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REGIONAL ANESTHESIA AND PAIN MANAGEMENT

Acute Phase Histopathological Study of Spinally Administered Midazolam in Cats

Tomoki Nishiyama, MD, PhD^*, Takashi Matsukawa, MD, PhD, and Kazuo Hanaoka, MD, PhD^*

*Department of Anesthesiology, The University of Tokyo, Faculty of Medicine, Tokyo, Japan; and Department of Anesthesia, Yamanashi Medical University, Yamanashi, Japan

Address correspondence and reprint requests to Tomoki Nishiyama, MD, PhD, 3-2-6-603, Kawaguchi, Kawaguchi-shi, Saitama, 332-0015, Japan.

Midazolam may be a useful analgesic when administered intrathecally. However, neurotoxicity must be excluded. The purpose of this study was to investigate whether spinally administered midazolam induces acute-phase histopathological or inflammatory reactions of the spinal cord. A lumbar laminectomy was performed on 40 cats, and their spinal cords were exposed. Midazolam 10 mg (2 mL, n = 20 cats) or saline 2 mL (20 cats) was administered directly to the spinal cord. At 1, 2, 4, or 6 h after the administration, cats were killed, and the lumbar spinal cord was removed and fixed in 10% formalin. Histology was examined using light microscopy with hematoxylin and eosin staining. Both groups showed slight to moderate changes in the spinal cord, but no severe damage was observed. Inflammatory reactions were seen in only one cat in the saline group with slight neutrophil infiltration. These changes were not different between the midazolam group and the saline group. In conclusion, up to 6 h after direct exposure to midazolam, no acute histological damage or inflammatory reaction of the spinal cord was seen in cats.

Implications: Spinally administered midazolam, even in large doses, does not cause acute neurotoxicity or inflammation of the spinal cord.

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