Anesthesia for diagnostic procedures and nonsurgical treatment in children with brain tumors.
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Journal Article↗
Biomedical subjects
S K Samra
Publications and source records attributed to S K Samra.
The relation between lorazepam-induced auditory amnesia and auditory evoked potentials.
We conducted a placebo-controlled double-blind investigation in 15 normal volunteers to study the time course of amnesia to auditory stimulation produced by lorazepam. We also studied the relationship between auditory amnesia and auditory evoked potentials to determine if long-latency auditory evoked potentials (LLAEPs) could be utilized as electrophysiologic predictors of memory. Amnesia was produced by administration of 0.05 mg/kg lorazepam intravenously. To separate the changes in LLAEPs due to generalized sedation from those associated with amnestic properties of a drug, a third group of subjects given 1.5 mg/kg secobarbital was included. Observed frequency and duration of amnesia to auditory stimulation after lorazepam was 58% and 3 hours, respectively (mean values), with marked diminuition of antirecall effect at 120 minutes. Administration of lorazepam increased the latency and decreased the amplitude of N1 and P3 components of LLAEPs. These changes appeared to be a result of generalized sedation rather than the amnestic properties of the drug. We failed to find a definite relationship between amnesia and changes in LLAEPs. We conclude that P3 component of LLAEPs cannot be utilized as an electrophysiologic predictor of amnesia in humans.
Adult↗
Differential effects of isoflurane on human median nerve somatosensory evoked potentials.
The effect of isoflurane on median nerve somatosensory evoked potentials (MN-SSEPs) was studied in 15 patients. Anesthesia was induced with thiamylal and maintained with oxygen and isoflurane. MN-SSEPs were recorded in awake patients and after achieving 0.5, 1.0, 1.5, and 2.0% stable end-tidal concentrations of isoflurane. Peak latencies and amplitudes of EP, N13, and N20 and conduction times EP-N13, N13-N20, and EP-N20 were measured. Peak latencies of all components increased after all concentrations of isoflurane compared with control values. N20 peak latencies after 1% and 1.5% isoflurane differed significantly, whereas EP and N13 latencies showed no significant difference. No significant change in conduction time EP-N13 resulted from 1% and 1.5% concentrations of isoflurane compared with control values. Isoflurane increased conduction time N13-N20 significantly when compared with control values, and this increase was dose related. Amplitude of EP and N13 did not show significant change with 1% and 1.5% isoflurane when compared with control values. Amplitude of N20 decreased significantly following isoflurane anesthesia compared with control values, and the difference between 1% and 1.5% isoflurane recordings was also statistically significant. N20 was not discernible in one out of 14 patients after 1.5% and in three out of ten patients after 2% isoflurane. These results indicate that subcortical potentials are less affected by isoflurane anesthesia than cortical potentials. Amplitude reduction of cortical potentials was more noticeable than either prolongation of peak latency or conduction time.(ABSTRACT TRUNCATED AT 250 WORDS)
Evoked Potentials, Somatosensory↗
Anticholinergics and human brain stem auditory evoked potentials.
The effect of premedication with morphine and anticholinergic drugs on absolute and interpeak latencies of brain stem auditory evoked potentials was studied in thirty patients. Two commonly used anticholinergics, glycopyrrolate and scopolamine, given in combination with morphine were studied. Patients premedicated with morphine alone served as a control group. No significant change in either absolute or interpeak latencies was noted in patients premedicated with either morphine alone or morphine and glycopyrrolate. Results in patients premedicated with morphine and scopolamine are inconclusive because of large intersubject variability.
Adolescent↗
Scopolamine, morphine, and brain-stem auditory evoked potentials in awake monkeys.
The effects of scopolamine and morphine sulfate on brain-stem auditory evoked potentials (BAEPs) were studied in 10 rhesus (Macaca mulatta) monkeys. Study drugs were given intravenously to unanesthetized animals and BAEPs recorded at 3-min and 30-min intervals after administration of 0.1 mg/kg and 0.32 mg/kg of scopolamine and 15 min after administration of 3.2 mg/kg morphine at the end of the experiment. No significant change in either latency or amplitude of different components of BAEPs was observed.
Animals↗
Evaluation of a hands-on workshop as a teaching tool for critical care medicine.
Many medical students have difficulty correlating the principles of cardiorespiratory physiology with the practice of critical care medicine. We developed a workshop to make this transition easier. After a computer-administered preworkshop test, groups of four students intubated a dog, and inserted arterial, peripheral, and pulmonary artery catheters. After baseline cardiorespiratory variables were measured, noncardiogenic pulmonary edema was created by administration of oleic acid via the right atrial port of the pulmonary artery catheter. Measurements were repeated after equilibration and again during the application of 5, 10, and 15 cm H2O of positive end-expiratory pressure. Monitoring techniques and calculation of physiologic variables and their significance were stressed; emphasis was also placed on the interrelationship between respiratory and cardiovascular manipulations. The educational validity of this workshop was confirmed by a significant improvement in the mean score of a post-workshop test over the mean preworkshop test score.
Anesthesiology↗
Subarachnoid hemorrhage and intraoperative electrocardiographic changes simulating myocardial ischemia--anesthesiologist's dilemma.
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Aged↗
Effect of halogenated anaesthetics on heart rate changes during reversal of neuromuscular block with glycopyrrolate and neostigmine.
The effect of halothane and enflurane on changes in heart rate during reversal of neuromuscular blockade was compared in 48 patients. Premedication and anaesthetic technique was standardized. Either halothane or enflurane was used as the primary anaesthetic. Neuromuscular block was reversed by injection of glycopyrrolate and neostigmine, given either separately or simultaneously. Heart rate changes were significantly different between the halothane and enflurane subgroups. Patients anaesthetized with enflurane showed less fluctuations in heart rate. Simultaneous injection of glycopyrrolate and neostigmine minimized the tachycardia in the halothane subgroups only.
Adult↗
Fentanyl anesthesia and human brain-stem auditory evoked potentials.
The effect of incremental doses of fentanyl on brain-stem auditory evoked potentials (BAEPs) was studied in 10 patients scheduled for elective surgery. Seven sets of BAEPs were recorded in each patient starting the day before surgery, after premedication and after 10 micrograms/kg increments of fentanyl up to 50 micrograms/kg. No significant effect on either absolute or interpeak latencies of wave I, III, and V of evoked potentials was observed.
Adult↗
Modification by halogenated anaesthetics of chronotropic response during reversal of neuromuscular blockade.
The effect of halothane and enflurane on changes in heart rate during reversal of neuromuscular block was compared in 48 adult patients. Premedication and anaesthetic technique were standardized. Either halothane or enflurane was the primary anaesthetic while pancuronium was used in all patients to achieve muscle relaxation. Ventilation was mechanically controlled and PaCO2 was between 30-40 mmHg. The neuromuscular block was reversed by an intravenous injection of atropine 1.2 mg and neostigmine 2.5 mg, given either separately or simultaneously, in different patient subgroups. Heart rate changes were significantly different between the halothane and enflurane groups. In general, reversal of neuromuscular block was accompanied by less fluctuations in heart rate after enflurane as compared to halothane anaesthesia. Simultaneous injection of atropine and neostigmine modified the tachycardiac response in the halothane sub-group only. Our observations suggest that use of enflurane offers an advantage over halothane in those patients in whom rapid fluctuations in heart rate during reversal of neuromuscular block may be dangerous.
Adult↗
The effect of a clinical clerkship on attitudes of medical students toward anesthesiology.
The study on which this article is based evaluated the effect of a clerkship in anesthesiology on medical students' attitudes toward anesthesiology as a specialty, the role of anesthesiologists as physicians, career choice, and the usefulness of this experience in their learning. Eighty-four participating students filled out questionnaires on the first and the last day of a four-week clerkship. Responses to common questions in the questionnaires administered before and after the clerkship were compared by paired t-test to determine statistical significance. The results suggest that the clerkship (a) significantly improved graduating students' attitudes toward anesthesiologists as physicians and (b) provided a worthwhile clinical experience.
Anesthesiology↗
Comparison of Teflon and polypropylene membranes for transcutaneous oxygen monitoring during anesthesia.
Performance of 2 electrodes used for transcutaneous oxygen monitoring, one covered with polypropylene and the other covered by fluorinated ethylene propylene Teflon, was compared in 11 patients during anesthesia. Both electrodes showed good correlation between transcutaneous (PtcO2) and arterial oxygen (PaO2) tension with a correlation coefficient of 0.96 with polypropylene and 0.88 with Teflon electrode. Although the ratio of transcutaneous to arterial tension varied from patient to patient, it was found to be fairly constant in any 1 patient and was not significantly affected by blood carbon dioxide tension.
Aged↗
Halothane interference with transcutaneous oxygen monitoring: in vivo and in vitro.
The effect of halothane on electrodes covered with polypropylene and FEP teflon membranes, used for monitoring transcutaneous oxygen tension, was compared in vitro and in patients anesthetized with halothane. In vitro experiments with halothane showed a false increase in PO2 measured by the electrode covered with polypropylene membrane while there was no increase in PO2 values recorded by an electrode covered with teflon membrane. In 15 patients anesthetized with halothane, no interference with transcutaneous oxygen measurement was seen with electrodes covered with either a polypropylene or FEP teflon membrane.
Adult↗
Migration of physicians to and from anesthesiology.
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Anesthesiology↗
Physostigmine fails to reverse clinical, psychomotor, or EEG effects of lorazepam.
Physostigmine salicylate (2.0 mg) or 0.9% NaCl (2.0 ml) was administered intravenously in a double-blind fashion to adult volunteers in an attempt to reverse the effects of a 0.05-mg/kg dose of lorazepam given intravenously 30 min earlier. No other medication affecting the central nervous system was given. No differences were observed between the two groups with regard to the frequency of amnesia, psychomotor impairment, or EEG changes during a period of 4 h. The only significant difference in the level of sedation between the two groups was observed 60 min into the study. This difference is attributed to the high incidence of nausea and vomiting that occurred at that time exclusively in one group. Time to complete recovery was the same in both groups. However, physostigmine, not saline, was associated with a high incidence of muscarinic and sympathetic stimulating effects. The results obtained indicate that at the dose used, physostigmine is of no clinical value in treating sedation induced by lorazepam.
Adult↗
Pneumocephalus after posterior fossa exploration in the sitting position.
Entrainment of air following exploration of posterior cranial fossa in the sitting position was studied in five patients. Intracranial pressure was monitored through a ventriculostomy catheter after closure of the dura. In three patients nitrous oxide was added to the breathing mixture only after the baseline intracranial pressure had stabilised following closure of the dura. A marked rise in intracranial pressure was observed immediately. A rapid decrease in intracranial pressure occurred when nitrous oxide administration was stopped. Two patients were nitrous oxide from the beginning. No change in intracranial pressure was noted. Computerised tomogram on the first postoperative day revealed a significant amount of air in eight cases.
Anesthesia, Inhalation↗
Time course of antirecall effect of diazepam and lorazepam following oral administration.
The time course of antirecall effect and grades of sedation after the oral administration of diazepam and lorazepam were determined in 120 patients. Three standard doses of each drug were employed. Grades of sedation following oral diazepam were dose related, with a latency of 30-60 min and duration of 120-150 min. All three doses of lorazepam produced significantly more sedation with a similar latency (30-60 min) but longer duration (more than 240 min). Peak frequencies of the antirecall effects of diazepam 10, 15, and 20 mg were 5, 20, and 30 per cent, respectively. The duration was about two hours. Peak frequencies of the antirecall effect after lorazepam 2, 3, and 4 mg were 30, 45, and 72 per cent, respectively. Latency of peak action was about 60-90 min for all the doses, but the duration, especially with 3 and 4 mg doses, was long (4 h).
Administration, Oral↗
Modification of chronotropic response to anticholinergics by halogenated anaesthetics in children.
Cardiac rate and rhythm changes were studied in 40 children after intravenous injection of atropine or glycopyrrolate following induction of anaesthesia with halothane and enflurane. Premedication was standardized in all groups and ventilation controlled to achieve normal end tidal carbon dioxide. Heart rate increased in all cases following anticholinergic medication and the increase in heart rate was significantly higher in children receiving halothane anaesthesia as compared to those given enflurane. There was no significant difference between atropine and glycopyrrolate groups. There was no difference in frequency of occurrence of junctional tachycardia, which was the only arrhythmia observed, in the four groups studied. Our findings suggest that, in clinical situations where development of marked tachycardia is a concern, the combination of enflurane and anticholinergic drugs offers an advantage over the combination of halothane and anticholinergic drugs in paediatric patients.
Age Factors↗