Tierärztliche Hochschule Hannover Vergleichende Studie zur

Publikation 2
resulting from procedures below the umbilicus (Kehlet 1984, Kehlet 1988). A
complete sympathetic and somatic blockade of the surgical site, affecting not only the
nociceptive, but also non-nociceptive pathways, such as the sympathetic innervation
to the adrenal glands however, requires an extensive epidural anaesthesia reaching
from T4 to S5 (Engquist et al. 1977). According to Meyer et al. (2007), a caudal
epidural application of 0.4 ml kg -1 BW (20 ml into a 50 kg calf) of contrast medium in a
calf migrated cranially as far as the T12, hence we assume that applying 0.6 ml kg -1
BW as performed in this study, will still be insufficient to induce the anaesthesia
necessary to induce complete sympathetic and somatic blockage. Thus, the local
release of stress response mediators from the surgical site extending cranially of the
umbilicus and the dose related lack of extent of neuronal blockage may explain the
incomplete effects of the EPI-anaesthesia on the stress response to umbilical
surgery. Application of higher volumes risks blocking the phrenical nerve, originating
in the fifth to seventh cervical segment, and thus causing a motor blockage of the
diaphragm, which would in turn require intubation and diligent monitoring by a
qualified assistant.
The effects of dorsal recumbancy in this study are in accordance with results of
Meyer et al. (2009). The change in positioning leads to compression of the caval vein
by abdominal viscera and, in consequence, reduces venous pre-load in all calves.
This, in addition to xylazines’ bradycardic effect and depression of cardiac
contractility (Campbell et al. 1979; Knight 1980) causes an initial significant reduction
in CO and MAP (Antonaccio et al. 1973). Statistically significant differences among
cardiovascular parameters of the three groups after inducing anaesthesia and before
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