Comparison of conventional averaged and rapid averaged, autoregressive-based extracted auditory evoked potentials for monitoring the hypnotic level during propofol induction

• Published in: Anesthesiology (Philadelphia) Vol. 97; no. 2; pp. 351 - 358
• Main Authors: LITVAN, Héctor, JENSEN, Erik W, GALAN, Josefina, LUND, Jeppe, RODRIGUEZ, Bernardo E, HENNEBERG, Steen W, CAMINAL, Pere, VILLAR LANDEIRA, Juan M
• Format: Journal Article
• Language: English
• Published: Hagerstown, MD Lippincott 01-08-2002
• Subjects: Anesthesia; Anesthesia. Intensive care medicine. Transfusions. Cell therapy and gene therapy; Anesthetics, Intravenous - pharmacology; Biological and medical sciences; Electrodiagnosis. Electric activity recording; Evoked Potentials, Auditory - drug effects; General anesthesia. Technics. Complications. Neuromuscular blocking. Premedication. Surgical preparation. Sedation; Humans; Investigative techniques, diagnostic techniques (general aspects); Medical sciences; Nervous system; Predictive Value of Tests; Propofol - pharmacology; Time Factors; Human; Electrodiagnosis; General anesthetic; Induction; Auditory evoked potential; General anesthesia; Electroencephalography; Propofol; Technique; Comparative study; Monitoring
• ISSN: 0003-3022; 1528-1175
• DOI: 10.1097/00000542-200208000-00011

The extraction of the middle latency auditory evoked potentials (MLAEP) is usually done by moving time averaging (MTA) over many sweeps (often 250-1,000), which could produce a delay of more than 1 min. This problem was addressed by applying an autoregressive model with exogenous input (ARX) that enables extraction of the auditory evoked potentials (AEP) within 15 sweeps. The objective of this study was to show that an AEP could be extracted faster by ARX than by MTA and with the same reliability.
The MTA and ARX methods were compared with the Modified Observer's Assessment of Alertness and Sedation Scale (MOAAS) in 15 patients scheduled for cardiac surgery and anesthetized with propofol. The peak amplitudes and latencies were recorded continuously for the MTA- and ARX-extracted AEP. An index, AAI, was derived from the ARX-extracted AEP as well.
The best predictors of the awake and anesthetized states, in terms of the prediction probability, Pk, were the AAI (Pk [SE] = 0.93 [0.01]) and Na-Pa amplitude (MTA, Pk [SE] = 0.89 [0.02]; ARX, Pk [SE] = 0.87[0.02]). When comparing the AAI at the MOAAS levels 5-3 versus 2-0, significant differences were achieved. During the transitions from awake to asleep, the ARX-extracted AEP were obtained with significantly less delay than the MTA-extracted AEP (28.4 s vs. 6 s).
The authors conclude that the MLAEP peaks and the AAI correlate well to the MOAAS, whether extracted by MTA or ARX, but the ARX method produced a significantly shorter delay than the MTA.