The effect of high-dose fentanyl on human median nerve somatosensory-evoked responses

Abstract

Median nerve somatoaensory evoked responses (MnSSERs) were recorded in nine neurologically normal adult cardiac patients before and during the administration of high-dose fentanyl. MnSSERs were recorded prior to induction and at r = 20rain and t = 45 rain postinduction. Fentanyl was administered as a slow bolus , followed by a continuous infusion at [10][11][12][13][14][15][16][17][18][19][20] From the Uniformed Services University of The Health Sciences, Naval Hospital, Bethesda, MD (AS) and the University of California, San Diego.The opinions expressed herein are those of the authnrs and me not to be construed as reflecting the views of the U.S, Navy Department, the U.S Naval Service at large or of the U.S. Department of Defense.Address correspot~lence to: Dr. John C. Drummond, Neuroanesthesia Research, M-029, La Jolla, CA 92093.High-dose fentanyl anaesthesia is frequently employed for patients undergoing major nenrologic and cardiovascular surgery. Sensory evoked response (SER) monitoring may be relevant during certain of these procedures. Accurate interpretation of SER changes requires a knowledge of the effect of the anaesthetic in use on the evoked response waveform, since anaesthetics can produce SER changes mimicking an injury pattern. We sought to define the effect of fentanyl in doses exceeding 30 p,g.kg-t on the human median nerve somatosensory evoked response (MnSSER). MethodsThis study was approved by the Committee on Investigations Involving Human Subjects of the University of California, San Diego. Nine neurologically normal adult subjects (mean age 66 -+ 11 years) scheduled for valve replacement or coronary artery bypass grafting were studied. Each gave informed consent. At the time of the study, the majority of the patients were taking one or more chronic medications for the treatment of their cardiovascular disease or other medico2 conditions, none of which are known to affect SERs.The night before surgery, patients received either Iorazepam 2 mg or flurazepam 30 mg PO. On the day of surgery, premedieation consisted of diazepam 0.1-0.2 mg PO and morphine 0.08-0.15rag IM (three patients received, in addition, scopolamine 0.2-04 mg IM) 30-60 rain prior to transfer to the operating suite. Radial, pulmonary artery, and intravenous catheters were inserted under local anaesthesia. The latter was placed in the forearm contralateral to the extremity to be stimulated for MnSSER recording.MnSSERs were recorded using a Pathfinder I1 Electrodiagnostic Monitor (Nicolet Biomedical, Madison WI 53711). The stimulation sites over the median nerve at the wrist were identified with a block electrode stimulator (intereleetrode distance = 3 era). Adhesive electrodes were applied and the stimuli, which consisted of 200 constant current impulses of 100 ~xsec duration, were CAN J ANAESTH 1987 / 24:1 / ppJ5-40

Estimation of Latency Changes and Relative Amplitudes in Somatosensory Evoked Potentials Using Wavelets and Regression

“…In theory, under normal conditions, the time difference is zero since no latency change should occur in the EPs observed. However, latency changes become nonzero when the neurological system condition changes (e.g., subject to change of depth of anaesthesia) (3)(4)(5)(6). Although there are many methods for extracting EPs from background EEGs, the most practical and popular method is still ensemble averaging (33,34) in which tens or hundreds of responses are averaged.…”

“…[4], h(n) is a low-pass filter, and g(n) is the quadrature mirror filter (QMF). The coefficients of both filters are related to the wavelet function (t).…”

“…Signals generated from within the central nervous system, such as the electroencephalogram (EEG) and evoked potentials (EP), are not influenced by neuromuscular blockers and show graded changes with increasing concentration of anesthetic agents. Somatosensory evoked potentials used as an index of depth of anesthesia have been shown to have delays in transmission of the sensory information (increased latency) and decreased amplitude with progressively increasing concentrations of most anesthetic agents except propofol and etomidate, whose amplitude either increases or shows no change when the dose increases (3)(4)(5)(6).…”

Evoked potential monitoring in anaesthesia and analgesia

“…reproducible SSEPs can be recorded [94]. Recently Langeron et al [95] observed that fentanyl (induction dose 6 mg.kg À1 and maintenance dose 3 mg.kg…”

“…Fentanyl causes dose-dependent increases in the latency of all waves, with cortical or late waves affected more than earlier waves, and decreases in amplitude. The changes in amplitude are more variable than the increases in latency [93,94]. Even at high doses of fentanyl (up to 60 mg.kg À1 )…”