Effects of sedation, anesthesia, and endotracheal intubation on respiratory mechanics in adult horses.
OBJECTIVE
To determine the effects of endotracheal intubation on respiratory mechanics during xylazine sedation and xylazine-diazepam-ketamine anesthesia in adult horses.


METHODS
5 healthy adult horses.


METHODS
Measurements were derived from recordings of respiratory gas flow, and transpulmonary and transtracheal pressures. Total pulmonary resistance (RT) was partitioned into upper airway resistance (extrathoracic portion of trachea, larynx, pharynx, nasal cavity, nares; RUA) and lower airway resistance (intrathoracic portion of trachea, bronchi, bronchioles). Baseline measurements were obtained in unsedated horses, after xylazine administration, and following nasotracheal intubation (ID, 18 mm). Measurements were obtained following induction of xylazine-diazepam-ketamine anesthesia and subsequent to endotracheal intubations (ID, 22, 20, and 16 mm). During recovery, horses were nasotracheally intubated (ID, 18 mm). Measurements were obtained upon standing, and repeated after extubation. Data were examined by use of ANOVA with repeated measures.


RESULTS
Significant increases in mean work of breathing (W), RT, and RUA observed with xylazine sedation were variably attenuated by nasotracheal intubation. During xylazine-diazepam-ketamine anesthesia, the highest mean values for W, RT, RUA, transpulmonary and transtracheal pressures developed during non-intubation periods. The magnitudes of resistance and pressure values were inversely proportional to the internal diameter of the endotracheal tube. At recovery, values of the W and all measurements of resistances and pressures were significantly increased, compared with presedation values. Extubation resulted in further increases in these measurements.


CONCLUSIONS
Work of breathing in horses is substantially increased when RUA is increased during xylazine sedation and xylazine-diazepam-ketamine anesthesia. Endotracheal intubation reduces W by reducing RUA.
Tomasic
M
M
Department of Clinical Studies/New Bolton Center, School of Veterinary Medicine, University of Pennsylvania, Kennett Square 19348, USA.
Mann
L S
LS
Soma
L R
LR
D000403:Airway Resistance / Q000187:drug effects / Q000502:physiology; D000704:Analysis of Variance; D000777:Anesthetics / Q000008:administration & dosage / Q000494:pharmacology*; D000778:Anesthetics, Dissociative / Q000008:administration & dosage / Q000494:pharmacology; D018686:Anesthetics, Intravenous / Q000008:administration & dosage / Q000494:pharmacology; D000818:Animals; D003975:Diazepam / Q000008:administration & dosage / Q000494:pharmacology; D004338:Drug Combinations; D006736:Horses / Q000502:physiology*; D006993:Hypnotics and Sedatives / Q000008:administration & dosage / Q000494:pharmacology*; D007442:Intubation, Intratracheal / Q000379:methods / Q000662:veterinary*; D007649:Ketamine / Q000008:administration & dosage / Q000494:pharmacology; D007830:Larynx / Q000502:physiology; D009305:Nasopharynx / Q000502:physiology; D015656:Respiratory Mechanics / Q000187:drug effects* / Q000502:physiology*; D014132:Trachea / Q000502:physiology; D014991:Xylazine / Q000008:administration & dosage / Q000494:pharmacology
D000777:Anesthetics; D000778:Anesthetics, Dissociative; D018686:Anesthetics, Intravenous; D004338:Drug Combinations; D006993:Hypnotics and Sedatives; D014991:Xylazine; D007649:Ketamine; D003975:Diazepam