Effectiveness in Preventing Surgical Site Infection by Using Prophylactic Occlusive Ionic Silver-containing Dressing in Abdominal Colorectal Surgery Patients - Randomized Controlled Trial
Phase: NA
Conditions: Surgical Site Infection
Sponsor: Princess Margaret Hospital, Hong Kong

Silver dressing RCT – protocol (Version 5; 14 September 2017) 
Protocol 
Effectiveness in Preventing Surgical Site Infection by Using Prophylactic Occlusive 
Ionic Silver-containing Dressing in Abdominal Colorectal Surgery Patients – 
Randomized Controlled Trial 
 
Principal investigator: CHEUNG Chi Yeung, RN, Surgery Department, PMH  
Co-investigators: Law Siu Ming Susan, NC, Central Nursing Division (Wound & Stoma Care), PMH and 
LEE Ho Yan, RN, Central Nursing Division (Wound & Stoma Care), PMH 
 
Abstract 
Background: Ionic silver-containing dressing has been proven as a broad spectrum antimicrobial 
agent to reduce inflammation of wounds and promote healing. However, surgical incisions are usually 
dressed with conventional gauze dressing in colorectal surgery.  
Objective: To compare the effectiveness in preventing surgical site infection (SSI) by using 
conventional gauze dressing and occlusive ionic silver-containing dressing.  
Methods: This is a single-blind two-arm parallel randomized controlled trial on occlusive ionic 
silver-containing dressing conducted in Surgery Department of Princess Margaret Hospital. Two 
hundred patients who undergo emergency or elective abdominal colorectal surgery will be recruited 
and randomly assigned to have the surgical incisional wound dressed with conventional gauze 
dressing or occlusive ionic silver-containing dressing. Subjects will be assessed for SSI on day 3, 15 and 
30 after operation in a clinical visit followed by phone interviews. 
 
Background 
Surgical site infections 
According to a Clean Care is safer programme by World Health Organization(WHO), the second most 
frequent and surveyed health care-associated infections in high-income countries is surgical site 
infections (SSI). The highest SSI is the colorectal surgery with 9.5% interlude per operations [1]. SSI 
develop negative influence on patient outcome, such as burden the morbidity, mortality and extra 
expenses to health care system. The length of stay increased 9.7 days due to SSI in 2005 in USA, and 
more expenses spend on the antibiotics and the advanced dressing materials [1]. Patient suffered 
from SSI will double the mortality rate in USA with increased cost and readmission for the treatment.  
 
Modern dressing 
There are many different treatment and dressing options for health care providers for wound care. 
The dressings with advanced technology become more popular in recent days. Many studies show the 
importance of moist wound dressing to enhance the wound healing process. It can provide a moist 
wound environment, absorb the excess exudate, move away the microorganism and prevent their 
replication, and provide a barrier from the external environment than the conventional gauze 
dressing [2-4]. Besides, a recommendation from the UK’s National Institution for Health and Clinical 
Excellence (NICE) suggest that all surgical incision wound should be dressed with low-adhesive 
dressing for at least 3-5 days after operation [5]. And a journal published in CINAHL Information 

Silver dressing RCT – protocol (Version 5; 14 September 2017) 
System stated that the use of dressing with moist wound healing effects can help to reduce the SSI 
rate by 50% that the conventional gauze [6]. On the other hand, there are studies commended that 
there are no significant different in prevention of SSI with the use of moist wound dressing [7-10]. 
Therefore, it is a controversial issue on the effectiveness of preventing SSI by using moist wound 
dressing versus conventional gauze dressing. 
 
Ionic silver-containing dressing 
Ionic silver (Ag+), is an active state silver oxidized biologically, is proved as a broad spectrum 
antimicrobial agent that is effective against aerobic, anaerobic, Gram-negative and Gram-positive 
bacteria, as well as fungi, viruses, and yeast with minimal development of bacterial resistance 
[7,8,11-13]. Silver is used commonly in many dressings for the antimicrobial effect. Silver containing 
dressing can reduce the inflammation of wounds and promotes healing, since silver cations in the 
dressing can destroy microorganism by inactivating bacterial enzymes, disrupting the functions of cell 
membrane and binding the bacterial DNA/RNA to cause cell death and inhibiting cell replication [12, 
14-15]. 
 
Abdominal Colorectal surgery and ionic silver-containing dressing in Hong Kong 
In Hong Kong, colorectal cancer is the commonest cancer, there were around 5000 new cases in 2014. 
And it is the second leading cause of cancer deaths, in 2015, around colorectal cancer caused 2000 
deaths [16]. An unpublished internal audit carried out in surgical department in Princess Margaret 
Hospital (PMH) in 2015 found that the day 30 post-operation SSI incidence among patients with 
colorectal surgery using occlusive ionic silver-containing dressing (20%; 19/95) was statistically lower 
than those using conventional gauze dressing (52.9%; 9/17) with p=0.012 (Table 1). Although the 
effect of using silver dressing to reduce SSI rate is controversial, there are no formal study has been 
published locally. Therefore, it is meaningful to carry out a randomized controlled trial (RCT) to prove 
the significance of silver dressing in reduce SSI rate. 
 
Table 1. Findings of unpublished internal audit in PMH on SSI among patients with colorectal surgery 
in 2015 
 
Conventional gauze dressing  
Occlusive ionic 
silver-containing dressing 
p value 
(n=17) 
(n=95) 
SSI 
Incidence (95%CI) 
SSI 
Incidence (95%CI) 
Day 3 
1 
5.9% (1.0%-27.0%) 
2 
2.1% (0.6%-7.4%) 
0.393 
Day 15 
8 
47.1% (26.2%-69.0%) 
14 
14.7% (9.0%-23.2%) 
0.005 
Day 30 
9 
52.9% (31.0%-73.8%) 
19 
20% (13.2%-29.1%) 
0.012 
 
Objective 
To compare the SSI incidence among patients with abdominal colorectal surgery patients using 
prophylactic occlusive ionic silver-containing dressing and conventional gauze dressing. 

Silver dressing RCT – protocol (Version 5; 14 September 2017) 
Methods 
Study design and setting 
This is a single-blind two-arm parallel randomized controlled trial on occlusive ionic silver-containing 
dressing conducted in Princess Margaret Hospital (PMH). PMH is a major acute general hospital in 
Kowloon West Cluster in Hong Kong, providing 1,542 beds to maintain a wide range of specialist care. 
There are around 150 abdominal colorectal surgery provided every year in our department. Both the 
subjects, data collectors and outcome assessors will be blinded to the type of dressing being used. 
Eligible inpatients receiving colorectal surgery from the department of surgery will be consecutively 
recruited in each surgical ward (namely, A4 ward, B4 ward and CD4 ward). 
 
Subjects 
Patient aged 18 years or above will be included if they undergo abdominal colorectal operation 
including colorectal cancer case and non-colorectal cancer case such as perforated diverticulitis, 
trauma, and so on. Patients with cognitive impairment and/or with known allergic reactions to silver, 
hydrofibre or hydrocolloid and/or with non-closed wound immediate after operation will be excluded.  
 
Subjects will be randomly assigned to use occlusive ionic silver-containing dressing (experimental 
group) or conventional gauze dressing (control group) with equal probability. Blocked randomization 
will be carried out by an independent party using computer-generated random number sequences 
(www.randomization.com) in random blocks of two, four, six and eight, allocated in sequentially 
numbered, sealed opaque envelopes. Those envelopes would be prepared and placed in each surgical 
ward. 
 
Data collection procedure 
On the day of admission, or an emergency operation is offered, written informed consent will be 
obtained from all eligible patients. Patients will be arranged by an independent primary nurse in two 
groups, the experimental and control group, according to the designed block randomized sequence. 
Relevant dressing materials will be prepared by the primary nurse and bring to the operation theatre. 
In order to blind the subject, the incisional wound will be covered by ionic silver containing and 
hydrocolloid dressing with gauze covered on the top for the experimental group, whereas only gauze 
dressing will be applied for the control group.  
 
Patient’s case doctor will be responsible to document in date collection form, if there are surgical site 
infection occur. A research team is responsible for the data collection. Data obtained includes age, 
gender, pre-operative albumin level, pre- and post-operative sepsis status, operation class (elective or 
emergency), 
operation 
duration, 
number 
of 
operation, 
wound 
classification 
(clean, 
clean-contaminated, contaminated, and dirty), types of stoma raised (colostomy or ileostomy), the 
use and length of duration of antibiotics (pre op and post op). Subjects will be assessed for SSI on Day 
3, 15 and 30 after operation in clinical area and followed by phone interviews. During hospitalization, 
patient’s case doctor, who are independent to the study, will be responsible for outcome assessment. 
After patient discharge, patient will be provide the information of SSI status. Data will be collection by 

Silver dressing RCT – protocol (Version 5; 14 September 2017) 
research team via phone contact, patient will be blind to the study as well. Carers of the patient, who 
are blind to the study, will be interviewed if the patient is unable to describe their surgical site 
condition. 
 
Outcomes 
Primary outcome is the SSI on day 30 after operation, whereas secondary outcomes are day 3 and 15 
SSI after operation. In view of updating patient’s condition after the operation and removal of stitches, 
the secondary outcomes are decided on day 3 and 15 after operation. Assessment of SSI will adopt 
the basis of criteria developed by the Centers for Disease Control and Prevention (CDC) [17]. 
 
Statistical analysis 
SSI incidence and relative risk with 95% confidence interval will be computed for the experimental 
and control groups. Differences in distribution of the clinical data and the development of an SSI in 
control and experimental groups were evaluated using Pearson’s chi-square test, Fisher’s exact test, 
independent t-test or Mann-Whitney U test, where appropriate. Statistical analyses will be performed 
using SPSS 22.0 for Windows (IBM Corp., Armonk, New York). A p value <0.05 will be regarded as 
statistically significant.  
 
Sample size estimation 
With reference to our previous internal audit, we might assume the day 30 SSI incidence in the 
experimental group and control group as 20% and 40%, respectively. Using PASS 13 for sample size 
calculation, the number of subjects needed in both groups will be 80 with a power of 0.8 and a 
significance level of 0.05. Assuming the response rate to be 80%, the total sample size required will be 
200. It is estimated that the ratio of eligible patients in A4 ward, B4 ward and CD4 ward will be around 
1:2:3, therefore the number of subjects needed will be 34, 66 and 100, respectively. 
 
Ethical consideration 
The protocol of this study will be submitted to KWC Research Ethics Committee for ethical approval 
and will be registered in ClinicalTrials.gov. Patients who meet the inclusion criteria will be given a 
comprehensive explanation of the wound dressing selection, including the experimental and control 
group, and the process of treatment allocation before the start of operation as well. Patient will be 
reassured the participation is voluntary and they may withdraw at any time during the study with no 
obligations. They will also be reminded that all detected SSIs are treated immediately and 
appropriately. Patients who developed an SSI will not be withdrawn from the study and will record as 
part of the data.  
 
Data handling and record keeping 
All data are for research purposes only. The data in paper form will be kept in a locked cupboard 
inside a locked room and the electronic data will be saved in encrypted file during the study. The hard 
copies of personal data will be discarded by shredding as confidential waste and all encrypted files 
with electronic personal data will be saved in CD-Rom for storage which will be destroyed at five  

Silver dressing RCT – protocol (Version 5; 14 September 2017) 
years after completion of the study. Principal investigator will be responsible for safekeeping of 
personal data during and after the study. 
 
 
Publication 
The research is for internal review and quality improvement but the publication right is still reserved. 
 
Tentative time table 
Protocol development 
July 2017 
Application of Ethical Approval 
Aug 2017 
Start of subject recruitment and data collection 
Sep 2017  
Interim analysis 
Apr 2018 
End of subject recruitment 
Dec 2018 
End of data collection 
Jan 2019 
Data cleaning and analysis 
Feb - Mar 2019 
Report writing 
Apr - May 2019 
 
References 
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WHO, 2016. 
 
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Journal of Surgery 1994; 167(1): S2-S6. 
 
[3] Vanessa, J., Joseph, E. G. & Keith, G. H. Wound Dressings. British Medical Journal 2006; 332:777. 
 
[4] Chen, W. Y. J., Rogers, A. A. & Lydon, M. J. Characterization of biologic properties of wound fluid 
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[7] Biffi, R., Fattori, L., Bertani, E., et al. Surgical site infection following colorectal cancer surgery: a 
randomized prospective trial comparing common and advanced antimicrobial dressing containing 
ionic silver. World Journal of Surgical Oncology 2012; 10: 94. 
 

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[16] http://www.chp.gov.hk/en/content/9/25/51.html 
 
[17] Horan, T. C., Gaynes, R. P. & Martone, W.J. CDC definitions of nosocomial surgical site infections: a 
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