Use of antibiotics in surgery Flashcards
What is the prophylactic administration of antimicrobials?
Involves the administration of an antimicrobial agent prior to contamination of the surgical site
What are antimicrobials?
General term that refers to a group of drugs that includes antibiotics, antifungals, antiprotozoals, and antivirals
What is an antibiotic?
Drug that is used to treat bacterial infection
What is the minimal inhibitory concentration (MIC)?
The lowest concentration that inhibits visible bacterial growth and represents the antimicrobial concentration necessary to have an inhibitory effect on bacteria in plasma or tissue
What is the minimal bactericidal concentration?
The lowest concentration that kills 99.9% of the bacteria in the animal’s plasma or tissues. A drug is classified as being bactericidal if the ratio of minimal bactericidal concentration to MIC is less than 4-6, if its more than 6, it may be not possible to administer the drug at a dose that is bactericidal and nontoxic
What are concentration dependent antimicrobials?
Successful therapy depends on the peak concentration above the MIC
What are time dependant antimicrobials?
Time above the MIC not the peak concentration that is important for successful use. An example is beta-lactam antimicrobials
What is the definition of contamination?
The introduction of microorganisms to living tissues, equipment, or materials
What is the definition of infection?
The growth of microorganisms in tissue
What is a surgical site infection and what are the three different classification of them?
Infection that is associated with a particular operative procedure and the facility in which it was performed.
SSIs are classified according to superficial, deep incisional or organ/space infections (centers for disease control)
What are some host and peri-operative factors that can increase the likelyhood of infection?
- Older age
- Immunosupression
- Intra-operative contamination
- Excessive tissue damage
What is the critical level of contamination?
10^5 bacteria per gram - but not all bacteria are equal and local wound factors do play a role
What are some examples of good surgical technique that can reduce the likelyhood of surgical wound infection?
copious saline lavage, gentle tissue handling, anatomical tissue apposition, closure of dead space, proper suture selection
What are some examples of common sources of surgical site infection?
- skin and hair
- bacteria colonies become re-infested 90 minutes after skin preparation
- exogenous - surgical equipment and operating room
- haematogenous routes (less common)
What is a clean infection site and what is an example of one?
Non-traumatic, no inflammation encountered, no break in technique resp. GI. urine. tracts not encountered
Examples: Castration, ovariohysterectomy
What is a clean contaminated procedure and what are some examples of some?
- GI, resp., urinary, bile tracts are entered or a minor break in technique
- examples include pyometra, cystotomy, pyometra etc.
What is a contaminated procedure and when might one occur?
- Often involves a major break in technique (could be gross spillage from GI tract) or a traumatic wound
- examples may include enterotomy or pyometra
What is a dirty procedure and what is an example of one?
- transection of “clean tissues” for the purpose of surgical access to collection of pus
- examples include leakage from perforated viscera, septic peritonitis, abscesses
When should prophylactic surgical antibiotic use primarily be given?
“clean contaminated” and selected “contaminated” wounds
Therapeutic antibiotic use is not primarily recommended for clean procedures what are some exceptions to this?
A procedure > 90 minutes
Procedures in which an implant was placed or when infection will be catastrophic to the outcome (eg. total hip replacement or pacemaker implantation)
When does the period of susceptibility to microbial infection begin and when does it end?
Starts from the moment of the first incision and typically ends within 24 hours of the procedure
What is the most likely pathogen to contribute to surgical site infection?
Staphylococci
What are the most commonly used prophylactics used in surgery?
Cephalosporins (Cephazolin, Ceftazidime, Cefoxitin)
Inhibit cell wall synthesis and promote destruction of bacterial cell walls - bactericidal
What generation of cephalosporins are commonly used in surgery?
Mainly only first generation is used - second and third rarely indicated and only used where absolutely necessary
Briefly explain the timing of giving antimicrobial prophylaxis in surgery:
It is important to maintain the inhibitory concentrations at the incision site for the duration of the procedure:
- Give 30-60 minutes prior to surgery to achieve adequate concentration
- Re-administration depends on pharmokinetic behaviour of drug
- Current recommendations - intra-operative doses @ 1-2 x elimination 1/2 life of drug (cephazolin - typically given @ 22 mg/kg every 90-120 minutes)
- no supportive evidence for giving antimicrobials beyond the immediate post-operative (>24 hours)
What are some additional precautions surrounding high risk procedures?
Prophylactic antimicrobial therapy is not warranted for most procedures where contamination is expected to be minor
What are some examples of systemic signs that could be associated with infection?
Fever, renal failure, leucocytosis with left shift
What are the steps to take in the confirming of infection?
- Culture of micro-organisms and sensitivity assessment for antibiotic selection
- Consider exit culture in high risk procedure
- Consider best sample - tissue culture best - deep rather than superficial to avoid contaminants
What are some considerations to factor into your response to a surgical site infection?
- If the type of infection is unknown and immediate therapy is warranted - broad spectrum or combination
- Consider toxicity and likely level of resistance
- If not clinical improvement in 3-5 days - consider antimicrobial selection and regime
