Effect of low dose rate ketamine infusions on thermal and mechanical thresholds in conscious cats

Effects of dexmedetomidine or tramadol continuous rate infusions on the propofol requirements and cardiorespiratory variables in propofol-ketamine-midazolam anaesthetised cats

The aim of this study was to compare the effects of midazolam-ketamine alone or in combination with dexmedetomidine or tramadol in a constant rate infusion (CRI) on the minimum infusion rate (MIR) of propofol and the cardiorespiratory function in cats undergoing an ovariohysterectomy (OH). This was a prospective, randomised, blinded clinical study. Twenty-four healthy female mixed-breed cats were premedicated with ketamine and midazolam. Propofol was used for the induction and maintenance of the anaesthesia (starting at 18 mg/kg/h). Cats were assigned to groups (n = 8) to receive one of the following intravenous treatments: midazolam-ketamine group (MKG; ketamine 0.6 mg/kg/h); midazolam-ketamine-dexmedetomidine group [MKDG; ketamine 0.6 mg/kg/h and dexmedetomidine loading dose (LD) 1 mg/kg, CRI 1 mg/kg/h)] or midazolam-ketamine-tramadol group [MKTG; ketamine 0.6 mg/kg/h and tramadol (LD 2 mg/kg, CRI 1 mg/kg/h)]. During the OH, the propofol infusion was adjusted based on the clinical signs to maintain adequate anaesthetic depth. Selected variables were measured before (T0) and after (T1) the anaesthesia induction and during six surgical time points (T2-T7). The mean arterial pressure was higher and the heart rate was lower in MKDG at T1 (than in MKG and MKTG). The mean ± SD MIR of propofol were 17.4 ± 3.2, 15.0 ± 2.8 and 12.6 ± 3.5 mg/kg/h for MKG, MKTG, and MKDG, respectively. We conclude that, compared to midazolam-ketamine alone, midazolam-ketamine-tramadol and midazolam-ketamine-dexmedetomidine reduced the MRI of propofol by 13.8% and 27.5%, respectively, without significant changes in the selected indicators.

Ketamine and sleep modulate neural complexity dynamics in cats

There is increasing evidence that the level of consciousness can be captured by neural informational complexity: for instance, complexity, as measured by the Lempel Ziv (LZ) compression algorithm, decreases during anaesthesia and non-rapid eye movement (NREM) sleep in humans and rats, when compared with LZ in awake and REM sleep. In contrast, LZ is higher in humans under the effect of psychedelics, including subanaesthetic doses of ketamine. However, it is both unclear how this result would be modulated by varying ketamine doses, and whether it would extend to other species. Here, we studied LZ with and without auditory stimulation during wakefulness and different sleep stages in five cats implanted with intracranial electrodes, as well as under subanaesthetic doses of ketamine (5, 10, and 15 mg/kg i.m.). In line with previous results, LZ was lowest in NREM sleep, but similar in REM and wakefulness. Furthermore, we found an inverted U-shaped curve following different levels of ketamine doses in a subset of electrodes, primarily in prefrontal cortex. However, it is worth noting that the variability in the ketamine dose-response curve across cats and cortices was larger than that in the sleep-stage data, highlighting the differential local dynamics created by two different ways of modulating conscious state. These results replicate previous findings, both in humans and other species, demonstrating that neural complexity is highly sensitive to capture state changes between wake and sleep stages while adding a local cortical description. Finally, this study describes the differential effects of ketamine doses, replicating a rise in complexity for low doses, and further fall as doses approach anaesthetic levels in a differential manner depending on the cortex.

Feline procedural sedation and analgesia: When, why and how

PRACTICAL RELEVANCE

Procedural sedation and analgesia (PSA) describes the process of depressing a patient's conscious state to perform unpleasant, minimally invasive procedures, and is part of the daily routine in feline medicine. Maintaining cardiopulmonary stability is critical while peforming PSA.

CLINICAL CHALLENGES

Decision-making with respect to drug choice and dosage regimen, taking into consideration the cat's health status, behavior, any concomitant diseases and the need for analgesia, represents an everyday challenge in feline practice. While PSA is commonly perceived to be an uneventful procedure, complications may arise, especially when cats that were meant to be sedated are actually anesthetized.

AIMS

This clinical article reviews key aspects of PSA in cats while exploring the literature and discussing complications and risk factors. Recommendations are given for patient assessment and preparation, clinical monitoring and fasting protocols, and there is discussion of how PSA protocols may change blood results and diagnostic tests. An overview of, and rationale for, building a PSA protocol, and the advantages and disadvantages of different classes of sedatives and anesthetics, is presented in a clinical context. Finally, injectable drug protocols are reported, supported by an evidence-based approach and clinical experience.

Evaluation of tumescent local anesthesia in cats undergoing unilateral mastectomy

OBJECTIVE

To evaluate the analgesic efficacy and safety of tumescent local anesthesia (TLA) in cats undergoing unilateral mastectomy.

STUDY DESIGN

Prospective clinical trial.

ANIMALS

A total of 12 ovariohysterectomized female cats.

METHODS

All animals were premedicated with pethidine (4 mg kg^-1) intramuscularly (IM), followed by induction of anesthesia with propofol (5 mg kg^-1) intravenously and maintenance with isoflurane in oxygen. A refrigerated TLA solution (15 mL kg^-1, 8 °C) was injected using a Klein cannula. The solution was composed of 0.5 mL of epinephrine (1 mg mL^-1) and 40 mL of 2% lidocaine added to 210 mL lactated Ringer's solution (final lidocaine concentration 0.32%). Heart and respiratory rates, systolic arterial blood pressure, temperature and oxygen saturation were measured during anesthesia. Blood samples were collected from the jugular vein for measurement of plasma lidocaine concentration using high performance liquid chromatography. Postoperative pain scores were evaluated hourly for 6 hours. Analgesic rescue was performed with tramadol (2 mg kg^-1) IM and meloxicam (0.15 mg kg^-1) subcutaneously.

RESULTS

Plasma lidocaine concentration peaked at 90 minutes after injection of TLA, but no concentration considered toxic for the species was measured. The median postoperative analgesia time was 6 hours after injection of TLA.

CONCLUSIONS

This study found that TLA prevented sympathetic response to noxious stimuli during anesthesia and provided satisfactory postoperative analgesia in cats submitted to total unilateral mastectomy, with no apparent signs of toxicity.

CLINICAL RELEVANCE

TLA can prevent sympathetic stimulation resulting from noxious stimuli during anesthesia, promoting good intraoperative conditions, proving to be a viable addition to analgesia in cats submitted to a total unilateral mastectomy.

Feline Neuropathic Pain

Neuropathic pain represents the extreme in maladaptive pain processing. In itself, it is a disease in which pain has become exaggerated in some combination of scope, severity, character, field, duration, and spontaneity. It is almost certainly an underappreciated, underdiagnosed cause of possible significant patient morbidity in cats. This article explores the basic mechanisms, recognition, known and suspect syndromes, and prospective treatment of feline maladaptive and neuropathic pain.

Use of nociceptive threshold testing in cats in experimental and clinical settings: a qualitative review

OBJECTIVE

The objective of this study was to review the scientific articles on the use of nociceptive threshold testing (NTT) in cats and to summarize the clinical and experimental applications in this species.

DATABASES USED

Pertinent literature was searched with PubMed, Scopus, Web of Science, Universitätsbibliothek Basel (swissbib Basel Bern) and Google Scholar. The search was then refined manually based first on article titles and abstracts, and subsequently on full texts.

CONCLUSIONS

Of the four classical acute nociceptive models used for NTT, thermal and mechanical are most commonly used in cats. Thermal stimulation is applicable in experimental settings and has been used in pharmacodynamics studies assessing feline antinociception. Although mechanical stimulation is currently less used in cats, in the future it might play a role in the evaluation of clinical feline pain. However, the low response reliability after stimulus repetition within a narrow time interval represents a major limitation for the clinical use of mechanical thresholds in this species. Challenges remain when thermal thresholds are used to investigate analgesics that have the potential to affect skin temperature, such as opioids and α2-adrenergic agonists, and when a model of inflammatory pain is reproduced in experimental cats with the purpose of evaluating non-steroidal anti-inflammatory drugs as analgesics.

Multimodal analgesia for treatment of allodynia and hyperalgesia after major trauma in a cat

Case summary

A 2-year-old polytraumatized male cat was admitted to a teaching hospital for correction of a defective inguinal herniorrhaphy. Upon arrival, the cat showed signs of neuropathic pain, including allodynia and hyperalgesia. Analgesic therapy was initiated with methadone and metamizole; however, 24 h later, the signs of pain continued. Reparative surgery was performed, and a multimodal analgesic regimen was administered (methadone, ketamine, wound catheter and epidural anesthesia). Postoperatively, the cat showed signs of severe pain, assessed using the UNESP-Botucatu multidimensional composite pain scale. Rescue analgesia was initiated, which included methadone, bupivacaine (subcutaneous wound-diffusion catheter) and transversus abdominis plane block. Because the response was incomplete, co-adjuvant therapy (pregabalin and electroacupuncture) was then implemented. Fourteen days after admission, the patient was discharged with oral tramadol and pregabalin for at-home treatment.

Relevance and novel information

Neuropathic pain is caused by a primary lesion or dysfunction in the nervous system and is a well-described complication following trauma, surgical procedures such as hernia repair, and inadequate analgesia. The aims of this report are to: (1) describe a presentation of neuropathic pain to highlight the recognition of clinical signs such as allodynia and hyperalgesia in cats; and (2) describe treatment of multi-origin, severe, long-standing, ‘mixed’ pain (acute inflammatory with a neuropathic component). The patient was managed using multiple analgesic strategies (multimodal analgesia), including opioids, non-steroidal anti-inflammatory drugs, locoregional anesthesia, co-adjuvant drugs and non-pharmacological therapy (electroacupuncture).

EEG 40 Hz Coherence Decreases in REM Sleep and Ketamine Model of Psychosis

Cognitive processes are carried out during wakefulness by means of extensive interactions between cortical and subcortical areas. In psychiatric conditions, such as psychosis, these processes are altered. Interestingly, REM sleep where most dreams occurs, shares electrophysiological, pharmacological, and neurochemical features with psychosis. Because of this fact, REM sleep is considered a natural model of psychosis. Ketamine is a non-competitive N-methyl-D-aspartate (NMDA) receptor antagonist that at sub-anesthetic dose induces psychotomimetic-like effects in humans and animals, and is employed as a pharmacological model of psychosis. Oscillations in the gamma frequency band of the electroencephalogram (EEG), mainly at about 40 Hz, have been involved in cognitive functions. Hence, the present study was conducted to analyze the EEG low gamma (30-45 Hz) band power and coherence of the cat, in natural (REM sleep) and pharmacological (sub-anesthetic doses of ketamine) models of psychosis. These results were compared with the gamma activity during alert (AW) and quiet wakefulness (QW), as well as during non-REM (NREM) sleep. Five cats were chronically prepared for polysomnographic recordings, with electrodes in different cortical areas. Basal recordings were obtained and ketamine (5, 10, and 15 mg/kg, i.m.) was administrated. Gamma activity (power and coherence) was analyzed in the abovementioned conditions. Compared to wakefulness and NREM sleep, following ketamine administration gamma coherence decreased among all cortical regions studied; the same coherence profile was observed during REM sleep. On the contrary, gamma power was relatively high under ketamine, and similar to QW and REM sleep. We conclude that functional interactions between cortical areas in the gamma frequency band decrease in both experimental models of psychosis. This uncoupling of gamma frequency activity may be involved in the cognitive features shared by dreaming and psychosis.