Antibiotics for surgical prophylaxis. Surgical site infections(SSIs) are a significant cause of morbidity and mortality. Approximately 2% to 5% of patients undergoing clean extra-abdominal operations and 20%undergoing intra-abdominal operations will develop an SSI. SSIs have become the second most common cause of nosocomial infection and these data are likely underestimated.

1. ANTIMICROBIAL PROPHYLAXIS IN
SURGERY
BY: DR.ZEEL NAIK

2. SURGICAL SITE INFECTIONS (SSI)
 Surgical site infections(SSIs) are a significant
cause of morbidity and mortality.
 Approximately 2% to 5% of patients
undergoing clean extra-abdominal operations
and 20%undergoing intra-abdominal
operations will develop an SSI.
 SSIs have become the second most
common cause of nosocomial infection and
these data are likely underestimated.

3. SSI
 SSIs negatively affect patient outcomes and increase
health care costs.
 Patients who develop SSIs are five times more likely to be
readmitted to the hospital and have twice the mortality of
patients who do not develop an SSI.
 A patient infected with an SSI is also 60% more likely to
be admitted to an intensive care unit.
 Clinical studies have shown that SSIs increase lengths of
hospital stay and costs.
 The type of SSI can also affect outcome.
 Deep SSIs, involving organs or spaces, result in longer
durations of hospital stay and higher costs compared to
SSIs that are limited to the incision.

4. SSI
 SSIs are defined and reported according to Centers for Disease
Control and Prevention (CDC) criteria.
 SSIs are classified as either incisional or organ/space.
 Incisional SSIs are further divided into superficial incisional SSI
(skin or subcutaneous tissue) and deep incisional SSI (deeper
soft tissues of the incision).
 Organ/space SSIs involve any anatomic site other than the
incised areas.
 For example, a patient who develops meningitis after removal of
a brain tumor could be classified as having an organ/space SSI.
 An infection is considered an SSI if any of the above criteria is
met and the infection occurs within 30 days of the operation.
 If a prosthetic is implanted, the timeline extends out to1 year.

5. EPIDEMIOLOGY AND ETIOLOGY
 Numerous risk factors for SSI have been identified.
 These factors can be divided into two categories: patient and
operative characteristics.
 Patient risk factors for SSI include: age, co-morbid disease
states (especially chronic lung disease and diabetes),
malnutrition, immunosuppression, nicotine or steroid use, and
colonization of the nares with Staphylococcus aureus.
 Many patients developing post-operative wound infections bring
the organism with them into the hospital.
 Modifying risk factors may decrease the threat of SSI.
 Studies have shown that the use of intranasal mupirocin can
decrease the incidence of SSI due to methicillin-sensitive
Staphylococcus aureus(MSSA)or methicillin-resistant
Staphylococcus aureus(MRSA).
 Malnutrition can be corrected using enteral or parenteral
feedings.

6. EPIDEMIOLOGY AND ETIOLOGY
 Operative characteristics are based on the actions of both the
patient and the operating staff.
 Shaving of the surgical site prior to operating can produce
microscopic lacerations and increase the chance of SSI.
 Maintaining aseptic technique and proper sterilization of medical
equipment is effective in preventing SSI.
 Surgical staff should wash hands thoroughly.
 Post-operative bacterial inoculums of clean surgeries are
generally small.
 However, subsequent patient contact with contaminated areas
(nares or rectum) and then the surgical site can lead to SSI.
 Finally, the appropriate use of antimicrobial prophylaxis can have
a significant impact on decreasing SSIs.

7. PATHOPHYSIOLOGY- PROPHYLAXIS VERSUS TREATMENT
 Properly identifying the state of an infection is important
when using antimicrobial prophylaxis in surgery.
 Antibiotic prophylaxis begins with the premise that no
infection exists but that during surgery there can be a low
level inoculum of bacteria introduced into the body.
 However, if sufficient antibiotic concentrations are
present, the situation can be controlled without infection
developing.
 This is the case when surgery is done under controlled
conditions, there are no major breaks in technique or
spillage of gastrointestinal (GI)contents, and perforation
or damage to the surgical site is absent.
 An example would be an elective hysterectomy done with
optimal surgical technique.

8. PATHOPHYSIOLOGY- PROPHYLAXIS VERSUS TREATMENT
 If an infection is already present, or presumed to
be present, then antimicrobial use is for
treatment, not prophylaxis, and the goal is to
eliminate the infection.
 This is the case when there is spillage of GI
contents, gross damage or perforation is
already present, or the tissue being operated on
is actively infected (pus is present and cultures
are positive).
 An example would be a patient undergoing
surgery for a ruptured appendix with diffuse
peritonitis.

9. PATHOPHYSIOLOGY- PROPHYLAXIS VERSUS TREATMENT
 The distinction between prophylaxis and treatment
influences the choice of antimicrobial and duration of
therapy.
 Appropriate antimicrobial selection, dosing, and
duration of therapy differ significantly between these
two situations.
 A regimen for antimicrobial prophylaxis ideally
involves one agent and lasts less than 24 hours.
 Treatment regimens can involve multiple
antimicrobials with durations lasting weeks to months
depending on desired antimicrobial coverage and the
surgical site.

10. TYPES OF SURGICAL OPERATIONS
 Surgical operations are classified as clean,
clean-contaminated, contaminated, or dirty.
 Antimicrobial prophylaxis is appropriate for
clean, clean-contaminated, and
contaminated operations.
 Dirty operations take place in situations of
existing infection and antimicrobials are used
for treatment, not prophylaxis.

11. TYPES OF SURGICAL OPERATIONS
 Clean — an incision in which no inflammation is encountered in a
surgical procedure, without a break in sterile technique, and during
which the respiratory, alimentary and genitourinary tracts are not
entered.
 Clean-contaminated — an incision through which the respiratory,
alimentary or genitourinary tract is entered under controlled conditions
but with no contamination encountered.
 Contaminated — an incision undertaken during an operation in which
there is a major break in sterile technique or gross spillage from the
gastrointestinal tract, or an incision in which acute, non-purulent
inflammation is encountered. Open traumatic wounds that are more than
12–24 hours old also fall into this category.
 Dirty or infected — an incision undertaken during an operation in which
the viscera are perforated or when acute inflammation with pus is
encountered during the operation (for example, emergency surgery for
faecal peritonitis), and for traumatic wounds where treatment is delayed,
and there is faecal contamination or devitalised tissue present”

13. MICROBIOLOGY
 Choosing the appropriate prophylactic antimicrobial
relies on anticipating which organisms will be
encountered during the operation.
 SSIs associated with extra-abdominal operations are
the result of skin flora organisms in nearly all cases.
 These organisms include gram-positive cocci, with S.
aureus and S. epidermidis being among the most
frequently isolated SSI pathogens according to the
National Nosocomial Infections Surveillance System
(NNIS).
 Streptococcus spp.and other gram-positive aerobes
may also be implicated.

14. MICROBIOLOGY
 Intra-abdominal operations involve a diverse flora with the
potential for polymicrobial SSIs.
 Escherichia coli make up a large portion of bowel flora and are
frequently isolated as pathogens according to the NNIS.
 Other enteric gram-negative bacteria, as well as anaerobes
(especially Bacteroides spp.), maybe encountered during intra-
abdominal operations.
 Candida albicansis being implicated as the cause of a growing
number of SSIs.
 Increased use of broad spectrum antibiotics and rising prevalence
of immunocompromised and humanimmunodeficiency virus–
infected individuals are factors in fungal SSIs.
 Despite this increase, antifungal prophylaxis for surgery is not
currently recommended.

16. CHOOSING AN ANTIBIOTIC
 An antimicrobial used in surgical prophylaxis should meet certain criteria.
 Selecting an antibiotic with a spectrum that covers expected pathogens is
crucial.
 The antibiotic should be inexpensive, available in a parenteral formulation, and
easy to use.
 Adverse event potential should be minimal.
 Choosing an agent with a longer half-life reduces the likely need to redose
unless the surgical procedure is prolonged.
 Operations can be separated into two basic categories: extra-abdominal and
intra-abdominal.
 SSIs resulting from extra-abdominal operations are frequently caused by gram-
positive aerobes.
 Thus, an antimicrobial with strong gram-positive coverage is useful.
 Cefazolin benefits from a benign adverse-event profile, simple dosing, and low
cost.
 These aspects have made cefazolin the mainstay for surgical prophylaxis of
extra-abdominal procedures.
 For patients with B-lactam allergy, clindamycin or vancomycin can be used as
an alternative.

17. CHOOSING AN ANTIBIOTIC
 Intra-abdominal operations necessitate broad-
spectrum coverage of gram-negative organisms
and anaerobes.
 Anti-anaerobic cephalosporins, cefoxitin and
cefotetan, are useful but suffer from limited
availability.
 Fluoroquinolones or aminoglycosides,paired
with clindamycin or metronidazole, should
provide ade-quate coverage for intra-abdominal
operations.

18. CHOOSING AN ANTIBIOTIC
 The Hospital Infection Control Practices Advisory Committee
allows for the use of vancomycin for surgical prophylaxis when
MRSA rates at an institution are “high.”
 Unfortunately, a “high” rate of MRSA has not been standardized,
but with most hospitals reporting MRSA rates greater than 50%,
the definition is irrelevant.
 The increasing prevalence of community-acquired methicillin-
resistant Staphylococcus aureus in patients admitted to the
hospital is a concern, although this pathogen is often sensitive to
clindamycin.
 Vancomycin use may not translate into a lower incidence of SSI.
 Finkelstein and associates found that the incidence of SSI
between patients on cefazolin or vancomycin did not differ despite
a high MRSA rate at the study institution.

19. CHOOSING AN ANTIBIOTIC
 However, patients who received cefazolin were
more likely to develop an SSI due to MRSA.
 Newer antimicrobials have not demonstrated
superiority in the prevention of SSI and should
be reserved for treatment only.
 Carbapenems, antipseudomonal penicillins,
and third-or fourth-generation cephalosporins
are not appropriate antibiotics for surgical
prophylaxis.
 Overuse of these antibiotics may contribute to
collateral damage and the development of
bacterial resistance.

20. BETA-LACTAM ALLERGY
 Penicillin allergy is one of the most common reported drug allergies.
 Concerns over cross-reactivity may limit the use of β-lactams for surgical
prophylaxis.
 A thorough drug allergy history should be taken to discern true allergy
(e.g., anaphylaxis)from adverse event (e.g., stomach upset).
 Allergy testing may be helpful in confirming a patient’s penicillin allergy
and could spare vancomycin.
 Cross-sensitivity between penicillin allergy and cephalosporins is low.
 Pichichero and colleagues stated that the increased risk of
cephalosporin allergy in patients with a history of penicillin allergy may
be as low as 0.4% when taking first-generation cephalosporins and
nearly zero for second- and third-generation agents.
 Apter and co-workers also found the risk of cross-reactivity to be very
low.
 However, in the case of severe penicillin allergy (anaphylaxis),
cephalosporins should be avoided.

21. PRINCIPLES OF ANTIMICROBIAL PROPHYLAXIS
 1. Route of Administration
 Intravenous antibiotic administration is the most common
delivery method for surgical prophylaxis.
 Intravenous administration ensures complete
bioavailability while minimizing the impact of patient-
specific variables.
 Oral administration is also used in some bowel
operations.
 Non-absorbable compounds like erythromycin base and
neomycin are given up to 24 hours prior to surgery to
cleanse the bowel.
 Note that oral agents are used adjunctively and do not
replace IV agents.

22. PRINCIPLES OF ANTIMICROBIAL PROPHYLAXIS
 2. Timing of First Dose
 Correct timing of antibiotic administration is
imperative to preventing SSI.
 The National Surgical Infection Prevention
Project recommends infusing antimicrobials for
surgical prophylaxis within 60 minutes of the
first incision.
 Exceptions to this rule are fluoroquinolones and
vancomycin, which can be infused 120 minutes
prior to avoid infusion-related reactions.

23. PRINCIPLES OF ANTIMICROBIAL PROPHYLAXIS
 2. Timing of First Dose
 Studies have found that administration of the
antimicro-bial should begin as close to the first
incision as possible.
 This is important for antibiotics with short half-lives so
that therapeutic concentrations are maintained during
the operation and reduce the need for redosing.
 Beginning the infusion after the first incision is of little
value in preventing SSI.
 Stone and associates found that administration of
the antimicrobial after the first incision had SSI rates
similar to patients who did not receive prophylaxis.

24. PRINCIPLES OF ANTIMICROBIAL PROPHYLAXIS
 3.Dosing and Redosing
 The goal of antimicrobial dosing for surgical prophylaxis is to
maintain antibiotic concentrations above the MIC of suspected
organisms for the duration of the operation.
 Dosing recommendations can vary between institutions and
guidelines.
 Clinical judgment should be exercised regarding dose
modifications for renal function, age, and especially weight.
 Obese patients often require higher doses than do non-obese
patients.
 Forse and associates showed that morbidly obese patients (body
mass index greater than 40) who received 2 g of cefazolin had a
lower incidence of SSI compared to patients receiving 1 g.

25. PRINCIPLES OF ANTIMICROBIAL PROPHYLAXIS
 3.Dosing and Redosing
 Guidelines suggest that if an operation exceeds two
half-lives of the selected antimicrobial, then another
dose should be administered.
 Repeat dosing has been shown to lower rates of SSI.
 For example, cefazolin has a half-life of about 2
hours, thus another dose should be given if the
operation exceeds 4 hours.
 The clinician should have extra doses of antibiotic
ready in case an operation lasts longer than planned.

26. PRINCIPLES OF ANTIMICROBIAL PROPHYLAXIS
 4.Duration
 The National Surgical Infection Prevention
Project and published evidence suggest that
the continuation of antimicrobial prophylaxis
beyond wound closure is unnecessary.
 Studies have not shown benefit for additional
doses of antibiotic and the duration of
antimicrobial prophylaxis should not exceed
24 hours.

27. TREATMENT- ANTIMICROBIAL PROPHYLAXIS IN SPECIFIC
SURGICALPROCEDURES
 Gynecologic and Obstetric
 Enteric gram-negative bacilli, anaerobes, group B strepto-cocci,
and enterococci are all possible pathogens that maybe
encountered in gynecologic or obstetric surgeries.
 For patients undergoing hysterectomy, cefoxitin or cefotetan are
appropriate therapies.
 Unfortunately, the availability of these drugs is an issue.
 Cefazolin or ampicillin/sulbactam may be used.
 In the case of β-lactam allergy, the following regimens are
appropriate: clindamycin combined with gentamicin, aztreonam,
or ciprofloxacin; metronidazole combined with gentamicin or
ciprofloxacin, or clindamycin monotherapy.
 Metronidazole monotherapy is also indicated but has been shown
to be less effective than other regimens.

28. TREATMENT- ANTIMICROBIAL PROPHYLAXIS IN SPECIFIC
SURGICALPROCEDURES
 Gynecologic and Obstetric
 Cesarean sections are stratified into low- and high-risk groups.
 Patients who undergo emergency operations or have cesarean
sections after the rupture of membranes and/or onset of labor are
considered high risk.
 Prophylactic antimicrobials are most beneficial for high-risk
patients but are used in both groups.
 Antimicrobial regimens similar to those for hysterectomy are
appropriate.
 Antimicrobials should not be administered until after the first
incision and the umbilical cord has been clamped.
 This practice prevents potentially harmful antibiotic
concentrations from reaching the new-born.

30. ORTHOPEDIC SURGERY
 Orthopedic surgery is generally a clean operation
done under controlled conditions.
 Likely pathogens include gram-positive cocci, mostly
staphylococci.
 In the case of total joint (knee and hip) arthroplasty,
cefazolin is the antimicrobial of choice.
 Patients with a β-lactam allergy should receive either
clindamycin or vancomycin.
 Antimicrobial prophylaxis should not exceed 24
hours and does not need to be continued until all
drains and catheters have been removed.

31. CARDIOTHORACIC AND VASCULAR SURGERY
 Cefazolin or cefuroxime are appropriate for prophylaxis in
cardiothoracic and vascular surgeries.
 In the case of β-lactam allergy, vancomycin or
clindamycin are advised.
 Debate exists on the duration of antimicrobial prophylaxis.
 The National Surgical Infection Prevention Project cites
data that extending prophylaxis beyond 24 hours does not
decrease SSI rates and may increase bacterial
resistance.
 SSIs are rare after cardiothoracic operations, but the
potentially devastating consequences lead some
clinicians to support longer periods of prophylaxis.

32. COLORECTAL SURGERY
 Antimicrobial prophylaxis for colorectal operations must cover a broad
range of gram-positive, gram-negative, and anaerobic organisms.
 Strategies include oral antimicrobial bowel preparations, parenteral
antimicrobials, or both.
 Oral prophylaxis combinations of neomycin and erythromycin or
neomycin and metronidazole are common.
 Oral antimicrobials should be administered at 19, 18, and 9 hours prior
to surgery.
 A delay in surgery may require a redose, depending on the length of
postponement.
 For parenteral prophylaxis, cefoxitin or cefotetan is appropriate.
 Cefazolin combined with metronidazole or ampicillin/sulbactam is an
effective alternative if antianaerobic cephalosporins are not available.
 For patients with β-lactam allergies, use clindamycin combined with
gentamicin, aztreonam, or ciprofloxacin; metronidazole combined with
gentamicin or ciprofloxacin is also appropriate.

33. COLORECTAL SURGERY
 Appendectomy is one of the most common
intra-abdominal operations.
 Antimicrobial prophylaxis used for
appendectomy is similar to that used for
colorectal regimens.
 In the case of ruptured appendix,
antimicrobials are used for treatment, not
prophylaxis.

34. DENTAL PROCEDURES
 The goal of antimicrobial prophylaxis in
dental procedures is to prevent endocarditis.
 According to American Heart Association
guidelines, at-risk individuals should receive
2 g of amoxicillin 1 hour prior to the
procedure.
 Patients with a β-lactam allergy may receive
clindamycin 600 mg 1 hour prior to the
procedure.

35. OUTCOME EVALUATION
 The clinician should consistently follow-up post-operative patients and screen for
any sign of SSI.
 According to CDC criteria, SSI may appear up to 30 days after an operation and
upto 1 year if a prosthesis is implanted.
 This period often extends beyond hospitalization so patients should be educated
on warning signs of SSI and be encouraged to contact a clinician immediately if
necessary.
 The presence of fever or leukocytosis in the immediate post-operative period
does not constitute SSI and should resolve with proper patient care.
 Distal infections, such as pneumonia, are not considered SSIs even if these
infections occur in the 30-day period.
 The appearance of the surgical site should be checked regularly and any
changes documented (e.g., erythema, drainage, or pus).
 The presence of pus or other signs suggestive of SSI must be treated
accordingly.
 Any wound requiring incision and drainage is considered an SSI regardless of
appearance.
 Prompt cultures should be collected and appropriate antimicrobial therapy
initiated to reduce any chance of morbidity and mortality.