Tierärztliche Hochschule Hannover Vergleichende Studie zur

Publikation 2
commencing surgery are only apparent in MAP, whereby the severity of hypotension
in the Group INH is greater compared to the Group INJ and EPI. Isofluranes’
vasodilatative and hypotensive effect is described in foals (Read et al. 2002), dogs
(Mutoh et al. 1997) and mice (Janssen et al. 2004), and accounts for the reduced
MAP and SVR in animals of Group INH.
Due to incomplete afferent somatic and sympathetic neural blockage, surgical stress
caused by abdominal surgery inevitably leads to a release of epinephrine and
norepinephrine immediately after incision, regardless of the anaesthetical protocol
used (Bromage et al. 1971; Traynor & Hall 1981). The positive chronotrope, inotrope
and dromotrope effects of these catecholamines on the heart are reflected in all
groups by an instantaneous increase in CO (as a product of HR and SV). In Group
EPI, HR is not elevated during the operation, yet CO is maintained by a
compensatory increase in SV. Vasoconstrictive effects of epinephrine and
norepinephrine lead to an increased SVR and MAP in Group INJ and INH, but
interestingly, not in Group EPI. Studies by Hogan et al. on rabbits (Hogan et al. 1994)
and Bromage et al. (1971) on man suggest a dilatation of capacitance vessels
evoked by sympathetic blockade following high volume caudal epidural anaesthesia.
This vasodilatation is postulated to result from passive distension of the mesenteric
veins by increased CVP, which was also observed in the Group EPI. To the best of
our knowledge, no such studies have been carried out in ruminants. If the same
mechanism applies in cattle, it would account for the reduced SVR and MAP in
Group EPI, compared to Group INH and INJ.
37