Surgical infection Flashcards
What does the severity of infectious disease depend on
Microbial virulence x numbers / host defences
What 3 factors is microbial virulence associated with
- Does not stimulate host defence
- Withstands host defence
- Causes host tissue damage (e.g toxin)
What 3 body surfaces act as defence
Mucocutaneous surface
Humoural (blood and tissue)
Celluluar (WBC)
What are 3 major proven factors increasing risk of surgical site infection
- degree of contamination, i.e. surgical wound class
- length of operation
- Pre-existing illness malignancy, DM, immunosuppression
Another proven factor increasing surgical infection risk
- patient related - age, obesity
What are 7 suggested but unproven factors that increase risk of surgical site infection
- length of pre-op hospital stay
- reoperation
- glove punctures, powder
- time of day
- month of year
- use of adhesive drapes
- use of wound irrigation
List 3 ways surgeons reduce surgical infections
- Where possible, wounds should be left alone for at least 48hrs post-operatively ! wetting, changing dressing too early can lead to contamination of tissues
- Patients get better from infection is probably only 40% antibiotics related ! the most important factor is host defence
- that’s why surgeons drain abscesses, remove necrotic tissues, and attempt to resurrect normal WBC function and numbers in
transplant or immunocompromised patients
When do infections generally become apparent in surgical patients
> 70% become apparent after patient has left the hospital
Have masks and gowns been shown to reduce post op surgical site infection
No
List 4 important infection control measures in peri-op care
- restriction in numbers and movement of theatre staff ! ?movement of air
- cleansing of skin in the operation field by antiseptics
- the administration of prophylactic antibiotics prior to skin incision
- hair clipping immediately prior to incision NOT razor shaving
When is it best to give prophylactic abx in surgery
is at time of induction of anaesthesia, i.e. around 20 minutes prior to incision
For elective procedures lasting 2 hours or less how many abx doses is warranted and why
a single dose of prophylactic Abx is enough; continuing therapy after wound
closure should be restricted because of unproven benefit and risk of selection of resistant bacteria
Should you cover all possible encountered microbes
no
How many abx for procedures > 2 hours or if there is blood loss
one or 2 further doses at intervals 2 times the plasma half
life (i.e. around 2hrly for most Abs) may be required. In such cases, a good time for the final dose is just before wound closure.
3 important principles for selecting abx peri-operatively
- should have minimal interaction with other drug likely to be used at the time of surgery,
- must be active against the microbes most likely to result in surgical site infection
- should always have staph aureus cover
In what circumstances may the antibiotic regimen be prolonged (6)
- during an emergency,
- likelihood of an active infection,
- an obstruction,
- unusual blood loss,
- trauma
- a high risk patient
Generally speaking what group of abx are suitable for surgical patients
First and second generation cephalosporins, in combination with metronidazole where appropriate, seem ideally suited for surgical prophylaxis
Is selective decontamination of the GI tract in critically ill patients of benefit
Highly debatable and largely unproven
What bugs need to be covered with abx in large bowel surgery
- Enteric coliforms, e.g. E. coli
- Obligate anaerobe, bacteroides fragilis
- staph aureus, important skin wound pathogen in all invasive surgical settings
Why isnt amoxicillin alone suitable for large bowel surgery prophylaxis
- amoxycillin is not enough to cover E. coli (>50% of E.coli are resistant to amoxicillin by B-lactamase)
- amoxycillin is not enough to cover staph aureus >80% produce penicillinases which inactivate amoxicillin
why isnt flucloxacillin alone suitable for large bowel surgery prophylaxis
flucloxacillin is not enough to cover against E. coli
Can aminoglycosides be used as large bowel surgery prophylaxis
- Tobramycin doen’t work against obligate anaerobe
- In addition, anaesthetic agents may potentiate the neuromuscular blocking effects of aminoglycosides ! so best avoid it
Most significant post op CABG bugs
- staph, both coagulase negative (e.g. epidermidis) and coagulase positive (e.g. aureus)
- E.coli, minor but still significant risk, if untreated, may adhere to any foreign material/implants, more relevant in valve replacement than CABG
Abx prophylaxis in CABG and what bug must be covered
- cefamandole is an acceptable choice
- cover against coagulase negative staph. Must be included in the antibiotic(s) chosen
Pathogens to cover for hip replacement surgery and what type of abx to use
- Staph both aureus and epidermidis
- Thus first or second generation cephalosporins are good, first generation better bone penetration and longer half life;
second generation better anti-staph effects
ABx to use in hip surgery
- Vancomycin should not be used unless MRSA are a major consideration
- cephazolin alone
Are gram negative coliforms implicated in hip operations
Can be, can result in significant post op infections
Incidence of post op hip infections
<1%
Where can peritonitis be located
- diffuse or localized
- intra or retroperitoneal space
- on viscera or mesentery
Where can intra-abdominal collections travel/ where are abscesses formed
- form around the involved organs
- walling off around SB or omentum
- traveling along paracolic gutters by gravity to pelvis
- travel up by negative pressure and lymphatic flow to subphrenic space
- travel to anywhere by operative anipulation
What are the 3 types of peritonitis
- primary (or spontaneous) peritonitis ! don’t know the source of infection, e.g. cirrhosis and ascites
- secondary peritonitis ! leakage of microbes from an injured or ruptured viscus (e.g. appendix)
- tertiary peritonitis ! persistent peritonitis in seriously ill patients, e.g. G –ve bacilli or yeasts ! generalized sepsis with shock
What is the classical management of peritonitis
- operative control of contamination/pathology
- antibiotic therapy
- intensive care support
Describe the biphasic development of secondary peritonitis
- initial phase, diffuse peritonitis, bacteremia with or without specific shock mainly a/w G-ve bacilli, e.g. E.coli,
pseudomonas aeruginosa - Second phase, survivors localize infection into abscesses in which bacteroides fragilis often in a/w facultative anaerobes
, synergy