A rigid barrier between the heart and sternum protects the heart and lungs against rupture during negative pressure wound therapy

Lindstedt et al. Journal of Cardiothoracic Surgery 2011, 6:90 http://www.cardiothoracicsurgery.org/content/6/1/90 RESEARCH ARTICLE Open Access A rigid barrier between the heart and sternum protects the heart and lungs against rupture during negative pressure wound therapy Sandra Lindstedt*, Richard Ingemansson and Malin Malmsjö Abstract Objectives: Right ventricular heart rupture is a devastating complication associated with negative pressure wound therapy (NPWT) in cardiac surgery. The use of a rigid barrier has been suggested to offer protection against this lethal complication, by preventing the heart from being drawn up and damaged by the sharp edges of the sternum. The aim of the present study was to investigate whether a rigid barrier protects the heart and lungs against injury during NPWT. Methods: Sixteen pigs underwent median sternotomy followed by NPWT at -120 mmHg for 24 hours, in the absence (eight pigs) or presence (eight pigs) of a rigid plastic disc between the heart and the sternal edges. The macroscopic appearance of the heart and lungs was inspected after 12 and 24 hours of NPWT. Results: After 24 hours of NPWT at -120 mmHg the area of epicardial petechial bleeding was 11.90 ± 1.10 cm2 when no protective disc was used, and 1.15 ± 0.19 cm2 when using the disc (p < 0.001). Heart rupture was observed in three of the eight animals treated with NPWT without the disc. Lung rupture was observed in two of the animals, and lung contusion and emphysema were seen in all animals treated with NPWT without the rigid disc. No injury to the heart or lungs was observed in the group of animals treated with NPWT using the rigid disc. Conclusion: Inserting a rigid barrier between the heart and the sternum edges offers protection against heart rupture and lung injury during NPWT. Introduction Cardiac surgery is complicated by poststernotomy mediastinitis in 1 to 5% of all procedures [1], and is a lifethreatening complication [2]. The reported early mortality using conventional therapy is between 8 and 25% [3,4]. In 1999, Obdeijn and colleagues described the treatment of poststernotomy mediastinitis using vacuum-assisted closure [5], now called negative pressure wound therapy (NPWT). The technique entails the application of negative pressure to a sealed wound. NPWT has remarkable effects on the healing of poststernotomy mediastinitis, and has reduced the rate of mortality considerably [6]. There are, however, increasing numbers of reports of deaths and serious complications associated with the * Correspondence: Department of Cardiothoracic Surgery, Lund University and Skåne University Hospital, Lund, Sweden use of NPWT, where right ventricle rupture and bypass graft rupture resulting in death are the most devastating complications; the incidence being 4 to 7% of the patients treated for deep sternal wound infection with NPWT after cardiac surgery [7-9]. We have previously described the cause of heart rupture in pigs using magnetic resonance imaging [10,11]. The heart was shown to be drawn up towards the thoracic wall, the right ventricle bulged into the space between the sternal edges, and the sharp edges of the sternum protruded into the anterior surface of the heart [11]. Placing multiple layers of paraffin gauze over the anterior portion of the heart did not prevent deformation of the heart. However, these events could be prevented by inserting a rigid plastic disc between the anterior part of the heart and the inside of the thoracic wall [11]. The present study was conducted to investigate whether a rigid disc offers protection against heart and lung injury during NPWT. Sixteen pigs underwent © 2011 Lindstedt et al; licensee BioMed Central Ltd. This is an Open Access article distributed under the terms of the Creative Commons Attribution License (http://creativecommons.org/licenses/by/2.0), which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. Lindstedt et al. Journal of Cardiothoracic Surgery 2011, 6:90 http://www.cardiothoracicsurgery.org/content/6/1/90 median sternotomy followed by NPWT at -120 mmHg for 24 hours, in the absence (eight pigs) or presence (eight pigs) of a rigid plastic disc between the heart and the sternal edges. In the present article we measure epicardial bleeding after NPWT of a sternotomy wound. Petechial refers to one of the three major classes of purpuric conditions. The most common cause of petechial is through physical trauma. In the present article we believe that the epicardial bleeding is caused by trauma from the NPWT. The macroscopic appearance of the heart and lungs was inspected and the area of epicardial petechial bleeding was measured after 12 and 24 hours of NPWT. Material and methods Animals A porcine sternotomy wound model was used. Sixteen domestic landrace pigs with a mean body weight of 70 kg were fasted overnight with free access to water. The study was approved by the Ethics Committee for Animal Research, Lund University, Sweden. All animals received humane care in compliance with the European Convention on Animal Care. Page 2 of 5 rigid plastic disc inserted between the heart and the sternum. A polyurethane foam dressing with an openpore structure was trimmed so as to be slightly larger than the wound. The first layer was placed between the sternal edges. A second layer of polyurethane foam dressing was placed between the soft tissue wound edges. The wound was sealed with a transparent adhesive drape and connected to a vacuum source set to deliver a continuous negative pressure -120 mmHg. Experimental procedure The pigs were divided into two groups of eight animals. In one group a rigid barrier disc was inserted between the heart and the sternum before the application of NPWT, while the other group was exposed to NPWT without a disc. The animals were treated with a continuous negative pressure of -120 mmHg for 24 hours. The NPWT dressing was changed after 12 hours. The heart and lungs were inspected with regard to injury after 12 and 24 hours. The length and width of the area affected by petechial bleeding on the epicardial surface were measured and the area was calculated (Figure 1). Calculations and statistics Anesthesia and surgery Premedication was performed with an intramuscular injection of xylazine (Rompun ® vet. 20 mg/ml; Bayer AG, Leverkusen, Germany; 2 mg/kg) mixed with ketamine (Ketaminol® vet. 100 mg/ml; Farmaceutici Gellini S.p.A., Aprilia, Italy; 20 mg/kg). Before surgery, a tracheotomy was performed and an endo-tracheal tube was inserted. Anesthesia was maintained with a continuous infusion of ketamine (Ketaminol® vet. 50 mg/ml; 0.4-0.6 mg/kg/h). Complete neuromuscular blockade was achieved by continuous infusion of pancuronium bromide (Pavulon; N.V. Organon, Oss, the Netherlands; 0.3-0.5 mg/kg/h). Fluid loss was compensated for by continuous infusion of Ringer’s acetate at a rate of 300 ml/kg/h. Mechanical ventilation was (...truncated)