August 1, 2013 Volume 77, Number 8
ACE Question

Administration of which of the following agents is MOST likely to be associated with an increase in intraocular pressure (IOP)?

(A) Thiopental

(B) Etomidate

(C) Propofol

(D) Ketamine

Intraocular pressure (IOP), normally 10–22 mm Hg, is determined by a combination of compliance of the sclera, extraocular pressure, and changes in volume of intraocular contents:

  • Scleral compliance. Normal aging is associated with increasing rigidity of the sclera (decreased compliance). Changes in the lens (e.g., enlargement) may also reduce scleral compliance.

  • Extraocular pressure. Contraction of the extraocular muscles and increased volume of other structures in the orbit will result in increased IOP. Increased venous blood volume in the orbit is one example of a change in orbital volume that produces an increase in IOP. Multiple factors (e.g., position, coughing, vomiting) can result in increased IOP through this mechanism.

  • Intraocular volume. The primary factors that are associated with a change in intraocular volume are the hydration status of the aqueous humor and the intraocular blood volume. Of these factors, changes in venous blood volume are the more important. Any factor that causes a decrease in venous return from the eye (e.g., Trendelenburg position, cervical collar) will produce an increase in IOP.

In the perioperative period, the events associated with increased IOP that generally receive most attention include coughing, straining, or vomiting (which may increase IOP by 40 mm Hg) and laryngoscopy/tracheal intubation (which may increase IOP even in the absence of coughing).

Administration of ketamine is associated with an increase in IOP, while all other intravenous induction agents (thiopental, propofol, etomidate) produce a reduction in IOP. The high risk of postoperative nausea and vomiting may limit the usefulness of etomidate for patients undergoing ophthalmologic surgery.

Answer: D

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