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30
A manual of basic microsurgical techniques
Respiraon rate
Any irregularies in breathing such as raspiness or wheezing
Presence of a blink reex
Rabbits
The main problem encountered during long periods of anaesthesia in rabbits is respiratory depression. It is therefore important to supply oxygen via a close-ng face
mask or an endotracheal tube (3.5 mm uncued paediatric tubes are ideal).
In the absence of inhalaonal anaesthec equipment, the safest injectable agents in rabbits are xylazine at 7 mg/kg, followed 5 minutes later by ketamine at 20 mg/kg IM. This
produces light surgical anaesthesia in 10–15 minutes. This will last for 30–60 minutes.
To extend the period of anaesthesia, 15 mg/kg of ketamine only IM can be administered
every 30–60 minutes as needed.
Having induced anaesthesia using xylazine and ketamine, long periods of anaesthesia
can also be maintained using inhalaonal anaesthec agents: 1–2% isourane with
1 L/min of oxygen via a mask or endotracheal tube should be sucient to maintain
anaesthesia for 3–4 hours.
Operating site preparation
It is far beer to clip the hair from the operang site with the nest grade of clipper
head (Oster 40®) rather than aempt to shave it. Loose hair should then be removed
with a small handheld vacuum cleaner. For the exercises described later, it is worth
clipping a wide area, including the lower abdomen, hind legs and scrotum (if males
are ulised).
Rats are then laid out in the supine posion on the operang board with the hind legs
taped close to the board. The forelimbs should not be taped, as this will make thoracic
excursions dicult and increase the likelihood of respiratory failure. The head and
neck should be slightly exed and not stretched straight, as this will diminish airway
patency.
List of useful pharmacological agents
Ancoagulant: Heparin sodium supplied at a concentraon of 1,000 IU/mL is useful both in the whole animal and diluted at 1,000 IU in 1,000 mL of isotonic 0.9%
saline for irrigang vessels and the immediate operave site. In rats, approximately
100 IU/100 g body weight provides adequate ancoagulaon.
Animal model
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Vasodilang agent: Lidocaine (2% soluon) is useful in rats applied undiluted directly
to the vessels and allowed at least 5 minutes to relieve spasm.
Respiratory smulant: Doxapram (Dopram® 20 mg/mL) is a direct smulant of the
central respiratory centre and is eecve in rats at 1.5 mg/kg IP to reverse respiratory
depression.
Euthanasia
Rats should be terminated via an intracardiac (IC) injecon of sodium pentobarbital at
0.6 mL/kg. Secondary conrmaon of death can be achieved by cung the femoral
vessels (exsanguinaon) or cervical dislocaon.
In rabbits, an overdose of sodium pentobarbital can be administered via an ear vein
(3–5 mL). Secondary conrmaon of death can be achieved by cung the femoral vessels (exsanguinaon) or onset of rigor mors.
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6
Factors affecting
anastomotic success
Gentle dissection
This requires adequate gentle dissecon of vessels. However good your anastomoc
skills are, the vessels will not ow if damaged during the preparaon stage.
Failure of patency in small blood vessels aer anastomosis is caused by:
● Faults in microsurgical technique
● Alteraons in the laminar ow of blood
● A tendency to coagulaon and thrombosis aer operaon due to release of coagu-
laon factors
● Spasm of the vessel musculature
● Or a combinaon of these
Poor surgical technique is undoubtedly the most important and is the most suscepble to improvement.
Microsurgical technique faults
The divided ends of vessels must never be grasped within the jaws of microsurgical forceps. Only grip the vessel by liing gently from underneath or by grasping the
advena.
● Gentle handling of the vessels is of prime importance, as the inma is very suscep-
ble to damage. Try to avoid vessel spasm
● Traumac placement of sutures, tearing of needle holes and mulple punctures are
likely to trigger platelet aggregaon
● Non–full-thickness needle penetraon
● Uneven gaps or bites
The correct bite and tension are indicated by a small suture loop whose diameter
is roughly equal to the wall thickness and which is visible from the inside of the
vessel.
● Inversion or eversion of the vessel edges leading to vessel narrowing
DOI: 10.1201/9781003413080-6
Factors affecting anastomotic success
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● Tension: Too much or too lile
Too much tension, which cannot be reduced within a double-approximator clamp,
will cause stenosis of the vessel and tearing at the suture holes.
If the whole anastomosis is put under longitudinal tension, either because the
natural elascity of a divided artery has allowed too big a gap to form or the vessels
have been traumased and need resecon, then it is preferable to bridge the gap
with an interposional vein gra.
● Suturing the front and back wall together, thus constricng the lumen
This is best avoided by using the triangulaon technique described in Chapter 3.
Keeping the walls widely separated whilst sutures are placed, repeated irrigaon of
the divided ends of the vessels and making a careful inspecon of the lumen before
tying the nal sutures can help avoid this.
● Non-removal of advena
In the case of arteries, it is important to remove the loose advenal ssue so that
it is clear of the suture line and less likely to be dragged into the anastomosis.
Tiny tags of advenal ssue can be carried into the lumen, and these are sufcient to form a nidus for platelet aggregaon.
● Kinking or longitudinal torsion will again alter laminar ow and predispose to loss of
patency. It can be a problem clinically when posioning free aps or replants (Figure 6.1).
33
● Clumsy tests for patency: This includes overusing the ‘milk’ technique (see Chapter 7),
parcularly on vessels below 1 mm.
Figure 6.1 Effects of releasing longitudinal torsion.
34
A manual of basic microsurgical techniques
Alterations in blood ow
Eddy currents and other forms of turbulent ow resulng from bends, kinks or gross
distoron at the anastomoc site are likely to propagate thrombi downstream.
Turbulent ow can be observed most easily in an end-to-side anastomosis, but these
cause surprisingly few problems so long as the suture line is not under tension and the
incoming vessel is set at an angle between 60° and 45° with the direcon of ow in
the recipient vessel.
More important in any ssue transfer is poor ow or even complete stasis, parcularly
at the venous anastomosis. The laer will be at double risk if the arterial ow is inadequate because of paral patency, and hence ow through the microcirculaon in the
ssue is sluggish.
If veins are anastomosed such that they have a ‘waist’, then they will fail due to slow
ow. Always anastomose veins at their maximum dilataon and this will not occur.
Most surgeons like to check the patency of the artery before proceeding to the venous
anastomosis.
If a clamp is released and then applied again, it is important to remove any stac blood
by vigorous irrigaon with heparinised saline before it starts to coagulate.
Release of coagulation factors
Any ssue or organ which has been compromised by hypoxia or ischaemia will build
up toxic metabolites, including lacc acid, hydrogen ions, oxygen-derived free radicals
and high concentraons of potassium.
These, together with thrombogenic factors such as bradykinins, serotonin and sensised platelets, will be washed out of the ssue through the venous anastomosis once
the clamps are released and further increase the risk of thrombogenesis.
Poor oulow is therefore the greatest risk in aps and replants and has led to many
aempts to improve results by local or systemic administraon of inhibitors or leeches.
Spasm of the vessel musculature
Spasm (Figure 6.2) is almost inevitable at some stage in a microvascular procedure and
may be provoked by:
● Surgical manipulaon
● Exposure at the operave site to an unusually low ambient temperature
● Allowing the operave site to become dry
Factors affecting anastomotic success
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● Allowing blood or blood products in the operave eld
● Abnormal pH and release of toxic factors from locally injured ssues
● It may also be provoked systemically via the sympathec system by release of
catecholamines
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Figure 6.2 Spasm in a carotid artery to a synthetic graft (pig).
Prevenon consists of careful dissecon and constant irrigaon of the immediate
vicinity of the anastomosis.
Treatment is best achieved by applying a suitable topical vasodilator and allowing
10–15 minutes for the spasm to be relieved.
It is important to relieve spasm before aempng an anastomosis; it becomes much
harder to space sutures evenly and the suture line may leak once it is relaxed.
Discrepancy in vessel size
There are various ways of coping with discrepancy in vessel size. The rst soluon is to do
an end-to-side anastomosis, but if this is not possible, three other techniques are available:
● If the discrepancy is relavely minor, then it is possible to dilate the smaller vessel
by gently inserng dilang forceps and spreading their ps, but there is a risk of
damaging the endothelial inma.
36
A manual of basic microsurgical techniques
● If the dierence is greater, then the end of the smaller vessel can be transected on
a 45° diagonal, thus providing a larger diameter edge for anastomosis (Figure 6.3).
Figure 6.3 Forty-ve-degree diagonal transection.
● Alternavely, the end of the small vessel can be incised longitudinally to create a
‘shtail’, which can then be sutured to the larger vessel (Figure 6.4).
Figure 6.4 ‘Fishtail’ of vessel.
In each of these methods, it is dicult to perform the simple triangulaon technique,
so great care must be taken not to suture the front wall of the vessel to the back. It
is also very important to ensure that the vessels are under no tension, or the smaller
vessel is likely to tear.
Factors affecting anastomotic success
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Similarly, you must ensure that the sutures are placed at the same relave posion
around the circumference of both vessels, or gaps will be le on inseron of the nal
sutures.
Summary of factors aecng anastomoc success:
● Rough handling
● Poor dissecon technique
● Stches too ght
● Stches too loose so that a loop of suture intrudes into the lumen
● Too many or too few stches
● Suture holes not equidistant from the edge so that the bite is not equal
● Uneven spacing between sutures
● Inversion or eversion of ssue edges
● Edges of ssue overlapping and heaped up on each other
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● Stch caught through both anterior and posterior walls
● Vessel stch tears
● Tension on vessel
● Vessel spasm
● Discrepant size
When to repair or redo
Be 100% sure of your anastomosis. If you are only 99% sure and there is any doubt at
all, then redo. This will save a lot of anguish later if you have a middle-of-the-night call
for a failed ap.
If ow is compromised in any way:
● Narrowing at anastomosis
● Stches caught through
● Stch tears
● Uneven, ght or loose stches
● Tension (gra if necessary)
38
A manual of basic microsurgical techniques
Repair
● If a stch has been misplaced, it is possible to carefully remove it and replace it,
preferably before clamp removal.
● For general oozing, replace the proximal clamp and wait for a few seconds more,
then recheck ow.
● For a pulsale leak: Reapply clamps, nd the gap, then ush all the blood out with
heparinised saline before placing an extra stch and then retesng.
● Trying to add an extra stch to a bleeding vessel will result in a misplaced stch; the
defect will be hard to see due to blood ow, so reapply the clamps and ush.
● More importantly thrombus will be ‘locked in’ if the stac blood is not removed,
and anastomoc failure will ensue.
Any ‘waist’ present on a venous anastomosis will almost certainly lead to failure.
Always anastomose veins at full horizontal stretch (maximum dilataon), and this will
be avoided.
Human factors affecting anastomotic success
Personal comfort
Standing for long periods can lead to bad backs and s necks. Make sure you stay as
upright as possible and comfortable at the microscope. We have found that the mountain pose (taken from yoga) facilitates long periods of standing.
Mental efciency
● Mental rehearsal and visualisaon techniques have been used in sports, music,
aviaon and recently, in training in laparoscopic surgery with successful results.
● The concept is to mentally rehearse the anastomosis in signicant detail so that
the surgeon can visualise each step vividly in their mind (including detailed imagery
cues) prior to undertaking the task itself (Figure 6.5).
Figure 6.5 Mental rehearsal.
Factors affecting anastomotic success
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Don’t panic
● When we start to panic, then ght, ight or freeze takes over and governs fear and
anger. This emoonal hijacking leads to strong emoons and makes us stupid.
● Panic and tremor set in and make the anastomosis doubly hard.
● Taking me to panic is me lost to set things right.
Coping mechanisms
Most surgeons are reluctant to let colleagues know that they are not coping or are
panicking if the anastomosis is not going well. We have some suggesons to help you
cope that can be done without anyone realising that you are suering.
The adrenalin surge experienced during this is accompanied by sharpened (foveal)
vision, a dry mouth and shallow breathing.
Mechanism 1
● To dampen the response, look away from the microscope. Go into peripheral
vision – soen your focus, bring saliva into the mouth and take three slow deep
breaths.
39
● You will nd your anxiety will lessen and you can start to think more raonally.
Mechanism 2
● 7/11 Breathing: To dampen the adrenalin response, try to breathe in for a count
of 1–7 then breathe out for a count of 1–11.
Mechanism 3
● Drop-through technique: This can be accessed again without anyone nocing.
● Think of the emoon you are experiencing e.g., frustraon.
● Then think of the next feeling e.g., anger.
● Carry on unl you can no longer access any emoon – you will come to a void.
● Think of the emoon under the void, and you will strangely nd a posive emo-
on e.g., calm.
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