A thorough history and physical is the cornerstone of preoperative risk assessment. Cardiac evaluation begins with the Revised Cardiac Risk Index (RCRI), which assigns one point each for: high-risk surgery (intraperitoneal, intrathoracic, suprainguinal vascular), ischemic heart disease, congestive heart failure, cerebrovascular disease, insulin-dependent diabetes, and preoperative serum creatinine >2.0 mg/dL. For patients with RCRI ≥2, consider further cardiac testing only if it will change management. Pulmonary risk is stratified using the STOP-Bang questionnaire (snoring, tiredness, observed apnea, pressure/hypertension, BMI >35, age >50, neck circumference >40 cm, male gender); a score ≥5 indicates high risk for obstructive sleep apnea and perioperative respiratory complications. A focused airway exam (Mallampati classification, thyromental distance, mouth opening) is essential for anesthesia planning. Functional capacity assessed in metabolic equivalents (METs) provides a practical measure of physiologic reserve; inability to climb two flights of stairs (<4 METs) is associated with increased perioperative morbidity and mortality.

Preoperative testing should be targeted rather than routine, guided by patient age, comorbidities, and surgical complexity. For low-risk procedures in healthy patients, no routine labs are indicated. For intermediate- to high-risk surgery or patients with significant comorbidities, obtain a CBC, basic metabolic panel, coagulation studies (PT/PTT/INR), and ECG in patients aged ≥65 or with cardiac risk factors. Type and screen or crossmatch is obtained for procedures with anticipated blood loss >500 mL. Chest X-ray is reserved for patients with unexplained respiratory symptoms or known cardiopulmonary disease. Pregnancy testing should be offered to all women of childbearing age. Echocardiography is indicated for patients with new or unexplained dyspnea, known heart failure with change in clinical status, or if valvular disease is suspected on exam. Stress testing is reserved for patients with three or more RCRI factors or poor functional capacity undergoing high-risk surgery.

Perioperative medication management requires balancing thrombotic and bleeding risks. For anticoagulation: warfarin is typically held 5 days preoperatively with INR checked the day before surgery; heparin bridging (LMWH or IV UFH) is used in patients at high thromboembolic risk (mechanical mitral valve, recent VTE within 3 months, atrial fibrillation with CHA2DS2-VASc ≥6 or prior stroke). DOACs (apixaban, rivaroxaban, dabigatran, edoxaban) are held 24-48 hours before surgery depending on renal function and bleeding risk; they do not require bridging. Antiplatelet therapy: aspirin is generally continued for primary prevention but held 5-7 days before surgery for high-bleeding-risk procedures; for secondary prevention (CAD, CVA, stents), aspirin is typically continued unless bleeding risk is prohibitive. For patients with coronary stents, elective surgery should be delayed: 4 weeks after bare-metal stent and 6 months after drug-eluting stent while continuing antiplatelet therapy. Perioperative beta-blockers: continue in patients already on them; initiation before surgery is recommended only if started at least 30 days before high-risk surgery. Statins should be continued perioperatively.

The ASA (American Society of Anesthesiologists) Physical Status Classification is a widely used global assessment tool: ASA I (normal healthy), ASA II (mild systemic disease), ASA III (severe systemic disease), ASA IV (severe disease that is a constant threat to life), ASA V (moribund, not expected to survive without surgery), and ASA VI (brain-dead organ donor). ASA class correlates with perioperative mortality: ASA I ~0.1%, ASA II ~0.2%, ASA III ~1.8%, ASA IV ~7.8%, ASA V ~9.4%. The NSQIP Surgical Risk Calculator provides procedure-specific, patient-specific risk estimates for 30-day morbidity and mortality based on 21 preoperative factors including age, functional status, ASA class, dyspnea, sepsis, ventilator dependence, ascites, and laboratory values. The NSQIP calculator is more accurate than clinical gestalt for predicting complications and should be used in shared decision-making. Frailty assessment using the 5-item Modified Frailty Index independently predicts postoperative complications, length of stay, and discharge disposition.

Informed consent is a legal and ethical requirement that must include discussion of the diagnosis, nature and purpose of the proposed procedure, material risks (including those with high probability and those with low probability but high severity), expected benefits, alternative treatment options including no treatment, and the probability of success. The consent must be obtained by the surgeon performing the procedure or a qualified designee with sufficient knowledge of the operation. Patients must be given adequate time to consider their options and ask questions. Advance directives (living will, durable power of attorney for healthcare) should be discussed with all patients, particularly the elderly and those with serious comorbidities. A goals-of-care conversation should document resuscitation preferences which may be temporarily modified during the perioperative period but must be explicitly reviewed and documented.

Standard NPO guidelines: clear liquids (water, black coffee, pulp-free juice, carbonated beverages) may be consumed up to 2 hours before anesthesia; a light meal up to 6 hours; and a full meal up to 8 hours prior to the procedure. Bowel preparation: for colorectal surgery, mechanical bowel preparation combined with oral antibiotics (neomycin + metronidazole or erythromycin base) reduces surgical site infection rates and anastomotic leak rates compared to mechanical preparation alone. Enhanced Recovery After Surgery (ERAS) protocols have shifted practice toward selective use of mechanical bowel preparation. Deep vein thrombosis (DVT) prophylaxis is the single most effective intervention for preventing venous thromboembolism in surgical patients. Risk stratification using the Caprini score determines the modality: low risk (Caprini 0-1): early ambulation; moderate risk (2-3): LMWH or unfractionated heparin or mechanical prophylaxis; high risk (≥4): pharmacologic + mechanical prophylaxis extended for 28 days after major cancer surgery or orthopedic procedures.

Surgical site infections (SSIs) are classified by depth: superficial incisional (involving skin and subcutaneous tissue within 30 days), deep incisional (involving fascia and muscle within 30-90 days), and organ/space (involving any anatomical structure deeper than the fascial layers within 30-90 days). The CDC NHSN risk index assigns 1 point each for: contaminated or dirty wound classification, ASA score ≥3, and operation duration exceeding the 75th percentile. Wound classification: Class I (clean) without entry into respiratory, GI, biliary, or GU tracts; Class II (clean-contaminated) with entry under controlled conditions; Class III (contaminated) from fresh accidental wounds or gross GI spillage; Class IV (dirty/infected) with existing clinical infection or perforated viscera. Patient-related risk factors include diabetes mellitus with HbA1c >8% doubling SSI risk, obesity with BMI >30, smoking, malnutrition with albumin <3.0 g/dL, immunosuppression, prolonged preoperative hospitalization, and nasal colonization with Staphylococcus aureus.

Surgical antibiotic prophylaxis is indicated for clean-contaminated procedures and clean procedures involving implant placement. The most critical principle is timing: the antibiotic infusion should be completed within 60 minutes before incision (120 minutes for vancomycin and fluoroquinolones). Cefazolin (1-2 g IV) is the most commonly used prophylactic agent for its excellent gram-positive coverage. For colorectal surgery, anaerobic coverage is added (cefoxitin or cefazolin + metronidazole). For patients with beta-lactam allergy, alternatives include clindamycin + gentamicin or vancomycin. Redosing is required if the procedure exceeds two half-lives of the antibiotic (2 hours for cefazolin) or if there is major blood loss (>1500 mL). Prophylaxis should be discontinued within 24 hours after wound closure; prolonged administration does not reduce SSI and promotes resistance.

Management depends on depth and severity. Superficial incisional SSI: remove skin staples or sutures, open the wound, obtain culture, and initiate twice-daily wet-to-dry dressing changes. Antibiotics are indicated only with systemic toxicity or cellulitis extending >2 cm from the wound edge. Deep incisional SSI: requires wound opening and exploration with debridement of necrotic tissue; obtain deep tissue cultures. Organ/space SSI: requires source control via percutaneous drainage or operative re-exploration with broad-spectrum antibiotics narrowed when culture results become available. Negative pressure wound therapy (VAC) accelerates granulation tissue formation in deep or complex SSIs. Optimize nutrition, maintain strict glucose control (target <180 mg/dL), and enforce smoking cessation.

Community-acquired complicated intra-abdominal infection requires empiric coverage for enteric gram-negatives and anaerobes. Preferred regimens include ertapenem, cefoxitin, piperacillin-tazobactam, or ceftriaxone + metronidazole. For healthcare-associated or severe infections, broader coverage including Pseudomonas and Enterococcus is warranted with meropenem, imipenem-cilastatin, or piperacillin-tazobactam. Duration of therapy: 4-7 days after source control; do NOT count days of preoperative antibiotics. Procalcitonin can guide antibiotic discontinuation. Source control via resection, repair, or drainage is the most critical intervention; antibiotics alone cannot compensate for inadequate source control.

Sepsis-3 defines sepsis as life-threatening organ dysfunction caused by a dysregulated host response to infection with a SOFA score change ≥2 points. Septic shock is sepsis with persistent hypotension requiring vasopressors to maintain MAP ≥65 mmHg and lactate >2 mmol/L despite adequate fluid resuscitation. The qSOFA uses altered mental status, respiratory rate ≥22/min, and systolic BP ≤100 mmHg. The Surviving Sepsis Campaign 1-hour bundle mandates: measure lactate, obtain blood cultures before antibiotics, administer broad-spectrum antibiotics within 1 hour, begin 30 mL/kg crystalloid for hypotension or lactate ≥4 mmol/L, and start vasopressors if MAP <65 despite fluids (norepinephrine first-line). Source control should be achieved within 6-12 hours of diagnosis. Adjunctive corticosteroids are reserved for refractory septic shock.

Empiric MRSA coverage (vancomycin 15-20 mg/kg, daptomycin, linezolid, or ceftaroline) is indicated for patients with known MRSA colonization, recent hospitalization, hemodialysis, long-term care facility residence, or severe sepsis. MSSA is better treated with cefazolin or nafcillin than vancomycin, as vancomycin is inferior for MSSA bacteremia with higher mortality. De-escalation based on culture data is a core principle. Duration of therapy for most surgical infections is 4-7 days post-source control. Procalcitonin algorithms reduce antibiotic duration without increasing adverse outcomes. C. difficile infection is a significant complication of perioperative antibiotics; fidaxomicin is superior to vancomycin for preventing recurrence.

Wound healing is a dynamic, overlapping biological process divided into four phases. Phase I (hemostasis, immediate to hours): vasoconstriction and platelet plug formation occur within minutes of injury. Activated platelets degranulate, releasing PDGF, TGF-beta, VEGF, and other growth factors that initiate the inflammatory cascade. The coagulation cascade generates fibrin strands forming a provisional matrix. Phase II (inflammation, day 1-6): neutrophils arrive within 24 hours to phagocytose debris and bacteria, while macrophages arrive at day 2-3 as master regulators secreting growth factors and orchestrating the transition to proliferation. Phase III (proliferation, day 3-21): angiogenesis, fibroblast proliferation with collagen synthesis, and re-epithelialization occur concurrently, forming granulation tissue. Phase IV (remodeling, day 21 to 1-2 years): collagen type III is replaced by type I, and tensile strength increases, reaching approximately 80% of original tissue strength by 12 weeks.

Primary intention: wound edges are approximated with sutures, staples, or adhesive strips, with minimal tissue loss. This is the ideal method for clean surgical incisions, and healing occurs by epithelial bridging across the narrow gap with minimal scar formation. Secondary intention: the wound is left open and fills in by granulation, contraction, and re-epithelialization from the wound edges. Used for contaminated wounds, abscess cavities, pressure ulcers, and wounds with significant tissue loss. Healing takes weeks to months with a more prominent scar. Tertiary intention (delayed primary closure): the wound is initially left open for 3-7 days to allow edema resolution and bacterial clearance, then surgically closed. Indicated for heavily contaminated wounds such as animal bites, farm injuries, delayed traumatic wounds, and infected wounds after source control. This approach reduces deep wound infection and dehiscence while achieving reasonable cosmetic outcomes.

Systemic factors include malnutrition with prealbumin <15 mg/dL signaling significant depletion; diabetes mellitus with HbA1c >8% impairing microvascular perfusion and neutrophil function; smoking causing nicotine-induced vasoconstriction and reduced oxygen delivery with 2-3 times higher wound complication rates; advanced age with delayed inflammatory response; obesity with hypovascular adipose tissue and increased wound tension; steroid therapy inhibiting inflammation and collagen synthesis (partially reversible with vitamin A 25,000 IU PO daily); chronic kidney disease with impaired platelet function; and jaundice impairing fibroblast proliferation. Local factors include tissue perfusion with PaO2 <40 mmHg halting collagen synthesis; infection with bacterial burden >10^5 organisms/g delaying healing; mechanical stress causing ischemia; wound desiccation; foreign bodies; and hematoma creating dead space that promotes infection. Perioperative warming and avoidance of hypothermia improve wound healing by maintaining tissue oxygen delivery.

Wound dehiscence occurs in 0.5-3% of abdominal incisions, most commonly at postoperative day 5-10 when tensile strength is lowest. Risk factors include technical error, infection, increased intra-abdominal pressure, malnutrition, steroid use, and obesity. A sudden gush of serosanguinous fluid from the wound may signal fascial disruption. Evisceration requires immediate wet sterile dressing coverage and operative re-closure. Hypertrophic scars remain within the original wound boundaries, develop within 4-8 weeks, and tend to regress over time. Keloids extend beyond the original wound boundaries, do not regress spontaneously, and are more common in darker skin types secondary to aberrant TGF-beta signaling. Treatment includes silicone sheeting first-line, intralesional corticosteroid injections, cryotherapy, laser therapy, and surgical excision with adjunctive radiotherapy for keloids.

Modern wound care follows the TIME principle: Tissue debridement, Infection control, Moisture balance, and Epithelial advancement. Debridement may be sharp, enzymatic, autolytic, mechanical, or biosurgical. Moisture-appropriate dressings include alginates for heavily exudating wounds, foams for moderate exudate, hydrocolloids for light exudate, and hydrogels for dry wounds. Negative pressure wound therapy (NPWT/VAC) applies continuous or intermittent subatmospheric pressure (-75 to -125 mmHg) to the wound bed. Mechanisms include wound contraction, micro-deformation stimulating cell proliferation, removal of interstitial fluid, improved local blood flow, and decreased bacterial burden. Indications include chronic wounds, diabetic foot ulcers, pressure ulcers, dehisced surgical wounds, open abdominal wounds, and as a bridge to skin grafting. Contraindications include active bleeding, untreated osteomyelitis, necrotic tissue, malignancy in the wound, and exposed blood vessels or organs.

Pressure ulcers are staged by NPUAP guidelines from Stage I (non-blanchable erythema) through Stage IV (full-thickness loss with exposed bone or muscle), including unstageable and deep tissue injury. Prevention includes turning q2h, pressure-relieving surfaces, moisture management, and nutritional optimization. Diabetic foot ulcers result from the triad of neuropathy, vascular insufficiency, and impaired healing. Wagner-Meggitt classification grades depth and osteomyelitis presence. Management includes offloading, revascularization if ABI <0.5, aggressive debridement, infection control, and advanced dressings. Marjolin ulcer is a squamous cell carcinoma arising in chronic wounds after 10-30 years latency, with high metastatic potential. Any chronic wound with a persistent non-healing area or heaped-up margins warrants biopsy. Treatment requires wide local excision with clear margins, often requiring amputation for extremity lesions.

The ATLS protocol prioritizes the ABCDE sequence. Airway with cervical spine protection (A): establish and maintain a patent airway while maintaining inline cervical immobilization. Assess for obstruction from foreign body, facial or neck trauma, blood or secretions, or altered mental status. Signs of obstruction include stridor, hoarseness, inability to speak, and see-saw respirations. Definitive airway indications: GCS ≤8, inability to maintain airway, need for ventilation, severe shock, or anticipated airway compromise. Options include orotracheal intubation with RSI and manual inline stabilization, nasotracheal intubation (avoid if basilar skull fracture), or cricothyroidotomy as surgical airway. All trauma patients maintain c-spine precautions with rigid cervical collar until clinical or radiographic clearance.

Breathing (B): assess ventilation by inspecting chest symmetry, tracheal deviation, and paradoxical motion. Six immediately life-threatening thoracic injuries must be treated during primary survey: tension pneumothorax (needle decompression at 2nd ICS midclavicular line), open pneumothorax (three-sided occlusive dressing), massive hemothorax (>1500 mL initial output requiring chest tube, operative thoracotomy if ongoing >200 mL/hr), flail chest (positive pressure ventilation), cardiac tamponade (pericardiocentesis or ED thoracotomy), and airway obstruction. Circulation (C): control external hemorrhage with direct pressure. Establish two large-bore IVs. Initiate balanced resuscitation at 1:1:1 ratio of PRBCs, FFP, and platelets for massive transfusion. FAST exam identifies intra-abdominal fluid, pericardial effusion, and hemothorax.

The secondary survey begins after the primary survey is complete and life threats are addressed. It is a head-to-toe systematic examination. Obtain AMPLE history: Allergies, Medications (especially anticoagulants and antiplatelets), Past medical history and pregnancy, Last meal, and Events/Environment related to injury. The head-to-toe exam includes scalp lacerations, facial fractures (LeFort classification), pupils, tympanic membranes, cervical spine, chest wall, abdomen with seatbelt sign, pelvis (compression pain suggests fracture), perineum (blood at meatus, vaginal bleeding), rectum (sphincter tone, high-riding prostate, occult blood), extremities (pulses, motor/sensory, compartment syndrome), and log-roll for spine and back. CT with IV contrast is standard for hemodynamically stable blunt trauma patients.

Damage control surgery is indicated for severely injured patients with physiologic exhaustion who cannot tolerate definitive repair. The lethal triad of hypothermia (<35deg;C), acidosis (pH <7.2), and coagulopathy (INR >1.5) drives mortality. Phase 1 (OR): abbreviated laparotomy with hemorrhage control via packing and vessel ligation, contamination control with bowel stapling, and temporary abdominal closure. Phase 2 (ICU): rewarming, balanced resuscitation at 1:1:1, correction of coagulopathy with cryoprecipitate for fibrinogen <100-150, and tranexamic acid 1g over 10 min then 1g over 8h if within 3h of injury. Phase 3 (reoperation): planned return to OR within 24-48h after normalization of physiology for definitive repair and primary fascial closure if possible.

Spleen: most commonly injured solid organ in blunt abdominal trauma. Hemodynamically stable patients with low-grade injuries (I-III) can be managed non-operatively with splenic artery angioembolization if contrast blush is present. Failure of non-operative management at 15-30% requires splenectomy with post-splenectomy vaccination. Liver: most low-grade injuries are managed non-operatively. The Pringle maneuver (compression of the portal triad) controls inflow hemorrhage. Deep lacerations may require perihepatic packing or hepatotomy with selective vessel ligation. Bowel: pneumoperitoneum or free fluid without solid organ injury suggests hollow viscus injury requiring primary repair. Retroperitoneal injuries include duodenal repair, distal pancreatectomy, and nephrectomy for non-salvageable kidney. Great vessel injuries require proximal and distal control. All diaphragmatic injuries require repair.

FAST examines four windows: perhepatic (Morison pouch), perisplenic, pelvic, and subxiphoid (pericardium). It has >90% specificity for hemoperitoneum but sensitivity of only 60-80%. eFAST adds thoracic windows for pneumothorax and hemothorax. Chest tube insertion: incision at 5th ICS mid-axillary line with blunt dissection and finger sweep, tube directed posteriorly and apically, connected to Pleur-evac at -20 cm H2O suction. ED thoracotomy: indicated for penetrating thoracic wounds with witnessed arrest <15 minutes; left anterolateral thoracotomy (clamshell for bilateral exposure). REBOA: endovascular balloon occlusion of the aorta in Zone I (supraceliac for intra-abdominal bleeding) or Zone III (infrarenal for pelvic/junctional hemorrhage), an alternative to ED thoracotomy with aortic cross-clamping.

The acute abdomen demands a systematic differential organized by location. Right upper quadrant: acute cholecystitis with Murphy sign, cholangitis with Charcot triad, hepatitis, hepatic abscess, perforated duodenal ulcer, pancreatitis, and right lower lobe pneumonia. Left upper quadrant: splenic abscess/infarct/rupture, pancreatitis, gastric perforation. Right lower quadrant: acute appendicitis (McBurney point, Rovsing, psoas, obturator signs), Crohn disease, cecal diverticulitis, mesenteric adenitis, Meckel diverticulitis, ovarian cyst/torsion, ectopic pregnancy, and incarcerated inguinal hernia. Left lower quadrant: diverticulitis, sigmoid volvulus with coffee bean sign on X-ray, ovarian pathology, and ureteral colic. Epigastric: pancreatitis radiating to back, perforated PUD, gastritis, and inferior wall MI. Diffuse peritonitis: perforated viscus with rigid board-like abdomen, intra-abdominal abscess, ischemic bowel with pain out of proportion, and hemoperitoneum from trauma or ruptured AAA.

Acute appendicitis is the most common surgical emergency with 7-8% lifetime risk. The Alvarado score (MANTRELS) stratifies risk: migration of pain (1), anorexia (1), nausea/vomiting (1), RLQ tenderness (2), rebound (1), fever >37.3deg;C (1), leukocytosis >10,000 (2), left shift (1). Score 0-3: low probability observe; 4-6: intermediate proceed to imaging; 7-10: high probability proceed to surgery. CT with IV contrast is the gold standard (sensitivity >95%) showing enlarged appendix >6mm and periappendiceal fat stranding. Ultrasound is preferred in children and pregnant patients. Laparoscopic appendectomy is standard via three-port technique. Complicated appendicitis with perforation or abscess requires antibiotics targeting gram-negatives and anaerobes for 3-5 days postoperatively. Interval appendectomy is performed 6-12 weeks after non-operative management of appendiceal abscess.

Acute cholecystitis is caused by gallstone impaction in the cystic duct leading to inflammation and potential progression to gangrene or perforation. Murphy sign (inspiratory arrest during right subcostal palpation) has ~97% positive predictive value. Tokyo Guidelines 2018 grade severity: Grade I (mild) treated with early laparoscopic cholecystectomy within 72h; Grade II (moderate) with marked inflammation requires early cholecystectomy by experienced surgeon; Grade III (severe) with organ dysfunction requires urgent biliary drainage via percutaneous cholecystostomy. Diagnosis requires one clinical sign plus one systemic sign plus one imaging finding. Laparoscopic cholecystectomy requires the critical view of safety with clear identification of cystic duct and artery. Conversion rate to open is 5-10% with higher rates in males, elderly, and acute cholecystitis.

Severity is assessed by Ranson criteria (11 parameters measured at admission and 48h), BISAP (BUN, Impaired mental status, SIRS, Age, Pleural effusion), and APACHE II. Management includes aggressive isotonic crystalloid resuscitation with LR preferred over NS as it reduces SIRS and hyperchloremic metabolic acidosis. Pain control with IV opioids. Antibiotics are NOT indicated for prophylaxis, only for documented infection. Enteral nutrition should be started within 48h of admission, significantly reducing mortality and infections compared to TPN. Necrotizing pancreatitis occurs in 10-20% with infected necrosis as the leading cause of late mortality. The step-up approach uses percutaneous or endoscopic drainage first, then minimally invasive necrosectomy if needed. Cholecystectomy for gallstone pancreatitis is performed during the same admission for mild cases.

SBO is most commonly caused by postoperative adhesions (60-70%), followed by hernias, neoplasms, Crohn disease, and other causes. Clinical presentation includes colicky abdominal pain, nausea and vomiting, obstipation, distension, and high-pitched bowel sounds. CT abdomen with IV contrast is the gold standard identifying the transition point, closed-loop obstruction (surgical emergency), and signs of ischemia. Management includes NGT decompression, NPO, IVF resuscitation, and serial exams. Non-operative management succeeds in 60-80% within 48h. Operative management is indicated for peritonitis, closed-loop obstruction, ischemia, failure of non-operative management beyond 3-5 days, or high-grade obstruction. Strangulated SBO carries 5-10x higher mortality if beyond 36h.

Classic peritonitis signs include involuntary guarding or rigidity suggesting perforated viscus, rebound tenderness indicating peritoneal irritation, and referred rebound tenderness. Special tests: psoas sign (pain on passive hip extension, suggests retrocecal appendicitis or psoas abscess), obturator sign (pain on internal rotation of flexed hip, suggests pelvic appendicitis), Rovsing sign (left lower quadrant palpation causes referred right lower quadrant pain), and Carnett sign (abdominal wall tenderness increases with head lift, differentiating wall from intra-abdominal pain). Cullen sign (periumbilical ecchymosis) and Grey-Turner sign (flank ecchymosis) indicate retroperitoneal hemorrhage from necrotizing pancreatitis or ruptured AAA. Kehr sign (referred left shoulder pain) suggests diaphragmatic irritation from splenic rupture. Diffuse peritonitis mandates emergent exploration.

Choledocholithiasis occurs in 10-15% of patients with symptomatic cholelithiasis. Clinical presentation includes RUQ pain, jaundice, dark urine, and elevated direct bilirubin, ALP, and GGT. MRCP is the non-invasive gold standard with >90% sensitivity. Charcot triad (RUQ pain, fever, jaundice) is present in 50-70% of acute cholangitis; Reynolds pentad adds hypotension and altered mental status indicating severe disease requiring urgent ERCP with sphincterotomy and stone extraction. Empiric antibiotics target gram-negatives, enterococci, and anaerobes. ERCP complications include post-ERCP pancreatitis (3-10%), hemorrhage (1-2%), and perforation (<1%). Prophylactic pancreatic stent placement and rectal indomethacin reduce the risk and severity of post-ERCP pancreatitis.

HCC is the most common primary liver malignancy, strongly associated with cirrhosis. Screening with abdominal US and AFP every 6 months is recommended for high-risk patients. Non-invasive diagnosis is made by LI-RADS classification on multiphase CT/MRI showing arterial phase hyperenhancement with delayed washout. BCLC staging guides treatment: BCLC 0 (very early) with curative resection or ablation; BCLC A (early) with resection, transplant, or ablation; BCLC B (intermediate) with TACE; BCLC C (advanced) with atezolizumab plus bevacizumab; BCLC D (terminal) with best supportive care. Milan criteria (single ≤5cm or up to 3 nodules ≤3cm) guide liver transplantation eligibility for HCC.

Pancreatic ductal adenocarcinoma has a 5-year survival of only 12%. Resectability is determined by CT assessment of tumor contact with SMA, SMV, celiac axis, and portal vein. The Whipple procedure (pancreaticoduodenectomy) is the standard operation for head tumors, involving en bloc resection of the pancreatic head, duodenum, CBD, gallbladder, and distal stomach with reconstruction via pancreaticojejunostomy, hepaticojejunostomy, and gastrojejunostomy. Morbidity is 30-50% including pancreatic leak (10-20%), delayed gastric emptying, and bleeding. Mortality at high-volume centers is <3%. Neoadjuvant FOLFIRINOX is standard for borderline resectable disease, increasing R0 resection rates. Adjuvant mFOLFIRINOX is standard for resected disease.

Liver trauma is classified by AAST grades I-VI. Non-operative management is standard for hemodynamically stable patients with grades I-IV injuries, with success rate >90%. Prerequisites include hemodynamic stability with <2U PRBC requirement, no peritonitis, and ability to perform serial exams. The Pringle maneuver (compression of the hepatoduodenal ligament) controls inflow hemorrhage and is the first step in operative management, allowing 15-20 minutes of inflow occlusion. Deep lacerations require finger fracture hepatotomy with selective vessel ligation. Perihepatic packing is a damage control technique. Juxtahepatic venous injuries carry ~80% mortality. Postoperative complications include rebleeding, bile leak (5-15%), abscess, and liver necrosis.

Portal hypertension is defined as HVPG >5 mmHg, most commonly from cirrhosis. Variceal bleeding management includes airway protection, restrictive resuscitation (Hb target 7-9 g/dL), vasoactive drugs (octreotide or terlipressin), prophylactic antibiotics (ceftriaxone), and urgent EGD within 12h with endoscopic band ligation. TIPS creates a connection between portal and hepatic veins, indicated for refractory variceal bleeding and refractory ascites. Complications include encephalopathy (20-30%) and shunt stenosis (50% at 1yr). Surgical shunts are rarely performed today given TIPS success and liver transplantation. Liver transplantation remains the definitive treatment for decompensated cirrhosis.

Biliary strictures are classified as benign (most commonly iatrogenic after cholecystectomy, Bismuth types I-IV) or malignant (cholangiocarcinoma, pancreatic cancer). Surgical repair uses Roux-en-Y hepaticojejunostomy for most types. Pancreatic pseudocyst is a fluid collection with well-defined wall ≥4wk after acute pancreatitis. Asymptomatic pseudocysts can be observed; symptomatic ones require endoscopic drainage (cystgastrostomy or cystduodenostomy) as first-line. Spleen-preserving distal pancreatectomy is the standard for benign and low-grade malignant tumors of the pancreatic body and tail, performed by dissecting the pancreas off the splenic vessels. This preserves immune function and reduces OPSI risk.

Colorectal cancer (CRC) is the 3rd most common cancer worldwide. Screening begins at age 45 for average-risk individuals with colonoscopy every 10 years, CT colonography every 5 years, or FIT annually. Earlier screening at age 40 or 10 years before youngest affected relative is recommended for Lynch syndrome (70-80% lifetime CRC risk) and FAP (nearly 100% by age 40). TNM staging determines treatment: Stage I with surgical resection alone; Stage II with resection plus adjuvant chemo for high-risk features; Stage III with resection plus adjuvant FOLFOX/CAPOX; Stage IV with resection of primary and metastases or palliative chemotherapy. Right hemicolectomy is performed for cecal and ascending colon tumors; left hemicolectomy for descending colon tumors; low anterior resection (LAR) with total mesorectal excision (TME) for mid to high rectal tumors; abdominoperineal resection (APR) for low rectal tumors involving the sphincter complex. TME reduces local recurrence from >30% to <10%.

The Hinchey classification grades severity based on intraoperative findings: Hinchey I with pericolonic abscess or phlegmon; Hinchey II with pelvic or intra-abdominal abscess; Hinchey III with generalized purulent peritonitis; Hinchey IV with generalized fecal peritonitis. Uncomplicated acute diverticulitis can be managed as outpatient with oral antibiotics or even without antibiotics in select patients. Inpatient management includes bowel rest, IV fluids, IV antibiotics, and CT-guided drainage of abscesses >3-4cm. Elective sigmoid colectomy is indicated after complicated diverticulitis with abscess or fistula, after multiple episodes, or for immunocompromised patients. Urgent sigmoidectomy (Hartmann procedure or primary anastomosis with diversion) is required for Hinchey III-IV with generalized peritonitis.

Surgery for Crohn disease is reserved for complications and is NOT curative. Indications include fibrostenotic strictures, internal fistulas, abscess, perforation, hemorrhage, and medical failure. Strictureplasty (Heineke-Mikulicz for short strictures, Finney for longer ones, Michelassi side-to-side for extensive disease) preserves bowel length. Resection is required for phlegmonous disease or fistulizing disease with abscess. Postoperative anti-TNF therapy within 2-4 weeks delays endoscopic recurrence. Surgery for ulcerative colitis is curative. Total proctocolectomy with ileal pouch-anal anastomosis (IPAA, J-pouch) is the standard restorative procedure. A diverting loop ileostomy is usually created and reversed at 8-12 weeks. Pouchitis (inflammation of the ileal pouch) occurs in 50% within 10 years and responds to metronidazole or ciprofloxacin. The alternative is total proctocolectomy with end ileostomy.

Ileostomy is created from the terminal ileum with semi-liquid, high-volume output (600-1500 mL/day) requiring continuous wear appliance and meticulous skin protection. High-output ileostomy (>1500-2000 mL/day) can cause dehydration requiring loperamide and oral rehydration solution. The Brooke ileostomy is the standard end ileostomy with a 2-3cm everted spout. Loop ileostomy temporarily diverts stool after distal anastomosis. Colostomy is created from the colon with thicker, formed output. Sigmoid colostomy output requires less frequent pouch changes. Transverse loop colostomy is usually temporary for emergency decompression. Complications include parastomal hernia (up to 50%), stomal prolapse, stenosis, skin breakdown, and obstruction. Preoperative stoma siting through the rectus abdominis muscle is essential.

Anorectal abscesses are classified by location: perianal (most common, 40-60%), ischiorectal (20-30%), intersphincteric (5-10%), and supralevator (<5%). All require incision and drainage. Anorectal fistula results from inadequately drained abscess. The Park classification describes the tract relationship to the sphincter complex: Type I (intersphincteric, 70%) treated by fistulotomy; Type II (transsphincteric, 25%) requiring fistulotomy for low tracts or sphincter-sparing technique for high tracts; Type III (suprasphincteric) requiring sphincter-sparing approach; Type IV (extrasphincteric) requiring rectal defect repair. Goodsall's rule predicts tract direction based on external opening location relative to the transverse anal line. MRI is the imaging modality of choice for complex fistulas. LIFT (ligation of intersphincteric fistula tract) has healing rates of 60-80% with minimal incontinence risk.

Lynch syndrome (HNPCC) is caused by germline mutations in DNA mismatch repair genes (MLH1, MSH2, MSH6, PMS2, EPCAM) with 50-80% lifetime CRC risk. Associated with right-sided tumors, MSI-high histology, and extracolonic malignancies including endometrial and ovarian cancer. Management includes colonoscopy q1-2 years starting at age 20-25. FAP (familial adenomatous polyposis) is caused by APC gene mutation with hundreds to thousands of polyps and nearly 100% CRC risk by age 40. Prophylactic total proctocolectomy with IPAA is performed by age 18-25. Anastomotic leak is the most feared colorectal complication with incidence 3-10% (higher with low rectal anastomosis, neoadjuvant chemoradiation, male sex, obesity, smoking). Tachycardia is the earliest sign. CT with rectal contrast has 70-90% sensitivity. Management: stable with contained leak requires bowel rest, IV antibiotics, and percutaneous drainage; unstable with peritonitis requires urgent reoperation with anastomotic takedown and diversion.

Breast cancer is the most common cancer in women worldwide. Screening mammography is recommended annually or biennially starting at age 40-50. Digital breast tomosynthesis improves sensitivity and reduces recall rates. Screening MRI is recommended for high-risk women including BRCA carriers and those with >20-25% lifetime risk. The BI-RADS classification standardizes reporting: Category 3 (probably benign, <2% malignancy) requires 6-month follow-up; Category 4 (suspicious, 2-95% malignancy) requires biopsy; Category 5 (highly suggestive, >95% malignancy) requires biopsy. Core needle biopsy is the standard for histologic diagnosis providing ER, PR, HER2, and Ki-67 assessment. Genetic testing is recommended for patients diagnosed at age ≤50, triple-negative at ≤60, or with family history of breast, ovarian, pancreatic, or prostate cancer. BRCA1/BRCA2 mutations confer 45-85% lifetime breast cancer risk.

Breast-conserving surgery (lumpectomy) with radiation is equivalent to mastectomy in overall survival for stage I-II breast cancer. Negative margins are defined as "no ink on tumor." Contraindications to lumpectomy include multicentric disease, diffuse malignant microcalcifications, inability to achieve negative margins, prior chest radiation, and first or second trimester pregnancy. Mastectomy options include total (simple), skin-sparing, and nipple-sparing mastectomy. Sentinel lymph node biopsy (SLNB) is the standard axillary staging for clinically node-negative breast cancer using dual injection of technetium-99m and blue dye. Per ACOSOG Z0011, completion ALND is no longer mandatory for T1-2 tumors with 1-2 positive SLNs undergoing breast-conserving surgery with whole-breast radiation. ALND is indicated for ≥3 positive SLNs, gross extranodal extension, neoadjuvant chemotherapy with residual nodal disease, or clinical N2/N3 disease.

Endocrine therapy for ER+ breast cancer: premenopausal patients receive tamoxifen 20mg PO daily for 5-10 years with or without ovarian suppression; postmenopausal patients receive aromatase inhibitors as first-line therapy. Chemotherapy is indicated for triple-negative, HER2+, and high-risk ER+ with Oncotype DX recurrence score >25. Neoadjuvant chemotherapy is increasingly used for triple-negative and HER2+ breast cancer to allow assessment of response and increase breast conservation rates. HER2+ therapy includes trastuzumab plus pertuzumab with chemotherapy; T-DM1 for residual disease after neoadjuvant therapy. PARP inhibitors are approved for germline BRCA-mutated breast cancer. Radiation therapy after lumpectomy reduces local recurrence from 30% to 10%. Post-mastectomy radiation is indicated for ≥4 positive lymph nodes, T3/T4 tumors, or positive margins.

Fibroadenoma is the most common benign breast tumor in women aged 15-35, presenting as a painless, firm, mobile mass (breast mouse). Classic imaging allows reassurance without excision; excision is indicated if enlarging, >4cm, or symptomatic. Intraductal papilloma presents with spontaneous unilateral serous or sanguinous nipple discharge and requires excision due to 5-10% malignancy risk. Mammary duct ectasia presents with thick greenish-brown discharge and is usually self-limiting. Mastitis is lactational in 90% of cases, treated with continued breastfeeding, warm compresses, and PO antibiotics. Breast abscess requires aspiration or incision and drainage. Central subareolar abscess has high recurrence and may require excision of the involved duct system (Hadfield operation).

Paget disease of the nipple presents as unilateral eczematous change of the nipple-areola complex caused by intraepidermal spread of underlying DCIS or invasive cancer. It is often misdiagnosed as dermatitis; key distinguishing feature is unilaterality. Nipple punch biopsy shows Paget cells (CK7+, HER2+). Treatment includes central lumpectomy with nipple-areola removal plus whole breast radiation versus mastectomy with SLNB. Inflammatory breast cancer (IBC) presents with rapid onset of breast erythema, edema (peau d'orange), warmth, and enlargement, often mistaken for mastitis. Criteria include ≥1/3 of breast skin involvement and dermal lymphatic invasion. IBC is always at least stage III (T4d). Treatment requires neoadjuvant chemotherapy followed by modified radical mastectomy with ALND and post-mastectomy radiation. Five-year survival is only 40-50%.

Gynecomastia is benign male breast enlargement from estrogen/androgen imbalance. Causes include physiologic (neonatal, pubertal, senescent), drugs (spironolactone, cimetidine, finasteride, anabolic steroids), and pathologic conditions (cirrhosis, hyperthyroidism, testicular tumors, Klinefelter syndrome). Workup includes history, exam, and mammogram/US for asymmetry or suspicious features. Tamoxifen is first-line for painful or persistent gynecomastia. Surgery (subcutaneous mastectomy with liposuction) is for cosmetic concerns or persistent severe gynecomastia. Breast implant complications include capsular contracture (Baker grade I-IV), rupture (requires MRI screening), infection, and anaplastic large cell lymphoma (ALCL) associated with textured implants presenting with late seroma. BIA-ALCL is treated with explantation and capsulectomy with excellent prognosis.

Thyroid nodules are found in 50-60% of adults on US with only <10% malignant. All patients require TSH and thyroid US. TI-RADS classifies nodules by composition, echogenicity, shape, margin, and echogenic foci to estimate malignancy risk. FNA is reported using the Bethesda System: Bethesda II (benign, 0-3% malignancy, follow); Bethesda III (AUS/FLUS, 5-15%, repeat FNA or molecular testing); Bethesda IV (follicular neoplasm, 15-30%, molecular testing or diagnostic lobectomy); Bethesda V (suspicious for malignancy, 60-75%, total thyroidectomy); Bethesda VI (malignant, 97-99%, total thyroidectomy). Molecular testing (Afirma GSC, ThyroSeq v3) for indeterminate cytology can reclassify up to 50% as benign, avoiding diagnostic surgery.

Papillary thyroid carcinoma (85%) has excellent prognosis with 10-year survival >95%. ATA risk stratification guides management: low risk (intrathyroidal, <4cm) may be treated with lobectomy alone; intermediate risk (microscopic extrathyroidal extension, central LN mets) requires total thyroidectomy with or without RAI; high risk (gross extrathyroidal extension, distant mets) requires total thyroidectomy plus RAI. Follicular thyroid carcinoma (10%) requires capsular or vascular invasion for diagnosis. Hrthle cell carcinoma (3-5%) is more aggressive with less RAI avidity. Medullary thyroid carcinoma (2%) from parafollicular C-cells secretes calcitonin as a tumor marker. All MTC requires RET mutation testing; RET inhibitors (selpercatinib, pralsetinib) are highly effective for advanced disease. Anaplastic thyroid carcinoma (<2%) is one of the most aggressive human cancers with median survival 4-6 months, requiring multimodality therapy.

Primary hyperparathyroidism presents with stones, bones, groans, and psychiatric moans. Diagnosis requires elevated calcium plus elevated or inappropriately normal PTH. Twenty-four hour urine calcium excludes familial hypocalciuric hypercalcemia (FHH) which does not require surgery. Localization uses sestamibi scan, US, or 4D-CT. Surgery is indicated for all symptomatic patients and for asymptomatic patients meeting NIH criteria (age <50, serum Ca >1 mg/dL above normal, Cr clearance <60 mL/min, T-score <-2.5, 24h urine Ca >400 mg). Parathyroidectomy can be focused (minimally invasive) for well-localized single adenoma or bilateral neck exploration for hyperplasia. Intraoperative PTH monitoring with the Miami criterion (≥50% drop at 5-10 minutes) predicts cure with >95% accuracy. Postoperative hypocalcemia (hungry bone syndrome) requires oral calcium and calcitriol supplementation.

Adrenal incidentaloma is found in 5% of CT scans. Workup includes hormonal evaluation (1mg dexamethasone suppression test for cortisol, plasma metanephrines for pheochromocytoma, aldosterone/renin ratio for hyperaldosteronism) and imaging characterization (<10 HU on non-contrast CT suggests benign adenoma). Size is the strongest predictor of malignancy: >4cm consider resection, >6cm resect. Pheochromocytoma presents with episodic headache, palpitations, and diaphoresis. Diagnosis uses plasma free metanephrines (sensitivity >96%). Preoperative preparation requires alpha-blockade (phenoxybenzamine or doxazosin) for 7-14 days then beta-blockade for tachycardia (NEVER beta-blocker alone). Laparoscopic adrenalectomy is standard for <6-8cm tumors. Cushing syndrome from adrenal adenoma requires laparoscopic adrenalectomy with perioperative steroid coverage. Primary hyperaldosteronism (Conn syndrome) is treated with laparoscopic adrenalectomy for unilateral disease or spironolactone/eplerenone for bilateral disease.

Recurrent laryngeal nerve (RLN) injury is a feared complication of thyroid and parathyroid surgery, presenting with hoarseness, vocal cord paralysis, and aspiration. Unilateral injury causes hoarseness and aspiration risk; bilateral injury causes stridor and airway obstruction requiring tracheostomy. The RLN should be identified along its course in the tracheoesophageal groove before division of any structures. Intraoperative nerve monitoring (IONM) is an adjunct to visual identification. Risk factors include malignant disease, reoperative surgery, large goiter, and Graves disease. Hypocalcemia after thyroidectomy results from hypoparathyroidism due to devascularization or inadvertent removal of parathyroid glands. Transient hypocalcemia occurs in 10-30% of total thyroidectomies, permanent in 1-3%. Symptoms include perioral numbness, tingling, Chvostek sign, Trousseau sign, and tetany. Treatment includes oral calcium carbonate with calcitriol; severe cases require IV calcium gluconate. Autotransplantation of devascularized parathyroid glands into the sternocleidomastoid muscle reduces permanent hypoparathyroidism.

Adrenal insufficiency (AI) can be primary (Addison disease), secondary (pituitary dysfunction), or tertiary (steroid withdrawal). Patients on chronic steroids (>20mg prednisone equivalent daily for >3 weeks) are at risk for tertiary AI and require perioperative stress-dose steroids. For minor surgery, give usual daily steroid dose plus 25-50 mg hydrocortisone IV at induction. For moderate surgery, give 50-75 mg hydrocortisone IV at induction then 25-50 mg q8h for 24-48h. For major surgery, give 100-150 mg hydrocortisone IV at induction then 50-100 mg q8h for 48-72h with rapid taper. Signs of adrenal crisis include hypotension refractory to fluids and vasopressors, hypoglycemia, hyponatremia, hyperkalemia, and metabolic acidosis. Treatment requires IV hydrocortisone 100 mg bolus then 100 mg q6h with aggressive fluid resuscitation. Undiagnosed AI presenting as unexplained postoperative hemodynamic instability should prompt a cosyntropin stimulation test.

PAD affects 12-20% of adults over 60 and is a marker of systemic atherosclerosis. Clinical stages: asymptomatic, claudication (muscle pain with exercise relieved by rest), rest pain (forefoot, critical limb ischemia), and tissue loss (ulceration/gangrene). Ankle-brachial index (ABI) is first-line: normal 1.0-1.4, PAD <0.9, severe <0.5. ABI >1.4 suggests non-compressible calcified vessels. The WIfI classification stratifies limb threat severity. Management: antiplatelet therapy, high-dose statin (atorvastatin 80mg), smoking cessation, and supervised exercise for claudication. Revascularization indications: disabling claudication failing medical therapy, rest pain, or tissue loss. Endovascular options include angioplasty with stenting (preferred for focal iliac/SFA disease). Surgical options include femoral endarterectomy with patch, femoral-popliteal bypass with vein/prosthetic graft, and femoral-tibial bypass.

Carotid stenosis accounts for 10-20% of ischemic strokes. Asymptomatic stenosis (>60-70%) has 2-3% annual stroke risk. Symptomatic stenosis (>50%) has 5-10% risk in 5 days and 10-15% at 90 days without intervention. Duplex ultrasound is the screening modality. Carotid endarterectomy (CEA) is the gold standard for symptomatic stenosis >50% and asymptomatic stenosis >60-70% in selected patients. Timing: CEA within 2 weeks of symptom onset is optimal. Carotid artery stenting (CAS) is for high surgical risk (hostile neck, prior CEA, radiation, contralateral laryngeal nerve palsy). Perioperative stroke risk is 2-5% for CEA and 4-8% for CAS. All patients receive dual antiplatelet therapy for CAS and aspirin alone for CEA. Beta-blocker and statin therapy are essential for perioperative stroke prophylaxis.

AAA is infrarenal aortic diameter ≥3cm, affecting 5-10% of men 65-79. Screening US recommended for men 65-75 with smoking history. Surveillance: 3.0-3.9cm US q3yr; 4.0-4.9cm q12mo; 5.0-5.4cm q6mo. Repair at ≥5.5cm (men) or ≥5.0cm (women), rapid growth >1cm/yr, or symptomatic. EVAR is preferred for suitable anatomy (proximal neck length ≥10-15mm, neck diameter ≤32mm) with lower 30-day morbidity but requires lifelong surveillance for endoleaks. Open repair with infrarenal aortic cross-clamping and Dacron/PTFE graft placement. Ruptured AAA: 50-80% pre-hospital mortality; management includes permissive hypotension (SBP 50-100 mmHg), immediate proximal control, and EVAR if anatomy suitable. Open repair as alternative.

VTE affects 1-2 per 1000 person-years. Diagnosis: DVT with US (non-compressible vein), PE with CTPA. Wells criteria stratify pretest probability. Treatment with DOACs or LMWH bridging to warfarin for 3-6 months (unprovoked indefinite). Massive PE (SBP <90) requires thrombolysis. IVC filter for anticoagulation contraindication or recurrent PE despite therapy. Chronic venous insufficiency from venous valve incompetence: CEAP classification C1 (telangiectasias) to C6 (active ulcer). Venous ulcers in gaiter area. Management: compression therapy (30-40 mmHg graduated stockings) is cornerstone, leg elevation, wound care. Venous ablation (endovenous laser, radiofrequency) for superficial reflux. Venous stenting for iliofemoral obstruction.

Acute compartment syndrome is a surgical emergency from increased pressure within a closed osteofascial compartment, causing irreversible muscle/nerve damage within 6 hours. Causes: fractures (tibia most common), crush injuries, reperfusion after ischemia, burns, tight casts. Clinical diagnosis: pain out of proportion (earliest sign), pain on passive stretch, paresthesia, pallor, poikilothermia, pulselessness (late). Compartment pressure >30 mmHg or delta pressure <30 mmHg indicates compartment syndrome. Treatment: emergent fasciotomy. Lower leg: two-incision, four-compartment release (anterior, lateral, superficial/deep posterior). Forearm: volar and dorsal fasciotomies. Wounds left open, dressed, closed 3-7 days later. Delay >6h causes Volkmann contracture, rhabdomyolysis, renal failure, limb loss.

Acute limb ischemia (ALI) presents with 6 Ps. Rutherford classification: Class I (viable) with elective revascularization; IIa (marginally threatened) within hours; IIb (immediately threatened) within minutes; III (nonviable) with primary amputation. Embolectomy with Fogarty catheter for embolic ALI; catheter-directed thrombolysis for acute thrombotic. Acute mesenteric ischemia (SMA embolus in atrial fibrillation): pain out of proportion, CT angiography diagnosis, emergent laparotomy with embolectomy/bypass and bowel resection with second-look at 24-48h. Mortality 50-80%. Amputation levels: toe/ray, transmetatarsal, below-knee (BKA), above-knee (AKA). BKA preserves knee function with 70-80% healing. Bilateral AKA has 50% 5-year survival.

Complete surgical resection with negative margins is the cornerstone of curative cancer surgery. R0 (microscopically margin-negative) is the goal; R1 (microscopically positive) has higher local recurrence; R2 (macroscopically positive) is palliative. Margin assessment requires surgeon-pathologist communication with oriented specimen and inked surfaces. Lymphadenectomy is integral: 12 nodes for colorectal, 15 for gastric, 10-30 for breast cancer. Sentinel lymph node biopsy (SLNB) has replaced elective lymphadenectomy for breast cancer and melanoma, reducing morbidity without compromising outcomes. Extended lymphadenectomy (D2 for gastric, complete mesocolic excision for right colon) improves staging but with higher morbidity. The concept of adequate margins varies by tumor type and organ.

AJCC TNM staging classifies T (primary tumor), N (lymph nodes), and M (metastasis) for prognosis and treatment. Grade (G1-G3) describes differentiation. Molecular markers guide therapy: EGFR, ALK, ROS1, BRAF, KRAS in lung; ER, PR, HER2 in breast; MSI/MMR in colorectal; IDH1/2 in glioma; CD20 in lymphoma; PD-L1 across tumor types. Next-generation sequencing (NGS) panels identify actionable mutations. Liquid biopsy (ctDNA) for minimal residual disease detection. Preoperative core needle biopsy for histologic and molecular diagnosis is essential before neoadjuvant therapy. Biomarker testing should be performed on all new cancer diagnoses to guide targeted therapy selection.

MIS (laparoscopy, robotics) reduces postoperative pain, length of stay, blood loss, and wound complications with equivalent oncologic outcomes for many cancers. Laparoscopic colectomy for colon cancer is equivalent to open (COST, COLOR, CLASICC trials). Robotic surgery provides improved ergonomics, 3D visualization, and wristed instruments for precise dissection in confined spaces (TME, prostatectomy, partial nephrectomy). Critical oncologic principles must not be compromised: R0 resection, adequate lymphadenectomy, avoidance of tumor spillage. Conversion to open is sound judgment when progress is unsafe. NOTES and SILS remain investigational for most oncologic applications. Laparoscopic liver, pancreatic, and esophageal resections are performed at specialized high-volume centers.

Cytoreductive surgery (CRS) with hyperthermic intraperitoneal chemotherapy (HIPEC) treats peritoneal carcinomatosis from selected primaries (appendiceal, colorectal, mesothelioma, ovarian). Complete removal of all visible peritoneal disease (peritonectomy, visceral resections) followed by heated chemotherapy (mitomycin C or cisplatin at 41-43deg;C for 60-90 min). Patient selection: Peritoneal Cancer Index (PCI, 0-39) <20 for most primaries. Completeness of cytoreduction (CC-0/1) predicts outcome. Morbidity 30-50% (bleeding, anastomotic leak, fistula, abscess, renal toxicity), mortality 2-5% at high-volume centers. Benefit established for appendiceal mucinous neoplasms and colorectal cancer with limited peritoneal spread.

Palliative surgery relieves symptoms and improves quality of life without cure. Indications: GI or biliary obstruction (bypass or stenting), hemorrhage, pain, infected/fungating tumors, pathologic fracture prevention. Gastrojejunostomy for gastric outlet obstruction; hepaticojejunostomy for biliary obstruction; intestinal stenting as alternative with lower morbidity but higher recurrence. Feeding tubes for malignant dysphagia. Pleurodesis or indwelling pleural catheter for malignant effusion. Debulking reduces tumor burden without complete resection. Decision requires assessment of operative risk, symptom burden, life expectancy, and patient preferences. Multidisciplinary approach essential. The principle "first do no harm" is paramount; high-risk palliation with prolonged recovery may negate benefit.

Cancer cachexia (involuntary weight loss >5% over 6 months, skeletal wasting) affects 50-80% of advanced cancer patients and contributes to 20-30% of cancer deaths. Pathophysiology: pro-inflammatory cytokines (TNF-alpha, IL-6), tumor-derived factors, metabolic alterations. Management: nutritional counseling, enteral supplements, appetite stimulants (megestrol acetate, corticosteroids). Preoperative malnutrition (albumin <3.0, weight loss >10%) predicts complications, warranting preoperative enteral nutrition. Immunotherapy: checkpoint inhibitors (anti-PD-1, anti-CTLA-4) neoadjuvantly produce pCR in 15-45% (melanoma, lung, MSI-high CRC). PARP inhibitors (olaparib, talazoparib) exploit synthetic lethality in BRCA1/2-mutant tumors (ovarian, breast, pancreatic, prostate). Surgical considerations: bone marrow suppression (myelosuppression, thrombocytopenia) requiring perioperative monitoring.

Maintenance fluids: 4-2-1 rule (4 mL/kg/hr for first 10kg, 2 mL/kg/hr for next 10kg, 1 mL/kg/hr beyond 20kg). Isotonic crystalloids for replacement: lactated Ringer is more physiologic; NS in large volumes causes hyperchloremic metabolic acidosis. Goal-directed fluid therapy using dynamic monitors (SVV, PPV, esophageal Doppler) optimizes cardiac output and reduces complications. The third space concept has been debunked; excessive crystalloid causes tissue edema, ileus, and impaired healing. Colloids have no proven benefit; hydroxyethyl starches increase AKI and mortality. Restrictive/balanced approach (0-2L net positive) is recommended for major surgery. For sepsis: 30 mL/kg crystalloid bolus then assess fluid responsiveness before further administration.

Hyponatremia (Na <135): correct ≤8 mEq/L/24h to avoid osmotic demyelination; 3% NaCl for seizures. Hypernatremia (Na >145): free water deficit with D5W, correct ≤10-12 mEq/L/24h. Hypokalemia (K <3.5): replete IV 10 mEq/hr peripheral, 20 mEq/hr central with cardiac monitoring. Hyperkalemia (K >5.5) with ECG changes: IV calcium gluconate for cardiac protection, then insulin/glucose, albuterol, kayexalate/loop diuretic. Hypocalcemia (Ca <8.5) after thyroid/parathyroid surgery: oral calcium + calcitriol; IV calcium gluconate for tetany. Hypercalcemia (Ca >10.5) of malignancy: IVF, bisphosphonates, calcitonin. Hypomagnesemia (Mg <1.7): causes refractory hypokalemia/hypocalcemia; IV MgSO4. Hypophosphatemia in refeeding syndrome: gradual feeding, IV phosphate.

Malnutrition affects 30-50% of surgical patients. Screening tools: MUST, NRS-2002, SGA. Severe malnutrition (albumin <3.0, weight loss >10-15%) warrants 7-14 days of preoperative nutritional optimization. Enteral nutrition (EN) is preferred over parenteral (PN) due to fewer infections, better wound healing, and lower cost. EN started within 24-48h postoperatively. PN when EN is not feasible for >7 days. Immunonutrition (arginine, omega-3, nucleotides, glutamine) for 5-7 days before major upper GI surgery reduces infections in malnourished patients. Refeeding syndrome: life-threatening electrolyte shifts (hypophosphatemia, hypokalemia, hypomagnesemia) in severely malnourished patients receiving feeding. Prevention: start at 10-20 kcal/kg/day, replete electrolytes, monitor phosphate, K, Mg, glucose daily.

Multimodal analgesia combines agents for maximal pain control with minimal opioid adverse effects: acetaminophen (1g q6h), NSAIDs (ketorolac 15-30mg q6h, avoid in renal impairment or bleeding risk), gabapentinoids (gabapentin 300-600mg preop), and regional anesthesia. Regional techniques: epidural (gold standard for major thoracic/abdominal surgery), paravertebral blocks (thoracotomy, breast), TAP blocks (abdominal), peripheral nerve blocks. Opioids: morphine, hydromorphone, fentanyl for PCA or infusion. Patient-controlled analgesia (PCA) allows patient-titrated delivery. ERAS emphasizes regional analgesia and opioid-sparing strategies for early mobilization and feeding. Avoid meperidine (normeperidine causes seizures). Scheduled acetaminophen and NSAIDs reduce opioid requirements by 30-50%.

ERAS is a multimodal perioperative pathway to reduce surgical stress and accelerate recovery. Core elements: preoperative counseling, carbohydrate loading (400 mL maltodextrin 2-3h before surgery), avoidance of prolonged fasting, multimodal opioid-sparing analgesia, goal-directed fluid therapy, normothermia maintenance, omission of routine NGT/drains, early catheter removal, early oral nutrition (clear fluids on POD0, solid diet POD1), early mobilization (out of bed POD0, ambulating POD1), and discharge criteria-based protocol. ERAS reduces length of stay by 2-4 days, complications by 30-50%, without increasing readmissions. Implementation requires multidisciplinary commitment, structured protocol, regular audit. Adapted across colorectal, gynecologic, urologic, HPB, and thoracic surgery. Barriers include resistance to change, insufficient resources, and incomplete adherence.

Postoperative fever: "Wind, Water, Wound, Walking, Wonder Drugs." POD 0-2: atelectasis (most common, treat with incentive spirometry/ambulation). POD 3-5: UTI (remove catheter, culture, antibiotics), wound infection, line infection, C. difficile. POD 5-7: wound infection, anastomotic leak, deep SSI. POD 7-21: DVT/PE (duplex US, CTPA), drug fever (diagnosis of exclusion, stop non-essential meds), abscess. Systematic evaluation: inspect wound, review cultures, examine lines, consider CT for intra-abdominal source. Anastomotic leak: sustained fever, tachycardia (earliest sign), abdominal pain, peritonitis, metabolic acidosis. CT with oral/IV contrast. Return to OR for peritonitis. DVT/PE: unilateral leg swelling, pleuritic chest pain, dyspnea, hypoxia. Start therapeutic anticoagulation after confirmation.