Ngai Liu

Titration of propofol for anesthetic induction and maintenance guided by the bispectral index: closed-loop versus manual control: a prospective, randomized, multicenter study.

Background: This report describes a closed-loop titration of propofol target control infusion based on a proportional-differential algorithm guided by the Bispectral Index (BIS) allowing induction and maintenance of general anesthesia and compares this to manual propofol target control infusion. Methods: One hundred sixty-four patients scheduled to undergo elective minor or major surgery were prospectively randomized in a multicenter study into the closed-loop (n = 83) or manual target control infusion group (n = 81). The goal was to reach a BIS target of 50 during induction and to maintain it between 40 and 60 during maintenance. For both groups, remifentanil target control infusion was adjusted manually, and ventilation was without nitrous oxide. Results: Closed-loop control was able to provide anesthesia induction and maintenance for all patients. During induction, propofol consumption was lower in the closed-loop group (1.4 ± 0.5 vs. 1.8 ± 0.6 mg/kg; P < 0.0001), but the duration was longer (320 ± 125 vs. 271 ± 120 s; P < 0.0002). Adequate anesthesia maintenance, defined as the BIS in the range of 40–60, was significantly higher in the closed-loop group (89 ± 9 vs. 70 ± 21%; P < 0.0001), with a decrease of the occurrence of BIS less than 40 (8 ± 8 vs. 26 ± 22%; P < 0.0001). Time from discontinuation of propofol infusion to tracheal extubation was shorter in the closed-loop group (7 ± 4 vs. 10 ± 7 min; P < 0.017). Unwanted somatic events and hemodynamic instability were similar. Conclusion: Automatic control of consciousness using the BIS is clinically feasible and outperforms manual control.

Clonidine Comparably Decreases the Thermoregulatory Thresholds for Vasoconstriction and Shivering in Humans

Background:Clonidine stops postoperative shivering, but its underlying mechanism of action is unknown. Clonidine may impair central control of thermoregulation or act on peripheral receptors. Accordingly, the authors tested the hypothesis that clonidine reduces both the vasoconstriction and shivering thresholds, a pattern consistent with central thermoregulatory impairment. Methods:Seven healthy volunteers participated in the study. Thermoregulatory vasoconstriction was evaluated using forearm minus fingertip, skin-temperature gradients; values exceeding 4° C were considered to be significant vasoconstriction. Systemic oxygen consumption (&OV0312;O2) was measured with a canopy system. In addition, shivering was qualitatively evaluated using a simple scale, graduated from 0 (no shivering) to 2 (intense shivering). The tympanic membrane temperatures triggering significant vasoconstriction and grade 1 shivering were considered to be the thresholds for the two thermoregulatory responses. Measurements were performed after a 10-min steady state period and during cooling by central venous infusion of Ringers lactate solution at 4° C. Each subject was evaluated at two sessions, separated by at least 48 h. They were randomly and blindly assigned to received either an intravenous bolus of 75 µg clonidine or a placebo before cooling. When the shivering score equaled 2, 75 µg clonidine was injected intravenously, and repeated if necessary, to completely stop shivering. Results:Clonidine significantly decreased the thermoregulatory threshold for shivering by 0.6 ± 0.3° C (mean ± SD). Similarly, the threshold for cutaneous vasoconstriction was significantly reduced by 0.5 ± 0.2° C. Additional clonidine administration always stopped shivering, at whatever temperature it occurred. Conclusions:This study confirms that clonidine administration stops shivering, and suggests that it acts by impairing central thermoregulatory control. That an additional dose of clonidine stops shivering in subjects already given one dose, indicates that the effect of clonidine is dose dependent.

Closed-loop Coadministration of Propofol and Remifentanil Guided by Bispectral Index: A Randomized Multicenter Study

BACKGROUND:We have developed a proportional-integral-derivative controller allowing the closed-loop coadministration of propofol and remifentanil, guided by a Bispectral Index (BIS) monitor, during induction and maintenance of general anesthesia. The controller was compared with manual target-controlled infusion. METHODS:In a multicenter study, 196 surgical patients were randomly assigned to dual closed-loop or manual administration of propofol and remifentanil. Comparison between groups was evaluated by calculating a global score that characterized the overall performance of the controller including the percentage of adequate anesthesia, defined as BIS between 40 and 60, the median absolute performance error, and wobble. Secondary outcomes included occurrence of burst suppression ratio, time to tracheal extubation, and drug consumption. RESULTS:Eighty-three patients assigned to dual-loop control and 84 patients assigned to manual control completed the study. The global score and the percentage of time with BIS between 40 and 60 were better in the dual-loop group (26 ± 11 vs 43 ± 40, P < 0.0001; 82% ± 12% vs 71% ± 19%, P < 0.0001). Overshoot (BIS <40), undershoot (BIS >60), and burst suppression ratio were all significantly less common in the dual-loop group. Modifications to the propofol and remifentanil infusions were more frequent, and adjustments smaller in the dual-loop group. Remifentanil consumption was greater (0.22 ± 0.07 vs 0.16 ± 0.07 &mgr;g · kg−1 · min−1; P < 0.0001) and the speed to tracheal extubation was shorter (10 ± 4 vs 11 ± 5 minutes; P = 0.02) in the dual-loop group. CONCLUSION:The controller allows the automated delivery of propofol and remifentanil and maintains BIS values in predetermined boundaries during general anesthesia better than manual administration.

The influence of a muscle relaxant bolus on bispectral and datex-ohmeda entropy values during propofol-remifentanil induced loss of consciousness.

Studies investigating the influence of muscle relaxants on the bispectral index have yielded contradictory results. In our prospective, randomized, double-blind experiments, patients received a fixed target concentration of remifentanil along with a target-controlled infusion of propofol, titrated until loss of consciousness. Two minutes after loss of consciousness, the study group received a bolus injection of atracurium, whereas the control group received a placebo. The following variables were recorded: bispectral index, spectral edge frequency, electromyographic activity, state entropy, and response entropy provided by the Datex-Ohmeda Entropy monitor. Similar values were obtained in both groups at loss of consciousness. Placebo administration induced a decrease in bispectral index (P < 0.002), spectral edge frequency (P < 0.05), electromyographic activ-ity (P < 0.02), state entropy (P < 0.05), and response entropy (P < 0.01) compared with the values measured at loss of consciousness. Atracurium administration induced a decrease in bispectral index (P < 0.0001), spectral edge frequency (P < 0.01), electromyographic activity (P < 0.0001), state entropy (P < 0.0001), and response entropy (P < 0.0001) values. Decreases in bispectral index (P < 0.05), electromyographic activity (P < 0.0001), and response entropy (P < 0.01) were larger after atracurium than placebo injection. In lightly anesthetized patients, myorelaxant administration decreases bispectral index and response entropy, but not state entropy values.

The Effects of Inhaled Nitric Oxide and Its Combination with Intravenous Almitrine on Pao2 During One-lung Ventilation in Patients Undergoing Thoracoscopic Procedures

The aim of this study was to assess whether hypoxemia during one-lung ventilation (OLV) can be prevented by inhaled nitric oxide (NO) (Part I) or by its combination with intravenous (IV) almitrine (Part II) in 40 patients undergoing thoracoscopic procedures. In Part I, 20 patients were divided into two groups: one received O2 (Group 1) and one received O2/NO (Group 2). In Part II, 20 patients were divided into two groups: one received O2 (Group 3) and one received O2/NO/almitrine (Group 4). In Groups 2 and 4, NO (20 ppm) was administered during the entire period of OLV, and almitrine was continuously infused (16 micro g [center dot] kg-1 [center dot] min-1) in Group 4. Arterial blood gases were measured during two-lung ventilation with patients in the supine position, after positioning in the lateral decubitus position, and then every 5 min for a 30-min period during OLV. During OLV, PaO2 values decreased similarly in Groups 1 and 2. After 30 min of OLV, the mean PaO2 values in Groups 1 and 2 were 132 +/- 14 mm Hg (mean +/- sem) and 149 +/- 27 mm Hg (not significant [NS]), and the PaO2 value was less than 100 mm Hg in four patients in Group 1 and five patients in Group 2. PaO2 values were greater in Group 4 than in Group 3 after 15 and 30 min of OLV. After 30 min of OLV, the mean PaO2 values were 146 +/- 16 mm Hg in Group 3 and 408 +/- 33 mm Hg in Group 4 (P < 0.001). PaO2 was less than 100 mm Hg during OLV (NS) in four patients in Group 3 and in no patient in Group 4. We conclude that NO inhalation alone has no effect on PaO2 evolution during OLV, although its combination with IV almitrine limits the decrease of PaO2 during OLV. This beneficial effect of NO/almitrine could be attributed to an improvement in ventilation-perfusion relationships. Implications: Decrease in oxygenation during one-lung ventilation is quite common. Our study showed that inhaled nitric oxide alone did not influence PaO2 evolution. We then tried adding intravenous almitrine to nitric oxide with amazingly good results on PaO2. This nonventilatory technique should be of great use during special thoracic acts, such as thoracoscopic procedures. (Anesth Analg 1997;85:1130-5)

Combined ultrasound and neurostimulation guidance for popliteal sciatic nerve block: a prospective, randomized comparison with neurostimulation alone.

BACKGROUND:Ultrasound imaging, an effective tool to localize peripheral nerves, may facilitate block performance. However, its usefulness during popliteal sciatic nerve block has not been assessed. METHODS:In this prospective, randomized, patient-blinded study, we compared the block time (as the primary end-point) of a popliteal sciatic nerve block with double-injection performed using anatomical landmarks and neurostimulation (NS group; n = 30) versus combined ultrasound and neurostimulation guidance (US-NS group; n = 30). Each block procedure was performed by a single operator. Correct needle placement was defined by a minimal stimulating current ≤0.5 mA, or, in the US-NS group, by mobilization of the nerve by the needle shaft even if the minimal stimulating current >0.5 mA. Ten milliliter levobupivacaine 0.5% was administered separately on the tibial and common peroneal nerves without needle adjustment to improve the spread of anesthetic in the US-NS group. All procedures were video-recorded, and a maximum of 7 min was allowed to perform the block. Successful block was defined as complete loss of cold sensation in the sciatic distribution and an inability to perform a plantar and dorsal flexion of the foot at 30 min. RESULTS:Five patients in the NS group and three in US-NS group were excluded from the study for prolonged procedure. Block time was not significantly different between groups. The number of needle passes was lower only for the detection of the first nerve in the US-NS group (1 [1–2] vs 2 [1–6]; P < 0.01). A greater success rate was observed at 30 min in the US-NS group (65% vs 16%; P < 0.001). CONCLUSIONS:Combined ultrasound and neurostimulation guidance does not decrease block time but increases the success rate of popliteal sciatic nerve block observed at 30 min.

A randomized, double-blinded comparison of intrathecal morphine, sufentanil and their combination versus IV morphine patient-controlled analgesia for postthoracotomy pain

We compared the analgesic effect of lumbar intrathecal (IT) 0.5 mg morphine (Group M, n = 10), 50 &mgr;g sufentanil (Group S, n = 10), and their combination (Group S-M, n = 10) given before general anesthesia and patient-controlled analgesia with IV morphine (Group C, n = 19) in a randomized, double-blinded study performed in patients undergoing thoracotomy. Pain visual analog scale (VAS) and morphine consumption were assessed for 24 h. In Group S-M the number of patients initially titrated with IV morphine was less than in group C (30 vs 84%, P < 0.05). Morphine requirement was higher in Group C (71 ± 30 mg) than in Groups S (46 ± 34 mg, P < 0.05), M (38 ± 31 mg, P < 0.05) and S-M (23 ± 16 mg, P < 0.01). VAS scores were significantly decreased during the first 0–11 postoperative h at rest and during the first 0–8 postoperative h on coughing in Groups M and S-M rather than in Group C. The incidence of side effects was infrequent except for urinary retention. Preoperative IT morphine or combined sufentanil and morphine could be given as a booster to achieve rapidly effective analgesia in the immediate postoperative period. IMPLICATIONS As compared with IV patient-controlled analgesia, intrathecal morphine or combined sufentanil and morphine provided superior postoperative pain relief both at rest (11 h) and on coughing (8 h) than did IV patient-controlled analgesia morphine alone. IV morphine requirement was decreased during the first postoperative day after posterolateral thoracotomy.

Assessment of systematic use of intraoperative transesophageal echocardiography during cardiac surgery in adults: A prospective study of 203 patients

OBJECTIVE To determine the usefulness of systematic intraoperative transesophageal echocardiography in a cardiac surgical unit. DESIGN Open prospective observational survey. SETTING University Hospital. PARTICIPANTS Consecutive adult patients (n = 203) undergoing elective or urgent cardiac operations. MEASUREMENTS AND MAIN RESULTS Pre-cardiopulmonary bypass imaging yielded unsuspected findings in 26 patients (12.8%) and changed the planned surgery in 22 patients (10.8%). Transesophageal echocardiography modified the diagnosis in eight patients (17%) operated on for mitral valvulopathy, in seven patients (15.5%) with aortic valvular disease, in four patients (4.6%) with coronary artery disease, in five patients operated on for thoracic aorta diseases regardless of their localization (18.5%), and in two miscellaneous cases. On the basis of the data obtained from the transesophageal echocardiography carried out at the end of cardiopulmonary bypass, an immediate reintervention was required in five cases (2.5%). CONCLUSIONS It is concluded that systematic intraoperative transesophageal echocardiography significantly affected decision making in this cardiac surgical unit. Its routine use in all cardiac surgical patients is recommended.

Feasibility of closed-loop titration of propofol and remifentanil guided by the spectral M-Entropy monitor.

Background: This randomized controlled trial describes automated coadministration of propofol and remifentanil, guided by M-Entropy analysis of the electroencephalogram. The authors tested the hypothesis that a novel dual-loop controller with an M-Entropy monitor increases time spent within predetermined target entropy ranges. Methods: Patients scheduled for elective surgery were randomly assigned in this single-blind study using a computer-generated list, to either dual-loop control using a proportional-integral-derivative controller or skilled manual control of propofol and remifentanil using target-controlled-infusion systems. In each group, propofol and remifentanil administration was titrated to a state entropy target of 50 and was subsequently targeted to values between 40 and 60. The primary outcome was the global score, which included the percentage of state entropy or response entropy in the range 40–60, the median absolute performance error and wobble. Data are presented as medians [interquartile range]. Results: Thirty patients assigned to the dual-loop group and 31 assigned to the manual group completed the study. The dual-loop controller was able to provide induction and maintenance for all patients. The Global Score of State Entropy was better maintained with dual-loop than manual control (25 [19–53] vs. 44 [25–110], P = 0.043), and state entropy was more frequently maintained in the range of 40–60 (80 [60–85] vs. 60 [35–82]%, P = 0.046). Propofol (4.1 [2.9–4.9] vs. 4.5 [3.4–6.3] mg · kg−1 · h−1) and remifentanil (0.18 [0.13–0.24] vs. 0.19 [0.15–0.26] &mgr;g · kg−1 · min−1) consumptions and the incidence of somatic side effects were similar. Conclusion: Intraoperative automated control of hypnosis and analgesia guided by M-Entropy is clinically feasible and more precise than skilled manual control.

Systematic transesophageal echocardiography for detection of mediastinal lesions in patients with multiple injuries

A prospective study assessing the interest in and the results of systematic transesophageal echocardiography (TEE) examination in nonselected intubated multiple injury patients was carried out from January 1992 through June 1993. Seventy patients were included and divided into two groups according to the results of admission screening, including clinical examination, EKG, CK-MB and chest radiograph. Group 1 (60 patients) had abnormalities on initial screening, while group 2 (10 patients) had no symptom of thoracic or mediastinal injury. TEE was performed within 48 hours following admission and its results were compared with those of the initial screening. TEE usefulness was evaluated on a score grade from 0 (no interest) to 4 (outstanding interest). Myocardial contusion was suspected in 25 patients. TEE invalidated 18 suspected and found 5 unsuspected myocardial contusions. Pericardial effusion was suspected in only one case, while TEE documented 13 additional cases. A mediastinal enlargement was seen in 13 patients, but TEE invalidated aortic lesions in all these cases and made an unsuspected diagnosis of aortic tears. Eight cases of severe hypovolemia and seven cases of left ventricle dysfunction were detected by TEE. The score of interest showed that TEE allowed new interesting diagnoses in 70% of group I patients and in 33% of group II patients. TEE is of utmost importance in multiple injury patients, with or without any evidence of thoracic or mediastinal injury, providing a safe and rapid examination of the mediastinal structures and an evaluation of the hemodynamic status.