Anaesthesia for cataract surgery

*Notes taken from local master student program 

Overview

· Cataract surgery is the commonest type of surgical procedure performed in ophthalmic practice.

· Before starting the surgical procedure every patient has to be anaesthetised properly to complete safe and uneventful surgery.

· For this purpose either local or general anaesthesia may be used.

· General anaesthesia is preferred for children, adults who desire to be unconscious during the surgery, prolonged operation, inflamed eyes, and acute trauma cases in which scleral perforation is a consideration.

· In some institutions general anaesthetic techniques have been developed to such a high level that their associated morbidity and mortality are not greater than those associated with local anaesthesia.

· Local anaesthesia is preferred whenever possible because it is safer, cheaper and quicker, has fewer postoperative complications and can be completely controlled by the surgeon.

· However, it is important to recognize that in our world of outpatient surgery and local anaesthesia, life threatening complications can occur.

· For this reason an intravenous line should be put as a routine in all the cases to be given local anaesthesia, and if possible, an anaesthesiologist should remain present during the procedure.

Preoperative Medication

· Regardless of the type of anaesthesia to be used, it is better that all the patients should be given preoperative medication.

· To ensure a well rested patient, 5-10 mg diazepam or 0.5 mg alprazolam orally, is recommended the night before surgery, which gives the patients better sleep and relieves them from unwanted psychological stress and anxiety because of the fear of surgery.

· On the morning of surgery, a combination of meperidine hydrochloride, 50 mg intramuscularly or injection fortwin 1 ampule intramuscularly, with an antihistamine such as hydroxyzine hydrochloride, 50 mg intramuscularly, or promethazine hydrochloride, 50 mg intramuscularly, is administered for an average built adults.

· The last two agents act synergistically with meperidine to produce analgesia, and they also have sedative and antiemetic properties.

· Diazepam 5 to 10 mg orally, is also an established tranquillizer with amnestic qualities.

· It reduces the frequency and severity of toxic reactions to local anaesthetic drugs.

Local Anaesthesia

· Various types of local anaesthesia methods are given for cataract surgery, which may be in the form of peribulbar, retrobulbar and topical anaesthesia.

· The anaesthetic agents used commonly are 4% xylocaine or 0.5% tetracaine drops for topical anaesthesia (4 times every 5 minutes in lower fornix) and 2% bupivacaine (Marcaine/sensoricaine) in the ratio of 60:40.

· Anaesthetic solution is prepared by adding one vial Hyalase (1500 IU) in 3 bottles of 30 ml each of xylocaine 2%.

· Use of hyalase helps in early infiltration of the anaesthetic solution around the periocular tissue and causes early akinesia.

· By this way it avoids undue excessive injection of the anaesthetic agent.

· Such prepared solution should be used on the same day.

A) Topical Anaesthesia

· Harold Ridley the pioneer of cataract surgery with intraocular lens (IOL) implants, routinely used topical cocaine for anaesthesia.

· However, topical anaesthesia alone is rarely used today for intraocular surgery except by a few very experienced surgeons.

· As mentioned above, the anaesthetic agent used is either in the form of 4% xylocaine or 0.5% preservative free tetracaine drops, which should be put in the lower fornix (not over cornea), to prevent the cornea from becoming hazy (epitheliotoxicity), before surgery.

· During intraoperative period, the topical anaesthetic drops should be put every 10 to 15 minutes or whenever required, till the surgery gets over.

B) Peribulbar Anaesthesia

· Anaesthesia and akinesia of the eye are obtained by injecting a local anaesthetic into the peribulbar space.

· The technique involves two injections of the above mentioned mixture of anaesthetic solution at least 20 to 30 minutes before surgery.

· The patient is asked to look upward (in supine position).

· In patients with advanced cataract, patient’s thumb is brought into the proper target position and ask to look towards it.

· Superior and inferior injections are given with a 1/2 inch, 26-guage needle.

· The superior injection is given superanasally beneath the superior orbital notch with the needle directed toward the roof of the orbit and remaining parallel to the nasal wall of the orbit.

· The inferior injection is given at the junction of the outer one third and inner two thirds of the lower orbital rim.

· With the patient looking up, the needle is directed away from the eye and toward the floor of the orbit.

· To ensure that the needle is in the proper peribulbar space, one should watch for the eversion of the lower lid when the hub of the needle touches the eyelid skin.

· Total 8 to 10 ml of anaesthetic solution (mixture) can be injected in both the sites.

· Some people prefer to inject the anaesthetic agent through the conjunctiva also.

· It is alleged that peribulbar anaesthesia is safer than retrobulbar anaesthesia because of less chances of retrobulbar haemorrhage and globe perforation.

· Optic nerve and CNS complications due to xylocaine being injected into the subarachnoid space around optic nerve are also avoided.

· It provides good hypotony but requires prolonged compression for effectiveness.

· It also has the disadvantage of causing chemosis which interferes in deep set eyes.

C).Retrobulbar anaesthesia

· Retrobulbar injection is given with a special one and half inch needle which is having a rounded tip which is bent 10 degree outward away from the globe.

· Anaesthesia and akinesia of the eye are obtained by injecting the local anaesthetic solution (mixture of xylocaine 2% and bupivacaine 0.5% with hyalase) into the retrobulbar space within the muscle cone.

· The patient is asked to look straight ahead upwards and/or slightly downward and outward.

· A 3.5 cm (one and half inch) 23 guage sharp edged rounded tipped needle is inserted in the quadrant between the inferior and the lateral rectus muscles and directed posteriorly until the resistance of the orbital septum, the needle is directed toward the apex of the orbit and advanced until it meets the resistance of the intermuscular septum.

· When this structure is penetrated, the needle tip is in the retrobulbar space.

· Approximately 2 to 3 ml of the anaesthetic mixtures injected into the retrobulbar space, taking care to minimize needle movement to prevent possible laceration of the blood vessels.

· After the injection, the globe should be intermittently compressed for several minutes to distribute the anaesthetic and to ensure haemostasis.

A properly placed retrobulbar injection is effective within seconds and blocks all extraocular muscles except the superior oblique muscle, affects the ciliary ganglion (resulting in pupillary dilatation), and anaesthetizes the entire globe.

· Complications of retrobulbar injection may be divided into those arising from the needle itself and those arising from the anaesthetic. The major complication of retrobulbar injection is retrobulbar haemorrhage (RBH). It can be recognize by proptosis, subconjunctival haemorrhage, eyelid ecchymosis, and elevated intraocular pressure (IOP). Since this last sign can lead to central retinal artery occlusion (CRAO), a lateral canthotomy should be performed immediately after an orbital haemorrhage is recognized, and IOP should be monitored. Surgery must be postponed for at least 1 week. The oculocardiac reflex is triggered by traction on the extraocular muscles and results in increased vagal tone, causing a sinus or nodal bradycardia and hypotension.

Dosage of anaesthetic used for retrobulbar injection are well below the reported maximum safe dosage a person may receive, and the initial signs of toxicity to the local anaesthetic on the CNS include tremors, agitation and slurred speech leading to generalised convulsions. Cases of CNS involvement after retrobulbar injection usually demonstrate increasing drowsiness, unconsciousness, respiratory depression and apnoea. The likely cause of these toxic signs is due to anaesthetic gaining access to the respiratory nucleus in the midbrain from a direct injection into the optic nerve sheath.

Digital pressure
Digital pressure is exerted against the closed eyelid for at least 15 to 20 minutes, with the fingers or the heel of the hand, or with the application of a superpinkie. In young, obese myopic and high risk (for vitreous loss) patients, pressure (by hand or superpinkie) is applied for 30 minutes. Cotton pads under superpinkie should spread the pressure uniformly and it should be possible to insert 2 fingers under the band of the pinkie ball. Care should be taken to keep the lids closed applying the superpinkie.

During digital massage, some consider steady pressure better than massage because there have massage because there have been reports of dislocation of the lens with the latter, though, we have never seen such a case. It is better to go for intermittent massage with release of pressure every 30 to 45 seconds to ensure against vascular occlusion. Digital pressure results in the following benefits:

1. Decreases vitreous volume
2. Decreases orbital volume
3. Provides better akinesia and anaesthesia
4. Haemostasis within the orbit

Akinesia of the orbicularis oculi
To prevent the squeezing action of the eyelids during cataract extraction, temporary paralysis of the orbicularis muscle is effected by one of the following methods using the same solution of anaesthetic mixture as described above. The methods used to anaesthetize orbicularis muscle are van lint akinesia (obtained in filtration anaesthetic solution in the region of the terminal branches of the facial nerve), Modified van Lint Akinesia, O’Brien akinesia technique (blocking the special nerve at the proximal trunk of the nerve, just in front of the tragus of the ear over the condyloid process of the mandible), Atksion akinesia (injection along the inferior edge of the zygomatic bone and then upward across the zygomatic arch toward the top of the ear). And Nadbath-Ellis akinesia (injection in the area of the

Different types of blocks for ocular anaesthesia

	Topical anaesthesia	Peribulbar anaesthesia	Retrobulbar anaesthesia
Anaesthetic agent	4% xylocaine or 0.5% tetracaine (preservative free)	0.5 bupivacaine + 2% xylocaine with hyalase (1500 IU in 3 vials of 30 ml xylocaine 2%)	0.5% bupivacaine + 2% xylocaine with hyalase (1500 IU in vials of 30 ml xlocaine 2%)
Amount of anaesthetic agent used	1 drop every 5 minutes 4 times before surgery	8-10 ml of above anaesthetic mixture	2 to 3 ml of above anaesthetic mixture
Site of injection	Lower fornix	Peribulbar space	Retrobulbar space
Time of action	Early	Takes time	Within second if placed in proper retrobulbar space.
Complication	Least	Occasional	More, and may be serous or life threatening
Needle parameter	Used as topical drops	1/2 inch, 26 G needle	3.5 cm (1/2 inch) sharp edged rounded tip needle.
Facial nerve block	Never comes	Usually orbicularis get anaesthetized and doesn’t require supplementation	Usually requires supplement injection by any one of the types of facial nerve blocks.
Currently in practice	Very rarely used alone. (only by very well experienced surgeons)	Preferred technique in current ophthalmic practice	Used only in situations where chemosis is to be avoided (e.g. squint, glaucoma surgery etc) and in camp settings.

Facial nerve as it emerges from the styllomastoid foramen and enters the parotid gland). Presently, during most ocular surgeries, Van Lint, modified Van Lint or O’Brien akinesia techniques are used and preferred whenever required. The reason being their simplicity and easy accessibility of the area to be blocked. Also a supplementary block can be given by these techniques, if required in the middle of the surgery.

CONCLUSION AND SUMMARY

1. The peribulbar though being equally effective as retrobulbar is still a better mode considering the patients comfort and in terms of prevention of the dreaded complications when used along with additives.

2. The local anaesthetic given with hyaluronidase enhances the effect of lignocaine.

3. The addition of Epinephrine 1:2 lacs is beneficial for prolonging the action and also prevents excessive bleeding by vascoconstriction.

4. Sensorcaine prolongs the duration of action. Greater the amount and concentration longer the action.

5. The minimum amount of anaesthetic for complete akinesia of globe and lids and decrease in IOP without supplementary injection is 6 ml.

6. Peribulbar through Conjunctival route is a faster mode of anaesthesia than cutaneous.

7. Ocular massage is important for even distribution of the local anaesthetic and to bring down the IOP.