The study was conducted between July 2010 and August 2012. Approval to conduct the study was received from the Carilion Clinic Institutional Review Board. The principal investigator (PI) formed a study team of nurses who screened patients for eligibility, informed them about the study, assisted with obtaining informed consent, applied the dressings, and completed assessments according to protocol. Manufacturers’ representatives provided extensive education on purpose, use, placement, and management of the silver dressings. To maximize adherence to the protocol, researchers conducted regular information sessions with the study team.
Participants/setting. A convenience sample of 351 inpatients awaiting cardiac surgery or outpatients seen in the presurgical testing area before admission for surgery were recruited for this study. Patients were eligible if they were: 1) adults at least 21 years of age, 2) undergoing cardiac surgery requiring sternotomy incisions, 3) hospitalized at the study setting, 4) English-speaking, 5) able to understand and give consent, 6) approved by their cardiothoracic surgeon to participate, 7) not sensitive to silver, and 8) not sensitive to alginates.
The study setting was a Magnet-designated, 703-bed Level I trauma center located in the southeastern United States. The center’s cardiac surgery program began in 1982; approximately 500 patients have surgeries performed there annually. All cardiac surgeries are performed in a dedicated operating area and patients are transferred to the Cardiac Surgery Intensive Care Unit (CSICU) immediately following surgery and to the Cardiac Surgery Progressive Care Unit (CSPCU) thereafter.
Study dressings. All study dressings were approved for marketing and received US Food and Drug Administration clearance for human use. The dry sterile dressing (DSD, Primapore®, Smith & Nephew, Andover, MA) is a 1-piece, peel-and-stick, nontransparent dressing. This dressing had been used in the facility for almost 30 years (since the initiation of the cardiac surgery program). This dressing was left in place for either 24 or 48 hours per standard facility protocol; it is only water-resistant and thus does not permit the patient to shower or bathe with the dressing in place. The dressing is indicated for postoperative wounds and other minor lesion sites.13
The metallic silver dressing (MSD, Acticoat Post-Op®, Smith & Nephew, St. Petersburg, FL) is a 1-piece, peel-and-stick, nontransparent, absorbent postoperative dressing. It consists of a nanocrystalline, silver-coated polyurethane layer, a white polyurethane foam layer, and an adhesive-coated waterproof polyurethane film layer. The MSD was left in place over the incision for 5 days. This dressing is indicated for a maximum 7-day wear time for postoperative surgical wounds with light to moderate drainage.14 It can cause transient discoloration of the skin and should not be used in patients with known silver allergies. Because the dressing is waterproof, the patient may shower or bathe with the dressing in place.
The ionic silver dressing (ISD, Dermanet® Ag+, DeRoyal, Powell, TN) is a semi-transparent dressing embedded with silver, alginate, and maltodextrin. The dressing was cut to fit the incision and then covered with a transparent dressing (Transeal®, DeRoyal, Powell, TN). The dressing was left in place for 5 days postoperatively. The ISD is indicated for a maximum wear time of 5 days for infected and noninfected wounds, including ulcers, burns, skin lesions, and skin graft donor sites.15 This ionic silver dressing should not be used on patients with known sensitivity to alginates (a seaweed-based component) or on third-degree burns. This dressing is waterproof, allowing patients to shower or bathe with it in place.
Procedure. Before surgery, all participants received sterile skin preparation using 2% chlorhexidine gluconate and 70% isopropyl alcohol (ChloraPrep with Tint®, CareFusion, El Paso, TX) per the standard protocol at the authors’ institution. All participants received intravenous antibiotics within the appropriate timeframe before surgery according to guidelines published by the Joint Commission in its Surgical Care Improvement Program (SCIP-Inf-1b).16 The surgical team closed chest incisions according to individual surgeon protocols.
Interventions. All dressings were applied to participants in the operating room following incision closure. Before placement of the silver dressings, a liquid barrier product (Skin Prep®, ConvaTec, Skillman, NJ) was applied to the area around the participant’s incision and permitted to dry to enhance adherence. The dry sterile dressing was the standard care for post-sternotomy patients at the study site at the initiation of the study. In the initial 8 months of the study, the facility’s incision care protocol dictated the dressing remain in place for 24 hours postoperatively. The facility changed the dressing policy during the study, and the research protocol was modified to leave the dry sterile dressing in place for 48 hours postoperatively. The silver dressings remained in place for 5 days postoperatively or until the patient was discharged from the hospital, whichever came first, and study nurses assessed and reported outcomes at this time.
Outcomes measured. The outcome measures in this study are described in Table 1. The primary outcome measure was wound healing, defined as the degree of wound approximation, skin integrity, exudate, and presence/absence of necrotic tissue. These parameters were assessed by study team nurses at postoperative day 5 (POD 5) or day of discharge. Wound approximation was assessed as total, partial (<2 cm of superficial separation), moderate (>2 cm of superficial separation), or dehisced (complete separation of layers). Skin integrity was evaluated as normal (pink, no redness), inflamed (heat, redness, swelling), or macerated within a 2.5 cm border of the incision. Exudate quality was assessed as purulent, bloody, serosanguinous, or serous. Presence or absence of necrotic tissue was noted.17
The secondary outcome measures in this study were patient comfort, specific dressing factors, and presence/absence of sternal wound infection. Patient comfort with the dressing in place and with dressing change was measured at POD 5 or day of discharge. Comfort was measured using a verbal rating 0–10 scale, with 0 signifying no pain and 10 signifying maximum pain.18 Dressing factors of ease of application, removal, and incision assessment were measured on a 5-point Likert-type scale (1 = very easy, 2 = moderately easy, 3 = neither easy nor difficult, 4 = moderately difficult, and 5 = very difficult). A standard wall clock in the operating room was used to measure the time to apply dressings. Dressing integrity was assessed as suture line exposed, poorly sealed (imperfect covering of the suture line with the potential for organism entry), or well-sealed.17 Sternal wound infection presence and type (superficial or deep) was evaluated using Centers for Disease Control/National Healthcare Safety Network surveillance definitions.19
Study nurses completed and documented assessments of participants on a standardized, investigator-developed, paper-and-pencil data collection tool. On POD 5 or on the patient’s day of discharge, a study nurse assessed the incision and the intactness of the silver dressing. Study participants who required premature removal of their sternotomy dressings (of any type) for any reason (additional chest surgery or catheter placement, need for closer incision assessment, patient request, patient confusion) were removed from the study. No dressing was removed for infection-related concerns. The patient’s electronic medical record was accessed to determine presence, absence, and type of sternal surgical site infection at POD 30. After thorough review, the PI entered all data into an Excel spreadsheet. All data were maintained under the control of the PI in a secure office. Patient confidentiality was maintained through use of a patient list stored separately from the data collection tools.
Sample size and randomization. A sample size of 339 patients with 113 patients in each group was determined adequate to achieve 80% power at a significance level (alpha) of 0.05 to detect a difference of 10% where 85% of DSD dressing patients achieved satisfactory wound approximation compared to 95% of silver dressing patients. Due to low infection rates at the study site, it was not possible to power the study to include infection as a primary outcome.
The PI used a statistician-generated, random numbers table to assign participants to each of the 3 dressing groups. Following randomization, the PI took the appropriate dressing to the operating room and communicated the dressing assignment directly to the nursing staff. Participants were not told of their group assignment until they awakened after surgery (see Figure 1). Due to the nature of the dressings, no aspect of this study was blinded.
Statistical analysis. SPSS software (Version 14.0 for Windows, SPSS, Chicago, IL) was used for data input and analysis. Fisher’s exact chi-squares and 1-way ANOVA were used to test the hypothesis that a larger proportion of patients with silver dressings would experience satisfactory wound approximation compared to patients with standard dressings. If ANOVA test results were statistically significant for any variable, the researchers conducted further analyses on the 2 silver dressings using Tukey’s test to look at each of the pairs individually. Statistical significance level was set at P <0.05.