{ kg}$ ( $10\text{ lbs}$ ). On admission, stool studies were negative for Clostridioides difficile toxin, Salmonella, Shigella, and Campylobacter. He was subsequently started on high-dose intravenous methylprednisolone.

Despite $5$ days of corticosteroid therapy, the patient's symptoms have rapidly deteriorated. He now reports $15$ bloody bowel movements a day and new-onset subjective fevers. His temperature is $38.6^{\circ}\text{C}$ ( $101.5^{\circ}\text{F}$ ), blood pressure is $108/68\text{ mmHg}$ , and pulse is $114/\text{min}$ . Physical examination reveals a distended abdomen with diffuse tenderness, but no rebound or guarding is present.

Laboratory studies show:
Hemoglobin: $7.8\text{ g/dL}$
Leukocyte count: $14,500/\text{mm}^3$
Erythrocyte sedimentation rate: $72\text{ mm/hr}$

An unprepared flexible sigmoidoscopy reveals diffuse mucosal erythema, friability, and several large, deep, punched-out ulcers in the descending colon. Histopathologic examination of the ulcer base biopsies demonstrates cytomegaly with prominent eosinophilic intranuclear inclusions surrounded by a clear halo.

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

Initiate intravenous ganciclovir

Administer intravenous infliximab

Begin intravenous ceftriaxone and metronidazole

Proceed to urgent subtotal colectomy

Initiate oral vancomycin

Show answer & explanation

Answer: Initiate intravenous ganciclovir

Answer

The most appropriate next step is to initiate targeted antiviral therapy with intravenous ganciclovir.

The correct answer targets the definitive histologic diagnosis provided in the vignette. The presence of enlarged cells with eosinophilic intranuclear inclusions surrounded by a clear halo ('owl's eye' appearance) is pathognomonic for Cytomegalovirus (CMV). CMV colitis frequently complicates severe inflammatory bowel disease, particularly in patients receiving systemic corticosteroids or other immunosuppressants. When a patient with an IBD flare becomes refractory to steroids, superimposed infections must be ruled out. Because this patient has confirmed tissue-invasive CMV, the immediate next step in management is the initiation of antiviral therapy with intravenous ganciclovir. Tapering of corticosteroids is also typically initiated.

Step-by-Step Solution

1

Identify the primary presentation and failure of initial therapy.

The patient has a severe ulcerative colitis flare that is refractory to 5 days of high-dose intravenous corticosteroids.

Recognizing steroid refractoriness prompts the search for complications, such as superimposed infections, rather than simply assuming worsening primary inflammation.

2

Interpret the biopsy findings from the flexible sigmoidoscopy.

The biopsy shows cytomegaly and 'eosinophilic intranuclear inclusions surrounded by a clear halo' (owl's eye inclusions).

These histologic findings are pathognomonic for Cytomegalovirus (CMV) infection.

3

Synthesize the clinical picture to establish the final diagnosis.

The diagnosis is CMV colitis complicating severe, immunosuppressed ulcerative colitis.

Patients with severe IBD on immunosuppressive therapy are at high risk for reactivation of latent CMV in the colon, which masquerades as a steroid-refractory flare.

4

Determine the optimal management for the specific complication.

Select intravenous ganciclovir to treat the CMV colitis.

Treating the underlying opportunistic infection is required before considering further biologic immunosuppression or irreversible surgical resection.

Key Concept

Cytomegalovirus (CMV) colitis is a common and severe complication of steroid-refractory inflammatory bowel disease; it is diagnosed by identifying pathognomonic 'owl's eye' intranuclear inclusions on colonic biopsy and is treated with intravenous ganciclovir.

Estimated Time:2m 30s

Question 7320Question →

A 52-year-old man is assessed on the surgical ward for an elevated temperature 24 hours after undergoing an elective open left hemicolectomy for recurrent, medically refractory diverticulitis. The patient reports expected, mild incisional pain and a dry throat from the endotracheal tube, but he specifically denies chills, chest pain, shortness of breath, dysuria, or productive cough. His medical history includes hypertension and hyperlipidemia. His temperature is 38.5°C (101.3°F), pulse is 94/min, respirations are 15/min, and blood pressure is 128/82 mmHg. Oxygen saturation is 98% on ambient air. The lungs are clear to auscultation bilaterally. Cardiac examination shows a regular rate and rhythm. The abdomen is soft but appropriately tender around the midline surgical incision. The surgical dressing is clean, dry, and intact with no surrounding erythema or drainage. A urinary catheter, placed preoperatively, is in place and draining clear, light-yellow urine. The lower extremities show no edema or calf tenderness. Which of the following is the most appropriate next step in management?

Observation and continuation of routine postoperative care

Order a portable chest radiograph and blood cultures

Obtain a urinalysis and urine culture

Perform bilateral lower extremity venous ultrasonography

Commence empiric intravenous piperacillin-tazobactam therapy

Show answer & explanation

Answer: Observation and continuation of routine postoperative care

Answer

Observation and continuation of routine postoperative care

The correct answer is observation and continuation of routine postoperative care. Fever occurring within the first 48 hours following a major surgery (postoperative days 1-2) is overwhelmingly physiologic. It is mediated by the release of inflammatory cytokines, such as interleukin-1 (IL-1), interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha), in response to the tissue trauma caused by the surgical procedure. This physiologic response is self-limiting and harmless. Because this patient is hemodynamically stable, has a normal physical examination for his postoperative day, and lacks any localizing signs of infection (e.g., no purulent wound drainage, no respiratory distress, no abnormal lung sounds), an infectious workup or empiric antibiotic therapy is not indicated. The best approach is clinical reassurance and continued routine postoperative care.

Step-by-Step Solution

1

Evaluate the timeline of the patient's postoperative fever.

The patient is on postoperative day 1 (approximately 24 hours after surgery).

The timing of a postoperative fever is the most critical initial factor in determining its underlying etiology.

2

Assess for localizing signs or symptoms of infection on physical examination.

The patient has clear lungs, a benign wound examination, clear urine, normal oxygen saturation, and no specific infectious complaints.

The absence of localizing signs suggests a systemic, physiologic response rather than a focal bacterial infection.

3

Determine the most appropriate management based on the clinical findings and timeline.

Observation and continuation of routine care.

Fever within the first 48 hours is typically caused by tissue trauma and cytokine release; without 'red flag' symptoms, it does not warrant an infectious diagnostic workup or empiric antibiotics.

Key Concept

Fever occurring within the first 48 hours postoperatively (postoperative days 1-2) is overwhelmingly physiologic due to tissue trauma and cytokine release. In the absence of localizing signs, no diagnostic workup or empiric antibiotics are required.

Answer

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