Nephrology

A 27-year-old woman is brought to the emergency department by her roommate due to persistent nausea, vomiting, and diffuse abdominal pain for the past 24 hours. She has a history of type 1 diabetes mellitus and reports that she ran out of her insulin prescription two days ago. On physical examination, she appears lethargic but is easily arousable. Her respiratory rate is $26/\text{min}$ and breaths are deep and rapid.

Laboratory testing reveals the following:

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

Match each clinical scenario with its most likely primary acid-base disorder.

Match each commonly prescribed medication with its primary mechanism of inducing acute kidney injury (AKI).

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 19-year-old college student presents to the student health clinic complaining of severe, watery diarrhea for the past 3 days after returning from a camping trip. He reports feeling profoundly weak and lightheaded when standing. His temperature is 37.2°C (99.0°F), blood pressure is 98/60 mm Hg while supine and 82/50 mm Hg while standing, and pulse is 115/min. Physical examination shows dry mucous membranes and delayed capillary refill. Laboratory results reveal:

Serum sodium: $138 \text{ mEq/L}$
Serum potassium: $3.1 \text{ mEq/L}$
Serum chloride: $112 \text{ mEq/L}$
Serum bicarbonate: $14 \text{ mEq/L}$

Arterial blood gas on room air:
pH: 7.28
$pCO_2$: 29 mm Hg
$pO_2$: 95 mm Hg

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

Match each complex clinical scenario and corresponding arterial blood gas/basic metabolic panel profile with the most accurate interpretation of the patient's mixed acid-base disorder. Evaluate the anion gap, delta gap (delta-delta), and appropriate respiratory compensation to determine the correct physiological state.

A 72-year-old man is brought to the emergency department from a nursing home due to altered mental status, fever, and rapid breathing for the past day. He has a history of benign prostatic hyperplasia and type 2 diabetes mellitus. His temperature is $39.1^\circ\text{C}$ ($102.4^\circ\text{F}$), blood pressure is $85/50\text{ mm Hg}$, pulse is $122/\text{min}$, and respiratory rate is $32/\text{min}$. Physical examination reveals a lethargic man with dry mucous membranes and right costovertebral angle tenderness.

Laboratory results are as follows:

Which of the following best describes this patient's primary and concurrent acid-base disturbances?

Match the following classic urinalysis sediment findings with their most likely associated renal pathology.

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?

Match each clinical scenario and associated arterial blood gas (ABG) profile with the most accurate description of the primary acid-base disturbance(s). Assume a normal anion gap is $8-12$ mEq/L.

A $42$-year-old male is evaluated in the urgent care clinic for persistent nausea and non-bilious emesis that has occurred multiple times daily over the past four days. He reports feeling profoundly weak and dizzy when standing up. His blood pressure is $98/60$ mm Hg while supine and drops to $82/50$ mm Hg upon standing. Heart rate is $112$/min. Physical examination reveals dry oral mucosa and decreased skin turgor. Laboratory studies show:

$Na^+$: $137$ mEq/L
$K^+$: $2.8$ mEq/L
$Cl^-$: $86$ mEq/L
$HCO_3^-$: $36$ mEq/L
$BUN$: $42$ mg/dL
Creatinine: $1.3$ mg/dL

Arterial blood gas reveals a $pH$ of $7.53$ and a $pCO_2$ of $46$ mm Hg.

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

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 $76$-year-old woman is brought to the emergency department by her daughter due to worsening confusion and rapid breathing that started earlier today. The daughter notes the patient has severe osteoarthritis and recently started taking a new "over-the-counter powder" for joint pain in addition to her prescribed medications. Temperature is $38.4^\circ\text{C}$ ($101.1^\circ\text{F}$), blood pressure is $110/70 \text{ mm Hg}$, pulse is $112/\text{min}$, and respiratory rate is $32/\text{min}$. Physical examination shows a confused, elderly woman. Mucous membranes are dry. Cardiopulmonary examination reveals clear lungs bilaterally and tachycardia without murmurs. Laboratory studies show:

Leukocyte count: $14,500/\text{mm}^3$
Serum sodium: $140 \text{ mEq/L}$
Serum potassium: $3.8 \text{ mEq/L}$
Serum chloride: $104 \text{ mEq/L}$
Serum bicarbonate: $12 \text{ mEq/L}$
Blood urea nitrogen: $32 \text{ mg/dL}$
Serum creatinine: $1.5 \text{ mg/dL}$
Thyroid-stimulating hormone (TSH): $0.2 \ \mu\text{U/mL}$ (Normal: $0.5-5.0$)
Free T4: $0.6 \text{ ng/dL}$ (Normal: $0.9-1.7$)

Arterial blood gas analysis on room air:
pH: $7.50$
$pCO_2$: $16 \text{ mm Hg}$
$pO_2$: $98 \text{ mm Hg}$

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

A 38-year-old woman comes to the clinic reporting progressive muscle weakness and fatigue over the past several weeks. She has a past medical history of Sjögren syndrome, for which she uses artificial tears and takes hydroxychloroquine. She denies recent diarrhea, vomiting, or changes in her medications. Vital signs are within normal limits.

Laboratory studies show:
Sodium: $139 \text{ mEq/L}$
Potassium: $2.6 \text{ mEq/L}$
Chloride: $113 \text{ mEq/L}$
Bicarbonate: $14 \text{ mEq/L}$

Arterial blood gas on room air:
pH: $7.26$
PaCO2: $29 \text{ mm Hg}$

Urinalysis reveals a pH of $6.8$ with no glucose, protein, or blood.

Which of the following is the most likely primary mechanism for this patient's acid-base and electrolyte abnormalities?

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?

An outpatient evaluation is requested for a 35-year-old woman complaining of new-onset profound generalized weakness and intermittent palpitations over the past two weeks. Her medical history is notable for rheumatoid arthritis and severe dry eyes, for which she frequently uses artificial tears. Her blood pressure is $118/76 \text{ mmHg}$ and heart rate is $92\text{/min}$. Laboratory studies show the following:

Urinalysis demonstrates a $pH$ of $6.5$, with no glucose, protein, or blood. Urine electrolytes reveal a sodium of $45 \text{ mEq/L}$, potassium of $25 \text{ mEq/L}$, and chloride of $50 \text{ mEq/L}$. Which of the following best describes the underlying pathophysiologic defect in this patient?

A 68-year-old man is brought to the emergency department from a nursing facility due to fever, cough, and progressive lethargy over the past 2 days. His medical history is significant for chronic kidney disease, hypertension, and benign prostatic hyperplasia. Temperature is 38.8°C (101.8°F), blood pressure is 88/54 mm Hg, pulse is 112/min, and respiratory rate is 22/min with shallow breathing. Physical examination reveals crackles in the right lower lung base and delayed capillary refill. The patient is somnolent and only arouses to painful stimuli.

Arterial blood gas (room air):
- pH: 7.08
- $pCO_2$: 35 mm Hg
- $pO_2$: 65 mm Hg

Serum chemistries:
- Sodium: 138 mEq/L
- Potassium: 4.5 mEq/L
- Chloride: 102 mEq/L
- Bicarbonate: 10 mEq/L
- Blood urea nitrogen: 45 mg/dL
- Creatinine: 2.8 mg/dL
- Lactate: 5.2 mmol/L (Normal 0.5-1.5 mmol/L)

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

A 24-year-old man is brought to the emergency department due to a 2-day history of generalized weakness, excessive urination, and diffuse abdominal pain. He was diagnosed with type 1 diabetes mellitus 10 years ago and recently missed several doses of his insulin regimen. On physical examination, he appears lethargic and his mucous membranes are dry. Laboratory studies reveal a serum bicarbonate level of 12 mEq/L and an arterial blood pH of 7.28. Which of the following is the expected arterial partial pressure of carbon dioxide ($PaCO_2$) in this patient if appropriate respiratory compensation has occurred?