Ch 10 Wound infections and antimicrobials Flashcards
surgical site infection (3)
pathophysiology of surgical site infections is complex > risk factors
Superficial SSI
Within 30 days
skin +/- SQ of the incision
One or more of:
* Purulent drainage
* Bacteria aseptically cultured
* Diagnosis by the surgeon
* Heat, redness, pain, OR localized swelling
**Deep SSI **
Within 30 days
Deep (fascia or muscle layers)
One or more of:
* Purulent drainage
* dehiscence of deeper incision OR fever, localized pain
* Abscess or other evidence of infection
**Organ/space SSI **
Within 30 days
Any area other than the incision
One or more of:
* Purulent drainage
* Bacteria
* Abscess or other evidence of infection on examination, reoperation, histology, or imaging
* Categorized into incisional vs organ space
Risk Factors (6)
Clean orthopedic surgeries 7.1% Whittem et al., 1999
* Duration of surgery
> Risk doubles for every hour
> bacteria to be exposed to and adhere w/in surgical wound
> Suppression of immune system via significant decrease in lymphocytes
-
Duration of anesthesia
>hypothermia
>impact on immune system
> 30% greater risk infectio each hour of anesthesia
surgical site prep
> Traumatic clipping or excessive scrubbing = microtrauma
> recontamination, inadequate contact time for biocides
> Clipping early allows bacterial proliferation on any traumatized areas
> In dogs, clipping before anesthetic induction was associated with increased risk
* Method of wound closure
> conflicting data, no RCT.
Staples may cause exaggerated inflame response and have increased bacterial attachment (decreased and no diff in prospective)
* Antimicrobial prophylaxis
o no specific protocols established, caution in unnecessary use as will cause patient effects (GI upset) and uncrease antimicrobial resistance
*Comorbidities
o Endocrinopathy (hyperadrenocorticism, hypothyroid), obesity
wound classification
clean/clean-contam/contam/dirty
Pathogens
opportunistic pathogens from patients, clinical personnel, environment
- S. pseud intermedius, Staphylococcus aureus, Enterobacteriaceae, Enterococcus spp, Pseudomonas spp
- Staphylococci of particular concern for SSI – widespread commensal nature and ability to become resistant to antimicrobials
S. pseudointermedius dominant in dog
Peri-operative ABs
recommended for:
-contaminated and dirty procedures
- some clean-contam procedures
- procedures involving implants
- clean procedures lasting >90m
appropriate use:
o Appropriate selection – pathogens expected to be present at site
o Timing of first dose – ensure peak drug conc at time of first incision
o Discontinuation postop – w/In 24 hrs
Time dependent (penicillins, cehpalosporins)
present at time of first incision and maintained
o Redosing every 2 half-lives of drug indicated
o Veterinary study – only 42.5% of dogs received prophylactic antimicrobials w/in 60min of first incision at appropriate dose
> > > > administration is included in surgical checklists
antimicrobials not substitute for meticulous surgical technique and strict adherence to the principles of surgical asepsis
cephazolin 1/2 life 47min
POSTOPERATIVE ANTIMICROBIALS
- Likely rarely indicated, low likelihood that bacteria would be present beyond 24 to 48 hours of treatment
TPLO
o Recurrent findings of protective effect – however most studies retrospective
o randomized trial in clean ortho cases – did not identify any difference in SSI rate between dogs treated postop for 5d vs those that only received periop
MANAGEMENT OF SURGICAL SITE INFECTIONS
Specimen collection and testing
> Deep culture prior to ab’s is ideal
or collect sample immediately before ab dose (potential for false-negative results)
> Cytology may help determine main bug present
Selection of antimicrobials
> ensure appropriate type based on expected pathogen (empirical), timing and duration
> concentration vs time dependent
- Why cephalosporins?
o Covers staph and enterobacteriaceae, second gen cephalosporins like cefoxitin are good for additional anaerobes when doing colonic or cecal surgery
pros/cons of perioperative antibiotics?
- Benefits
o Shown to prevent SSI in orthopedic procedures, conflicting results for clean ST procedures - Cons
o Infected wounds post operatively often resistant to perioperative AB. 43% in human spinal study.
concentration dependent abs
killing dependent on the concentration being well above the minimum inhibitory concentration of the organism.
best responses occurring when Cmax is ≥10 times the minimum inhibitory concentration for the target organism at the site of infection
Ex: quinolones, metronidazole, amphotericin, and the aminoglycosides
time depenedant
dependent on the duration of pathogen exposure to an antibiotic, concentration above MIC for a specific time
Optimal response when above the MIC is equal to or greater than 50% of the dosing interval
Ex: B lactams, clindamycin, macrolides, azoles, vancomycin
Antibiotic MOA (6)
- cell wall synthesis via via competitive inhibition of the transpeptidase enzyme (penicillin, cephalosporin)
- protien synthesis inhibitors (clindamycin)
i.e 30s ribosonal subunit (aminoglycosides) - DNA synthesis inhibitors (fluoroquinolone, metronidazole))
- RNA synthesis inhibitor (rifampin)
- Mycolic acid synthesis inhibitor
- folic acid synthesis inhibitor (TMS)
ab spectrum of activity
Advances in bacterial isolation including matrix-assisted laser desorption ionization–time-of-flight mass spectrometry and 16S rRNA sequencing provide a promising future for a more accurate and timely diagnosis when combined with culture and antimicrobial susceptibility in cases of synovial sepsis across species
positive culture rates from synovial sepsis cases often remain < 50%
