Postoperative changes in visual evoked potentials and cognitive function tests following sevoflurane anaesthesia

The p-ERG spatial acuity in the biomedical pig under physiological conditions

Pigs are becoming an important pre-clinical animal species for translational ophthalmology, due to similarities with humans in anatomical and physiological patterns. Different models of eye disorders have been proposed, and they are good candidates to assess biocompatibility/functionality of retinal prostheses. Electroretinography is a common tool allowing to gain information on retinal function, with several types of electroretinogram (ERG) been implemented including full field (ff-ERG), multifocal (mf-ERG) and pattern (p-ERG). p-ERG represents a valuable tool to monitor Retinal Ganglion Cells (RGCs) activity and can be used to calculate p-ERG spatial acuity. Unfortunately, scarce methodological data are available regarding recording/interpretation of p-ERG and retinal acuity in biomedical pigs yet enhancing knowledge regarding pig vision physiology will allow for more refined and responsible use of such species. Aim of this study was to record p-ERG in juvenile pigs to functionally assess visual acuity. Six female hybrid pigs underwent two p-ERG recording sessions at 16 and 19 weeks of age. Photopic ff-ERG were also recorded; optical coherence tomography (OCT) and histology were used to confirm retinal integrity. ff-ERG signals were repeatable within/across sessions. All p-ERG traces consistently displayed characterizing peaks, and the progressive decrease of amplitude in response to the increment of spatial frequency revealed the reliability of the method. Mean p-ERG spatial acuities were 5.7 ± 0.14 (16 weeks) and 6.2 ± 0.15 cpd (19 weeks). Overall, the p-ERG recordings described in the present work seem reliable and repeatable, and may represent an important tool when it comes to vision assessment in pigs.

Low-hemorrhage-risk surgical approach to expose the optic nerve in rabbits without bony removal and rectus resection

OBJECTIVE

A low-hemorrhage-risk surgical approach to expose the optic nerve (ON) in rabbits through the orbital process of the frontal bone without removal of the bony orbit and resection of the rectus muscle was explored and assessed in this study. This approach will be used to investigate a new visual prosthesis that requires intraorbital ON stimulation with penetrating electrodes. Animals Chinese Albino rabbits (n = 10).

METHODS

Rabbits were classified into a surgery and a control group (five in each). In the surgery group, the ON exposure was explored by the newly proposed surgical approach. Surgical time, blood loss, visually evoked potentials (VEP) at four different scheduled time points, and H&E-stained histology of the ON at one month after surgery were recorded and analyzed to assess the ease and safety of the approach.

RESULTS

The average surgical time for the ON exposure was 16.40 +/- 1.14 min with average blood loss of 0.52 +/- 0.08 mL. Within the one-month follow-up, the ON exhibited a naturally reversible conduction change in terms of VEP amplitude. Histological examination of the ON was unremarkable. A postoperative mild ptosis of the surgical eye resolved within one month after surgery.

CONCLUSION

The ease and safety of this new surgical approach allowed it to be easily used by non-expert operators and widely applied in rabbit experiments for various research purposes requiring exposure of the ON.

Recovery of dynamic balance after additional small divided doses of midazolam given intravenously for sedation

We have previously reported that a dynamic balance test with perturbation stimuli and computerised dynamic posturography sensitively reflected the inhibitory effect on balance of intravenous midazolam sedation given intravenously as a single dose, and recovery time was within 80 min. The purpose of this study was to investigate the recovery of dynamic balance after additional doses of midazolam. Eighteen young adult male volunteers were sedated with midazolam given intravenously. The initial dose was given until the Wilson sedation score reached 3, and an additional dose was given until the same score was obtained 40 min later. They were tested with perturbation stimuli 40, 80, 100, and 120 min after the additional doses had been given. Their recovery time was recorded. The mean (S.D.) initial dose of midazolam was 0.07 (0.005) mg kg(-1), and additional doses were 41 (7)% of the initial dose. The serial changes in bispectral index after initial and additional doses were similar. The recovery time for the dynamic balance test (within 80 min) was the same as that recorded in the previous single-dose study. The recovery time of the psychomotor function test was within 75 min. Additional doses of midazolam aiming for a Wilson sedation score of 3 at a dose about 40% of the initial dose and given 40 min after the initial dose are valid in terms of the maintenance of sedation and recovery of dynamic balance. Complete recovery time, including psychomotor function, was within 80 min of the additional dose of the drug.

Pharmacology of modern volatile anaesthetics

The volatile anaesthetics sevoflurane and desflurane feature new and promising properties. Their low blood and tissue solubility enables rapid onset of and emergence from anaesthesia, thus enhancing patient safety and comfort. This article is designed as an up-to-date review of the pharmacokinetic and pharmacodynamic properties of modern volatile anaesthetics. The first part focuses on pharmacokinetic issues such as substance properties, uptake and elimination. The second part covers the effects of inhaled anaesthetics on organ systems, with emphasis on the central nervous system, the cardiovascular system, the respiratory tract, liver and kidneys.