Infection

Systemic infection affects healing as the wound has to compete with any infection for white cells and nutrients. Healing may not take place until after the body has dealt with the infection. Systemic infection is frequently associated with pyrexia. Pyrexia causes an increase in the metabolic rate, thus increasing catabolism or tissue breakdown.

All wounds are contaminated with bacteria, especially open wounds. This does not affect healing. However, clinical infection will certainly do so. Infection prolongs the inflammatory stage of healing as the cells combat the large numbers of bacteria. It also appears to inhibit the ability of fibroblasts to produce collagen (Senter & Pringle, 1985).

Infection in a burn wound increases the metabolic rate and thereby increases the time of negative nitrogen balance. Kinney (1977) has shown that there may be a loss of 20-30% of the initial body weight in the presence of major sepsis. Infection also causes pain which raises the metabolic rate (Arturson, 1978).

There have been several major studies of surgical wound infection rates, including those of Cruse and Foord (1973, 1980), Bibby et al. (1986) and Emmerson et al. (1996). These studies, especially that of Cruse and Foord, have highlighted factors which may predispose the patient to wound infection. It should be noted that the infection rates are usually compared with the expected infection rate of 1.5% for clean surgery. These factors include the following.

Age It has been found that patients over 65 years are six times more likely to develop an infection in a clean surgical wound than a child under 14 years (Cruse & Foord, 1973). Mishriki et al. (1990) found a significantly higher incidence of wound infection in patients over the age of 55 years. Moro et al. (1996) used logistical regression to identify factors associated with increased risk of surgical wound infection. They found that age greater than 85 years was a significant factor.

Build/weight for height Obesity increases clean wound infection rate to 13.5% (Cruse & Foord, 1973). Martens et al. (1995) found obesity to be a significant factor in wound infection following Caesarian section. These findings are supported by Moro et al. (1996), who found obesity to be a significant factor for infection in a wide range of surgical cases, and also by He et al. (1994) and Birkmeyer et al. (1998). Researchers in these latter two studies found a significantly higher incidence of sternal wound infection following bilateral internal mammary artery grafting and coronary artery bypass surgery respectively.

Nutritional status Poor nutrition increases the infection risk. McPhee et al. (1998) found preoperative protein depletion to be a significant factor for wound infection in patients undergoing spinal surgery. (See also Eating and drinking; Section 2.2.4)

Diabetes The management of diabetic patients undergoing surgery must be carefully monitored. Surgery can cause de-stabilisation which increases the risk of infection. In turn, infection can also affect the diabetic state. Hyperglycaemia affects the body's defence mechanism by impairing the response of white cells -neutrophils in particular. Cruse and Foord (1973) found a clean wound infection rate of 10.7% in diabetic patients. Borger et al. (1998) found diabetes to be a predictor of deep sternal wound infection for patients undergoing cardiac surgery.

Special risks Irradiation, steroids, and immunosuppressive drugs cause greatly increased infection rates (Bibby et al., 1986). Chmell and Schwartz (1996) found that preoperative chemotherapy was a significant factor in wound infection following musculoskeletal sarcoma resections.

Length of preoperative stay The longer the stay in hospital, the more chance there is that the patient's skin will become colonised by bacteria against which the patient has no resistance. Cruse and Foord (1980) found that the clean wound infection rate increased from 1.2% for a one-day preoperative stay to 2.1% for seven days and to 3.4% for more than 14 days.

Bed occupancy Occupancy of more than 25 beds in an open ward increases wound infection (Bibby et ai, 1986).

Shave It is impossible to carry out a shave without causing injury to the skin. Bacteria flourish and multiply rapidly in these minute cuts. The clean wound infection rate was found to be 2.5% in shaved patients compared with 1.7% for those who had had their pubic hair clipped and 0.9% for those who were not shaved (Cruse & Foord, 1980). Mishriki et al. (1990) and Moro et ai. (1996) also found shaving to be a significant factor in the development of infection. Mishriki et al. suggest that this is particularly so when contaminated and dirty procedures are undertaken and bacteria are shed on the skin. It is generally recommended that if a patient needs to be shaved preoperatively, it should be done just prior to surgery.

Type of surgery Infection rates are much higher in some types of surgery than others. This is discussed in more detail in Chapter 6. The appearance of infected wounds will be discussed in Chapter 3.

The elderly

Elderly people have an increased incidence of underlying disease. Some may directly affect the healing process. Others may cause a level of disability which can affect the patient's ability to maintain safe standards of hygiene, thus increasing the risk of infection.

Socioeconomic problems

Poor housing may not only cause hazards such as badly lit stairs, but other problems - damp or rodent infestation - which make it difficult to maintain cleanliness. This predisposes to disease as well as increasing the risk of infection.

(1) Infection: (a) identify those at risk (see Table 2.1)

(b) assess wound (see Chapter 3)

(c) monitor temperature regularly.

(2) The elderly: evidence of relevant underlying disease?

(3) Socioeconomic problems: relevant if a patient with a chronic wound is to be cared for at home.

Table 2.1 Infection risk factors.

General factors

Age

Very young or very old.

Nutrition

Emaciated; thin; obese; dehydrated.

Mobility

Limited; immobile; temporary; permanent.

Mental state

Confused; depressed; senile.

Incontinence

Urine; faeces; temporary; permanent.

General health

Weak; debilitated.

General hygiene

Dependence; mouth/teeth; skin.

Local factors

Oedema

Pulmonary; ascites; effusion.

Ischaemia

Thrombus; embolus; necrosis.

Skin lesions

Trauma; burns; ulceration.

Foreign body

Accidental; planned.

Invasive procedures

Cannulation

Peripheral; central; parenteral.

Catheterisation

Intermittent; closed; drainage; irrigation.

Surgery

Wound; wound drainage; colostomy; implant.

Intubation

Endobronchial suction; ventilation; humidification.

Drugs

Cytotoxics; antibiotics; steroids.

Diseases

Carcinoma; leukaemia; aplastic anaemia; severe anaemia; diabetes.

Liver disease; renal disease; transplantation; AIDS.

Based on Bowell (1992)

Based on Bowell (1992)

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