Effects of low-dose ketamine on neuropathic pain: An electroencephalogram-electrooculogram/behavioral study

Effects of S-ketamine on Postoperative Recovery Quality and Inflammatory Response in Patients Undergoing Modified Radical Mastectomy

INTRODUCTION

S-ketamine plays an important role in reducing postoperative pain, but its impact on the quality of recovery in breast cancer has not been clarified. We designed this trial to explore the effects of s-ketamine on the quality of postoperative recovery and inflammatory response in modified radical mastectomy.

METHODS

A total of 138 patients were randomly assigned to group C (group control), group K1 (group of s-ketamine dose 1) and group K2 (group of s-ketamine dose 2). Groups K1 and K2 were given 0.1 mg/kg, 0.2 mg/kg s-ketamine intravenous (IV) after induction, followed by 0.1 mg/kg/h or 0.2 mg/kg/h continuous intravenous infusion, respectively. Group C received the same volume of saline. A 40-item Quality of Recovery Questionnaire (QoR-40) was used to assess the quality of recovery at 24 h postoperatively. Changes in inflammatory markers, nociceptive thresholds, and the occurrence of adverse events were recorded at 24 h postoperatively.

RESULTS

The QoR-40 scores at 24 h postoperatively were higher in group K2 [182.00 (179.00-185.00)] compared to group K1 [174.00 (169.50-180.50)] and group C [169.00 (163.75-174.25)] (group K2 vs. group K1, P < 0.001; group K2 vs. group C, P < 0.001). At 24 h postoperatively, the neutrophil count, NLR (neutrophil-lymphocyte ratio), and CRP (C-creative protein) were all significantly lower in group K2 than group C(P < 0.05), no differences were observed between group K1 and C(P > 0.05), group K1 and K2(P > 0.05), respectively. There was no significant difference in the incidence of adverse effects among the three groups (P > 0.05).

CONCLUSIONS

A high dose of s-ketamine improved the quality of recovery at 24 h after surgery, as well as alleviated the inflammatory response without increasing the incidence of adverse effects.

Resting-state electroencephalography and magnetoencephalography as biomarkers of chronic pain: a systematic review

ABSTRACT

Reliable and objective biomarkers promise to improve the assessment and treatment of chronic pain. Resting-state electroencephalography (EEG) is broadly available, easy to use, and cost efficient and, therefore, appealing as a potential biomarker of chronic pain. However, results of EEG studies are heterogeneous. Therefore, we conducted a systematic review (PROSPERO CRD42021272622) of quantitative resting-state EEG and magnetoencephalography (MEG) studies in adult patients with different types of chronic pain. We excluded populations with severe psychiatric or neurologic comorbidity. Risk of bias was assessed using a modified Newcastle-Ottawa Scale. Semiquantitative data synthesis was conducted using modified albatross plots. We included 76 studies after searching MEDLINE, Web of Science Core Collection, Cochrane Central Register of Controlled Trials, and EMBASE. For cross-sectional studies that can serve to develop diagnostic biomarkers, we found higher theta and beta power in patients with chronic pain than in healthy participants. For longitudinal studies, which can yield monitoring and/or predictive biomarkers, we found no clear associations of pain relief with M/EEG measures. Similarly, descriptive studies that can yield diagnostic or monitoring biomarkers showed no clear correlations of pain intensity with M/EEG measures. Risk of bias was high in many studies and domains. Together, this systematic review synthesizes evidence on how resting-state M/EEG might serve as a diagnostic biomarker of chronic pain. Beyond, this review might help to guide future M/EEG studies on the development of pain biomarkers.

Ketamine pharmacology: an update (pharmacodynamics and molecular aspects, recent findings)

For more than 50 years, ketamine has proven to be a safe anesthetic drug with potent analgesic properties. The active enantiomer is S(+)-ketamine. Ketamine is mostly metabolized in norketamine, an active metabolite. During "dissociative anesthesia", sensory inputs may reach cortical receiving areas, but fail to be perceived in some association areas. Ketamine also enhances the descending inhibiting serotoninergic pathway and exerts antidepressive effects. Analgesic effects persist for plasma concentrations ten times lower than hypnotic concentrations. Activation of the (N-Methyl-D-Aspartate [NMDA]) receptor plays a fundamental role in long-term potentiation but also in hyperalgesia and opioid-induced hyperalgesia. The antagonism of NMDA receptor is responsible for ketamine's more specific properties. Ketamine decreases the "wind up" phenomenon, and the antagonism is more important if the NMDA channel has been previously opened by the glutamate binding ("use dependence"). Experimentally, ketamine may promote neuronal apoptotic lesions but, in usual clinical practice, it does not induce neurotoxicity. The consequences of high doses, repeatedly administered, are not known. Cognitive disturbances are frequent in chronic users of ketamine, as well as frontal white matter abnormalities. Animal studies suggest that neurodegeneration is a potential long-term risk of anesthetics in neonatal and young pediatric patients.

Psychiatric side effects of medications prescribed in internal medicine

Several pharmacological treatments used in internal medicine can induce psychiatric side effects (PSEs) that mimic diagnoses seen in psychiatry. PSEs may occur upon withdrawal or intoxication, and also at usual therapeutic doses. Drugs that may lead to depressive, anxious, or psychotic syndromes include corticosteroids, isotretinoin, levo-dopar mefloquine, interferon-a, and anabolic steroids, as well as some over-the-counter medications. PSEs are often difficult to diagnose and can be very harmful to patients. PSEs are discussed in this review, as well as diagnostic clues to facilitate their identification.

Ketamine, an NMDA-antagonist, increases the oscillatory frequencies of alpha-peaks on the electroencephalographic power spectrum

BACKGROUND

Ketamine, an N-methyl-D-aspartate (NMDA) antagonist, is known to activate the electroencephalogram (EEG), despite its sedative effects. Spindle oscillations are known to be related to the sedative actions of the reticular thalamic nucleus with links to thalamocortical neurons. This study was designed to examine the effect of ketamine on the spindle oscillations to understand the simultaneous sedative effect and EEG activation that occurs with ketamine, by comparing the EEG in emergence.

METHODS

Anesthesia was induced with propofol using a target-controlled infusion (TCI) system (3.5 microg/ml). Seventeen patients, scheduled for non-cranial surgery under general anesthesia combined with epidural anesthesia, were randomly divided into two groups: (i) anesthesia was maintained with TCI-propofol alone (n= 8) and (ii) anesthesia was maintained with TCI-propofol and intravenously administered ketamine (n= 9). The EEG was continuously monitored and EEG indices and power spectra were determined.

RESULTS

Propofol alone caused the alpha-peaks of the power spectra to occur at an average frequency of 10.4 +/- 0.9 Hz; the addition of ketamine shifted the peaks to higher frequencies of 15.1 +/- 1.4 Hz (P < 0.05). On the other hand, when the EEG was activated by discontinuation of propofol, the corresponding alpha-peaks disappeared.

CONCLUSIONS

Ketamine increased the frequencies of alpha-spindle waves induced by propofol, but did not block their formations. The phenomena have the possibility to underlie the cooperative effect between propofol and ketamine concerning sedation and anesthesia.

A treatment algorithm for neuropathic pain

BACKGROUND

Neuropathic pain is a chronic pain syndrome caused by drug-, disease-, or injury-induced damage or destruction of sensory neurons within the dorsal root ganglia of the peripheral nervous system. Characteristic clinical symptoms include the feeling of pins and needles; burning, shooting, and/or stabbing pain with or without throbbing; and numbness. Neuronal hyperexcitability represents the hallmark cellular mechanism involved in the underlying pathophysiology of neuropathic pain. Although the primary goal is to alleviate pain, clinicians recognize that even the most appropriate treatment strategy may be, at best, only able to reduce pain to a more tolerable level.

OBJECTIVE

The purpose of this review is to propose a treatment algorithm for neuropathic pain that health care professionals can logically follow and adapt to the specific needs of each patient. The algorithm is intended to serve as a general guide to assist clinicians in optimizing available therapeutic options.

METHODS

A comprehensive review of the literature using the PubMed, MEDLINE, Cochrane, and Toxnet databases was conducted to design and develop a novel treatment algorithm for neuropathic pain that encompasses agents from several drug classes, including antidepressants, antiepileptic drugs, topical antineuralgic agents, narcotics, and analgesics, as well as various treatment options for refractory cases.

RESULTS

Any of the agents in the first-line drug classes (tricyclic antidepressants, antiepileptic drugs, topical antineuralgics, analgesics) may be used as a starting point in the treatment of neuropathic pain. If a patient does not respond to treatment with at least 3 different agents within a drug class, agents from a second drug class may be tried. When all first-line options have been exhausted, narcotic analgesics or refractory treatment options may provide some benefit. Patients who do not respond to monotherapy with any of the first- or second-line agents may respond to combination therapy or may be candidates for referral to a pain clinic. Because the techniques used at pain clinics tend to be invasive, referrals to these clinics should be reserved for patients who are truly refractory to all forms of pharmacotherapy.

CONCLUSIONS

Neuropathic pain continues to be one of the most difficult pain conditions to treat. With the proposed algorithm, clinicians will have a framework from which to design a pain treatment protocol appropriate for each patient. The algorithm will also help streamline referrals to specialized pain clinics, thereby reducing waiting list times for patients who are truly refractory to traditional pharmacotherapy.

Muscimol prevents NMDA antagonist neurotoxicity by activating GABAA receptors in several brain regions

N-Methyl-D-aspartate (NMDA) glutamate receptor antagonists are being developed as therapeutic agents for several clinical conditions. However, the ability of these agents to produce neurotoxicity and psychosis can compromise their clinical usefulness. In addition, an NMDA receptor hypofunction (NRHypo) state may play a role in neurodegenerative and psychotic disorders. A better understanding of the mechanism underlying these adverse effects should allow for the safer use of these agents and might clarify mechanisms underlying certain clinical disorders. NRHypo neurotoxicity is mediated by a complex disinhibition mechanism in which NMDA antagonists abolish GABAergic inhibition, resulting in the simultaneous excessive release of acetylcholine and glutamate onto the vulnerable retrosplenial cortex (RSC) neurons. Systemically administered GABAergic agents are potent protectors against NRHypo neurotoxicity. To determine where in brain GABAergic agents could be acting to protect against NRHypo neurotoxicity, we injected the GABAergic agonist, muscimol, into different brain regions of rats treated systemically with a neurotoxic dose of the potent NMDA antagonist, MK-801. We report that muscimol injections into the anterior thalamus or diagonal band of Broca provide substantial protection, suggesting that disinhibition of neurons in these regions underlies NRHypo neurotoxicity. Muscimol injections into the RSC also provide substantial protection possibly by directly inhibiting the vulnerable RSC neuron. Injections of muscimol into other areas known to project to the RSC (ventral orbital cortex, anterior cingulate cortex and subiculum) provide only minimal protection. We conclude that GABAergic agents prevent NRHypo neurotoxicity mainly by activating GABA receptors in the anterior thalamus, diagonal band of Broca and RSC.