USMLE USMLE Certifications USMLE-STEP-3 Questions & Answers

• Question 561:

  The most common site of aortic transection in deceleration injuries is which of the following?

  A. the root of the aorta

  B. at the level of the right innominate artery

  C. at the level of the left innominate artery

  D. near the origin of the left subclavian artery

  E. in the middle portion of the descending thoracic aorta

  Correct Answer: D Section: (none)

  Explanation:

  In deceleration injuries, laceration involving the aorta most frequently occurs just distal to the left subclavian artery at the level of the ligamentum arteriosum. This is where the aorta is fixed and thus more susceptible to shear forces. The tear may be complete or partial. Diagnosis is difficult, but is suggested by a widened mediastinum on chest x-ray and confirmed with a CT scan of the chest or an aortogram.

• Question 562:

  Vital capacity is best described as the volume of air which is:

  A. inhaled during normal respiration

  B. expelled during passive expiration

  C. remaining in the lungs after passive expiration

  D. actively exchanging with pulmonary venous blood

  E. able to be expelled following maximal inspiration

  Correct Answer: E Section: (none)

  Explanation:

  Vital capacity is an important measure of respiratory function. It is defined as the maximum volume of air a person can expel following a maximum inspiratory effort. When vital capacity is normal, significant restrictive pulmonary disease is not present. Acutely decreased vital capacity indicates decreased ventilatory reserve.

• Question 563:

  A man who underwent total thyroidectomy 24 hours ago now complains of a generalized "tingling" sensation and muscle cramps. Appropriate treatment would include which of the following?

  A. intravenous infusion of calcium gluconate

  B. administration of oxygen by mask

  C. administration of an anticonvulsant

  D. administration of a tranquilizer

  E. neurologic consultation

  Correct Answer: A Section: (none)

  Explanation:

  During total thyroidectomy, parathyroid glands may inadvertently be removed or their vascular supply interrupted. Hypoparathyroidism may then develop, the manifestations of which include tingling, muscle cramps, convulsions, and a positive Chvostek's sign (contraction of facial muscles after tapping the facial nerve). These symptoms are dramatically relieved by intravenous administration of calcium. Oral calcium and vitamin D are administered for long-term correction of hypocalcemia.

• Question 564:

  A severely traumatized patient who has been receiving prolonged parenteral alimentation develops diarrhea, mental status changes, alopecia, and perioral and periorbital dermatitis. Administration of which of the following trace element is most likely to reverse these complications?

  A. iodine

  B. zinc

  C. selenium

  D. silicon

  E. tin

  Correct Answer: B Section: (none)

  Explanation:

  Symptoms of zinc deficiency include diarrhea, mental status changes, alopecia, and periorbital, perinasal, and perioral dermatitis. Persons who have cirrhosis, who are receiving steroids, who have excessive loss of GI secretions, or who are severely traumatized are at risk for zinc deficiency. Deficiency states resulting from inadequate ingestion of selenium, silicon, and tin have not been described. Deficiency of iodine produces hypothyroidism.

• Question 565:

  A 30-year-old male is brought to the ED after being hit in the head by a baseball. He is making incomprehensible sounds, but no words. He opens his eyes and withdraws to painful stimuli.

  The most appropriate next step in the treatment of this patient is:

  A. neurosurgery consultation

  B. intubation and mechanical ventilation

  C. CT scan of head to evaluate for intracranial blood

  D. administration of mannitol to prevent cerebral herniation

  E. blood and urine toxicology screens

  Correct Answer: B Section: (none)

  Explanation: The Glasgow Coma Scale is used to quantify a neurologic examination in patients with a head injury. It is based on three elements: eye opening, motor response, and verbal response. The total score ranges from 3 (worst) to 15 (best) with a score of 8 or lower indicating a coma. The scale is shown below. This patient has a score of 2E. + 4(M) + 2(V) = 8. This patient has evidence of a severe head injury. The initial step should be to protect his airway and prevent hypoxia, which could adversely affect his head injury. Thus, the initial step should be endotracheal intubation. Neurosurgical expertise, imaging to define the injury, and screens to rule out drugs or alcohol as contributions are all important, but should be performed after airway, breathing, and circulation are addressed. Mannitol is indicated in patients with evidence of herniation, such as those with pupillary dilatation.

  

• Question 566:

  A 30-year-old male is brought to the ED after being hit in the head by a baseball. He is making incomprehensible sounds, but no words. He opens his eyes and withdraws to painful stimuli. His Glasgow Coma Scale score is:

  A. 10

  B. 9

  C. 8

  D. 7

  E. 6

  Correct Answer: C Section: (none)

  Explanation:

  The Glasgow Coma Scale is used to quantify a neurologic examination in patients with a head injury. It is based on three elements: eye opening, motor response, and verbal response. The total score ranges from 3 (worst) to 15 (best) with a score of 8 or lower indicating a coma. The scale is shown below. This patient has a score of 2E. + 4(M) + 2(V) = 8. This patient has evidence of a severe head injury. The initial step should be to protect his airway and prevent hypoxia, which could adversely affect his head injury. Thus, the initial step should be endotracheal intubation. Neurosurgical expertise, imaging to define the injury, and screens to rule out drugs or alcohol as contributions are all important, but should be performed after airway, breathing, and circulation are addressed. Mannitol is indicated in patients with evidence of herniation, such as those with pupillary dilatation.

  

• Question 567:

  Which of the following structures can be found outside of the spermatic cord during a hernia repair?

  A. direct hernia sac

  B. indirect hernia sac

  C. vas deferens

  D. testicular artery

  E. ovary

  Correct Answer: A Section: (none)

  Explanation:

  A direct hernia comes through the medial inguinal canal floor and is found behind the spermatic cord. An indirect hernia passes though the internal inguinal ring, and thus can be found within the spermatic cord. The spermatic cord also contains the vas deferens, the testicular artery, lymphatics, and nerve fibers.

• Question 568:

  Patients with septic arthritis of the hip joint usually present with which position?

  A. internal rotation and flexion

  B. internal rotation and extension

  C. internal rotation and abduction

  D. external rotation and flexion

  E. external rotation and abduction

  Correct Answer: D Section: (none)

  Explanation:

  The joint space is most relaxed when the hip is flexed and externally rotated. This tends to be the least painful position for patients with septic arthritis

• Question 569:

  A 21-year-old male presents to the ED after sustaining a gunshot wound to the neck. After evaluation, it is determined that he has C6 quadriplegia.

  Which of the following activities will be limited by this injury?

  A. wrist extension

  B. elbow extension

  C. elbow flexion

  D. shoulder flexion

  E. raising his arms above his shoulders

  Correct Answer: B Section: (none)

  Explanation:

  This patient should be able to perform any activity that requires innervation from C6 or above. The biceps and deltoid are innervated by C5, so he should be able to lift his arms above his head, have shoulder flexion, and elbow flexion. C6 innervates the extensor carpi radialis, so wrist extension should be preserved. The triceps rely on C7, so he would not be able to perform elbow extension.

• Question 570:

  During laparoscopic abdominal procedures, the abdominal cavity is usually insufflated with carbon dioxide to a pressure of 15 mmHg. Increasing the intra-abdominal pressure to these levels produces which of the following1 physiologic responses?

  A. decreased afterload

  B. depressed cardiac output

  C. hypercarbia

  D. depressed diaphragm

  E. alkalosis

  Correct Answer: C Section: (none)

  Explanation:

  Increasing abdominal pressures for laparoscopic procedures has several systemic effects. By increasing the carbon dioxide, patients become hypercarbic and acidotic. There is decreased venous return and increased afterload. The peritoneum is distended and the diaphragm elevated. In patients with normal cardiac function, cardiac output is not affected until the abdominal pressures reach about 20 mmHg.