62. Penetrating eye injury Flashcards
You are asked to anaesthetise a 15-year-old girl who sustained a
penetrating eye injury 1 hour ago. She is fit and well but had fish and
chips just prior to her injury.
What are the issues here?
There are two major and conflicting priorities in this case.
- The need to minimize the risk of aspiration in a patient requiring
emergency anaesthesia with a full stomach. - The need to avoid a rise in intra-ocular pressure (IOP).
What are the determinants of intra-ocular pressure?
Normal IOP is 12–20 mmHg.
The eye can be thought of in a similar way to the skull. If any of the
contents of this ‘rigid’ sphere (such as blood or aqueous humour) increase,
then the IOP will increase.
Raised IOP may be caused by direct pressure on the eye, raised CVP,
hypertension, hypercarbia, hypoxia, coughing, straining or alterations in
production/drainage of aqueous humour.
When the globe is open, the IOP is equal to atmospheric pressure, therefore
anything that would normally lead to raised IOP will lead to extrusion of
intra-ocular contents.
How do induction agents alter IOP?
Most reduce IOP with the exception of ketamine, which may cause an increase
via hypertension. (Ketamine may also cause nystagmus and blepharospasm.)
How do volatile anaesthetics alter IOP?
All modern inhalational agents reduce IOP in proportion to the depth of
anaesthesia.
The fall in BP with increasing depth of anaesthesia reduces
choroidal blood volume and relaxes the extra-ocular muscles.
The pupillary constriction aids aqueous drainage.
There may also be a direct action on
central control mechanisms.
How do muscle relaxants alter IOP?
Non-depolarising agents have minimal effect on IOP.
Suxamethonium increases IOP by around 5–10 mmHg for 5–10 minutes.
Why does suxamethonium have this effect?
The extra-ocular muscles have a more prolonged contraction compared with
other skeletal muscles due to their innervation by multiple neuromuscular
junctions (‘en-grappe’ – bunch of grapes) on each muscle fibre.
How will you manage this case?
Local anaesthesia is not suitable, as IOP will be raised by injecting around the
globe. Discuss the degree of urgency with the surgeon. It may be possible to
delay surgery until an adequate starvation time has elapsed though eye injury
may result in gastric stasis and the surgery is likely to be urgent.
The surgeon feels that the surgery is urgent and must be performed
straight away.
What will you do?
Reduce the risk of aspiration and its consequences as much as possible.
Rapid sequence induction
Obtund response to suxamethonium/laryngoscopy/intubation
This is not a life-threatening emergency. However, the surgery is urgent.
Giving metoclopramide will encourage gastric emptying, ranitidine will raise
the pH of any remaining contents and 0.3M sodium citrate will neutralise
remaining gastric acid.
Induction
The patient will require a rapid sequence induction with cricoid pressure.
The main issue is the use of suxamethonium.
If airway assessment suggests
that intubation will be straightforward, then rocuronium could be considered,
but if there is any doubt then protection of the airway should come first.
If rocuronium is used, then it is important to give it adequate time to work (at
least 60 seconds). Coughing at this stage may be disastrous. In a study of RSI
using suxamethonium in 228 patients with penetrating eye injury, there was
no loss of vitreous through the eye wound (Libonati et al., 1985).
induction agents
Fentanyl (3–5 mcg/kg), alfentanil (20 mcg/kg) or lignocaine (1.5 mg/kg)
could be used to obtund the hypertensive response to laryngoscopy.
Pre-treatment with a non-depolarising muscle relaxant will also reduce the IOP
rise associated with suxamethonium.
Remifentanil (1 mcg/kg immediately prior to induction) has also been shown
to effectively obtund the IOP response to suxamethonium and intubation.
Attention should be given to general measures to prevent a rise in IOP.
These are similar to those used in the management of raised intracranial
pressure. Anti-emetics should be given to try to prevent vomiting in the
post-operative period.
Coughing on the tube at emergence is a risk. However, if the patient is
deemed to be at risk of aspiration, then protection of the airway takes priority
and the patient should be extubated awake. If the risk is low, then consider
changing the tube for an LMA whilst still paralysed or under deep
anaesthesia.
If IOP increases intra-operatively what would you do?
Look for a cause and treat.
Other therapeutic measures
Ensure adequate depth of anaesthesia and analgesia.
Hypercarbia and hypoxia should be addressed as
should any obstruction to venous flow.
Mannitol (0.5 g/kg) or acetazolamide (500 mg) could be considered.
What is the oculo-cardiac reflex and how is it managed?
It may occur following pressure on the eyeball, traction on the extra-ocular
muscles, pain or raised IOP. There may be bradycardia, nodal rhythm, ectopic
beats, sinus arrest or even ventricular fibrillation.
The afferent passes via the ophthalmic division of the trigeminal nerve to
the sensory nucleus in the fourth ventricle. The efferent is supplied via the
vagus.
Management involves asking the surgeon to stop operating for the time
being, ensuring adequate depth of anaesthesia and analgesia and
administering atropine or glycopyrrolate if it persists.
