Anesthesia for Head and Neck Surgery - Anesthesia for Ophthalmic Surgery

Anesthesia for Head and Neck Surgery - Anesthesia for Ophthalmic Surgery is a topic covered in the Clinical Anesthesia Procedures.

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General Considerations

General Considerations

  1. Intraocular pressure (IOP; normal range 10 to 22 mm Hg) is principally determined by (1) aqueous volume (the rate of production of aqueous humor in relation to its rate of drainage) and (2) the blood volume within vessels of the eye. Due to scleral inelasticity, small volume changes result in large changes in IOP.
    1. Factors that may increase IOP include hypertension, hypercarbia, hypoxia, laryngoscopy and endotracheal intubation, venous congestion, vomiting, coughing, straining, bucking, external pressure on the eye, succinylcholine, and ketamine.
    2. Factors that may decrease IOP include hypocarbia, hypothermia, central nervous system depressants, ganglionic blockers, most volatile and intravenous (IV) anesthetics, nondepolarizing muscle relaxants, mannitol, diuretics, acetazolamide, and head elevation.
  2. Glaucoma
    1. Open-angle glaucoma usually arises from chronic obstruction of the aqueous humor drainage and is characterized by a progressive, insidious course that may be painless.
    2. Closed-angle glaucoma results from acute aqueous outflow obstruction due to a narrowing of the anterior chamber. This occurs as a result of pupillary dilation or lens edema and is painful.
  3. Oculocardiac reflex
    1. The oculocardiac reflex (OCR) is mediated by afferent impulses via the ophthalmic branch (CN VI) of the trigeminal nerve to the ciliary ganglion and efferents from the vagus nerve (CN X). Increases in IOP, manipulation of the globe, or traction on the extrinsic eye muscles may result in bradycardia or asystole. Administration of ocular regional anesthesia may also elicit this response. OCR is common in patients undergoing strabismus surgery.
    2. The OCR should be promptly treated by cessation of the stimulus. Atropine (0.01 to 0.02 mg/kg IV) may be administered if bradyarrhythmias persist. The reflex fatigues quickly with repeated stimulation. However, if the reflex persists, infiltration of local anesthetic near the extrinsic eye muscles or placement of a peribulbar or retrobulbar block is effective. Alternatively, atropine prophylaxis can be helpful in preventing the reflex.
  4. Commonly used drugs
    1. Topical. Most ophthalmic medications are highly concentrated solutions that are administered topically and may produce systemic effects.
      1. Mydriatics
        1. Phenylephrine eye drops may cause hypertension and reflex bradycardia, especially when administered as a 10% solution. For this reason, a 2.5% solution is commonly used. It dilates the pupil and constricts periocular blood vessels.
        2. Cyclopentolate, atropine, and scopolamine are anticholinergic agents that can produce central nervous system toxicity (e.g., confusion and seizures), particularly in the elderly and young. Additional effects include flushing, thirst, dry skin, and tachycardia.
        3. Epinephrine 2% topical solution reduces IOP in open-angle glaucoma by decreasing aqueous secretion while improving outflow. Complications can include hypertension, tachycardia, dysrhythmias, and syncope.
      2. Miotics. Cholinergic drugs (e.g., pilocarpine 0.25% to 4% solution) may produce bradycardia, salivation, bronchorrhea, and diaphoresis.
      3. Drugs that decrease IOP
        1. β-Adrenergic antagonists (e.g., timolol or betaxolol) may cause bradycardia, hypotension, congestive heart failure, and bronchospasm.
        2. Anticholinesterases, such as echothiophate, depress plasma cholinesterase activity for 2 to 4 weeks and may prolong recovery from succinylcholine and mivacurium.
        3. Apraclonidine, an α2-adrenergic agonist, is used to reduce IOP by decreasing aqueous production and improving outflow. Systemic side effects may include sedation and drowsiness. Rebound hypertension may result from acute withdrawal after chronic therapy.
    2. Systemic
      1. Acetazolamide, a carbonic anhydrase inhibitor, is administered systemically to control aqueous humor secretion. Chronic use can lead to the development of hyponatremia, hypokalemia, and metabolic acidosis.

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