Propofol inhibits epileptiform activity in rat hippocampal slices

Seizure protection by intrapulmonary delivery of propofol hemisuccinate

The lung provides a portal of entry for drug delivery that could be used to administer anticonvulsant substances to prevent or abort seizures. Here, we demonstrate that intrapulmonary propofol hemisuccinate (PHS) rapidly confers seizure protection in various rodent chemoconvulsant models. Propofol is a powerful anticonvulsant substance at subanesthetic doses, but it is a viscous, water-immiscible oil that is not suitable for intrapulmonary administration. We found that PHS can be formulated as an aqueous solution that is well tolerated when instilled into the lung. High-dose intraperitoneally administered PHS induced loss-of-righting reflex in rats and mice. The onset of action of PHS was delayed in comparison with propofol, suggesting that conversion to propofol is required for activity. A lower dose of PHS (40 mg/kg i.p.) did not cause general anesthesia but protected against pentylenetetrazol (PTZ)-induced seizures in rats. Intrapulmonary administration of an aqueous PHS solution via a tracheal cannula at lower doses (5 and 10 mg/kg) conferred equivalent seizure protection without acute motor toxicity. In mice, intraperitoneal PHS (60-80 mg/kg) was associated with an elevation in PTZ, bicuculline, picrotoxin, and kainic acid seizure thresholds. Intratracheal PHS was markedly more potent, producing seizure threshold elevations at doses of 10 to 15 mg/kg. In the PTZ threshold model in mice, PHS was active at 5 min, maximally active at 10 min, and no longer active at 20 min. Intratracheal PHS also prolonged the onset of 4-aminopyridine-induced convulsions but did not affect the threshold for N-methyl-D-aspartate-induced convulsions. We conclude that intratracheal administration of an aqueous solution of PHS, a putative propofol prodrug, provides potent seizure protection of rapid onset and brief duration. Intrapulmonary PHS may be useful for preventing the spread of seizures or aborting seizure clusters without causing prolonged sedation.

Propofol infusion syndrome in patients with refractory status epilepticus: an 11-year clinical experience

OBJECTIVES

Propofol is a sedative, anesthetic, and antiepileptic agent that is frequently used in patients with refractory status epilepticus. Propofol infusion syndrome is a feared complication of propofol use, especially at high infusion rates for prolonged periods. The present study describes the use of propofol and its associated complications in patients with refractory status epilepticus.

DESIGN

: Retrospective study with outcome assessment.

SETTING

Intensive care units at Mayo Clinic.

PATIENTS

Intensive care unit admissions with refractory status epilepticus.

INTERVENTIONS

None.

MEASUREMENTS AND MAIN RESULTS

A computer-assisted search identified 41 consecutive patients from January 1997 to September 2008 admitted to our intensive care unit with refractory status epilepticus, defined by the need for continuous intravenous infusion of anesthetic agents to control seizures. Propofol infusion syndrome was defined per previously published criteria. The study population consisted of 24 males and 17 females with a median age of 51 yrs (range, 0.25- 80). Propofol was used in 31 (76%) of these patients (propofol group), and other agents like midazolam, lorazepam, and pentobarbital were used in the other ten (24%) patients (nonpropofol group). Median hospital (12 days; range, 2-112) and intensive care unit length of stay (9 days; range, 2-95) did not differ among the two groups. Propofol was used for a median of 63 hrs (range, 2-391) with a median cumulative dosage of 12,750 mg (range, 336-57,545). The median peak infusion rate was 67 microg/kg/min (range, 19-200). There were three sudden unexplained cardiorespiratory arrests in the propofol group (3 of 31, 10%), of which two were fatal. These three patients were aged 37, 46, and 55 yrs and had no prior cardiopulmonary disease. Eleven additional patients (11 of 31, 35%) had non-life-threatening features of propofol infusion syndrome. There were no such events noted in the nonpropofol group.

CONCLUSIONS

The prolonged use of large doses of propofol to treat refractory status epilepticus was associated with significant mortality and morbidity.

The experimental and clinical pharmacology of propofol, an anesthetic agent with neuroprotective properties

Propofol (2,6-diisopropylphenol) is a versatile, short-acting, intravenous (i.v.) sedative-hypnotic agent initially marketed as an anesthetic, and now also widely used for the sedation of patients in the intensive care unit (ICU). At the room temperature propofol is an oil and is insoluble in water. It has a remarkable safety profile. Its most common side effects are dose-dependent hypotension and cardiorespiratory depression. Propofol is a global central nervous system (CNS) depressant. It activates gamma-aminobutyric acid (GABA A) receptors directly, inhibits the N-methyl-d-aspartate (NMDA) receptor and modulates calcium influx through slow calcium-ion channels. Furthermore, at doses that do not produce sedation, propofol has an anxiolytic effect. It has also immunomodulatory activity, and may, therefore, diminish the systemic inflammatory response believed to be responsible for organ dysfunction. Propofol has been reported to have neuroprotective effects. It reduces cerebral blood flow and intracranial pressure (ICP), is a potent antioxidant, and has anti-inflammatory properties. Laboratory investigations revealed that it might also protect brain from ischemic injury. Propofol formulations contain either disodium edetate (EDTA) or sodium metabisulfite, which have antibacterial and antifungal properties. EDTA is also a chelator of divalent ions such as calcium, magnesium, and zinc. Recently, EDTA has been reported to exert a neuroprotective effect itself by chelating surplus intracerebral zinc in an ischemia model. This article reviews the neuroprotective effects of propofol and its mechanism of action.

Effect of propofol on seizure-like phenomena and electroencephalographic activity in children with epilepsy vs children with learning difficulties

There is an ongoing debate as to whether propofol exhibits pro- or anticonvulsant effects, and whether it should be used in patients with epilepsy. We prospectively assessed the occurrence of seizure-like phenomena and the effects of intravenous propofol on the electroencephalogram (EEG) in 25 children with epilepsy (mean (SD) age: 101 (49) months) and 25 children with learning difficulties (mean (SD) age: 52 (40) months) undergoing elective sedation for MRI studies of the brain. No child demonstrated seizure-like phenomena of epileptic origin during and after propofol sedation. Immediately after stopping propofol, characteristic EEG changes in the epilepsy group consisted of increased beta wave activity (23/25 children), and suppression of pre-existing theta rhythms (11/16 children). In addition, 16 of 18 children with epilepsy and documented EEG seizure activity demonstrated suppression of spike-wave patterns after propofol sedation. In all 25 children with learning difficulties an increase in beta wave activity was seen. Suppression of theta rhythms occurred in 11 of 12 children at the end of the MRI study. In no child of either group was a primary occurrence or an increase in spike-wave patterns seen following propofol administration. The occurrence of beta wave activity (children with learning difficulties and epilepsy group) and suppression of spike-wave patterns (epilepsy group) were transient, and disappeared after 4 h. This study demonstrates characteristic, time-dependent EEG patterns induced by propofol in children with epilepsy and learning difficulties. Our data support the concept of propofol being a sedative-hypnotic agent with anticonvulsant properties as shown by depression of spike-wave patterns in children with epilepsy and by the absence of seizure-like phenomena of epileptic origin.

[Refractory status epilepticus: diagnosis, therapy, course, and prognosis]

Status epilepticus (SE) is a frequent neurological emergency with an annual incidence of 10-20/100,000 individuals. The overall mortality is about 10-20%. Patients present with long-lasting fits or series of epileptic seizures or extended stupor and coma. Furthermore, patients with SE can suffer from a number of systemic complications possibly also due to side effects of the medical treatment. In the beginning, standardized treatment algorithms can successfully stop most SE. A minority of SE cases prove however to be refractory against the initial treatment and require intensified pharmacologic intervention with nonsedating anticonvulsive drugs or anesthetics. In some partial SE, nonpharmacological approaches (e.g., epilepsy surgery) have been used successfully. This paper reviews scientific evidence of the diagnostic approach, therapeutic options, and course of refractory SE, including nonpharmacological treatment.

The anticonvulsant action of propofol on epileptiform activity in rat hippocampal slices

We used extracellular electrophysiological recordings from the CA1 region in rat hippocampal slices to investigate the effects of propofol on the field excitatory postsynaptic potential (fEPSP), population spike, and epileptiform activity induced by a Mg(2+)-free condition. Propofol depressed the population spike, fEPSP, and epileptiform activity. Both aminophylline, a nonselective adenosine receptor antagonist, and 8-cyclopentyl-1,3-dipropylxanthine, an A(1) receptor antagonist, significantly reduced the effect of propofol on fEPSP amplitude. However, 3,7-dimethyl-1-propagylxanthine, an A(2) receptor antagonist, did not alter the effect of propofol on fEPSP amplitude. Picrotoxin, a specific chloride channel blocker, partly reduced the effect of propofol on epileptiform activity, but bicuculline, a competitive gamma-aminobutyric acid(A) receptor antagonist, failed to antagonize it. Aminophylline significantly reduced the action of propofol on the epileptiform activity. The anticonvulsant action of propofol was partly reduced by 8-cyclopentyl-1,3-dipropylxanthine, whereas 3,7-dimethyl-1-propagylxanthine failed to affect it. Adenosine depressed the amplitude of fEPSPs in a dose-dependent manner, and propofol enhanced this inhibition. The results demonstrated that, in rat hippocampal slices, propofol inhibits epileptiform activity. In addition, adenosine neuromodulation through the A(1) receptor may contribute to the anticonvulsant action of propofol.

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.

Propofol suppresses a hyperpolarization-activated inward current in rat hippocampal CA1 neurons

We examined the effect of propofol and thiopental, intravenous anesthetics, on the hyperpolarization-activated inward current (I(H)), whose functional role on the neuronal activity has been evaluated. Whole-cell recordings of I(H) evoked by hyperpolarizing step pulses were taken from hippocampal CA1 neurons in rat brain slices. Propofol reduced I(H) current in a dose-dependent manner. However, thiopental had no significant effect on the activation of I(H). According to the functional role of I(H), the suppression of I(H) should result in a reduction of neuronal activity. We suggest that the effectiveness of propofol as an anticonvulsant or an antiemetic is associated with the blockade of the I(H) channel.

Sustained plateau activity precedes and can generate ictal-like discharges in low-Cl(-) medium in slices from rat piriform cortex

Interictal and ictal discharges represent two different forms of abnormal brain activity associated with epilepsy. Ictal discharges closely parallel seizure activity, but depending on the form of epilepsy, interictal discharges may or may not be correlated with the frequency, severity, and location of seizures. Recent voltage-imaging studies in slices of piriform cortex indicated that interictal-like discharges are generated in a two-stage process. The first stage consists of a sustained, low-amplitude depolarization (plateau activity) lasting the entire latent period prior to discharge onset. Plateau activity takes place at a site distinct from the site of discharge onset and serves to sustain and amplify activity initiated by an electrical stimulus. In the second stage a rapidly accelerating depolarization begins at the onset site and then spreads over a wide region. Here, we asked whether ictal-like discharges can be generated in a similar two-stage process. As with interictal-like activity, the first sign of an impending ictal-like discharge is a sustained depolarization with a plateau-like time course. The rapidly accelerating depolarization that signals the start of the actual discharge develops later at a separate onset site. As found previously with interictal-like discharges, local application of kynurenic acid to the plateau site blocked ictal-like discharges throughout the entire slice. However, in marked contrast to interictal-like activity, blockade of synaptic transmission at the onset site failed to block the ictal-like discharge. This indicates that interictal- and ictal-like discharges share a common pathway in the earliest stage of their generation and that their mechanisms subsequently diverge.

Midazolam coma for refractory status epilepticus in children

OBJECTIVE

To implement and retrospectively evaluate a therapeutic algorithm for the treatment of refractory status epilepticus with midazolam coma.

METHODS

Eight consecutive patients with refractory status epilepticus were mechanically ventilated. Their arterial and central venous blood pressures were continuously monitored by indwelling vascular catheters. These patients were also continuously monitored by a 16-channel video electroencephalogram (EEG). A midazolam bolus of 0.15 mg/kg was administered, and a continuous infusion of 1-2 microg/kg/min was started. If seizures continued, the infusion was increased every 15 mins by 1-2 microg/kg/min. If seizures stopped and/or burst suppression was achieved, the patients continued to receive that dose for 48 hrs and were then weaned by decrements of 1-2 microg/kg/min every 15 mins.

RESULTS

The patients' ages ranged from 17 days to 16 yrs, and they had various underlying diseases. In five of the eight patients, cessation of seizures occurred before achieving burst suppression on EEG, in two patients, cessation occurred during burst suppression, and in one patient, no response before or during burst suppression was encountered. The maximal midazolam doses required to achieve cessation of seizures and/or burst suppression, whichever came first, ranged from 4-24 microg/kg/min, with a mean of 14 +/- 6 microg/kg/min. The patients maintained stable cardiovascular function while receiving the maximal dose of midazolam and did not require inotropic support.

CONCLUSION

Midazolam infusion, as per our described algorithm, is effective in terminating refractory status epilepticus. This treatment is not associated with cardiovascular instability, even at doses resulting in burst suppression. In the majority of cases, cessation of seizures occur before burst suppression is achieved on EEG.

Propofol anesthesia

Although questions may still remain regarding the use of this unique sedative-hypnotic drug with anesthetic properties in high-risk patients, our studies have provided cardiopulmonary and neurological evidence of the efficacy and safety of propofol when used as an anesthetic under normal and selected impaired conditions in the dog. 1. Propofol can be safely and effectively used for the induction and maintenance of anesthesia in normal healthy dogs. Propofol is also a reliable and safe anesthetic agent when used during induced cardiovascular and pulmonary-impaired conditions without surgery. The propofol requirements to induce the safe and prompt induction of anesthesia prior to inhalant anesthesia with and without surgery have been determined. 2. The favorable recovery profile associated with propofol offers advantages over traditional anesthetics in clinical situations in which rapid recovery is important. Also, propofol compatibility with a large variety of preanesthetics may increase its use as a safe and reliable i.v. anesthetic for the induction and maintenance of general anesthesia and sedation in small animal veterinary practice. Although propofol has proven to be a valuable adjuvant during short ambulatory procedures, its use for the maintenance of general anesthesia has been questioned for surgery lasting more than 1 hour because of increased cost and marginal differences in recovery times compared with those of standard inhalant or balanced anesthetic techniques. When propofol is used for the maintenance of anesthesia in combination with a sedative/analgesic, the quality of anesthesia is improved as well as the ease with which the practitioner can titrate propofol; therefore, practitioners are able to use i.v. anesthetic techniques more effectively in their clinical practices. 3. Propofol can induce significant depression of respiratory function, characterized by a reduction in the rate of respiration. Potent alpha 2 sedative/analgesics (e.g., xylazine, medetomidine) or opioids (e.g., oxymorphone, butorphanol) increase the probability of respiratory depression during anesthesia. Appropriate consideration of dose reduction and speed of administration of propofol reduces the degree of depression. Cardiovascular changes induced by propofol administration consist of a slight decrease in arterial blood pressures (systolic, mean, diastolic) without a compensatory increase in heart rate. Selective premedicants markedly modify this characteristic response. 4. When coupled with subjective responses to painful stimuli, EEG responses during propofol anesthesia provide clear evidence that satisfactory anesthesia has been achieved in experimental dogs. When propofol is used as the only anesthetic agent, a higher dose is required to induce an equipotent level of CNS depression compared with the situation when dogs are premedicated. 5. The propofol induction dose requirement should be appropriately decreased by 20% to 80% when propofol is administered in combination with sedative or analgesic agents as part of a balanced technique as well as in elderly and debilitated patients. As a general recommendation, the dose of propofol should always be carefully titrated against the needs and responses of the individual patient, as there is considerable variability in anesthetic requirements among patients. Because propofol does not have marked analgesic effects and its metabolism is rapid, the use of local anesthetics, nonsteroidal anti-inflammatory agents, and opioids to provide postoperative analgesia improves the quality of recovery after propofol anesthesia. 6. The cardiovascular depressant effects of propofol are well tolerated in healthy animals, but these effects may be more problematic in high-risk patients with intrinsic cardiac disease as well as in those with systemic disease. In hypovolemic patients and those with limited cardiac reserve, even small induction doses of propofol (0.75-1.5 mg/kg i.v.) can produce profound hypotens

Ictal epileptiform activity in the CA3 region of hippocampal slices produced by pilocarpine

Pilocarpine, a muscarinic agonist, produces status epilepticus that is associated with the later development of chronic recurrent seizures. When applied to rat hippocampal slices, pilocarpine (10 microM) produced brief (<200 ms) epileptiform discharges that resembled interictal activity that occurs between seizures, as well as more prolonged synchronous neuronal activation that lasted seconds (3-20 s), and was comparable to ictal or seizures-like discharges. We assessed the factors that favored ictal patterns of activity and determined the biophysical properties of the ictal discharge. The probability of observing ictal discharges was increased when extracellular potassium ([K+]o) was increased from 5 to 7.5 mM. Raising [K+]o to 10 mM resulted in loss of ictal patterns and, in 20 of 34 slices, desynchronization of epileptiform activity. Making the artificial cerebrospinal fluid (ACSF) hyposmotic favored ictal discharges at 5 mM [K+]o, but shifted 7.5 mM [K+]o ACSF patterns to interictal discharges or desynchronized activity. Conversely, increasing osmolality suppressed ictal patterns. The pilocarpine-induced ictal discharges were blocked by atropine (1 microM, n = 5), a muscarinic antagonist, and pirenzepine (1 microM, n = 6), a selective M1 receptor antagonist. Kainate/alpha-amino-3-hydroxy-5-methyl-4-isoxazoleproprionic acid receptor blockade stopped all epileptiform activity (n = 8). The N-methyl--aspartate antagonist ,-2-amino-5-phosphonovaleric acid (100 microM, n = 34) did not change the pattern of epileptiform activity but significantly increased the rate of interictal discharges and prolonged the duration of ictal discharges. The ictal discharge was characterized intracellularly by a depolarization that was associated with action potential generation and persisted as a membrane oscillation of 4-10 Hz. The ictal oscillations reversed in polarity at -22.7 +/- 2.2 mV (n = 11) with current-clamp recordings and -20.9 +/- 3.1 mV (n = 7) with voltage-clamp recordings. The reversal potential of the ictal discharge in the presence of the gamma-aminobutyric acid-A blocker bicuculline (10 microM, n = 6) was -2.2 +/- 2.6 mV and was significantly different from that measured without bicuculline. Bicuculline added to 7.5 mM [K+]o and 10 microM pilocarpine did not cause epileptiform activity to change pattern but significantly increased the rate of interictal discharges and prolonged the ictal discharge duration. Both synaptic and nonsynaptic mechanisms are important for the generation of ictal patterns of epileptiform activity. Although the synchronous epileptiform activity produced by pilocarpine required fast glutamate-mediated synaptic transmission, the transition from an interictal to ictal pattern of activity depended on [K+]o and could be influenced by extracellular space.

The epidemiology and management of status epilepticus

Status epilepticus refers to a prolonged seizure state, usually taken as lasting 30 min or longer. This review considers recent studies of the epidemiology of status epilepticus; these have confirmed the high incidence and the high associated mortality and morbidity. Advances in the management of status epilepticus are also reviewed but despite these advances there is still a lack of good comparative studies on which to base treatment regimens.