Objective—To characterize respiratory reflexes elicited
by nasal administration of sevoflurane (Sevo),
isoflurane (Iso), or halothane (Hal) in anesthetized
Animals—8 healthy Beagles.
Procedure—A permanent tracheostomy was created
in each dog. Two to 3 weeks later, dogs were anesthetized
by IV administration of thiopental and α-chloralose.
Nasal passages were isolated such that
inhalant anesthetics could be administered to the
nasal passages while the dogs were breathing 100%
O2 via the tracheostomy. Respiratory reflexes in
response to administration of each anesthetic at 1.2
and 2.4 times the minimum alveolar concentration
(MAC) and the full vaporizer setting (5%) were recorded.
Reflexes in response to administration of 5% of
each anesthetic also were recorded following administration
of lidocaine to the nasal passages.
Results—Nasal administration of Sevo, Iso, and Hal
induced an immediate ventilatory response characterized
by a dose-dependent increase in expiratory time
and a resulting decrease in expired volume per unit of
time. All anesthetics had a significant effect, but for
Sevo, the changes were smaller in magnitude.
Responses to administration of each anesthetic were
attenuated by administration of lidocaine to the nasal
Conclusions and Clinical Relevance—Nasal administration
of Sevo at concentrations generally used for
mask induction of anesthesia induced milder reflex
inhibition of breathing, presumably via afferent neurons
in the nasal passages, than that of Iso or Hal.
Respiratory reflexes attributable to stimulation of the
nasal passages may contribute to speed of onset and
could promote a smoother induction with Sevo, compared
with Iso or Hal. (Am J Vet Res 2001;62:311–319)