Commentary on selected evidence
With advice from topic experts we selected 3 studies for further commentary.
Intraoperative phase – antiseptic skin preparation
We selected the studies by Ngai et al. (2015) and Tuuli et al. (2016) for full commentary because they assessed skin antisepsis with chlorhexidine in alcohol compared with povidone-iodine in alcohol. Previous studies, for example, Darouiche et al. (2010), compared chlorhexidine in alcohol with povidone-iodine in water, which may not have been a 'fair' comparison.
Current guidance recommends preparing the skin at the surgical site immediately before incision using an antiseptic (aqueous or alcohol-based) preparation: povidone-iodine or chlorhexidine are most suitable.
Both studies were randomised controlled trials that assessed skin antisepsis with chlorhexidine in alcohol compared with povidone-iodine in alcohol in women undergoing scheduled or unscheduled caesarean section. Both studies excluded emergency caesarean sections.
Ngai et al. (2015) compared 3 methods of skin antisepsis (n=1,404): povidone-iodine in alcohol (n=463); chlorhexidine in alcohol (n=474); and dual antisepsis with povidone-iodine then chlorhexidine in alcohol applied immediately after (n=467). The report did not specify the concentrations of antiseptics, or specific antiseptic products used in the study. The primary outcome was the rate of surgical site infections 30 days after delivery in the dual antisepsis group compared with the povidone-iodine-only or chlorhexidine-only control groups. Surgical site infection was defined as patient-reported use of antibiotics for a wound infection or documented wound infection at a post-discharge outpatient appointment.
Tuuli et al. (2016) compared povidone-iodine 8.3% in 72.5% isopropyl alcohol with chlorhexidine 2% in 70% isopropyl alcohol. The primary outcome was surgical site infection (superficial or deep) diagnosed by the treating physician and validated by an investigator blind to treatment allocation. The surgical site infection had to be diagnosed within 30 days after the caesarean delivery.
In Ngai et al. (2015), rates of surgical site infection were 4.6% in the povidone-iodine group (21 of 463); 4.5% in the chlorhexidine group (21 of 474); and 3.9% in the dual antisepsis group (18 of 467). There was no clear evidence of a difference in surgical site infection between the dual antisepsis group and the povidone-iodine-only group (odds ratio [OR] 0.85, 95% confidence interval [CI] 0.44 to 1.61) or the chlorhexidine-only group (OR 0.99, 95% CI 0.53 to 1.84).
Ngai et al. (2015) also conducted multivariable regression analyses to identify risk factors for surgical site infection, which were: estimated blood loss greater than 1,000 ml (OR 2.44, 95% CI 1.29 to 4.62) and pre-eclampsia (OR 2.61, 95% CI 1.25 to 5.44).
In Tuuli et al. (2016), rates of surgical site infection were 7.3% in the povidone-iodine group (42 of 575) and 4.0% in the chlorhexidine group (23 of 572). The rate of surgical site infection was significantly lower in the chlorhexidine group than in the povidone-iodine group (risk ratio [RR] 0.55, 95% CI 0.34 to 0.90, p=0.002). Subgroup analyses suggested that the effect was not affected by whether caesarean section was scheduled or unscheduled, type of skin closure, or by the presence of other chronic conditions including diabetes or obesity. When deep and superficial surgical site infections were analysed separately, there was no clear evidence of a difference between the antiseptics.
Both studies included a power calculation and recruited more participants into each group than the power calculation suggested was necessary. Additionally, both studies included all randomised participants in the analyses.
Both studies appeared to have low risk of bias in most aspects of study design. However, neither study blinded the operating team, which would be difficult because of differences in smell and colour of the antiseptics.
Although Ngai et al. (2015) enrolled more people than necessary according to the power calculation, it was based on an expected rate of surgical site infections of 12%. The rate of surgical site infections was much lower than expected at around 4.5% in the 2 groups that had skin antisepsis with a single agent, meaning that the study was underpowered. The authors noted that a sample size of around 3,000 people would be needed to detect a significant difference.
Both studies were conducted at single institutions, so other aspects of care unique to the institution could have influenced the results.
The impact on the guideline is not clear because of the inconsistent results. The 2 trials do not have any obvious differences in design that would explain the higher rate of surgical site infection with povidone-iodine in 1 study but not the other. Therefore, a systematic review of studies of these antiseptic agents in an update to the guideline is necessary to determine whether there are significant differences in the effectiveness of povidone-iodine and chlorhexidine.
Intraoperative phase – triclosan sutures
We selected the systematic review by Guo et al. (2016) for a full commentary because studies of triclosan sutures have shown inconsistent results, so a systematic review and meta-analysis may give a robust estimate of the efficacy of this intervention.
No recommendations on suture material or technique were made in the guideline because of insufficient and inconsistent evidence.
The systematic review included 13 randomised controlled trials (n=5,256) of triclosan-coated sutures compared with uncoated sutures in people older than 18 years who were having surgery. Studies that included additional measures to prevent surgical site infection were excluded. Subgroup and sensitivity analyses were performed.
The overall analysis showed a significantly lower rate of surgical site infection with triclosan-coated sutures compared with uncoated sutures (RR 0.76, 95% CI 0.65 to 0.88, p<0.001; 13 studies, n=5,256). Heterogeneity was not significant and sensitivity analysis showed that removing any single study did not substantially affect the results.
In subgroup analysis, abdominal surgeries showed a significant reduction in surgical site infections with triclosan-coated sutures compared with uncoated sutures (RR 0.70, 95% CI 0.50 to 0.99, p=0.04; 5 studies, n=3,020). However, there was no significant effect of triclosan sutures in cardiac surgery (RR 0.77, 95% CI 0.54 to 1.08, p=0.13; 3 studies, n=1,207), breast surgery (RR 0.64, 95% CI 0.33 to 1.26, p=0.2; 3 studies, n=303), or 'other' types of surgery (RR 0.72, 95% CI 0.35 to 1.48, p=0.37, 2 studies, n=726).
This systematic review was generally well conducted, with many aspects quality-assured by a second author. The main results were explored further in subgroup and sensitivity analyses, which was useful in attempting to explain inconsistent results between individual studies.
Studies that used additional measures to prevent surgical site infection were reported to be excluded from analysis; however, there was no information to explain what this meant. For example, several included studies used antibiotic prophylaxis, which may be considered to be an additional measure to prevent surgical site infection.
A funnel plot was included to assess possible publication bias, which the authors noted showed no evidence of publication bias. However, there was an absence of smaller studies showing no benefit of triclosan-coated sutures, which indicates possible publication bias. The authors excluded unpublished work, so it is not possible to tell whether any such studies exist.
The new evidence suggests that triclosan-coated sutures may be associated with lower rates of surgical site infections compared with uncoated sutures when used after abdominal surgery. The evidence-base on triclosan-coated sutures has grown substantially from the single study (n=135) considered when developing the guideline to the 13 studies (n=5,256) included in this systematic review. An update to this aspect of the guideline may result in the development of recommendations on the use of antimicrobial-coated sutures.
This page was last updated: 30 January 2017