The impact of closed incision negative pressure therapy on prevention of median sternotomy infection for high risk cases: a single centre retrospective study

Sternal wound infection (SWI) is a devastating postoperative complication for any patient [1]. Despite the recent advances in cardiac surgery, the rate of sternal wound complications has seen minimal improvement [2]. SWI has a reported incidence between 0.5 and 10% and has an associated 1-year mortality of 0.5 to 9% [2, 3]. We have reported previously a deep sternal wound infection (DSWI) incidence of 0.59% with an associated 1-year mortality rate of 9.1% with older age, obesity, diabetes and chronic obstructive pulmonary disease (COPD) as the associated risk factors in our department [4].

There is currently no universal guideline for the treatment of SWI [1]. However, recent studies have reported a reduced incidence of SWI complications in centres utilizing closed incision negative pressure therapy (ciNPT) [2]. The ciNPT system is a closed system that can maintain an intact environment. Compared to a standard sterile dressing, the ciNPT canister can hold excess fluids removed from the incision. It may be used over anatomically challenging incision locations whilst maintaining its seal, thus minimizing the risk from external contamination. The ciNPT unit is small so a patient can mobilise freely and the ciNPT dressing is waterproof allowing the patient to shower with the dressing in place [5].

This study aims to assess the effect of ciNPT use over a closed incision post-median sternotomy on the incidence of sternal wound infection (SWI) in high-risk patients with two or more risk factors with focus on the hypothesis that the use of ciNPT would reduce the rate of infection.

The clinical and economic burden of wound infection particularly in cardiac surgery has shifted focus to prevention rather than treatment alone [7]. This clinical investigation was a retrospective study to evaluate the clinical benefit of ciNPT among high risk patients who underwent cardiac surgery. In our dataset, we have demonstrated that the application of ciNPT to manage sternal incisions among patients with ≥2 risk factors may lower the incidence of SWIs with patients having longer postoperative stay if they develop an infection..

The absence of consensus concerning the clinical efficacy and broader adoption of ciNPT after median sternotomy is constrained by several factors, such as the dearth of medical literature and the lack of large and robust health economic studies. Incision management modalities that employ subatmospheric pressure are generally more expensive than standard care, and controversy arises as to whether the wider use of ciNPT would significantly mitigate SSI risk and reduce the economic burden posed by post-sternotomy SSIs.

SWI is a debilitating postoperative complication for patients, and we have reported previously an incidence of DSWI of 0.59% with an associated 1-year mortality rate of 9.1% with older age, obesity, diabetes or respiratory compromise as risk factors [4]. According to consensus recommendations by Willy et al. [8], obesity (BMI ≥ 30 kg/m2), diabetes mellitus, respiratory insufficiency, and tobacco use were among the most common patient comorbid risk factors that elevate the risk of SSI development. In their two-centre (n = 996 patients) randomized controlled trial (RCT), Schimmer et al. [9] identified a preoperative BMI > 30 kg/m2 as an independent predictor for an increased rate of sternal surgical site infections (SSI). However, Allen et al. [10] demonstrated via a multivariate exact logistic regression model that BMI was not a significant predictor of sternal complications and SSIs. Our previous work identified 4 risk factors (age, BMI, COPD and diabetes) that elevated the incidence of post-sternotomy SWIs [4]. The patient is considered high-risk for developing SWI if they have 2 out of the 4 risk factors identified [4]. Diabetes and obesity represented the most common comorbidities in the study cohorts; however, patient demographics and comorbidities were similar between control and ciNPT cohorts. The current study also takes into consideration a patient’s critical preoperative state by calculating the logistic EuroSCORE to assign a preoperative mortality risk grade. Although we had identified a statistical significance comparing mean logistic EuroSCORE of the overall control cohort versus the ciNPT study cohorts this was not the case for the High Risk Groups.

Select surgical procedures present an elevated risk of delayed healing that can foster the development of an SSI. As sternotomy is characterized as a high-risk incision, complications after CABG and the harvest of bilateral internal thoracic arteries or mammary arteries can be considered operation-related risk factors [9, 11]. CABG was the most common cardiac procedure in our study indicating an elevated surgical risk factor of the development of SWI in our study population.

Few studies have been conducted on the use of ciNPT as a preventative measure in cardiac surgery, although they have yielded positive results. Some of these studies focused on the high-risk population group [12, 13]. Agarwal and colleagues [14] recommended that ciNPT be considered as a standard treatment for patients with SWI.

However, this trial focussed solely on treating patients, who had developed complication with the sternal incision, as opposed to mitigating the incidence of this complication [14].

Grauhan et al. [5] assessed the effect of ciNPT on incision management in 150 consecutive obese patients undergoing sternotomy. The patients were split into two groups, those who received conventional dressing (n = 75) and those who received ciNPT (n = 75) [5]. Significantly lower rates of infection were reported in the ciNPT group compared to the control group [5]. Grauhan et al. [15] followed up this research with a further trial looking at the effect of ciNPT in a general population of post-sternotomy patients (n = 237) compared to a historical cohort that received conventional dressings (n = 3508). The authors found the ciNPT group had a significantly lower infection rate compared to the historical control group [15]. The authors found that the ciNPT group had a significantly lower infection rate compared to the historical group (1.3% for ciNPT vs. 3.4% for control; P ≤ 0.05) [15]. In our study, ciNPT had a lower infection rate among patients with 2 or more risk factors Our results appear to match those reported in the current published literature. The positive impact of the ciNPT might be a result of enhanced tissue perfusion facilitated by applying ciNPT to the sternal incision which may promote healing and sequestere the incision from external contamination; thereby, accounting for the reduced incidence of SWI among ciNPT patients.

The management of deep SWI after cardiac surgery represents a persistent challenge and can extend hospitalization. Protracted length of hospitalization is associated with the incidence of SSIs, evidenced by patients affected with an SSI after undergoing cardiac surgery spending an additional 23 days in hospital [16]. In a review of data of 999 consecutive patients who underwent coronary artery bypass grafting (CABG) during a 24-month period, Findeisen et al. [17] evaluated protracted LOS due to SSIs.

The SSI-related mean additional LOS was estimated to be 9.3 days [17]. In a retrospective, nonrandomized review of patients receiving median sternotomy procedures, Miyahara et al. [18] reported significantly longer length of intensive care unit (ICU) stay and hospital LOS in patients with deep SWI. In our study, the mean extended LOS for ciNPT was shorter than the control group (11.4 days for ciNPT vs. 218.4 days for control). Further, we report that the mean post-operative LOS of patients with superficial SWI in the ciNPT group was longer, which might be accounted for by the larger number of acute patients enrolled in the ciNPT group as evidenced by an elevated EuroSCORE. There was no further analysis done to identify whether the patients experienced a longer LOS due to ciNPT use or patient EuroSCORE.

Poststernotomy surgical site occurrences, particularly SSIs exert a significant pecuniary impact on individual patients, healthcare systems, and resource utilization. Not all patients require ciNPT, individuals at high-risk for complications have been reported to receive cost-effective clinical benefit from ciNPT use [10, 17]. Nussbaum et al. [19] characterized surgical infection and surgical wounds among the most prevalent and the most expensive (ranging from $11.7 to $38.3 billion) wound aetiologies. Individual Medicare spending per wound costing $3364 + $2604 ($5968) to $14,153 + $6585 ($20,738) for Medicare beneficiaries in 2014 [19]. Limited evidence exists regarding economics aspects of ciNPT use in the post-sternotomy population. Grauhan et al. [15] considered the economic aspects of ciNPT in post-sternotomy patients. Their report suggested that comprehensive use of ciNPT in Germany would yield an annual cost of approximately €30,000,000, which would represent an appreciable reduction from the avoidable economic loss of €60,000,000 to €90,000,000 associated with patients with 302 wound infections requiring surgical revision [15]. Citing the additional 23 days in hospital and additional cost of £11,003.31 for SSI following cardiac surgery, Philip et al. [16] recommended ciNPT be given consideration for patients at risk of developing post-sternotomy SSIs. This was compared to three representative cases of post-sternotomy SSIs at their institution where patient LOS was extended by 12–25 days and additional costs ranging from €12,214 to €22,456 [16]. This is obviously can be extended to our patient population although we have not conducted a detailed financial implication analysis.

SWI following cardiac surgery is a recognised major complication. In this study, ciNPT reduced the incidence of SWI after median sternotomy in patients at an elevated risk for developing SWI. Reduced SWI incidence may result in a shorter inpatient hospital stay, a decreased rate of mortality, and tentatively reduced financial cost although not demonstrated in this study. Nonetheless, our results indicate that ciNPT can be a valuable tool in reducing the incidence of SWI in high-risk patients.