ANESTHESIA FOR EYE SURGERY

ANESTHESIA FOR EYE SURGERY : 

ANESTHESIA FOR EYE SURGERY ALI SHAHABBASI, MD BOARD CERTIFIED IN ANESTHESIOLOGY, CRITICAL CARE & PAIN MEDICINE

Regional Anesthesia : 

Regional Anesthesia health care costs population continues to age Patients with : chronic spontaneous cough shortness of breath while lying flat parkinsonian head tremor Alzheimer's disease Claustrophobia may be very difficult to manage with regional anesthesia and light sedation

Regional Anesthesia : 

Regional Anesthesia Hearing aids and dentures should be left in place. presence of an interpreter patient's usual medication regimens should not be interrupted proper sedation levels can be achieved by intravenous titration patient should be monitored and provided with supplemental oxygen

Drugs and combinations used for sedation during MAC : 

Drugs and combinations used for sedation during MAC Alfentanil Remifentanil (0.3 to 0.6 µg/kg IV) has a 30- to 60-second onset time and a 5- to 10-minute duration (decrease narcotic doses in the elderly) Midazolam (is synergistic with narcotics and increases the risk of temporary apnea) Propofol in small (20 mg) incremental intravenous doses (achieve amnesia) Infusions of propofol or narcotic are not necessary

Monitoring : 

Monitoring arterial blood pressure electrocardiogram (ECG) pulse oximeter Respiration may be monitored by direct vision and placing a carbon dioxide sampler near the mouth A facemask delivering an air-oxygen mixture at a total flow rate of at least 10 L/min

Regional Eye Blocks : 

Regional Eye Blocks Retrobulbar block Peribulbar block Disadvantages: larger injected volumes (6 to 8 mL) slower onset (5 to 10 minutes) potential for perforation of the globe vertical diplopia Sub-Tenon Block Topical Anesthesia

Complications of Regional Eye Blocks: : 

Complications of Regional Eye Blocks: oculocardiac reflex (OCR) Hemorrhage brainstem anesthesia globe perforation Myotoxicity optic nerve damage anticoagulant therapy allergic responses generally occur within 15 minutes of injection Hypotension, bradycardia, cardiac arrest, diaphoresis, and nausea are usually responses to fear or pain of injection or to manipulation of the eyeball.

OCR : 

OCR a trigeminal-vagal reflex response that is manifested as cardiac arrhythmias and hypotension and may be elicited by pain, pressure, or manipulation of the eyeball afferent pathway: long and short ciliary nerves ciliary ganglion gasserian ganglion along the ophthalmic division of the trigeminal nerve (the fifth cranial nerve)main trigeminal sensory nucleus in the floor of the fourth ventricle. efferent pathway: start in the vagal cardiac depressor nerve  negative inotropic and conduction effects

OCR : 

OCR Occurs: most often during strabismus surgery in children occasionally during retinal surgery at the time of injection for retrobulbar block during nonophthalmic surgery if pressure is placed on the eyeball. The more acute the onset and the stronger and more sustained the traction, the more likely OCR is to occur Hypoventilation and increased arterial carbon dioxide partial pressure significantly increase the incidence of bradycardia during strabismus surgery

OCR : 

OCR To reduce the incidence and severity of OCR: Intramuscular (?) administration of atropine gentle manipulation of the extraocular muscles control of ventilation to maintain normocapnia surgeon and anesthesiologist communication treating OCR: The first step in is to stop stimulation by the surgeon before the arrhythmia progresses to sinus arrest atropine (0.007 mg/kg IV) local injection of lidocaine near the eye muscle ensure that the depth of general anesthesia is adequate, the patient is normocapnic, and surgical manipulation is gentle.

Shivering : 

Shivering occurs in approximately 0.64% of patients, probably because of absorption of local anesthetic along the optic nerve sheath into the CNS brainstem anesthesia clinical picture of brainstem anesthesia can include amaurosis, gaze palsy (ductional defects), dysphagia, cardiac arrest, shivering, apnea, tachycardia, hypertension, loss of consciousness, and dilatation of the contralateral pupil. Full recovery from brainstem anesthesia is the expectation, provided that the condition is detected early and proper treatment is instituted.

brainstem anesthesia : 

brainstem anesthesia The onset of symptoms may be delayed 2 to 40 minutes after injection. If recognized early and treated promptly, patients usually recover within 1 to 3 hours and do well. Brainstem anesthesia has not yet been reported with the peribulbar method of eye anesthesia.

intra-arterial injection of local anesthetic: : 

intra-arterial injection of local anesthetic: retrograde flow through the ophthalmic artery into the cerebral circulation and midbrain area. The onset is usually immediate and may be associated with seizure activity. Treatment includes: oxygen assisted ventilation intravenous fluids pharmacologic circulatory support suppression of convulsions if necessary, intubation and cardiopulmonary resuscitation.

Topical Eye Anesthesia : 

Topical Eye Anesthesia Advantages : no risk of hemorrhage, brainstem anesthesia, optic nerve damage, or perforation of the globe. Limitations : lack of eye akinesis treatment of uncomplicated cataracts only need for cooperative, communicative patients who are not anxious, claustrophobic, or demented Usually, little or no sedation is necessary, If necessary, a small dose of midazolam (0.01 mg/kg IV) is generally sufficient. Oversedation, especially in the elderly, can lead to hypoventilation, hypoxia, and disorientation.

Intraocular Pressure : 

Intraocular Pressure Management of anesthesia for ophthalmic surgery requires control of IOP before, during, and after the procedure. Events such as coughing, straining, the Valsalva maneuver, or vomiting can cause transient, but significant increases in IOP. IOP will also tend to increase in response to respiratory acidosis, hypercapnia and hypoxia. direct relationship exists between central venous pressure and IOP. A slight head-up tilt during intraocular surgery helps counteract the effects of central venous pressure. Injecting a large volume (8 to 10 mL) of fluid into the orbit (e.g., a peribulbar block) may significantly increase IOP. If IOP reaches the level of retina arterial pressure, retinal ischemia can result.

Anesthesia and Intraocular Pressure : 

Anesthesia and Intraocular Pressure In general, narcotics, tranquilizers, and anesthetics reduce IOP. Only succinylcholine and ketamine may increase IOP. IOP will also increase in response to the stimulus of laryngoscopy and endotracheal intubation. anticholinergic drugs applied topically to the eye may cause mydriasis and increase IOP. Several pretreatment regimens have been advocated to control the sympathetic response to tracheal intubation: intravenous administration of lidocaine (1.5 mg/kg), sufentanil(0.05 to 0.15 µg/kg), or remifentanil (0.5 to 1.0 µg/kg) 3 to 5 minutes before induction. Oral administration of the centrally acting antihypertensive drug clonidine (5 µg/kg) 2 hours before induction of anesthesia. Intranasal administration of nitroglycerin or a β-adrenergic receptor blocking drug.

Specific Clinical Situations and Complications : 

Specific Clinical Situations and Complications Intravitreal Injection of Gas (SF6 & C3F8) Nitrous oxide (N2O) is 117 times more diffusible than SF6 and rapidly enters the gas bubble. Washout of N2O from the lung is 90% complete within 10 minutes, so administration of N2O should be discontinued at least 20 minutes before an intravitreal injection of gas. N2O should be avoided in any patient returning for a general anesthetic within 3 to 4 weeks of undergoing intravitreal gas injection. patients with intravitreal gas bubbles may risk ocular damage during air travel.

Penetrating Eye Injuries : 

Penetrating Eye Injuries Management of emergency anesthesia requires balancing the need to prevent aspiration of gastric contents against prevention of sudden significant increases in IOP. early administration of metoclopramide (0.15 mg/kg IV) Intravenous administration of lidocaine (1.5 mg/kg) and remifentanil (0.7 µg/kg) 3 to 5 minutes before induction. A β-adrenergic receptor blocking drug such as labetalol (0.05 to 0.10 mg/kg IV) may also be useful in blocking the cardiovascular response to tracheal intubation, especially in patients with angina or hypertension. A dose of thiopental (6 mg/kg IV) or propofol (3.0 mg/kg IV)

Penetrating Eye Injuries : 

Penetrating Eye Injuries a modified rapid-sequence technique consisting of preoxygenation, thiopental or propofol induction, a large dose of nondepolarizing muscle relaxant, and application of cricoid pressure for 2 minutes has been advocated for open eye surgery. During general anesthesia for open eye surgery, the depth of anesthesia must be sufficient to ensure lack of movement or coughing. Smooth emergence from anesthesia can be aided by administering an antiemetic drug before or during surgery and by giving lidocaine (1.5 mg/kg IV) or remifentanil (0.5 µg/kg IV) approximately 5 minutes before the patient awakens.

Pediatric Eye Injuries : 

Pediatric Eye Injuries may also have cranial injuries If administration of narcotics is necessary to control pain, an antiemetic should also be given. Regional eye anesthesia is not suitable in patients with eye trauma. With the aid of a topical anesthetic cream it is usually possible to gently start an intravenous line OR rapid, gentle induction of anesthesia by mask (with 7% to 8% sevoflurane). administration of metoclopramide and an H2 receptor antagonist as with adults. The stomach should be decompressed during surgery and the patient extubated while awake. To facilitate tolerance of the endotracheal tube and minimize bucking in an awakening patient, a narcotic may be given 10 to 20 minutes before the end of surgery and lidocaine (1.5 mg/kg) administered intravenously 5 minutes before extubation of the trachea.

Retinopathy of Prematurity : 

Retinopathy of Prematurity ROP is an abnormal proliferation of undifferentiated primitive mesenchymal cells in the retina Though usually associated with hyperoxic periods during neonatal care, the cause of ROP is complex and uncertain. arterial oxygen tension maintained at around 70 mm Hg (arterial oxygen saturation at 90% to 95% by finger-pulse oximetry) in premature infants to balance the risk of hypoxic damage with the respiratory problems frequently encountered in these sick, frail preterm infants. immature patients, prolonged exposure to high intraoperative concentrations of oxygen is best avoided during the period of retinal immaturity (i.e., until 8 months of age).

Strabismus : 

Strabismus Three problems associated with strabismus are of particular interest for the anesthetist: the possible increased risk of malignant hyperthermia the high incidence of postoperative nausea and vomiting (PONV) the likelihood of an OCR. The risk of malignant hyperthermia may be lessened by avoiding succinylcholine and halothane. Droperidol (75 µg/kg IV) successfully reduces the incidence of nausea and vomiting Intravenous administration of lidocaine (1.5 mg/kg) before tracheal intubation also reduces the incidence of PONV using a combined low-dose ondansetron (50 µg/kg) and dexamethasone (150 µg/kg) regimen.

to decrease the incidence of nausea and vomiting after strabismus surgery: : 

to decrease the incidence of nausea and vomiting after strabismus surgery: Minimal use of opioids for pain management The use of propofol and a potent volatile anesthetic to maintain general anesthesia Decrease or avoid the use of N2O Administration of a serotonin 5-HT3 antagonist such as ondansetron (0.1 mg/kg IV) during anesthesia Use of dexamethasone (0.15 mg/kg IV) Insertion and removal of an orogastric tube to decompress the stomach after the induction of anesthesia Gentle surgical manipulation of the eye muscles Maintenance of adequate hydration with intravenous crystalloids Placement of lidocaine near the extraocular muscle during surgery to minimize afferent impulses and postoperative pain on awakening.

Systemic Effects of Eye Medications : 

Systemic Effects of Eye Medications Phenylephrine can cause severe hypertension, arrhythmias, headache, tremulousness, and myocardial ischemia. Epinephrine can cause tachyarrhythmia and premature ventricular beats. Timolol Systemic effects include bradycardia, hypotension, congestive heart failure, and exacerbation of asthma and myasthenia gravis. Echothiophate can reduce plasma cholinesterase activity significantly for 4 to 6 weeks prolonged response to succinylcholine or to mivacurium