Surgery

Let's talk about the non-negotiable foundation of surgery — asepsis. Think of it as a hierarchy: at the very top, , whether through steam autoclaving at 121-134°C, ethylene oxide gas for heat-sensitive instruments, or hydrogen peroxide plasma for your delicate endoscopic kit. One rung down, disinfection kills pathogenic organisms but doesn't guarantee total elimination — that's what glutaraldehyde and peracetic acid are for, reserved for semi-critical items that don't need full sterilization.

Sterilization Methods Comparison

Method	Temp/Pressure	Time	Best For	Cannot Use On
Autoclave (steam)	121°C/15 psi or 134°C/30 psi	15-30 min	Surgical instruments, drapes, gowns	Heat-sensitive items, plastics, electronics
Ethylene Oxide (ETO)	37-55°C	2-6h + 12h aeration	Endoscopes, electrical equipment, cameras	None — needs long aeration time
Hydrogen Peroxide Plasma	<50°C	28-75 min	Heat-sensitive instruments, scopes	Cellulose/linen (absorbs H2O2), long lumens
Gamma Radiation	Ambient	Variable	Disposables, sutures, implants (industrial)	Not for hospital use (industrial only)

Surgical Scrub

The surgical scrub remains a critical component, with chlorhexidine gluconate (4%) or povidone-iodine (7.5%) providing rapid broad-spectrum antimicrobial activity. The timed scrub technique (5 minutes for the first case, 3 minutes for subsequent cases) or the counted-brush-stroke technique (20 strokes per surface) ensures adequate reduction of transient and resident skin flora. Alcohol-based hand rubs (70% ethanol or isopropanol with emollients) are equally effective and associated with reduced dermatitis.

Scrub Agent	Onset	Residual Activity	Spectrum	Preferred For
Chlorhexidine 4%	Rapid	Superior (6+ hours)	Broad (gram+, gram−, viruses)	Most clean-contaminated procedures
Povidone-Iodine 7.5%	Moderate	Limited (1-3 hours)	Broad (includes spores)	Contaminated/dirty cases
Alcohol 70%	Fastest	None (no residual)	Excellent bactericidal	Hand rub between cases

Gowning, Gloving, and the Sterile Field

Surgical gowning and gloving establish a sterile barrier. The sterile field must be maintained with constant vigilance:

Operating Room Environment

Operating room environment parameters include positive-pressure ventilation (>15 air changes per hour, with at least 3 fresh air changes), HEPA filtration (99.97% efficiency at 0.3 μm), temperature maintained at 20-23°C, and humidity at 30-60%. Laminar airflow systems reduce bacterial counts in orthopaedic and transplant surgery. Traffic in and out of the OR should be minimized, as each opening of the door reduces positive pressure and increases particle counts.

Surgical Site Infection Prevention

Surgical site infection (SSI) prevention bundles include preoperative showers with chlorhexidine, appropriate hair removal (clippers, not razors — ), prophylactic antibiotics within 60 minutes before incision (120 minutes for vancomycin), perioperative normothermia (), glucose control (perioperative hyperglycemia >180 mg/dL increases SSI risk), and appropriate wound closure techniques. The CDC classification of surgical wounds (Class I Clean, Class II Clean-Contaminated, Class III Contaminated, Class IV Dirty-Infected) determines postoperative infection risk and guides antibiotic management.

CDC Wound Classification — NEET PG High-Yield

Class	Definition	Infection Rate	Prophylaxis	Example
I — Clean	No infection, no viscus entry	1-3%	Not routinely indicated	Hernia repair, breast biopsy, thyroidectomy
II — Clean-Contaminated	Controlled entry into viscus	5-8%	Single dose preop	Cholecystectomy, colectomy, gastrectomy
III — Contaminated	Spillage/acute inflammation no pus	15-20%	Preop + 24h postop	Perforated diverticulitis, trauma <4h
IV — Dirty-Infected	Established infection at surgery	25-40%	Therapeutic (not prophylactic)	Abscess drainage, perforation with peritonitis

1. Chlorhexidine-alcohol reduces SSI by 40% compared to povidone-iodine per WHO guidelines
2. Preoperative nasal mupirocin for S. aureus carriers reduces SSI in cardiothoracic and orthopaedic surgery
3. Most common SSI organism: Staphylococcus aureus (20-30%)
4. Hyperglycemia >180 mg/dL increases SSI risk by 2-3x
5. MRSA SSI: requires vancomycin — cefazolin does NOT cover MRSA

Phases of Wound Healing

Wound healing follows a predictable cascade of overlapping phases: haemostasis (immediate to minutes), inflammation (1-7 days), proliferation (3-21 days), and remodelling (21 days to 2 years). Haemostasis begins with platelet aggregation and degranulation, releasing platelet-derived growth factor (PDGF), transforming growth factor-beta (TGF-β), and vascular endothelial growth factor (VEGF). The coagulation cascade generates fibrin, forming a provisional matrix scaffold.

Inflammatory Phase

The inflammatory phase features neutrophil infiltration within 24-48 hours, serving as the primary antibacterial defence. Macrophages appear at 48-96 hours and are the master regulators of wound healing — they phagocytose debris, secrete cytokines (IL-1, TNF-α, PDGF, TGF-β, FGF), and coordinate the transition to the proliferative phase. Lymphocytes arrive later and modulate collagen synthesis and remodelling.

Proliferative Phase

The proliferative phase encompasses three key processes: angiogenesis (new capillary formation driven by hypoxia-inducible factor 1α and VEGF, creating granulation tissue), fibroplasia (fibroblast migration and proliferation with collagen synthesis — predominantly type III collagen initially), and epithelialisation (keratinocyte migration from wound edges and residual adnexal structures). Wound contraction, mediated by myofibroblasts expressing α-smooth muscle actin, reduces wound surface area by up to 80% in secondary healing.

Remodelling Phase

Remodelling involves the gradual replacement of type III collagen with type I collagen, increased cross-linking (mediated by lysyl oxidase), and a reduction in cellularity and vascularity. Collagen turnover in a scar continues for years, with a net balance between metalloproteinase-mediated degradation and continued synthesis.

Phases of Wound Healing — NEET PG Mnemonic Table

Phase	Timing	Dominant Cell	Key Events	Collagen
Haemostasis	Immediate — minutes	Platelets	PDGF, TGF-β, VEGF release; fibrin clot forms	None
Inflammation	Day 1-7	Neutrophils (day 1-3) → Macrophages (day 3+)	Debridement, cytokine secretion, transition signal	None
Proliferation	Day 3-21	Fibroblasts, Myofibroblasts	Granulation tissue, angiogenesis, Type III collagen	Type III (immature)
Remodelling	3 weeks — 2 years	Fibroblasts	Type III → Type I, cross-linking, scar maturation	Type I (mature)

Factors Impairing Wound Healing

Key Vitamins and Minerals in Wound Healing

Nutrient	Role	Deficiency Effect	Daily Requirement (Postop)
Vitamin C (Ascorbic Acid)	Prolyl and lysyl hydroxylase cofactor — cross-linking	Scurvy: impaired collagen, wound dehiscence, bleeding	500-1000 mg
Vitamin A	Epithelialisation, macrophage function, reverses steroid effects	Impaired immunity, poor epithelial growth	25,000 IU (caution: toxicity)
Zinc	Matrix metalloproteinase cofactor, protein synthesis	Delayed wound healing, poor epithelialisation	15-30 mg elemental zinc
Protein	Substrate for collagen synthesis, immune cell production	Impaired granulation tissue, poor fibroblast activity	1.5-2.0 g/kg/day

Wound Closure Types

Closure Type	Timing	Indications	Infection Risk
Primary intention	Immediate (within hours)	Clean surgical wounds, acute uncontaminated lacerations	Lowest
Delayed primary closure	3-5 days after injury	Contaminated wounds, bites, wounds with delayed presentation	Moderate
Secondary intention	Heals by granulation (weeks)	Infected wounds, chronic ulcers, wounds with tissue loss	Highest
Tertiary intention	After granulation tissue forms	Wounds left open initially then closed surgically	Moderate

Wound Dehiscence and Evisceration

Dehiscence vs Evisceration	Definition	Management
Wound Dehiscence	Fascial separation without bowel protrusion	Open wound care, NPWT, delayed closure when clean
Wound Evisceration	Fascial separation WITH bowel protrusion	SURGICAL EMERGENCY: cover with saline-soaked sterile towels, urgent return to OR

Hypertrophic Scar vs Keloid

Feature	Hypertrophic Scar	Keloid
Growth pattern	Confined to wound borders	Extends beyond original wound margins
Onset	Within weeks of injury	Delayed (months to years)
Natural history	May regress spontaneously	Does NOT regress
Common sites	Over joints, sternum, flexor surfaces	Earlobes, sternum, shoulders, upper back
Histology	Type III > Type I collagen, parallel bundles	Thick, hyalinised collagen bundles (Type I, disorganised)
Treatment	Silicone sheeting, steroid injection	Surgical excision + intralesional triamcinolone + pressure therapy

The pathogenesis follows the interaction between the bacterial inoculum (dose, virulence), the host immune response, and the local wound environment. The critical bacterial load for wound infection is generally >10⁵ organisms per gram of tissue, though lower counts can cause infection in the presence of foreign material (suture, implant) or devitalised tissue.

SSI Classification by Depth

SSI Type	Depth	Onset	Features	Management
Superficial Incisional	Skin + subcutaneous tissue only	Within 30 days	Erythema, pain, purulent drainage from incision	Open wound, local care, oral antibiotics
Deep Incisional	Deep soft tissues (fascia/muscle)	Within 30-90 days	Fever, pain, fascial dehiscence, purulent drainage	Open/debride, IV antibiotics, NPWT
Organ/Space	Organ or anatomic space	Within 30-90 days	Intra-abdominal abscess, empyema, peritonitis	Percutaneous/surgical drainage + IV antibiotics

Common Pathogens by Surgical Site

The most common pathogens are Staphylococcus aureus (20-30%), coagulase-negative staphylococci (15-20%), Enterococcus species (10-15%), Escherichia coli (10-15%), and Pseudomonas aeruginosa (5-10%).

SSI Pathogen by Surgical Site

Surgery Type	Most Common Pathogen	Second Most Common
Clean (hernia, breast, thyroid)	S. aureus (40-50%)	Coagulase-negative staphylococci
Colorectal	E. coli (30%) and Bacteroides fragilis (25%)	Enterococcus spp.
Biliary	E. coli, Klebsiella	Enterococcus, Clostridium
Gastroduodenal	Oral streptococci, Enterobacteriaceae	Anaerobes
Vascular/orthopaedic implant	S. aureus (including MRSA)	Coagulase-negative staphylococci

Antibiotic Prophylaxis Guidelines

The first dose should be administered within 60 minutes before incision (120 minutes for vancomycin and fluoroquinolones, which require longer infusion times). Redosing is required after 2 half-lives of the antibiotic.

Prophylaxis by Procedure — NEET PG Must-Know

Procedure Type	Recommended Agent(s)	Alternative (Allergy)	Key NEET Fact
Clean (cardiac, ortho, vascular)	Cefazolin 2g IV (3g if >120 kg)	Clindamycin 600-900 mg OR Vancomycin 1g	Cefazolin covers S. aureus + S. epidermidis
Colorectal	Cefoxitin 2g or Cefotetan 2g + Metronidazole 500 mg	Gentamicin + Metronidazole + Amoxicillin	Must cover anaerobes AND gram-negatives
Head and neck (mucosal)	Ampicillin-Sulbactam 3g IV	Clindamycin + Gentamicin	Oral anaerobes + skin flora coverage needed
Biliary (high risk)	Cefazolin 2g IV	Gentamicin + Metronidazole	High risk = age >70, jaundice, acute cholecystitis, prior ERCP
Urologic (bacteriuria)	Ciprofloxacin 400 mg or Ceftriaxone 1g IV	Aztreonam + Metronidazole	Must treat bacteriuria preop (culture at least 7 days prior)

SIRS, Sepsis, and Septic Shock

The quick Sequential Organ Failure Assessment (qSOFA) screening tool identifies patients at risk: altered mental status (GCS <15), respiratory rate ≥22/min, systolic blood pressure ≤100 mmHg — 2 or more criteria predict poor outcomes. Septic shock is defined by vasopressor requirement to maintain MAP ≥65 mmHg and serum lactate >2 mmol/L despite adequate volume resuscitation.

Shock in Surgical Patients

Type	Hemodynamics	Common Causes in Surgery	Key Features	NEET PG Clue
Hypovolemic	↓CVP, ↓CO, ↑SVR	Hemorrhage, dehydration, burns	Flat neck veins, oliguria, cool extremities	Most common shock in surgical patients
Distributive (septic)	↓CVP, ↑CO, ↓SVR	Sepsis, anaphylaxis, spinal shock	Warm extremities, bounding pulse, fever	"Warm shock" — vasodilation with normal/high CO
Cardiogenic	↑CVP, ↓CO, ↑SVR	MI, arrhythmia, cardiac tamponade	Distended neck veins, pulmonary edema, cool extremities	Elevated JVP + hypotension
Obstructive	↑CVP, ↓CO, ↑SVR	Tension pneumothorax, PE, tamponade	Distended neck veins, pulsus paradoxus	JVP elevated + hypotension + clear lungs (PE) or hyperresonance (PTx)

Hemodynamic Patterns in Shock — NEET PG Must-Know

Parameter	Hypovolemic	Cardiogenic	Distributive	Obstructive
CVP/PCWP	↓	↑	↓	↑
CO/CI	↓	↓	↑	↓
SVR	↑	↑	↓	↑
Mixed SvO2	↓	↓	↑	↓

Body Fluid Compartments

Perioperative fluid management requires understanding of body fluid compartments: total body water constitutes 60% of body weight (50% in females, 45% in elderly), distributed as intracellular fluid (40%) and extracellular fluid (20%, of which 75% is interstitial and 25% is intravascular). Maintenance fluid requirements are calculated using the 4-2-1 rule (4 mL/kg/hour for the first 10 kg, 2 mL/kg/hour for the second 10 kg, 1 mL/kg/hour for each kg above 20 kg) or the Holliday-Segar method.

Fluid Compartments — NEET PG Memorisation Table

Compartment	% Body Weight	% TBW	60 kg Adult Volume	Major Cation	Major Anion
Total Body Water (TBW)	60% (M); 50% (F)	100%	36 L	—	—
Intracellular Fluid (ICF)	40%	67%	24 L	K⁺ (150 mmol/L)	Phosphate, Protein
Extracellular Fluid (ECF)	20%	33%	12 L	Na⁺ (140 mmol/L)	Cl⁻ (100 mmol/L), HCO₃⁻
— Interstitial Fluid	15%	75% of ECF	9 L	Na⁺	Cl⁻
— Intravascular (Plasma)	5%	25% of ECF	3 L	Na⁺	Cl⁻, Protein

Maintenance Fluids: 4-2-1 Rule

Body Weight Segment	Rate	Example: 70 kg patient
First 10 kg	4 mL/kg/h	10 × 4 = 40 mL/h
Second 10 kg (11-20 kg)	2 mL/kg/h	10 × 2 = 20 mL/h
Each kg above 20 kg	1 mL/kg/h	50 × 1 = 50 mL/h
TOTAL		110 mL/h ≈ 2640 mL/day

Stress Response and Fluid Shifts

The stress response to surgery induces fluid shifts through increased antidiuretic hormone (ADH), aldosterone, and cortisol secretion. This results in sodium and water retention, making goal-directed fluid therapy essential to avoid both hypovolaemia (which impairs tissue perfusion and increases the risk of acute kidney injury) and hypervolaemia (which causes tissue oedema, impaired wound healing, anastomotic dehiscence, and pulmonary complications).

Crystalloid Comparison for NEET PG

Solution	Na⁺	K⁺	Cl⁻	Ca²⁺	Buffer	Osmolality	pH
0.9% Normal Saline	154	0	154	0	None	308	5.0-5.5
Ringer's Lactate (Hartmann's)	130	4	109	3	Lactate 28	273	6.5
Plasma-Lyte	140	5	98	0	Acetate 27, Gluconate 23	294	7.4
5% Dextrose	0	0	0	0	None	278	4.5
3% Hypertonic Saline	513	0	513	0	None	1026	5.0

Electrolyte Disturbances

Electrolyte disturbances are common in surgical patients. Hyponatraemia (Na <135 mmol/L) is classified by volume status: hypovolaemic (GI losses, diuretics) requires 0.9% saline repletion; euvolemic (SIADH — common postoperatively due to pain, nausea, opioids) requires fluid restriction; and hypervolaemic (heart failure, cirrhosis) requires diuresis. Treatment includes intravenous calcium gluconate for myocardial membrane stabilisation, insulin-dextrose infusion, beta-agonists (salbutamol nebulised), and potassium-binding resins or haemodialysis for refractory cases.

Surgical Electrolyte Emergencies

Electrolyte	Emergency Value	ECG Change	Immediate Treatment	Surgical Context
Hyperkalaemia	K⁺ >6.5 or any K⁺ >5.5 with ECG change	Peaked T → prolonged PR → loss P → wide QRS → sine wave	Ca gluconate 10 mL 10% IV (cardioprotective)	Renal failure, crush injury, reperfusion, Addisonian crisis
Hyponatraemia (severe)	Na⁺ <120 or symptomatic (seizure)	Non-specific ST-T changes	3% hypertonic saline 1-2 mL/kg/h (correct no faster than 8 mEq/L/day)	TURP syndrome, SIADH, excessive hypotonic IVF
Hypocalcaemia	Total Ca <6.5 corrected OR ionised Ca <0.8	Prolonged QT interval	Ca gluconate 1-2 g IV over 10-20 min	Post-parathyroidectomy, thyroid surgery, massive transfusion

Nutritional Support

Nutritional assessment in surgical patients uses the Subjective Global Assessment (SGA) and objective measures including serum albumin (<3.5 g/dL indicates malnutrition but is confounded by inflammation), prealbumin (shorter half-life of 2-3 days, better reflects acute nutritional changes), and the NRS-2002 or MUST screening tools.

Enteral vs Parenteral Nutrition

Parameter	Enteral Nutrition	Parenteral Nutrition
Route	NG/ND/NDJ tube or oral	Central line (PICC or tunnelled catheter)
Gut barrier	Preserved	Atrophy + bacterial translocation risk
Infectious complications	10-15%	25-35% (CLABSI risk)
Cost	1/10th of TPN	10x more expensive
Indications	Functional gut, always preferred	GI failure: obstruction, SBO, high-output fistula, short bowel

Even trophic feeding (10-30 mL/hour) provides significant benefits. Parenteral nutrition is indicated when the gut is non-functional (prolonged ileus, bowel obstruction, short bowel syndrome, high-output fistulae).

Blood Transfusion Triggers in Surgery

Patient Category	Restrictive Threshold	NEET PG Note
Stable non-cardiac surgery patient	Hb <7 g/dL	TRICC trial: 7 g/dL threshold as safe as 9-10 g/dL
Active cardiac disease (CAD, MI)	Hb <8 g/dL	Higher threshold for myocardial oxygen demand
Active haemorrhage with shock	No threshold — massive transfusion protocol	1:1:1 PRBC:FFP:Platelets (PROPPR trial)