Respiratory reflexes in response to nasal administration of halothane to anesthetized, spontaneously breathing dogs.
OBJECTIVE
To characterize and determine the sensory innervation of respiratory reflexes elicited by nasal administration of halothane to dogs.


METHODS
10 healthy Beagles.


METHODS
Dogs underwent permanent tracheostomy and, 2 to 3 weeks later, were anesthetized with thiopental and alpha-chloralose administered IV. The nasal passages were functionally isolated so that halothane could be administered to the nasal passages while dogs were breathing 100% O2 via the tracheostomy. Respiratory reflexes in response to administration of halothane at concentrations of 1.25, 1.75, and 2.5 times the minimum alveolar concentration (MAC), and 5% (administered in 100% O2 at a flow rate of 5 L/min) were recorded. Reflexes in response to administration of 5% halothane were also recorded following transection of the infraorbital nerve, transection of the caudal nasal nerve, and nasal administration of lidocaine.


RESULTS
Nasal administration of halothane induced an inhibition of breathing characterized by a dose-dependent increase in expiratory time and a resultant decrease in expired volume per unit time. Effects were noticeable immediately after the onset of halothane administration and lasted until its cessation. Reflex responses to halothane administration were attenuated by transection of the caudal nasal nerve and by nasal administration of lidocaine, but transection of the infraorbital nerve had no effect.


CONCLUSIONS
Nasal administration of halothane at concentrations generally used for mask induction of anesthesia induces reflex inhibition of breathing. Afferent fibers in the caudal nasal nerve appear to play an important role in the reflex inhibition of breathing induced by halothane administration.
Mutoh
T
T
Laboratories of Veterinary Surgery, Graduate School of Agricultural and Life Sciences, The University of Tokyo, Japan.
Kanamaru
A
A
Tsubone
H
H
Nishimura
R
R
Sasaki
N
N
D000281:Administration, Intranasal; D018685:Anesthetics, Inhalation / Q000008:administration & dosage*; D018686:Anesthetics, Intravenous; D000779:Anesthetics, Local / Q000008:administration & dosage; D000818:Animals; D002698:Chloralose; D004285:Dogs / Q000502:physiology*; D004305:Dose-Response Relationship, Drug; D005260:Female; D006221:Halothane / Q000008:administration & dosage*; D008012:Lidocaine / Q000008:administration & dosage; D008297:Male; D009297:Nasal Mucosa / Q000294:innervation; D012018:Reflex / Q000187:drug effects*; D012119:Respiration / Q000187:drug effects*; D012129:Respiratory Function Tests / Q000662:veterinary; D013874:Thiopental; D014139:Tracheostomy / Q000662:veterinary; D014276:Trigeminal Nerve / Q000502:physiology
D018685:Anesthetics, Inhalation; D018686:Anesthetics, Intravenous; D000779:Anesthetics, Local; D002698:Chloralose; D008012:Lidocaine; D013874:Thiopental; D006221:Halothane