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Abstract

Effects of isoflurane on peripheral microvascular function

Crystal L. Keeley 1, Christopher M. Quick 1, 2, 3

1Department of Physiology and Pharmacology,

2Department of Biomedical Engineering,

3Michael E. Debakey Institute,

Texas A&M University, College Station, TX 77843

Abstract

Objective – The goal of this study is to characterize the microvascular response to isoflurane anesthesia and to evaluate the potential of isoflurane to induce local vascular steal phenomena.

Animals or Sample Population – Our unique in vivo model for studying the microvasculature is the wing of the Pallid bat (Antrozous pallidus), which allows evaluation of both the anesthetized and unanesthetized states.

Procedure – Before looking at the microvasculature under isoflurane anesthesia, we established the correct dosage for Pallid bats by finding the minimum alveolar concentration (MAC).  We determined MAC by varying the isoflurane dose and testing to see at which dosage the withdrawal response reappeared.

In order to characterize the direct microvascular response to isoflurane, we recorded the diameter of three vessels of different sizes before and after induction of anesthesia.  To evaluate the potential for steal, we will occlude a blood vessel and measure the changes in blood flow in downstream vessels both down and across the vascular tree, then compared the response with and without isoflurane.

Results – MAC was found to be 3.025% (0.78).  Preliminary data suggest that isoflurane causes significant vasodilation in vessels larger than 30 Ám when delivered at 3.5%, or 1.16 MAC.  Unexpectedly, vasoconstriction was seen in vessels under 30 Ám, perhaps due to the myogenic response.

Conclusions and Clinical Relevance – At clinically relevant doses, isoflurane causes large amounts of vasodilation in microvessels larger than 30 μm, but not in smaller vessels.