Few data about the electroencephalogram and its calculated indices, such as the bispectral index (BIS), have been reported in rabbits. We aimed to evaluate whether a clinically stable anesthesia was mirrored by consistent and stable BIS values and to investigate the effects of modified cerebral blood supply, due to bilateral carotid clamping and re-opening, on BIS values. We also investigated the effects of fentanyl, as an antinociceptive drug, on the BIS. Sixty-eight rabbits undergoing general anesthesia for surgical creation of carotid bifurcation aneurysms were enrolled. The BIS values were recorded at nine selected time points (TPs) during each procedure and before and after fentanyl administration. The BIS values over time were compared with two-way repeated-measures analysis of variance followed by Tukey test, while the Wilcoxon signed rank test was performed to compare values at clamping and re-opening of the carotids as well as before and after fentanyl administration. The BIS values were significantly lower during anesthesia than at the end of anesthesia and at tracheal extubation; no significant differences were found among other TPs. Adequate depth of anesthesia was mirrored by consistent BIS values among rabbits, and alteration of cerebral blood supply did not modify BIS values, except once. Following fentanyl, BIS values did not change in a clinically relevant way.

Minipigs are widely used in biomedical research for translational studies. However, information about pain elicited by experimental procedures is lacking. Non-invasive methods as quantitative sensory testing and conditioned pain modulation are particularly attractive. Our overarching aim was to explore and refine these methods for assessing post-operative pain in minipigs after myocardial infarction. As first step, we aimed at defining mechanical and thermal thresholds in healthy adults Göttingen Minipigs, evaluating their reliability, and testing their modifications after the application of a conditioning stimulus. Thresholds were assessed at different body sites before and after a painful conditioning stimulus (CS) (cuffed tourniquet) and sham CS (uncuffed tourniquet) in eleven animals. Thresholds’ reliability was assessed using interclass correlation coefficient (ICC). The effect of the CS was assessed calculating absolute change, percentage change of the thresholds and standard error of measurement. Baseline mechanical thresholds (Newton) were: left hindlimb 81 [73; 81]; left forearm 81 [72.1; 81]; right forearm 81 [76; 81]; left chest 80.5 [68; 81]; right chest 81 [76.5; 81]; left neck 81 [70.3; 81]; right neck 74.8 [62.3; 80.5]. Reliability of mechanical thresholds was good at right chest (ICC = 0.835) and moderate at left chest (ICC = 0.591), left hindlimb (ICC = 0.606) and left neck (ICC = 0.518). Thermal thresholds showed poor reliability in all the tested sites. A modulatory effect was present at right chest, but it was seen when both a painful CS and a sham CS was applied. Minipigs tendentially showed a pro-nociceptive profile (i.e. conditioning pain facilitation). The measured thresholds are a reference for future trials in this species. Mechanical thresholds showed to be more reliable and, therefore, more useful, than thermal ones. The pain facilitation might be explained by the phenomenon of stress induced hyperalgesia, but this finding needs to be further investigated with a stricter paradigm.

Introduction: Use of veno-arterial extracorporeal membrane oxygenation (VA-ECMO) is still in the focus of research, in which pigs are commonly involved. During VA-ECMO, cardiovascular parameters are artificially manipulated and therefore not reliable indicators of nociception. Nociceptive withdrawal reflex (NWR) thresholds can be a suitable alternative in such a context. This study aimed at recording and comparing NWR thresholds before and after administering spinal analgesia in healthy pigs undergoing VA-ECMO.Methods: Sixteen pigs were sedated with a mixture of ketamine, midazolam, and methadone; general anesthesia was induced with propofol and maintained with propofol and fentanyl in continuous rate infusion. Before surgery, ropivacaine 0.75% and morphine (RM) were injected via a spinal catheter (T13-L1). Nociceptive withdrawal reflex thresholds were recorded before RM (baseline) and at 40 min, end of surgery, 240, 300, 360, 420 and 480 min afterward. If after spinal analgesia NWR thresholds increased ≥20% from their baseline values, the increase was deemed clinically relevant. If NWR thresholds decreased at least 20% from their baseline values, ropivacaine alone was injected (rescue analgesia). Thresholds were compared with baseline using ANOVA on Ranks followed by Dunn’s method. At each time point, the number of pigs showing a clinically relevant increase in thresholds, thresholds higher than the maximum stimulation intensity and the need of rescue analgesia, was assessed. Nine animals were included in the final data analysis.Results: A clinically relevant increase of the thresholds was achieved in all the pigs at 240 min after the injection of RM. A statistically significant increase in NWR thresholds was found at 300 and 360 min (p = 0.009 and 0.048, respectively) compared to baseline. Rescue analgesia was required at 300 (one pig) and 420 (two pigs) and 480 (one pig) minutes.Discussion and conclusion: Nociceptive withdrawal reflex thresholds increased significantly, both clinically and statistically following spinal injection. Their increase suggests that the combination of spinal morphine and ropivacaine can last on average up to 6 h. Particularly in those scenarios where cardiovascular variables are unreliable, NWR thresholds could be useful for evaluating antinociception following spinal analgesia in pigs.

Etomidate, an agonist of the GABA A receptors, is available for clinical use either in combination with 35% propylene glycol or in a lipid emulsion. Its recognized ability to minimally impact the cardiovascular system made etomidate a suitable option for cardiac-compromised patients. Myoclonus and pain at the injection site are recognized side effects of etomidate in propylene glycol, affecting both human and veterinary species. There is no information available concerning potential side effect in minipigs. In the present case series, we report the side effects related to the use of etomidate in 35% propylene glycol in five Ellegaard Göttingen Minipigs that underwent general anesthesia for cardiac magnetic resonance imaging days or weeks after experimentally induced myocardial infarction. Following intravenous injection of etomidate, laryngeal edema and hyperemia were observed in one case. In another case, tachycardia, apnea, and decreased oxygen saturation, accompanied by laryngeal edema and hyperemia, were observed, which resolved spontaneously in a few minutes. In the arterial or venous samples collected shortly after the induction of general anesthesia, hemolysis was macroscopically visible and subsequently confirmed with a hematological exam in all five cases, as well as hemoglobinuria. Necropsies carried out immediately after euthanasia confirmed macroscopic laryngeal edema, marked diffuse lung alveolar and interstitial edema and hyperemia at histology in one animal, and marked acute lung congestion in another animal. These side effects were not observed when etomidate in a lipid emulsion was injected into another 24 animals. The role played by the different formulations (propylene glycol versus lipidic formulation) has not yet been fully elucidated. Based on our observations, we recommend caution in using the formulation of etomidate in 35% propylene glycol in Göttingen Minipigs.

To report rate of unintentional spinal puncture and compare intraoperative effects of a combination of morphine and ropivacaine at a volume of 0.2 mL kg^-1 in the lumbosacral epidural or subarachnoid space. Prospective, observational, experimental study. A total of 36 Edelschwein pigs (34 males and two females) 4 ± 0.5 months old, 55.6 ± 6.5 kg bodyweight (mean ± standard deviation). With pigs anaesthetized in sternal recumbency, an 18 gauge Tuohy needle was inserted at the lumbosacral intervertebral space intending to reach the epidural space. If the dural sac was accidentally punctured, the same volumes of ropivacaine 0.75% (1.45 mg kg^-1) and morphine (0.1 mg kg^-1) were administered spinally. Invasive blood pressure (IBP) and heart rate (HR) (n = 36) and electroencephalogram variables (n = 17) were recorded before and at regular intervals after injection. Differences in IBP over time and between groups were investigated with two-way repeated measures (RM) ANOVA. Remaining values were compared with RM ANOVA on ranks (over time) and U test (between groups, only for HR). p < 0.05. Need for rescue analgesia was reported in the 11 animals that underwent sternotomy before circulatory death. Rate of accidental spinal puncture was 36%. After epidural or spinal injection, IBP significantly decreased over time but mean arterial pressure did not decrease below the treatment cut-off (65 mmHg). There was no significant difference between groups. HR did not vary significantly over time, nor did electroencephalogram variables. Overall antinociceptive efficacy was 81.8%. Lumbosacral epidural or spinal administration of ropivacaine and morphine (0.2 mL kg-1) caused mild cardiovascular alterations, prevented autonomic responses during sternotomy and did not worsen electroencephalographic cortical depression. In pigs, reducing the volume injected when the dural sac is accidentally punctured does not seem necessary.