Asian Cardiovasc Thorac Ann 2006;14:452-457
© 2006 Asia Publishing EXchange Ltd
Pneumatic Pump Reduces Leg Wound Complications in Cardiac Patients
Cally K L Ho, MRCS,
Man Ping Sun, BSc,
Timmy W K Au, FRCS,
Clement S W Chiu, FRCS
Division of Cardiothoracic Surgery, Department of Surgery, Grantham Hospital, The University of Hong Kong, Hong Kong, China
For reprint information contact: Cally KL Ho, MRCS, Tel: 852 2518 2639, Fax: 852 2553 3436, Email: callykalai{at}yahoo.com, Division of Cardiothoracic Surgery, 3/F Grantham Hospital, 125 Wong Chuk Hang Road, Hong Kong, China.
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ABSTRACT
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Leg wound complications at the site of vein harvest for coronary artery bypass graft, although infrequent, cause significant morbidity. Pneumatic pressure therapy is valuable in venous and lymphatic diseases, but its usefulness after leg vein harvest has not been determined. A prospective randomized controlled trial was conducted on 200 patients, half of whom had sequential pneumatic leg pump therapy postoperatively. Wound healing, extent of lower limb edema, patient satisfaction, and the financial implications of pneumatic pressure therapy were assessed. In the study group, 71 patients had satisfactory wound healing vs. 23 in the control group. The leg wound infection rate in the study group was 3% vs. 15% in the control group ( p = 0.003). Lower limb edema was significantly reduced in the study group in the early postoperative period ( p < 0.05), and the mean postoperative length of hospital stay was reduced by 2.6 days in patients given pneumatic pressure therapy ( p = 0.003). The sequential pneumatic leg pump is an effective, inexpensive, and convenient device that reduces leg wound complications after coronary artery bypass grafting.
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INTRODUCTION
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Despite a general preference for arterial grafts, saphenous vein grafts are still the most commonly used vascular conduit for coronary revascularization. Many patients requiring coronary artery bypass grafting (CABG) are smokers or have diabetes mellitus (DM), peripheral vascular disease (PVD), obesity, or renal failure, which all predispose to leg wound complications. Previous reports have focused on sternal wound infection; very few discussed leg wound complications, which may result in substantial morbidity and increased costs. The incidence of leg wound complications after CABG ranges from 1% to 44%.1 The risk factors for leg wound infection include obesity, advanced age, female sex, PVD, and DM. There have been some studies on intraoperative techniques to improve wound healing, such as skin closure methods and use of saline lavage, but few on postoperative methods.2,3 Pneumatic pressure therapy is effective in the treatment of lymphedema, post-thrombotic venous ulcers, and prevention of thromboembolism.4,5 After CABG, there is often edema at the leg vein harvest site. Improvement in venous function can reduce edema and thus improve wound healing. Blackshear and colleagues6 hypothesized that the use of sequential pneumatic compression would improve venous function by direct mechanical pressure on the vessel wall or by the Venturi effect through increased velocity in the vena cava, but there has been no study on its usefulness in reducing leg wound complications in patients undergoing CABG.
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PATIENTS AND METHODS
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A prospective randomized controlled trial of 200 patients was carried out from January 2000 to August 2001. The study protocol was approved by the hospital’s Research Ethics Committee, and informed consent was obtained from all participants. Data were collected by the Outcome Management Working Group of the Cardiothoracic Surgical Unit. Briefing sessions were organized for group members to standardize their skills of data collection and instrument usage. Demographic data including sex, age, body mass index, and risk factors comprising left ventricular ejection fraction (LVEF), history of DM, PVD, renal impairment, smoking, preoperative serum albumin, and hematocrit were recorded. Operative characteristics including EuroSCORE, length of hospital stay, cardiopulmonary bypass time, aortic cross clamp time, number of vein grafts used, total units of red blood cells transfused, use of an intra-aortic balloon pump (IABP), leg wound drain, postoperative morbidity, and hospital mortality were noted.7
Patients undergoing elective isolated CABG with the great saphenous vein harvested from the lower leg to above knee level were included. Those with physical or psychological disturbances or contraindications to leg pumping (severe PVD, uncompensated cardiac failure, renal failure, deep vein thrombosis, acute inflammatory skin disease, or malignancy of the lower limbs) were excluded. Randomization of patients to the study or control groups was carried out by drawing lots. Those assigned to the study group had sequential pneumatic leg pump therapy during the postoperative period. All patients were given prophylactic ceftriaxone 1 gm on induction, then every 24 hr intravenously, until all surgical drains were removed, unless further indication for continued antibiotic usage was found postoperatively. Those allergic to penicillin or the cephalosporin group of antibiotics were given vancomycin 500 mg instead. Vein harvest sites were prepared with 10% povidone-iodine solution, allowed to dry, and draped. Conventional open venectomy with one long continuous incision over the course of the vein was performed in all patients. Hemostasis was achieved with diathermy and ligation of the branches with 3/0 silk, the subcutaneous layer was closed with 2 layers of 0/0 Vicryl, and the skin was closed with 3/0 Monocryl subcuticular suture or metal clips. The procedures were performed by either cardiothoracic fellows or trainees, using the same technique in all patients. The Vasoflow 200 (Medizintechnik GmbH, Germany) 3-chamber gradient system was used for pneumatic leg pumping (Figure 1
). The sleeves were filled with air from the distal to the proximal chambers until the assigned pressure (20–70 mm Hg for 15 min) was attained. The air was released in all chambers simultaneously and the cycle was repeated. During the 30 min procedure, patients were lying semi-supine with the leg elevated by 30 degrees; their subjective feelings and vital signs were monitored.
The ASEPSIS score, which is a fully evaluated wound scoring method, was used in this study.8 It is composed of objective and subjective criteria, and was devised specifically for cardiac surgery. Points are given for additional treatment such as antibiotics, drainage of pus and debridement of the wound, the presence of serous discharge, erythema, purulent exudates, separation of deep tissues, isolation of bacteria, and prolonged hospital stay of more than 14 days. The wound condition was divided into 5 categories according to ASEPSIS score: satisfactory healing, disturbance in healing, minor wound infection, moderate wound infection, and severe wound infection. In this study, an ASEPSIS score of 21 or above was classified as wound infection. For assessing edema of the lower limbs, standard tape measurements were taken at 2 points on the venectomized lower limb: the mid calf, 5 cm below the tip of the patella; and at the ankle, 10 cm above the sole, around the medial and lateral malleolus. Any increase in circumference above the preoperative baseline was documented.
All CABG patients with lower limb vein harvest were offered elastic stockings, given elevation therapy, and recommended exercise during postoperative days 1 to 7. Those in the study group received additional sequential pneumatic leg pump therapy for 30 min daily from postoperative day 3 to 5 (30 mm Hg on day 3, 40 mm Hg on day 4, 50 mm Hg on day 5). Wound assessment and measurement of lower limb edema were carried out prior to application of the leg pump (Table 1). Patient satisfaction with the use of the leg pump was measured using the Likert scale, with 1 being excellent and 5 being very unsatisfactory.
Statistical analysis was carried out using SPSS version 10.0 software (SPSS Inc., Chicago, IL, USA). All continuous variables were measured as group means and standard deviations. Categorical and dichotomous variables were analyzed by the chi-squared test. Continuous variables were analyzed by the independent sample t test or Fisher’s exact test if low event frequency occurred. A p value less than 0.05 was considered to be statistically significant.
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RESULTS
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There were 100 patients in each group, the mean age of the study group was younger than the control group ( p < 0.05); otherwise, there were no significant differences in demographic data or risk factors between the 2 groups (Table 2). The mean EuroSCORE was higher in the study group than in controls ( p < 0.05). More surgical trainees were involved in vein harvest in the control group ( p < 0.05). There were no significant differences in the other operative variables (Table 3). Most of the patients (71%) in the study group had satisfactory wound healing, while in the control group, most (62%) had disturbed wound healing (Table 4). Only 3% of the study group had a wound infection compared to 15% of the control group. The overall leg wound infection rate in our study was 9%. All patients with wound infection had either minor or moderate degree of infection according to the ASEPSIS score; however, two of them needed wound exploration and debridement under local anesthesia. It was found that use of the leg pump reduced leg wound infection 5-fold. Seventeen of 18 infected leg wounds had positive bacterial cultures. Of the causative organisms, 29% were methicillin-resistant Staphylococcus aureus, 24% were methicillin-sensitive Staphylococcus aureus, 24% were methicillin-sensitive coagulase-negative staphylococci, 12% were Pseudomonas, 6% were Acinetobacter, and 6% were Enterobacter. Only one patient with a clinically infected wound had no culture-positive bacterial growth. With risk factor analysis of the infected and non-infected group (Table 5), use of the leg pump was the only significant factor in leg wound infection ( p = 0.003); the other common risk factors were not significantly different between the two groups.
Use of the leg pump caused a significant reduction in edema over the ankle and mid calf compared with that of the control group ( p < 0.05) during the early postoperative period (Figure 2). On the Likert scale, 52 of the 100 patients in the study group were satisfied with the use of the pump: 44 found it excellent; 3 had no comment after the treatment; and only one was dissatisfied. The mean postoperative length of hospital stay in the study group was 10.5 days (range, 6 to 27 days; mode, 8 days); in the control group it was 13.1 days (range, 6 to 44 days; mode, 10 days; p = 0.001). There was a difference of 2.6 days in the mean postoperative hospital stay between the 2 groups. Before 2003, the daily maintenance rates in a general ward at The Grantham Hospital was HK$3,300 and the extra cost for CABG patients with leg wound infection was HK$8,580 per patient. In addition, there was an increase in dressing frequency in patients without leg pump treatment, which added to the financial burden on the healthcare system.
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Figure 2. The mean (with 95% confidence interval) increase in calf circumference in (A) the study group, (B) the control group, and the increase in ankle circumference in (C) the study group and (D) control group. For both parameters, p < 0.05 for the study group vs controls on postoperative days 4 to 7.
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DISCUSSION
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Vein harvest sites in CABG patients are prone to edema and local complications due to the systemic inflammatory response after cardiopulmonary bypass, impaired venous drainage, and extensive lymphatic and soft tissue damage; all these lead to significant fluid accumulation in the interstitial space, poor tissue oxygenation, and thus poor wound healing. Pneumatic pressure therapy is a standard treatment for venous and lymphatic diseases.4–6 Mechanical compression enhances the venous and lymphatic drainage over the lower extremities, hence reducing edema and improving microcirculation in the cutaneous tissue. We postulated that by reducing edema, there would be improved tissue approximation in the wounds, and wound tension would be decreased. Moreover, with increased lymphatic drainage, there should be less tissue fluid around the wounds and this would reduce the culture medium for bacterial growth. With these hypotheses, we proposed that use of pneumatic pressure therapy would enhance wound healing and reduce leg wound complications in CABG patients.
A limitation of this study is that the observer, who was a nursing officer, was not blinded to which patients had leg pump therapy. With such a big machine, it was difficult for anyone taking care of the patients not to know who was having such therapy. However, this limitation was recognized and the assessment was carried out using objective criteria. A better method that we could use in the future would be to assess individual patients by two different assessors each time; although time consuming, observer bias could be minimized. Lower limb infection rates in CABG patients vary among studies, ranging from 1% to 44%.1 The infection rate is dependent on the definition of wound infection. One study included only patients with a limb-threatening condition or those requiring additional surgical intervention on the lower limb.9 Rosenfeldt and colleagues10 utilized the Centers for Disease Control and Prevention definition to classify superficial and deep-wound infection. Very often the diagnosis of wound infection was based on the surgeon’s discretion. We adopted the ASEPSIS score for wound infection as it is objective and universally accepted.
A number of seriously ill patients were excluded from our study because of underlying uncontrolled medical conditions that contraindicated the use of a leg pump. This group might be more prone to wound complications. Olsen and colleagues11 identified an old cerebrovascular accident, postoperative transfusion > 5 units, obesity, female sex, and advanced age as independent risk factors for leg wound infection in their retrospective analysis of 1,689 patients. Paletta and colleagues12 noted a minor leg wound infection rate of 4.1% in 3,525 CABG patients, of whom 0.65% required additional surgical treatment for lower leg wound complications. The major risks factors identified as contributing to wound complications were female sex, PVD, and postoperative IABP. However, we failed to show any independent risk factors contributing to leg harvest site infection; use of the leg pump was the only independent factor contributing to the reduction in leg wound infection.
Our results are compatible with those of other major studies demonstrating that lower limb infection leads to significant morbidity, a greater burden on healthcare, and less patient satisfaction. It was concluded that sequential pneumatic leg pumping reduces leg wound complications during the early postoperative period after saphenous vein harvest.
The long-term effect of this inexpensive and convenient procedure should be further assessed by recruiting a larger number of patients, and with a longer follow-up period.
Presented at the 13th Annual Meeting of the Asian Society for Cardiovascular Surgery, Chiang Mai, Thailand, February 5–8, 2005.
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ACKNOWLEDGMENTS
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We thank all our nurses for their assistance in application of the leg pump. We thank Dr. Mansha Khemlani for proofreading the paper.
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REFERENCES
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ABSTRACT
INTRODUCTION
