A study of cardiovascular function under controlled and spontaneous ventilation in isoflurane-medetomidine anaesthetized horses.
OBJECTIVE
To determine, in mildly hypercapnic horses under isoflurane-medetomidine balanced anaesthesia, whether there is a difference in cardiovascular function between spontaneous ventilation (SV) and intermittent positive pressure ventilation (IPPV).


METHODS
Prospective randomized clinical study.


METHODS
Sixty horses, undergoing elective surgical procedures under general anaesthesia: ASA classification I or II.


METHODS
Horses were sedated with medetomidine and anaesthesia was induced with ketamine and diazepam. Anaesthesia was maintained with isoflurane and a constant rate infusion of medetomidine. Horses were assigned to either SV or IPPV for the duration of anaesthesia. Horses in group IPPV were maintained mildly hypercapnic (arterial partial pressure of carbon dioxide (PaCO(2)) 50-60 mmHg, 6.7-8 kPa). Mean arterial blood pressure (MAP) was maintained above 70 mmHg by an infusion of dobutamine administered to effect. Heart rate (HR), respiratory rate (f(R)), arterial blood pressure and inspiratory and expiratory gases were monitored continuously. A bolus of ketamine was administered when horses showed nystagmus. Cardiac output was measured using lithium dilution. Arterial blood-gas analysis was performed regularly. Recovery time was noted and recovery quality scored.


RESULTS
There were no differences between groups concerning age, weight, body position during anaesthesia and anaesthetic duration. Respiratory rate was significantly higher in group IPPV. Significantly more horses in group IPPV received supplemental ketamine. There were no other significant differences between groups. All horses recovered from anaesthesia without complications.


CONCLUSIONS
There was no difference in cardiovascular function in horses undergoing elective surgery during isoflurane-medetomidine anaesthesia with SV in comparison with IPPV, provided the horses are maintained slightly hypercapnic.


CONCLUSIONS
In horses with health status ASA I and II, cardiovascular function under general anaesthesia is equal with or without IPPV if the PaCO(2) is maintained at 50-60 mmHg.
Kalchofner
Karin S
KS
Vetsuisse Faculty, Equine Hospital, University of Zurich, Zurich, Switzerland. kkalchofner@vetclinics.uzh.ch
Picek
Stephanie
S
Ringer
Simone K
SK
Jackson
Michelle
M
Hässig
Michael
M
Bettschart-Wolfensberger
Regula
R
D000768:Anesthesia, General / Q000662:veterinary; D000769:Anesthesia, Inhalation / Q000009:adverse effects / Q000662:veterinary*; D018685:Anesthetics, Inhalation / Q000008:administration & dosage / Q000494:pharmacology*; D000818:Animals; D005260:Female; D006734:Horse Diseases / Q000601:surgery; D006736:Horses; D006993:Hypnotics and Sedatives / Q000008:administration & dosage / Q000494:pharmacology*; D007530:Isoflurane / Q000008:administration & dosage / Q000494:pharmacology*; D008297:Male; D020926:Medetomidine / Q000008:administration & dosage / Q000494:pharmacology*; D012119:Respiration; D012121:Respiration, Artificial / Q000662:veterinary
D018685:Anesthetics, Inhalation; D006993:Hypnotics and Sedatives; D007530:Isoflurane; D020926:Medetomidine