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H L Edmonds

Publications and source records attributed to H L Edmonds.

At least 37 records · Page 2Linked to original sources
PubMed1994

Auditory steady-state response, upper facial EMG, EEG and heart rate as predictors of movement during isoflurane-nitrous oxide anaesthesia.

We have studied the relationship between patient movement and changes in the auditory steady-state evoked potential, upper facial muscle electromyogram (FEMG), electroencephalographic-zero crossing frequency (EEG-ZCF) and heart rate during emergence from anaesthesia. Twelve healthy patients underwent surgery during stable isoflurane-nitrous oxide-oxygen anaesthesia without neuromuscular block. After skin closure, anaesthesia was discontinued abruptly while mechanical ventilation was continued until the patient moved. The magnitude of change in each physiological signal was evaluated in decibels (dB). Both the auditory steady state evoked potential and FEMG showed significant increases in amplitude during the last 5-min period before movement (6.1 and 10.7 dB, respectively). EEG-ZCF increased rapidly after anaesthesia was discontinued (2.5 dB) but there was no further increase in activity before movement. Heart rate did not change before movement. The use of the decibel transformation offers a promising method of displaying and interpreting changes in physiological variables during anaesthesia.

Adult↗
PubMed1994

Stability of thrombosis induced by electrocoagulation of rat middle cerebral artery.

BACKGROUND AND PURPOSE: Although it is often assumed in experimental stroke studies that cautery-induced occlusion is permanent, surgeons commonly expect cauterized vessels to recanalize spontaneously. We used the rat middle cerebral artery to determine if electrocoagulation would produce a permanent occlusion in this preparation. METHODS AND RESULTS: A standard bipolar coagulator, calibrated to determine actual power output, was adjusted to induce platelet aggregation in the middle cerebral artery of anesthetized Sprague-Dawley rats without inducing bleeding through the arterial wall. A reliable temporary thrombosis was induced by a Malis Bipolar Coagulator set to deliver 10 bursts of 1.5 seconds each at a rate of 24 min-1 and a power setting of 3 W. This thrombus was responsive to the antithrombotic agent flunarizine. An apparently permanent occlusion was produced by 30 bursts at 3 W followed by 20 bursts at 5 W. To our surprise, seven of seven such occlusions recanalized spontaneously within 4 hours. CONCLUSIONS: The electrocoagulation process commonly used in experimental stroke studies may produce only a temporary occlusion of the rat middle cerebral artery.

Animals↗
PubMed1993

Quantitative EEG analysis during cardiac surgery in a case of spontaneous recall.

A case of spontaneous postoperative recall of intraoperative events during tricuspid valvuloplasty is presented. In this case, EEG activity was continuously monitored and quantitatively processed to detect brain dysfunction during the procedure. Anesthetic maintenance was provided by fentanyl, isoflurane and midazolam. A retrospective analysis of the relative power distribution, median frequency and fast/slow ratio was conducted to characterize the recall and non-recall periods during the surgery. Analysis of the quantitative descriptors suggested that no specific EEG pattern was associated with the periods of recall. The use of several anesthetics with different effects on the EEG precludes the establishment of a single relationship between descriptors and changes in vigilance during episodes of recall.

Adult↗
PubMed1993

Correlation of motor-evoked potentials, somatosensory-evoked potentials, and the wake-up test in a case of kyphoscoliosis.

The ability to monitor the descending motor pathways of the spinal cord during surgery is an important goal in neurophysiologic monitoring of spinal deformities. This report describes a case of a severe spinal deformity for which instrumentation and reduction carried a significant risk of neurologic complications. During the procedure, changes in neurologic status were monitored simultaneously using both SSEPs and tcMMEPs. The reliability of these two complimentary modalities was then verified by concurrent wake-up tests. This case provides documentation of the reliability of tcMMEP responses when an accurate assessment of motor function was necessary.

Adult↗
PubMed1992

Quantitative electroencephalographic monitoring during myocardial revascularization predicts postoperative disorientation and improves outcome.

We evaluated computerized quantitative electroencephalography for the intraoperative detection of cerebral dysfunction. The quantitative electroencephalogram was recorded continuously during 96 myocardial revascularizations involving hypothermic cardiopulmonary bypass using Cerebrovascular Intraoperative MONitor (CIMON) software. CIMON relies on an adaptive statistical approach to detect subtle, but clinically relevant, changes in electroencephalographic activity indicative of cerebrocortical dysfunction. Relative (percent of total) low-frequency (1.5 to 3.5 Hz) power was chosen as the single quantitative electroencephalographic descriptor because it is an established hallmark of cortical dysfunction and is surprisingly insensitive to moderate changes in body temperature and level of opioid anesthesia. Reference values for this measure were established for each patient after anesthetic induction before sternotomy. The large sample variance often seen in low-frequency power was dramatically decreased by using log-transformed data and allowing each patient to serve as his own control. Quantitative electroencephalographic changes in standard deviation units or z-scores were determined from the individualized reference self-norm. Prolonged (greater than 5 minutes) and statistically significant (greater than 3 standard deviation) focal increases in relative low-frequency power were temperature-corrected to determine a standardized cerebrocortical dysfunction time at 37 degrees C. (CDT37). In phase I (n = 48), this objective quantitative electroencephalogram-based numeric descriptor was used to predict neuropsychologic outcome. These CDT37 greater than 5-minute episodes occurred 38 times in 19 patients. The quantitative electroencephalogram-based descriptor predicted the occurrence of such disorientation (n = 14 or 29%) with a 68% false positive rate but only an 8% false negative rate. Since these intraoperative quantitative electroencephalographic episodes were often (19/38) associated with low (less than 50 mm Hg) pump pressures, phase II (n = 48) sought to correct the quantitative electroencephalographic abnormality and prevent postoperative disorientation by appropriate increases in cerebral perfusion. Although the number of episodes of quantitative electroencephalographic abnormality was similar (n = 31) in phase II, these ischemic events disappeared after prompt elevation of perfusion pressure. The phase II disorientation rate fell significantly (p less than 0.002) to 4%. Thus statistically significant increases in low-frequency electroencephalographic relative power persisting for a temperature-corrected duration of 5 minutes or more are a reliable means of alerting the surgical/anesthesia team to the presence of cerebrocortical dysfunction and provide a rational and objective basis for corrective intervention. This form of electroencephalographic monitoring appears to offer an opportunity for the timely correction of perfusion abnormalities or the administration of cerebroprotectant compounds.

Aged↗
PubMed1991

Is defibrillation testing safe?

Determination of defibrillation thresholds (DFTs) and implantable cardioverter defibrillator (ICD) testing requires repeated inductions of ventricular fibrillation (VF) and defibrillation attempts using known energy outputs. Little is known about the individual and cumulative effects of repetitive brief episodes of VF and hypoperfusion on cerebral function. The potential clinical utility of quantitative electroencephalographic (QEEG) monitoring during intraoperative ICD testing, by using processed 19-channel EEG (0.5-35 Hz bandwidth), was examined in ten anesthetized patients, five males and five females (mean age 62 +/- 10 years), who underwent ICD implantation and testing. Ischemic QEEG patterns were defined as those with a 3 standard deviation increase (P less than 0.01) in absolute delta (1.5-3.5 Hz) power persisting for greater than or equal to 2.5 minutes. The majority (80%) of the VF episodes (70) were accompanied by QEEG "slowing" (doubling of the pre-VF low frequency delta waves amplitude). All the patients (5/5) experiencing greater than 6 VF episodes showed a statistically significant increase in the low frequency amplitude. In contrast, this EEG abnormality was apparent in only one of five patients experiencing less than 6 VF episodes. These results suggest a cumulative QEEG depression associated with ICD testing. QEEG may provide an objective means for establishing an individualized upper safe limit of DFT testing and the total number of induced VF episodes.

Electric Countershock↗
PubMed1989

Transcranial magnetic motor evoked potentials (tcMMEP) for functional monitoring of motor pathways during scoliosis surgery.

Transcranial magnetic motor evoked potentials (tcMMEP) were used to assess the functional integrity of the descending motor pathways. The tcMMEP, recorded bilaterally from anterior tibialis muscles, were evoked by an electric current induced in the motor cortex by a high-intensity transient magnetic field applied to the scalp surface. Potentials were recorded from ten of 12 volunteer subjects and preoperatively in 11 of 11 scoliotic patients. Group mean latency in the volunteers (32.0 +/- 2.1 msec) did not differ from that of the scoliotics (28.6 +/- 5.0 msec), but values in the latter group were more variable. During nitrous oxide-narcotic anesthesia, tcMMEP with reproducible latencies were obtained in 9 of 11 (82%) cases. A small, but statistically significant, increase in latency occurred during anesthesia. Compared with preoperative values (523 +/- 490 microV), individual tcMMEP amplitudes were significantly decreased intraoperatively (163 +/- 153 microV). Although the absolute amplitudes varied widely, the minimum recorded value was over 20 microV. Thus, intraoperative tcMMEP waveforms were readily discriminable from background electrical noise. These results demonstrate the technical feasibility of intraoperative tcMMEP monitoring. Combined somatosensory evoked potential and tcMMEP monitoring may provide a more complete picture of spinal cord function, intraoperatively.

Electromagnetic Fields↗
PubMed1989

Assessment of anaesthetic adequacy with upper facial and abdominal wall EMG.

We compared changes in biopotentials arising from upper facial (FEMG) and abdominal (AEMG) muscles associated with alterations in alveolar enflurane concentration and neuromuscular block. Induction of anaesthesia significantly reduced both FEMG and AEMG mean amplitudes (-60% and -43%, respectively). Neuromuscular blocker-induced abolition of the electrically evoked thenar EMG response did not prevent FEMG and/or AEMG activation during endotracheal intubation. Decreasing the alveolar enflurane concentration was associated with an increase in FEMG amplitude prior to visible signs of arousal in half of the patients. Movement and other signs of inadequate anaesthesia were associated with distinct increases in FEMG amplitude in 29 out of 30 patients. Recovery from neuromuscular block during unchanged alveolar enflurane concentration was associated with increasing amplitudes of both FEMG and AEMG. Finally, very low-amplitude FEMG recordings were always associated with relaxed abdominal muscles.

Abdominal Muscles↗
PubMed1988

Comparison of neuromuscular blockade in upper facial and hypothenar muscles.

Facial and hand muscles are used frequently for monitoring neuromuscular blockade. Therefore, we compared changes in electrically evoked muscle potential magnitude in upper facial and hypothenar muscles after fixed doses of neuromuscular blockers (succinylcholine, 750 micrograms/kg; pancuronium, 70 micrograms/kg; vecuronium, 50 micrograms/kg; and atracurium, 300 micrograms/kg). Face-hand comparisons were made in both anesthetized (nitrous oxide/narcotic, n = 51) and comatose (closed-head injuries, n = 5) patients. In 24 anesthetized patients, complete blockade of the hypothenar muscles prevented quantitative comparison. In the remaining 27 patients, the relaxant effect (as determined by the percentage change from prerelaxant baseline muscle potentials) was significantly smaller (P less than 0.0001) in the upper facial muscles (65 +/- 24% versus 92 +/- 8%, mean +/- SD). All four evoked muscle responses to train-of-four stimulation were detectable in upper facial muscles of the 19 patients receiving non-depolarizing neuromuscular blocking drugs; this pattern was seen in hand muscles of only 7 patients (P less than 0.001). The neuromuscular blockade in both the hand (49 +/- 54%) and the upper facial area (68 +/- 28%, P greater than 0.05) of comatose patients was smaller and more variable than that seen during anesthesia. These results illustrate the value of quantitative monitoring of neuromuscular function, especially during highly variable and unpredictable drug-induced blockade in the comatose state. We conclude that during narcotic-based anesthesia the upper facial and hand muscles are differentially sensitive to commonly used neuromuscular blockers.

Anesthesia, General↗
PubMed1988

Objective assessment of opioid action by facial muscle surface electromyography (SEMG).

1. Activity of the mimetic muscles of the upper face were recorded from awake and anesthetized patients by surface electromyography (SEMG). 2. High amplitude SEMG accompanied ketamine anesthesia and/or the presentation of pain-provoking stimuli. 3. During periods of elevated facial muscle activity, fentanyl or butorphanol decreased SEMG amplitude. 4. The opioid-induced SEMG depression was not consistently associated with either lowered vigilance or analgesia but did provide an objective measure of drug effect.

Adult↗
PubMed1988

Pitfalls in the use of brain slices.

In vitro brain slices are the preparation of choice for the detailed examination of local circuit properties in mammalian brain. However it is the investigator's responsibility to verify that the circuits under investigation are indeed confined within the boundaries of the functional region of the slice used. The medium in which the slice is maintained is under the full control of the investigator. This places the burden on the investigator to ensure that: (1) the properties of the medium are fully under control; (2) the effects of the medium on the slice are known; (3) the conditions under which the slice is being maintained bear some reasonable relation to those it enjoys (or endures) in vivo. Generalizations to in vivo conditions must be made with caution. If at all possible, similar studies (perhaps less extensive, due to the greater technical difficulties) should be done in vivo to provide a basis for comparison. Investigators using drugs should be aware of, and respect, the basic pharmacological principles cited in the text. In particular, the substantial freedom the investigator has in defining the extracellular medium should not be abused.

Animals↗
PubMed1987

Cerebral resuscitation: pathophysiology and therapy.

The interest in the possibility of cerebral resuscitation has been growing exponentially during the last decade. It became clear that pharmacotherapeutic interaction can possibly alter the outcome of cerebral hypoxia/ischemia. The present review is an attempt to provide an organizational framework for a systematic integration of studies specifically dealing with pharmacological treatment post-insult.

Animals↗
PubMed1986

Quantitative surface electromyography in anesthesia and critical care.

The frontalis muscle spontaneous (SEMG) and electrically evoked (EEMG) electromyograms were recorded in 4 different clinical settings. Using a standardized isoflurane-based anesthetic protocol. Study 1 examined the SEMG response to both surgical and acoustic stimuli. The acoustic SEMG response was also examined in comatose head-injured patients. Study 2 used the EEMG to compare the extent of vecuronium-induced neuromuscular blockade on the frontalis and hypothenar muscles in both anesthetized and comatose patients. In Study 3 head-injured comatose patients were used to investigate the relationship between SEMG changes and transient elevations in intracranial pressure (ICP). The effect of opiate analgesics on the pain-activated SEMG in conscious post-operative patients was investigated in Study 4. These studies illustrate the following phenomena. First, in conscious, unparalyzed or lightly anesthetized patients, painful (stressful) stimuli are associated with increases in SEMG amplitude. Thus, the SEMG may indicate periods of inadequate analgesia, not only post-operatively (Study 4) but also intra-operatively (Study 1), since we found the frontalis to be relatively insensitive to a non-depolarizing neuromuscular blocker (Study 2). However, the interpretation of intra-operative SEMG changes may be confounded by opiates (Study 4) and perhaps other agents capable of influencing the frontalis through either non-nociceptive central or peripheral mechanisms. Second, the opiate analgesics consistently decreased SEMG amplitude in non-tolerant conscious patients (Study 4. Although this opiate-induced decrease is not necessarily indicative of opiate analgesia, it may provide an objective, quantifiable measure of a central opiate effect. The SEMG is particularly well-suited to determine the precise timecourse of this effect. Third, in deeply anesthetized or comatose patients, unresponsive to either surgical or electrical stimulation. SEMG amplitude may increase in response to elevated ICP or certain sounds (Study 3). The stress (pain) and auditory-evoked SEMGs may thus provide measures of brainstem function that are independent of the level of consciousness.

Adult↗
PubMed1986

Effect of electrical stimulation on the viability of the hippocampal slice preparation.

Continuous electrical stimulation of rat hippocampal slices at a frequency of 1 Hz brought about a 50% decline in the evoked population spike amplitude at a rate 5 times faster than that caused by very low frequency (1/600 Hz) stimulation. Within 2 hr after the high frequency stimulation began the evoked response totally disappeared. By contrast low frequency stimulated slices maintained an evoked response for at least 9 hr. Continuous electrical stimulation, especially at high frequency seems to facilitate the deterioration of the in vitro hippocampal slice preparation.

Animals↗