The main bacteria and viruses involved in surgical infections have been described in Chapter 3. The chief sources of infection are the patients themselves (particularly bowel flora), less commonly the hospital environment, food or cross-infection from other patients, and occasionally bacteria and viruses carried by ward staff or theatre personnel. Rare sources of infection are contaminated surgical instruments or equipment, dressings or parenteral drugs and fluids. The viruses causing hepatitis B and C and particularly human immunodeficiency virus (HIV) pose sinister risks of transmitting infection from patient to operating staff and vice versa. These risks make it mandatory to observe universal blood and body fluid precautions as described in Chapter 3.

The risk of postoperative bacterial infection depends on the extent of contamination of the wound or body cavity at operation or, in the case of intestinal perforation, before operation. Bacteria enter a wound by five possible routes:

• Direct inoculation from instruments and operating personnel

• Airborne bacteria-laden particles

• From the patient’s skin

• From the flora of the patient’s internal viscera, especially large bowel

• Via the bloodstream

Modern operating theatre design and correctly observed aseptic procedures minimise wound contamination but when infections occur, results can be devastating especially in relation to artificial prostheses, skin grafts, bone and the eye. Furthermore, some patients are particularly vulnerable to infection, notably neonates, the immunosuppressed, the debilitated and the malnourished. Note that treatment of established infection is no substitute for prevention.

The use of preoperative prophylactic antibiotics began in the 1970s and has revolutionised the outcome of certain types of operative surgery in a manner comparable to the changes heralded by Lister’s introduction of antisepsis in the late nineteenth century.

The operating environment

Modern operating theatre design plays a key role in control of airborne wound contamination. This is important mainly for staphylococci carried on airborne skin scales.

The main factors influencing airborne operating theatre infection rates are:

• The concentration of organisms in the air

• The size of bacteria-laden particles

• The duration of exposure of the open wound

The first two are influenced mainly by theatre design and air supply, and the last can be minimised by avoiding unnecessarily long procedures. Operating theatre complexes are laid out so as to minimise introduction of infection from outside via air, personnel or patients. Air is drawn from the relatively clean external environment, filtered and then supplied to the theatres at a slightly higher pressure than outside to ensure a constant outward flow. Air turnover is the most important factor; the aim is to ensure 3–15 air changes per hour which ‘scrubs out’ the theatre air by dilution. Standard air delivery systems aim to achieve a constant flow of clean air towards the operating table, which is then exhausted from the theatre. Despite this, convection currents allow some recirculation of air, which may be contaminated, into the operation site.

The crucial importance of preventing infection in joint replacement surgery led to the development of sophisticated ultra-clean air delivery systems. These reduce postoperative infection two- to four-fold in joint replacement surgery, but the cost is very high. Enclosure of the patient in a sterile tent in which the surgeons wear space-type suits can reduce infection rates by a further 5–7.5%.

Minimising infection from operating theatre personnel: Only a modest proportion of wound infections derive from theatre personnel. Bacteria reach the wound via the air or by direct inoculation, often from viscera within the wound. About 30% of healthy people carry Staphylococcus aureus in the nose but pathogenic organisms may also be present in axillae and the perineal area, the last probably being the most important source of wound infections from theatre personnel. In addition, skin abrasions are usually infected, as are skin pustules and boils; thus personnel with these lesions must ensure that they are effectively covered with occlusive dressings or else should not enter the operating area.

Airborne, personnel-derived infection is reduced by changing from potentially contaminated day clothes to clean theatre clothes and shoes which should not be worn outside the theatre complex. Trouser cuffs should be elasticated or tucked into boots. Females should wear trousers instead of dresses, in order to reduce ‘perineal fallout’. Face masks are worn to deflect bacteria-containing droplets in expired air, but most types become ineffective after a very short period, especially when wet. With the exception of nasal Staph. aureus (particularly important in prostheses infection), bacteria derived from the head do not generally cause wound infection. The effectiveness of wearing masks and hair coverings to reduce infection is unknown.

Sterile gloves and gowns are worn by surgeons and staff directly involved in the operation to prevent inoculation of bacteria. Gloves are impermeable to bacteria but hands and forearms need washing before gloving and gowning with antiseptics that persist on the skin. This minimises bacterial contamination if a glove is punctured (as often happens) or the sleeve of the gown becomes wet. The traditional ritual of scrubbing with a brush for 3 minutes is actually less effective than washing the hands thoroughly because it causes microtrauma and brings bacteria to the surface.

Despite the protection given by wearing gloves and gown, the less a wound is handled the better. This principle applies particularly when aseptic conditions are less than ideal. On the ward, minor procedures such as bladder catheterisation or chest drain insertion should be performed using sterile precautions and a no-touch technique. Catheters, for example, should not be handled directly but only within their wrapper or with instruments.

Minimising infection from the patient’s skin: The patient’s skin, especially the perineal area, is the source of up to half of all wound infections. These may be minimised by the following measures:

• Removing body hair—body hair was thought to be a source of wound contamination but this is no longer believed. Hair is removed only to allow the incision site to be seen and the wound to be closed without including hair. Shaving produces abrasions which rapidly become colonised with skin commensals. Most surgeons now restrict hair removal to clipping away just enough to provide skin access.

• Painting the skin with antiseptic solutions—povidone-iodine or chlorhexidine in alcoholic or aqueous solution is applied to a wide area around the proposed operation site (‘skin prep’). In the past, patients were subjected to ineffective applications of antiseptics such as gentian violet for several days beforehand!

• Draping the patient—the operating area is isolated by placing sterile, (ideally self-adhesive) drapes made of impermeable paper or coated waterproof material over all but the immediate field of operation.

Reducing infection from internal viscera: The large bowel teems with potentially pathogenic bacteria and the peritoneal cavity inevitably becomes contaminated in any operation where large bowel is opened. Pathogenic bacteria are also found in obstructed small bowel. The same applies to the stomach and small bowel of patients on proton pump inhibitors where the normal bactericidal effect of gastric acid is lost. Great care should be taken at operation to minimise this contamination. Bowel preparation of the colon before operation may help this process. All patients having bowel operations should be given prophylactic antibiotics before operation.

Sterilisation of instruments and other supplies: (see Table 10.1)

Table 10.1

Time and temperature requirements for sterilisation by different methods

In modern surgical practice, infection from instruments, swabs, equipment and intravenous fluids has been virtually eliminated by the use of sterile packs from central sterile supply departments (CSSD). Reusable instruments and drapes are sterilised by high-pressure steam autoclaving according to strict regulations. Most disposable items are purchased in pre-sterilised, sealed packs. Sterilisation in small autoclaves near the operating theatre should only be performed if instruments in short supply are required for successive operations. Sterilisation by any method is ineffective unless all organic material is first removed by thorough cleaning. It is also important to transport soiled instruments promptly to CSSD as proteinaceous material becomes fixed to metal and resistant to removal. This is especially true for small and microsurgical instruments (e.g. in ophthalmology), where channels easily become blocked by organic matter and prevent effective sterilisation.

Instruments which would be damaged by heat, including plastics, cystoscopic lenses, flexible endoscopes and electrical equipment, can be sterilised using a variety of chemical methods such as ethylene oxide gas. The Sterilox method is commonly used for endoscopic instruments that need to be reused several times during a session; the endoscopes are bathed in an electro-chemically activated water system through which an electrical current is passed.

World-wide, many surgical instruments are prepared by boiling water ‘sterilisers’. Boiling water is markedly inferior to other methods but is included here as it may be the only practical method in developing countries because of cost and technical difficulties. Boiling water kills most vegetative organisms within 15 minutes but spores are not killed. All organic debris should, as always, be scrupulously removed first, then the instruments immersed in visibly boiling water, returned to the boil and boiled continuously for at least 30 minutes to ensure hepatitis and human immunodeficiency viruses are destroyed.

Surgical technique

Surgical technique plays an important part in minimising the risk of operative infection. Non-vital tissue and collections of fluid and blood are vulnerable to colonisation by infecting organisms, which may enter via the bloodstream even if direct contamination has been avoided by aseptic technique. Tissue damage should be kept to a minimum by careful handling and retraction and by avoiding unnecessary diathermy coagulation. Haematoma formation is minimised by careful haemostasis and placing drains into potential sites of fluid collection; closed-drainage or suction-drainage systems reduce the risk of organisms tracking back into the wound from the ward environment.

During extensive resections of bowel, early ligation of its blood supply allows bacteria to permeate the wall (translocation) and this may contaminate the peritoneal cavity.

Faecal contamination is associated with a high risk of infection and great care needs to be taken in operations where bowel is opened. In emergency operations for large bowel perforation, free faecal matter is meticulously removed. A planned ‘second look’ laparotomy after 48 hours is advisable to deal with remaining contamination and new abscesses even if the patient appears well.

Prevention of cross-infection (nosocomial infection): Cross-infection is the term used for infection transmitted from other patients in the nearby hospital environment and should be distinguished from colonisation with other patients’ bacteria. Cross-infection is mainly spread via staff, medical equipment, food or ward furnishings. Doctors are probably the worst offenders as regards transfer of infection—by removing dressings to inspect wounds in the open ward, by failing to cleanse hands between patients and by careless aseptic technique when performing ward procedures such as bladder catheterisation. Minimising patient movements between wards and hospital units also decreases cross-infection rates.

A patient with an infection that is potentially dangerous to other patients, such as meticillin-resistant Staph. aureus (MRSA), should be isolated and barrier-nursed in a single room.

Prophylactic antibiotics: Despite using the best aseptic techniques, some operations carry a high risk of wound infection as well as other infective complications; these can be dramatically reduced by using prophylactic antibiotics. The chosen antibiotics should be matched to the organisms likely to occur in the area of the operation and should be bactericidal rather than bacteriostatic (see Table 10.2). The relative risk of postoperative infection in different types of operation is summarised in Box 10.2.

Box 10.2 Relative risk of infection in surgical wounds

Risk 2–5%

Clean operations with no preoperative infection and no opening of gastrointestinal, respiratory or urinary tracts (e.g. inguinal herniorrhaphy, breast lump excision, ligation of varicose veins)

Risk less than 10%

Clean operations with gastrointestinal, respiratory or urinary tracts opened but with minimal contamination (e.g. elective cholecystectomy, transurethral prostatectomy excision of un-inflamed appendix)

Risk about 20%

Operations where tissues inevitably become contaminated but without pre-existing infection (e.g. elective large bowel operations, appendicectomy where the appendix is perforated or gangrenous, fresh traumatic skin wounds (except on the face))

Risk greater than 30%

Operations in the presence of infection (e.g. abscesses within body cavities, small bowel perforation, delayed operations on traumatic wounds)

Risk greater than 50%

Emergency colonic surgery (bowel unprepared) for perforation or obstruction

Table 10.2

As a general principle, pre or peroperative prophylactic antibiotics are indicated if the anticipated risk of infection exceeds 10%, e.g. all emergency abdominal surgery and all elective colonic operations. Prophylactic antibiotics are also used by many surgeons for operations in the 5–10% risk category, e.g. cholecystectomy. Prophylactic antibiotics are also indicated for inherently low-risk cases where the consequences of infection would be catastrophic, e.g. operations employing prosthetic implants, or in patients with mitral stenosis or other cardiac defects at risk of infective endocarditis. Prophylactic antibiotics can reduce postoperative infection rates in high-risk cases by 75%, and may almost entirely eliminate infection where the risk is lower.

In most wound-related infections, the organisms are introduced during the operation and become established during the next 24 hours. Thus, for prophylactic antibiotics to be effective, high blood levels must be achieved during the operation when contamination occurs. To achieve this, the first dose should be given 1 hour before operation or preferably intravenously at induction of anaesthesia; prophylactic antibiotics should not be given earlier as this may encourage resistant organisms to proliferate (Box 10.3). A single preoperative dose of antibiotic is generally sufficient if it is rapidly bactericidal and the inoculum of bacteria is small; long operations with heavy blood loss, e.g. ruptured abdominal aortic aneurysm, merit a second perioperative dose of antibiotics later in the operation. Longer courses of prophylactic antibiotics are of no advantage.

Box 10.3 Principles of antimicrobial prophylaxis

• A single dose of antibiotic is adequate for most purposes

• Never continue prophylaxis for more than 48 hours

• Dose should be administered immediately before the procedure

• If the patient is already suspected of having an infection, go straight to treatment

In general, intravenous antibiotics give the most predictable blood levels and peak tissue levels are achieved within 1 hour of injection. However, for prophylaxis against anaerobes, metronidazole administered rectally gives blood and tissue levels equivalent to intravenous administration but later, 2–4 hours after administration.

Operations involving bowel and biliary system: Patients having these operations are at risk mainly from a mixture of Gram-negative bacilli (Enterobacteriaceae family), faecal anaerobes (Bacteroides fragilis) and Staph. aureus. Less commonly, enterococci cause surgical infection, notably E. faecalis (formerly Strep. faecalis).

The most commonly used prophylactic antibiotic regimens are shown below. A more comprehensive list is given in Table 10.2:

• For biliary surgery—co-amoxicillin-clavulanate

• For colonic and other bowel surgery—either co-amoxicillin-clavulanate or a combination of gentamicin, benzylpenicillin (or ampicillin) and metronidazole

• For appendicectomy—rectal metronidazole alone, given 2 hours before operation; this has proved as effective as any other regimen. The evidence for the beneficial effect of metronidazole in preventing infection after appendicectomy is now so strong that it may be negligent not to use it

The choice of antibiotics for prophylaxis must be kept under review because organisms change their sensitivities. Aminoglycosides such as gentamicin have the important advantage do not alter the bowel flora because their concentration in the lumen is low; this is in contrast to the cephalosporins and ampicillin, which have caused a rising tide of beta-lactam-resistant bowel organisms insensitive to cephalosporins and ampicillin but sensitive to aminoglycosides. If resistant staphylococci are a problem, vancomycin or other newer antibiotics may become necessary for prophylaxis.

Operations involving implantation of prostheses: Vascular grafts and joint replacements are at particular risk from Staph. aureus infection. Coagulase-negative slime-forming staphylococci (e.g. Staph. epidermidis) are a common source of chronic infection. Coliforms are a very rare cause. Flucloxacillin is the agent of first choice for prophylaxis but gentamicin is usually added for extra protection. Rifampicin can be used to soak vascular grafts as it is effective against Staph. epidermidis. Meticillin-resistant Staph. aureus (MRSA) is becoming a common cause of prosthetic infection. In areas where the risk is substantial, prophylaxis with vancomycin is appropriate.

Operations where ischaemic or necrotic muscle may remain: Lower limb amputations for arterial insufficiency and major traumatic injuries involving muscle are susceptible to gas gangrene and tetanus. Clostridia are highly sensitive to benzylpenicillin and metronidazole, one of which should be given in high dose as early as possible after major trauma, and before major amputations for ischaemia. Co-amoxicillin-clavulanate is a good alternative.

Basic surgical techniques

Anaesthesia

General principles: Some form of anaesthesia is needed for almost every surgical procedure, with the aim of preventing pain in all cases, minimising stress for the patient in most, and providing special conditions for some operations, e.g. muscular relaxation in abdominal surgery. The choice of anaesthetic techniques includes topical (surface) anaesthesia, local anaesthetic infiltration or peripheral nerve block, spinal or epidural anaesthesia and general anaesthesia. Methods other than general anaesthesia may be supplemented with intravenous sedation if the patient is anxious or agitated (e.g. with benzodiazepines). Intravenous sedation with these drugs produces relaxation, anxiolysis and amnesia whilst retaining protective reflexes. However, these drugs can also cause unconsciousness and they must be carefully titrated to produce just the desired effects. Intravenous sedation of this type does not provide pain relief; if needed, this is achieved with local anaesthesia or intravenous analgesics.

Choice of anaesthetic technique: Combining local or regional anaesthesia (for pain relief) with general anaesthesia can minimise postoperative respiratory and cardiovascular depression compared with general anaesthesia alone, reducing morbidity. An example is the use of caudal anaesthesia in perineal operations. Local or regional anaesthesia with bupivacaine or levobupivacaine can also be administered during an operation to provide postoperative pain relief; for example, intercostal nerve blocks during an abdominal operation allow more comfortable breathing and coughing, reducing respiratory complications. Another common example is wound infiltration with the same long-acting local anaesthetics. The main factors influencing choice of anaesthesia are summarised in Box 10.4.

Box 10.4 Choice of anaesthetic technique

1 Local anaesthesia

In general, this safest form of anaesthesia is used for calm and rational patients when no autonomic discomfort is anticipated:

• Minor operations, e.g. excision of small skin lesions or dental operations

• Minor but painful procedures, e.g. insertion of chest drain, siting of peripheral venous cannulae

• Unavailability of general anaesthetic expertise, e.g. in developing countries

• Patients unfit for general anaesthesia, e.g. cardiac and respiratory cripples

• Ambulatory (‘day case’) surgery especially if co-morbidity

• Patients unwilling to undergo general anaesthesia

• Use of combined local anaesthetic and vasoconstrictor to provide a relatively bloodless operative field. (Note: this must never be used in the extreme peripheries, i.e. digits, penis, nose)

2 Regional nerve block

• Minor surgery requiring wide field of anaesthesia, e.g. femoral nerve block for varicose vein surgery, pudendal block for forceps delivery

• When it is undesirable to inject local anaesthetic into the operation site, e.g. drainage of an abscess (local anaesthesia works less well in inflamed tissue)

• To avoid tissue distortion from local infiltration in delicate surgery

• Short-lived, wide-field ambulatory anaesthesia for reduction of forearm fractures or hand surgery (Bier’s intravenous regional anaesthesia)

3 Epidural and spinal anaesthesia

• Lower limb surgery, e.g. amputations

• Lower abdominal, groin, pelvic and perineal surgery, e.g. Caesarean sections, inguinal hernia repair, prostatectomy, bladder and urethral surgery

4 Intravenous sedation or intravenous analgesia alone

• Short-lived uncomfortable procedures where local anaesthesia is impractical, e.g. gastrointestinal endoscopy, musculoskeletal manipulation

5 Intravenous sedation combined with local anaesthesia

• Potentially unpleasant procedures despite adequate local anaesthesia, e.g. wisdom tooth extraction, toenail operations, siting of central venous lines

6 Regional analgesia with light general anaesthesia

• Caudal epidural plus general anaesthesia for operations in the perineal area, e.g. transurethral prostatectomy or resection of bladder tumours, haemorrhoidectomy, circumcision. This provides perioperative and postoperative analgesia

7 General anaesthesia

• Where all of the above are unsuitable or difficult to achieve

• Severe patient apprehension or patient preference for general anaesthesia

• Major or prolonged operations

• Abdominal or thoracic operations requiring muscle relaxation

• Where it is necessary to secure the airway by intubation

• Special indications, e.g. neurosurgery

Incision technique

Choice of incision: The purpose of most skin incisions is to gain access to underlying tissues or body cavities. When planning an incision, the first concern is to achieve good access and also allow it to be extended if necessary. It must also be sited in such a way that it can be effectively closed to give the best chance of primary healing and the lowest chance of an incisional hernia later. Despite patients’ impressions, the length of an incision (and the number of sutures) has little bearing on the rate of healing, and the success of an operation should not be put at risk by inadequate access.

Secondary considerations in the choice of incision are as follows:

• Orientation of skin tension lines (based on Langer’s lines) and skin creases—where possible, incisions should be made parallel to the lines of skin tension determined by the orientation of dermal collagen (e.g. a ‘collar’ incision for thyroid operations) as the wound is less likely to break down, there is minimal distortion, and healing occurs with little scar tissue to give the best cosmetic result

• Strength and healing potential of the tissues—the nature and distribution of muscle and fascia influences the strength of the repair, particularly in different parts of the abdominal wall. For example, a vertical lower midline incision along the linea alba, a strong layer of fascia, is less prone to incisional herniation than a paramedian incision lateral to the midline

• The anatomy of underlying structures, particularly nerves—the incision line should run parallel to, but some distance away from the expected course of underlying structures, reducing the risk of damage. For example, to gain access to the submandibular gland, the incision is made 2 cm below the lower border of the mandible to avoid the mandibular branch of the facial nerve

• Cosmetic considerations—wherever possible, incisions should be placed in the least conspicuous position, such as in a skin crease or a site that will later be concealed by clothing or hair, e.g. a transverse suprapubic (Pfannenstiel or bucket-handle) incision below the ‘bikini’ line for operations on the bladder, uterus or ovary, or a peri-areolar incision for breast biopsy

Dissection and handling of deeper tissues: The skin consists of thin epidermis and dense, somewhat thicker dermis, as well as the underlying fatty hypodermis which may be 10 cm or more thick in an obese individual.

Once the skin incision has been made, the scalpel is mainly reserved for incising fascia and other fibrous structures such as breast tissue and very fine dissection. Anatomical detail is exposed and displayed by a combination of blunt and sharp dissection. Blunt dissection involves teasing or stripping tissues apart using fingers, swabs or blunt instruments, following natural tissue planes. Sharp dissection with scissors and forceps or scalpel is used where tissues have to be cut and also to display small structures. Some surgeons prefer sharp to blunt dissection in general, believing it causes less tissue trauma. Most dissection, however, involves a combination of both.

Principles of haemostasis

Bleeding is an unavoidable part of surgery. Blood loss should be minimised because bleeding obscures the operative field and hampers operative technique (the finer the surgery, the more bleeding affects visibility and quality of outcome), and because the loss has to be made up later. Excessive bleeding can be averted by judicious dissection with control of bleeding as the operation proceeds, and by minimising the area of raw tissue exposed at the operation site by accurately siting the incision and by avoiding opening unnecessary tissue planes.

Clipping, ligation and under-running: Ligation or specialised bipolar diathermy is obligatory when large vessels are divided and is desirable for vessels larger than about 1 mm calibre (see Fig. 10.1). If the end of a bleeding vessel cannot be grasped by haemostat forceps, a suture can be used to encircle the vessel and its surrounding tissues, a technique often described as under-running. It is particularly useful for a bleeding artery in the fibrous base of a peptic ulcer.

Fig. 10.1 Techniques of haemostasis

Diathermy: Diathermy achieves haemostasis by local intravascular coagulation and contraction of the vessel wall caused by heating (-thermy), generated by particular electrical waveforms. However, enough heat is also produced to burn the tissues and these may be needlessly damaged by careless use, particularly near the skin or nerves. Ordinary diathermy is ineffective for large vessels, which should be ligated. There are three main variants of diathermy, illustrated in Figure 10.2, and all three modes are available on modern diathermy machines.

Fig. 10.2 Three modes of diathermy

Monopolar diathermy is the most widely used for operative haemostasis but there is wide dispersion of coagulating and heating effects, making it unsuitable for use near nerves and other delicate structures. Since the current passes through the patient’s body, there is a risk of coagulating vessels en passant (e.g. monopolar diathermy used in circumcision may cause penile thrombosis), as well as provoking arrhythmias in patients with cardiac pacemakers. Monopolar diathermy may also result in skin burns at the indifferent electrode plate if skin contact is poor or if the plate becomes wet during operation. To improve contact, hair should be shaved from the skin where the plate is placed.

Bipolar diathermy is used mainly for finer surgery. The current passes only between the blades of the forceps and it requires fairly accurate grasping of the bleeding vessel. It uses low levels of electrical power, there is almost no electrical dispersion from the tip of the forceps and much less heat is generated. The main advantages are minimal tissue damage around the point of coagulation and safety in relation to nearby nerves, blood vessels and cardiac pacemakers. Specialised computer controlled bipolar diathermy is often used for larger vessels during laparoscopic surgery.

Cutting diathermy is mainly used for dividing large masses of muscle (e.g. during thoracotomy or access to the hip joint) and cutting vascular tissues (e.g. breast). The intention is a form of sharp dissection, at the same time coagulating the numerous small blood vessels as the tissue is cut; unfortunately this is not always wholly effective. A blend of cutting and coagulation is sometimes used.

Tourniquet and exsanguination: This technique is used in surgery of the limbs and hands where a bloodless field is desirable. For the whole limb, a pneumatic tourniquet is placed proximally. The limb is exsanguinated by elevation and spiral application of a rubber bandage (Esmark) or a ring exsanguinator from the periphery; the tourniquet is then inflated. Upper limb tourniquets must not be left inflated for more than 30 minutes and lower limb tourniquets for more than about 1 hour to avoid the risk of necrosis.

Pressure: Pressure is a useful means of controlling bleeding until platelet aggregation, reactive vasoconstriction and blood coagulation take over. It can be used for emergency temporary control of severe arterial or venous bleeding but is equally useful for controlling diffuse small-vessel bleeding from a raw area, e.g. liver bed after cholecystectomy. Pressure is usually applied with gauze swabs which must be kept in position for at least 10 minutes. Even if bleeding is not arrested completely, this process usually allows a clearer view and allows haemostasis by standard means.

For intractable bleeding which is not amenable to ligature, diathermy or suture, various resorbable packing materials, e.g. oxidised cellulose, can be left in position until haemostasis occurs, allowing the wound to be closed. If bleeding simply cannot be controlled—for example, after liver injury—the bleeding cavity can be packed with gauze swabs which are left in situ and removed 48–72 hours later at a further operation. Bleeding, once controlled by this method, rarely recurs.

When a raw cavity has been created beneath the skin, external pressure dressings are sometimes a useful method of controlling potential superficial postoperative oozing and minimising haematoma formation.

Suturing and surgical repair

Types of suture material and needles: Numerous types of suture are available (see Box 10.5), with the most important distinction being between absorbable and non-absorbable materials. The groups can be subdivided into natural and synthetic materials (although natural materials are being phased out) and further subdivided into monofilament and polyfilament (braided) materials. The choice of suture material depends upon the task at hand, the handling qualities and personal preference.