anesthesia. Its high lipid content allows for rapid absorption through the corneal epithelium resulting in fast peak onset. However, the duration of anesthesia is limited to just 15–20 min, making it appropriate for examination techniques or short procedures only [3].

Tetracaine hydrochloride 0.5–1% ophthalmic solution or 0.5% ophthalmic ointment has similar onset and duration of action as proparacaine, but confers more corneal epithelial toxicity. Overuse may cause ocular irritation and pain. The duration of effect for proparacaine and tetracaine may be prolonged by repeat instillation [3].

Lidocaine hydrochloride 1–4% solution or 2% gel may also be applied topically to the ocular surface. It has rapid onset like proparacaine and tetracaine, with a significantly longer duration of action. Lidocaine without preservatives is used routinely inside the anterior chamber (intracamerally) of the eye during cataract surgery. In addition, injectable lidocaine can be dropped on the cornea prior to its local injection for blepharoplasty to minimize the sting of prep agents that may contact the eye (Author’s (J.A.W) anecdotal experience).

Table 5.1 reviews and compares these topically applied ophthalmic drops.

5.2.2Topical Skin Creams

Topical skin creams are used for laser skin resurfacing, laser hair removal, superficial skin surgery, placement of intravenous catheters, suture removal, and neurotoxin and fillers injections. They provide a degree of surface anesthesia for these procedures, and when necessary can be augmented with regional sensory nerve blocks or diffuse local infiltration. These preparations have allowed the performance of appropriate procedures in a less invasive manner (no injections) which has led to higher patient acceptance.

The maximum dose for topical lidocaine is 4.5 mg/kg up to 300 mg [4]. There is a case report of a woman who died from administration of anesthetic cream over one third of her body’s surface area for a prolonged period of time [5]. Consequently, many hospitals will not formulate high concentrations of lidocaine creams. They will however allow preformulated preparations such as eutectic mixture of local anesthetics (EMLA™) and LMX™.

EMLA™ consists of lidocaine 2.5% and prilocaine 2.5% in eutectic mixture (5% oil in water). It is applied under an

occlusive dressing for 60 min to achieve maximum effect (onset/duration). It is packaged in 5 and 30 g tubes. It also comes in a patch form. LMX™ is a lidocaine cream available in both 4 and 5% that is also applied for 60 min under occlusive dressing.

A compounding pharmacy can be used to manufacture higher concentration creams of local anesthetics (up to 30% lidocaine). These are not recommended for use on areas greater than 5 cm2, as significant lidocaine toxicity (seizure) can result from larger surface area applications.

5.3Local Injectable Anesthesia

Local injectable anesthetic agents act internally on neuronal axon sodium channels to prevent conduction of nerve impulses. Smaller and nonmyelinated nerve fibers are affected more quickly than larger or myelinated fibers. The effects are reversible as the local anesthetic diffuses away from the site of injection with no permanent effects on nerve function. Lidocaine, bupivacaine, mepivacaine, and prilocaine are the most commonly used medications. Structurally, these are amides, which are metabolized in the liver, and carry only rare risk of allergic reactions. Esters such as tetracaine and cocaine, which require plasma pseudocholinesterase for breakdown, carry a higher risk of allergy and are less commonly used for infiltration. Locally injected anesthetic agents have potential systemic toxicity directly related to the total dose and the site of administration. This usually manifests with central nervous system signs (drowsiness, paresthesias, and seizures) or cardiovascular issues (dysrhythmias and cardiac arrest). These agents have pKa’s of approximately 8, but are prepared as ionized hydrochloride salts in a weak acid solution with a pH of 4.5–6 to increase their shelf life and water solubility. This acidic environment leads to variable degrees of pain with injection. The advantage of using local anesthetics is that they can mitigate the need for intraoperative monitoring, significantly lowering patient costs.

Local anesthetics are administered via local infiltration into subcutaneous tissues and also as nerve blocks. Lidocaine hydrochloride 1–2% solution confers the least pain on injection. The maximum dose is 5 mg/kg, but if combined with epinephrine 1:200,000, the maximum dose raises to 7 mg/kg. It confers a rapid onset of action with an effect lasting up to 1–2 h. Bupivacaine hydrochloride 0.5–0.75% solution has a

slower onset with a longer duration (4–12 h) when compared to lidocaine. Its maximum safe dose is 2.5 mg/kg with epinephrine, and it carries the risk of significant cardiac toxicity with overdose. Mepivacaine 1–3% has a rapid onset of action and intermediate duration of 2–3 h with a maximum safe dose of 7 mg/kg. Lidocaine and bupivacaine are often mixed prior to administration in order to maximize speed of onset and duration of action. In order to decrease the pain on injection, sodium bicarbonate 8.4% (9:1 mixture) is often added. This has the added benefit of deprotonating the local anesthetics, making them able to cross into neurons freely and work more rapidly. Further pain upon injection can be reduced by slow injection and use of small-bore needles.

Table 5.2 reviews and compares the local anesthetics described above.

The addition of epinephrine to these anesthetics decreases the rate of systemic absorption through vasoconstriction, resulting in diminished diffusion of anesthetic away from the injection site. This effect allows greater maximal dosing and potentially extended duration of effect. These anesthetics may be formulated with 1:100,000, 1:200,000, or 1:400,000 epinephrine.

The addition of hyaluronidase (0.5 cc hyaluronidase to 9.5 cc lidocaine) helps improve the spread of the anesthetic and speed of onset. The improved spread allows for fewer needle sticks as gentle massage disperses the solution well. Hyaluronidase acts by depolymerizing hyaluronic acid and facilitating diffusion of local anesthetic agents. However it may reduce duration of anesthesia as the anesthetic diffuses away from the surgical site. Epinephrine should be used with hyaluronidase in the solution mixture to improve its duration. The combination may also help maintain surgical planes [6, 7].

5.4Tumescent Anesthesia

Significant regional anesthesia of skin and subcutaneous tissue can be accomplished with subcutaneous infiltration of large amounts of dilute lidocaine and epinephrine solution (mixed in saline) until the skin feels hardened (tumesced). The technique is typically used for liposuction, but can also be given for rhytidectomy, laser resurfacing, scalp surgery, and other soft tissue procedures. Prior to the development of this technique, the maximum established safe dose of

injectable lidocaine was 5 mg/kg, and 7 mg/kg when mixed with epinephrine. With the tumescent technique, developed by dermatologist Klein [4], the maximum safe dose for lidocaine is 50 mg/kg. This is related to the action of epinephrine and to the mechanical effect of the high volume of dilute solution injected. Both act as a vascular tourniquet preventing spread of lidocaine systemically where it can become toxic. The technique provides excellent hemostasis, pain control, and possibly a decreased rate of infection due to the acidity of the lidocaine [4].

5.5Oral Sedation

Anxiety can play an important role in anesthetic choices and surgical decision-making. Even minor procedures can be extremely stressful for patients, regardless of adequate pain control. Systemic anxiolytics are useful in these situations, particularly when a healthy patient undergoes a simple procedure that does not require systemic monitoring.

Benzodiazepines such as oral diazepam (Valium) and lorazepam (Ativan) are useful adjuncts to help relax patients. Both bind to the GABA receptor, facilitating influx of chloride, producing membrane hyperpolarization, and decreasing neuronal activity. Care should be taken with benzodiazepines and other drugs such as barbiturates, opioids, and antidepressants, as their effects are often synergistic [8].

Zolpidem tartrate (Ambien®) is a short-acting nonbenzodiazepine that potentiates GABA receptors similarly to benzodiazepines. This medication has benefits over benzodiazepines, including a low risk of habit-formation and an improved safety profile in elderly patients [9].

Table 5.3 reviews the properties of the oral sedatives described earlier. For certain painful procedures, these medications can be given with oxycodone/acetaminophen (Percocet 5/325) or meperidine (Demerol) PO prior to the procedure, for combined pain control and sedation.

5.6Monitored Anesthesia Care

Monitored anesthesia (conscious sedation) care (MAC) refers to monitored intravenous sedation and analgesia without endotracheal intubation. It can be administered by the surgeon or anesthesia specialist. Certification is required for

surgeons to administer this form of sedation. Most surgeons prefer a certified registered nurse anesthetist (CRNA) or anesthesiologist to provide IV sedation so that they can concentrate on the procedure itself. This also minimizes the surgeon’s liability. In determining if MAC will suffice or whether deeper sedation with endotracheal intubation is warranted, the surgeon and anesthesia practitioner should work together. This would include a full physical examination and review of the patient’s health condition to assess anesthesia risk.

Benzodiazepines are commonly used in MAC. They produce sedation, retrograde amnesia, anxiolysis, and muscle relaxation. Risks include hypotension and respiratory depression. Use benzodiazepines with caution in patients with liver disease as they can be hepatotoxic. They also increase the seizure threshold for lidocaine allowing for safer injection.

Useful IV benzodiazepines include midazolam, diazepam, and lorazepam. Midazolam is a potent amnestic and has short redistribution and elimination half-lives, making it useful during injection of local anesthetics. It has all, but replaced diazepam and lorazepam for outpatient procedures. Diazepam is longer acting but often causes irritation at the injection site and localized thrombophlebitis. Lorazepam is potent but has a delayed onset which makes it less useful in ambulatory surgical cases. Overdose or toxicity from benzodiazepines can be reversed with flumazenil, a benzodiazepine antagonist, which reversibly competes with benzodiazepines at GABA receptor binding sites.

Opioids are useful IV anesthetic agent utilized to provide analgesia. Unfortunately, they carry a long list of side effects including drowsiness, respiratory depression, pruritis, miosis, bradycardia, nausea, and vomiting. Fentanyl (Sublimaze®) is commonly used for the initial phase of sedation to facilitate a short period of deep anesthesia. Morphine or other long-acting opioids can be utilized when postoperative pain is expected. Overdose (sedation and respiratory depression) from opioid use can be reversed with Naloxone (Narcan®), a competitive antagonist which reversibly binds to opioid receptors. It should however be used judiciously since it effectively unmasks the pain for which the opioids were initially administered. Acute pain can significantly increase patient’s stress which can result in poor outcome (hypertension, tachycardia, etc.), particularly if they have comorbid cardiovascular disease. To help combat nausea and vomiting associated with opioids, antiemetics such as decadron or ondansetron (Zofran®) can be administered intraor postoperatively [8, 10].

Propofol (Diprivan®) is a widely used short-acting sedative-hypnotic useful for induction of anesthesia. It has all but replaced barbiturate use in the surgical arena. It is formulated in a 1% egg lecithin and soy lipid emulsion and has rapid onset and recovery. It is not an analgesic and often causes a burning pain upon injection, so it is often preceded by or mixed with IV lidocaine. Opioids such as fentanyl are often administered immediately prior to propofol as well. Propofol is generally well tolerated by healthy patients, but carries side effects including hypotension from vasodilation, or cardiac depression and transient apnea [8].

Dexmedetomidine hydrochloride (Precedex®) is a relatively new centrally acting alpha-2 agonist that controls stress, anxiety, and pain while keeping patients cooperative. It is also desirable because it is not a respiratory or cardiac depressant. This drug has had increasing popularity in recent years [11].

5.7General Anesthesia

General anesthesia aims to induce reversible amnesia, analgesia, loss of responsiveness, and muscle relaxation. These attributes may be achieved through a careful balance of the above-described anesthetic agents. To be sure, trained anesthetists should be consulted to administer and to manage general anesthesia. These professionals are responsible for patient preoperative evaluations, intraoperative anesthetic management, and postoperative anesthetic recovery. General anesthesia can be useful in a variety of situations. Medically frail, severely anxious, disinhibited, developmentally delayed, and infants or children should be considered for this type of anesthesia. Procedural constraints are also important to consider, as prolonged surgeries or those with the potential for significant blood loss may warrant general anesthesia for strict control of fluids and patient comfort.

Preoperatively, systemic conditions must be evaluated. A history of cardiovascular disease, including myocardial infarction, angina, valvular disorders, and hypertension increases the risk of intraor postoperative myocardial ischemia. Respiratory disorders such as chronic obstructive pulmonary disease and obstructive sleep apnea are associated with chronic hypoxemia, which could influence anesthetic decision-making. Undertreated asthma can be particularly problematic perioperatively as well. Both cardiovascular and pulmonary disease can present practical problems preand

postoperatively, as these patients often have difficulty lying flat for surgery and may require supplemental oxygen.

Finally, some agents administered in general anesthesia have particular ophthalmic or systemic side effects that need to be kept in mind. The potent inhaled anesthetics and propofol lower intraocular pressure, while ketamine increases it. Isoflurane and the modern, less soluble agents – sevoflurane and desflurane are the potent inhaled anesthetics utilized in the United States today. They are rapidly exhaled, allowing tight titration of wake-up timing. Nitrous oxide, a nonpotent inhaled anesthetic, is a useful adjunct to the other agents for lowering overall anesthetic concentration demands. It has low blood solubility and is as rapidly exhaled as desflurane [8].

5.8Issues for Consideration

Anesthesia medications are associated with side effects from minor to life-threatening. Allergic (type 1 hypersensitivity) reactions require previous sensitization to a drug and may range from minor (pruritis, urticaria, and angioedema) at the injection site to severe anaphylaxis (wheezing, hypotension, and cardiovascular collapse). Anaphylactoid reactions are toxic nonimmune mediated reactions to a medication. Treatment for minor reactions includes immediate discontinuation of suspected triggering medications and the prompt administration of antihistamines such as diphenhydramine and glucocorticoids such as dexamethasone. Severe anaphylaxis requires prompt administration of epinephrine and generous IV fluids.

Malignant hyperthermia (MH) is a rare, life-threatening reaction seen only in genetically susceptible patients who have been exposed to either potent inhaled anesthetics or succinylcholine. MH is a medial emergency. Early signs are tachycardia, clenching of jaw muscles, and systemic muscular rigidity. Increased metabolic demand by the musculature causes acidosis, hyperthermia, and free release of myoglobin into the bloodstream. Initial treatments include discontinuation of all volatile anesthetics, conversion to an IV anesthetic, administration of 100% oxygen, and active cooling. It is important to treat any electrolyte imbalances, particularly hyperkalemia, and maintain urine output. Intravenous dantrolene, a muscle relaxant, should be given immediately to depress skeletal muscle excitation. Mortality from episodes of MH has decreased from 90% to less than 10% since the introduction of dantrolene [3, 8].

5.9Postoperative Care

Anesthesia and pain management does not end with the surgical procedure. Patient perception of pain during and after a procedure varies widely. A basic postoperative

method of attaining patient comfort is the use of ice packs for reduction of pain and swelling. Also, keeping the patient’s head elevated helps to avoid dependent edema around the face.

Postoperative pain control can be initiated at the conclusion of the case. Local anesthetic injection of long-act- ing amides, such as bupivacaine, can diminish postoperative pain and is a useful tool to decrease the need for narcotics. Intravenously or intramuscularly administered narcotics, such as fentanyl, morphine, and hydromorphone also bridge patients through the immediate postoperative period. Oral narcotic agents including codeine with or without acetaminophen, oxycodone with or without acetylsalicylic acid, or acetaminophen may provide longerduration effects, and are excellent agents for responsible outpatient controlled analgesia. Notably, these agents may be associated with frustrating or dangerous side effects, including habit-formation, nausea and vomiting, respiratory depression, and/or orthostatic hypotension. Finally, nonsteroidal anti-inflammatory (NSAID) agents, such as ibuprofen, naproxen, and ketorolac (Toradol®), which inhibit prostaglandin synthesis, are generally well-tolerated and may be useful to avoid narcotic side effects. If all else fails, pain consultation should be considered for refractory patients.

5.10Regional Nerve Blocks

Regional nerve blocks in the periorbital region are a very useful adjunct to surgery and can be divided into motor or sensory type. The term regional refers to the area supplied by the nerve. A motor block causes akinesia, while a sensory block leads to loss of sensation.

The motor nerve of the face is the facial nerve (seventh cranial nerve). It exits the facial skeleton at the stylomastoid foramen. Its main trunk separates into five component branches within the parotid gland: temporal (frontal), zygomatic, buccal, mandibular, and cervical. The temporal, zygomatic, and buccal branches travel superomedially to innervate the frontalis, orbicularis oculi, corregator supraciliaris, and procerus muscles [11]. The temporal branch innervates the brow and upper lids. The zygomatic and buccal branches contribute to the movement of the lower lids (Fig. 5.1). There are significant anastomoses between these branches [12].

In ophthalmology, regional motor blocks are used to prevent forceful eyelid closure during intraocular surgery [13]. On occasion, these blocks may be useful during eyelid surgery. An example would be an awake patient who is squeezing the lids making surgery more difficult and less precise. This can be encountered with canthal suspension. In this setting, lid squeezing can significantly reduce the surgical field