Systemic and local effects of lidocaine or mepivacaine when used for intravenous regional anaesthesia of the distal limb in standing sedated horses.

BACKGROUND: Local anaesthetics are being combined clinically with amikacin in intravenous regional limb perfusion (IVRLP), with limited knowledge on the analgesia provided and its onset and duration of action after tourniquet application and release. OBJECTIVE: To evaluate the systemic clinical effect, limb withdrawal to nociceptive stimulation, and plasma and synovial fluid concentrations after IVRLP with lidocaine or mepivacaine in standing sedated horses. STUDY DESIGN: Prospective, controlled, randomised, cross-over study. METHODS: Six healthy adult horses were sedated and received IVRLP with lidocaine, mepivacaine or saline (negative control), or perineural anaesthesia of the medial and lateral palmar and palmar metacarpal nerves (positive control) in one forelimb with a 3-week washout period between trials. Electrical and mechanical stimuli were used to test nociceptive threshold of the limb before and after IVRLP/perineural anaesthesia. For lidocaine and mepivacaine trials, blood was collected from the jugular vein and synovial fluid from the radiocarpal joint before, during and out to 24 hours after IVRLP. Drug concentrations were measured using high-performance liquid chromatography. RESULTS: Nociceptive thresholds for lidocaine, mepivacaine and perineural anaesthesia trials were significantly increased compared with saline and baseline values at 10, 20 and 30 minutes, with no differences between anaesthetic trials. During this time, horses had lower heart rates than IVRLP with saline. After tourniquet release at 30 minutes, nociceptive thresholds for lidocaine and mepivacaine trials gradually returned to baselines, whereas perineural anaesthesia trial remained unchanged out to an hour. Plasma lidocaine and mepivacaine concentrations were ≤50 ng/mL while the tourniquet was in place, significantly increasing 10 minutes after tourniquet release. Maximal lidocaine and mepivacaine concentrations in synovial fluid were reached 25 minutes after IVRLP injection. MAIN LIMITATIONS: Amikacin was not included in the perfusate. CONCLUSION: Similar to perineural anaesthesia, IVRLP with lidocaine or mepivacaine provides anti-nociception to the distal limb in standing sedated horses while a tourniquet is applied with concentrations remaining below toxic levels in plasma and synovial fluid.

Anesthetic effects of isoflurane and propofol on cerebrospinal fluid biochemical markers in healthy dogs.

BACKGROUND: The study of brain energy metabolism (BEM) markers in the cerebrospinal fluid (CSF) is a potential diagnostic and prognostic tool for many central nervous system (CNS) diseases. To date, in veterinary medicine, few studies are reporting physiologic ranges for some BEM markers. Recently, the influence of anesthetic drugs on BEM markers has been described in mice; subsequently, the study of CSF-BEM markers has gained increasing attention. OBJECTIVES: The effects of anesthetic agents on BEM are poorly understood in dogs. The aim of this study was to evaluate the influence of propofol, isoflurane, and the duration of anesthesia on CSF-BEM markers in dogs. METHODS: Nine dogs were anesthetized at two different periods, one month apart. In the first period, the dogs were intravenously anesthetized with propofol (PRO-group), and in the second period, the dogs received inhalant anesthesia with isoflurane (ISO-group). In both cases, CSF and blood were collected 15 minutes (T0) and 3 hours after induction (T3) and analyzed for lactate, pyruvate, glucose, creatine kinase, glutamate, and electrolyte concentrations. RESULTS: CSF lactate (CSF-L) showed variation depending on the anesthetic agent and time, being significantly lower after 3 hours of anesthesia in the PRO-group and showing a trend to increase over time in the ISO-group. No changes were detected over time or between groups in CSF glutamate, glucose, or electrolytes. CONCLUSIONS: The results of this study support that the anesthetic drug choice and length of the general anesthesia should be considered when CSF-L analyses are interpreted in dogs.

Anaesthetic and cardiorespiratory effects of a constant rate infusion of fentanyl in isoflurane-anaesthetized sheep.

OBJECTIVE: To determine the anaesthetic and cardiorespiratory effects of a constant rate infusion of fentanyl in sheep anaesthetized with isoflurane and undergoing orthopaedic surgery. STUDY DESIGN: Prospective, randomised, 'blinded' controlled study. ANIMALS: Twenty healthy sheep (weight mean 41.1 ± SD 4.5 kg). METHODS: Sheep were sedated with intravenous (IV) dexmedetomidine (4 µg kg(-1) ) and morphine (0.2 mg kg(-1) ). Anaesthesia was induced with propofol (1 mg kg(-1)  minute(-1) to effect IV) and maintained with isoflurane in oxygen and a continuous rate infusion (CRI) of fentanyl 10 µg kg(-1)  hour(-1) (group F) or saline (group P) for 100 minutes. The anaesthetic induction dose of propofol, isoflurane expiratory fraction (Fe'iso) required for maintenance and cardiorespiratory measurements were recorded and blood gases analyzed at predetermined intervals. The quality of recovery was assessed. Results were compared between groups using t-tests or Mann-Whitney as relevant. RESULTS: The propofol induction dose was 4.7 ± 2.4 mg kg(-1) . Fe'iso was significantly lower (by 22.6%) in group F sheep than group P (p = 0). Cardiac index (mean ± SD mL kg(-1)  minute(-1) ) was significantly (p = 0.012) lower in group F (90 ± 15) than group P (102 ± 35). Other measured cardiorespiratory parameters did not differ statistically significantly between groups. Recovery times and recovery quality were statistically similar in both groups. CONCLUSIONS AND CLINICAL RELEVANCE: Fentanyl reduced isoflurane requirements without clinically affecting the cardiorespiratory stability or post-operative recovery in anaesthetized sheep undergoing orthopaedic surgery.