Wednesday, October 24, 2007

Poststernotomy Mediastinitis and Repair

In the United States, mediastinitis most commonly occurs in the postoperatively. It occurs in 1-2% of patients who have a sternotomy. Most of these patients are cardiac surgery patients (more than 300,000 cases per year in the US). Most of these are coronary bypass patients rather than heart valve or transplant patients. Some other causes of mediastinitis, other than postoperative, include 1) esophageal perforation; 2) trauma, especially blunt trauma to the chest or abdomen; 3) tracheobronchial perforation, due to either penetrating or blunt trauma or instrumentation during bronchoscopy; 4) descending infection following surgery of the head and neck, great vessels, or vertebrae; 5) progressive odontogenic infection (Ludwig angina); 6) mediastinal extension of lung infection; and 7) chronic fibrosing mediastinitis due to granulomatous infections. (photo credit)

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

TREATMENT
Medical
Most patients have already received prophylactic antibiotics, usually a first-generation cephalosporin. Very broad and deep antibiotic coverage that includes Pseudomonas species (20% are gram negative) and methicillin-resistant S aureus (20% are MRSA) is needed. Culture results should then guide antibiotic use as multiple regimens are available for use with patients who have mediastinitis. Therapy is usually prolonged, ranging from weeks to months (4-6 weeks of therapy is adequate for most patients). Nutritional support is often necessary. This may be enteral or hyperalimentation.

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)

Although many closures are accomplished with a single pedicled pectoralis flaps both muscles may be used if necessary on their respective pedicles to provide extensive coverage for the heart and the sternal defect and particularly exposed grafts. Many bypass patients have had the left and on occasion the right internal mammary arteries taken, thus limiting the use of “turnover” pectoralis flaps, which rely on perforators from these arteries. The rectus muscle is very hardy and can provide excellent coverage of sternal defects, especially those involving the lower sternal areas.

Recently, vacuum-assisted closure has been used alone or in conjunction with muscle flap closure for mediastinitis in an attempt to decrease the incidence of this bleeding.

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

Photo credit.

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.

References

Part II, Department of Health and Human Services Centers for Medicare & Medicaid Services ; 42 CFR Parts 411, 412, 413, and 489 Medicare Program; Changes to the Hospital Inpatient Prospective Payment Systems and Fiscal Year 2008 Rates; Final Rule --surgical infections

Mediastinitis by Dale K Mueller, MD--eMedicine article

Sternal Wound Reconstruction: 252 Consecutive Cases. The Lenox Hill Experience; Plastic & Reconstructive Surgery. 114(1):44-48, July 2004; Schulman, Norman H. M.D.; Subramanian, Valavanur M.D.

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

3 comments:

Allen said...

Nice review, thanks!

GruntDoc

Ana said...

Wow-wish I had come across this blog a long time ago! Very informative and fun to read. You should write a medical book if you haven't already. (I'm studying for USMLE Step 3-lots of reading as you know).

rlbates said...

Thank you Ana. Best to you