Preoperative antibiotic prophylaxis is defined as the administration of antibiotics prior to performing surgery to help decrease the risk of postoperative infections. The evidence supporting routine preoperative use of antibiotic prophylactic administration continues to grow, with a 2008 study highlighting the effectiveness of its administration during total hip and knee replacement, reducing the absolute risk of wound infection by over 80% compared to patients treated with no prophylaxis. The routine administration of prophylactic antibiotics is standard in cases in which a patient will have an artificial implant or foreign body implanted as part of the procedure, in bone grafting procedures, and other surgeries in which large dissections and higher amounts of anticipated blood loss is expected.
The timing of antibiotic administration may vary, but the goal of administering preoperative systemic prophylactic antibiotics is to have the concentration in the tissues at its highest at the start and during surgery. The literature supports at least 30 minutes, but no greater than 60 minutes before the skin incision is made as to the optimal timing for the pre-operative administration of most commonly used antibiotics. Special consideration is given for ideal preoperative timing when using a tourniquet, as the administration is least effective when the antibiotic is given after the application of a tourniquet.
The most common organisms implicated as causes of surgical site infections include:
- staphylococcus aureus
- staphylococcus epidermidis
- aerobic streptococci
- anaerobic cocci
Other organisms, such a cutibacterium acnes is characteristically isolated in the setting of postoperative infections following shoulder surgery.
In general, the preoperative antibiotic selection is based on the anatomic region undergoing the specific surgical procedure. The goal when determining appropriate antibiotic selection is to have achieved a relatively narrow spectrum of activity while ensuring the most common organisms are targeted. Additionally, preoperative antibiotics are chosen based on a multitude of factors including cost, safety, ease of administration, pharmacokinetic profile, bacteriocidal activity, and hospital resistance patterns. By addressing all of these factors during antibiotic selection, surgical site infections (SSIs) are minimized. SSIs, in aggregate, constitute a significant factor driving negative patient-reported outcomes and independent risk factors for increasing financial burden to the entire healthcare system.
Cefazolin is used most often for surgical prophylaxis in patients with no history of beta-lactam allergy, a history of MRSA infection, or when consideration is given to surgical sites in which the most probable organisms that are not covered by cefazolin alone (e.g., appendectomy, colorectal).
In patients requiring only cefazolin for preoperative surgical prophylaxis, clindamycin or vancomycin are often used as alternatives in those with significant beta-lactam allergies. In the case of MRSA colonization, or in select patients at high-risk for MRSA (i.e. patients residing in nursing homes, patients with a history of MRSA infection, or patients with current positive MRSA colonization testing) vancomycin is the alternative unless additional antibiotics are required for possible gram-negative or anaerobic organisms. For patients requiring additional microbe coverage (e.g., colorectal), multiple options may be considered including cefazolin plus metronidazole, cefoxitin, or ertapenem. Additional antibiotics are options based on specific surgical sites in addition to hospital-specific and patient-specific antibiotic resistance.
Weight-based dosing should be followed per standardized protocol, and administration should occur within 1 hour of skin incision and continue for 24 hours postoperatively. Furthermore, surgical durations of greater than 4 hours or estimated blood loss over 1,500 mL necessitates repeat intraoperative dosing of antibiotics. Weight-based guidelines include the following:
- Cefazolin: 2 g (3 g for weight >120 kg) —standard adult surgical prophylaxis guidelines
- Vancomycin: 15 mg/kg
Wound classifications 
Wound types can be classified as clean, clean-contaminated, contaminated, or dirty/infected according to the Centers for Disease Control and Prevention's (CDC) National Healthcare Safety Network (NHSN). Clean wounds are not infected, without inflammation, primarily closed, and do not include the organ systems that are outlined in a clean-contaminated wound. Clean-contaminated wounds involve the respiratory, alimentary, genital, and urinary tract as long as the tract is entered without unusual contamination. Contaminated wounds include open, fresh accidental wounds including those with non-purulent inflammation. Contaminated wounds also include procedures with major breaks in sterile technique or gross spillage from the gastrointestinal tract. Dirty or infected wounds are old traumatic wounds with devitalized tissue or involve existing clinical infection or perforated viscera. During clean procedures, skin florae such as coagulase-negative staphylococci (e.g., Staphylococcus epidermidis or Staphylococcus aureus) are predominant pathogens in surgical site infections. In clean-contaminated procedures, the most commonly found organisms causing surgical site infections are skin flora, gram-negative rods, and Enterococci.
Other preoperative actions include basic infection control strategies, instrument sterilization, and a patient's skin preparation (e.g., methicillin-resistant Staphylococcus aureus [MRSA] decolonization, appropriate hair removal, skin antiseptic). In regards to the latter, it is commonly recommended that patients about to undergo surgery perform a combination of a standard soap-and-water shower and chlorhexidine gluconate cloth wash prior to surgery. Murray et al. previously demonstrated that the combined protocol resulted in a 3-fold reduction in colony count for coagulase-negative Staphylococcus (CNS), a significant decrease in the rate of positive cultures for CNS and Corynebacterium, and a significant decrease in overall bacterial burden compared to soap-and-water shower alone.
Screening for MRSA via swabs of the anterior nares weeks before elective arthroplasty procedures and reflexively treating patients based on culture results is generally institution dependent. Positive MRSA culture results can be treated with either 2% mupirocin twice daily for 5 days preoperatively to the nares or 5% povidone-iodine solution to each nostril for 10 seconds per nostril, 1 hour prior to surgery, in addition to vancomycin administration at the time of surgery.
Another area requiring special attention and consideration is in regard to infection prevention in patients with hyposplenism (or status post splenectomy). Davies et al. provided updated guidelines for the prevention and treatment of infections in patients with dysfunctional (or absent) splenic function:
- Pneumococcal immunization
- Haemophilus influenza type B vaccination
- Meningococcal group C conjugate vaccination
- Yearly influenza immunization
- Lifelong prophylactic antibiotics (oral phenoxymethylpenicillin or erythromycin)