The impact of VAC Therapy on management of sternal wound infections after cardiac surgery - Literature review Example

of the of the Nursing June 8, A Literature Review about the impact of VAC Therapy on management of sternal wound infections after cardiac surgery Introduction Sternal wound infection after cardiac surgery is a serious problem resulting in increased patient morbidity; mortality and duration of hospital stay (Luckraz et al 2003). The infection may become chronic and have significant repercussions in terms of pain, cost and quality of life. Expensive antibiotic therapy and repeat surgical procedures will cause significant economic morbidity in addition to pain (Popov et al 2011; Graf et al 2010). The incidence of this infection has been variably reported as 0.5 to 5% and the resultant mortality as 10 to 25% (Sjogren et al 2006; Schimer et al 2008). Conventionally, many management techniques have been recommended to treat this complication like surgical debridement with open dressings, closed irrigation of the infected wound, or reconstruction with vascularised omental or pectoral muscle flaps (Domkowski et al 2003). Vacuum assisted closure (VAC) therapy is one of the newer modalities to treat this complication (Evans & Land 1997) which has been widely adopted. Application of negative pressure was successfully used for treating chronic wounds such as diabetic foot ulcers (Eneroth & van Houtum 2008; Ubbink et al 2008). After it was found successful in achieving faster healing in these wounds, use of this therapy has been extended for the management of sternal wound infections as well (Luckraz et al 2003; Domkowski et al 2003; Hersh et al 2003; Sjogren et al 2006). However, it hasn’t been proven yet with good evidence that its efficacy is more than the conventional treatment (Raja & Berg 2007, Ubbink et al 2008). Thus, the main objective of this review is to determine the effectiveness of vacuum assisted closure therapy in the management of wound infection after cardiac surgery. The therapy being reviewed In vacuum assisted closure therapy, also called negative pressure therapy, negative pressure is created to drain exudate fluid from the wound and this alters the wound in such a way mechanically that healing is hastened (Evans & Land, 1997). It has been said to decrease bacterial colonization of the wound and promote granulation tissue proliferation (Hersh et al 2001). Also, it allows re-examination of the wound and bedside debridement, as and when required. To apply negative pressure, wound area is packed with special dressing (polyurethane sponge/foam or polyvinyl alcohol foam) and covered with a transparent tape which seals the wound. A drain tube passes through this tube which is connected to a vacuum tube which sucks out the fluid through this drain tube. Negative pressure applied is in the range of -75 to -125 mm Hg (MAS 2006). Conventionally, medical (antibiotics) and various surgical modalities have been used in the treatment of deep sternal wound infections (DSWI) (Singh, Anderson & Harper 2011). Surgical management options include closed suction antibiotic irrigation system, omental flap reconstruction, pectoralis major, latissimus dorsi or rectus abdominis muscle advancement or rotation flap, and microsurgical free flap. Early wound exploration is combined with any of these techniques. Regimen of sternal fixation with sternal plating system is also getting popular (Singh, Anderson & Harper 2011). Traditional methods of wound care involve regular cleaning and dressing of the wound different kinds of dressing materials from simple gauzes to chemical impregnated gauzes as per the type of the wound. However, VAC therapy is being projected as one solution for multiple wound types. Search strategy A manual search was conducted for the journals, books and other data related to the subject. Internet was also accessed for searching for journal articles pertaining to the subject. CINAHL database via the EBSCO host platform was utilized to perform a literature search because it is the most wide-ranging nursing database and is easy to search. MEDLINE and COCHRANE database was also searched. Key words were a combination of vacuum assisted closure therapy, VAC, topical negative pressure (TNP) ‘and’ cardiac surgery, CABG, cardiothoracic surgery, thoracic surgery ‘and’ postoperative wound infection, deep sternal wound infection (DSWI), postoperative mediastinitis. The search was for observational studies and trials that provided information about impact of VAC therapy on clinical outcomes. Search yielded various articles and the inclusion criteria for the article to be included in the review were based on recent articles between the years 2005 & 2012, published in English in peer reviewed journals, human trials, and sample size. Five papers were selected for this literature review (Lee et al, 2005, Bapat et al, 2008, Simek et al, 2008 & 2011 and Sjogren et al, 2008). All of these articles deal with the use of VAC therapy in treatment of postoperative sterna wound infections after cardiac surgery. The articles chosen were published in peer reviewed journals and were well referenced. They were chosen depending upon the extent of their literature search, study quality, research methodology and publication bias (Burnes & Groves 2009). Sample sized ranged between 9 patients (Lee et al 2005) to 62 patients (Simek et al 2008) and the studies were longitudinal in that the same patients were observed over a period of time. This study design is appropriate when a patient related intervention is being used and the data is recorded over multiple time periods (Cowman et al 2008). The available evidence will be analysed and summed up in terms of efficacy (morbidity, mortality, long term survival & duration of hospital stay), safety (complications) and cost effectiveness to answer the question that whether there is a role of routine application of VAC therapy in the management of wound infections in cardiac surgery setting. Baseline characteristics, Study design & sampling In order for conclusions to be drawn from a study and its application to the clinical practice, the study must be representative of the population the results are intended for. Ideally, the baseline characteristics of the patients should be similar, the cohorts of the patients should be studied in the same time period, randomly selected and studied in a prospective manner, and power of the study should be adequate. If sample size is less, errors creep in and the evidence will be weak. This has been the flaw in most of the studies dealing with VAC intervention in the management of DWSI. Bapat et al determined an incidence of 1.9% DSWI in their study. The incidence of sternal wound infection was 1.39% in the study of Simek et al (2011) and 0.9% in the study of Sjogren et al (2008). Rest of the authors did not mention about the incidence of DSWI in their setting. For a study to assess the effect on an intervention related to wound infection, the incidence of wound infection should be noted as it may pertain to the quality of disinfection, microbial level hygiene and nursing care aspects such as hand washing and dressings change. These factors which caused the infection in the first place may then impact upon the performance and effectiveness of the intervention being studied. Also, the intrinsic factors which are likely to impact wound healing such as the nutritional status of the patient, diabetes, immunosuppressive therapy, renal impairment etc. should be assessed for the patients to make the groups comparable. Simek et al (2011) identified 58% patients with diabetes in their study. Similarly, Simek et al (2008) mentioned in their article that no significant difference was observed in patients’ demographic and operative characteristics, making their study groups comparable. The centre for disease control (CDC) criteria as proposed by Garner et al (1988) was adopted by Sjogren et al (2008) and Bapat et al (2008)to diagnose DSWI. Others authors have not mentioned the criteria followed to establish the diagnosis of DSWI. The grading commonly used to classify postoperative mediastinitis was proposed by El Oakley and Wright (1996). This grading to classify DWSI was used by Sjogren et al (2008), Lee et al (2005) and Simek et al (2008). Even though, the demographic data was similar in early and late group as studied by Sjogren et al (2008), the late group had a higher Oakley grade of the wound as compared to the late group. This surprisingly did not have any influence on the mortality and the survival which they had set out to measure with their study was similar in both the groups. Also, the details of preoperative antibiotic prophylaxis and the antibiotic regimen followed after the diagnosis of infection have been mentioned only by Sjogren et al (2008). Lee et al (2005) reported a series of 9 patients who received VAC therapy to achieve healthy wounds with vascularised beds. Surgical reconstruction was then performed to attain closure. Only patients who developed refractory deep sternal wound infection after primary closure were included in the study. However, their case series has an inadequate number of patients and power of the study to be able to draw any meaningful conclusions from the study. Bapat et al (2008) conducted a prospective observational study and recruited 49 patients with sternal wound infection. They divided patients into 4 groups of deep or superficial sternal infection treated solely with VAC therapy or with VAC therapy plus surgery. These studies did not perform any comparative analysis with the patients treated with conventional therapy in the same hospital setting. The only study in this review which did this comparison was by Simek et al (2008). Simek et al (2008) studied 62 patients who underwent treatment for DSWI at their institution during study period. Out of these patients, first 28 patients consecutively underwent conventional treatment and next 34 patients underwent TNP. However, again the limitation of this study was the small number of patients treated, although larger than the other studies. To have an adequate power of the study, they should have recruited at least 90 patients. Moreover, the patients were not treated in the same time period, that is, synchronously. This can lead to the confounding effect of the learning curve of the surgical technique and the management of that particular infection. A study specifically conducted to assess the impact of learning curve on the outcomes following VAC therapy has revealed no impact (Sjogren et al 2008). This, however, needs more confirmation before it can be extrapolated to other surgeons and hospital settings. In fact, their study can be compared to that of Sjogren et al (2005) who performed a similar comparative study between conventional and VAC therapy. The study by Sjogren et al (2005) had a large sample size but suffered from the same possibility of bias in that the patients were treated and data was collected in different time frames. Simek et al (2011) reported their experience with first line application of TNP on 50 consecutive patients. Sjogren et al (2008) conducted a study to assess the impact of learning curve of VAC therapy on survival and to identify the predictors of mortality in patients of DWSI treated with VAC. They divided patients into early (26 patients) and late (27 patients) groups. None of the studies were randomised trials resulting in diminished quality and strength of evidence gathered from the trials. The authors however defended this fact by arguing that it is seldom possible for the trials like these and in these settings to be randomised (Sjogren et al 2008). Similarly, no blinding has been mentioned in any of the trials regarding the assessment of the wounds and application of the technique in wounds treated by conventional therapy or VAC. In the study by Bapat et al (2008) decision to apply VAC alone or VAC followed by surgical reconstruction was based on wound characteristics and surgeon’s choice. Also, the retrospective nature of the trials and the earlier mentioned factors make the quality of evidence low and suspect and the studies cannot be really compared due to different aims, characteristics, outcomes, study designs and analysis. Treatment regimen In the series of Lee et al (2005), patients were initially treated with conventional methods. In those with persistent infection, extensive debridement was followed by 125 mm negative pressure application. Every other day, the dressing was changed. On an average, 2.2 debridements were done and 20.2 days was the average duration for which TNP was applied. 2 patients received exclusive VAC therapy while the rest went under surgical reconstruction procedures post VAC. Bapat et al (2008) surgically debrided all patients on diagnosis and placed VAC on the debrided wounds. Dressing change was done every 48 hours. In both the studies, Simek et al (2008 & 2011) followed the similar protocol of surgical debridement and TNP application every 48 hours till granulation tissue was healthy. Chest was closed when C reactive protein (CRP) dropped below 30 mg/l. However, in their later study Simek et al (2011) introduced a newer VAC technique in which negative pressure therapy is combined with intermittent instillation of antiseptic irrigation solution. This difference in the therapy technique has obvious implication on the state of bacterial colonisation and consequently, rate of healing. Sjogren et al (2008) performed dressing change 3 times a week and a level of CRP between 50 and 70 mg/l was used to support the decision to stop VAC therapy and/or close the chest. Thus, in all of these studies no consistent criteria have been adopted to stop the treatment. The decision has been variably guided by the state of the wound and the granulation tissue which is a very subjective measurement and prone to observer bias, and the level of CRP whose levels again differ in guiding the closure of the chest. Thus, the question of how long the VAC therapy should last remains unanswered by these studies. Outcome measures including adverse events In Lee et al series, two of the nine patients died due to flap related procedures. One patient died due to aorta rupture due to severe mediastinitis, which the authors correlated to insufficient duration of TNP. This directly contrasts with the finding of Bapat et al (2008) who determined that the patients who had prolonged VAC therapy had more wound related complications and their patients who had briefest periods of VAC followed by earliest possible surgical closure had no problems. Main focus of Bapat et al (2008) was to report chronic sternal wound complications after prolonged use of VAC. Length of hospital stay was recorded. Twenty three patients of superficial sternal wound infection received VAC therapy alone which was prolonged (17 to 38 days). Four patients of this group died, although authors have considered the causes unrelated. Nine patients needed surgical procedures for treatment of recurrent problems with the wound. Five patients who had VAC therapy followed by earliest possible surgical closure had no problem. Twelve patients of deep sternal infection received prolonged VAC therapy. Four of them died (3 due to infection related complications, 1 due to right ventricular rupture) and the remaining 8 had recurrent wound healing problems. Debridement under GA was required in these patients which in turn led to prolonged hospitalisation (median length 57 days). In the last group of deep sternal infections, VAC was applied followed by earliest possible surgical repair. One patient died due to septic complications and remaining 8 remained free of any problems. In the study of Simek et al (2008) although duration of primary therapy was less in conventional group, the failure rate of primary therapy was also higher in this group. Overall, duration of therapy was comparable in both the groups. In hospital mortality, ICU stay and 1 year mortality was significantly less in the TNP group. One patient died of bleeding complications and 1 died because of multiorgan failure in TNP group. Six patients died of septic complications and 1 patient died of bleeding complications. Their later study (2011) revealed mean length of TNP therapy 12.6±8 days, 5.4±2.5 dressing changes and duration of hospitalisation38.1±14.6 days. Four patients died, 3 from multiorgan failure and 1 from bleeding right ventricle. 30 day mortality was 4%, in hospital mortality was 8 % and 1 year mortality was 14 % and although they did not compare these results concomitantly with another group treated with conventional therapy, these results show an improvement over previous conventional therapy results. Sjogren et al (2008) reported zero percent ninety day mortality in both early and late groups. All patients underwent sternal rewiring without any flap procedure or VAC related complications. No significant difference in the duration of VAC therapy and hospitalisation (median 20.5 and 21 days respectively) between 2 groups. There were18 deaths in total at the follow up. Survival was comparable in both groups. Univariate analysis could not identify any variable which was different between survivors and non survivors. However, multivariate analysis identified 2 independent predictors of late mortality. These were the number of days between cardiac surgery and the diagnosis of DWSI and the duration of VAC therapy. Both were significantly increased in the patients who died. They did not encounter the complication of right ventricular rupture. This could be due to their method of using paraffin gauze or slicon dressing as an organ barrier to prevent adhesions between heart and VAC foam. Thus, so far as complications are concerned, mostly these studies reported about the rupture of right ventricle which is a major complication, fatal sepsis and related complications such as multi organ failure along with other chronic complications such as osteomyelitis and sinus formation. Bacteriological analysis revealed predominantly gram positive bacteria in study by Lee et al (2005) and Bapat et al (2008). Staph aureus and coagulase negative staphylococcus aureus was found by simek et al (2008). No significant differences between the 2 groups (conventional vs TNP) were found in simek et al. This spectrum of bacteriological findings could have an implication on the rate of wound healing. So far as the follow up period of these studies is concerned, surviving patients were followed up for 35 months in Lee’s series. The variable monitored was recurrence of wound infection. Bapat et al (2008) followed patients every 3 to 6 months for earlier detection of chronic wound problems. The duration for which this was done has not been mentioned in their article. One year follow up was done by simek et al (2008) and follow up was done after 3 and half years of completion of the study period. None of the studies could comment on the 5 year survival rate. Only one of these studies conducted a cost analysis (Simek et al 2008) and found the cost as 208 Euros per dressing change. There is no data from any other studies in this review to compare the validity of their results. Statistical analysis The nature and type of statistical analysis was not mentioned for Lee et al (2005) and Bapat et al (2008). Kaplan Meier actuarial analysis plot for survival was plotted by simek et al in both their studies (2011 & 2008). Continuous variables were expressed as mean ± SD and categorical variables were presented as absolute numbers as well as percentages and were compared by chi square test and Fisher exact test. Continuous data was analysed with Student?s t test or Mann-Whitney test. Thus, all the applied statistical tests were in line with the recommendations and existing protocols. Sjogren et al (2008) used univariate analysis with Student’s t-test for continuous variables. Fisher’s exact test was used for categorical variables if the expected frequencies were less than 5. Multivariate analysis was used to determine the independent predictors of late mortality after treatment of DSWI with VAC. In order to compare the difference in survival between the two groups, log-rank test was used. Statistical analysis was performed with the Intercooled Stata version 9.2 statistical package (Stata Corporation, TX) by Sjogren et al and with SPSS for Windows (version 14, SPSS Inc. Chicago, USA) by Simek et al (2008). A P value < 0.05 was considered significant by both the authors. Even though, the statistical analysis is appropriate, the basic flaws in the study designs with inadequate power, lack of randomisation and blinding, possibility of different biases and heterogeneous mixture of the studies included in this review, it is not possible to draw any results with conviction about the routine application of VAC therapy in DSWI. Conclusions drawn Lee et al (2005) hypothesised that infection persists due to collection of the exudates at the bottom of the wound. Negative pressure acts against gravity and removes these exudates from the wound. No significant conclusion can anyhow be achieved by such a small series of patients. After their results, Bapat et al (2008) changed their approach from prolonged VAC therapy to VAC therapy followed by earliest possible closure of wound by surgical methods. They postulated that prolonged use of VAC can cause deeper infections such as sternal osteomyelitis. Their recommendation calls for further research into effects of long term TNP. Also, their approach appears to be in direct conflict of Lee et al who recommended early and adequate debridement followed by TNP till the infection is fully cured before surgical reconstruction. From their results, Simek et al (2008 & 2011) concluded that TNP therapy has reduced rates of therapy failure, and short and midterm mortality and recommended its first line application for DSWI management in cardiac surgery. Conclusion Although, many studies and trials have demonstrated benefits of using VAC therapy in deep sternal wound infections, conclusive evidence is still lacking regarding its effectiveness in this particular setting. More randomized controlled trials comparing this therapy with conventional management are needed for the evidence that application of negative pressure leads to increased healing in deep sternal wound infections after cardiac surgery. Other outcomes such as safety and cost effectiveness also need to be addressed in the future research. As the therapy has been widely adopted, there are implications for nursing practice as well. Nurses are involved in all aspects of wound care. Preoperative aseptic preparation, intraoperative asepsis and maintenance of sterility, postoperative infection control measures and wound infection surveillance are the measures which go a long way in preventing deep sternal wound infections in the first place. So far as VAC therapy is concerned, nurses should be aware of the therapy being used, its application and evidence related to its use. As it is, more effective and faster wound healing will have a positive influence on utilisation of human and capital resources. Reference list Bapat, V, El-Muttardi, N, Young, C, Venn, G & Roxburgh, J 2008, ‘Experience with vacuum-assisted closure of sternal wound infections following cardiac surgery and evaluation of chronic complications associated with its use’, Journal of Cardiac Surgery, vol. 23, pp. 227-233. Burns, K & Groves, S 2009, 6th Edn, The Practice of nursing Research. Appraisal, synthesis and Generation Evidence, Saunders Elsevier, USA. Cowman, S, Keady, J, Mckenna, J & Watson, R 2008, Understanding Nursing Research, designs & Method, Churchill Livingstone, Philadelphia. 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