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Effects of acepromazine on pulmonary gas exchange and circulation during sedation and dissociative anaesthesia in horses

Authors

  • Stina Marntell DVM,

    1. Department of Large Animal Clinical Sciences, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Uppsala, Sweden
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  • Görel Nyman DVM, PhD, Diplomate ECVA,

    1. Department of Large Animal Clinical Sciences, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Uppsala, Sweden
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  • Pia Funkquist DVM, PhD,

    1. Department of Large Animal Clinical Sciences, Faculty of Veterinary Medicine, Swedish University of Agricultural Sciences, Uppsala, Sweden
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  • Göran Hedenstierna MD, PhD

    1. Department of Medical Sciences, Clinical Physiology, Uppsala University, Uppsala, Sweden
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Stina Marntell, Department of Large Animal Clinical Sciences, Swedish University of Agricultural Sciences, Box 7018, SE-75007 Uppsala, Sweden. E-mail: gorel.nyman@kirmed.slu.se

Abstract

Objective  To study pulmonary gas exchange and cardiovascular responses to sedation achieved with romifidine and butorphanol (RB) alone, or combined with acepromazine, and during subsequent tiletamine–zolazepam anaesthesia in horses.

Animals  Six (four males and two females) healthy Standardbred trotters aged 3–12 years; mass 423–520 kg.

Study design  Randomized, cross-over, experimental study.

Materials and methods  Horses were anaesthetized on two occasions (with a minimum interval of 1 week) with intravenous (IV) tiletamine–zolazepam (Z; 1.4 mg kg−1) after pre-anaesthetic medication with IV romifidine (R; 0.1 mg kg−1) and butorphanol (B; 25 µg kg−1 IV). At the first trial, horses were randomly allocated to receive (protocol ARBZ) or not to receive (protocol RBZ) acepromazine (A; 35 µg kg−1) intramuscularly (IM) 35 minutes before induction of anaesthesia. Each horse was placed in left lateral recumbency and, after tracheal intubation, allowed to breathe room air spontaneously. Respiratory and haemodynamic variables and ventilation–perfusion (inline image; multiple inert gas elimination technique) ratios were determined in the conscious horse, after sedation and during anaesthesia. One- and two-way repeated-measures anova were used to identify within- and between-technique differences, respectively.

Results  During sedation with RB, arterial oxygen tension (PaO2) decreased compared to baseline and increased inline image mismatch was evident; there was no O2 diffusion limitation or increase in intrapulmonary shunt fraction identified. With ARB, PaO2 and inline image remained unaffected. During anaesthesia, intrapulmonary shunt occurred to the same extent in both protocols, and inline image mismatching increased. This was less in the ARBZ group. Arterial O2 tension decreased in both protocols, but was lower at 25 and 35 minutes of anaesthesia in RBZ than in ARBZ. During sedation, heart rate (HR) and cardiac output (Q̇t) were lower while arterial-mixed venous oxygen content differences and haemoglobin concentrations were higher in RBZ compared with ARBZ. Total systemic vascular resistance, mean systemic, and mean pulmonary arterial pressures were higher during anaesthesia with RBZ compared to ARBZ.

Conclusions and clinical relevance  Acepromazine added to RB generally improved haemodynamic variables and arterial oxygenation during sedation and anaesthesia. Arterial oxygenation was impaired as a result of increased shunt and inline image mismatch during anaesthesia, although acepromazine treatment reduced inline image disturbances and falls in PaO2 to some extent. Haemodynamic variables were closer to baseline during sedation and anaesthesia when horses received acepromazine. Acepromazine may confer advantages in healthy normovolaemic horses.

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