Download anaesthesia for common ophthalmic surgeries

ANAESTHESIA FOR COMMON OPHTHALMIC SURGERIES
Dr. M.V. Bhimeshwar
Professor of Anaesthesiology
Sarojini Devi Eye Hospital
Hyderabad
INTRODUCTION :
Most of the ophthalmic surgeries are performed under local anaesthesia.
However all the paediatric ophthalmic procedures and long duration cases are
performed under General Anaesthesia. There are several aspects of anaesthesia
which are pertinent for the successful conduct of ophthalmic surgeries. These
aspects include preoperative screening, selection of patient, preparation of the
patient, choice of anaesthetic and reassurance. In addition there are several
intricaries of ophthalmic anaesthesia which the anaesthesiologists should be
aware of for the successful conduct of ophthalmic anaesthesia. These include
the regulation of IOP ; prevention of Occulo cardiac reflex and its management,
the control of intra ocular gas expansion and knowledge of the systemic effects
of all the drugs used in ophthalmic practice.
Ophthalmic surgeries can be
broadly classified as extra ocular, intra ocular and specialities. The specialities
surgeries fall in either extra ocular or intra ocular surgeries. The anaesthetic
management differs for the type of surgery.
ANATOMY OF THE EYE :
The orbit is an irregularly shaped pyramid in the skull with the base at
the front and the apex pointing posterior medially. The medial walls of the (R)
and (L) orbits are parallel to each other. The eye sits in the orbit with the globe
occupying the anterior part of orbit. The globe sits high and lateral in the orbit.
The muscles of the eye are (4) Recti and 2 oblique.
The
recti
muscles
are
superior, inferior, medial and lateral are responsible for the movement of eye
up, down, in and out. The oblique muscle superior and inferior help in rotation
of the eye. The (4) Recti muscles insert into the globe just forward of equator
and forms a cone forming a boundary between the (2) compartment a) Central
compartment (Retrobulbar) and (b) Peripheral compartment (Peribulbar).
Within the cone the structures present are optic nerves ; ophthalmic artery and
vein ; ciliary ganglion. The nerve supply to the Eye : Sensory is by the
ophthalmic division of trigeminal nerve. The motor supply is through the III, IV
and VI nerves.
The facial nerve VII supplies secretomotor parasympathetic
fibres to the lacrimal glands, nasal and palatine mucosal glands.
The blood
supply to the eye is by the ophthalmic artery which is a branch of the internal
carotid artery.
PHYSIOLOGY OF INTRA OCULAR PRESSURE :
The eye is a hollow sphere with a rigid wall. The normal IOP ranges from
12-20mmHg. The IOP is maintained in the normal range by a dynamic balance
between the aquous humour formation and its elimination through the canal of
Schelm. The aquous humour is secreted by the ciliary processes in the ciliary
body in the posterior chamber, enters the anterior chamber through the pupil.
From the AC it is eliminated through the canal of Schelm through the episcleral
veins to the Cavernous sinus. The IOP should be maintained in the normal
range while operating with in the globe. Any rise in the IOP during the surgery
can cause impaired operating conditions and expulsion of intra ocular contents.
There are several factors which effect the intra ocular pressure.
The factors
which raise the IOP are a) An increase in the arterial or venous pressure, 2)
Hypoxia 3) Hypercarbia, 4) Anaesthetic drugs like Suxamethonium and
ketamine and Laryngoscopy and intubation.
The factors which decrease the
IOP include a fall in the arterial or venous pressure. Hypocarbia, I.V inducing
agents except ketamine Inhalatinal agents, non depolarizing muscles relaxants.
Drugs like acatazolamide and Mannitol.
SYSTEMIC EFFECTS OF OPHTHALMIC DRUGS
Most of the drugs used in ophthalmology are either in the form of
ointments or drops. These drugs though used in minimal quantity by virtue of
high concentration can get absorbed from the conjunctive or nasal mucosa and
produce systemic effects – the drugs are used to produce miosis mydriasis and
cycloplegia
Atropine :
Atropine is used to produce mydriasis and cycloplegia. It is used as a
1% solution and contains 0.2 to 0.5mg/drop.
This causes tachycardia,
flushing, thirst, dry skin and agitation. This is contraindicated in close angle
glaucoma.
Scopolamine :
This is used to cause mydriasis. A 0.5% solution contains 0.2mg (drop
and causes disorientation and hallucination.
Physostigmine 0.015mg/kg IV.
These can be managed by Inj.
This drug is contraindicated in close angle
glaucoma.
Phenylephrine Hydrochloride :
This is used to produce ciliary decongestion and pupillary dilatation. It
is available in 2.5%, 5% and 10% solution. 2.5% solution is used (4mg/drop).
This causes tachycardia palpitation, nervousness, headache, nausea, vomiting,
severe HTN, Reflex bradycardia and sub arachnoid haemorrhage.
Epinephrine :
This is used as a mydriatic to decrease the aqueous secretion, improve
outflow and lower IOP in narrow angle glaucoma. 2% solution of epinephrine
contain 0.5mg – 1mg / drop.
This can cause hypertension ; palpitations,
tachycardia and fainting.
Timolol Maleate :
This is a beta blocker used in the treatment of glaucoma. This drug can
cause light headedness ; fatigue, disorientation, exacerbation of bronchial
asthma, bradycardia an bronchospasm.
Acetylcholine / Pilocarpine
This is used to produce miosis intra operatively following cataract
surgery.
This causes hypotension, bradycardia, bronchospasm, increased
bronchial secretions and is managed by Inj. Atropine.
Echothiophate Iodide
This is a cholinesterase inhibitor used as a miotic agent. The use of this
drug for 2 weeks reduces the levels of pseudocholinestrase by 80%.
It also
prolongs the effects of Suxamethonium and ester type of local anaesthetics.
Cyclopentolate :
This drugs is used as a 2% solution for dilating the pupil. This causes
disorientation ; dysarthria, and seizures (CNS toxicity)
OCULO CARDIAC REFLEX
This reflex is a Trigemino vagal reflex. The afferent pathway is by the
long and short ciliary nerves to the ciliary ganglion and Gessarian ganglion
along the ophthalmic division of the Trigeminal nerve ; to the main sensory
nucleus in the 4th ventricle. The efferent pathways is through the vagus nerve.
The triggering factors for this reflux are the traction on the muscles and
pressure on the globe (Eye muscle surgery ; RD repair ; Enucleation). The side
effects include bradycardia, Bigemeny ; Ectopics ; Nodal rhythm A-V block, and
cardiac arrest.
Other contributory factors are preoperative anxiety, lighter
planes of GA ; Hypoxia ; Hypercarbia, old age ( vagal tone). ECG monitoring is
mandatory.
The management is by stopping the stimulus, maintaining
adequate ventilation and depth of anaesthesia and by Inj. Atropine.
INTRA OCULAR GAS EXPANSION
In the surgery for correcting the retinal detatchment the surgeon injects
a gas bubble which keeps the retina in place by pressure effect. This air bubble
will get absorbed in 5 days. N2O used in GA is 35 times more soluble and it
diffuses into the air bubble and increases its size, thereby increasing the IOP.
In some centres, Sulfur Hexafluoride (SF6) and Carbon Octafluoride (C3H8) are
used instead of air, because they are less soluble than N2 or N2O, has longer
duration of Action (10days).
They are inert, insoluble in water and poorly
diffusible. In all these surgeries N2O has to be stopped at least 20min before
the injection of the gas. These patients have a risk of loss of eye during air
travel.
TECHNIQUES OF ANAESTHESIA :
Most of the procedures in ophthalmic surgery are performed under local
anaesthesia. The various techniques employed in anaesthetizing the eye are
1.
Local anaesthesia : Topical ; Sub conjunctival ; 2) Regional :
Retrobulbar ; Peribublar ; Sub-Tenon’s block and 3) General anaesthesia.
The aim of any anaesthesia should be complete anaesthesia of the globe
and conjunctiva ; and a normal or soft eye. If Akinesia is not required topical
and subconjunctival injections are sufficient. If akinesia of the globe, eyelids,
and orbicularis oculi muscle are required then Akinetic methods, Retrobulbar,
peribulbar or sub Tenon’s block are used.
Topical Anaesthesia :
For the success of topical anaesthesia very careful patient selection and
very skilled surgeon are required. There are several benefits to this technique
like : No physiological disturbances, No PONV ; and economical. This technique
is non invasive and has no complications.
This techniques is increasingly
becoming popular for phaecoemulsification of cataract surgery. The commonly
used drugs are 1% Amethocaine, 4% lignocaine and 0.75% Bupivacaine.
In
addition sedation ; I.V access, supplemental oxygen ; topical NSAID and
hydriatic are also used.
Procedure : About 20 to 30 mins before surgery.
2 to 3 drops of the local
anaesthesia is instilled every 5 minutes. The effect lasts for 30 mins.
Sub conjunctival injection :
Topical anaesthesia combined with a small volume of LA (0.5ml) is
injected under the conjunctiva near the superior limbus. There is no effect on
the motor nerves to the globe or periorbital structures.
simple and safe.
This procedure is
REGIONAL ANAESTHESIA :
There are several advantages to Regional Anaesthesia, like good akinesia
and anaesthesia, minimal effects on IOP, all are day cases, minimal equipment
is required.
However this is not suitable for all patients, needs skill and is
associated with several complications. It is unsuitable for certain surgeries like
paediatric and long procedures. The different types of regional anaesthesia are
a) Retrobublar block (intra cone)
b) Peribulbar block (peri conc) and
c) Sub Tenon’s block.
Retrobulbar Block (Intra Cone)
In this block a long needle is used (35 – 50mm) to inject the LA into the
muscular cone close to orbital apex.
This block is largely replaced by the
peribulbar block because of high incidence of complications.
Procedure : The injection is introduced at the junction of the inner 2/3 and
outer 1/3 is directed backwards under the globe. Once part the equator
upwards and inwards, aiming to enter the space behind the globe behind the
inferior and lateral recti.
Peribulbar block (peri cone)
In this block a large volume of LA is injected around the cone using a
short needle (25mm).
This block is safer than the retrobulbar block as the
needle is directed further away from the vital structures and are not inserted so
deep.
Procedure : In the past this block and performed with two injections in the skin
is inferotemporal and superonasal region. The techniques is now modified and
only one injection is made in the inferotemporal region. After securing an IV
access topical LA solution is applied to conjunctiva.
asked to look straight.
The supine patient is
The lower lid is retracted and at the junction of the
inner 2/3 and outer 1/3 the needle is advanced about 25mm in the saggital
plane. Once past the equator of the globe, it is turned medially and cephalad.
In this block the drug is deposited outside the cone rather than behind the
globe and has slower onset of action. The LA solution used is 2.5-5ml of 0.75%
bupivacaine, 2.5 to 5% of 2% lignocaine.
Inj. Hyaluronidase 5 IU/ml,
adrenaline 5ugm/ml 1 : 4,00,000 . The eye is closed, covered with gauze and
pressure is applied which helps in lowering IOP and facilitates periorbital
spread of LA. The signs of a good block are ptosis, akinesia and inability to
fully close eye once opened.
Sub Tenon’s Block :
This block is an alternative to Retro and Peribulbar blocks. In this block
a trans conjunctival injection of LA is injected into the potential sub Tenon’s
space and is now being frequently used for cataract surgery.
The Tenon’s
capsule is a dense facial sheath surrounding the globe and extra ocular muscle
from limbus to optic Nerve.
Procedure : After instilling topical LA drops the speculum is used to retract the
eye lids.
A small incision is made in the conjunctiva at the infero medial
quadrant. Blunt dissection is made to bare the sclera. A curved blunt sub
Tenon’s cannula is inserted and 5ml of LA is injected which tracks back to the
retrobulbar space.
This block can be used for patient on Anticoagulants. The advantages of
the block are safe and simple to teach, blunt cannula and provides reliable
anaesthesia
and
akinesia.
The
disadvantages
are
sub
conjunctival
haemorrhage, conjunctival chemosis, inferior rectus injury and care in a patient
with previous eye surgery.
COMPLICATIONS OF REGIONAL ANAESTHESIA :
The complications of RA are 1) Intra vascular injections of LA, 2)
Anaphylaxis, 3)Retrobulbar haemorrhage 4) Sub conjunctival oedema 5)
Penetration / Perforation of the globe 6) CNS spread 7) Brain stem anaesthesia
8) Injury to optic nerve.
CARE OF THE PATIENT :
As these patients are conscious reassurance and comfort of the patient
should be ensured.
The patient should be given O2 via nasal prongs and
monitored for O2 sat, ECG and NIBP.
GENERAL ANAESTHESIA :
The indication for GA is ophthalmology are
1. Patient refusal for LA
2. All paediatric cases
3. Major and lengthy procedures and inability of the patient to be still for
long time.
While selecting the patient for GA we need to take into
consideration the co-morbid conditions and the ophthalmic drugs that
the patients might be on.
The goals of GA for eye surgery are
1. A quiet surgical field, immobile eye, stable intra ocular pressure, minimal
bleeding and avoidance of OCR and smooth emergence.
The usually performed paediatric procedures are
Emergency : Perforating eye injury : FB in the eye,
Elective : Strabismers ; Retrinoblastoma ; Congenital Cataract : Chronic
dacryocystis ; Stye.
Pre medication :
The aim is to have a calm patient.
These patients should be
premedicated with anxiolytic, antiemetic, analgesic and anti sailagogue.
Induction :
Thiopentone 5-7mg/kg is the drug of choice as it reduces the IOP.
Ketamine should be avoided as it raises the IOP.
Intubation : The intubation should be smooth. NDMR are used for intubation
(Vecuronium or Atracurium)
Inj. Succinylcholine is avoided as it causes a rise in IOP.
Maintenance : the GA is maintained on O2 and N2O and inhlational
(sevoflurane ; isoflurane or halothane).
Reversal and Recovery : Should be smooth to avoid coughing which might
increase IOP.
COMMON OPHTHALMIC PROCEDURES :
1. Cataract :
Usually performed under LA. However these patients are likely to have
co-morbid conditions which should be ruled out before surgery.
2. Strabismus :
This
procedure
is
usually
done
under
GA
in
children.
The
anaesthesiologist should keep in mind the associated neuromuscular disorders,
OCR and malignant hyperpepxia which are associated with this procedure and
avoid excess manipulation, Halothane and Suxamethonium.
3. Penetrating Eye injuries :
These patients should be treated as full stomach but should weigh the
pros and cons of using Suxamethonium for Rapid sequence induction (RSI).
The judgment of whether the condition is life threatening or sight threatening
should be considered.
Retinal detachment : The possibility of intra vitreal Gas expansion, increased
IOP and OCR should be considered.
4.
Retinoblastoma :
To anticipate problems of severe blood loss intra
operatively and treat accordingly.
5. Retrolental Fibroplasia : Is associated with premature infants and ARDS.
6. Eye Donation :
The cornea of dead patient is taken under strict aseptic
conditions within 6hrs of death. This button is kept in NK medium and stored
in a refrigerator. This is sutured to the recipient after removing the damaged
cornea.
CONCLUSION :
To conclude anaesthesia for ophthalmic procedures have certain intricacies
which the anaesthesiologist have to keep in mind like
1. Maintaining of IOP
2. Prevention of OCR and its management
3. Control of Intraocular gas expansion and need to deal with the systemic
effects of ophthalmic drugs
In addition all GA cases should be calm and sedated, have smooth induction,
laryngoscopy, intubation, good pain relief.
Smooth recovery and extubation.
Avoid coughing, crying, hypoxia, hypercarbia, hypotension and hypertension.
In addition each case has to be dealt with keeping in mind the unique nature of
each case.
REFERENCES
1. Ronald D Miller Anaesthesia 3rd edition.
2. Parsons’ : Disease of the Eye
3. Wylie and Churchill Davidson – A Practice of Anaesthesia
4. Dr Shika Mehrotra – Ophthalmic Regional Anaesthesia.
Conference
Proceedings ISACON 2006.
5. Satish Deshpande : Anaesthesia management of paediatric ophthalmic
surgical procedure. Conference proceedings ISACON 2006.