A 52-year-old man comes to the emergency department with a 24-hour history of pain and swelling of his right knee.  He has no fevers, chills, or recent trauma to the knee.  In addition, the patient has had constipation, excessive urination, and fatigue for the past several months.  His medical history is notable for a kidney stone a year ago that passed with intravenous and oral hydration.  The patient does not take any prescription medications, and does not use tobacco, alcohol, or illicit drugs.  His temperature is 37.2 C (98.9 F) and blood pressure is 130/76 mm Hg.  Examination shows tenderness, erythema, and swelling of the right knee.  The remainder of the examination is unremarkable.  Laboratory results are as follows:

Arthrocentesis is performed.  Which of the following is most likely to be found on synovial fluid assessment in this patient?

A 40-year-old man is intubated and receiving mechanical ventilation after being found unresponsive on the floor of his apartment.  The patient is sedated and initiates no spontaneous breaths.  The ventilator triggers 14 breaths/min, each delivering 500 mL of tidal volume.  Because of difficulty in ventilating the patient’s airway, an inspiratory hold maneuver is performed to further evaluate his respiratory mechanics.  During this maneuver, the ventilator is paused for 2 seconds after the entire tidal volume is delivered.  The pressure at the mouthpiece, measured when there is no flow, is found to be elevated.

The measured pressure most likely reflects which of the following?

A 28-year-old woman comes to the emergency department due to bilateral upper extremity weakness and abdominal pain.  The patient has had progressive weakness of the upper extremities for 2 days and severe, diffuse, poorly localized abdominal pain for 1 day.  Temperature is 37.3 C (99.1 F), blood pressure is 148/86 mm Hg, and pulse is 112/min.  On physical examination, the patient appears restless and is diaphoretic.  There is no scleral icterus.  The abdomen is soft and nontender, with no organomegaly, guarding, or rebound tenderness.  Bowel sounds are decreased.  Neurological examination shows normal cranial nerves, weakness of the proximal upper extremity muscles, and loss of the biceps and triceps reflexes on both sides.  Laboratory results are as follows:

Which of the following is most likely to yield the diagnosis in this patient?

A 24-year-old man is brought to the office by his parents due to hand shaking and involuntary movements, which have progressively worsened over the last 6 months.  A year ago, he was diagnosed with depression and treated with fluoxetine for 5 months but stopped the medication and did not follow up with his psychiatrist.  His medical history is otherwise unremarkable.  The patient has smoked cigarettes intermittently in the past but does not drink alcohol or use illicit drugs.  He dropped out of college and has worked as a delivery man for the last several years.  Blood pressure is 122/82 mm Hg supine and 120/84 mm Hg standing.  Physical examination reveals clear breath sounds and no cardiac murmurs.  The liver is enlarged, firm, and nontender, and the spleen is not palpable.  There is tremor of both hands that increases with activity.  Occasional rapid, jerky contractions of the distal extremities are also seen.  Laboratory results are as follows:

Viral hepatitis panel is negative.  Which of the following is the most likely diagnosis?

A 75-year-old man is brought to the emergency department from home after being found unresponsive by his son.  His medical history is significant for coronary artery disease with coronary stenting 2 years ago, diabetes mellitus, hypertension, and stroke.  He was hospitalized 2 months ago with pneumonia and upper gastrointestinal bleeding, during which time he received intravenous antibiotics and a transfusion of 4 units of packed red blood cells.  In the emergency department today, temperature is 39.1 C (102.4 F), blood pressure is 70/40 mm Hg, pulse is 120/min, respiratory rate is 32/min, and oxygen saturation is 79% on room air.  Laboratory results are notable for leukocytosis but are otherwise unremarkable.  Chest x-ray reveals a new right upper lobe infiltrate.  He is treated with normal saline, antibiotics, vasopressors, and mechanical ventilation.  The next day, laboratory analyses reveal the following:

Which of the following most likely accounts for the abnormal liver function panel?

A 54-year-old woman comes to the emergency department due to several hours of severe epigastric abdominal pain.  The patient began having mild colicky upper abdominal pain after dinner last night and took acetaminophen before going to bed.  In the night, the patient awoke with severe abdominal pain radiating to her back.  She has also had nausea and several episodes of vomiting.  The patient has a history of occasional upper abdominal pain after eating but has never had such severe symptoms.  She has no other medical issues and takes no medications.  Temperature is 37.6 C (99.6 F), blood pressure is 110/66 mm Hg, pulse is 118/min, and respirations are 24/min.  The patient appears to be in moderate distress.  Mucous membranes are dry.  The abdomen is distended with marked epigastric tenderness.  Bowel sounds are decreased.  Laboratory results are as follows:

Which of the following sets of renal findings are most expected in this patient?

A 65-year-old man comes to the emergency department due to lower extremity swelling and a 9.1-kg (20.1-lb) weight gain over the last month.  He also reports some shortness of breath at night.  The patient has a history of hypertension and coronary artery disease and underwent coronary artery bypass graft surgery 10 years ago.  The patient does not smoke or use recreational drugs.  Temperature is 36.7 C (98.1 F), blood pressure is 140/92 mm Hg, pulse is 98/min, and respirations are 18/min.  Examination shows jugular venous distension.  Breath sounds are decreased at the bilateral bases.  The point of maximal impulse is laterally displaced.  S1 and S2 are normal, and a II/VI holosystolic murmur is present at the apex.  There is 3+ pretibial edema bilaterally.  Laboratory results are as follows:

Chest x-ray reveals an enlarged cardiac silhouette and pulmonary vascular congestion.  The patient is treated with intravenous furosemide for 4 days, with a return to his baseline weight and resolution of his edema.  Serum chemistry shows an improvement in creatinine to 1.1 mg/dL.  Which of the following is the most likely mechanism by which this drug therapy led to improved renal function?

A 17-year-old girl is brought to the emergency department due to acute abdominal pain, nausea, and vomiting.  She has no chronic medical conditions and has had no surgery.  The patient has had irregular menstruation and is not sexually active.  Family history is significant for deep venous thrombosis following knee replacement in her mother, who takes apixaban.  Temperature is 38.3 C (101 F).  BMI is 18 kg/m².  Physical examination shows right lower quadrant abdominal tenderness.  CT scan of the abdomen reveals acute appendicitis, and laparoscopic appendectomy is planned.  Preoperative laboratory studies demonstrate a platelet count of 400,000/mm³.  Coagulation study results are as follows:

Mixing the patient’s plasma sample with normal plasma fails to correct the coagulation abnormalities.  Which of the following best explains this patient’s coagulation study results?

A 60-year-old man is brought to the emergency department due to fever, chills, and confusion.  The patient was fishing in the ocean yesterday and cut his foot on a jagged rock while wading through shallow water.  He was unable to clean the wound right away, and overnight, it became increasingly red and painful.  The patient was awakened several times by fever and chills, and this morning, his wife found him disoriented.  Medical history includes hypertension.  Temperature is 38.8 C (101.8 F), blood pressure is 86/62 mm Hg, pulse is 118/min, and respirations are 24/min.  On physical examination, the patient is in moderate distress.  Heart sounds are rapid and regular with no murmurs.  The lungs are clear to auscultation.  Breathing is fast and shallow.  The right foot shows a laceration with purulent drainage and erythema spreading to the midshin.  The results of arterial blood gas testing on room air are as follows:

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

A 34-year-old woman comes to the office for evaluation of skin lesions.  For the past year, she has noticed darkening and thickening of the skin over her neck and groin areas.  These areas occasionally feel itchy.  Blood pressure is 130/80 mm Hg.  Skin examination findings are shown in the image below.

Similar hyperpigmented, velvety lesions are found on the axilla and groin.  This patient’s skin manifestations are most likely associated with which of the following underlying conditions?

A 30-year-old man comes to the office due to 2 months of lower extremity swelling and skin lesions on his groin.  The lesions are not painful.  Review of systems is positive for frequent loose stools and a 10% weight loss from baseline.  The patient used intravenous heroin in the past and was hospitalized 3 years ago for right upper extremity cellulitis near an injection site.  Temperature is 37.2 C (99 F), blood pressure is 132/78 mm Hg, and pulse is 92/min.  BMI is 22 kg/m².  Oral mucosa appears normal.  Bilateral inguinal lymphadenopathy and mild lower extremity edema are present.  Skin examination of the groin region is shown below:

This patient would benefit most from which therapy?

A 60-year-old man comes to the office after he was found to have a “low blood count” when attempting to donate blood.  The patient is in his usual state of health and feels well.  He has no chronic medical problems but has been treated for pneumonia twice during the past year.  The patient takes no medications and does not use tobacco or alcohol.  Temperature is 37 C (98.6 F), blood pressure is 120/80 mm Hg, and pulse is 76/min.  Physical examination reveals mucosal pallor.  There are no enlarged lymph nodes.  The abdomen is soft and nontender.  The spleen tip is palpable 5 cm below the left costal margin; the liver is normal in size.  Stool guaiac is negative.  Complete blood count results are as follows:

Peripheral blood smear shows predominant lymphocytes with features as seen in the image below.

Which of the following is the most likely diagnosis?

A 68-year-old woman with a history of advanced chronic obstructive pulmonary disease comes to the emergency department due to increased shortness of breath and cough for 12 hours.  She took 2 extra nebulizer treatments at home with no relief of symptoms.  She has no fever, nausea, vomiting, or hemoptysis.  The patient has been oxygen dependent for the last 2 years.  She has a 45-pack-year smoking history and quit about 6 years ago.  Medications include tiotropium daily, fluticasone/salmeterol twice daily, and albuterol by metered-dose inhaler or nebulizer as needed.  Temperature is 36.7 C (98.1 F), blood pressure is 110/65 mm Hg, pulse is 110/min, and respirations are 28/min.  The patient appears dyspneic and in moderate distress.  She is given intravenous antibiotics, methylprednisolone, and 2 treatments of nebulized ipratropium with albuterol.  Following these measures, the patient remains dyspneic and uses accessory muscles of respiration but is alert and follows commands.  On 4 L/min O₂, her pulse oximetry is 89%, and arterial blood gas shows pH of 7.30, PCO₂ of 63 mm Hg, and PO₂ of 54 mm Hg.  Chest x-ray, shown in the image below, demonstrates hyperinflation:

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

A 34-year-old man is brought to the emergency department due to confusion.  The patient recently lost his job and moved in with his parents yesterday because he could no longer afford housing.  Today, his mother found him disoriented and unsteady.  He has no known chronic medical conditions and takes no medications.  Temperature is 38.5 C (101.3 F), blood pressure is 164/90 mm Hg, pulse is 108/min, and respirations are 22/min.  The patient appears restless and is constantly picking at the bed linens, yelling, “Get these bugs off me.”  The lungs are clear on auscultation, and cardiac examination is unremarkable with the exception of regular tachycardia.  The abdomen is soft and nontender.  No extremity edema is present.  Laboratory results are as follows:

Which of the following would be most helpful to improve this patient’s current condition?