How reliable is the ‘wound’ item in the POMS

5.1 Introduction

Surgical site infection (SSI) following arthroplasty is a potentially devastating complication. It can require revision surgery, and in the worst-case scenario, can lead to limb amputation. To avoid these complications, every effort is made to keep infection rates to a minimum. In order to monitor infection rates, a reliable and reproducible method of diagnosing infection must be used.

This chapter will examine the accuracy of the wound domain of the POMS. The POMS definition of wound morbidity is ‘wound dehiscence requiring surgical exploration or drainage of pus from operative wound with or without isolation of organisms’. The POMS aims to identify morbidity that warrants inpatient

hospital care. Therefore, the wound domain of the POMS would be expected to identify SSI that requires intravenous antibiotics or surgical treatment. The POMS would not be expected to identify mild superficial wound infections that can be treated with oral antibiotics and outpatient monitoring.

In order to test accuracy, the wound domain of POMS needs to be compared to a ‘gold standard’. There are several definitions of wound infection, as

197 (CDC) definition, the English Nosocomial Infection National Surveillance

Scheme (NINSS) definition and the English ASEPSIS definition (Additional treatment, Serous discharge, Erythema, Purulent exudate, Separation of deep tissues, Isolation of bacteria and Stay as inpatient prolonged over fourteen days), all of which have undergone some psychometric analysis. Substantial gaps exist in the literature regarding the validity of these definitions. The CDC definition is known to be weak since 3 out of the 4 defining criteria are

subjective. CDC is also known to be unreliable35_{. NINSS evolved in an attempt} to increase the reliability of CDC but evaluation has confirmed that

reproducibility remains low36_{. The original ASEPSIS method has been shown to} be both objective and repeatable38 _{for sternal wounds but a more recent revised} version has not been psychometrically evaluated. A recent systematic review concluded that ASEPSIS is the ‘gold standard’ for scoring surgical site

infections168_{. It was therefore decided to compare the wound domain of POMS} to ASEPSIS to test its accuracy.

Patient follow-up is essential to record accurately SSI rates since half of infections present after hospital discharge33_{. Therefore SSI rates cannot be} simply defined as a ‘short-term’ outcome measure. ASEPSIS defines wound infection as occurring up to 2 months post-surgery. This presents a problem when comparing it to the wound domain of the POMS. The POMS only

identifies wound morbidity during the inpatient episode, where as the ASEPSIS considers both the inpatient episode and outpatient follow-up. Furthermore, the POMS only identifies wound morbidity that is sufficiently serious to warrant

198 inpatient care. ASEPSIS identifies mild wound morbidity that could be treated as an outpatient as well more serious morbidity requiring inpatient care. For these two reasons, the incidence of wound morbidity defined by the POMS could be expected to be lower than the incidence defined by ASEPSIS.

In an attempt to overcome this problem, and make a fair comparison, the wound domain of the POMS was compared to two different ASEPSIS scores: the inpatient ASEPSIS score (based on information from the inpatient episode only) and the overall ASEPSIS score. In this way, the wound domain of POMS could be directly compared to another inpatient assessment of wound morbidity.

At the time of the POMS study, ASEPSIS scores were routinely collected on all patients who remained in the hospital for at least 2 days. Therefore ASEPSIS data was available for all patients in the POMS study.

5.2 Methods

5.2.1 General methodology

The methods used to collect the POMS data are described fully in Chapter 2. The patient demographics are also described. POMS data was collected on post-operative days (POD) 3, 5, 8 and 15 if the patient remained in hospital.

ASEPSIS data was collected on the same patients. A member of a specialist wound surveillance team, made up of 4 nurses and a health care assistant,

199 assessed each wound. The sole role of these five members of staff was to collect and record wound infection data, and all received specialist training in the diagnosis of surgical site infection.

Each patient was reviewed on 3 separate occasions: once pre-operatively and twice post-operatively. The same standardized data collection sheet was completed for each patient. Details collected pre-operatively included patient age, height, weight, clinical team and consultant in charge. Operative

information and microbiology results were recorded from a direct interface with hospital computer databases. Microbiology tests, such as wound swabs or tissue cultures, were performed according to clinical judgment. No specific microbiology tests were requested for study purposes alone.

Surgical wounds were inspected on POD 2 or 3, and again on POD 4 or 5 (if the patient remained in hospital). The proportion of each wound exhibiting

erythema, serous discharge, purulent discharge or dehiscence was recorded. Wounds were directly inspected by surveillance staff if undressed, but if a dressing was present, the relevant information was gained by questioning nursing staff. This was done to avoid an unnecessary increase in the risk of infection. Nurses were encouraged to fill out the data collection sheet at the time of dressing change.

200 prescription of therapeutic antibiotics and the opening of a wound or drainage of an abscess were recorded.

At the time of discharge patients were given a simple ‘yes/no’ questionnaire regarding their wound. They were asked to complete and return the

questionnaire in a pre-paid envelope 2 months post-surgery. Patients were contacted by telephone if no postal questionnaire was returned. The

questionnaire was used to ascertain if a wound infection had been diagnosed since discharge, if antibiotics had been prescribed for the wound, if any further surgery had been necessary, and if the hospital stay had been longer than 14 days.

Data was stored on a modified Access 97® database which was only

accessible to surveillance team members. A single patient episode was defined as an operation with post-operative follow-up of either 3 months or until a further operation was performed, whichever was shorter. SSI resulting in readmission at any time was recorded in the database.

5.2.2 Calculation of the ASEPSIS score

ASEPSIS is a quantitative wound scoring method. The score is calculated using objective criteria based both on visual characteristics of the wound and the consequences of infection.