Silver-Based Dressings in the Prevention of the Incisional Surgical Site Infection: A Prospective Multicenter Observational Controlled Trial

Abstract

Background:

A new silver-based dressing has been designed to reduce surgical sited infections.

Patients and Methods:

A prospective multicenter observational study was conducted from January 2020 to October 2021. Patients with and without silver-based dressing after surgical incision were observed and their data analyzed. The study aimed to assess the incidence of incisional surgical site infection and primary healing after general surgery procedures.

Results:

Overall, 218 patients with silver-based (n = 109) and conventional silver-free dressing (n = 109) were analyzed. Surgical site infection (SSI) and primary incision healing were reported in 10 (9.2%) versus 21 (19.3%) (p = 0.037) and in 95 (87.2%) versus 86 (78.9%) (p = 0.107) patients treated with and without silver-based dressing, respectively.

Conclusions:

Silver-based dressing demonstrated a lower incidence of incisional SSI and improved primary healing in comparison with patients in whom conventional non-silver–based dressing has been used.

The silver dressing is a generally accepted treatment for not only contaminated surgical incisions but also for therapy of diabetic foot ulcers, burns, chronic venous leg ulcers, and others. The principle is based on the antimicrobial effect of silver in its ionic form, where an aqueous environment such as wound exudates favors activation of silver into silver cations (Ag+). There are many products containing silver in different forms, such as alginate, film, cream, gauze, hydrocolloid, hydrofiber, hydrogel, powder, and others. Some of the examples of many products are Algicell Ag^® (AllegroMedical, Bolingbrook, IL), Melgisorb Ag^® (Mölnlycke Health Care, Peachtree Corners, GA), Mepilex Ag^® (Mölnlycke Health Care), and Aquacel Ag^® (Convatec, Oklahoma City, OK).¹

One of the new silver-based antimicrobial dressing StopBac^® (Grade Medical, Prague, Czech Republic) has been tested in the two previous Czech studies. Those studies have reported favorable outcomes in reducing surgical site infection (SSI). They also confirmed a lower frequency of changing dressings and excellent patient tolerance with satisfactory handling by healthcare professionals.^2,3 However, both studies have weakness in a low number of patients and are missing a control matched group. The present study aimed to compare the incidence of incisional SSI and primary healing between patients treated with and without silver-based dressing after general surgery procedures. We test a hypothesis that the novel silver-based dressing decreases the incidence of superficial surgical site infections and improves primary healing.

Patients and Methods

Study characteristics

A prospective multicenter observational study was conducted from January 2020 to October 2021 and was approved by the ethics committee. Data of patients with incisions dressed with or without silver dressing were collected and analyzed. Four surgical departments of university hospitals from the Czech Republic participated in the study: University Hospital Královské Vinohrady in Prague, Thomayer University Hospital in Prague, the University Hospital Olomouc, and the University Hospital Brno. The recruitment of the patients was consecutive, and the application of the silver-based dressing was randomly applied in a ratio of 1:1. The follow-up of the patients was during their hospital stay and after being discharged from the hospital. The follow-up was finished when the incision had healed completely.

Inclusion criteria

All consecutive patients who underwent elective or urgent general surgical procedures via open or laparoscopic approach. The definition of surgical procedure follows that of the World Health Organization.⁴

Exclusion criteria

Patients who were admitted and diagnosed with an already infected wound, non-compliant patients, patients who were severe acute respiratory syndrome coronavirus-2 (SARS-CoV-2)-positive, patients enrolled in other studies, and patients allergic to silver were excluded. All patients who died or had to undergo re-operation in the first 30 days post-operatively were also excluded from the analysis. Prisoners and pregnant women were not involved in this study.

Dressing technique and post-operative care

All patients included in the study had the surgical site dressed either with silver-based dressing StopBac or with standard non-silver gauze. The dressing was first applied immediately after the surgical procedure when the incision was closed in the operating room. The patients received the same type of dressing until the incision was completely healed and stitches extracted or until SSI was established.

If the healing course was uncomplicated, the first change of silver-based dressing was not done until three days after surgery. If the SSI was suspected SSI before three days, the dressing was changed sooner. Depending on the findings during the first and each other change of dressing, the physician in charge decided whether to apply the silver dressing again or in the case of good healing, to keep the wound uncovered by any dressing. If SSI was diagnosed, the physician recorded the day when the SSI appeared and details of the local finding. Once the diagnosis of SSI was established, the frequency of dressing change and local care was customized to the local finding according to the physician in charge.

The control group received standard of care. The patients treated with non-silver gauze had their incisions treated according to the local findings and the customs of the surgical departments. The frequency of dressing change depended on the local finding and the physician in charge. The local findings were carefully observed, and every dressing was recorded. If an SSI appeared, the day and details of local findings were documented.

There were no alterations in the use of antibiotic, anticoagulation, or immunosuppressive therapy in the silver-based group and the control group. Both groups received a non-altered standard of care. The prophylactic and therapeutic use of antibiotic agents followed the customs of the surgical departments. The prophylactic use was administered for maximum of 24 hours for procedures on gastrointestinal tract, hepato-pancreato-biliary procedures, and breast resection for carcinoma, whereas the first dose was administered usually 30-60 minutes (in certain cases 120 minutes) prior to surgery. The antibiotic agents of first choice were cephazolin or amoxicillin-clavulanate or ampicillin-sulbactam or metronidazole. If the patients were allergic, a different antibiotic agent was used. The doses were accommodated to the patient's weigh and renal functions. The therapeutic use of antibiotic agents was applied when diagnosis of infection was established. The type of antibiotic agents was indicated individually, based on local finding, antimicrobial screening, result of sample cultivation and sensitivity to antibiotic agents, and patient's allergy.

Definition of outcome parameters

The diagnosis of SSI was made following the definition of the U.S. Centers for Disease Control and Prevention⁵ and was established as the primary outcome parameter. The secondary outcome was primary incision healing, and the tertiary outcome was an adverse effect of the dressing. Adverse effect was defined as any type of incision complication not including SSI or incision healing and causing discomfort to the patient.

Statistical analysis

Data analysis was performed using software R version 4.1.2.⁶ An exploratory data analysis was performed for all parameters. Continuous parameters were tested using the Shapiro-Wilk test. If the test was not significant (p > 0.05), the parameters were considered normally distributed and are reported as mean and standard deviation. Non-normally distributed continuous parameters are presented as median with 25th and 75th percentile. Categorical parameters are reported as counts and frequencies. Comparisons of normally distributed continuous parameters were made using Welch t-test. If the parameters were not distributed normally, a Wilcoxon unpaired test was used. Comparison of categorical parameters was made using χ² or Fisher exact test. Fisher exact test was used if the expected frequencies of the χ² test were below five. We performed univariable logistic regression for primary and secondary outcomes (binary parameters SSI and primary healing). For SSI, the time-to-event analysis was further performed by using the Kaplan-Meier method and log-rank test.

We also performed a multivariable logistic regression for SSI and primary healing, where we adjusted the use of silver dressing on confounders and outcome predictors, to eliminate their effect on the outcome if they were non-equally distributed between the silver dressing group and the control group, and predictors of the outcome. We defined confounders as parameters associated (p < 0.1 in univariable analysis) with both the use of silver dressing and outcome parameters (SSI, primary healing) and outcome predictors as parameters associated with the outcome only (primary healing, SSI; Supplementary Figure S1). For SSI, univariable and multivariable Cox regression was performed. We used forward and backward stepwise approaches for the selection of the final multivariate model (both logistic and Cox). Results of models are expressed as odds ratio (OR) in case of logistic regression or hazard ratio (HR) in case of Cox regression and 95% confidence interval (CI). A p value <0.05 was considered statistically significant. Finally, the fragility index for the primary outcome (SSI) was calculated.

Power analysis

The frequency of incisional SSIs after general surgery procedures are reported in the literature as ranging from 12% to 22%.^7–10 Because we expected a high number of urgent procedures and contaminated wounds in our study centers, the anticipated incidence of SSI was 20%. We expected a reduction of SSIs in the silver-based cohort by two-thirds, which was calculated as 13%. The power analysis calculation estimated a necessary number of patients as 107 in each group with the required number of patients in a total of 214 (for α 0.05 and power 0.8). We aimed to screen a higher number of patients as we expected approximately 10% dropout.

Results

Patient recruitment

A total of 244 patients were screened in the study; 10 patients were excluded from our study. Eight patients were considered non-compliant, one patient developed SARS-CoV-2, and one patient was enrolled in another study. No patient had an allergy to silver. Two hundred thirty-four patients were recruited, 116 in the silver-based dressing group and 118 in the control group. Seven patients from the silver-based dressing group were excluded (three underwent re-operation and four died). Nine patients were excluded from the control group (eight underwent re-operation and one died). There were 218 patients who had their data analyzed further (Fig. 1).

FIG. 1.

Flowchart demonstrating patients' inclusion.

Baseline characteristics

One hundred nine (50%) patients received standard of care and 109 (50%) patients received silver-based dressing. All patients were involved in the analysis and all patients were followed up until the incision was completely healed. One hundred fourteen patients were male and 104 patients were female. The male to female ratio was 1.1:1, p = 0.28. The mean age was 60.4 years (standard deviation [SD] ± 16.0). The average patient body mass index was 26.7 (SD ±4.9). Statistical difference was noted between the silver-based dressing group and conventional dressing in a varicose vein, cancer, chemotherapy treatment, use of alcohol, pancreatic, gallbladder, biliary tract and liver cancer, appendicitis, cholecystectomy, and liver resection. In terms of the type of wound, clean-contaminated wound was noted more frequently in the silver-based group (74 [67.9%] vs. 55 [50.5%]; p = 0.009), contrary to contaminated wound, which was more noted more frequently in the control group (10 [9.2%) vs. 23 [21.1%]; p = 0.017).

Prophylactic use of antibiotic agents before surgery was documented in 79 patients (72.5%) in the silver-based dressing group and 76 patients (69.7%) in the control group, p = 0.65. The antibiotic agents after surgery were reported in 26 (23.9%) and 29 cases (26.6%), in the silver-based and in the control group, respectively, p = 0.64. The median number of days during which patients were treated with antibiotic agents was 1 (0; 1.0) in the silver-based dressing group and 1 (0; 1.2) in the control group (p = 0.72). Details regarding patient characteristics, diagnosis, comorbidities, medication, types of surgeries, and types of wounds are presented in Table 1.

Table 1.

Patient Baseline Characteristics

Parameter	Silver-based group n (%)	Non-silver-based group n (%)	p
Comorbidities
Arterial hypertension	49 (45%)	53 (48.6%)	0.587
Diabetes mellitus	28 (25.7%)	23 (21.1%)	0.424
Ischemic heart disease	11 (10.1%)	12 (11%)	0.826
Peripheral arterial disease	5 (4.6%)	2 (1.8%)	0.445^a
Varicose vein	25 (22.9%)	13 (11.9%)	0.032
History of peripheral vein thrombosis	11 (10.1%)	5 (4.6%)	0.119
Dyslipidemia	34 (31.2%)	34 (31.2%)	1.000
Cancer	71 (65.1%)	51 (46.8%)	0.006
Smoking	29 (26.6%)	38 (34.9%)	0.186
Alcohol	75 (68.8%)	44 (40.4%)	0.000
Medication
Anticoagulation	54 (49.5%)	42 (38.5%)	0.102
Immunosuppression	5 (4.6%)	3 (2.8%)	0.721^a
Chemotherapy	21 (19.3%)	7 (6.4%)	0.005
Antibiotic agents before surgery	79 (72.5%)	76 (69.7%)	0.654
Antibiotic agents after surgery	26 (23.9%)	29 (26.6%)	0.640
Diagnosis
Pancreatic cancer	30 (27.5%)	14 (12.8%)	0.007
Bowel cancer	16 (14.7%)	26 (23.9%)	0.086
Hernia	13 (11.9%)	18 (16.5%)	0.332
Gallbladder, biliary tract, and liver cancer	22 (20.2%)	6 (5.5%)	0.001
Appendicitis	5 (4.6%)	16 (14.7%)	0.012
Cholecystolithiasis, cholecystitis	6 (5.5%)	12 (11%)	0.140
Other diagnoses	9 (8.3%)	10 (9.2%)	0.810
Other bowel diagnoses	8 (7.3%)	7 (6.4%)	0.789
Procedure
Urgent procedure	26 (23.9%)	39 (35.8%)	0.054
Procedure on intestine	30 (27.5%)	45 (41.3%)	0.032
Pancreatic resection	31 (28.4%)	15 (13.8%)	0.008
Hernia repair	13 (11.9%)	20 (18.3%)	0.186
Cholecystectomy	6 (5.5%)	15 (13.8%)	0.039
Liver resection	14 (12.8%)	2 (1.8%)	0.002
Other procedures	15 (13.8%)	12 (11%)	0.537
Type of wound^b
Type 1: Clean	20 (18.3%)	27 (24.8%)	0.250
Type 2: Clean-contaminated	74 (67.9%)	55 (50.5%)	0.009
Type 3: Contaminated	10 (9.2%)	23 (21.1%)	0.017
Type 4: Dirty	5 (4.6%)	4 (3.7%)	0.734

Note: p values are calculated using χ² test unless marked with ^a where p values are calculated using Fisher exact test.

Type of wound is by the definition of the U.S. Centers for Disease Control and Prevention.

Outcome parameters

Univariate analysis: SSI

Information regarding SSI incidence was available for all patients. It was established in 31 cases (14.2%). Ten patients (9.2%) had silver-based dressing and 21 patients (19.3%) had non-silver-based dressing (χ² test; p = 0.033). Silver-based dressing revealed less SSI in 30-day follow-up compared with the control group (OR, 0.42, 95% CI, 0.18–0.93; p = 0.037; HR, 0.45; 95% CI, 0.21–0.96; p = 0.038), log-rank test p = 0.033, Supplementary Figure S2; see Kaplan-Meier curve on Figure 2.

FIG. 2.

Kaplan-Meier curves display surgical site infection in time for silver-based group and control group including 95% confidence intervals. The number of patients at risk at different time points is displayed on the graph. The log-rank test indicates a significant difference between the curves. Black = silver-free dressing group, Gray = silver-based dressing group.

Primary healing

All patients had type of healing documented. Ninety-five patients (87.2%) had their incision healed primarily in the silver-based cohort and 86 patients (78.9%) in the control group, (χ² test p = 0.104). Logistic regression of primary healing versus silver-based dressing showed OR 1.82 (95% CI, 0.89–3.83; p = 0.11; Supplementary Figure S3).

Adverse effects

Side effects of incision dressings were identified only in two patients in the non-silver–based group. Those patients developed mild and moderate signs of local allergic reactions to the dressing. There was no report of allergic or other undesirable skin reactions among patients treated by silver-based dressing.

Multivariable analysis: SSI

Identified confounders (parameters associated with SSI and silver dressing) were cancer, chemotherapy, pancreatic resection, and liver resection. Binarized wound type (type 1 and 2 versus type 3 and 4) was considered a confounder for its clinical importance despite a non-significant association with SSI and primary healing (p = 0.144). For silver-based dressing adjusted OR was 0.28 (95% CI, 0.11–0.67; p = 0.006), adjusted HR was 0.33 (95% CI, 0.15–0.73; p = 0.006; Table 2; Supplementary Tables S1 and S2). Identified outcome predictors were primary healing, diabetes mellitus, history of thrombosis, diagnosis of hernia and hernia repair, antibiotic agents before and after surgery, and complications. Parameters excluded for high correlation were primary healing, complications, diagnosis of hernia, and hernia repair. Parameters that were found in multivariable analysis to be strongly non-significant were also excluded.

Table 2.

Multivariable Regression Models for SSI and Primary Healing

Multivariable logistic regression analysis for SSI
Variable	Adjusted OR	p
Silver-based dressing (yes vs. no)	0.28 (95% CI, 0.11–0.67)	0.006
Wound type (3 + 4 vs. 1 + 2)	0.2 (95% CI, 0.04–0.7)	0.022
Antibiotic agents before operation (yes vs. no)	10.9 (95% CI, 2.13–200.1)	0.022
Antibiotic agents after the operation (yes vs. no)	4.82 (95% CI, 2.0–12.2)	0.001
History of thrombosis (yes vs. no)	4.4 (95% CI, 1.1–16.0)	0.025

Cox regression analysis for SSI
Variable	Adjusted HR	p
Silver-based dressing (yes vs. no)	0.33 (95% CI, 0.15–0.73)	0.006
Wound type (3 + 4 vs. 1 + 2)	0.26 (95% CI, 0.08–0.9)	0.032
Antibiotic agents before operation (yes vs. no)	9.6 (95% CI, 1.3–71.5)	0.028
Antibiotic agents after the operation (yes vs. no)	3.7 (95% CI, 1.8–7.8)	<0.001
History of thrombosis (yes vs. no)	3.1 (95% CI, 1.1–8.6)	0.027

Multivariable logistic regression analysis for primary healing
Variable	Adjusted OR	p
Silver-based dressing (yes vs. no)	2.62 (95% CI, 1.18–6.11)	0.021
Wound type (3 + 4 vs. 1 + 2)	3.59 (95% CI, 1.14–13.64)	0.041
Varices (yes vs. no)	0.32 (95% CI, 0.12–0.84)	0.018
Diabetes mellitus (yes vs. no)	0.57 (95% CI, 0.25–1.37)	0.199
Antibiotic agents before operation (yes vs. no)	0.39 (95% CI, 0.11–1.13)	0.109
Antibiotic agents after operation (yes vs. no)	0.21 (95% CI, 0.09–0.51)	0.001

OR = odds ratio; HR = hazard ratio; SSI = surgical site infection; CI = confidence interval.

Results of the multivariable logistic regression analysis for SSI: adjusted OR with 95% CI.

Results of the Cox regression analysis for SSI: adjusted HR with 95% CI.

Results of the multivariable logistic regression analysis for primary healing: adjusted OR with 95% CI.

Primary wound healing

Identified confounders (parameters associated with primary healing and silver dressing) were SSI, chronic venous disease, chemotherapy, pancreatic resection, and liver resection. Identified outcome predictors were diabetes mellitus, antibiotic agents before and after surgery, and complications. Parameters excluded for perfect prediction of outcome were SSI and complications. Parameters that were found in multivariable analysis to be strongly non-significant were also excluded. Multivariable logistic regression of primary healing versus silver-based dressing adjusted for confounders showed that adjusted odds ratio was 2.6 (95% CI, 1.18–6.1; p = 0.021).

Number of dressings

The median number of dressings in total in the silver-based group was two (interquartile range [IQR], 1;3, range 1–12). In the control group, the median number of dressings was three (IQR 2;4.8, range 1–21), p = 0.037 (Wilcoxon rank-sum test; Supplementary Figure S4).

Post-operative complications

Recorded complications in the silver-based dressing cohort were two urologic infections, non-inflammatory collection in the abdominal cavity, pancreatic fistula, biliary leak, and heart failure. The complications reported in the control group were one abdominal non-inflammatory collection, bleeding necessitating successful radiologic intervention, delayed gastric emptying, and pancreatic fistula. The remaining complications in both groups were related to the SSIs and are reported above.

Discussion

Because incision infection remains a significant cause of morbidity and mortality¹¹ with increasing bacterial resistance to antibiotics,¹² the effort of finding an ideal protocol to prevent incision infections and improve healing is immense. Silver-based dressings have been used in medicine for many decades.^13,14 Initially it was used predominantly in burn surgery and gradually spread throughout other surgical fields. Silver-based dressing found its place in healing chronic and infected wounds.¹⁵ Several studies demonstrated a beneficial effect on pain relief, decreased frequency of dressing changes, decreased wound odor, and cost-effectiveness.^16–19 The recommendations for using silver-based dressing are however controversial. Results of some studies do not support improved healing or lower incidence of infections. Most of the studies, however, reported the low quality of available evidence.^19–21

In 2009, Lo et al.¹⁹ published a meta-analysis on the effectiveness of silver-releasing dressings on a non-healing chronic wound. They selected eight randomized clinical trials (RCTs) and analyzed data for 1,366 patients. They demonstrated significantly improved wound incision healing, as well as reduced odor, pain-related symptoms, incision exudates, and prolonged wear time.

A Cochrane Review from 2010 involving 26 RCTs with 2,066 patients (20 studies on burns, six studies on acute, chronic, non-surgical wounds, and surgical incisions) reported insufficient evidence on improved healing and prevention of wound infection of silver-containing dressings. The overall methodological quality of the studies was low. The majority of the studies had less than 80 participants and a high or uncertain risk of bias.²⁰

In 2011, Krieger et al.²² reported a significant reduction of superficial and deep SSI incidence in their prospective randomized study with 110 patients. Their study compared silver nylon versus standard gauze after colorectal surgeries.

In 2012, Leaper et al.¹ published the international consensus document on the appropriate use of silver dressings in wounds. The authors reviewed all available evidence and published recommendations for the use of silver-based dressings. They recommend silver-based dressing use for the initial two weeks on infected wounds. After two weeks, the wound, the patient, and the management should be re-evaluated and if infect continues but with improvement, continued use of silver-based dressing is recommended. If there is no more sign of an infection, the recommendation is to discontinue the use of the silver-based dressing. If there is no improvement, the use of silver-based dressing should be discontinued. However, they recommend that silver-based dressings should not be used unnecessarily on wounds, where bioburden is not a problem, which applies to clean wounds that are not at high risk of infection.

In 2017 Li et al.²¹ presented a systematic review and meta-analysis of RCTs focusing on silver-based dressing for SSI in clean and clean-contaminated operations. Their analysis involved nine studies with a total of more than 2,000 patients. The results did not confirm decreased incidence of SSI in patients treated with silver-containing dressings compared with patients treated with silver-free dressings. The authors evaluated the evidence and available studies as being of very low quality with recommendations for further higher-quality studies.²¹

In 2018, researchers in The Netherland published their results with carboxymethylcellulose dressing after breast cancer surgery on 230 women. Although the silver dressing did not substantially reduce the incidence of SSI, they reported better patient satisfaction, fewer dressing changes in the first 48 hours after surgery, fewer re-operations, and lower mean wound-related treatment costs.²³

Our study focuses on the new silver-based antimicrobial dressing, StopBac. The dressing consists of an organic-inorganic hybrid oligomer containing silver cations in silver nitrate colloid solution. It has a hybrid nanolayer prepared with a sol-gel method. The antibacterial sol is applied on an upper side of composite medical dressing in contact with the incision by using spray atomization. The unique modern technique using advanced nanotechnological procedures ensures the exact height of the hybrid nanolayer. This layer warrants the controlled ions release ensuring a long-lasting antimicrobial effect. The sol itself provides mechanical protection. The hybrid matrix also demonstrates hydrophobic properties, which further supports the creation of conditions unsuitable for bacteria and other micro-organisms and minimizes the risk of adherence to the incision and its traumatization. The effective absorbent properties enable a lower frequency of dressing that additionally prevents the incision from bacterial contamination.³ It can be applied for up to five to seven days on clean wounds (Fig. 3).

FIG. 3.

StopBac dressing. Perforated mat with antibacterial treatment: three-dimensional perforated low-density polyethylene with low wound adhesion and one-sided drainage of fluid and organic-inorganic hybrid oligomer nanolayer purposed for sustained release of Ag ions. Hypoallergenic binder: non-irritating hot-melt adhesive. A highly absorbent layer: a mixture of bicomponent fiber processed by air-laid technology. Transparent carrier film with an adhesive thermoplastic film based on polyurethanes, covered with a solvent-free acrylic copolymer. Handling foil: polyethylene foil purposed for easier handling of the dressing by personnel (removed during application).

Results of our study revealed the incidence of SSI after common general surgery procedures were lower in patients with silver-based dressing compared to patients treated with casual silver-free gauze. This supports the theory that the new antimicrobial silver-based dressing can decrease incisional SSIs after surgical procedures. Its effect on improved healing was also shown. After adjusting the analysis on confounders, the results were statistically significant.

The main confounder in the multivariable analysis was the binarized wound type (types 1 and 2 and types 3 and 4). Types 3 and 4 were less represented in the silver-based group (13.8% vs. 24.8%; p = 0.039; Supplementary Figure S5). Wound types 1 and 2 had a paradoxically higher risk of infection in the studied population in comparison to wound types 3 and 4 (15.9% SSI vs. 7.1%), although marginally insignificant (p = 0.144; Supplementary Figure S6).

Pre-operative and post-operative use of antibiotic agents was homogeneously distributed between the silver-based group and the control group (72.5% vs. 69.7%; p = 0.65 and 23.9% vs. 26.6%; p = 0.64, respectively; Table 1). However, patients with wound types 3 and 4 had higher use of antibiotic agents after the surgery (50% vs. 19.3%; p < 0.001; Supplementary Figures S7 and S8). That is probably the reason why wound type 1 and 2 are at higher risk of SSI and non-primary healing in our study population than wound types 3 and 4.

We could think that the pre-operative and post-operative use of antibiotic agents were paradoxically significant risk factors for the development of SSI in our population (OR >1). This is probably not because the use of antibiotic agents would lead to a higher frequency of SSI, but because of a decision by physicians who indicate antibiotic agents more often in wound types 3 and 4.

The statistical significance of the effect of silver-based dressing on SSI and primary healing increased in the multivariable analysis, after the adjustment on the type of the wound. In this case, the wound type acts as a special type of confounder, a suppressor that partially masks the effect of the silver-based dressing. Silver-based dressing also has approximately the same effect, 11% decrease in SSI, for wound types 1 and 2 (10.6% vs. 22%; p = 0.041) and types 3 and 4 (0% vs. 11.1%; p = 0.54; Supplementary Figure S9). The difference in wound types 3 and 4 was not statistically significant despite the similar effect size as in the wound type 1 and 2.

In previous non-controlled studies with StopBac, the authors reported zero and one SSI. In the first case, the authors presented a prospective observational study with 21 patients who underwent planned clean procedures. All incisions were healed primarily. The total number of dressing changes was an average of 4.2 (±0.7).² The second study reported a case series of 32 patients who underwent hepato-pancreato-biliary, colorectal, or hernia repair surgery. This cohort represented aseptic and potentially contaminated wounds. The only case of SSI was in a patient who developed a pancreatic fistula after pancreatic resection, which drained into the surgical site. The average number of dressings in that study was 1.8 (median, 2; range, 1–3). Our study involved a variety of wounds from clean to dirty, and the incidence of SSI in the silver-based dressing group was in 10 patients (9.2%) and the median of dressing changes was two (IQR 1;3, range, 1–12). Our study confirms the results of the previous two studies, which is decreased number of SSI. The difference in several dressing can be probably explained by different protocols of dressing change used in the studies.

We have been able to demonstrate a statistically significant reduction of necessary dressing changes after operation. The decreased necessity of frequent wound changing makes the dressing popular among health care professionals and patients. Non-hospitalized patients particularly can benefit from its easy, infrequent use when caring for their incisions at home with a limited supply of dressing materials.

The dressing claims that its glue is hypoallergenic. As our cohort of 109 patients did not report any cases of allergic reaction to this dressing, we can support this statement.

Our study provides favorable results for the use of this silver-based dressing in general surgery. On the contrary, some of the abovementioned studies focusing on silver-based dressings do not support our outcomes. Our results are in concordance with previously published Czech studies. For a better understanding of our results, a well-designed prospective RCT with this dressing is recommended.

The probable cause of the reported positive results of the silver-based dressing is the combination of properties given by the specific production technology of the manufacturer. Optimal kinetics of silver ion release are essential to achieve a long-lasting antibacterial effect to ensure minimal inhibitory concentration in the wound, but while minimizing the naturally cytotoxic effect of silver on human cells. The manufacturer declares a long-lasting antibacterial effect and the results obtained do not contradict this. The indicated sol-gel technology is often used for the synthesis of silver nanoparticles,^24,25 which have been shown to have a weaker but long-lasting antibacterial effect and lower cytotoxicity,²⁶ however, available technical data on StopBac dressing does not allow an evaluation of the possible contribution of this form of silver.

The limitation of the present study is its observational character and no implementation of a randomization method. Although the physicians randomly assigned patients into groups, there was a non-equal division of surgery procedures and diagnoses in the groups (Supplementary Figures S1, S10, and S11). The fragility index was one and therefore one more diagnosis of SSI in the silver group within the same cohort size would lead to a not statistically significant difference in univariable analysis. The next considerable weakness of this study could be its open nature because the involved physicians were not blinded to the method of treatment. Because of the clinical nature of this trial, the blinded method was not practically applicable here. The standard of care in each surgical department could differ in some ways, which could be another possible source of bias. We also clarify that our study involved only incisional SSI and not organ/space SSI because the focus of the study was on the local effect of the wound dressings.

Conclusions

The silver-based dressing seems to be an effective method for primary incision dressing after a general surgery procedure that was confirmed with a lower incidence of SSI and better primary healing of the incision in comparison with standard non-silver-based dressing.

Footnotes

Authors' Contributions

Investigation: Lawrie, Baláž, Drozd, Loveček, Klos, Skalický, Kurečková, Kráčmar, Kala, Makajevová, Hodačová, Šimša. Validation: Lawrie, Drozd, Loveček, Klos, Skalický, Kurečková, Kráčmar, Kala, Makajevová, Hodačová, Šimša, Gürlich. Writing original draft: Lawrie, Waldauf, Baláž. Review and editing draft: All authors. Conceptualization: Gürlich. Resources: Gürlich.

Funding Information

No funding was received.

Author Disclosure Statement

Petr Btat'ka worked for GRADE MEDICAL s.r.o. All remaining authors declare no conflicts of interest.

Supplementary Material

References

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