Ch 10 Wound infections and antimicrobials Flashcards

1
Q

surgical site infection (3)

pathophysiology of surgical site infections is complex > risk factors

A

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

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2
Q

Risk Factors (6)

Clean orthopedic surgeries 7.1% Whittem et al., 1999

A

* 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

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3
Q

wound classification

clean/clean-contam/contam/dirty

A
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4
Q

Pathogens

opportunistic pathogens from patients, clinical personnel, environment

A
  • 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

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5
Q
A
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6
Q

Peri-operative ABs

A

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

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7
Q

POSTOPERATIVE ANTIMICROBIALS

A
  • 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

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8
Q

MANAGEMENT OF SURGICAL SITE INFECTIONS

A

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

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9
Q
  • Why cephalosporins?
A

o Covers staph and enterobacteriaceae, second gen cephalosporins like cefoxitin are good for additional anaerobes when doing colonic or cecal surgery

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10
Q

pros/cons of perioperative antibiotics?

A
  • 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.
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11
Q

concentration dependent abs

A

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

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12
Q

time depenedant

A

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

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13
Q

Antibiotic MOA (6)

A
  1. cell wall synthesis via via competitive inhibition of the transpeptidase enzyme (penicillin, cephalosporin)
  2. protien synthesis inhibitors (clindamycin)
    i.e 30s ribosonal subunit (aminoglycosides)
  3. DNA synthesis inhibitors (fluoroquinolone, metronidazole))
  4. RNA synthesis inhibitor (rifampin)
  5. Mycolic acid synthesis inhibitor
  6. folic acid synthesis inhibitor (TMS)
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14
Q

ab spectrum of activity

A
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15
Q

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

A

positive culture rates from synovial sepsis cases often remain < 50%

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16
Q

Synovial sepsis diagnostics and antimicrobial resistance: a one-health perspective
Pearson 2023

Reducing AMR requires a coordinated one-health directive from the human, veterinary, and environmental sectors to develop or repurpose antimicrobials, utilize alternative therapies, improve diagnostics, and prevent infection.

A

resistance

generation of AMR by upregulating the rate of mutation and gene transfer

targeting antimicrobial therapy appropriately, reinforcing the importance of accurate and timely diagnostics

antimicrobial selection important, but dosing should be based on pharmacokinetics studies to ensure efficacy. Exposure to subtherapeutic concentrations or inappropriate frequency of administration contributes to development of resistance.

few surveillance studies in the canine literature, evidence points toward an increase in multidrug-resistant isolates

17
Q

Wound swabs versus biopsies to detect methicillin resistant
Staphylococcus aureus in experimental equine wounds
Brock 2022

A

Study design: Experimental in vivo study.
Animals: Three light-breed adult horses.

Bacterial load and diversity did not differ between sampling techniques
but MRSA was detected more often from the cultures of tissue biopsies