Block-dependent sedation during epidural anaesthesia is associated with delayed brainstem conduction

Efficacy of intraoperative thoracoscopic intercostal nerve blocks in nonintubated and intubated video-assisted thoracic surgery: A randomized study

BACKGROUND

The efficacy of thoracoscopic intercostal nerve blocks (TINBs) for noxious stimulation from video-assisted thoracic surgery (VATS) remains unclear. The efficacy of TINBs may also be different between nonintubated VATS (NIVATS) and intubated VATS (IVATS). We aim to compare the efficacy of TINBs on analgesia and sedation for NIVATS and IVATs intraoperatively.

METHODS

Sixty patients randomized to the NIVATS or IVATS group (30 each) received target-controlled propofol and remifentanil infusions, with bispectral index (BIS) maintained at 40-60, and multilevel (T3-T8) TINBs before surgical manipulations. Intraoperative monitoring data, including pulse oximetry, mean arterial pressure (MAP), heart rate, BIS, density spectral arrays (DSAs), and propofol and remifentanil effect-site concentration (Ce) at different time points. A two way ANOVA with post hoc analysis was applied to analyze the differences and interactions of groups and time points.

RESULTS

In both groups, DSA monitoring revealed burst suppression and α dropout immediately after the TINBs. The Ce of the propofol infusion had to be reduced within 5 min post-TINBs in both NIVATS (p < 0.001) and IVATS (p = 0.252) groups. The Ce of remifentanil infusion was significantly reduced after TINBs in both groups (p < 0.001), and was significantly lower in NIVATS (p < 0.001) without group interactions.

CONCLUSION

The surgeon-performed intraoperative multilevel TINBs allow reduced anesthetic and analgesic requirement for VATS. With lower requirement of remifentanil infusion, NIVATS presents a significantly higher risk of hypotension after TINBs. DSA is beneficial for providing real-time data that facilitate the preemptive management, especially for NIVATS.

Electroencephalographic assessment of infant spinal anesthesia: A pilot prospective observational study

INTRODUCTION

Spinal anesthesia is utilized as an alternative to general anesthesia in infants for some surgeries. After spinal anesthesia, infants often become less conscious without administration of sedative medications. The aim of this study was to assess electroencephalographic (EEG) correlates after spinal anesthesia in a cohort of infants.

PATIENTS AND METHODS

This pilot study included 12 infants who underwent spinal anesthesia. Unprocessed electroencephalography was recorded. The electroencephalogram was interpreted by four neurologists. Processed analyses compared electroencephalogram changes 30 min after spinal anesthesia to baseline.

RESULTS

Following spinal anesthesia, all 12 infants became sedated. Electroencephalography in all 12 demonstrated Stage 2 sleep with the appearance of sleep spindles (12-14 Hz) in the frontal and central leads in 8/12 (67%) of subjects. The median time to onset of sleep spindles was 24.7 interquartile range (21.2, 29.9) min. The duration of sleep spindles was 25.1 interquartile range (5.8, 99.8) min. Voltage attenuation and background slowing were the most common initial changes. Compared to baseline, the electroencephalogram 30 min after spinal anesthesia showed significantly increased absolute delta power (p = 0.02) and gamma power (p < 0.0001); decreases in beta (p = 0.0006) and higher beta (p < 0.0001) were also observed. The Fast Fourier Transform power ratio difference for delta/beta was increased (p = 0.03). Increased coherence was noted in the delta (p = 0.02) and theta (p = 0.04) bandwidths.

DISCUSSION

Spinal anesthesia in infants is associated with increased electroencephalographic slow wave activity and decreased beta activity compared to the awake state, with appearance of sleep spindles suggestive of normal sleep. The etiology and significance of the observed voltage attenuation and background slowing remains unclear.

CONCLUSIONS

The EEG signature of infant spinal anesthesia is distinct from that seen with general anesthesia and is consistent with normal sleep. Further investigation is required to better understand the etiology of these findings. Our preliminary findings contribute to the understanding of the brain effects of spinal anesthesia in early development.

Effect of lumbar epidural blockade and propofol on mean arterial pressure, cardiac output and bispectral index: A randomised controlled and pharmacodynamic modelling study

BACKGROUND

It is generally accepted that a neuraxial blockade strengthens the sedative effects of propofol. Deafferentation caused by neuraxial blockade is thought to play a key role.

OBJECTIVES

The objective is to determine whether epidural blockade affects the bispectral index (BIS) of propofol and two other pharmacodynamic endpoints, mean arterial pressure (MAP) and cardiac output (CO).

DESIGN

Randomised, placebo-controlled study.

SETTING

University hospital.

PATIENTS

Patients scheduled for surgery needing epidural analgesia.

INTERVENTION

28 ASA one or two patients received 0, 50, 100 or 150 mg of epidural ropivacaine. After stabilisation of the epidural blockade, propofol was given by target-controlled infusion. The propofol plasma target concentrations were increased at 6-min intervals from 0 to 1, 2.5, 4 and 6 μg ml-1. The study was performed before surgery.

MAIN OUTCOME MEASURES

Three endpoints, BIS, mean arterial blood pressure and CO were measured from baseline (prior to the administration of epidural ropivacaine) until 2 h after the start of propofol infusion. The propofol concentration-effect data were analysed to determine the interaction between epidural blockade and propofol sedation.

RESULTS

In the absence of propofol, the increase in number of epidural blocked segments from 0 to 15.5 (range 6 to 21) reduced the MAP by 30%, without affecting BIS or CO. In the absence of epidural blockade, the increase in propofol concentration to 6 μg ml-1 reduced BIS, MAP and CO. When combined, epidural anaesthesia and intravenous propofol exhibited no pharmacodynamic interaction on any of the three endpoints. In addition, epidural blockade did not affect the propofol effect-site equilibration half-life for its haemodynamic effects (11.5 ± 0.5 min) or for its effects on the BIS (4.6 ± 0.4 min).

CONCLUSION

Epidural blockade reduces the propofol requirements for sedative end points. This is not the result of a pharmacodynamic interaction.

TRIAL REGISTRATION

Dutch trial register CCMO, Central Committee on Research Involving Human Subjects, trial number NL 32295.058.10.

Dose Comparison of Dexmedetomidine Sedation following Spinal Anesthesia: Parturient versus Nonpregnant Women-A Randomized Trial

Background

This study was designed to investigate and compare the effective doses of dexmedetomidine for sedation in parturient patients who underwent Cesarean section (CS) and nonpregnant women who underwent elective gynecologic surgery.

Methods

The study comprised 60 females aged between 25 and 35. They were divided into two groups. The parturient group received a bolus dose of dexmedetomidine over 15 min after the delivery of the fetus and placenta. In the nonpregnant women group, a bolus of dexmedetomidine was administered intravenously upon the completion of spinal anesthesia. The subsequent dose required by patients in each group was then determined through a modified two-stage Dixon up-and-down sequential method. Probit analysis was used to calculate the ED50 and the ED95 of dexmedetomidine for adequate sedation.

Results

The ED50 of dexmedetomidine for adequate sedation in parturient patients was 1.58 μg/kg (1.51–1.66 μg/kg); in nonpregnant women, it was 0.96 μg/kg (0.91–1.01 μg/kg) (95% CI). The ED95 of dexmedetomidine in parturients was 1.80 μg/kg (1.70–2.16) μg/kg and that of nonpregnant women was 1.10 μg/kg (1.04–1.30 μg/kg) (95% CI). The ED50 in parturients was significantly higher than that in nonpregnant women (P < 0.05).

Conclusion

The ED50 of dexmedetomidine for target sedation in parturients who received spinal anesthesia for CS is greater than 1.5 times that in nonpregnant women who received spinal anesthesia for lower abdominal gynecologic surgery. This study postulates that the dose of dexmedetomidine required to achieve optimal sedation following spinal anesthesia is much higher in parturients than in nonpregnant women undergoing gynecologic surgeries. This trial is registered with NCT02111421.

Effects of intrathecal bupivacaine on the NR2B/CaMKIIα/CREB signaling pathway in the rat lumbar spinal cord

Neuraxial anesthesia produces an anesthetic-sparing, sedative effect. The mechanism underlying this effect potentially involves decreased spinal afferent input. However, the neurochemical mechanisms at the spinal level remain unknown. The N-methyl-D-aspartate receptor 2B subunit/calcium-calmodulin-dependent protein kinase II α/cAMP response element-binding protein (NR2B/CaMKIIα/CREB) signaling pathway serves an important role in regulating the transmittance of peripheral noxious stimulation to supraspinal regions in the process of nociception. The present study investigated the effects of intrathecal bupivacaine on the NR2B/CaMKIIα/CREB signaling pathway. Following catheterization, 36 male Sprague-Dawley rats were randomly assigned to a normal saline (NS) or bupivacaine treatment group, in which each rat intrathecally received 20 µl normal saline or 0.5% bupivacaine, respectively. The expression levels of NR2B, CaMKIIα/p-CaMKIIα, and CREB/phosphorylated (p)-CREB in the lumbar spinal cord were investigated by western blotting, reverse transcription-quantitative polymerase chain reaction and immunohistochemistry (IHC). Following bupivacaine treatment, western blot analysis demonstrated that the protein expression levels of NR2B, p-CaMKIIα, and p-CREB in the spinal cord were reduced by approximately 54, 56 and 33%, respectively, compared with NS control rats. Similar alterations in expression were observed by IHC analysis. Additionally, mRNA expression levels of NR2B, CaMKIIα, and CREB were also downregulated following the intrathecal administration of bupivacaine. Therefore, the sedative effect of subarachnoid blockade with bupivacaine possibly occurs through de-afferentation, which may reduce cortical arousal by downregulating the spinal NR2B/CaMKIIα/CREB pathway in vivo, however further investigation is required in order to verify this.

Transient Coma Due To Epidural Anesthesia: The Role of Loss of Sensory Input

Patient: Female, 22

Final Diagnosis: Coma due to loss of sensory input

Symptoms: Coma

Medication: Lidocaine

Clinical Procedure: Epidural

Specialty: Anesthesiology

A study of the effect of caudal epidural block on bispectral index targeted propofol requirement in children: A comparative study

Caudal epidural block is one of the most commonly performed neuraxial block techniques with reliable peri-operative and post-operative analgesia in pediatric patients. In our randomized, prospective, double-blinded, open level, parallel group study, we have established the effect of caudal epidural block on maintenance requirement of intravenous (IV) propofol in targeted bispectral (BIS) monitored patients.

Context:

Neuraxial anesthesia exhibits sedative properties that may reduce the requirement for general anesthesia. TIVA with propofol has been administered as an established method of maintaining general anesthesia in children. Caudal analgesia being a type of neuraxial block, also seems to reduce the requirement of sedative hypnotics in pediatric patients. Numerous studies show that for patients, administered with caudal epidural block, they require reduced intra-operative volatile inhalation anesthetics. In the present study, we have established the anesthetic sparing effect of Caudal Epidural Analgesia in children undergoing infra-umbilical surgical procedure and calculated the efficacy of propofol-infusion in maintaining adequate depth of anesthesia.

Aims:

(1) To study and compare the dose requirements of propofol using caudal epidural analgesia. (2) To calculate the efficacy of propofol as maintenance anesthetic agent in both groups and to compare hemodynamic stability of patients in both the techniques.

Settings and Design:

In our study, after administering general anesthesia to pediatric patients, we have administered caudal analgesia and IV analgesia to monitor the requirement of intra-operative propofol infusion using BIS monitor with a target value of 40-60 in both groups.

Materials and Methods:

82 patients (aged between 3 and 6 years) have been selected undergoing infra-umbilical surgery and randomly allocated into two groups containing 41 patients in each group. Both the groups group B and group A then intubated with glycopyrrolate, 2 mg/kg injection fentanyl, propofol till loss of verbal contact and atracurium at the rate of 0.5 mg/kg and group B has been administered caudal epidural blockade with 1 ml/kg 0.2% ropivacaine. Propofol infusion at the rate of 10 mg/kg/h is given as maintenance. BIS value has been recorded throughout and propofol requirement at the end of surgery has been calculated.

Statistical Analysis Used:

Numerical variables between groups have been analyzed using the Student's t-test and the Mann-Whitney U-test as applicable. Categorical variables have been analyzed using the Pearson's Chi-square test. P < 0.05 is considered statistically significant.

Results:

Consumption of propofol at the start of operation in the group A is 2.9 ± 0.17 and group B is 2.91 ± 0.17, which is not statistically significant (P > 0.05), whereas at the end of the operation in the group A is 11.33 ± 0.17 and group B is 7.83 ± 0.63, which is statistically significant (P < 0.05). Incidence of adverse effects is statistically insignificant between the two groups. The time for administration of rescue analgesic is 2.1 ± 0.88 in group A and 6.5 ± 0.17 in group B, which is statistically significant due to caudal analgesia.

Conclusions:

We conclude that in BIS-monitored patients (3-6 years) with infra-umbilical surgeries have shown a reduction in consumption of IV propofol due to caudal epidural blockade.

Effect of deafferentation from spinal anesthesia on pain sensitivity and resting-state functional brain connectivity in healthy male volunteers

Patients may perceive paradoxical heat sensation during spinal anesthesia. This could be due to deafferentation-related functional changes at cortical, subcortical, or spinal levels. In the current study, the effect of spinal deafferentation on sensory (pain) sensitivity was studied and linked to whole-brain functional connectivity as assessed by resting-state functional magnetic resonance imaging (RS-fMRI) imaging. Deafferentation was induced by sham or spinal anesthesia (15 mg bupivacaine injected at L3-4) in 12 male volunteers. RS-fMRI brain connectivity was determined in relation to eight predefined and seven thalamic resting-state networks (RSNs) and measured before, and 1 and 2 h after spinal/sham injection. To measure the effect of deafferentation on pain sensitivity, responses to heat pain were measured at 15-min intervals on nondeafferented skin and correlated to RS-fMRI connectivity data. Spinal anesthesia altered functional brain connectivity within brain regions involved in the sensory discriminative (i.e., pain intensity related) and affective dimensions of pain perception in relation to somatosensory and thalamic RSNs. A significant enhancement of pain sensitivity on nondeafferented skin was observed after spinal anesthesia compared to sham (area-under-the-curve [mean (SEM)]: 190.4 [33.8] versus 13.7 [7.2]; p<0.001), which significantly correlated to functional connectivity changes observed within the thalamus in relation to the thalamo-prefrontal network, and in the anterior cingulate cortex and insula in relation to the thalamo-parietal network. Enhanced pain sensitivity from spinal deafferentation correlated with functional connectivity changes within brain regions involved in affective and sensory pain processing and areas involved in descending control of pain.

Intrathecal fentanyl decreases the optimal effect site concentration of propofol during spinal anaesthesia

BACKGROUND

The aim of this study was to assess the possible difference in the optimal effect site concentration of propofol for conscious sedation during spinal anaesthesia with or without intrathecal fentanyl in patients undergoing urologic surgery. The hypothesis was that intrathecal fentanyl would decrease the effect site concentration of propofol needed for conscious sedation.

METHODS

Among 43 patients, 23 patients received fentanyl 25 mcg and 20 patients received normal saline in addition to hyperbaric bupivacaine 10 mg during spinal anaesthesia. Propofol was infused at a dose determined by a modified Dixon's up-and-down method. The Cerebral State Index was recorded once target effect site concentration was reached to determine the effect of the successfulness of the conscious sedation.

RESULTS

The half maximal effective concentration (EC50) of the effect-site concentration of propofol for sedation was 1.67 ± 0.28 mcg/ml in the control group and 0.87 ± 0.15 mcg/ml in the fentanyl group (P = 0.02). The propofol dose for conscious sedation during spinal anaesthesia was decreased by 48% when intrathecal fentanyl 25 mcg was added to local anaesthetics.

CONCLUSION

The EC50 of the effect-site concentration of propofol for sedation decreased from 1.67 ± 0.28 mcg/ml to 0.87 ± 0.15 mcg/ml with the addition of 25 mcg fentanyl to a spinal anaesthetic in patients undergoing urologic surgery.

Thiopental dose requirements for induction of anaesthesia and subsequent endotracheal intubation in patients with complete spinal cord injuries

BACKGROUND

Dose requirements of thiopental depend on patient characteristics and infusion rate. We determined thiopental dose requirements for induction of anaesthesia, and the effects of remifentanil on cardiovascular and bispectral index (BIS) responses to tracheal intubation in spinal cord-injured (SCI) patients undergoing general anaesthesia.

METHODS

Twenty patients with traumatic complete SCI undergoing elective surgery were enrolled. Twenty patients without SCI served as control. Anaesthesia was induced with thiopental, followed by remifentanil 1 μg/kg and rocuronium 0.8 mg/kg, and maintained with 2% sevoflurane and 50% nitrous oxide in oxygen after tracheal intubation. Thiopental was administered at a rate of 50 mg/15 s until abolition of the eyelash reflex. Thiopental doses, BIS values, systolic arterial blood pressure (SAP), heart rate (HR) and plasma catecholamine concentrations were measured.

RESULTS

Total thiopental dose required to abolish the eyelash reflex based on total body weight (BW) (5.26 ± 0.87 vs. 3.91 ± 1.07 mg/kg, P < 0.001) or lean BW (6.56 ± 1.37 vs. 5.24 ± 1.36 mg/kg, P < 0.01) were significantly smaller in the SCI group than in the control. SAP was decreased by induction of anaesthesia with thiopental and remifentanil, and increased by tracheal intubation in both groups. However, the peak SAP after intubation was smaller in the SCI patients. HR increased significantly above baseline values following intubation in both groups with no significant intergroup differences. Hypertension was more frequent in the control group. Norepinephrine concentrations remained unaltered following intubation in both groups.

CONCLUSIONS

These results suggest that the dose requirements of thiopental for induction of general anaesthesia and subsequent tracheal intubation are reduced in the SCI patients.

Effect of epidural neuraxial blockade-dependent sedation on the Ramsay Sedation Scale and the composite auditory evoked potentials index in surgical intensive care patients

BACKGROUND/PURPOSE

Peripheral deafferentation induced by neuraxial anesthesia reduces the degree of cortical arousal. This study investigated whether epidural analgesia blockade decreased sedation, as measured by the rapidly extracted auditory evoked potentials index, A-line autoregressive index (AAI) and Ramsay Sedation Scale (RSS) in sedated surgical intensive care patients, and looked at whether this was a concentration-dependent effect of lidocaine.

METHODS

Forty patients underwent major lower abdominal surgery and received epidural analgesia in the surgical intensive care unit. Patients were continuously sedated with propofol to achieve an RSS value of 3, randomly divided into two groups, and received epidural analgesia with 10 mL of 0.5% or 1% lidocaine. Sedation was evaluated using the RSS and AAI, and analgesia was evaluated using a visual analog scale (VAS). RSS, AAI, electromyography (EMG) activity of AAI and VAS values were recorded at 5 minutes before and 30, 60 and 90 minutes after epidural lidocaine administration.

RESULTS

Epidural 0.5% lidocaine produced a reduction of AAI, EMG and VAS at 30, 60 and 90 minutes after administration. For 1% epidural lidocaine administration, AAI, EMG and VAS were also reduced at 30, 60 and 90 minutes after epidural lidocaine administration. However, there was no difference in the AAI between the two concentrations; moreover, no significant change was observed in the RSS.

CONCLUSION

Epidural lidocaine analgesia could potentiate sedation in patients evaluated by the AAI, but had no effect on the RSS. The present study suggests that the AAI could provide an objective and more precise index than the RSS in evaluation of sedation level in patients who are undergoing epidural pain management in the intensive care unit.

Caudal analgesia reduces the sevoflurane requirement for LMA removal in anesthetized children

Background

An anesthetic state can reduce adverse airway reaction during laryngeal mask airway (LMA) removal in children. However, the anesthetic state has risks of upper airway obstruction or delayed emergence; so possibly less anesthetic depth is advisable. Caudal analgesia reduces the requirement of anesthetic agents for sedation or anesthesia; it is expected to reduce the sevoflurane requirement for LMA removal. Therefore, we determined the EC₅₀ of sevoflurane for LMA removal with caudal analgesia and compared that to the EC₅₀ without caudal analgesia.

Methods

Forty-three unpremedicated children aged 1 to 6 yr were enrolled. They were allocated to receive or not to receive caudal block according to their parents' consent. General anesthesia were induced and maintained with sevoflurane and oxygen in air. EC₅₀ of sevoflurane for a smooth LMA removal with and without caudal analgesia were estimated by the Dixon up-and-down method. The LMA was removed when predetermined end-tidal sevoflurane concentration was achieved, and the sevoflurane concentration of a subsequent patient was determined by the success or failure of the previous patient with 0.2% as the step size; success was defined by the absence of an adverse airway reaction during and after LMA removal. EC₅₀ of sevoflurane with caudal block, and that without caudal block, were compared by a rank-sum test.

Results

The EC₅₀ of sevoflurane to achieve successful LMA removal in children with caudal block was 1.47%; 1.81% without caudal block. The EC₅₀ were significantly different between the two groups (P < 0.001).

Conclusions

Caudal analgesia significantly reduced the sevoflurane concentration for a smooth LMA removal in anesthetized children.

Neostigmine decreases bupivacaine use by patient-controlled epidural analgesia during labor: a randomized controlled study

BACKGROUND

Intrathecal neostigmine not only produces analgesia but also severe nausea. In contrast, epidural neostigmine enhances opioid and local anesthetic analgesia without causing nausea. Previous studies examined only single epidural neostigmine bolus administration and did not assess the efficacy of continuous epidural infusion or several aspects of maternal and fetal safety. We therefore tested the hypothesis that epidural neostigmine in combination with bupivacaine by continuous infusion during labor would reduce the amount of bupivacaine required.

METHODS

Twelve healthy women scheduled for elective cesarean delivery were assigned to receive epidural neostigmine, 40 microg (first six subjects) or 80 microg (second six subjects) as a single bolus, with fetal heart rate (FHR) and uterine contractions monitored for 20 min. In a subsequent experiment, 40 healthy laboring women were randomized to receive bupivacaine 1.25 mg/mL alone or with neostigmine 4 microg/mL by patient-controlled epidural analgesia. The primary outcome measure was hourly bupivacaine use.

RESULTS

Epidural neostigmine bolus did not alter baseline FHR, induce contractions, or produce nausea. Epidural neostigmine infusion reduced bupivacaine requirement by 19% in all patients and 25% in those with >4 h of treatment (P < 0.05 for both) but might have contributed to the incidence of mild sedation. Mode of delivery, incidence of maternal nausea, and FHR abnormality were similar between groups.

CONCLUSIONS

These data show that adding epidural neostigmine 4 microg/mL reduces the hourly bupivacaine requirement by 19%-25% with patient-controlled epidural analgesia during labor. Administered as a bolus and by continuous infusion at the studied doses, epidural neostigmine does not cause nausea and does not induce uterine contractions or FHR abnormalities, but mild sedation can occur.

Depth of sedation using Cerebral State Index in infants undergoing spinal anesthesia

BACKGROUND

Infants are noted to frequently sleep during spinal anesthesia, with a concomitant fall in Bispectral Index. However, there are suggestions that EEG derived anesthesia depth monitors have inferior performance in infants. The aim of this study was to quantify the degree of sedation during spinal anesthesia in infants using another EEG derived measure of anesthesia effect--the Cerebral State Index (CSI).

METHODS

Twelve infants, <52 weeks postconceptual menstrual age, scheduled for bilateral inguinal hernia repair under spinal anesthesia were enrolled. Patients received a standard anesthetic protocol with a subarachnoid dose of 1 mg x kg(-1) of levobupivacaine 0.5%. No premedication, sedatives, opioids or anticholinergics were administrated during the perioperative period and patients were left undisturbed during the surgical time, without tactile stimulation or loud auditory stimuli. CSI score (0-100) and bust suppression (BS) (0-100%) were continuously recorded during the surgical time and then statistically re-evaluated.

RESULTS

In all patients the CSI fell during the procedure and there were significant levels of BS recorded by the CSI monitor. The BS occurred between 12 and 34 min after spinal anesthesia with the peak being at 30 min and mean onset time being 15 (2.6) min after spinal block. A statistical significant difference was found between the lowest mean CSI as well as the highest BS if compared with their baseline values. A negative correlation was found between CSI and BS.

CONCLUSIONS

The degree of burst suppression detected by the CSI in our study supports the hypothesis that infants may have discontinuous patterns of EEG during spinal anesthesia similar to those seen during emergence from general anesthesia. Moreover, the limitations in the application of the adult algorithms to infant EEG may lead to an overestimation of the degree of sedation.

[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.

Sedation and regional anaesthesia in the adult patient

This review discusses sedation for regional anaesthesia in the adult population. The first section deals with general aspects of sedation and shows that the majority of patients receiving sedation for regional anaesthesia are satisfied and would choose it again. Methods of assessing the level of sedation are discussed with emphasis on clinical measures. The pharmacology of the drugs involved in sedation is discussed, with propofol and remifentanil appearing to be the combination of choice for sedation in regional anaesthesia. The techniques for administering sedation are discussed and replacement of the traditional repeated boluses or continuous infusion with pharmacokinetic and patient-controlled systems is supported. Patient satisfaction studies suggest that patient-controlled systems are preferred.

Influence of the baricity of a local anaesthetic agent on sedation with propofol during spinal anaesthesia

BACKGROUND

This study examined the effect of different levels of spinal anaesthesia, induced by solutions of different baricity but containing the same amount of local anaesthetic agent, on the requirement for sedation with propofol.

METHODS

Thirty-six patients undergoing varicose vein surgery under spinal anaesthesia were randomly allocated to receive tetracaine 15 mg in 3 ml of either glucose 5% (hyperbaric) or CSF (isobaric). I.V. propofol was started 5 min after the intrathecal injection and was titrated to maintain a bispectral index (BIS) score of 65-75. The propofol requirements to maintain this range in the two groups were compared every 5 min.

RESULTS

The propofol requirement was always lower in the hyperbaric group, with the differences becoming statistically significant 20 min after the intrathecal injection. Total consumption of propofol over the 55 min of the study was also less in the hyperbaric group.

CONCLUSION

The known difference in level of spinal anaesthetic block induced by solutions of different baricity, but the same dose of local anaesthetic, was associated with different requirements for propofol sedation as determined by BIS assessment.

Using EEG to monitor anesthesia drug effects during surgery

The use of processed electroencephalography (EEG) using a simple frontal lead system has been made available for assessing the impact of anesthetic medications during surgery. This review discusses the basic principles behind these devices. The foundations of anesthesia monitoring rest on the observations of Guedel with ether that the depth of anesthesia relates to the cortical, brainstem and spinal effects of the anesthetic agents. Anesthesiologists strive to have a patient who is immobile, is unconscious, is hemodynamically stable and who has no intraoperative awareness or recall. These anesthetic management principles apply today, despite the absence of ether from the available anesthetic medications. The use of the EEG as a supplement to the usual monitoring techniques rests on the observation that anesthetic medications all alter the synaptic function which produces the EEG. Frontal EEG can be viewed as a surrogate for the drug effects on the entire central nervous system (CNS). Using mathematical processing techniques, commercial EEG devices create an index usually between 0 and 100 to characterize this drug effect. Critical aspects of memory formation occur in the frontal lobes making EEG monitoring in this area a possible method to assess risk of recall. Integration of processed EEG monitoring into anesthetic management is evolving and its ability to characterize all of the anesthetic effects on the CNS (in particular awareness and recall) and improve decision making is under study.

Sedation during spinal anaesthesia in infants

BACKGROUND

Neuraxial anaesthesia in adults decreases the dose of i.v. or inhalational anaesthetic needed to reach a desired level of sedation. Furthermore, spinal anaesthesia alone has a sedative effect. The mechanism behind this phenomenon is presumed to be decreased afferent stimulation of the reticular activating system after sympatholysis. We hypothesized that this mechanism is equally active in infants undergoing spinal anaesthesia.

METHODS

In total, 20 unpremedicated former preterm infants underwent surgery under spinal anaesthesia with hyperbaric bupivacaine 0.5% 1 mg kg(-1) with epinephrine 10 microg kg(-1). No additional sedatives or anaesthetics were administered. Sedation was evaluated using the bispectral index (BIS) score and the 95% spectral edge frequency (SEF(95)).

RESULTS

After spinal anaesthesia, mean (SD) BIS began to decrease significantly from baseline 97.0 (1.1) to 83.9 (14.4) after 15 min (P=0.006). BIS decreased further, reaching the lowest values after 30 min [62.2 (14.0); P<0.00001]. Mean (SD) SEF(95) declined from baseline 26.1 (1.8) Hz to 24.3 (3.1) after 5 min (P=0.02) and further to 9.9 (3.8) after 30 min (P<0.00001). Mean arterial pressure also decreased significantly from 66.5 (4.7) mm Hg within 10 min to 56.1 (5.6) after spinal anaesthesia (P=0.0002), while heart rate remained stable.

CONCLUSIONS

These results suggest that sedation after spinal anaesthesia in infants is at least as pronounced as in adults. The sedative effect of spinal anaesthesia should be kept in mind when additional sedatives are administered, especially in former preterm infants.

Bispectral index does not correlate with observer assessment of alertness and sedation scores during 0.5% bupivacaine epidural anesthesia with nitrous oxide sedation

The bispectral index (BIS) has been used as a measure of the degree of sedation and level of hypnosis for IV hypnotics and sedatives, potent volatile anesthetics. We evaluated the effect of increasing concentrations of nitrous oxide (N2O) on BIS and compared it with the Observer's Assessment of Alertness and Sedation (OAA/S) scale in patients undergoing regional anesthesia. We studied 48 unpremedicated, ASA physical status I-II adult patients scheduled for lower extremity surgery under lumbar epidural anesthesia. N2O was given in oxygen to achieve measured end-tidal concentrations of 33%, 50%, and 67% N2O by a tight-fitting facemask, and each N2O concentration was maintained for 20 min. Paired measurements of BIS and OAA/S scores were obtained just before each increase in N2O concentration. Forty of the 48 subjects completed the study. Increasing N(2)O concentrations produced no changes in BIS despite a significant decrease in OAA/S scores at 50% and 67% N2O concentrations. The prediction probability for BIS and OAA/S calculated by Somers' d(x.y) were 0.60 and 0.84, respectively. Anesthesiologists should be aware that the BIS monitor may not be sensitive enough to provide an adequate measure of the depth of sedation and hypnosis when using N2O alone for sedation. It may be better to monitor sedation clinically (e.g., with the OAA/S scale) to determine the dose requirement and the adequacy of depth of sedation and hypnosis.

The effects of caudal local anesthesia blockade on the Bispectral Index during general anesthesia in children

BACKGROUND

Peripheral deafferentation induced by epidural or spinal anesthesia reduces the degree of cortical arousal in adults. This study aimed at determining if caudal blockade decreases the level of arousal, as measured by Bispectral Index (BIS) in unstimulated children, and to determine if this effect differed between age groups.

METHODS

Hospital ethics committee approval and parental consent was obtained. Children (age between 24 months and 5 years) and infants (between 6 and 24 months of age) were recruited if they were scheduled for below umbilical surgery that would usually require caudal local anesthesia blockade. Before the procedure, subjects within each age group were randomized to either caudal group (1 ml.kg(-1) 0.25% bupivacaine), or control group (no caudal). In all groups, anesthesia was induced with sevoflurane and maintained at a constant endtidal concentration of 1.5% sevoflurane without N(2)O. Five minutes after induction a baseline BIS was recorded (BIS(1)). In the caudal groups, a caudal block was then performed while in the control groups no block was performed. Fifteen minutes later, the BIS was again recorded (BIS(2)). The change in BIS over this time period was the primary outcome (BIS(Delta)). After measurement, subjects in the control groups received a caudal block before the start of surgery.

RESULTS

Twenty-nine infants and 18 children completed the study protocol. In children, BIS(Delta) was significantly different between the caudal group and control (-5.7 vs -0.7, P = 0.04). In infants, no significant difference was detected in BIS(Delta) between caudal and control groups.

CONCLUSIONS

Caudal blockade decreased the degree of arousal, as measured by BIS, in unstimulated children aged 2-5 years. No change in arousal was detected in infants.

Haemodynamic effects of thoracic epidural anaesthesia during induction of anaesthesia: an investigation into the effects of tracheal intubation during target-controlled infusion of propofol

We compared haemodynamic changes following induction of anaesthesia with propofol during tracheal intubation with and without epidural anaesthesia. Nineteen patients were divided into two groups to receive epidurally administered saline (Group C) or lidocaine 1.5% (Group E). The propofol infusion was started to produce blood concentrations of 3 microg.ml(-1), and following fentanyl and vecuronium administration, tracheal intubation was performed. Mean arterial blood pressure (MBP), heart rate (HR), Bispectral index and effect-site propofol concentration were recorded. Time to loss of consciousness was significantly shorter in Group E than in Group C. The effect-site propofol concentration at loss of consciousness was significantly lower in Group E than in Group C. MBP and HR were significantly lower following propofol induction in both groups, and were significantly increased following intubation in Group C but not in Group E. In conclusion, epidural anaesthesia did not produce profound hypotension following induction of anaesthesia and produced a reduction in the haemodynamic response to tracheal intubation during a target controlled infusion of propofol.