Effects of methoxyflurane on intraocular and cerebrospinal fluid pressure in dogs with spontaneous or artificial respiration

Abstract

Methoxyflurane (0.2 ml/kg over 5 min), administered by inhalation to dogs with spontaneous respiration, resulted approximately 10 minutes later in a significant increase of intraocular pressure (IOP) (13.3 mm Hg), cerebrospinal fluid pressure (CSFP) (9.4 mm Hg), and venous pressure (VP) (6 mm Hg), as well as a significant decrease in arterial pressure (AP) (23.3 mm Hg), respiratory frequency (3.2 mov/min) and respiratory amplitude (7.1 mm). These alterations occurred concomitantly with respiratory acidosis, an increase in serum K+ and Cl-, increased osmolarity of the aqueous humor, and an elevation of K+ and Cl- in cerebrospinal fluid (CSF). However, if CSF was allowed to drain freely so that no increase of CSFP occurred, there was only a small increase of IOP (3.7 mm Hg). Under these latter conditions, there also was a decrease of arterial pressure (20.7 mm Hg), respiratory frequency (9.5 mov/min) and respiratory amplitude (2.1 mm). When dogs were ventilated artificially the above changes were greatly attenuated. They were limited to a small but significant rise of CSFP (4.7 mm Hg), a decrease in AP (20.7 mm Hg) and a decrease of HCO3- (7.6 mEq/) of arterial blood. The possible mechanisms involved in the action of methoxyflurane on IOP were discussed and it was pointed out that this anesthetic agent might be used for inducing anesthesia; however, it would be necessary to avoid respiratory depression, in order to prevent intracranial and ocular hypertension.