|Year : 2018 | Volume
| Issue : 3 | Page : 167-172
Monitored anesthesia care in ophthalmic surgeries
Manickavasagan Rangaswamy, Jeyakumar Veeraiyan, Divya Malarvannan
Department of Anaesthesiology, Sundaram Medical Foundation, Chennai, Tamil Nadu, India
|Date of Web Publication||23-Oct-2018|
509, MTH Road, Ambattur, Chennai - 600 053, Tamil Nadu
Source of Support: None, Conflict of Interest: None
Monitored anesthesia care (MAC) is a specific anesthesia service for diagnostic and therapeutic procedures. It includes safe conscious sedation, adequate pain relief, and measures to allay anxiety. Even though it involves minimal anesthetic intervention, it is essential for an anesthetist to know about the patient history. Many ophthalmic drugs have significant anesthetic implications, and many anesthetic drugs cause significant intraocular pressure changes. In this article, we have highlighted the importance of MAC in ophthalmic procedures and implications of various anesthetic agents in eye surgeries. The various ophthalmic blocks and their complications and the toxicity which can occur with the use of local anesthetics have also been touched upon.
Keywords: Local anesthetic systemic toxicity, monitored anesthesia care, sedation
|How to cite this article:|
Rangaswamy M, Veeraiyan J, Malarvannan D. Monitored anesthesia care in ophthalmic surgeries. TNOA J Ophthalmic Sci Res 2018;56:167-72
| Introduction|| |
Monitored anesthesia care (MAC) is a specific anesthesia service for diagnostic and therapeutic procedures which are performed under local anesthesia (LA). It includes sedation and analgesia, titrated to a level that preserves spontaneous breathing and airway reflexes, according to the latest American Society of Anesthesiologists update in 2008.
The three basic components of MAC are as follows:
- A safe conscious sedation
- Measures to allay patient's anxiety
- Effective pain control.
Ideally, it is suited for daycare procedures as it helps in fast tracking of patient.
MAC is an anesthesiologist-led service as it is very important for the provider to be qualified and skilled to rescue an airway and/or convert to general anesthesia if the situation demands. It also involves intravenous (IV) administration of drugs alone and/or supplementation to LA/regional anesthesia.
The standard of care is similar to that of general or regional anesthesia, which includes a proper preanesthetic examination, standard intraoperative monitoring, and postoperative care. Monitoring comprises continuous communication with a patient, observation of parameters such as oxygenation, ventilation, circulation, temperature, as well as vigilance for LA toxicity.
Sedation is a continuum which ranges from minimal (anxiolysis), to moderate (also called conscious sedation, where the patient remain asleep but is easily arousable), to deep sedation (where the patient can be aroused only by painful stimuli) [Table 1].
Assessment of the depth of sedation enables in titrating drug administration to prevent awareness and to avoid excessive anesthetic depth, thereby ensuring patient safety and early recovery.
An ideal sedative agent should be consistently effective in having rapid onset, easy titration, high clearance, and minimal side effects, particularly a lack of cardiovascular and respiratory depression.
Due to dearth of an ideal agent, sedation techniques for MAC often utilize a combination of agents to provide analgesia, amnesia, and hypnosis with complete and rapid recovery that suits a particular operative procedure with minimum side effects, such as postoperative nausea and vomiting, prolonged sedation, and cardiorespiratory depression.
Duration of procedure, clinical condition, age of the patient, and the need to convert to general or regional anesthesia help to guide toward the selection of appropriate sedation technique.
Fewer sedative drugs are required in geriatric population as chances of desaturation and cardiovascular instability are more. Apart from distribution and elimination half-life, factors such as context sensitive half-time, effect-site equilibration, and potential of interaction with other drugs need to be taken into account while choosing the drugs.
| Goals of Monitored Anesthesia Care|| |
- To maintain patient safety and sense of well-being
- To alleviate pain and minimize discomfort
- To minimize the psychological response – adequate anxiolysis and amnesia
- To control behavior
- To return to preprocedural state
- Safe discharge.
| End Point|| |
- Providing patient comfort
- Maintaining cardiorespiratory stability
- Improving operating condition
- Prevent recall of unpleasant perioperative event.
| Preoperative Assessment|| |
It should be the same as for patients who are undergoing procedures under regional or general anesthesia. There should be no compromise of any sorts just because the patient is to undergo the procedure under MAC.
Moreover, it is very important to assess the patient's ability.
- To remain motionless
- To cooperate
- To communicate.
| Ophthalmic Surgeries|| |
Most patients belong to geriatric population. Aging involves a progressive loss of functional reserve in all organ systems. Moreover, to this, the presence of other coexisting diseases will further contribute to the decline. In general, geriatric patients are more sensitive to anesthetic agents. Hence, lesser medication is usually required to achieve a desired clinical effect, and the drug effect is also often prolonged. Some common comorbid conditions seen in elderly are as follows:
- Diabetes mellitus
- Coronary artery disease
- Congestive heart failure
- Cardiac arrhythmias
- Chronic bronchitis
- Decreased cough
- Parkinsonism More Details
- Restless leg syndrome
| Monitoring during Monitored Anesthesia Care|| |
- Pulse oximetry
- Noninvasive blood pressure
- Bispectral index/entropy.
| Effects of Anesthesia and Adjuvant Drugs on Intraocular Pressure|| |
Majority of the anesthetic drugs cause a decrease in intraocular pressure (IOP), except succinylcholine and ketamine  both of which have known to increase the IOP [Table 2].
|Table 2: Effects of anesthesia and adjuvant drugs on intraocular pressure|
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| Anesthetic Implications of Ophthalmic Drugs|| |
Ophthalmic drugs have several anesthetic implications. [Table 3]. Routinely used drugs such as phenylephrine and beta-blockers can cause hypertensive crisis and bradycardia and bronchospasm, respectively. Mannitol can increase the circulating blood volume and can precipitate congestive cardiac failure (CCF) in patients with poor ventricular function. Similarly, atropine can cause tachycardia and echothiophate which is an anticholinesterase can cause prolongation of succinylcholine action. In procedures such as retinal detachment, sulfur hexafluoride bubble is used. In such procedures, the use of N20 can cause increase in size of bubble and increase IOP [Table 3].
| Complications of Ophthalmic Blocks|| |
The complications of ophthalmic blocks are summarized in [Table 4].
| Anticoagulants in Ophthalmic Procedures|| |
Oral anticoagulants showed no significant increase in potentially sight-threatening complications with regional anesthesia.
IV anticoagulants showed that it is better to avoid regional anesthesia and prefer to administer general anesthesia.
| Oculocardiac Reflex (Trigemino-Vagal Reflex)|| |
It is also known as Aschner phenomenon, Aschner reflex, or Aschner-Dagnini reflex.
The incidence of occurrence of about 14%–90% is seen in pediatric patients, especially those undergoing strabismus surgery, although it can be evoked in all age groups and during a variety of other ocular procedures.
- Afferent pathway: Ophthalmic branch of the trigeminal cranial nerve [Figure 1]
- Efferent pathway: Vagus nerve.
| Triggers|| |
There are various stimulus that can lead to oculocardiac reflex, few most common stimulus are traction of extraoccular muscle (especially medial rectus), conjunctiva, pressure on globe, retrobulbar block, ocular trauma, pressure on tissue remaining after enucleation.
| Effects|| |
Oculocardiac reflex leads to bradycardia, arrythmia including ventricular tachycardia and rarely asystole.
| Treatment|| |
- Inform surgeon – removal of stimulus
- Verify adequate ventilation and oxygenation
- Check depth of anesthesia
- Atropine (20 μg/kg) or glycopyrrolate (10–20 μg/kg)
- In recalcitrant episodes, infiltration of the rectus muscles with LA.
The reflex eventually fatigues with repeated traction on the EOMs. Intramuscular atropine is not useful due to delayed onset. In children, injection glycopyrrolate 0.01 mg/kg IV before commencing surgery is indicated. In adults, prophylaxis is not usually indicated.
To summarize, the plan for monitored anaesthesia care in opthalmic surgeries is that after the preoperative assessment and consent is obtained, stabilizing of patient comorbidities is done. On the day of surgery, the patient should be accompanied by a responsible attendant. Clear liquids are allowed 2 hours before procedure. Make sure patient voids and then the patient is connected to monitors and intravenous cannula is secured. Local anaesthetic is administered and the patient is intraoperatively monitored with ECG/SPO2/ NIBP/EtCO2. At the end of surgery, the patient is shifted to the recovery ward and later discharged after satisfying the discharge criteria.
| Local Anesthetics|| |
Local Anesthetics (LA) agents can be divided into two groups based on their structure, esters and amides [Table 5].
Local anesthetic toxicity
While generally safe, LA agents can be toxic if administered inappropriately, and in some cases, it may cause unintended reactions even when properly administered [Figure 2]. Adverse effects are usually caused by high plasma concentrations of the agent, which may result from one of the following:
- Inadvertent intravascular injection
- Excessive dose or rate of injection
- Delayed drug clearance
- Administration into vascular tissue.
Signs and symptoms of systemic toxicity
Manifestations of LA toxicity typically appear 1–5 min after the injection, but onset may range from 30 s to as long as 60 min. Toxicity manifestations are shown in [Figure 2] which can be categorized as follows:
- Central nervous system (CNS)
- Cardiovascular system
- Hematologic system.
Central nervous system manifestations
Systemic toxicity begins with symptoms of CNS excitement such as the following:
- Circumoral and/or tongue numbness
- Metallic taste
- Visual and auditory disturbances (difficulty focusing and tinnitus)
With higher doses, initial CNS excitation is often followed by a rapid CNS depression, with the following features:
- Muscle twitching
- Respiratory depression and arrest
- Cardiovascular depression and collapse.
- Chest pain
- Shortness of breath
Methemoglobinemia is mostly with prilocaine. It may be accompanied by any of the following complaints:
- Cutaneous discoloration (grey)
- Exercise intolerance
- Dizziness and syncope.
Risk factors for toxicity
These relate to the LA, the block, and the patient.
Local anesthesia-related factors
The type and dose of LA injection influence toxicity risk.
- Bupivacaine > levobupivaciane, ropivacaine > lignocaine.
Site of block
The site is important since some sites have a higher risk of direct intravascular injection (e. g. interscalene or stellate ganglion block) and others carry an increased risk of rapid absorption and toxicity due to the injection being in a highly vascularized area. IV > intercostal > caudal > epidural > brachial plexus > subcutaneous.
- Comorbidities (renal, liver, and cardiac disease)
- Elderly patients
- Pediatric patients
- Pregnant patients.
| Prevention|| |
- Avoid multiple simultaneous blocks
- Use low dose
- Use adrenaline as marker or IV injection
- Aspirate before injection
- Inject in graded aliquots.
- Use relatively less toxic drugs
- Restrict total anesthetic dosage to lowest effective dose
- Avoid rapid injections
- Use adjuvants to reduce dosage of LA
- Avoid excessive sedation to allow early detection of LA systemic toxicity.
Reduce dose in
- Extremes of age
- Cardiac patients
- Renal disease
- Liver disease.
| Diagnosis|| |
The evaluation of patients with possible toxicity from a LA should be guided by the clinical presentation. Blood levels of the anesthetic may be measured although blood levels may not correlate with toxicity or may not be obtained at a clinically useful time.
| Management|| |
- Stop LA injection
- Protect airway if necessary
- Supplemental oxygen
- Anticonvulsants such as thiopentone and midazolam
- Cardiac arrest – ACLS protocol-based resuscitation
- Avoid lignocaine for ventricular arrhythmias
- IV Lipid emulsion therapy [Figure 3]
- Cardiopulmonary bypass.
Financial support and sponsorship
Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3], [Table 4], [Table 5]