Remifentanil: a novel, short-acting, mu-opioid

Synergic Difficulties in an Anticipated Physiologically and Anatomically Difficult Airway in a Trauma Patient: A Case Report

The American Society of Anesthesiologists (ASA) defines a difficult airway as a clinical situation in which a physician who is trained in anesthesiology experiences difficulty or fails in either face mask ventilation, laryngoscopy, using a supraglottic airway, tracheal intubation, extubation, or front-of-neck airway. Classically, this has been defined in relation to anatomic factors, but the concept of a physiologically difficult airway has been growing in relevance, in which physiologic factors, such as hypoxemia and hypercapnia, act to reduce safe apnea times. The case reports on a trauma patient with an unstable thoracic vertebral fracture requiring correction via the posterior approach. Our patient had multiple anatomical difficult airway predictors, namely, a short neck, greatly limited neck mobility, and a Mallampati class IV airway, among others, and multiple physiological difficult airway predictors, such as a baseline hypoxemic respiratory failure and severe sleep apnea, in addition to the restrictions on mobility imposed by the fracture itself. We describe a successful perioxygenation strategy, using high-flow nasal oxygen (HFNO) during the preoxygenation, intubation, extubation, and post-anesthesia care phases, and with an awake fiberoptic intubation technique for securing the airway.

Changes in pontine and preBötzinger/Bötzinger complex neuronal activity during remifentanil-induced respiratory depression in decerebrate dogs

Introduction: In vivo studies using selective, localized opioid antagonist injections or localized opioid receptor deletion have identified that systemic opioids dose-dependently depress respiratory output through effects in multiple respiratory-related brainstem areas. Methods: With approval of the subcommittee on animal studies of the Zablocki VA Medical Center, experiments were performed in 53 decerebrate, vagotomized, mechanically ventilated dogs of either sex during isocapnic hyperoxia. We performed single neuron recordings in the Pontine Respiratory Group (PRG, n = 432) and preBötzinger/Bötzinger complex region (preBötC/BötC, n = 213) before and during intravenous remifentanil infusion (0.1-1 mcg/kg/min) and then until complete recovery of phrenic nerve activity. A generalized linear mixed model was used to determine changes in Fn with remifentanil and the statistical association between remifentanil-induced changes in Fn and changes in inspiratory and expiratory duration and peak phrenic activity. Analysis was controlled via random effects for animal, run, and neuron type. Results: Remifentanil decreased Fn in most neuron subtypes in the preBötC/BötC as well as in inspiratory (I), inspiratory-expiratory, expiratory (E) decrementing and non-respiratory modulated neurons in the PRG. The decrease in PRG inspiratory and non-respiratory modulated neuronal activity was associated with an increase in inspiratory duration. In the preBötC, the decrease in I-decrementing neuron activity was associated with an increase in expiratory and of E-decrementing activity with an increase in inspiratory duration. In contrast, decreased activity of I-augmenting neurons was associated with a decrease in inspiratory duration. Discussion: While statistical associations do not necessarily imply a causal relationship, our data suggest mechanisms for the opioid-induced increase in expiratory duration in the PRG and preBötC/BötC and how inspiratory failure at high opioid doses may result from a decrease in activity and decrease in slope of the pre-inspiratory ramp-like activity in preBötC/BötC pre-inspiratory neurons combined with a depression of preBötC/BötC I-augmenting neurons. Additional studies must clarify whether the observed changes in neuronal activity are due to direct neuronal inhibition or decreased excitatory inputs.

Structural Modification in Anesthetic Drug Development for Prodrugs and Soft Drugs

Among the advancements in drug structural modifications, the increased focus on drug metabolic and pharmacokinetic properties in the anesthetic drug design process has led to significant developments. Drug metabolism also plays a key role in optimizing the pharmacokinetics, pharmacodynamics, and safety of drug molecules. Thus, in the field of anesthesiology, the applications of pharmacokinetic strategies are discussed in the context of sedatives, analgesics, and muscle relaxants. In this review, we summarize two approaches for structural optimization to develop anesthetic drugs, by designing prodrugs and soft drugs. Drugs that both failed and succeeded during the developmental stage are highlighted to illustrate how drug metabolism and pharmacokinetic optimization strategies may help improve their physical and chemical properties.

Opioid-induced analgesia among persons with opioid use disorder receiving methadone or buprenorphine: A systematic review of experimental pain studies

BACKGROUND

Treating acute pain among persons with opioid use disorder (OUD) on opioid agonist therapy (OAT) is complex, and the therapeutic benefits of opioids remain unclear when weighted against their abuse potential and respiratory depressant effects.

METHODS

We conducted a systematic review of experimental pain studies examining opioid-induced analgesia among persons with OUD on OAT. We searched multiple databases from inception to July 30, 2021. Study quality was assessed by previously established validity measures.

RESULTS

Nine studies were identified, with a total of 225 participants, of whom 63% were male, and 37% were female. Six studies included methadone-maintained persons with OUD; four studies included buprenorphine-maintained persons with OUD; and three studies included healthy persons as comparison groups. Either additional doses of OAT or other opioids - morphine, oxycodone, hydromorphone, or remifentanil - were administered. In seven studies, persons with OUD on OAT did not experience analgesia, despite receiving opioid doses up to 20 times greater than those clinically used to treat severe pain among the opioid naïve. Conversely, in two studies, high-potency opioids did produce analgesia, albeit with greater abuse potential. Notably, persons with OUD on OAT remained vulnerable to respiratory depression.

CONCLUSIONS

Although persons with OUD on OAT can derive analgesic effects from opioids, high-potency compounds may be required to achieve clinically significant pain relief. Further, persons with OUD on OAT may remain vulnerable to opioid-induced abuse potential and respiratory depression. Together, these finding have clinical, methodological, and mechanistic implications for the treatment of acute pain in the context of OAT.

Gas Chromatography-Mass Spectrometry Analysis of Synthetic Opioids Belonging to the Fentanyl Class: A Review

The rising number of deaths caused by fentanyl overdosing in the US due to the overwhelming illicit use of this synthetic opioid has started a global campaign to develop efficient ways to control its production and distribution as well as discovering efficient antidotes to mitigate its lethal effects. Another important vein of focused research established by various agencies lies in the development of efficient and practical protocols for the detection of this opioid and analogs thereof in various matrices, whether environmental or biological in nature, particularly in the field of gas chromatography-mass spectrometry (GC-MS). The following review will cover the literature dealing with the detection and identification of synthetic opioids belonging to the fentanyl class by GC-MS means and hyphenated versions of the technique. Detailed descriptions will be given for the GC-MS methods employed for the analysis of the opioid, starting with the nature of the extraction protocol employed prior to analysis to the actual findings presented by the cited reports. Great effort has gone into describing the methods involved in each paper in a detailed manner and these have been compiled by year in tables at the end of each section for the reader's convenience. Lastly, the review will end with concluding remarks about the state of GC-MS analysis with regards to these powerful opioids and what lies ahead for this analytical field.

Accurate prediction of terahertz spectra of molecular crystals of fentanyl and its analogs

Fentanyl is a potent synthetic opioid pain reliever with a high bioavailability that can be used as prescription anesthetic. Rapid identification via non-contact methods of both known and emerging opioid substances in the fentanyl family help identify the substances and enable rapid medical attention. We apply PBEh-3c method to identify vibrational normal modes from 0.01 to 3 THz in solid fentanyl and its selected analogs. The molecular structure of each fentanyl analog and unique arrangement of H-bonds and dispersion interactions significantly change crystal packing and is subsequently reflected in the THz spectrum. Further, the study of THz spectra of a series of stereoisomers shows that small changes in molecular structure results in distinct crystal packing and significantly alters THz spectra as well. We discuss spectral features of synthetic opioids with higher potency than conventional fentanyl such as ohmefentanyl and sufentanil and discover the pattern of THz spectra of fentanyl analogs.

Cardiovascular and renal effects of constant rate infusions of remifentanil, dexmedetomidine and their combination in dogs anesthetized with sevoflurane

We evaluated changes in cardiovascular and renal functions as well as arginine vasopressin (AVP) secretion, with remifentanil and dexmedetomidine administration alone or in combination in sevoflurane-anesthetized dogs. Six healthy adult Beagle dogs received one of the following four treatments in a randomized crossover study: saline (C), remifentanil alone at successively increasing doses (R; 0.15, 0.60, and 2.40 µg/kg/min), dexmedetomidine alone (D; 0.5 µg/kg intravenously for initial 10 min followed by a constant rate infusion at 0.5 µg/kg/hr), and a combination of remifentanil and dexmedetomidine at the above-mentioned doses (RD). Sevoflurane doses were adjusted to 1.5 times of minimum alveolar concentration (MAC) equivalent according to MAC-sparing effects with remifentanil and dexmedetomidine as previously reported. Cardiovascular measurements, renal function data, and plasma AVP concentrations were determined before and every 60 min until 180 min after drug administration as per each treatment. In the R, D and RD, heart rate significantly decreased and mean arterial pressure significantly increased from baseline or with C. Cardiac index significantly decreased and systemic vascular resistance index increased with D and RD. Oxygen extraction ratio, renal blood flow, and glomerular filtration rate were not affected. The plasma AVP concentrations significantly decreased in D and RD, but increased in R. Only in D, the natriuresis was elicited. The combination of remifentanil and dexmedetomidine in sevoflurane-anesthetized dogs was acceptable in terms of the hemodynamics, oxygenation, and renal function. Remifentanil may interfere with dexmedetomidine-induced diuresis and inhibition of AVP secretion.

Remifentanil infusion during desflurane anesthesia reduces tissue blood flow while maintaining blood pressure and tissue oxygen tension in the masseter muscle and mandibular bone marrow

The aim of this study was to compare changes in tissue blood flow and tissue oxygen tension in the masseter muscle and mandibular bone marrow induced by remifentanil under desflurane or sevoflurane anesthesia. Eleven male tracheotomized Japan White rabbits were anesthetized with desflurane or sevoflurane under mechanical ventilation. The order of the inhalation of desflurane or sevoflurane was randomized. Desflurane or sevoflurane was administered at 1.0 minimum alveolar concentration and remifentanil was infused at 0.4 µg/kg/min. Observed variables included heart rate (HR), blood pressure (BP), common carotid artery blood flow (CCBF), mandibular bone marrow tissue blood flow (BBF), masseter muscle tissue blood flow (MBF), mandibular bone marrow tissue oxygen tension (PbO₂), and masseter muscle tissue oxygen tension (PmO₂). Two way repeated measures ANOVA showed no interaction between volatile anesthetics and remifentanil infusion except for MBF. There were significant differences in HR, SBP, DBP, MAP and CCBF between desflurane and sevoflurane groups. There were also significant differences in HR, SBP, DBP, MAP, CCBF, BBF and PbO₂ before, during and after remifentanil infusion. Desflurane reduced tissue blood flow in the masseter muscle and mandibular bone marrow while better maintained HR and BP than sevoflurane. Under remifentanil infusion, although both anesthetics reduced tissue blood flow, tissue oxygen tension was maintained in masseter muscle and mandibular bone marrow.

Analgosedation during flexible fiberoptic bronchoscopy: comparing the clinical effectiveness and safety of remifentanil versus midazolam/propofol

Background

There are limited data regarding the efficacy and safety of remifentanil sedation for diagnostic bronchoscopy. The aim of this study was to evaluate the clinical efficacy and safety of remifentanil by comparing it with those of conventional drugs, midazolam and propofol.

Methods

A retrospective study of 186 patients who underwent diagnostic bronchoscopy at Chonbuk National University Hospital was performed. Patients were classified into the remifentanil group and midazolam/propofol group according to the drugs used during bronchoscopy.

Results

Of the 186 patients, 111 patients received remifentanil and 75 received midazolam/propofol during the bronchoscopy. The proportion of patients who required bronchoscopy for endobronchial inspection alone was significantly higher in the midazolam/propofol group than in the remifentanil group (93.3% vs. 73.0%; p <  0.001). In contrast, the proportion of patients who required more invasive procedures, such as bronchoscopic biopsy, bronchoalveolar lavage, or transbronchial lung biopsy, was significantly higher in the remifentanil group than in the midazolam/propofol group (27.0% vs. 6.7%; p <  0.001). The recovery time was significantly shorter in the remifentanil group than in the midazolam/propofol group (mean 6.4 min vs. 11.6 min, p <  0.001). There were no significant differences between the groups with regard to safety events including desaturation, hypotension, and arrhythmia.

Conclusions

Despite the higher proportion of patients who underwent more invasive procedures in the remifentanil group than in the midazolam/propofol group, there was no significant difference in safety events between the groups. Those in the remifentanil group also demonstrated a faster recovery time than those in the midazolam/propofol group.

Remifentanil-Sparing Effect of Pectoral Nerve Block Type II in Breast Surgery under Surgical Pleth Index-Guided Analgesia during Total Intravenous Anesthesia

The pectoral nerve block type II (Pecs II block) can provide adequate perioperative analgesia in breast surgery. The surgical pleth index (SPI) is used to monitor the nociception balance using pulse oximetry. We investigated the remifentanil-sparing effect of Pecs II block under SPI guided analgesia during total intravenous anesthesia (TIVA). Thirty-nine patients undergoing breast surgery under remifentanil-propofol anesthesia were randomly assigned to the intervention (Pecs group, n = 20) or control group (n = 19). Remifentanil and propofol concentrations were adjusted to maintain an SPI of 20–50 and a bispectral index of 40–60, respectively. The Pecs group received an ultrasound-guided Pecs II block preoperatively using 30 mL of 0.5% ropivacaine. Total infused remifentanil during the surgery was significantly less in the Pecs group than in the control group (6.8 ± 2.2 μg/kg/h vs. 10.1 ± 3.7 μg/kg/h, p = 0.001). Pain scores on arrival at the postanesthetic care unit (PACU) (3 (2–5) vs. 5 (4–7)) and the rescue analgesic requirement in the PACU (9 vs. 2) was significantly lower in the Pecs group than in the control group. In conclusion, Pecs II block was able to reduce the intraoperative remifentanil consumption by approximately 30% and improve the postoperative pain in PACU in patients undergoing breast surgery under SPI-guided analgesia during TIVA.

Indispensable role of β-arrestin2 in the protection of remifentanil preconditioning against hepatic ischemic reperfusion injury

Our previous study demonstrated that remifentanil, an opioid agonist, conferred profound liver protection during hepatic ischemia reperfusion injury (HIRI), in which Toll-like receptors (TLRs) played a crucial role in mediating the inflammatory responses. β-arrestin2, a well-known mu opioid receptor desensitizer, is also a negatively regulator of Toll-like receptor 4 (TLR4)-mediated inflammatory reactions in a mitogen-activated protein kinase (MAPK)-dependent manner. Using the rodent models of hepatic ischemia reperfusion injury both in wild type and TLR4 knockout (TLR4 KO) mice, we found that remifentanil preconditioning could inhibit the expression of TLR4 and reduce the inflammatory response induced by HIRI in wild type but not in TLR4 KO mice. For the in-vitro study, LPS was used to treat RAW264.7 macrophage cells to mimic the inflammatory response induced by HIRI. Remifentanil increased β-arrestin2 expression both in vivo and in vitro, while after silencing β-arrestin2 RNA, the effect of remifentanil in reducing cell death and apoptosis, as well as decreasing phosphorylation of ERK and JNK were abolished in RAW264.7 cells. These data suggested that remifentanil could ameliorate mice HIRI through upregulating β-arrestin2 expression, which may function as a key molecule in bridging opioid receptor and TLR4 pathway.

Postmortem Toxicology of New Synthetic Opioids

One hundred fifteen Americans die every day from opioid overdose. These overdose fatalities have been augmented by the increased availability of potent synthetic opioids, such as fentanyl and its derivatives. The death rate of synthetic opioids, other than methadone, increased by 72.2% from 2014 to 2015, and doubled from 2015 to 2016, situating the USA in the midst of an opioid overdose epidemic. The analytical identification of these opioids in postmortem samples and the correct toxicological data interpretation is critical to identify and implement preventive strategies. This article reviews the current knowledge of postmortem toxicology of synthetic opioids and the chemical and pharmacological factors that may affect drug concentrations in the different postmortem matrices and therefore, their interpretation. These factors include key chemical properties, essential pharmacokinetics parameters (metabolism), postmortem redistribution and stability data in postmortem samples. Range and ratios of concentrations reported in traditional and non-traditional postmortem specimens, blood, urine, vitreous humor, liver and brain, are summarized in tables. The review is focused on fentanyl and derivatives (e.g., acetyl fentanyl, butyryl fentanyl, carfentanil, furanyl fentanyl, 4-methoxybutyrylfentanyl, 4-fluorobutyrylfentanyl, ocfentanil) and non-traditional opioid agonists (e.g., AH-7921, MT-45, U-47700). All of these data are critically compared to postmortem data, and chemical and pharmacological properties of natural opioids (morphine), semi-synthetic (oxycodone, hydrocodone, hydromorphone, and oxymorphone), and synthetic opioids (methadone and buprenorphine). The interpretation of drug intoxication in death investigation is based on the available published literature. This review serves to facilitate the evaluation of cases where synthetic opioids may be implicated in a fatality through the critical review of peer reviewed published case reports and research articles.

Drug Interactions With New Synthetic Opioids

Fentanyl, fentanyl analogs, and other new synthetic opioids (NSO) have burst onto the illegal drug market as new psychoactive substances (NPS). They are often sold as heroin to unsuspecting users and produce euphoria through their agonist action on μ- opioid receptors. Their high consumption, often combined with other substances, has led to multiple intoxications during recent years. In some countries, such as the United States, the consumption of opioids, whether for medical or recreational purposes, has become epidemic and is considered a public health problem. Fentanyl analogs are more potent than fentanyl which in turn is 50 times more potent than morphine. Furthermore, some fentanyl analogs have longer duration of action and therefore interactions with other substances and medicines can be more serious. This review is focused on the potentially most frequent interactions of opioid NPS taking into account the drugs present in the reported cases of poly-intoxication, including other illegal drugs of abuse and medication. Substances involved are mainly antidepressants, antihistamines, antipsychotics, benzodiazepines, analgesics, anesthetics, psychostimulants, other opioids, alcohol, and illegal drugs of abuse. The interactions can be produced due to pharmacokinetic and pharmacodynamic mechanisms. Naloxone can be used as an antidote, although required doses might be higher than for traditional opioid intoxications. It is crucial that doctors who habitually prescribe opioids, which are often misused by patients and NPS users, be aware of designer opioids' potentially life-threatening drug-drug interactions in order to prevent new cases of intoxication.

Remifentanil suppresses increase in interleukin-6 mRNA in the brain by inhibiting cyclic AMP synthesis

PURPOSE

Neuronal inflammation is caused by systemic inflammation and induces cognitive dysfunction. IL-6 plays a crucial role in therapies for neuronal inflammation and cognitive dysfunction. Remifentanil, an ultra-short-acting opioid, controls inflammatory reactions in the periphery, but not in the brain. Therefore, the anti-inflammatory effects of remifentanil in neuronal tissue and the involvement of cAMP in these effects were investigated in the present study.

METHODS

Mice were divided into 4 groups: control, remifentanil, LPS, and LPS + remifentanil. Brain levels of pro-inflammatory cytokine mRNA, and serum levels of corticosterone, catecholamine and IL-6 were measured in the 4 groups. The co-localization of IL-6 and astrocytes in the mouse brain after the LPS injection was validated by immunostaining. LPS and/or remifentanil-induced changes in intracellular cAMP levels in cultured glial cells were measured, and the effects of cAMP on LPS-induced IL-6 mRNA expression levels were evaluated.

RESULTS

Remifentanil suppressed increase in IL-6 mRNA levels in the mouse brain, and also inhibited the responses of plasma IL-6, corticosterone, and noradrenaline in an inflammatory state. In the hypothalamus, IL-6 was localized in the median eminence, at which GFAP immunoreactivity was specifically detected. In cultured cells, remifentanil suppressed increase in IL-6 mRNA levels and intracellular cAMP levels after the administration of LPS, and this enhanced IL-6 mRNA expression in response to LPS.

CONCLUSION

Remifentanil suppressed increase in IL-6 mRNA levels in the brain in an inflammatory state, and this effect may be attributed to its direct action on neuronal cells through the inhibition of intracellular cAMP rather than corticosterone.

Does glycopyrrolate premedication facilitate tracheal intubation with a rigid video-stylet?: A randomized controlled trial

BACKGROUND

A rigid video-stylet intubation device provides safe and accurate access to the trachea by enabling visualization of the airway structures during tracheal intubation. The primary purpose of this study was to examine the effects of glycopyrrolate premedication on tracheal intubation with a rigid video-stylet.

METHODS

In this prospective, randomized, double-blinded study, 78 patients were randomly assigned to the control group (n = 39; no glycopyrrolate administration) or the glycopyrrolate group (n = 39; 0.005 mg/kg glycopyrrolate, intramuscular injection). A rigid video-stylet was used for tracheal intubation. The degree of oral secretion observed through the video-stylet monitor was assessed using the OptiScope laryngeal view and graded on a 4-point scale (1, excellent; 2, good; 3, poor; and 4, unacceptable). The time to intubation and hemodynamic variables at baseline and 1, 3, and 5 minutes after intubation were recorded.

RESULTS

The OptiScope laryngeal view grades of the glycopyrrolate group (grade 1 = 16 [41.0%], 2 = 17 [43.6%], 3 = 6 [15.4%], and 4 = 0 [0%]) were significantly higher than those of the control group (grade 1 = 9 [23.1%], 2 = 11 [28.2%], 3 = 18 [46.2%], and 4 = 1 [2.6%]; P = .02). The intubation time was shorter in the glycopyrrolate group (18.5 seconds [15.0-22.0]) than the control group (22.0 seconds [17.9-26.4], P = .02). There was no significant difference in the hemodynamic variables between groups.

CONCLUSION

Glycopyrrolate facilitated tracheal intubation with a rigid video-stylet by decreasing oral secretions and providing better visualization and faster intubation with hemodynamic stability.

TRIAL REGISTRY

www.clinicaltrials.gov; Identifier: NCT03050242.

Population Pharmacokinetic Modeling of Remifentanil in Infants with Unrepaired Tetralogy of Fallot

BACKGROUND

Although there is literature suggesting that pathophysiologic changes in children with congenital heart disease alter the pharmacokinetics of anesthetics and may result in dosage adjustment, limited information exists regarding the pharmacokinetics of remifentanil in infants with unrepaired tetralogy of Fallot (TOF). The objectives of the current analysis were to characterize the population pharmacokinetics of remifentanil in infants, and to evaluate the effects of TOF on remifentanil's pharmacokinetics.

METHODS

Twenty-seven infants (16 with TOF and 11 with normal cardiac anatomy; aged 114-360 days) scheduled to undergo elective surgery under general anesthesia were recruited in the study. All children received remifentanil 1 μg/kg/min intravenously for anesthesia induction and early maintenance [until ~ 20 min before cardiopulmonary bypass (CPB) for patients with TOF]. Serial arterial blood samples were drawn and analyzed. Population pharmacokinetics of remifentanil was characterized using NONMEM software. The estimates were standardized to a 70-kg adult using a per-kilogram model.

RESULTS

A two-compartment disposition model adequately described the pharmacokinetics of remifentanil. Besides body weight, the introduction of any other covariates, including TOF status, did not improve the model significantly (P > 0.05). The population parameter estimates for systemic clearance (Cl₁) and inter-compartment clearances (Cl₂) were 6.03 × (WT/70 kg) and 1.23 × (WT/70 kg) L/min, respectively, and central volume of distribution (V₁) and peripheral volumes of distribution (V₂) were 19.6 × (WT/70 kg) and 21.7 × (WT/70 kg) L, respectively.

CONCLUSIONS

Unrepaired TOF does not change the pharmacokinetics of remifentanil, suggesting a similar dosage for infants with TOF compared to normal cardiac anatomy infants.

CLINICAL TRIAL REGISTRATION

The patient enrollment in this study started at 2012, so we do not have clinic trial number, but we still think this is a valuable research and hope it could be considered for publication.

The effect of remifentanil on the minimum alveolar concentration (MAC) and MAC derivatives of sevoflurane in dogs

Remifentanil is an ultra-short-acting µ-opioid receptor agonist. The purpose of this study was to determine the relationship of the minimum alveolar concentration (MAC) of sevoflurane and other MAC derivatives, including the MAC for blocking adrenergic responses (MAC-BAR) and the MAC at which tracheal extubation is occurred (MAC-extubation), with or without remifentanil infusion. Six healthy adult beagle dogs were randomly anesthetized three times for determining the MAC-BAR (SEV_MAC-BAR), MAC (SEV_MAC), and MAC- extubation (SEV_{MAC-extubation}) of sevoflurane under infusion of saline and remifentanil at rates of 0.15, 0.30, 0.60, 1.20, and 2.40 µg/kg/min. The ratio of the SEV_MAC-BAR and SEV_MAC and that of the SEV_{MAC-extubation} and SEV_MAC were not significantly different at baseline and during treatment. The MAC-BAR₉₅ and MAC₉₅ decreased in a dose-dependent manner until reaching 1.20 µg/kg/min, and the MAC-extubation₅ decreased in a dose-dependent manner until reaching 0.60 µg/kg/min. The percentage reduction of SEV_MAC-BAR, SEV_MAC, and SEV_{MAC-extubation} increased in a dose-dependent manner during remifentanil infusion. The heart rate significantly decreased in the MAC-BAR and MAC groups, and the systolic and mean arterial pressures increased after remifentanil infusion compared with the baseline values. Remifentanil infusion caused reduction of the SEV_MAC-BAR, SEV_MAC, and SEV_{MAC-extubation} in a dose-dependent manner, and ceiling effects were observed in the dogs. Higher doses of remifentanil and sevoflurane were necessary for blocking the sympathetic response to the supramaximal stimulus to prevent movement and extubation in dogs.

Intraoperative Nefopam Reduces Acute Postoperative Pain after Laparoscopic Gastrectomy: a Prospective, Randomized Study

BACKGROUND

We assessed whether intraoperative nefopam would reduce opioid consumption and relieve postoperative pain in patients undergoing laparoscopic gastrectomy.

METHODS

The 60 enrolled patients were randomly assigned to the control (n = 32) or nefopam (n = 28) group. All patients were blinded to their group assignment. We administered 100 ml of normal saline only (control group) or 20 mg of nefopam mixed in 100 ml normal saline (nefopam group) after anesthesia induction and at the end of surgery. The cumulative amount of fentanyl via intravenous patient-controlled analgesia (PCA), incidence of rescue analgesic medication, and numerical rating scale (NRS) for postoperative pain were evaluated along with the total remifentanil consumption.

RESULTS

The mean infusion rate of remifentanil was significantly lower in the nefopam group (0.08 ± 0.05 μg/kg/min) than in the control group (0.13 ± 0.06 μg/kg/min) (P < 0.001). Patients in the nefopam group required less fentanyl via intravenous PCA than those in the control group during the first 6 h after surgery (323.8 ± 119.3 μg vs. 421.2 ± 151.6 μg, P = 0.009). Additionally, fewer patients in the nefopam group than in the control group received a rescue analgesic during the initial 6 h postoperatively (78.6 vs. 96.9%, P = 0.028). The NRS measured while patients were in the post-anesthetic care unit was significantly lower in the nefopam group than in the control group (3.8 ± 1.1 vs. 4.8 ± 1.4, P = 0.012). The subsequent NRS obtained after patients had been transferred to the general ward was comparable between the two groups during the following postoperative period.

CONCLUSIONS

Intraoperative nefopam decreased postoperative pain and opioid consumption in the acute postoperative period after laparoscopic gastrectomy. Hence, nefopam may be considered as a component of multimodal analgesia after laparoscopic gastrectomy.

Intraoperative electroacupuncture relieves remifentanil-induced postoperative hyperalgesia via inhibiting spinal glial activation in rats

Background

Accumulating studies have suggested that remifentanil, the widely-used opioid analgesic in clinical anesthesia, can activate the pronociceptive systems and enhance postoperative pain. Glial cells are thought to be implicated in remifentanil-induced hyperalgesia. Electroacupuncture is a complementary therapy to relieve various pain conditions with few side effects, and glial cells may be involved in its antinociceptive effect. In this study, we investigated whether intraoperative electroacupuncture could relieve remifentanil-induced postoperative hyperalgesia by inhibiting the activation of spinal glial cells, the production of spinal proinflammatory cytokines, and the activation of spinal mitogen-activated protein kinases.

Methods

A rat model of remifentanil-induced postoperative hyperalgesia was used in this study. Electroacupuncture during surgery was conducted at bilateral Zusanli (ST36) acupoints. Behavior tests, including mechanical allodynia and thermal hyperalgesia, were performed at different time points. Astrocytic marker glial fibrillary acidic protein, microglial marker Iba1, proinflammatory cytokines, and phosphorylated mitogen-activated protein kinases in the spinal cord were detected by Western blot and/or immunofluorescence.

Results

Mechanical allodynia and thermal hyperalgesia were induced by both surgical incision and remifentanil infusion, and remifentanil infusion significantly exaggerated and prolonged incision-induced pronociceptive effects. Glial fibrillary acidic protein, Iba1, proinflammatory cytokines (interleukin-1β and tumor necrosis factor-α), and phosphorylated mitogen-activated protein kinases (p-p38, p-JNK, and p-ERK1/2) were upregulated after surgical incision, remifentanil infusion, and especially after their combination. Intraoperative electroacupuncture significantly attenuated incision- and/or remifentanil-induced pronociceptive effects, spinal glial activation, proinflammatory cytokine upregulation, and phosphorylated mitogen-activated protein kinase upregulation.

Conclusions

Our study suggests that remifentanil-induced postoperative hyperalgesia can be relieved by intraoperative electroacupuncture via inhibiting the activation of spinal glial cells, the upregulation of spinal proinflammatory cytokines, and the activation of spinal mitogen-activated protein kinases.

A Subregion of the Parabrachial Nucleus Partially Mediates Respiratory Rate Depression from Intravenous Remifentanil in Young and Adult Rabbits

BACKGROUND

The efficacy of opioid administration to reduce postoperative pain is limited by respiratory depression. We investigated whether clinically relevant opioid concentrations altered the respiratory pattern in the parabrachial nucleus, a pontine region contributing to respiratory pattern generation, and compared these effects with a medullary respiratory site, the pre-Bötzinger complex.

METHODS

Studies were performed in 40 young and 55 adult artificially ventilated, decerebrate rabbits. We identified an area in the parabrachial nucleus where α-amino-3-hydroxy-5-methyl-4-isoxazolepropionic acid microinjections elicited tachypnea. Two protocols were performed in separate sets of animals. First, bilateral microinjections of the μ-opioid receptor agonist [D-Ala, N-MePhe, Gly-ol]-enkephalin (100 μM) into the "tachypneic area" determined the effect of maximal μ-opioid receptor activation. Second, respiratory rate was decreased with continuous IV infusions of remifentanil. The opioid antagonist naloxone (1 mM) was then microinjected bilaterally into the "tachypneic area" of the parabrachial nucleus to determine whether the respiratory rate depression could be locally reversed.

RESULTS

Average respiratory rate was 27 ± 10 breaths/min. First, [D-Ala, N-MePhe, Gly-ol]-enkephalin injections decreased respiratory rate by 62 ± 20% in young and 45 ± 26% in adult rabbits (both P < 0.001). Second, during IV remifentanil infusion, bilateral naloxone injections into the "tachypneic area" of the parabrachial nucleus reversed respiratory rate depression from 55 ± 9% to 20 ± 14% in young and from 46 ± 20% to 18 ± 27% in adult rabbits (both P < 0.001). The effects of bilateral [D-Ala, N-MePhe, Gly-ol]-enkephalin injection and IV remifentanil on respiratory phase duration in the "tachypneic area" of the parabrachial nucleus was significantly different from the pre-Bötzinger complex.

CONCLUSIONS

The "tachypneic area" of the parabrachial nucleus is highly sensitive to μ-opioid receptor activation and mediates part of the respiratory rate depression by clinically relevant administration of opioids.

Postoperative nausea and vomiting after thyroidectomy: a comparison between dexmedetomidine and remifentanil as part of balanced anesthesia

BACKGROUND

Postoperative nausea and vomiting (PONV) is the major complication related to general anesthesia, occurring in 60-80% of patients after thyroidectomy. The objective of this study was to compare the effects of an intraoperative dexmedetomidine infusion with remifentanil, as anesthetic adjuvants of balanced anesthesia, on PONV in patients undergoing thyroidectomy.

METHODS

Eighty patients scheduled for thyroidectomy were randomized into the following two groups: 1) The dexmedetomidine group (Group D), who received an initial loading dose of dexmedetomidine (1 µg/kg over 10 min) during the induction of anesthesia, followed by a continuous infusion at a rate of 0.3-0.5 µg/kg/h; 2) the remifentanil group (group R), who received remifentanil at an initial target effect site concentration of 4 ng/ml during the induction of anesthesia, followed by a target effect site concentration of 2-3 ng/ml. PONV was assessed during the first 24 hours in 2 time periods (0-2 h and 2-24 h). The pain intensity, sedation score, extubation time, and hemodynamics were also assessed.

RESULTS

During the 2 time periods, the incidence and severity of PONV in group D were significantly lower than in group R. In addition, the need for rescue antiemetics was significantly lower in group D than in group R. The effect of dexmedetomidine on postoperative pain relief (2-24 h) was superior to that of remifentanil. The hemodynamics were similar in both groups, whereas eye opening and extubation time were delayed in group D.

CONCLUSIONS

Adjuvant use of intraoperative dexmedetomidine infusion may be effective for the prevention of PONV.

Activation of spinal alpha-7 nicotinic acetylcholine receptor shortens the duration of remifentanil-induced postoperative hyperalgesia by upregulating KCC2 in the spinal dorsal horn in rats

Background Accumulating evidence has shown that the signal from spinal brain-derived neurotrophic factor/tyrosine receptor kinase B-K+-Cl- cotransporter-2 plays a critical role in the process of pain hypersensitivity. The activation of alpha-7 nicotinic acetylcholine receptors could have an analgesic effect on remifentanil-induced postoperative hyperalgesia. Nevertheless, whether intrathecal administration of PNU-120596, an alpha-7 nicotinic acetylcholine receptors selective type II positive allosteric modulator, before surgery could affect the duration of remifentanil-induced postoperative hyperalgesia remains unknown, and the effects of alpha-7 nicotinic acetylcholine receptors activation on the brain-derived neurotrophic factor/tyrosine receptor kinase B-K+-Cl- cotransporter-2 signal in the spinal dorsal horn of rats with remifentanil-induced postoperative hyperalgesia is still enigmatic. Results We demonstrated that the brain-derived neurotrophic factor/tyrosine receptor kinase B-K+-Cl- cotransporter-2 signal played a critical role in the development of remifentanil-induced postoperative hyperalgesia. Intrathecal administration of PNU-120596 (8 µg/kg, 15 min before surgery) was associated with earlier signs of recovery from remifentanil-induced postoperative hyperalgesia. Simultaneously, remifentanil-induced postoperative hyperalgesia-induced K+-Cl- cotransporter-2 downregulation was partly reversed and coincided with a decreased expression of brain-derived neurotrophic factor/tyrosine receptor kinase B in the spinal dorsal horn, approximately correlating with the time course of the nociceptive behavior. Moreover, intrathecal administration of the K+-Cl- cotransporter-2 inhibitor VU0240551 significantly reduced the analgesic effect of PNU-120596 on remifentanil-induced postoperative hyperalgesia. Conclusions The activation of alpha-7 nicotinic acetylcholine receptors induced a shorter duration of remifentanil-induced postoperative hyperalgesia by restoring the brain-derived neurotrophic factor/tyrosine receptor kinase B-K+-Cl- cotransporter-2 signal in the spinal dorsal horn of rats, which provides new insight into treatment in clinical postoperative pain management.

Comparison of the effect of continuous intravenous infusion and two bolus injections of remifentanil on haemodynamic responses during anaesthesia induction: a prospective randomised single-centre study

BACKGROUND

Remifentanil is an effective drug for protecting against adverse haemodynamic responses to tracheal intubation. We compared the haemodynamic responses during anaesthesia induction between continuous intravenous (IV) infusion and two bolus injections of remifentanil.

METHODS

This prospective, randomised, open-label, single-centre study included patients with American Society of Anesthesiologists physical status I-II, scheduled to undergo elective surgery under general anaesthesia. Patients were randomised into two groups based on remifentanil administration type: the continuous IV infusion group (Group C) receiving a 0.3-μg/kg/min remifentanil infusion for 5 min followed by a 0.1-μg/kg/min remifentanil infusion, and the IV bolus group (Group B) receiving a combination of two bolus injections of remifentanil (first bolus of 0.4 μg/kg and second bolus of 0.6 μg/kg after 3 min) and 0.1 μg/kg/min remifentanil. General anaesthesia was induced with 1 mg/kg propofol and 0.6 mg/kg rocuronium 3 min after remifentanil infusion (Group C) or immediately after the first bolus of remifentanil (Group B). Tracheal intubation was performed 4 min after the injection of propofol and rocuronium. Heart rate and non-invasive blood pressure were recorded at 1-min intervals from baseline (i.e., before induction) to 5 min after tracheal intubation.

RESULTS

A total of 107 patients were enrolled (Group C, 55; Group B, 52). Normotensive patients with no history of antihypertensive medication use were assigned to the normotensive subgroup (41 each in both groups), while those with hypertension but without a history of antihypertensive medication use were assigned to the untreated hypertensive subgroup (Group C vs. B, n = 7 vs. 4). Finally, patients with a history of antihypertensive medication use were assigned to the treated hypertensive subgroup (7 each in both Groups C and B). No differences in heart rate and blood pressure were observed between Groups C and B within each subgroup.

CONCLUSIONS

Haemodynamic responses during anaesthesia induction were similar between continuous infusion and two bolus injections of remifentanil within both normotensive and hypertensive patients with or without medication.

TRIAL REGISTRATION

The trial was retrospectively registered with Japanese Clinical Trial Registry "UMIN-CTR" on 20 October 2016 and was given a trial ID number UMIN000024495 .

Comparison of an Intraoperative Infusion of Dexmedetomidine, Fentanyl, and Remifentanil on Perioperative Hemodynamics, Sedation Quality, and Postoperative Pain Control

We aimed to compare fentanyl, remifentanil and dexmedetomidine with respect to hemodynamic stability, postoperative pain control and achievement of sedation at the postanesthetic care unit (PACU). In this randomized double-blind study, 90 consecutive total laparoscopic hysterectomy patients scheduled for elective surgery were randomly assigned to receive fentanyl (1.0 μg/kg) over 1 minute followed by a 0.4 μg/kg/hr infusion (FK group, n = 30), or remifentanil (1.0 μg/kg) over 1 minute followed by a 0.08 μg/kg/min infusion (RK group, n = 30), or dexmedetomidine (1 μg/kg) over 10 minutes followed by a 0.5 μg/kg/hr infusion (DK group, n = 30) initiating at the end of main procedures of the operation to the time in the PACU. A single dose of intravenous ketorolac (30 mg) was given to all patients at the end of surgery. We respectively evaluated the pain VAS scores, the modified OAA/S scores, the BIS, the vital signs and the perioperative side effects to compare the efficacy of fentanyl, remifentanil and dexmedetomidine. Compared with other groups, the modified OAA/S scores were significantly lower in DK group at 0, 5 and 10 minutes after arrival at the PACU (P < 0.05), whereas the pain VAS and BIS were not significantly different from other groups. The blood pressure and heart rate in the DK group were significantly lower than those of other groups at the PACU (P < 0.05). DK group, at sedative doses, had the better postoperative hemodynamic stability than RK group or FK group and demonstrated a similar effect of pain control as RK group and FK group with patient awareness during sedation in the PACU. (World Health Organization registry, KCT0001524).

Metabolism of Carfentanil, an Ultra-Potent Opioid, in Human Liver Microsomes and Human Hepatocytes by High-Resolution Mass Spectrometry

Carfentanil is an ultra-potent synthetic opioid. No human carfentanil metabolism data are available. Reportedly, Russian police forces used carfentanil and remifentanil to resolve a hostage situation in Moscow in 2002. This alleged use prompted interest in the pharmacology and toxicology of carfentanil in humans. Our study was conducted to identify human carfentanil metabolites and to assess carfentanil's metabolic clearance, which could contribute to its acute toxicity in humans. We used Simulations Plus's ADMET Predictor™ and Molecular Discovery's MetaSite™ to predict possible metabolite formation. Both programs gave similar results that were generally good but did not capture all metabolites seen in vitro. We incubated carfentanil with human hepatocytes for up to 1 h and analyzed samples on a Sciex 3200 QTRAP mass spectrometer to measure parent compound depletion and extrapolated that to represent intrinsic clearance. Pooled primary human hepatocytes were then incubated with carfentanil up to 6 h and analyzed for metabolite identification on a Sciex 5600+ TripleTOF (QTOF) high-resolution mass spectrometer. MS and MS/MS analyses elucidated the structures of the most abundant metabolites. Twelve metabolites were identified in total. N-Dealkylation and monohydroxylation of the piperidine ring were the dominant metabolic pathways. Two N-oxide metabolites and one glucuronide metabolite were observed. Surprisingly, ester hydrolysis was not a major metabolic pathway for carfentanil. While the human liver microsomal system demonstrated rapid clearance by CYP enzymes, the hepatocyte incubations showed much slower clearance, possibly providing some insight into the long duration of carfentanil's effects.

Procedural sedation and analgesia for respiratory-gated MR-HIFU in the liver: a feasibility study

BACKGROUND

Previous studies demonstrated both pre-clinically and clinically the feasibility of magnetic resonance-guided high-intensity focused ultrasound (MR-HIFU) ablations in the liver. To overcome the associated problem of respiratory motion of the ablation area, general anesthesia (GA) and mechanical ventilation was used in conjunction with either respiratory-gated energy delivery or energy delivery during induced apnea. However, clinical procedures requiring GA are generally associated with increased mortality, morbidity, and complication rate compared to procedural sedation and analgesia (PSA). Furthermore, PSA is associated with faster recovery and an increased eligibility for non- and mini-invasive interventions.

METHODS

In this study, we investigate both in an animal model and on a small patient group the kinetics of the diaphragm during free-breathing, when a tailored remifentanil/propofol-based PSA protocol inducing partial respiratory depression is used. Subsequently, we demonstrate in an animal study the compatibility of the resulting respiratory pattern of the PSA protocol with a gated HIFU ablation in the liver by direct comparison with gated ablations conducted under GA. Wilcoxon signed-rank tests were performed for statistical analysis of non-perfused and necrosed tissue volumes. Duty cycles (ratio or percentage of the breathing cycle with the diaphragm in its resting position, such that acoustic energy delivery with MR-HIFU was allowed) were statistically compared for both GA and PSA using student's t tests.

RESULTS

In both animal and human experiments, the breathing frequency was decreased below 9/min, while maintaining stable vital functions. Furthermore an end-exhalation resting phase was induced by this PSA protocol during which the diaphragm is virtually immobile. Median non-perfused volumes, non-viable volumes based on NADH staining, and duty cycles were larger under PSA than under GA or equal.

CONCLUSIONS

We conclude that MR-HIFU ablations of the liver under PSA are feasible and potentially increase the non-invasive nature of this type of intervention.

Optimal effect-site concentration of remifentanil for minimizing cardiovascular changes caused by fiberoptic nasotracheal intubation

BACKGROUND

Endotracheal intubation induces clinically adverse cardiovascular changes. Various pharmacological strategies for controlling these responses have been suggested with opioids being widely administered. In this study, the optimal effect-site concentration (Ce) of remifentanil for minimizing hemodynamic responses to fiberoptic nasotracheal intubation was evaluated.

METHODS

Thirty patients, aged 18-63 years, scheduled for elective surgery were included. Anesthesia was induced with a propofol and remifentanil infusion via target-controlled infusion (TCI). Remifentanil infusion was initiated at 3.0 ng/mL, and the response of each patient determined the Ce of remifentanil for the next patient by the Dixon up-and-down method at an interval of 0.5 ng/mL. Rocuronium was administered after propofol and remifentanil reached their preset Ce; 90 seconds later fiberoptic nasotracheal intubation was initiated. Non-invasive blood pressure and heart rate (HR) were measured at pre-induction, the time Ce was reached, immediately before and after intubation, and at 1 and 3 minutes after intubation. The up-and-down criteria comprised a 20% change in mean blood pressure and HR between just prior to intubation and 1 minute after intubation.

RESULTS

The median effective effect-site concentration (EC₅₀) of remifentanil was 3.11 ± 0.38 ng/mL by the Dixon's up-and-down method. From the probit analysis, the EC₅₀ of remifentanil was 3.43 ng/mL (95% confidence interval, 2.90-4.06 ng/mL). In PAVA, the EC50 and EC95 of remifentanil were 3.57 ng/mL (95% CI, 2.95-3.89) and 4.35 ng/mL (95% CI, 3.93-4.45). No remifentanil-related complications were observed.

CONCLUSIONS

The EC₅₀ of remifentanil for minimizing the cardiovascular changes and side effects associated with fiberoptic nasotracheal intubation was 3.11-3.43 ng/mL during propofol TCI anesthesia with a Ce of 4 ug/mL.

Opioid-induced Respiratory Depression Is Only Partially Mediated by the preBötzinger Complex in Young and Adult Rabbits In Vivo

BACKGROUND

The preBötzinger Complex (preBC) plays an important role in respiratory rhythm generation. This study was designed to determine whether the preBC mediated opioid-induced respiratory rate depression at clinically relevant opioid concentrations in vivo and whether this role was age dependent.

METHODS

Studies were performed in 22 young and 32 adult New Zealand White rabbits. Animals were anesthetized, mechanically ventilated, and decerebrated. The preBC was identified by the tachypneic response to injection of D,L-homocysteic acid. (1) The μ-opioid receptor agonist [D-Ala2,N-Me-Phe4,Gly-ol]-enkephalin (DAMGO, 100 μM) was microinjected into the bilateral preBC and reversed with naloxone (1 mM) injection into the preBC. (2) Respiratory depression was achieved with intravenous remifentanil (0.08 to 0.5 μg kg(-1) min(-1)). Naloxone (1 mM) was microinjected into the preBC in an attempt to reverse the respiratory depression.

RESULTS

(1) DAMGO injection depressed respiratory rate by 6 ± 8 breaths/min in young and adult rabbits (mean ± SD, P < 0.001). DAMGO shortened the inspiratory and lengthened the expiratory fraction of the respiratory cycle by 0.24 ± 0.2 in adult and young animals (P < 0.001). (2) During intravenous remifentanil infusion, local injection of naloxone into the preBC partially reversed the decrease in inspiratory fraction/increase in expiratory fraction in young and adult animals (0.14 ± 0.14, P < 0.001), but not the depression of respiratory rate (P = 0.19). PreBC injections did not affect respiratory drive. In adult rabbits, the contribution of non-preBC inputs to expiratory phase duration was larger than preBC inputs (3.5 [-5.2 to 1.1], median [25 to 75%], P = 0.04).

CONCLUSIONS

Systemic opioid effects on respiratory phase timing can be partially reversed in the preBC without reversing the depression of respiratory rate.

Comparison between remifentanil and dexmedetomidine for sedation during modified awake fiberoptic intubation

Cricothyroid membrane injections and the application of a coarse fiberoptic bronchoscope (FOB) below the vocal cords for topical anesthesia have a number of limitations for certain patients. Thus, the aim of the present observational study was to assess the effect of a novel modified topical anesthesia method using the effective sedation drugs, remifentanil (Rem) or dexmedetomidine (Dex), during awake fiberoptic orotracheal intubation (AFOI). In total, 90 adult patients, who had been classified as American Society of Anesthesiologists I-II, were included in the study. The patients had anticipated difficult airways and were to undergo orotracheal intubation for elective surgery. The patients were enrolled in the double-blinded randomized pilot study and received Rem or Dex for sedation during the modified AFOI procedure. The two groups received 2% lidocaine for topical anesthesia via an epidural catheter, which was threaded through the suction channel of the FOB. The main clinical outcomes were evaluated by graded scores representing the conditions for intubation and post-intubation. Additional parameters analyzed included airway obstruction, hemodynamic changes, time required for intubation, amnesia level and subjective satisfaction. All 90 patients were successfully intubated using the modified AFOI technique. The comfort scores and airway events during intubation did not significantly differ between the two groups. However, the Rem group experienced less coughing, and less time was required for tracheal intubation when compared with the Dex group. No statistically significant differences were observed in the changes to the mean arterial pressure and heart rate at any time point between the two groups. Therefore, the current study demonstrated that the modified AFOI method is feasible and effective for difficult airway management, and that Dex and Rem exhibit similar efficacy as adjuvant therapies.

Bispectral index monitoring during anesthesiologist-directed propofol and remifentanil sedation for endoscopic submucosal dissection: a prospective randomized controlled trial

PURPOSE

Endoscopic submucosal dissection (ESD) is a technically difficult and lengthy procedure requiring optimal depth of sedation. The bispectral index (BIS) monitor is a non-invasive tool that objectively evaluates the depth of sedation. The purpose of this prospective randomized controlled trial was to evaluate whether BIS guided sedation with propofol and remifentanil could reduce the number of patients requiring rescue propofol, and thus reduce the incidence of sedation- and/or procedure-related complications.

MATERIALS AND METHODS

A total of 180 patients who underwent the ESD procedure for gastric adenoma or early gastric cancer were randomized to two groups. The control group (n=90) was monitored by the Modified Observer's Assessment of Alertness and Sedation scale and the BIS group (n=90) was monitored using BIS. The total doses of propofol and remifentanil, the need for rescue propofol, and the rates of complications were recorded.

RESULTS

The number of patients who needed rescue propofol during the procedure was significantly higher in the control group than the BIS group (47.8% vs. 30.0%, p=0.014). There were no significant differences in the incidence of sedation- and/or procedure-related complications.

CONCLUSION

BIS-guided propofol infusion combined with remifentanil reduced the number of patients requiring rescue propofol in ESD procedures. However, this finding did not lead to clinical benefits and thus BIS monitoring is of limited use during anesthesiologist-directed sedation.

The Comparison of Patient-Controlled Remifentanil Administered by Two Different Protocols (Bolus and Bolus+Infusion) and Intramuscular Meperidine for Labor Analgesia

OBJECTIVE

Nowadays, there are many pain relief methods for reducing the pain and stress of labor and delivery. In our study, two different remifentanil protocols (bolus and bolus+infusion) administered by patient-controlled analgesia method were compared with intramuscular meperidine for labor analgesia.

METHODS

Ninety parturients who were scheduled for vaginal delivery were included in this study. Patients were randomly divided into 3 groups, with 15 primiparous and 15 multiparous patients in each group. Whenever a patient requested analgesics during the labor, Group M was given 1 mg kg(-1) intramuscular meperidine, Group B was given intravenous bolus patient-controlled remifentanil, and Group IB was given intravenous bolus+infusion patient-controlled remifentanil. Patients' systolic and diastolic blood pressure, heart rate, pain-comfort and sedation scores, remifentanil consumption, side effects, and Apgar scores of the newborns were evaluated during the labor and delivery.

RESULTS

Patients' mean pain and comfort scores were significantly lower in Groups B and IB than in Group M at all time intervals except the first minute. Compared with Group IB, mean pain and comfort scores at 15, 30, 60, and 120 minutes were significantly higher in Group B. The mean sedation scores were similar among the groups. Total remifentanil consumption was lower in Group IB than in Group B, but it was not statistically significant.

CONCLUSION

Patient-controlled intravenous bolus or bolus+infusion remifentanil provided more effective analgesia and patient comfort than intramuscular meperidine for labor analgesia. Especially during labor, bolus+infusion remifentanil administration provided better pain and patient comfort scores than bolus alone, without increasing remifentanil consumption.

Factors that affect intravenous patient-controlled analgesia for postoperative pain following orthognathic surgery for mandibular prognathism

The predictors of postoperative pain and analgesic consumption were previously found to include preoperative pain, anxiety, age, type of surgery, and genotype, but remaining unclear was whether intraoperative factors could predict postoperative pain. In the present study, we investigated the time-course of fentanyl consumption using intravenous patient-controlled analgesia records from patients who underwent orthognathic surgery for mandibular prognathism and analyzed the influence of anesthesia methods and surgical methods together with sex on the time course. A significant difference in the time course of fentanyl administration was found (P<0.001). No significant difference in the time course of fentanyl administration was found between males and females (P = 0.653), with no interaction between time course and sex (P = 0.567). No significant difference in the time course of fentanyl administration was found among anesthesia methods, such as fentanyl induction followed by fentanyl maintenance, fentanyl induction followed by remifentanil maintenance, and remifentanil induction followed by remifentanil maintenance (P = 0.512), but an interaction between time course and anesthesia method was observed (P = 0.004). A significant difference in the time course of fentanyl administration was found between surgical methods, such as bilateral mandibular sagittal split ramus osteotomy (BSSRO) and BSSRO combined with Le Fort I osteotomy (bimaxillary; P = 0.008), with no interaction between time course and surgical method (P = 0.535). Total postoperative 24 h consumption associated with the bimaxillary procedure was significantly higher than with BSSRO (P = 0.008). The present results indicate that administration patterns and total 24 h consumption were different among the three groups of anesthesia methods and between the two groups of surgical methods, respectively. Although more research on patient-controlled analgesia patterns and consumption is necessary, the present study will contribute to adequately relieving individual patients from postoperative pain.

Intraoperative use of remifentanil and opioid induced hyperalgesia/acute opioid tolerance: systematic review

INTRODUCTION

The use of opioids has been increasing in operating room and intensive care unit to provide perioperative analgesia as well as stable hemodynamics. However, many authors have suggested that the use of opioids is associated with the expression of acute opioid tolerance (AOT) and opioid-induced hyperalgesia (OIH) in experimental studies and clinical observations in dose and/or time dependent exposure even when used within the clinically accepted doses. Recently, remifentanil has been used for pain management during anesthesia as well as in the intensive care units because of its rapid onset and offset.

OBJECTIVES

Search of the available literature to assess remifentanil AOT and OIH based on available published data.

METHODS

We reviewed articles analyzing remifentanil AOT and OIH, and focused our literature search on evidence based information. Experimental and clinical studies were identified using electronic searches of Medline (PubMed, Ovid, Springer, and Elsevier, ClinicalKey).

RESULTS

Our results showed that the development of remifentanil AOT and OIH is a clinically significant phenomenon requiring further research.

DISCUSSIONS AND CONCLUSIONS

AOT - defined as an increase in the required opioid dose to maintain adequate analgesia, and OIH - defined as decreased pain threshold after chronic opioid treatment, should be suspected with any unexplained pain report unassociated with the disease progression. The clinical significance of these findings was evaluated taking into account multiple methodological issues including the dose and duration of opioids administration, the different infusion mode, the co-administrated anesthetic drug's effect, method assessing pain sensitivity, and the repetitive and potentially tissue damaging nature of the stimuli used to determine the threshold during opioid infusion. Future studies need to investigate the contribution of remifentanil induced hyperalgesia to chronic pain and the role of pharmacological modulation to reverse this process.

Effect of intraoperative high-dose remifentanil on postoperative pain: a prospective, double blind, randomized clinical trial

BACKGROUND

Remifentanil, an ultra-short-acting opioid, is widely used for pain control during surgery. However, regular dose (RD) remifentanil exacerbates postoperative pain in a dose-dependent manner. Recent studies suggest that high-dose (HD) remifentanil offers sustained analgesia in experimental studies. We thus hypothesized that intraoperative administration of high-dose remifentanil may attenuate postoperative pain.

METHODS

In this prospective, randomized, double blind, controlled clinical study, sixty patients undergoing thyroidectomy (18-60 years-of-age) received an intraoperative infusion of 0.2 (RD group) or 1.2 μg kg(-1) min(-1) (HD group) remifentanil during thyroidectomy. A visual analogue scale (VAS) was used to measure pain intensity. Mechanical pain threshold on the forearm was assessed using von Frey filaments before surgery (baseline), 2 h postoperatively and 18-24 h postoperatively. The primary outcome was to compare the difference of VAS score at different time points after operation and morphine consumption 24 h postoperatively between RD and HD groups. The second outcome was to compare the difference of mechanical pain thresholds in the forearm postoperatively between RD and the HD groups.

RESULTS

VAS scores were lower 30 min postoperatively in the HD group (1.29 ± 1.67, 95% CI 0.64-1.94) compared with the RD group (2.21 ± 1.67, 95% CI 1.57-2.84) (t = 3.427, p = 0.0043, RD group vs. HD group). Postoperative morphine consumption was much lower in the HD group compared with the RD group (1.27 ± 1.88 mg vs. 0.35 ± 1.25 mg, p = 0.033). In both groups, mechanical pain threshold was decreased 18-24 h postoperatively (2.93 ± 0.209 Ln(g) vs. 3.454 ± 2.072 Ln(g), p = 0.032 in RD group; 2.910 ± 0.196 Ln(g) vs. 3.621 ± 0.198 Ln(g), p = 0.006 in HD group, 18-24 h postoperatively vs baseline).

CONCLUSIONS

Intraoperative administration of high-dose remifentanil decreased VAS scores and morphine consumption postoperatively. Thus, modulation of intraoperative opiates may be a simple and effective method of postoperative pain management.

TRIAL REGISTRATION

This trial is registered in ClinicalTrials.gov, with the Name: Effect of Higher Doses of Remifentanil on Postoperative Pain in Patients Undergoing Thyroidectomy, and ID number: NCT01761149.

Fentanyl-related compounds and derivatives: current status and future prospects for pharmaceutical applications

Fentanyl and its analogs have been mainstays for the treatment of severe to moderate pain for many years. In this review, we outline the structural and corresponding synthetic strategies that have been used to understand the structure-biological activity relationship in fentanyl-related compounds and derivatives and their biological activity profiles. We discuss how changes in the scaffold structure can change biological and pharmacological activities. Finally, recent efforts to design and synthesize novel multivalent ligands that act as mu and delta opioid receptors and NK-1 receptors are discussed.

Interaction between postoperative shivering and hyperalgesia caused by high-dose remifentanil

BACKGROUND

High-dose remifentanil-based anesthesia is associated with opioid-induced hyperalgesia (OIH) and postanesthetic shivering (PAS). These effects can be prevented by N-methyl-d-aspartate (NMDA) receptor antagonists. This study aimed to investigate correlations between OIH and PAS caused by high-dose remifentanil and the effects of low-dose ketamine on OIH and PAS.

METHODS

Seventy-five patients scheduled for single-port laparoscopic gynecologic surgery were randomly allocated into three groups, each of which received intraoperative remifentanil: group L at 0.1 µg/kg/min; group H at 0.3 µg/kg/min; and group HK at 0.3 µg/kg/min plus 0.25 mg/kg ketamine just before incision, followed by a continuous infusion of 5 µg/kg/min ketamine until skin closure.

RESULTS

PAS, postoperative tactile pain threshold, and the extent of hyperalgesia in group H were significantly different (P < 0.05) than in the other two groups. PAS was significantly correlated with OIH, including mechanically evoked pain such as postoperative tactile pain threshold (r = -0.529, P = 0.01) (r = -0.458, P = 0.021) and the extent of hyperalgesia (r = 0.537, P = 0.002) (r = 0.384, P = 0.031), respectively, in group H and group HK. Notably, both groups were treated with high-dose remifentanil. Tympanic membrane temperature, time to first postoperative analgesic requirement, postoperative pain scores, analgesic consumption, and cumulative patient-controlled analgesia volume containing morphine were comparable in all three groups.

CONCLUSIONS

OIH, including the enhanced perception of pain, and PAS were both associated with high-dose remifentanil, were significantly correlated and were attenuated by a low dose of ketamine. This suggests that a common mechanism in part mediated through activation of the central glutamatergic system (e.g., NMDA receptors), underlies the two effects caused by high doses of remifentanil.

Comparison of the effects of remifentanil and alfentanil on intraocular pressure in cataract surgery

Background:

Anesthesia for ophthalmic surgery requires management of intraocular pressure (IOP) during perioperative period. In an open eye, in conditions such as after traumatic injury or during cataract surgery, IOP increase can lead to permanent vision loss. Administration of narcotics concomitant with anesthetics has the ability to reduce this increase of IOP. This clinical trial aims to compare the efficacy of remifentanil and alfentanil in preventing an increase in IOP after administration of succinylcholine, intubation and during anesthesia.

Methods:

This double-blind clinical trial was conducted on 50 patients undergoing elective general surgery for cataracts. Patients were randomly divided into two groups. Alfentanil (20 μg/kg in 30 s) for group 1 and remifentanil (1 μg/kg in 30 s) for group 2 were injected before induction of anesthesia, and 0.5 μg/kg/min alfentanil for group 1 and 0.1 μg/kg/min remifentanil for group 2 were infused during the anesthesia. Systolic and diastolic blood pressure, heart rate, and IOP from normal eye were measured before the induction, after administration of thiopental and succinylcholine, after tracheal intubation, and 2 min later, and were repeated in 2-min intervals until the end of operation.

Results:

IOP decreased after injection of anesthetics and remained lower all through the operation in both groups, but IOP decreased after injection of succinylcholine in remifentanil group while it increased in alfentanil group (P<0.05).

Conclusions:

Results of this study indicate benefits of both remifentanil and alfentanil in managing IOP after induction and during anesthesia. It seems that remifentanil is better than alfentanil in controlling the IOP after injection of succinylcholine.

Antihyperalgesic effects of dexmedetomidine on high-dose remifentanil-induced hyperalgesia

Background

Dexmedetomidine is a highly selective α2 adrenergic agonist that has been shown to decrease the intensity of opioid-induced hyperalgesia (OIH). We aimed to investigate the antihyperalgesic effects of dexmedetomidine on high-dose remifentanil-induced hyperalgesia.

Methods

Ninety American Society of Anesthesiologists physical status I-II patients undergoing laparoscopically assisted vaginal hysterectomy (LAVH) were randomly assigned to one of the following three groups, each of which received either dexmedetomidine (an initial dose of 1.0 µg/kg for 10 min, followed by a continuous infusion of 0.7 µg/kg/hr) or placebo saline 15 min before the induction of anesthesia and intraoperative remifentanil infusion: group C received a placebo and 0.05 µg/kg/min remifentanil; group RH received a placebo and 0.3 µg/kg/min remifentanil; and group DRH received dexmedetomidine and 0.3 µg/kg/min remifentanil.

Results

The mechanical hyperalgesia threshold 24 hr after surgery was significantly lower in group RH than in the other two groups. Postoperative pain intensity using visual analog scale (VAS) and cumulative volume of a patient-controlled analgesia (PCA) containing morphine over 24 hr were significantly greater in group RH than in group DRH. The time to the first postoperative analgesic requirement was significantly shorter in group RH than in the other two groups. The desflurane requirement was significantly greater in group C than in the other groups. The frequency of hypotension and bradycardia was significantly higher, but shivering and postoperative nausea and vomiting were significantly lower in group DRH than in the other two groups.

Conclusions

High-doses of remifentanil induced hyperalgesia, which presented a decreased mechanical hyperalgesia threshold, enhanced pain intensity, a shorter time to first postoperative analgesic requirement, and greater morphine consumption, but dexmedetomidine efficiently alleviated those symptoms. Dexmedetomidine may be a novel and effective treatment option for preventing or attenuating OIH.

Effect of oral pregabalin on opioid-induced hyperalgesia in patients undergoing laparo-endoscopic single-site urologic surgery

Background

Pregabalin is an antiepileptic drug that is effective for treating postoperative pain, neuropathic pain, anxiety, and hemodynamic instability. The aim of this study was to investigate the effect of a single preoperative dose of pregabalin in patients with opioid-induced hyperalgesia (OIH).

Methods

Ninety ASA I-II patients undergoing laparoendoscopic single-site urologic surgery were randomly assigned to one of the following three groups that received either pregabalin or placebo 1 h before anesthesia and an intraoperative remifentanil infusion. Group plL received placebo and 0.05 µg/kg/min remifentanil, group plH received placebo and 0.3 µg/kg/min remifentanil, and group prH received 300 mg pregabalin plus 0.3 µg/kg/min remifentanil. The primary endpoint was pain intensity upon movement 1, 6, 12, and 24 h after surgery. Secondary endpoints were the area of hyperalgesia and mechanical hyperalgesia threshold 24 h after surgery, time to first postoperative analgesic requirement, and cumulative postoperative volume of morphine administered via a patient-controlled analgesia (PCA) pump over 24 h.

Results

The time to first postoperative analgesic requirement in group plH was significantly shorter than that in group plL. The injected PCA volume was significantly greater in group plH than that in the other two groups. Postoperative pain intensity in group plH was significantly greater than that in the other two groups at 6, 12, and 24 h after surgery. The mechanical hyperalgesia threshold and the area of hyperalgesia around the surgical incision 24 h after surgery in group plH differed significantly from those in the other two groups, which were not significantly different. Adverse effects were comparable among groups.

Conclusions

High-dose remifentanil induced hyperalgesia, including increased pain intensity, increased area of hyperalgesia, and decreased mechanical hyperalgesia threshold. These effects were attenuated by oral administration of a single preoperative dose of pregabalin (300 mg) in patients undergoing laparo-endoscopic single-site urologic surgery.

Usefulness of Intravenous Anesthesia Using a Target-controlled Infusion System with Local Anesthesia in Submuscular Breast Augmentation Surgery

Background

Patients have anxiety and fear of complications due to general anesthesia. Through new instruments and local anesthetic drugs, a variety of anesthetic methods have been introduced. These methods keep hospital costs down and save time for patients. In particular, the target-controlled infusion (TCI) system maintains a relatively accurate level of plasma concentration, so the depth of anesthesia can be adjusted more easily. We conducted this study to examine whether intravenous anesthesia using the TCI system with propofol and remifentanil would be an effective method of anesthesia in breast augmentation.

Methods

This study recruited 100 patients who underwent breast augmentation surgery from February to August 2011. Intravenous anesthesia was performed with 10 mg/mL propofol and 50 µg/mL remifentanil simultaneously administered using two separate modules of a continuous computer-assisted TCI system. The average target concentration was set at 2 µg/mL and 2 ng/mL for propofol and remifentanil, respectively, and titrated against clinical effect and vital signs. Oxygen saturation, electrocardiography, and respiratory status were continuously measured during surgery. Blood pressure was measured at 5-minute intervals. Information collected includes total duration of surgery, dose of drugs administered during surgery, memory about surgery, and side effects.

Results

Intraoperatively, there was transient hypotension in two cases and hypoxia in three cases. However, there were no serious complications due to anesthesia such as respiratory difficulty, deep vein thrombosis, or malignant hypertension, for which an endotracheal intubation or reversal agent would have been needed. All the patients were discharged on the day of surgery and able to ambulate normally.

Conclusions

Our results indicate that anesthetic methods, where the TCI of propofol and remifentanil is used, might replace general anesthesia with endotracheal intubation in breast augmentation surgery.

Dexmedetomidine versus remifentanil sedation during awake fiberoptic nasotracheal intubation: a double-blinded randomized controlled trial

BACKGROUND

Awake fiberoptic nasotracheal intubation is usually performed in patients with an anticipated difficult airway. This study compares dexmedetomidine and remifentanil for conscious sedation during fiberoptic intubation.

METHODS

Forty patients undergoing elective awake fiberoptic nasotracheal intubation were allocated randomly to receive either dexmedetomidine (n = 20) or remifentanil (n = 20). Primary outcome measures were endoscopy, intubation, and post-intubation conditions as scored by the attending anesthesiologist. Other parameters included the time taken to achieve the desired level of sedation, endoscopy time, intubation time, and hemodynamic changes during the procedure. An interview was conducted 24 h after surgery to evaluate patients' recall of and satisfaction with the procedure.

RESULTS

The median [interquartile range] endoscopy score (graded 0-5) in the dexmedetomidine group (2 [1-2]) was significantly better than in patients who received remifentanil (3 [2-3]; p < 0.01). Recall of intubation was significantly lower in the dexmedetomidine group (p = 0.027). Dexmedetomidine provided better patient satisfaction than remifentanil (2 [1-2] and 2 [2-3], respectively; p = 0.022). Patients in the dexmedetomidine group had fewer heart rate responses during endoscopy and intubation as compared to the remifentanil group (p < 0.001 and p = 0.004, respectively). Peripheral oxygen saturation was less in the remifentanil group during endoscopy (p = 0.003). There were no significant differences in intubation and post-intubation conditions.

CONCLUSIONS

Both dexmedetomidine and remifentanil were effective as sedatives in patients undergoing awake fiberoptic nasotracheal intubation. Compared with remifentanil, dexmedetomidine offered better endoscopy scores, lower recall of intubation, and greater patient satisfaction, with minor hemodynamic side effects.

Remifentanil used as adjuvant in general anesthesia for spinal fusion does not exhibit acute opioid tolerance

Background

Although acute tolerance to opioids, especially to remifentanil, has been demonstrated consistently in animal studies, the results of clinical trials in humans are controversial. The aim of this study was to determine whether intraoperative infusions of remifentanil used as an adjuvant in general anesthesia result in acute tolerance, an event manifested by increased postoperative pain and a higher opioid requirement than usual.

Methods

Sixty patients who underwent surgery under general anesthesia for spinal fusion were randomly assigned to receive sevoflurane-nitrous oxide-oxygen (group SO, n = 20), sevoflurane-remifentanil-nitrous oxide-oxygen (group SR, n = 20), or propofol-remifentanil-oxygen (group PR, n = 20) in a double-blinded manner. All patients within 1 hour after induction received PCA (fentanyl 0.4 µg/kg/ml and ondansetron 16 mg) administered intravenously at a basal infusion rate of 1 ml/h, after being intravenously injected with a loading dose of fentanyl (1 µg/kg). Data for fentanyl requirement, verbal Numerical Rating Scale (NRS) pain score at rest, and presence of nausea or vomiting were collected at 1, 24, and 48 hours after surgery.

Results

We did not find any significant difference in postoperative PCA fentanyl requirements, NRS or side effects among the groups.

Conclusions

Remifentanil as an adjuvant to sevoflurane or propofol in general anesthesia for adults having surgery for spinal fusion does not appear to cause acute opioid tolerance or hyperalgesia in patients. However, further studies are needed to elucidate whether sevoflurane and propofol exert a clinically significant effect on opioid-induced tolerance or hyperalgesia and whether this effect is related to the age of the patient, the dose and duration of remifentanil given and the intensity of pain experienced postoperatively.

Pontine μ-opioid receptors mediate bradypnea caused by intravenous remifentanil infusions at clinically relevant concentrations in dogs

Life-threatening side effects such as profound bradypnea or apnea and variable upper airway obstruction limit the use of opioids for analgesia. It is yet unclear which sites containing μ-opioid receptors (μORs) within the intact in vivo mammalian respiratory control network are responsible. The purpose of this study was 1) to define the pontine region in which μOR agonists produce bradypnea and 2) to determine whether antagonism of those μORs reverses bradypnea produced by intravenous remifentanil (remi; 0.1-1.0 μg·kg(-1)·min(-1)). The effects of microinjections of agonist [D-Ala(2),N-Me-Phe(4),Gly-ol(5)]-enkephalin (DAMGO; 100 μM) and antagonist naloxone (NAL; 100 μM) into the dorsal rostral pons on the phrenic neurogram were studied in a decerebrate, vagotomized, ventilated, paralyzed canine preparation during hyperoxia. A 1-mm grid pattern of microinjections was used. The DAMGO-sensitive region extended from 5 to 7 mm lateral of midline and from 0 to 2 mm caudal of the inferior colliculus at a depth of 3-4 mm. During remi-induced bradypnea (~72% reduction in fictive breathing rate) NAL microinjections (~500 nl each) within the region defined by the DAMGO protocol were able to reverse bradypnea by 47% (SD 48.0%) per microinjection, with 13 of 84 microinjections producing complete reversal. Histological examination of fluorescent microsphere injections shows that the sensitive region corresponds to the parabrachial/Kölliker-Fuse complex.

The proper effect site concentration of remifentanil for prevention of myoclonus after etomidate injection

BACKGROUND

Etomidate frequently induces myoclonus when administered intravenously with bolus injection during anesthetic induction. This can be bothersome for the anesthesiologist. The dose of remifentanil appropriate for preventing myoclonus without side effects was investigated.

METHODS

All patients with American Society of Anesthesiologists (ASA) physical status I-III were divided into three groups (n = 33 per group) according to the pretreatment effect site concentration of remifentanil (Ultiva, Glaxo-Wellcome, München, Germany) of 0, 2 or 4 ng/ml (Group N: 0 ng/ml, Group R: 2 ng/ml, Group Q: 4 ng/ml) by a target controlled infusion (TCI) system. After a 0.3 mg/kg dose of etomidate was injected intravenously for over 1 minute for anesthetic induction, myoclonus was observed. Before the etomidate injection, the patients were pretreated with remifentanil and their side effects were monitored.

RESULTS

The number of patients showing myoclonus was significantly different among the groups. The incidence of myoclonus was 81%, 12% and 0% (groups N, R, and Q, respectively, P < 0.01). Side effects including bradycardia and hypotension did not occur in either Group R or Q. Chest wall rigidity occured in 45% of patients in Group Q.

CONCLUSIONS

Administration with a 2 ng/ml effect site concentration of remifentanil could reduce the incidence of myoclonus caused by etomidate bolus injection without chest wall rigidity.

Perioperative care of a child with non-ketotic hyperglycinemia

Non-ketotic hyperglycinemia (NKGH) is an autosomal recessive disorder of glycine metabolism. Defective glycine cleavage results in elevated concentrations of glycine in plasma, urine and cerebrospinal fluid. The accumulation of glycine, an inhibitory neurotransmitter, leads to a clinical presentation of apnea, lethargy, hypotonia, seizures, and severe psychomotor retardation. There are four clinical variants of NKHG, which have been described in the medical literature. Neonatal NKHG is the most common as well as the most devastating and lethal form of the disorder. Given the multi-system involvement of the disorder, there are several perioperative concerns of such patients with delayed emergence requiring supported ventilation being a common postoperative outcome for NKHG patients. We report the perioperative management of a 4-year-old boy with NKGH who required anesthetic care during an adenoidectomy and tonsillectomy for obstructive sleep apnea.

Sedation and analgesia in gastrointestinal endoscopy: What’s new?

Various types of sedation and analgesia technique have been used during gastrointestinal endoscopy procedures. The best methods for analgesia and sedation during gastrointestinal endoscopy are still debated. Providing an adequate regimen of sedation/analgesia might be considered an art, influencing several aspects of endoscopic procedures: the quality of the examination, the patient’s cooperation and the patient’s and physician’s satisfaction with the sedation. The properties of a model sedative agent for endoscopy would include rapid onset and offset of action, analgesic and anxiolytic effects, ease of titration to desired level of sedation, rapid recovery and an excellent safety profile. Therefore there is an impulse for development of new approaches to endoscopic sedation. This article provides an update on the methods of sedation today available and future directions in endoscopic sedation.

Clinically relevant infusion rates of mu-opioid agonist remifentanil cause bradypnea in decerebrate dogs but not via direct effects in the pre-Bötzinger complex region

Systemic administration of mu-opioids at clinical doses for analgesia typically slows respiratory rate. Mu-opioid receptors (MORs) on pre-Bötzinger Complex (pre-BötC) respiratory neurons, the putative kernel of respiratory rhythmogenesis, are potential targets. The purpose of this study was to determine the contribution of pre-BötC MORs to the bradypnea produced in vivo by intravenous administration of clinically relevant infusion rates of remifentanil (remi), a short-acting, potent mu-opioid analgesic. In decerebrate dogs, multibarrel micropipettes were used to record pre-BötC neuronal activity and to eject the opioid antagonist naloxone (NAL, 0.5 mM), the glutamate agonist D-homocysteic acid (DLH, 20 mM), or the MOR agonist [D-Ala(2), N-Me-Phe(4), gly-ol(5)]-enkephalin (DAMGO, 100 microM). Inspiratory and expiratory durations (T(I) and T(E)) and peak phrenic nerve activity (PPA) were measured from the phrenic neurogram. The pre-BötC was functionally identified by its rate altering response (typically tachypnea) to DLH microinjection. During intravenous remi-induced bradypnea (approximately 60% decrease in central breathing frequency, f(B)), bilateral injections of NAL in the pre-BötC did not change T(I), T(E), f(B), and PPA. Also, NAL picoejected onto single pre-BötC neurons depressed by intravenous remi had no effect on their discharge. In contrast, approximately 60 microg/kg of intravenous NAL rapidly reversed all remi-induced effects. In a separate group of dogs, microinjections of DAMGO in the pre-BötC increased f(B) by 44%, while subsequent intravenous remi infusion more than offset this DAMGO induced tachypnea. These results indicate that mu-opioids at plasma concentrations that cause profound analgesia produce their bradypneic effect via MORs located outside the pre-BötC region.