This chapter reviews techniques used in surgical practice and invasive procedures.
The operating room
The operating room is a dedicated area for surgical procedures and must be conducive to performing surgery to the highest standards of safety for patients and staff. The principal purpose of such a dedicated area is to reduce the risk of infection of patients. The operating room must be large enough for complex procedures to be undertaken, for storage of appropriate equipment, movement of staff, as well as the maintenance of a sterile area around the operative field. By changing the operating room air 20–25 times each hour at positive pressure relative to outside the room, low concentrations of airborne bacteria and particulate matter can be maintained. The number of people in the room and their movement should be minimised. Ambience should be calm and professional, and the air temperature such that inadvertent patient hypothermia does not occur. The operative field must be well illuminated by direct bright light, and surgeons sometimes wear a head light for procedures in body cavities which cannot be illuminated easily by standard operating room lights.
The surgeon's assistant has the important role of assisting and supporting the surgeon in the smooth conduct of operations. It is important to concentrate on the task at hand, to carry out the surgeon's instructions with speed and accuracy, to have a sense of anticipation, and to notify the surgeon of any potential hazard during the operation.
A face mask which covers the nose and mouth prevents droplet spread of bacteria, is worn for any invasive procedure and is changed after each case. Eye protection in the form of plain plastic glasses or a visor attached to the face mask must be worn to protect against droplet spray of infected body fluids. Gloves are worn if there is a possibility of coming into contact with patients' body fluids. Clean theatre attire, dedicated theatre shoes, and a disposable hair cover are worn while in the operating suite.
Aseptic techniques are clinical practices which aim to prevent infection occuring in the patient as a result of the surgical procedure by:
- Preparation and cleaning the patient's skin with antiseptic fluid before it is cut or punctured.
- Use of sterilised instruments, equipment or surgical materials which might come into contact with the operative field and surgical wound.
Personnel involved directly in the operative procedure (surgeon, surgical assistant and ‘scrub’ nurse) wash their hands and forearms with antiseptic soap for 5 minutes before the first operation of the day and for 3 minutes before each subsequent case to reduce skin flora. Hands are dried with sterile towels, and a moisture-impermeable sterile gown is worn. One or two pairs of sterile gloves prevent transfer of bacteria from the surgeon's hands to the patient and also protect the surgeon from infected blood and body fluids from the patient.
The patient should shower or bathe with an antiseptic soap before going to the operating room. After induction of anaesthesia, hair is removed from the operative site by shaving with a razor or electric clippers. The skin is cleansed with an antiseptic solution starting at the site where the incision will be made and working away from the area, so that approximately 10–20 cm of skin around the incision site is prepared. The patient is covered with sterile linen or impermeable drapes, leaving exposed only the cleansed area around the incision site, which may be covered by a sterile adhesive plastic drape.
The commonest source of bacterial contamination in the operating room is from the patient. Therefore, topical antiseptic agents are used to reduce the number of skin organisms prior to any skin incision or puncture, and include:
- Aqueous chlorhexidine (0.5%) is used to disinfect mucous membranes and parts of the body adjacent to structures which would be adversely affected by more stringent antiseptics (e.g. the skin around the eyes). Aqueous chlorhexidine is bactericidal and has low tissue toxicity.
- Cetrimide (2%) is bactericidal.
- Iodine-based antiseptics (e.g. povidone iodine (10%) [Betadine], alcoholic iodine solution) destroy a wide range of bacteria, especially staphylococci, by iodisation of microbial proteins.
- Alcohol-based (70%) antiseptics kill bacteria by evaporation.
Anything that comes into contact with the surgical wound must be sterile. The method of sterilisation depends on the item being sterilised (<a href="Surgical techniques#ch4-box1">Methods of sterilisation</a>).
The risk of transmission of infectious agents from patients to staff (and vice versa) is reduced by practising universal precautions. Thus, it is assumed that all patients harbour potentially dangerous pathogens (e.g. hepatitis C, HIV) no matter how innocuous they appear, because carrier status cannot definitely be excluded without repeated, expensive and time consuming investigations. The principle of universal precautions is to establish a physical barrier between the patient and the carer to prevent direct contact with any potentially infected body fluid or tissue in either direction (<a href="Surgical techniques#ch4-box2">Universal precautions</a>).
In addition to infection, there are many potential sources of hazard in the operating environment. Hazards, other than those intrinsic to the anaesthetic and surgical operation, are organisational, or related to operating room equipment or the transfer and positioning of the patient on the operating table.
Organisational hazards should be entirely preventable. A full history and examination of the patient must be made before surgery, including the past medical history, drug history and allergies, so that elementary errors are not made (e.g. unwittingly operating on a patient with a pacemaker or who is anticoagulated, or prescribing a drug to which the patient is allergic). Before surgery commences, the reason for and nature of the operation, together with its potential common and serious complications, and the reasonable expectations from the procedure, are discussed with the patient and family who are free to ask any questions. A consent or request for treatment form, which states the nature of the operation and the side on which the operation is to be performed if the operation is a unilateral procedure, is signed by the patient and the surgeon or deputy.
Once in the operating suite, a check is made that the patient is the correct one for that procedure, that the correct side or limb is identified and marked with an indelible pen, and that the lesion or lump is similarly marked to ensure that there is no confusion after the patient has been anaesthetised. All relevant case notes, investigation results and X-rays must be available in the operating room.
Diathermy is used universally in surgical practice. High frequency alternating current passes from a small point of contact (active electrode) through the patient to a large contact site (indifferent electrode or diathermy plate) to produce localised heat which coagulates protein. Diathermy produces either (a) coagulation - haemostasis with a small amount of adjacent tissue damage, (b) cutting - tissue cutting with minimal tissue damage, or (c) fulgaration - haemostatsis with considerable tissue necrosis. Potential hazards include electrocution, inadvertent burn to the patient at a remote site and to the surgeon, fire associated with pooled alcohol-based antiseptics, explosion of flammable anaesthetic gases, and interference with the function of cardiac pacemakers.
A variety of lasers with different wavelengths and effects on cells and tissues are used in surgical practice for highly accurate tissue destruction (e.g. mucosal surgery, CNS tumours, dermatological lesions, aerodigestive tumours), coagulating blood vessels (e.g. gastrointestinal tract, retinal photocoagulation), and for photo-activation of intra-tumour haematoporphyrin for malignant tumour destruction (photodynamic therapy). Hazards include eye damage, explosion of anaesthetic gases, and shattering and destruction of other equipment.
Limb torniquets are used to provide a blood-less field in which to operate. The limb is elevated and exsanguinated by a rubber bandage or compressive sleeve, and the proximal torniquet inflated to 50 mm Hg (upper limb) or 100 mm Hg (lower limb) above systolic blood pressure. A torniquet should not be kept inflated for more than 60-90 minutes. Hazards include arterial thrombosis, distal ischaemia, nerve compression and skin traction.
Positioning of the patient
The patient is positioned on the operating table in such a way that the procedure is facilitated and the airway can be protected. Pressure points are padded, and limbs are positioned so that peripheral nerves, major blood vessels, joints and ligaments are not stretched or compressed. The anaesthetised patient must be in a stable position on the operating table and may need to be strapped on with broad adhesive tape. There must be no contact between the skin and any metallic surface because of the risk of diathermy burn and pressure necrosis. Sections of the operating table can be angled so that the patient is optimally positioned for the particular procedure (e.g. flexed while lying supine or on one side, head-down, head-up).
Endoscopy is performed by inserting a fibre-optic telescope containing a light source and instrument channels into the gastrointestinal, respiratory and urinary tracts. The operator undertakes the procedure by manipulating the endoscope while viewing a video screen or looking down the eye piece of the instrument.
Endoscopy of the gastrointestinal tract allows the endoscopist to view the lumen of the oesophagus, stomach and proximal half of the duodenum (oesophagogastroduodenoscopy), colon (colonoscopy), and rectum and distal sigmod colon (sigmoidoscopy), and distal rectum and anal canal (proctoscopy). It is usually performed under sedation. Intestinal endoscopy can also be performed at laparotomy (enteroscopy) by making a small incision in the intestine and the surgeon passes the endoscope along the intestinal lumen. Procedures, such as dilatation of strictures, biospy and diathermy ablation of polyps, injection of adrenaline around bleeding gastric and duodenal ulcers, cholangio-pancreatography, removal of common bile duct calculi, injection of haemorrhoids, and tumour phototherapy can be performed using fibreoptic endoscopes.
The upper airway, trachea and proximal bronchi can be inspected by bronchoscopy, which may be performed under local or general anaesthesia. Bronchoscopy is used for diagnosis (e.g. inspection and biopsy of lung tumours) or therapy (e.g. removal of foreign bodies, aspiration of secretions). Anaesthetists ocassionally use the fibre-optic bronchoscope to facilitate difficult endotracheal intubation. (see also <a href="Common topics in thoracic surgery#ch58">Common topics in thoracic surgery</a>).
The urethra (urethroscopy), bladder (cystoscopy), and ureters (ureteroscopy) can be inspected for diagnostic purposes. Extensive therapeutic procedures (e.g. resection of the prostate, diathermy and excision of bladder tumours, extraction of calculi) can be performed safely with far less morbidity than the equivalent open procedures.
Endoscopic surgery is performed by inserting a microchip video camera with a light source and specially crafted long-handled surgical instruments into a body cavity by way of small incisions. The surgeon undertakes the procedure by manipulating the instruments while viewing a video screen.
The advantages of endoscopic or ‘closed’ surgery are reduced post-operative pain and analgesic requirements, earlier discharge from hospital, and earlier return to normal function. However, many surgical procedures either cannot be undertaken endoscopically because of their very nature, or cannot be completed endoscopically because of difficulty or patient safety, in which case the operation is converted to an ‘open’ procedure. Some procedures use endoscopic techniques to assist with the procedure and an incision is made to either complete the operation or deliver the resected specimen (e.g. bowel resection, nephrectomy, splenectomy). The range of endoscopically performed operations in many surgical specialties has increased enormously over the last 10–15 years.
Laparoscopy refers to the technique of insufflating the peritoneal cavity with gas, inserting a camera through a 10–15-mm sub-umbilical incision and inspecting the abdominal contents. Usually, three additional ports are inserted through 5–10-mm incisions in the abdominal wall and instruments (e.g. scissors, grasping devices, retractors, staplers, needle holders) are introduced and manipulated by the surgeon to perform the operation. Procedures such as cholecystectomy, gastric fundoplication, hiatus hernia repair, division of adhesions, appendicectomy, splenectomy, adrenalectomy, nephrectomy, oophorectomy, tubal ligation, and hernia repair can be undertaken laparoscopically with less morbidity than if undertaken as an open or conventional operation. Endoscopic surgery has allowed some procedures to be undertaken as day cases, whereas the same procedure performed as an open operation would require an inpatient stay of several days (e.g. cholecystectomy, hernia repair).
Thorascopy involves inserting a camera with a light source and instruments into the thoracic cavity. The technique is used diagnostically and therapeutically for procedures such as drainage of the thoracic cavity (haemothorax, pleural effusion and empyema), lung biopsy, pleurodesis, and excision of lung bullae. The mediastinum can be inspected and mediastinal lymph nodes can be biopsied by mediastinoscopy, which may prevent the need for an exploratory thoracotomy.
Large joints (e.g. knee, hip, ankle, shoulder, wrist) can be inspected by arthroscopy. Therapeutic procedures include removal of bone chips, cartilage excision and removal, and ligament repair. Arthroscopic surgery has been enormously beneficial for orthopaedic patients and has allowed far more rapid return to function.
Open surgery is the traditional or conventional method of operating. In general terms, open surgery involves making a surgical wound, dissecting tissues to gain access to and mobility of the structure or organ of interest, completing the therapeutic procedure, ensuring haemostasis is complete, and then closing the wound with sutures. Open surgey is performed more with the hands and direct touch than endoscopic procedures, and fingers may be used for ‘blunt’ dissection. The surgical wound accounts for much of the morbidity of open surgery, particularly the cutting of muscle. The range of open operations is extremely wide, as evidenced by the procedures described throughout this book.
Surgical operations are performed by well worked out, standardised steps which progress in logical sequence. An operative plan is worked out by the surgeon for every operation.
There are literally thousands of surgical instruments, some simple and others extremely complex, but each designed for a specific function. The surgical incison is made with a scalpel which consists of a re-usable handle and a disposable blade. Scissors are used to cut other tissues and sutures, and for blunt dissection with the blades closed. Diathermy is used for haemostasis and to cut through tissue layers beneath the skin. Tissues are held with dissecting or tissue grasping forceps rather than the fingers. Hand-held forceps either have teeth which tend to dig into and damage tissues, or are non-toothed with poorer grasping ability. Needle holders are used to grasp needles for suturing and eliminate the need for hand-held needles, and are therefore safer. They have a ratchet so that the needle can be contained securely in the holder while not in the surgeon's hand. Retractors allow the surgeon to operate in an adequately exposed field. Self-retaining retractors keep the wound edges apart without the aid of an assistant. Retractors held by the assistant provide tissue retraction in awkward parts of the wound and in situations where retraction of specific tissues is required so that intricate parts of the operation can be performed. A sucker is used to aspirate blood and body fluids from the operative field and to remove smoke created by the diathermy. There are many instruments designed specifically for surgical specialties and procedures.
Surgical incisions are made so that:
- The operation can be undertaken with adequate exposure of the area or structure of interest.
- The procedure can be performed and completed safely and expeditiously.
- The wound heals satisfactorily with a cosmetically acceptable scar.
Thus, incisions are to be of adequate but not excessive length and, if possible, placed in skin creases, particularly when operating on exposed areas of the body such as the face, neck and breast. Parallel skin incisions (tram tracking) and V- or T-shaped incisions are avoided because of ischaemia of intervening tissue and pointed flaps.
Ideally, surgical dissection should be performed along tissue planes which tend to be relatively avascular. The aim is to isolate (mobilise) the structure(s) of interest from surrounding connective tissue and other structures with the least amount of trauma and bleeding. Tissues should be handled with great care and respect and as little as possible. Dissection is undertaken by using a scalpel or scissor (sharp dissection), a finger, closed scissor, gauze pledget, or scalpel handle (blunt dissection), or the diathermy. Gentle counter traction on tissues by the assistant facilitates the dissection.
Surgical haemostasis refers to stopping bleeding which occurs with transection of blood vessels. The majority of cases of operative and post-operative bleeding are due to inadequate surgical haemostasis rather than disorders of clotting and coagulation. Haemostasis is essential in order to prevent blood loss during surgery and haematoma formation post-operatively. Methods of surgical haemostasis include:
- Application of a haemostatic clamp to a blood vessel and then ligation with a surgical ligature (see <a href="Care of the critically ill patient#ch6">Care of the critically ill patient</a>).
- Suture ligation of a vessel - under-running a bleeding vessel with a figure-of-8 suture which is tied firmly.
- Diathermy coagulation (see <a href="Anaesthesia and pain management#ch2">Anaesthesia and pain management</a>).
- Localised pressure for several minutes to allow coagulation to occur naturally.
- Application of surgical materials (e.g. oxidised cellulose, Surgicell) which promote coagulation.
- Application of topical agents to promote vasoconstriction (e.g. adrenaline) or coagulation (e.g. thrombin).
- Packing of a bleeding cavity with gauze packs as a temporary measure until definitive haemostasis can be achieved.
Sutures have been used to close surgical wounds for thousands of years, and initially were made from human or animal hair, animal sinews, and plant material. Today, a wide variety of material is available for suturing and ligating tissues (<a href="Surgical techniques#ch4-box3">Sutures</a>).
Sutures are selected for use according to the required function. For example, arteries are sutured together with non-absorbable polypropylene or polytetrafluoroethylene (PTFE) sutures which are nonthrombogenic, cause virtually no tissue reaction, and maintain their instrinsic strength indefinitely so that the anastomotic scar (which is under constant arterial pressure) does not stretch and become aneurysmal. Skin wounds, for example, are sutured with either non-absorbable sutures, which are removed after several days (see <a href="Care of the critically ill patient#ch6">Care of the critically ill patient</a>), or absorbable sutures hidden within the skin (subcuticular sutures) and which are not removed surgically but are absorbed after several weeks.
Sutures are available in diameters ranging from 0.02–0.50 mm. The minimum calibre of suture should be used, compatible with its function. Non-absorbable sutures are avoided for suturing the luminal aspects of the gastrointestinal and urinary tracts because substances within the contained fluids (e.g. bile, urine) may precipitate on persisting sutures and produce calculi.
The requirements of suture material are:
- Tensile strength - the suture must be strong enough to hold tissues in apposition for as long as required.
- Durability - the suture must remain until either healing is advanced or indefinitely if the healed tissue is under constant pressure.
- Reactivity - tissue reaction (i.e. an inflammatory response) allows absorbable sutures to be removed by phagocytosis but results in chronic inflammation if non-absorbable sutures remain in situ.
- Handling characteristics - sutures must be easy to grasp, handle and tie.
- Knot security - sutures must be able to be tied effectively so that knots do not come undone or slip. Sutures are classified as:
- Absorbable or non-absorbable. The rate of absorption of absorbable sutures depends on what they are made of and their thickness. Disappearance of the suture occurs through inflammatory reaction, hydrolysis or enzymatic degradation.
- Synthetic or natural material. Sutures of natural (animal) origin are being phased out of surgical practice because of the very minimal risk of disease transmission. A wide variety of synthetic suture materials are available.
- Monofilament or multifilament. Monofilament sutures pass through tissues easily, are generally less reactive, and are more difficult to handle and knot securely. Multifilament sutures are braided or twisted thread, and are easier to handle and knot, but are more likely to harbour micro-organisms within the suture.
Knots are tied to ensure that ligatures and sutures remain in place and do not slip or unravel. The ability to tie a secure knot is a fundamental technique in surgery, and patients' lives literally depend on knot security (e.g. the knot in a ligature used to tie off an artery). Knot security depends on friction between the throws of the ligature material, the number of throws used to tie the knot, the strength of the ligature material, and the tightness of the knot. Usually, multiple throws are used to secure the knot (e.g. two reef knots, one on the other).
The technique of suturing depends on the tissue and wound being sutured. Sutures may be either continuous (e.g. subcuticular skin sutures, abdominal closure, vascular anastomosis), or interrupted (e.g. skin sutures, sternal wires). The function of sutures is to hold the adjacent edges of sutured tissues in apposition and to immobilise them in that position so that wound healing (i.e. neovascularisation, connective tissue ingrowth and collagen formation) is facilitated. It is essential that sutures are not tied so tightly that the tissues encompassed by them become ischaemic. Skin sutures may be supported by adhesive paper tapes.
Retention sutures (incorrectly referred to as tension sutures) are used to close abdominal incisions which are thought to be at increased risk of dehiscence, and are inserted to encompass a large amount of fascial tissue and are placed 3–5 cm apart.
Within the last two decades, stainless steel staples have been used to close skin wounds and to perform gastrointestinal anastomoses. Staples are quicker to use than sutures, but are relatively expensive and produce a worse cosmetic result for skin closure than subcuticular absorbable sutures.
Sutures are removed as early as possible to minimise the risk of infection and scarring, so long as tissue healing is sufficently advanced that the wound will not open when the sutures are removed. Sutures are therefore removed at different times, depending on tissue and general patient factors (<a href="Surgical techniques#ch4-box4">Timing of suture removal</a>). for example, sutures are left in situ for a longer time in patients who are immunosuppressed, malnourished, jaundiced, or undergoing chemotherapy; who have renal failure, and in tissues judged to be relatively ischaemic, subject to increased stress and tension, and which have been irradiated.
Drains are used widely in surgical practice to
- Remove blood or serous fluid, which would otherwise accumulate in the operative area (e.g. wound drain).
- Provide a track or line of minimal resistance so that potentially harmful fluids can drain away from a particular site (e.g. drain placed into an intra-abdominal abscess cavity).
Several different methods of drainage may be used depending on the required function.
- Open drainage - a drain tube or strip of soft flexible latex rubber is placed so secretions or pus can drain along the track of the drain into gauze or other dressing covering the external end of the drain tube (e.g. drain placed in an abscess cavity, drain placed prohylactically near a bowel anastomosis in case of subsequent anastomotic leak).
- Closed drainage - a tube is placed into an area or viscus to drain fluid contents into a collecting bag so that there is no contamination of the drained area from outside the system (e.g. chest drain, urinary catheter, cholecystostomy drain).
- Closed suction drain - the drain tube is connected to a bottle at negative atmospheric pressure so that fluid is sucked out of the area (e.g. wound drain, drain under skin flaps).
It is important to note both the amount and the type of fluid which drains. Large volumes of fluid drainage may need to be replaced as intravenous fluids (e.g. duo-denal fistula fluid). Depending on the particular situation, it may be necessary to culture drain fluid or send it for estimation of haemoglobin, creatinine, electrolytes, amylase or protein. A radiological contrast study may be performed along the drain tube, for example to estimate the size of a cavity being drained.
Drain tubes are removed when they are no longer required, for example when there is minimal fluid being drained, or when a cavity being drained has contracted and is small. Drains are removed simply by cutting the suture which anchors them to the skin and withdrawing the tube from the patient.
Venepuncture involves removing blood from a superficial vein, usually in the antecubital fossa or dorsum of the hand, by inserting a needle attached to a syringe or collection tube at negative pressure (vacutainer system). A venous torniquet is applied around the arm, which is hung in a dependent position; the patient vigorously opens and closes the hand, and the vein is gently patted to encourage venous dilatation. The skin is cleansed with antiseptic and the needle is inserted through the skin into the dilated vein at an angle of 30–45 degrees. Only the required volume is aspirated, the torniquet is released, the needle is withdrawn, the puncture site is immediately covered with a cotton wool swab, and light pressure is applied for 1–2 minutes. The site is covered with an adhesive dressing. Complications include bruising, haematoma, and rarely, infection and damage to deeper structures. Inadvertent needlestick injury to the venepuncturist is avoided by careful technique.
Intravenous (i.v.) cannulation is used commonly for administration of fluids and drugs. Superficial veins on the forearms and dorsum of the hands are used for i.v. cannulation. Antecubital fossa veins are best avoided for cannulation because the elbow has to be kept extended to avoid kinking of the cannula. Leg veins may have to be used in the absence of useable upper limb veins. Cannulas have a soft outer Teflon sheath attached to a hub, and a central hollow needle attached to a small chamber.
A suitable vein is identified as for venepuncture. Local anaesthetic cream is applied to the skin overlying the vein or local anaesthetic (1% lignocaine without adrenaline) is injected intradermally next to the vein after cleansing the skin with antiseptic. The cannula (needle and sheath) is inserted through the skin into the vein at an angle of 10–30 degrees and advanced into the vein in the same movement. The needle is removed from the sheath and a closed three-way tap or i.v. giving set is joined to the hub of the sheath. The cannula is secured to the skin with adhesive tape.
Intravenous infusion is painful when the infusate is cold or contains irritants (e.g. potassium, calcium, drugs of low or high pH), or if the cannula pierces the vein wall and fluid extravasates subcutaneously. Thrombophlebitis develops at the insertion site after about three days, and i.v. cannulas should be re-sited if infusions are required for longer periods.
Central venous catheterisation
Percutaneous catheterisation of a central vein is used for
- Short- or long-term venous access when peripheral veins are unsuitable or cannot be used (e.g. prolonged fluid infusion, total parenteral nutrition, ultrafiltration, haemodialysis, plasma exchange, chemotherapy).
- Short-term monitoring of central venous pressure A central venous catheter (CVC) may be inserted into the internal or external jugular vein or the subclavian vein. Temporary CVCs are made of semi-rigid Teflon, are approximately 25 cm in length and, depending on their function, are between 1 and 4 mm in diameter and have one, two or three lumens. Long-term CVCs are made of barium-impregnated silastic and are quite flexible. They have a Dacron cuff bonded to the part of the catheter which lies subcutaneously and becomes incorporated by fibrous tissue after several weeks so that organisms cannot track along the catheter from the skin into the circulation.
Some long-term single lumen CVCs are available with a small volume chamber attached to the extravenous end of the catheter (Portacath, Infusaport). The chamber is implanted subcutaneously after the vein is catheterised and can be accessed for chemotherapy or blood sampling by inserting a needle into it through the skin.
CVC insertion is best performed in an operating theatre, under local or general anaesthesia, and with ultrasound localisation of the central vein. The patient is placed in a supine, slightly head-down position, and the surface anatomy of the vein is marked. Aseptic technique is essential. A hollow wide-bore needle is inserted into the vein, a guidewire is passed down the needle and the needle is removed. The guidewire position is checked radiologically. A plastic dilator is passed over the guidewire to dilate a track for the catheter and is removed, and the CVC is passed over the guide wire which is removed after the CVC is in place. A chest X-ray is performed to check the final position of the CVC and also to ensure that a pneumo- or haemothorax has not occurred due to inadvertent puncture of the pleura or lung. The catheter is sutured to the skin to prevent dislodgement and the exit site is dressed with an adhesive dressing.