Surgical infections

From SurgWiki

Jump to: navigation, search


Contents

Introduction

Infection is the main enemy of the surgeon. There are a number of reasons for this:

  • cosmetic and functional outcomes after surgery are compromised by infection
  • trauma often results in infection due to the contamination and devitalisation of tissues
  • deep infections in mesothelial cavities are life threatening
  • lives can be ruined by careless exposure to bloodborne viruses.

Those who care for surgical patients can never be complacent in their efforts to diminish the risk of infection.

The main ways of achieving this are:

  • the washing of hands
  • adherence to antiseptic and asepsis rituals
  • aggressive attention to basic surgical principles
  • compliance with antibiotic guidelines
  • patiently accepting the measures that are necessary to prevent the spread of resistant organisms
  • the adoption of universal precautions to prevent diseases due to blood-borne viruses.

In this chapter, particular emphasis is placed upon the prevention and management of infections related to surgical procedures.

Acute infection

Surgical infections occur because of a breakdown of the equilibrium that exists between organisms and the host. This may be due to a breach in a protective surface, changes in host resistance, or particular characteristics of the organism. The possible outcomes are resolution, abscess formation, extensive local spread with or without tissue death, and distant spread.

Host defence mechanisms

Areas of the body that are in contact with an external environment are protected by elaborate barrier mechanisms. Parts of these barriers are mechanical in nature, such as the keratinised layer of skin. Such physical barriers are augmented by powerful innate immune mechanisms (e.g. the low pH and fatty acid content of normal skin inhibits bacterial growth). An additional factor is that all mucous membranes are protected by lymphocyte-mediated events that result in the secretion of immunoglobulin A (IgA) antibodies. In the gut, the rapid turnover of the mucosal cells along the crypto-villus axis has a protective function because enteropathogens must adhere to enterocytes in order to cause clinical problems.

Tissue injury stimulates a cascade of events that lead to the formation of granulation tissue and eventual healing. However, extensive tissue damage inhibits the inflammatory response (e.g. the low oxygen tensions in poorly vascularised tissues impairs the oxidative killing of microbes by phagocytes). Damaged tissue also forms a nidus for bacterial growth. These factors explain the need to debride wounds in order to avoid infection.

The response of the body to microbes can be affected by immunodeficiencies of genetic origin (which are rare) or by acquired deficiencies (e.g. protein-energy undernutrition; diseases such as diabetes, cancer and AIDS; or by the administration of immunosuppressive or cytotoxic drugs). Infections often arise in immunocompromised individuals with microbes that are not usually regarded as pathogens (e.g. opportunistic infections caused by Candida albicans and fungi).

The organisms

The pathogenicity of microbes is determined by their capacity to adhere to and damage host cells, and then to produce and release a variety of enzymes and exotoxins. Staphylococcus has surface receptors that allow it to bind to host cells and extracellular matrix proteins, especially those covered by protein A molecules, which bind to the Fc portion of antibodies. Streptococcus and Haemophilus secrete proteases that degrade antibodies, and other enzymes such as haemolysins and kinases that assist in the spread of infection in the form of cellulitis or erysipelas. Escherichia coli carries K-antigen, which prevents the activation of complement via the alternate pathway.

Foreign bodies increase the pathogenicity of microbes by impairing local defence mechanisms. It is important to explore deep wounds adequately in order to remove foreign bodies and devitalised tissues. This is a critical issue because the use of antibiotics is no substitute for poor surgical technique. It should also be appreciated that although prosthetic materials are made of ‘inert materials’ they are still foreign bodies, and it is difficult to control associated infections without removing the offending prosthesis. Examples of this range from infected central venous lines to infected vascular grafts and orthopaedic implants.

Cellulitis

Cellulitis is a spreading inflammation of connective tissues that is often due to β-haemolytic Streptococcus. The invasiveness of this organism is due to the production of hyaluronidase (dissolution of the intercellular matrix) and streptokinase (dissolution of the fibrin inflammatory barrier). Cellulitis may be accompanied by obvious inflammation of the draining lymphatics (lymphangitis) and the draining lymph nodes (lymphadenitis). There may also be associated septicaemia. The treatment is immobilisation with elevation, antibiotic therapy, and drainage of any residual abscesses.

There is a group of patients who present with cellulitis of the lower limb complicating lymphoedema from any cause. There is usually no obvious entry site for bacteria, the cellulitis tends to be low grade and brawny in nature, and it is usually slow to recover to antibiotic therapy. Compression stockings are a useful long-term measure, but recurrence is common.

Abscesses

An abscess is a localised collection of pus. Abscesses start as inflammatory lesions, which then soften and become fluctuant because of the presence of liquefied tissues and the remnants of the inflammatory response. The only effective treatment for abscesses is drainage. In the absence of therapeutic drainage, abscesses may discharge spontaneously onto the surface or into an adjacent viscus or body cavity (e.g. a colo-vesical fistula as a result of a peridiverticular abscess in the sigmoid colon). Deep abscesses can often be localised and drained under the guidance of ultrasound. Antibiotic therapy is appropriate if there is clinical evidence of sepsis. However, failure to drain an abscess in the presence of inappropriate and prolonged antibiotic therapy can result in a troublesome chronic ‘smouldering’ abscess.

Bacteraemia and septicaemia

Spread of organisms into the bloodstream may be either as a transient bacteraemia, which is asymptomatic, or as septicaemia with symptoms such as fever and chills (sepsis). It should be noted that critically ill patients may exhibit a systemic response, due to cytokines and other biologically active molecules, in the absence of positive blood cultures (Systemic Inflammatory Response Syndrome). The failure of multiple organs in the presence of sepsis is referred to as ‘severe sepsis’.

It is advisable to administer antibiotics when draining an abscess because of the associated sepsis and the risk of metastatic infection, especially if the patient has a prosthetic device in situ or a damaged heart valve. Other examples of metastatic infection include portal pyaemia with liver abscesses secondary to suppurative appendicitis and a localised staphylococcal infection, such as an infected hair follicle (a boil or furuncle), spreading to multiple systemic sites (e.g. osteomyelitis, brain abscess, perinephric abscess).

Nosocomial infections

Nosocomial infections are infections that are acquired while a patient is in hospital. More than 10% of patients admitted to the surgical wards of large hospitals develop a clinically significant infection. Hence, there is a special need for stringent precautions against crossinfection when caring for debilitated patients undergoing major surgery. Surgical wounds are classified into categories to aid the monitoring and interpretation of wound infection rates (Classification of wounds).

The commonest organisms isolated from hospitalacquired infections are Staphylococcus aureus and a range of Gram-negative bacilli. Multiple antibiotic resistance is a particular problem. Besides multi-drugresistant Staphylococcus aureus, Gram-negative organisms may become resistant to many of the antibiotics in common use. Cross-infection can occur by many routes, but of particular concern are those caused by the inappropriate activity of the attending medical staff. The main problems are failure to wash hands between attending patients (which is the single most important preventative measure), not employing antiseptic and asepsis techniques when performing ward procedures, and the careless management of infected wounds.

Wound infections

Wound infection is usually defined as the discharge of either pus or serous fluid containing pathogens. However, on occasions, cellulitis can cause considerable morbidity, such as after breast surgery. The main factors associated with wound infection are the extent of intraoperative soiling (as discussed in the classification of wounds), the presence of pre-existing comorbidity (diseases and situations associated with immunodeficiency), age (the risk escalates when patients are over 70 years of age), and the performance of major surgery. A useful global measure of co-morbidity is the American Society of Anesthesia (ASA) classification, which is routinely recorded by many anaesthetists (see Anaesthesia and pain management).

The prevention of wound infection relates to the avoidance of contamination and the judicious use of antibiotics. Strict adherence to aseptic techniques is essential, but it is now appreciated that aggressive ‘escrubbing up’ is counterproductive because it results in bacteria being brought to the surface of the skin. In addition, unless performed immediately prior to surgery, removing hair by razor causes skin abrasions that become colonised with bacteria leading to an increased incidence of wound infection. Post-operative dressings should be left in place for at least 24 hours after surgery; after this time wounds are relatively impervious to external contamination.

Urinary tract infection

Urinary tract infections can occur after either instrumentation of the urinary tract or the insertion of a urethral catheter. Urinary catheters are foreign bodies that irritate the urethral mucosa and predispose to the colonisation of urine with bacteria. They must only be used for a good reason and then removed as soon as possible. Urinary tract infections may present as a pyrexia of unknown origin during the post-operative period, and the temperature may be in excess of 38°C; a characteristic that only tends to be shared with atelectasis and phlebitis. Many patients experience transitory dysuria after the removal of a urethral catheter and resolution of this problem may be aided by the induction of a mild diuresis.

Phlebitis

Intravenous cannulae, especially those used for the infusion of hypertonic nutrients and drugs, are particularly prone to infection. It is important to observe strict asepsis when inserting intravenous cannulae because it has been reported that one-third of them can become colonised with bacteria within 48 hours. The risk of phlebitis increases in an exponential manner after cannulae are left in situ for more than 72 hours. Intravenous cannulae, as with other indwelling devices, are foreign bodies and should be removed as soon as possible. If removal is not possible then they should be changed to another site within 72 hours; this is only possible if the time of their insertion has been carefully documented.

Enterocolitis

The normal flora of the gut is altered by the use of broad-spectrum antibiotics, the stasis that accompanies a lack of peristalsis after abdominal surgery, and the acquisition of organisms that are prevalent within hospitals. These factors increase the likelihood of overgrowth by enteropathogens such as Clostridium difficile (so named because of the difficulty of growing it in culture), which secretes toxins responsible for symptoms that range from mild watery diarrhoea to profound diarrhoea associated with a florid colitis. The latter is characterised by the presence of creamy fibrinous plaques that coalesce to form a pseudomembrane (pseudomembranous colitis). Treatment includes the cessation of broad-spectrum antibiotic therapy and the introduction of either oral metronidazole or oral vancomycin. It is essential that stool cultures and toxin assays are performed on all patients with profuse diarrhoea after surgery.

Post-operative pulmonary complications

The vast majority of post-operative pulmonary complications are due to atelectasis, which is usually transitory and self-limiting. This is a mechanical event and antibiotics are contraindicated unless there is objective evidence of infection (e.g. the production of purulent sputum or radiographic evidence of pneumonia).

Antimicrobial therapy

It should be evident that the most important weapons against infection are compliance with infection control measures, adherence to basic surgical principles (debridement of dead tissue, removal of foreign bodies, drainage of pus), and the judicious use of antibiotics. A major step towards the appropriate use of antibiotics is adherence to institutional antibiotic guidelines and, in particular, drawing a clear distinction between prophylaxis and treatment.

Prophylaxis

Antibiotic prophylaxis is appropriate whenever its benefits outweighs its disadvantages. For example, it is difficult to justify the side effects and costs of administering prophylactic antibiotics for healthy patients undergoing the excision of a skin lesion. In contrast, it would be negligent not to provide antibiotic prophylaxis for a patient undergoing any form of gastrointestinal surgery; afterall, no ethics committee would now agree to an antibiotic trial in such patients that included a ‘no treatment’ control group. Antibiotic prophylaxis is particularly important if the infection of prosthetic material would be extremely adverse (e.g. joint replacements, vascular prostheses, revisional breast surgery with insertion of an implant). The principles of antibiotic prophylaxis are given in Principles of antibiotic prophylaxis.

Treatment

Treatment courses of antibiotics are used to manage specific infections, but they may also be employed after surgery if there is residual infection (e.g. purulent peritonitis) or if gross contamination occurred at the time of surgery (e.g. spillage of liquid bowel contents).

As a general principle, antibiotic therapy should cease after 5 days when there is no clinical evidence of infection, the patient has been afebrile for 48 hours, and there is a normal polymorphonuclear neutrophil count. The most extreme form of antibiotic therapy relates to ‘salvage therapy’ within ICUs using powerful broad-spectrum agents, such as imipenum, while waiting for specific culture and sensitivity results. The factors influencing the choice of antibiotic are given in Factors influencing the choice of antibiotic.

Resistant microbes

The resistance of Gram-positive and Gram-negative bacteria to antimicrobial agents is a major problem. This is especially so when multi-resistant pathogens cause an outbreak of infection within a hospital. Microbes have evolved elaborate mechanisms to ensure their survival, and resistance strains emerge regardless of innovations in the mechanism of action of new antibiotics. Hence, it is important for surgical staff to be fully compliant with antibiotic guidelines and infection control measures. Antibiotics should never be regarded as ‘golden bullets’.

Blood-borne viral infections

The blood-borne viruses that raise special concerns are human immunodeficiency virus (HIV), hepatitis B virus, and hepatitis C virus. They all have the properties of chronicity, transmission via body fluids, and long-term health consequences. The main route of infection in health-care workers is by percutaneous inoculation. There is no evidence of transmission of any of the common blood-borne viruses by the air-borne route or from occupational or social contact that does not involve exposure to body fluids. History suggests that it is wise to presume that other blood-borne viruses will present similar problems in the future.

Universal precautions

It is crucial that all health-care workers recognise how to reduce the risks of exposure to blood-borne viruses. It must be appreciated that it is neither cost-effective nor reliable to embark on routine screening of patients for blood-borne viruses. The concept of universal precautions is based on the reality that it is impossible to identify all patients with a nosocomial virus infection and it is therefore prudent to adopt policies that regard all patients as being potentially infectious. Because percutaneous inoculation is the major route of infection, care must be taken when handling sharp instruments. Sharp instruments should only be passed to others when they are in a rigid container such as a kidney dish and never passed by hand. All sharps should be disposed of into dedicated ‘sharps containers’, and needles should never be resheathed. Cuts and abrasions should be covered with waterproof dressings, and disposable gloves should be worn if there is a risk of contamination of the hands with blood or any other body fluid. Protective eye-wear and a mask should be worn if there is a risk of splashing with blood or any other body fluid. It is particularly important not to abandon universal precautions during emergencies; this is the time when junior staff are at the greatest risk.

Vaccination

It is important that all health-care workers maintain their immunisation when appropriate vaccines are available. Active immunisation against hepatitis B is available but as yet there is no active immunisation against hepatitis C or HIV.

Exposure

Advice should be sought immediately after exposure to blood or any other body fluid. It is important to commence post-exposure prophylactic drugs for HIV without delay, and ideally within 1 hour of exposure. Most hospitals have an infection control manual that outlines specific requirements and policies relating to blood-borne infections.
Personal tools