Neurotoxicity of perineural vs intraneural-extrafascicular injection of liposomal bupivacaine in the porcine model of sciatic nerve block

Liposomal bupivacaine is a prolonged-release local anaesthetic, the neurotoxicity of which has not yet been determined. We used quantitative histomorphometric and immunohistochemical analyses to evaluate the neurotoxic effect of liposomal bupivacaine after perineural and intraneural (extrafascicular) injection of the sciatic nerve in pigs. In this double-blind prospective randomised trial, 4 ml liposomal bupivacaine 1.3% was injected either perineurally (n = 5) or intraneurally extrafascicularly (n = 5). Intraneural-extrafascicular injection of saline (n = 5) was used as a control. After emergence from anaesthesia, neurological examinations were conducted over two weeks. After harvesting the sciatic nerves, no changes in nerve fibre density or myelin width indicative of nerve injury were observed in any of the groups. Intraneural injections resulted in longer sensory blockade than perineural (p < 0.003) without persistent motor or sensory deficit. Sciatic nerve block with liposomal bupivacaine in pigs did not result in histological evidence of nerve injury.

Total intravenous anaesthesia with propofol or propofol/ketamine in spontaneously breathing dogs premedicated with medetomidine

The cardiorespiratory parameters, the depth of anaesthesia and the quality of recovery were evaluated in six spontaneously breathing dogs that had been premedicated with medetomidine (40 microg/kg, supplemented with 20 microg/kg an hour later), administered with either propofol (1 mg/kg followed by 0.15 mg/kg/minute, intravenously), or with ketamine (1 mg/kg followed by 2 mg/kg/hour, intravenously) and propofol (0.5 mg/kg followed by 0.075 mg/kg/minute, intravenously). The dogs' heart rate and mean arterial blood pressure were higher and their minute volume of respiration and temperature were lower when they were anaesthetised with propofol plus ketamine, and a progressive hypercapnia leading to respiratory acidosis was more pronounced. When the dogs were anaesthetised with propofol/ketamine they recovered more quickly, but suffered some unwanted side effects. When the dogs were anaesthetised with propofol alone they recovered more slowly but uneventfully.

Influence of electrical stimulation on regeneration of the radial nerve in dogs

The effects of biphasic electric fields on nerve regeneration that follows injury to the left radial nerve were studied in dogs by electromyography (EMG). Left and right radial nerves were crushed with a serrated haemostat. Stimulating electrodes were positioned proximally and distally to the site of the injury. The left nerves received rectangular, biphasic and current pulses (30 microA, 0.5 Hz) through the injury for two months. The right radial nerves were treated as controls and regenerated without electrical stimulation. EMG activities were recorded intramuscularly from the left and right musculus extensor digitalis communis (MEDC). Results obtained at the end of the two-month stimulation period showed a significant difference in EMG activity between the left (stimulated) and the right (non-stimulated) MEDC, suggesting that electrical treatment enhanced nerve regeneration.

Selective recording of neuroelectric activity from the peripheral nerve

Electroneurograms (ENGs) from superficial regions of the sciatic nerve of a dog, innervating the tibialis anterior (TA) and gastrocnemius muscles (GM), arising mainly from muscle spindles and Golgi tendon organs were recorded selectively with an implanted 33-electrode spiral cuff (cuff). Relative positions of superficial regions within the cuff were defined by delivering stimulating pulses on groups of three electrodes (GTEs) within the cuff which were in contact with them. It was found that GTEs eliciting maximum contractions of muscles were GTE No. 3 for the TA muscle and GTE No. 8 for the GM muscle. In the first experiment the implanted leg was mounted into a special electronic brace. Extending forces were applied to the ankle rotating it by up to +/-37 degrees according to the neutral position, thus eliciting torques in the TA muscle of up to 1.2 Nm. Channel 1 of the 4-channel preamplifier was connected to GTE No. 8, channel 2 to GTE No. 2, channel 3 to GTE No. 11 and channel 4 to GTE No. 5. Results show that only ENG recorded with GTE No. 8, being close to the region innervating the TA muscle, correspond to the mechanical load. In the second experiment the calcanean tendon (CT) of an implanted leg was dissected. The proximal end of the CT was connected to a force transducer and repetitive pull forces (about 12 N) were applied to the CT. Channel 1 of the preamplifier was connected to GTE No. 5, channel 2 to GTE No. 1, channel 3 to the GTE No. 11 and channel 4 to GTE No. 8. Results show that only ENG recorded with GTE No. 5, being close to the region innervating the GM muscle, correspond to the mechanical load applied on CT.

Regeneration of the radial nerve in a dog influenced by electrical stimulation

The effect of biphasic electric fields on nerve regeneration that follows injury to the left radial nerve of a dog was examined using electromyography (EMG). The left and right radial nerves were crushed with a serrated hemostat and the stimulating electrodes were positioned proximally and distally relative to the site of the injury. The left nerves received rectangular, biphasic current pulses (30 microA, 0.5 Hz) through the lesion for two months. The right radial nerves were treated as controls and regenerated without electrical stimulation. EMG activity was recorded intramuscularly from left and right musculus extensor digitorum (from Medical dictionary) communis (MEDC). Results obtained at the end of the two-month stimulation period showed a significant difference between the EMG activity of the stimulated and the unstimulated MEDC suggesting that the electrical treatment enhanced the nerve regeneration.