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

Simple Summary

Standing surgery and diagnostic procedures in equine patients under deep sedation reduce the risk associated with general anesthesia. Sedation protocols must be safe, provide a good quality of sedation without producing cardiorespiratory depression and severe ataxia. The use of adrenergic alpha-2 receptors agonist in combination with opioids and/or ketamine can achieve an adequate sedation and provide sufficient analgesia for surgical procedures. Medetomidine and medetomidine with morphine in intravenous constant rate infusion have been evaluated for standing sedation but have not been compared directly. Although ketamine has been combined with other alpha-2 agonists successfully, it has not been evaluated in combination with medetomidine. The objective of this study was to compare four medetomidine-based protocols with the addition of morphine and/or ketamine, including cardiorespiratory, sedative and mechanical antinociceptive variables. All four protocols produced a similar degree of sedation and mechanical antinociception without clinically relevant impact on cardiorespiratory variables.

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.

Transition from dexmedetomidine to enteral clonidine for ICU sedation: an observational pilot study

INTRODUCTION

Enteral clonidine represents a potentially less costly alternative to dexmedetomidine for sedation in intensive care unit (ICU) patients. This study describes our practice of transitioning selected adult ICU patients from dexmedetomidine to clonidine with a focus on efficacy, safety, and drug acquisition costs.

METHODS

We conducted a single-center prospective observational pilot study from January through March 2014. Consecutive patients 18 years and older treated with dexmedetomidine and transitioned to clonidine were followed. The transition was assessed in five phases: dexmedetomidine maintenance, transition, clonidine maintenance, clonidine taper, and post clonidine. Efficacy data included any occurrence of significant pain, excessive agitation or oversedation, delirium, and need for ancillary psychoactive medications. Safety data included any occurrence of bradycardia, hypotension, new second- or third-degree atrioventricular node blockade, and clonidine withdrawal syndrome. Drug acquisition cost avoidances were estimated using average wholesale price.

RESULTS

Twenty patients were evaluated. Fifteen (75%) were successfully transitioned from dexmedetomidine within 48 hours of starting clonidine. The initial and maintenance clonidine regimens were 0.3 mg every 6 hours. Clonidine was the sole α2A -receptor agonist administered for 45 hours while in the ICU and for 54 hours outside the ICU. Fentanyl requirements were lower when clonidine was administered as the sole α2A -receptor agonist as compared to dexmedetomidine alone (387 vs. 891 μg/day, p = 0.03). Otherwise, there were no statistically significant differences in efficacy data during the dexmedetomidine and clonidine maintenance phases. No statistically significant differences in safety data were observed. Clonidine withdrawal syndrome criteria were met in one patient. The potential drug acquisition cost avoidance was $819-$2338 per patient during the 3-month study.

CONCLUSIONS

Transitioning from dexmedetomidine to clonidine may be an efficacious, safe, and less costly method of maintaining α2A -receptor agonist therapy in critically ill adults; these results warrant confirmation in expanded studies.

Continuous intravenous anaesthesia with sufentanil and midazolam in medetomidine premedicated New Zealand White rabbits

BACKGROUND

Anaesthesia in rabbits is associated with a high mortality rate, compared to that in cats and dogs. Total intravenous anaesthesia (TIVA) with drugs that provide cardiovascular stability and are rapidly metabolised could be of benefit for use in rabbits. The aim was to evaluate cardiorespiratory effects of TIVA with sufentanil-midazolam in eight New Zealand White rabbits. Subcutaneous premedication with medetomidine (0.1 mg/kg BW) was followed by IV administration of a mixture of 2.5 μg/mL sufentanil and 0.45 mg/mL midazolam at a rate of 0.3 mL/kg BW/h for anaesthetic induction. Additionally, intravenous boluses of 0.1 mL of the mixture were administered every 20 s until the righting reflex was lost. Following endotracheal intubation, anaesthesia was maintained for 60 min with an infusion rate adjusted to supress the pedal withdrawal reflex. Air and oxygen (1:2) were delivered at 3 L/min. Physiological variables were recorded before induction and at predefined time points during and after anaesthesia.

RESULTS

Righting and pedal withdrawal reflexes were lost within 3 and 5 min, respectively. Doses of sufentanil and midazolam were 0.48 μg/kg BW and 0.09 mg/kg BW for induction, and 0.72 μg/kg BW/h and 0.13 mg/kg BW/h for maintenance. Apnoea occurred in two rabbits. Induction of anaesthesia caused a significant increase in heart rate, cardiac output and arterial CO2 partial pressure and a decrease in mean arterial pressure, respiratory rate and pH. Mean time from stopping the infusion to endotracheal extubation was 5 min, and to return of the righting reflex 7 min. Anaesthesia was characterized by induction and recovery without excitation, with muscle relaxation, and absence of the pedal withdrawal reflex.

CONCLUSIONS

TIVA with sufentanil-midazolam provided smooth induction and recovery of anaesthesia in rabbits but with marked hypotension and respiratory depression, requiring mechanical ventilation. Further evaluation is needed to establish if the protocol is useful for rabbits undergoing surgery.