Comparison of the effects of three different combinations of general anesthetics on the electroretinogram of dogs

Abstract

The objective of this study is to compare the effects of three different anesthetic combinations on the electroretinogram in the same animals under similar laboratory conditions. Thiopental-isoflurane (TI), medetomidine-ketamine (MK), and xylazine-ketamine (XK) were used on each of 12 healthy miniature schnauzer dogs (MS) with a period of at least 3 weeks in between subsequent anesthesia protocols, using the Dog Standard Protocol. The scotopic ERGs consisted of scotopic low stimulus strength (S) responses designated S1, S2, S3, S4, and S5, at 1, 5, 10, 15, and 20 min after dark adaptation, respectively, and scotopic standard stimulus strength (S-ST) responses. The photopic ERGs consisted of a photopic single flash (P) response and 31 Hz flicker (P-FL) responses. For S-ST (2.5 cd s/m(2)), the amplitude of the a-wave using TI was significantly lower than that using MK (adjusted P = 0.05) and XK (adjusted P = 0.03), and the implicit time of the a-wave was significantly shorter than that using MK (adjusted P = 0.04). For P (2.5 cd s/m(2)), the amplitude of the b-wave using XK was significantly higher than that using MK (adjusted P = 0.01). The implicit times of the b-wave using TI was significantly longer and shorter than that of MK for S1, S2 and P-FL and for S4 and S-ST, respectively, and than that of XK for S2 and P-FL and for S5 and S-ST, respectively. The results of the present study showed that TI affected both the amplitude and the implicit time of the a-wave for S-ST and the implicit time of the b-wave relatively more so than was the case when using XK or MK. Therefore, it appears that either XK or MK could be advantageous to use rather than TI for clinical studies.

Effects of chemical restraint on electroretinograms recorded sequentially in awake, sedated, and anesthetized dogs

“…Although some clinicians may consider sedation an acceptable alternative to anesthesia for ERG, some of the same financial, time, and health concerns can remain. Additionally, use of sedatives and anesthesia alters the ERG a-and b-wave amplitudes and implicit times [3][4][5][6][7][8] and these effects must be taken into consideration when evaluating the ERG response.…”

Penetrating eye injury in a dog: a case report

“…The studies by Kommonen et al (1988) and Jeong et al (2009) showed that a combination of xylazine and ketamine resulted in the lowest changes in a-wave and b-wave implicit times and amplitudes. In addition, the combination of these anaesthetics does not induce lower rotation of the eyeball or myosis.…”

Electroretinography in the normal koala (Phascolarctos cinereus)

“…The anesthetic protocol utilized in this case was selected as it widely and safely used in koalas by wildlife veterinarians . It is well known that general anesthesia decreases ERG responses, although this reduction is probably less important in ERG interpretation than the large artifacts often seen in recordings performed on awake animals Considering the temperament of koalas, ERG would not be reliable or safe in a conscious koala.…”