Desflurane induces more cerebral vasodilation than isoflurane at the same A-line autoregressive index level

BACKGROUND: Clinical use of desflurane in neuroanesthesia remains under debate. Comparison of dose-dependent vasodilatory properties between desflurane and isoflurane, the more traditional volatile agent for clinical neuroanesthesia, requires equianesthetic dosing of the agents. Reproducible neurophysiological measurements of the level of anesthesia in an individual, e.g. the A-line autoregressive index (AAI), can be used for an equipotent dosage of two volatile agents in the same individual. METHODS: Desflurane and isoflurane, in randomized order, were titrated to a stable AAI level of 15-20 in 18 ASA I or II patients. The mean flow velocity (Vmca) and pulsatility index (PI) in the middle cerebral artery were then measured with transcranial Doppler at an end-tidal CO(2) concentration of 4.4%. RESULTS: For desflurane Vmca was 11% higher [95% confidence interval (CI), 5-18%; P = 0.0020] and PI was 13% lower (95% CI, 3-23%; P = 0.0083) than for isoflurane. The mean arterial blood pressure did not differ between the agents. The fraction of MAC necessary for the intended AAI level was 35% lower (95% CI, 20-49%; P = 0.00016) with desflurane than with isoflurane. CONCLUSION: Desflurane was associated with more cerebral vasodilation than isoflurane at the same depth of anesthesia, as indicated by the AAI. This attributes further reason for caution in the use of desflurane in clinical neuroanesthesia. The difference between desflurane and isoflurane in the MAC fractions required for the same AAI level confirms the limitations of MAC in defining the level of anesthesia.     

Does the use of electroencephalographic bispectral index or auditory evoked potential index monitoring facilitate recovery after desflurane anesthesia in the ambulatory setting?

BACKGROUND: Analogous to the Bispectral Index (BIS) monitor, the auditory evoked potential monitor provides an electroencephalographic-derived index (AAI), which is alleged to correlate with the central nervous system depressant effects of anesthetic drugs. This clinical study was designed to test the hypothesis that intraoperative cerebral monitoring guided by either the BIS or the AAI value would facilitate recovery from general anesthesia compared with standard clinical monitoring practices alone in the ambulatory setting. METHODS: Sixty consenting outpatients undergoing gynecologic laparoscopic surgery were randomly assigned to one of three study groups: (1) control (standard practice), (2) BIS guided, or (3) AAI guided. Anesthesia was induced with 1.5-2.5 mg/kg propofol and 1-1.5 microg/kg fentanyl given intravenously. Desflurane, 3%, in combination with 60% nitrous oxide in oxygen was administered for maintenance of general anesthesia. In the control group, the inspired desflurane concentration was varied based on standard clinical signs. In the BIS- and AAI-guided groups, the inspired desflurane concentrations were titrated to maintain BIS and AAI values in targeted ranges of 50-60 and 15-25, respectively. BIS and AAI values, hemodynamic variables, and the end-tidal desflurane concentration were recorded at 5-min intervals during the maintenance period. The emergence times and recovery times to achieve specific clinical endpoints were recorded at 1- to 10-min intervals. The White fast-track and modified Aldrete recovery scores were assessed on arrival in the PACU, and the quality of recovery score was evaluated at the time of discharge home. RESULTS: A positive correlation was found between the AAI and BIS values during the maintenance period. The average BIS and AAI values (mean +/- SD) during the maintenance period were significantly lower in the control group (BIS, 41 +/- 10; AAI, 11 +/- 6) compared with the BIS-guided (BIS, 57 +/- 14; AAI, +/- 11) and AAI-guided (BIS, 55 +/- 12; AAI, 20 +/- 10) groups. The end-tidal desflurane concentration was significantly reduced in the BIS-guided (2.7 +/- 0.9%) and AAI-guided (2.6 +/- 0.9%) groups compared with the control group (3.6 +/- 1.5%). The awakening (eye-opening) and discharge times were significantly shorter in the BIS-guided (7 +/- 3 and 132 +/- 39 min, respectively) and AAI-guided (6 +/- 2 and 128 +/- 39 min, respectively) groups compared with the control group (9 +/- 4 and 195 +/- 57 min, respectively). More importantly, the median [range] quality of recovery scores was significantly higher in the BIS-guided (18 [17-18]) and AAI-guided (18 [17-18]) groups when compared with the control group (16 [10-18]). CONCLUSION: Compared with standard anesthesia monitoring practice, adjunctive use of auditory evoked potential and BIS monitoring can improve titration of desflurane during general anesthesia, leading to an improved recovery profile after ambulatory surgery.     

Is the ARX index a more sensitive indicator of anesthetic depth than the bispectral index during sevoflurane/nitrous oxide anesthesia?

BACKGROUND: During general anesthesia, hypnotic components have been monitored with electroencephalogram. The bispectral index is derived from a cortical electroencephalogram, but the A-line ARX index is the electroencephalographic response to auditory stimuli. The purpose of this study was to compare the changes of the A-line ARX index and the bispectral index during sevoflurane - nitrous oxide anesthesia. METHODS: One hundred females aged 30-60 years, and scheduled for partial mastectomy, were divided into two groups. Anesthesia was induced with sevoflurane 5% and nitrous oxide in oxygen for 3 min. A laryngeal mask airway was inserted, and anesthesia was maintained with sevoflurane 1-2% and nitrous oxide in oxygen. During surgery, the sevoflurane end-tidal concentration was kept at 0.5%, 1%, or 2% for 5 min before each measurement. Blood pressure, heart rate, and the A-line ARX index (n = 50), and the bispectral index (n = 50) were measured. RESULTS: Blood pressure and heart rate increased following laryngeal mask airway insertion and blood pressure decreased at 2% sevoflurane in both groups similarly. The A-line ARX index, but not the bispectral index, increased significantly by laryngeal mask airway insertion and skin incision. The A-line ARX index decreased at 2% sevoflurane compared with 0.5%, while the bispectral index remained unchanged. CONCLUSION: During sevoflurane-nitrous oxide anesthesia, the A-line ARX index might be a more sensitive indicator of anesthetic depth than the bispectral index.     

Effect of sevoflurane on the mid-latency auditory evoked potentials measured by a new fast extracting monitor

BACKGROUND: Mid-latency auditory evoked potentials (MLAEP) are widely suppressed during general anesthesia and may therefore be useful for assessment of the depth of anesthesia. However, interpretation of amplitudes and latencies in the AEP signal is time consuming. A new monitor (A-line) that quantifies the MLAEP into an index has therefore been developed. The present study aimed to assess the precision of a prototype of the new monitor and to test the hypothesis that the depth of anesthesia index shows a graded response with changing steady-state end-expiratory concentrations of sevoflurane. METHODS: We studied 10 ASA physical status I or II patients undergoing elective hysterectomy under combined epidural and general anesthesia by sevoflurane. Baseline auditory evoked potentials were recorded in the conscious patient immediately before induction of general anesthesia. Depth of anesthesia indices were recorded before anesthesia and at decreasing end-expiratory steady-state sevoflurane concentrations of 2.0%, 1.5%, 1.0% and 0.5%. All indices were recorded in duplicate 6 s apart. By use of an autoregressive model with exogenous input (ARX-model), the monitor extracted the AEP within 6 s. The depth of anesthesia AEP index calculated in this way was defined as the A-line ARX index (AAI). RESULTS: Approximately 95% of the differences between repeated recordings were 5 AAI-units or less. A wide interindividual variation was observed at each observation point. AAI at 1%, 1.5% and 2% end-expiratory concentration was significantly less than the baseline AAI obtained before induction of anesthesia (P < 0.001). AAI did not change significantly in the 1-2% concentration range. CONCLUSION: The new monitor was precise. Attenuation of the A-line ARX-index (AAI) for mid-latency auditory evoked potentials (MLAEP) during general anesthesia was profound. However, the monitor did not show a graded response with changing end-expiratory steady-state concentrations of sevoflurane.     

Does the Use of Electroencephalographic Bispectral Index or Auditory Evoked Potential Index Monitoring Facilitate Recovery after Desflurane Anesthesia in the Ambulatory Setting?

Background: Analogous to the Bispectral Index(R) (BIS(R)) monitor, the auditory evoked potential monitor provides an electroencephalographic-derived index (AAI), which is alleged to correlate with the central nervous system depressant effects of anesthetic drugs. This clinical study was designed to test the hypothesis that intraoperative cerebral monitoring guided by either the BIS or the AAI value would facilitate recovery from general anesthesia compared with standard clinical monitoring practices alone in the ambulatory setting.

Methods: Sixty consenting outpatients undergoing gynecologic laparoscopic surgery were randomly assigned to one of three study groups: (1) control (standard practice), (2) BIS guided, or (3) AAI guided. Anesthesia was induced with 1.5-2.5 mg/kg propofol and 1-1.5 [mu]g/kg fentanyl given intravenously. Desflurane, 3%, in combination with 60% nitrous oxide in oxygen was administered for maintenance of general anesthesia. In the control group, the inspired desflurane concentration was varied based on standard clinical signs. In the BIS- and AAI-guided groups, the inspired desflurane concentrations were titrated to maintain BIS and AAI values in targeted ranges of 50-60 and 15-25, respectively. BIS and AAI values, hemodynamic variables, and the end-tidal desflurane concentration were recorded at 5-min intervals during the maintenance period. The emergence times and recovery times to achieve specific clinical endpoints were recorded at 1- to 10-min intervals. The White fast-track and modified Aldrete recovery scores were assessed on arrival in the PACU, and the quality of recovery score was evaluated at the time of discharge home.

Results: A positive correlation was found between the AAI and BIS values during the maintenance period. The average BIS and AAI values (mean +/- SD) during the maintenance period were significantly lower in the control group (BIS, 41 +/- 10; AAI, 11 +/- 6) compared with the BIS-guided (BIS, 57 +/- 14; AAI, 18 +/- 11) and AAI-guided (BIS, 55 +/- 12; AAI, 20 +/- 10) groups. The end-tidal desflurane concentration was significantly reduced in the BIS-guided (2.7 +/- 0.9%) and AAI-guided (2.6 +/- 0.9%) groups compared with the control group (3.6 +/- 1.5%). The awakening (eye-opening) and discharge times were significantly shorter in the BIS-guided (7 +/- 3 and 132 +/- 39 min, respectively) and AAI-guided (6 +/- 2 and 128 +/- 39 min, respectively) groups compared with the control group (9 +/- 4 and 195 +/- 57 min, respectively). More importantly, the median [range] quality of recovery scores was significantly higher in the BIS-guided (18 [17-18]) and AAI-guided (18 [17-18]) groups when compared with the control group (16 [10-18]).     

Neuromuscular block with vecuronium reduces the rapidly extracted auditory evoked potentials index during steady state anesthesia

PURPOSE: During clinical monitoring, vecuronium appeared to reduce the rapidly extracted auditory evoked potentials index (A-line ARX index or AAI) to some extent. A prospective and randomized study was designed to analyze this phenomenon. METHODS: Forty adult patients undergoing elective surgery were studied. After tracheal intubation, anesthesia was maintained with an end-tidal isoflurane concentration (F(ET)ISO) of 1.0% for 20 min, then a 10-mL dose of either vecuronium 0.05 mg*kg(-1), 0.1 mg*kg(-1), 0.2 mg*kg(-1) or saline was administered in a randomized, double-blind design. The AAI and bispectral index (BI(hx)) were monitored throughout the study and analyzed off-line. RESULTS: BI(hx) was unaltered after the administration of saline or vecuronium. The mean of the averaged (per patient) AAI values recorded from two minutes to ten minutes after the administration of saline or vecuronium 0.05 mg*kg(-1) did not differ significantly from the corresponding mean recorded from 15 min to 20 min after F(ET)ISO maintained 1.0% (P = 0.678, 0.169), however after the administration of vecuronium 0.1 mg*kg(-1) or 0.2 mg*kg(-1), AAI was reduced from 18.3, 18.0 to 14.8, 13.4 (P = 0.016, 0.017). CONCLUSIONS: Neuromuscular block with vecuronium reduces AAI in patients during steady state anesthesia without surgical stimuli, while BI(hx) is unaltered. The cut-off values of AAI for events should be determined according to the level of neuromuscular blockade when monitoring the depth of anesthesia/sedation.     

Sevoflurane induces less cerebral vasodilation than isoflurane at the same A-line autoregressive index level

BACKGROUND: The use of sevoflurane in neuroanesthesia is still under debate. Comparison of dose-dependent vasodilatory properties between sevoflurane and isoflurane, the more traditional neuroanesthetic agent, requires comparable dosing of the agents. A-line autoregressive index (AAI) provides reproducible individual measurement of anesthetic depth. METHODS: Sevoflurane and isoflurane, in randomized order, were titrated to a stable AAI of 15-20 in each of 18 ASA I or II patients. The mean flow velocity (Vmca) and pulsatility index (PI) in the middle cerebral artery were measured with transcranial Doppler at an end-tidal CO2 of 4.5%. RESULTS: For sevoflurane Vmca was 18% lower [95% confidence interval (CI) 12-22%; P < 0.00001] and PI was 23% higher (95% CI 12-33%; P = 0.0013) than for isoflurane. Mean arterial blood pressure did not differ between the two agents. The minimum alveolar concentration (MAC) fraction necessary to reach the intended AAI level was 13% higher (95% CI 5-20%; P = 0.0079) with sevoflurane than with isoflurane. CONCLUSION: Sevoflurane induced less cerebral vasodilation than isoflurane at the same depth of anesthesia, measured by AAI, and hence seems more favorable for clinical neuroanesthesia. In our opinion the difference between sevoflurane and isoflurane in the MAC fraction required to attain the same AAI level demonstrates the limitations of MAC in defining the level of anesthesia.     

Effect of Auditory Evoked Potential Index Monitoring on Anesthetic Drug Requirements and Recovery Profile after Laparoscopic Surgery: A Clinical Utility Study

Background: The auditory evoked potential (AEP) monitor provides an electroencephalogram-derived index (AAI) that has been reported to correlate with the central nervous system depressant effects of anesthetic drugs. This clinical utility study was designed to test the hypothesis that AAI-guided administration of the maintenance anesthetics and analgesics would improve their titration and thereby provide a faster recovery from general anesthesia.

Methods: Seventy consenting patients undergoing elective general surgery procedures were randomly assigned to either a control (standard clinical practice) or AEP-monitored group. Although the AEP monitor was connected to all patients, the information from the monitor was only made available to the anesthesiologists assigned to patients in the AEP-monitored group. In the AEP-monitored group, the inspired desflurane concentration was titrated to maintain an AAI value of 15-20. In the control group, the inspired desflurane concentration was varied based on standard clinical signs. The AAI values and hemodynamic variables, as well as end-tidal desflurane concentrations, were recorded at 3- to 5-min intervals. The recovery times to achieve a White fast-track score greater than 12 and an Aldrete score of 10, as well as the actual duration of the PACU stay, were evaluated at 5- to 10-min intervals. Patient satisfaction with recovery from anesthesia was assessed using a 100-point verbal rating scale at 24 h after surgery.

Results: The average intraoperative AAI value in the AEP-monitored group was significantly higher than in the control group (16 +/- 5 vs. 11 +/- 8, P < 0.05). Use of the AEP monitor reduced the desflurane requirement by 26% compared to the control group (P < 0.01). In addition, the AEP-monitored group received less intraoperative fentanyl (270 +/- 120 vs. 390 +/- 203 [mu]g, P < 0.05) and more rapidly achieved fast-track eligibility (29 +/- 19 vs. 56 +/- 41 min, P < 0.05). The time required to achieve an Aldrete score of 10 (60 +/- 31 vs. 98 +/- 55 min) and the duration of stay in the recovery room (78 +/- 32 vs. 106 +/- 54 min) were also significantly reduced in the AEP-monitored (vs. control) group (P < 0.05).     

The A-line ARX index may be a more sensitive detector of arousal than the bispectral index during propofol-fentanyl-nitrous oxide anesthesia: A preliminary investigation

PURPOSE: To compare changes in the A-line ARX index (AAI) by the Alaris AEP monitor(TM) with those of the bispectral index (BIS) during propofol-fentanyl-nitrous oxide anesthesia. METHODS: Eighty female patients undergoing partial mastectomy were randomly allocated to AAI or BIS (40 per group). Anesthesia was induced with propofol 2 mg x kg(-1) and fentanyl 3 micro g x kg(-1) during the inhalation of oxygen. A laryngeal mask airway (LMA) #3 was inserted. Anesthesia was maintained with propofol 4 mg x kg(-1) x hr(-1), fentanyl 1 micro g x kg(-1) given at the start of surgery, and nitrous oxide 4 L x min(-1) in oxygen 2 L x min(-1). Blood pressure, heart rate, and AAI or BIS were monitored, including recovery time of the index after disturbance by electrocautery. RESULTS: The AAI but not the BIS increased significantly with LMA insertion and skin incision, while blood pressure and heart rate did not change. The BIS decreased from 87 +/- 7 to 30-60 while the AAI decreased from 75 +/- 8 to 10-25 during anesthesia. The increase of the AAI was larger than that of the BIS at recovery from anesthesia. The variation of the index was smaller in the AAI than in the BIS. Recovery time of the index after electrocautery was significantly longer in the BIS group (21 +/- 9 sec) than that in the AAI group (5 +/- 3 sec). CONCLUSIONS: During propofol-fentanyl-nitrous oxide anesthesia, the AAI responded to LMA insertion or surgical incision, but not the BIS, and the AAI had smaller variations. The AAI recovered faster from the disturbance by electrocautery than the BIS. Thus, the AAI may be a more sensitive and useful detector of arousal than the BIS.     

Auditory evoked potential monitoring with the AAITM-index during spinal surgery: decreased desflurane consumption

Background: The auditory evoked potential (AEP) is sensitive to the depth of anesthesia. The A-line monitor is a novel device that processes the amplitude and latency of the AEP during the mid-latency time window to provide a simple numerical index, the AAI™-index. The hypothesis of the present study was that titration of anesthetic depth (desflurane) by means of the AAI™-index could decrease the consumption of the main anesthetic and shorten emergence times.
Methods: Thirty ASA I–II patients scheduled for elective open spine surgery under general anesthesia were randomly allocated to two groups. Group I (n=15), the main anesthetic, desflurane, was titrated with a target AAI™-index of 20±5. Group II (n=15), desflurane was titrated according to routine clinical signs, including heart rate, blood pressure, sweating and tears. No fixed MAC-multiple was sought. The primary study variable was desflurane consumption; and secondary study variables were time to extubation and orientation.
Results: All patients had an uncomplicated course and no patients showed signs of awareness or had any recall postoperatively. AAI™-index guidance reduced desflurane consumption by 29% and improved emergence. Time until extubation and orientation and ability to state name and date of birth was significantly shortened among AAI™-index titrated patients.
Conclusion: Titrating depth of desflurane anesthesia using AAI™-index guidance decreased main anesthetic consumption and improved emergence during spine surgery.     

Comparison of auditory evoked potentials and the A-line ARX Index for monitoring the hypnotic level during sevoflurane and propofol induction

BACKGROUND: Extraction of the middle latency auditory evoked potentials (AEP) by an auto regressive model with exogenous input (ARX) enables extraction of the AEP within 1.7 s. In this way, the depth of hypnosis can be monitored at almost real-time. However, the identification and the interpretation of the appropriate signals of the AEP could be difficult to perform during the anesthesia procedure. This problem was addressed by defining an index which reflected the peak amplitudes and latencies of the AEP, developed to improve the clinical interpretation of the AEP. This index was defined as the A-line Arx Index (AAI). METHODS: The AEP and AAI were compared with the Modified Observers Assessment of Alertness and Sedation Scale (MOAAS) in 24 patients scheduled for cardiac surgery, anesthetized with propofol or sevoflurane. RESULTS: When comparing the AEP peak latencies and amplitudes and the AAI, measured at MOAAS level 5 and level 1, significant differences were achieved. (mean(SD) Nb latency: MOAAS 5 51.1 (7.3) ms vs. MOAAS 1: 68.6 (8.1) ms; AAI: MOAAS 5 74.9 (13.3) vs. MOAAS 1 20.7 (4.7)). Among the recorded parameters, the AAI was the best predictor of the awake/anesthetized states. CONCLUSION: We conclude that both the AAI values and the AEP peak latencies and amplitudes correlated well with the MOAAS levels 5 (awake) and 1 (anesthetized).     

听觉诱发电位指数监测患者吸入异氟醚麻醉深度的准确性

Objective To evaluate the accuracy of auditory evoked potential index (AAI) in monitoring the anesthetic depth during isoflurane anesthesia.Methods Thirty ASA Ⅰ or Ⅱ patients aged 18-55 years and undergoing elective surgery under general anesthesia were enrolled in this study. The patients were unpremedicated. Anesthesia was induced with midazolam 0.05 mg/kg, fentanyl 3 μg/kg and propofol 1 mg/kg. Tracheal intubation was facilitated with recuronium 0.1 mg/kg. The patients were mechanically ventilated (VT:40 mm Hg. Anesthesia was maintained with isoflurane inhalation and intermittent intravenous boluses of vecuronium. Isoflurane was started with high-flow (FGF, 3 L/min) for 12 min followed by low-flow (LGF, 0.5 L/min). The inspired isoflurane concentration was set at 3%. The electrocardiogram (ECG), mean arterial pressure (MAP), heart rate (HR), pulse oxygen saturation (SpO2), end-tidal isoflurane concentration and AAI were continuously monitored during anesthesia and recorded before induction of anesthesia (baseline, To ), immediately after induction (T1), immediately before isoflurane inhalation (T2), at 3 min(T3), 6 min (T4), 9 min (T5) and 12 min (T6) during high-flow wash-in and at the end-tidal isoflurane concentrations of 0.8 MAC (T7), 1.0 MAC (T8) and 1.3 MAC (T9) during low-flow inhalation of isoflurane, respectively.Results AAI decreased gradually while the end-tidal isoflurane concentration increased during high-flow wash-in. And AAI was negatively correlated with the end-tidal isoflurane concentrations ( r = -0.896, P ＜ 0.01 ) during low-flow inhalation of isoflurane anesthesia.     

Effect of auditory evoked potential index monitoring on anesthetic drug requirements and recovery profile after laparoscopic surgery: a clinical utility study

BACKGROUND: The auditory evoked potential (AEP) monitor provides an electroencephalogram-derived index (AAI) that has been reported to correlate with the central nervous system depressant effects of anesthetic drugs. This clinical utility study was designed to test the hypothesis that AAI-guided administration of the maintenance anesthetics and analgesics would improve their titration and thereby provide a faster recovery from general anesthesia. METHODS: Seventy consenting patients undergoing elective general surgery procedures were randomly assigned to either a control (standard clinical practice) or AEP-monitored group. Although the AEP monitor was connected to all patients, the information from the monitor was only made available to the anesthesiologists assigned to patients in the AEP-monitored group. In the AEP-monitored group, the inspired desflurane concentration was titrated to maintain an AAI value of 15-20. In the control group, the inspired desflurane concentration was varied based on standard clinical signs. The AAI values and hemodynamic variables, as well as end-tidal desflurane concentrations, were recorded at 3- to 5-min intervals. The recovery times to achieve a White fast-track score greater than 12 and an Aldrete score of 10, as well as the actual duration of the PACU stay, were evaluated at 5- to 10-min intervals. Patient satisfaction with recovery from anesthesia was assessed using a 100-point verbal rating scale at 24 h after surgery. RESULTS: The average intraoperative AAI value in the AEP-monitored group was significantly higher than in the control group (16 +/- 5 vs. 11 +/- 8, P < 0.05). Use of the AEP monitor reduced the desflurane requirement by 26% compared to the control group (P < 0.01). In addition, the AEP-monitored group received less intraoperative fentanyl (270 +/- 120 vs. 390 +/- 203 microg, P < 0.05) and more rapidly achieved fast-track eligibility (29 +/- 19 vs. 56 +/- 41 min, P < 0.05). The time required to achieve an Aldrete score of 10 (60 +/- 31 vs. 98 +/- 55 min) and the duration of stay in the recovery room (78 +/- 32 vs. 106 +/- 54 min) were also significantly reduced in the AEP-monitored (vs. control) group (P < 0.05). CONCLUSION: Use of AEP monitoring as an adjunct to standard clinical monitors improved titration of anesthetic drugs, thereby facilitating the early recovery process after laparoscopic surgery.     

Epidural lidocaine decreases sevoflurane requirement for adequate depth of anesthesia as measured by the Bispectral Index monitor

BACKGROUND: Epidural anesthesia potentiates sedative drug effects and decreases minimum alveolar concentration (MAC). The authors hypothesized that epidural anesthesia also decreases the general anesthetic requirements for adequate depth of anesthesia as measured by Bispectral Index (BIS). METHODS: After premedication with 0.02 mg/kg midazolam and 1 microg/kg fentanyl, 30 patients aged 20-65 yr were randomized in a double-blinded fashion to receive general anesthesia with either intravenous saline placebo or intravenous lidocaine control (1-mg/kg bolus dose; 25 microg x kg(-1) x min(-1)). A matched group was prospectively assigned to receive epidural lidocaine (15 ml; 2%) with intravenous saline placebo. All patients received 4 mg/kg thiopental and 1 mg/kg rocuronium for tracheal intubation. After 10 min of a predetermined end-tidal sevoflurane concentration, BIS was measured. The ED50 of sevoflurane for each group was determined by up-down methodology based on BIS less than 50 (MAC(BIS50)). Plasma lidocaine concentrations were measured. RESULTS: The MAC(BIS50) of sevoflurane (0.59% end tidal) was significantly decreased with lidocaine epidural anesthesia compared with general anesthesia alone (0.92%) or with intravenous lidocaine (1%; P < 0.0001). Plasma lidocaine concentrations in the intravenous lidocaine group (1.9 microg/ml) were similar to those in the epidural lidocaine group (2.0 microg/ml). CONCLUSIONS: Epidural anesthesia reduced by 34% the sevoflurane required for adequate depth of anesthesia. This effect was not a result of systemic lidocaine absorbtion, but may have been caused by deafferentation by epidural anesthesia or direct rostral spread of local anesthetic within the cerebrospinal fluid. Lower-than-expected concentrations of volatile agents may be sufficient during combined epidural-general anesthesia.     

Level of sedation evaluation with Cerebral State Index and A-Line Arx in children undergoing diagnostic procedures

BACKGROUND: Monitoring of anesthesia depth is difficult clinically, particularly in children. The aim of this study was to assess the correlation existing between CSI (Cerebral State Index), or AAI (A-line ARX) and a clinical sedation scale such as UMSS (University of Michigan Sedation Scale), during deep sedation with propofol in children undergoing diagnostic procedures. METHODS: Twenty ASA I and II children, scheduled to undergo deep sedation for magnetic resonance imaging (MRI) or Esophagogastroduodenoscopy (EGDS), were enrolled. The patients were randomly assigned to receive depth of anesthesia monitoring with CSI or AAI. The anesthetist administered repeated doses of propofol every 10 s to a UMSS score of 3-4. An attending anesthetist, not involved in drug administration, recorded time and doses of sedation medications, vital signs, UMSS score and CSI or AAI score. All the evaluations were recorded at awake state (baseline), every 10 s until an UMSS score of 3-4 and every 3 min until the children were awake. RESULTS: We enrolled 13 males and seven females ranging in age from 8 months to 7 years. After induction of anesthesia CSI and AAI scores decreased and from the end of the procedure to emergence the two scores increased. The CSI data showed a strong correlation with the UMSS scores (r = -0.861; P < 0.0001); we found a similar correlation between the AAI data and the UMSS scores (r = -0.823; P < 0.0001). CONCLUSIONS: Our study suggests that CSI and AAI may be two, real-time and objective tools to assess induction and emergence during propofol sedation in children undergoing EGDS and MRI.     

Desflurane increases brain tissue oxygenation and pH

Background Desflurane anesthesia can produce cerebral metabolic depression and increase cerebral blood flow. We evaluated the effect of desflurane on brain tissue oxygen pressure (PO₂), carbon dioxide pressure (PCO₂) and pH during neurosurgery.
Methods: Following a craniotomy, the dura was opened and a Paratrend 7 sensor, which measures PO₂, PCO₂, pH and temperature, was inserted into brain tissue. In 6 control patients in group 1, anesthesia was maintained constant with 3% end-tidal desflurane over 60 min, including a 30-min stabilization period. In group 2, 9 patients were ventilated with 3% desflurane under baseline conditions. After a 30-min stabilization period, baseline tissue gases and pH were measured and end-tidal desflurane was increased to 6% and then 9% for 15-min intervals. Mean arterial pressure (MAP) was maintained with intravenous phen-ylephrine.
Results: Under baseline conditions, cardiovascular and brain tissue measures were similar between the 2 groups. Increasing end-tidal desflurane from 3% to 9% produced burst-suppression EEG in all patients and significantly increased tissue PO₂ and pH and decreased PCO₂. No parameters changed significantly in the control group during steady-state anesthesia.
Conclusion: These results show that 9% desflurane can improve brain tissue metabolic status before temporary brain artery occlusion if cerebral perfusion pressure is maintained. This may be particularly important in patients with symptoms of ischemia before surgery.     

Does epidural anesthesia have general anesthetic effects? A prospective, randomized, double-blind, placebo-controlled trial

BACKGROUND: Clinically, patients require surprisingly low end-tidal concentrations of volatile agents during combined epidural-general anesthesia. Neuraxial anesthesia exhibits sedative properties that may reduce requirements for general anesthesia. The authors tested whether epidural lidocaine reduces volatile anesthetic requirements as measured by the minimum alveolar concentration (MAC) of sevoflurane for noxious testing cephalad to the sensory block. METHODS: In a prospective, randomized, double-blind, placebo-controlled trial, 44 patients received 300 mg epidural lidocaine (group E), epidural saline control (group C), or epidural saline-intravenous lidocaine infusion (group I) after premedication with 0.02 mg/kg midazolam and 1 microg/kg fentanyl. Tracheal intubation followed standard induction with 4 mg/kg thiopental and succinylcholine 1 mg/kg. After 10 min or more of stable end-tidal sevoflurane, 10 s of 50 Hz, 60 mA tetanic electrical stimulation were applied to the fifth cervical dermatome. Predetermined end-tidal sevoflurane concentrations and the MAC for each group were determined by the up-and-down method and probit analysis based on patient movement. RESULTS: MAC of sevoflurane for group E, 0.52+/-0.18% (+/- 95% confidence interval [CI]), differed significantly from group C, 1.18+/-0.18% (P < 0.0005), and from group I, 1.04+/-0.18% (P < 0.001). The plasma lidocaine levels in groups E and I were comparable (2.3+/-1.0 vs. 3.0+/-1.2 microg/ml +/- SD). CONCLUSIONS: Lidocaine epidural anesthesia reduced the MAC of sevoflurane by approximately 50%. This MAC sparing is most likely caused by indirect central effects of spinal deafferentation and not to systemic effects of lidocaine or direct neural blockade. Thus, lower concentrations of volatile agents than those based on standard MAC values may be adequate during combined epidural-general anesthesia.     

Effect of preoperative epidural morphine administration on desflurane requirements during gynecologic surgery

BACKGROUND AND OBJECTIVES: The goal of this study is to examine the influence of epidural morphine on the end-tidal desflurane concentration titrated to maintain the bispectal index (BIS) values between 40 and 60 during gynecologic surgery. METHODS: Forty patients undergoing transabdominal hysterectomy under general anesthesia were randomly and prospectively assigned to 1 of 2 study groups: group saline (group S) and group morphine (group M). After placing an epidural catheter at L3-4 or L4-5, patients received either 10 mL of saline or 4 mg of morphine in 10 mL of saline approximately 60 minutes before anesthesia induction. Anesthesia maintenance was provided with desflurane and nitrous oxide in oxygen with a ratio of 2:1 by an anesthesiologist blinded to the group. Measurements included BIS value, end tidal desflurane concentration, heart rate, and blood pressure before surgery and every 10 minutes during surgery. RESULTS: Although there was a tendency to slightly lower end-tidal desflurane concentrations in the morphine group, this difference did not reach statistical significance at any time. In the morphine group, the heart rate was lower than in the saline group at 20, 30, 40, and 50 minutes of surgery (P < .05). BIS values were similar throughout surgery. CONCLUSIONS: Preoperative administration of epidural morphine does not reduce desflurane requirements in patients undergoing gynecologic surgery.     

硬膜外复合全身麻醉对梗阻性黄疸术后肠屏障功能的影响

目的探讨硬膜外复合全身麻醉对梗阻性黄疸患者术后肠屏障功能的影响。方法选择梗阻性黄疸拟行手术治疗患者40例,男15例,女25例,年龄26~65岁,ASAⅠ~Ⅲ级,手术时间90~320min,血清总胆红素(TBIL)水平100μmol/L。所有患者随机分为全凭静脉麻醉组(GA组)和硬膜外复合全麻组(GE组),每组20例。GA组患者面罩吸氧后快速诱导气管插管行全身麻醉,GE组患者取左侧卧位行T8~9或T9~10间隙硬膜外穿刺并置管,改平卧位后予以2%利多卡因5ml试验量,5min确认无麻醉并发症及其他异常后行全身麻醉。于入手术室后(T1)、术毕(T2)、术后24h(T3)和术后48h(T4)分别采集外周静脉血,采用ELISA法测定血浆D-乳酸(D-LA)浓度;PCR技术定性检测大肠杆菌特异性β-半乳糖苷酶基因BG;提取血浆标本中的细菌DNA,进行PCR扩增,凝胶电泳后扫描凝胶并分析结果。结果与T1时比较,T2~T4时两组血浆D-LA浓度明显逐步升高(P0.05);T2~T4时GA组D-LA浓度明显高于GE组(P0.05)。PCR技术定性检测大肠杆菌特异性半乳糖苷酶基因BG,扩增长度为762bp。T1时两组患者大肠杆菌DNA检测结果均为阴性,术后两组患者大肠杆菌DNA阳性例数随时间依次增多,且T4时GA组明显高于GE组(P0.05)。结论与全凭静脉麻醉比较,硬膜外复合全身麻醉能够减轻梗阻性黄疸患者术后肠屏障功能的损伤。     

A-line, bispectral index, and estimated effect-site concentrations: a prediction of clinical end-points of anesthesia

Autoregressive modeling with exogenous input of middle-latency auditory evoked potentials (A-Line AEP index, AAI) has been developed for monitoring depth of anesthesia. We investigated the prediction of recovery and dose-response relationship of desflurane and AAI or bispectral index (BIS) values. Twenty adult men scheduled for radical prostatectomy were recruited. To minimize opioid effects, analgesia was provided by a concurrent epidural in addition to the general anesthetic. Electrodes for AAI and BIS monitoring and a headphone for auditory stimuli were applied. Propofol and remifentanil were used for anesthetic induction. Maintenance of anesthesia was with desflurane only. For comparison to AAI and BIS monitor parameters, pharmacokinetic models for desflurane and propofol distribution and effect-site concentrations were used to predict clinical end-points (Prediction probability P(K)). Patients opened their eyes at an AAI value of 47 +/- 20 and a BIS value of 77 +/- 14 (mean +/- sd), and the prediction probability for eye opening was P(K) = 0.81 for AAI, P(K) = 0.89 for BIS, and P(K) = 0.91 for desflurane effect-site concentration. The opening of eyes was best predicted by the calculated desflurane effect-site concentration. The relationship between predicted desflurane effect-site concentration versus AAI and BIS was calculated by nonlinear regression analysis (r = 0.75 for AAI and r = 0.80 for BIS). The correlation between BIS and clinical end-points of anesthesia or the desflurane effect-compartment concentration is better than for the AAI.