Two hours after admission to the intensive care unit, a 56-year-old man with necrotizing pancreatitis develops profound hypotension. His blood pressure is 80/50 mm Hg and he is started on vasopressors. A central venous access line is placed. Which of the following is most likely to decrease the risk of complications from this procedure?

Preparation of the skin with chlorhexidine and alcohol

Placement of the central venous line in the femoral vein

Replacement of the central venous line every 7-10 days

Initiation of anticoagulation after placement

Initiation of periprocedural systemic antibiotic prophylaxis

A 43-year-old woman comes to the physician because of a 3-month history of a painless ulcer on the sole of her right foot. There is no history of trauma. She has been dressing the ulcer once daily at home with gauze. She has a 15-year history of poorly-controlled type 1 diabetes mellitus and hypertension. Current medications include insulin and lisinopril. Vital signs are within normal limits. Examination shows a 2 x 2-cm ulcer on the plantar aspect of the base of the great toe with whitish, loose tissue on the floor of the ulcer and a calloused margin. A blunt metal probe reaches the deep plantar space. Sensation to vibration and light touch is decreased over both feet. Pedal pulses are intact. An x-ray of the right foot shows no abnormalities. Which of the following is the most appropriate initial step in management?

Sharp surgical debridement of the ulcer

Surgical revascularization of the right foot

Amputation of the right forefoot

Total contact casting of right foot

A previously healthy 5-year-old boy is brought to the emergency department 15 minutes after sustaining an injury to his right hand. His mother says that she was cleaning the bathroom when he accidentally knocked over the drain cleaner bottle and spilled the liquid onto his hand. On arrival, he is crying and holding his right hand in a flexed position. His temperature is 37.7°C (99.8°F), pulse is 105/min, respirations are 25/min, and blood pressure is 105/65 mm Hg. Examination of the right hand shows a 4 x 4 cm area of reddened, blistered skin. The area is very tender to light touch. His ability to flex and extend the right hand are diminished. Radial pulses are palpable. Capillary refill time is less than 3 seconds. Which of the following is the most appropriate next step in management?

Apply split-thickness skin graft

A 38-year-old, working, first-time mother brings her 9-month-old male infant to the pediatrician for "wounds that simply won't heal" and bleeding gums. She exclaims, "I have been extra careful with him making sure to not let him get dirty, I boil his baby formula for 15 minutes each morning before I leave for work to give to the caregiver, and he has gotten all of his vaccinations." This infant is deficient in a molecule that is also an essential co-factor for which of the following reactions?

Conversion of dopamine to norepinephrine

Conversion of homocysteine to methionine

Conversion of alpha ketoglutarate to succinyl-CoA

Conversion of pyruvate to acetyl-CoA

Conversion of pyruvate to oxaloacetate

A 15-year-old boy is brought to the emergency department by ambulance after his mother found him having muscle spasms and stiffness in his room. His mother stated he scraped his foot on a rusty razor on the bathroom floor 2 days prior. On presentation, his temperature is 102.0°F (38.9°C), blood pressure is 108/73 mmHg, pulse is 122/min, and respirations are 18/min. On physical exam, he is found to have severe muscle spasms and rigid abdominal muscles. In addition, he has a dirty appearing wound on his right foot. The patient's mother does not recall any further vaccinations since age 12. Finally, he is found to have difficulty opening his mouth so he is intubated. Which of the following treatment(s) should be provided to this patient?

Wound debridement, antitoxin, and booster vaccine

Wound debridement and antitoxin

Wound debridement and booster vaccine

A 39-year-old man comes to the physician for a follow-up examination. He was treated for a urinary tract infection with trimethoprim-sulfamethoxazole 2 months ago. He is paraplegic as a result of a burst lumbar fracture that occurred after a fall 5 years ago. He has hypertension and type 2 diabetes mellitus. Current medications include enalapril and metformin. He performs clean intermittent catheterization daily. He has smoked one pack of cigarettes daily for 19 years. His temperature is 37.1°C (98.8°F), pulse is 95/min, respirations are 14/min, and blood pressure is 120/80 mm Hg. He appears malnourished. Examination shows palpable pedal pulse. Multiple dilated tortuous veins are present over both lower extremities. There is a 2-cm wound surrounded by partial-thickness loss of skin and a pink wound bed over the right calcaneum. Neurologic examination shows paraparesis. His hemoglobin A1c is 6.5%, and fingerstick blood glucose concentration is 134 mg/dL. Which of the following is most likely to have prevented this patient's wound?

Broad-spectrum antibiotic therapy

A 63-year-old man comes to the emergency department because of pain in his left groin for the past hour. The pain began soon after he returned from a walk. He describes it as 8 out of 10 in intensity and vomited once on the way to the hospital. He has had a swelling of the left groin for the past 2 months. He has chronic obstructive pulmonary disease and hypertension. Current medications include amlodipine, albuterol inhaler, and a salmeterol-fluticasone inhaler. He appears uncomfortable. His temperature is 37.4°C (99.3°F), pulse is 101/min, and blood pressure is 126/84 mm Hg. Examination shows a tender bulge on the left side above the inguinal ligament that extends into the left scrotum; lying down or applying external force does not reduce the swelling. Coughing does not make the swelling bulge further. There is no erythema. The abdomen is distended. Bowel sounds are hyperactive. Scattered rhonchi are heard throughout both lung fields. Which of the following is the most appropriate next step in management?

Surgical exploration of the testicle

Surgical wound classification for USMLE Step 2 CK: High-Yield Surgery Lessons

Wound Classes - A Clean Sweep

Class	Description & Tract Entry	Examples	Infection Risk (%)
I: Clean	Uninfected; no inflammation. Resp, GI, GU tracts not entered.	Hernia repair, breast biopsy	<2%
II: Clean-Contaminated	Resp, GI, GU tracts entered under controlled conditions.	Elective cholecystectomy, appendectomy	~5-10%
III: Contaminated	Open, fresh, accidental wounds; major break in sterile technique.	Penetrating trauma, gross GI spillage	~10-20%
IV: Dirty/Infected	Existing clinical infection or perforated viscera.	Abscess I&D, perforated diverticulitis	>20-40%

⭐ Most surgical site infections (SSIs) are caused by the patient's endogenous skin flora, most commonly Staphylococcus aureus.

The 4 Tiers - From Clean to Catastrophe

Surgical wounds are classified by contamination level at the time of surgery, which directly predicts the risk of surgical site infection (SSI).

Class I: Clean
- Uninfected, non-inflammatory wound; no hollow viscus (GI, respiratory, GU tracts) entered.
- Examples: Hernia repair, breast biopsy, elective orthopedic surgery.
- SSI Risk: <2%.
Class II: Clean-Contaminated
- Hollow viscus entered under controlled conditions without unusual contamination.
- Examples: Elective cholecystectomy, uncomplicated appendectomy.
- SSI Risk: 2-10%.
Class III: Contaminated
- Open, fresh, accidental wounds; or major break in sterile technique; or gross spillage from GI tract.
- Examples: Penetrating abdominal trauma, inflamed appendectomy with spillage.
- SSI Risk: 10-20%.
Class IV: Dirty/Infected
- Old traumatic wounds, existing clinical infection, or perforated viscera.
- Examples: Incision & drainage of an abscess, perforated diverticulitis.
- SSI Risk: >20%.

⭐ The classification dictates antibiotic use. Class I wounds may not require prophylaxis unless hardware (e.g., mesh, prosthesis) is implanted. Class III/IV wounds require therapeutic antibiotics.

Class & Consequences - The Bug Battle Plan

Wound Class → Infection Risk

Class I (Clean): Elective, non-traumatic, primarily closed. No acute inflammation.
- Ex: Hernia repair, breast biopsy.
Class II (Clean-Contaminated): GI/GU/respiratory tract entered, but controlled.
- Ex: Elective cholecystectomy, lung lobectomy.
Class III (Contaminated): Major sterile break; gross spillage; acute inflammation.
- Ex: Inflamed appendectomy, open fracture <4 hrs old.
Class IV (Dirty/Infected): Existing infection, perforated viscera, old traumatic wound.
- Ex: Abscess drainage, perforated diverticulitis.

⭐ Most surgical site infections (SSIs) are caused by the patient's endogenous skin flora, with Staphylococcus aureus being the most common pathogen across all wound classes.

High‑Yield Points - ⚡ Biggest Takeaways

Class I (Clean) wounds have an infection risk of <2%; they are uninfected with no entry into visceral tracts.

Class II (Clean-Contaminated) involves controlled entry into tracts, with an infection risk of ~5-10%.

Class III (Contaminated) includes open, fresh accidental wounds or major sterile breaks; risk is ~10-20%.

Class IV (Dirty/Infected) involves pre-existing infection or perforation, with a risk of ~25-40%.

This classification directly predicts Surgical Site Infection (SSI) risk and guides antibiotic use.

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