Medetomidine-ketamine anaesthesia induction followed by medetomidine-propofol in ponies: infusion rates and cardiopulmonary side effects.
BACKGROUND
To search for long-term total i.v. anaesthesia techniques as a potential alternative to inhalation anaesthesia.


OBJECTIVE
To determine cardiopulmonary effects and anaesthesia quality of medetomidine-ketamine anaesthesia induction followed by 4 h of medetomidine-propofol anaesthesia in 6 ponies.


METHODS
Sedation consisted of 7 microg/kg bwt medetomidine i.v. followed after 10 min by 2 mg/kg bwt i.v. ketamine. Anaesthesia was maintained for 4 h with 3.5 microg/kg bwt/h medetomidine and propofol at minimum infusion dose rates determined by application of supramaximal electrical pain stimuli. Ventilation was spontaneous (F(I)O2 > 0.9). Cardiopulmonary measurements were always taken before electrical stimulation, 15 mins after anaesthesia induction and at 25 min intervals.


RESULTS
Anaesthesia induction was excellent and movements after pain stimuli were subsequently gentle. Mean propofol infusion rates were 0.89-0.1 mg/kg bwt/min. No changes in cardiopulmonary variables occured over time. Range of mean values recorded was: respiratory rate 13.0-15.8 breaths/min; PaO2 29.1-37.9 kPa; PaCO2 6.2-6.9 kPa; heart rate 31.2-40.8 beats/min; mean arterial pressure 90.0-120.8 mmHg; cardiac index 44.1-59.8 ml/kg bwt/min; mean pulmonary arterial pressure 11.8-16.4 mmHg. Recovery to standing was an average of 31.1 mins and ponies stood within one or 2 attempts.


CONCLUSIONS
In this paper, ketamine anaesthesia induction avoided the problems encountered previously with propofol. Cardiovascular function was remarkably stable. Hypoxaemia did not occur but, despite F(I)O2 of > 0.9, minimal PaO2 in one pony after 4 h anaesthesia was 8.5 kPa.


CONCLUSIONS
The described regime might offer a good, practicable alternative to inhalation anaesthesia and has potential for reducing the fatality rate in horses.
Bettschart-Wolfensberger
R
R
Department of Farm Animal and Equine Medical Surgery, The Royal Veterinary College, University of London, Hatfield, UK.
Bowen
I M
IM
Freeman
S L
SL
Weller
R
R
Clarke
K W
KW
D000778:Anesthetics, Dissociative / Q000008:administration & dosage* / Q000009:adverse effects; D018686:Anesthetics, Intravenous / Q000008:administration & dosage* / Q000009:adverse effects; D000818:Animals; D001794:Blood Pressure / Q000187:drug effects; D004359:Drug Therapy, Combination; D006339:Heart Rate / Q000187:drug effects; D006736:Horses / Q000502:physiology*; D006993:Hypnotics and Sedatives / Q000008:administration & dosage* / Q000009:adverse effects; D007262:Infusions, Intravenous / Q000662:veterinary; D007649:Ketamine / Q000008:administration & dosage* / Q000009:adverse effects; D020926:Medetomidine / Q000008:administration & dosage* / Q000009:adverse effects; D015742:Propofol / Q000008:administration & dosage* / Q000009:adverse effects; D012119:Respiration / Q000187:drug effects
D000778:Anesthetics, Dissociative; D018686:Anesthetics, Intravenous; D006993:Hypnotics and Sedatives; D007649:Ketamine; D020926:Medetomidine; D015742:Propofol