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• Asepsis and antisepsis
• Asepsis and antisepsis
• Antisepsis is the use of chemical solutions for disinfection
• Asepsis is the absence of infectious organisms
• Aseptic techniques are those aimed at minimising infection
• Asepsis usually involves
• The use of sterile instruments
• The use of a gloved no touch technique
• Antisepsis is the removal of transient microorganisms from the skin and a
reduction in the resident flora
Preoperative skin preparation
• Bacterial flora of the patient is the principle source of surgical wound infection
• Focal sources of sepsis should be treated prior to surgery
• In patients with active infection consideration should be given to delaying surgery
• Pre-operative showing with an antiseptic solution does not reduce infection rate
• Skin shaving
• Aesthetic and makes surgery, suture and dressing removal easier
• Wound infection rate lowest when performed immediately prior to surgery
• Infection rate increased from 1% to 5% if performed more than 12 hours prior to surgery
• Abrasions can cause colonisation which can lead to wound infection
• Clippers or depilatory creams reduce infection rates to less than 1%.
Skin preparation
• 70% Isopropyl alcohol
• Acts by denaturing proteins
• Is bactericidal but short acting
• Effective against gram-positive and gram-
negative organisms
• Also fungicidal and virucidal
• Chlorhexidine
• Quaternary ammonium compound
• Acts by disrupting the bacterial cell wall
• Bactericidal but does not kill spore forming organisms
• It is persistent and has a long duration of action (up to
6 hours)
• More effective against gram-positive organisms
70% Povidone - iodine
• Acts by oxidation / substitution of free iodine
• Bactericidal and active against spore forming organisms
• Effective against both gram-positive and gram-negative
organisms
• Rapidly inactivated by organic material such as blood
• Patient skin sensitivity is occasionally a problem
• Chlorhexidine may be more effective than iodine
Sterilisation
• Removal of viable microorganisms including spores and viruses
• Can be achieved by:
• Autoclaves
• Hot air ovens
• Ethylene oxide
• Low-temperature steam and formaldehyde
• Sporicidal chemicals
• Irradiation
• Gas plasma
Disinfection
• a reduction in the number of viable organisms
• Can be achieved by:
• Low-temperature steam
• Boiling water
• Chemical disinfectants
Tourniquets
• Commonly used in surgical practice
• When properly used they provide excellent
haemostasis
• When incorrectly used they are dangerous
• Cuff failure can be disastrous with rapid systemic
absorption of drugs (e.g. local anaesthetics)
• Ensure correct placement and connection
• Use adequate padding
• Exsanguinate limb before inflation
• Use minimal pressure - usually 100 mmHg above systolic blood pressure
• Use for minimal duration - no longer than 90 minutes
• Avoid multiple inflations or deflations
• Be aware of relative contraindications to use
• Previous DVT or PE
• Arterial disease
• Vasculitic disorders
• Sickle cell anaemia
Complications
• Nerve injury
• Vascular injury
• Postoperative embolic events
• Post-tourniquet syndrome
• Myoglobinuria
• Increased blood viscosity
• Increased postoperative pain
• Tourniquet burns
Diathermy
• Diathermy is the use of high frequency electric current to produce
heat
• Used to either cut or destroy tissue or to produce coagulation
• Mains electricity is 50 Hz and produces intense muscle and
nerve activation
• Electrical frequency used by diathermy is in the range of 300 kHz
to 3 MHz
• Patients body forms part of the electrical circuit
• Current has no effect on muscles
Monopolar diathermy
• Electrical plate is placed on patient and acts as
indifferent electrode
• Current passes between instrument and indifferent
electrode
• As surface area of instrument is an order of magnitude
less than that of the plate
• Localised heating is produced at tip of instrument
• Minimal heating effect produced at indifferent electrode
Bipolar diathermy
• Two electrodes are combined in the instrument
(e.g. forceps)
• Current passes between tips and not through
patient
Effects of diathermy
• The effects of diathermy depends on the current intensity and
wave-form used
• Coagulation
• Produced by interrupted pulses of current (50-100 per second)
• Square wave-form
• Cutting
• Produced by continuous current
• Sinus wave-form
Risk and complications
• Can interfere with pacemaker function
• Arcing can occur with metal instruments and implants
• Superficial burns if use spirit based skin preparation
• Diathermy burns under indifferent electrode if plate
improperly applied
• Channeling effects if used on viscus with narrow
pedicle (e.g. penis or testis)
Staphylococcal infections
• More than 30 staphylococcal species exist
• All are part of normal skin and mucous
membrane flora
• They are either coagulase-positive or negative
• The most important coagulase-positive species is
Staph. aureus
Staph aureus• 30% adults carry Staph. aureus in their anterior nares
• Carriers transfer the organism to skin allowing a portal of entry
• Toxins (e.g. haemolysins and leukocidins)
• Enzymes (e.g. coagulase, protease, hyaluronidase)
• The organism is both aerobic and anaerobic on blood agar
• Microscopically it is gram-positive
• Forms clusters on solid media
• There is increasing spread of clones resistant to beta-lactam antibiotics
(e.g. MRSA)
Coagulase-negative
staphylococci• Staph. epidermidis and Staph. saprophyticus are the commonest
human pathogens
• Staph. epidermidis is a common cause of nosocomial
bacteraemia
• Often associated with indwelling catheters and prosthetic
materials
• Is a common cause of prosthetic valve endocarditis
• Its is often multiply antibiotic resistant
• Treatment may require removal of line or prosthesis
Streptococcal infections
• Streptococci are gram-positive cocci
• More than 30 species have been identified
• On solid media they grow in pairs or chains
• They are catalase negative
• Beta-haemolytic streptococci are classified
according to their Lancefield group
MRSA
• MRSA is a major nosocomial pathogen
• Causes severe morbidity and mortality worldwide
• Endemic in many European and American hospitals
• 40% of nosocomial Staph. aureus infections are methicillin resistant
• Many in-patients are colonised or infected
• 25% hospital personnel may be carriers
• Found on inguinal, perinea, or axillary skin and anterior nares
• Spread by hand, usually of health care workers
• Staph aureus is a gram-positive coccus
• Forms clusters on culture medium
• Methicillin resistance is mediated by the mecA
gene
• Encodes a single additional penicillin binding
protein PBP2a
• Expression of mecA can be either constitutive or
inducible
Risk factors for MRSA
colonisation• Advanced age
• Male gender
• Previous hospitalisation
• Length of hospitalisation
• Stay in ICU
• Chronic medical illness
• Prior and prolonged antibiotic therapy
• Presence and size of a wound
• Exposure to colonised or infected patient
• Presence of invasive indwelling device
Infection control
• Screening of patients and staff
• Hand washing
• Use of gowns and gloves
• Topical antimicrobials
• Isolation of patients
• Environmental cleaning
Antibiotics
• An antibiotic is an agent that either kills or inhibits
the growth of a microorganism
Types
• Acting on
• cell wall / membrane
• Folic acid
• DNA
• RNA
• Protein synthesis
Types