Seizures during opioid anesthetic induction--are they opioid-induced rigidity?

An electroencephalogram biomarker of fentanyl drug effects

Opioid drugs influence multiple brain circuits in parallel to produce analgesia as well as side effects, including respiratory depression. At present, we do not have real-time clinical biomarkers of these brain effects. Here, we describe the results of an experiment to characterize the electroencephalographic signatures of fentanyl in humans. We find that increasing concentrations of fentanyl induce a frontal theta band (4 to 8 Hz) signature distinct from slow-delta oscillations related to sleep and sedation. We also report that respiratory depression, quantified by decline in an index of instantaneous minute ventilation, occurs at ≈1700-fold lower concentrations than those that produce sedation as measured by reaction time. The electroencephalogram biomarker we describe could facilitate real-time monitoring of opioid drug effects and enable more precise and personalized opioid administration.

Acute Opioid-Induced Myoclonic Reaction after Use of Fentanyl as an Anesthetic Drug for an Emergency Cesarean Section

Myoclonus is an abnormal involuntary movement that has been previously reported with administration of high doses of opioids for prolonged periods of time. In this case, however, we report an acute myoclonic reaction and review the literature on the possible causative pathophysiology. We report the case of a 24-year-old woman who was admitted for postdated cesarean section. She started to have abnormal involuntary movements after administration of an epidural anesthesia containing 700 μg of fentanyl with 115 mL (0.5) bupivacaine and 40 mL (2%) lidocaine. Upon examination, the patient was conscious, alert, and oriented. Her vital signs were stable. Her movements can be described as generalized, sudden, involuntary, jerking movements, involving the upper limbs, head, torso as well as the lower limbs. The frequency of these jerks was about every 1–2 min lasting for 10 s. There was no change in level of consciousness during these abnormal movements. The rest of the neurological examination was normal. Laboratory values showed normoglycemia and normal serum biochemistry. A routine electroencephalogram showed no epileptiform activity. Brain imaging was normal. Based on history, examination, and laboratory findings, we made the diagnosis of drug-induced myoclonus, which in this clinical scenario was secondary to fentanyl. We discontinued fentanyl and, gradually, the intensity and frequency of the abnormal movements decreased and disappeared after a few hours. A clear definitive explanation of the acute effect of opioids is still to be reached. It involves an interaction of complex neuroanatomical pathways and neurophysiological receptors. Nonetheless, a unanimous effort is needed to raise awareness about the role of opioids in the development of abnormal movements and their clinical management, to insure that they do not go unnoticed in the clinical scenarios, and to further add more scientific content that could help in reaching an explanatory theory.

Does remifentanil improve ECT seizure quality?

Studies have reported that co-adjuvant remifentanil can enhance electroconvulsive therapy (ECT) seizure quality, putatively by allowing a reduction in the dosage of the main anaesthetic agents, as the latter have anticonvulsant properties. However, whether remifentanil also has direct effects on ECT seizure quality, and by implication, treatment efficacy, is unknown. This is the first study examining the effect of adjuvant remifentanil on ECT seizure quality when the dose of conventional anaesthesia remained unchanged. A total of 96 ECT sessions (from 36 patients) were retrospectively analysed. Subjects received ECT with and without remifentanil (1 µg/kg), while the dose of thiopentone (3-5 mg/kg) or propofol (1-2 mg/kg) was unchanged. Seizure quality indices (time to slow wave activity or TSLOW, amplitude, regularity, stereotypy, post-ictal suppression) and duration were assessed through a structured rating scale by a single trained blinded rater. Linear mixed-effects models with random subject effects analysed the effect of remifentanil on seizure parameters, controlling for other variables that can affect seizure quality or duration. Remifentanil was given in 47.9 % of the ECT sessions. Co-adjuvant remifentanil had no effects on any of the seizure quality parameters analysed [TSLOW (E = -0.21, p > 0.1), amplitude (E = 0.08, p > 0.5), regularity (E = -0.05, p > 0.5), stereotypy (E = -0.02, p > 0.5), suppression (E = -0.3, p > 0.05)] or on seizure duration (E = -0.25, p > 0.1). While adjuvant remifentanil may be a useful strategy for reducing anaesthetic dosage in ECT, present evidence suggests that remifentanil does not have intrinsic properties that enhance ECT seizures.

Intravenous sufentanil-midazolam versus sevoflurane anaesthesia in medetomidine pre-medicated Himalayan rabbits undergoing ovariohysterectomy

Objective

To compare physiological effects of sufentanil-midazolam with sevoflurane for surgical anaesthesia in medetomidine premedicated rabbits.

Study design

Prospective, randomized controlled experimental study.

Animals

Eighteen female Himalayan rabbits, weight 2.1 ± 0.1 kg.

Methods

Premedication with 0.1 mg kg⁻¹ medetomidine and 5 mg kg⁻¹ carprofen subcutaneously, was followed by intravenous anaesthetic induction with sufentanil (2.3 μg mL⁻¹) and midazolam (0.45 mg mL⁻¹). After endotracheal intubation, anaesthesia was maintained with sufentanil-midazolam (n = 9) or sevoflurane (n = 9). Ovariohysterectomy was performed. Intermittent positive pressure ventilation was performed as required. Physiological variables were studied perioperatively. Group means of physiologic data were generated for different anaesthetic periods. Data were compared for changes from sedation, and between groups by anova. Post-operatively, 0.05 mg kg⁻¹ buprenorphine was administered once and 5 mg kg⁻¹ carprofen once daily for 2–3 days. Rabbits were examined and weighed daily until one week after surgery.

Results

Smooth induction of anaesthesia was achieved within 5 minutes. Sufentanil and midazolam doses were 0.5 μg kg⁻¹ and 0.1 mg kg⁻¹, during induction and 3.9 μg kg⁻¹ hour⁻¹ and 0.8 mg kg⁻¹ hour⁻¹ during surgery, respectively. End-tidal sevoflurane concentration was 2.1% during surgery. Assisted ventilation was required in nine rabbits receiving sufentanil-midazolam and four receiving sevoflurane. There were no differences between groups in physiologic data other than arterial carbon dioxide. In rabbits receiving sevoflurane, mean arterial pressure decreased pre-surgical intervention, heart rate increased 25% during and after surgery and body weight decreased 4% post-operatively. Post-operative problems sometimes resulted from catheterization of the ear artery.

Conclusion

Sevoflurane and sufentanil-midazolam provided surgical anaesthesia of similar quality. Arterial blood pressure was sustained during sufentanil-midazolam anaesthesia and rabbits receiving sevoflurane lost body weight following ovariohysterectomy. Mechanical ventilation was required with both anaesthetic regimens.

Clinical relevance

Anaesthesia with sufentanil-midazolam in medetomidine premedicated healthy rabbits is useful in the clinical and the research setting, as an alternative to sevoflurane.

Sedation in traumatic brain injury

Several different classes of sedative agents are used in the management of patients with traumatic brain injury (TBI). These agents are used at induction of anaesthesia, to maintain sedation, to reduce elevated intracranial pressure, to terminate seizure activity and facilitate ventilation. The intent of their use is to prevent secondary brain injury by facilitating and optimising ventilation, reducing cerebral metabolic rate and reducing intracranial pressure. There is limited evidence available as to the best choice of sedative agents in TBI, with each agent having specific advantages and disadvantages. This review discusses these agents and offers evidence-based guidance as to the appropriate context in which each agent may be used. Propofol, benzodiazepines, narcotics, barbiturates, etomidate, ketamine, and dexmedetomidine are reviewed and compared.

Sufentanil preserves hemodynamics and left ventricular function in patients with ischemic heart disease

OBJECTIVE

Sufentanil has been reported to provide stable hemodynamics similar to other opioids. However, it has not been reliably established whether this stability can be attributed only to Sufentanil and translates into fully preserved left ventricular (LV) function. The purpose of this study was to evaluate the effect of Sufentanil on hemodynamics and LV systolic and diastolic function using invasive monitoring and echocardiography in patients with ischemic heart disease.

METHODS

Prospective observational study of thirty patients acting as their own control undergoing echocardiographic imaging before and after bolus Sufentanil 1.5-2.0 μg/kg. Full invasive hemodynamic monitoring was established before Sufentanil administration. Global LV systolic function was evaluated with a global longitudinal peak systolic strain (GLPSS) by speckle tracking ultrasound; systolic displacement by tissue tracking (TT) and diastolic function was evaluated using Doppler tissue imaging and pulse wave Doppler.

RESULTS

Hemodynamic monitoring showed a minor decline in systolic blood pressure from 159 to 154 mmHg (P=0.046). No changes were observed in the cardiac index, stroke volume index and heart rate. An unchanged TT score index (9.9 vs. 10.2 mm, P=0.428) and GLPSS (14.3 vs. 14.5%, P=0.658) indicated preserved LV global systolic function and unchanged E'/A' (0.95 vs. 0.89, P=0.110) and E/E' ratio (15.4 vs. 14.9, P=0.612) indicated unchanged diastolic function.

CONCLUSION

Sufentanil preserves hemodynamic parameters as well as echocardiographic indices of LV systolic and diastolic function in patients with ischemic heart disease (IHD).

Anesthetic management of the patient with epilepsy or prior seizures

PURPOSE OF REVIEW

Epilepsy is a clinical disorder of paroxysmal recurring seizures, the diagnosis 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.

RECENT FINDINGS

New antiepileptic drugs (AEDs) have been a major change in the approach to management of patients with epilepsy. These drugs tend to have fewer significant drug interactions and less severe side effects. Nonetheless, first-generation AEDs are still widely used. Propofol and desflurane have reliable anticonvulsant effects, whereas remifentanil in larger doses and sevoflurane appear to support epileptiform activity, although the clinical significance of these observations is unclear.

SUMMARY

The primary concerns for providing anesthesia to the patient with epilepsy are the capacity of anesthetics to modulate or potentiate seizure activity and the interaction of anesthetic drugs with AEDs. Proconvulsant and anticonvulsant properties have been reported for virtually every anesthetic such that these properties become elements of the anesthetic plan in the patient with epilepsy. Moreover, AEDs have many physiologic and pharmacologic effects that can have an impact on an anesthetic.

Pro-epileptic effect of alfentanil in rats subjected to pilocarpine-induced chronic epilepsy

Pharmacological induction of epileptiform activity is a complementary method to study the epileptogenic area in drug-resistant epileptic patients. Among the different activation methods, fentanyl derivatives (e.g. alfentanil) provide one of the most efficient tools in triggering epileptiform abnormalities in surgical candidates. In this study, we tested the pro-epileptic effect of different concentrations of alfentanil in hippocampal slices obtained from control and pilocarpine-treated chronic epileptic rats. The pro-convulsant action of alfentanil was also studied in control and pilocarpine-treated epileptic rats implanted with subdural and hippocampal electrodes for electroencephalographic recordings. In 90% of slices from control animals, application of alfentanil (0.1-5 microM) induced a significant enhancement in amplitude and number of population spikes recorded in the hippocampal CA1 region. In contrast, alfentanil produced a significant reduction in the amplitude of population spikes in slices from pilocarpine-treated epileptic rats. These changes were accompanied by a significant increase in the number of population spikes in the form of epileptiform multispike responses of epileptic slices. Naloxone (20 microM) antagonized the effect of alfentanil in both control and epileptic slices, reducing the number of population spikes in slices from epileptic rats. In control rats, alfentanil induced epileptiform abnormalities in the hippocampal and cortical electroencephalographic recordings but only at concentrations higher than 200 microg/kg (e.g. 350 microg/kg). Lower doses of alfentanil (25 microg/kg) elicited epileptiform abnormalities only in chronic epileptic rats. The potent action of a minimal dose of alfentanil in inducing epileptiform activity suggests an enhancement of the pro-convulsant action of mu-receptor opioids in chronic temporal lobe epilepsy.

The safety of remifentanil by bolus injection

Remifentanil is the newest of the fentanyl family of short-acting phenylpiperidine derivatives to be released into clinical practice. Remifentanil is a pure agonist at the mu opioid receptor with relatively little binding at the kappa, sigma or delta receptors. This is precisely the same profile as the other opioids currently popular in anaesthetic practice (fentanyl, alfentanil, sufentanil) and it offers the same advantages (profound analgesia, sedation, attenuation of the stress response). This has led to widespread use of remifentanil as an adjunct to general anaesthesia in a variety of clinical settings. The unique pharmacology of remifentanil, in particular its rapid offset, has more recently attracted clinicians and investigators to the use of remifentanil by bolus injection, especially for procedures requiring a brief, intense, opioid effect. The clinical effects of remifentanil, both therapeutic and adverse, are consistent with that of the other fentanyl congeners. However, the pharmacokinetic profile of remifentanil, that is, its rapid effect site equilibration, has also revealed a significant potential for therapeutic misadventure. The untoward effects of remifentanil, given by continuous infusion, are well-described in the literature. They are predictable and easily managed by experienced clinicians. This review will concentrate on the adverse effects of remifentanil given by bolus injection, either alone or in the context of a background infusion.

Propofol treatment of refractory status epilepticus: a study of 31 episodes

PURPOSE

Refractory status epilepticus (RSE) is a critical medical condition with high mortality. Although propofol (PRO) is considered an alternative treatment to barbiturates for the management of RSE, only limited data are available. The aim of this study was to assess PRO effectiveness in patients with RSE.

METHODS

We retrospectively considered all consecutive patients with RSE admitted to the medical intensive care unit (ICU) between 1997 and 2002 treated with PRO for induction of EEG-monitored burst suppression. Subjects with anoxic encephalopathy showing pathological N20 on somatosensory evoked potentials were excluded.

RESULTS

We studied 31 RSE episodes in 27 adults (16 men, 11 women; median age, 41.5 years). All patients received PRO, and six also subsequently thiopental (THP). Clonazepam (CZP) was administered with PRO, and other antiepileptic drugs (AEDs) concomitant with PRO and THP. RSE was successfully treated with PRO in 21 (67%) episodes and with THP after PRO in three (10%). Median PRO injection rate was 4.8 mg/kg/h (range, 2.1-13), median duration of PRO treatment was 3 days (range, 1-9), and median duration of ICU stay was 7 days (range, 2-42). In 24 episodes in which the patient survived, shivering after general anesthesia was seen in 10 episodes, transient dystonia and hyperlipemia in one each, and mild neuropsychological impairment in five. The seven deaths were not directly related to PRO use.

CONCLUSIONS

PRO administered with CZP was effective in controlling most of RSE episodes, without major adverse effects. In this setting, PRO may therefore represent a valuable alternative to barbiturates. A randomized trial with these drug classes could definitively assess their respective role in RSE treatment.

Excitatory effects of fentanyl upon the rat electroencephalogram and auditory-evoked potential responses during anaesthesia

BACKGROUND AND OBJECTIVE

Previous studies have shown existence of inconsistent data concerning the use of auditory-evoked potential (AEP) and electroencephalogram (EEG) changes to measure the depth of anaesthesia in regimens involving the use of opioids. The present studies characterize the effects of fentanyl on those responses in rats.

METHODS

The effects of a bolus of fentanyl (6-10 microg kg(-1) intravenously) alone or following naloxone (100 microg kg(-1) intravenously) were examined using brain responses in rats during light anaesthesia with either propofol (20-30 mg kg(-1) h(-1)) or isoflurane (0.8%). Electrophysiological data were recorded using silver ball electrodes. The rats' tracheas were intubated and a femoral artery cannula was inserted to monitor blood pressure. Body temperature, respiratory and pulse rate, and pedal withdrawal data were also collected. Parameters measured before and following administration of naloxone and fentanyl or of fentanyl alone were compared using repeated-measures ANOVA.

RESULTS

Fentanyl significantly increased the latency of the major peak from the AEP during propofol and isoflurane anaesthesia (F = 13.2 and 13.5, respectively; P < 0.05) and the amplitude differential between two waveform complexes, and the second differential index (F = 28.3 and 57.2, respectively; P < 0.01). The spectral edge frequency and median frequency from the EEG tended to increase. These effects were abolished by the prior administration of naloxone.

CONCLUSIONS

These excitatory effects were inconsistent with the classical concept of brain activity depression indicating a deepening of anaesthesia.

Safety of injectable opioid maintenance treatment for heroin dependence

BACKGROUND

There is a growing debate about injectable opioid treatment programs in many Western countries. This is the first placebo-controlled study of the safety of injectable opioids in a controlled treatment setting.

METHODS

Twenty-five opioid-dependent patients on intravenous (IV) heroin or IV methadone maintenance treatment were randomly assigned to either their individual prescribed IV maintenance dose or placebo. Acute drug effects were recorded, focusing on electrocardiography, respiratory movements, arterial blood oxygen saturation, and electroencephalography (EEG).

RESULTS

After heroin injection, marked respiratory depression progressing to a Cheyne-Stokes pattern occurred. Peripheral arterial blood oxygenation decreased to 78.9 +/- 8.7% (mean +/- SD) ranging from 52%-90%. During hypoxia, 7 of the 16 subjects experienced intermittent and somewhat severe bradycardia. Five subjects exhibited paroxysmal EEG patterns. After methadone injection, respiratory depression was less pronounced than after heroin injection. No relevant bradycardia was noted.

CONCLUSIONS

Opioid doses commonly prescribed in IV opioid treatment induce marked respiratory and circulatory depression, as well as occasionally irregular paroxysmal EEG activity. Further studies are needed to optimize the clinical practice of IV opioid treatment to prevent serious complications. Moreover, the extent of the observed effects raises questions about the appropriateness of IV opioid treatment in the present form.

Fentanyl-induced rigidity during emergence from general anesthesia potentiated by venlafexine

PURPOSE

To present and discuss a case of opioid-induced rigidity with low-dose fentanyl during recovery from anesthesia.

CLINICAL FEATURES

A 41-yr-old woman underwent laparotomy for total abdominal hysterectomy and bilateral salpingo- oophorectomy under general anesthesia. She received a total of 500 micro g of fentanyl by iv intermittent boluses during the three-hour anesthetic. During emergence from anesthesia, while intubated, the patient presented with rigidity. No changes in ventilatory parameters were measured during the episode. The only notable predisposing factor was treatment with venlafexine, an antidepressant that modifies serotonin and norepinephrine levels. She was successfully treated with iv naloxone 20 micro g. The rest of the postoperative period was uneventful.

CONCLUSION

We observed an atypical case of opioid-induced rigidity in contrast to the classical syndrome, which presents at induction with high-dose opioids. This syndrome has many clinical presentations with neurologic and ventilatory signs of varying intensity. Early recognition of the syndrome and adequate treatment is crucial. If treated adequately, opioid-induced rigidity is self-limited with few complications.

Effects of sevoflurane on electrocorticography in patients with intractable temporal lobe epilepsy

Fentanyl-droperidol technique is the choice for epilepsy surgery. It requires intraoperative electrocorticography (ECoG), but a large dose of fentanyl is needed for this technique. On the other hand, sevoflurane reportedly may be beneficial for intraoperative ECoG. To reveal whether the combined technique with fentanyl and sevoflurane is beneficial for epilepsy surgery, we investigated ECoG in 10 patients with intractable temporal lobe epilepsy without sevoflurane, with 0.5 minimum alveolar concentration (MAC) sevoflurane, and with 1.5 MAC sevoflurane under fentanyl-based anesthesia. The mean number of spikes for 1 minute decreased from 38.3 to 14.1 after 1.5 MAC sevoflurane was induced, which was statistically significant ( P <.05). Our results showed that balanced technique with neurolepto-analgesia (NLA) and sevoflurane is not suitable for epilepsy surgery requiring intraoperative ECoG. When epilepsy surgeries are performed under sevoflurane anesthesia, it is important to consider that sevoflurane may suppress electric activities when it is used with other anesthetic agents.

Generalized tonic-clonic activity after remifentanil administration

IMPLICATIONS

This is the first report of seizure-like activity in an adult who received remifentanil. This report confirms that opioid administration can be associated with generalized tonic-clonic seizure-like activity. It is suggested that this reaction could be referred to as the "opioid-seizure syndrome."

Alfentanil-induced epileptiform activity: a simultaneous surface and depth electroencephalographic study in complex partial epilepsy

PURPOSE

Alfentanil is a high potency mu opiate receptor agonist commonly used during presurgical induction of anesthesia. This and other opiate receptor agonists have demonstrated proconvulsant effects in animals, but these properties have been less consistently demonstrated in humans. Most human scalp EEG studies have failed to demonstrate induction of epileptiform activity with these agents, which is inconsistent with findings using intracranial EEG. Simultaneous scalp and depth EEG recordings have yet to be performed in this setting. The relationship between opiate dose and proconvulsant activity is unclear.

METHODS

Simultaneous scalp and depth electrode recordings were performed on five patients with complex partial epilepsy (CPE) who underwent alfentanil anesthesia induction before depth electrode removal. Consecutive equal bolus doses of alfentanil were administered to each patient according to strict time intervals so as to assess their correlation with any induced epileptiform activity.

RESULTS

Epileptiform activity was induced by alfentanil in three of five patients. Two of these patients had electrographic seizures. Epileptiform activity was only detected from the depth electrodes, occurring within 2 min of the first bolus dose in all three cases. Further increase or spread of epileptiform activity did not occur despite cumulative bolus doses of alfentanil.

CONCLUSIONS

Alfentanil is proconvulsant in patients with CPE. Induced seizures may be subclinical and lack a scalp EEG correlate. There is a complex dose-response relationship. Alfentanil induction of anesthesia should be approached with caution in patients with CPE.

Alfentanil-induced activation: a promising tool in the presurgical evaluation of temporal lobe epilepsy patients

Pharmacologic activation of epileptic foci has been used experimentally with the hope that it may accelerate the presurgical evaluation of patients with medically intractable epilepsy. In this article, we will review the existing literature on these activating tests giving emphasis on the opioid analogs, and particularly alfentanil. Alfentanil is an opioid analog with rapid anesthetic effect, which has been known to trigger epileptiform discharges in epilepsy patients. 58 temporal lobe epilepsy (TLE) patients were studied with alfentanil activation during electrocorticography, at the Epilepsy Surgery Unit (ING, Brazil). An increase of the interictal epileptiform discharges was observed originating from hippocampal and parahippocampal regions (96.5%). To a lesser extent, alfentanil activated the basal and lateral temporal regions. Electrographic seizures were observed in 38%. In addition, we performed continuous video-EEG (VT/EEG) monitoring, with scalp and bilateral foramen ovale electrodes, in 12 TLE patients. The results of spontaneously observed seizures were compared with the electrographic changes following alfentanil activation (50-75 microg/kg, i.v.). In seven cases, alfentanil triggered focal electrographic seizures, ipsilaterally to the side generating the spontaneous seizures and in two patients it produced bilateral sequential activation of the temporal lobes. Ictal SPECTs during the alfentanil test showed hyperperfusion at the lateral temporal regions, ipsilaterally to the activated area or bilaterally. In summary, our study confirms the activating effect of alfentanil, and provides a strong evidence for its selective activating effect on the temporal lobes of TLE patients. The ictal SPECT during alfentanil activation did not offer any additional advantage for the localization of the ictal onset.

Intraoperative localization of an epileptogenic focus with alfentanil and fentanyl

We evaluated the effectiveness of alfentanil and fentanyl in stimulating epileptogenic activity during surgery for intractable temporal lobe epilepsy under general anesthesia. Ten patients received a standardized anesthetic induction with i.v. fentanyl 5 microg/kg, propofol 3-5 mg/kg, and atracurium 0.5 mg/kg. Maintenance was with isoflurane, 70% N2O/30% O2, and an atracurium infusion. After dural opening, droperidol 0.02 mg/kg was administered i.v.. Both inhaled anesthetics were discontinued and verified to be at 0 end-tidal concentration before the study. Baseline electrocorticography over the surface of the temporal lobe and depth electrode recordings in the amygdala and hippocampus were obtained, followed by 10 min of recording before and after the i.v. administration of both alfentanil 50 microg/kg and fentanyl 10 microg/kg. Any changes in cardiovascular variables were documented. The number of interictal epileptiform spikes at the most active site for each patient was tabulated before and after the administration of each drug. Both alfentanil and fentanyl induced an increase in spike activity in all patients. Alfentanil was more potent, increasing the median number of spikes per epoch from 18 to 58, compared with fentanyl (20 to 42 spikes) (P < 0.05). Alfentanil had a shorter duration of action (4.9+/-1.3 min) compared with fentanyl (8.5+/-2 min) (P < 0.009). In nine patients, the most active site was the hippocampus or amygdala. There was a decrease in mean blood pressure, but only after the administration of alfentanil (P < 0.05). Two patients had electrographic evidence of seizure activity. These opioids can be used to assist in the localization of the epileptogenic focus during surgery.

IMPLICATIONS

Both alfentanil and fentanyl activate epileptiform activity in patients with temporal lobe epilepsy. These opioids can be used to assist in the localization of the epileptogenic focus during surgery.

Role of propofol in refractory status epilepticus

OBJECTIVE

To provide a review of the proposed mechanism of action, clinical efficacy, adverse effects, and therapeutic considerations associated with the use of propofol in the management of patients with refractory status epilepticus.

DATA SOURCES

A MEDLINE database (January 1966-April 1998) was searched for literature pertaining to status epilepticus and propofol. Additional literature was obtained from the references of selected articles identified in the search. Information from all articles published in English was considered for inclusion in the article.

DATA SYNTHESIS

Propofol is a unique, nonbarbiturate, anesthetic agent possessing anticonvulsant properties, although the exact anticonvulsant mechanism is unknown. Several case reports and two small, open, uncontrolled studies have described the efficacy of propofol in refractory status epilepticus. Most of these clinical reports discuss the utility of propofol after traditional treatment regimens have failed or are not tolerated. Initiation of propofol usually resulted in termination of seizure activity and/or electroencephalographic burst suppression within seconds that was sustained during the drug's use. Additionally, propofol was well tolerated. Advantages of propofol compared with traditional barbiturate anesthetic agents include better cardiovascular tolerability and a more favorable pharmacokinetic profile, allowing for rapid assessment of efficacy and neurologic assessment upon drug withdrawal. Propofol has been associated with a variety of neuroexcitatory adverse events such as opisthotonos, muscle rigidity, and choreoathetoid movements. Additionally, although the data are inconclusive, propofol has also been reported to cause seizures.

CONCLUSIONS

Propofol has shown promising results in the management of refractory status epilepticus when traditional therapies have failed or were not tolerated; however, controlled clinical trials are needed to better assess the comparative efficacy, neurologic adverse effects, and clinical outcome to better define its role in refractory status epilepticus.

Evaluating a possible pharmacokinetic interaction between remifentanil and esmolol in the rat

Remifentanil (Ultiva) is a novel, ultra-short-acting opioid which has recently been approved for use as an analgesic during induction and maintenance of general anesthesia. Esmolol is a short-acting beta-blocker used during surgical procedures to reduce heart rate and blood pressure. Both drugs are metabolized by nonspecific esterases in the blood and other tissues and may be administered concomitantly during surgery. The goal of this study was to determine if coadministration of esmolol significantly alters the pharmacokinetics of remifentanil in the rat. Two groups of rats were dosed with remifentanil [25 micrograms/kg/min (n = 8)] and remifentanil plus esmolol [25 and 200 mg/kg/min (n = 7)] for 20 min. Cardiovascular measurements were collected continuously over the course of the study. Serial blood samples (12) were collected over 25 min into test tubes containing 0.5 mL of acetonitrile. Blood samples were extracted (liquid-liquid) with methylene chloride and then analyzed by a validated GC-MS assay. Compartmental data analysis was performed using PCNONLIN. The mean(+/- SD) for Cl and t1/2 observed in treatment I were 390(+/- 98) mL/min/kg and 0.69(+/- 0.27) min and in treatment II were 421(+/- 164) mL/min/kg and 0.56(+/- 0.22) min, respectively. Comparison of clearance, volume of distribution, and terminal half-life between the two groups showed that coadministration of esmolol had no significant (p < 0.05) effect on the pharmacokinetics of remifentanil in the rat.

Alfentanil Mediated Activation of Epileptiform Activity in the Electrocorticogram During Resection of Epileptogenic Foci

Purpose:

Alfentanil is a potent, short-acting opioid agent which has been used during balanced anaesthesia in children undergoing the surgical excision of epileptic foci. After the observation that this agent had the potential to induce epileptic seizures, we questioned the frequency of this occurrence in this group of patients.

Method:

Twelve patients (6 males, 6 females) undergoing surgical excision of an epileptic foci were prospectively followed. For each patient an electrocorticogram was recorded for 30 minutes before and after receiving alfentanil 20 pg/kg intravenously. The frequency of epileptiform abnormalities before and after drug administration was evaluated. When the electrocorticogram no longer showed the effects of alfentanil administration, methohexital 0.5 ug/kg was given intravenously.

Results:

Alfentanil induced significant activation of epileptiform discharges among 83% of these patients. Twenty-five per cent had an electrographic seizure. In comparison, methohexital induced significant activation of epileptiform discharges in 50% of these patients. None experienced electrographic seizures.

Conclusions:

As alfentanil can induce electrographic seizures in patients known to have epilepsy, caution is advised in its use in this group of patients.

Sedation for the critically ill neurologic patient

OBJECTIVE

To review the scientific basis for sedation of critically ill neurologic patients by summarizing the distinct neurophysiologic disturbances present in this population and presenting the central nervous system effects of sedative agents to permit optimal drug therapy.

DATA SOURCES

Review of the English language clinical and scientific literature using MEDline data search.

STUDY SELECTION

Literature references were selected through a key word search of sedative therapy, drugs used for sedation, and specific neurologic disorders and processes to provide an in-depth overview of sedative drug mechanisms of action, effects on neurophysiology and intracranial dynamics, pharmacokinetics, and toxicity profile. Special emphasis was placed on neurologic side effects.

DATA EXTRACTION

Clinical and scientific literature was reviewed and data relevant to neurophysiologic effects of sedative drug therapy were summarized. Recommendations for institution of sedative therapy and of particular agents were made as a result of analysis of all pooled data.

DATA SYNTHESIS

Critically ill patients with neurologic pathology present as a unique subset of individuals cared for in an acute care setting. Because monitoring of neurologic patients requires frequent assessment of the neurologic examination, the goal of sedative therapy should be to enhance, or to minimally perturb elicitation of the examination. Neurophysiologic disturbances introduce distinct risks for sedation and require their identification and understanding before the initiation of any sedative therapy. Sedative drugs, in particular, act to disturb central nervous system function and their effects may result in diagnostic confusion and further neurologic deterioration. The pharmacokinetic and neurophysiologic actions of the common classes of sedative agents, such as benzodiazepines, opioids, barbiturates, and neuroleptics, as well as ketamine, propofol, and clonidine are discussed. Recommendations are presented based on the specific type of sedation required and the underlying neurologic disturbance. Several specific examples, including head trauma, neuromuscular disease, and alcohol withdrawal, are provided.

CONCLUSIONS

Preservation of the neurologic examination is paramount in documenting clinical improvement or deterioration in the critically ill neurologic patient. Pharmacologic sedation in this unique population of acute care patients requires careful consideration of the underlying neurophysiologic disturbances and potential adverse effects introduced by sedative drugs.

Opioid-induced muscle activity: implications for managing chronic pain

OBJECTIVE

To increase awareness of opioid-induced involuntary muscle hyperactivity and to present management options.

CASE SUMMARY

A ventilator-dependent 71-year-old man presented with pain caused by metastatic lung cancer. Transdermal fentanyl therapy was titrated to 200 micrograms/h. Two days later a continuous morphine infusion was initiated because of frequent administration of oral morphine solution for breakthrough pain. The patient became progressively less responsive and began exhibiting involuntary muscle hyperactivity thought to represent breakthrough pain. Despite the inability to assess pain control effectively in this unresponsive patient, the morphine infusion rate was increased from 22 to 717 mg/h within 7 days. No change in muscle hyperactivity was observed.

DISCUSSION

Over the last decade involuntary muscle hyperactivity has been documented as an adverse effect of chronic opioid therapy. The literature describing the incidence of this toxicity, possible risk factors for its development, and recommendations for its management are discussed.

CONCLUSIONS

The occurrence of muscle hyperactivity in an unresponsive patient receiving chronic opioid therapy may represent opioid toxicity. Recommendations for managing opioid-induced muscle hyperactivity include reduction of the opioid dosage and/or administration of clonazepam therapy.

Pharmacokinetic/dynamic assessment in drug development: application to the investigational opioid mirfentanil

The safety, pharmacokinetics, and pharmacodynamics of the investigational partial opioid agonist, mirfentanil, were determined in a dose-escalating, Phase 1 study in healthy male volunteers. Hemodynamic, central nervous system, and respiratory monitoring were used for safety assessment. The electroencephalogram (EEG) was evaluated as a surrogate measure of drug effect. Butorphanol was chosen as the control drug. In the mirfentanil group (n = 8) the dose was increased in sequential subjects from 25 micrograms.kg-1.min-1 for 30 min to 450 micrograms.kg-1.min-1 for 15 min, and in the butorphanol group (n = 10) from 2 micrograms.kg-1.min-1 for 30 min to 25 micrograms.kg-1.min-1 for 15 min. In the mirfentanil group, serious side effects were observed at plasma concentrations more than 2000 ng/mL: heart rates exceeded 130 bpm (n = 2), epileptiform EEG potentials (n = 2), and a convulsion (n = 1). The clearance of mirfentanil was high (5.8-7.2 L/min), and the volume of distribution large (247-348 L). The EEG of the subjects receiving mirfentanil showed no changes typical for opioids. Butorphanol however, caused intermittent slowing in the delta and theta ranges. The results of our study define the upper limit of safe plasma concentrations in future mirfentanil studies.

Intrathecal administration of high-dose morphine solutions decreases the pH of cerebrospinal fluid

Terminally ill patients suffering from intractable cancer pain are treated in our hospital on an outpatient basis with a percutaneous intrathecal (i.t.) catheter and a portable pump delivering morphine continuously. In a patient showing an increased demand of morphine the dose was raised from 1.5 to 2 mg/h, but pain intensity did not decrease. Subsequently a 1.5 ml dose of 5% lidocaine was administered; however, no motor or sensory block was observed. After controlling the catheter position and passage through the catheter, a sample of cerebrospinal fluid (CSF) was taken and the pH was measured. It was found to be outside the physiological range of 7.19 (normal range: 7.27-7.37), possibly explaining the decreased activity of the local anesthetic. The purpose of this study was to determine the influence of morphine, with or without sodium metabisulfite, on pH in vitro, using artificial CSF (ACSF) and on pH in vivo during i.t. administration of morphine. An in vitro model was used to measure pH changes by adding a morphine solution (concentrations of 0.5, 2, 5 and 10 mg/ml) with and without sodium metabisulfite to ACSF solutions (Elliott B). Fourteen patients were consecutively selected for continuous administration of morphine. An i.t. catheter was inserted, tunnelled and connected with an external pump (Provider 5500, Abbott, Chicago, IL). CSF was aspirated and pH was measured with a blood-gas system (Ciba-Corning 288, Medfield, USA). In vitro, morphine solutions with or without sodium metabisulfite added to an Elliott B solution (pH = 7.47, 37 degrees C) caused a concentration-related decrease in pH.(ABSTRACT TRUNCATED AT 250 WORDS)

Epileptiform activity during opioid anesthesia

The proconvulsant properties of exogenously administered opioids in man are not established. We prospectively evaluated relationships between epileptiform activity and opioid dose in 20 patients undergoing coronary artery revascularization. Baseline electroencephalograms were performed before surgery. Ten subjects were given fentanyl and 10 sufentanil, at 100 micrograms/kg and 10 micrograms/kg, respectively, in 4 divided doses, 3 min apart. Midazolam (4 mg) was given 3 min after the last dose of narcotic. Serum opioid concentrations were measured by radioimmunoassay. Within 3 min of the first opioid dose, 19 of 20 patients developed epileptiform activity, characterized by generalized single and multiphasic, low-to-moderate voltage spike discharges, similar in appearance to benign epileptiform transients of sleep (BETS). Despite continuously increasing serum concentrations of opioid, the number of spike discharges initially increased during the first and second dose intervals and then declined during the third and fourth dose intervals. This dissociation between epileptiform discharges and measured serum opioid concentration was unexpected and remained unexplained. Spike activity was consistently attenuated (P = 0.000003) within 20 sec of midazolam administration. Abrupt cessation of discharges after administration of the anticonvulsant, midazolam, suggests an epileptogenic mechanism for the opioid-induced activity.

The effects of midazolam on the EEG during sedation of critically ill patients

Patients who require mechanical ventilation are often sedated with midazolam. As clinical signs of sedation are often confusing or nonexistent, and there are few adverse side effects when large doses are infused over a period of days, substantial drug accumulation can result in these critically ill patients, despite the short half-life of midazolam. An objective monitor of sedation would help maintain sedation at a constant level despite changing pharmacokinetic values in patients. We undertook this study to describe the electroencephalographic changes which occur with intravenous midazolam in critically ill patients, and to determine if a relationship exists between these changes and the depth of sedation as measured using a clinical scoring method. A series of 31 critically ill patients who required intravenous midazolam during mechanical ventilation were studied. Four different levels of sedation were defined ranging from execution of verbal commands to no response to suctioning through the tracheal tube or sternal rub. Electroencephalographic recordings were obtained in patients on a daily basis and a concurrent sedation level was determined. High frequency electroencephalogram activity decreased as sedation level increased. This was reflected in decreases in the spectral edge (17.61 to 10.56 Hz (p = 0.0024)), the median frequency (4.27 to 2.56 Hz (p = 0.0278)), and the logarithm of the absolute power in the beta 1 (p = 0.0012), and beta 2 (p < 0.0001) bands. An incidental finding of asymmetry in power between right and left frontal electrodes was observed, with right-sided power being 9-18% greater (p < 0.001).(ABSTRACT TRUNCATED AT 250 WORDS)

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.

Apparent focal motor seizure with a jacksonian march induced by fentanyl: a case report and review of the literature

This report describes an unusual presentation of focal motor activity resembling Jacksonian march, which developed during fentanyl induction of general anesthesia. Simultaneous spectral-edge activity recording of electroencephalography (EEG) failed to show evidence of an epileptic focus. A negative history of previous seizures, as well as failure to show postoperative postictal symptoms or seizure activity by 16-lead EEG, suggested a myoclonic rather than epileptic nature of the observed muscle activity. Pertinent literature and current theories regarding opioid-induced seizures are discussed.

Postoperative opisthotonus and torticollis after fentanyl, enflurane, and nitrous oxide

Most drug-induced extrapyramidal symptoms are due to blockade of dopaminergic receptors and are treated with anticholinergic drugs. We report a patient with severe postoperative extrapyramidal symptoms which responded to physostigmine and indicated a different aetiology. A young, healthy female outpatient developed severe extrapyramidal symptoms after an uneventful 50 min anaesthetic with thiopentone, fentanyl (100 micrograms), enflurane, and nitrous oxide. Although the trachea was not extubated until she obeyed commands, the patient developed opisthotonus, which resolved initially after treatment with thiopentone (40 mg), diazepam (5 mg), and diphenhydramine (50 mg). The opisthotonus recurred approximately 25 min later, in association with torticollis, obtundation, and periodic apnoea. A tentative diagnosis of central anticholinergic syndrome was proposed, and fentanyl was considered to have been responsible. Naloxone (0.4 mg) induced no improvement, but physostigmine (2 mg) reversed the dystonic symptoms and periodic apnoea and improved her mental status. The response to physostigmine may have been due specifically to increased levels of acetylcholine at the cholinergic receptors, or to a nonspecific analeptic effect.