Overview of Anesthesia for Eye Surgery
The most common eye-related surgeries today involve treating cataracts, glaucoma, and issues with the retina (the back part of the eye). About 26 million people in the United States have symptomatic cataracts, meaning they experience vision problems due to this condition. Cataract surgery, where the cloudy lens causing the cataract is removed, is the most frequently performed surgical procedure in the county. Each year, nearly 3.6 million cataract extractions are performed.
Furthermore, glaucoma, another common eye condition, affects around 67 million people in the United States. All these eye surgeries need some form of anesthesia, which is tailored based on the specific procedure.
According to the Anesthesia Closed Claims Program, which studies claims related to anesthesia, eye injury accounted for 3% of all claims. This highlights the importance of taking extra care of the eyes during anesthesia and minimizing the risks that come with regional anesthetic techniques. Regional anesthesia is a method where only a specific area of the body is numbed for surgery.
So this document reviews the anesthetic considerations and implications for eye surgeries, covering general, regional, and topical anesthetic techniques. General anesthesia makes you completely unconscious, regional anesthesia numbs a select area, and topical anesthesia, usually in the form of eye drops, numbs the surface of the eye. The document also discusses the indications (when to use), contraindications (when not to use), complications, and clinical significance of these anesthetic techniques, and the role of the healthcare team in caring for patients undergoing eye surgeries that require an anesthetic approach.
Anatomy and Physiology of Anesthesia for Eye Surgery
The orbit, or eye socket, is a crucial part of our anatomy if we are to understand regional anesthesia and how to make the eye immobile, or “akinesis of the globe”. Imagine the orbit as a deep pocket of bone that’s mostly filled with fat and houses our eyeball, which stays at the frontmost part of it. This bony socket is home to many important structures, such as the optic nerve, which enables us to see, and various blood vessels.
Feeling in the eye is provided by the ophthalmic branch of the trigeminal nerve while three other nerves (oculomotor, trochlear, and abducens) help control the movements of the muscles around our eyes. All these nerves, except for the trochlear nerve, pass through something called the muscular cone of the orbit.
When anesthetic is injected into this area, it can effectively block motor and sensory function, resulting in a numb and immobile eye, paralysis of the muscles around the eye, and freedom from pain. It’s important to inject the local anesthetic carefully to avoid hitting important structures and causing potential vision loss, nerve damage, or bleeding.
Pressure within the eye, known as intraocular pressure, may rise substantially during eye procedures. Normal intraocular pressure usually falls within 10 to 20 mm Hg. An increase in pressure can cause damage to different parts of the eye, including the retina and optic nerve. Even a small amount of pressure increase – say, from injecting 0.5 mL of any substance into the intravitreal space (inside part of the eye) – could raise the intraocular pressure by more than 150% compared to normal levels. Such spikes in pressure can risk damaging the retina and optic nerve, possibly leading to problems with vision after the procedure.
Why do People Need Anesthesia for Eye Surgery
There are different methods for giving anesthesia to patients who are having eye surgeries. The plan for anesthesia should be personalized for each patient and the specific surgery to maximize their comfort, safety and cooperation, and to take into account their overall health. Anesthesia methods can include moderate sedation, close anesthesia observation, or full general anesthesia. Adding local and area-specific anesthesia to the plan has improved patient care and result after surgery.
If using local or area-specific anesthesia as part of monitored anesthesia care, the patient must be able to follow instructions, respond properly, and be comfortable with the surgery and body position. Most eye surgeries are done with the patient laying flat on their back. However, certain health conditions, such as heart failure, chronic obstructive pulmonary disease (a long-term lung disease), or obstructive sleep apnea, could prevent a person from being able to be in this position. The use of sterile covers for eye surgeries also limits doctors’ access to the patient’s airway, which is important if the patient has trouble breathing during surgery. People with cognitive disorders may have difficulty interacting and cooperating. Young patients may have trouble staying still and could benefit from being completely asleep from general anesthesia.
The anesthesia plan also depends on the specific surgery. Most cataract or glaucoma surgeries are often done under moderate sedation along with local and area-specific anesthesia. Here in the United States, for the removal of cataracts, peribulbar and topical anesthesia techniques are most commonly used. The peribulbar anesthesia involves numbing the area around the eye, while topical anesthesia involves applying medication directly to the surface of the eye. However, when patients have vitreoretinal surgeries, they generally receive both a regional anesthesia and general anesthesia in the United States. Vitreoretinal surgery involves procedures to treat eye problems involving the retina, macula, and vitreous fluid. We don’t use topical anesthesia for these surgeries because they usually take a long time. In contrast, these vitreoretinal surgeries are usually performed with peribulbar anesthesia in India and other countries.
When a Person Should Avoid Anesthesia for Eye Surgery
There are certain reasons why a person might avoid using anesthesia during eye procedures. The most definitive reason is if the patient chooses not to have it.
Having a history of severe allergic reactions (anaphylaxis) to local anesthetics could potentially make it unsafe to have a regional block, which is a type of anesthesia injected around nerves in a specific part of the body. In eye procedures, local anesthetics used are either aminoesters or aminoamides. Lidocaine, an aminoamide, is commonly used in local and regional anesthesia techniques. However, true severe allergic reactions to lidocaine are extremely uncommon. Most of these severe allergies are actually due to an ingredient used to preserve the drug, called methylparaben. An alternative version of lidocaine that doesn’t contain this preservative is also available.
A condition called malignant hyperthermia where the body’s temperature rises quickly and dangerously, can make general anesthesia (which makes you sleep during surgery) risky. However, careful preparation, which includes picking the right kind of anesthesia and being ready for potential complications, can allow patients with malignant hyperthermia to go under general or local anesthesia safely.
Nitrous oxide, a type of gas commonly used in general anesthesia, is not recommended for use in certain types of eye surgeries. During an operation to fix a detached retina (the light-sensitive layer of tissue at the back of the eye), the surgeon might put a gas bubble, made of either sulfur hexafluoride or perfluoropropane, into the eye to help aid in the repair. If the patient can’t naturally eliminate this gas bubble from their eye before receiving nitrous oxide, it can enlarge the bubble, which increases pressure inside the eye. This pressure increase might lead to blindness.
Having an eye infection or an increased size of the eye globe (the round part of the eye) could make it not advisable to use certain anesthesia plans.
Equipment used for Anesthesia for Eye Surgery
Eye surgery anesthesia uses common anesthesia tools including equipment that monitors the levels of oxygen in your body, how well you’re breathing, your heart rate and temperature. Your oxygen level can be checked with a method called pulse oximetry, your breathing with a method called capnography, and your heart rate and blood pressure can also be continuously monitored.
An anesthesia machine, which usually includes a device to analyze gases, may be necessary for delivering mixed air and oxygen under pressure and for providing the anesthesia gases that make you sleep during the procedure.
Quick access is needed to emergency drugs like epinephrine and atropine, muscle relaxing drugs, and airway devices. A special solution called lipid emulsion should also be available to quickly treat any potential side effects from accidental injection of the local anesthesia into the bloodstream. Local and regional anesthetics – these are drugs used to numb specific areas – are needed depending on the anesthesia plan.
A drug called hyaluronidase can help spread the local anesthetic in your eye to make it remain still during surgery while reducing the volume of anesthetic needed.
Depending on the method used, local and regional anesthesia applications require needles that are 25- to 27-gauge, which refers to the diameter or size of the needle.
Who is needed to perform Anesthesia for Eye Surgery?
Eye-related surgical procedures involve a medical team that gives you anesthesia, which is medication to help you not feel any pain during the operation. This team includes special assistants and nurse anesthesiologists, who are specially trained nurses that manage anesthesia. They all work under the guidance of an anesthesiologist, a doctor who specializes in providing and managing anesthesia. The anesthesiologist leads the team to ensure that the anesthesia is administered correctly and safely.
Preparing for Anesthesia for Eye Surgery
Before undergoing eye surgery where anesthesia is required, a complete health check-up is needed. This includes an extensive medical history and physical examination. This health check-up helps to identify any other existing illnesses, like obesity, heart disease, lung problems, anxiety, claustrophobia, and chronic back pain, which may make it difficult for the patient to lie flat on their back, as is commonly needed during eye operations. It also helps the doctor to come up with the safest anesthesia plan, fitting to both the patient’s needs and the surgical procedure, facilitating better outcomes.
It’s important to know what medications the patient is currently taking, especially those that may affect anesthesia. Some eye drops, commonly given in eye conditions, can get absorbed in the body through the nose and can change heart behavior during the operation. Plus, blood-thinning medications can also impact the use of regional anesthetics, which are medicines applied to a specific area of the body to numb it before surgery.
The physical examination also involves evaluating the patient’s ability to understand and communicate effectively. This is particularly vital as eye surgeries are commonly done on children and elderly individuals. These groups of patients may not have the needed mental function to cooperate during procedures that require them to be awake or semi-conscious, yet numb in a specific area due to local or regional anesthesia.
How is Anesthesia for Eye Surgery performed
Topical anesthesia refers to a simple and frequently used method of pain relief for certain eye surgeries, specifically for cataracts or glaucoma. This method involves numbing the eye area with local anesthetic drops or gels, like lidocaine, proparacaine, or tetracaine. Topical anesthesia doesn’t require patients to remain absolutely still or freeze their eye movement, and it’s often selected for patients on blood thinners as it reduces bleeding risk.
Regional anesthesia, on the other hand, provides relief and restricts movement within the eye area. It’s important that a patient can cooperate and follow instructions for these types of anesthesia, as the method requires a sharp needle injection near the eye. To keep the eye and its nerves safe, the doctor will confirm there’s no aspiration (accidental inhalation) before the local anesthetic is injected.
There are three main techniques for regional anesthesia: retrobulbar, peribulbar, or sub-Tenon (episcleral) block. The retrobulbar block is an early method which places the anesthetic behind the eye for maximum effect. The peribulbar block is considered safer than the retrobulbar because the injection doesn’t penetrate as deeply, reducing risk of injury. Both the retrobulbar and peribulbar blocks involve anatomical landmarks to accurately place the injections. The sub-Tenon block is performed by creating a small cut, inserting a catheter, and then injecting the anesthetic.
When it comes to eye surgery, sometimes general anesthesia might be necessary. Although not commonly used, it’s chosen based on the patient and the specific surgical requirements. Vitreoretinal surgery, which treats eye disorders in the retina and the vitreous fluid, is an example of a common ophthalmic procedure performed under general anesthesia. It’s important for the anesthesiologist to know how the anesthesia medicine affects eye pressure, the state of the patient’s airway, and to manage any emergencies effectively. Anesthesia can be maintained with intravenous and other medical agents, which on the whole, lead to a decrease in eye pressure. The decision to secure the airway either with an endotracheal tube or a supraglottic airway device (SGA) will depend on the patient’s health conditions.
Possible Complications of Anesthesia for Eye Surgery
If local anesthetic is accidentally injected into a blood vessel instead of the area being treated, it can cause serious health problems by affecting your entire body.
Sometimes, anesthetics are used to numb the area behind the eyes (a procedure known as a retrobulbar block), but this can have side effects. The most serious ones can include injuries around the eye, even accidentally poking a hole in the eyeball if the eye is longer than normal. Other risks include trouble breathing if the anesthetic accidentally enters the area surrounding the brain, and severe vision loss. Vision loss can happen if the pressure inside your eye goes up because of bleeding or pressing on the optic nerve (which sends signals from your eye to your brain) from local anesthetic. When this bleeding happens, it’s called a retrobulbar hemorrhage. Signs that suggest you might have a retrobulbar hemorrhage include swelling or “bulging” of the eye and increased pressure inside the eye (like a very bad headache in just one eye). In such cases, doctors may need to release the pressure with a small cut at the edge of your eyelid (known as lateral canthotomy).
To inject anesthesia around the eyeball (peribulbar blocks) is usually considered safer and has quickly become a popular method due to less serious and less common side effects. A common side effect of this method includes temporary eye swelling due to the buildup of anesthetic within the confined space of the eye socket. When a blunt needle is used to inject anesthesia beneath the thin tissue covering the white of the eye (a sub-Tenon block), the risks are lower. This method is often suggested for patients on blood thinners or those with longer eyes, because using a sharp needle could increase the risk of complications.
In surgery, it’s possible for something called the oculocardiac reflex to be triggered. This can happen if pressure is placed on the eyeball, if the eye is in pain, if the eye is moved a lot, or if a specific eye muscle (the medial rectus muscle) is pulled. This reflex involves two cranial nerves (the trigeminal and vagus nerves) and can lead to severe slowing of the heart rate, heart rhythm abnormalities, and low blood pressure. This needs to be addressed right away. First the surgical team will stop whatever they’re doing that could be causing the reflex. Then they might give drugs like atropine or glycopyrrolate to help increase the heart rate again. Atropine is usually the first choice because it starts working faster.
What Else Should I Know About Anesthesia for Eye Surgery?
When having an eye surgery, it’s important to note that the level of pressure in your eyes (IOP) may change due to the anesthesia. Most anesthetics, whether inhaled or given through a vein, can lower IOP. Other body changes like low carbon dioxide levels, body temperature drops, and lower average blood pressure can also reduce eye pressure.
However, there are instances when eye pressure can increase. This can happen when certain drugs are used, like succinylcholine and ketamine, or during certain activities like straining (Valsalva maneuver) or if pressure is applied to the eye. Throwing up can drastically increase your eye pressure, so it’s important to prevent nausea and vomiting before and after the surgery. It’s crucial to remember, though, that a drug called scopolamine, which is normally used to prevent nausea, can cause a sudden form of glaucoma, so it has to be avoided if you have a higher risk of getting glaucoma.
If you’ve had a type of eye surgery known as vitreoretinal surgery, which involves injecting a gas bubble into your eye, you should steer clear of nitrous oxide for 4 to 6 weeks. This is because it can expand the gas bubble in your eye and potentially harm your optic nerve.
Many people preparing for eye surgery use eye drops that contain medications. Some of these, like echothiophate, phenylephrine, beta-blockers, and acetazolamide, can have effects on other parts of your body. Echothiophate can cause a longer paralysis if succinylcholine is used during intubation (a process where a tube is placed down your throat to help you breathe). Beta-blockers and phenylephrine eye drops can affect your heart rate and blood pressure.
Lastly, during the surgery, something called an oculocardiac reflex can occur. This condition can cause severe low heart rate, low blood pressure, and even a complete stop of the heart. A light sedation or certain conditions that can happen under general anesthesia, like low oxygen and high carbon dioxide levels in your body, can increase this risk during your operation.
