Psychomotor recovery after three methods of sedation during spinal anaesthesia

The Role of GABA Receptors in Anesthesia and Sedation: An Updated Review

GABA (γ-aminobutyric acid) receptors are constituents of many inhibitory synapses within the central nervous system. They are formed by 5 subunits out of 19 various subunits: α1-6, β1-3, γ1-3, δ, ε, θ, π, and ρ1-3. Two main subtypes of GABA receptors have been identified, namely GABAA and GABAB. The GABAA receptor (GABAAR) is formed by a variety of combinations of five subunits, although both α and β subunits must be included to produce a GABA-gated ion channel. Other subunits are γ, δ, ε, π, and ϴ. GABAAR has many isoforms, that dictate, among other properties, their differing affinities and conductance. Drugs acting on GABAAR form the cornerstone of anesthesia and sedation practice. Some such GABAAR agonists used in anesthesia practice are propofol, etomidate, methohexital, thiopental, isoflurane, sevoflurane, and desflurane. Ketamine, nitrous oxide, and xenon are not GABAR agonists and instead inhibit glutamate receptors-mainly NMDA receptors. Inspite of its many drawbacks such as pain in injection, quick and uncontrolled conversion from sedation to general anesthesia and dose-related cardiovascular depression, propofol remains the most popular GABAR agonist employed by anesthesia providers. In addition, being formulated in a lipid emulsion, contamination and bacterial growth is possible. Literature is rife with newer propofol formulations, aiming to address many of these drawbacks, and with some degree of success. A nonemulsion propofol formulation has been developed with cyclodextrins, which form inclusion complexes with drugs having lipophilic properties while maintaining aqueous solubility. Inhalational anesthetics are also GABA agonists. The binding sites are primarily located within α+/β- and β+/α- subunit interfaces, with residues in the α+/γ- interface. Isoflurane and sevoflurane might have slightly different binding sites providing unexpected degree of selectivity. Methoxyflurane has made a comeback in Europe for rapid provision of analgesia in the emergency departments. Penthrox (Galen, UK) is the special device designed for its administration. With better understanding of pharmacology of GABAAR agonists, newer sedative agents have been developed, which utilize "soft pharmacology," a term pertaining to agents that are rapidly metabolized into inactive metabolites after producing desired therapeutic effect(s). These newer "soft" GABAAR agonists have many properties of ideal sedative agents, as they can offer well-controlled, titratable activity and ultrashort action. Remimazolam, a modified midazolam and methoxycarbonyl-etomidate (MOC-etomidate), an ultrashort-acting etomidate analog are two such examples. Cyclopropyl methoxycarbonyl metomidate is another second-generation soft etomidate analog that has a greater potency and longer half-life than MOC-etomidate. Additionally, it might not cause adrenal axis suppression. Carboetomidate is another soft analog of etomidate with low affinity for 11β-hydroxylase and is, therefore, unlikely to have clinically significant adrenocortical suppressant effects. Alphaxalone, a GABAAR agonist, is recently formulated in combination with 7-sulfobutylether-β-cyclodextrin (SBECD), which has a low hypersensitivity profile.

The Role of GABA Receptor Agonists in Anesthesia and Sedation

GABA (γ-aminobutyric acid) receptors, of which there are two types, are involved in inhibitory synapses within the central nervous system. The GABA_A receptor (GABAAR) has a central role in modern anesthesia and sedation practice, which is evident from the high proportion of agents that target the GABAAR. Many GABAAR agonists are used in anesthesia practice and sedation, including propofol, etomidate, methohexital, thiopental, isoflurane, sevoflurane, and desflurane. There are advantages and disadvantages to each GABAAR agonist currently in clinical use. With increasing knowledge regarding the pharmacology of GABAAR agonists, however, newer sedative agents have been developed which employ 'soft pharmacology', a term used to describe the pharmacology of agents whereby their chemical configuration allows rapid metabolism into inactive metabolites after the desired therapeutic effect(s) has occurred. These newer 'soft' GABAAR agonists may well approach ideal sedative agents, as they can offer well-controlled, titratable activity and ultrashort action. This review provides an overview of the role that GABAAR agonists currently play in sedation and anesthesia, in addition to discussing the future role of novel GABAAR agonists in anesthesia and sedation.

Psychomotor and cognitive effects of 15-minute inhalation of methoxyflurane in healthy volunteers: implication for post-colonoscopy care

Background and study aims: Colonoscopy with portal inhaled methoxyflurane (Penthrox) is highly feasible with low sedation risk and allows earlier discharge. It is unclear if subjects can return to highly skilled psychomotor skill task shortly after Penthrox assisted colonoscopy. We evaluated the psychomotor and cognitive effects of 15-minute inhalation of Penthrox in adults. Patients and methods: Sixty healthy volunteers (18 to 80 years) were studied on 2 occasions with either Penthrox or placebo in a randomized, double-blind fashion. On each occasion, the subject's psychomotor function was examined before, immediately, 30, 60, 120, 180 and 240 min after a 15-minute inhalation of studied drug, using validated psychomotor tests (Digit Symbol Substitution Test (DSST), auditory reaction time (ART), eye-hand coordination (EHC) test, trail making test (TMT) and logical reasoning test (LRT). Results: Compared to placebo, a 15-minute Penthrox inhalation led to an immediate but small impairment of DSST (P < 0.001), ART (P < 0.001), EHC (P < 0.01), TMT (P = 0.02) and LRT (P = 0.04). In all subjects, the performance of all 5 tests normalized by 30 minutes after inhalation, and was comparable to that with placebo. Although increasing age was associated with a small deterioration in psychomotor testing performance, the magnitude of Penthrox effects remained comparable among all age groups. Conclusions: In all age groups, a 15-minute Penthrox inhalation induces acute but short-lasting impairment of psychomotor and cognitive performance, which returns to normal within 30 minutes , indicating that subjects who have colonoscopy with Penthrox can return to highly skilled psychomotor skills tasks such as driving and daily work the same day.

Anaesthetic interventions for prevention of awareness during surgery

BACKGROUND

General anaesthesia is usually associated with unconsciousness. 'Awareness' is when patients have postoperative recall of events or experiences during surgery. 'Wakefulness' is when patients become conscious during surgery, but have no postoperative recollection of the period of consciousness.

OBJECTIVES

To evaluate the efficacy of two types of anaesthetic interventions in reducing clinically significant awareness:- anaesthetic drug regimens; and- intraoperative anaesthetic depth monitors.

SEARCH METHODS

We searched the Cochrane Central Register of Controlled Trials (CENTRAL, ISSUE 4 2016); PubMed from 1950 to April 2016; MEDLINE from 1950 to April 2016; and Embase from 1980 to April 2016. We contacted experts to identify additional studies. We performed a handsearch of the citations in the review. We did not search trial registries.

SELECTION CRITERIA

We included randomized controlled trials (RCTs) of either anaesthetic regimens or anaesthetic depth monitors. We excluded volunteer studies, studies of patients prior to skin incision, intensive care unit studies, and studies that only randomized different word presentations for memory tests (not anaesthetic interventions).Anaesthetic drug regimens included studies of induction or maintenance, or both. Anaesthetic depth monitors included the Bispectral Index monitor, M-Entropy, Narcotrend monitor, cerebral function monitor, cerebral state monitor, patient state index, and lower oesophageal contractility monitor. The use of anaesthetic depth monitors allows the titration of anaesthetic drugs to maintain unconsciousness.

DATA COLLECTION AND ANALYSIS

At least two authors independently scanned abstracts, extracted data from the studies, and evaluated studies for risk of bias. We made attempts to contact all authors for additional clarification. We performed meta-analysis statistics in packages of the R language.

MAIN RESULTS

We included 160 studies with 54,109 enrolled participants; 53,713 participants started the studies and 50,034 completed the studies or data analysis (or both). We could not use 115 RCTs in meta-analytic comparisons because they had zero awareness events. We did not merge 27 of the remaining 45 studies because they had excessive clinical and methodological heterogeneity. We pooled the remaining 18 eligible RCTs in meta-analysis. There are 10 studies awaiting classification which we will process when we update the review.The meta-analyses included 18 trials with 36,034 participants. In the analysis of anaesthetic depth monitoring (either Bispectral Index or M-entropy) versus standard clinical and electronic monitoring, there were nine trials with 34,744 participants. The overall event rate was 0.5%. The effect favoured neither anaesthetic depth monitoring nor standard clinical and electronic monitoring, with little precision in the odds ratio (OR) estimate (OR 0.98, 95% confidence interval (CI) 0.59 to 1.62).In a five-study subset of Bispectral Index monitoring versus standard clinical and electronic monitoring, with 34,181 participants, 503 participants gave awareness reports to a blinded, expert panel who adjudicated or judged the outcome for each patient after reviewing the questionnaires: no awareness, possible awareness, or definite awareness. Experts judged 351 patient awareness reports to have no awareness, 87 to have possible awareness, and 65 to have definite awareness. The effect size favoured neither Bispectral Index monitoring nor standard clinical and electronic monitoring, with little precision in the OR estimate for the combination of definite and possible awareness (OR 0.96, 95% CI 0.35 to 2.65). The effect size favoured Bispectral Index monitoring for definite awareness, but with little precision in the OR estimate (OR 0.60, 95% CI 0.13 to 2.75).We performed three smaller meta-analyses of anaesthetic drugs. There were nine studies with 1290 participants. Wakefulness was reduced by ketamine and etomidate compared to thiopental. Wakefulness was more frequent than awareness. Benzodiazepines reduces awareness compared to thiopental, ketamine, and placebo., Also, higher doses of inhaled anaesthetics versus lower doses reduced the risk of awareness.We graded the quality of the evidence as low or very low in the 'Summary of findings' tables for the five comparisons.Most of the secondary outcomes in this review were not reported in the included RCTs.

AUTHORS' CONCLUSIONS

Anaesthetic depth monitors may have similar effects to standard clinical and electrical monitoring on the risk of awareness during surgery. In older studies comparing anaesthetics in a smaller portion of the patient sample, wakefulness occurred more frequently than awareness. Use of etomidate and ketamine lowered the risk of wakefulness compared to thiopental. Benzodiazepines compared to thiopental and ketamine, or higher doses of inhaled anaesthetics versus lower doses, reduced the risk of awareness.

Antagonistic effect of flumazenil after midazolam sedation on arterial-cardiac baroreflex

BACKGROUND

Flumazenil is generally administered to antagonise the sedative effect of midazolam. However, although flumazenil completely antagonises the sedative effect of midazolam, a few effects remain unantagonised. Hence, it is unclear whether flumazenil restores the attenuation of the arterial-cardiac baroreflex (i.e. arterial-heart rate reflex) induced by midazolam. We investigated the antagonistic effect of flumazenil administered after midazolam on cardiac baroreflex, to reveal whether complete recovery from midazolam-induced sedation by flumazenil administration is accompanied by restoration of midazolam's attenuating effects on the cardiac baroreflex.

METHOD

Twelve healthy male subjects received midazolam followed by flumazenil until complete recovery from midazolam sedation. Before and during midazolam sedation, and after flumazenil administration, cardiac baroreflex function was assessed by sequence analysis and transfer function analysis between spontaneous oscillations in systolic arterial pressure and R-R interval.

RESULTS

During midazolam sedation, defined by an Observer's Assessment of Alertness/Sedation scale score of 3, BIS value decreased significantly. Simultaneously, the baroreflex indices of the two analyses decreased significantly compared with baseline, suggesting attenuated cardiac baroreflex function. With complete recovery from midazolam sedation by flumazenil, indicated by an Observer's Assessment of Alertness/Sedation scale score of 5, BIS values returned to the baseline level. Simultaneously, cardiac baroreflex indices also returned to baseline levels.

CONCLUSION

The present results suggest that complete recovery from midazolam sedation by flumazenil is accompanied by restoration of the attenuated cardiac baroreflex function induced by midazolam.

[Sedation in surgical procedures using regional anesthesia in adult patients: results of a survey of Spanish anesthesiologists]

OBJECTIVE

To analyze the frequency and methods of sedation used in the context of regional anesthesia in adults by means of a national survey.

MATERIAL AND METHODS

We carried out a survey of participants at the courses of an anesthesiology training organization (Fundación Europea de Enseñanza en Anestesiología), held in Spain in 2006. The survey questionnaires asked about indications for sedation used during surgery under regional anesthesia as well as the form of administration, follow-up, and complications.

RESULTS

A total of 375 questionnaires were sent out and 185 responses were received (49.3%). Sedation is always used to accompany regional anesthesia by 69.2% of the respondents; 13.5% of them discuss the technique to be used with the patient and come to an agreement. The same type of sedation, regardless of the regional block performed, is used by 49.2% of respondents, and 64.3% use a scale to evaluate the level of sedation. The most favored sedation technique is continuous infusion, followed by target controlled infusion and boluses on demand. The most commonly used technique is sedation with bolus injections. Sixty percent use a single agent and 38.9% use combinations. The most commonly reported adverse effects are variability of patient response (53.5%) and respiratory complications (27%). In cases of ineffective regional blockade, 49.2% of those surveyed switch to general anesthesia.

CONCLUSIONS

Sedation is very often used to complement regional anesthesia in adult patients. Even though continuous infusion is considered to be the most appropriate form of administration, the most commonly used form is injection of boluses. Sedation with a single drug is used more frequently than drug combinations. Variability of individual response is the complication most commonly reported by the respondents.

Propofol infusion for sedation during spinal anesthesia

PURPOSE

The dose and time course of propofol infusion required to induce rapid sedation without oversedation during spinal anesthesia were investigated.

METHODS

Forty patients scheduled for spinal and epidural anesthesia were studied. After premedication with intramuscular midazolam 0.04 mg.kg(-1), an epidural catheter was inserted, followed by spinal anersthesia at L4-L5 with 0.5% hyperbaric tetracaine with epinephrine. The infusion of propofol was started with 10 mg.kg(-1).h(-1) and was decreased to 5 mg.kg(-1).h(-1) at spontaneous eye closure. According to the increase or decrease of the sedation level, the infusion does was decreased or increased to half or twice the initial dose, respectively, to keep the Observer's Assessment of Alertness Sedation (OAAS) score at 3 or 4.

RESULTS

Eye closure was observed at 1.0 +/- 0.4 min after the start of insusion. The maintenance insusion dose to keep the OAAS score at 3 or 4 was about 2.5 mg.kg(-1).h(-1).

CONCLUSION

Propofol infusion, starting with 10 mg.kg(-1).h(-1), decreasing to 5 mg.kg(-1).h(-1) after 1 minute, and then decreasing to 2.5 mg.kg(-1).h(-1) after another min induced rapid onset of sedation and kept the OAAS score at 3 or 4 during spinal anesthesia.

Remifentanilversus propofol for radio frequency treatment of atrial flutter

PURPOSE

Radio frequency treatment in cardiology generates short acute pain during the heating process. The present study evaluates two techniques used for sedation/analgesia for this procedure.

METHODS

Two groups of 20 patients each were studied prospectively. Patients were randomized to receive sedation for the procedure using either a patient-controlled analgesia device with remifentanil (Group R), or a target controlled infusion of propofol (Group P). Patients in Group R had a basal infusion of remifentanil 0.02-0.04 microg x kg(-1) x min(-1) with self administered bolus doses of 0.3 microg x kg(-1) i.v. every minute as required, with a delivery time greater than 30 sec. Patients in Group P had an initial plasma target concentration set at 3-4 microg x mL(-1).

RESULTS

Sedation scores were significantly higher in Group P, and two patients required supplementation with remifentanil and insertion of an laryngeal mask airway. Pain scores were higher in Group R, and two patients experienced muscular rigidity, one with transient apnea. Systolic blood pressure decreased significantly in Group P, and at the end of the procedure, PaCO(2) values were higher in that group (P < 0.01). Recovery time was significantly longer in Group P. Patient and physician satisfaction scores were similar in the two groups.

CONCLUSIONS

A basal infusion of remifentanil plus remifentanil patient controlled analgesia and target controlled infusion of propofol were adequate but not optimal techniques for sedation/analgesia for radio frequency treatment of atrial flutter.

Sedation with sufentanil and midazolam decreases pain in patients undergoing upper limb surgery under multiple nerve block

Multiple nerve blocks may be painful and a source of discomfort. We assessed the efficacy of sufentanil 5 microg combined with midazolam 1 mg in decreasing pain in outpatients after a midhumeral multiple nerve stimulation technique. Visual analog scores for pain were significantly lower in those patients who received sedation before the block, both at the time of block performance (14 +/- 1 vs 27 +/- 2 mm, P < 0.0001) and at discharge (11 +/- 1 vs 24 +/- 2 mm, P < 0. 0001). We conclude that the association of sufentanil and midazolam produced minimal sedation while significantly reducing pain experienced by patients undergoing multiple nerve stimulation.

Patient evaluation and comparison of the recovery profile between propofol and thiopentone as induction agents in day surgery

The patient's subjective perception of the quality of his/her recovery after day case anaesthesia with propofol or thiopentone as induction agents is still controversial. The authors investigated the perception and quality of awakening after anaesthesia during the recovery period and at 24 hours and 72 hours, in outpatients undergoing anaesthesia induced either with propofol or thiopentone and maintained with a volatile anaesthetic. In a double-blind study in adults undergoing knee arthroscopy in a day surgery unit, propofol and thiopentone were compared as induction agents in 60 randomized outpatients. A Critical Flicker Fusion Threshold test (CFFT), verbal test for anxiety, visual analog scale for anxiety and pain, and questionnaires were used to assess objectively and subjectively the quality of anaesthesia and awakening during the postoperative period. Demographic data and mean duration of anaesthesia were similar. In the propofol group, patients awoke more rapidly (9.2 +/- 5.8 vs 12.3 +/- 5.8 min) (P < 0.05); however, the CFFT measurements did not show any significant difference between the groups, except at time = 0 min, when 17 patients in the propofol group were able to perform the test versus only 10 patients in the thiopentone group (P < 0.05). At 4, 24, and 72 hours postoperatively, the authors were unable to detect any difference between the two groups. Except for early recovery, there were no differences between the intermediate and late recovery profiles, when propofol or thiopentone was used as the anaesthetic induction agent in day surgery.

Conscious sedation for interventional neuroradiology: a comparison of midazolam and propofol infusion

PURPOSE

The aim of this study was to compare two conscious sedation techniques, midazolam (M) and propofol (P), for interventional neuroradiology by assessment of the incidence of complications and satisfaction scores.

METHODS

Forty patients were randomized to receive 0.75 micrograms.kg-1 fentanyl and a M or P bolus followed by an infusion (M 15 micrograms.kg-1 + 0.5 micrograms.kg-1.min-1; P 0.5 mg.kg-1 + 25 micrograms.kg-1 min-1). The incidences of complications and untoward events requiring intervention were documented. These included respiratory depression, excessive pain, inappropriate movements and the inability to examine the patient. The satisfaction of the anaesthetic technique from the perspective of both the neuroradiologist and the patient was scored.

RESULTS

The incidence and types of complications were no different between the two groups. Pain occurred in 12 patients (6M, 6P), inappropriate movements in 17 (7M, 10P) and respiratory changes in 10 patients (2M, 8P).

CONCLUSIONS

Both techniques were satisfactory and the incidence of complications was similar for both groups.

Flumazenil and midazolam in anaesthesia

Flumazenil, the first benzodiazepine antagonist, is currently used widely as an emergency drug, and has also been utilized in planned procedures, to time arousal intra- or post-operatively. It is known that flumazenil, used at the end of a procedure, causes instant recovery by reversing the residual effects of, for example, midazolam. An agonist-antagonist concept, midazolam-flumazenil, where benzodiazepine sedation or anaesthesia is terminated at will, is, therefore, finding increasing application. In neuroanaesthesia, for example, it facilitates immediate recovery, cardiovascular stabilization and the use of midazolam as an alternative to thiopentone and inhalational agents, and in ear, nose and throat endoscopies, it permits more rapid turnover of patients and is a good choice for haemodynamic stability in patients with a high cardiovascular risk factor. There continues to be debate over the term used to describe the level of sedation remaining after the effects of the antagonist have worn off. 'Resedation' is often used incorrectly to describe what is in reality residual sedation. Given the correct use of midazolam or the exploitation of synergism using opioids, flumazenil will cause arousal, while maintaining the benefit of opioid analgesia. Such a technique may eliminate the need for formal recovery facilities in many ambulatory patients, thereby reducing dependence on trolleys, beds and nurses. This has major implications for health economics, particularly in relation to endoscopy clinics and when co-induction of anaesthesia is employed.

An assessment of resedation following flumazenil-induced antagonism of intravenous midazolam: comparison of psychomotor and amnesic recovery with a non-sedated reference group

The specific benzodiazepine antagonist flumazenil can enhance patient recovery following local anaesthetic day-case surgery performed under sedation. However, in view of its short elimination half-life, concerns have been expressed about the risk of resedation following its use. An open, randomised, parallel group study was designed to explore this question. Eighty-five patients were studied. Group A (n=43) patients underwent local anaesthetic cystoscopy with intravenous (i.v.) midazolam sedation. Following cystoscopy, and 30 min after the injection of midazolam, a bolus dose of flumazenil (0.5 mg i.v.) was given. Group B (n=42) patients underwent no operation and received no drugs but, in all other respects, were treated in an identical fashion to patients in group A. Tests of psychomotor function and memory were administered at baseline and again at 0.5, 1, 2, 3 and 4 h (or equivalent times for group B patients) following the injection of flumazenil. The test results showed no evidence of resedation, but there was evidence of incomplete reversal, as shown by significant differences in critical flicker fusion and delayed word recall at the 0.5-h test point. Group B patients showed no evidence of practice effects but did demonstrate an impairment in test performance possibly related to motivational factors. In conclusion, this study provides no evidence of resedation when using flumazenil to reverse the acute effects of midazolam. Incomplete reversal of amnesia need not delay patient discharge but has important implications with respect to the timing and nature of information imparted to patients prior to their release from hospital.

Sedation with midazolam during regional anaesthesia: is there a role for flumazenil?

The aim of this study was to reassess the efficacy of flumazenil for reversal of sedation with midazolam. Twenty-four ASA I or II patients undergoing elective surgery under epidural anaesthesia participated. Following epidural block, midazolam was administered to keep the patient sleepy but still responsive to verbal commands. At the end of surgery the patients were randomly allocated to receive, in a double-blind manner, either flumazenil (0.1 mg.ml-1) or placebo. The study drug (maximum dose: 10 ml) was titrated until the patient became fully awake. Sedation was assessed with the Modified Steward Coma Scale (MSCS), the Trieger test (TT) and Critical Flicker Frequency (CFF). The assessments were done before anaesthesia (baseline), at the end of surgery immediately before administration of study drug, and serially afterwards, at 10, 30, 60, 90, 120, 150 and 180 min. Analyses of variance for repeated measures and pooled t tests were used. The duration of surgery was (mean +/- SD) 0.72 +/- 0.25 hr in the flumazenil group and 0.74 +/- 0.28 hr in the placebo group. The total dose of midazolam was 7.2 +/- 2.2 mg for the flumazenil group and 8.9 +/- 2.7 mg for the placebo group. The volume of study drug administered was 5.5 ml +/- 1.9, equivalent to 0.55 mg, for the flumazenil group and 6.7 +/- 2.2 ml for the placebo group. Critical Flicker Frequency is the only measure which revealed a difference (P < 0.005) between the flumazenil and placebo groups and this occurred only at the ten-minute assessment.(ABSTRACT TRUNCATED AT 250 WORDS)

Propofol versus midazolam for monitored sedation: a comparison of intraoperative and recovery parameters

STUDY OBJECTIVE

To compare intraoperative and recovery parameters in patients who received either propofol infusion (PI), propofol bolus (PB), or midazolam bolus (MZ) for sedation.

DESIGN

Randomized clinical study.

SETTING

Medical/surgical patients in a specialized hospital.

PATIENTS

Ninety patients, aged 18 to 85 years, scheduled for central venous access for chemotherapy and/or total parenteral nutrition.

INTERVENTIONS

In 30 patients, sedation was induced with MZ 0.02 mg/kg intravenously (i.v.), repeated every 2 to 3 minutes to achieve a sedation level of 3 (eyes closed, responds to verbal stimulus) (SL3). Maintenance was with MZ 0.005 mg/kg i.v. repeated as necessary to maintain SL3. In both propofol groups (30 patients each), induction of sedation was with a bolus of propofol 0.75 to 1.0 mg/kg i.v. Maintenance in the PB group was with propofol 0.25 mg/kg IV, repeated as necessary to maintain SL3. Maintenance in the PI group was with propofol 2 to 4 mg/kg/hr or 33 to 66 micrograms/kg/min to maintain SL3.

MEASUREMENTS AND MAIN RESULTS

Blood pressure, heart rate, respiratory rate, oxygen saturation, and sedation level were monitored each minute for 5 minutes and then at 5-minute intervals during the procedure. A right atrial blood sample was taken for pH and partial pressure of carbon dioxide at maximum sedation. Adequate sedation was achieved in all three groups. The time to reach SL3 was significantly shorter in the PB group than in the PI and MZ groups (p < 0.05 and p < 0.01, respectively). Cardiovascular and respiratory parameters were remarkably stable. Immediate recovery, as judged by spontaneous eye opening, response to commands, and ability to state date of birth, was significantly shorter in both the PB and PI groups than in the MZ group (p < 0.0001). Intermediate recovery, as measured by sedation score at recovery entry, Aldrete score, and time to standing, was slower in the MZ group (p < 0.05 for the MZ group vs. the PB and PI groups for sedation score and Aldrete score; p < 0.05 for the MZ group vs. the PI group in time to standing). Psychomotor recovery, judged by digit symbol substitution tests, was significantly faster in the PB and PI groups (p < 0.05 vs. the MZ group). Amnesia, measured by picture recall, was significantly greater in the MZ group than in the PI and PB groups (p < 0.05). Mood changes were measured on a visual analog scale. All groups showed improvement. Nausea, headache, dizziness, blurred vision, appetite, tension, pain, depression, drowsiness, and ability to concentrate were evaluated in the preoperative and postoperative periods. The frequency did not differ significantly between groups due to confounding factors such as postoperative chemotherapy and premedicant drugs.

CONCLUSION

The PI, PB, and MZ groups all gave excellent sedation for patients undergoing surgical procedures with local anesthesia. Amnesia was greatest with midazolam, and recovery was more rapid with propofol.

Role of angiotensin II and AT1 receptors in hippocampal LTP

Results of a previous study showed that angiotensin II (AII) inhibited the induction of long-term potentiation (LTP) in hippocampal granule cells in response to dorsomedial perforant path stimulation in urethane-anesthetized rats. The results of present experiments demonstrate a dose-dependent inhibition of LTP induction under the same conditions due to ethanol (EtOH) administered by stomach tube and diazepam (DZ) injected IP. The inhibition of LTP induction by EtOH and DZ can be blocked by saralasin (SAR) applied directly to the dorsal hippocampus and by lorsartan (DuP 753) administered IP. Lorsartan or a metabolite crosses the blood-brain barrier because it also blocks the inhibition of LTP induction due to AII administration directly into the dorsal hippocampus. Lorsartan is a competitive antagonist of the AT1 subtype AII receptor. Therefore, the AII and the EtOH and DZ inhibition of LTP induction are mediated by the AII subtype receptor AT1. AIII and the AT2 antagonist PD123319 did not produce any significant effects. These in vivo effects can be reproduced in brain slices and therefore cannot be attributed to other factors, such as the urethane. In addition, electrical stimulation of the lateral hypothalamus (LH) inhibits LTP induction, and the inhibition can be blocked by SAR. These data on LH stimulation indicate that LH AII-containing neurons send axons into the hippocampus that inhibit the induction of LTP. These results not only provide new information on a neurotransmitter involved in the amnesic effects of benzodiazepines and ethanol-induced memory blackouts, but also testable hypotheses concerning recent observations that angiotensin converting enzyme (ACE) inhibitors elevate mood and improve certain cognitive processes in the elderly.

Ethanol and diazepam inhibition of hippocampal LTP is mediated by angiotensin II and AT1 receptors

Angiotensin II (AII) inhibits the induction of hippocampal long-term potentiation (LTP), a frequency-dependent model of learning and memory. These results demonstrate that the dose-dependent inhibition of LTP due to ethanol (EtOH) and diazepam (DZ) involves AII. Inhibition of LTP induction by AII, EtOH, and DZ can be blocked by AII receptor antagonists saralasin and lorsartan (DuP 753). Lorsartan is a competitive antagonist of the AT1 subtype AII receptor. Therefore, the EtOH and DZ inhibition of LTP induction is mediated by AT1 receptors. These results indicate a new role for AII in the brain in the possible mediation of memory deficits associated with alcohol and the benzodiazepines.

Assessing the behavioral effects and abuse potential of propofol bolus injections in healthy volunteers

Propofol is a recently introduced intravenous anesthetic agent, commonly administered to surgical patients because it induces anesthesia smoothly (i.e., provides loss of consciousness rapidly and usually with no complications) and is associated with rapid recovery. Propofol has psychoactive effects that could be construed as pleasant, although little abuse liability testing has been done on this agent in humans. Accordingly, we examined various effects of this agent at different subanesthetic doses (0.2-0.6 mg/kg) in order to characterize this drug's abuse potential (for recreational use or potential for diversion). Using a double-blind, randomized, crossover design, healthy normal volunteers (N = 10) were injected intravenously with the drug or with placebo. Before the injection and for up to 1 h afterwards, mood (including drug liking), memory and psychomotor performance were assessed. Propofol impaired memory and psychomotor performance and produced changes in 10 of 20 VAS mood ratings. Although there was variability in self-reported drug liking, some subjects clearly liked the effects of propofol, especially at the two higher doses. At the debriefing interview held after completion of the study, five subjects said if they had to participate in one more session in which they were given a choice between being injected with the highest dose (0.6 mg/kg) or a placebo, they would choose propofol. These preliminary results suggest that this agent may have some potential for abuse/diversion and perhaps stricter accountability procedures should be established for this drug in settings where general anesthesia or conscious sedation procedures are done.

Measuring recovery from general anaesthesia using critical flicker frequency: a comparison of two methods

Critical flicker frequency (CFF) is the frequency at which a flickering light appears steady. It is a sensitive measure for assessing recovery from anaesthesia. The CFF is almost always determined with the method of limits by which the flickering frequency is progressively decreased (or increased) until the patient reports a change from fusion to flicker (or flicker to fusion). This method has two disadvantages: it is influenced by the response bias (i.e., the subjective criterion used by the subject to decide that flicker is present or absent) and by the response delay (i.e., the interval between the perceptual change and the response). To avoid these problems, the method of forced choice is recommended. For each trial, the subject observes the light during two short successive periods. The light flickers during only one period, according to chance. The patient must indicate the period during which flickers occur. If uncertain, the patient has to make a guess. The aim of this study was to compare the two methods for assessing recovery from general anaesthesia. Two induction agents were used to obtain different recovery profiles. Twenty patients undergoing uncomplicated surgery lasting less than two hours were tested. They received either thiopentone or midazolam for induction, according to a randomized design. Vecuronium was used to facilitate tracheal intubation and anaesthesia was maintained with fentanyl, isoflurane and nitrous oxide. The CFF was measured before induction and at 60, 120 and 180 minutes after arrival in the recovery room. The person measuring CFF was unaware of the induction agent used.(ABSTRACT TRUNCATED AT 250 WORDS)

Flumazenil. A reappraisal of its pharmacological properties and therapeutic efficacy as a benzodiazepine antagonist

Flumazenil is a specific benzodiazepine antagonist which is indicated when the central effects of a benzodiazepine need to be attenuated or terminated. Following intravenous administration of up to 1 mg, flumazenil effectively reverses sedation and improves psychomotor performance following administration of short and longer acting benzodiazepines used for sedation, or general anaesthesia supplemented with benzodiazepines. The duration of action is short at generally 30 to 60 minutes and supplemental doses of flumazenil may be needed to maintain the desired level of consciousness in some patients. After poisoning with high dosages of benzodiazepines alone or combined with other drugs, the initial single dose of flumazenil will require supplementing with repeated low intravenous doses or an infusion to maintain wakefulness. In such patients, flumazenil also facilitates differential diagnosis and reduces the necessity for interventions. Flumazenil thus enhances recovery and allows more rapid discharge of patients sedated with benzodiazepines for diagnostic procedures and facilitates management of patients during the initial recovery period following general anaesthesia supplemented with benzodiazepines, but does not preclude normal monitoring during the recovery period. Flumazenil is clearly very useful in treating drug poisoning when benzodiazepines are a major component. By virtue of its specific benzodiazepine antagonist effects, flumazenil provides an innovative and well tolerated approach in clinical situations requiring rapid reversal of benzodiazepine-induced central nervous system depressant effects.