Mediastinitis is a life-threatening condition with an extremely high mortality rate if recognized late or treated improperly. Although small in proportional terms (one out of one hundred post-sternotomy), the actual number of patients affected by mediastinitis is substantial (1% of 300,000 equals 3000). This significantly increases mortality and cost.
Even though poststernotomy mediastinits is considered by the Department of Health and Human Services as a "never event" it will still occur. Hopefully, it will decrease to a much smaller (though I doubt ever be a "never") in number event. Prevention guidelines—The CDC surgical site infection prevention guidelines are backed by evidence based medicine.
Risk factors for the development of mediastinitis postoperatively include the following:
- Bilateral internal mammary artery grafts
- Diabetes mellitus
- Emergency surgery
- External cardiac compression (conventional cardiopulmonary resuscitation)
- Obesity (>20% of ideal body weight)
- Postoperative shock, especially when multiple blood transfusions are required
- Prolonged bypass and operating room time
- Reoperation and/or Reexploration following initial surgery (check out Grunt Doc's post)
- Sternal wound dehiscence
- Surgical technical factors (eg, excessive use of electrocautery, bone wax, paramedian sternotomy
Surgical options for mediastinitis after cardiac surgery
Effective treatment for simple sternal dehiscence without infection is rewiring the sternum. This usually yields reasonable long-term results. Cultures should be taken to exclude active infection in the cases of sternal dehiscence.
Failure to adequately debride and sterilize the mediastinum during the first reoperation is the most common cause of repeat postoperative mediastinitis. Options for mediastinitis after cardiac surgery are immediate closure after sternal debridement, delayed closure after sternal debridement, and sternal irrigation after sternal debridement. Each has its advantages and disadvantages. The best strategy for accomplishing this depends on the duration of the infection, the condition of the mediastinal structures, and the experience of the surgeon. Below is a diagram of the main pathways for treatment selection as per the presenting wound as per Dr. Norman Schulman (reference 3).
Most surgeons prefer to leave the wound open for subsequent debridement efforts after initial sternal reexploration. In this case, the wound is packed daily until it appears clean with adequate granulation tissue. At this point, muscle flap closure is achieved. The workhorse flap is the unipedicled pectoralis major muscle flap. It is based on its primary blood supply from the acromioclavicular axis. By detaching the muscle from its sternal, rib, humeral, and medial clavicular attachments and separating it from the clavicular head of the deltoid, it can usually be extended to the level of the xiphoid. Back cutting the superior medial segment of the pectoralis muscle for a distance of 4 to 6 cm maintains its blood supply and permits it to be tucked into an upper manubrial dead space. Distal closure at the level of or below the xiphoid is accomplished by approximating the upper medial ends of the rectus sheath with large no. 1 sutures. (photo credit)
The lack of a bony anterior sternal wall may be unacceptable to some patients and has prompted some surgeons to attempt sternum-sparing procedures, even in more advanced cases. This is often a difficult decision, requiring excellent surgical judgment. Advanced cases of sternal osteomyelitis are extremely difficult to cure, and most patients with muscle or omental flaps do very well from a functional standpoint.
Vacuum assisted closure (also called vacuum therapy, vacuum sealing or topical negative pressure therapy) is a sophisticated development of a standard surgical procedure, the use of vacuum assisted drainage to remove blood or serous fluid from a wound or operation site. A piece of foam with an open-cell structure is introduced into the wound and a wound drain with lateral perforations is laid on top of it. The entire area is then covered with a transparent adhesive membrane, which is firmly secured to the healthy skin around the wound margin. When the exposed end of the drain tube is connected to a vacuum source, fluid is drawn from the wound through the foam into a reservoir for subsequent disposal.
The plastic membrane prevents the ingress of air and allows a partial vacuum to form within the wound, reducing its volume and facilitating the removal of fluid. The foam ensures that the entire surface area of the wound is uniformly exposed to this negative pressure effect, prevents occlusion of the perforations in the drain by contact with the base or edges of the wound, and eliminates the theoretical possibility of localised areas of high pressure and resultant tissue necrosis.
Mediastinitis by Dale K Mueller, MD--eMedicine article
Chest Reconstruction, Sternal Dehiscence by Sanjay K Sharma, MD--eMedicine article
Bipedicle Muscle Flaps in Sternal Wound Repair; Plastic & Reconstructive Surgery. 101(2):356-360, February 1998; Solomon, Mark P. M.D.; Granick, Mark S. M.D.
Use of the Omentum in the Management of Sternal Wound Infection after Cardiac Transplantation; Plastic & Reconstructive Surgery. 95(4):697-702, April 1995; Wornom, Isaac L. III M.D.; Maragh, Hallene M.D.; Pozez, Andrea M.D.; Guerraty, Albert J. M.D.
Mechanisms Governing the Effects of Vacuum-Assisted Closure in Cardiac Surgery; Plastic & Reconstructive Surgery. 120(5):1266-1275, October 2007; Malmsjo, Malin M.D., Ph.D.; Ingemansson, Richard M.D., Ph.D.; Sjogren, Johan M.D., Ph.D.
An introduction to the use of vacuum assisted closure by Steve Thomas, PhD--World Wide Wounds