Brain Monitoring

EEG monitoring during cardiac surgery

Harvey L. Edmonds, Jr. Ph.D.
Professor & Director of Research
Department of Anesthesiology
University of Louisville, Louisville, KY, USA

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Cardiac surgery provides the best opportunity to demonstrate the benefits of intraoperative EEG monitoring. First, in developed countries, cardiac surgery represents the most common and expensive major surgery. Second, considering all types of surgery, that involving cardiopulmonary bypass results in the largest number of potentially preventable perioperative brain injuries. This large clinical problem also represents a major opportunity for improvement in health care delivery. Thus, our ten year experience in over 4,000 cardiac procedures has shown the cost-benefit and cost-effectiveness of intraoperative EEG monitoring, especially as part of multimodality neuromonitoring using the complementary technologies of transcranial Doppler ultrasound (TCD) and cerebral oximetry.

Cost-benefit derived from the ability of EEG monitoring to reduce major neurologic complications. Our initial experience in 600 monitored cases (1) demonstrated that, in the absence of rapid cooling or anesthetic bolus, the odds were >500:1 that a sudden loss of EEG activity would precede a serious cerebral injury. From this experience, an EEG-based intervention algorithm was developed to treat such episodes with hopes of ameliorating ischemic injury (2). Subsequently, we reviewed the records of 1,792 consecutive myocardial revascularizations at one hospital. The use of monitoring was a pseudo-random event that depended on both surgeon choice and monitorist availability. The incidence of neurologic complications in the cohort with multimodality neuromonitoring was 0.3% (n=1,036) compared with 1.9% (n=756; P=.002) in the unmonitored group. The relatively low incidence in both groups seem, in part, the result of retrospective analysis. Monetization of this apparent benefit varies enormously, based on the regional differences in stroke cost estimate. Nevertheless, the benefit of EEG-guided multimodality neuromonitoring is statistically and clinically significant.

Cost-effectiveness is based on the use of EEG to improve perioperative efficiency. Unnecessarily large anesthetic doses result in ultrahypnosis, consuming unneeded anesthetic and prolonging utilization of very expensive surgical and critical care facilities and personnel. Univariate (i.e., suppression ratio) or multivariate (i.e., bispectral index or BIS) quantitative EEG descriptors provide a simple method for minimizing ultrahypnosis, particularly during surgery’s final 30 min. We recently demonstrated (3) that during this interval, cardiac patients with <5 BIS-minutes below 40 (n=21) recovered twice as fast as those with >15 BIS-min below 40 (n=10; 45± 31 vs 91± 49 min; P=.005). In a 1,037 patient subset from the larger study population (4), we found that the critical care unit stay for the monitored cohort (n=671) was 43 hr shorter than the unmonitored cohort (P=.001). At an estimated hospital cost of $90 U.S./hr (5), the EEG-guided neuromonitoring saved $3,870/case. EEG monitoring played a key role in this savings, since 28% of the interventions were to correct ultrahypnosis and another 8% prevented subhypnosis (i.e., BIS>70).

The multimodal approach helps overcome limitations inherent in each of the modalities. Especially when coupled with TCD and cerebral oximetry, EEG monitoring during cardiac surgery is clearly effective in reducing both complications and cost.

References

1. Edmonds HL Jr et al. Perfusion 1993;8(3):270
2. Edmonds HL Jr et al. J Cardiothorac Vasc Anesth 1996;10(1):15-23
3. Yu Q-J et al. Anesth Analg 1999;88:SCA35
4. Edmonds HL Jr et al. Anesth Analg 1999;88:SCA26
5. McCarthy TP et al. Resp Care 1998;43:114-9

Last updated: 1 June 2001Created
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