Nephrology

A 54-year-old female is brought to the emergency department by her husband due to progressive lethargy and confusion over the past $24$ hours. Her husband reports she has had severe, large-volume, watery diarrhea for the last $5$ days. She has not urinated since yesterday. Vital signs include a temperature of $37.2^\circ$ C ($99.0^\circ$ F), blood pressure of $82/50$ mm Hg, heart rate of $132$/min, and respiratory rate of $26$/min. Physical examination reveals delayed capillary refill, dry mucous membranes, and cold extremities.

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

Match the following clinical scenarios with their most likely characteristic finding on microscopic urinalysis.

A $45$-year-old man is brought to the emergency department by emergency medical services after a witnessed generalized tonic-clonic seizure on the street. Bystanders report the seizure lasted approximately $3$ minutes. The patient has a known history of severe alcohol use disorder and was found unresponsive outside a liquor store. On arrival, he is lethargic and arousable only to painful stimuli. His temperature is $36.8^\circ C$ ($98.2^\circ F$), blood pressure is $112/72$ mm Hg, heart rate is $108$/min, and respiratory rate is $10$/min. Pulse oximetry shows $92\%$ on room air.

Laboratory studies show:

Arterial blood gas on room air:

Which of the following best explains this patient's acid-base findings?

A 68-year-old man is evaluated in the hospital for decreased urine output. He was admitted 3 days ago for severe gastroenteritis and has had poor oral intake. His blood pressure is $96/60 \text{ mm Hg}$ and heart rate is $112/\text{min}$. Physical examination reveals dry oral mucosa and delayed capillary refill. Laboratory studies show:

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

A 19-year-old woman is brought to the emergency department by her college roommate due to confusion, nausea, and ringing in her ears that started 4 hours ago. The roommate reports that the patient was distraught after a recent argument, and an empty bottle of over-the-counter pain medication was found on her desk. Vital signs show a temperature of $37.8^\circ$ C ($100.0^\circ$ F), blood pressure of $110/70$ mmHg, pulse of $115$/min, and respiratory rate of $28$/min. Physical examination reveals an oriented but lethargic patient. Lungs are clear to auscultation. Laboratory studies are obtained and show the following:

Serum sodium: $142$ mEq/L
Serum potassium: $4.0$ mEq/L
Serum chloride: $104$ mEq/L
Serum bicarbonate: $14$ mEq/L
Blood urea nitrogen: $18$ mg/dL
Serum creatinine: $0.9$ mg/dL

Arterial blood gas (room air):
pH: $7.42$
pCO $_2$: $20$ mmHg
pO $_2$: $105$ mmHg

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

A 42-year-old man is brought to the emergency department by ambulance after being found unresponsive in his garage. His wife reports that he has a history of major depressive disorder and recently lost his job. On physical examination, he is unarousable. Blood pressure is 115/75 mm Hg, pulse is 112/min, and respirations are 24/min and deep.

Laboratory studies show:
Serum sodium: 140 mEq/L
Serum potassium: 4.6 mEq/L
Serum chloride: 105 mEq/L
Serum bicarbonate: 10 mEq/L
Blood urea nitrogen (BUN): 28 mg/dL
Serum creatinine: 1.8 mg/dL
Serum glucose: 108 mg/dL
Measured serum osmolality: 320 mOsm/kg H2O

What is this patient's serum osmolar gap in mOsm/kg H2O?

Paramedics transport a $34$-year-old male construction worker to the emergency department after he was trapped under a collapsed concrete wall for $6$ hours. En route to the hospital, he was administered $2$ mg of intravenous hydromorphone due to severe pain in his legs. Upon arrival, the patient appears lethargic and somnolent. Vital signs include a blood pressure of $110/70$ mm Hg, pulse of $112$/min, and respiratory rate of $10$/min. Physical examination reveals tense, swollen, and exquisitely tender bilateral lower extremities.

Laboratory results are as follows:

Arterial blood gas analysis on room air:

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

A $35$-year-old woman with a history of Sjögren syndrome comes to the clinic due to progressive generalized weakness and fatigue for the past month. Her blood pressure is $110/70$ mm Hg and her physical examination is unremarkable except for dry oral mucosa.

Laboratory studies show:
- Serum sodium: $140$ mEq/L
- Serum potassium: $2.8$ mEq/L
- Serum chloride: $115$ mEq/L
- Serum bicarbonate: $13$ mEq/L
- Urine sodium: $45$ mEq/L
- Urine potassium: $25$ mEq/L
- Urine chloride: $40$ mEq/L

The patient's serum anion gap is calculated to be $12$ mEq/L (normal: $10-14$ mEq/L), indicating a normal anion gap metabolic acidosis. To help determine whether the acidosis is due to renal or gastrointestinal etiology, what is this patient's calculated urine anion gap (in mEq/L)?

Match each clinical presentation with its corresponding classic arterial blood gas and basic metabolic panel profile.

A $24$-year-old woman is brought to the emergency department by her roommate due to severe, progressive muscle weakness, dizziness, and palpitations over the past $3$ days. She has a history of generalized anxiety disorder. She takes no prescribed medications but admits to using over-the-counter supplements to help with weight loss. She denies any recent vomiting, diarrhea, or illicit drug use. On physical examination, her body mass index is $18.2$ kg/m $^2$. Blood pressure is $98/60$ mm Hg while supine and $82/50$ mm Hg upon standing. Pulse is $105$/min supine and $125$/min standing. Respiratory rate is $12$/min. Her mucous membranes are dry, and skin turgor is decreased. Neurologic examination reveals symmetrical $3/5$ strength in the proximal upper and lower extremities with diminished deep tendon reflexes.

Laboratory results are as follows:
Serum sodium: $135$ mEq/L
Serum potassium: $2.2$ mEq/L
Serum chloride: $84$ mEq/L
Serum bicarbonate: $38$ mEq/L
Blood urea nitrogen: $35$ mg/dL
Serum creatinine: $1.2$ mg/dL

Arterial blood gas (room air):
pH: $7.52$
pCO $_2$: $49$ mm Hg
pO $_2$: $92$ mm Hg

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

A $45$-year-old man with a history of severe alcohol use disorder is brought to the emergency department after $3$ days of intractable vomiting and generalized weakness. On physical examination, he appears lethargic and has dry mucous membranes with decreased skin turgor. Vital signs show a blood pressure of $95/60 \text{ mmHg}$, heart rate of $118/\text{min}$, and respiratory rate of $24/\text{min}$. Laboratory evaluation reveals the following:

- Serum sodium: $138 \text{ mEq/L}$
- Serum potassium: $3.2 \text{ mEq/L}$
- Serum chloride: $86 \text{ mEq/L}$
- Serum bicarbonate: $10 \text{ mEq/L}$
- Blood urea nitrogen: $42 \text{ mg/dL}$
- Serum creatinine: $1.9 \text{ mg/dL}$
- Plasma beta-hydroxybutyrate: elevated

Based on the provided laboratory values, the physician suspects a mixed acid-base disorder and decides to calculate the delta-delta (corrected) bicarbonate. Assuming a normal anion gap of $12 \text{ mEq/L}$, what is the patient's calculated delta-delta bicarbonate level?

A $32$-year-old man is brought to the emergency department by paramedics following a generalized tonic-clonic seizure. His roommate witnessed the event, reporting that the seizure lasted for approximately $10$ minutes before stopping on its own. On arrival, the patient is deeply lethargic and only withdraws to painful stimuli. His temperature is $37.2^\circ C$ ($99.0^\circ F$), blood pressure is $118/76$ $mmHg$, pulse is $110/min$, and respiratory rate is $8/min$. Pulse oximetry shows $92\%$ on room air.

Laboratory results are as follows:
Sodium: $140$ $mEq/L$
Potassium: $4.5$ $mEq/L$
Chloride: $100$ $mEq/L$
Bicarbonate: $12$ $mEq/L$
Blood urea nitrogen: $16$ $mg/dL$
Serum creatinine: $1.2$ $mg/dL$

An arterial blood gas drawn on room air reveals:
pH: $7.15$
pCO $_2$: $40$ $mmHg$
pO $_2$: $65$ $mmHg$

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

A $64$-year-old man comes to the clinic for a routine follow-up. He has a $15$-year history of type 2 diabetes mellitus, hypertension, and hyperlipidemia. His current medications include lisinopril, amlodipine, atorvastatin, and insulin glargine. Blood pressure is $138/86 \text{ mm Hg}$, and pulse is $76\text{/min}$. Physical examination reveals decreased sensation to monofilament testing in the bilateral feet. Laboratory studies show the following:

Which of the following is the most likely primary mechanism responsible for this patient's laboratory findings?

Match each characteristic urinalysis sediment finding with its most likely underlying renal pathology.

During morning rounds in the medical intensive care unit, a physician evaluates a patient admitted for severe hypovolemia secondary to intractable diarrhea.

The patient, a $55$-year-old male, reports four days of unremitting watery stools. Intravenous fluid resuscitation is planned but has not yet been initiated. Vital signs show a blood pressure of $90/60\text{ mm Hg}$ and a heart rate of $110/\text{min}$. Physical examination is notable for poor skin turgor, delayed capillary refill, and dry oral mucosa. Laboratory analysis of blood and urine samples obtained simultaneously reveals the following values:

Based on these findings, what is the patient's calculated fractional excretion of sodium (in percent)?

A 19-year-old woman is brought to the emergency department by her roommate due to nausea, vomiting, and "ringing" in her ears. The roommate reports that the patient was distraught after a severe argument and ingested an unknown quantity of an over-the-counter pain medication approximately 5 hours ago. On physical examination, her temperature is 37.8°C (100.0°F), blood pressure is 112/68 mm Hg, pulse is 115/min, and respirations are 32/min. She appears agitated and is breathing deeply and rapidly. Her lungs are clear to auscultation bilaterally.

Laboratory studies show:
* Serum sodium: $139$ mEq/L
* Serum potassium: $3.7$ mEq/L
* Serum chloride: $103$ mEq/L
* Serum bicarbonate: $14$ mEq/L
* Blood urea nitrogen: $16$ mg/dL
* Serum creatinine: $0.9$ mg/dL

Arterial blood gas analysis on room air reveals:
* pH: $7.46$
* $PaCO_2$: $20$ mm Hg
* $PaO_2$: $105$ mm Hg
* $HCO_3^-$: $14$ mEq/L

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

A series of patients undergo evaluation for various nephritic and nephrotic syndromes. Based on the underlying pathophysiologic mechanisms, match each specific glomerular disease with its characteristic defining renal biopsy finding.