Overview of surgery

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2 Overview of surgery

This chapter reviews conditions and generic problems common to all surgical specialties.

Wound healing and management

Understanding the principles of wound healing and management is essential in all forms of surgery. Careful wound management reduces complications such as wound breakdown, infection and poor cosmetic result. Oxygen is the crucial ingredient for wound healing. Adequate oxygen delivery depends on heart and lung function, haemoglobin level and blood supply to the wounded tissue. Box 2.1 highlights local and systemic factors affecting wound healing. These same factors apply whether the healing wound is of skin, bone or any other tissue, e.g. a bowel anastomosis.

First intention

Rapid wound healing occurs by the approximation of wound edges soon after injury. This results in a narrow scar formation with superior cosmetic result. Most surgical skin incisions are closed, to heal by first intention.

There are three phases of wound healing:

Inflammatory phase

Acute inflammatory processes cascade in response to cellular injury. Clot formation, tissue oedema, and increased vascular permeability occur, with fibrin formed in the wound helping to hold the edges together. Clean, healthy surgical incisions are typically approximated with sutures, adhesive strips or glues. There is no inherent strength of the wound during this phase, which lasts up to 3 days.

Reparative phase

There is formation of new capillaries and collagen is deposited by fibroblasts during this phase. Collagen, fibroblasts and capillaries together are known as ‘granulation tissue’. The wound becomes stronger as collagen aligns and then contracts. Epithelialisation occurs. This phase usually lasts 3 weeks.

Consolidative phase

The scar matures and becomes paler as vascularity decreases. Abnormal collagen deposition can result in hypertrophic or keloid scar formation. Eighty per cent of original tissue tensile strength is regained at 6 months. This phase is completed after 1 year.

Second intention

Contaminated wounds can be left open to heal by secondary intention. They may require debridement of debris and dead tissue first. The wound heals from the base upward with granulation tissue, and re-epithelialisation occurs from the skin edges.

Delayed primary closure

This is suitable for wounds where bacterial contamination is high and wound breakdown likely if closed immediately, e.g. anal surgery for fistula-in-ano. Healthy-looking wounds are closed after irrigation, debridement and a period of observation have occurred.

Skin grafting

This may be suitable for large, non-infected, healthy granulating wounds. Indications include burns, traumatic skin loss, ulcers, and wounds following excision of large skin tumours.

Classification of surgical wounds

Clean (low risk of postoperative infection)

Incisions are made under aseptic conditions where the gastrointestinal (GI), biliary and genitourinary (GU) tracts and respiratory organs are not cut open. Antibiotic prophylaxis is not usually needed except in operations where prosthetic materials are required, e.g. joint replacement, hernia repair, abdominal aortic aneurysm (AAA) repair.

Clean/contaminated (medium risk of postoperative infection)

Operations involve incisions into the GI, biliary, GU or respiratory tracts. A low level of contamination is expected, e.g. small bowel resection, gallbladder removal. Prophylactic antibiotics are usually indicated.

Contaminated (high risk of postoperative infection)

A high bacterial load is encountered during surgery, e.g. perforated peptic ulcer, perforated appendicitis. Antibiotics are always needed pre- and post-surgery. Broad-spectrum antibiotics are usually given, e.g. cefuroxime 750 mg to 1.5 g three times a day IV and metronidazole 500 mg three times a day IV. Seek regular advice from a microbiologist where severe infection is anticipated. All hospitals in the UK have their own anti-microbial policy for reference in these situations.

Management of bleeding (haemostasis)

The optimal environment for wound healing is a dry wound with minimal ooze. Inadequate control of bleeding:

• prevents apposition of wound edges, leading to increased fibrous tissue deposition and delayed healing

• may lead to a haematoma which has to be released before the wound edges can be opposed

• increases the risk of postoperative infection – bacteria thrive in a haematoma.

The main techniques used to stop bleeding are:

• compression

• ligation/clipping of vessels

• diathermy coagulation.

Wound closure

Wound closure can be achieved in a number of ways:

• adhesive tape

• staples/glue

• plastic surgery procedures to close defects which cannot be treated with the above methods, e.g. skin grafting, flap transfer.

Details of these techniques are given in Chapter 23.

Contaminated wounds require adequate debridement, often in the operating theatre. These result from road traffic accidents, farming accidents or bomb injuries in civilian life. Gravel must be removed and all foreign bodies (FBs) extracted along with bits of clothing etc. X-rays to exclude deeper FBs are mandatory. Bites, human or animal, should be thoroughly cleaned and disinfected. Clean wounds may be primarily sutured but others should be left to granulate.

Blood products

The components of blood, e.g. red cells, platelets, fresh frozen plasma (FFP), are prepared from single donors whilst plasma derivatives, coagulation factor concentrates etc. are made from many donors.

• Whole blood is rarely used, as blood is a very scarce commodity. Specific use of the required component is a more effective use of these products. Packed red cells are used for acute haemorrhage in combination with colloid or crystalloid solutions and correction of anaemia after the diagnosis has been established. Platelets may be given to prevent bleeding, whilst FFP is given often in severe coagulopathy states, e.g. leaking aortic aneurysm surgery.

• Cryoprecipitate contains fibrinogen, factor VIIIc and von Willebrand factor. Its use is confined in surgery to patients with severe coagulopathy, e.g. severe sepsis.

• Albumin may be used for correction of hypoalbuminaemic states.

• Immunoglobulins are used to prevent infection in patients with idiopathic thrombocytopenic purpura and specific immunoglobulins may be used for patients who have contracted infections, e.g. antihepatitis B immunoglobulin. Consultation with a haematologist is mandatory in situations where these products are needed. Protocols for massive transfusion exist in all UK hospitals.

Blood groups

Blood groups are determined by antigens on the red cell surface. There are over 400 different types, the most important being the ABO and rhesus (Rh) systems. Incompatibility transfusion reactions involving other blood groups can occur, resulting in haemolytic anaemia. Compatibility testing is always done by the transfusion service; donor blood of the same ABO and Rh group as the recipient is chosen. The patient’s serum is also screened for antibodies against other red cell antigens.

Most hospitals now have strict guidelines for the use and ordering of blood for operations and with new technology blood can be available within 20–30 minutes of a request even if the blood is not ‘grouped and saved’. The blood transfusion checking procedure is shown in Box 2.2.

Box 2.2

Blood transfusion checking procedure

(from Ballinger & Patchett 2003 Pocket Essentials of Clinical Medicine, 3rd edn, Saunders, Edinburgh, with permission)

Blood transfusion

Blood transfusion is not without risk. Other therapies must always be considered before prescribing a blood transfusion, e.g. plasma substitutes or iron therapy. The introduction of screening programmes for hepatitis B and C and HIV have now made transfusion safer. For the first 48 hours after transfusion, donated blood does not have the same oxygen-carrying capacity as normal blood due to red blood cell depletion of 2,3-biphosphoglycerate (2,3-BPG), which shifts the oxygen-haemoglobin dissociation curve to the left. Blood transfusion also deranges fluid balance, electrolytes and coagulation (Box 2.3). For this reason, when required, preoperative blood transfusions should wherever possible be given at least 48 hours preoperatively. It is now possible for patients to store their own blood prior to big operations.

Complications of blood transfusion

Early

Volume overload

Patients with limited cardiac and renal reserve are prone to pulmonary oedema if transfused too quickly; 20 mg furosemide administered IV with every second unit is a common precaution for these patients. This does NOT apply in the emergency situation with a shocked patient.

Hyperkalaemia

Transfused red cells are tired and leaky and allow potassium to diffuse out. This increases the serum potassium concentration. Patients with normal kidneys will clear this without difficulty but those with renal impairment may develop dangerously high potassium levels. In such patients, the urea and electrolytes should be checked before starting transfusion and after every 2–4 units.

Coagulation problems

Transfused blood consists of packed red cells only, so transfusion dilutes the patient’s own platelets and coagulation factors. Transfused blood contains citrate, which is an anticoagulant, to prevent the blood clotting during storage. Blood is stored at 4°C and it is easy inadvertently to cause hypothermia by a large blood transfusion (ameliorated by blood warming devices). For these reasons it is important to monitor a patient’s clotting after every 4 units and correct impaired coagulation by administering clotting factors in the form of FFP.

Incompatibility reactions

Transfusion reactions vary from anaphylaxis to a mild rash/headache/temperature. The former is usually the result of administering the wrong blood to the wrong patient, leading to a major ABO mismatch. The latter are due to lesser antibodies, which are not included in the cross-match.

Impaired oxygen-carrying capacity

Due to 2,3-BPG depletion, transfused red cells take 48 h before they deliver oxygen to the tissues.

Because of these potential early complications of blood transfusion, if an anaemic patient requires a transfusion preoperatively, it is most unwise to do it the day before. Allow at least 48 hours for the volume, potassium, coagulation and 2,3-BPG to equilibrate.

Late

Transfer of infection

The viruses hepatitis C and HIV are the most important infections caused by transfusion of infected blood. Malaria (a protozoan) can also be transmitted by transfusion and there is a risk of spreading diseases caused by prions, e.g. CJD.

Depression of cell-mediated immunity

There is some evidence that wound infections and metastases are commoner in patients who receive blood transfusions at the time of cancer surgery.

Haemochromatosis

Patients with haemoglobinopathies who need multiple transfusions over many years may suffer from the effects of iron overload. This is seldom seen in the surgical setting.

Alternatives to blood transfusion

Concerns about blood transfusion safety have resulted in alternative strategies for its use. Artificial haemoglobin solutions are being developed along with autologous blood transfusion and intraoperative blood salvage (e.g. the cell saver system).

Fluid balance

Water

The basic principle behind fluid balance is that what goes out must come in. Water losses occurring through the skin, the lungs as water vapour, kidneys as urine and GI tract as faeces approximate to 2500 mL/day (Table 2.1).

Table 2.1 24-hour intake and output of water and electrolytes in health

Substance	Intake	Excretion and route
Water	2000–2500 mL (plus 500 mL of water of oxidation – needs consideration if renal excretion is limited)	Kidney (1500 mL) and insensible loss (respiratory and sweating, 1000 mL)
Sodium	100 mmol	Kidney (but sweat also up to 120 mmol/L)
Potassium	Up to 100 mmol	Kidney; restricted input not followed by fall in excretion

These losses can be much greater due to pyrexia, vomiting and diarrhoea, bowel preparation, or intestinal obstruction. On average, 3 litres of fluid per day will be adequate for normal losses, but much greater volumes are required when there is a deficit to be made up.

Electrolytes

The main electrolytes are Na⁺ and K⁺. Sodium is lost mainly in the urine at 100 mmol/day with an additional 40 mmol lost in sweat. Potassium (also lost in urine) loss is 80 mmol/day. These amounts should be added to water replacement. A typical regime in a surgical patient might be 1 L 0.9% saline plus 20 mmol KCl in 8 hours followed by 1 L dextrose 5% plus 20 mmol KCl in 8 hours followed by another litre of dextrose 5% plus 20 mmol KCl in the final 8 hours of a 24-hour period. This gives 150 mmol Na⁺ and 60 mmol K⁺; this regime would of course only replace losses in a healthy patient, as these totals are the normal daily requirement. Alternating sodium-rich fluid with dextrose solution may be required if sodium-rich fluid is lost pre- or perioperatively.

In addition to losses suffered during an operation, surgical patients can also ‘lose’ fluids in the postoperative phase, e.g. during paralytic ileus into interstitial spaces (third space losses). These fluids will return to the normal spaces upon recovery, often seen in the diuretic phase after intestinal surgery or recovery from shock.

Specific electrolyte problems

Hyponatraemia

This is usually due to water overload with inappropriate administration of dextrose 5%. If mild, fluid restriction is all that is required with furosemide diuresis, but if severe with symptoms (convulsions, confusion, and coma), hypertonic saline may have to be given with full support.

Hypernatraemia

This occurs with dehydration in the postoperative surgical patient or when too much saline is given when aldosterone secretion is high. It may be a complication of Conn’s syndrome (see Ch. 11). In the former case, rehydration is needed, and in the latter case, sodium restriction. Electrolytes need to be checked twice daily in these situations.

Hypokalaemia

Hypokalaemia may be a preoperative problem secondary to the disease state (e.g. villous adenoma of the rectum or pyloric stenosis) or as a result of diuretic therapy, but inadequate replacement postoperatively is the most common cause. Muscle weakness and ECG changes (T-wave flattening) are seen and corrected by potassium replacement. Care should be taken with rate of administration to prevent cardiac arrhythmia.

Hyperkalaemia

Hyperkalaemia may be caused by crush syndrome, massive blood transfusion or chronic renal failure preoperatively. Postoperatively excessive administration is the usual cause, often asymptomatic. Treatment by intravenous insulin and glucose should be given with calcium gluconate if ECG changes are present. A level of >7 mmol/L is dangerously high and is considered an emergency. Calcium resonium orally and rectally may also be given to further reduce the levels on the subsequent days.

Acid–base balance

The pH of body fluids is slightly alkaline maintained between 7.36 and 7.44. If it moves outside this range, body metabolism is deranged. A pH <7 or >7.8 is usually fatal. The constant production of CO₂ in the body forms carbonic acid in solution (H₂CO₃), which together with the bicarbonate ion of the sodium salt (NaHCO₃) forms the most important buffer system in the body. Carbonic acid dissociates to H⁺ and HCO₃^–, the mixture being in equilibrium (H₂CO₃ = H⁺ + HCO₃^–). The addition of hydrogen ions causes a shift to the left and withdrawal a shift to the right. The equilibrium keeps the hydrogen ion concentration constant.

Because there is a constant production of H₂CO₃ and therefore hydrogen ions these must be eliminated. The major routes excreting CO₂ are the lungs (fast) and the kidney (slowly). Dehydration reduces the efficacy of the buffering system, promoting acidosis. Haemoglobin is an additional important base buffer after oxygen has been removed.

Metabolic acidosis

This is commonly seen in surgery where there is a failure of oxygen transport and excess acid production due to anaerobic metabolism (lactic acidosis). Fluid loss, bleeding or sepsis may cause peripheral circulatory failure (see Ch. 3). Initial compensation occurs in the lungs but when, for example, sepsis is prolonged, ventilatory failure also occurs. Mechanical ventilation often restores the balance whilst additional compensation is provided by the kidneys. If acidosis is persistent despite the above measures, intravenous administration of sodium bicarbonate may correct the situation.

Respiratory acidosis

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