Summary
Normal intraocular pressure (IOP) ranges between 10 and 22 mmHg. This pressure represents a balance between aqueous humor production and drainage [1]. An increase in IOP is harmful because it can decrease blood supply to the optic nerve [2]. Special care must be taken if the globe is open during surgery, as increased IOP in a patient with an open globe can lead to expulsion of ocular contents and permanent damage or blindness [2]. Surgeries in which there is an open globe include cataract extraction, corneal laceration repair, corneal transplant, trabeculectomy, vitrectomy, and ruptured globe repair. Other complications of increased IOP include acute glaucoma and retinal hemorrhage [1].
Ocular
Factors that Influence Intraocular Pressure
Normal intraocular pressure (IOP) ranges between 10 and 22 mmHg. This pressure represents a balance between aqueous humor production and drainage [Reference Pardo and Miller1]. An increase in IOP is harmful because it can decrease blood supply to the optic nerve [Reference Miller2]. Special care must be taken if the globe is open during surgery, as increased IOP in a patient with an open globe can lead to expulsion of ocular contents and permanent damage or blindness [Reference Miller2]. Surgeries in which there is an open globe include cataract extraction, corneal laceration repair, corneal transplant, trabeculectomy, vitrectomy, and ruptured globe repair. Other complications of increased IOP include acute glaucoma and retinal hemorrhage [Reference Pardo and Miller1].
Most anesthetic drugs, including nondepolarizing neuromuscular blocking drugs (NMBDs), lead to decreased IOP. Exceptions include succinylcholine and ketamine [Reference Pardo and Miller1].
During induction, increased IOP can be caused by straining, coughing, mask ventilation, laryngoscopy, and intubation, whereas it is less likely with laryngeal mask airway (LMA) placement. This response can be attenuated by administering lidocaine (1.5 mg kg−1), a beta-blocker, or an opioid prior to laryngoscopy. Intubation should not occur under light anesthesia or inadequate muscle relaxation. The Trendelenburg position can increase IOP by preventing drainage of aqueous humor. Hypoxemia, hypercarbia/hypoventilation, and systemic hypertension can also increase IOP [Reference Pardo and Miller1].
Choosing Pharmacologic Agents
Succinylcholine transiently increases IOP by 5–10 mmHg for <10 minutes, due to prolonged contracture of the extraocular muscles (EOMs) [Reference Pardo and Miller2]. While this effect is transient, care must be taken in patients with pathology leading to an elevated preinduction IOP.
The effect of ketamine on IOP is controversial. While the classic teaching is that ketamine should be avoided in ocular cases due to a theoretical increase in IOP, studies have shown that this effect is not clinically significant unless doses of >4 mg kg−1 are used [Reference Drayna, Estrada and Wang3].
The ophthalmologist may inject a gas bubble, such as sulfur hexafluoride (SF6) or perfluoropropane (C3F8), into the posterior chamber during vitreoretinal surgery. Nitrous oxide (N2O) is 35 times more soluble in blood than in nitrogen. Thus, it can expand this bubble, leading to increased IOP. If used during vitreoretinal surgery, it should be turned off 15 minutes before injection of the gas bubble, and should not be used for at least 7–10 days after SF6 or 1 month after C3F8 injection [Reference Jaffe4]. The safest practice is to provide patients with a wristband stating this restriction.
Ophthalmologic Drugs
Topical eye drops have some degree of systemic absorption. Epinephrine eye drops can cause hypertension, tachycardia, and arrhythmias, whereas timolol eye drops can cause bradycardia. Atropine eye drops may cause central anticholinergic syndrome, especially in the elderly.
Topical echothiophate, which is used for glaucoma, is an irreversible acetylcholinesterase inhibitor. Systemic absorption reduces plasma cholinesterase activity, leading to prolonged duration of action of succinylcholine. This effect can last up to 3–7 weeks [Reference Pardo and Miller1].
Regional Anesthesia
Benefits/Drawbacks
Benefits of regional anesthesia include akinesia (immobility) and analgesia of the eye, suppression of the oculocardiac reflex, lower incidence of postoperative nausea and vomiting (PONV), significant postoperative analgesia, and faster recovery leading to shorter stay in the postoperative care unit (PACU). Regional anesthesia may not be a good choice for patients who are very anxious and unable to lie still for the nerve block and/or surgery. Additionally, the oculocardiac reflex can be elicited during placement of regional nerve blocks [Reference Miller2].
Types of Blocks
Retrobulbar and peribulbar blocks (see Table 22.1) are the most common regional blocks used for eye surgery. In a retrobulbar block, local anesthetic is injected into the orbital cone formed by the EOMs, whereas in a peribulbar block, it is injected outside the muscle cone. Since retrobulbar blocks involve direct injection into the muscle cone, they are associated with a more rapid onset and more complete akinesia and anesthesia, requiring a smaller volume of local anesthetic, but are also associated with a higher risk of complications [Reference Pardo and Miller1].
Table 22.1 Bulbar anesthesia
| Retrobulbar block | Peribulbar block | |
|---|---|---|
| Location of injection |
|
|
| Onset and density | Faster onset and denser block | Slower onset and less dense block |
| Local anesthetic volume | Small volume | Large volume |
| Advantages | Faster onset and denser block |
|
| Complications |
|
|
| Contraindications |
| |
| Contraindications to EITHER |
|
See reference [Reference Pardo and Miller1].
Oculocardiac Reflex
The oculocardiac reflex manifests as sudden bradycardia, in response to traction on the EOMs or pressure on the globe. The afferent limb is the ophthalmic division (V1) of the trigeminal nerve (CN5). The efferent limb is the vagus nerve (CN10). Eliciting the oculocardiac reflex can lead to bradycardia, atrioventricular (AV) block, ventricular ectopy, ventricular fibrillation, and asystole. It is more likely to occur in children, particularly during strabismus surgery.
If this reflex occurs, the first step in management is to alert the surgeon, so that they can temporarily stop causing traction on the eye muscles or pressure on the eye. Typically, this will resolve the bradycardia. If bradycardia persists, then after assessing for other causes of bradycardia, including inadequate ventilation and oxygenation, intravenous (IV) atropine (10 μg kg−1) can be given. Local anesthetic infiltration of the EOMs, via a retrobulbar block, also prevents this reflex. However, the reflex can also be elicited during placement of a retrobulbar block [Reference Butterworth IV, Mackey and Wasnick.5].
Postoperative Eye Injuries
Painful
Corneal abrasion is the most common cause of postoperative eye pain. Other symptoms include foreign body sensation and tearing. It is caused by direct trauma from objects touching the cornea, such as surgical drapes or the anesthetic mask. It can be prevented by taping the eyelids carefully, using an ocular lubricant, and preventing patients from rubbing their eyes as they emerge from anesthesia. Although bothersome, corneal abrasions usually heal spontaneously within 24–72 hours. Antibiotic ointment may be given to prevent infection [Reference Pardo and Miller1].
Acute glaucoma presents with painful vision loss, which may be associated with the appearance of halos around lights, headache, nausea, and vomiting. This is an ophthalmic emergency, requiring time-sensitive evaluation by an ophthalmologist to prevent blindness [Reference Pardo and Miller1].
Painless
Postoperative vision loss (POVL) is usually painless. It is predominantly caused by ischemic optic neuropathy (ION), but can be caused also by central retinal artery occlusion (CRAO) [Reference Miller2]. It is more likely to occur during spine surgery in the prone position, as well as in cardiac surgery. Risk factors include hypotension, significant blood loss, administration of large volumes of crystalloid, and anemia. Patient risk factors include smoking, diabetes, and obesity [Reference Jaffe4].
Ophthalmology consultation should be obtained as soon as possible [Reference Pardo and Miller1].
Surgeries
Strabismus Surgery
Strabismus surgery is the most common eye procedure in children. Strabismus is a condition in which there is eye misalignment. It often occurs in healthy children, but there is a higher incidence in Down syndrome and cerebral palsy. It can also be associated with other myopathies, which increases the risk of malignant hyperthermia. Strabismus surgery is associated with severe PONV and frequent triggering of the oculocardiac reflex [Reference Miller2].
Cataract Extraction
Cataract surgery is one of the most common surgical procedures. Cataracts are lens opacifications, which may cause blurred vision or even blindness. Surgery involves removal of the patient’s lens, with subsequent insertion of an intraocular lens (IOL) implant. Removal of the lens may include phacoemulsification, in which ultrasound energy is used to break the lens into fragments to allow easier removal. This procedure is most commonly performed using only topical local anesthetics, without sedation [Reference Jaffe4].
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