Effect of sevoflurane concentration on visual evoked potentials with pattern stimulation in dogs

Comparison of the effect of sedation and general anesthesia on pattern and flash visual evoked potentials in normal dogs

Background

Visual evoked potentials (VEPs) can provide objective functional assessment of the post-retinal visual pathway. This study compared the effects of sedation (butorphanol and dexmedetomidine) and general anesthesia (propofol and sevoflurane) on pattern and flash VEPs. Dogs (n = 13) underwent sedation or anesthesia and VEPs were obtained from 3 subcutaneous recording electrodes placed on the head (O1, Oz, O2).

Results

Pattern VEPs could only be recorded under sedation and a maximum of 3 peaks were identified (N75, P100, N135). Flash VEPs could be recorded under both sedation and anesthesia and a maximum of 5 peaks were identified (N1, P1, N2, P2, N3). The latency of the N1 peak and the baseline-N1 amplitude were significantly longer under general anesthesia.

Conclusion

Visual evoked potentials should be preferentially recorded in dogs sedated with dexmedetomidine and butorphanol, regardless of the stimulus.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12917-022-03375-5.

Effects of pupil size on canine visual evoked potential with pattern stimulation

The purpose of this study was to investigate the effects of pupil diameter on canine visual evoked potentials with pattern stimulation (P-VEP). Atropine eye drop (1.0%) was applied to both eyes as a cycloplegic drug, and tafluprost eye drop (0.015%) was applied to one eye that was selected randomly for miosis (miosis group). The other eye did not receive tafluprost (mydriasis group). P-VEP was recorded at three pattern sizes. The P100 implicit time at a small pattern size in the mydriasis group was significantly prolonged compared to the miosis group. We hypothesized that the prolonged P100 implicit time under mydriatic conditions was due to increased spherical aberrations and concluded that mydriatic conditions affected P100 implicit time in canine P-VEP recordings.

Measurement of visual acuity in Beagle dog by visual evoked potential with pattern stimulation

We tried measurement of visual acuity in laboratory beagle using pattern stimulus visual evoked potential (P-VEP). We recorded P-VEP in 6 beagles which were corrected refractive power. The stimulus pattern size was 1.22 mm. The testing distance were 0.5, 1.0, and 2.0 m. The visual angles and spatial frequency were calculated from stimulus pattern size and distance. In all subjects, P-VEP was clearly recorded in all testing distance, and this result means that the eye could recognized grid pattern on the stimulus monitor. When stimulus monitor was set up 2.0 m, spatial frequency was 14.29 cpd. From our results, it was founded that the visual acuity in laboratory beagle which was corrected refractive power was 14.29 cpd and more.

Electrophysiologic evaluation of the visual pathway at different depths of sevoflurane anesthesia in diabetic rats

Our study investigated the changes produced by diabetes on the visual pathway in a Wistar rat model. The impact of diabetes at 10 weeks after intraperitoneal streptozotocin (STZ) injection was evaluated through electrophysiological methods like visual evoked potentials (VEP) and electroretinogram (ERG). VEP and ERG were recorded simultaneously under different sevoflurane anesthetic depths. In all tested concentrations, sevoflurane affected the amplitude and latency of VEP and ERG component elements. With increasing anesthetic depths, sevoflurane increased the latencies of VEP N1, P1 and N2 peaks and ERG a- and b- waves in both control and diabetic animals. On the other hand, the amplitude of VEP showed enhancement in higher concentrations of sevoflurane, contrariwise to the drop of amplitude seen in the ERG. Diabetes additionally increased the latencies of VEP peaks and decreased the N1-P1 amplitude of the VEP when compared to control at the same anesthetic depth. The a- and b- waves were also delayed by diabetes at 10 weeks post-STZ diabetic induction, with the exception of highly profound anesthetic depth in which the result for the b wave were conflicting. We found a reduction in amplitude of the a-b wave in diabetic animals, when ERG was recorded under 6% and 8% sevoflurane concentration. In conclusion, neurophysiological studies like VEP and ERG are useful in the assessment of retinal and optic nerve dysfunctions produced by diabetes, yet considering the alterations that occur during anesthesia if this is used.

Effect of refractive error on visual evoked potentials with pattern stimulation in dogs

The purpose of this study was to investigate the effects of refractive error on canine visual evoked potentials with pattern stimulation (P-VEP). Six normal beagle dogs were used. The refractive power of the recorded eyes was measured by skiascopy. The refractive power was corrected to −4 diopters (D) to +2 D using contact lens. P-VEP was recorded at each refractive power. The stimulus pattern size and distance were 50.3 arc-min and 50 cm. The P100 appeared at almost 100 msec at −2 D (at which the stimulus monitor was in focus). There was significant prolongation of the P100 implicit time at −4, −3, 0 and +1 D compared with −2 D, respectively. We concluded that the refractive power of the eye affected the P100 implicit time in canine P-VEP recording.