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Background: During endoscopic neurosurgery, direct mechanical stimulation of the brain by the endoscope and increased intracranial pressure (ICP) caused by the continuous rinsing can induce potentially lethal haemodynamic reflexes, brain ischaemia, and excessive fluid resorption., Methods: In a newly presented rat model of endoscopic neurosurgery, stereotactic access to the cerebrospinal fluid was secured and the ICP was increased by controlled infusion until complete suppression of the cerebral perfusion pressure (CPP). The haematocrit (Hct) level was determined before and after the procedure. During the whole procedure, invasive arterial pressure, ICP, and heart rate were continuously recorded and evaluated in a subsequent offline analysis. After the procedure, the animals were allowed to recover and 7 days later they were killed for histological examination., Results: Suppression of the CPP resulted in a severe hypertension combined with tachycardia or mild bradycardia. The Hct decreased from 41 to 35 over the minutes of CPP suppression. After cessation of the infusion, the ICP decreased to 37% of the plateau pressure within 2.5 s. In the first few minutes after restoration of normal ICP, five animals died because of pulmonary oedema., Conclusions: Upon complete suppression of the CPP, an obvious hypertension developed, often together with tachycardia, but no severe bradycardia. At high ICP levels, we observed an important translocation of irrigation fluid to the vascular space. Fatality was not caused by ischaemia or arrhythmia but due to pulmonary oedema.

During the last decennium, a growing number of depth of anesthesia monitors, extracting information from the spontaneous electroencephalogram (EEG) have been developed and commercialized. The growing interest in depth of anesthesia monitoring resulted in an intensified technological progress. Innovations on both hardware and mathematical algorithms were introduced for improving the extraction of data. Because of the abundance of monitors now commercially available, it becomes increasingly important to develop a standardized reproducible methodology for comparing depth of anesthesia monitors. In this review, the authors present a strategy to compare monitors of the hypnotic component of anesthesia, based on the available literature and their own experience with validation studies. They also discuss the level of validation of the most commonly used EEG derived depth of anesthesia monitors.

Background: Choice of opioid may influence postoperative pain, recovery, and respiratory homeostasis in morbid obesity. The aim of this study was to compare the effects of target-controlled infusions (TCIs) of remifentanil or sufentanil on postoperative analgesia, recovery, and pulmonary function after laparoscopic gastric banding., Methods: Forty morbidly obese patients undergoing laparoscopic gastric banding received BIS-guided desflurane anaesthesia combined with remifentanil TCI (Group R) or sufentanil TCI (Group S). Intraoperative haemodynamic stability, BIS controllability, and immediate recovery in the operating room were measured. Pulmonary function, modified Aldrete score, modified Observers Assessment of Alertness and Sedation score, blood gas analysis, and visual analogue score for pain and postoperative nausea and vomiting were measured on admission to the post-anaesthesia care unit and 30, 60, 120 min afterwards. After operation, patients received patient-controlled analgesia with morphine., Results: During the first two postoperative hours, cumulative morphine consumption was higher in the remifentanil group compared with the sufentanil group, but was equal values after that time. Recovery profiles and spirometry showed no significant differences. During maintenance, remifentanil gave a better haemodynamic stability., Conclusions: As few differences occurred in the postoperative period, the theoretical advantage of remifentanil over the longer acting sufentanil can be questioned when using TCI technology.

Background: The surgical stress index (SSI) is based on a sum of the normalized pulse beat interval (PBI) and the pulse wave amplitude (PPGA) time series of the photoplethysmography. As a measure of the nociception-anti-nociception balance in response to a standardized pain stimulus, SSI was compared with EEG changes in state and response entropy (SE and RE), PPGA, and heart rate (HR) during various targeted pseudo-steady-state concentrations of propofol and remifentanil., Methods: Forty ASA I patients were allocated to one of the four groups to receive a remifentanil step-up/-down effect-compartment target-controlled infusion (Ce(remi)) of 0, 2, 6, 2, 0 ng ml(-1), or 6, 2, 0, 2, 6 ng ml(-1), and an effect-compartment target-controlled propofol infusion (Ce(prop)) to keep the SE between 30 and 50 or 15 and 30, respectively. At each steady-state Ce(remi), maximum change in SSI, SE, RE, PPGA, and HR after a noxious stimulus was compared with the baseline value. A correlation and prediction probability (P(K)) with Ce(prop) and Ce(remi) was measured., Results: Static and dynamic values of SSI correlated to Ce(remi) better than SE, RE, HR, and PPGA. SSI was independent of Ce(prop), in contrast to SE and RE. The P(K) for Ce(remi) both before and during a noxious stimulus was better with SSI., Conclusions: SSI appeared to be a better measure of nociception-anti-nociception balance than SE, RE, HR, or PPGA.

Background: Facial electromyography (FEMG) may have utility in the assessment of nociception during surgery. The difference between state entropy (SE) and response entropy (RE) is an indirect measure of FEMG. This study assesses an automated algorithm for remifentanil administration that is based on maintaining an entropy difference (ED) that is less than an upper boundary condition and greater than a lower boundary condition., Methods: The algorithm was constructed with a development set (n = 40), and then automated and studied with a validation set (n = 20) of patients undergoing anterior cruciate ligament repair. The percentage of time that the ED was maintained between the two boundary conditions was determined. Remifentanil and propofol predicted effect-site concentrations (Ce) were determined at surgical milestones and, after drug discontinuation, the time to response to verbal stimulation and orientation was measured., Results: The median (25th-75th percentile) per cent of time that the ED was recorded between the boundary conditions was 99.3% (98.1-99.8%). Predicted propofol (microg ml(-1)) and remifentanil (ng ml(-1)) Ce (sd), respectively, were 3.5 and 4.0 at induction, 1.9 (0.8) and 7.2 (3.7) at the end of surgery, and 1.1 (0.5) and 3.2 (2.2) at eye opening. The median time to eye opening and orientation was 3.8 and 6.8 min, respectively., Conclusion: This feasibility study supports the concept that remifentanil may be delivered using an algorithm that maintains the difference between SE and RE between the upper and lower boundary condition.

Background: The aim of this study was to determine whether, after propofol, rocuronium and remifentanil rapid sequence induction, inhaled anaesthetic agents should be started before intubation to minimize autonomic and arousal response during intubation., Methods: One hundred ASA I and II patients were randomized to receive 1 MAC of desflurane or sevoflurane during manual ventilation or not. Anaesthesia was induced with an effect-site-controlled infusion of remifentanil at 2 ng ml(-1) for 3 min. Patients then received propofol to induce loss of consciousness (LOC). Rocuronium (0.6 mg kg(-1)) was given at LOC and the trachea was intubated after 90 s of manual breathing support (=baseline) with or without inhaled anaesthetics. Vital signs and bispectral index (BIS) were recorded until 10 min post-intubation to detect autonomic and arousal response., Results: A significant increase in BIS value after intubation was seen in all groups. The increases were mild, even in those not receiving pre-intubation inhaled anaesthetics. However, in contrast to sevoflurane, desflurane appeared to partially blunt the arousal response. Heart rate, systolic and diastolic pressure increase similarly in all groups., Conclusions: Desflurane and sevoflurane were unable to blunt the arousal reflex completely, as measured by BIS, although the reflex was significantly less when desflurane was used. Rapid sequence induction with remifentanil, propofol and rocuronium and without inhaled anaesthetics before intubation can be done without dangerous haemodynamic and arousal responses at intubation after 90 s.

Depth of anaesthesia monitors might help to individualize anaesthesia by permitting accurate drug administration against the measured state of arousal of the patient. In addition, the avoidance of awareness or excessive anaesthetic depth might result in improved patient outcomes. Various depth of anaesthesia monitors based on processed analysis of the EEG or mid-latency auditory-evoked potentials are commercially available as surrogate measures of anaesthetic drug effect. However, not all of them are validated to the same extent.

Background: During an endoscopic neurosurgical procedure a sudden increase in intracranial pressure may occur at any time. We present a prospective study of haemodynamic changes during such procedures., Methods: Physiological data were recorded during the whole operative procedure in 17 consecutive patients who underwent an endoscopic neurosurgical procedure under general anaesthesia. Monitoring included invasive blood pressure, intracranial pressure, electrocardiogram, end-expired carbon dioxide, pulse oximetry and heart rate. Pressure and ECG waveforms were recorded at 100 Hz and evaluated in a subsequent offline analysis., Results: In almost every case, the occurrence of hypertension and tachycardia was clearly the result of an increase in intracranial pressure. Also, a Cushing reflex developed in almost every case where the cerebral perfusion pressure dropped below 15 mm Hg. The occurrence of bradycardia was not systematically associated with a low cerebral perfusion pressure., Conclusion: In this study, we describe the haemodynamic effects of increased intracranial pressure during endoscopic neurosurgical procedures and their respective sequence of events at high temporal resolution. Although most clinicians rely on the occurrence of bradycardia to diagnose intracranial hypertension during endoscopic neurosurgical procedures, we show that a simultaneous onset of hypertension and tachycardia is a better indicator of impaired brain perfusion. Waiting for a persistent bradycardia to alert the surgeon during endoscopic neurosurgical procedures could allow severe bradycardia or even asystole to develop.

Background: The aim of this study was to detail the time-course, defined as the changes in end-tidal drug concentration with time, and consumption of inhaled anaesthetics when using a multifunctional closed-circuit anaesthesia machine in various drug delivery modes, and to compare it with a classical anaesthesia machine using an out-of-circle vaporizer under high and low fresh gas flow conditions., Methods: Using an artificial test lung, sevoflurane and desflurane time-course and consumption were compared when using the Zeus apparatus (Dräger, Lubeck, Germany) with direct injection of inhaled anaesthetics or the Primus apparatus (Dräger, Lubeck, Germany) using a classical out-of-circle vaporizer. Anaesthetics were targeted at 1 and 2 MAC end-tidal during 15 min. For both apparatus, out-of-circle high and low fresh gas control (FGC) and for Zeus, auto-control (AC) modes (fixed fresh gas flow at 6 and 1 litre min(-1) and uptake mode) were compared. Time to reach target, initial overshoot and stability at target, and wash-out times were compared., Results: In FGC, an initial overshoot in end-tidal drug concentration is seen when using 6 litre min(-1) fresh gas flow and a slower time course is observed when using only 1 litre min(-1) in both apparatus. In auto-control mode, the time course of both sevoflurane and desflurane was very fast and not influenced by the changes in fresh gas flow. No overshoot at target was seen. At all settings, the wash-out times were faster when using Zeus than Primus. Inhaled anaesthetic consumption was lowest with the Zeus ventilator in uptake AC mode., Conclusion: A combination of the fastest time course and lowest consumption of sevoflurane and desflurane was found when using the Zeus apparatus in AC uptake mode.

Background: We compared two spectral entropies, state entropy (SE) and response entropy (RE), based on the irregularity of the EEG, to measure loss of response to verbal command (LOR(verbal)) and noxious stimulus (LOR(noxious)) with the bispectral index (BIS) during propofol infusion with and without remifentanil., Methods: Three groups of 20 patients received an effect-site controlled propofol infusion (Ce(PROP)) starting at 1 microg ml(-1) and increased in steps of 0.5 microg ml(-1) at 4 min intervals. In addition, a remifentanil infusion was maintained at a group-dependent, fixed effect-site target concentration (Ce(REMI)) (0, 2 or 4 ng ml(-1)). The ability of BIS, SE or RE to predict LOR(verbal) and LOR(noxious) were compared with the changes in BIS, SE and RE using logistic regression, prediction probability (P(K)), and sensitivity/specificity., Results: In all groups, BIS, SE and RE decreased with increasing Ce(PROP). However, BIS decreased more smoothly than SE and RE at deeper levels of sedation. At LOR(verbal), BIS(50), SE(50) and RE(50) increased with increasing Ce(REMI). BIS, SE and RE all detected LOR(verbal) accurately but BIS performed better at 100% sensitivity. Sensitivity/specificity for detection of LOR(verbal) decreased for all methods with increasing Ce(REMI). LOR(noxious) was poorly described by all measures., Conclusion: LOR(verbal) was detected accurately by BIS, SE and RE except for 100% sensitivity, where BIS performed better. Though BIS, SE and RE were influenced by remifentanil during propofol administration, their ability to detect LOR(verbal) remained accurate. None of the measures predicted LOR(noxious).

Background: The concept of an 'inhalation bolus' can be used to optimize inhaled drug administration. We investigated the depth of anaesthesia, haemodynamic stability, and recovery time in morbidly obese patients resulting from bispectral index (BIS)-guided sevoflurane or desflurane administration and BIS-triggered inhalation boluses of sevoflurane or desflurane combined with titration of remifentanil., Methods: Fifty morbidly obese patients undergoing laparoscopic gastroplasty received either BIS-guided sevoflurane or desflurane anaesthesia in combination with a remifentanil target-controlled infusion. Intraoperative haemodynamic stability and BIS control were measured. Immediate recovery was recorded., Results: Intraoperatively, the BIS was between 40 and 60 for a greater percentage of time in the sevoflurane (78 (13)% of case time) than in the desflurane patients (64 (14)% of case time), owing to too profound anaesthesia in the desflurane patients at the start of the procedure. However, fewer episodes of hypotension were found in the desflurane group, without the occurrence of more hypertensive episodes. During immediate recovery, eye opening, extubation, airway maintenance, and orientation occurred sooner in the desflurane group., Conclusions: Immediate recovery was significantly faster in the desflurane group. Overall hypnotic controllability measured by BIS was less accurate with desflurane. Overall haemodynamic controllability was better when using desflurane. Fewer episodes of hypotension were found in the desflurane group. The use of the inhalation bolus was found to be appropriate in both groups without causing severe haemodynamic side effects. Minimal BIS values were significantly lower after a desflurane bolus.