1.20 Intraocular Pressure

Question 1

List factors affecting IOP perioperatively

Answer 1

External factors

Internal factors

Drugs

Question 2

External factors

Answer 2

Extraocular compression

1. Anaesthetic equipment - masks
2. Surgical equipment
   Honan balloon retractors surgical hand
3. Block complications
   - high vol LA / Haematoma
4. Tumours
5. Increase tone of extrinsic eye muscles
   - fasiculations

Question 3

Internal Factors

Answer 3

Globe contents

1. Aqueous humour volume
2. Vitreous Humour Volume
   (haemorrhage increases it)
3. Choroid Volume
   2nd to Blood volume depends on
   Arterial pressure - low vol SBP<90
   Venous pressure - increae when venous drainage from head is impaired or cough / strain / Laryngoscopy
4. Presence of foreign body
   Sulphur hexafluoride
   carbon octofluoride bubble
5. Tumours

Question 4

Drugs

Answer 4

1. All IV inductions ↓
   (ketamine increase)
2. All volatile ↓ moderate
3. Sux ↑ up to 50%
4. N2O will ↑
   if sulphur hex / carb octa is used
5. Acetazolamide (inhibit carbonic anhydrase) ↓ aqueous humour production
6. Mannitol ↓ vitreous humour contents
   - water removal

Question 5

Anaesthetic techniques

Induction

Answer 5

1. Careful mask ventilation to avoid globe compression
2. Ensure adequate depth prior to airway placement
   avoid cough strain
3. LMA if approp avoid laryngoscopy pressor response

4. Intubation necessary
consider lidocaine spray
opiate
short acting bbloq 
obtund pressor response to laryngoscopy

Question 6

Maintenance

Answer 6

5. IV maintenance tci prop remi
   smooth intraop course
   emergence
   NDMB intraop PRN
6. Aim minimise venous congestion
   - normal etCO2 w/ IPPV
   - Tape airway securely (tying)
   - neutral neck
   - 15-20’ reverse trendelenburg position
7. IV anti emetics
   PONV
8. Avoid surgery in BP
   Adequate anaesthesia / analgesia / muscle relax
9. Avoid N2O if sulphur hexafluoride used