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142 Cards in this Set

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Criteria of clean surgical wounds:
elective, primarily closed, undrained, nontraumatic, uninfected, no break in technique, no inflammation encountered, respiratory, urogenital or gi tract not entered
Criteria of clean-contaminated surgical wounds:
GI or respiratory tract entered without significant spillage, oropharynx entered, vagina entered, GU entered in absence of infected urine, minor break in technique
Criteria of contaminated surgical wounds:
major break in technique, gross spillage from gi tract, fresh traumatic wound, entrance of GU or biliary tract in presence of infected bile or urine
Criteria of dirty surgical wounds:
acute bacterial inflammation entered, transection of clean tissues to gain access to pus, traumatic wound with retained devitalized tissue, foreign bodies, fecal contamination, or delayed treatment
Sources of bacterial contamination in a surgical procedure:
air, patient, surgeon, instrumentation
Recommendations for reducing airborne bacteria:
positive air pressure in OR, filtering >90% of air, exchanging air 15 time/ hr, air introduced from ceiling and exhausted at floor
How does hair removal affect risk of SSI?
Hair removal did not reduce # of CFU compared with leaving hair; shaving increases risk of SSI compared with clipping
Why is shaving associated with an increase risk of SSI?
Results in microscopic cuts to the skin that serve as foci for bacterial multiplication
What is the most common source of bacteria in SSI?
Direct inoculation by endogenous flora
What is the most common pathogen associated with musculoskeletal SSI?
Staphylococcus aureus
What is the most common pathogen associated with long bone fracture or arthrodesis SSI?
Enterobacter
Equation for risk of SSI:
risk of SSI = dose of bacterial contamination x virulence / resistance of host
Examples of microbial virulence factors:
bacterial adhesion molecules, exotoxins, secreted proteins, production of biofilm
Define biofilm:
adherence to and production of a glycocalyx film
Examples of patient related risk factors for SSI:
extremities or age, female gender, immunocompromise due to corticosteroid use, FPT, weight, distant sites of infection, local or systemic hypoxemia, presence of foreign material
What is the relationship between duration of surgery and risk of SSI?
General ortho procedures over 90 minutes increased risk by 3.6; as duration increased for long bone fracture repair the risk of SSI increased; incisional complications are twice as likely if abdominal surgery is > 2 hours
What is the rate of MRSA colonization in hospitalized horses?
2.3%
What is the rate of clinical MRSA nosocomial infection in hospitalized horses?
0.18%
What acute phase proteins are commonly measured?
Fibrinogen, serum amyloid A, haptoglobin
What are the differences in fibrinogen and SAA measurements for SSI detection?
Fibrinogen has a lengthy response to inflammation so is insensitive for SSI detection, SSA has rapid and large changes so more sensitive for SSI
Methods to improve bacterial culture growth:
use of enrichment broth, obtain before administering antibiotics or withhold antibiotics for 24 hours prior to sample selection
Most common isolates in long bone fracture SSI:
gram negative- enterobacter cloacae, gram positive- coagulase negative staphylococcus
Most common isolate in post-operative synovial infections:
staphylococcus aureus
What are the basic principles for treating SSI?
Drain infected tissues aided by gravity; debride devitalized and infected tissue; appropriate therapeutic antimicrobial therapy based on culture & sensitivity
How do concentration dependent antibiotics function?
Rely on the ration of the peak plasma concentration of the antibiotic to the MIC of the bacteria
What is the optimal peak plasma antibiotic concentration to MIC ration for concentration dependent antibiotics?
10:1 or 12:1
How do time dependent antibiotics function?
Depend on a saturable concentration effect for bacterial killing (at some point there is no additional benefit of higher concentration of drug)
How do concentration and time dependent antibiotics differ in dosing?
Because concentration dependent reliant on ratio dosing interval is long and higher doses, time dependent antimicrobials have more frequent dosing with smaller doses to be effective
What is the difference between antimicrobial prophylaxis and therapeutic antimicrobials?
Antimicrobial prophylaxis is a very short term administration protocol given prior to surgical intervention, therapeutic antimicrobial therapy refers to treatment of an established infection
What are the principles of prophylactic antimicrobials?
Antimicrobials only used when benefits have be demonstrated by clinical trial or the risk of SSI would be catastrophic; safe, inexpensive, bactericidal antimicrobial chosen with activity against most likely pathogens; appropriate time of administration; tissue levels of antimicrobial maintained throughout surgery and for a few hours after incision closed
When should prophylactic antibiotics be administered in relation to surgery?
Within 1 hour of incision
When does prophylactic antimicrobial administration become unnecessary?
After 24 hours
What is post antibiotic effect?
Period of time after the antimicrobial concentration has fallen below MIC when growth of targeted bacteria continues to be suppressed
What does the post antibiotic effect depend on?
Antibiotic concentration, duration of exposure to the antibiotic, bacterial species, antimicrobial used
What is the benefit of extended interval dosing?
Concentration dependent antimicrobial activity maximized by optimizing peak plasma concentrations, time dependent toxicity minimized, post antibiotic effect maximized, adaptive resistance is limited
MOA of sulfonamides:
competitive substitution of PABA in conversion of PABA to dihydrofolic acid
MOA of trimethoprim:
inhibit dihydrofolic acid reductase which would convert dihydrofolic acid to tetrahydrofolic acid
What are the advantages of local antimicrobial therapy?
Exposure of pathogen to extremely high concentrations of antimicrobial drugs; avoid adverse effects of systemic doses; deliver high dose of drugs that would be cost-prohibitive systemically
What are the disadvantages of PMMA?
Not absorbable and heat labile antibiotics can not be incorporated
What is the ratio of antibiotic to PMMA?
1-2g antibiotic to 10g PMMA
What can weaken the biomechanical properties of PMMA?
greater than 10% antibiotic to PMMA
What antibiotics have been incorporated into PMMA?
Gentamicin, amikacin, tobramycin, cephalosporins, enrofloxacin
How are PMMA beads re-sterilized?
Ethylene oxide sterilization
What are the benefits of POP over PMMA?
POP is less expensive and will slowly degrade over time
What is the rate of elution of antibiotics from POP?
80% within the first 2 days
What are the disadvantages of POP vs. PMMA?
The set up time of POP is slower
What is the usual dosing recommendation for RLP?
1/3 of systemic dose diluted to 30mL (distal limb) or 60 mL(upper limb)
What is the MOA of renal toxicity of aminoglycosides?
Drug accumulation in the proximal renal tubules by the organic ion transport system
What is the cause of resistance in MRSA?
Production of an altered penicillin-binding protein called PBP2a
What gene is responsible for the production of PBP2a by MRSA and where is it located?
mecA is located in the staphylococcal cassette chromosome (SCCmec)
What is the significance of staphylococcal cassette chromosome mec?
The mec gene is responsible for PBP2a which confers resistance to beta lactams and cephalosporins and downstream from mec in this cassette is a variable segment in which other genes conferring resistance can be added
How are MRSA strains seen in horses different from human and small animals?
The strains common to horses are uncommon in humans and small animals (although strains common in humans are common in small animals) humans can acquire horse strains of MRSA, veterinarians exposed to horse strains of MRSA are likely to carry these strains in nasal passages (8-15.6%)
MIC:
minimum concentration of antibiotic that will visible inhibit bacterial growth after overnight inoculation
Penicillin static or cidal
Bactericidal
Penicillin MOA
Inhibit cell wall synthesis by binding to penicillin-binding proteins, leading to cell lysis
Penicillin adverse effects
Autoimmune hemolytic anemia, anaphylaxis, transient hypotension, increased large intestinal motility, cardiac arrhythmia
Cephalosporins static or cidal
Bactericidal
Cephalosporins MOA
Inhibit cell wall synthesis by binding to penicillin-binding proteins, leading to cell lysis
Cephalosporins adverse effects
Enterocolitis
Bacterial resistance mechanisms to beta lactams:
altered or different PBP, efflux through specific pumps, loss or change in porins, inactivation by beta-lactamases
Aminoglycoside static or cidal
Bactericidal
Aminoglycoside MOA
Inhibit protein synthesis by binding to 30S ribosomal subunit, required oxygen!
Aminoglycoside adverse effects
Nephrotoxicity, neuromuscular blockade, ototoxicity
Bacterial resistance mechanisms to aminoglycosides:
decreased cell entry, altered ribosome structure, destruction by microbial enzymes within cell
Fluoroquinolone static or cidal
Bactericidal
Fluoroquinolone time or concentration:
concentration
Fluoroquinolone MOA
Inhibits bacterial DNA gyrase
Fluoroquinolone adverse effects
Cartilage disorders in young (< 3 years old) horses, oral ulceration
Metronidazole static or cidal
Bactericidal
Metronidazole MOA
Disrupts bacterical DNA by free radicals and unstable intermediate compounds after structural change once in target organism; causes DNA breakage and inhibition of DNA repair
Metronidazole adverse effects
Enterocolitis, inappetence
Trimethoprim sulfonamides static or cidal
Bactericidal when combined. Sulfa static.
Trimethoprim sulfonamides MOA
Synergistic action to inhibit folic acid synthesis (sulfonamides block first step and trimethoprim blocks second stop in folic acid synthesis pathway)
Trimethoprim sulfonamides adverse effects
Idiosyncratic reaction
Tetracyclines static or cidal
Bacteriostatic
Tetracyclines MOA
Inhibit protein synthesis by reversibly binding to 30S ribosomal subunit
Tetracycline adverse effects
Nephrotoxicity, discoloration of urine and erupting teeth
Bacterial mechanisms of resistance to tetracyclines:
plasmid mediated
Chloramphenicol static or cidal
Bacteriostatic
Chloramphenicol, florfenicol MOA
Inhibit protein synthesis by reversibly binding to 50S ribosomal subunit
Chloramphenicol adverse effects
Reversible aplastic anemia (idiosyncratic anemia in humans)
Bacterial mechanisms of resistance to phenicols:
destruction by microbial enzymes (chloro > florfen)
Macrolides static or cidal
Bacteriostatic
Macrolides MOA
Inhibit protein synthesis by reversibly binding to 50S ribosomal subunit
Macrolide adverse effects
Intestinal prokinetic
Bacterial mechanisms of resistance to macrolides:
pump efflux from cell, altered ribosome
Concentration dependent antibiotics
Aminoglycosides, sulphas, rifampin, macrolides, tetracyclines, chloramphenicol, metronidazole, vancomycin, fluoroquinolones
Time dependent antibiotics
Beta lactams, cephalosporins
Common aminoglycosides
Amikacin, gentimicin
Common beta lactams
Penicillins (PPG, Potassium pen), ampicillin, amoxicillin
Common macrolides
Erythromycin, clarithromycin, azithromycin, in FA tulathromycin ("Draxxin") and tilmicosin ("Micotil")
Common fluoroquinolones
Enrofloxacin
Spectrum of penicillins
Excellent gram +, poor gram -, good anaerobes
Spectrum of ceftiofur
excellent gram + and -, good anaerobes
Spectrum of aminoglycosides
Poor gram +, excellent gram -, no anaerobes
Spectrum of sulphas
Excellent gram +, -, good anaerobes
Spectrum of macrolides
Excellent gram +, poor gram -, poor anaerobes
Spectrum of fluoroquinolones
Poor gram +, excellent gram -, no anaerobes
Spectrum of tetracyclines
Excellent gram +, -, anaerobes
Spectrum of chloramphenicol
Excellent gram +, -, anaerobes
Spectrum of metronidazole
Only anaerobes
Spectrum of vancomycin
Only gram +
Penicillins time or concentration
Time
Cephalosporins time or concentration
Time
Aminoglycosides time or concentration
Concentration
Sulphas time or concentration
Concentration
Rifampin time or concentration
Concentration
MOA rifampin:
inhibits RNA synthesis
Spectrum of rifampin:
primarily gram +
Macrolides time or concentration
Concentration
Fluoroquinolones time or concentration
Time
Tetracyclines time or concentration
Concentration
Metronidazole time or concentration
Concentration
Vancomycin time or concentration
Concentration
MOA lincosamides:
inhibit 50S ribosomal subunit
what is an s-type infection?
infection in foals with only the synovial membrane and synovial fluid involvement
conditions related to s-type infections:
very young foals (< 1 week) usually larger joints and usually multiple joints
what is an e-type infection?
infection of the epiphyseal complex in foals
conditions related to e-type infections:
weeks old foals, usually multiple joints, history of FPT or other disease such as pneumonia or diarrhea, mild or intermittent lameness with or without fever
what is a p-type infection?
infection of a long bone physis in foals with or without joint involvement
conditions related to p-type infections:
usually older foals, extension into joint usually at attachment of joint capsule, no history of pre-existing disease, usually only a single site of infection
clinical pathology associated with septic arthritis in foals:
hyperfibrinogenemia with type e and p infections
common p-type bacteria:
strep, rhodococcus, actinobacillus, enterbacteriaeae
most common pathogen in post-injection septic arthritis
staph aureus
most common pathogen in traumatic septic arthritis
enterobacteriaceae
radiographic evidence of type s infection
soft tissue density with marked effusion
radiographic evidence of type e infections
subchondral lytic defect
radiographic evidence of type p infections
large lytic lesion extending to the outer cortex of the bone
cause of sequestrum formation
stripping of the periosteum and loss of blood supply leads to necrosis of a segment of bone
what is a seqestrum
necrotic bone separated from healthy bone
what is an involucrum?
reactive bone that forms around a sequestrum
what is a cloaca?
draining tract to the skin connecting to the opening of the sequestrum
treatment of bone sequestra:
if there is minimal tissue reaction and a small piece of bone, time and appropriate antimicrobial therapy should resolve the infection otherwise removal of the sequestrum and debridement are indicated with local antibiotic therapy or bone graft at the site of debridement
disadvantage of gentamicin collagen sponges
short elution, quick absorption
advantage of antibiotic plaster of paris
very inexpensive
disadvantage of antibiotic plaster of paris
slow to harden
examples of biodegradable biomaterials for local antibiotic delivery
collagen sponges, plaster of paris, hydroxyapatite, dextran gel (R gel)
disadvantage of hydroxyapatite for local antibiotic delivery
expensive
advantages of dextran gel (R gel)
variety of antibiotics available, easy to use
example of non biodegradable biomaterial for local antimicrobial delivery
PMMA
advantage of antibiotic PMMA
easy to use, good elution properties, excellent biocompatibility
disadvantage of antibiotic PMMA
very exothermic curing so can not be used with heat sensitive antibiotics