Anesthesia For Eye Surgery

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Continuing Education Activity

This activity reviews the anesthetic implications associated with patients undergoing eye surgeries. This article will highlight major anesthetic topics related to common eye procedures and will include a brief discussion regarding the various anesthetic approaches and intraoperative management of common eye surgeries. Understanding the basic principles of intravenous and volatile anesthetics concerning intraocular pressure and preparing for potential complications is essential to providing excellent patient care. This activity is intended to guide the multidisciplinary and interprofessional operative team consisting of nurses, surgical technicians, and specialty physicians in working together to provide a safe and uneventful perioperative experience.

Objectives:

  • Review the anatomy of the orbit and describe changes in intraocular pressure that result from intravenous and volatile agents.
  • Explain the oculocardiac reflex and review the hemodynamic changes that can result.
  • Describe complications that may result from regional anesthesia for eye blocks.
  • Outline the anesthetic techniques used by the interprofessional team and indications for providing regional anesthesia for patients undergoing eye surgery.

Introduction

Understanding the anesthetic implications and approaches to ophthalmic surgery is very important for providing anesthetic care in the perioperative period. The goals of anesthesia during elective eye surgery should focus on patient safety and providing analgesia to elicit a pain-free experience and create optimal surgical conditions to facilitate the procedure in collaboration with the perioperative staff, including the ophthalmologic surgeons and surgical technicians. It is paramount to minimize risks that may present during eye surgery under anesthesia and sedation while anticipating and managing any potential outcomes associated with eye surgeries. The most common eye surgeries performed today are cataracts, glaucoma, and vitreoretinal surgery. It is estimated that nearly 26 million Americans are suffering from cataracts, and approximately 3.6 million cataract extractions are completed annually, making it the most commonly performed surgical procedure in the united states.[1] 

Moreover, glaucoma affects nearly 67 million people in the united states, and understanding the concept of intraocular pressure concerning intravenous and volatile anesthetics becomes increasingly important to providing anesthetic care, especially in patients with comorbidities.[2] Another commonly performed ophthalmic surgery is vitreoretinal. The important anesthetic consideration for this surgery would concern the need for general versus local anesthesia and the necessary avoidance of nitrous oxide with intraoperative use of sulfur hexafluoride (SF6).

This article aims to understand the anesthetic considerations and implications along with the general and regional anesthetic techniques, including topical, retrobulbar, peribulbar, and sub-Tenon blocks, that can be used to provide anesthesia. The anatomy and physiology will be reviewed as well to provide a complete understanding of the structures of the eye and the important hemodynamic manifestations of the oculocardiac reflex. Management of perioperative complications will be discussed as the adverse events can result in significant life-threatening harm and permanent visual impairments for patients presenting for ophthalmic surgeries. According to the anesthesia closed claims project, eye injury occurred in 3% of all claims in the database, further indicating the importance of protecting and caring for the eyes during anesthesia, especially in mitigating the risk associated with peripheral nerve blocks.[3]

Anatomy and Physiology

It is important to understand the anatomic considerations of the orbit as it pertains to completing nerve blocks for regional anesthesia and achieving an akinetic globe. The orbit consists primarily of adipose tissue, and the globe itself is located in the anterior part. The ophthalmic nerve, a branch of the trigeminal nerve, is responsible for the sensory innervation of the globe.[4] Motor innervation to the extraocular muscles passes through the muscular cone of the eye. This knowledge is important because the deposition of local anesthetic will provide anesthesia, analgesia, and akinesia of both the globe and extraocular muscles. The extraocular muscles are innervated by the oculomotor, trochlear, and abducens nerves in orbit.[4] 

All of these nerves except the trochlear nerve transverse through the muscular cone of the orbit, thus injection of local anesthetic in this area can reliably provide akinesia to the globe, thereby blocking both sensory and motor innervation. Because of the proximity to these nerves in the muscular cone, there is a risk for inadvertent puncture of the optic nerve and vasculature of the orbit.

When injecting the local anesthetic, it is important to keep the injection needle extraconal when possible to minimize the risk of puncturing important structures resulting in vision loss, nerve damage, and bleeding. In terms of physiology, the understanding of intraocular pressure is an important concept in regards to delivering and managing anesthesia in eye surgeries. Intraocular pressure is described as the pressure the contents of the eyes produce on the surrounding wall. Increases in this pressure can have detrimental effects secondary to impairments in perfusion, resulting in a decrease in blood flow to ocular structures, including the retina, choroid, and optic nerve. Normal intraocular pressure is considered approximately to be 10 mm Hg to 21 mm Hg.[5]

There is a substantial increase in intraocular pressures during ophthalmic surgeries. Moreover, an injection of 0.5 mL into the intravitreal space has the potential to increase intraocular pressure by over 150% compared to pre-injection levels. These fluctuations in pressure can compromise perfusion to the retina and optic nerve, resulting in visual impairment following surgery.

Indications

There are many approaches to providing anesthetic care for patients undergoing eye surgeries. Anesthetic plans may vary from moderate sedation to monitored anesthesia care to full general anesthesia. The inclusion of topical and regional anesthesia has improved the anesthetic techniques that can be performed to facilitate eye surgeries while providing excellent patient care. Developing an anesthetic plan should always be specific to the comorbidities of the patient in addition to particular factors that may influence cooperation, comfort, and safety in the perioperative period. For instance, most eye surgeries are performed in the supine position.

If the decision to pursue regional or topical anesthesia is selected in conjugation with monitored anesthesia care, then the patient must be able to follow directions, respond appropriately, and tolerate the procedure and positioning. Comorbidities like heart failure, chronic obstructive pulmonary disease (COPD), and obstructive sleep apnea, for example, may cause patient harm and discomfort from the inability to lie flat on the operating room table. Also, securing an airway in the event of respiratory distress can be more challenging in these situations as there is limited access to the patient's head which is typically covered with drapes to perform eye surgeries.

Moreover, patient cooperation must be assessed when developing an anesthetic plan because cognitive decline and diseases such as Parkinson disease and dementia may preclude patients from responding appropriately. Similarly, pediatric patients may have difficulty remaining still, and thus, general anesthesia may be the best option. The type of eye surgery performed will have separate indications that will influence anesthetic care as well. For example, most cataract and glaucoma surgeries are completed under monitored anesthetic care combined with topical anesthesia and regional anesthetic techniques. Peribulbar and topical anesthetic techniques are the most commonly utilized approaches in the united states for cataract procedures.[6] 

This is in contrast to patients who present for vitreoretinal surgeries and will typically receive a combination of a regional anesthetic technique with general anesthesia. The use of topical anesthesia is not utilized because vitreoretinal surgeries may take longer to perform. This avoids the possibility of the local anesthetic wearing off and thus limiting operating conditions for the ophthalmologist. However, vitreoretinal surgeries are usually performed under peribulbar block in India and other countries. As stated earlier, general anesthesia is typically reserved for pediatric patients and for those who may have difficulty in cooperating and communicating through the procedure.

Contraindications

There are very few contraindications when performing anesthesia for eye surgeries, and many are based on patient factors. An absolute contraindication would be patient refusal and anaphylactic reactions to local anesthetics when anesthetic care for regional blocks is selected. Local anesthetics used for eye surgeries may consist of aminoesters and aminoamides. The most commonly used local anesthetic is lidocaine which is an aminoamide. True anaphylactic reactions are rare and mainly result from the preservative (methylparaben), commonly added to lidocaine.[7] In terms of providing general anesthesia, absolute contraindications are malignant hyperthermia as well as the use of nitrous oxide for vitreoretinal surgeries.[8]

During retinal detachment surgeries, the ophthalmologist may inject a gas bubble of either sulfur hexafluoride (SF6) or perfluoropropane (C3F8) that will be used to intentionally tamponade the retinal break. This gas bubble must be completely reabsorbed, which may take several weeks before nitrous oxide can be used as part of an anesthetic under general anesthesia. This is an absolute contraindication because of the permanent blindness that may result in weeks later as nitrous oxide enters and expands this gas bubble, thereby increasing intraocular pressure. Other relative contraindications which may guide anesthetic care to improve surgical outcomes are based on the age of the patient in pediatric patients, diseases that inhibit cooperation such as dementia or Parkinson disease, inability to tolerate supine positioning secondary to comorbidities, localized eye infections, and increased long axial length of the eye undergoing the operation.[9]

Equipment

The equipment needed to perform anesthesia care during eye surgeries is the standard equipment normally present in modern-day operating rooms in the United States. Standard anesthesia monitors should always be present when providing any type of anesthesia to evaluate the patient, focusing on oxygenation, ventilation, circulation, and temperature monitoring when significant changes are anticipated. Oxygenation can be assessed via pulse oximetry, ventilation can be assessed via capnography, and circulation can be evaluated via continuous electrocardiogram and blood pressure readings every 5 minutes. An anesthesia machine may be required as well to assist in the delivery of positive pressure ventilation, fresh oxygen gas flows, and volatile anesthetics. These anesthesia machines will typically include gas analyzers as well.

In terms of pharmacotherapy, there should be easy access to emergency drugs such as epinephrine and atropine. A ready supply of neuromuscular blocking agents and airway equipment to rapidly secure an airway in the event of adverse events should be present. The anesthesia provider should also have ready access to lipid emulsification if an inadvertent intravascular injection occurs, resulting in local anesthetic systemic toxicity. Other medications needed to provide anesthesia, if regional anesthesia is selected, are local anesthetics as well as a medication called hyaluronidase, which may assist in the spread of local anesthetic to accomplish akinesia while reducing the volume of infiltration of the local anesthetic. Equipment for surgical blocks with local anesthetic involves small gauge needles (25 to 27 mm) that can be either sharp or blunt depending on the block technique.

Personnel

The perioperative team for patients undergoing eye surgery consists of surgical technicians, operating room nurses, physician assistants, nurse anesthetists, anesthesiologists, and ophthalmologists.

Preparation

Patients should undergo a thorough preoperative consultation to allow for the opportunity to assess comorbidities and deliver an anesthetic plan that is safest for the patient while facilitating the ophthalmologic surgeon. This pre-operative examination should assess patient cooperation and the ability to communicate effectively. Eye surgeries are common in elderly patients, and thus, assessing cognitive function is paramount to predict if the patient will be able to respond and communicate appropriately if the anesthetic plan involves monitored anesthesia care under sedation in conjunction with topical or regional anesthesia. Elderly patients may have a higher incidence of undiagnosed cardiac disease, and thus, an accurate assessment of their cardiac risk factors and metabolic equivalents should be performed prior to surgery.

Moreover, patients lie in the supine position, and the head may be strapped to a headrest on a specific operating room table designed for performing eye surgeries. Patients must be able to tolerate this position, and there are various patient factors that may make this challenging such as obesity, heart failure, COPD, claustrophobia, and chronic cervical or spinal pain. Anxiety and claustrophobia may make certain patients unable to tolerate this positioning, especially when sterile drapes are placed over their head and body, which is standard for operating room surgeries. A focused medical history is also essential and is primarily important for identifying medications that have anesthetic implications. For instance, many patients presenting for eye surgeries may be on topical drops like timolol, carteolol, pilocarpine, and phenylephrine. Many of these drugs are absorbed (usually through the nasal mucosa) and can have hemodynamic effects intraoperatively.[10] Moreover, many patients may be on anti-coagulant medications, which is an important anesthetic concern when performing regional anesthesia.

Technique

There are various techniques to provide anesthetic care for eye surgery. Topical anesthesia is one of the most commonly performed approaches, particularly for procedures involving cataracts or for patients with glaucoma. This is an option for patients on anticoagulation therapy where it is necessary to mitigate risks of intraocular bleeding that may occur with needle insertion for local anesthetic injection, especially for retrobulbar blocks. Choice of anesthesia will also depend on the type of surgery as well. For instance, complete akinesia may not be required for cataract surgery, making topical anesthesia the superior choice, which would eliminate adverse effects present with regional anesthesia. Topical anesthesia is achieved by placing local anesthetic drops or gels such as lidocaine, proparacaine, and tetracaine directly to the cornea and conjunctiva.

Another approach to providing anesthesia care is accomplished using regional techniques, which can provide varying degrees of akinesia and analgesia of the eye through transconjunctival or percutaneous injections. When sharp needles are being used for injection, patient cooperation is paramount as they must be able to follow instructions when requested to look straight ahead, which is otherwise known as the primary gaze position. Looking straight before injection will help protect the ophthalmic artery and optic nerve from damage caused by the injection needle. After needle injection has occurred, the next step is to confirm negative aspiration of the syringe to identify possible intravascular injection when injecting the local anesthetic.

The three most common approaches to providing regional anesthesia via nerve blocks are the retrobulbar block, peribulbar block, and the sub-Tenon block, which is not typically performed in the United States. One of the earliest blocks to be performed in ophthalmologic surgery is the intraconal, retrobulbar block. This is completed using anatomical landmarks by identifying the space slightly lateral of the junction of middle and lateral thirds of the inferior orbital rim.[9] The decision to perform this block via the transconjunctival versus the percutaneous routes should depend on physician comfort and skill level as well as the anatomy of the patient landmarks. If a percutaneous approach is chosen, slight pressure is applied above the rim of the eye to create a space between the globe and infraorbital bone. This space is used to guide the trajectory of the needle that helps in decreasing the risk of potential globe perforation. If a transconjunctival route is chosen, slight pressure is applied in a downward motion near the inferior orbit to retract the lid of the eye. The needle is then advanced upward and inward until the space behind the globe is entered. A small amount of local anesthetic of 2- 5 mL is injected after negative aspiration through a 23 to 25 gauge needle with a length of less than 1.5 inches to avoid damage to the adjacent ophthalmic nerve and vasculature.[11] The smaller needle length decreases the risk of globe perforation as well. The major benefit of the retrobulbar block is the deposition of local anesthetic in the intraconal portion of the eye, which will provide maximum akinesia to the extraocular muscles with a success rate of approximately 85%.[12]

The peribulbar block is another regional eye block that can be performed with a 25 to 27 gauge needle with a maximum length of 1.25 inches. It is a safer alternative than the retrobulbar block and is becoming more popular when providing anesthetic care.[13] This is mainly because the injection needle with local anesthetic remains extraconal, so the depth of insertion is significantly decreased, which allows for a shorter needle length. The trajectory of the needle is less steep compared to a retrobulbar block which can help to decrease the likelihood of particular adverse events such as globe perforation, damage to the optic nerve, and central nervous depression resulting from direct local anesthetic injection into the intrathecal space.[14] 

Inferotemporal and medial peribulbar approaches have been described when performing peribulbar blocks. The inferotemporal approach is similar to the retrobulbar block regarding anatomical landmarks. However, the needle does not enter inside the myofascial cone of the orbit. This block has the added benefit of blocking the orbicularis oculi muscle (which is responsible for closing the eyelid) compared to the retrobulbar block. This can help facilitate the surgeon and improve operating conditions when performing surgery on the eye.[15] The medial peribulbar block is an alternative peribulbar block approach that is also a relatively safe area to deposit local anesthetic. There is approximately a 10 mm space between the medial orbital wall and the fat pad equator of the orbit. Larger amounts of local anesthetic in volumes of 6 to 12 mL are placed to achieve akinesia and analgesia of the eye for this block. The larger amounts in volume used for this block are intended to result in the local anesthetic spread in all directions in the extraconal space of the orbit. Although this peribulbar block is considered safer since there is less exposure to the posterior globe and intraconal anatomical structures, this block requires more time (approximately 5 minutes) to affect. Moreover, there is a higher incidence of conjunctival chemosis secondary to a higher volume of injectate compared to retrobulbar blocks.[16]

The last regional anesthesia block to be discussed is the sub-Tenon block. This technique is performed by creating a small incision through the conjunctiva and Tenon capsule. These anatomical structures are secured via forceps followed by careful dissection of the sclera with blunt scissors. A small 19 gauge catheter is then placed through the incision hole. Approximately 2 to 5 mL of local anesthetic is deposited into this space. This local anesthetic can spread to the posterior portion of the globe via this anterior approach. Similar to the peribulbar block, this block may take approximately 5 minutes to affect analgesia and akinesia. Regardless of the type and technique used for regional anesthesia, it is important to evaluate the success of the performed block by assessing for any motion of the globe or extraocular muscles.

Another technique in which eye surgery can be performed is under general anesthesia. Although this may be rare, this decision is based on patient factors and the details of the specific type and approach of the eye surgery being completed. Under general anesthesia, it is necessary to maintain a deep and stable plane of anesthesia to create the best surgical outcomes. Vitreoretinal surgery is one of the most common ophthalmic procedures performed under general anesthesia.[17] 

It is important to be mindful of the anesthetic implications under general anesthesia, which would include knowledge of intravenous and volatile anesthetic agents for induction and maintenance, pharmacotherapy concerns of opioids and neuromuscular blocking agents, airway management, and emergencies. Additionally, the relationship between these anesthetics and intraocular pressure (IOP) must be continuously evaluated to improve surgical outcomes. Most induction agents, including propofol, thiopental, and etomidate, decrease IOP by approximately 30%.[18] Similarly, volatile anesthetics, commonly used to maintain anesthesia after induction, cause a decrease in IOP. The combination of propofol and sevoflurane decreases IOP significantly and is a reasonable approach to counter the increase in IOP from the sympathetic response to laryngoscopy for airway management.[19]

In terms of airway management, the anesthetic plan to secure the airway via endotracheal intubation or through a supraglottic airway device (SGA) is important as both airway devices have advantages and disadvantages. The benefit of an SGA is that it produces a smaller increase in IOP and allows for a smoother emergence upon removal as compared to endotracheal intubation.[20] However, endotracheal intubation is more of a secure airway and should be used if the patient has a risk of aspiration secondary to a history of gastric reflux disease, obesity, hiatal hernias, or comorbid conditions that slow gastric motility like gastroparesis from diabetes mellitus. The disadvantage of endotracheal intubation is that there will be an increase in IOP. This can be attenuated with pretreatment of fentanyl, remifentanil, dexmedetomidine, and clonidine before laryngoscopy.[21] 

If the intubation route is selected, it may be beneficial to avoid depolarizing neuromuscular blocking agents as this may cause a transient increase in IOP.[22] Also, many patients presenting for eye surgery may be on a medication called Ecothiophate. This is clinically relevant as it is an irreversible inhibitor of pseudocholinesterase responsible for the degradation of succinylcholine, resulting in a prolonged duration of paralysis.

Additionally, if the nondepolarizing neuromuscular blockade is pursued, it may be beneficial to reverse the paralytic using sugammadex instead of neostigmine and glycopyrrolate, which are anticholinergic agents that have been known to increase IOP.[23] Regardless of the type of airway device, it is crucial to maintain a deep plane of anesthesia to avoid laryngospasm if SGA is utilized and to prevent even the slightest movements that can be detrimental to surgical outcomes. General anesthesia under volatile anesthetics can cause severe postoperative nausea and vomiting, which can increase intraocular pressure drastically. Thus, important steps must be taken to prevent the likelihood of this happening following general anesthesia.

Complications

Many perioperative complications may arise during ophthalmic surgeries. The retrobulbar block has the highest incidence of adverse events associated with damage to anatomical structures compared to peribulbar and sub-Tenon blocks.[9] Some of the most feared complications associated with retrobulbar blocks include globe perforation (increased risk when the axial length of eye exceeds 26 mm), respiratory arrest secondary to intrathecal spread to the brainstem from inadvertent puncture through the optic nerve dura, severe vision loss from increased intraocular pressure related to retrobulbar hemorrhage or from optic nerve compression from local anesthetic infiltration.[24] A retrobulbar hemorrhage can be sight-threatening, and thus clinical signs like proptosis and increased IOP should suggest prompt treatment via a lateral canthotomy.

Complications for peribulbar blocks are less severe and are less common. This is the main reason that peribulbar blocks are becoming exceptionally popular. The main complication from a peribulbar block is temporary swelling of the conjunctiva, which is attributed to the accumulation of local anesthetics since larger volumes are used for anesthesia within the confined space of the orbit. Similarly, a sub-Tenon block has lower rates of complications because anesthesia can be achieved without using a sharp needle. This block would be a reasonable approach in patients who are on anticoagulation therapy or have a greater axial length of the eye, as using a sharper needle may cause complications. It is important to note that inadvertent intravascular injection can occur in all of these nerve blocks and can result in systemic toxicity due to local anesthetic.

Another feared complication that may result in hemodynamic compromise is a result of the oculocardiac reflex. The afferent for this reflex is the trigeminal nerve, and the efferent is the vagus nerve. The risk factors for this reflex include traction on ocular muscles (especially the medial rectus), pressure on the globe, ocular pain, and manipulation of the eye.[25] This reflex results in severe bradycardia, bradyarrhythmias, and hypotension. This must be immediately recognized and promptly treated via cessation of surgical stimulation and with pharmacotherapy such as atropine or glycopyrrolate to increase heart rate. Atropine is the better choice in emergent situations as it has a faster onset compared to glycopyrrolate.

Clinical Significance

IOP is an important concept, and understanding changes that may result during the perioperative experience is essential. A decrease in IOP can be achieved by most inhaled and intravenous anesthetics and other physiological changes like hypocarbia, hypothermia, and decreased mean arterial pressure. Increases in IOP can be achieved with certain drugs like succinylcholine and ketamine, as well as certain events such as Valsalva maneuvers and external pressure applied to the eye by the ophthalmologists. It is important to note that vomiting can increase IOP by approximately 30 to 40 mm Hg, so postoperative prophylaxis of nausea and vomiting should be given. When considering scopolamine for postoperative nausea and vomiting prophylaxis, it is important to remember that this can precipitate acute angle-closure glaucoma and should be avoided in susceptible patients.

Moreover, nitrous oxide should be avoided for 4 to 6 weeks if the patient underwent recent eye surgery that involved using an injected gas bubble of SF6 as nitrous oxide can enter and expand this gas bubble causing ischemia of the optic nerve. Many patients presenting for eye surgery may be taking topical eye medications. Some of these significant medications are echothiophate, phenylephrine, beta-blockers, and acetazolamide. All of these medications can be absorbed and can have systemic effects. Echothiphate may result in prolonged paralysis if succinylcholine is used for intubation. Topical beta-blockers and phenylephrine can have hemodynamic effects by influencing heart rate and blood pressure by acting on their corresponding receptors. A major clinical significance that may result is the oculocardiac reflex resulting in severe bradycardia, hypotension, and asystole. This can be aggravated by a light plane of anesthesia and physiological conditions that may arise under general anesthesia, including hypoxia and hypercarbia.

Enhancing Healthcare Team Outcomes

Management of patients presenting for eye surgery in the perioperative period needs an interprofessional team of healthcare providers who share the responsibility of providing a safe and successful perioperative experience. This experience includes the preoperative, intraoperative, and postoperative time until discharge from the recovery room.

The preoperative nurse plays a crucial role in preparing the patient for surgery and obtaining intravenous access for medication delivery. The preoperative nurses are also instrumental in preparing documents for consent to surgery and anesthesia, which improves communication for all team members involved. The intraoperative nurses and surgical technicians play an essential role in preparing the equipment that is needed in the operating room to perform the surgery. Recovery room nurses assess the patient as they recover from surgery. They share the responsibility of monitoring the patient and observing any changes in clinical status. This interprofessional, patient centered-care has the ability to improve outcomes and enhance team performance, resulting in better patient outcomes. [Level 5]

Nursing, Allied Health, and Interprofessional Team Interventions

An interprofessional team is essential for providing patient-centered care. One example that requires a team-centered intervention is the occurrence of the oculocardiac reflex, which can result in severe bradycardia progressing to asystole, hypotension, or other bradyarrhythmias. When this is recognized, the anesthesiologist must immediately communicate with the ophthalmologist to remove the surgical stimulation causing this reflex while making the operating room technicians, nurses, and midlevel providers aware of this hemodynamic compromise in the event that advanced cardiac life support becomes indicated. Nurses may assist in drawing up medications or assisting the head of the bed to assist the anesthesiologist in securing the airway if needed.

Nursing, Allied Health, and Interprofessional Team Monitoring

All team members are responsible for monitoring the patient to ensure a safe and successful perioperative experience. Every team member is involved in monitoring the patient. For instance, the anesthesia provider continuously monitors the patient's blood pressure, oxygenation, ventilation, and cardiac function. The operating room nurse may assist in monitoring safe patient positioning when placing and moving the patient on the operating room table.

The surgical technicians should monitor sterile techniques that are practiced to prevent infection or breaks in sterilization. The ophthalmologist is essential for monitoring the intraocular pressure of the eye and changing operating conditions based on anatomy and progression of surgery. Every team member monitors a specific part of the surgery, which collectively increases safety to deliver excellent patient care.


Article Details

Article Author

Osman Lodhi

Article Editor:

Koushik Tripathy

Updated:

8/21/2021 7:57:03 AM

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