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Contact us at email@example.com 5 Anaesthetic Management in Cataract Surgery Alparslan Apan Department of Anaesthesiology and Reanimation, Kırıkkale University Faculty of Medicine, Turkey
1. Introduction Cataract surgery is one of the most commonly performed surgical procedures in our ageing world. The majority of patients have concurrent disorders including hypertension, diabetes mellitus and coronary artery disease. The anaesthetic management varies between topical anaesthetic applications, regional blocks to general anaesthesia. The patients’ medical/mental condition and current medications are of prime importance in terms of their implications for anaesthesia. It is also prudent to define and prevent drug interactions of ocular medication that are required during the perioperative or postoperative period. The type of intervention and skill of the surgeon are variables that influence the selection of the anaesthetic regimen. Preoperative evaluation is therefore as important as anaesthetic care for this surgical population.
Cataract surgery performed in the setting of an office-based, day case surgical set-up is considered in this chapter. Unsutured incisions and less invasive techniques are increasingly popular. Extraocular muscle akinesia is important for an optimum operating field.
Topical anaesthesia includes local anaesthetic applied to the cornea as drops or ointment.
Benoxinate, tetracaine, ametocaine, lignocaine, and bupivacaine are common ester and amide types of local anaesthetic used for this purpose. Lack of ocular akinesia and insufficient analgesia are considered as disadvantages of topical methods.
Retrobulbar block was one of the most frequently implemented techniques. It is performed via introduction of a needle at the infero-lateral rim of the lower eyelid passing through the muscle cone with advancement in a medial and superior direction at about 10° and injecting 4-8 mL of local anaesthetic / hyaluronidase mixture behind the globe. Maintaining a short advancement distance and use of blunt-tipped needles are advised for this practice. Besides the advantages, including obtaining ocular akinesia and sufficient analgesia, the procedure can for this reason still be considered and useful where other procedures are unsuitable, though this is rare. There is a risk of damage to surrounding structures including globe perforation, as well as penetration into the cerebrospinal fluid and vascular structures behind the eye, causing respiratory depression and cardiovascular collapse. While rare these are significant and limit its use in practice, especially in view of newer ‘blunt needle’ techniques.
Peribulbar block is performed as a retrobulbar block with straight advancement of a short needle from the infero-lateral border of the lower eyelid. This technique is infrequently utilized due to the disadvantages such as high rate of chemosis, lower quality of akinesia, increased local anaesthetic requirements and longer latent period requirement for akinesia.
54 Cataract Surgery Sub-Tenon’s block (a type of ‘blunt needle’ block) is performed by introducing a cannula between the conjunctiva and Tenon’s capsule after delicate but mainly blind dissection of the sub-Tenon’s space. Advantages are reduction of complication rates especially in myopic eyes and it offers the option of re-injections to top up the anaesthetic during surgery. Local anaesthetic leakage, need for dissection and possible need for sutures are limitations.
Gentle pressure application on the globe for local anaesthetic spread after regional blocks are useful for avoiding the oculocardiac reflex. Local anaesthetic infiltration for facial nerve branches might be indicated for eyelid akinesia.Sedation and analgesia may be required during topical anaesthesia or regional blocks. In continuum and during surgery verbal contact between the anaesthetist and the surgeon is important for reducing complications at an early a stage as possible. Depending on the operation it might be preferable to use sedatives/hypnotics or opioid analgesics with a shorter half-life. In the case of repeated drug administrations, accumulating drugs should be avoided and/or a specific antidote should be given if necessary. It is not always possible to approximate additive effects of drug combinations in elderly patients and patients with co-morbidities, and using the lower doses might be important for preventing unforeseen complications though must be balanced with the need to prevent pain or awareness of surgery. Midazolam, propofol and dexmedetomidine, might be frequently used alone as a bolus or infusion, or in combination with fentanyl or remifentanil.
General anaesthesia might be preferred in patients with limited co-operation or advanced co-existing disorders. With a few exceptions, all general anaesthetics decrease intraocular pressure. Laryngeal mask insertion with a smooth induction using etomidate, propofol or thiopentone with or without a non-depolarizing muscle relaxant is frequently chosen.
Propofol infusion with fentanyl or remifentanil might be delivered alone or with volatile anaesthetics. Besides the anti-emetic effects of propofol, the emetic and depressive effects of opioids should be remembered in the postoperative period. General anaesthesia may offer almost motionless optimal surgical conditions (though the Bell’s reflex can persist at lower doses), allows bilateral surgery (rarely needed in intraocular surgery) and possesses virtually no major complication risk related to the injection. On the other hand it needs anaesthetic staff and equipment during administration and is increasingly expensive.
Analgesics and anti-inflammatory drugs might be combined with topical local anaesthetic during the postoperative period. It is important to ensure patients are free from side-effects or residual drug effects of medications to prevent further complications and rehospitalisation.
Cataract surgery is one of the most common interventions made in day-case surgery (Cullen et al., 2009). Although lens opacification is generally a time-related process, it can be observed at an earlier period of life such as in newborns related to congenital metabolic errors and in all age groups due to trauma. The majority of the patients have concurrent disorders including hypertension, diabetes, rheumatoid arthritis, coronary artery or chronic pulmonary disease and take medication. Pre-operative evaluation, including anaesthetic and surgical planning should be performed as per the demands of co-morbidities. Cataract surgery is major surgery as it is intra-ocular surgery, technically challenging, with abundant scope for devastating complications like loss of sight, but it is from an anaesthetic perspective limited in terms of stress to the body overall. Advances in techniques including phacoemulsification and intraocular foldable silicone lens implantation through suture-less mini incisions decrease the surgical recovery period with lower complication rates and improved surgical outcomes.
55 Anaesthetic Management in Cataract Surgery
2. Preoperative evaluation The responsibility of the anaesthetist is to ensure that the patient is in an optimal condition before undergoing surgery. Pre-operative interview with anaesthetic and surgical staff may reduce anxiety and stress concerning the operation. Patients may also be informed about unexpected visual experiences during anaesthesia and surgery in order to prevent undesirable outcomes (Tan et al., 2006).
The pre-operative visit includes determinations concerning the patient’s history, habits, current disease with medications, complete systemic physical evaluation, and occult disease if not diagnosed. Patients may be referred to other physicians when concurrent pathology is not stable. Potential airway problems with a difficult airway must be evaluated and an anaesthetic plan should also be explained with informed consent. Patients may be categorized according to the American Society of Anesthesiologists (ASA) Physical Classification System that is shown in Table 1 to document their status before surgery (Davenport et al., 2006). Mild asthma or well controlled hypertension are examples of ASA Class II patients that are unlikely to have an impact on anaesthesia and surgery. More advanced disease such as renal failure on dialysis or class II congestive heart failure indicates ASA class III patients and is likely to have an impact on anaesthesia and surgery.
Patients are classified as ASA class IV if disease requires special medical care e.g., acute myocardial infarction, and respiratory failure that requires mechanical ventilation with major impact on anaesthesia and surgery. The physical condition of patient over ASA III generally requires hospitalization even when performing surgery with otherwise comparatively limited potential for major systemic stress like cataract surgery.
Class Description I Healthy patient without organic, biochemical, or psychiatric disease.
II A patient with mild systemic disease. No significant impact on daily activity.
III Significant or severe systemic disease that limits normal activity. Significant impact on daily activity.
IV Severe disease that is a constant threat to life or requires intensive therapy.
Serious limitation of daily activity.
V Moribund patient who is likely to die without surgery.
VI Brain-dead organ donor.
Table 1. American Society of Anaesthesiologists physical status (ASA PS) classification The history of the patient may include social habits, cigarette and alcohol consumption, illicit drug use, allergies, past medical history including operations with enquiries about possible adverse outcomes, current medications, and questioning relatives on whether there is a family history of attack from malignant hyperthermia – thus halogenated volatile anaesthetic agents, which may trigger malignant hyperthermia, may be avoided.
Systemic evaluation must include careful examination for a difficult airway, including jaw and neck movements, mouth opening, and intra-oral pathology. Special precautions or devices must be prepared to be used for patients who are likely to have an airway problem.
Patients, especially with increased body mass index, must also be questioned about snoring during their sleep and evaluated for possible sleep apnoea syndrome. The physical capacity of patients can be determined with simple questions on for instance being able to do daily activities, climbing stairs, swimming or other sports.
56 Cataract Surgery Physicians may require symptom-oriented laboratory investigations instead of ordering a battery of tests (Schein et al., 2000). Laboratory results and an electrocardiogram (ECG) performed within 6 months is sufficient to determine the gravity of most cardiac conditions.
The consensus is to obtain an ECG from all elderly patients to determine the baseline cardiac condition. Haemoglobin levels may also be necessary to exclude anaemia that can precipitate cardiac events. Levels under 7 g/dL require transfusion therapy.
Chronic medical conditions such as congestive heart failure or chronic obstructive pulmonary disease must be optimized before surgery. Patients with a recent attack of angina, arrhythmia, ischemia or infarction must be identified and elective cataract surgery may be postponed for month(s). A recent cerebrovascular attack or exacerbation of a chronic cerebral disorder e.g. multiple sclerosis is also a reason for postponing elective surgery. For patients with chronic renal failure it is necessary to determine the status of the ECG, plasma electrolytes, blood urea nitrogen (BUN) and creatinine levels. In the case of acute hepatitis or its exacerbation, surgery must be postponed until return to systemic baseline levels, requiring monitoring using a liver enzyme profile.
Hypertension must be controlled and blood pressure must be decreased to the acceptable levels, 140/90 mmHg if possible. Blood pressure of 200/110 mmHg or more before the operation requires postponement of elective surgery.
It is not usually necessary to discontinue current medication but herbal medicines should be withdrawn due to possible drug interference or due to the possibility of postoperative complications at least 1 week beforehand. Patients on anticoagulation therapy may also continue their medication as the risk of cessation of treatment outweighs the risk of bleeding (Hirschman & Morby, 2006) though clotting needs to be checked before surgery to ensure patients are not over-anticoagulated. Patients receiving aspirin, clopidogrel or warfarin may switch to low molecular weight or regular heparin should they be felt to be at risk of deep vein thrombosis during prolonged general anaesthesia.
Patient who are unable to lie flat due to their disorder, musculoskeleteal disease such as kyphoscoliosis, paediatric patients, those with claustrophobia, altered cognitive function or orientation such as in Alzheimer’s Disease, deafness, language problems that affect cooperation and abnormal movements or tremor such as in Parkinson’s Disease are often unable to undergo surgery under local or regional anaesthesia.