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Both the anesthesiologist and the ophthalmologist must be aware that eyedrops are readily absorbed through hyperemic incised conjunctivae. Though small in volume, these drops contain highly concentrated medication that can produce systemic results. Infants and elderly patients are most susceptible. The systemic effects can be minimized by using lower concentrations, limiting instillation to only 1 or 2 drops, and promptly occluding the nasolacrimal duct at the time of instillation. [2] [92]
Eye medications that cause systemic effects include phenylephrine, epinephrine, timolol, echothiophate iodide, acetylcholine, cyclopentolate, scopolamine, atropine, and cocaine (also see Chapter 14 and Chapter 16 ).
Phenylephrine eyedrops can cause severe hypertension, arrhythmias, headache, tremulousness, and myocardial ischemia. Because a single drop of 10% phenylephrine ophthalmologic solution contains 4 mg of phenylephrine, 2.5% solutions are recommended.
Topical ocular epinephrine (a 2% solution contains 0.8 mg per drop) can cause tachyarrhythmia and premature ventricular beats.
Timolol is a β-adrenergic receptor blocking drug administered as eyedrops to treat glaucoma. Systemic effects include bradycardia, hypotension, congestive heart failure, and exacerbation of asthma and myasthenia gravis.
Echothiophate iodide eyedrops can reduce plasma cholinesterase activity significantly. Four to 6 weeks is required for activity to recover after cessation of the drops. Patients treated with these eyedrops may have a prolonged response to succinylcholine or to mivacurium
Acetylcholine may be used to produce miosis after cataract surgery. Systemic effects include bradycardia, hypotension, bronchospasm, and increased bronchial secretions and salivation. These undesirable effects may be prevented by the intravenous administration of atropine.
Cyclopentolate eyedrops are used in a 2% concentration to dilate the pupils. CNS toxicity resulting in effects such as disorientation, dysarthria, and seizures has been reported. Less concentrated (0.5%) solutions are recommended for pediatric use.
Scopolamine eyedrops can cause disorientation and hallucinations in elderly and very young patients.
Cocaine blocks reuptake of norepinephrine at the nerve terminal and usually produces sympathomimetic effects. However, after ocular instillation, very low plasma levels of cocaine can produce severe bradycardia. Topical application of cocaine is no longer recommended for ophthalmic surgery. However, during dacryocystorhinostomy, cocaine may be used topically for vasoconstriction and topical anesthesia.
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