Cardiorespiratory, Sedative and Antinociceptive Effects of a Medetomidine Constant Rate Infusion with Morphine, Ketamine or Both

Abstract

Standing surgery under sedation reduces anesthetic-related mortality in horses. Medetomidine, alone and combined with morphine in a constant rate infusion (CRI), has been described for standing surgery but their cardiorespiratory, sedative and antinociceptive effects have never been compared. The addition of ketamine could improve analgesia in these procedures with minimal cardiorespiratory consequences. The objectives were to compare the cardiorespiratory effects, quality of sedation, antinociception and ataxia produced by administration of a medetomidine-based CRI with morphine, ketamine or both, in standing horses. A prospective, blind, randomized crossover, experimental design with six healthy adult horses was performed, in which four treatments were administered to all horses with at least two weeks of washout period: medetomidine (M); medetomidine and ketamine (MK); medetomidine and morphine (MMo); and medetomidine, morphine and ketamine (MMoK). Dosages were the same in all treatment groups: medetomidine at 5 µg/kg bwt followed by 5 µg/kg bwt/h, ketamine at 0.4 mg/kg/h and morphine at 50 µg/kg bwt, followed by morphine 30 µg/kg bwt/h. Drug infusions were maintained for 120 min. Cardiorespiratory variables, sedation degree and antinociceptive effects were evaluated during the procedure. All combinations produced similar sedation and antinociceptive effects and no clinically relevant alterations in cardiorespiratory variables occurred. Medetomidine CRI combined with morphine, ketamine or both are suitable and safe protocols for standing sedation in horses and the addition of morphine and/or ketamine did not cause any negative effect but no improving effect on sedation and antinociception was detected.

Comparison of Detomidine or Romifidine in Combination with Morphine for Standing Magnetic Resonance Imaging in Horses

“…During long-term standing procedures for horses, alpha-2 agonists are commonly used as a single bolus followed by a CRI [ 4 , 5 , 6 ]. Several studies have shown that combining alpha-2 agonists with opioids increases the level of sedation and analgesia, improves chemical restraint, and decreases the response of the animal to environmental stimulation [ 4 , 7 , 8 , 9 ]. Two studies have demonstrated that the combination of methadone and the infusion rate of detomidine improves sedation and analgesia in horses [ 14 , 22 ].…”

“…The antinociceptive, cardiorespiratory, and sedative effects of a medetomidine constant rate infusion with morphine, ketamine, or both were recently investigated in a horse [ 9 ], demonstrating that a CRI administration of 5 μg/kg of medetomidine combined with 50 μg/kg of morphine is safe and provides a proper degree of antinociception and sedation, in the absence of clinically relevant changes in cardiorespiratory variables. Similar results were obtained in this study, where the range of HR and RR remained constant in both groups, with the exception of one horse in Group D that presented tachycardia 5 min after the end of morphine inoculation.…”

“…However, the physiologic advantages of standing sedation are counterbalanced by the intrinsic complication of maintaining appropriate patient restraint [ 4 ]. To perform a surgical or diagnostic standing procedure in horses, alpha-2 adrenergic receptor agonists alone or in combination with opioids and/or ketamine are used as a single bolus, multiple boluses, or a loading dose followed by a constant rate infusion (CRI), with the aim of providing more balanced and steady-state sedation and reducing adverse effects, episodes of excessive or inadequate sedation, and ataxia [ 4 , 5 , 6 , 7 , 8 , 9 ].…”

Opioid‐free sedation for atlantoaxial cerebrospinal fluid collection in adult horses

“…Sedation protocols vary greatly in clinical practice, and objective methods for assessing sedation depth and quality are critical for studies seeking to identify optimal protocols for potentially painful procedures. Published methods of sedation assessment in horses often rely on the height of the head above the ground (HHAG) and observation of behaviors such as ataxia, or observation of behaviors such as ataxia; and chewing and head movement 20‐23 . More recently, a facial scale has been described for evaluating sedation in horses 24 .…”

“…Published methods of sedation assessment in horses often rely on the height of the head above the ground (HHAG) and observation of behaviors such as ataxia, or observation of behaviors such as ataxia; and chewing and head movement. [20][21][22][23] More recently, a facial scale has been described for evaluating sedation in horses. 24 While well-suited for assessing sedation depth in standing, undisturbed horses, these methods are not easily applied to sedated horses undergoing a potentially painful stimulus.…”