Anesthesia for Cataract Surgery






Definition


Procedures and medications given to allow successful completion of lens removal with minimal risk, pain, and anxiety.




Key Features





  • Consideration of patient characteristics.



  • Local anesthesia: considerations, sedatives used, local anesthetics used.



  • Local techniques: topical, retrobulbar—advantages, disadvantages; peribulbar and sub-Tenon’s—comparison.



  • General anesthesia: techniques, advantages, disadvantages, and complications.





Introduction


The advent of small, self-sealing cataract incisions has allowed a change in the practice of anesthesia for cataract surgery. Local and topical techniques are now the norm, with less than 2% of patients requiring general anesthesia. However, anesthesiology input remains important, as even topical techniques have been shown to require anesthesiologist intervention for 22%–28% of cases.


A team approach is important because it allows the surgeon to concentrate on the operation while the anesthesiologist cares for the patient.




Medical Aspects of Anesthesia for Cataract Surgery


Cataract Type and Associated Medical Conditions


Cataracts can be either congenital or acquired and may be an ocular manifestation of a systemic disease. Younger patients may have uncommon medical conditions, whereas those with acquired cataracts are usually older (average age 75 years) and have comorbidities, such as ischemic heart disease and chronic obstructive airway disease. In an audit of 1000 cases in Auckland, 43% were identified as American Society of Anesthesiologists (ASA) grades 3–4. There is also a significant increase in overall mortality in those with concurrent hypertension (48%), ischemic heart disease (38%), and diabetes (16%).


Routine preoperative investigations, however, are not usually indicated, with the exception of testing for clotting in some patients taking oral anticoagulants, for electrolytes in those having dialysis, and for blood sugar in those with a history of diabetes. An assessment of the patient’s ability to lie flat and still is important.


Specific Conditions


Ischemic Heart Disease


Ischemia can be provoked by stress and anxiety at the prospect of surgery and anesthesia. If possible, surgery should be avoided for 3 months after myocardial infarction, angioplasty, or coronary revascularization. Phenylephrine drops may result in a significant rise in blood pressure and should be limited to a 2.5% solution. The oxidative damage resulting in cataract formation is linked to free radical formation and atherosclerosis, which explains the high proportion of patients with coexisting ischemic heart disease.


Anticoagulants


Patients on oral anticoagulants and antiplatelet therapy, including aspirin and clopidogrel, should continue with these throughout surgery. The risks of cardiovascular complications if these agents are stopped outweigh the potential risks of hemorrhage. General anesthesia, sub-Tenon’s block, or topical local anesthesia is recommended.


Diabetes Mellitus


Local anesthesia causes the least disruption to diabetic management and is preferred. Normally, patients do not need to fast (see below).




Cataract Type and Associated Medical Conditions


Cataracts can be either congenital or acquired and may be an ocular manifestation of a systemic disease. Younger patients may have uncommon medical conditions, whereas those with acquired cataracts are usually older (average age 75 years) and have comorbidities, such as ischemic heart disease and chronic obstructive airway disease. In an audit of 1000 cases in Auckland, 43% were identified as American Society of Anesthesiologists (ASA) grades 3–4. There is also a significant increase in overall mortality in those with concurrent hypertension (48%), ischemic heart disease (38%), and diabetes (16%).


Routine preoperative investigations, however, are not usually indicated, with the exception of testing for clotting in some patients taking oral anticoagulants, for electrolytes in those having dialysis, and for blood sugar in those with a history of diabetes. An assessment of the patient’s ability to lie flat and still is important.




Specific Conditions


Ischemic Heart Disease


Ischemia can be provoked by stress and anxiety at the prospect of surgery and anesthesia. If possible, surgery should be avoided for 3 months after myocardial infarction, angioplasty, or coronary revascularization. Phenylephrine drops may result in a significant rise in blood pressure and should be limited to a 2.5% solution. The oxidative damage resulting in cataract formation is linked to free radical formation and atherosclerosis, which explains the high proportion of patients with coexisting ischemic heart disease.


Anticoagulants


Patients on oral anticoagulants and antiplatelet therapy, including aspirin and clopidogrel, should continue with these throughout surgery. The risks of cardiovascular complications if these agents are stopped outweigh the potential risks of hemorrhage. General anesthesia, sub-Tenon’s block, or topical local anesthesia is recommended.


Diabetes Mellitus


Local anesthesia causes the least disruption to diabetic management and is preferred. Normally, patients do not need to fast (see below).




Ischemic Heart Disease


Ischemia can be provoked by stress and anxiety at the prospect of surgery and anesthesia. If possible, surgery should be avoided for 3 months after myocardial infarction, angioplasty, or coronary revascularization. Phenylephrine drops may result in a significant rise in blood pressure and should be limited to a 2.5% solution. The oxidative damage resulting in cataract formation is linked to free radical formation and atherosclerosis, which explains the high proportion of patients with coexisting ischemic heart disease.




Anticoagulants


Patients on oral anticoagulants and antiplatelet therapy, including aspirin and clopidogrel, should continue with these throughout surgery. The risks of cardiovascular complications if these agents are stopped outweigh the potential risks of hemorrhage. General anesthesia, sub-Tenon’s block, or topical local anesthesia is recommended.




Diabetes Mellitus


Local anesthesia causes the least disruption to diabetic management and is preferred. Normally, patients do not need to fast (see below).




Local Anesthesia


Local anesthesia can be classified into topical, retrobulbar, peribulbar, and sub-Tenon’s block.


General Considerations


The main advantage of local anesthesia is minimal disruption for the patient. Sedation may be useful, particularly in the anxious. Patients given local anesthesia without sedation or with “minimal” sedation (as defined by the ASA) need not be starved. Guidelines for standard fasting times should be followed for deeper sedation or general anesthesia.


Minimal monitoring should include electrocardiography (ECG) and pulse oximetry. Older adults and those with systemic illnesses should be anesthetized in an appropriate environment with backup facilities if inpatient or critical care is required. Supplemental oxygen is given to avoid hypoxia and to minimize claustrophobia. Rebreathing can occur under the drapes even at 6 L/min of oxygen.


Nonmedical personnel often perform an assessment prior to surgery. Accurate listing for local or general anesthesia can be a problem because many patients have comorbidities. A questionnaire filled in by patients has been shown to be a good initial screening tool, with supplemental medical input as required.


Many patients have visual experiences under local anesthesia; in one survey 16% found this distressing. Counseling preoperatively has been shown to be beneficial in reducing this distress.


All operating room personnel must be trained in basic life support, and at least one member should have advanced training. The Joint Royal Colleges in the United Kingdom recommend that an anesthetist be present throughout, whether general or local anesthesia is used, and this is essential if sharp needle technique or sedation is contemplated. For patients undergoing topical anesthesia or sub-Tenon’s block, an anesthetist does not need to be present, unless the site is isolated.


There are few absolute contraindications to local anesthesia, but patient refusal and the possibility of noncooperation during surgery remain the commonest.


Topical Anesthesia (see Box 5.8.1 )


More than 60% of all cataract operations are performed with the patient under topical anesthesia in the United States and around 33% in the United Kingdom. Oxybuprocaine (benoxinate) 0.4%, an ester anesthetic, is frequently used. Proparacaine (proxymetacaine) 0.5% is less toxic to the corneal epithelium, does not sting on application, but has a shorter duration of action (20 minutes). Other agents, including tetracaine (amethocaine) 0.5%–1%, lidocaine 1%–4%, and bupivacaine 0.5%–0.75%, have longer durations of action but increased corneal toxicity and pain on application.



Box 5.8.1

Advantages and Disadvantages of Topical Anesthesia


Advantages





  • No risk associated with needle insertion



  • Reduced risk of periocular hemorrhage



  • Functional vision is maintained; advantageous for uniocular patients



  • Reduced postoperative diplopia and ptosis



Disadvantages





  • An awake and talkative patient can be distracting for the surgeon



  • No akinesia of the eye



  • Less effective anesthesia compared with sub-Tenon’s block



  • Increased risk of surgical complications; if difficulties or problems occur, anesthesia may be inadequate



  • May be unsuitable for less experienced surgeons



Adverse Effects of Topical Ocular Anesthetics





  • Direct corneal effects—alteration of lacrimation and tear film stability



  • Epithelial toxicity—healing has been shown to be delayed when an epithelial defect occurs (lidocaine does not appear to affect healing)



  • Endothelial toxicity—this occurs when penetrating trauma is present and appears to be related to the preservative benzalkonium



  • Systemic effects—lethal toxicity (this is only a problem with cocaine)



  • Allergy and idiosyncratic reactions



Secondary Adverse Effects





  • Surface keratopathy




Topical anesthesia may be combined with subconjunctival or, more commonly, intracameral anesthesia to improve patient comfort. Preservative-free lidocaine 1% 0.3–0.5 mL appears to be effective and safe.


As visual perception is not lost, the patient is asked to focus on a light, the intensity of which is reduced. Subconjunctival injection of antibiotics can be painful and can be avoided by intracameral administration.


Use of topical anesthesia has been increasing throughout the United States and Europe despite several studies demonstrating inferior analgesia compared with both peribulbar and sub-Tenon’s blocks and a possible increase in surgical complication rate (4.3% posterior capsular tear for topical compared with 2.1% for sub-Tenon’s anesthesia).


With correct selection of patients and surgery performed by experienced surgeons, many centers have shown good results, but because there is no akinesia of the eye, it may not be suitable for inexperienced surgeons or uncooperative patients.


Retrobulbar Block (see Box 5.8.2 )


With this technique, the aim is to block the oculomotor nerves before they enter the four rectus muscles by depositing the local anesthetic directly into the posterior intraconal space ( Fig. 5.8.1 ). Although the resultant akinesia is usually profound, serious complications, such as brainstem anesthesia, globe perforation, and myotoxicity, have rendered the technique relatively obsolete. For sharp needle anesthesia, peribulbar block offers a safer, equally effective method.



Box 5.8.2

Advantages and Disadvantages of Retrobulbar Block


Advantages





  • Reliable akinesia



  • Onset of block is quicker than with peribulbar anesthesia



  • Low volumes of anesthetic result in a lower intraorbital tension and less chemosis than with peribulbar blocks



  • Temporary loss of visual acuity occurs more reliably than for peribulbar block



Disadvantages





  • Risk of brainstem anesthesia—reason for the development of the peribulbar block



  • Risk of myotoxicity and globe perforation





Fig. 5.8.1


Advancement of needle in retrobulbar block.


Peribulbar Block (see also Table 5.8.1 )


The principle of this technique is to instill the local anesthetic outside the posterior muscle cone and thereby avoid accidental injection into the optic nerve (which would cause brainstem anesthesia). This utilizes higher volumes (6–10 mL) of the local anesthetic compared with the traditional retrobulbar block, and the application of a pressure device is often needed.



TABLE 5.8.1

Comparison of Peribulbar and Sub-Tenon’s Block






















Peribulbar Block Sub-Tenon’s Block
More pronounced akinesia Less akinesia
Lower rates of chemosis and subconjunctival hemorrhage High rates of chemosis and subconjunctival hemorrhage
Risk of globe perforation, retrobulbar hemorrhage, myotoxicity Complications rarely serious
Improved analgesia
Lower dose and volume of anesthetic agent are used
Less painful to perform
Small risk of brainstem anesthesia


Technique


With the eye in primary gaze, local anesthetic drops are applied to the cornea. At the inferotemporal lower orbital margin, a 25-gauge, 25-mm needle is advanced parallel to the plane of the orbital floor either transcutaneously or transconjunctivally. A degree of upward and inward angulation may be needed once the needle goes past the equator of the globe. Local anesthetic (4–6 mL) is injected at a depth of about 20 mm from the inferior orbital rim (in an eye of normal axial length). No resistance to injection should be felt, and prior aspiration should be performed ( Fig. 5.8.2 and Fig. 5.8.3 ).




Fig. 5.8.2


Inferotemporal peribulbar injection. (A) The needle enters the orbit at the junction of its floor with the lateral wall, very close to the bony rim. (B) The needle passes backward in a sagittal plane parallel to the orbit floor. (C) It passes the globe equator when the needle–hub junction reaches the plane of the iris. (D) After test aspiration, up to 10 mL anesthetic solution is injected.

(Adapted from Hamilton RC. Techniques of orbital regional anaesthesia. Br J Anaesth 2001;86:473–6.)



Fig. 5.8.3


Transconjunctival peribulbar injection technique.


After 5 minutes, the degree of akinesia is assessed. If a second mediocanthal injection is required, a 25-gauge, 25-mm needle is inserted between the medial canthus and the caruncle and directed immediately backward. The medial check ligament is often penetrated. At a depth of 15 mm, after prior aspiration, another 4–6 mL of solution is injected to produce a more complete block, with akinesia of the orbicularis oculi and levator palpebrae superioris. A Honan balloon or pressure-lowering device is often applied for 5–10 minutes.


Peribulbar block has been reported to be more painful than using topical anesthesia. It is important that adequate training be given to decrease complications from the use of all of these blocks.


Local Anesthetic Agent


The most common agent used is lidocaine 2% plus hyaluronidase 15 IU/mL. If greater duration of anesthesia is required, the lidocaine can be mixed in a ratio of 50 : 50 with bupivacaine 0.5%.


Other agents used include 2-chloroprocaine 2%–3%, mepivacaine 1%–2%, bupivacaine 0.25%–0.75%, prilocaine 3%, and ropivacaine 0.75%. Levobupivacaine is the l -isomer of bupivacaine with a higher safety index, especially in terms of cardiac toxicity. Articaine 2%–4% is an amide local anesthetic of low toxicity used predominantly in dentistry. Because of its rapid onset, short duration of action, low toxicity, and better penetration of tissues, it has been shown to produce good quality blocks.


Epinephrine 5 µg/mL is sometimes added to improve onset time, quality, and duration of the block. However, it should be avoided in older patients with atherosclerosis and has been implicated in optic artery thrombosis secondary to vasoconstriction. A 50% decrease in pressure in the ophthalmic artery has also been noted.


Hyaluronidase is an enzyme derived from the testicles of rams (previously from the testicles of cattle), although a recombinant version is now available. It hydrolyzes C1–C4 bonds between glucosamine and glucuronic acid in connective tissue, thus enabling the local anesthetic to penetrate tissues more effectively. The required quantity of the local anesthetic, therefore, is reduced, and the time to onset decreased. Hyaluronidase may also help prevent damage to the extraocular muscles, especially the inferior rectus muscle, preventing diploplia.


Complications


Most serious complications of peribulbar anesthesia are associated with the use of sharp needles.




  • Globe perforation/penetration. Incidence 1.4–1.9 per 10 000. More common in high myopes (>26 mm axial length) and with inexperience. Usually results in marked visual loss because of permanent retinal damage.



  • Retrobulbar hemorrhage. Incidence 0.6–4.2 per 10 000. More common in those taking anticoagulants. May require surgical decompression.



  • Extraocular myotoxicity. Incidence 25–100 per 10 000. Related to inadvertent direct injection of the local anesthetic into the muscle belly. Myocyte cell death is followed by hypertrophic regeneration and shortening.



These serious complications have led some authorities to recommend abandoning sharp needle techniques altogether. The UK Royal College of Ophthalmologists has also stated:


“Sharp needle local anaesthetic techniques have a higher risk of ocular and systemic complications than sub-Tenon’s or topical techniques and should only be used when the anaesthetist and surgeon consider it absolutely necessary.”


In 2017 the UK National Institute for Health and Care Excellence (NICE) concluded that peribulbar anesthesia should no longer be used for routine cataract surgery where Topical or sub-Tenon’s anesthesia is possible.


Certainly, sharp needle blocks are responsible for the majority of ophthalmic anesthesia–related problems and are the most common cause of regional anesthesia–related litigation after centroneuraxial blockade in the United Kingdom (average settlement £24 000).


Sub-Tenon’s Block (see also Table 5.8.1 )


This was first described by Turnbull in 1884 when he used open dissection of Tenon’s layer followed by instillation of cocaine. Later modifications were introduced by Stevens, Greenbaum and Allman.


Sub-Tenon’s block involves surface anesthesia and surgical access to sub-Tenon’s space. In the United Kingdom, this now is the most common method used in cataract surgery, comprising 47% of cases.


Anatomy


This is described in more detail elsewhere in this text. Briefly, Tenon’s capsule (after Jacques René Tenon [1724–1816], French anatomist/surgeon) is a facial sheath, a thin membrane enveloping the eyeball and separating it from orbital fat. The inner surface is smooth and shiny, separated from the outer surface of the sclera by a potential space, the episcleral or sub-Tenon’s space. Anteriorly, the capsule fuses with conjunctiva 5–10 mm from the limbus. Posteriorly, it fuses with the meninges around the optic nerve. It has been suggested that it is a lymph space and is crossed by numerous delicate bands.


Technique


The conjunctiva is anesthetized first with a topical local anesthetic of choice. The most common approach is via the infranasal quadrant because this allows for good distribution of the anesthetic while decreasing the risk of damage to the vortex veins. The eye is cleaned with 5% iodine, and the patient is asked to look upward and outward. Aseptically, the conjunctiva and Tenon’s capsule are held 3–5 mm from the limbus using nontoothed Moorfield’s forceps ( Fig. 5.8.4 ). A small incision is made through these layers using blunt-tipped, sprung Westcott scissors, exposing the sclera. A cannula is then advanced into the sub-Tenon’s space and around the globe.




Fig. 5.8.4


Incision for sub-Tenon’s block. Arrows point to conjunctiva, Tenon’s capsule, and shining sclera under the Tenon’s capsule.

(Reprinted with kind permission from Kumar CM, Williamson S, Manickham B. A review of sub-Tenon’s block: current practice and recent development. Eur J Anaesthesiol 2005;22:567–7, Figure 2c, European Academy of Anaesthesiology, published by Cambridge University Press.)


Sub-Tenon’s anesthesia can be broadly divided into anterior and posterior techniques. In the former, the cannula tip remains anterior to the globe equator. This reduces the risk of inadvertent misplacement but increases the rate of chemosis and can make akinesia difficult to achieve. For more profound akinesia, the cannula tip should be placed posterior to the equator but must be positioned with care, gently following the curve of the globe ( ).



Numerous cannulae have been described. The plastic Greenbaum cannula (12-mm 15-gauge) is suitable for anterior blocks, whereas a metal Stevens cannula (25-mm 19-gauge) is most suitable for posterior techniques ( Fig. 5.8.5 ).




Fig. 5.8.5


Three cannulae used for sub-Tenon’s anesthesia. (A) Greenbaum cannula 15-gauge 12-mm. Middle, Triport cannula (Eagle Laboratories) 21-gauge 25-mm. (B) Steven’s cannula (Visitec) 19-gauge 25-mm.




An alternative technique that requires no prior conjunctival incision uses a pencil-point cannula (25-mm 21-gauge Triport cannula; Eagle Laboratories). This reduces the amount of conjunctival damage and decreases reflux of the local anesthetic. The blunt cannula entry site leaves a very small, self-sealing wound, which then heals rapidly with less conjunctival scarring compared with traditional techniques ( ).



The sub-Tenon’s (or episcleral) space also can be accessed using a “B” beveled needle, as described by Jacques Ripart. Although a useful and reliable technique, this somewhat negates the advantages of using a blunt cannula.


The local anesthetic in a dose of 3 to 5 mL is injected; the greater the volume, the greater is the degree of akinesia. Lidocaine 2% is usually used in combination with hyaluronidase. Addition of hyaluronidase reduces the median effective volume (EV50) needed from 6.4 to 2.6 mL. Articaine 2%–4% may be even more effective.


A Honan’s balloon can be used to increase dispersal; however, it is not usually needed.


Complications are mainly minor (chemosis and subconjunctival hemorrhage), although orbital inflammation, scleral perforation, cardiovascular collapse, and sight-threatening and life-threatening complications have all been reported.




General Considerations


The main advantage of local anesthesia is minimal disruption for the patient. Sedation may be useful, particularly in the anxious. Patients given local anesthesia without sedation or with “minimal” sedation (as defined by the ASA) need not be starved. Guidelines for standard fasting times should be followed for deeper sedation or general anesthesia.


Minimal monitoring should include electrocardiography (ECG) and pulse oximetry. Older adults and those with systemic illnesses should be anesthetized in an appropriate environment with backup facilities if inpatient or critical care is required. Supplemental oxygen is given to avoid hypoxia and to minimize claustrophobia. Rebreathing can occur under the drapes even at 6 L/min of oxygen.


Nonmedical personnel often perform an assessment prior to surgery. Accurate listing for local or general anesthesia can be a problem because many patients have comorbidities. A questionnaire filled in by patients has been shown to be a good initial screening tool, with supplemental medical input as required.


Many patients have visual experiences under local anesthesia; in one survey 16% found this distressing. Counseling preoperatively has been shown to be beneficial in reducing this distress.


All operating room personnel must be trained in basic life support, and at least one member should have advanced training. The Joint Royal Colleges in the United Kingdom recommend that an anesthetist be present throughout, whether general or local anesthesia is used, and this is essential if sharp needle technique or sedation is contemplated. For patients undergoing topical anesthesia or sub-Tenon’s block, an anesthetist does not need to be present, unless the site is isolated.


There are few absolute contraindications to local anesthesia, but patient refusal and the possibility of noncooperation during surgery remain the commonest.




Topical Anesthesia (see Box 5.8.1 )


More than 60% of all cataract operations are performed with the patient under topical anesthesia in the United States and around 33% in the United Kingdom. Oxybuprocaine (benoxinate) 0.4%, an ester anesthetic, is frequently used. Proparacaine (proxymetacaine) 0.5% is less toxic to the corneal epithelium, does not sting on application, but has a shorter duration of action (20 minutes). Other agents, including tetracaine (amethocaine) 0.5%–1%, lidocaine 1%–4%, and bupivacaine 0.5%–0.75%, have longer durations of action but increased corneal toxicity and pain on application.



Box 5.8.1

Advantages and Disadvantages of Topical Anesthesia


Advantages





  • No risk associated with needle insertion



  • Reduced risk of periocular hemorrhage



  • Functional vision is maintained; advantageous for uniocular patients



  • Reduced postoperative diplopia and ptosis



Disadvantages





  • An awake and talkative patient can be distracting for the surgeon



  • No akinesia of the eye



  • Less effective anesthesia compared with sub-Tenon’s block



  • Increased risk of surgical complications; if difficulties or problems occur, anesthesia may be inadequate



  • May be unsuitable for less experienced surgeons



Adverse Effects of Topical Ocular Anesthetics





  • Direct corneal effects—alteration of lacrimation and tear film stability



  • Epithelial toxicity—healing has been shown to be delayed when an epithelial defect occurs (lidocaine does not appear to affect healing)



  • Endothelial toxicity—this occurs when penetrating trauma is present and appears to be related to the preservative benzalkonium



  • Systemic effects—lethal toxicity (this is only a problem with cocaine)



  • Allergy and idiosyncratic reactions



Secondary Adverse Effects





  • Surface keratopathy




Topical anesthesia may be combined with subconjunctival or, more commonly, intracameral anesthesia to improve patient comfort. Preservative-free lidocaine 1% 0.3–0.5 mL appears to be effective and safe.


As visual perception is not lost, the patient is asked to focus on a light, the intensity of which is reduced. Subconjunctival injection of antibiotics can be painful and can be avoided by intracameral administration.


Use of topical anesthesia has been increasing throughout the United States and Europe despite several studies demonstrating inferior analgesia compared with both peribulbar and sub-Tenon’s blocks and a possible increase in surgical complication rate (4.3% posterior capsular tear for topical compared with 2.1% for sub-Tenon’s anesthesia).


With correct selection of patients and surgery performed by experienced surgeons, many centers have shown good results, but because there is no akinesia of the eye, it may not be suitable for inexperienced surgeons or uncooperative patients.




Retrobulbar Block (see Box 5.8.2 )


With this technique, the aim is to block the oculomotor nerves before they enter the four rectus muscles by depositing the local anesthetic directly into the posterior intraconal space ( Fig. 5.8.1 ). Although the resultant akinesia is usually profound, serious complications, such as brainstem anesthesia, globe perforation, and myotoxicity, have rendered the technique relatively obsolete. For sharp needle anesthesia, peribulbar block offers a safer, equally effective method.



Box 5.8.2

Advantages and Disadvantages of Retrobulbar Block


Advantages





  • Reliable akinesia



  • Onset of block is quicker than with peribulbar anesthesia



  • Low volumes of anesthetic result in a lower intraorbital tension and less chemosis than with peribulbar blocks



  • Temporary loss of visual acuity occurs more reliably than for peribulbar block



Disadvantages





  • Risk of brainstem anesthesia—reason for the development of the peribulbar block



  • Risk of myotoxicity and globe perforation





Fig. 5.8.1


Advancement of needle in retrobulbar block.




Peribulbar Block (see also Table 5.8.1 )


The principle of this technique is to instill the local anesthetic outside the posterior muscle cone and thereby avoid accidental injection into the optic nerve (which would cause brainstem anesthesia). This utilizes higher volumes (6–10 mL) of the local anesthetic compared with the traditional retrobulbar block, and the application of a pressure device is often needed.



TABLE 5.8.1

Comparison of Peribulbar and Sub-Tenon’s Block






















Peribulbar Block Sub-Tenon’s Block
More pronounced akinesia Less akinesia
Lower rates of chemosis and subconjunctival hemorrhage High rates of chemosis and subconjunctival hemorrhage
Risk of globe perforation, retrobulbar hemorrhage, myotoxicity Complications rarely serious
Improved analgesia
Lower dose and volume of anesthetic agent are used
Less painful to perform
Small risk of brainstem anesthesia


Technique


With the eye in primary gaze, local anesthetic drops are applied to the cornea. At the inferotemporal lower orbital margin, a 25-gauge, 25-mm needle is advanced parallel to the plane of the orbital floor either transcutaneously or transconjunctivally. A degree of upward and inward angulation may be needed once the needle goes past the equator of the globe. Local anesthetic (4–6 mL) is injected at a depth of about 20 mm from the inferior orbital rim (in an eye of normal axial length). No resistance to injection should be felt, and prior aspiration should be performed ( Fig. 5.8.2 and Fig. 5.8.3 ).




Fig. 5.8.2


Inferotemporal peribulbar injection. (A) The needle enters the orbit at the junction of its floor with the lateral wall, very close to the bony rim. (B) The needle passes backward in a sagittal plane parallel to the orbit floor. (C) It passes the globe equator when the needle–hub junction reaches the plane of the iris. (D) After test aspiration, up to 10 mL anesthetic solution is injected.

(Adapted from Hamilton RC. Techniques of orbital regional anaesthesia. Br J Anaesth 2001;86:473–6.)



Fig. 5.8.3


Transconjunctival peribulbar injection technique.


After 5 minutes, the degree of akinesia is assessed. If a second mediocanthal injection is required, a 25-gauge, 25-mm needle is inserted between the medial canthus and the caruncle and directed immediately backward. The medial check ligament is often penetrated. At a depth of 15 mm, after prior aspiration, another 4–6 mL of solution is injected to produce a more complete block, with akinesia of the orbicularis oculi and levator palpebrae superioris. A Honan balloon or pressure-lowering device is often applied for 5–10 minutes.


Peribulbar block has been reported to be more painful than using topical anesthesia. It is important that adequate training be given to decrease complications from the use of all of these blocks.


Local Anesthetic Agent


The most common agent used is lidocaine 2% plus hyaluronidase 15 IU/mL. If greater duration of anesthesia is required, the lidocaine can be mixed in a ratio of 50 : 50 with bupivacaine 0.5%.


Other agents used include 2-chloroprocaine 2%–3%, mepivacaine 1%–2%, bupivacaine 0.25%–0.75%, prilocaine 3%, and ropivacaine 0.75%. Levobupivacaine is the l -isomer of bupivacaine with a higher safety index, especially in terms of cardiac toxicity. Articaine 2%–4% is an amide local anesthetic of low toxicity used predominantly in dentistry. Because of its rapid onset, short duration of action, low toxicity, and better penetration of tissues, it has been shown to produce good quality blocks.


Epinephrine 5 µg/mL is sometimes added to improve onset time, quality, and duration of the block. However, it should be avoided in older patients with atherosclerosis and has been implicated in optic artery thrombosis secondary to vasoconstriction. A 50% decrease in pressure in the ophthalmic artery has also been noted.


Hyaluronidase is an enzyme derived from the testicles of rams (previously from the testicles of cattle), although a recombinant version is now available. It hydrolyzes C1–C4 bonds between glucosamine and glucuronic acid in connective tissue, thus enabling the local anesthetic to penetrate tissues more effectively. The required quantity of the local anesthetic, therefore, is reduced, and the time to onset decreased. Hyaluronidase may also help prevent damage to the extraocular muscles, especially the inferior rectus muscle, preventing diploplia.


Complications


Most serious complications of peribulbar anesthesia are associated with the use of sharp needles.




  • Globe perforation/penetration. Incidence 1.4–1.9 per 10 000. More common in high myopes (>26 mm axial length) and with inexperience. Usually results in marked visual loss because of permanent retinal damage.



  • Retrobulbar hemorrhage. Incidence 0.6–4.2 per 10 000. More common in those taking anticoagulants. May require surgical decompression.



  • Extraocular myotoxicity. Incidence 25–100 per 10 000. Related to inadvertent direct injection of the local anesthetic into the muscle belly. Myocyte cell death is followed by hypertrophic regeneration and shortening.



These serious complications have led some authorities to recommend abandoning sharp needle techniques altogether. The UK Royal College of Ophthalmologists has also stated:


“Sharp needle local anaesthetic techniques have a higher risk of ocular and systemic complications than sub-Tenon’s or topical techniques and should only be used when the anaesthetist and surgeon consider it absolutely necessary.”


In 2017 the UK National Institute for Health and Care Excellence (NICE) concluded that peribulbar anesthesia should no longer be used for routine cataract surgery where Topical or sub-Tenon’s anesthesia is possible.


Certainly, sharp needle blocks are responsible for the majority of ophthalmic anesthesia–related problems and are the most common cause of regional anesthesia–related litigation after centroneuraxial blockade in the United Kingdom (average settlement £24 000).




Technique


With the eye in primary gaze, local anesthetic drops are applied to the cornea. At the inferotemporal lower orbital margin, a 25-gauge, 25-mm needle is advanced parallel to the plane of the orbital floor either transcutaneously or transconjunctivally. A degree of upward and inward angulation may be needed once the needle goes past the equator of the globe. Local anesthetic (4–6 mL) is injected at a depth of about 20 mm from the inferior orbital rim (in an eye of normal axial length). No resistance to injection should be felt, and prior aspiration should be performed ( Fig. 5.8.2 and Fig. 5.8.3 ).




Fig. 5.8.2


Inferotemporal peribulbar injection. (A) The needle enters the orbit at the junction of its floor with the lateral wall, very close to the bony rim. (B) The needle passes backward in a sagittal plane parallel to the orbit floor. (C) It passes the globe equator when the needle–hub junction reaches the plane of the iris. (D) After test aspiration, up to 10 mL anesthetic solution is injected.

(Adapted from Hamilton RC. Techniques of orbital regional anaesthesia. Br J Anaesth 2001;86:473–6.)



Fig. 5.8.3


Transconjunctival peribulbar injection technique.


After 5 minutes, the degree of akinesia is assessed. If a second mediocanthal injection is required, a 25-gauge, 25-mm needle is inserted between the medial canthus and the caruncle and directed immediately backward. The medial check ligament is often penetrated. At a depth of 15 mm, after prior aspiration, another 4–6 mL of solution is injected to produce a more complete block, with akinesia of the orbicularis oculi and levator palpebrae superioris. A Honan balloon or pressure-lowering device is often applied for 5–10 minutes.


Peribulbar block has been reported to be more painful than using topical anesthesia. It is important that adequate training be given to decrease complications from the use of all of these blocks.




Local Anesthetic Agent


The most common agent used is lidocaine 2% plus hyaluronidase 15 IU/mL. If greater duration of anesthesia is required, the lidocaine can be mixed in a ratio of 50 : 50 with bupivacaine 0.5%.


Other agents used include 2-chloroprocaine 2%–3%, mepivacaine 1%–2%, bupivacaine 0.25%–0.75%, prilocaine 3%, and ropivacaine 0.75%. Levobupivacaine is the l -isomer of bupivacaine with a higher safety index, especially in terms of cardiac toxicity. Articaine 2%–4% is an amide local anesthetic of low toxicity used predominantly in dentistry. Because of its rapid onset, short duration of action, low toxicity, and better penetration of tissues, it has been shown to produce good quality blocks.


Epinephrine 5 µg/mL is sometimes added to improve onset time, quality, and duration of the block. However, it should be avoided in older patients with atherosclerosis and has been implicated in optic artery thrombosis secondary to vasoconstriction. A 50% decrease in pressure in the ophthalmic artery has also been noted.


Hyaluronidase is an enzyme derived from the testicles of rams (previously from the testicles of cattle), although a recombinant version is now available. It hydrolyzes C1–C4 bonds between glucosamine and glucuronic acid in connective tissue, thus enabling the local anesthetic to penetrate tissues more effectively. The required quantity of the local anesthetic, therefore, is reduced, and the time to onset decreased. Hyaluronidase may also help prevent damage to the extraocular muscles, especially the inferior rectus muscle, preventing diploplia.




Complications


Most serious complications of peribulbar anesthesia are associated with the use of sharp needles.




  • Globe perforation/penetration. Incidence 1.4–1.9 per 10 000. More common in high myopes (>26 mm axial length) and with inexperience. Usually results in marked visual loss because of permanent retinal damage.



  • Retrobulbar hemorrhage. Incidence 0.6–4.2 per 10 000. More common in those taking anticoagulants. May require surgical decompression.



  • Extraocular myotoxicity. Incidence 25–100 per 10 000. Related to inadvertent direct injection of the local anesthetic into the muscle belly. Myocyte cell death is followed by hypertrophic regeneration and shortening.



These serious complications have led some authorities to recommend abandoning sharp needle techniques altogether. The UK Royal College of Ophthalmologists has also stated:


“Sharp needle local anaesthetic techniques have a higher risk of ocular and systemic complications than sub-Tenon’s or topical techniques and should only be used when the anaesthetist and surgeon consider it absolutely necessary.”


In 2017 the UK National Institute for Health and Care Excellence (NICE) concluded that peribulbar anesthesia should no longer be used for routine cataract surgery where Topical or sub-Tenon’s anesthesia is possible.


Certainly, sharp needle blocks are responsible for the majority of ophthalmic anesthesia–related problems and are the most common cause of regional anesthesia–related litigation after centroneuraxial blockade in the United Kingdom (average settlement £24 000).




Sub-Tenon’s Block (see also Table 5.8.1 )


This was first described by Turnbull in 1884 when he used open dissection of Tenon’s layer followed by instillation of cocaine. Later modifications were introduced by Stevens, Greenbaum and Allman.


Sub-Tenon’s block involves surface anesthesia and surgical access to sub-Tenon’s space. In the United Kingdom, this now is the most common method used in cataract surgery, comprising 47% of cases.


Anatomy


This is described in more detail elsewhere in this text. Briefly, Tenon’s capsule (after Jacques René Tenon [1724–1816], French anatomist/surgeon) is a facial sheath, a thin membrane enveloping the eyeball and separating it from orbital fat. The inner surface is smooth and shiny, separated from the outer surface of the sclera by a potential space, the episcleral or sub-Tenon’s space. Anteriorly, the capsule fuses with conjunctiva 5–10 mm from the limbus. Posteriorly, it fuses with the meninges around the optic nerve. It has been suggested that it is a lymph space and is crossed by numerous delicate bands.


Technique


The conjunctiva is anesthetized first with a topical local anesthetic of choice. The most common approach is via the infranasal quadrant because this allows for good distribution of the anesthetic while decreasing the risk of damage to the vortex veins. The eye is cleaned with 5% iodine, and the patient is asked to look upward and outward. Aseptically, the conjunctiva and Tenon’s capsule are held 3–5 mm from the limbus using nontoothed Moorfield’s forceps ( Fig. 5.8.4 ). A small incision is made through these layers using blunt-tipped, sprung Westcott scissors, exposing the sclera. A cannula is then advanced into the sub-Tenon’s space and around the globe.




Fig. 5.8.4


Incision for sub-Tenon’s block. Arrows point to conjunctiva, Tenon’s capsule, and shining sclera under the Tenon’s capsule.

(Reprinted with kind permission from Kumar CM, Williamson S, Manickham B. A review of sub-Tenon’s block: current practice and recent development. Eur J Anaesthesiol 2005;22:567–7, Figure 2c, European Academy of Anaesthesiology, published by Cambridge University Press.)


Sub-Tenon’s anesthesia can be broadly divided into anterior and posterior techniques. In the former, the cannula tip remains anterior to the globe equator. This reduces the risk of inadvertent misplacement but increases the rate of chemosis and can make akinesia difficult to achieve. For more profound akinesia, the cannula tip should be placed posterior to the equator but must be positioned with care, gently following the curve of the globe ( ).



Numerous cannulae have been described. The plastic Greenbaum cannula (12-mm 15-gauge) is suitable for anterior blocks, whereas a metal Stevens cannula (25-mm 19-gauge) is most suitable for posterior techniques ( Fig. 5.8.5 ).


Oct 3, 2019 | Posted by in OPHTHALMOLOGY | Comments Off on Anesthesia for Cataract Surgery
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