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Chapter: Clinical Cases in Anesthesia : Open-Eye Injury And Intraocular Pressure

How does one minimize the deleterious side-effects of these agents in the presence of a rup-tured globe?

What neuromuscular blocking agents are appropriate for the patient who is at risk for loss of intraocular contents? How does one minimize the deleterious side-effects of these agents in the presence of a rup-tured globe?

What neuromuscular blocking agents are appropriate for the patient who is at risk for loss of intraocular contents? How does one minimize the deleterious side-effects of these agents in the presence of a rup-tured globe?

Selection of a neuromuscular blocking agent for the patient at increased risk for both aspiration of abdominal contents and extrusion of ocular contents has long been controversial. For many years, succinylcholine, which is recognized to increase IOP by causing tonic contractions of extraocular muscles, was thought to be contraindicated, and the use of nondepolarizing agents was recommended. The dilemma occurred at a time when only relatively long acting agents, such as pancuronium, d-tubocurarine, and dimethylcurarine were available. Over the last 15 years, with the introduction of the intermediate-acting agents, suitable substitutes have become available. Caveats to the use of these agents under the circumstances of this case suggest that very large doses (4 times the ED95) of these drugs must be used to effect good intubating conditions. Consequently, there may be a prolonged duration of neuromuscular blockade. Using larger intubating doses of rocuronium offers intubating times and conditions similar to succinylcholine but prolongs the duration of action to similar times as vecuronium. Using similar doses of mivac-urium has a shorter duration of action than rocuronium but mivacurium has a longer onset time that may be cru-cial to securing the airway. In general, the issue of succinyl-choline and the open globe is no longer controversial. Clinicians may rest assured that there are no contraindica-tions to its use. Two separate studies by Libonati et al. (1985) and Donlon (1986) demonstrated that succinylcholine offers ideal intubating conditions with minimal risk. This is true provided that defasciculation with a nondepolarizing neuro-muscular blocker and administration of lidocaine and fen-tanyl were accomplished before intubation.

 

The ideal neuromuscular blocking agent will be one that offers rapid onset, short duration, and absence of fas-ciculations. Prolonged or difficult laryngoscopy will have a more deleterious effect on raising IOP and subsequent extrusion of intraocular contents than the choice of neuro-muscular blocking agent itself. It is important to remember during preoxygenation that suboptimal placement of the facemask can result in pressure on the globe, predisposing to extrusion of intraocular contents.

 

In this particular patient with a smoking history, airway reactivity increases the risk of coughing during patient management. The use of intravenous lidocaine and fentanyl will aid in cough suppression. Equally important is the timing of laryngoscopy and endotracheal intubation, which requires use of a neuromuscular blockade monitor. Although laryngotracheal topical anesthesia may reduce airway reactivity, it is probably ill advised. The act of spraying the larynx and trachea with local anesthesia in the awake state may cause retching or coughing. Abolition of laryn-gotracheal reflexes increases the risk of gastric content aspi-ration before endotracheal intubation and after extubation in both the awake and anesthetized patient.

 

Intravenous induction agents, such as propofol, thiopen-tal, and methohexital, reduce IOP. Narcotics, sedatives, and major tranquilizers also lower IOP, as long as ventilation is controlled because increases in PaCO2 will raise IOP.

 

Ketamine may cause nystagmus and blepharospasm, resulting in suboptimal surgical conditions. Etomidate, which reduces IOP, may cause myoclonus, which may ultimately result in an increase in IOP. Additionally, both ketamine and etomidate have been associated with higher rates of postoperative nausea and vomiting, which also detract from their usefulness in the case of the ruptured globe.

 

As previously stated, any form of respiratory acidosis will increase IOP, and respiratory alkalosis will decrease IOP. Normal ranges of PaCO2 will have little effect on IOP. Interestingly, metabolic acidosis actually reduces IOP, whereas metabolic alkalosis will increase IOP.

 

Hypoxemia and hyperthermia will lead to increased IOP. Hypothermia will reduce IOP.


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Clinical Cases in Anesthesia : Open-Eye Injury And Intraocular Pressure : How does one minimize the deleterious side-effects of these agents in the presence of a rup-tured globe? |


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