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Titration of barbiturate therapy by auditory brain-stem evoked response monitoring in neurosurgical patients
S145 PSA on averaged auditory evoked potentials (AEPs) recorded from bilateral temporal scalp locations in response to monaural stimulation suggested that, in audiologically normal subjects, AEP frequency components in the high alpha range (11-14 Hz) were the most sensitive to dominance of the contralateral auditory pathway. We now present research in which we attempted to replicate this finding with a larger subject sample. Monopolar EEG recordings were taken from T 3, T 4, C 3 and C 4 scalp sites, referred to linked ear-lobes. The stimuli were monaural tones (1000 Hz, 75 dB SPL) delivered pseudo-randomly to lhe left and right ears under three conditions: 1) passive attention: 2) attend left ear; 3) attend right ear. Order of presentation of the latter two conditions was counterbalanced across subjects. We will compare time and frequency domain measures of the AEPs obtained under each condition, with particular reference to their sensitivity to the interaction between ear of stimulation and hemisphere.
P21.08 TITRATION OF BARBITURATE THERAPY BY AUDITORY BRAIN-STEM EVOKED R E S P O N S E MONITORING IN N E U R O S U R G I C A L PATIENTS. A. Hirc~vama and S. Yamasaki (Osaka, Japan) When barbiturate coma therapy fails eventually in spite of its initial success, the manner of administration is controversial. In the present study, monitoring of auditory brain-stem evoked response (ABR) instead of EEG was instituted for administration of moderate dose pentobarbital. Of 8 patients studied and saved, 3 had a diffuse traumatic cerebral swelling associated with unilateral acute subdural haematoma (operated), one had a deep frontal glioblastoma, and 4 had thalamic haematoma perforating into the ventricular system. ABR showed electrical silence other than wave 1 at the stage when the low dose barbiturate therapy was started, as 24 hr. high dose therapy (4-7 m g / K g / h r thiopental or pentobarbital) caused hypotension and either epidural or ventricular ICP was over 45 mmHg. The subsequent doses of pentobarbital were titrated to maintain wave V even with delayed latency and decreased amplitude (about 1 2 m g / K g / h r ) . The results suggest that switching to low dose barbiturate therapy but with the guide of ABR monitoring could reverse the catastrophic vicious circle of ischemia and oedema caused by high barbiturate with possible uncoupling of CBF and ICP.
P21.09 EXPERIENCE WITH A C O N T I N U O U S MONITORING A L G O R I T H M F O R BAEP D U R I N G R E T R O M A S T O I D CRANIECTOMIES. J . R Boston, L.G. Deneault, L. Kronk and P.J. Jannetta (Pittsburgh, PA, USA) Brain-stem auditory evoked potentials (BAEP) offer a noninvasive method to monitor auditory function that can be used during surgery. We have used the technique in over 135 retromastoid craniectomies for microvascular decompression. Because important latency changes can occur over periods of seconds to minutes, we have implemented a continuous averaging algorithm with automatic measurement of peak latency. This algorithm indicates large changes in the BAEP within 30 seconds, while providing immediate and stable data on latency trends. We observed systematic changes in both peak I latency and in the 1 II1 interval. Peak 1 latency changes were most common and usually showed substantial recovery by the end of the procedure. Changes in the I-lII interval were less common and smaller, but they were less likely to show substantial recovery. In most cases the surgeons were able to modify their technique and to obtain a reduction in latency increases: the sooner they were notified of an increase, the more effectively they could control it. Fifteen percent of the patients had a hearing deficit in the immediate post-operative period. The post-operative deficits were small (5-20dB) and generally transient except for one patient in whom the BAEP was lost and not recovered during the procedure. Patients with post-operative hearing losses showed greater BAEP changes than those without post-operative hearing changes, although there was extensive overlap of the two groups.
P21.10 EFFECT OF H Y P O T H E R M I A ON BRAIN-STEM AUDITORY (BAERs) A N D S O M A T O S E N S O R Y (SERs) EVOKED R E S P O N S E S . O.N. Markand and C.H. Warren (Indianapolis, IN, USA) Thirty adult patients had BAERs and SERs during cardiac surgery under cardio-pulmonary bypass and moderate hypothermia (19°-25°C). With cooling, the latency of all components of BAERs and SERs increased in a linear fashion; the later the component the more severe was the change. The regression data are summarized below: BAER BAER BAER SER SER SER Wavel WavelI1 WaveV N10 NI4 N19 -0.12 -0.28 -0.48 -0.61 - 0 . 9 7 -1.45 Slope 5.97 15.00 23.23 33.42 50.12 72.97 Constant Corr. -0.79 -0.89 0.88 - 0 . 8 9 -0.88 - 0 . 9 0 Coeff. r
P21.08 TITRATION OF BARBITURATE THERAPY BY AUDITORY BRAIN-STEM EVOKED R E S P O N S E MONITORING IN N E U R O S U R G I C A L PATIENTS. A. Hirc~vama and S. Yamasaki (Osaka, Japan) When barbiturate coma therapy fails eventually in spite of its initial success, the manner of administration is controversial. In the present study, monitoring of auditory brain-stem evoked response (ABR) instead of EEG was instituted for administration of moderate dose pentobarbital. Of 8 patients studied and saved, 3 had a diffuse traumatic cerebral swelling associated with unilateral acute subdural haematoma (operated), one had a deep frontal glioblastoma, and 4 had thalamic haematoma perforating into the ventricular system. ABR showed electrical silence other than wave 1 at the stage when the low dose barbiturate therapy was started, as 24 hr. high dose therapy (4-7 m g / K g / h r thiopental or pentobarbital) caused hypotension and either epidural or ventricular ICP was over 45 mmHg. The subsequent doses of pentobarbital were titrated to maintain wave V even with delayed latency and decreased amplitude (about 1 2 m g / K g / h r ) . The results suggest that switching to low dose barbiturate therapy but with the guide of ABR monitoring could reverse the catastrophic vicious circle of ischemia and oedema caused by high barbiturate with possible uncoupling of CBF and ICP.
P21.09 EXPERIENCE WITH A C O N T I N U O U S MONITORING A L G O R I T H M F O R BAEP D U R I N G R E T R O M A S T O I D CRANIECTOMIES. J . R Boston, L.G. Deneault, L. Kronk and P.J. Jannetta (Pittsburgh, PA, USA) Brain-stem auditory evoked potentials (BAEP) offer a noninvasive method to monitor auditory function that can be used during surgery. We have used the technique in over 135 retromastoid craniectomies for microvascular decompression. Because important latency changes can occur over periods of seconds to minutes, we have implemented a continuous averaging algorithm with automatic measurement of peak latency. This algorithm indicates large changes in the BAEP within 30 seconds, while providing immediate and stable data on latency trends. We observed systematic changes in both peak I latency and in the 1 II1 interval. Peak 1 latency changes were most common and usually showed substantial recovery by the end of the procedure. Changes in the I-lII interval were less common and smaller, but they were less likely to show substantial recovery. In most cases the surgeons were able to modify their technique and to obtain a reduction in latency increases: the sooner they were notified of an increase, the more effectively they could control it. Fifteen percent of the patients had a hearing deficit in the immediate post-operative period. The post-operative deficits were small (5-20dB) and generally transient except for one patient in whom the BAEP was lost and not recovered during the procedure. Patients with post-operative hearing losses showed greater BAEP changes than those without post-operative hearing changes, although there was extensive overlap of the two groups.
P21.10 EFFECT OF H Y P O T H E R M I A ON BRAIN-STEM AUDITORY (BAERs) A N D S O M A T O S E N S O R Y (SERs) EVOKED R E S P O N S E S . O.N. Markand and C.H. Warren (Indianapolis, IN, USA) Thirty adult patients had BAERs and SERs during cardiac surgery under cardio-pulmonary bypass and moderate hypothermia (19°-25°C). With cooling, the latency of all components of BAERs and SERs increased in a linear fashion; the later the component the more severe was the change. The regression data are summarized below: BAER BAER BAER SER SER SER Wavel WavelI1 WaveV N10 NI4 N19 -0.12 -0.28 -0.48 -0.61 - 0 . 9 7 -1.45 Slope 5.97 15.00 23.23 33.42 50.12 72.97 Constant Corr. -0.79 -0.89 0.88 - 0 . 8 9 -0.88 - 0 . 9 0 Coeff. r