Observer's Assessment Of Alertness/Sedation Research Articles

Evaluation of Auditory Evoked Potential and Bispectral Index in Patient-Controlled Sedation with Propofol

Background: The auditory evoked potential (AEP) index and bispectral (BIS) index have been proposed as methods to measure the depth of sedation. A prospective study was designed to assess the performance of both these methods for measuring the depth of sedation induced by propofol patient-controlled sedation (PCS) under spinal anesthesia. Methods: Forty ASA I and II adult patients under spinal anesthesia using 0.5% hyperbaric bupivacaine were studied. Group 1 (10mg bolus, 30 mg loading) and Group 2 (20 mg bolus, 60 mg loading) received propofol and maintained PCS with 1min lockout interval and 100 mg/hr continuous infusion. AEP, BIS and Observer's assessment of alertness/sedation (OAA/S) scale were monitored during the operation. Results: AEP and BIS decreased and increased following the changes on the patient's OAA/S scores and correlated with sedation significantly. There were no significant difference in mean AEP index (group 1; 13.4 8.4, group 2; 8.9 6.2), BIS index (group 1; 76.2 9.7, group 2; 71.2 9.8), and OAA/S scale (group 1; 3.8 1.3, group 2; 3.2 1.5) between the groups. Incidence of perioperative respiratory depression was significantly higher in group 2 (25%) than group 1 (5%), and incidence of involuntary movement was significantly higher in group 1 (20%) than group 2 (5%) (P

Does Level of Sensory Block by Epidural Anesthesia Affect the Degree of Sedation?

Background: Epidural anesthesia has been shown to have a direct sedative effect, and to markedly reduce the hypnotic requirement of intravenous anesthetics. The purpose of this study was to investigate whether the level of sensory block by epidural anesthesia is related with the degree of sedation, and to the hypnotic requirement of propofol. In addition, we tested whether bispectral index (BIS) monitoring can quantify the sedative effects of epidural anesthesia. Methods: Thirty two patients scheduled for elective upper abdominal or lower extremity surgery were allocated into two groups. 2% lidocaine 15 ml was administered through an epidural catheter at the level (group T, n = 16) or at the level (group L, n = 16). Observer's assessment of alertness/sedation (OAA/S) and BIS were evaluated 20 min after the epidural injection. Hypnotic doses of propofol were then determined by evaluating the loss of open eyes in response to a verbal command as an end point while propofol was administered by target controlled infusion (target effect concentration 5/ml, induction time 3 min). At the time of induction of hypnosis, the target effect concentration and BIS were recorded. Results: The average level of sensory block was up to T3 in group T, and up to T11 in group L. Compared with the group L, more decreases were noticed in group T in terms of the hypnotic dose of propofol (1.13 0.31 mg/kg vs. 1.67 0.36 mg/kg; P = 0.03). A decrease in the OAA/S scale from 5 to 4 was more frequently noticed in group T than in group L (93.7% vs. 12.5%, P 7 2.8 vs. 82.6 2.2; P

The Effect of Monitored Anesthesia Care using Alfentanil and Ketorolac in Patients Undergoing Endoscopic Sinus Surgery

Background: Monitored anesthesia care (MAC) has become increasingly important as a means of ensuring patient comfort, safety and satisfaction during surgery under local anesthesia. The purpose of this study was to evaluate the effect of monitored anesthesia care using alfentanil and ketorolac in patients undergoing endoscopic sinus surgery (ESS). Methods: We studied 47 adult patients premedicated with glycopyrrolate 0.2 mg and midazolam 0.02 mg/kg IV. Using a 5.0 endotracheal tube, 5 L/min of oxygen was delivered via mouth. A mixture of 30 mg of ketorolac and 2,500g of alfentanil in 25 ml of saline was infused to patients at a rate of 1g/kg/min alfentanil after a bolus injection of 5g/kg alfentanil before operation. During operations we monitered vital signs, SpO2, OAA/S (Observer’s Assessment of Alertness/Sedation) scale and BIS scores. Six hours postoperatively we assessed patient degree of satisfaction via NRS (1-10) with the anesthetic technique and side effects. Results: Mean duration of drug infusion was 35 10.1 min, and the mean infusion rate of alfentanil was 1.09 y 0.23g/kg/min. Significant differences were observed between OAA/S scale scores at 10 min and 30 min after drug infusion and those in the waiting room (4.63, 4.65 vs 5, P

Patient-Controlled Sedation for Local Anesthesia Patients in Plastic Surgery

Background: Patient-controlled sedation (PCS) involves the patient self administering the sedative agent to the point at which the patient is satisfied with the level of sedation with the advantage to overcome the phamacodynamic differences between individual patients. We performed the PCS with two different dosages of propofol and compared the efficacy and side effects for local anesthesia patients in plastic surgery. Methods: Thirty patients underwent propofol PCS with fm (B. Braun, Germany) PCA pump during nasal inhalation of 3 L/min with continuous monitoring of . PCS settings were 10 mg of bolus dose, 30 mg of initial loading dose, 1 min of lockout interval, 100 mg/hr of continuous infusion in group 1 and 20 mg of bolus dose, 60 mg of initial loading dose, 1 min of lockout interval, 100 mg/hr of continuous infusion in group 2. All the patients received local anesthesia with 1% lidocaine before operation. Observer's assessment of alertness/sedation (OAA/S) scale, , mean infusion rate of propofol, duration of induction and recovery, recall of operative procedure, and patient's and surgeon's satisfaction were checked. Results: The mean infusion rate (group 1; 32.2 19.4, group 2; 38.3 20.5 ug/kg/min), duration of induction (group 1; 4.9 1.9, group 2; 3.1 1.4 min), duration of recovery (group 1; 1.7 1.2, group 2; 2.5 1.3 min), and mean OAA/S scale (group 1; 3.8 1.6, group 2; 3.1 1.5) were not significantly different between the groups (mean SD). Inadequate sedation occurred more frequently in group 1 (13%) than group 2 (0%), and incidences of respiratory depression (

Automated responsiveness test and bispectral index monitoring during propofol and propofol/N2O sedation.

Sedation practice, especially when non-anaesthesia personnel are involved, requires efficient anaesthetic depth monitoring. Therefore, we used prediction probability (PK) to evaluate the performance of the bispectral index (BIS) of the EEG and automated responsiveness test (ART) to predict sedation depth and loss of subject's responsiveness during propofol sedation, with and without N2O. Twenty volunteers were studied during propofol administration with (N2O) and without (Air) N2O. The protocol consisted of sequential 15-min cycles. After a control period, propofol was infused to a target effect-site concentration of 0.25 microg/ml (N2O) or 1.5 microg/ml (Air), which was subsequently increased by 0.25 or 0.5 microg/ml, respectively, until loss of responsiveness was detected by loss of response to command [observer's assessment of alertness/sedation (OAA/S) score <or= 2]. Deeply sedated patients did not respond to ART indicating that the sensitivity was 1.0 with or without N2O. The specificity of ART was 0.24 with Air and 0.98 with N2O. The BIS was better than ART in predicting OAA/S score (PK = 0.84 vs. 0.77) and loss of responsiveness (PK = 0.87 vs. 0.69) during the Air trial. Nitrous oxide decreased the performance of BIS in predicting OAA/S score (PK = 0.76), but increased the performance of ART to predict loss of responsiveness (PK = 0.85). BIS and ART comparably predict sedation and loss of responsiveness. However, ART, because of its resistance to false-normal responses, might prove to be more useful on an individual patient basis - especially in the presence of agents that impair BIS sensitivity.

Self-reports are not related to objective assessments of cognitive function and sedation in patients with cancer pain admitted to a palliative care unit.

Cancer patients often report complaints of cognitive impairment and sedation. It is not well known if subjective complaints reflect objective assessments of cognitive function (CF) and sedation. We obtained self-reports of sedation and CF from 29 patients admitted to a palliative care unit and receiving morphine treatment. Sedation was reported on a verbal rating scale (VRS) and CF was reported using the EORTC QLQ-C30 health-related quality-of-life questionnaire CF scale. The self-reports were compared with objective assessments of sedation and CF by applying the Observer's Assessment of Alertness/Sedation (OAA/S) scale and Mini Mental State Examination (MMS), respectively. The assessments were repeated for seven patients who were readmitted to the palliative care unit. The patient self-reports of memory, concentration and sedation were dichotomized into noncomplainers and complainers. The percentages of complainers were 54%, 46% and 37% for memory, concentration and sedation, respectively. Patients who complained from difficulties with concentration or memory did not score differently from noncomplainers on objective assessments of CF (MMS score), but had a significantly higher level of fatigue. Patients complaining from sedation did not score differently from noncomplainers on objective assessments of sedation (OAA/S score). We observed no significant correlations between EORTC QLQ-C30 CF scale scores and MMS scores, or between VRS sedation scores and OAA/S scores. The study demonstrates a lack of relationship between patient self-reports and objective methods for assessing sedation and cognitive failure. This finding illustrates the importance of differentiating between observations and patient self-reports. The results also question the validity of patient self-reports for measurements of cognitive failure and sedation.

Changes in the rapidly extracted auditory evoked potentials index and the bispectral index during sedation induced by propofol or midazolam under epidural block

The bispectral index (BIS) and the rapidly extracted auditory evoked potentials index (A-line ARX Index or AAI) have been proposed as methods to measure the depth of sedation. A prospective study was designed to assess the performance of both these methods for measuring the depth of sedation induced by propofol or midazolam under epidural block. Thirty-two ASA I and II adult patients undergoing elective gynaecological surgery under low-thoracolumbar epidural block were studied. Eighteen patients received propofol (Group P: 20 mg bolus every 3 min) and 14 received midazolam (Group M: 0.5 mg bolus every 5 min) until an observer's assessment of alertness/sedation (OAA/S) scale score of 1 was achieved. AAI and BIS were monitored for different OAA/S scores. AAI and BIS decreased and increased following the changes on the patients' OAA/S scores and correlated with sedation significantly. During the onset phase, the coefficients of Spearman's rank correlation for AAI and BIS were respectively 0.958 and 0.898 (P < 0.001) for Group P, and 0.973 and 0.945 (P < 0.001) for Group M. During the recovery phase in Group P, the coefficients were respectively 0.946 and 0.702 (P < 0.001). Linear regression analysis showed that both AAI and BIS were linearly related to the OAA/S scores. The coefficients of Spearman's rank correlation and linear regression for AAI were all greater than those for BIS (P < 0.05). Both AAI and BIS correlated well with the depth of sedation induced by propofol or midazolam under epidural block. AAI may be more valuable when monitoring depth of sedation.

Automated responsiveness test (ART) predicts loss of consciousness and adverse physiologic responses during propofol conscious sedation.

The authors evaluated a device designed to provide conscious sedation with propofol (propofol-air), or propofol combined with 50% nitrous oxide (N2O; propofol-N2O). An element of this device is the automated responsiveness test (ART), a method for confirming that patients remain conscious. The authors tested the hypotheses that the ART predicts loss of consciousness and that failure to respond to the ART precedes sedation-induced respiratory or hemodynamic toxicity. The protocol consisted of sequential 15-min cycles in 20 volunteers. After a 15-min control period, propofol was infused to an initial target effect-site concentration of 0.0 microg/ml with N2O or 1.5 microg/ml with air. Subsequently, the propofol target effect-site concentration was increased by a designated increment (0.25 and 0.5 microg/ml) and the process repeated. This sequence was continued until loss of consciousness, as defined by an Observer's Assessment of Alertness/Sedation (OAA/S) score of 10/20 or less, or until an adverse physiologic event was detected. The OAA/S score at which only 50% of the volunteers were able to respond to the ART (P50) during propofol-N2O was 11.1 of 20 (95% confidence interval [CI]: 10.6-11.8); the analogous P50 was 11.8 of 20 (95% CI: 11.4-12.3) with propofol-air. Failure to respond to the ART occurred at a plasma propofol concentration of 0.7 +/- 0.6 microg/ml with propofol-N2O and 1.6 +/- 0.6 microg/ml with propofol-air, whereas loss of consciousness occurred at 1.2 +/- 0.8 microg/ml and 1.9 +/- 0.7 microg/ml, respectively. There were no false-normal ART responses. The ART can guide individual titration of propofol because failure to respond to responsiveness testing precedes loss of consciousness and is not susceptible to false-normal responses. The use of N2O with propofol for conscious sedation decreases the predictive accuracy of the ART.

EEG complexity as a measure of depth of anesthesia for patients.

A new approach for quantifying the relationship between brain activity patterns and depth of anesthesia (DOA) is presented by analyzing the spatio-temporal patterns in the electroencephalogram (EEG) using Lempel-Ziv complexity analysis. Twenty-seven patients undergoing vascular surgery were studied under general anesthesia with sevoflurane, isoflurane, propofol, or desflurane. The EEG was recorded continuously during the procedure and patients' anesthesia states were assessed according to the responsiveness component of the observer's assessment of alertness/sedation (OAA/S) score. An OAA/S score of zero or one was considered asleep and two or greater was considered awake. Complexity of the EEG was quantitatively estimated by the measure C(n), whose performance in discriminating awake and asleep states was analyzed by statistics for different anesthetic techniques and different patient populations. Compared with other measures, such as approximate entropy, spectral entropy, and median frequency, C(n) not only demonstrates better performance (93% accuracy) across all of the patients, but also is an easier algorithm to implement for real-time use. The study shows that C(n) is a very useful and promising EEG-derived parameter for characterizing the (DOA) under clinical situations.

Bispectral index monitoring of sedation during endoscopy

Background: No objective measure of the level of sedation is universally accepted. However, bispectral index monitoring is currently used to objectively measure sedation levels in several clinical settings. This study compares the temporal relationship of bispectral index levels versus the Observer's Assessment of Alertness/Sedation (OAA/S) scale for sedation during endoscopy and proposes a functional bispectral index range for endoscopic procedures. Methods: Fifty consecutive adults undergoing endoscopic retrograde cholangiopancreatography, colonoscopy, or esophagogastroduodenoscopy by a single endoscopist were studied. Intravenous sedation was achieved with diazepam and meperidine. Bispectral index levels (0 to 100) and OAA/S scores (1 to 5) were recorded every 3 minutes by a single trained observer. Results: There were significant temporal correlations between bispectral index levels and OAA/S scores (r = 0.59, p < 0.0001). Bispectral index levels and OAA/S scores corresponded with the need for additional sedation as determined clinically by the endoscopist. An OAA/S score of 3 corresponded to a bispectral index level of 81.49 ± 9.78. Conclusions: Bispectral index monitoring temporally correlates with the OAA/S scale and therefore provides an objective measure of sedation during endoscopy. This preliminary, observational study suggests that a bispectral index level near 82 corresponds with sufficient and functional sedation levels for endoscopy. (Gastrointest Endosc 2000;52:192-6.)

Correlations among Bispectral Index, Observer's Assessment of Alertness/sedation (OAA/S) Scale and Blood Concentration during Anesthesia Induction with Etomidate

Correlations among Bispectral Index, Observer's Assessment of Alertness/sedation (OAA/S) Scale and Blood Concentration during Anesthesia Induction with Etomidate

Remifentanil as an analgesic adjunct in local/regional anesthesia and in monitored anesthesia care.

Remifentanil as an analgesic adjunct in local/regional anesthesia and in monitored anesthesia care.

Clinical assessment of target-controlled infusion of propofol during monitored anesthesia care.

To determine the plasma concentrations of propofol required to achieve different levels of sedation during monitored anesthesia care. Sixty ASA I-II, 18-65 yr-old patients, received a target-controlled continuous iv infusion of propofol. The target plasma concentration of propofol (Cpt) was initially set at 0.4 microg x ml(-1). Two minutes after calculated equilibrium between plasma and effect-site concentrations, the Cpt of propofol was increased by 0.2 microg x ml(-1) steps until the patient showed no reaction to squeezing the trapezius. The level of sedation was assessed immediately before each increase in propofol Cpt using the Observer's Assessment of Alertness/Sedation (OAA/S) scale. The Cpt of propofol required to induce lethargic response to name was 1.3 microg x ml(-1) (5 degrees and 95 degrees percentiles: 1.0 - 1.8 microg x ml(-1)), to obtain response after loud and repeated calling name was 1.7 microg x ml(-1) (1.2 - 2.2 microg x ml(-1)), to obtain response after prodding or shaking was 2.0 microg x ml(-1) (1.6 - 2.6 microg x ml(-1)), to obtain response after squeezing the trapezius was 2.4 microg x ml(-1) (1.8 - 3.0 microg x ml(-1)). Patients showed no response after squeezing the trapezius at 2.8 microg x ml(-1) (2.0 - 3.6 microg x ml(-1)). Correlation between Cpt propofol and sedation scores were r = 0.76, P < 0.0001. Target-controlled infusion of propofol provided easy and safe management of intraoperative sedation, allowing fast and predictable deepening in the level of sedation, while minimizing systemic side effects of intravenous sedation due to the minimal risk of overdosing the drug.

ANESTHETIC OF CHOICE FOR OUTPATIENT IMMERSION LITHOTRIPSY

S319 INTRODUCTION: Epidural anesthesia has been considered the anesthetic technique of choice for immersion lithotripsy. However, more recent studies have demonstrated that both intravenous sedation-analgesia [1] and general anesthesia [2] can offer advantages over epidural anesthesia with respect to an improved recovery profile. This study was designed to compare intravenous sedation-analgesic and volatile anesthetic-based techniques in outpatients undergoing immersion lithotripsy procedures. METHODS: 49 consenting adult outpatients undergoing extracorporeal shock wave lithotripsy (ESWL) were randomly assigned to one of two anesthetic treatment groups according to an IRB-approved protocol. All patients received midazolam 2 mg iv, and fentanyl, 0.5 [micro sign]g/kg iv, for premedication. In Group 1 received propofol, 50 [micro sign]g[center dot]kg-1[center dot]min-1, which was subsequently titrated to maintain an observer's assessment of alertness/sedation (OAA/S) score >3, with 1=awake/alert to 5=asleep. If the patient complained of pain during the procedure, fentanyl 12.5-25 [micro sign]g iv was administered. In Group 2, anesthesia was induced with propofol 1.5 mg[center dot]kg-1 iv, and following loss of consciousness, a cuffed oropharyngeal airway (COPA) device was inserted and connected to the airway circuit. Maintenance of anesthesia consisted of desflurane 2-4% and nitrous oxide (N2 O) 60% in oxygen. Tachypnea (respiratory rate >20 bpm) was treated with fentanyl 12.5-25 [micro sign]g iv. At the end of the procedure, the inhaled anesthetics were discontinued and droperidol 0.625 mg iv, was administered as a prophylactic antiemetic. Recovery times were recorded from discontinuation of the anesthetic drugs until the patient was awake and oriented. In addition, times to achieving an OAA/S score of 1 and to discharged home were noted. Postoperative side effects were assessed in the recovery area (Phase II step-down unit) and at 24 hr after the procedure. Data were analyzed using Students' t-test and Chi-square test, with a p-value <0.05 considered statistically significant (*). Values are means +/- SD. RESULTS: The two anesthetic treatment groups were similar demographically (Table 1). Although the general anesthetic group required a longer time interval to awaken, the time required for the patients to return to an OAA/S score of 1 and to be discharged home were similar in both anesthetic treatment groups. Finally, there were no significant differences in the incidences of perioperative side effects.Table 1DISCUSSION: General anesthesia with propofol-desflurane-N2 O was an acceptable alternative to an intravenous sedative-analgesic technique involving propofol and fentanyl for outpatient ESWL procedures. The ability to "bypass" the recovery room after general anesthesia was facilitated by using a COPA airway device and resulted in recovery times that were comparable to a sedation-analgesia technique for outpatient immersion lithotripsy.

Use of Alfentanil and Propofol for Outpatient Monitored Anesthesia Care

Propofol and alfentanil are both rapid and short-acting drugs that can be used for sedation and analgesia during monitored anesthesia care (MAC). This study was designed to determine the optimal infusion rates of propofol and alfentanil when administered during local anesthesia. In this randomized, double-blind study, we evaluated the effects of different propofol infusion rates on the alfentanil requirement, level of sedation, intraoperative recall, respiratory and cardiovascular variables, and recovery. Seventy-two consenting ASA physical status I or II female outpatients undergoing breast biopsy procedures with local anesthesia were randomly assigned to one of four treatment groups. All patients received midazolam, 2 mg intravenously (IV) for premedication. Propofol was infused at 0, 25, 50, or 75 micro g [center dot] kg-1 [center dot] min-1 during the operation. Sedation was evaluated using the Observer's Assessment of Alertness/Sedation (OAA/S) scale at 5-min intervals by a blinded observer. Two minutes before the infiltration of the local anesthetic solution, a bolus of alfentanil, 2.5 micro g/kg IV, was administered, followed by a maintenance infusion of 0.5 micro g [center dot] kg-1 [center dot] min-1. The alfentanil infusion rate was subsequently varied to maintain patient comfort and stable cardiovascular and respiratory function. Pictures were shown at the start of the propofol infusion, upon initiating the alfentanil infusion, and at 45 min after the skin incision to evaluate recall of intraoperative events. Propofol produced dose-dependent increases in the level of sedation (with median OAA/S scores of 2-4, P < 0.05). Higher infusion rates of propofol (50-75 micro g [center dot] kg-1 [center dot] min-1) produced significant amnesia, opioid-sparing effects (alfentanil 0.3 +/- 0.2 vs 0.6 +/- 0.2 micro g [center dot] kg-1 [center dot] min-1), and less postoperative nausea and vomiting (P < 0.05). However, episodes of transient hemoglobin oxygen desaturation were more common in the deeply sedated patients. Thus, in healthy outpatients premedicated with midazolam, 2 mg IV, a propofol infusion of 25-50 micro g [center dot] kg-1 [center dot] min-1 in combination with an alfentanil infusion of 0.2-0.4 micro g [center dot] kg-1 [center dot] min (-1) is recommended for sedation and analgesia during MAC in the ambulatory setting. Implications: Sedation is often given during local anesthesia. This study demonstrated that administration of an intravenous anesthetic, propofol, in combination with an opioid infusion (i.e., alfentanil) to provide sedation analgesia and amnesia with a low incidence of side effects, such as nausea and vomiting and respiratory depression in outpatients premedicated with midazolam. (Anesth Analg 1997;85:566-72)

Electroencephalographic bispectral index correlates with intraoperative recall and depth of propofol-induced sedation.

The bispectral (BIS) index and 95% spectral edge frequency (SEF) of the electroencephalograph (EEG) have been used to study the anesthetic and sedative effects of intravenously (i.v.) administered drugs. This prospective study was designed to evaluate the effectiveness of the BIS index and 95% SEF for assessing the level of propofol-induced sedation and amnesia during regional anesthesia. Ten consenting adult patients undergoing surgery with regional anesthesia were administered propofol in increments of 10-20 mg i.v., every 5-10 min until they became unresponsive to tactile stimulation (i.e., mild prodding or shaking). The BIS index and 95% SEF were continuously recorded from a bifrontal montage (Fp1-Cz and Fp2-Cz) using the Aspect B500 monitor. The depth of sedation was assessed clinically at 5- to 10-min intervals using the observer's assessment of alertness/sedation (OAA/S) scale, with 1 = no response to tactile stimulation to 5 = wide awake. Each patient was shown a picture of an animal (cat) prior to administration of an initial dose of propofol, 40 mg i.v.. Subsequently, patients were administered intermittent bolus doses of propofol, 10-20 mg i.v., and shown different pictures upon achieving OAA/S scores of 4, 3, and 2 during the onset of and recovery from propofol-induced sedation. Picture recall was tested upon arrival of the patient in the postanesthesia care unit (PACU). Of the two EEG variables studied, the BIS index exhibited a better correlation with the OAA/S scores during both the onset (Spearman's rho = 0.744) and recovery (Spearman's rho = 0.705) phases of propofol-induced sedation. With the increasing depth of sedation, there was a progressive decrease in the BIS index (OAA/S score of 5, BIS = 94.5 +/- 2.9; 4, 93.3 +/- 3.3; 3, 89 +/- 6.1; 2, 80.1 +/- 8.7; 1, 75.6 +/- 7.5; mean +/- SD). Conversely, there was a progressive increase in the BIS value during recovery from propofol sedation (OAA/S score of 1, BIS = 75.6 +/- 7.5; 2, 82.4 +/- 10.5; 3, 84.9 +/- 5.9; 4, 93.8 +/- 0.8). Although the changes in the 95% SEF values were less consistent during the onset phase, this EEG variable increased from 16.4 +/- 5.0 to 19.3 +/- 5.6 as the OAA/S score increased from 1 to 4 during the recovery phase. Patient recall of the intraoperative pictures decreased with increasing depth of sedation and decreasing BIS values (OAA/S:% BIS:% recall = 5:94.5 +/- 2.9:100%; 4:93.4 +/- 3:63%; 3:87.3 +/- 6.1:40%; 2:80.8 +/- 8.3:0%; 1:75.6 +/- 7.5:0%). The BIS index appears to be a useful variable for assessing the depth of propofol-induced sedation. Increasing depth of sedation was associated with a significant decrease in intraoperative picture recall.

Electroencephalogram Bispectral Analysis Predicts the Depth of Midazolam-induced Sedation

The electroencephalogram (EEG) has been used to study the effects of anesthetic and analgesic drugs on central nervous system function. A prospective study was designed to evaluate the accuracy of various EEG parameters for assessing midazolam-induced sedation during regional anesthesia. Twenty-six consenting adult patients were administered 4.5-20 mg intravenous midazolam (in increments of 0.5-1 mg bolus doses every 6-10 min) until they became unresponsive to tactile stimulation (i.e., mild prodding or shaking). The EEG was continuously recorded from a bifrontal montage (FP1-Cz and FP2-Cz) to obtain the bispectral index (BI), 95% spectral edge frequency (SEF), median frequency (MF), and delta, theta, alpha, and beta power bands. Sedation was assessed clinically at 6-10-min intervals using the Observers' Assessment of Alertness/Sedation (OAA/S) scale, with 1 = no response (unconsciousness) to tactile stimulation to 5 = wide awake. The EEG parameters were correlated with the OAA/S scores using nonparametric Spearman's rank-correlation analysis. Kruskal-Wallis analysis of variance was used to determine significant changes in EEG parameters during the onset of and recovery from midazolam-induced sedation. Of the EEG parameters studied, the BI exhibited the best correlation with OAA/S scores during both the onset (Spearman's Rho = 0.815) and recovery (Spearman's Rho = 0.596) phases. With increasing sedation, there was a progressive decrease in the BI (OAA/S score of 5: BI = 95.4 +/- 2.3; 4: 90.3 +/- 4.5; 3:86.6 +/- 4.6; 2:75.6 +/- 9.7; 1:69.2 +/- 13.9). A similar pattern was found for the 95% SEF as the OAA/S score decreased from 4 to 1. Similarly, EEG-BI increased with recovery from the sedative effects of midazolam (OAA/S score = 2:BI = 75.2 +/- 10.2; 3:82.3 +/- 7.3; 4:90.8 +/- 6). However, no consistent changes were found with the other EEG parameters. The mean EEG values between OAA/S scores 3 and 2 and between OAA/S scores 2 and 1 during the onset and recovery phases from midazolam-induced sedation, defined as EEG50 values for response to verbal command (EEG50-VC) and to shaking of the head (EEG50-SH), were 79.3 +/- 8 and 70.8 +/- 14.3, respectively, for EEG-BI. The EEG-BI displayed the smallest coefficients of variation for the EEG50-VC and EEG50-SH values. The EEG-BI appears to be a useful parameter for assessing midazolam-induced sedation and can predict the likelihood of a patient responding to verbal commands or to shaking of the head during midazolam-induced sedation.

Comparison of Propofol Administration Techniques for Sedation During Monitored Anesthesia Care

Sixty-three outpatients undergoing breast biopsy procedures with local anesthesia were randomly assigned to receive propofol by intermittent bolus injections (n = 21), a conventional syringe infusion pump (n = 21), or a target-controlled infusion (TCI) device (n = 21) for intraoperative sedation. In the first two groups, an initial intravenous (IV) bolus of propofol (0.3 mg/kg) was administered and an attempt was made to maintain the sedation level at an Observer's Assessment of Alertness/Sedation (OAA/S) score of 3 or 4 with either intermittent bolus injections of propofol (10 mg) or a variable-rate infusion (25-100 micro gram centered dot kg-1 centered dot min-1). In the TCI group, the initial target concentration of propofol was set at 2 micro gram/mL and the target concentration was adjusted between 1 and 4 micro gram/mL in an attempt to maintain an OAA/S score of 3 or 4. Recovery was assessed using clinical criteria, visual analog scales (VAS), and the digit-symbol substitution test (DSST). The overall quality of sedation, operating conditions, and clinical recovery profiles were similar in all three treatment groups. The anesthesiologist had to intervene more frequently in the intermittent bolus injection group than in the two infusion groups. We conclude that the use of an infusion technique may allow the anesthesiologist more time for monitoring the patient by decreasing the number of interventions necessary to administer supplemental doses of the sedative medication during the operation. However, the cost of the IV drug delivery system may become an increasingly important factor in the future. (Anesth Analg 1995;81:486-91)

Validity and Reliability of the Observer??s

The Observer's Assessment of Alertness/Sedation (OAA/S) Scale was developed to measure the level of alertness in subjects who are sedated. This scale was tested in 18 subjects in a three-period crossover study to assess its reliability and its criterion, behavioral, and construct validity. After receiving either placebo or a titrated dose of midazolam to produce light or heavy sedation, each subject was administered two sedation scales (OAA/S Scale and a Visual Analogue Scale) and two performances tests (Digit Symbol Substitution Test and Serial Sevens Subtraction). Two raters individually evaluated the subject's level of alertness on each of the two sedation scales. The results obtained on the OAA/S Scale were reliable and valid as measured by high correlations between the two raters and high correlations between the OAA/S Scale and two of the three standard tests used in this study. The OAA/S Scale was sensitive to the level of midazolam administered; all pairwise comparisons were significant (p less than 0.05) for all three treatment levels at both test periods.