Veterinary · Clinical · also MSVE VSR-411
The surgical principles common to every species: wounds and healing, asepsis, sutures, haemorrhage, shock, inflammation, tumours, hernias, burns and fluid therapy.
In the exams: China clinical paper surgery 30 (its largest clinical component); ICAR AICE-JRF core group 07; ICAR AIEEA-PG 13 (Surgery & Radiology); PRC Surgery 10%; Nepal NLEV 8 (with radiology and anaesthesia); BCSE 22-25 items; EGEL Plus surgery 15
General veterinary surgery is the set of principles under every operation in every species: how tissue is injured and heals, how infection is kept out of a wound, how bleeding is stopped, how shock is recognised and treated, how sutures and instruments are chosen, and how tumours, hernias, burns and fractures are approached before any species-specific technique is learned. The rules are the same for a cat in a referral theatre and a bullock cast on straw in a village; what changes is the equipment, the anaesthesia, the economics and the species biology.
Halsted's principles, the phases of wound healing, the contamination classes of surgical wounds, the choice between absorbable and non-absorbable sutures, and the arithmetic of fluid deficits are used on every working day. An infected clean-contaminated wound, a slipped pedicle ligature, unrecognised hypovolaemic shock, or a strangulated hernia lanced as an abscess each traces back to a principle in this manual.
The subject is examined heavily worldwide: it underpins the Surgery & Radiology papers of India's ICAR PG and PhD entrance exams (MSVE course VSR-411) and state veterinary officer papers, is the largest part of the clinical paper in China's national veterinary exam, is a named subject in the Philippine licensure exam, a scored domain of the BCSE and Mexico's EGEL, and a practical station in the Australasian, Canadian, American and British clinical exams. Doses are given only where they are standard textbook values, each with a reminder to check the label and national formulary; where practice differs by country or species, the manual says so.
A wound is a break in the continuity of tissue caused by physical, chemical or thermal injury. In a closed wound the skin is intact over the injury: a contusion (bruise) is bleeding into tissue from a blunt blow, and a haematoma is a localised collection of blood in a tissue space. In an open wound the skin or mucosa is breached. Open wounds are described by how they were made. An incised wound is made by a sharp edge; it has clean margins, bleeds freely and heals well if closed. A lacerated wound is torn, with irregular edges and variable devitalised tissue; wire and barbed-fence injuries in horses and cattle are the classic example. A punctured wound is narrow and deep relative to its opening, carries contamination deep, and favours anaerobes such as Clostridium tetani, which is why tetanus prophylaxis matters in horses and small ruminants. An avulsion tears tissue away from its attachments. A crush wound combines skin damage with severe underlying tissue death. Bite wounds are a special case: a small skin puncture may hide extensive crushing and tearing of muscle beneath, the so-called iceberg effect, and bites carry a heavy mixed bacterial load.
Every traumatic wound is contaminated; not every wound is infected. Contamination is the presence of bacteria; infection is bacterial multiplication with tissue invasion and a host response. The commonly quoted threshold is about 100,000 (10 to the power 5) organisms per gram of tissue, above which infection is likely, although the threshold falls when there is dead tissue, a foreign body, soil, or poor blood supply. The time between wounding and bacterial multiplication to that level is called the golden period, traditionally six to eight hours. Surgical wounds are classified by contamination risk. Clean wounds are non-traumatic, with no inflammation and no entry into the respiratory, alimentary or urogenital tracts. Clean-contaminated wounds enter those tracts under controlled conditions without unusual spillage. Contaminated wounds include fresh traumatic wounds, a major break in asepsis, or gross spillage from the gut. Dirty or infected wounds are old traumatic wounds with devitalised tissue or those involving existing infection or perforated viscera.
The patient comes before the wound. Airway, breathing, circulation and neurological status are assessed first, because a dramatic limb wound may distract from a pneumothorax or internal haemorrhage. Once the animal is stable the wound is protected with a sterile moistened dressing or water-soluble gel, the surrounding hair is clipped with the wound covered to stop hair falling in, and the skin around it is prepared. The wound is then explored under sedation or anaesthesia: its depth, involvement of joints, tendons, tendon sheaths, nerves, major vessels, body cavities and bone are recorded. Lavage is the most important single step in reducing bacterial load. Large volumes of warm isotonic fluid, such as 0.9 percent sodium chloride or lactated Ringer's solution, are used at moderate pressure; a 35 mL syringe with an 18- or 19-gauge needle gives roughly 7 to 8 pounds per square inch, enough to dislodge bacteria without driving them into tissue. Debridement removes dead and heavily contaminated tissue, either all at once or in stages.
Soft-tissue healing is a continuous process described in overlapping phases. The inflammatory phase begins at injury. Vessels constrict briefly, then dilate; platelets aggregate and the clot of fibrin fills the wound, stops bleeding and forms a scaffold. Neutrophils arrive within hours and remove bacteria and debris; monocytes follow, become macrophages, and are the key cell of the whole process because they both clean the wound and release growth factors that call in fibroblasts and new vessels. The proliferative (repair) phase begins after about three to five days. Fibroblasts lay down collagen and ground substance, capillaries bud into the wound, and the red, granular, bleeding-on-touch tissue that results is granulation tissue. Granulation tissue resists infection, provides a surface for epithelium, and contains myofibroblasts that pull the wound edges together (contraction). Epithelial cells migrate from the edges across the granulation bed. The maturation (remodelling) phase begins around the third week and can last months or years: collagen is reorganised, early type III collagen is replaced by type I, and fibres realign along lines of stress. The first three to five days are called the lag phase because the wound has almost no strength of its own; it is held by sutures and fibrin. A wound gains strength rapidly during repair, but a healed scar never quite regains the strength of uninjured skin, reaching roughly 70 to 80 percent of it.
Healing by first intention (primary union) occurs when clean edges are apposed soon after injury, as in a surgical incision; there is little granulation tissue and a thin scar. Delayed primary closure is suturing a contaminated wound after a few days of open management but before granulation tissue appears. Secondary closure is suturing after a granulation bed has formed, usually after about five days. Healing by second intention leaves the wound open to heal by granulation, contraction and epithelialisation; it suits wounds that are too contaminated or have too much tissue loss to close. Species matter. In the horse, wounds of the distal limb are prone to exuberant granulation tissue (proud flesh), which rises above the skin edges and blocks epithelialisation and contraction; it is managed by trimming, pressure bandaging and sometimes grafting. Cats form granulation tissue more slowly than dogs and second-intention healing in cats is slower. Factors that delay healing in any species include infection, dead space, foreign bodies, movement, poor blood supply, excessive tension, hypoproteinaemia, corticosteroids, cytotoxic drugs, radiation, hyperadrenocorticism and diabetes mellitus.
Debridement removes tissue that will not survive or that harbours bacteria. Surgical debridement is the fastest, using scalpel and scissors in layers, or en bloc excision of a whole contaminated wound when anatomy allows. Mechanical debridement uses adherent dressings, the classic being wet-to-dry gauze, which remove debris when changed but also remove healthy cells and are painful. Enzymatic agents, autolytic debridement under moisture-retentive dressings, and maggot (larval) therapy are alternatives. Honey and granulated sugar are used in many countries; their osmotic and antibacterial effects help early in open wound management. A bandage has three layers. The primary (contact) layer touches the wound and is chosen for the stage: adherent in early debridement, non-adherent or moisture-retentive once a healthy granulation bed forms. The secondary layer absorbs exudate, pads and supports. The tertiary layer holds everything in place and protects it. Drains, either passive (a soft latex drain that relies on gravity and capillary action, exiting at a dependent point) or active (closed suction), prevent fluid collecting in dead space.
A fracture is a break in the continuity of bone. It is described by whether it is open (communicating with the skin) or closed; by pattern (transverse, oblique, spiral, comminuted, segmental, greenstick, fissure, avulsion, impacted); by location (diaphyseal, metaphyseal, articular, physeal); and by displacement. Physeal fractures in young animals follow the Salter-Harris classification, types I to V, with type V (a crushing injury of the growth plate) carrying the worst prognosis for further growth. Bone heals in two ways. Direct (primary) healing occurs when fragments are anatomically reduced and rigidly fixed, as with compression plating; bone remodels across the line without callus. Indirect (secondary) healing occurs when there is some movement: a haematoma organises, soft callus of fibrocartilage forms, then mineralises and is remodelled to bone. Perren's strain theory explains why: granulation tissue tolerates high strain, fibrocartilage less, and lamellar bone only about 2 percent, so bone can bridge a gap only when movement falls within its tolerance. Management follows principles: treat life-threatening injuries first; immobilise the joint above and the joint below; reduce the fracture; stabilise it so that the chosen fixation neutralises the forces acting (bending, torsion, compression, tension, shear); preserve blood supply; and restore early function. Options include external coaptation (splints, casts, the Robert Jones bandage for temporary support), intramedullary pins and interlocking nails, bone plates and screws, external skeletal fixators and cerclage wire. Complications include delayed union, non-union, malunion, osteomyelitis and fracture disease (joint stiffness and muscle atrophy).
Asepsis is the absence of pathogenic organisms; aseptic technique is the set of practices that keeps organisms out of a surgical wound. Sterilisation destroys all microorganisms, including bacterial spores. Disinfection destroys most pathogenic organisms on inanimate objects but not necessarily spores. Antisepsis is the same aim applied to living tissue, such as skin. Sanitisation reduces microbial numbers to a level judged safe by public health standards. The Spaulding classification ranks items by risk: critical items enter sterile tissue or the vascular system and must be sterile; semicritical items contact mucous membranes and need at least high-level disinfection; non-critical items touch only intact skin. William Halsted's principles, taught in every veterinary school, summarise good technique: gentle handling of tissue, accurate haemostasis, preservation of blood supply, strict aseptic technique, minimal tension on tissues, accurate apposition of tissue, and obliteration of dead space. Most surgical infections come from the patient's own flora, so asepsis includes patient preparation, the surgeon's preparation, the instruments and the theatre.
Steam under pressure in an autoclave is the most widely used and most reliable method for heat-tolerant items. Moist heat kills by coagulating proteins. The standard gravity-displacement cycle is 121 degrees Celsius at about 15 pounds per square inch (roughly 103 kilopascals) above atmospheric pressure for at least 15 minutes of exposure once the load reaches temperature; higher temperatures such as 134 degrees Celsius allow much shorter exposure. Dry heat (hot-air oven) kills by oxidation and needs higher temperatures and longer times, classically 160 degrees Celsius for about two hours or 170 degrees for about one hour; it suits glassware, powders and oils that steam cannot penetrate. Ethylene oxide gas sterilises heat- and moisture-sensitive items such as endoscopes, plastics and electrical equipment at low temperature; it is toxic, flammable, mutagenic and carcinogenic, and items must be aerated before use. Ionising (gamma) radiation is used industrially to sterilise disposable items and most packaged sutures. Liquid chemical sterilants such as 2 percent glutaraldehyde achieve sterilisation only after prolonged immersion (hours) and are otherwise used as high-level disinfectants; items must be rinsed with sterile water. Boiling is not sterilisation because spores survive. A sterile pack is only as good as the evidence that the cycle worked. Mechanical monitoring is the reading of time, temperature and pressure gauges. Chemical indicators change colour on exposure to sterilising conditions: indicator tape on the outside of a pack shows only that the pack went through a process, while an internal indicator strip placed in the centre of the pack shows that conditions reached the inside. Biological indicators are the definitive test because they contain resistant bacterial spores; after the cycle they are incubated and should show no growth. Spores of Geobacillus stearothermophilus are used for steam and hydrogen peroxide systems, and spores of Bacillus atrophaeus for ethylene oxide and dry heat.
The patient is bathed if needed, the surgical site clipped widely (clipping close to surgery causes less skin infection than shaving the day before), and loose hair vacuumed away. The initial scrub removes gross dirt; the final sterile preparation starts at the incision site and moves outward in a spiral or in parallel lines, never returning from a dirty area to a clean one. Chlorhexidine gluconate and povidone-iodine are the main antiseptics, often alternated with alcohol. Chlorhexidine has a broad spectrum and a residual effect that persists on the skin for hours and is relatively little inactivated by organic matter; povidone-iodine is broad-spectrum including some spores with longer contact, but organic matter inactivates it and it may irritate skin. The surgeon removes jewellery, wears cap and mask, performs a timed or counted-stroke scrub or an alcohol-based surgical hand rub, dries with a sterile towel, and dons sterile gown and gloves, most commonly by closed gloving. Drapes isolate the site; towel clamps (Backhaus type) fix them. Antimicrobial prophylaxis is justified for clean-contaminated procedures, for clean procedures lasting longer than about 90 minutes or involving implants, and when infection would be catastrophic. It works only when effective tissue concentrations are present at incision: the drug is given intravenously within 60 minutes before the first cut and repeated during long surgery at intervals of about two half-lives. Cefazolin at 22 mg/kg intravenously in dogs and cats is the commonly cited regimen, repeated every 90 to 120 minutes during surgery — confirm against the product label and your national formulary. Prophylaxis is normally stopped within 24 hours; longer courses add resistance without benefit.
A suture holds tissue in apposition until the tissue can hold itself. Its properties decide where it can be used. Absorbable sutures lose most of their tensile strength within weeks and are then removed by the body; non-absorbable sutures keep strength for long periods and either stay in place (buried) or are removed (skin). Absorption occurs by two mechanisms: natural materials such as surgical gut are removed by proteolytic enzymes and phagocytosis, which causes more inflammation and is unpredictable (faster in infected, catabolic or acidic tissue); synthetic absorbables are broken down by hydrolysis, which is predictable and causes little reaction. Monofilament sutures are single strands: they pass through tissue with less drag, have no interstices to harbour bacteria, and are preferred in contaminated sites, but they have more memory and need more throws for a secure knot. Multifilament (braided or twisted) sutures handle and knot well but show capillarity, the wicking of fluid and bacteria along the strand. Other properties are tensile strength, knot security, elasticity, plasticity, memory (the tendency to return to the packaged shape), and tissue reactivity. Suture diameter is expressed in the United States Pharmacopeia (USP) scale: sizes run from 0 downward as 2-0, 3-0, 4-0 and so on, each smaller than the last, and upward as 1, 2, 3 and so on, each larger.
Surgical gut (catgut) is collagen from the submucosa of sheep intestine or the serosa of cattle intestine. Plain gut is absorbed quickly; chromic gut is tanned with chromium salts to slow absorption and reduce reaction. It is cheap and still used widely in large-animal work, but it is reactive and loses strength unpredictably, and it is avoided in infected sites. Synthetic absorbables include polyglycolic acid and polyglactin 910 (both braided), and the monofilaments poliglecaprone 25 (rapid strength loss, useful for subcutaneous and intradermal closure), polyglyconate and polydioxanone (prolonged strength, used where healing is slow, such as fascia and tendon). Non-absorbable natural materials include silk, which handles superbly and knots securely but is braided, capillary and among the most reactive; it gradually loses strength in tissue and is not recommended in contaminated sites or hollow organs. Stainless steel wire is the strongest and least reactive suture but is difficult to handle and can cut tissue; it is used in bone (cerclage) and sternal closure. Synthetic non-absorbables include polyamide (nylon), which is commonly used for skin; polypropylene, which is the least thrombogenic and is preferred for vascular work; polyester, which is strong and braided; and polybutester.
A surgical needle has an eye (or swage), a body and a point. Eyed needles must be threaded and pull a double strand through tissue, making a larger hole; swaged (atraumatic) needles have the suture fixed into the end so a single strand follows. Needle shapes are straight or curved, curved needles being described as a fraction of a circle (1/4, 3/8, 1/2, 5/8); 3/8 and 1/2 circle are the workhorses. The body and point decide how the needle penetrates. Taper-point (round-bodied) needles spread tissue rather than cut it and are used in soft, easily penetrated tissues such as intestine, bladder and subcutis. Conventional cutting needles have a cutting edge on the inside (concave) curvature, facing the wound edge, and can cut out through tissue under tension. Reverse cutting needles have the third edge on the outside (convex) curvature, which makes them less likely to tear out; they are used for skin and dense tissue.
Scalpel handle number 3 takes small blades (numbers 10, 11, 12 and 15); number 4 takes larger blades (20 to 25). Mayo scissors cut heavy tissue such as fascia; Metzenbaum scissors are lighter, for delicate dissection, and must not cut suture. Thumb forceps may be toothed (Adson, Brown-Adson) for skin and fascia or atraumatic (DeBakey) for vessels and viscera. Haemostatic forceps differ in size and serrations: Halsted mosquito forceps are small, for small vessels; Kelly forceps have transverse serrations on the distal half of the jaw; Crile forceps have them along the whole jaw; Rochester-Carmalt forceps have longitudinal serrations with cross-hatching at the tip and are used to clamp large tissue pedicles such as in ovariohysterectomy. Needle holders include Mayo-Hegar (without scissors) and Olsen-Hegar (with a scissor blade built in). Allis tissue forceps grasp firmly but traumatically; Babcock forceps are gentler, used for hollow organs; Retractors are hand-held (Senn, Army-Navy) or self-retaining (Gelpi, Weitlaner, Balfour for the abdomen, Finochietto for the ribs).
Suture patterns are described in two ways. The first is whether each stitch is tied separately (interrupted) or the suture runs as one strand with a knot at each end (continuous). Interrupted patterns take longer and leave more suture, but a single broken knot does not open the whole wound and tension can be adjusted stitch by stitch. Continuous patterns are fast, use less material, give an airtight or watertight seal, and distribute tension along the line, but depend on each end knot. The second description is the effect on the tissue edges. Appositional patterns bring the edges together side by side; everting patterns turn the edges outward, away from the patient; inverting patterns turn them inward, away from the surgeon, burying the edges. Skin heals best with accurate apposition or very slight eversion; the gut and hollow organs are closed either with appositional patterns (the current preference for intestine, because inversion narrows the lumen) or inverting patterns (bladder, uterus, rumen and stomach, where a seal and serosal contact are wanted). The strongest layer for holding sutures in the intestine is the submucosa, and every intestinal suture must include it.
The simple interrupted suture is the basic appositional pattern for skin and many other tissues. The simple continuous pattern is appositional and quick, used for linea alba, subcutis and intestine in many hands. The Ford interlocking pattern is a continuous skin pattern in which each pass locks through the previous loop; it is used widely for long skin incisions in large animals such as flank laparotomy in cattle. Horizontal mattress sutures run parallel to the wound edge and are tension-relieving and everting; they can compromise blood supply to the edges. Vertical mattress sutures run perpendicular to the edge (a far-far then near-near bite) and are stronger tension-relieving sutures with less interference with blood supply than horizontal mattress. The cruciate (cross mattress) pattern resists moderate tension and is quick to place in skin. The intradermal (subcuticular) pattern buries the suture in the dermis so no external suture needs removal. Inverting patterns include Lembert (interrupted or continuous, passes perpendicular to the wound through serosa, muscularis and submucosa without entering the lumen), Cushing (continuous, parallel to the wound edge, into submucosa, not penetrating the lumen), Connell (like Cushing but penetrating all layers into the lumen), and Utrecht (a modified Cushing with oblique bites, designed for the bovine uterus after caesarean section). The purse-string suture runs around an opening and is tightened to close it; it is used around the anus in rectal prolapse (leaving room for defecation) and to secure tubes.
Wounds under tension heal poorly, so tension is managed before closure: undermining skin, walking sutures that advance skin gradually, tension-relieving patterns such as vertical mattress or far-near-near-far, stents (tubing under mattress sutures), and relaxing incisions. The square (reef) knot is the basic secure knot; two throws in opposite directions lie flat. The surgeon's knot adds an extra twist in the first throw to reduce loosening while the second throw is laid. A granny knot, with both throws in the same direction, slips and should not be used. Dead space, the gap left between tissue layers, fills with fluid and invites infection; it is closed with buried sutures in layers, or managed with drains or pressure bandages. For continuous closure of the abdominal wall, many texts quote a suture-length to wound-length ratio of about 4 to 1 (from human surgery) so that the line is neither too tight nor too loose. Skin sutures are commonly removed after about 10 to 14 days, later in areas of tension, poor healing or in patients on corticosteroids.
Haemorrhage is the escape of blood from vessels. It is classified by the vessel: arterial bleeding is bright red and spurts in time with the pulse; venous bleeding is darker and flows steadily; capillary bleeding oozes from a raw surface; parenchymatous bleeding comes from a cut organ such as liver or spleen. It is classified by time: primary haemorrhage occurs at injury or operation; intermediate or reactionary haemorrhage occurs within about 24 hours as blood pressure recovers, a ligature slips, or vasoconstriction relaxes; secondary haemorrhage occurs days later (classically 7 to 14) when infection erodes a vessel wall or clot. It is also external, internal or concealed (into a body cavity or tissue). Blood volume varies by species: it is commonly given as about 80 to 90 mL/kg in dogs and about 50 to 60 mL/kg in cats. A healthy animal compensates for acute loss of about 10 to 15 percent of blood volume; losses above roughly 30 to 40 percent threaten life. The packed cell volume does not fall immediately after acute haemorrhage because cells and plasma are lost together; it falls over hours as interstitial fluid moves into the vessels or as fluids are given. In the dog, splenic contraction can also briefly hold up the PCV.
Haemostasis has three overlapping parts. Primary haemostasis is vasoconstriction and the formation of a platelet plug: exposed subendothelial collagen binds von Willebrand factor, platelets adhere, activate and aggregate. Secondary haemostasis is coagulation, the sequential activation of clotting factors that produces thrombin and converts fibrinogen to fibrin to stabilise the plug. It was taught as extrinsic (tissue factor and factor VII), intrinsic (factors XII, XI, IX and VIII) and common (factors X, V, II and fibrinogen) pathways. Fibrinolysis, mediated by plasmin, then breaks the clot down as the vessel heals. Tests: platelet count; buccal mucosal bleeding time, which tests platelet function when the count is adequate; prothrombin time (PT), which tests the extrinsic and common pathways; activated partial thromboplastin time (aPTT) and activated clotting time (ACT), which test the intrinsic and common pathways; fibrinogen; and fibrin degradation products or D-dimers. Common veterinary disorders include thrombocytopenia; von Willebrand disease, the most common inherited bleeding disorder of dogs; haemophilia A (factor VIII) and B (factor IX), both X-linked so seen mainly in males; anticoagulant rodenticide poisoning, which blocks vitamin K recycling and so depletes factors II, VII, IX and X, prolonging PT first because factor VII has the shortest half-life; and disseminated intravascular coagulation.
The first measure is direct pressure with a swab for several minutes; wiping a bleeding surface dislodges clots, so swabs are pressed, not rubbed. Ligatures tie off vessels; a transfixing (transfixation) ligature passes through the tissue of a large pedicle before tying so it cannot slip, and double ligation is standard for major vessels and pedicles such as the ovarian and uterine stumps. Electrosurgery coagulates by heat: monopolar units pass current through the patient to a ground plate, while bipolar forceps pass current only between their tips and are safer near nerves and in small patients. A tourniquet stops flow to a limb temporarily to allow a bloodless field; it must be applied correctly and for a limited time, commonly quoted as up to about 90 minutes to 2 hours, because prolonged ischaemia damages nerves and muscle. Topical haemostats include gelatin sponge, oxidised regenerated cellulose, microfibrillar collagen, thrombin and fibrin sealants; bone wax plugs bleeding from bone surfaces but impairs bone healing. Blood loss can be estimated by weighing swabs (1 gram of blood is about 1 mL) and measuring suction volumes. Significant loss is replaced with crystalloids, and with whole blood or blood components when oxygen-carrying capacity or clotting factors are needed.
Shock is a state in which cells cannot produce enough energy to maintain function, most often because oxygen delivery to tissues is inadequate for their demand. Oxygen delivery depends on cardiac output (heart rate times stroke volume) and arterial oxygen content (mainly haemoglobin and its saturation), so shock can arise from lost volume, failed pumping, obstructed flow, maldistributed flow, or too little oxygen in the blood. Hypovolaemic shock follows loss of circulating volume from haemorrhage, severe dehydration, vomiting, diarrhoea or burns; it is the most common form in surgical patients. Cardiogenic shock is pump failure, as in dilated cardiomyopathy or severe arrhythmia. Obstructive shock arises when flow is physically blocked: pericardial tamponade, tension pneumothorax, and gastric dilatation-volvulus, where the distended stomach compresses the caudal vena cava. Distributive shock results from loss of vascular tone and maldistribution of flow: septic shock (infection with a dysregulated host response), anaphylactic shock and neurogenic shock.
Shock progresses through stages. In the compensated stage, sympathetic activation and hormonal responses (catecholamines, the renin-angiotensin-aldosterone system, antidiuretic hormone) raise heart rate and constrict peripheral vessels to hold blood pressure; dogs show tachycardia, often bright pink mucous membranes and a fast capillary refill, with normal or mildly reduced blood pressure. In early decompensated shock the vasoconstriction becomes obvious: pale mucous membranes, prolonged capillary refill time (more than two seconds), cool extremities, weak pulses, falling blood pressure and dull mentation. In late decompensated (terminal) shock, anaerobic metabolism, acidosis and cell failure lead to bradycardia, severe hypotension, grey mucous membranes and organ failure that may not respond to treatment. Cats differ: a cat in shock often shows bradycardia, hypothermia and hypotension together rather than tachycardia, and must be warmed alongside resuscitation. Monitoring uses heart rate, pulse quality, mucous membrane colour, capillary refill, mentation, rectal temperature, arterial blood pressure (hypotension is usually taken as systolic below about 90 mmHg or mean below about 60 to 65 mmHg), blood lactate (normal is usually under about 2 to 2.5 mmol/L in dogs; hyperlactataemia signals anaerobic metabolism, and falling lactate signals response), urine output (normal about 1 to 2 mL/kg/h), PCV and total solids. The shock index (heart rate divided by systolic pressure) above 1 in dogs suggests shock.
Treatment aims to restore oxygen delivery and remove the cause. Oxygen is supplemented. Hypovolaemic and distributive shock are treated first with intravenous fluid through a large-bore catheter, or an intraosseous needle in neonates and very small patients. Isotonic crystalloids are the first choice. The traditional full shock volume is about one blood volume, 90 mL/kg in dogs and about 40 to 60 mL/kg in cats, but the modern practice is to give a quarter to a third of that as a bolus over 10 to 15 minutes (for example 22 to 30 mL/kg in dogs) and reassess, repeating as needed — confirm against the product label and your national formulary. Cats are more prone to fluid overload and receive smaller boluses. Hypertonic saline (7 to 7.5 percent) at about 4 to 5 mL/kg in dogs draws interstitial water into vessels rapidly and is useful in large dogs and horses and in head trauma, but must be followed by crystalloid — confirm against the product label and your national formulary. In haemorrhage from an uncontrolled source, hypotensive (limited) resuscitation aims for a lower target blood pressure until surgery controls the bleeding, so that clots are not blown off. Obstructive shock requires relief of the obstruction: pericardiocentesis, thoracocentesis, or gastric decompression. Cardiogenic shock is not treated with large fluid volumes; it needs drugs that support contractility (such as dobutamine), control of arrhythmias, and diuretics if congestion is present. Septic shock needs early broad-spectrum antimicrobials and source control, with vasopressors such as noradrenaline (norepinephrine) if pressure stays low after fluid. Anaphylaxis is treated with adrenaline (epinephrine), fluids and airway support. Routine corticosteroids are not recommended for hypovolaemic shock.
Inflammation is the local response of vascularised tissue to injury, aimed at removing the cause and preparing for repair. Its cardinal signs were described by Celsus as rubor (redness), tumor (swelling), calor (heat) and dolor (pain); functio laesa (loss of function) was added later and is usually attributed to Virchow. The vascular events are a brief arteriolar constriction, then vasodilatation (redness and heat) and increased vascular permeability, so protein-rich fluid leaks into the tissue (swelling). Fluid rich in protein and cells is an exudate; fluid low in protein from altered pressure without inflammation is a transudate. The cellular events are margination of leucocytes to the vessel wall, rolling (mediated by selectins), firm adhesion (integrins), emigration through the wall (diapedesis), chemotaxis towards the injury, and phagocytosis. Neutrophils dominate early acute inflammation; macrophages and lymphocytes dominate chronic inflammation, which may form granulomas around persistent agents or foreign material. Chemical mediators include histamine and serotonin (immediate permeability), prostaglandins and leukotrienes from arachidonic acid, bradykinin (pain and permeability), complement fragments (C3a and C5a as anaphylatoxins, C5a as a strong chemotactic agent) and cytokines such as interleukin-1 and tumour necrosis factor, which also produce fever.
An abscess is a localised collection of pus in a cavity formed by tissue destruction, surrounded by a wall (the pyogenic membrane) of granulation and fibrous tissue. Common pyogenic organisms include Staphylococcus and Streptococcus species; Trueperella pyogenes in cattle, sheep and pigs; Pasteurella multocida and anaerobes in cat-bite abscesses; Streptococcus equi subspecies equi in the lymph node abscesses of equine strangles; and Corynebacterium pseudotuberculosis in caseous lymphadenitis of sheep and goats. An acute (hot) abscess is warm, painful and soft to fluctuant as it matures; a chronic (cold) abscess has a thick fibrous wall and little heat or pain. A diffuse spreading infection through tissue planes without a wall is cellulitis (phlegmon), which is more dangerous and is not drained in the same way. Diagnosis rests on palpation, and on needle aspiration when uncertain, which is important because a hernia, haematoma, seroma, cyst or tumour may look like an abscess; lancing a hernia is a serious error. Treatment: an immature abscess can be encouraged to localise with hot fomentation; once fluctuant it is lanced at the most dependent point, drained, the cavity explored for foreign bodies, lavaged with dilute antiseptic, and left open to heal by second intention, with a drain if needed. Systemic antimicrobials are used when there is cellulitis, fever or a risk of spread, and for specific infections. Some abscesses, such as caseous lymphadenitis and strangles, are contagious: pus must be contained and disposed of safely, and affected animals isolated.
A cyst is an abnormal closed sac lined by epithelium containing fluid or semisolid material; examples are sebaceous (epidermal inclusion) cysts, dentigerous cysts and salivary mucocoele (which, strictly, is a pseudocyst because it is lined by granulation tissue rather than epithelium). A haematoma is blood collected in tissue; aural haematoma between the cartilage layers of the ear flap is the commonest veterinary example, usually secondary to head shaking from otitis, and it is treated by drainage or incision with measures to hold the layers together while the ear heals, and by treating the cause. A sinus is a blind tract lined by granulation tissue that leads from a deep focus to a surface opening; it persists because of a foreign body, sequestrum, necrotic tissue or infection at its base. A fistula is an abnormal passage connecting two epithelial surfaces, such as a rectovaginal or oronasal fistula. Both are cured by removing the cause and the tract. Gangrene is death of tissue with putrefaction or desiccation: dry gangrene follows slow arterial obstruction in tissue that dries and mummifies (for example from ergot poisoning or frostbite of extremities); moist gangrene follows venous obstruction or infection, and the tissue is swollen, dark and foul; gas gangrene is caused by Clostridium species producing gas and toxins in muscle. Gangrenous tissue is removed surgically, with amputation where needed, and the patient supported.
A tumour (neoplasm) is an abnormal mass of tissue whose growth exceeds and is uncoordinated with that of normal tissue and continues after the stimulus has stopped. Benign tumours grow slowly by expansion, are often encapsulated, resemble their tissue of origin, and do not metastasise; they harm by pressure, obstruction or hormone secretion. Malignant tumours grow faster, invade surrounding tissue, show cellular atypia and loss of differentiation (anaplasia), and can metastasise via lymphatics, blood or across body cavities (transcoelomic spread). Names follow a pattern. Benign tumours end in -oma after the tissue of origin: lipoma, fibroma, papilloma, adenoma, osteoma. Malignant epithelial tumours are carcinomas (adenocarcinoma, squamous cell carcinoma); malignant mesenchymal tumours are sarcomas (fibrosarcoma, osteosarcoma, haemangiosarcoma). Some names break the pattern and must be learned: lymphoma is malignant, and melanoma is often malignant though some are benign, so the terms benign and malignant melanoma are used. Grade describes how aggressive the tumour looks under the microscope; stage describes how far it has spread. The World Health Organization TNM system stages by the primary Tumour, regional lymph Nodes and distant Metastasis. Paraneoplastic syndromes are effects distant from the tumour: hypercalcaemia (lymphoma, apocrine gland anal sac adenocarcinoma), hypoglycaemia (insulinoma), hypertrophic osteopathy (thoracic masses), and histamine release from mast cell tumours causing gastric ulceration.
No mass should be removed with a definitive surgery before its type is known when the answer would change the plan. Fine-needle aspiration cytology is quick and cheap and distinguishes many tumours (mast cell tumour, lipoma, lymphoma) and inflammation. Tissue biopsy gives architecture and grade: needle-core biopsy, punch biopsy, incisional (wedge) biopsy of part of the mass, or excisional biopsy of the whole mass when it will not change the treatment (small, benign-appearing masses). Biopsy rules: take the sample so the tract can be removed with the definitive excision; avoid contaminating new tissue planes; include the junction with normal tissue in an incisional biopsy; avoid necrotic centres; and handle and fix tissue correctly (usually 10 percent neutral buffered formalin at about ten times the tissue volume). Staging combines physical examination, regional lymph node aspiration, thoracic radiography or computed tomography for lung metastases, abdominal ultrasonography, and blood tests. Surgical margins are described as intracapsular (inside the tumour capsule, leaving tumour behind), marginal (through the reactive zone just outside it), wide (through normal tissue with a margin, including a fascial plane deep to the tumour), and radical (removal of the whole anatomical compartment, such as amputation). The first surgery offers the best chance of cure: residual tumour in a scar is harder to remove. Oncological technique includes gentle handling, early ligation of draining vessels, en bloc removal of the biopsy tract, and changing gloves and instruments before closure to avoid seeding tumour cells.
Mammary tumours are common in intact bitches; roughly half of canine mammary tumours are malignant, whereas in cats the large majority (commonly quoted as around 85 to 90 percent) are malignant adenocarcinomas. Spaying before the first oestrus greatly reduces risk in bitches; the classic figures are about 0.5 percent risk if spayed before the first oestrus, about 8 percent after one, and about 26 percent after two. Mast cell tumours are the commonest malignant skin tumours of dogs; manipulating them can release histamine, causing local swelling and redness (Darier's sign), so antihistamines are often given before surgery and wide margins are planned. Osteosarcoma affects the metaphyses of long bones of large and giant breed dogs, classically 'away from the elbow and toward the knee' (distal radius, proximal humerus, distal femur, proximal tibia), and metastasises early to the lungs. Canine transmissible venereal tumour spreads by coitus and contact and responds well to chemotherapy with vincristine. Squamous cell carcinoma arises in unpigmented, sun-exposed skin: the eye and eyelids of cattle with white faces, the ear tips of white cats and sheep, and the base of the horn (horn cancer) in zebu bullocks in parts of India. The equine sarcoid, linked to bovine papillomavirus, is the commonest skin tumour of horses; melanomas are common in older grey horses. Non-surgical options include radiotherapy (often after marginal excision), chemotherapy (for systemic disease such as lymphoma and for metastatic control), cryosurgery (freezing with liquid nitrogen for small superficial lesions such as ocular squamous cell carcinoma and some sarcoids), immunotherapy and palliative care, which includes pain control.
A hernia is the protrusion of an organ or tissue through an abnormal opening, or a normal opening that has become abnormally large, in the wall of the cavity that contains it. A true hernia has four parts: the ring (the opening in the wall), the sac (a pouch of parietal peritoneum or other serous lining pushed through the ring), the contents (omentum, intestine, bladder, uterus or other organs) and the coverings (skin and subcutaneous tissue over the sac). A false hernia lacks a peritoneal sac, as when viscera pass through a torn abdominal wall into the subcutis after trauma. Terminology for abdominal wall ruptures varies between textbooks: eventration is generally used for protrusion of viscera through a ruptured abdominal wall beneath intact skin, and evisceration for protrusion of viscera through an open wound so that they are outside the body. Hernias are congenital or acquired (traumatic, incisional after surgery, or from weakening). They are reducible when contents can be pushed back into the cavity, irreducible (incarcerated) when adhesions, swelling or a narrow ring prevent reduction, and strangulated when the blood supply of the contents is obstructed, which leads to ischaemia, necrosis and, if intestine is involved, obstruction, toxaemia and death. An obstructed hernia blocks the lumen of the gut without yet cutting off its blood supply.
Umbilical hernias are common in calves, foals, piglets and puppies; many are congenital and some breeds are predisposed, suggesting inheritance, which matters for breeding advice. In calves they must be distinguished from umbilical infections involving the umbilical vein, arteries or urachus, which can coexist with a hernia; ultrasound helps. Inguinal hernias occur through the inguinal canal; in bitches they are seen in middle-aged intact females and may contain the uterus, sometimes gravid. Scrotal hernias, a form of inguinal hernia in males where contents reach the scrotum, are common in boars and piglets and occur in stallions, where acquired inguinal/scrotal herniation causes colic and is an emergency. Ventral hernias follow trauma such as horn injuries in cattle and kicks, or incisional breakdown. Perineal hernia occurs mainly in older intact male dogs: the pelvic diaphragm muscles (levator ani and coccygeus) weaken and separate, allowing rectal deviation or sacculation, and sometimes herniation of the bladder or prostate. Retroflexion of the bladder into a perineal hernia is an emergency because of urinary obstruction. Hormonal influences are implicated, and castration at repair reduces recurrence. Diaphragmatic hernia in dogs and cats is usually traumatic (road accidents), producing dyspnoea, muffled heart and lung sounds, and abdominal organs in the thorax on radiographs; peritoneopericardial diaphragmatic hernia is congenital.
Diagnosis is by palpation of the swelling and the ring, attempts at reduction, auscultation for gut sounds, and imaging. Radiography with or without contrast is used for diaphragmatic and perineal hernias. Signs of strangulation are a hot, painful, tense, irreducible swelling with systemic illness such as colic, vomiting, tachycardia and toxaemia; strangulation is a surgical emergency. Repair aims to return viable contents, remove non-viable tissue (resecting devitalised intestine), and close the ring securely without tension. In an open herniorrhaphy the sac is opened, contents inspected and returned, excess sac trimmed and the ring closed; in a closed herniorrhaphy the sac is inverted without opening, suitable for small, reducible hernias with no adhesions. The ring edges are freshened and closed with strong suture material that keeps strength for a long time, using simple interrupted, mattress, or overlapping (vest-over-pants) patterns. Large defects that cannot be closed without tension are repaired with a synthetic mesh, commonly polypropylene, or with muscle flaps. In perineal hernia repair the internal obturator muscle is commonly elevated and transposed to reinforce the ventral part of the defect. Diaphragmatic hernia repair requires positive-pressure ventilation because opening the abdomen to the thorax collapses the lungs; the patient is first stabilised, and chronically collapsed lungs are re-expanded gradually to avoid re-expansion pulmonary oedema.
A burn is tissue injury from heat, chemicals, electricity, radiation or friction. Depth is the main guide to treatment. A superficial (first-degree) burn involves only the epidermis; it is red, painful and heals without scarring. A partial-thickness (second-degree) burn involves the epidermis and part of the dermis; superficial partial-thickness burns are very painful and heal from surviving adnexa, while deep partial-thickness burns heal slowly with scarring. A full-thickness (third-degree) burn destroys the entire dermis; the skin is leathery or charred, hair pulls out easily, and it is often painless at the centre because nerve endings are destroyed; it heals only by contraction and epithelialisation from the edges or by grafting. Some texts describe a fourth-degree burn extending into muscle, tendon or bone. In animals with a thick hair coat the true extent of a burn is often hidden for several days, until the dead skin separates, so the prognosis should be guarded early on.
The extent of a burn is expressed as a percentage of total body surface area (TBSA). The rule of nines, developed for humans, has been adapted for dogs and cats: each forelimb about 9 percent, each hindlimb about 18 percent, head and neck about 9 percent, and the dorsal and ventral trunk about 18 percent each, with the rest distributed differently by author. Burns covering more than about 15 to 20 percent of TBSA produce systemic effects: fluid, protein and electrolytes are lost from the damaged capillaries and the burn surface, leading to hypovolaemic (burn) shock; the loss of the skin barrier invites infection and sepsis. Burns over about 50 percent of TBSA carry a poor prognosis, and euthanasia is often considered on welfare grounds. Smoke inhalation causes airway injury, pulmonary oedema and carbon monoxide poisoning; oxygen supplementation (ideally 100 percent) is the first treatment because it shortens the half-life of carboxyhaemoglobin, and pulse oximetry is misleading because it reads carboxyhaemoglobin as oxygenated haemoglobin. Fluid resuscitation for major burns is guided by human formulas adapted to animals; the Parkland formula (4 mL/kg per percent TBSA of crystalloid over the first 24 hours, half in the first 8 hours) is often cited as a starting point, with the rate then titrated to perfusion and urine output — confirm against the product label and your national formulary.
First aid is cooling the burn with cool (not ice-cold) water for a period, which limits the depth of injury and relieves pain; ice worsens tissue damage and cooling large areas risks hypothermia. The wound is clipped and cleaned gently. Topical antimicrobials such as silver sulfadiazine cream are widely used to limit infection of burn wounds; honey and other dressings are also used. Dead tissue (eschar) is debrided, either in stages or by early excision, and full-thickness burns of large area need reconstruction with flaps or grafts once a granulation bed exists. Circumferential full-thickness burns of limbs or the thorax may need escharotomy to release constriction. Chemical burns are flushed immediately and copiously with water; neutralising agents are not recommended because the reaction generates heat. Electrical burns in puppies and kittens typically affect the lips, commissures of the mouth, tongue and palate and can be followed by non-cardiogenic pulmonary oedema, so these patients need thoracic assessment and monitoring. Oral burns may slough several days later and leave oronasal fistulae. Cold injury (frostbite) affects poorly insulated extremities: ear tips, tail, scrotum, teats and digits, especially in wet, windy conditions and in debilitated or neonatal animals. The tissue is pale and cold, then red, swollen and painful after thawing, and may become dry and gangrenous. It is treated by rapid rewarming in warm water (around 40 to 42 degrees Celsius), not by rubbing, then analgesia and delayed surgical removal once the line between living and dead tissue is clear, which may take one to two weeks. Refreezing must be avoided because it causes more damage than the original injury.
Total body water is about 60 percent of body weight in adult animals, higher in neonates and lower in obese animals. Two thirds of it (about 40 percent of body weight) is intracellular fluid; one third (about 20 percent of body weight) is extracellular fluid, of which roughly three quarters is interstitial (about 15 percent of body weight) and a quarter is plasma (about 5 percent). Dehydration is loss of water from the interstitial and intracellular spaces; hypovolaemia is loss of circulating (intravascular) volume. They often coexist but are treated at different speeds: hypovolaemia over minutes with boluses, dehydration over hours. Dehydration is estimated clinically. Below about 5 percent there are no reliable signs. At about 5 to 6 percent there is slight loss of skin elasticity and tacky mucous membranes. At about 6 to 8 percent skin tenting is clear, capillary refill may be slightly prolonged, and the eyes may be slightly sunken. At about 10 to 12 percent the skin tent persists, the eyes are sunken, the mucous membranes dry, and signs of shock appear. At 12 to 15 percent the animal is in shock and near death. Skin tenting is affected by age and body condition (old and thin animals tent more, obese animals less), so the estimate is combined with PCV and total protein, urine specific gravity, body weight change, history of losses and, for perfusion, heart rate, pulse and lactate.
A fluid plan has three parts. The deficit (replacement) volume in litres equals body weight in kilograms multiplied by the percentage dehydration expressed as a decimal; for example a 20 kg dog 8 percent dehydrated has a deficit of 1.6 litres. The deficit is usually replaced over 12 to 24 hours, faster when there is no heart disease. Maintenance covers normal losses in urine, faeces, respiration and skin. Commonly used maintenance figures are about 40 to 60 mL/kg/day for adult dogs and cats, cats at the lower end; formulas based on metabolic body weight are also used and give relatively more per kilogram to small animals. Adult horses and cattle are commonly given about 50 mL/kg/day; neonates need more per kilogram. Ongoing losses from vomiting, diarrhoea, polyuria, drains and third-space accumulation are measured or estimated and added. During anaesthesia, the traditional rate of 10 mL/kg/h has been replaced in many guidelines by lower starting rates, commonly about 5 mL/kg/h in dogs and 3 mL/kg/h in cats, adjusted to the patient — confirm against the product label and your national formulary. The drip rate for a gravity set equals volume (mL) times drop factor (drops per mL) divided by time in minutes. Standard giving sets deliver 10, 15 or 20 drops per mL (macro-drip) and paediatric sets 60 drops per mL (micro-drip). Signs of overload are serous nasal discharge, chemosis, restlessness, increased respiratory rate and effort, crackles on auscultation, rapid weight gain and subcutaneous oedema; cats and patients with heart disease are most at risk.
Crystalloids are water with electrolytes or glucose. Isotonic replacement crystalloids such as lactated Ringer's solution, balanced multiple-electrolyte solutions and 0.9 percent sodium chloride have sodium concentrations near that of plasma and are used for resuscitation and deficit replacement; about three quarters of an infused isotonic crystalloid redistributes to the interstitium within an hour. Lactated Ringer's contains lactate, which the liver converts to bicarbonate, so it is mildly alkalinising. Sodium chloride 0.9 percent contains no potassium and more chloride than plasma; it is acidifying and is preferred in hypochloraemic metabolic alkalosis (such as pyloric obstruction or abomasal displacement with sequestration of chloride), hypercalcaemia and when balanced solutions are unavailable. Five percent dextrose in water is effectively free water once the glucose is metabolised; it is used for free-water deficits and never as a resuscitation fluid. Potassium is added when serum potassium is low, using a sliding scale; the widely taught maximum infusion rate is 0.5 mEq/kg/h, because faster rates cause cardiac arrhythmias — confirm against the product label and your national formulary. Metabolic acidosis in diarrhoeic calves is corrected with sodium bicarbonate; the bicarbonate requirement in mmol equals body weight in kg times base deficit times a distribution factor, commonly 0.3 for adults and about 0.5 to 0.6 for neonatal calves. Routes: intravenous is used for shock and severe dehydration (cephalic or saphenous veins in small animals, jugular in large animals, ear veins in pigs); intraosseous access (femur, humerus, tibia) in neonates and very small patients; subcutaneous for mild dehydration in small animals, with isotonic fluids only; and oral rehydration, which is the cheapest and physiologically ideal route in calves with a working gut and a suckle reflex.
In the clinics you will be asked to scrub, gown and glove without contamination, prepare a surgical site from the centre outward, name every instrument in a general pack, tie square and surgeon's knots, and place simple interrupted, mattress, Ford interlocking, Lembert and Cushing sutures on a model. You will calculate fluid deficits and drip rates at the bedside, estimate dehydration in a calf, and write a wound-management plan for a dog hit by a car. Learn Halsted's principles, the healing phases and the sterilisation parameters until you can recite them, because every exam from state service papers to the RCVS and BCSE asks them, and because they explain every decision you will watch a surgeon make.
Five years into practice, general surgery is daily decisions: whether a laceration can be closed or must be left open, which suture to use in a contaminated field, how to drain and manage a cat-bite abscess, whether a calf's umbilical swelling is a hernia or an abscess, and how much fluid a vomiting dog needs before anaesthesia. You recognise compensated shock early, stop reaching for antimicrobials where lavage and debridement do the work, send biopsies correctly fixed, and know when a mass needs wide margins and referral. You audit your own infection rates and sterilisation indicators, and you explain prognosis and costs clearly to owners and farmers.
After twenty-five years you run the system that makes surgery safe: sterilisation validation and biological indicator logs, theatre protocols, antimicrobial stewardship policies and infection surveillance. You teach interns tissue handling and decision-making, review complications, and decide which cases to treat in the field and which to refer. You manage mass-casualty events such as barn fires, write standard operating procedures for burns, shock and fluid therapy, and advise on herd-level issues such as inherited umbilical hernias or castration technique in pigs. You also act as expert witness when a surgical complication becomes a dispute.
At research level the questions are about mechanism and evidence: growth factors and cellular signalling in wound healing and why horse limb wounds form exuberant granulation tissue; bone biology under different fixation strains; new biomaterials, sutures, meshes, haemostats and wound dressings; antimicrobial prophylaxis and resistance; resuscitation fluids and the evidence against some colloids; and surgical oncology outcomes. You design controlled trials and cohort studies, set standards for reporting surgical site infection, translate comparative findings between species, and review and write the textbooks and guidelines on which this manual is built.
This manual covers the general principles only. It does not yet cover anaesthesia and analgesia protocols, diagnostic imaging, regional (species- and organ-specific) surgery, detailed orthopaedic implant technique, ophthalmic, dental or neurosurgery, laparoscopy and minimally invasive surgery, detailed skin flap and graft design, blood-typing and cross-matching, or drug doses beyond the few standard values given. Figures such as the golden period, blood volumes, dehydration bands, maintenance fluid rates and burn formulas are approximations from textbooks and guidelines; they vary between sources and species and must be applied with clinical judgement. Laws on who may perform which procedures, drug availability and withdrawal periods in food animals differ by country and are not covered here.
Original practice questions written to the syllabus and pattern of the exams named in each question's examTags. They are not past papers and do not reproduce any board's questions.
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