6. Gastrointestinal System
6A. GI Tract — Structure & Function
| Structure | Function | Surgical Relevance |
|---|---|---|
| Esophagus | Propels food from pharynx to stomach; ~25 cm; passes through diaphragm at esophageal hiatus (T10) | Esophagectomy; hiatal hernia repair (Nissen fundoplication); esophagoscopy; GERD |
| Stomach | Storage and initial digestion; produces HCl, pepsin, intrinsic factor; regions: cardia, fundus, body, pylorus. | Gastrectomy (partial/total); bariatric surgery (sleeve, bypass); peptic ulcer; gastrostomy |
| Small Intestine | Primary site of digestion and absorption; ~6–7 m; three segments: duodenum (25 cm), jejunum, ileum | Small bowel resection; Crohn’s disease; ileostomy; Meckel’s diverticulum |
| Large Intestine (Colon) | Water/electrolyte absorption; fecal formation; ~1.5 m; cecum → ascending → transverse → descending → sigmoid → rectum → anus | Colectomy; colostomy; hemorrhoidectomy; colonoscopy; colorectal cancer resection |
| Appendix | Vestigial; attached to cecum; lymphoid tissue | Appendectomy (most common emergent abdominal surgery); McBurney’s point |
| Rectum / Anus | Fecal storage and defecation; internal sphincter (involuntary) + external sphincter (voluntary) | Anterior resection; abdominoperineal resection (APR); hemorrhoidectomy; lithotomy position |
6B. Accessory Digestive Organs
| Organ | Function | Surgical Relevance |
|---|---|---|
| Liver | Bile production; detoxification; protein synthesis (albumin, clotting factors); glycogen storage; drug metabolism; largest internal organ (1,200–1,500 g); 2 lobes (right is larger); receives dual blood supply (portal vein 75% + hepatic artery 25%) | Hepatectomy (Pringle maneuver to control inflow); liver transplant; TIPS procedure; cirrhosis complications |
| Gallbladder | Stores and concentrates bile (produced by liver); contracts when CCK released after fatty meal → bile flows into duodenum via common bile duct | Cholecystectomy (laparoscopic vs. open); choledochoscopy; cholelithiasis; Calot’s triangle (cystic artery, cystic duct, common hepatic duct) |
| Pancreas | Exocrine: digestive enzymes (amylase, lipase, trypsinogen) into duodenum via pancreatic duct; Endocrine: insulin (beta cells) and glucagon (alpha cells) from islets of Langerhans | Whipple procedure (pancreaticoduodenectomy) for head of pancreas tumors; distal pancreatectomy; pancreatitis; ERCP |
| Spleen | Largest lymphoid organ; filters blood; removes old RBCs; immune function; located LUQ behind 9th–11th ribs; highly vascular (fragile) | Splenectomy; highest risk of injury in abdominal trauma; post-splenectomy → increased infection risk (especially encapsulated bacteria: Strep pneumoniae, H. flu, N. meningitidis) → vaccinate |
7. Genitourinary System
7A. Urinary System
- Kidneys — paired retroperitoneal organs at T12–L3; right kidney slightly lower (displaced by liver); receive 20–25% of cardiac output; functional unit = nephron (glomerulus + tubules)
- Nephron function — glomerular filtration → tubular reabsorption → tubular secretion → urine formation; kidneys filter ~180 L/day; produce ~1–2 L urine/day; normal urine output ≥0.5 mL/kg/hr
- Renal hilum — where renal artery, renal vein, ureter, lymphatics enter/exit; left renal vein longer (crosses aorta) — used in live donor nephrectomy
- Ureters — ~28 cm; carry urine from renal pelvis → bladder; three natural narrowings (UPJ, pelvic brim, UVJ) — sites for stone impaction; at risk during hysterectomy (“water under the bridge”)
- Urinary Bladder — pelvic organ; detrusor muscle; trigone = fixed triangle (two ureteral orifices + internal urethral orifice); cystoscopy port of entry
- Urethra — male ~20 cm (longer, higher risk of catheter trauma); female ~4 cm (shorter, higher UTI risk); prostatic urethra passes through prostate gland
| Procedure | Anatomy Involved | Key Notes |
|---|---|---|
| Nephrectomy (open/laparoscopic) | Kidney, renal vessels, adrenal gland, ureter | Lateral flank or supine; flank position requires kidney rest elevation |
| Cystoscopy / TURBT | Bladder via urethra | Lithotomy position; glycine or sterile water irrigation |
| TURP | Prostate via urethra | Glycine 1.5% irrigation; TURP syndrome risk; lithotomy position |
| Ureteroscopy / Lithotripsy | Ureter, renal pelvis | Kidney stones; laser lithotripsy (holmium laser); stone basket retrieval |
7B. Female Reproductive System
- Ovaries — produce ova and sex hormones (estrogen, progesterone); held by broad ligament and ovarian ligament
- Fallopian tubes — transport ova from ovary to uterus; site of fertilization; fimbriae sweep ova in; ectopic pregnancy most common here (ampulla)
- Uterus — fundus (top), body, cervix (bottom); endometrium (inner lining — shed during menstruation), myometrium (muscular middle), perimetrium (serosal outer)
- Cervix — connects uterus to vagina; os (opening); cervical cancer — Pap smear; LEEP procedure
- Broad ligament — double fold of peritoneum supporting uterus, tubes, ovaries; contains uterine vessels
- Key GYN procedures: TAH-BSO (total abdominal hysterectomy + bilateral salpingo-oophorectomy); laparoscopic hysterectomy; D&C; myomectomy; ovarian cystectomy; tubal ligation; cesarean section
7C. Male Reproductive System
- Testes — produce sperm (spermatogenesis) and testosterone; located in scrotum (cooler temp required for sperm); covered by tunica albuginea; seminoma = most common testicular tumor
- Epididymis — comma-shaped; site of sperm maturation and storage; posterior to testis; epididymitis = infection
- Vas deferens (ductus deferens) — carries sperm from epididymis to ejaculatory duct; vasectomy performed here
- Seminal vesicles, prostate, bulbourethral glands — accessory glands contributing to semen; prostate surrounds prostatic urethra; BPH causes urinary obstruction → TURP
- Key urologic procedures: Radical prostatectomy; orchiectomy; vasectomy; orchiopexy (undescended testis — cryptorchidism); hydrocelectomy; circumcision
8. Endocrine System
| Gland | Location | Key Hormones | Surgical Relevance |
|---|---|---|---|
| Pituitary | Sella turcica (sphenoid bone); “master gland” | GH, TSH, ACTH, FSH, LH, ADH (posterior), oxytocin | Transsphenoidal hypophysectomy (pituitary adenoma); Cushing’s disease |
| Thyroid | Anterior neck; 2 lobes + isthmus; butterfly-shaped | T3, T4 (metabolism), Calcitonin (↓Ca²⁺) | Thyroidectomy (total/partial); recurrent laryngeal nerve at risk; parathyroids at risk; thyroid storm perioperatively; hyperthyroidism prep with beta-blockers + iodine |
| Parathyroid | 4 glands on posterior thyroid | PTH → ↑Ca²⁺ (↑bone resorption, ↑renal reabsorption, ↑GI absorption) | Parathyroidectomy (hyperparathyroidism); inadvertent removal → hypocalcemia → tetany; intraoperative PTH assay used |
| Adrenal Glands | Atop each kidney; cortex + medulla | Cortex: cortisol (stress), aldosterone (Na/K), androgens; Medulla: epinephrine, norepinephrine | Adrenalectomy; pheochromocytoma (medulla tumor → hypertensive crisis); Cushing’s syndrome (excess cortisol); Conn’s syndrome (excess aldosterone) |
| Pancreas (Endocrine) | Islets of Langerhans: alpha (glucagon) and beta (insulin) cells | Insulin ↓blood glucose; Glucagon ↑blood glucose | Diabetic patients require perioperative glucose monitoring; insulinoma (hypoglycemia); perioperative glucose target <200 mg/dL |
| Gonads | Testes / Ovaries | Testosterone, estrogen, progesterone | Orchiectomy (testicular cancer, prostate cancer); oophorectomy (ovarian cancer, endometriosis) |
9. Integumentary System (Skin)
9A. Skin Layers
- Epidermis — outermost; avascular; 5 layers (from deep to superficial: stratum basale, spinosum, granulosum, lucidum, corneum); no pain receptors; barrier to infection; keratinocytes predominate; melanocytes produce melanin (deeper = less UV penetration)
- Dermis — vascularized; collagen (strength) and elastin (flexibility) from fibroblasts; contains hair follicles, sweat glands, sebaceous glands, sensory receptors (Meissner’s, Pacinian corpuscles); papillary dermis (superficial) and reticular dermis (deep)
- Hypodermis (subcutaneous) — not true skin layer; adipose tissue; insulation; shock absorption; site of SQ injections
9B. Burn Classification
| Degree | Depth | Appearance | Pain | Healing |
|---|---|---|---|---|
| 1st Degree (Superficial) | Epidermis only | Red, dry, no blisters | Painful | 3–5 days; no scarring |
| 2nd Degree (Partial Thickness) | Epidermis + superficial/deep dermis | Blisters; moist; red; blanches | Very painful | 2–3 weeks (superficial); skin grafting for deep |
| 3rd Degree (Full Thickness) | All skin layers; may include subcutaneous | White/brown/black; leathery; dry; no blisters | Painless (nerve destruction) | Requires skin grafting; significant scarring |
| 4th Degree | Full thickness + muscle/bone/tendon | Charred; eschar | Painless | May require amputation |
Rule of Nines (adult burn % TBSA): Head/neck = 9%; each arm = 9%; anterior trunk = 18%; posterior trunk = 18%; each leg = 18%; perineum = 1%. Used to calculate fluid resuscitation (Parkland formula: 4 mL/kg/% TBSA burned — half in first 8 hrs, half in next 16 hrs).
10. Lymphatic & Immune System
- Lymphatic vessels — collect interstitial fluid (lymph), returns it to circulation via thoracic duct (left side) and right lymphatic duct (right upper body) → subclavian veins
- Thoracic duct — largest lymphatic vessel; drains most of body (left side + both legs + abdomen) → left subclavian vein junction; injury during esophagectomy or neck surgery → chylothorax
- Lymph nodes — filter lymph; produce lymphocytes; regional nodes are sampled in oncologic surgery to determine metastasis (sentinel node biopsy)
- Sentinel lymph node — first node(s) receiving drainage from primary tumor; identified with isosulfan blue dye and/or technetium-99m radiotracer; biopsy determines whether cancer has spread (staging)
- Key lymph node groups (surgical): Axillary (breast/upper extremity drainage; sampled in mastectomy); cervical (head/neck cancers); inguinal (lower extremity/perineal drainage); para-aortic (abdominal/pelvic cancers)
- Spleen — largest lymphoid organ; filters blood; removes senescent RBCs; immune surveillance; splenectomy → increased risk of overwhelming post-splenectomy infection (OPSI) with encapsulated organisms
- Thymus — located in anterior mediastinum; T-lymphocyte maturation; atrophies after puberty; thymoma may cause myasthenia gravis → thymectomy
11. Obstetric & Breast Anatomy
11A. Cesarean Section Anatomy (C-Section)
The most commonly performed major surgery in the world. Layers incised (from superficial to deep):
- Skin (Pfannenstiel or vertical midline incision)
- Subcutaneous fat (Camper’s fascia)
- Fascia of Scarpa
- Fascia of the rectus abdominis (anterior rectus sheath)
- Rectus abdominis muscles (separated, not cut in Pfannenstiel)
- Peritoneum (visceral and parietal)
- Uterus (low transverse incision — lower uterine segment)
11B. Breast Anatomy
- Overlies pectoralis major muscle (2nd–6th ribs); suspensory ligaments of Cooper attach to skin and pectoralis fascia
- Quadrants: UOQ (upper outer), UIQ, LOQ, LIQ; axillary tail of Spence extends into axilla; most breast cancers occur in UOQ (50%)
- Lymph drainage: Primarily to axillary nodes (Level I–III); also internal mammary nodes; sentinel node biopsy standard for staging
- Key procedures: Lumpectomy (breast-conserving); mastectomy (simple/modified radical/radical); sentinel node biopsy; axillary node dissection; breast reconstruction (TRAM, DIEP, tissue expanders, implants)
12. Surgical Positioning — Anatomical Risks & Nerve Injuries
Understanding anatomy is critical to preventing positioning injuries. The CST exam frequently tests which nerves and structures are at risk in each position.
| Position | Anatomy / Nerves at Risk | Padding / Prevention | Common Procedures |
|---|---|---|---|
| Supine | Brachial plexus (arm abducted >90°); ulnar nerve (elbow); heel pressure (skin/achilles); occiput pressure | Arms ≤90° abduction; padded arm boards; pillow under knees; heel protectors | Abdominal, cardiac, vascular, GYN, orthopedic |
| Trendelenburg | Brachial plexus (shoulder braces push on nerve); increased ICP; airway edema; aspiration risk | Avoid shoulder braces; use non-slip mattress; head elevated slightly; limit duration | GYN laparoscopy, lower abdominal surgery, central line placement |
| Reverse Trendelenburg | Venous pooling in legs → hypotension; sliding off table | Padded footboard; sequential compression devices (SCDs) | Head/neck, thyroid, upper GI laparoscopy |
| Lithotomy | Common peroneal nerve at fibular head (most common positioning injury); femoral nerve; obturator nerve; lower extremity compartment syndrome; lumbar strain | Pad lateral knee/leg supports; lower both legs simultaneously; limit duration (<2 hrs if possible); avoid hip hyperflexion | GYN (perineal), urologic, rectal, obstetric |
| Prone | Eyes (corneal abrasion, retinal ischemia from direct pressure — MUST protect); brachial plexus; ulnar nerve (elbow); femoral nerve; breast/genitalia pressure; IVC compression → hypotension | Foam face rest or pins (Mayfield) for head; chest rolls/Wilson frame; arms in Superman or at side; protected eyes checked frequently; padded elbows and knees | Spinal/posterior neurosurgery, posterior orthopedic, posterior urologic |
| Lateral (Decubitus) | Brachial plexus (down-side axillary compression); common peroneal nerve (down-side fibular head); ear; dependent eye; down-side shoulder/hip | Axillary roll (chest roll distal to axilla — NOT in axilla); pillows between knees; head neutral; “bean bag” or lateral positioners; pad fibular head | Thoracic, renal, hip, shoulder |
| Sitting (Beach Chair / Fowler’s) | Venous air embolism (VAE) — open veins above heart level; hypotension; sciatic nerve (hip flexion); cervical spine injury during head positioning | Monitor for VAE (precordial Doppler, EtCO₂ drop); flex head carefully; SCDs; careful blood pressure management | Posterior fossa craniotomy, shoulder (beach chair), ENT |
| Kidney / Flank | Brachial plexus; lateral femoral cutaneous nerve; IVC compression; vena caval compression causing hypotension when kidney rest elevated | Kidney rest raised gradually; monitor BP; flex table at iliac crest; axillary roll; all bony prominences padded | Nephrectomy, ureteroscopy, renal surgery |
⚠️ Most Common Positioning Nerve Injury: The common peroneal (fibular) nerve at the fibular head is the most frequently injured peripheral nerve from surgical positioning — particularly in lithotomy position. Injury causes foot drop (inability to dorsiflex foot). Always pad the lateral knee/fibular head area.
13. Physiology Concepts Critical to OR Practice
13A. Homeostasis & Fluid/Electrolyte Balance
- Homeostasis — maintenance of stable internal environment; disrupted by surgery (blood loss, fluid shifts, temperature changes, anesthetic effects)
- Sodium (Na⁺) — primary extracellular cation; controls osmolality and water distribution; hyponatremia (<135) → neurological symptoms; hypernatremia (>145) → dehydration
- Potassium (K⁺) — primary intracellular cation; critical for cardiac conduction; hypokalemia → arrhythmias, muscle weakness; hyperkalemia → peaked T waves, cardiac arrest; succinylcholine raises K⁺
- Calcium (Ca²⁺) — muscle contraction, nerve transmission, coagulation; hypocalcemia → tetany, perioral numbness, Chvostek’s sign (facial nerve tapping → facial twitch), Trousseau’s sign; risk after thyroid/parathyroid surgery
- pH / Acid-Base — normal arterial pH 7.35–7.45; acidosis <7.35 (respiratory: ↑CO₂; metabolic: ↓HCO₃); alkalosis >7.45 (respiratory: ↓CO₂; metabolic: ↑HCO₃)
13B. Hemostasis & Coagulation
- Primary hemostasis — vascular spasm → platelet adhesion (vWF bridges collagen and platelets) → platelet aggregation → platelet plug
- Secondary hemostasis (coagulation cascade) — intrinsic pathway (factors XII, XI, IX, VIII — measured by PTT) + extrinsic pathway (tissue factor + VII — measured by PT/INR) → common pathway (X, V, II, I) → thrombin → fibrin clot
- PT/INR — measures extrinsic pathway; elevated in warfarin use, liver disease; goal INR <1.5 before elective surgery
- PTT (aPTT) — measures intrinsic pathway; used to monitor heparin; normal 25–35 sec; therapeutic heparin: 60–100 sec
- Platelets — normal 150,000–400,000/µL; <50,000 = surgical bleeding risk; <20,000 = spontaneous bleeding risk
- Fibrinolysis — plasmin breaks down fibrin; antifibrinolytics (tranexamic acid, aminocaproic acid) prevent this; used to reduce blood loss in major surgery
13C. Thermoregulation
- Normal body temperature: 36.5–37.5°C (97.7–99.5°F); controlled by hypothalamus
- Perioperative hypothermia (<36°C) — most common thermal complication of surgery; causes: cold OR, open body cavities, cold IV fluids, anesthetic-induced vasodilation and impaired thermoregulation
- Consequences of hypothermia: Impaired coagulation, wound infection (impaired neutrophil function), cardiac arrhythmias, increased anesthetic requirements, prolonged drug metabolism, shivering (increased O₂ demand)
- Prevention: Forced-air warming blankets (Bair Hugger); warm IV fluids; warm irrigation; head covering; minimize patient exposure; OR temperature ≥68°F (20°C)
- Hyperthermia in OR — infection, transfusion reaction, malignant hyperthermia (see Pharmacology section); fever >38.3°C postoperatively within first 24 hrs likely from atelectasis or physiologic response, not infection
13D. Shock — Types & Physiological Response
| Type | Mechanism | Signs | Treatment Principle |
|---|---|---|---|
| Hypovolemic | ↓ blood volume (hemorrhage, fluid loss) | ↑HR, ↓BP, pale/cool/clammy skin, ↓UO | Control hemorrhage; IV fluids/blood products |
| Distributive | Vasodilation → relative hypovolemia (sepsis, anaphylaxis, neurogenic) | Warm/flushed skin (sepsis/anaphylaxis); ↓BP; ↑HR | Vasopressors; epinephrine (anaphylaxis); antibiotics (sepsis) |
| Cardiogenic | Pump failure (MI, heart failure, dysrhythmia) | ↓BP, ↑HR, crackles, ↑JVD, ↓CO | Inotropes; IABP; treat arrhythmia; careful fluids |
| Obstructive | Mechanical block to circulation (tension pneumothorax, cardiac tamponade, PE) | Beck’s triad (tamponade: ↓BP, ↑JVD, muffled heart sounds); ↓BP, ↑HR | Remove obstruction: needle decompression (pneumo), pericardiocentesis (tamponade), embolectomy (PE) |
13E. Blood Products
| Product | Contents | Indication | Notes |
|---|---|---|---|
| pRBC (Packed Red Blood Cells) | RBCs; Hgb/Hct; small plasma volume | Anemia; hemorrhage; Hgb <7–8 g/dL typically | 1 unit raises Hgb ~1 g/dL; must be ABO-compatible; infuse through blood filter with NS only |
| FFP (Fresh Frozen Plasma) | All clotting factors + fibrinogen + albumin | Coagulopathy; warfarin reversal; massive transfusion | Must be ABO-compatible; thaw before use; given for elevated PT/INR or PTT; 1 unit raises coagulation factors ~5% |
| Platelets | Platelets in plasma | Thrombocytopenia (<50,000 for surgery); platelet dysfunction | 1 apheresis unit raises count ~50,000; room temperature storage (5 days); agitated to prevent clumping |
| Cryoprecipitate | Fibrinogen, Factor VIII, vWF, Factor XIII | Fibrinogen deficiency, DIC, hemophilia A, vWD | High fibrinogen per volume; pooled; given when fibrinogen <100–150 mg/dL; 10-unit pool is standard |
| Albumin | Colloid protein | Hypoalbuminemia; volume expansion; paracentesis replacement | 5% (iso-oncotic) or 25% (hyper-oncotic); no blood type required; expensive |
✅ Blood Administration Safety: Blood products must ALWAYS be administered through a filter (170–260 micron). Only Normal Saline (0.9% NaCl) is compatible — do NOT infuse with LR (calcium causes clotting) or D5W (hemolysis). Two licensed personnel must verify blood product against patient ID before administration.
14. CST Exam Strategy — A&P Edition
How A&P Appears on the CST Exam
A&P is rarely tested in isolation on the CST exam. Instead, it is embedded in questions about:
- Surgical procedures — “Which structure is most at risk during a thyroidectomy?” → Recurrent laryngeal nerve
- Patient positioning — “Which nerve is most commonly injured in lithotomy position?” → Common peroneal nerve
- Instrumentation & retractors — you must know what structures are being retracted
- Pathology identification — “What organ was resected?” requires knowing anatomy
- Complications — “A patient develops hoarseness postoperatively after a neck dissection — which nerve was injured?” → Recurrent laryngeal (vagus)
Top Tips for A&P on the CST Exam
- Know your at-risk nerves by procedure: Facial nerve (parotid/mastoid); RLN (thyroid/esophageal); brachial plexus (supine/lateral); peroneal nerve (lithotomy). These appear repeatedly.
- Memorize organ locations by quadrant: Know which RUQ/LUQ/RLQ/LLQ organs to identify what surgery is being performed based on incision location.
- Know blood flow through the heart perfectly: Questions about cardiac surgery require knowing the sequence of chambers and valves.
- Master the layers of the abdomen: Skin → fat → fascia → muscle → peritoneum → organ. Every abdominal case closes in reverse. Know what you’re counting in sponge counts.
- Understand dermatomes for spinal anesthesia: T4 = nipples; T10 = umbilicus. A spinal block to T4 is needed for cesarean section.
- Know the right bronchus rule: Right main bronchus is shorter, wider, and more vertical — this is why foreign body aspiration and inadvertent right mainstem intubation occur here.
- Know the ureter trick: Ureters pass under the uterine artery during hysterectomy (“water under the bridge”) — most common site of ureteral injury during GYN surgery.
- Triangles matter: Triangle of Calot (cholecystectomy) → cystic artery identification. Femoral triangle (inguinal surgery) → femoral nerve, artery, vein, lymphatics (NAVEL from lateral to medial).
- Coagulation pathways on the exam: PT/INR = extrinsic = warfarin; PTT = intrinsic = heparin. This is always tested.
- Body cavities and incisions: Know which incision provides access to which cavity. Midline = widest abdominal access; Pfannenstiel = pelvic/GYN; McBurney’s = appendix.
⚡ High-Yield A&P Quick Reference Cards
Heart Valves — Mnemonic
“Try Pulling My Aorta”
Tricuspid (right AV) → Pulmonic → Mitral (left AV) → Aortic
AV valves open during diastole; Semilunar valves open during systole.
Cranial Nerve Mnemonic
“Oh Oh Oh To Touch And Feel Very Good Velvet — Ah Heaven!”
I Olfactory, II Optic, III Oculomotor, IV Trochlear, V Trigeminal, VI Abducens, VII Facial, VIII Vestibulocochlear, IX Glossopharyngeal, X Vagus, XI Accessory, XII Hypoglossal
Femoral Triangle — NAVEL
Lateral → Medial:
Nerve (femoral) | Artery (femoral) | Vein (femoral) | Empty space | Lymphatics
Key for inguinal hernia, femoral access, groin dissection.
Coagulation Labs
PT/INR = Extrinsic pathway = Warfarin effect → factors II, VII, IX, X
PTT/aPTT = Intrinsic pathway = Heparin monitoring
Platelets = Primary hemostasis; <50,000 = surgical bleeding risk
Right vs. Left Bronchus
Right bronchus: shorter, wider, more vertical → foreign body aspiration and inadvertent endobronchial intubation occur here. Right lung has 3 lobes; Left has 2 (room for heart).
Dermatome Landmarks
T4 = Nipple line (spinal level needed for C-section)
T10 = Umbilicus
L4 = Knee
S3–S5 = Perineum/saddle area
C3–C5 = Diaphragm (“phrenic nerve keeps diaphragm alive”)
Abdominal Layers (Outside → In)
Skin → Subcutaneous fat (Camper’s / Scarpa’s fascia) → External oblique → Internal oblique → Transversus abdominis → Transversalis fascia → Preperitoneal fat → Peritoneum → Organ
Most Common Positioning Injury
Common peroneal (fibular) nerve at fibular head — lithotomy/lateral position.
Injury = foot drop (cannot dorsiflex).
Always pad lateral knee and fibular head.
Cushing’s Triad (↑ICP)
↑ Blood Pressure + ↓ Heart Rate + Irregular Respirations = Brain herniation warning. Notify surgeon immediately. Treat with mannitol, hyperventilation, HOB elevation.
Structures at Risk by Surgery
Thyroidectomy: RLN, parathyroids
Parotidectomy: Facial nerve (CN VII)
Hysterectomy: Ureters (“water under the bridge”)
CEA: Hypoglossal, vagus nerves
Cholecystectomy: Common bile duct
Beck’s Triad — Cardiac Tamponade
↓ Blood pressure + ↑ JVD (jugular venous distension) + Muffled heart sounds
Treatment: pericardiocentesis (needle aspiration of pericardial sac) or surgical pericardial window.
Appendix / McBurney’s Point
Located at 1/3 distance from the ASIS to the umbilicus in the RLQ. Appendix attaches to base of cecum. Classic appendicitis: pain starts periumbilical → migrates to McBurney’s point.
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