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Biomedical subjects

H L Bennett

Publications and source records attributed to H L Bennett.

9 recordsLinked to original sources
PubMed1992

EEG power changes are more sensitive than spectral edge frequency variation for detection of cerebral ischemia during carotid artery surgery: a prospective assessment of processed EEG monitoring.

To investigate the basis of ambiguous reports of the validity and utility of processed electroencephalogram (EEG) detection of cerebral ischemia, 19 patients monitored during surgical procedures requiring clamping of the carotid artery were studied. The EEG was recorded and observed for detection of alteration of spectral edge frequency versus EEG power. Electrodes were positioned at the P3-C3' locations over the left hemisphere and P4-C4' areas over the right hemisphere (10-20 system of electrode placement). Maximum sensitivity was used for recordings of the processed EEG. Twelve of 19 patients had bilateral carotid vascular stenosis. Nine of 19 patients studied with EEG monitoring had EEG changes suggestive of cerebral ischemia during interruption of carotid artery blood flow by surgical manipulation, defined as a decline in EEG power of greater than 40% or a decline in spectral edge frequency of at least 3 Hz. Eight of these episodes occurred at the time of carotid vascular clamp placement. These changes were confirmed by the raw EEG. Whereas power band monitoring detected 9 episodes of suspected ischemia, alteration of spectral edge frequency was sufficient to detect only 2 of these episodes. One patient sustained a right hemispheric stroke detected intraoperatively by a 47% decline in EEG power; however, these changes were unaccompanied by intraoperative alteration of spectral edge frequency. It is concluded that monitoring of EEG power with processed EEG devices is a more sensitive indicator of cerebral ischemia than monitoring only the spectral edge frequency of the EEG.

Aged↗
PubMed1992

Effects of isoflurane and nitrous oxide in subanesthetic concentrations on memory and responsiveness in volunteers.

Awareness, defined as conscious memory during anesthesia, has been a problem in anesthesia practice. To determine the effect of isoflurane and nitrous oxide (N2O) on memory, 17 healthy adult volunteers were randomly assigned to receive isoflurane or N2O and received the alternate agent 1-2 weeks later. Each volunteer was studied at four end-tidal concentrations of each agent, consecutively 0.15, 0.3, 0.45, and 0.15 times the minimum alveolar concentration (MAC) for isoflurane or 0.3, 0.45, 0.6, and 0.3 times MAC for N2O. After 15-min equilibration at each end-tidal concentration, volunteers were tested for voluntary response to command and were presented with verbal information to be recalled after anesthesia. Volunteers were interviewed on the day after the study and tested for conscious and unconscious memory of the information presented during anesthetic administration. MAC-awake (the end-tidal concentration preventing voluntary response in 50% of volunteers) was 0.38 (0.35-0.42) times MAC for isoflurane and 0.64 (0.61-0.68) MAC for N2O (means, 95% confidence limits), indicating isoflurane to be more potent than N2O in suppressing voluntary response (P = .0001). Memory data were analyzed in 12 volunteers who completed the study and in whom the allocation of information to be recalled was counterbalanced among agents and concentrations of agents. Memory was decreased by increasing concentrations of both agents. Conscious memory of the information presented during anesthetic administration was prevented by 0.45 MAC isoflurane but not completely prevented by 0.6 MAC N2O. Unconscious memory (defined as memory of information without conscious recognition) occurred during administration of both agents and was prevented by 0.45 MAC isoflurane but not by 0.6 MAC N2O. Isoflurane was more potent in suppressing memory than MAC-equivalent concentrations of N2O. Using models of the relationship between dose of agent and suppression of memory, a dose of both agents was estimated that suppressed memory by 50% (ED50). The ED50 was 0.20 MAC for isoflurane (95% confidence intervals, 0.15-0.25), and 0.50 MAC for N2O (95% confidence intervals 0.43-0.55). We conclude that isoflurane and N2O suppress memory in a dose-dependent manner, and that isoflurane is more potent in preventing memory and voluntary response to command than MAC-equivalent concentrations of N2O.

Adolescent↗
PubMed1992

Isoflurane anesthesia prevents unconscious learning.

We investigated whether greater than or equal to 0.6 minimum alveolar concentration (MAC) of isoflurane suppresses learning of information presented verbally. Preoperatively, we asked 45 healthy patients (aged 23-58 yr) undergoing elective surgery 15 general knowledge questions designed to arouse their curiosity. They were told that they would be given the answers during anesthesia. Anesthesia was induced with isoflurane and nitrous oxide (25 subjects also received 1.1 +/- 0.6 mg/kg of propofol). The trachea was intubated with the aid of vecuronium (0.07 mg/kg IV). Isoflurane in oxygen was given to provide 0.6 MAC before and 1.0 and 1.4 MAC during surgery. After 10 min at each of two of the three MAC levels, the answers were given to five of the questions. At the remaining concentration, patients received a message to either touch an ear (n = 30) or keep their arms still (n = 15) during the postoperative interview. Twenty-four hours later, patients were asked whether they recalled intraoperative events. They were then asked to answer the 15 questions, choosing from five possible answers to each, one of which was correct. The number of times each patient touched an ear during this interview was noted. No patient consciously recalled events during anesthesia. The number of questions answered correctly postoperatively did not differ according to whether the answers had been provided during anesthesia (at any isoflurane concentration) or had not been provided (control questions). The number of ear-touches postoperatively did not differ between those who had and had not received the intraoperative message encouraging ear-touching.(ABSTRACT TRUNCATED AT 250 WORDS)

Adult↗
PubMed1989

Somatosensory evoked potentials for orthopaedic spine trauma.

Monitoring somatosensory evoked potentials (SSEPs) for intraoperative assessment of spinal cord activity provides a reliable and valid measure of sensory function during manipulation of structures placing cord function at risk. We describe a multichannel technique with artifact reductions that has proved successful in 415 spine cases including 146 posttraumatic injuries. Accurate prediction of sensory function in near or at 100% of cases is possible. No patient has recovered with less than the predicted sensory function. Statistics and cases are presented. A professional-level consultant role for SSEP monitoring is suggested as necessary for valid use of the technique.

Adult↗
PubMed1987

Expressive and perceptual asymmetries of the resting face.

Lateral facial composites reveal the asymmetry of the resting face. In the current research, we created lateral composites of 30 resting faces, then had subjects compare the two composites of a face with a depiction of the whole face in either normal- or mirror-image. Results indicate that the side of the face in a subject's left visual hemi-space dominates facial recognition. The magnitude of this bias can be altered by priming tasks. It is a bias in facial perception, not memory.

Adult↗
PubMed1985

Non-verbal response to intraoperative conversation.

In a double-blind study, 33 patients (herniorraphy, cholecystectomy and orthopaedic) were randomly assigned to either suggestion or control groups. Under known clinical levels of nitrous oxide and enflurane or halothane anaesthesia, suggestion patients were exposed to statements of the importance of touching their ear during a postoperative interview. Compared with controls, suggestion patients did touch their ear (tetrachoric correlation 0.61, P less than 0.001) and they did so more frequently (Mann-Whitney U test, P less than 0.02). All suggestion patients were completely amnesic for the intraoperative spoken suggestion, despite inquiries which included hypnotic regression to the operation.

Adult↗