case 40 - open eye injury and IOP Flashcards
What is normal intraocular pressure (IOP) and what effects IOP?
- normal IOP = 10-20 mm Hg
-
IOP effected by:
- aqueous humor
- choroidal blood volume
- CVP
- extraocular muscle tone
explain the factors that effect IOP?
- aqueous humor, choroidal blood volume, CVP, extraocular muscle tone
- *globe is noncompliant and surrounded by rigid orbit*
Aqueous humor
- secreted from ciliary process in posterior chamber
- eliminates through space of Fontana and Schlemm canal (corner of eyes)
- mydriatic drugs decrease these spaces, therefore decrease elimination of aqueous humor –> inc IOP
Choroidal blood volume
- increase in MAP or CVP will increase blood volume
- although vessels do not autoregulate, affected same way as CBF: PaCo2, Pa02, o2 metabolic rate, MAP.
- inc MAP, inc PaCO2, decrease PaO2, inc metbolic rate –> all inc IOP
CVP
- inc CVP will inhibit flow of aqueous humor through shlemm canal –> inc IOP
Extraocular muscle tone
- contraction inc IOP
What is the anesthetic goals for repair of open eye injury?
- Main goal - do not elevate IOP
- prevent increase IOP by manipulating the factors that affect IOP: aqueous humor elimination, CVP, choroidal blood volume (MAP/CVP), extraocular muscle tone
How can you reduce/prevent increase in IOP during eye surgery?
Reduce IOP
- elevate head to allow venous drainage
Prevent increase in IOP
- minimize pre-op sedation to avoid PaCo2 increase (hypoventilation/sedation)
- deep anesthesia - hemodynamic response to laryngoscopy and intubation
- hyperventilate (lower PaCo2)
- avoid bucking/coughing through surgery –> deep anesthesia & muscle relxation
- smooth emergence to avoid coughing
what is your anesthesia plan for open eye surgery?
prior to induction
- RSI if full stomach
- elevate head of bed (facilitate venous drainage)
- careful placement of facemask
Induction
- propofol - dec IOP
- Etomidate - dec IOP; myoclonus may cause eye injury
- SUX - ? inc IOP?; shortest time for intubation
- ROC - prolong mask ventilation may predispose to eye trauma from mask
- ETT vs LMA - LMA does not protect against laryngospasm or aspiration; no access to airway during sx
Maintenance
- deep anesthesia to dec IOP
- muscle relaxation motionless field
- hypocapnia (dec blood flow to eye), maintain adequate SaO2 (hypoxia cause inc blood flow)
Emergence
- smooth emergence
- prevent PONV
Is SUX contraindicated in open eye sx?
- major concern –> inc IOP leading to extrusion of intraocular contents
- controversial, does temporarily increase IOP, exact mech unknown
- crying, bucking & coughing (during suboptimal intubation conditions) inc IOP more (inc CVP)
-
overall - can use SUX; however, optimize other conditions that may increase IOP.
- can pre-tx to attenuate inc IOP with SUX
what can you pre-tx to attentuate IOP increase with sux?
Lidocaine
- blunts inc IOP via decrease airway reactivity and HD response to intubation
Opioid
- provides deeper anesthesia, attenuates laryngoscopy response
Defasciculating dose
- potential benefit if fasciculations inc IOP (debated mechanism of sux and IOP affect)
What are advantages and disadvantages for Roc during induction?
Advantages
- avoid acute increase in IOP
Disadvantage
- duration of action may outlast length of sx
- problamatic if cannot intubate cannot ventilate situation
- onset is a little longer than SUX:
- mask ventilation applied longer awaiting peak effect of NMBDs –> eye injury with facemask
- longer period of unprotected airway
Use of ROC depends on:
- NPO status
- difficult airway??
- optimal intubaitng conditions
- minimizing increase in IOP that occurs with mask application
what nonanesthstic phamacologic agents can decrease IOP?
Mannitol
- dec aq humor formation
Azetazolamide
- carbonic anhydrase inhibitor
- interferes with aq humor formation
how do you determine wheter surgical repair of an open injury is emergent or urgent?
Always talk to the opthalmologist. Team Work.
Things to Consider
1) Is the patient “full stomach”?
2) is the eye viable or not viable?
3) risk of blindness vs risk of aspiration
* if delaying surgery places eye viablity at greater risk, sx may need to proceed despire risk of aspiration
4) Look at the whole picture… open eye injury occur with extensive trauamtic events. are there any other bodily injuries that need more immediate attention (ex intracranial trauma)?
