Skin preparation for preventing infection following caesarean section
Abstract
This is a protocol for a Cochrane Review (Intervention). The objectives are as follows:
To compare the effectiveness of different forms and methods of preoperative skin preparation for preventing postcaesarean infection.
Background
Caesarean section is the most common major surgical procedure performed on women. The increasing rate of caesarean birth worldwide is well established and a concern to many (Thomas 2001). The risk of maternal morbidity and mortality is higher in caesarean section than in vaginal delivery, with postoperative infection a common component of morbidity. With the increase in caesarean section, it is important that the risks to the mother are minimised as far as possible. This review focuses on different forms and methods for preoperative skin preparation to prevent infection.
Women who give birth by caesarean section are exposed to both endogenous (internal) and exogenous (external) sources of infection during delivery. Exposure to a hospital environment places these women at risk of developing hospital‐acquired infections. The rate of postcaesarean infection has been estimated to be 10 times greater than that after vaginal delivery (Henderson 1995).
The Centers for Disease Control and Prevention (CDC) estimates that 27 million surgical procedures are performed in the United States each year. The CDC's National Nosocomial Infections Surveillance system reports that surgical site infections are the third most frequently reported nosocomial infection, accounting for 14% to 16% of all such infections (CDC 2005). Preventing infection by properly preparing the skin before incision is thus a vital part of the overall care given to women during caesarean delivery.
Proper preparation of an incision site involves removal of surface dirt and oil by a soap or detergent scrub plus application of a topical antimicrobial agent that will reduce the bacterial population to a minimal level. In surgical patients, the choice of surgical scrub and the duration of scrubbing have not been shown to make any significant difference in the rate of wound infection in clean or clean‐contaminated (such as caesarean skin incision) wounds (Edwards 2004; Mangram 1999).
Antiseptics to prevent infection have been in use for over 150 years. Antiseptic handwash solution was first introduced by Semmelweis in 1847 at the Vienna Maternity Hospital to reduce maternal mortality due to puerperal sepsis (Loudon 2002). Later in 1864, Lister introduced carbolic acid spray preparation for the operative site. Since then many solutions (including alcoholic iodine, mercuric compounds and ether) have been used to prepare the operative site. However, as a Cochrane review has shown, there is uncertainty about which antiseptic skin preparation is the most effective for preventing postoperative surgical wound infections (Edwards 2004).
The incidence of abdominal incisional infections following caesarean section ranges from 3% to 15%. A postcaesarean wound infection is a bacterial infection in the surgical incision following an abdominal delivery. Women who develop a postcaesarean wound infection typically experience a temperature of 38.0°C (100.4°F) or higher and lower abdominal pain (Williams 2005). Abdominal incisional abscesses that develop following caesarean delivery usually cause fever on about the fourth postoperative day. In many cases, these are preceded by uterine infection and fever persists from the first or second postoperative day. Wound erythema and drainage may also be present. Organisms causing these infections are usually the same as those isolated from amniotic fluid at caesarean delivery, but hospital‐acquired pathogens may also be the cause.
Some women are more likely than others to develop a postcaesarean wound infection. High‐risk women include those who are obese; have diabetes or an immunosuppressive disorder (HIV infection); have chorioamnionitis (infection of the amniotic fluid and fetal membrane) during labour; anaemia; or are taking corticosteroids (by mouth or intravenously) (Williams 2005).
In addition to wound infections, another common source of morbidity is postcaesarean metritis, including endometritis, an infection that develops within the lining of the uterus after delivery. Despite the use of routine perioperative prophylaxis, estimates of metritis following caesarean range form 10% to 20% (Normand 2001).
The removal of transient bacteria and reduction of the number of commensal organisms by antiseptic is recommended prior to surgery by several organisations, for example, the Royal College of Surgeons of England (Leaper 2001), the Centers for Disease Control and Prevention (Mangram 1999) and the Association of Operating Room Nurses (AORN 2002). Several antiseptic agents are available for preoperative preparation of skin at the incision site. Leclair 1990 describes an antiseptic as 'a chemical agent that reduces the microbial population on the skin'. It is suggested that the ideal agent would kill all bacteria, fungi, viruses, protozoa, tubercle bacilli and spores; be nontoxic, hypoallergenic and safe to use in all body regions; not be absorbed; have residual activity and be safe for repetitive use (Edwards 2004; Hardin 1997).
Antiseptics for preoperative skin preparation should be broad‐spectrum and fast‐acting and contain an antimicrobial ingredient that results in significant reductions in the numbers of micro‐organisms on intact skin (Larson 1988). The primary action of antiseptics includes both the mechanical removal and chemical killing and inhibition of both contaminating and colonising flora.There are six types of antiseptics that are designed for topical application: iodine/iodophors, alcohol, chlorhexidine gluconate, hexachlorophene, parachlorometaxylenol, triclosan (Edwards 2004; Larson 1988).
There is an existing Cochrane review on the use of preoperative skin antiseptics for preventing infections (Edwards 2004). However, although the scope of the Edwards review includes all clean surgical operations, including caesarean section, the focus is on preventing surgical wound infections. In this review, the focus extends to preventing all types of infection, such as metritis. This review is only concerned with different methods of skin preparation. There is another Cochrane review looking at alternative methods of surgical incisions for caesarean section (Mathai 2007). For the purpose of this review, antiseptic agents can be applied in the form of liquids, solutions, powders or delivered on impregnated drapes.
Objectives
To compare the effectiveness of different forms and methods of preoperative skin preparation for preventing postcaesarean infection.
Methods
Criteria for considering studies for this review
Types of studies
We will include all published and unpublished randomised and quasi‐randomised trials, including cluster‐randomised trials, evaluating any described type of preoperative skin preparation agents, forms and methods of application for caesarean section.
Types of participants
All pregnant women undergoing elective or emergency caesarean section.
Types of interventions
Comparisons between different antiseptic agents used for caesarean section skin preparation (e.g. alcohol, povidone‐iodine), different methods of antiseptic application (e.g. scrub, paint, drape) or different forms of antiseptic (e.g. powder, liquid). We will only include skin incision area preparation and will exclude preoperative handwashing of the surgical team or preoperative bathing.
Types of outcome measures
Primary outcomes
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Surgical site infection
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Metritis or endometritis, or both
Secondary outcomes
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Length of stay
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Maternal mortality
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Repeat surgery
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Re‐admission resulting from infection
Search methods for identification of studies
Electronic searches
We will contact the Trials Search Co‐ordinator to search the Cochrane Pregnancy and Childbirth Group’s Trials Register.
The Cochrane Pregnancy and Childbirth Group’s Trials Register is maintained by the Trials Search Co‐ordinator and contains trials identified from:
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quarterly searches of the Cochrane Central Register of Controlled Trials (CENTRAL);
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weekly searches of MEDLINE;
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handsearches of 30 journals and the proceedings of major conferences;
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weekly current awareness alerts for a further 44 journals plus monthly BioMed Central email alerts.
Details of the search strategies for CENTRAL and MEDLINE, the list of handsearched journals and conference proceedings, and the list of journals reviewed via the current awareness service can be found in the ‘Specialized Register’ section within the editorial information about the Cochrane Pregnancy and Childbirth Group.
Trials identified through the searching activities described above are each assigned to a review topic (or topics). The Trials Search Co‐ordinator searches the register for each review using the topic list rather than keywords.
In addition, we will search the Cochrane Central Register of Controlled Trials (The Cochrane Library) using the search strategy in Appendix 1. We will adapt this strategy to search MEDLINE (January 1996 to current), EMBASE (January 1974 to current) and CINAHL (January 1982 to current) by selecting appropriate MeSH and/or keywords from the respective thesauri. If necessary, we will contact researchers to provide further information. We will also search the reference lists of trials and review articles. We will not apply any language restrictions.
Data collection and analysis
Selection of studies
We will assess for inclusion all potential studies we identify as a result of the search strategy. We will resolve any disagreement through discussion or if required consult an outside person.
Data extraction and management
We will design a form to extract data. For eligible studies, two review authors will extract the data using the agreed form. We will resolve discrepancies through discussion or, if required, we will consult a third author. We will enter data into Review Manager software (RevMan 2008) and check them for accuracy.
When information regarding any of the above is unclear, we will attempt to contact authors of the original reports to provide further details.
Assessment of risk of bias in included studies
Two review authors will independently assess risk of bias for each study using the criteria outlined in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2008). Any disagreement will be resolved by discussion or by involving a third assessor.
(1) Sequence generation (checking for possible selection bias)
We will describe for each included study the method used to generate the allocation sequence in sufficient detail to allow an assessment of whether it should produce comparable groups. We will assess the method as:
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adequate (any truly random process, e.g. random number table; computer random‐number generator);
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inadequate (any non random process, e.g. odd or even date of birth; hospital or clinic record number); or
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unclear.
(2) Allocation concealment (checking for possible selection bias)
We will describe for each included study the method used to conceal the allocation sequence in sufficient detail and determine whether intervention allocation could have been foreseen in advance of, or during recruitment, or changed after assignment. We will assess the methods as:
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adequate (e.g. telephone or central randomisation; consecutively numbered sealed opaque envelopes);
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inadequate (open random allocation; unsealed or non‐opaque envelopes, alternation; date of birth);
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unclear.
(3) Blinding (checking for possible performance bias)
We will describe for each included study the methods used, if any, to blind study participants and personnel from knowledge of which intervention a participant received. Blinding will be assessed separately for different outcomes or classes of outcomes. We will assess the methods as:
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adequate, inadequate or unclear for participants;
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adequate, inadequate or unclear for personnel;
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adequate, inadequate or unclear for outcome assessors.
(4) Incomplete outcome data (checking for possible attrition bias through withdrawals, dropouts, protocol deviations)
We will describe for each included study, and for each outcome or class of outcomes, the completeness of data including attrition and exclusions from the analysis. We will state whether attrition and exclusions were reported, the numbers included in the analysis at each stage (compared with the total randomised participants), reasons for attrition or exclusion where reported, and whether missing data were balanced across groups. Where sufficient information is reported, or can be supplied by the trial authors, we will re‐include missing data in the analyses which we undertake. We will assess methods as:
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adequate;
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inadequate;
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unclear.
Missing data greater than 20% will be considered inadequate.
(5) Selective reporting bias
We will describe for each included study how we investigated the possibility of selective outcome reporting bias and what we found. We will assess the methods as:
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adequate (where it is clear that all of the study’s prespecified outcomes and all expected outcomes of interest to the review have been reported);
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inadequate (where not all the study’s prespecified outcomes have been reported; one or more reported primary outcomes were not prespecified; outcomes of interest are reported incompletely and so cannot be used; study fails to include results of a key outcome that would have been expected to have been reported);
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unclear.
(6) Other sources of bias
We will describe for each included study any important concerns we have about other possible sources of bias, for example, source of funding and extreme baseline imbalance. We will assess whether each study was free of other problems that could put it at risk of bias:
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yes;
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no;
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unclear.
(7) Overall risk of bias
We will make explicit judgements about whether studies are at high risk of bias, according to the criteria given in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2008). With reference to (1) to (6) above, we will assess the likely magnitude and direction of the bias and whether we consider it is likely to impact on the findings. We will explore the impact of the level of bias through undertaking sensitivity analyses ‐ see 'Sensitivity analysis'.
Measures of treatment effect
Dichotomous data
For dichotomous data, we will present results as summary risk ratio with 95% confidence intervals.
Continuous data
For continuous data, we will use the mean difference if outcomes are measured in the same way between trials. We will use the standardised mean difference to combine trials that measure the same outcome, but use different methods.
Unit of analysis issues
Cluster‐randomised trials
We will include cluster‐randomised trials in the analyses along with individually randomised trials. Their sample sizes or standard errors will be adjusted using the methods described in the Cochrane Handbook for Systematic Reviews of Interventions (Higgins 2008) using an estimate of the intracluster correlation co‐efficient (ICC) derived from the trial (if possible), or from another source. If ICCs from other sources are used, this will be reported and sensitivity analyses conducted to investigate the effect of variation in the ICC. If we identify both cluster‐randomised trials and individually‐randomised trials, we plan to synthesise the relevant information. We will consider it reasonable to combine the results from both if there is little heterogeneity between the study designs and the interaction between the effect of intervention and the choice of randomisation unit is considered to be unlikely.
We will also acknowledge heterogeneity in the randomisation unit and perform a separate meta‐analysis.
Crossover trials
Crossover trials will not be included for analysis.
Dealing with missing data
For included studies, we will note levels of attrition. We will explore the impact of including studies with high levels of missing data in the overall assessment of treatment effect by using sensitivity analysis.
For all outcomes, we will carry out analyses, as far as possible, on an intention‐to‐treat basis, i.e. we will attempt to include all participants randomised to each group in the analyses. The denominator for each outcome in each trial will be the number randomised minus any participants whose outcomes are known to be missing.
Assessment of heterogeneity
We will use the I² statistic to measure heterogeneity among the trials in each analysis. If we identify substantial heterogeneity (above 50%), we will explore it by prespecified subgroup analysis.
Assessment of reporting biases
Where we suspect reporting bias (see selective reporting bias above), we will attempt to contact study authors asking them to provide missing outcome data. Where this is not possible, and the missing data are thought to introduce serious bias, we will explore the impact of including such studies in the overall assessment of results by a sensitivity analysis.
Data synthesis
We will carry out statistical analysis using the Review Manager software (RevMan 2008). We will use fixed‐effect inverse variance meta‐analysis for combining data where trials are examining the same intervention, and the trials’ populations and methods are judged sufficiently similar. Where we suspect clinical or methodological heterogeneity between studies sufficient to suggest that treatment effects may differ between trials we will use random‐effects meta‐analysis. If substantial heterogeneity is identified in a fixed effect meta‐analysis this will be noted and the analysis repeated using a random‐effects method.
The different possible combinations of interventions could result in a large number of comparisons. As far as possible, we will limit the number of comparisons by grouping together interventions that are sufficiently similar. For example, studies in which the comparison is between the same classes of antimicrobials will be included in the same meta‐analysis. If the interventions are not sufficiently similar we will consider performing subgroup analyses.
Subgroup analyses
We plan to carry out the following subgroup analyses when it is not clinically appropriate to combine in the same meta‐analysis:
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Risk of infection (high versus low risk)
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Duration of skin preparation
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Dose of preparation
For fixed‐effect meta‐analyses we will conduct planned subgroup analyses classifying whole trials by interaction tests as described by Deeks 2001. For random‐effects meta‐analyses we will assess differences between subgroups by inspection of the subgroups’ confidence intervals; non‐overlapping confidence intervals indicate a statistically significant difference in treatment effect between the subgroups.
Sensitivity analyses
We will carry out a sensitivity analysis to explore the effects of allocation concealment and blinded outcome assessment on the results of the review. Studies in which either allocation concealment or blinded outcome assessment (for surgical site infection) is inadequate (i.e. high risk of bias) or unclear will be excluded from the analysis to assess for any substantive difference to the overall result. We will also carry out a sensitivity analysis to explore the effects of fixed‐ or random‐effects analyses for outcomes with statistical heterogeneity.
