All practice questions

An 82-year-old man with advanced Alzheimer dementia is brought to the emergency department from a skilled nursing facility due to progressive lethargy over the past 3 days. The facility staff report that he has been refusing meals and liquids. On examination, temperature is 37.1°C (98.8°F), blood pressure is 98/60 mm Hg, pulse is 112/min, and respiratory rate is 16/min. The patient appears cachectic with profoundly dry mucous membranes and poor skin turgor. His current weight is 60 kg (132 lb).

Laboratory studies show:
Serum sodium: 168 mEq/L
Serum potassium: 4.1 mEq/L
Serum chloride: 129 mEq/L
Serum bicarbonate: 24 mEq/L
Blood urea nitrogen: 56 mg/dL
Serum creatinine: 1.8 mg/dL

Based on an estimated total body water of 50% of his body weight, what is this patient's calculated free water deficit in liters?

A 72-year-old man is evaluated in the hospital for decreased urine output. He was admitted 3 days ago for an acute exacerbation of heart failure with reduced ejection fraction. His treatment regimen includes intravenous furosemide, lisinopril, carvedilol, and spironolactone. His weight has decreased by 4 kg (8.8 lb) since admission, and his peripheral edema has significantly improved. However, his urine output over the last 12 hours has been only 250 mL.

Vitals:
Blood pressure: 102/60 mm Hg
Heart rate: 94/min

Laboratory results from today:
Serum:
Sodium: 135 mEq/L
Potassium: 4.8 mEq/L
Chloride: 98 mEq/L
Bicarbonate: 28 mEq/L
Blood urea nitrogen: 80 mg/dL
Creatinine: 2.4 mg/dL

Urine:
Sodium: 75 mEq/L
Creatinine: 120 mg/dL
Urea nitrogen: 600 mg/dL

Based on the laboratory findings, what is this patient's calculated fractional excretion of urea (expressed as a percentage)?

A 68-year-old man is brought to the emergency department with 3 days of severe, watery diarrhea and poor oral intake. He reports feeling lightheaded upon standing. His temperature is $37.1^\circ$ C ($98.8^\circ$ F), blood pressure is $112/72$ mm Hg supine and $90/60$ mm Hg standing, and pulse is 92/min supine and 116/min standing. Physical examination reveals dry mucous membranes and delayed capillary refill.

Laboratory results are as follows:

Serum studies:
Sodium: $140$ mEq/L
Potassium: $3.5$ mEq/L
Chloride: $110$ mEq/L
Bicarbonate: $20$ mEq/L
Blood urea nitrogen: $42$ mg/dL
Creatinine: $1.4$ mg/dL

Urine studies:
Sodium: $20$ mEq/L
Creatinine: $40$ mg/dL

Based on these findings, what is the patient's fractional excretion of sodium?

A 24-year-old woman with a history of type 1 diabetes mellitus presents to the emergency department with a 3-day history of intractable nausea, vomiting, and diffuse abdominal pain. She reports that her insulin pump malfunctioned four days ago. On physical examination, she appears lethargic and has dry mucous membranes. Her pulse is 118/min, blood pressure is 98/60 mm Hg, and respirations are 26/min and deep.

Laboratory studies show:
Serum:
Sodium: $140 \text{ mEq/L}$
Potassium: $4.8 \text{ mEq/L}$
Chloride: $88 \text{ mEq/L}$
Bicarbonate: $16 \text{ mEq/L}$
Blood urea nitrogen: $42 \text{ mg/dL}$
Creatinine: $1.6 \text{ mg/dL}$
Glucose: $520 \text{ mg/dL}$

Arterial blood gas (room air):
pH: 7.34
$\text{pCO}_2$: $31 \text{ mm Hg}$
$\text{pO}_2$: $95 \text{ mm Hg}$

Assume a normal serum anion gap of $12 \text{ mEq/L}$ and a normal serum bicarbonate of $24 \text{ mEq/L}$.

What is this patient's delta-delta ratio ($\frac{\Delta \text{AG}}{\Delta \text{HCO}_3^-}$)?

During a routine follow-up at the nephrology clinic, a 42-year-old woman is evaluated for persistent hypokalemia and mild muscle weakness. She has a history of Sjögren syndrome and has had two episodes of calcium phosphate nephrolithiasis in the past five years. She reports no diarrhea, vomiting, or recent dietary changes. Her blood pressure is 118/76 mm Hg. Laboratory studies show:

Serum sodium: 140 mEq/L
Serum potassium: 2.9 mEq/L
Serum chloride: 115 mEq/L
Serum bicarbonate: 15 mEq/L
Blood urea nitrogen: 12 mg/dL
Serum creatinine: 0.8 mg/dL

Urine studies obtained simultaneously show:
Urine sodium: 55 mEq/L
Urine potassium: 25 mEq/L
Urine chloride: 60 mEq/L

What is this patient's urine anion gap in mEq/L? (Provide your answer as a number only)

A 65-year-old man is admitted to the hospital for acute decompensated heart failure and is treated with aggressive intravenous furosemide. On hospital day 3, his blood pressure is 105/65 mm Hg and heart rate is 92/min. Over the past 24 hours, his urine output has decreased to 400 mL. His serum creatinine rises from a baseline of 1.1 mg/dL to 2.8 mg/dL.

Laboratory studies are obtained to evaluate his acute kidney injury:

Serum chemistry:
Sodium: 136 mEq/L
Potassium: 3.8 mEq/L
Chloride: 98 mEq/L
Bicarbonate: 28 mEq/L
Blood urea nitrogen (BUN): 84 mg/dL
Creatinine: 2.8 mg/dL

Urine chemistry:
Sodium: 70 mEq/L
Urea nitrogen: 420 mg/dL
Creatinine: 56 mg/dL

Because recent loop diuretic administration impairs tubular sodium reabsorption, the fractional excretion of sodium ($FE_{Na}$) can be misleadingly elevated. Instead, the fractional excretion of urea ($FE_{Urea}$) is preferred to differentiate between prerenal azotemia and intrinsic acute tubular necrosis in this clinical scenario.

Calculate the patient's $FE_{Urea}$. Express your answer as a percentage.

A 45-year-old man with a history of poorly controlled type 2 diabetes mellitus is brought to the emergency department due to confusion, nausea, and abdominal pain for the past 2 days. He has missed his last several doses of insulin. His temperature is 37.1°C (98.8°F), blood pressure is 100/65 mm Hg, pulse is 112/min, and respirations are 24/min. Physical examination shows dry mucous membranes and a fruity breath odor.

Laboratory studies show:

What is this patient's serum anion gap (in mEq/L)?

Paramedics are dispatched to the home of a 42-year-old man after he was discovered unresponsive in his garage. According to his husband, the patient has a history of severe depression and recently experienced a job loss. An empty, unlabeled container of sweet-smelling fluid was found nearby. Vital signs upon arrival at the hospital include a temperature of $36.5^\circ\text{C}$ ($97.7^\circ\text{F}$), blood pressure of $110/70 \text{ mm Hg}$, heart rate of $105/\text{min}$, and respiratory rate of $24/\text{min}$. The patient is obtunded, responding only by withdrawing from painful stimuli.

Laboratory studies are obtained:

Serum chemistry:
Sodium: $138 \text{ mEq/L}$
Potassium: $4.5 \text{ mEq/L}$
Chloride: $102 \text{ mEq/L}$
Bicarbonate: $12 \text{ mEq/L}$
Blood urea nitrogen (BUN): $28 \text{ mg/dL}$
Creatinine: $1.2 \text{ mg/dL}$
Glucose: $108 \text{ mg/dL}$

Arterial blood gas (room air):
pH: $7.22$
$\text{pCO}_2$: $26 \text{ mm Hg}$
$\text{pO}_2$: $95 \text{ mm Hg}$

Additional diagnostics:
Measured serum osmolality: $335 \text{ mOsm/kg H}_2\text{O}$

Based on the provided laboratory data, what is this patient's serum osmolar gap? (Enter the numerical value in $\text{mOsm/kg H}_2\text{O}$)

A 68-year-old man with a history of type 2 diabetes mellitus is brought to the emergency department due to progressively worsening confusion and profound weakness over the past 4 days. He recently recovered from a mild upper respiratory illness. On examination, he is lethargic but arousable. Vital signs show a blood pressure of $92/58\text{ mm Hg}$, a heart rate of $118/\text{min}$, and a respiratory rate of $16/\text{min}$. His mucous membranes are parched, and skin turgor is significantly decreased.

Initial laboratory evaluation reveals:
Serum sodium: $129\text{ mEq/L}$
Serum potassium: $4.4\text{ mEq/L}$
Serum chloride: $95\text{ mEq/L}$
Serum bicarbonate: $22\text{ mEq/L}$
Blood urea nitrogen: $48\text{ mg/dL}$
Serum creatinine: $1.9\text{ mg/dL}$
Serum glucose: $600\text{ mg/dL}$

In order to properly select the composition of intravenous fluids for resuscitation, the patient's true sodium status must be evaluated.

What is the patient's corrected serum sodium concentration in $\text{mEq/L}$? (Assume a correction factor of $1.6\text{ mEq/L}$ for each $100\text{ mg/dL}$ increase in glucose above $100\text{ mg/dL}$).

Paramedics arrive at the emergency room with a 52-year-old man who was discovered unresponsive in a public park. The patient has a documented medical history of severe alcohol use disorder. Upon initial evaluation, his body temperature is $36.2^\circ\text{C}$ ($97.2^\circ\text{F}$), pulse is $102/\text{min}$, blood pressure is $110/70\text{ mm Hg}$, and respirations are $24/\text{min}$. He is unarousable to painful stimuli. Cardiopulmonary examination is unremarkable. Initial laboratory studies show the following:

Arterial blood gas (room air) shows a pH of $7.22$ and a $\text{PaCO}_2$ of $26\text{ mm Hg}$.

Based on the provided laboratory results, what is the patient's serum osmolar gap in $\text{mOsm/kg}$?

A 25-year-old female with a history of type 1 diabetes mellitus is brought to the emergency department by her roommate due to severe lethargy and abdominal pain. Over the preceding 48 hours, she has experienced intractable nonbilious emesis and has consequently withheld her scheduled insulin doses. On physical examination, she appears confused and has markedly dry mucous membranes with decreased skin turgor.

Laboratory results:
- Serum $Na^+$: $140 \text{ mEq/L}$
- Serum $K^+$: $3.4 \text{ mEq/L}$
- Serum $Cl^-$: $86 \text{ mEq/L}$
- Serum $HCO_3^-$: $14 \text{ mEq/L}$
- Serum glucose: $545 \text{ mg/dL}$
- Blood urea nitrogen: $38 \text{ mg/dL}$
- Serum creatinine: $1.6 \text{ mg/dL}$

Assuming a normal anion gap of $12 \text{ mEq/L}$ and a normal serum bicarbonate of $24 \text{ mEq/L}$, what is this patient's calculated delta-delta ratio?

A 60-year-old man is brought to the emergency department by a neighbor who found him lethargic and confused in his apartment. The neighbor notes that the patient has a history of severe alcohol use disorder and has been drinking heavily for the past week. He has also had multiple episodes of non-bilious vomiting over the last three days. Physical examination reveals dry mucous membranes and decreased skin turgor. Laboratory studies are obtained:

Arterial blood gas on room air reveals a pH of $7.30$ and PaCO $_2$ of $32\text{ mm Hg}$.

Calculate the patient's delta-delta ratio, defined as the change in anion gap divided by the change in serum bicarbonate ($\frac{\Delta \text{AG}}{\Delta \text{HCO}_3^-}$). Assume a normal anion gap of $12\text{ mEq/L}$ (calculated without potassium) and a normal serum bicarbonate of $24\text{ mEq/L}$.

A 38-year-old mechanic is evaluated in the hospital after being found confused and lethargic in his workshop. He has a history of alcohol use disorder. Vital signs show a temperature of 37.1°C (98.8°F), blood pressure of 135/85 mmHg, pulse of 92/min, and respiratory rate of 22/min. Physical examination reveals a disoriented patient with dry mucous membranes.

Initial laboratory evaluation reveals the following:

Based on the provided laboratory results, what is this patient's serum anion gap?

A 35-year-old man is brought to the emergency department after sustaining injuries in a kitchen grease fire. On examination, he is alert and oriented. His blood pressure is 125/80 mm Hg, heart rate is 98/min, and respiratory rate is 16/min. Physical examination reveals deep partial-thickness burns involving the entire anterior surface of his chest and abdomen, as well as the entire anterior surface of both arms. His airway is patent with no signs of inhalational injury. Using the Rule of Nines, what is the estimated total body surface area (TBSA) percentage affected by these burns?

A 50-year-old construction worker is evacuated by helicopter to the trauma center following a localized industrial explosion. The patient weighs $80\text{ kg}$. Paramedics report the incident occurred exactly $2\text{ hours}$ prior to arrival. Primary survey reveals a patent airway with no signs of inhalation injury, clear breath sounds bilaterally, and a heart rate of $115\text{ beats/min}$. Secondary survey is notable for deep partial-thickness and full-thickness thermal burns covering the entirety of his posterior trunk (including buttocks), his entire left lower extremity, and his entire right upper extremity. Superficial (first-degree) burns are noted on his face but are not blistering. Large-bore intravenous access is established. The trauma team initiates fluid resuscitation using lactated Ringer solution according to current Advanced Trauma Life Support (ATLS) guidelines ($2\text{ mL/kg/\%TBSA}$ for adult thermal burns).

What should be the initial rate of the fluid infusion (in $\text{mL/hr}$) programmed on the intravenous pump for the time remaining in the first 8-hour post-injury window?

A $35$-year-old man weighing $70 \text{ kg}$ is brought to the emergency department $2 \text{ hours}$ after being rescued from a structural fire. On examination, he is hemodynamically stable, and his airway is secure with no evidence of inhalational injury. He has sustained deep partial-thickness and full-thickness burns involving his anterior chest, anterior abdomen, entire right arm, and the anterior aspect of his left leg. The remainder of his skin is intact. Intravenous access is obtained. According to current Advanced Trauma Life Support (ATLS) guidelines for adult thermal burns, what should be the initial rate of intravenous lactated Ringer solution administration for this patient? (Enter the value in $\text{mL/hr}$)

A 32-year-old male utility worker is brought to the emergency department after sustaining a high-voltage electrical injury while repairing a power line. The incident occurred exactly 2 hours prior to his arrival. On presentation, he is awake, alert, and complains of severe pain in his extremities. His temperature is $36.8^\circ \text{C}$ ($98.2^\circ \text{F}$), heart rate is $112/\text{min}$, and blood pressure is $110/70 \text{ mm Hg}$. Physical examination reveals deep, full-thickness burns involving his entire anterior trunk and his entire right lower extremity. There are also deep, charred entry and exit wounds on his right hand and left foot, though these cover a negligible surface area. His body weight is estimated at $75 \text{ kg}$. A Foley catheter is inserted to monitor urine output, and large-bore intravenous access is obtained. According to the Advanced Trauma Life Support (ATLS) guidelines for high-voltage electrical injuries, what is the appropriate initial intravenous fluid infusion rate (in $\text{mL/hour}$) for this patient?

A 35-year-old man is brought to the emergency department after a motor vehicle collision. On initial evaluation, he opens his eyes only when the physician loudly calls his name. When asked what happened, he responds with single, random words that do not form coherent sentences. When pressure is applied to his right fingernail bed, he briskly flexes his elbow to pull his right arm away from the stimulus, but does not reach toward the examiner's hand. What is this patient's Glasgow Coma Scale (GCS) score?

A 24-year-old man is brought to the emergency department after a high-speed motorcycle collision. He complains of severe pain in his left leg. Physical examination reveals a deformed left knee with an obvious posterior dislocation. The dislocation is promptly reduced in the emergency department. Afterward, palpation of the left pedal pulses reveals they are diminished compared to the right side. The patient remains hemodynamically stable. To evaluate for potential popliteal artery injury, the physician measures systolic blood pressures using a continuous-wave Doppler ultrasound and a sphygmomanometer. The following systolic pressures are recorded:

What is the Ankle-Brachial Index (ABI) of the injured extremity?

A 45-year-old industrial worker is brought to the emergency department after a chemical vat exploded. He sustained deep partial-thickness burns. Physical examination reveals burns covering his entire anterior trunk (chest and abdomen), his entire right upper extremity (both anterior and posterior surfaces), and his entire right lower extremity (both anterior and posterior surfaces). No other areas of the body are affected.

Based on the Rule of Nines, what is the estimated total body surface area (TBSA) percentage affected by burns in this patient?