Ch.7 Surgical Site Infection and the Use of Antimicrobials Flashcards
1
Q
What is the reported SSI rate of fracture repair
A
27.6%
2
Q
How does SSI of fracture repairs influence likelihood of survival to DC
A
7.25 times less likely to survive to DC
3
Q
What is the SSI rate for horses undergoing radial fx repair and how does it influence the implant success
A
44%
17 times more likely to have implant failure
4
Q
Incisional site infection occurs in up to what % of procedures
A
43%
5
Q
A repeat laparotomy does what to the odds of SSI
A
Doubles it
6
Q
How does the centre of disease control classify SSI
A
According to depth and tissue spaces involved
1 - Superficial incisional
2 - Deep incisional
3 - Organ/space involvement
7
Q
The likelihood that a SSI will occur is a complex relationship between
A
1) Microbial characteristics -virulence and pathogen
2) Host characteristics - immune status, age
3) Wound characteristics - hemostasis, foreign material
8
Q
When is the greatest risk for SSI
A
Time of open to time of closure
9
Q
What are the most significant contributors to SSI
A
The hosts innate immune system
The dose and virulence of the bacteria
10
Q
What are the criteria for a superficial incisional infection
A
Within 30 days of sx
Involves only skin or subq
Purulent drainage from the superficial incision
Organism isolated aseptically from sup incision
Pain or tenderness, localised swelling
Superficial incision is opened by surgeon unless it cultures negative
11
Q
What are the criteria for a deep incisional infection
A
Within 30 days of sx
Within 1 year if an implant in place and infection appears to be related to the operation and involves deep soft tissue
Purulent drainage, fever, tender
An abscess
12
Q
What are the criteria for an organ/space SSI
A
Within 30 days if no implant
Within 1 year if implant
13
Q
Host related risk factors for SSI
A
- Extremities of age
- Gender - female
- Immunocompromised
- Weight >250-300kg
- Distant site of infection
- Hypoxia
- Foreign material
14
Q
Surgery related factors for SSI
A
- Emergency procedure
- Patient and surgeon prep
- Duration of sx
- Sx skill
- Foreign material
- Bandage
15
Q
A stent left in place for how long increases SSI
A
> 3 days
16
Q
Within how long after closure is an incision resistant to microbial entry
A
24 hours
17
Q
What % of bacterial skin flora are present in sebaceous glands, hair follicles and sweat glands
A
20%
18
Q
What is the most common musculoskeletal pathogen
A
Staph aureus
19
Q
What is the most common isolate of equine long bone fracture repair
A
Enterobacter spp.
20
Q
What is considered to contribute most to SSI
A
Intraoperative pathogen burden
21
Q
Contamination of a wound with how many microorganisms will lead to SSI
A
100,000
22
Q
What are the main commensuals of the equine distal limb
A
Enterobacter spp.
Bacillus spp.
Micrococcus spp.
23
Q
What methods can be used to reduce the minimum inoculum of Staph aureus
A
Surgical sutures
Polytetrafluoroethylene grafts
Dextran beads
24
Q
How does biofilm evade the host response and antimicrobials
A
Physical barrier against antimicrobials, antibodies, activity of granulocytic cells
Microorganisms is encased
25
What are the primary exogenous bacteria of SSI
G+ Aerobes - Staph and Strep
26
What type of airflow is best for high risk procedures
Laminar air flow - fresh filtered air is blown down onto Sx site pushing air present, aerosols etc to the periphery
27
What are the guidelines from the centre of disease control and preventions recommendations on airflow
1. Maintain positive air pressure in the OR
2. Filtration of >90% of the air
3. Exchange of air 15 times an hour
4. Air introduced from ceiling exits at floor level
28
Clipping/removal of hair prior to intra-articular injection has shown an increased or decreased risk of septic arthritis
20 times greater risk
29
Microscopic skin trauma from clipping with a razor increases the risk of SSI by how much
5.6%
30
Staph aureus, coag-neg Staph and Enterococcus faecalis have what specific virulence factors
MSCRAMMs -
microbial
surface components
recognising
adhesive
matrix molecules
which allow improved adhesion to collagen, fibrin, fibronectin and other extracellular matrix proteins
Also the ability to develop biofilm
31
What is biofilm
An organised community of bacteria attached to a surface and enveloped within a self produced matrix
32
What is unique about the biofilm produced by Staph. aureus
1. Forms a unique matrix of fibrin and glycocalyx
2. that anchors to the cell or inert device
3. and functions as a partial physical barrier
4. against antibiotics, antibodies, and granulocytic cell populations
33
Biofilm producing bacteria possess what unique characteristic
Phenotypic heterogeneity
- allows them to survive and grow at a slow rate
in localised nutrient and oxygen depletion
compared with other planktonic organisms in the same niche.
34
What is SarA and what does it do
1. Regulatory element - controls Staph. virulence factors
Is essential for polysaccharide intercellular adhesion (PIA) synthesis
and therefor biofilm development.
a central regulatory element that controls the production of Staphylococcus aureus virulence factors, is essential for the synthesis of PIA/PNAG and the ensuing biofilm development in this species
35
How does biofilm survive
Release planktonic seeds
stim host immune response
derives nutrients from host exudate
36
What type of antimicrobials and biocides are effect against biofilm
Chlorhexidine
Gentamicin
can bind to sites within biofilm and limit it temporarily
37
What novel techniques are being developed to counteract biofilm
1. surfactant surface modifications
2. sol gel coating
3. covalent antimicrobial tethering
4. hydrophobic poly cat ionic coatings
38
How has age been associated with SSI
Horses <1yr reduced SSI at colic sx 15% compared with adults 43%
Horses >20yrs - 17 times greater risk of incisional site infection
39
Which gender has been associated with more SSI
Female
40
How has temperature been shown to affect SSI
Development of hypothermia (<36*) or decrease in body temp by 2* intro can triple the risk of SSI
41
How is temperature thought to affect immune function
Hypothermia impairs neutrophil function
either through vasoconstriction or hypoxia
can affect platelet function resulting in increased blood loss and hematoma formation
42
How does surgical trauma affect immune function
25% less antimicrobial activity in neutrophils
reduced helper T cell response and proliferation
43
How has hyperbaric oxygen therapy been shown to affect wound healing
Has not been shown any adjunctive effect
44
How has hypoxia been shown to affect wound healing
Low intraop PaO2 <80mmHg increases risk of ventral midline infection
45
How do open fractures compare to closed for SSI
Open 4.2 times more likely to become infected
46
How has suture material been associated with SSI
Silk - 3.4 times more likely to develop a SSI compared with polyglactin 910
A single strand of silk can reduce the number of staph aureus required to cause infection by a factor of 10.
47
What helps bacteria to grow on an implant
Low vascularity at the site of the new implant
Adhesion of serum proteins
formation of a fibrous coating
48
What are the most commonly used implant materials
Stainless steel
Titanium
Titanium alloys
49
Which implant material has been associated with a higher rate of infection and why
Stainless steel
Development of a fibrous fluid-filled capsule at the bone-implant interface that
creates an ideal medium for bacterial proliferation
Latent infection development at a mean of 70months after sx
SSI rate of 4.6% compared with 1.3% for Titanium
50
Pros of titanium and titanium alloy
Decrease fibroblastic adhesion properties
Pure titanium - increased biocompatibility and increased soft tissue adherence
51
Rate of SSI in laparoscopic and arthroscopic procedures
Lap crypt - 0%
Arthroscopy 0.5-1.5%
Risk- draft breed/tarsocrural joint
52
Rate of SSI in celiotomy -emergency vs elective
Risk factors which increase SSI
Emergency - 7.4 - 39%
Risks -
Inexperienced surgeon,
near-far-far-near,
staples,
polyglactin 90
Sx time>2hrs
Protective - lavage linea, topical abs
Elective - 9%
53
How does closed reduction and fixation of a fx compare to open
2.5 times lower SSI
54
SSI incidence of extensive long bone fx compared to articular surface only
5.1 times more likely to develop an SSI
55
SSI rate of P3 fx repair
37.5%
56
SSI infection of clean orthopaedic and clean-contaminated orthopaedic procedures
Clean - 8.1%
Clean contaminated - 52.6%
Risks - Sx duration >90mins
57
SSI rate of long bone fx
A sx time of what duration increases the risk
What else related to the fx can increase the risk of SII
28-32%
Risks - Sx duration >180mins.
Open fx, configuration
58
SSI rate of routine castration
2-3.2%
59
SSI rate of laryngoplasty
0-4%
60
Alcohol based solutions pro and con
Rapid bactericidal effect
Limited persistent antimicrobial effect
Avagard, Sterillium, Monorapid - more effective than aqueous solutions
61
What % of surgical gloves become defective (in small animal procedures)
26.2%
62
Risk of SSI increases by how much when 1st/2nd yr resident closes the abdomen
Doubles
63
How does time affect SSI rates
Double with every hour (clean wounds)
64
Post op incisional infection are more likely in abdominal surgeries exceeding how long and what % occurrence
>2 hours
47%
65
Orthopedic procedures >90mins are how many times more likely to develop a SSI
3.6
66
Is polyglycolic acid for closure of the subcutaneous tissue associated with an increased or decreased risk of SSI?
Increased
67
How does the use of surgical staples affect the SSI rate in celiotomy
Increases it 4 fold
1.3 times the likelihood of incisional drainage
68
Does irrigation of the SS with antibiotic containing sterile fluids decrease the SSI
Yes
Use drugs not commonly used systemically - vancomycin/polymixin
69
Pros and cons of using a stent bandage
Pro: 2.7% SSI vs 21.8% without a stent
Con: If left in place for 3 days or more have an increased rate of SSI
70
Use of belly bandage on a paramedian celiotomy ...
Increased SSI
71
What % of hospital admissions develop nosocomial infections
20%
72
Horses undergoing celiotomy are how likely to develop nosocomial Salmonella infections
2 - 8 times
73
Clinical indicators associated with acute salmonellosis
Fever >103
Abnormal leukocyte count
Acute colitis
74
Horses presenting with acute colic that become more lethargic and inappetent are how likely to shed salmonella
17 times
75
C. diff has been isolated from what % of veterinary hospital samples
3-17%
76
What % of horses experience catheter site inflammation and infection
9%
77
Most commonly isolated pathogens from catheters
Staph
Corynebacterium
Bacillus
Enterobacter
Pseudomonas
78
Catheter related complications are high in IVC left in place for how long
>3.5 days
79
Nasal colonisation of MRSA in vet personnel is how prevalent
9.4-22.2%
80
In horses undergoing complicated orthopaedic procedures SSI increased the hospitalisation and duration of antimicrobial therapy by how long
32.1 days in Hospital
17.3 days abx
81
When is incisional drainage likely to occur
6-10 days post op
82
How long after injury does fibrinogen peak
7-10 days
83
How many mg/dl fibrinogen has been associated with osteomylitis
900mg/dl
84
When does SAA peak and return to baseline
36-48hrs
Returns to baseline in 1-2weeks
85
Cell/uL, %Neutrophils and TP of normal synovial fluid
1000 cells/uL
10% Neutrophils
2 g/dl TP
86
A nucleated cell count of what is pathognomonic for infection
75,000 cells/uL
87
Intraarticular TP concentrations have been shown to increase how long after arthrocenthesis
4 hours
88
Normal synovial fluid lactate
3.9mmol/L
89
What difference between peritoneal fluid glucose and peripheral indicates peritonitis
>50mg/dl
90
Obtaining a positive culture is dependent on
1. Method of culture
2. Number and virulence of the organism
3. Defence mechanism of the organism
91
Tissue culture vs swab culture sens/specif
Tissue sensitivity 98% specificity 93%
Swab sensitivity 89% specificity 70%
92
Incidence of positive culture from synovial fluid
64-89%
93
How large a volume of fluid is required for most blood culture vials
8-10ml
94
How much bone demineralisation must occur before it is radiographically evident
50%
95
What MRI sequences are advised for imaging of SSI
T1-weighted
T-2 weighted
Short Tau inversion recovery
96
Photopenia in nuclear scintigraphy may be an indication of
osteitis
97
Common isolate of cellulitis
60% Staph. aureus
Strep
98
Most common isolates of post op synovial structures
34-52% Staph. aureus
22% haemolytic staph
25% gram neg
99
Most commonly isolated pathogens of neonates
Escherichia coli
Actinobacillus
Klebsiella
100
% G+ vs G- isolates from joints of septic foals
62.5% G-
37.5% G+
101
Which is the most commonly isolated G- in musculoskeletal inf
Enterobacter cloacae
102
Penetrating wounds are most likely to culture what bacteria
Staph
Pseudomonas
Proteus
Enterobacter
Yeast
Fungi
103
Most common isolates of foot wounds
Enterobacter
Strep zooepidemicus
104
Post op peritonitis is associated with which bacteria
Strep
Enterobacteriaceae
Actinobacillus
Anaerobes
105
Most common isolates of paranasal sinus and guttural pouch
Strep equi asp equo
Strep zooepidemicus
Aspergillus
Cryptococcus
106
Most common isolates of septic physitis/arthritis in foals
Escherichia coli
Rhodococcus equi
107
Most common isolates of chronic wounds
Pseudomonas
Staph
Serratia
Enterococcus
Providencia
108
Most common isolates of orthopaedic sx
Enterobacteriaceae
Staph
Strep
Pseudomonas
109
Most common isolates of penetrating wounds to synovial structures
Enterobacteriaceae
Anaerobes
110
Common time dependent antimicrobials
Beta lactams
Trimethoprom sulphonamides
Macrolides
Tetracyclines
Chloramphenicol
111
Common concentration dependent antimicrobials
Aminoglycosides
Fluoroquinolones
Metronidazole
112
What is the optimal ratio for peak concentration to MIC of concentration dependent drugs
10:1 or 12:1
113
How is the peak concentration of conc dependent drugs monitored
Serum sample 60 mins after IV or 90 mins after IM administration
114
What through level of amikacin is advised to reduced nephrotoxicity
<1ug/ml
115
When should antimicrobials be redosed in surgery
If surgical procedure exceeds 1 to 2 times the half life of the antibiotic
116
When should prophylactic antibiotics be used
When risk of SSI is >5% without their use or if a SSI would be life threatening
117
Within how long of surgical incision should abs be administered
1 hour
118
The risk of SSI increases from 6.3-28% for surgeries lasting longer than...
2 hours
119
Failure to redose abs during long surgeries increases the SSI risk by how much?
4.5 times more likely
120
Mechanism of action and adverse effects of penicillin
Bactericidal - Time dependent
Inhibit cell wall synthesis by binding to penicillin-binding proteins, leading to cell lysis
Adverse effects
Autoimmune haemolytic anemia anaphylaxis
Transient hypotension
Increased large intestine motility
Cardiac arrhythmia
121
Mechanism of action and adverse effects of cephalosporins
Bactericidal - Time dependent
Inhibit cell wall synthesis by binding to penicillin-binding proteins, leading to cell lysis
Adverse effects
Enterocolitis
122
Mechanism of action and adverse effects of Aminoglycosides
Bactericidal - Concentration dependent
Inhibit protein synthesis by binding to 30S ribosomal subunit
Adverse effects
Nephrotoxicity
Neuromuscular blockade
Ototoxicity
123
Mechanism of action and adverse effects of Fluoroquinolones
Bactericidal
Inhibit bacterial DNA gyrase
Adverse effects
Cartilage disorders in young <3yo
Oral ulceration
124
Mechanism of action and adverse effects of metronidazole
Bactericidal
Disrupt bacterial DNA by free radicals and unstable intermediate compounds after structural change once in target organism
Adverse effects
Enterocolitis
Inappetence
125
Mechanism of action and adverse effects of trimethoprim/sulfonamide
Bactericidal
Synergistic action to inhibit folic acid Synthesis
Sulfa block 1st step:
Para-aminobenzoic acid to dihydrofolic acid
Bacteriostatic when used alone
Trimethoprim 2nd step
Inhibits dihydrofolic acid reductase
Adverse effects
Idiosyncratic
126
Mechanism of action and adverse effects of Tetracyclines
Bacteriostatic
Inhibit protein synthesis by reversibly binding to 30S Ribosomal subunit
Adverse effects
Nephrotoxicity
Discolouration of urine and erupting teeth
127
Mechanism of action and adverse effects of Chloramphenicol
Bacteriostatic
Inhibit protein synthesis by reversibly binding to 50S ribosomal subunit
Adverse effects
Reversible aplastic anaemia
128
Mechanism of action and adverse effects of Microlides
Bacteriostatic
Inhibit protein synthesis by reversibly binding to 50S Ribosomal subunit
Adverse effects
Intestinal pro-kinetic
129
Common bacteriostatic antimicrobials in equine medicine
Tetracyclines
Chloramphenicol
Macrolides - foals
130
Common bactericidal antimicrobials in equine medicine
Penicillin
Cephalosporins
Aminoglycosides
Fluoroquinolones
Metronidazole
Trimethoprim/sulfonamide
131
Why do neonates require a higher dose of aminoglycosides than adults up to 4-6 weeks
Aminoglycosides are distributed within the extracellular space - foals have a larger ecf than adults
132
Nephrotoxicity occurs due to prolonged exposure of renal tubules or exposure to a high concentration
Prolonged
133
Ratio of Potentiated sulphonamides to trimethoprim
1:5
134
Local concentration of abs from PMMA beads reach what level compared to systemic
200 times greater than systemic
135
How long do AIPOP beads remain active when stored at room temperature
5 months
136
At what % antimicrobial is there
a- inhibition of hardening process
b- weakening of biomechanics properties
of PMMA
>20% of antimicrobial inhibits hardening
>10% weakens the biomechanics
137
Which antibiotics are not suitable for PMMA beads
Non heat stabile ones - must be stable to 100*C (low tissue toxicity)
Not suitable:
Polymyxin B
Chloramphenicol
Tetracyclines
138
Drug combinations which enhance elution
Vancomycin-amikacin
Gentamicin-metronidazole
Cefazolin-amikacin
139
Alternative delivery systems to PMMA and AIPOP
Bovien collagen sponge
Hydroxyapatite (HAP)
Beta tricalcium phosphate (B-TCP)
140
Complication rate of RLP using 22g butterfly catheter
12%
141
What dose of an abx is advised in a RLP
One third of the systemic dose
However doses less than 0.5g are not effective
142
Parenteral antimicrobial tx increases the risk of developing Salmonellosis
1) by how much?
2) if combined with enteral abx
6.4 times
40 times if combined with enteral
