Faculty Collaboration Database

Region of epidural blockade determines sympathetic and mesenteric capacitance effects in rabbits. Anesthesiology 1995 Sep;83(3):604-10

Date

09/01/1995

Pubmed ID

7661361

DOI

10.1097/00000542-199509000-00020

Scopus ID

2-s2.0-0029078529 (requires institutional sign-in at Scopus site)   60 Citations

Abstract

BACKGROUND: The mechanisms producing hemodynamic changes during epidural anesthesia are incompletely understood. The role of capacitance changes in the splanchnic venous bed can be clarified by comparing blocks of differing segmental distributions. Specifically, we speculated that blocks that include the innervation to the mesenteric circulation alter hemodynamics, sympathetic activity, and venous capacitance to a greater extent than blocks without blockade of sympathetic nerves to this critical vascular bed.

METHODS: Rabbits were studied during alpha-chloralose anesthesia and mechanical ventilation. Sympathetic efferent nerve activity to the mesenteric vessels was measured by surgically placed electrodes, and mesenteric vein diameter was measured by videomicroscopy. Heart rate and mean arterial pressure were monitored by intraarterial cannulation. Responses were compared after administration of epidural lidocaine using a dose and catheter level that limited anesthetic to lumbar levels (lumbar group) or thoracic levels (thoracic group). In addition, hemodynamic responses were recorded after thoracolumbar block in animals receiving alpha-chloralose but breathing spontaneously (spontaneous ventilation group) and in awake animals (awake group).

RESULTS: Mean arterial pressure decreased 38.3 +/- 5.8% in the thoracic group but only 16.5 +/- 2.8 in the lumbar group. Sympathetic efferent nerve activity decreased in the thoracic group but increased in the lumbar group. An increase in vein diameter followed thoracic epidural anesthesia, but venoconstriction was observed after lumbar epidural block. The addition of intravenous sedation with alpha-chloralose did not increase the hypotensive effect of epidural anesthesia in this model.

CONCLUSIONS: Block of sympathetic fibers to the splanchnic circulation with thoracic epidural lidocaine produces mesenteric venodilatation that contributes to hypotension in rabbits. A lesser decrease in blood pressure follows blocks limited to lower segments, because baroreceptor stimulation produces increased splanchnic sympathetic activity and mesenteric venoconstriction. Responses in this model are comparable with and without general anesthesia and mechanical ventilation. To minimize hemodynamic consequences, epidural blockade should ideally be confined to the fewest necessary segments, avoiding splanchnic innervation if possible.

Author List

Hogan QH, Stekiel TA, Stadnicka A, Bosnjak ZJ, Kampine JP

Author

Quinn H. Hogan MD Professor in the Anesthesiology department at Medical College of Wisconsin

MESH terms used to index this publication - Major topics in bold

Anesthesia, Epidural
Animals
Hemodynamics
Male
Mesenteric Veins
Rabbits
Respiration
Splanchnic Circulation
Sympathetic Nervous System