Source: Anesth Analg 2001;93:697-702

Reviewer:  John F. Heath, M.D.

Summary:

• Twenty-eight dogs were studied (in two groups of fourteen each) to determine the effects of ketamine on cerebral arterioles.
• Part 1
• dogs induced with pentobarbital
• maintenance anesthetic of pentobarbital (2 mg/kg/hr) or isoflurane (1-1.2 MAC).
• After intubation, invasive lines were placed (arterial and sagittal sinus catheters) and a closed cranial window technique was used to directly observe the pial arterioles.
• The dogs received three different concentrations of topical ketamine (1:10 million, 1:100,000, and 1:1000 Molar).
• Measurements of inner diameters of four pial arterioles were taken using a videomicrometer attached to a microscope.
• Part 2
• dogs were given a baseline hypercapnic challenge (paCO2 60mmHg)
• measurements of pial arteriole inner diameters were taken as previously described.
• Next, dogs were given IV ketamine in doses of 1mg/kg and (one hour later) 5mg/kg.
• Measurements of pial arteriole inner diameters were repeated after another hypercapnic challenge within 10 minutes of each dose of IV ketamine.
• Results
• Part 1
• no changes in pial arteriole diameter at any concentration of topical ketamine.
• no significant changes in MAP, heart rate, ABG's, or sagittal sinus pH.
• Part 2
• no significant changes in hemodynamic values (including cerebral oxygen extraction) or pial arteriole diameters with either concentration of IV ketamine.
• However, there was a tendency for IV ketamine to increase vasoconstriction in the isoflurane group compared to the pentobarbital group.  Larger arterioles were affected at the 1mg/kg dose, and smaller arterioles were also affected at the 5mg/kg dose of IV ketamine.
• Also, IV ketamine significantly attenuated the pial arteriolar reactivity induced by hypercapnia as compared to control conditions (i.e. less cerebral arteriolar vasodilation after ketamine).
• Conclusions
• Therefore, IV ketamine may not produce cerebral vasodilation or significant changes in MAP or cerebral oxygen extraction depending on the background anesthetic.
• In addition, IV ketamine may attenuate the cerebral arteriole vasodilation seen in response to hypercapnia.