• 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