EUROPEAN TISSUE REPAIR SOCIETY

PHYSICAL FORCES III

PHYSICAL FORCES III

PRETREATMENT WITH RADIANT HEAT – ACUTE SURGICAL WOUNDS

CLEAN wounds are defined as surgical wounds that have been made into tissues in which no inflammation is encountered, nor are the respiratory, alimentary or genitourinary tracts entered.¹ This definition has stood the test of time, but two major unresolved controversies persist. Firstly, what the true incidence of wound infection is after clean surgery and secondly whether antibiotic prophylaxis is effective. Clean surgical wounds can be subdivided into those which involve an implant (such as a vascular graft or arthropaedic prosthesis) and those which do not. It has been recognised since seminal work by Elek and Conen, that the presence of an implant, or a foreign body such as silk, logarithmically reduces the inoculum of a pathogen which is required to produce a wound infection.² There is no controversy that prophylactic antibiotics are just as effective in preventing wound infections in prosthetic surgery as they are in elective cleancontaminated and contaminated general surgical wounds. Clean, implant wounds are not considered further.

Prevention of infection after clean non-implant surgery, which constitutes the largest group of operations, is as important as for any other type of surgery. Apart from inconvenience, distress and delay in returning to normal life wound infections have a financial cost. Estimates are difficult to make, but the management of a wound infection alone may cost the hospital over £1500.^3,4 After clean, non-implant wound surgery, most of which is undertaken as day case procedures, these costs are passed on to primary health care, as infections present several days postoperatively.^5–7 The importance of infection rates in clean surgery should not be underestimated as they may be seen as an indicator of quality and used to determine surgical performance.^8,9 Therefore, the methods and definition used to determine the presence of infection need to be carefully defined.

Definition of infection after clean, non-implant surgery

The true incidence of wound infection after clean, nonimplant surgery depends on the definition. Most infections are endogenous and caused by contamination of the patient’s own resident, potential pathogens, at surgery. Some, the proportion of which is hard to define, are exogenous and are probably nosocomially acquired during surgery or by poor post-operative wound management. We probably take for granted that operating theatres and wards provide satisfactory environments in which to undertake surgery and manage wounds. There is no room for complacency, however, and any change from established surgical and nursing rituals should not be made without evidence- based medicine to show it is safe to do so, supported by adequate acceptable randomised controlled trials. Adequate handwashing is widely regarded as the single most important preventative factor.¹⁰

A simple clinical definition of wound infection is easy – a purulent discharge in, or exuding from, the wound or a painful, spreading erythema indicative of cellulitis.¹¹ The definition of wound infection adopted by the Center for Disease Control is similar, but insists on a thirty-day surveillance. ¹² Severity scoring of wound infection allows even more precise definition using the Southampton⁸ or ASEPSIS¹³ systems.

Incidence of infection after clean, non-implant surgery

The incidence of post-operative wound infection may be underestimated even with these appropriate definitions. If surveillance is to be accurate it needs to be labour intensive and undertaken by a blinded, trained observer for at least thirty days post-operatively. The ideal of daily observation is difficult to achieve for out-patients and some compromise has to be made. Errors occur when hospital notes, telephone or postal follow up, or primary care (an external observer) are used.⁹ The majority of published studies suggest that the infection rate after this type of surgery is under 5%.^3,14–21 Cruse and Foord^14–16 have shown a consistent rate of wound infections over a twenty-year period with surveillance of 100,000 wounds. The wound infection rate of <2% after clean operations is widely quoted and sets a high standard. The method of recording a wound infection was based on a final telephone call to the respective surgeons’ offices twenty-eight days after the operation. However, when surveillance has more depth, involving follow up into the community and out-patients using a trained unbiased observer with strict definitions of infection, or a diary system and close communication over a sixweek period with primary health care then much higher infection rates (up to 17–18%) have been reported.^{5-8, 22-23} Low and colleagues5 found that 59% of wound infections were recognised after discharge from hospital with 70% of infections occurring at home. Keeling and Morgan⁷ discovered that the recorded in-hospital incidence of wound infections was increased ten-fold when patients were followed up in the community. It was found in another study that hospital case notes recorded a 3% wound infection rate, whereas community surveillance showed a 9% rate.⁸

Value of antibiotic prophylaxis in clean nonimplant surgery

The use of antibiotic prophylaxis in clean non-implant operations (principally hernia and breast surgery) is controversial. Platt and colleagues showed a statistically significant reduction of postoperative infections in patients undergoing breast and hernia surgery who received cefonicid compared with a placebo.²⁴ However, if wound infections alone were considered the difference was not significant (1.9% to 1.3% in hernia surgery and 8.6% to 5.6% for breast surgery). An extension of the study involving breast patients alone, with a larger patient sample but not acceptably randomised, did give a statistically significant advantage in lowering wound infections.²⁵ The studies were partially flawed by the use of telephone follow- up in some patients, unclear randomisation and trial design and being of multicentre nature.

Since then there have been two further reports of the use of co-amoxyclav as a prophylactic antibiotic in hernia²² and breast²³ surgery. Amoxycillin combined with clavulanic acid is an acceptable antistaphyloccocal agent. Two things emerged from these trials; first that in depth surveillance with accepted definitions produces a high overall infection rate (9% after hernia surgery and 17–18% after breast surgery), and secondly that antibiotic prophylaxis made no difference whatsoever to postoperative wound infection rates. Both studies were multicentre but contained adequate numbers of patients in their trial design which was also acceptable.

Several experimental and clinical studies have shown that intraoperative hypothermia increases the risk of wound infection.^26–28 This probably relates to poor skin perfusion and tissue hypoxia which makes the wound more susceptible to infection, even if contamination is minimal (as in clean wound surgery). Day-case surgical patients may fall into this category; they may be relatively cold waiting for surgery, they may be relatively dry with overnight fasting, and they may have apprehension not usually counteracted by the use of anxiolytics.

Patients and Methods

In a randomised controlled trial we have compared wound infection after standard clean wound surgery (mostly varicose vein, breast or hernia day case operations) with that after preoperative warming using either a local warming device (Warm-Up^®, Augustine Medical) or a systemic forced warmed-air device (Bair Hugger^®, Augustine Medical). Initial calculations based on past publications, estimated that a sample size of 402 patients was needed with a 90% power of showing a statistically significant difference. The majority of patients were randomly assigned to one of these three groups on the same day as their surgery.

The groups assigned to Warm-Up or Bair Hugger were warmed for 30–60 minutes immediately prior to surgery. Patients were reviewed at two and six weeks (out-patients or at home) by a single trained observer who was blinded to the treatment allocation. A patient diary and patient questionnaire were also used and any wound problems were recorded and discussed with the district nurse, general practitioner or at a review. Wounds were defined as being infected using four systems.^{8, 11–13}

Results

Over a 14-month period 421 patients were recruited into the study. One operation was cancelled and four patients were lost to follow-up leaving 139 in the standard group, 138 in the Warm-Up group and 139 in the Bair Hugger group. There were nine protocol violations in the warmed groups. The three patient groups were demographically similar (age, sex, body mass index, type of surgery, etc) and their overall wound infection rate was 7.7%. There were 19/139 (13.7%) infections in the standard group compared with 13/277 (4.7%) in the warmed groups (P < 0.001). The ASEPSIS scores were also significantly lower in the warmed groups but there was no difference between the two warmed groups. Interestingly, only 18 patients in the warmed groups (6.5%) were given post-operative antibiotics by their general practitioners compared with 22 (15.9%) in the standard group (P < 0.002). Breast surgery has the highest associated wound infection rate (10.3%) compared with hernia (6.5%) or varicose vein surgery (4.7%). High body mass index was the only significant variable relating to infection (P < 0.05).

Discussion

It is clear that clean non-implant surgery is associated with a higher than generally accepted surgical site infection rate if surveillance is undertaken with precise definitions, by detailed follow-up using a trained unbiased (blinded) observer. The value of antibiotic prophylaxis is not proven and probably further well-designed, randomised controlled trials are needed. The value of prophylaxis in implant surgery is not contestable.

There is little evidence that antibiotics used prophylactically cause a significantly increased risk of resistance. When used in more than one dose there is a definite theoretical risk of resistance with added complications of allergy, toxicity (in some cases) and emergence of organisms such as Clostridium difficile. Warming does seem to offer an effective alternative. Certainly warming using radiant heat increases tissue pO2 and this persists for three hours after removal of the Warming card.29 It also reduces wound infection as shown in the study presented above, probably by improving host defences. This has an obvious benefit to the day-case surgical patients of the study, who are most at risk of skin capillary shut down because of being relatively cold, over anxious, having prolonged fasting and of course a general anaesthetic.

References

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Professor David J Leaper
Professorial Unit of Surgery
North Tees General Hospital
Stockton-on-Tees
Cleveland
TS19 8PE
United Kingdom