Ophthalmic anaesthesia

• An insensate eye (anaesthesia)
• A stationary eye attached to a stationary patient (akinesia)
• An unobstructed surgical field
• No increase in intra-ocular pressure (especially for eye injuries)
• A fast, cheap and efficient day-case list (where possible)

How invasive is the surgery and how long is it going to take?

• Corneal surgery is usually done under topical anaesthesia
• As are conjunctival procedures

Things like measuring intra-ocular pressure, removing superficial foreign bodies, minimal incision cataract surgery.

• Procedures going deeper into the eye such as vitreoretinal surgery often need a regional block to keep the eye still and ensure complete sensory blockade
• Long procedures or those needing strange positioning will often need general anaesthesia for patient tolerance and to ensure the eye doesn't move

Is the patient amenable to lying still for the procedure, and are they psychologically going to be able to cope with potentially seeing instruments coming towards their eye?

• Comorbidities will influence suitability and requirement for general anaesthesia
• Age - kids usually need a GA
• Axial length - a longer globe carries increased risk of blebs called staphylomata which can get punctured during regional procedures
• Of course the ol'-reliable 'allergy to local anaesthetics'
• Active significant eye infection

• Topical - quick, cheap, easy and safe but doesn't stop the eye from moving
• Regional - less quick, less cheap, less easy and less safe but better pain relief and better akinesis
• General - even more less quick and cheap but may be needed for patients who won't tolerate loco-regional anaesthesia
• Also - what is the anaesthetist most comfortable and experienced in using?

Topical

• 0.5 - 1% tetracaine
• 3.5% lidocaine
• 0.5% proxymetacaine

This theoretically anaesthetises the iris as well, because some leaches into the aqueous humour.

Lidocaine can also be directly injected into the anterior chamber by the surgeon.

Procedures can be done under local anaesthesia with or without light sedation or anxiolysis.

If you're giving very light sedation then you can just about get away without fasting the patient, however as a general rule if you're thinking a patient is going to need moderate or heavy sedation, then they need fasting like normal.

Oral

• Midazolam
• Tempazepam
• Clonidine

Intravenous

• Midazolam
• Propofol
• Remifentanil
• Fentanyl
• Alfentanil
• Dexmedetomidine

While we do love ketamine more than life itself, it does increase intra-ocular pressure, so we tend to avoid it here.

• Patients tend to have lots of comorbidities putting them at risk
• Tricky to access the head intra-operatively
• Airways can make operative field more tricky for the surgeon
• Coughing on a tube or airway can be disastrous for the eye
• Surgeon often needs to check intraocular pressure, which drugs can affect
• Often want a fast turnover day-case list
• More expensive
• Patients need to fast

To answer the question 'what are the benefits of loco-regional anaesthesia for ophthalmic surgery?', just say all of these in reverse.

The same as always - TIVA or gas and neither is convincingly better than the other.

• Volatile anaesthesia seems better at maintaining a neutral gaze
• TIVA may have a greater risk of oculo-cardiac reflex activation
• Avoid nitrous in vitreoretinal surgery if they're planning gas tamponade
• Use rocuronium to keep them seriously steady

A trigemino-vagal reflex causing bradycardia when the eye is stimulated.

How it works

Afferent Limb:

• Cranial nerve V1 (ophthalmic nerve) is triggered by stretch or pressure to the globe or extraocular muscles
• This is conducted via the trigeminal sensory nucleus to the vagus

Efferent Limb:

• Vagal stimulation of the SA node causes bradycardia or arrhythmias
• This in turn can cause hypotension

Triggers:

• Pressure on the globe
• Traction on extra-ocular muscles (particularly medial rectus)

Risk Factors:

• Age: more common in kids due to increased vagal tone
• Type of Surgery: strabismus correction, retinal detachment surgery
• Depth of Anaesthesia: more pronounced in light planes of anaesthesia

Management:

Prevention:

• Avoid lots of traction and pressure where possible
• Ensure adequately asleep if using GA
• Avoid hypercapnoea
• Atropine or glycopyrrolate prophylaxis or as emergency meds on standby

Children with a positive oculocardiac reflex are more likely to have post operative nausea and vomiting.

• Unstable angina chest pain
• Significant tachycardia or bradycardia
• Haemodynamic instability or heart failure
• Shortness of breath and evidence of anaemia
• Decreased urine output and fatigue
• Jaundice and malaise
• Severe hypertension >180/110 with evidence of organ dysfunction*

Most other issues can just be managed on the fly apparently.

*Even this is a 'consider' rather than an absolute reason to cancel.

It's often the reason they're here in the first place:

• Predisposes to cataracts
• Predisposes to retinopathy

A high HbA1c and hyperglycaemia at the time of operation unsurprisingly increases the rate of post operative complications.

Hyperglycaemia in the perioperative period can lead to:

• Endophthalmitis
• Cystoid macular oedema
• Choroidal haemorrhage
• Cardiac complications
• Wound infections
• Increased overall mortality

Elective surgery should be postponed if:

• Blood glucose <4 mmol/L with symptoms
• Blood glucose >17 mmol/L with signs or symptoms

For diabetic patients, glycaemic control can be made easier by removing the fasting requirement and doing everything under local anaesthesia, so that's nice.

The Venn diagram of patients that get neurodegenerative conditions and cataracts is rather overlappy.

Think carefully about the following:

• Dementia affects visual perception
• Cataracts affect cognition via visual perception, so operating may improve their condition
• Early or mild dementia may be amenable to local anaesthesia
• Severe or late stage dementia may require general anaesthesia
• General anaesthesia can then make post-operative cognitive decline worse
• Consent is tricky as the neurodegenerative disease progresses, and the patient may need an MDT best interest meeting

Not exactly an easy decision.

You can use the Global deterioration Scale and consider regional anaesthesia if the score is 5 or less.

• Most procedures done under local or regional anaesthesia
• Makes glycaemic control easier
• Avoids dizziness, dehydration, nausea, headache
• Some patients with gastroparesis, reflux and diabetic gastropathy would still have a full stomach after six hours anyway
• Severe complications of local techniques that end up requiring GA (brainstem anaesthesia, anaphylaxis) are very rare
• Risk of severe outcome after unfasted GA actually not that awful

If a patient definitely needs a general anaesthetic, then preoperative fasting guidelines are generally adhered to, but this isn't all that common.

Some surgeons now use a digital alignment system that requires taking pictures of the eye and retina pre- and intra-op. They use the conjunctival blood vessels as reference points, so conjunctival haemorrhage can make this difficult.

• If you're doing a needle-based block then do this after all the pictures are done

Other surgeons do femtosecond laser-assisted cataract surgery, which requires a special suction cup to hold the eye in the right place. If you've filled their conjunctiva and orbit with local anaesthetic, it can make the suction more tricky.

• You might consider topical or sub-Tenon's rather than a peribulbar block for this procedure

Some surgeons use phenylephrine in the eye to prevent floppy iris syndrome, which probably does what it says on the tin.

• Be aware of cardiovascular side effects if this gets absorbed into their blood via the nasolacrimal ducts and conjunctival and iris veins

• This carries the highest risk of all the eye goop falling out, or expulsive choroidal haemorrhage
• Therefore many surgeons prefer a deep general anaesthetic
• This allows longer time to fix things in the anterior chamber and prevents any movement that could result in bad news for all involved

Say that quickly five times.

This is an endoscopic nasal procedure that has historically been done under GA with a throat pack.

• The throat packs don't seem to add much and increase the risk of airway disaster, so don't use them routinely

• Globe perforation
• Expulsive haemorrhage (suprachoroidal or orbital)
• Brainstem anaesthesia

• You can mix local anaesthetic agents - 2% lidocaine and 0.5% bupivacaine gives the speed of lidocaine and the duration of bupivacaine
• Hyaluronidase - 5 - 150 IU/ml - is often added to increase membrane permeability

• Reduced risk of globe perforation compared to standard needle blocks
• Reduced bleeding in patients on antiplatelet and anticoagulant therapy

• Pain
• Hypertension
• Hypoxia
• Hypercarbia
• Coughing on emergence
• • Deep extubation or airway exchange for SGA if spontaneously breathing, fasted and appropriate to do so
  • Extubate on remifentanil infusion
  • Lidocaine prior to extubation
• Vomiting
• • Antiemetics
  • NG tube and gastric suction (remove tube before waking up)
  • Multimodal analgesia with reduced opioid use
• Crying
• Screaming - mainly paeds
• Eye rubbing - mainly paeds
• Breath-holding - mainly paeds
• Drugs
• • Keep them deep and paralysed to avoid hypertension and movement
  • Suxamethonium causes transient 5 - 10 mmhg increase in IOP
  • Opioids to avoid laryngeal hypertensive response
  • • Alfentanil 10 - 20 μg/kg
    • Fentanyl 3 - 5 μg/kg
    • Remifentanil at a Ce of around 4 ng/ml
    • Lidocaine 1 - 1.5 mg/kg
    • Esmolol 4 - 5 μg/kg
• Position with head up tilt
• Tape rather than tie endotracheal tube
• Avoid high airway pressures
• Aim for low-normal PaCO2
• Acetazolamide and mannitol can be considered in certain cases