Micro - Wound, Bone, and Joint infections Flashcards
Which organisms cause surgical site infections
Staph. aureus (including MSSA and MRSA)
E. coli
Pseudomonas aeruginosa
What are the levels of surgical site infections
Superficial Incisional: skin and subcutaneous tissues
Deep Incisional: fascial and muscle layers
Organ/Space Infection: any part of the anatomy other than the incision
What are the pre-operative methods for preventing surgical site infections
Determine their risk (age, ASA score, co-morbs, medications, obesity, smoking)
Day of /day before surgery showering
Hair removal using an electric clipper on the day of the surgery
Nasal decontamination if carrying S. aureus
Abx prophylaxis
What is the most powerful risk factors for surgical site infections following cardiothoracic surgery
Staph. aureus carriage in the nostrils
What are the intra-operative management options to prevent surgical site infections
Limiting no. of people in theatre
Positive pressure
Sterilisation of surgical instruments
Skin prep: chlorhexidine in 70% alcohol
Maintain normothermia
Oxygenation >95%
Why must normothermia be maintained in patients during surgery
Hypothermia → increase risk of SSIs by causing vasoconstriction and decreasing oxygen delivery to wound space with impairment of neutrophil function
What are the risk factors for septic arthritis
Rheumatoid arthritis
Osteoarthritis
Crystal arthritis
Joint prosthesis
IVDU
Diabetes, chronic renal disease, chronic liver disease
Immunosuppression (e.g. steroids)
Trauma – intra-articular injection, penetrating injury
What is the pathophysiology of septic arthritis
Organisms adhere to synovial membrane
Bacterial proliferation in synovial fluid → host inflammatory response → joint damage
Joint damage → exposure of host derived protein (e.g. fibronectin) to which bacteria can adhere
What are the most common causative organisms for septic arthritis
Staph aureus (46%)
Streptococci pyogenes/pneumoniae/agalactiae
Gram -ves: E. Coli, H. influenzae, N. gonorrhoea, salmonella
Coagulase-negative staph
Lyme disease, Brucellosis, Mycobacteria, fungi
What are the factors that contribute to septic arthritis
Bacterial: Staph. aureus has fibronectin-binding protein and may produce cytotoxin PVL
Kingella kingae: synovial adherence via bacterial pili
Leucocyte → proteases and cytokines → cartilage and bone damage
Raise intra-articular pressure → impedes capillary blood flow → cartilage and bone ischaemia/necrosis
Genetic deletion of macrophage-derived cytokines
Absence of IL-10 → increases severity of staph.aureus joint disease
What investigations should be done for septic arthritis
Blood cultures
US with Synovial fluid aspiration for MC&S → synovial count >50,000 WBCs = septic arthritis
ESR/CRP
CT - check for erosive bone change, soft tissue extension
MRI - joint effusion, articular cartilage destruction, abscess, contiguous osteomyelitis
What is the management for septic arthritis
ABx, 4-6 weeks (outpatient setting)
- IV cephalosporin or flucloxacillin
- MRSA risk: vancomycin
Drainage of the joint - arthroscopic washout
What are the causes of spinal epidural abscesses and vertebral osteomyelitis
Acute haematogenous spread or exogenous (disc surgery, implants)
Staph. aureus
Coagulase negative staph
Gram -ve rods
Streptococcus
What is the most common site of Spinal epidural abscesses and Vertebral Osteomyelitis
Lumbar (45%)
Cervical
Cervico-thoracic
What investigations should be done for Spinal epidural abscesses and Vertebral Osteomyelitis
MRI (90% sensitivie)
blood cultures
CT-guided/open biopsy