Anaesthesia for reconstructive surgery
Anaesthesia for reconstructive surgery

https://doi.org/10.1016/j.mpaic.2011.12.002Get rights and content

Abstract

Reconstructive surgery is aimed at the restoration of shape and function following tissue loss due to trauma, oncological surgery, burns and infection. Techniques range from simple primary wound closure at the bottom to complex microvascular free tissue transfer at the top rung of the reconstructive ladder.

Free flap surgery involves separation of the flap from its original vascular supply and microvascular reanastomosis at a distant site and is associated with substantial transient ischaemia of the transferred tissue. Anaesthetic management plays an important role in successful free flap surgery.

All factors promoting vasoconstriction need to be eliminated in order to facilitate blood flow through the transferred tissue.

In this respect, maintenance of an adequate arterial blood pressure, normothermia and normocarbia, institution of moderate hypervolaemic haemodilution and effective pain management are the main principles.

In spite of studies describing the effects of particular drugs on the microcirculation no single ideal anaesthetic agent has yet been identified for this type of surgery.

Free flap failure occurs mainly during the first 48 hours postoperatively with venous thrombosis being more common than arterial occlusion. Prompt surgical revision is the mainstay of flap salvage. The overall success rate of microvascular free tissue transfer in high volume centres exceeds 90%.

Section snippets

Preoperative assessment

The transfer of a free flap constitutes major surgery that may take in excess of 6 hours and involves institution of a hyper-dynamic circulatory state with vasodilation and a high cardiac output to maintain perfusion pressures at a sufficient level.

A thorough workup of the patient’s cardiovascular status will therefore be at the core of the preoperative assessment.

Smoking, diabetes mellitus and peripheral vascular disease are both predictive indicators for anaesthetic complications and

Anaesthesia and microcirculation

The primary role of the cardiovascular system is to supply tissues and cells with the required oxygen and nutrients and to eliminate metabolic waste products.

Microcirculation is defined as the blood flow through the terminal portion of the cardiovascular system. There are three fundamental conditions for a functioning microcirculation: (1) the resistance vessels are functioning properly; (2) vessels responsible for the transfer process are in an appropriate condition; (3) vessels for the

Preparation of theatre environment and induction

To avoid hypothermia the operating theatre should be preheated to 22–24° C. If induction is performed in an anaesthetic room, two sets of hot air blankets can be used, one for the patient and one can be left on the operating table. It is important that the patient remains covered as much as possible, that is, only expose body areas during procedures such as line insertion and keep hot-air down-time during skin preparation to a minimum.

After induction of anaesthesia an endotracheal tube is

Monitoring

The insertion of an arterial line is essential for blood pressure monitoring and useful for repeated blood gas analysis and haemoglobin level checks.

Central venous pressure monitoring has been used for many years to guide fluid administration during free flap transfers. Although not yet validated for free flap surgery, alternative methods such as oesophageal Doppler or LiDCO® are increasingly being used for the guidance of fluid management. The decision whether to dispense with a central venous

Providing for optimal macro- and microcirculation of the flap

Blood flow through a free flap follows the law of Hagen–Poiseuille, in which:Flow=δ(P)×r4×π/η×l×8

From a practical perspective that translates into maintaining mean arterial pressure, avoiding vasoconstriction and aiming for optimal viscosity.

There is no evidence for a threshold blood pressure value that has to be maintained in order to avoid hypoperfusion of the flap, to aim for the patient’s preoperative baseline mean arterial pressure from the time of anastomosis until 48 hours

Pain management and postoperative care

During the first 48 hours the flap is particularly vulnerable and most flap complications occur in that period. Postoperative care is guided by the principle ‘keep the patient warm, well filled and pain free’.

If a regional or epidural catheter technique has been part of the anaesthetic regime this will provide excellent analgesia in the postoperative setting.

If the patient’s volume status is addressed adequately the vasodilation associated with regional and epidural blocks supports regional

Monitoring of the flap and flap failure

Clinical evaluation, pinprick testing and surface Doppler monitoring are the cornerstones of free flap monitoring. Implantable Doppler probes attached to the venous outflow are particularly useful in case of buried flaps. Once a compromise of the flap has been suspected, there should be a low threshold for return to the operating theatre as rapid re-exploration is crucial in flap salvage.

The most common causes of flap failure are pedicle obstruction/thrombosis (venous:arterial = 2:1) caused by:

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