The effects of clonidine premedication and scalp infiltration of lidocaine on hemodynamic responses to laryngoscopy and skull pin head-holder insertion during skull base procedures

This study was designed to determine if oral clonidine or lidocaine, injected into the scalp before head-holder (H-H) insertion, would attenuate the hemodynamic effects associated with intubation and H-H placement. Thirty-four patients undergoing skull base procedures were randomized to four groups. Group 1 received clonidine 5 mcg/kg po before surgery with 10 to 15 ml of 1% lidocaine infiltrated at pin insertion sites; Group 2 received clonidine with saline infiltration; Group 3 received a placebo preoperatively and had lidocaine infiltrated at pin sites; and Group 4 received a placebo with saline infiltrated. All patients had a standard anesthetic titrated to a 10 to 14 Hz EEG endpoint during laryngoscopy and H-H placement. Mean arterial pressure (MAP) was similar between groups during intubation, but heart rate (HR) increased in patients who did not receive clonidine. H-H application increased HR and MAP in Group 4. HR also increased after H-H placement in patients who received oral clonidine, while patients receiving scalp lidocaine or both clonidine and scalp lidocaine had little change in either value. Clonidine attenuated HR increases after laryngoscopy but not after H-H placement. Lidocaine injected at the pin sites reduced HR, and MAP increased after H-H insertion. The combination of oral clonidine and scalp lidocaine blunted hemodynamic responses to both intubation and H-H placement.

The effect of prone positioning on intraocular pressure in anesthetized patients

BACKGROUND

Ocular perfusion pressure is commonly defined as mean arterial pressure minus intraocular pressure (IOP). Changes in mean arterial pressure or IOP can affect ocular perfusion pressure. IOP has not been studied in this context in the prone anesthetized patient.

METHODS

After institutional human studies committee approval and informed consent, 20 patients (American Society of Anesthesiologists physical status I-III) without eye disease who were scheduled for spine surgery in the prone position were enrolled. IOP was measured with a Tono-pen XL handheld tonometer at five time points: awake supine (baseline), anesthetized (supine 1), anesthetized prone (prone 1), anesthetized prone at conclusion of case (prone 2), and anesthetized supine before wake-up (supine 2). Anesthetic protocol was standardized. The head was positioned with a pinned head-holder. Data were analyzed with repeated-measures analysis of variance and paired t test.

RESULTS

Supine 1 IOP (13 +/- 1 mmHg) decreased from baseline (19 +/- 1 mmHg) (P < 0.05). Prone 1 IOP (27 +/- 2 mmHg) increased in comparison with baseline (P < 0.05) and supine 1 (P < 0.05). Prone 2 IOP (40 +/- 2 mmHg) was measured after 320 +/- 107 min in the prone position and was significantly increased in comparison with all previous measurements (P < 0.05). Supine 2 IOP (31 +/- 2 mmHg) decreased in comparison with prone 2 IOP (P < 0.05) but was relatively elevated in comparison with supine 1 and baseline (P < 0.05). Hemodynamic and ventilatory parameters remained unchanged during the prone period.

CONCLUSIONS

Prone positioning increases IOP during anesthesia. Ocular perfusion pressure could therefore decrease, despite maintenance of normotension.

Visual loss after spine surgery: a survey

OBJECTIVE

To survey a large number of neurosurgical spine surgeons for data regarding the presence of risk factors in patients experiencing visual loss after spine surgery.

METHODS

A survey was sent to current members (as of 1997) of the American Association of Neurological Surgeons/Congress of Neurological Surgeons, Section on Disorders of the Spine and Peripheral Nerves, with questions focusing on intraoperative factors that may predispose patients to perioperative visual loss.

RESULTS

Two hundred ninety surveys were returned, and 24 patients with visual loss after spine surgery were reported by 22 surgeons. Although many of these patients had probable causative factors for visual loss after surgery (e.g., hypotension, low hematocrit level, coexisting disease), some did not (n = 8).

CONCLUSION

These results suggest the necessity of a high index of suspicion for evolving perioperative visual loss even in the absence of risk factors.

Anesthesia and epilepsy

The patient with epilepsy is an anesthetic challenge. New drugs and surgical procedures are being used to treat epilepsy. Certain anesthetics have been reported to cause perioperative seizures. This discussion will focus on advances in the treatment of epilepsy, as well as the pro- and anti-convulsant effects of the newer anesthetic agents.

Anesthetic implications of epilepsy, status epilepticus, and epilepsy surgery

Epilepsy is a clinical paroxysmal disorder of recurring seizures, excluding alcohol or drug withdrawal seizures or such recurring exogenous events as repeated insulin-induced hypoglycemia. Epilepsy has a profound impact on each individual diagnosed with this disease. Seizures have been and are thought to arise as a result of abnormalities in (a) neural circuits, (b) excitation/inhibition balance, (c) potassium, and (d) genetic abnormalities. Therapy for epilepsy is either medical, entailing the use of a variety of antiepileptic drugs, or surgical. An urgent approach to seizure control is indicated when status epilepticus occurs. When all standard therapy fails, general anesthesia can be used to control status epilepticus. Surgery is an option in the treatment of epilepsy and requires extensive preoperative evaluation. The primary concerns for the neuroanesthesiologist anesthetizing the patient with epilepsy are the capacity of anesthetics to modulate or potentiate seizure activity and the interaction of anesthetic drugs with antiepileptic drugs. Proconvulsant and anticonvulsant properties have been reported for nearly every anesthetic. If seizure spikes are to be evoked during seizure surgery, then light anesthesia with a proconvulsant anesthetic is used. Conscious analgesia can be used for awake seizure surgery. However, if electrocorticography is not planned, then a general anticonvulsant anesthetic maintenance regimen is used. The latter technique also may be useful in patients whose anesthetic management is complicated by an incidental history of epilepsy.

Convection versus conduction cooling for induction of mild hypothermia during neurovascular procedures in adults

Hypothermia for cerebral protection is usually achieved by administration of intravenous fluids at room temperature, cooling ambient air, ice packs, and a temperature-adjustable circulating water mattress. We compared cooling by conduction by using a water mattress to cool by convection by using a forced-air cooling device. Twenty patients were prospectively randomized to two groups: 10 patients cooled by convection (CC) and 10 patients cooled by traditional methods (TC). Two patients in the CC group were withdrawn from the study and excluded from the analysis; one patient for failure to cool despite the use of both techniques, and the other for the abrupt onset of arrhythmias and myocardial depression during hypothermia. Temperature was measured at the tympanic membrane, pulmonary artery, and esophageal probe sites and recorded every 15 min. The time required to reach the target temperature range of 33-34 degrees C was recorded. We found no differences in the temperatures measured at the three sites during cooling and rewarming. Baseline temperatures recorded from the pulmonary artery catheter before beginning "active cooling" were similar in both groups (TC, 35.0 +/- 0.2 degrees C vs. CC, 35.3 +/- 0.1 degrees C). We found no difference in the time to target temperature between TC and CC (TC, 178 +/- 25 min vs. CC, 142 +/- 21 min). One patient had some arrhythmias on cooling in the convective group, but her preoperative condition may have been responsible. In conclusion, cooling by convection appears to be a safe alternative to conduction cooling.

Anesthesia for carotid endarterectomy: a survey

Indications for carotid endarterectomy (CEA) have been expanded recently, and a consensus statement has been made regarding these changes. However, the debate regarding the "ideal" anesthetic for CEA remains on-going. This study was designed to evaluate the actual anesthetic techniques used by anesthesiologists for CEA. A total of 426 1-page questionnaires were mailed to all current (1995) members of the Society of Neurosurgical Anesthesia and Critical Care (SNACC). Of these, 216 (50.7%) were completed and returned. The majority of these respondents (84.7%) administered general anesthesia (GA) for CEA. Regional anesthesia (RA) was the anesthetic method of choice for 16.7%, whereas 2.8% each chose either local anesthesia (LOC) or a combined regional/general (RA/GA) technique. Despite the controversial role of nitrous oxide in neuroanesthesia, 74.6% of those returning the survey use nitrous oxide during CEA. Intraoperative neuromonitoring use was reported by 90% of the respondents, with the electroencephalography (EEG) the favored modality (67.5%). Specific intraoperative neuroprotective measures were provided by only 22.2% of all respondents, with barbiturates as the favorite method (50.0%). The technique of intraoperative hypertension is practiced by a majority of those surveyed (61.1%), with the most common target blood pressures being either preoperative baseline or preoperative baseline plus 20%. Although there is some trend towards nonintensive care setting for postoperative care, the intensive care remains the location of choice for overnight care of CEA patients (71.8%). The results of this study show that despite arguments for RA over GA, the majority of anesthesiologists surveyed choose GA for CEA.

Etomidate and thiopental-based anesthetic induction: comparisons between different titrated levels of electrophysiologic cortical depression and response to laryngoscopy

STUDY OBJECTIVE

To determine whether etomidate-based induction can provide better hemodynamics than a standard thiopental sodium-based anesthetic induction.

DESIGN

Prospective, single-blind clinical trial.

SETTING

Multicenter university neurosurgical operating room.

PATIENTS

66 ASA physical status II and III inpatients undergoing neurosurgical procedures for intracranial tumor or other pathology.

INTERVENTIONS

Patients were divided into two groups for anesthetic induction. The first group (control) was divided into two subgroups, with the first subgroup receiving "low-dose" etomidate (LET) 0.4 to 0.6 mg/kg titrated to an electroencephalographic (EEG) spectral edge frequency (SEF) of 10 to 12 Hz. The second subgroup received thiopental sodium (THIO) 3 to 6 mg/kg titrated to the same EEG endpoint. The study group was given high-dose etomidate (HET) 0.5 to 1.7 mg/kg titrated to an early burst suppression pattern.

MEASUREMENTS AND MAIN RESULTS

Baseline (awake) measurements of mean arterial pressure (MAP) heart rate (HR), and SEF were obtained prior to anesthetic induction that was accomplished using a small bolus plus an infusion of the induction drug titrated to the EEG target. MAP, HR, and SEF were recorded just prior to laryngoscopy and intubation (T1), 30 seconds after laryngoscopy and intubation (T2), and 90 seconds after (T3) laryngoscopy and intubation. Times to reach EEG endpoint, along with total dose of anesthetic given, were also recorded. Compared with baseline values, the THIO group had the highest increase in both HR (22.9 +/- 4.4 bpm.) and MAP (16.8 +/- 4.2 mmHg) (P < 0.05) after laryngoscopy and intubation. The LET group also had significant increases compared with the HET group that demonstrated the least hemodynamic variability. No correlations could be made between age and dose of induction drug.

CONCLUSIONS

Etomidate-based anesthetic induction, titrated to EEG burst suppression, produced stable hemodynamics during laryngoscopy and intubation as compared with lower dose, more "classic" inductions with etomidate or thiopental.

Intravenous agents and intraoperative neuroprotection. Beyond barbiturates

The authors discuss the role of intravenous anesthetic agents in brain protection. The newer intravenous anesthetics, etomidate and propofol, have been proposed as neuroprotective agents. Thiopental remains the drug of choice, however, for use prior to intraoperative ischemic events. The anesthetic ketamine presents surprising similarities to other N-methyl-D-aspartate receptor inhibitors, but remains controversial in its use in neurologically compromised patients.

Large-dose propofol alone in adult epileptic patients: electrocorticographic results

The primary objective of this study was to evaluate the electrophysiologic effects of large-dose propofol, used as the sole anesthetic in patients with epilepsy. Nine patients with medically intractable complex partial epilepsy undergoing a three-stage approach to the surgical management of epilepsy were recruited. State I involved placement of the intracranial electrode array, while Stage II consisted of extraoperative localization of the seizure focus. The patients were studied during induction of anesthesia for Stage III (removal of electrodes and resection of seizure focus). Unpremedicated patients were induced with a propofol infusion (0.5 mg.kg-1.min-1) until one of the following occurred: 1) electrical seizure activity, 2) burst suppression, or 3) total dose of 10 mg/mg. Electrocorticography (ECoG) was recorded continuously during this period. Two patients were excluded from the study after experiencing delayed awakening after the Stage I procedure. Both had received propofol along with other anesthetics. No ECoG evidence of seizure activity was detected in the seven patients completing the study. Burst suppression was attained in six patients using a mean dose of 5.7 mg/kg +/- 2.6. We conclude that large dose propofol alone does not trigger electrical epileptiform activity on the ECoG of seizure patients.

Jugular bulb temperature: comparison with brain surface and core temperatures in neurosurgical patients during mild hypothermia

Blood temperature at the jugular bulb was monitored in 10 patients undergoing neurovascular procedures that used induced mild hypothermia, and its correlation with surface brain, core, and peripheral temperatures was determined. The study was motivated by the difficulty encountered in directly measuring global brain temperature and the poor correlations between various core and peripheral sites temperatures and brain temperature, particularly during deep hypothermia. Although not statistically significant, previous studies have suggested a trend toward higher brain temperatures. Temperatures from the jugular bulb (collected using a No. 5 French Swan-Ganz catheter) as well as from subdural, pulmonary artery, esophagus, tympanic membrane, and bladder sites were analyzed during three surgical conditions: prior to incision, with the dura open, and after closure of the dura. No complications related to placement of the jugular bulb catheter, induced hypothermia, or temperature monitoring were seen. The authors found that jugular bulb temperature was similar to pulmonary artery and esophageal temperatures; although prior to incision it tended to be higher than that found at the pulmonary artery, most commonly by 0.2 degrees C. Surface brain temperature was cooler than all other temperatures (p < 0.05), except that of the tympanic membrane, and was particularly sensitive to environmental variations. Finally, as has been shown by others, bladder temperature lagged substantially behind core temperatures particularly during rapid cooling and rewarming of the patient. In summary, monitoring of jugular bulb temperature is a feasible technique, and temperatures measured in the jugular bulb are similar to core temperatures.

Recovery from mivacurium-induced neuromuscular blockade is not affected by anticonvulsant therapy

Long-term chronic anticonvulsant therapy produces a resistance to the effects of all nondepolarizing neuromuscular blocking agents studied to date. Since the metabolism of mivacurium is unique among the nondepolarizing neuromuscular blocking agents, the effect of anticonvulsants on its recovery parameters was examined. Forty-five patients were separated into three groups based on the number of chronic anticonvulsant medications the subjects were taking: subjects in group 1, the control group, took no anticonvulsant medication; group 2 subjects took one medication; and group 3 subjects took two medications. Mivacurium, 0.15 mg/kg i.v., was administered after induction of general anesthesia with thiopental sodium, 4-6 mg/kg, and fentanyl 2-4 micrograms/kg i.v. Maintenance anesthesia consisted of N2O in O2. 0.2-0.3% end-tidal isoflurane, and a fentanyl infusion. The evoked compound electromyograph (ECEMG) of the adductor pollicis-brevis muscle was measured for time of onset, T-1 (time at which ECEMG signal reaches 5, 25, 50, and 75% of baseline), TR (TOF ratio), and recovery index. T-1 at 25% was 18.2 +/- 1.8, 20.7 +/- 1.9, and 21.5 +/- 1.4 min for groups 1, 2, and 3, respectively, with TR at 25% being 23.7 +/- 2.3, 26.9 +/- 2.4, and 27.3 +/- 2.3 min. No significant differences were noted in neuromuscular recovery between groups at any time point. These results fail to demonstrate the resistance to the nondepolarizing neuromuscular blockade of mivacurium that has been observed with other nondepolarizing agents.

[Cerebral protection: contribution of intravenous anesthetic agents]

The administration of an intravenous anaesthetic agent before experimental cerebral ischaemia in animals improves the functional and histological outcome. Cerebral ischaemia may be global or focal, complete or incomplete. Intravenous anaesthetic agents reduce the cerebral metabolic demand for oxygen (CMRO2) and abolish electrophysiological activity. This reflects a discontinuation of the functional neuronal activity with maintenance of its basic metabolic activity. The oxygen spared by the decrease in consumption, while reducing the functional activity, might be used by the neurons to sustain longer periods of ischaemia. This protective effect is also observed after pretreatment with either lidocaine or volatile agents, but their potentially deleterious vasodilating effect must be considered. Ketamine has recently been shown to antagonize NMDA receptors. The protective effect of barbiturates was experimentally demonstrated more than 30 years ago. They are still used as a reference. They reduce CMRO2, optimise the ratio between oxygen consumption and oxygen delivery and thus reduce cerebral blood flow and cerebral blood volume, as a result of the decrease of the metabolic demand. This might explain why a protective effect is seen in case of global or focal hypoxia with increased intracranial pressure, while no protection is documented in case of global cerebral ischaemia, such as after cardiac arrest, where EEG is immediately flat and ICP low. However, at doses required to obtain a protective effect, barbiturates induce deleterious side effects such as severe arterial hypotension, which limits their use. Cerebrovascular and cardiac surgery or surgery of the carotids are characterised by potentially ischaemic episodes which can be predicted.(ABSTRACT TRUNCATED AT 250 WORDS)

EEG-controlled "overdosage" of anesthetics in a patient with a history of intra-anesthetic awareness

In spite of the ever-growing pharmacologic arsenal available for induction and maintenance of anesthesia, to our knowledge no treatment regimen exists that will provide full protection against intraoperative awareness. To date, no single monitoring technique is able to detect awareness or predict recall. Although the frequency of these complications is rare, the occurrence of any such event can be very distressful for the patient. Based on our clinical experience with a patient with a history of recall and a marked resistance to benzodiazepines, we present electroencephalogram-based anesthetic management as a technique to address this difficult problem.

Accelerated recovery from pipecuronium in patients treated with chronic anticonvulsant therapy

STUDY OBJECTIVE

To determine whether chronic anticonvulsant therapy affects recovery time from pipecuronium.

DESIGN

Open-labeled, controlled study.

SETTING

Inpatient neurosurgical service at a university medical center.

PATIENTS

ASA physical status II and III patients within 30% of their ideal body weight and without significant history of ethanol abuse or renal or hepatic disease. Nineteen patients were admitted into the study and were divided into three groups based on the number of anticonvulsant medications (MED) they were taking: MED = 0, control group (6 patients); MED = 1, one anticonvulsant (6 patients); MED = 2, two or more anticonvulsants (7 patients).

INTERVENTIONS

Intravenous (IV) administration of pipecuronium 80 micrograms/kg with general anesthesia after thiopental sodium 4 to 6 mg/kg IV, maintained with 70% nitrous oxide in oxygen, 0.2% to 0.3% end-tidal isoflurane, and fentanyl.

MEASUREMENTS AND MAIN RESULTS

The evoked compound electromyogram (ECEMG) of the adductor pollicis brevis muscle was measured after stimulation of the ulnar nerve by train-of-four (TOF) supramaximal impulses at 2 Hz repeated every 20 seconds. Measurements include T-1% (ECEMG signal at 25%, 50%, and 75% of baseline), TR% (TOF ratio), and recovery index (RI). Patients administered chronic anticonvulsant therapy recovered more rapidly from pipecuronium than untreated patients. For instance, time to 25% recovery of baseline (T-1 25%) was 123 +/- 13 minutes for MED = 0, 91 +/- 7 minutes for MED = 1, and 58 +/- 5 minutes for MED = 2 (p < 0.05). TOF recovery to 20% (TR 20%) and RI were similarly affected.

CONCLUSIONS

Patients treated with chronic anticonvulsant therapy recovered from pipecuronium more rapidly than unmedicated patients. Furthermore, there seemed to be a dose-effect relationship between the number of anticonvulsants received and a decreased time to recovery from pipercuronium neuromuscular blockade.

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.

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.

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.

EEG-Assisted Titration of Propofol Infusion During Neuroanesthesia

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.

Propofol vs. Thiopental-Isoflurane for Neurosurgical Anesthesia

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.

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.

[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.

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)

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.

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.

[Monitoring of cerebral ischemia: current data and review of results based on the ischemic carotid model]

Recent studies appear to indicate that computerized electroencéphalogram (CEEG) monitoring is a reliable method for early detection of cerebral ischemia. This article summarizes the current status of this type of monitoring during cerebro-vascular procedures.

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.

Use of computerized electroencephalographic monitoring during aneurysm surgery

The clinical usefulness of intraoperative electroencephalographic (EEG) monitoring of cerebral perfusion during aneurysm surgery has received little attention, primarily due to problems with electrode placement over the operative site, which is the area of maximal risk. In this report, 27 patients undergoing surgery for anterior circulation aneurysms were monitored intraoperatively with a two-channel computerized EEG complex using a bilateral frontal-occipital montage. In 16 patients, a normal EEG pattern was observed throughout surgery; all 16 awoke neurologically intact and their postoperative angiograms did not reveal cerebral vasospasm. In the other 11 patients, one of two patterns of persistent EEG abnormalities was identified. 1) In six of these patients a marked attenuation of EEG activity was observed ipsilaterally which coincided with various intraoperative events including brain retraction, hypotension, and aneurysm dissection/clipping. Five of these six patients awoke with new neurological deficits which persisted beyond 12 hours in two, both of whom had angiographically proven vasospasm 24 hours after surgery. 2) In the remaining five patients, a distinct abnormal EEG pattern consisting of marked hyperactivity in the delta, theta, and alpha frequency ranges was observed ipsilaterally. Four of these five patients had a poor neurological outcome and vasospasm on their angiogram 24 hours after surgery. Thus, EEG monitoring which spans the operative area during aneurysm surgery is practicable and appears to be of value in the detection of compromised cerebral perfusion during aneurysm surgery. The possible significance of the two abnormal EEG patterns identified in this report is discussed.

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.