[Effect of premedication and barbiturate hypnotics on motor evoked potentials induced by magnetic cortex stimulation].
OBJECTIVE
The aim of this study was to investigate the influence of the premedication and the influence of the two barbiturates methohexital and thiopental on magnetically evoked compound muscle action potentials (magnet MEP) in humans.


METHODS
40 Patients (ASA-PS I-II) undergoing lumbar nucleotomy were included in this study after obtaining written informed consent. The study was approved by the local ethical committee. All patients were premedicated with 0.5 mg atropine, 25 mg promethazine and 50 mg pethidine. For induction of anaesthesia patients randomly received methohexital or thiopental by continuous infusion with increasing infusion rates every 15 seconds up to a minimal anaesthesia level in 15 minutes. Transcranial magnetic stimulation was delivered by the magstim 200 magnetic stimulator. Magnetic MEPs were recorded from the surface of the short abductor pollices muscle. MEP-examination was performed preoperatively, after premedication and every two minutes during the induction of anaesthesia. Every other two minutes the patients level of consciousness were assessed and documented. Statistical calculations were performed with the U-test.


RESULTS
No statistical differences were found for the mean induction time in the two groups. No statistical difference in amplitude and latency could be observed between the preoperative values and the values measured after premedication. During anaesthesia induction the amplitude decreased in both groups. In 25 of the 40 cases, the MEP disappeared completely before the patients fell asleep. The thiopental group showed a significantly lower incidence of MEP preservation (20%) compared to methohexital (50%).


CONCLUSIONS
Premedication with atropine, promethazine and pethidine has no influence on magnetic MEP. Methohexital allows the highest incidence of successful MEP recordings with sufficient anaesthesia. A success rate of only 50% even in cases without motorpathway affection makes the application of magnetic MEP an unreliable tool for intraoperative monitoring.
Klinik und Poliklinik für Anästhesiologie und Spezielle Intensivmedizin, Rheinischen Friedrich-Wilhelms-Universität Bonn.
J
J
Nadstawek
M
M
Taniguchi
U
U
Langenbach
C
C
Thees
U
U
Pechstein
N
N
Schnitzler
D000759:Adjuvants, Anesthesia; D000328:Adult; D000368:Aged; D000771:Anesthesia, Intravenous; D001143:Arousal / Q000187:drug effects / Q000502:physiology; D001285:Atropine / Q000008:administration & dosage; D002540:Cerebral Cortex / Q000187:drug effects* / Q000503:physiopathology; D017586:Diskectomy; D004569:Electroencephalography / Q000187:drug effects; D004574:Electromagnetic Fields; D019054:Evoked Potentials, Motor / Q000187:drug effects* / Q000502:physiology; D005260:Female; D006801:Humans; D006993:Hypnotics and Sedatives; D007273:Injections, Intramuscular; D007405:Intervertebral Disc Displacement / Q000503:physiopathology / Q000601:surgery*; D008159:Lumbar Vertebrae / Q000294:innervation / Q000601:surgery*; D008297:Male; D008614:Meperidine / Q000008:administration & dosage; D008723:Methohexital; D008875:Middle Aged; D016343:Monitoring, Intraoperative; D011229:Preanesthetic Medication; D011398:Promethazine / Q000008:administration & dosage; D011930:Reaction Time / Q000187:drug effects / Q000502:physiology; D013874:Thiopental
D000759:Adjuvants, Anesthesia; D006993:Hypnotics and Sedatives; D001285:Atropine; D008614:Meperidine; D008723:Methohexital; D011398:Promethazine; D013874:Thiopental
Einfluss von Prämedikation und Barbiturathypnotika auf motorisch evozierte Potentiale mittels magnetischer Kortexstimulation.