Propofol can be given as a constant rate infusion or intermittently as needed. Injectable agents may also be used for certain procedures. Nitrous oxide can also be used but is not recommended for intraocular procedures as nitrous oxide diffuses into closed, air-filled spaces and can increase IOP if air bubbles are present.
Maintenance of anesthesia is usually with volatile inhalant anesthetics such as isoflurane or sevoflurane. A patient undergoing extraocular surgery where IOP is of less concern may receive any standard induction drug or drug combo and ketamine may actually be helpful as it provides additional analgesia for painful surgeries.
Mask and box inductions should also be avoided since excess struggling often occurs. Ketamine and ketamine combinations should be avoided since this drug increases IOP. Induction of patients with intraocular disease or those that are undergoing intraocular surgery can be achieved with thiopental, propofol or etomidate depending on the needs of the individual. An anticholinergic drug should always at least be available and can be given as needed. The pre-emptive administration an anti-cholinergic drug should be considered based on the patient and the preferences of the clinician and/or anesthetist.
ANESTHESIA FOR RETINA DETACHMENT SURGERY ELDERLY FULL
One drawback to opioid use is that full agonist opioid drugs (morphine, hydromorphone) can cause vomiting after administration and thus can increase IOP. Analgesia is often provided by the use of opioid drugs as they provide excellent pain control as well as sedation. Sedation is generally adequate in patients that are debilitated in some way. In some patients a benzodiazepine tranquilizer, such as midazolam or diazepam, is preferable. This drug should be used with care in pediatric or geriatric patients and avoided in patients with hepatic disease. This drug provides excellent anxiolysis and can lower blood pressure. Sedation can be provided by a tranquilizer such as acepromazine in many patients. The goals of premedication in the ophthalmic patient are to minimize stress, to decrease or maintain IOP and to prevent stimulation of the OCR. Anti-cholinergic drugs, such as glycopyrrolate, can be administered as needed or as part of the premedication to prevent or treat this physiologic response. Pediatric/neonatal patients and brachycephalic patients tend to have high vagal tone and are pre-disposed to activation of the OCR. Certain patients are more likely to have this drop in heart rate than others. Traction on the eye puts pressure on the trigeminal / vagus nerves of the parasympathetic nervous system leading to bradycardia and brady-arrhythmias such as atrioventicular block or sinus arrest. The oculo-cardiac reflex or OCR refers to a sudden drop in heart rate associated with traction on the eye and/or surrounding structures. Even physiologic factors such as sudden increases in blood pressure and hypercapnia from hypoventilation can increase IOP and potentially lead to damage or blindness. Endotracheal intubation, as well as many anesthetic drugs can also cause increased pressure. Restraint, neck leads, jugular compression for blood draws, coughing, gagging or vomiting can result in increased IOP. There are many factors that can affect IOP in the peri-anesthetic period. Significant increases in intraocular pressure can lead to globe prolapse or rupture, damage to the optic nerve, or retinal detachment. Normal IOP in the dog ranges from 10-26 mmHg. The goals for anesthesia in the ophthalmic patient include providing appropriate analgesia for the particular procedure or condition, maintaining or lowering intraocular pressure (IOP), preventing activation of the oculo-cardiac reflex (OCR), and providing a level of anesthesia that will allow surgical manipulation of eye and surrounding structures while maintaining normal cardiovascular function
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