Transcranial motor-evoked potentials monitoring can detect spinal cord ischemia more rapidly than spinal cord-evoked potentials monitoring during aortic occlusion in rats

Abstract

In this study, we evaluated the efficacy of transcranial motor-evoked potentials (tc-MEPs), compared with segmental spinal cord-evoked potentials (SCEPs), for detecting spinal cord ischemia (SCI) and assessed the relationship between neurological outcome and tc-MEPs or SCEPs in the rat aortic occlusion model. In the rats, SCI was induced by aortic occlusion for 10 min with a balloon catheter. At first, tc-MEPs (Group A: n = 6) or segmental SCEPs (Group B: n = 6) was recorded during SCI. Second, in using the quantal bioassay for the relationship between an interval of aortic occlusion and the probability of positive response in tc-MEPs or segmental SCEPs, the P50(MEP) and P50(SCEP) which represent the interval of aortic occlusion associated with 50% probability of assessment of ischemic spinal cord dysfunction by tc-MEP and SCEP were analyzed. The amplitude of tc-MEPs decreased significantly at 30 s and disappeared completely at 2 min after aortic occlusion. In Group B, it took about 6 min after aortic occlusion to diminish SCEP signal amplitude by approximately 50%. P50(MEP) obtained in the quantal analysis was 0.3 +/- 0.1 min. P50(SCEP) was calculated as 6.2 +/- 0.5 min that was significantly (P < 0.01) longer than P50(MEP). Our data indicated that tc-MEP monitoring could detect the onset of SCI so rapidly in comparison with segmental SCEP monitoring, which could provide therapeutic windows in a surgical approach that includes spinal cord protection.

Fig. 1

Typical waveforms of tc-MEP (a) and segmental SCEP (b) before aortic occlusion. The amplitudes were measured from peak to peak in tc-MEP (a) and from baseline to peak in segmental SCEP (b)

Fig. 2

Myogenic tc-MEPs recorded from the right soleus muscle and segmental SCEP. tc-MEPs in Group A disappeared at 2 min after aortic occlusion. In Group B, it took about 6 min after aortic occlusion to diminish SCEP signal amplitude by approximately 50%. Neither tc-MEP (Group C) nor segmental SCEP (Group D) changed throughout this experiment

Fig. 3

Time course changes in the amplitude of myogenic tc-MEPs and segmental SCEPs. Data were expressed as mean ± standard deviation. The amplitudes of tc-MEPs decreased significantly and disappeared within a minute after spinal cord ischemia. (** ## P < 0.01, ## and ** compared with baseline in Group A and in Group B, respectively

Fig. 4

Relation of duration of ischemia to probability of paraplegia, probability of amplitude less than 25% of baseline in tc-MEPs and less than 50% of baseline in segmental SCEP. Horizontal bars represent standard errors at the P50 required to produce paraplegia, amplitude less than 25% of baseline in tc-MEPs and less than 50% of baseline in segmental SCEP. ** Significant differences (P < 0.01) in P50_SCEP from P50_MEP