ntibiotic administration during the perioperative period has recently been proposed as a quality metric.¹ Anesthesiologists are frequently responsible for ensuring the timely administration of antibiotics for surgical site infection and infective endocarditis (IE) prophylaxis in the operating room or procedure suite. Knowledge of the indications and appropriate antibiotics and dose are necessary for appropriate prophylactic antimicrobial therapy.

In the United States, 15,000 new patients each year are diagnosed with IE.² Despite advances in diagnosis and treatment, IE remains associated with significant morbidity and mortality. The vast majority of IE cases (~85 percent) are caused by streptococci, enterococci or staphylococci.³ Risk factors for developing IE have changed over time, from rheumatic valve lesions and congenital cardiac abnormalities to myriad other risk factors, including intravenous drug abuse, prosthetic valves, degenerative valve disease and bacteremia associated with invasive procedures. Since 1955, the American Heart Association (AHA) has periodically published guidelines for the prevention of IE, most recently in October 2007.⁴

These latest guidelines were revised for several reasons. IE is now thought more likely to result from frequent bacteremias associated with daily activities than from bacteremia caused by dental, gastrointestinal (GI) or genitourinary (GU) tract procedures or skin incision. For example, maintenance of optimal oral health and hygiene can reduce the incidence of bacteremia and thereby have a more important role than prophylactic antibiotics in reducing the risk of IE. Furthermore, there is little evidence to suggest that prophylactic antibiotic administration prevents IE. Finally, even if 100-percent effective, universal antibiotic prophylaxis would prevent a minimal number of IE cases. Consequently, it was the opinion of the AHA guideline panel that the risk of antibiotic-associated adverse events exceeded the potential benefit of routine prophylactic therapy, except in high-risk individuals undergoing high-risk procedures (see below).




Compared to previous guidelines, the 2007 AHA IE prevention guidelines have been greatly simplified. Several important concepts summarize the current recommendations:

1. The need for IE antibiotic prophylaxis is based not only on the risk of developing IE but also on the severity of outcome if IE were to occur. Highest-risk patients include those with:

a. Presence of a prosthetic cardiac valve;

b. Previous IE;

c. Unrepaired cyanotic congenital heart disease (including palliative shunts and conduits);

d. Completely repaired congenital heart defects with prosthetic material or device, whether placed by surgery or by percutaneous catheter intervention, during the six months after the procedure;

e. Repaired congenital heart disease with residual defects at the site, or adjacent to the site, of a prosthetic patch or prosthetic device (which inhibit endothelialization); and

f. Previous cardiac transplantation with subsequent cardiac valvulopathy (substantial leaflet pathology and regurgitation).

It is noteworthy that highest-risk patients no longer include those with common valvular lesions, including bicuspid aortic valve, acquired aortic or mitral valve disease (including mitral valve prolapse with an audible click or murmur) or hypertrophic cardiomyopathy.

2. Highest-risk patients who undergo dental procedures that involve manipulation of gingival tissue or the periapical region of teeth or perforation of the oral mucosa should receive antibiotic prophylaxis. Almost all dental procedures are included except:

a. Routine anesthetic injections through noninfected tissue;

b. Dental radiographs;

c. Placement of removable prosthodontic or orthodontic appliances;

d. Placement or adjustment of orthodontic appliances;

e. Shedding of deciduous teeth; and

f. Bleeding from trauma to the lips or oral mucosa.

In addition to dental procedures, excluding those listed above, highest-risk patients should receive IE antibiotic prophylaxis prior to procedures that involve incision or biopsy of respiratory tract mucosa, such as tonsillectomy, adenoidectomy or biopsies. Antibiotic prophylaxis is not recommended for endotracheal intubation or routine bronchoscopy.

3. Antibiotic prophylaxis for dental and respiratory tract procedures in highest-risk patients is focused against viridans group streptococci and consists of a single pre-procedure dose. No repeat dosing is advised. Recommended drugs and dosages are listed in Table 1.

4. Antibiotic prophylaxis solely to prevent IE is no longer recommended for GI or GU procedures. These procedures include diagnostic esophagogastroduodenoscopy, colonoscopy, vaginal delivery and hysterectomy. However, patients with established or suspected GI or GU infections undergoing a GI or GU procedure should receive, as part of routine infection management, an antibiotic active against enterococci. In these scenarios, IE prophylaxis is redundant. Infectious disease consultation is recommended if an infection is known or suspected to be caused by a resistant strain of enterococcus.

5. In highest-risk patients, antibiotic prophylaxis is recommended to prevent IE in procedures involving infected skin, skin structure or musculoskeletal tissue. Despite the polymicrobial nature of these infections, only staphylococci and beta-hemolytic streptococci are likely to cause IE; thus therapeutic antibiotic regimens need to be active against these pathogens, in addition to other potential site-specific organisms.
These changes may violate longstanding expectations of patients and practice patterns of physicians and dentists. As previous guidelines contained inconsistencies and were based on minimal published data, conflicting interpretations among patients, health care providers and attorneys often resulted. In the past, various interpretations may have resulted in unnecessary treatment by physicians and dentists who felt an obligation (professionally and legally) to protect their patients from IE.

In summary, the updated 2007 AHA Guidelines for Prevention of Infective Endocarditis recommend antibiotic prophylaxis for a decreased number of indications in fewer patients. These simplified guidelines are based on the best available, albeit minimal, data and should result in less confusion regarding appropriate therapy. Future studies will be necessary to monitor the effects of these changes.

References:
1. American Medical Association Web site. Available at www.ama-assn.org/ama1/pub/upload/mm/370/perioperativews1206.pdf. Accessed on February 11, 2008.
2. Mylonakis E, Calderwood SB. Infective endocarditis in adults. N Engl J Med. 2001; 345:1318-1330.
3. Hoen B. Epidemiology and antibiotic treatment of infective endocarditis: An update. Heart. 2006; 92:1694-1700.
4. Wilson W, Taubert KA, Gewitz M, et al. Prevention of infective endocarditis: Guidelines from the American Heart Association. Circulation. 2007; 116:1736-1754.

James A. Onigkeit, M.D., is a Fellow, Division of Critical Care Medicine, Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota.

Daniel R. Brown, M.D., Ph.D., F.C.C.M., is Chair, Division of Critical Care Medicine, Department of Anesthesiology, Mayo Clinic, Rochester, Minnesota.