Anaesthesia for reconstructive free flap surgery

Anaesthesia for
Reconstructive Free Flap
Surgery
BY
Dr. Chamika Huruggamuwa
(Registrar in Anaesthesia)

• Reconstructive free flap surgery is a complex method of wound
closure for large wounds not amenable to linear (primary) closure.
• It involves the transfer of free tissue (skin, muscle, bone, bowel
or a combination) to a site of tissue loss where its circulation is
restored via microvascular anastomoses
• The defect may be caused by trauma, infection or extensive
surgery (e.g. mastectomy, head and neck cancer)

• The most commonly used flaps are the gracilis muscle for lower
leg trauma;
• latissimus dorsi and rectus abdominis for breast reconstruction;
• pectoralis major and radial forearm flap for head and neck
reconstruction.
• In patients with multiple trauma, any life-threatening injuries
must be addressed first and the patient’s haemodynamic status
stabilized before reconstructive surgery is contemplated.

Properties of free vascularised tissue
• • Subject to ischaemia during transfer
• • Denervated
• • Still responds to physical and chemical stimuli
• • Blood flow frequently decreases to half its original (in situ) flow
• • No intact lymphatic drainage leading to increased risk of
• interstitial oedema

• The stages of flap transfer are:
• flap elevation and clamping of vessels
• primary ischaemia as blood flow ceases and intracellular
metabolism becomes anaerobic (this is dependent on surgical time
and lasts 60–90 minutes)
• reperfusion as the arterial and venous anastomoses are completed
and the clamps released
• secondary ischaemia is subsequent to hypoperfusion of the flap
(minimized by appropriate anaesthetic management).

Physiological considerations
• Laminar flow through a rigid tube is described by the Poiseuille-
Hagen equation:
• Blood flow = ∆P π r 4 /8 η l
• The systemic arterial pressure is the main determinant of the
pressure gradient across the transplanted tissue.
• As flow is related to the fourth power of the radius, a small
decrease in vessel cross-sectional area will result in a large fall in
flow

• Laplace’s law states that intraluminal pressure will itself influence
blood vessel diameter.
• Transmural pressure is decreased by either an increase in
extravascular pressure (e.g. oedema, haematoma, dressings) or a
decrease in intravascular pressure
• There is a non-linear relationship between blood viscosity and
haematocrit;

• Haemodilution increases blood flow but also decreases the oxygen
carrying capacity of the blood
• A haematocrit of approximately 30% is thought to give the best
balance between blood viscosity and oxygen content for oxygen
transport to the tissues.

Vasodilatation
• Vessel radius is the most important determinant of flow, for the
vessels supplying the flap as well as those in the flap.
• Temperature
• – the patient should be kept warm in theatre, the recovery room
and the ward for the first 24–48 hours.
• In addition to vasoconstriction, hypothermia also produces a rise
in haematocrit and plasma viscosity, the aggregation of red blood
cells into rouleaux, and platelet aggregation. These effects may
reduce the microcirculatory blood flow in the flap.

• Fluid – peripheral vasoconstriction due to an underestimation of
fluid losses is common.
• Modest hypervolaemia reduces sympathetic vascular tone and
dilates the supply vessels to the flap.

• Vasospasm of the transplanted vessels may occur after surgical
handling or after damage to the intima of the vessels, and can
occur during surgery or postoperatively. The surgeons may use
topical vasodilators such as papaverine, lidocaine (lignocaine) or
verapamil during the operation to relieve the vasospasm.
• Sympathetic blockade – epidural, brachial plexus or interpleural
local anaesthetic infusions, used intraoperatively and
postoperatively, provide sympathetic blockade to further dilate
vessels.

Anaesthesia
Pre-operative assessment
• All patients presenting for free flap surgery must be thoroughly
assessed and investigated prior to anaesthesia
• Elderly patients
• heavy smokers and drinkers
• poor nutritional state.
• Airway anatomy may be distorted- previous chemotherapy or
radiotherapy, and a difficult intubation must be anticipated.
• Paediatric patients may have associated abnormalities of
anaesthetic importance (e.g. congenital cardiac disease)

• Baseline investigations should include ,
• full blood count, urea and electrolytes, clotting screen and blood
sugar.
• Chest X-ray, ECG, respiratory function tests, arterial blood gases
and echocardiogram should be considered in patients with cardiac
and respiratory risk factors.
• All patients require a ‘group and save’ and blood should be cross-
matched for all surgery requiring extensive dissection and
reconstruction.

Conduct of anaesthesia
• The basic requirements for free tissue transfer are the provision of
a full hyperdynamic circulation and maintenance of a normal body
temperature.
• All patients usually require large bore intravenous access, an
arterial cannula and central venous catheter.
• Positioning of the patient requires meticulous attention to detail
in order to avoid well recognised problems
• Pneumatic calf compression should be utilised routinely; some
recommend regular passive limb movements during prolonged
surgery.

• Eyes are taped and lightly padded to reduce the incidence of
corneal abrasion and prevent drying of the cornea.

Induction
• The ambient temperature in theatre is raised to about 22–24oC, a
level high enough to reduce patient heat loss, but not too hot to
be uncomfortable for the theatre staff.
• The patient is covered in a hot air blanket before induction of
anaesthesia and this remains in place while the patient is
prepared for theatre.
• Once in theatre, the blanket is moved to enable surgical access,
but with as much surface area coverage as possible.

• Anaesthesia – isoflurane has the advantage over other volatile
anaesthetics and propofol that it causes vasodilatation with
minimal myocardial depression.
• Propofol inhibits platelet aggregation which could reduce the risk
of thrombosis

• Nitrous oxide diffusion into air in the stomach combined with
gastric stasis results in gastric distension, with associated
postoperative nausea and vomiting. A nasogastric tube is therefore
sited at intubation, left on free drainage, then aspirated and
removed at the end of the operation.
• Fluid, administered through a fluid warmer, is started in the
anaesthetic room to compensate for preoperative dehydration.

• The patient is ventilated to normocapnia. Hypocapnia increases
peripheral vascular resistance and reduces cardiac output, while
hypercapnia causes sympathetic stimulation.
•
• If the surgeon uses the microscope for vessel preparation or
anastomosis on the chest or abdomen, the tidal volume is reduced
to minimize movement in and out of the surgeon’s field of vision.
The respiratory rate is then increased to maintain minute
ventilation.

• Controlled hypotension is useful during the initial dissection and is most
easily achieved using epidural local anaesthetic and/or isoflurane.
• Crystalloids are used to replace the preoperative fluid deficit from
starvation and to cover intraoperative insensible losses.
• The latter are high because the warm theatre increases evaporative
losses from the two operating sites. Excessive use of crystalloid may
precipitate oedema in the flap.
• Hypervolaemic haemodilution is achieved using colloids. Blood gas
analysis and haematocrit measurement should be carried out at the start
of the operation and repeated every 2 hours.

• By the time the flap is reperfused, the patient should be warm,
well-filled and sympathetically blocked with a high cardiac
output.
• As the duration of surgery is often > 5 h, nitrous oxide is best
avoided. Most anaesthetists favour air and oxygen in combination
with a volatile agent or a propofol infusion
• The addition of a remifentanil infusion has also become very
popular. This short-acting opioid provides excellent intra-operative
analgesia, rapid control of blood pressure and marked
vasodilatation. It usually obviates the need for a muscle relaxant

Extubation
• Whilst it is desirable to have an awake co-operative patient, it is
also important to avoid excessive surges in blood pressure
associated with coughing and retching
• Techniques used to reduce the risk of blood pressure surges at the
time of extubation include:

• Allowing the patient to wake gradually, breathing spontaneously with the
endotracheal cuff deflated
• • Exchanging the endotracheal tube for a laryngeal mask airway prior to
reversing muscle relaxation
• • Intravenous lidocaine 0.5 mg kg–1 may reduce coughing during waking
and extubation
• • Carefully titrated boluses of a short-acting β-blocker (e.g. esmolol)
• If surgery has been particularly prolonged and there is concern about the
anastomosis, a period of ventilation on the intensive care unit may be
considered.

Fluid therapy
• A hyperdynamic circulation with a high cardiac output, peripheral
vasodilatation and a large pulse pressure is required to maintain
adequate microcirculatory perfusion of the transplanted tissue.
• Most patients can tolerate a drop in haematocrit to 18–20%,
although oxygen delivery to the tissues is probably optimal at
around 30%.
• very low haematocrit is associated with increased bleeding time.

• CVP trends are more useful and should be considered with other
relevant information such as urine output and Δt (difference
between core and peripheral temperatures).
• Patients with documented ischaemic heart disease or left
ventricular dysfunction may not tolerate volume loading well and
are probably better managed with normovolaemic haemodilution.
• Fluids should be administered cautiously whilst monitoring for
signs of ischaemia and hypoperfusion
(e.g. ST segment depression, fall in urine output, rising blood
lactate concentration and increasing Δt)

• A combination of crystalloid and colloid infusions is used.
• Electrolyte solutions alone are less effective in producing volume
expansion and haemodilution; resultant interstitial oedema may
put the flap at risk.
• In the UK, gelatin and albumin solutions are usually used for
volume expansion.
• Synthetic colloids have the advantage that they are readily
available, stable, relatively inexpensive and without the risk of
transmitting infectious diseases.

• In Europe, dextran solutions, starch solutions and hypertonic
saline are very popular as plasma substitutes in microvascular
surgery.
• Dextran - more efficient plasma substitute than both large
volumes of crystalloids and gelatin
-have beneficial effects on the microcirculation. It has
antithrombotic effects through a reduction in platelet adhesiveness
and depression of Factor VIII activity.
-This is an advantage in terms of thromboprophylaxis
but limits the amount that can be given during major blood loss.

• hydroxyethyl starch and pentastarch
- They are efficient plasma volume expanders,
-Have a low incidence of anaphylactic reactions
-reduce reperfusion injury and capillary
hyperpermeability after temporary ischaemia.
Their disadvantages
-prolonged bleeding time
-if used in excessive amounts and a high incidence of
postoperative pruritus.

• Hypertonic saline
-effective plasma volume expanders
- have beneficial cardiovascular effects
(i.e. increased myocardial contractility, decreased afterload and
increased preload).
• potential disadvantages include hypernatraemia, and intracellular
hypovolaemia.

policy in adults
#infuse 10–20 ml kg–1 of 0.9% NaCl followed by 1000–1500 ml of 4.5%
human albumin solution over the next 1–2 h.
#Thereafter, fluid therapy is guided by urine output, CVP and haematocrit
measurement.
#Blood loss may be extensive during a prolonged procedure and may be
covert (e.g. latissimus dorsi donor site).
#Red cells should only be transfused if the Hb falls below 8 g dl-1.
#Clotting factors and platelets may be required if blood loss is significant

Analgesia
• The main choices are an opioid technique, regional block or a
combination of the two.
• NSAIDs -usually avoided in the acute peri-operative period
because of the risk of bleeding and flap haematoma formation.
• Regional anaesthesia usually consists of a lumbar epidural for
lower limb flaps or a brachial plexus block for upper limb work.
• a catheter technique allows continuation of the block into the
postoperative period.

• Other advantages of epidural analgesia include a
# Reduction in intraoperative and postoperative blood loss
and vessel spasm;
# A lower incidence of deep venous thrombosis;
# Improved diaphragmatic function and more rapid
postoperative recovery.
# Good analgesia reduces the level of circulating
catecholamines and avoids the vasoconstrictor response to pain.

• An opioid may be required to provide analgesia for the donor site
(e.g. latissimus dorsi flap, rectus abdominis flap)
• Prophylactic anti-emetics should be given to prevent retching and
vomiting.

Temperature regulation
• Patients must not be allowed to become hypothermic.
• Anaesthetic agents may interfere with the normal thermoregulatory
mechanisms.
• Cold induces vasoconstriction, an increase in haematocrit, increased
aggregation of red cells, and increased whole blood and plasma
viscosity.
• Patients must be actively warmed by means of
• Underheating mattresses,
• Forced air warming blankets (e.g. Bair Hugger),
• warmed intravenous fluids,
• Humidification of anaesthetic gases

• Both core and peripheral temperatures should be monitored and
the difference between them (Δt ideally < 1°C)
• Core temperature is usefully measured by means of a specially
adapted urinary catheter which allows continuous measurements,
easily continued in the postoperative period.
• At the end of surgery, patients should be immediately transferred
to a dedicated warmed area for continued monitoring.

• Postoperative shivering should be treated . It can,
#double the oxygen consumption,
#increase circulating catecholamine concentrations
#cause peripheral vasoconstriction
#profound drop in free flap blood flow.
• CAN BE stopped with
#External warming together with
#IV Meperidine (10–20 mg),
#chlorpromazine (2.5–5 mg)
#clonidine (100–150 µg).
However, flap blood flow may not return to normal for over an hour

Control of blood pressure
• Controlled hypotension -to improve the surgical field and reduce blood
loss.
• Other measures which may assist include positioning to improve venous
drainage or local anaesthetic infiltration.
• Anaesthetic techniques include,
#vapour and remifentanil infusion ± glyceryl trinitrate infusion
#(ii) propofol and remifentanil total intravenous anaesthesia
• During harvesting and anastomosis of the flap, mean arterial blood
pressure should be maintained at a normal or slightly elevated level to
ensure an adequate perfusion pressure through the graft tissue bed.

• pharmacological agents have been utilised in the past in an attempt to
improve flap survival.
#α-receptor blockers (e.g. chlorpromazine)
#Direct-acting vasodilators (e.g. sodium nitroprusside)
• Systemic sodium nitroprusside -reduction in flap blood flow and may
lead to reflex vasoconstriction in the postoperative period when the
infusion is stopped.
• Hypotension is usually secondary to blood loss or vasodilatation and
should be treated with fluid replacement.
• catecholamines are avoided.

Postoperative care
• It is essential that all measures taken to ensure adequate tissue
perfusion during surgery are continued in to the postoperative
period.
• maintenance of circulating volume with crystalloid infusions and
colloid boluses,
• Maintenance of normothermia
• provision of effective analgesia
• Prevention of PONV

Monitoring the flap
• Observation of skin colour, capillary return and temperature are
the traditional methods of monitoring free skin flaps.
• Other more invasive methods include use of radiolabelled
erythrocytes, ultrasound Doppler.
• The best of the currently available methods is laser Doppler
flowmetry which allows monitoring of superficial and buried flaps
and is reportedly reliable for skin, muscle, bowel and bone
transfers.

Anaesthesia for reconstructive free flap surgery

Anaesthesia for reconstructive free flap surgery

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Anaesthesia for reconstructive free flap surgery