Repeated anaesthesia with isoflurane and medetomidine-midazolam-fentanyl in guinea pigs and its influence on physiological parameters

Abstract

Repeated anaesthesia may be required in experimental protocols and in daily veterinary practice, but anaesthesia is known to alter physiological parameters in GPs (Cavia porcellus, GPs). This study investigated the effects of repeated anaesthesia with either medetomidine-midazolam-fentanyl (MMF) or isoflurane (Iso) on physiological parameters in the GP. Twelve GPs were repeatedly administered with MMF or Iso in two anaesthesia sets. One set consisted of six 40-min anaesthesias, performed over 3 weeks (2 per week); the anaesthetic used first was randomized. Prior to Iso anaesthesia, atropine was injected. MMF anaesthesia was antagonized with AFN (atipamezole-flumazenil-naloxone). Abdominally implanted radio-telemetry devices recorded the mean arterial blood pressure (MAP), heart rate (HR) and core body temperature continuously. Additionally, respiratory rate, blood glucose and body weight were assessed. An operable state could be achieved and maintained for 40 min in all GPs. During the surgical tolerance with MMF, the GPs showed a large MAP range between the individuals. In the MMF wake- up phase, the time was shortened until the righting reflex (RR) returned and that occurred at lower MAP and HR values. Repeated Iso anaesthesia led to an increasing HR during induction (anaesthesias 2–6), non-surgical tolerance (anaesthesias 3–6) and surgical tolerance (anaesthesias 4, 6). Both anaesthetics may be used repeatedly, as repeating the anaesthesias resulted in only slightly different physiological parameters, compared to those seen with single anaesthesias. The regular atropine premedication induced HR increases and repeated MMF anaesthesia resulted in a metabolism increase which led to the faster return of RR. Nevertheless, Iso’s anaesthesia effects of strong respiratory depression and severe hypotension remained. Based on this increased anaesthesia risk with Iso, MMF anaesthesia is preferable for repeated use in GPs.

Evaluation of injectable anaesthesia with five medetomidine-midazolam based combinations in Egyptian fruit bats (Rousettus aegyptiacus)

“…17,53 Although medetomidine, midazolam, and opioids are classified as sedatives and not anaesthetics, combinations of medetomidine-midazolam-opioid have been reported to produce surgical anaesthesia in several animal species. 17,28,54,55 Moreover, these combinations were used for conducting surgical procedures in experimental settings. 25,[29][30][31] In the present study, all five combinations induced loss of withdrawal reflex for periods of over an hour, indicating their effectiveness in inducing anaesthesia.…”

“…25 This combination was described in several animal species and is often used in research settings. 23,24,26,27 Although none of the MM-Fen components are anaesthetics per se, this combination has been shown to induce anaesthesia with surgical tolerance, 17,28 and has been used in various surgical procedures in several species, 29,30 including bats. 25,31 MM-Fen offers several advantages: (a) significant analgesia provided by fentanyl, a rapid acting synthetic opioid, 32 and medetomidine; 33 (b) good muscle relaxation, provided by midazolam and medetomidine; 33,34 (c) amnesia, an important feature of surgical anaesthesia, 35 provided by midazolam; 36,37 and (d) rapid and complete antagonization with atipamezole, flumazenil, and naloxone, 23 reducing the risk of anaesthetic related morbidity or mortality.…”

Nitrous oxide improves cardiovascular, respiratory, and thermal stability during prolonged isoflurane anesthesia in juvenile guinea pigs

“…Animals were randomized using a computerized method (RAND function in Microsoft Excel) at commencement of study, 34 to isoflurane alone (ISO: 1.5%) or isoflurane + N 2 O (ISO+ N 2 O: 0.8% +70%). A 3‐day recovery washout period was given between anesthetic regimens 16,35 . Guinea pigs were housed individually in a 12:12 h light and temperature‐controlled environment, with ad libitum access to standard guinea pig chow (Specialty Feeds, Glen Forrest, Australia) and vitamin C‐enriched water.…”

“… 12 Currently, the favored agents in guinea pigs are ketamine/xylazine and isoflurane 4,13–15 . While injectable agents induce less cardiorespiratory depression in guinea pigs, 16 establishing and maintaining stable vascular access necessary to sustain an appropriate anesthetic plane is difficult to achieve. As such, isoflurane is often preferred due to its ease of titration, steady maintenance, and rapid withdrawal 13 .…”

Tendencies and perspectives of central alpha2-adrenomimetic application in medicobiological research

“…With sedation caused by α2-AM, a decrease in body temperature may occur. In general, a decrease in temperature under the influence of α2-AM may be associated with inhibition of CNS and a decrease in motor activity [38].…”