Download Anaesthesia, surgery preparation and monitoring for

Natasha Mitchell MVB DVOphthal MRCVS
Anaesthesia, surgery preparation and monitoring for the ophthalmic
patient
Abstract:
Anaesthesia of the ophthalmic patient presents some unique aspects including considerations of
the intraocular pressure, oculo-cardiac reflex, and ocular pain. Routine surgical preparation of
the skin for surgery would not be appropriate for the eye and orbit. Careful surgical preparation
of the ophthalmic patient will minimise peri-operative infection and ensure that there is
minimal irritation of the area that could lead to post-operative inflammation and discomfort.
Monitoring of the ocular patient presents many challenges because of the position of and the
lack of access to the patient’s head, and recovery considerations.
Ophthalmic patients often require gentle handling because they may have a fragile eye (for
example, a deep corneal ulcer), a painful eye (for example, a corneal foreign body) or an eye
with glaucoma where the intraocular pressure is high. They also will need special consideration
if they are blind. It is important not to pull on their collar or have a choke chain on their necks,
as this could raise the intraocular pressure or rupture a fragile eye. The use of a harness is to be
encouraged.
Pre-operative medications are beneficial for several reasons:
•
Non-steroidal anti-inflammatory agents may reduce swelling associated with eyelid
manipulation, clipping and surgery.
•
Analgesics such as opioids and non-steroidal anti-inflammatory agents are important for
the welfare of the patient and also reduce post-operative discomfort, and therefore the
likelihood of self-trauma.
•
Antibiotic use topically and / or systemically may reduce the bacterial burden on and
around the eye.
•
Application of topical anaesthesia (e.g. proxymetacaine, Minims vials) is very useful if
the cornea or conjunctiva is ulcerated and painful. This will reduce stimulation of the patient
while under anaesthesia, avoiding deep anaesthesia. Topical anaesthetic is epitheliotoxic, but
judicious use in this situation is beneficial.
However some medications need to be avoided.
Face masks must not touch the eye.
The intraocular pressure is raised during intubation if a light plane of anaesthesia allows the
patient to cough. Acepromazine and benzodiazepams tend to have no ill effects on intraocular
pressure (they may reduce it slightly). Opioids generally have little effect on intraocular
pressure unless they cause vomiting (e.g. morphine), and they also cause pupil constriction
which is not desirable for intraocular surgery (lens surgery). Ketamine can raise the intraocular
pressure and result in rupture of a fragile globe.
The oculo-cardiac reflex is a reaction which occurs upon stimulation of the eye resulting in
bradycardia or arrythmias. Pressure on the eye such as surgical manipulation or traction
transmits an impulse down the Trigeminal Nerve (Cranial Nerve V) which in turn stimulates the
Vagus Nerve (Cranial Nerve X) and results in slowing of the heart rate. It is important to be
aware of the reflex so that the cause is understood. Manipulation of the eye should be stopped to
allow the heart rate to return to normal, but urgent administration of intravenous atropine is
required if this does not occur quickly.
An intravenous catheter is highly recommend for all ocular procedures. It is good practice, and
also because there is limited to the head of the patient, problems may not be apreciated as
quickly. Ideally the saphenous vein is catheterised rather than the cephalic vein so that the
catheter is further away from the operation site, but in practical terms it is more commonly
placed in the front leg.
Surgical preparation of the eye or orbital area is a common requirement in small animal
practice. Preparing a safe surgical environment includes practices that will eliminate or greatly
reduce the potential for contamination of the site by ensuring that microorganisms are brought
to an irreducible minimum in the effort to protect the animal from postoperative infection.
Standard preparation for aseptic surgery that is appropriate for other areas of the body is not
suitable for the eye area. The factors that make this area unique include:
•
Delicate eyelids which have thin skin and a rich vascular supply
•
The conjunctival and corneal epithelia are susceptible to damage by alcohol, detergents
and dessication
•
Commensal bacterial flora are present on the ocular surfaces and eyelids
•
The deep conjunctival fornices contain tears and mucous, and may harbour hairs and
pathogens
•
The third eyelid can also trap hairs, pathogens and mucous.
Equipment / disposables needed
•
Sterile saline solution
•
Povidone-iodine solution
•
Disposable gloves
•
Gauze swabs
•
Cotton wool
•
Cotton-tipped applicators
•
Syringe
•
Lubricant such as carbomer eye gel, KY jelly or bland petrolatum ointment
•
Clippers
Choice of ocular disinfectant:
Povidone-iodine is the ocular disinfectant of choice. It is essential that the solution contains no
detergent (avoid scrub solutions) or alcohol, as these can damage the epithelium of the cornea
and conjunctiva, causing ulceration. A 1:50 dilution is made with sterile saline, compound
sodium lactate or distilled water. This is easily achieved by adding 10ml of 10% povidoneiodine to a 500ml bag of saline. There is no data available as to how long this solution remains
stable, but it should be replaced at least weekly. Chlorhexidine gluconate (not diacetate)
solution (rather than scrub) may be diluted with distilled water (not saline) to a 0.05%
concentration, and this is an acceptable alternative. The consequences of inappropriate ocular
disinfectants include post-operative infection due to inadequate bactericidal action, corneal
ulceration or oedema, conjunctival ulceration or chemosis, and post-operative self-trauma.
Technique:
There are some differences in the surgical preparation of the eye depending on whether
corneal, conjunctival, eyelid or orbital surgery is required. The globe rolls downwards with
standard general anaesthetic techniques and with deep sedation, and this makes surgical
preparation of the cornea more difficult.
•
The endotracheal tube should be secured around the lower jaw rather than the upper jaw.
This is because the ties could contaminate the surgery site.
•
The animal is placed in the position that will be required for surgery – usually lateral
recumbency but sometimes they are placed in sternal recumbency.
•
Gloves are worn for hygiene reasons, and because some people have allergies to iodine
solutions. Adverse reactions due to dilute iodine have not been reported in small animals.
•
Water-soluble gel such as KY jelly or carbomer gel tears is applied to the cornea in order to
trap clipped hairs and make it easier to flush them out. In the case of a unilateral procedure,
gel should be also applied to the fellow cornea to protect it.
•
A small scissors may be used to carefully trim long lashes. Coating the scissors blade with
gel or a bland petrolatum ointment to collect hair and debris will allow for the lashes to be
easily collected and reduce potential contamination of the surgical field.
•
Hair does not usually need to be removed for conjunctival, third eyelid, corneal or intraocular surgery. A sterile adhesive drape is normally used for these procedures, which keeps
the contaminated hair from the sterile operating field. However, a small area at the lateral
canthus may be clipped in animals with small palpebral fissures in case a lateral canthotomy
is required. In breeds with long hair, it is useful to clip the area beneath the medial canthus,
as this will make it easier for the owner to wipe discharge from this area post-operatively.
•
For eyelid and orbital surgery (for example, enucleation), clipping is required. However it is
kept to a minimum because the eyelid skin is very thin and delicate, and eyelid swelling and
small cuts can result which may lead to self-trauma in the recovering animal. Clippers with a
size 40 blade are adequate but it is also possible to purchase smaller clippers which will
allow a more precise clip. The eyelid skin is pulled taut and the hair is clipped against the
direction of growth. For eyelid surgery, the area on which surgery is anticipated plus a small
extra margin is clipped (1-2 cm depending on the surgeon’s preference). If the eyelids
appear damaged, a small amount of Fucithalmic eye ointment may be rubbed onto the area
post-operatively. If the rash is severe, this could be continued twice daily post-operatively,
along with systemic anti-inflammatories and antibiotics.
•
After clipping, the hair is best removed with moistened cotton wool or gauze swabs
although a light suction vacuum cleaner could be used with care. Sticky tape may be used if
there is a small quantity of hair.
•
The eye gel is removed with moistened cotton wool or gauze swabs.
•
The conjunctival sac is flushed with 10-20ml 1:50 dilution povidone-iodine using a syringe
or irrigating bottle. Both the contact time with the disinfectant and the volume used are
important to achieve adequate disinfection of the eyelids and conjunctival sac. A contact
time of at least two minutes is recommended.
•
To gain access to the deep conjunctival fornices and to clean both sides of the third eyelid, it
is useful to use sterile cotton-tipped applicators soaked in the same disinfectant.
•
The conjunctival sac may then be flushed with 10ml of saline or compound sodium lactate to
remove residual disinfectant. It is important not to flush too liberally or vigorously, as
backwash from the adjacent skin would contaminate the surgical field.
•
The eyelids may be prepared with a 1:10 dilution of povidone-iodine, although so long as
good contact time is allowed, the 1:50 dilution is sufficient. If the 1:10 dilution contacts the
cornea during the process of cleaning the eyelids, it can be flushed with sterile saline or
Hartmann’s solution. The solution is soaked on non-woven swabs which are soft, absorbent
and almost lint-free. Soaked cotton wool is an acceptable alternative although there is more
of a risk of cotton fibres being shed. Gauze swabs may also be used gently but they are not as
soft as non-woven swabs and therefore will create more friction on the delicate peri-ocular
region. Usually three cleanses are required, but this varies with the amount of ocular
discharge and the anatomy of the eyelids – for example the St Bernard conjunctival sac is
very large and would require several cleanses.
Things to avoid:
•
Alcohol and detergent in the prep solution
•
Clipper blade trauma
•
If the cornea is perforated, the use of gel or disinfectants is contraindicated. In this
situation, the eye should be gently flushed with sterile saline or compound sodium lactate.
•
Desiccation of the conjunctiva or cornea – if there is a delay before surgery, ensure that
the eye is not left open underneath a bright surgical light for a prolonged period, which would
dry the ocular surfaces and potentially damage the light-sensitive retina. Lubricate the open eye
every minute with a flush of sterile saline or compound sodium lactate solution.
•
Drying of the fellow eye – the other eye may also need topical lubrication, especially if
ketamine is used in the anaesthetic protocol.
Positioning for surgery:
The surgeon may operate sitting down, in which case the table needs to be as low as possible.
The exact positioning of the head is greatly assisted by the use of a vacuum (Buster) cushion.
Negative pressure removes the air from a bean bag and when it is sealed, it remains in position
unless it has a leak. They are water-proof so can be easily cleaned after the procedure, and of
course the nurse and vet both have to be very careful not to puncture it. The surgeon may wish
to position the head themselves.
Monitoring during the procedure:
Ideally a pulse oximeter is clipped securely onto the tongue and a capnograph or ap-alert used
to monitor breathing. An oesophageal stethoscope may be pre-placed as access to the chest is
more difficult due to draping. The palpebral reflex can’t be checked in an eye that has been
surgically prepared. The position of the eye (i.e. whether or not the eye rolled down) may be
difficult to see with the positioning of the head and after the surgery site is draped. The nurse
monitoring anaesthesia of the ophthalmic patient relies on monitoring equipment and also
watching the anaesthetic circuit bag move while feeling the femoral pulse or listening to the
heart by chest stethoscope or oesophageal stethoscope. The patient should be kept warm (for
example by heated blanket) and rectal temperature can be monitored throughout. If facilities
are available to monitor blood pressure, this should also be carried out.
If the patient under-going anaesthesia is diabetic, blood glucose should be measured intraoperatively. A useful way of obtaining blood for this is by clipping the back nails slightly too
short in order to draw a drop of blood.
Recovery after the procedure:
Recovery of the ophthalmic patient should be slow and gentle. It is useful to place the buster
collar before they wake up, as often the first instinct is to rub the eye. If a corneal or conjunctival
procedure was done, a single drop of topical anaesthetic could be applied to prevent the animal
from traumatizing the eye area. In cases where a buster collar isn’t practical, the dew claws
should be bandaged, as these are usually what does most of the rubbing. Of course they
shouldn’t be applied too tightly, and the owner needs to be told to remove them a couple of days
later.
Pain-relief is very important in recovery, and animals with painful procedures might require
additional opioids. The vet should be alerted if the animal is uncomfortable in recovery. A
harness should be applied to walk the animal back down to the kennels when they are
sufficiently recovered.
Further reading:
Veterinary Ophthalmology - a manual for nurses and technicians. Sally Turner. 2005. Elsevier.
ISBN 0750688416
Chapter 5: Surgical nursing: equipment, instruments and the duties of the ophthalmic
theatre nurse
Chapter 6: Anaesthesia for ophthalmic surgery
BSAVA Manual of Small Animal Ophthalmology. Simon Peterson-Jones and Sheila Crispin 2002.
BSAVA. ISBN 0 905214 54 4
Chapter 2: Ophthalmic surgery and anaesthesia