Arab Board Surgery Part 1 cheat sheet

Right recurrent laryngeal nerve loops under the right subclavian artery; the left loops under the aortic arch at the ligamentum arteriosum; both ascend in the tracheoesophageal groove and are at risk in thyroid and oesophageal surgery.

Femoral triangle: inguinal ligament superiorly, sartorius laterally, adductor longus medially; from lateral to medial lie femoral nerve, artery, vein and the empty femoral canal (NAVEL).

Hesselbach's triangle: lateral border of rectus abdominis, inguinal ligament, inferior epigastric vessels - herniation here is a direct inguinal hernia; indirect hernias pass lateral to the inferior epigastric vessels through the deep ring.

Calot's triangle is bounded by the cystic duct, the common hepatic duct and the inferior surface of the liver; it contains the cystic artery and the node of Lund.

The midgut rotates 270 degrees counterclockwise around the superior mesenteric artery during the 10th week; the caecum settles in the right iliac fossa and the duodenojejunal flexure at the ligament of Treitz.

The ureter has three constrictions where stones lodge: the pelviureteric junction, the crossing of the iliac vessels, and the vesicoureteric junction.

Superior parathyroid glands arise from the fourth pharyngeal pouch and inferior glands from the third; both are supplied mainly by the inferior thyroid artery, which must be preserved during thyroidectomy.

The axillary artery is divided into three parts by pectoralis minor; the brachial plexus cords are named by their relation to its second part as lateral, posterior and medial.

Cardiac output = heart rate × stroke volume (normal 4–8 L/min); cardiac index = cardiac output divided by body surface area (2.5–4.0 L/min/m²).

Fick principle: cardiac output = oxygen consumption divided by the arteriovenous oxygen content difference.

Oxygen delivery DO2 = cardiac output × CaO2, where CaO2 = (1.34 × haemoglobin × SaO2) + (0.003 × PaO2); normal DO2 is about 1000 mL/min and consumption about 250 mL/min.

Starling equation: net filtration = Kf[(Pc − Pi) − σ(πc − πi)]; plasma colloid oncotic pressure is approximately 25 mmHg.

Renal autoregulation holds renal blood flow and GFR constant between mean arterial pressures of 80 and 180 mmHg; GFR is about 125 mL/min and filtration fraction about 20%.

Henderson–Hasselbalch: pH = 6.1 + log([HCO3−] ÷ (0.03 × PaCO2)); a rise in PaCO2 causes respiratory acidosis and a fall in HCO3− causes metabolic acidosis.

Gastric acid secretion is stimulated by acetylcholine (M3), gastrin (CCK2) and histamine (H2); the parietal cell H+/K+-ATPase is blocked by proton pump inhibitors.

West's lung zones: zone 1 at the apex (PA > Pa > Pv), zone 2 in the mid-zone (Pa > PA > Pv), zone 3 at the base (Pa > Pv > PA).

Virchow's triad - endothelial injury, stasis or turbulence, and hypercoagulability - underlies both arterial and venous thrombosis.

Acute inflammation causes vasodilatation and increased vascular permeability; neutrophils dominate the first 6–24 hours and macrophages predominate after 24–48 hours.

Wound healing sequence: haemostasis, inflammation, proliferation (granulation tissue, angiogenesis, epithelialisation) and remodelling, in which type III collagen is replaced by type I.

Oncogenes (RAS, MYC, HER2) gain function from a single mutation; tumour suppressors (p53, RB, APC, BRCA1/2) require loss of both alleles, as described by Knudson's two-hit hypothesis.

Features of malignancy include invasion through the basement membrane, metastasis, anaplasia, pleomorphism, a high nuclear-to-cytoplasmic ratio and atypical mitoses.

Metaplasia is a reversible change of one mature cell type to another and may progress to dysplasia (disordered growth) and then carcinoma in situ, in which the basement membrane remains intact.

Necrosis causes cell swelling and inflammation; apoptosis is caspase-mediated, energy-dependent, non-inflammatory and shows internucleosomal DNA laddering.

A granuloma is a collection of activated macrophages (epithelioid cells and Langhans giant cells) seen in tuberculosis, sarcoidosis and foreign-body reactions.

Sepsis (Sepsis-3): suspected infection with an acute rise in SOFA score of ≥2; septic shock is vasopressor need to keep MAP ≥65 mmHg plus lactate >2 mmol/L despite adequate fluid resuscitation.

Surgical site infection is most often caused by Staphylococcus aureus, coagulase-negative staphylococci and Escherichia coli; prophylaxis is given within 60 minutes of incision (120 minutes for vancomycin or fluoroquinolones).

Cefazolin 2 g (3 g if over 120 kg) is standard prophylaxis for clean-contaminated surgery, redosed every 4 hours and after about 1500 mL blood loss; metronidazole is added for anaerobic cover.

Steam sterilisation uses 121 °C for 15 minutes at 15 psi or 134 °C for 3 minutes; heat-sensitive items require ethylene oxide or hydrogen peroxide plasma, and sterilisation fails without prior cleaning.

Spaulding classification: critical items entering sterile tissue need sterilisation, semicritical items contacting mucosa need high-level disinfection, and noncritical items touching intact skin need low-level disinfection.

Clostridium perfringens alpha-toxin causes gas gangrene; treatment is urgent surgical debridement with high-dose penicillin plus clindamycin.

MRSA is treated with vancomycin or linezolid; anaerobes respond to metronidazole; Pseudomonas requires an antipseudomonal beta-lactam or an aminoglycoside.

Hand hygiene is the single most effective measure against healthcare-associated infection; use alcohol rub for 20–30 seconds and soap and water when hands are soiled or after Clostridioides difficile exposure.

Induction agents: propofol causes hypotension and apnoea; ketamine, an NMDA antagonist, preserves blood pressure and bronchodilates; etomidate is cardiovascularly stable but suppresses adrenal steroidogenesis.

Succinylcholine is a depolarising blocker with rapid onset and 5–10 minute duration; it causes hyperkalaemia and raised intraocular pressure and triggers malignant hyperthermia, so it is avoided in burns, denervation and spinal injury.

Rocuronium is reversed by sugammadex; neostigmine, given with glycopyrrolate, reverses nondepolarising blockade by inhibiting acetylcholinesterase.

Local anaesthetics are weak bases that block voltage-gated sodium channels from the cytoplasmic side; onset depends on pKa, potency on lipid solubility and duration on protein binding.

Maximum lidocaine dose is 3 mg/kg plain and 7 mg/kg with adrenaline; bupivacaine is the most cardiotoxic local anaesthetic and is contraindicated for intravenous regional anaesthesia.

Malignant hyperthermia: stop triggering agents, give dantrolene 2.5 mg/kg IV, use 100% oxygen, cool actively and treat hyperkalaemia and arrhythmias; dantrolene has cut mortality from about 70% to under 5%.

Heparin acts through antithrombin and is monitored by aPTT and reversed by protamine; warfarin inhibits vitamin K epoxide reductase, is monitored by INR and is reversed by vitamin K, prothrombin complex or fresh frozen plasma.

MAC (minimum alveolar concentration) is the alveolar concentration at which 50% of patients do not move to surgical stimulus; it is additive with nitrous oxide and reduced by hypothermia, pregnancy, sepsis and opioids.

Cuthbertson's response: an ebb phase of hypovolaemia and reduced metabolic rate, then a flow phase of fever, tachycardia, raised catecholamines, cortisol, glucagon and antidiuretic hormone with insulin resistance and negative nitrogen balance.

Body fluid compartments: total body water is about 60% of body weight, with 40% intracellular and 20% extracellular (15% interstitial, 5% plasma).

Energy requirement is about 25–30 kcal/kg/day with protein 1.2–1.5 g/kg/day in catabolic patients; maximal glucose oxidation is about 5 mg/kg/min.

Nitrogen balance = nitrogen intake − (24-hour urinary urea nitrogen + 4 g); 6.25 g of protein supplies 1 g of nitrogen, and a positive balance indicates anabolism.

Respiratory quotient is 1.0 for carbohydrate, 0.8 for protein and 0.7 for fat; a mixed diet gives about 0.85 and lipogenesis from overfeeding pushes it above 1.0.

Refeeding syndrome: an insulin surge drives phosphate, potassium and magnesium into cells, causing arrhythmias and cardiac failure; give thiamine first and start feeding at about 10 kcal/kg/day.

Starvation: glycogen stores are exhausted by 24 hours, then gluconeogenesis uses amino acids and glycerol; prolonged starvation shifts to ketone bodies and spares protein.

Enteral nutrition is preferred to parenteral nutrition because it maintains gut mucosal integrity, reduces septic complications and costs less; parenteral nutrition is reserved for a non-functioning gut.

Wound tensile strength is about 5% at 2 weeks, 20–30% at 1 month and 70–80% at 1 year; final strength depends more on collagen cross-linking than on collagen quantity.

Holliday–Segar maintenance: 100 mL/kg/day for the first 10 kg, 50 mL/kg/day for the next 10 kg and 20 mL/kg/day thereafter, equivalent to 4-2-1 mL/kg/hour.

Absorbable sutures include catgut, polyglactin (Vicryl), poliglecaprone (Monocryl) and polydioxanone (PDS); non-absorbable sutures include silk, nylon, polypropylene (Prolene) and polyester (Ethibond).

Monofilament sutures such as nylon, polypropylene and PDS resist bacterial colonisation and slide easily but have memory; braided sutures handle better but can harbour bacteria and potentiate infection.

Chronic hyponatraemia should be corrected by no more than 8–10 mmol/L in 24 hours to avoid osmotic demyelination; 3% saline is reserved for seizures or sodium below 120 mmol/L.

Hyperkalaemia with ECG changes: give intravenous calcium gluconate first, then insulin with dextrose, salbutamol and sodium bicarbonate, with dialysis for refractory cases.

Haemostasis: primary haemostasis forms the platelet plug via von Willebrand factor and GPIIb/IIIa; secondary haemostasis uses the intrinsic (XII, XI, IX, VIII) and extrinsic (VII, tissue factor) pathways converging on factor X, thrombin and fibrin.

Monopolar diathermy returns current through a patient pad and can burn if the pad is loose; bipolar diathermy confines current between the forceps tips and is safer in patients with pacemakers.

ATLS sequence: A airway with cervical spine protection, B breathing, C circulation with haemorrhage control, D disability (Glasgow Coma Scale, pupils), E exposure with prevention of hypothermia.

Haemorrhagic shock classes: I under 15% loss (normal vitals), II 15–30% (tachycardia, narrow pulse pressure), III 30–40% (hypotension, confusion, oliguria), IV over 40% (profound hypotension, lethargy).

Hypotension after trauma is haemorrhagic until proven otherwise; give 1 L warm crystalloid then blood products in a 1:1:1 ratio of red cells, plasma and platelets, with tranexamic acid within 3 hours of injury.

Tension pneumothorax is a clinical diagnosis: perform immediate needle decompression in the fifth intercostal space at the anterior axillary line or the second space midclavicular, then insert a chest drain; never wait for imaging.

Cardiac tamponade shows Beck's triad of hypotension, distended neck veins and muffled heart sounds, with pulsus paradoxus and an enlarged cardiac silhouette; treat by pericardiocentesis or thoracotomy.

Glasgow Coma Scale: eye opening 4, verbal response 5, motor response 6; a total of 8 or less indicates the need for airway protection and intubation.

Burns: Parkland formula gives 4 mL/kg per percent total body surface area of lactated Ringer's in 24 hours, half in the first 8 hours; rule of nines gives 9% per arm, 18% per leg, 18% anterior trunk, 18% posterior trunk, 9% head, 1% perineum.

ARDS (Berlin criteria): onset within 1 week, bilateral infiltrates not explained by cardiac failure, and PaO2/FiO2 ≤300 with PEEP ≥5 cmH2O; ventilate at 6 mL/kg predicted body weight.

Valid informed consent requires capacity, adequate disclosure, comprehension, voluntariness and consent for the specific procedure; the emergency exception applies when life is at risk and no proxy can be reached.

Four ethical principles: autonomy (respect for patient choice), beneficence (act in the patient's interest), non-maleficence (avoid harm) and justice (fair distribution of scarce resources).

Confidentiality may be breached with consent, under statutory duty (notifiable diseases, knife wounds) or where public interest overrides it; disclose only the minimum necessary information.

The WHO Surgical Safety Checklist has three phases - sign in before induction, time out before incision and sign out before leaving theatre - and reduces mortality and complications.

Sensitivity = TP/(TP + FN) and specificity = TN/(TN + FP); positive and negative predictive values change with disease prevalence, whereas sensitivity and specificity do not.

A randomised controlled trial is the strongest design for causation; cohort studies yield incidence and relative risk; case-control studies yield odds ratios and suit rare outcomes.

Type I error (alpha) is rejecting a true null hypothesis; type II error (beta) is failing to reject a false null hypothesis, and power equals 1 − beta, conventionally set at 80%.

Number needed to treat = 1 ÷ absolute risk reduction, where absolute risk reduction = control event rate − treatment event rate; number needed to harm = 1 ÷ absolute risk increase.