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Biomedical subjects

R Tempelhoff

Publications and source records attributed to R Tempelhoff.

At least 37 records · Page 2Linked to original sources
PubMed1992

Intracranial pressure during induction of anaesthesia and tracheal intubation with etomidate-induced EEG burst suppression.

This study was designed to determine if induction of anaesthesia with etomidate titrated to an early EEG burst suppression pattern would produce minimal changes in cerebral perfusion pressure, and prevent increases in intracranial pressure (ICP) associated with tracheal intubation. Eight patients, 18-71 yr, with intracranial space-occupying lesions, were studied. In each patient ICP was monitored via a lateral ventriculostomy catheter placed preoperatively. In the operating room, an ECG, a radial arterial line, and a two-channel computerized EEG were placed. Control (awake) measurements of MAP (mmHg), ICP (mmHg), CPP (mmHg), heart rate (HR-bpm), EEG power (picowatts-pW), and spectral edge frequency (SEF, Hz) were obtained. Anaesthesia was induced with etomidate, 0.2 mg.kg-1 iv, followed immediately by an etomidate infusion, 20 mg.min-1, iv, and vecuronium 0.2 mg.kg-1 iv. When early burst suppression was achieved, the etomidate infusion was stopped and tracheal intubation performed. The etomidate dose (bolus plus infusion) required to reach burst suppression was 1.28 +/- 0.11 mg.kg-1. Compared with awake control values (mean +/- SE), the period from induction to burst suppression was associated with a 50% decrease in ICP (22 +/- 1 vs 11 +/- 1 mmHg, P less than 0.01), but there were no changes in MAP, CPP, or HR. The decrease in ICP was maintained during the first 30 sec and the following 60 sec after intubation as MAP and HR remained unchanged. Our results suggest that when etomidate was administered to early burst suppression pattern on EEG, minimal changes in CPP occurred during induction of anaesthesia and a marked reduction in ICP was maintained following tracheal intubation.

Adolescent↗
PubMed1992

EEG-assisted titration of propofol infusion during neuroanesthesia: effect of nitrous oxide.

Total intravenous anesthesia (TIVA) with propofol is an alternative to standard techniques for neuroanesthesia. The present study compared the hemodynamic and recovery profiles of 46 neurosurgical patients randomly assigned to one of three different anesthetic treatment groups. Group 1 was anesthetized with a TIVA technique in which propofol was titrated using an EEG-assisted quantification method. Group 2 received a similar propofol-based infusion technique in combination with nitrous oxide. Group 3 (control) received a standard anesthetic technique consisting of thiopental, nitrous oxide, fentanyl, and isoflurane. Significantly less propofol was required in group 2 than in group 1 (7.4 +/- 1.9 vs. 9.0 +/- 1.0 mg/kg/h, respectively). The propofol blood concentration at the first appearance of EEG burst suppression was also higher in group 1 compared to group 2 (5.8 +/- 1.1 vs. 4.8 +/- 0.8 microg/ml). However, 25% of the patients in group 2 were treated for hypotension after induction, compared to none in groups 1 and 3. Hypertensive episodes, on the other hand, were more frequent in groups 1 (43%) and 3 (31%) than in group 2 (12%). Time to awakening was significantly shorter in the control group (6 +/- 6 min) than in groups 1 (14 +/- 10 min) or 2 (12 +/- 16 min). In conclusion, titration of propofol to achieve a burst suppressive EEG pattern resulted in a slower emergence from anesthesia than a standard "balanced" technique. Use of nitrous oxide with propofol produced more hypotension during induction; however, its use improved hemodynamic stability during the maintenance period.

Journal Article↗
PubMed1992

Computerized electroencephalographic monitoring and selective shunting: influence on intraoperative administration of phenylephrine and myocardial infarction after general anesthesia for carotid endarterectomy.

During carotid endarterectomy (CEA), phenylephrine infusions are commonly used to induce hypertension during carotid clamping in an attempt to increase collateral cerebral blood flow and prevent cerebral ischemia. Although this practice appears to increase the incidence of intraoperative myocardial ischemia during CEA when general anesthesia is employed, whether the limited use of phenylephrine infusions in specific instances of cerebral ischemia, as shown on an electro-encephalogram, results in low perioperative rates of both myocardial infarction (MI) and cerebral infarction remains unclear. We studied 171 CEAs done under general anesthesia performed with selective shunting based on the identification of cerebral ischemia by a two-channel computerized electroencephalographic monitor. The use of a phenylephrine infusion was restricted to the following instances of cerebral ischemia: 1) ischemia associated with hypotension that did not resolve within 2 minutes of decreases in anesthetic administration and treatment with fluid and/or colloid; 2) ischemia poorly or slowly responsive to shunt placement, accompanied by either hypo- or normotension; and 3) ischemia poorly or slowly responsive to removal of the carotid clamp, accompanied by either hypo- or normotension. Two non-Q wave MIs (1.2%) occurred, both nonfatal. There were two cerebral infarctions (1.2%) and three deaths not related to MI (1.8%). Based on these findings, in order to decrease the incidence of both MI and cerebral infarction after general anesthesia for CEA, we recommend the restrictive use of phenylephrine-induced hypertension for specific instances of slowly or poorly reversible cerebral ischemia, as shown on the electroencephalogram.

Adult↗
PubMed1992

Fentanyl-induced electrocorticographic seizures in patients with complex partial epilepsy.

Although electrical seizure activity in response to opioids such as fentanyl has been well described in animals, scalp electroencephalographic (EEG) recordings have failed to demonstrate epileptiform activity following narcotic administration in humans. The purpose of this study was to determine whether fentanyl is capable of evoking electrical seizure activity in patients with complex partial (temporal lobe) seizures. Nine patients were studied in whom recording electrode arrays had been placed in the bitemporal epidural space several days earlier to determine which temporal lobe gave rise to their seizures. The symptomatic temporal lobe was localized by correlating clinical and electrical seizure activity obtained during continuous simultaneous videotape and epidural EEG monitoring. In each patient, clinical seizures and electrical seizure activity were consistently demonstrated to arise unilaterally from one temporal lobe (four on the right, five on the left). During fentanyl induction of anesthesia in preparation for secondary craniotomy for anterior temporal lobectomy, eight of the nine patients exhibited electrical seizure activity at fentanyl doses ranging from 17.7 to 35.71 micrograms.kg-1 (mean 25.75 micrograms.kg-1). More importantly, four of these eight seizures occurred initially in the "healthy" temporal lobe contralateral to the surgically resected lobe from which the clinical seizures had been shown to arise. These findings indicate that, in patients with complex partial seizures, moderate doses of fentanyl can evoke electrical seizure activity. The results of this study could have important implications for neurosurgical centers where electrocorticography is used during surgery for the purpose of determining the extent of the resection.

Adult↗
PubMed1991

Propofol vs. thiopental-isoflurane for neurosurgical anesthesia: comparison of hemodynamics, CSF pressure, and recovery.

Sixty otherwise healthy patients with no clinical signs of intracranial hypertension who were undergoing elective intracranial surgery were randomly assigned to receive anesthesia with either thiopental, 3-6 mg/kg i.v., and isoflurane, 0.5-1.5% (group 1, N = 30) or propofol, 1-2.5 mg/kg i.v., and propofol infusion, 40-200 microg/kg/h (group 2, N = 30). Both groups received 50% nitrous oxide in O2 subsequent to dural opening. During induction, the changes in heart rate (HR), mean arterial pressure (MAP), cerebrospinal fluid pressure (CSFP), and cerebral perfusion pressure (CPP) were similar between the groups, except at 3 min when the findings (mean +/- SEM) for CPP (81 +/- 3.3 vs. 70.3 +/- 2.8 mm Hg, p <0.05) were significantly lower in group 2. At intubation, the highest level of MAP (103.1 +/- 3.3 vs. 88.9 +/- 2.7 mm Hg, p <0.05) was significantly greater in group 1. At pinhead-holder application, the highest values of HR (81.8 +/- 3 vs. 73.9 +/- 2.1 beats/min, p <0.05), MAP (112.2 +/- 3.6 vs. 98.3 +/- 3 mm Hg, p <0.05), CSFP (15.2 +/- 1.3 vs. 11.6 +/- 1.1 mm Hg, p <0.05), and CPP (97.0 +/- 3.9 vs. 86.7 +/- 3.3 mm Hg, p <0.05) were significantly greater in group 1. During early (20-30 min) recovery, group 2 had higher Glasgow Coma Scale scores and a greater percentage of patients in whom eye opening, response to commands, extubation, speech, and time/space orientation were present. In conclusion, when compared to thiopentalisoflurane for intracranial surgery, propofol produces similar HR, MAP, CSFP, and CPP responses during induction, adequate control of these responses during nociceptive stimulation, and faster recovery for cerebral function postoperatively.

Journal Article↗
PubMed1990

Anticonvulsant therapy increases fentanyl requirements during anaesthesia for craniotomy.

This study was designed to determine whether patients receiving chronic anticonvulsant therapy demonstrate an altered requirement for fentanyl during anaesthesia. Sixty-one patients undergoing craniotomy were studied; 20 controls (MED = 0) who had never received anticonvulsants and 41 epileptics in whom therapeutic plasma concentrations of either one (MED = 1), two (MED = 2), or three (MED = 3) different anticonvulsants were documented. During anaesthesia with 60-70 per cent N2O in O2 and 0.2 per cent isoflurane, a maintenance dose (MD) of fentanyl was administered using a continuous variable-rate IV fentanyl infusion, supplemented by intermittent 50 micrograms IV boluses. In order to define the minimal dosage of fentanyl required, the MD was titrated according to increases or decreases in the heart rate and/or mean arterial pressure exceeding 15 per cent of baseline ward values. A progressively higher fentanyl MD was required in the epileptic patients (MED = 1-4.3 +/- 0.5 microgram.kg-1.hr-1; MED = 2-5.4 +/- 0.6; MED = 3-7.6 +/- 0.6) compared with the control MD (MED = 0-2.6 +/- 0.5) (P less than 0.001). These findings indicate that there appears to be a dose-effect relationship between the number of anticonvulsants received and the maintenance dose of fentanyl required during balanced anaesthesia.

Adolescent↗
PubMed1990

Pro- and anticonvulsant effects of anesthetics (Part I)

Many inhaled anesthetics and intravenous analgesics have been alleged to produce both proconvulsant and anticonvulsant activity in humans. The reasons for these contrasting actions on the CNS are poorly understood at the present time. However, biologic variability plays an important role in determining individual patient's responses to anesthetic and analgesic drugs. In addition, variations in the responsiveness of inhibitory and excitatory neurons to the central depressant effects of these drugs could also explain these apparently conflicting data. Depending on the brain concentration, centrally active drugs may produce differing effects on the CNS inhibitory and excitatory neurotransmitter systems. The availability of increasingly powerful magnetic resonance imaging techniques to provide noninvasive information about tissue chemistry (e.g., neurotransmitters and citric acid cycle metabolites) and positron emission tomography to noninvasively evaluate CNS drug-receptor interactions should lead to a more in-depth understanding of the in vivo effects of anesthetics and analgesics on the CNS. In the second part of this review article, we discuss the pro- and anticonvulsant effects of the sedative-hypnotics, local anesthetics, and other anesthetic adjuvant drugs.

Analgesics↗
PubMed1990

Pro- and anticonvulsant effects of anesthetics (Part II)

Perioperative seizures have numerous potential etiologies. In general, when seizures occur during surgery, their onset often coincides with the introduction of a specific anesthetic or analgesic drug. Conversely, postoperative seizures are more commonly due to nonanesthetic causes. However, there have been reports of postoperative convulsions that appeared to be caused by anesthetic or analgesic drugs administered intraoperatively via inhalation or injection (e.g., intravenous, epidural, or peripheral nerve block). Some anesthetics appear to possess both proconvulsant and anticonvulsant properties. One possible factor is an inherent pharmacodynamic variability in the responsiveness of inhibitory and excitatory target tissues in the CNS. This is well illustrated by the anticonvulsant and proconvulsant effects of progressively higher doses of local anesthetic drugs. This variability in neuronal responsiveness could also explain the conflicting findings for low versus high doses of fentanyl and etomidate. Furthermore, biological variation in the individual patient's responsiveness to certain anesthetic drugs could be an additional contributory factor. Differing structure-activity relationships might also explain why some anesthetic agents possess both proconvulsant and anticonvulsant properties. Relatively minor modifications in a drug's structure can influence its affinity for a specific receptor site and its intrinsic pharmacologic activity. For example, when methohexital was first introduced, convulsions were commonly encountered in patients with and without a history of epilepsy. Subsequent fractionation of the original compound into its two isomeric forms resulted in the identification of the isomer primarily responsible for this convulsive activity. In its present formulation (Brevital; Eli Lilly, Indianapolis, Ind.), the epileptogenic properties of methohexital are limited to patients with psychomotor epilepsy. However, compared with thiopental, excitatory effects are still more common with methohexital. The excitatory effects of methohexital are presumably due to its methylated structure. The inhaled anesthetic flurothyl (hexaflurodiethyl) ether and the intravenous anesthetic ketamine also illustrate how subtle changes in stereoisomerism can result in significant changes in structure-activity relationships. Flurothyl, a fluorinated ether analogue, reliably produces convulsions in nonepileptic patients, whereas its structural isomer isoindoklon has not been associated with seizure activity. Other examples of isomer or structural analogue relationships that produce differential effects on neuronal hyperexcitability include enflurane-isoflurane and meperidine-normeperidine. In conclusion, the patient population (epileptic or nonepileptic), the method of documentation (EEG study or clinical observation), and the method of EEG analysis (cortical or depth electrodes) must be considered to properly analyze the proconvulsant and/or anticonvulsant properties of an anesthetic or analgesic drug.(ABSTRACT TRUNCATED AT 400 WORDS)

Adjuvants, Anesthesia↗
PubMed1990

Resistance to atracurium-induced neuromuscular blockade in patients with intractable seizure disorders treated with anticonvulsants.

Previous studies have demonstrated that, with the exception of atracurium, resistance to the neuromuscular blocking effects of various muscle relaxants develops in patients receiving anticonvulsant therapy. We studied the effects of 0.5 mg/kg IV atracurium in 53 neurosurgical patients: 21 nonepileptic patients receiving no anticonvulsant therapy (MED = 0); 14 epileptic patients treated with carbamazepine for years (MED = 1); and 18 epileptic patients treated with carbamazepine plus either phenytoin or valproic acid for years (MED = 2). The evoked compound electromyogram of the adductor pollicis brevis was recorded, and results were analyzed using analysis of covariance, with weight and age as covariables. The onset time was not significantly different among the three groups. Times for recovery of baseline and train-of-four responses to stimuli were significantly shorter in the MED = 1 and MED = 2 groups than in control patients (MED = 0). The recovery index (time between 25% and 75% recovery of baseline electromyogram values) was progressively shorter in the three groups (MED = 0: 8.02 min; MED = 1: 5.93 min; MED = 2: 1.96 min; P less than 0.001). This study demonstrates that atracurium, when used on epileptic patients requiring long-term (that is, years of) anticonvulsant therapy, has a shorter duration of action than when used in nonepileptic patients.

Adolescent↗
PubMed1990

[Cerebral monitoring during surgery of intracranial aneurysm: review of various techniques and contribution of computerized EEG].

Recent studies have demonstrated that the computerized EEG (CEEG) is a reliable indicator for the early detection of brain ischemia during carotid surgery. During intracranial aneurysm surgery, different cerebral monitoring techniques are proposed, and the benefits and limitations of conventional EEG, evoked potentials and transcranial doppler are discussed. The authors also give the results of their experience with the CEEG monitoring during intracranial aneurysm surgery. In conclusion, they insist on the necessity for some type of cerebral monitoring during this type of surgery.

Brain Ischemia↗
PubMed1989

A comparison of computerized EEG with internal carotid artery stump pressure for detection of ischemia during carotid endarterectomy.

Previous investigations appear to indicate that an ischemic EEG is not observed during carotid cross-clamping when the stump pressure is >/=60 mm Hg. In this report of 124 carotid endarterectomies (CEA) performed with selective shunting based on computerized EEG (CEEG), we compared the CEEG and this previously established critical stump pressure level of 60 mm Hg as methods of detecting cerebral ischemia during carotid clamping. A significant association between stump pressure and CEEG findings during clamping existed (p <0.05). Only 1 of 44 patients with a stump pressure >/=60 mm Hg received a shunt based on CEEG signs of cerebral ischemia. However, 62 of the remaining 80 patients did not receive a shunt and awoke neurologically intact despite a stump pressure <60 mm Hg. A highly significant association between the postoperative neurologic exam and the CEEG findings during carotid clamping was demonstrated (p <0.001). In contrast, for stump pressure, a correlation with the neurologic exam was not found. Compared to CEEG, these results appear to indicate that a critical stump pressure of 60 mm Hg is a sensitive but not specific indicator for the placement of a shunt selectively during CEA. The combined use of these two monitors should lead to reliable shunt selection, especially when stump pressure is <60 mm Hg.

Journal Article↗
PubMed1989

Selective shunting during carotid endarterectomy based on two-channel computerized electroencephalographic/compressed spectral array analysis.

The reliability of selective shunting based on computerized electroencephalographic (EEG) monitoring has not been addressed. In this study, 103 carotid endarterectomies were performed with selective shunting based on a two-channel computerized EEG monitor that processed the on-line, raw electroencephalogram (EEG) to produce a compressed spectral array (CSA). Ischemic EEG events were identified by amplitude attenuation of the raw EEG and/or loss of high-frequency activity on the CSA. Fourteen patients (13.6%) received a bypass shunt, and postoperative neurological examinations showed 97 patients (94.2%) to be intact. A correlation between total (cumulative) ischemic EEG time and the postoperative neurological exam was demonstrated (P less than 0.0001). Six postoperative deficits (5.8%) occurred, five in patients whose computerized EEGs demonstrated an ischemic EEG event late during carotid clamping, when it was no longer possible to place a shunt. The sixth deficit was found in a patient whose EEG did not demonstrate any patient whose EEG did not demonstrate any signs of cerebral ischemia. Five of these six new deficits resolved within 12 hours, and only one persisted for 72 hours, when the patient died of a pulmonary embolism (cerebral infarction and mortality rate of 1%). These results appear to demonstrate that two-channel monitoring of both the CSA and the unprocessed (raw) EEG simultaneously can be used as a reliable indicator of whether a bypass shunt is required during carotid cross-clamping in all patients, regardless of their preoperative neurological history or angiographic findings.

Brain Damage, Chronic↗