bone and joint infections Flashcards
consequences of surgical site infections
Increased length of stay ( THR- 11 days longer);
additional surgical procedures,
treatment in ITU,
higher mortality
what are the major pathogens involved in surgical site infections
Staph.aureus (MSSA and MRSA)
E.coli
Pseudomonas aeruginosa
bacteria depends on site of infection
intra-abdo - more likely gram -ve eg E coli
hip replacement - more likely S aureus
pathogenesis of surgical site infection
contamination of wound at op
> 10(5) microorganisms per gram of tissue, risk of SSI is increased.
dose of bacteria needed is lower if foreign material present
whether infection happens depends on:
pathogenicity and innoculum of microorganisms
host immune response
ie strep A more virulent than staph viridans
if immunosuppressed more likely infection
what are the 3 levels of surgical site infection
superficial incisional - affect skin and subcut tissue
deep incisional - fascial and muscle layers
organ/space infection - any part of anatomy other than incision
what are underlying conditions/states that lead to surgical site infections
ASA score of 3 or more
diabetes - 2-3x increase, association with post-op hyperglycaemia. control blood glucose, HbA1c <7
malnutrition
low serum albumin
radiotherapy
steroid use - taper steroids pre surgery
RA - stop disease modifying agents 4wk pre and 8wk post op
how does obesity increase risk of surgical site infections
adipose tissue poorly vascularised
poor oxygenation + poor functioning of immune response
risk increase 2-7x with BMI of 35 or more
how does smoking increase surgical site infection risk
duration and number smoked
nicotine delays primary wound healing
peripheral vascular disease
vasoconstrictive effect of reduced oxygen-carrying capacity of blood
encourage tobacco cessation pre-op
how does pre-op showering alter surgical site infections
microorganisms colonising the skin can contaminate exposed tissues -> SSI
no difference in SSI incidence when chlorhexidine or detergent/bar soap is used
advise to shower on day of surgery or day before
how does hair removal alter surgical site infections
Micro-abrasions caused by shaving with a razor may -> multiplication of bacteria
Use electric clippers on the day of surgery with single-use head on day of op
Hair should not be removed unless it will interfere with the operation
should nasal decontamination happen to prevent surgical site infections
S.aureus is carried in the nares of 20-30%
carriage is the most powerful independent RF for SSI
so should have decontamination
antibiotic prophylaxis for SSI
given at induction of anaesthesia
Bactericidal concentration of the drug should be established in serum and tissues at time of incision.
additional doses needed if sig blood loss or op prolonged
how many people should be in theatre - in terms of surgical site infection
all carry bacteria on skin
microbial load in theatre is related to number of people present
so keep people to a min
how should theatres be ventilated to prevent SSIs
maintain positive pressure ventilation
20 air changes per hour (of which at least 3must be fresh air)
filter all air
keep op room doors closed
Consider laminar flow for orthopaedic implant surgery
what skin prep should be done to prevent SSIs
antiseptic prep
chlorhexidine in 70% alcohol used
what temperature should people be kept at to prevent SSIs
normothermia
mild hypothermia increases risk of SSIs -> vasoconstriction -> reduced oxygen to wound space and impairment of neutrophil function
measure temp before anaesthesia
start forced air warmining of temp <36 (warm IV fluid and irrigation fluid)
what level of oxygenation should patients be kept at to prevent SSIs
keep Hb sats above 95%
higher ox = reduced SSIs
epidemiology of septic arthritis
Incidence is 2-10 cases per 100,000
Mortality is 7-15%
Morbidity is 50%
incidence higher if have rheumatoid arthritis
RF for septic arthritis
rheumatoid arthritis
osteoarthritis
crystal induced arthritis
joint prosthesis
IVDU
dm
chronic renal disease
chronic liver disease
immunosuppression - steroids
trauma - intra-articular injection, penetrating injury
pathophysiology of septic arthritis
organisms adhere to synovial membrane
bacterial proliferation in synovial fluid - generation of host inflammatory immune response
joint damage -> exposure of host derived proteins such as fibronectin that bacteria adhere to
bacterial factors that contribute to pathogenesis of septic arthritis
S.aureus: receptors eg fibronectin binding protein that recognise selected host proteins.
Kingella kingae: synovial adherence is via bacterial pili (cause septic arth in children)
Some strains produce the cytotoxin PVL ( Panton-Valentine Leucocidin) which have been associated with fulminant infections.
host factors that contribute to pathogenesis of septic arthritis
Leucocyte derived proteases and cytokines -> cartilage degradation and bone loss.
Raised intra-articular pressure reduces capillary blood flow -> cartilage and bone ischaemia and necrosis.
Genetic variation in expression of cytokines may -> differential susceptibility to septic arthritis.
causative organisms of septic arthritis
Staph. aureus 46%
- Coagulase negative staphylococci 4%
Streptococci 22%
* Streptococcus pyogenes
* Streptococcus pneumoniae
* Streptococcus agalactiae
Gram negative organisms
* E.coli
* Haemophilus influezae
* Neisseria gonorrhoeae
* Salmonella
Rare- Lyme, brucellosis, mycobacteria, fungi
clinical features of septic arthritis
1-2 week history of red, painful, swollen restricted joint
mainly monoarticular
knee half the time
if rheumatoid arthritis - signs more subtle
investigations for septic arthritis
blood culture before abx if pyrexial
synovial fluid aspiration fro MC&S
ESR
CRP
a synovial count> 50,000 cells/mm3 used to suggest septic arthritis
negative culture doesnt exclude septic arthritis
US - confirm effusion and guide needle aspiration
MRI - joint effusion, articular cartilage destruction, abscess, contiguous osteomyelitis
