Essential Notes for MRCS - Book 2(B)

SECTION 4

Surgical infections

In a nutshell ...

You will come across infections that are:
Primary conditions (eg any surgical condition ending in -itis) • Community-acquired (eg UTI,

gastroenteritis) • Hospital-acquired (nosocomial)
Always attempt to identify the organism in order to tailor antibiotic treatment, ie send specimens before
starting empirical treatment.
Do not delay treatment if clinically septic (ie treat with a ‘best guess’ antibiotic after sending
specimens).
Take advice from microbiologists. This is essential in immunocompromised individuals and patients
previously treated with multiple antibiotics.

4.1 Recognition of a septic patient

Definitions of ‘sepsis’

Sepsis: clinical evidence of infection • Sepsis syndrome: clinical evidence of infection plus evidence of
altered organ perfusion • Septic shock: septic syndrome plus evidence of decreased blood pressure
unresponsive to fluid therapy

Clinical indicators of infection

Consider sepsis as a diagnosis in cases of:
Changes in core temperature
• Fever: >37.8°C
• Hypothermia: <36°C (especially in elderly people) • Unexplained hypotension
Oliguria
Confusion

Patients should be thoroughly examined and a septic screen performed.

Examination for sepsis



Possible foci of infection
Abdominal examination
Bowel: eg inflammatory bowel disease, perforation, anastomotic leak, abscess • Hepatobiliary: eg
cholecystitis, cholangitis, hepatitis • Genitourinary: eg urinary tract infection (UTI), pyelonephritis
Respiratory examination (eg pneumonia) Cardiovascular examination (eg endocarditis) Skin:
surgical wound inspection, percutaneous lines including Venflon, abscesses Joints: septic arthritis,
prosthetic infection CNS: meningitis, encephalitis
Haematological: recent travel (eg malaria)



Septic screen
Blood tests
Full blood count (for leucocytosis)
Acute phase proteins: C-reactive protein, fibrinogen • Urea, creatinine and electrolytes
Liver function tests (LFTs)/amylase
Clotting
Arterial blood gases (ABGs) for acidosis
Radiology
Chest radiograph
Abdominal radiograph
CT
Cardiac echo
Microbiology
Blood cultures
Sputum
Urine

Septic screen

The nature of the septic screen should be directed by findings at patient examination. In particular,
radiological investigation of sepsis should be targeted to the most likely focus.

Blood tests for sepsis

Leucocytosis
The white cell count (WCC) may be elevated, referred to as ‘leucocytosis’. Differential diagnosis of
leucocytosis is discussed in Chapter 3. Features of leucocytosis pertinent to sepsis will be outlined here.
Very high WCCs may be indicative of abscess formation (>20). The WCC may be low if there is
overwhelming sepsis (NB, the elderly may exhibit signs of sepsis without a rise in the WCC).
Neutrophils: increases in the neutrophil count are commonly due to bacterial infection. Neutropenia may
occur due to underlying conditions (eg immune deficiency, chemotherapy) or to overwhelming sepsis.
Chemical mediators produced by leucocytes cause increased numbers of neutrophils to form in the bone
marrow; these are released early into the bloodstream, producing a neutrophilia indicative of an acute
inflammatory response • Lymphocytes: a low lymphocyte count is indicative of sepsis; a high lymphocyte
count may indicate viral illness

Acute phase proteins
CRP is commonly used as a marker for sepsis as levels respond within 24 hours to inflammatory change
(compared with the ESR, which takes days). The range for CRP is commonly <8 to >285 in most labs.
Elevated CRP of >100 is strongly indicative of bacterial infection. CRP is commonly elevated
postoperatively (as an acute response to trauma) so should be interpreted with care. Fibrinogen levels are
also elevated postoperatively.

U&Es and LFTs
Urea, creatinine and electrolytes are important to assess renal function (severe sepsis can result in ARF).
Renal function is also important in the administration of certain antibiotics (eg gentamicin). Albumin
levels fall in acute sepsis and LFTs may become elevated in cholangitis or sepsis syndrome. Elevation in
amylase may occur as a result of pancreatitis or inflammation near the pancreas.

Arterial blood gases
ABGs are important to demonstrate acidosis. Metabolic acidosis may occur in sepsis as a result of low
BP and poor tissue perfusion.

Clotting screen
There may also be a non-specific thrombocytosis (increased platelet count). It is not clear whether this
translates into increased risk of thrombosis. Sepsis may also result in DIC, with deranged clotting
parameters such as increasing prothrombin time (PT) and falling platelet count.

Radiology
Chest radiograph may show consolidation or demonstrate free intra-abdominal gas (indicative of
perforation of a viscus). Remember that changes in the chest radiograph may lag behind clinical signs.
Abdominal collections are best demonstrated by CT but can sometimes be seen on ultrasonography.

Microbiology
See section 4.6, Specimen collection page 329.

4.2 Fever in a postoperative patient

Postoperative pyrexia

A low-grade pyrexia postoperatively often doesn’t require further investigation. However, if pyrexia
persists you should investigate potential foci of infection.


Common postop infections
Surgical site infection
Respiratory infection
Urinary tract infection
Line-associated infection

While a patient remains systemically well with stable haemodynamic and respiratory parameters, there is
time to perform adequate septic screen investigations and seek microbiological advice in order to define
appropriate antibiotic therapy. Patients who are unstable or demonstrating septic syndrome or shock
should have microbiological specimens taken and then be treated with a ‘best guess’ antibiotic (see
Section 6).

For a discussion of sepsis, systemic inflammatory response syndrome (SIRS) and multiorgan dysfunction
syndrome (MODS) see Chapter 3.

Surgical site infection


Surgical site infection includes:

Superficial wound infection
Deep abscess formation:
Intra-abdominal abscess after abdominal surgery
Intrathoracic abscess after cardiothoracic surgery • Intracranial abscess after neurosurgery
Periprosthetic infection/abscess formation (eg around orthopaedic prosthesis or vascular graft)

Implantation of prosthetic materials carries a higher risk of infection, and such infection is often very
difficult to eradicate. For detailed discussions of infection in vascular surgery see Chapter 9, Vascular
Surgery in Book 2, and for infection in orthopaedic surgery see Chapter 9, Orthopaedic Surgery.

Common organisms in surgical site infection

Organism related to wound type
Clean wounds – skin commensals (eg Staphylococcus epidermidis, S. aureus, enterobacteria) •
Contaminated wounds – site-specific organisms (eg from soil, saliva after bites, perforated viscus) •
Dirty wounds – site-specific organisms
Necrotising fasciitis – mixed flora or group A streptococci • Infected prostheses – may be skin flora or
nosocomial • Burns – Pseudomonas spp.
Nosocomial infection, eg meticillin-resistant S. aureus (MRSA)

Management includes:
Wound swab ± blood cultures if indicated
Empirical treatment with a broad-spectrum agent likely to cover organisms involved (see Section 6) • Pus
won’t resolve with antibiotics – it needs formal radiological or surgical drainage

Note that surgical site infections may be due to an organism resistant to the antibiotic administered
prophylactically.

Respiratory infection

Postoperative respiratory tract infection may be due to nosocomial infection or aspiration (in the
critically unwell). Patients are more prone to respiratory infection after surgery due to:
General anaesthetic and basal atelectasis
Supine positioning (prevents full expansion of lung bases) • Immunosuppression (comorbid conditions)

Common organisms in respiratory infection

Community-acquired: Streptococcus pneumoniae, Haemophilus influenzae, Mycoplasma pneumoniae
Nosocomial: often aerobic Gram-negative bacteria – includes Klebsiella spp., Escherichia coli,
Enterobacter spp., S. aureus
• Common in ventilated patients (50% prevalence) • May be opportunistic infection in the
immunosuppressed (eg Pneumocystis jiroveci) • Empyema (pus in thoracic cavity): commonly due to S.
pneumoniae but occasionally S. aureus secondary to: • Primary lung infection
• Haematogenous or lymphatic spread
• Direct extension from diaphragmatic, mediastinal or cervical foci • Inoculation by penetrating trauma •
Lung abscesses: result from aspiration (anaerobic organisms) or granulomatous disease (eg TB)

Urinary infection

See also Urology and Transplantation chapters in Book 2.

Common organisms in urinary tract infection

Community-acquired: commonly E. coli; may also be due to Proteus and Klebsiella spp.
Abnormalities of the renal tract: Pseudomonas spp.
Catheterisation/instrumentation of the renal tract: Staphylococcus epidermidis, Enterococcus faecalis

Line-associated infection

Common organisms in line-associated infection

S. aureus, coagulase-negative staphylococci, streptococci, enterococci and Gram-negative species •
Incidence increases with length of time since line insertion (keep sites clean, record date of insertion,
observe site regularly, change lines before they become infected, re-site if infection documented)

Management includes:
Change lines if evidence of infection: may require at least 24-hour antibiotic treatment before re-insertion
of tunnelled lines. NEVER pass a guidewire through an infected line and insert a new line along the same
guidewire
Take blood cultures from two separate sites (one through the infected line before it is removed and one
from a distant peripheral site; label them accordingly)
Discuss antibiotic choice with on-call microbiologist



Possible causes of PUO
Infection (23%)
Abscesses (lung, liver, subphrenic, perinephric, pelvic) • Empyema
Endocarditis
Unusual bacterial infection (Salmonella, Brucella, Borrelia spp. or leptospirosis) • TB and other
granulomatous diseases (actinomycosis, toxoplasmosis) • Parasites (amoebic liver abscess, malaria,
schistosomiasis) • Fungi
HIV
Neoplasia (20%)
Lymphoma
Solid tumour (GI, renal cell)
Connective tissue diseases (22%)
Rheumatoid arthritis
SLE
Still’s disease
PAN (polyarteritis nodosa)
Kawasaki’s disease
Drugs (3%)
Other causes (14%)
Pulmonary emboli
Inflammatory bowel disease (Crohn’s/ulcerative colitis) • Sarcoid
Amyloid
It is impossible to reach a diagnosis in up to 25% cases.

Pyrexia of unknown origin

Pyrexia of unknown origin (PUO) is defined as a prolonged fever (of >3 weeks) that remains undiagnosed
after sufficient hospital investigation (about a week). Management should involve an infectious diseases
physician.

4.3 Abscess management



In a nutshell ...

An abscess is a localised collection of pus in a cavity. The cavity may be naturally occurring or caused
by tissue destruction or displacement.
If there is pus about, let it out!

Diagnosis of abscesses

Abscess may be difficult to distinguish from cellulitis. The former require surgical drainage, the latter
may respond to antibiotics. Abscess may be inferred if the area is pointing or the centre is fluctuant. If in
doubt, needle aspiration or ultrasonography may help. Left alone, many abscesses will drain
spontaneously. Pus may track through tissue planes, causing the base of the abscess to be much deeper
than initially thought.

Common sites for superficial abscesses

Infection of a pre-existing sebaceous cyst
Axillary:
• Exclude hidradenitis suppurativa
• Exclude breast disease
Anorectal (eg perianal, ischiorectal):
• Exclude inflammatory bowel disease by rigid sigmoidoscopy ± biopsy • Exclude fistula in ano by
proctoscopy
Groin (beware the femoral pseudoaneurysm masquerading as groin abscess in IV drug users – get an
ultrasound scan before incising it!)

Treatment of abscesses

Superficial skin abscesses may be lanced. Local anaesthetics do not work satisfactorily in inflamed tissue
(because the injection is more painful, there is a risk that the needle track will spread the infection, and
inflamed tissue has a low pH, reducing the dissociation and binding of the anaesthetic compound). Deeper
abscesses under the skin require a surgical procedure under general anaesthetic (GA). Abscesses deep in
body cavities may be drained percutaneously under radiological guidance or at open surgery.



Procedure box: Superficial abscess drainage

Indications
Area of fluctuance
Pointing of an abscess
Identification of a superficial collection of pus by imaging • Region (axilla, anorectal, groin)

Patient position
Anaesthetic: the skin may be frozen with ethyl chloride spray or the patient placed under GA • Anorectal

abscesses should only be drained under GA because they require thorough colorectal investigation for
underlying cause • Positioning should be appropriate to the site of the abscess, thus: • Perianal and
ischiorectal abscesses require the patient to be placed in the lithotomy position • Axillary abscesses
require elevation of the arm
Procedure
Make a cruciate incision over the point of greatest fluctuance (this should be extended into a circular
incision once the cavity is defined to deroof the abscess and allow easier packing)
Release pus (and send for microbiological analysis; targeted antibiotics can then be started if cellulitis
persists) • The cavity may be irrigated or curetted down to the base (removes dead tissue) • Gently
pack the cavity (eg with gauze ribbon soaked in Betadine) • Note that packs are changed frequently until
the cavity closes and this is performed initially on the ward and then by the district nurse – it is
essential that the incision allows for this to be done with ease. The cavity will granulate from the base
regardless of its size but the abscess will recur if its ‘roof’ (ie the skin) closes before the cavity has
healed. Antibiotics are not usually indicated
Risks
Inadequate drainage (especially loculated abscesses) • Recurrence
Persistent cellulitis (may require antibiotics)
Hazards
Consider the relationship to nearby important structures, eg: • Anal sphincters in anorectal abscesses
Cervical and mandibular branches of facial nerve around the jaw • Femoral vessels in the groin
For a detailed discussion of anorectal abscess, incision and drainage see the abdominal surgery chapter
in Book 2.

Special cases

Neck abscesses may be due to simple abscess, furuncle, infected epidermal cysts or branchial cysts,
abscess in lymph node, dental abscesses, actinomycosis or TB (cold abscess). They should be operated
on by a suitably experienced surgeon • Perianal abscesses are usually infection in the anal glands (other
causes include fistulae, Crohn’s disease, tumours and HIV). See Abdomen chapter in Book 2. An on-table
rigid sigmoidoscopy should always be performed • Breast or axillary abscesses are occasionally related
to underlying malignancy. A biopsy should always be sent and follow-up should always be arranged in a
breast clinic
Groin abscesses may be due to suppurating lymph nodes, TB or psoas abscess (tracking down from the
kidney or lumbar spine). An ultrasound scan should be done on anyone at risk of an infected femoral
artery aneurysm (such as drug addicts) before incision

4.4 Necrotising fasciitis

This is an infection that spreads along fascial planes, secondarily affecting muscle, subcutaneous tissue
and skin.

Aetiology of necrotising fasciitis

Typically polymicrobial (streptococci; haemolytic staphylococci; Bacteroides spp.; coliforms) • Postop
Trauma
Untreated perineal wound

Contaminated needle

Pathology of necrotising fasciitis

Appears benign in initial stages
If untreated: results in massive subcutaneous oedema and dermal gangrene • Fournier’s gangrene is dermal
gangrene of scrotum and penis

Management of necrotising fasciitis

Rapid aggressive resuscitation
Broad-spectrum antibiotics
Skin incisions down to fascia
Aggressive debridement of soft tissue with excision of necrotic tissue • Colostomy if perineal area is
involved
Nutritional support
Mortality rate is 30%

4.5 Gangrene

Gangrene is essentially irreversible tissue death due to loss of its blood supply.

Causes of gangrene

Progressive tissue ischaemia (eg vascular disease) • Trauma (eg crush injury, burns, frostbite)
Infection resulting in tissue necrosis

Differentiating between dry and wet gangrene

Gangrene may be dry, resulting in mummification of the tissues, or wet, in which the tissues become
infected and purulent. Odour is associated with infection. Gas gangrene occurs when infection occurs by a
gas-forming organism such as Clostridium perfringens and gas may be palpable or visible between the
tissue planes on plain film.

Investigations for gangrene

Proximal blood supply (eg arteriogram)
Cultures for infective organism
Plain film for gas tracking between tissue planes

Management of gangrene

Gangrene is painful due to tissue ischaemia so pain relief is essential • Dry gangrene can be managed
expectantly because digits usually autoamputate • Wet gangrene will need debriding back to healthy tissue

4.6 Specimen collection

The microbiological data available from specimens are often related to the manner of collection and
should be interpreted in the light of the patient’s clinical condition. Most specimens are processed during
working hours but specimens that will be processed out of hours in most labs include:
Cerebrospinal fluid (CSF)
Aspirates of sterile sites (eg intra-abdominal abscess, thoracic cavity, joints) • Intraoperative specimens
from deep surgical infections (eg debridement of osteomyelitis) • HIV/hepatitis B and C in transplant
donors (recipient status usually known)

Skin swabs

Wound infections: overt infections (with pus) can be swabbed for causative organism to tailor therapy.
Often the organism is related to the site of surgery (eg bowel flora in abdominal wounds) but swabs may
exclude organisms such as MRSA • Ulcers: little value in swabbing ulceration because this gives only an
indication of colonising organisms and will not help in tailoring therapy
Abscess cavities: may be of use if taken from deep in the abscess cavity. Remember that abscesses do not
respond to antibiotics but require surgical drainage of pus. Surrounding cellulitits may benefit from
therapy tailored to the causative organism

Urine samples

Midstream urine (MSU): this is optimal because it is a clean-catch sample and results may determine
antibiotic choice • Catheter-stream urine (CSU): urine from catheters may demonstrate colonisation
rather than overt infection (particularly if the catheter is long term). Treat only if the patient is
symptomatic

Stool samples

Stool culture: useful in the returning traveller with diarrhoea. Document region of travel and duration of
request card • Clostridium difficile toxin (CDT): useful in patients who develop diarrhoea on
antibiotics. It is a highly sensitive assay. Document antibiotic treatment and specifically request a CDT
test. The test remains positive after treatment so there is little point in repeating it

Blood cultures

Blood cultures should be taken if the patient is presumed to be septic before the start of empirical
treatment. Cultures do not have to be taken during a temperature ‘spike’ because patients will remain
bacteraemic for many hours. Cultures can be sent even if the patient is afebrile but has other features of
sepsis and may provide the elusive diagnosis in elderly people.



Taking a blood culture
Use aseptic technique with gloves and swab the skin several times with alcohol before puncture to
prevent skin contamination.
Try to take two sets from different peripheral venepuncture sites (eg antecubital fossa) – groin and line
cultures are likely to be contaminated (however, cultures can also be taken from intravenous lines, eg
arterial lines, central venous pressure [CVP] lines, and may help in the diagnosis of line infection).

If considering endocarditis, three sets of cultures should be taken from three sites at three separate
times.
Inoculate aerobic and anaerobic bottles with 10 ml blood each (do not touch the bottle lids). Label each
bottle with the patient details, site of venepuncture, time of sample, any current antibiotic therapy and
current diagnosis. Indicate if the sample is high risk (eg hepatitis, HIV).

Processing of blood cultures

Once in the lab
Specimens are placed in an oscillating incubator • Bacteria present produce CO2 which reacts with a disc
at the bottom of the bottle, producing a colour change that is detected by the machine, flagging the sample
up as being positive
Blood is aspirated from positive bottles for Gram staining (positive or negative) and microscopy (rods or
cocci) • Blood is inoculated on to Agar plates with discs impregnated with common antibiotics • After 24
hours bacterial growth has occurred apart from in the region of antibiotics to which the organism is
sensitive • Additional tests may be employed to identify the organism • The microbiologists phone
positive results and antibiotic sensitivities to the ward (so it is important to correctly identify this on the
request form)

Common results from blood cultures

Growth in both bottles
Staphylococci: in the face of sepsis these are likely to be a significant finding. In a hospital setting this may
represent MRSA bacteraemia, so microbiological advice may include a dose of vancomycin
Coliforms: almost always significant. Consider GI and urosepsis. Will require tailored antibiotic therapy

Growth in one bottle
May represent contamination and should be interpreted in the light of the clinical context • May therefore
require repeat sample

Joint aspirates

Joint aspiration technique is discussed in the Orthopaedics chapter. It should be performed using aseptic
technique to produce a sterile specimen.

Sputum

These are poor-quality specimens and usually represent oral flora. For this reason many labs do not
process these. Specimens obtained by BLA are, however, of much higher quality and can be used to tailor
antibiotic therapy (eg in a critical care setting).



Advice from your microbiologist
To get the best advice and answers to questions such as Which antibiotic? or How long should we
continue antibiotics for? the microbiologist will want to know:
Patient age, gender and occupation
Date of admission
Premorbid conditions (eg diabetes, malignancy, steroid or other immunosuppressant, elderly, pregnant) •
Date and details of surgery or injury
Current and previous antibiotic therapy
Results or outstanding microbiological samples
MRSA status
Details of current clinical condition: examination findings (temperature, haemodynamic status,
chest/abdo/cardiovascular exam) • Results of septic screen (blood results with WCC differential) •
Allergies (confirmed or suspected)

SECTION 5

Prevention and control of infection

5.1 Infection control

Identify patients at risk

All patients need careful thought and planning to prevent infection. Some are at increased risk if they have
or undergo:
Trauma (including major surgery itself)
Burns
Shock
Pre-existing sepsis syndrome
Coexisting metabolic disease (diabetes mellitus, renal failure, liver failure) • Haematological problems
Nutritional problems (malnutrition, obesity) • Malignancy
Chemotherapy and/or radiotherapy
Immunosuppression (steroids, previous splenectomy, transplantation, congenital or acquired immune
deficiency)

Infection control teams and hospital policy

Infection control teams are multidisciplinary and should include:
A consultant microbiologist
Infection control nurses
Representatives from medical and surgical specialities • Occupational health personnel
Management personnel

The infection control team should:
Meet regularly
Perform audit evaluations of current hospital status, by: • Surveillance of nosocomial infection rates •
Comparison with published countrywide rates • Implementation of alterations to policy • Advise and
implement hospital policy

Patient isolation and ward discipline

Patient isolation

Patients may be isolated because they are:
Infectious (and require barrier nursing to protect others from the spread of transmissible infection) • At
increased risk of infection (and require ‘reverse’ barrier nursing to protect them from the spread of
transmissible infection; barrier nursing and reverse-barrier nursing are essentially the same – they use
barrier methods to prevent the spread of infection, eg gloves, plastic aprons, filtered air and masks to
prevent droplet infections)

Ward discipline

After examining every patient always wash your hands or use an alcohol rub • Always wear gloves to
handle or change dressings, take blood, etc • Observe isolation procedures
For MRSA-positive patients always wear gloves and an apron and spray stethoscope with alcohol after
examining • Contact infection control team if there are any doubts

5.2 Skin preparation



In a nutshell ...

Preparation of the patient
Skin (shaving, skin disinfection, adhesive wound drapes) • Bowel (laxatives/enemas)

Preparation of the theatre
Cleanliness, airflow issues, personnel movements

Preparation of the surgical team
Scrubbing up, caps, gowns, gloves, masks, shoes

Preop skin preparation

Antiseptics

Include Betadine (iodine-based) and chlorhexidine (colourless) • Should be applied to the skin in circular
or sweeping motion (friction on the skin removes some bacterial colonisation) • Apply several times to
high-risk areas:
• Perineum
• Groin
• Axilla
There is no evidence that Betadine placed in the wound during closure reduces the rate of wound infection
• Alcoholic antiseptics are much more effective than aqueous preparations but pooled areas on the skin
may can ignite if using diathermy

Preop shaving

Causes skin abrasion
Disrupts deeper flora layers; increased bacterial count on skin surface • Increased tendency to postop

wound sepsis • Therefore shave immediately preoperatively with surgical clippers or use depilatory
cream before theatre

Adhesive wound drapes

Do not prevent infection
Reported to reduce wound contamination by 50% BUT no decrease in wound infection • Trapped bacteria
may multiply

Preparation of theatre

Theatre design

Theatre design is discussed in Chapter 1, Perioperative care.

Control of air quality

Aim: to decrease number of airborne particles carrying bacteria from skin flora • Positive pressure-
filtered ventilation (PPFV) prevents bacteria gaining entry to the air • Laminar flow plus ultraclean air
systems give twofold reduction in postop wound infections

Greater numbers of people in theatre and movement through doors have been correlated with infection
rates.

Preparation of the surgical team

Scrub up

Aim: to decrease bacterial skin count
Chlorhexidine gluconate or povidone-iodine solutions: stiff brushes damage the epidermis; use on
fingernails only • One nail scrub at beginning of operating list is sufficient

Clothing

Cotton gowns reduce the bacterial count in the air by only 30%
Bacteria-impermeable fabrics may reduce bacterial air counts by 40–70%. There is no evidence of
reduced wound infection

Caps

Useful because S. aureus can be carried on the scalp • Prevents hair from falling in the wound

Masks

Deflect forceful expirations such as coughs and sneezes that carry bacteria (normal speech does not expel
bacteria) • May rub off bacteria-carrying skin squames from the face • No effect on infection rates

Prudent use in implant surgery

Gloves

Effective hand disinfection before gloving up • Glove punctures or tears do not affect incidence of wound
infection • Double-glove if implanting prosthesis (eg orthopaedic) or if high-risk patient

Shoes

Plastic overshoes have not been proved to reduce wound infection

5.3 Asepsis and sterilisation



In a nutshell ...

Asepsis is prevention of introduction of bacteria to the surgical field • Antisepsis is destruction of pre-
existing bacteria in the surgical field • Sterilisation: complete destruction of all viable
microorganisms, including spores and viruses by means of heat, chemicals or irradiation. Inanimate
objects only (eg not skin because it damages tissue) • Disinfection: treatment of tissue or hard surface
in an attempt to decrease the bacterial count • Antiseptics: disinfectants used in living tissue •
Cleaning: physically removes contamination – does NOT necessarily destroy microorganisms

Asepsis

Development of asepsis

In the 1860s Joseph Lister introduced carbolic acid as a disinfectant for hands and surgical instruments
and to be sprayed into the air. A few years later he published in The Lancet a reduction in mortality rates
during major amputations of from 45% to 15%.

Principles of asepsis

Invasive procedures should always be performed in line with aseptic techniques (may be incomplete in
times of life-threatening emergency).


Principles of asepsis
Skin preparation with disinfectant
Bowel preparation preoperatively
Draping to surround the sterile field
‘Scrubbing up’ with disinfectant
Use of sterile gloves and gowns
Use of sterile instrumentation and no-touch technique • Good surgical technique

Sterilisation
Sterilisation methods

Autoclave sterilisation
Saturated steam at high pressure
Kills ALL organisms, including TB, viruses, heat-resistant spores • Holding times depend on temperature
and pressure (eg 134°C at 30 lb/in2 has a 3-minute holding time; 121°C at 15 lb/in2 has a 15-minute
holding time)
Wrapped instruments: use a porous load autoclave – steam penetration monitored with Bowie–Dick test •
Unwrapped instruments: use a Little Sister II portable autoclave • Fluids: use a bottle autoclave

Dry heat sterilisation
Hot-air ovens
For moisture-sensitive instruments (no corrosion), non-stainless metals, surgical instruments with fine
cutting edges • Able to process airtight containers and non-aqueous liquids • Effective BUT inefficient
(160°C for at least 2 hours kills ALL microorganisms) • Monitor with Browne’s tubes type III

Ethylene oxide sterilisation
Highly penetrative gas
Kills vegetative bacteria, spores and viruses • Effective at ambient temperatures and pressures • Effective
as a liquid or a gas
Efficient for heat-sensitive equipment (eg rubber, plastics, electrical equipment, lenses) • Used for sutures
and single-use items
Flammable if vapour >3% volume in air • Toxic, irritant, mutagenic, carcinogenic • Limited availability
and expensive (predominantly industrial process)

Low-temperature steam and formaldehyde sterilisation
Physicochemical method
Kills vegetative bacteria, spores and viruses • 73°C for heat-sensitive items
NOT suitable for sealed, oily or greasy items

Irradiation sterilisation
Use of gamma rays limited to industry
Use for large batches of single-use items (catheters, syringes)

Disinfection

Disinfection aims to bring about a reduction in the number of viable organisms. Some viruses and
bacterial spores may remain active.

Disinfection of inanimate objects can be carried out with:
Low-temperature steam
Boiling water
Formaldehyde gas

Alcohols

Broadest spectrum at 70% concentration
Rapidly effective against Gram-positive and Gram-negative bacteria; some antiviral activity • No residual
activity
Relatively inactive against spores and fungi • Denature proteins
Use of alcohols: skin preparation (note: ensure dryness before using diathermy – explosions – and pooling
may irritate sensitive areas such as the groin)

Diguanides

Chlorhexidine
Good activity against S. aureus
Moderate activity against Gram-negative bacteria • Some activity against Pseudomonas aeruginosa,
although may multiply in deteriorating solutions • Non-toxic to skin and mucous membranes
Poor activity against spores, fungi and viruses • Inactivated by pus, soap and some plastics • Causes
bacterial cell-wall disruption
Uses of chlorhexidine:
• In local antisepsis
• 4% chlorhexidine in detergent (Hibiscrub) • Chlorhexidine-cetrimide mixture for some dirty wounds •
0.5% chlorhexidine in 70% alcohol

Iodophors and iodine
Broad spectrum of activity against bacteria, spores, fungi and viruses (including hepatitis B and HIV) •
Easily inactivated by blood, faeces and pus • Need optimum freshness, concentration and pH <4
Stains skin and fabrics
Irritant; may cause local hypersensitivity • Use of iodophors and iodine:
• Preoperative skin disinfection
• Wound antisepsis

Hydrogen peroxide
Only weak bactericidal activity

Aldehydes (glutaraldehyde and formaldehyde)

Rapidly active against vegetative bacteria and viruses (including hepatitis B and HIV) • Slowly effective
against spores
Only fair activity against tubercle bacilli • Exposure of at least 3 hours to kill ALL microbes (most
bacteria killed in <10 minutes) • Toxic, with sensitivity reactions in skin, eyes and lungs (glutaraldehyde
is safer) • Endoscopes are heat-sensitive – disinfect by immersion in 2% glutaraldehyde between each
case

5.4 Surgical measures to reduce infection

If you become aware of changes in the rate of postop infections you should contact the infection control
team. They will analyse the cases and identify any linking factors. This is often reassuring because cases
often only represent a statistical cluster rather than a true increase.



In a nutshell ...

Surgical infection may be caused by:
Endogenous organisms
Exogenous organisms

Surgical infection can be reduced or prevented by:
Environmental factors
Patient factors
Surgeon factors
Surgical technique
Prophylactic antibiotics

Endogenous infection

This is clinical infection with organisms normally found in the patient as commensals. All surgical
procedures result in a transient bacteraemia. Good preparation, surgical technique and prophylactic
antibiotics minimise the chance of these becoming a significant problem.
Lower GI tract:
• ‘Coliforms’ (eg Gram-negative bacilli such as E. coli, Klebsiella and Proteus spp.) • Enterococci
• Anaerobes (eg Bacteroides fragilis) • Pseudomonas spp.
• Enterobacter spp.
Urogenital tract:
• Vagina: anaerobes, lactobacilli
• Urethra: skin flora (eg staphylococci, diphtheroids) • Upper respiratory tract:
• Streptococci, Haemophilus spp., S. aureus, diphtheroids
Conditional pathogens colonise when use of antimicrobials destroys normal flora – this is known as
superinfection.

Prevention of endogenous infection

Patient preparation
Skin disinfection
Bowel preparation
Appropriate antibiotic prophylaxis Avoid disrupting normal flora (give antibiotics only for specific

infection). Treat sepsis with full course of antibiotics, not prophylaxis (inadequately treated infections
encourage bacterial resistance).

Exogenous infection

This is clinical infection acquired from an external source. Incidence is low (2%), affecting:
Hospital staff
Hospital environment
Other patients

Wound sepsis

Asepsis means no organisms are present during surgery. A truly aseptic environment is needed in
immunocompromised patients. Antisepsis involves prevention of sepsis. Total abolition of organisms is
not achieved.

Clean wounds
Incise through non-inflamed tissue
Ensure no entry into genitourinary, GI or respiratory tracts • Contamination rate <2% (exogenous sepsis)

Clean-contaminated wounds
Entry into a hollow viscus other than the colon, with minimal, controlled contamination • Contamination
rate 8–10%



Prevention of wound sepsis In exogenous infection
Control of surgical conditions
Sterilisation (air and instruments)
Aseptic technique
Good surgical technique
Preparation of patient and surgeon

In clean wounds
No-touch technique
Careful and gentle dissection
Careful haemostasis
Minimisation of operation duration
Skin preparation
Prophylactic antibiotics (only if insertion of prosthetic material)

In clean–contaminated wounds
Measures as for clean wounds plus:
Single-shot antibiotic prophylaxis
Minimisation of spillage (swabs, suction)
In contaminated wounds
Full course of antibiotics
Debridement of devitalised tissues (samples to microbiology for causative organism and sensitivity) •
Removal of foreign material
Cleaning of tissues
Lavage
In dirty wounds
Full course of antibiotics
Thorough removal of pus
Wound debridement
Thorough lavage
Simplest shortest operation (life-saving) • Avoidance of anastomosis (eg Hartmann’s procedure) •
Consideration of delayed primary closure

Contaminated wounds
Breaching of hollow viscus with more spillage: opening the colon, open fractures, penetrating animal or
human bites • Contamination rate 12–20%

Dirty wounds
Gross pus, perforated viscus (eg faecal peritonitis) or traumatic wounds >4 hours • Contamination rate
>25%

5.5 Vaccination



In a nutshell ...

Vaccines act by inducing active or passive immunity. Vaccination is used in groups who are susceptible
to certain diseases:
Children (diseases of childhood)
Travellers to endemic areas of disease
Healthcare professionals exposed to high-risk patients

Principles of immunisation

Active vs passive immunisation

Active immunisation stimulates the immune system to produce a response, resulting in the formation of
immunological memory and thus protection against subsequent exposure. Antigens used for immunisation:
Live-attenuated organism (bacterium or virus such as TB (BCG), MMR) • Dead organism (eg tetanus,
pneumococci, influenza virus) • Characteristic protein from organism (eg purified viral protein coat)

Passive immunisation involves the transfer of preformed antibodies to provide immediate protection
against disease exposure, eg:
Maternal transfer of immunoglobulin in breast milk • Immunoglobulins, eg against hepatitis, tetanus,
varicella zoster, hepatitis A, rabies

Reasons for immunisation

For eradication of dangerous childhood disease • For those who are immunocompromised or who have
increased susceptibility (eg splenectomy, extremes of age) • For healthcare professionals with exposure
to infection • For travel to areas of endemic disease

Immunisation of surgical patients

Consider immunisation in the following surgical patients.

Patients with dirty or soil-contaminated wounds
Tetanus toxoid (intramuscularly)
Human tetanus immunoglobulin

Splenectomy patients
Give Haemophilus influenzae type b (Hib), meningococcal and pneumococcal vaccines • Re-immunise
every 5–10 years
Give annual influenza vaccine
For elective cases give immunisations at least 2 weeks preoperatively • For traumatic cases immunise
after a few weeks to maximise immune response

Immunisation of healthcare professionals

The most serious health risks are posed by blood-borne viruses:
Hepatitis B
Hepatitis C
HIV

Infections may be passed in either direction:
From patients to healthcare staff (many infections may be undiagnosed – adopt universal protective
precautions at all times) • From healthcare staff to patients during exposure-prone procedures when there
is a risk of exposure to blood (eg cuts) or accidental injury to hands (eg bony spurs, sharp instruments)



Common mode of transmission is exposure to any bodily fluid
Blood (needlestick or sharps injury; bleeding, eg haematemesis, melaena, epistaxis; invasive

procedures; spray from arteries during surgery; bone fragments, eg trauma and orthopaedic surgery)
Saliva
Urine and stools
CSF
Semen

Healthcare professionals should be immunised against the following diseases capable of nosocomial
transmission:
Hepatitis B
Varicella zoster
± Rubella
± Measles
± Mumps

Additional immunisation may be required for workers dealing with outbreaks of disease (eg influenza
pandemics, meningococcal C disease) or workers commonly encountering other diseases in endemic
countries or among certain patient groups (eg hepatitis A).

The Hospital Infection Control Practices Advisory Committee (HIPAC) guidelines suggest that the
following personnel should be immunised, or be capable of demonstrating immunity to the diseases listed
above (as all may come into contact with needles or bodily fluids):
Doctors
Nurses
Emergency service personnel
Dental professionals

Students (medical and nursing)
Laboratory personnel
Hospital volunteers
Housekeeping personnel

5.6 Sharps injury

Causes of sharps injury

Needlestick or sharps injury may occur in situations involving:
Syringes and hypodermic needles
Taking of blood/venous access
Invasive procedures
Suturing
Sharp instruments

It commonly occurs with practices such as:
Re-sheathing needles
Transferring body fluids between containers • Poor disposal of needles (use sharps bins)

Post-injury procedure

In the event of sharps injury follow hospital protocol, which involves:
Encouraging bleeding by squeezing the wound • Washing with water/soap/disinfectant (do not suck the
wound) • Reporting the incident (to on-call microbiologist if out of hours) • Attending the appropriate
department immediately (occupational health, A&E) • Counselling and testing of recipient and donor (for
hepatitis B, hepatitis C and HIV status) if required • Postexposure prophylactic treatment (eg triple
therapy started immediately in the event of high-risk exposure to HIV) – this should be discussed with a
microbiologist or infectious disease physician

High-risk patients

Note that many infectious patients do not exhibit symptoms and signs of the disease so precautions should
be taken with all patients (eg wear gloves for taking blood and for cannulation, catheterisation and
intubation).

Precautions in hepatitis and HIV patients

Surgeons, anaesthetists, theatre nurses, operating department practitioners and other theatre personnel also
need protection from potentially infectious agents, in the following situations:
Contact (with blood, saliva, urine, tears, CSF, stools) • Air (eg after use of power tools)
Inoculation (via sharps, scalpel or bone fragment injuries)

Universal precautions

These precautions serve to protect theatre staff from infection in all cases (eg surgical gloves, gowns,

masks, no-touch surgical technique).

Special precautions

These are used for high-risk surgical patients (eg hepatitis and HIV patients). In an ideal world all
procedures would be performed using special precautions, but in practice the level of precaution is
limited by expense, time, etc. Precautions include:
Disposable drapes and gowns
Double-gloving and ‘indicator’ glove systems • Face visors
Blunt suture needles
Passing of instruments in a kidney dish
No-touch technique
Minimal theatre staff
Only vital equipment in theatre

Some of the special precautions should be undertaken with all patients (eg high-risk patients or in high-
risk areas). Special precautions are also used for infective cases to prevent spread of infection to other
patients (eg MRSA).

SECTION 6

Antibiotic control of infection

6.1 Types of antibiotic



In a nutshell ...

Antibiotic action is either:
Bactericidal (results in death of current bacterial population) or • Bacteriostatic (prevents bacterial

replication)
These actions may be achieved by inhibition of protein synthesis, nucleic acid synthesis or membrane
functions. Different classes of antibiotics have different spectrums of activity against different
organisms.

Mode of action of antibiotics

Bactericidal antibiotics
Include β-lactams, vancomycin, aminoglycosides and chloramphenicol • Indications for bactericidal
antibiotics include: • Life-threatening sepsis
• Infective endocarditis
• Opportunistic infections in immunocompromised patients

Bacteriostatic antibiotics
Include tetracycline, erythromycin, clindamycin and chloramphenicol • Bacteria can multiply again
Final elimination of pathogens depends on host defence mechanisms with effective phagocytosis

Mechanisms of action

Inhibition of cell-wall synthesis
Leads to osmotic lysis of bacteria with defective peptidoglycan molecules in the cell wall. Antibiotics
with bactericidal action: • β-Lactams (penicillin, ampicillin, cephalosporin) • Vancomycin

Inhibition of protein synthesis
Occurs at the following stages of the bacteria life cycle:
Transfer RNA – amino acid attachment (eg by tetracyclines, bacteriostatic agents) • Translocation (eg by
chloramphenicol and erythromycin, which are bacteriostatic at low concentration; clindamycin and
fusidic acid, which are bactericidal at high concentrations)

Attachment of mRNA to ribosome (eg by aminoglycosides, bactericidals)

Inhibition of nucleic acid synthesis
Bactericidal mechanisms include:
Decreased RNA replication, eg by:
• Sulfonamides
• Trimethoprim
• Quinolones (ciprofloxacin, nalidixic acid) • Metronidazole
Decreased mRNA, eg by:
• Rifampicin

Alteration of cell membrane function
Antibiotics called ionophores alter the permeability of bacterial cell membranes causing lysis. Polymyxin
has bactericidal actions against Gram-negative bacilli

Antibiotic classes

β-Lactams
Penicillins:
• Examples: benzylpenicillin, flucloxacillin, ampicillin • Bactericidal
• Good penetrance of tissues and body fluids • Renal excretion
• Hypersensitivity (rash alone) occurs in up to 10% of patients (anaphylaxis in 0.05%) and may occur
with other β-lactams (similar molecular structures). There is a 1 in 10 risk of hypersensitivity to
cephalosporins in patients with penicillin hypersensitivity • May cause antibiotic-associated colitis •
Cephalosporins:
• Broad-spectrum antibiotics (for septicaemia, pneumonia, meningitis, biliary tract and urinary tract
infections) • Pharmacology similar to penicillins
• 10% penicillin-allergic patients will be hypersensitive to cephalosporins • First-generation
cephalosporins include cephradine • Second-generation cephalosporins include cefuroxime • Third-
generation cephalosporins include cefotaxime, ceftazidime, ceftriaxone • Other β-lactam agents:
• Carbapenems, eg imipenem, meropenem
• Broad spectrum activity against anaerobes and aerobic Gram-positive and Gram-negative bacteria

Tetracyclines
Examples: tetracycline, doxycycline, minocycline • Work by attacking bacterial ribosomes (note increasing
bacterial resistance) • Used against Chlamydia spp., Haemophilus influenzae, Rickettsia and Brucella
spp. and spirochaetes • Generally safe but should not be used in pregnancy

Aminoglycosides
Examples: gentamicin, neomycin, streptomycin • Active against Gram-negative and some Gram-positive
organisms • Not absorbed from the gut (given intravenously) • Excreted via the kidney
Side effects are dose-related (ototoxicity, nephrotoxicity) – as a general guide you can give a single dose
of 5–7 mg/kg if renal function is normal; reduce to 3 mg/kg if there is any compromise in renal function

Macrolides
Examples: erythromycin, clarithromycin
Antibacterial spectrum similar to penicillins (used for respiratory infections, Campylobacter spp.,
Legionnaires’ disease, Chlamydia spp.)
Clarithromycin has higher tissue concentrations than erythromycin • Side effects include nausea, vomiting
and diarrhoea

Glycopeptides
Examples: first line vancomycin, second line teicoplanin • Anaerobes and aerobes; Gram-positive bacteria
– used against MRSA • Side effects are dose-related (ototoxicity, nephrotoxicity) – dose should be
reduced in renal failure

Sulfonamides
Examples: co-trimoxazole, trimethoprim
Used for PCP, urinary and respiratory tract infections, and Salmonella infection • Side effects include
nausea, vomiting and diarrhoea

Metronidazole
Effective against anaerobic and protozoal infections

Quinolones
Examples: ciprofloxacin, norfloxacin
Ciprofloxacin is particularly active against Gram-negative bacteria • Used for respiratory tract and biliary
infections • Same bioavailability orally as intravenously (and much cheaper) • Side effects include GI
disturbance, rash, headache, tendinitis • Avoid in elderly people and people with epilepsy (lowers
seizure threshold)

6.2 Empirical treatment

Sometimes it is not possible to wait for microbiological results to guide your choice of antibiotics. The
following should act as a guide. If in doubt, discuss with your local microbiologist.

Which antibiotic? Narrow-spectrum or broad-spectrum?

Narrow-spectrum antibiotics
These are selected for specific infections. They cause less disturbance of normal flora and are associated
with:
Reduced risk of superinfection
Fewer resistant strains

Broad-spectrum antibiotics
Use of these is associated with acquiring Clostridium difficile (pseudomembranous colitis).

Wound infection and cellulitis