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Local anesthesia helps achieve safe, comfortable oculofacial surgery
It is important to understand the anesthetics, sedatives and techniques that are involved.
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 Jeremiah Tao |
Anesthesia for eyelid and periocular surgery calls for safety to the eye, optic nerve and other vital structures, in addition to procuring comfort. When appropriately administered, significant pain can be eliminated during a procedure.
Regional techniques alone or in combination with intravenous agents are often preferred for oculofacial surgery because they may reduce the inherent risks of general anesthesia and allow quicker recovery. Several safe and reliable medications and techniques have been adopted for the use of local anesthesia to relieve discomfort safely in eyelid and periocular surgery.
Anesthetic medications
A spectrum of topical and injectable anesthetic agents may be utilized in eyelid and periocular surgery. The choice of local anesthetic depends on a variety of factors including half-life properties and side effects.
Most local anesthetics have a lipophilic group attached to an ionizable group via an intermediate, which is an ester or an amide. Amide types include lidocaine and bupivacaine; esters include procaine and cocaine. Both create a local nerve block by reducing the influx of sodium ions into the cytoplasm of nerve cells, which prevents nerve depolarization. Hydrolysis of ester compounds yields para-aminobenzoic acid, a well-known allergic compound; thus, amides are generally preferred. Local anesthetics can be administered topically or through injection.
Topical anesthetics
Topical anesthetics are applied to mucous membranes or skin for short, effective analgesia. Forms of administration include creams, ointments, aerosol sprays and eye drops. Adverse reactions with topical medications are rare but include allergic reaction, contact dermatitis or epithelial injury.
Anesthetic solution eye drops are instilled into the fornix. This provides analgesia to the cornea and ocular surface but does not anesthetize intraocular structures or surrounding soft tissues. Tetracaine 0.5%, proparacaine 0.5%, lidocaine 4% and bupivacaine 0.5% are options. Generally, all are short acting with duration of less than 30 minutes. Alone, these are rarely sufficient for conjunctival or anterior cornea surgery, but topical agents are often applied to reduce eye irritation due to povidone iodine skin preparation (or other solution) or corneal shield placement during periocular surgery.
Common skin cream anesthetics include lidocaine 4% and combination lidocaine 2.5% with prilocaine 2.5%. These are applied directly over the cutaneous surgical sites. Alone, these are usually not sufficient for incisional surgery, but pretreatment with these creams may minimize discomfort associated with needle penetration of the skin. Additionally, many surgeons use these medications before administration of botulinum toxin or injectable facial fillers. Typically, the maximum effect occurs 30 to 40 minutes after application.
Intradermal or subcutaneous anesthetics
Injectable local anesthetics are usually administered through a needle and syringe. They have relatively immediate onset after intradermal or subcutaneous injection.
Lidocaine
Lidocaine is an amide local anesthetic. Half-time distribution is 10 minutes, and half-life elimination rate is 1.5 hours. It has an intermediate duration of action of approximately 30 to 60 minutes. Toxic dose for infiltration anesthesia is 4.5 mg/kg. At very high concentrations, local anesthetics can block calcium channels, resulting in decreased myocardial contractility and hypotension.
Epinephrine
Epinephrine acts on adrenergic receptors in the vasculature, causing vasoconstriction, which leads to less blood loss and improved surgical visualization during the procedure. The analgesic effects are limited, but epinephrine also prolongs the anesthetic effect. Lidocaine with epinephrine lasts approximately 2 to 4 hours, in comparison to 30 to 60 minutes for lidocaine alone.
Bupivacaine
Like lidocaine, bupivacaine is an amide local anesthetic. Half-time distribution is 28 minutes, and half-life elimination is 3.5 hours. Duration of action is approximately 120 to 240 minutes. Maximum single dose is up to 175 mg of bupivacaine 0.25%. In addition to toxic effects mentioned above for lidocaine, the use of bupivacaine for intravenous regional anesthesia has been linked to cardiovascular collapse.
Cocaine
Cocaine is an ester anesthetic; unlike other local anesthetics, cocaine has direct sympathomimetic effects. Generally, 4% solution is recommended. Doses should not exceed 1 mg/kg due to the increased risk of systemic toxicity. For topical use, cocaine has duration of action ranging from 20 to 60 minutes. Some lacrimal surgeons apply intranasal cocaine for anesthetic and pronounced vasoconstriction effect. Cocaine must be used with caution because it may easily be absorbed systematically with risk for an acute cardiac vaso-occlusive event, even in patients with no prior heart disease.
Sodium bicarbonate
The addition of sodium bicarbonate to lidocaine or bupivacaine can minimize stinging sensation by balancing acidity.
Hyaluronidase
Hyaluronidase, which breaks down connective tissue, can be added to allow better penetration and stasis of an anesthetic.
Combination injectable regimens
Combinations of anesthetics can be used to help minimize pain and prolong desired effects. Lidocaine and bupivacaine come premixed with epinephrine in various concentrations.
We prefer the mix of 4.5 cc 1% lidocaine with 1:100,00, 4.5 cc 0.5% bupivacaine, and 1 cc of NaHCO3 in a 10 cc syringe. This combination has been associated with good intraoperative and postoperative analgesia and hemostasis. The addition of sodium bicarbonate aids in injection discomfort.
Techniques
An optimal and safe experience depends upon the choice of drug and good administration technique. An understanding of periocular anatomy and physiology is important in providing effective local anesthesia.
Direct tissue infiltration
Commonly, the soft tissue operative sites are directly infiltrated with local anesthesia. A generous amount of injectable anesthetic is also given to the surrounding area.
The anesthetic agents such as lidocaine or bupivacaine inactivate local sensory nerves. Epinephrine, usually included within the mix, aids in hemostasis. A mild blanching of the skin is usually observed secondary to vasoconstriction. The decreased blood flow improves surgical visualization and minimizes the amount of electrocautery necessary during the procedure. Distortion of anatomy and fluid tissue expansion may be one disadvantage.
Smaller-bore needles, such as 30 gauge, may be better tolerated but may require longer injection times. Additionally, slow administration of anesthetics may cause less discomfort.
We prefer a 30-gauge needle with local-only procedures. A 25.5-gauge needle is preferred when local anesthesia is administered in concert with brief conscious sedation due to quicker infiltration through a larger-bore needle.
 Figure 1: Longer needles allow for fewer penetrations, which may improve the patient's experience. Image: submitted by Dr. Tao
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Longer needles are advantageous to minimize the number of times the skin is penetrated by the needle, which may improve the experience. Additionally, fewer needle penetrations may minimize hematoma and infection. The needle should always be aimed away from the globe or other vital structures to forestall injury due to inadvertent movement (Figure 1).
Retrobulbar block
An anesthetic is injected inside the muscle cone, leading to paralysis of cranial nerves III, V and VI, ciliary nerves and ciliary ganglion. The trochlear nerve (cranial nerve IV) is often spared because it is not located within the muscle cone.
Proper technique involves injecting at the inferior orbital rim, perpendicular to the plane of the patient's face. Risks include retrobulbar hemorrhage, globe penetration and optic nerve injury. The optic nerve sheath is in continuum with the subarachnoid space. Thus, if the sheath is penetrated, systemic effects from brain stem anesthesia such as disorientation, respiratory depression or arrest, or unconsciousness can occur. Intra-arterial injection and reversal of blood flow from the ophthalmic artery to the internal carotid artery can produce seizures. Some needles, such as the Atkinson needle, have a less acute tip, which may forestall surrounding injury to vital structures during retrobulbar blockade.
Typically unnecessary for eyelid and surrounding facial surgery, a retrobulbar block is more often utilized for intraocular or ocular surface surgery. In oculoplastic surgery, a retrobulbar block is commonly administered at the end of enucleation or evisceration to aid in postoperative analgesia. A retrobulbar injection of alcohol or chlorpromazine injection may be considered to treat a blind, painful eye. However, these injections are associated with mixed success rates. Additionally, motor nerve denervation, with adverse effects such as ptosis, is a risk.
Peribulbar block
In contrast to retrobulbar block, local anesthetic is injected outside the muscle cone, which significantly decreases the risk of injuring the optic nerve. Disadvantages include a longer onset time and increased likelihood that complete akinesia has not
been achieved. The risks include globe or optic nerve penetration.
Sub-Tenon's block
Sub-Tenon's space is anatomically defined as a potential space between the capsule and the sclera. Using a blunt cannula, local anesthesia is injected into this potential space. By diffusion, local anesthesia infiltrates the retrobulbar space, causing akinesia and anesthesia. Although the risk of brain stem anesthesia, globe rupture and intravascular injection remains, it is significantly reduced. More commonly, subconjunctival edema and hemorrhage can occur.
Infraorbital nerve block
The infraorbital nerve, part of the terminating branches of the maxillary branch (V2) of the trigeminal nerve, supplies sensory innervation to the lower eyelid, the side of the nose and the upper lip. Infraorbital blocks are helpful with lower eyelid and midfacial surgery.
Intravenous agents
Intravenous agents are often administered in concert with or just before local anesthesia. These help reduce patient anxiety that may exacerbate pain and discomfort. The goals of conscious sedation include protecting airway reflexes and hemodynamic stability, while alleviating patient's anxiety and discomfort. No single ideal agent exists for conscious sedation, and frequently combination regimens are preferred. Benzodiazepines, opioids and propofol are the most common intravenous medications for eyelid and periocular surgery. Barbiturates and ketamine are sometimes utilized but may be less desirable due to central nervous system side effects.
Benzodiazepines
Benzodiazepines bind to inhibitory GABA receptors and promote GABA binding. Such binding increases the frequency of the receptor-linked chloride channel, resulting in an inhibition of neuronal firing. Benzodiazepines are classified based on their duration of action. Midazolam, lorazepam and diazepam are short, intermediate and long acting, respectively. They all have hypnotic, sedative, anxiolytic and amnesic effects. Sedation has slower onset and is longer lasting for lorazepam because of its longer half-life. Intravenous midazolam has quick onset and offset, making it a suitable choice for conscious sedation. Results are a mild decrease in blood pressure and mild to significant respiratory depression. Hypotension can be exacerbated when used with opioids due to a synergistic effect. Potentially unfavorable side effects including postoperative amnesia, respiratory depression and prolonged sedation can be reversed with flumazenil, a benzodiazepine antagonist.
Barbiturates
Like benzodiazepines, barbiturates are anxiolytic and hypnotic drugs that act on GABAA receptors of the central nervous system. They prolong the duration of ligand-gated chloride channel opening. Methohexital and thiopental share similar pharmacokinetic
and pharmacodynamic properties with the exception of elimination half-lives. Methohexital has an elimination half-life of 4 hours, in comparison to 12 hours for thiopental. Side effects include dose-dependent cardiovascular and respiratory depression. In
addition, thiopental causes more excitatory symptoms such as coughing and tremors compared with methohexital, which should be taken into consideration to avoid needle stick injury to the patient or surgeon.
Ketamine
Ketamine is an NMDA receptor antagonist that produces an analgesic and sedative effect. In contrast to other sedatives discussed, ketamine produces dissociative anesthesia, characterized by a cataleptic state. It has minimal effect on cardiovascular and
respiratory function. Undesirable side effects include psychological disturbance upon emergence; patients often experience vivid dreams and illusions. In regards to ophthalmic surgery, ketamine may be contraindicated in patients with an open eye injury or other ophthalmologic disorder because it can increase IOP.
Propofol
Propofol is a nonbarbiturate intravenous anesthetic. Although its mechanism of action is incompletely understood, it is believed to potentiate GABAA receptors and inhibit NMDA-glutamate excitatory receptors. Continuous IV infusion of propofol allows for quick onset of sedation that is rapidly terminated when infusion is stopped. Unlike other anesthetics, propofol has antiemetic properties, and thus patients are less prone to nausea and vomiting during the postoperative period. Side effects of propofol include respiratory depression, hypotension or dystonia. Alone or with concomitant benzodiazepines, propofol may exacerbate sneezing during periocular injections. Commonly, it can cause pain on injection, which can be reduced by pre-administering intravenous lidocaine.
Opioid
Opioids are natural alkaloids derived from the opium poppy or synthetic variations thereof. They act on mu, kappa and delta receptors located in the central nervous system and other tissues to provide analgesia. Common opioids used in oculofacial surgery are fentanyl, alfentanil and remifentanil. These medications provide analgesia only, with no sedative or amnestic properties. Alfentanil is a shorter-acting agent. Remifentanil is extremely short acting, with a half-life of approximately 7 minutes, which allows for rapid emergence from anesthesia without significant respiratory depression. Side effects include respiratory depression, nausea and vomiting.
Combination regimens and other considerations
Benzodiazepines, opioids and propofol, when taken alone, in the various tandem combinations or all three together, are generally preferred in non-general anesthesia oculofacial surgery. Barbiturates and ketamine may be less frequently utilized due to central nervous system side effects.
Some agents may be more highly associated with abrupt movement. Needle and local agents into periorbital soft tissues, orbit or eyelids may activate the afferent arm of sternutatory (sneeze) reflex. Propofol hypnosis may suppress sneeze inhibitory neurons. Consequently, sneezing or a head thrust upon injection can be dangerous with a needle near vital structures. Midazolam with propofol may further increase the risk of sneezing. The concomitant use of an opioid with propofol, with or without midazolam, may suppress the sneeze reflex.
The authors recommend the administration of an opioid minutes before propofol sedation and periocular injection to eliminate the sneeze reflex. Forestalling this abrupt head movement may minimize the risk for needle damage to surrounding structures. Conclusion
Proper local anesthesia, with or without intravenous sedation, helps achieve a safe and comfortable oculofacial surgical experience. An understanding of anesthetic and sedative pharmacology combined with proper technique is important in eyelid and periocular surgery.
References:
- Barash PG. Clinical Anesthesia. 6th ed. Philadelphia: Wolters Kluwer/Lippincott Williams & Wilkins; 2009.
- Friedman NJ, Kaiser PK Kaiser, Trattler WB. Review of Ophthalmology. Philadelphia: Elsevier Saunders; 2005.
- Katzung BG. Basic & Clinical Pharmacology. New York: Lange Medical Books/McGraw Hill; 2009.
- Miller RD. Miller's Anesthesia. 7th ed. Philadelphia: Churchill Livingstone/Elsevier; 2010.
- Rewari V, Madan R, Kaul HL, Kumar L. Remifentanil and propofol sedation for retrobulbar nerve block. Anaesth Intensive Care. 2002;30(4):433-437.
- Riordan-Eva P, Whitcher J, Vaughan D, Asbury T. Vaughan & Asbury's General Ophthalmology. New York: Lange Medical Books/McGraw-Hill Medical Pub Division; 2008.
- Tao J, Nunery W, Kresovsky S, Lister L, Mote T. Efficacy of fentanyl or alfentanil in suppressing reflex sneezing after propofol sedation and periocular injection. Ophthal Plast Reconstr Surg. 2008;24(6):465-467.
- Yee JB, Burns TA, Mann JM, Crandall AS. Propofol and alfentanil for sedation during placement of retrobulbar block for cataract surgery. J Clin Anesth. 1996;8(8):623-626.
- Jeremiah Tao, MD, FACS, can be reached at The Gavin Herbert Eye Institute, University of California, Irvine, 118 Med Surge I, Bldg. 810, Mail Code: 4375, Irvine, CA 92697; 949-824-2020; 949-824-0327; email: j.tao@uci.edu.
- Disclosure: The authors have no relevant financial disclosures.