N-methyl-d-aspartate receptors and glycinergic transmission, respectively, mediate muscle relaxation and immobility of pentobarbital in mice

Pentobarbital-induced anesthesia is believed to be mediated by enhancement of the inhibitory action of γ-aminobutyric acid (GABA)ergic neurons in the central nervous system. However, it is unclear whether all components of anesthesia induced by pentobarbital, such as muscle relaxation, unconsciousness, and immobility in response to noxious stimuli, are mediated only through GABAergic neurons. Thus, we examined whether the indirect GABA and glycine receptor agonists gabaculine and sarcosine, respectively, the neuronal nicotinic acetylcholine receptor antagonist mecamylamine, or the N-methyl-d-aspartate receptor channel blocker MK-801 could enhance pentobarbital-induced components of anesthesia. Muscle relaxation, unconsciousness, and immobility were evaluated by grip strength, the righting reflex, and loss of movement in response to nociceptive tail clamping, respectively, in mice. Pentobarbital reduced grip strength, impaired the righting reflex, and induced immobility in a dose-dependent manner. The change in each behavior induced by pentobarbital was roughly consistent with that in electroencephalographic power. A low dose of gabaculine, which significantly increased endogenous GABA levels in the central nervous system but had no effect on behaviors alone, potentiated muscle relaxation, unconsciousness, and immobility induced by low pentobarbital doses. A low dose of MK-801 augmented only the masked muscle-relaxing effects of pentobarbital among these components. Sarcosine enhanced only pentobarbital-induced immobility. Conversely, mecamylamine had no effect on any behavior. These findings suggest that each component of anesthesia induced by pentobarbital is mediated through GABAergic neurons and that pentobarbital-induced muscle relaxation and immobility may partially be associated with N-methyl-d-aspartate receptor antagonism and glycinergic neuron activation, respectively.

Mild hypothermia fails to protect infant macaques from brain injury caused by prolonged exposure to Antiseizure drugs

Barbiturates and benzodiazepines are GABA_A-receptor agonists and potent antiseizure medications. We reported that exposure of neonatal macaques to combination of phenobarbital and midazolam (Pb/M) for 24 h, at clinically relevant doses and plasma levels, causes widespread apoptosis affecting neurons and oligodendrocytes. Notably, the extent of injury was markedly more severe compared to shorter (8 h) exposure to these drugs. We also reported that, in the infant macaque, mild hypothermia ameliorates the apoptosis response to the anesthetic sevoflurane. These findings prompted us explore whether mild hypothermia might protect infant nonhuman primates from neuro- and gliotoxicity of Pb/M. Since human infants with seizures may receive combinations of benzodiazepines and barbiturates for days, we opted for 24 h treatment with Pb/M. Neonatal rhesus monkeys received phenobarbital intravenously, followed by midazolam infusion over 24 h under normothermia (T > 36.5 °C-37.5 °C; n = 4) or mild hypothermia (T = 35 °C-36.5 °C; n = 5). Medication doses and blood levels measured were comparable to those in human infants. Animals were euthanized at 36 h and brains examined immunohistochemically and stereologically. Treatment was well tolerated. Extensive degeneration of neurons and oligodendrocytes was seen at 36 h in both groups within neocortex, basal ganglia, hippocampus and brainstem. Mild hypothermia over 36 h (maintained until terminal perfusion) conferred no protection against the neurotoxic and gliotoxic effects of Pb/M. This is in marked contrast to our previous findings that mild hypothermia is protective in the context of a 5 h-long exposure to sevoflurane in infant macaques. These findings demonstrate that brain injury caused by prolonged exposure to Pb/M in the neonatal primate cannot be ameliorated by mild hypothermia.

Brain pathology caused in the neonatal macaque by short and prolonged exposures to anticonvulsant drugs

Barbiturates and benzodiazepines are potent GABAA receptor agonists and strong anticonvulsants. In the developing brain they can cause neuronal and oligodendroglia apoptosis, impair synaptogenesis, inhibit neurogenesis and trigger long-term neurocognitive sequelae. In humans, the vulnerable period is projected to extend from the third trimester of pregnancy to the third year of life. Infants with seizures and epilepsies may receive barbiturates, benzodiazepines and their combinations for days, months or years. How exposure duration affects neuropathological sequelae is unknown. Here we investigated toxicity of phenobarbital/midazolam (Pb/M) combination in the developing nonhuman primate brain. Neonatal rhesus monkeys received phenobarbital intravenously, followed by infusion of midazolam over 5 (n = 4) or 24 h (n = 4). Animals were euthanized at 8 or 36 h and brains examined immunohistochemically and stereologically. Treatment was well tolerated, physiological parameters remained at optimal levels. Compared to naïve controls, Pb/M exposed brains displayed widespread apoptosis affecting neurons and oligodendrocytes. Pattern and severity of cell death differed depending on treatment-duration, with more extensive neurodegeneration following longer exposure. At 36 h, areas of the brain not affected at 8 h displayed neuronal apoptosis, while oligodendroglia death was most prominent at 8 h. A notable feature at 36 h was degeneration of neuronal tracts and trans-neuronal death of neurons, presumably following their disconnection from degenerated presynaptic partners. These findings demonstrate that brain toxicity of Pb/M in the neonatal primate brain becomes more severe with longer exposures and expands trans-synaptically. Impact of these sequelae on neurocognitive outcomes and the brain connectome will need to be explored.

Thiamylal anaesthetic therapy for febrile refractory status epilepticus in children

PURPOSE

To evaluate barbiturate anaesthetic therapy using thiamylal for febrile refractory status epilepticus (fRSE) in children.

METHODS

This was a review of a prospectively-collected database between April 2012-March 2016 for fRSE cases treated with thiamylal anaesthetic therapy in a single paediatric hospital in Japan. The sample comprised 23 children (median age, 23 months) with fRSE that underwent thiamylal anaesthetic therapy for convulsive seizures lasting longer than 60 min, sustained after intravenous administration of benzodiazepine and non-benzodiazepine anticonvulsants. The intervention comprised protocol-based thiamylal anaesthetic therapy with bolus administration. We measured the dose and time required to achieve the burst suppression pattern (BSP) on electroencephalography, seizure recurrence, death, neurological sequelae, and complications.

RESULTS

All patients except one reached the BSP. The thiamylal median dose until reaching the BSP was 27.5 mg/kg, and the median time from thiamylal administration to reaching the BSP was 109.5 min. There was one case of immediate treatment failure and one of withdrawal seizure, but no breakthrough seizure. No deaths occurred during treatment, and neurological sequelae occurred in four cases (17%). Vasopressors were administered in all cases. Other complications included 11 cases of pneumonia and one of enterocolitis.

CONCLUSION

We revealed the time and dose required to reach the BSP with thiamylal anaesthetic therapy using bolus administration in children. Our results suggested that reaching the BSP with bolus administration requires markedly less time than without bolus administration, rarely causes seizure recurrence in paediatric fRSE, and causes haemodynamic dysfunction and infections as often as observed without bolus administration.

Barbiturates enhance itch-associated scratching in atopic dermatitis mice: A possible clue to understanding nocturnal pruritus in atopic dermatitis

In chronic pruritic diseases such as atopic dermatitis, pruritus is exacerbated during nocturnal sleep; however, the underlying mechanism remains unclear. We previously demonstrated that acute administration of the sedative-hypnotics ethanol markedly enhanced itch-associated spontaneous scratching in a diet-induced mouse model of atopic dermatitis. In the present study, to expand our previous finding and provide a general mechanism for the central modulation of chronic itch, we examined whether other hypnotic drugs, such as barbiturates and benzodiazepines, also enhance scratching, and further investigated the underlying mechanism. Barbiturates markedly enhanced spontaneous scratching in the atopic dermatitis model but not controls. However, unexpectedly, benzodiazepines only slightly increased scratching, and the selective γ-aminobutyric acid type A (GABA_A) receptor agonist, muscimol, had no effect. Local injection studies have demonstrated that barbiturates act at the supraspinal level to enhance scratching. Barbiturate-induced scratching was inhibited not only by GABA_A receptor antagonists but also by an L-type voltage-dependent calcium channel (L-VDCC) agonist and an α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid (AMPA) glutamate receptor agonist. An intracisternally injected AMPA receptor antagonist alone or in combination with an L-VDCC antagonist sufficiently enhanced scratching. Barbiturate-induced scratching enhancement was observed in another atopic dermatitis model, NC/Nga, but not in histamine-induced acute itch model in normal healthy mice. Overall, our results suggest that a synergistic effect among AMPA receptor inhibition, GABA_A receptor activation, and L-VDCC inhibition in the brain mediates barbiturate-induced scratching in atopic dermatitis mice. This observation may provide a novel clue to understanding a supraspinal itch mechanism in chronic diseases such as atopic dermatitis.

Neuroprotective Action of the CB1/2 Receptor Agonist, WIN 55,212-2, against DMSO but Not Phenobarbital-Induced Neurotoxicity in Immature Rats

The developing brain is uniquely susceptible to drug-induced increases in programmed cell death or apoptosis. Many compounds, including anticonvulsant drugs, anesthetic agents, and ethanol, when administered in a narrow postnatal window in rodents, result in increased pruning of neurons. Here, we report that dimethyl sulfoxide (DMSO) triggers widespread neurodegeneration in the immature (postnatal day, P7) rat brain, an effect consistent with a prior report in neonatal mice. We found that the synthetic cannabinoid receptor agonist WIN 55,212-2 (WIN) exerts a neuroprotective effect against DMSO-induced cell death. We extended these findings to determine if WIN is neuroprotective against another drug class known to increase developmental cell death, namely antiseizure drugs. The antiseizure drug phenobarbital (PB) remains the primary treatment for neonatal seizures, despite significantly increasing cell death in the developing rodent brain. WIN exerts antiseizure effects in immature rodent seizure models, but increases the toxicity associated with neonatal ethanol exposure. We thus sought to determine if WIN would protect against or exacerbate PB-induced cell death. Unlike either the prior report with ethanol or our present findings with DMSO, WIN was largely without effect on PB-induced cell death. WIN alone did not increase cell death over levels observed in vehicle-treated rats. These data suggest that WIN has a favorable safety profile in the developing brain and could potentially serve as an adjunct therapy with phenobarbital (albeit one that does not attenuate PB-induced toxicity).

Extracorporeal elimination of butalbital in acute aspirin-butalbital-caffeine-codeine (Fiorinal with Codeine) poisoning

BACKGROUND

Butalbital is a small molecule (approximately 220 Da), with 26% protein binding, a 0.8 L/kg volume of distribution, and is eliminated nearly 80% unchanged in the urine. Although hemodialysis has been used to treat overdoses of other barbiturates, the extracorporeal clearance of butalbital is unknown. The objective of this case is to describe the use of extracorporeal therapy to augment elimination of butalbital after an overdose of aspirin 325 mg-butalbital 50 mg-caffeine 40 mg with codeine 30 mg (Fiorinal with Codeine).

METHODS

This is a case report of a single patient.

RESULTS

A 67-year-old female was admitted to the medical intensive care unit approximately 3 h after ingestion of 40 tablets of Fiorinal with Codeine. Her presentation was notable for a decline in mental status, preserved renal function and a relatively low peak salicylate concentration at 46.4 mg/dL (3.4 mmol/L). Approximately 8 h after ingestion of 2000 mg of butalbital, our patient's serum concentration was 26.9 mg/L (normal <10 mg/L). At the end of a four-hour hemodialysis session, the total body elimination of butalbital was approximately 60% which corresponded to an intradialytic clearance of 233-300 mL/min.

CONCLUSIONS

The extracorporeal clearance of butalbital observed in this case demonstrates the utility of dialysis to augment drug elimination in a Fiorinal with Codeine overdose.

Intravenous theophylline is the most effective intervention to prolong EEG seizure duration in patients undergoing electroconvulsive therapy

BACKGROUND

Seizure duration in electroconvulsive therapy (ECT) is positively related with patients' outcome. This study sought to investigate the impact of anesthetic management on seizure duration, and the impact of selected drugs (theophylline, remifentanil, S-ketamine) on seizure duration.

METHODS

Retrospective analysis of all patients undergoing ECT at our institution from January 2011 to April 2012 was performed based on electronic medical chart and review of existing quality improvement data. Patient data (N = 78), including gender, age, height, weight, and administered drugs, energy levels, and electroencephalic seizure duration were analyzed. Statistical analysis was performed using a generalized linear model.

RESULTS

A total of 78 patients (male = 39, female = 39, age 51 ± 12 years) were included. Average number of session was 10 ± 6 (1-30). In our patient population, theophylline administration was the only parameter, which significantly prolonged seizure duration, whereas S-ketamine, remifentanil, thiopental, age, sex, session or energy level had no significant effect.

CONCLUSION

Theophylline can be a useful adjunct for patients with inadequate seizure duration. If there is a concomitant beneficial effect on patients' outcome needs to be investigated in further studies.

A Fatal Adverse Effect of Barbiturate Coma Therapy: Dyskalemia

The management guideline for traumatic brain injury (TBI) recommends high-dose barbiturate therapy to control increased intracranial pressure refractory to other therapeutic options. High-dose barbiturate therapy, however, may cause many severe side effects; the commonly recognized ones include hypotension, immunosuppression, hepatic dysfunction, renal dysfunction, and prolonged decrease of cortical activity. Meanwhile, dyskalemia remains relatively uncommon. In this study, we report the case of a hypokalemic patient with severe rebound hyperkalemia, which occurred as a result of barbiturate coma therapy administered for TBI treatment.

Status epilepticus caused by nefopam

Nefopam, a centrally acting analgesic, has been used to control postoperative pain. Reported adverse effects are anticholinergic, cardiovascular or neuropsychiatric. Neurologic adverse reactions to nefopam are confusion, hallucinations, delirium and convulsions. There are several reports about fatal convulsive seizures, presumably related to nefopam. A 71-year-old man was admitted for surgery for a lumbar spinal stenosis. He was administered intravenous analgesics : ketorolac, tramadol, orphenadrine citrate and nefopam HCl. His back pain was so severe that he hardly slept for several days; he even needed morphine and pethidine. At 4 days of administration of intravenous analgesics, the patient suddenly started generalized tonic-clonic seizures for 15 seconds, and subsequently, status epilepticus; these were not responsive to phenytoin and midazolam. After 3 days of barbiturate coma therapy the seizures were controlled. Convulsive seizures related to nefopam appear as focal, generalized, myoclonic types, or status epilepticus, and are not dose-related manifestations. In our case, the possibility of convulsions caused by other drugs or the misuse of drugs was considered. However, we first identified the introduced drugs and excluded the possibility of an accidental misuse of other drugs. Physicians should be aware of the possible occurrence of unpredictable and serious convulsions when using nefopam.

Successful use of sustained low efficiency dialysis in a case of severe phenobarbital poisoning

A 30-year-old female presented with coma and subsequent cardiac arrest caused by phenobarbital overdosage, requiring ventilatory and vasopressor support. She had also developed severe hypoxia following gastric aspiration. Initial therapy, including activated charcoal and forced alkaline diuresis, failed to significantly lower her drug levels and there was minimal neurological improvement. As she was hemodynamically unstable, and unsuitable for conventional dialysis, she was put on sustained low efficiency dialysis (SLED) to facilitate drug removal. SLED resulted in marked reduction in plasma level of phenobarbital, which eventually led to early extubation, improved cognition and aided full recovery. Thus, we concluded that SLED can be an effective alternative in cases of severe phenobarbital poisoning, where conventional hemodialysis or hemoperfusion cannot be initiated, to hasten drug elimination and facilitate early recovery.

Does the use of thiopental provide added cerebral protection during deep hypothermic circulatory arrest?

A best evidence topic in cardiac surgery was written according to a structured protocol. The question addressed was: Does the use of thiopental provide added cerebral protection during deep hypothermic circulatory arrest (DHCA)? Altogether, more than 62 papers were found using the reported search, of which 7 represented the best evidence to answer the clinical question. The authors, journal, date and country of publication, patient group studied, study type, relevant outcomes and results of these papers are tabulated. Four of the seven papers used thiopental alongside other neuroprotective methods and agents. The methods included the use of ice packs to the head and core systemic hypothermia. Agents used alongside thiopental included nicardipine and mannitol. Thiopental was found to have the ability to lower oxygen consumption, where oxygen consumption was measured using the phosphocreatinine and adenosine triphosphate ratio. The neuroprotective effect of thiopental was evaluated by assessing the electrical activity of the brain during circulatory arrest, by which it was shown to be advantageous. However, other trials suggested that adding thiopental during circulatory arrest did not provide any extra protection to the brain. The timing of thiopental administration is of importance in order to gain positive outcomes, as it's ability to lower the cerebral energy state may result in unfavourable results if added before hypothermic circulatory arrest, where this may lead to an ischaemic event. We conclude that the use of thiopental during deep hypothermic circulatory arrest is beneficial, but if administered too early, it may replete the cerebral energy state before arrest and prove to be detrimental.

Comparative Study of Brain Protection Effect between Thiopental and Etomidate Using Bispectral Index during Temporary Arterial Occlusion

OBJECTIVE

This study was conducted to compare the effect of etomidate with that of thiopental on brain protection during temporary vessel occlusion, which was measured by burst suppression rate (BSR) with the Bispectral Index (BIS) monitor.

METHODS

Temporary parent artery occlusion was performed in forty one patients during cerebral aneurysm surgery. They were randomly assigned to one of two groups. General anesthesia was induced and maintained with 1.5-2.5 vol% sevoflurane and 50% N(2)O. The pharmacological burst suppression (BS) was induced by a bolus injection of thiopental (5 mg/kg, group T) or etomidate (0.3 mg/kg, group E) according to randomization prior to surgery. After administration of drugs, the hemodynamic variables, the onset time of BS, the numerical values of BIS and BSR were recorded at every minutes.

RESULTS

There were no significant differences of the demographics, the BIS numbers and the hemodynamic variables prior to injection of drugs. The durations of burst suppression in group E (11.1±6.8 min) were not statistically different from that of group T (11.1±5.6 min) and nearly same pattern of burst suppression were shown in both groups. More phenylephrine was required to maintain normal blood pressure in the group T.

CONCLUSION

Thiopental and etomidate have same duration and a similar magnitude of burst suppression with conventional doses during temporary arterial occlusion. These findings suggest that additional administration of either drug is needed to ensure the BS when the temporary occlusion time exceed more than 11 minutes. Etomidate can be a safer substitute for thiopental in aneurysm surgery.