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Biomedical subjects

M Struys

Publications and source records attributed to M Struys.

At least 19 recordsLinked to original sources
PubMed2004

Pitfalls and challenges when assessing the depth of hypnosis during general anaesthesia by clinical signs and electronic indices.

The objective of this article was to review the present methods used for validating the depth of hypnosis. We introduce three concepts, the real depth of hypnosis (DHreal), the observed depth of hypnosis (DHobs), and the electronic indices of depth of hypnosis (DHel-ind). The DHreal is the real state of hypnosis that the patient has in a given moment during the general anaesthesia. The DHobs is the subjective assessment of the anaesthesiologist based on clinical signs. The DHel-ind is any estimation of the depth of hypnosis given by an electronic device. The three entities DHreal, DHobs and DHel-ind should in the ideal situation be identical. However, this is rarely the case. The correlation between the DHobs and the DHel-ind can be affected by a number of factors such as the stimuli used for the assessment of the level of consciousness or the administration of analgesic agents or neuro muscular blocking agents. Opioids, for example, can block the response to tactile and noxious stimuli, and even the response to verbal command could vanish, hence deeming the patient in a lower depth of hypnosis than the real patient state. The DHel-ind can be disturbed by the presence of facial muscular activity. In conclusion, although several monitors and clinical scoring scales are available to assess the depth of hypnosis during general anaesthesia, care should be taken when interpreting their results.

Acoustic Stimulation↗
PubMed2003

Cardiovascular changes during endoscopic third ventriculostomy.

During an endoscopic third ventriculostomy (ETV) a sudden increase in intracranial pressure (ICP) may occur at any time. In the literature little attention has been paid to the early detection of such an increase. In particular the occurrence of a 'Cushing reflex' has not been discussed in this context. Therefore, we have now analysed retrospectively the anesthesia charts of 88 patients with obstructive hydrocephalus who had undergone ETV under general anesthesia. Monitoring included invasive blood pressure, electrocardiogram, end-expired carbon dioxide, pulse oximetry and heart rate. These variables were now evaluated before and after the introduction of the endoscope and during and after the occurrence of any change. In 67 patients the procedure had been uneventful. In 6 patients the occurrence of tachycardia and hypertension followed by bradycardia and hypertension was clearly the result of an increase in ICP, which we call a Cushing reflex. In his classical description of this pressure response Cushing reported the occurrence of hypertension, bradycardia and apnoea. However, many investigators have shown that beside systemic hypertension, both tachycardia and bradycardia are essential components of the Cushing reflex. Waiting for a persistent bradycardia to alert the surgeon during ETV can allow a fatal asystole.

Adolescent↗
PubMed2002

Postoperative residual curarization with cisatracurium and rocuronium infusions.

BACKGROUND AND OBJECTIVE: Monitoring of neuromuscular blockade still often relies on clinical judgement. Moreover, there are substantial national differences in the use of agents to 'reverse' their effects. We investigated the recovery characteristics and incidence of postoperative residual curarization after cisatracurium and rocuronium infusions for long duration interventions without systematic antagonism. METHODS: In 30 patients undergoing major surgery, we measured infusion dose requirements for rocuronium and cisatracurium during propofol anaesthesia. Infusions were discontinued at the beginning of surgical closure; spontaneous recovery of neuromuscular function was awaited in both groups. Neostigmine (50 microg kg(-1)) was administered only when a patient started to wake without a train-of-four ratio (TOF) of 0.9. RESULTS: In the cisatracurium and rocuronium groups, four (27%) and one (7%) patients, respectively, had a TOF ratio > or = 0.9 at the end of surgery. The TOF ratio in each group at that time was 51 +/- 32% for cisatracurium and 47 +/- 31% for rocuronium (P = 0.78). Six patients (40%) in the cisatracurium group and seven (47%) in the rocuronium group required neostigmine. The TOF ratio at the time of reversal was 63 +/- 7% for cisatracurium and 40 +/- 19% for rocuronium (P = 0.01). The time interval between the end of surgery and a TOF ratio of 0.9 was 10 +/- 9 min for cisatracurium and 18 +/- 13 min for rocuronium (P = n.s.). CONCLUSIONS: Patients receiving a cisatracurium or rocuronium infusion have a high incidence of postoperative residual curarization when the block is not antagonized. When 'reversal' is not attempted, cisatracurium seems to be safer than rocuronium.

Androstanols↗
PubMed2001

Compound A production from sevoflurane is not less when KOH-free absorbent is used in a closed-circuit lung model system.

In an in vitro study, less compound A was formed when a KOH-free carbon dioxide absorbent was used. To confirm this observation we used a lung model in which carbon dioxide was fed in at 160 ml min(-1) and sampling gas was taken out for analysis at 200 ml min(-1); ventilation aimed for a PE'CO2 of 5.4 kPa. The soda lime canister temperatures in the inflow and outflow ports (Tin and Tout) were recorded. In six runs of 240 min each, a standard soda lime, Sodasorb (Grace, Epernon, France) was used and in eight runs KOH-free Sofnolime (Molecular Products, Thaxted, UK) was used. Liquid sevoflurane was injected using a syringe pump to obtain 2.1% E'. Compound A was measured by capillary gas chromatography combined with mass spectrometry. Median (range) compound Ainsp increased to a maximum of 22.7 (7.9) ppm for Sodasorb and 33.1 (20) for Sofnolime at 60 min and decreased thereafter; the difference between groups was significant (P<0.05) at each time of analysis up to 240 min. The canister temperatures were similar in both groups and increased to approximately 40 degrees C at 240 min. Contrary to expectation, compound A concentrations were greater with the KOH-free absorbent despite similar canister temperatures with both absorbents.

Absorption↗
PubMed2000

Influence of intravenous clonidine pretreatment on anesthetic requirements during bispectral EEG-guided sevoflurane anesthesia.

STUDY OBJECTIVE: To assess the anesthetic effects of clonidine during sevoflurane anesthesia guided by the bispectral index (BIS), which is a processed EEG variable correlated with anesthetic-hypnotic depth. DESIGN: Placebo-controlled, double-blind clinical trial. SETTINGS: Elective laparoscopic surgery. PATIENTS: 60 ASA physical status I patients scheduled for laparoscopic surgery. INTERVENTIONS: Patients received either clonidine (3 micrograms/kg, 15 min before induction) or placebo premedication for a sevoflurane-induced and sevoflurane-maintained anesthesia. Sevoflurane was titrated against a BIS held between 40 and 50. Analgesia was provided by local infiltration with bupivacaine. Need for postoperative analgesia was recorded. RESULTS AND CONCLUSION: Mean sevoflurane requirements were not lower with clonidine pretreatment. There was statistically better perioperative hemodynamic stability (i.e., fewer episodes of hypertension and tachycardia) without clinical relevance. A decreased need for postoperative analgesia was observed.

Adolescent↗
PubMed2000

Therapeutic coma or neuroprotection by anaesthetics.

Some surgical patients are at an increased risk for developing cerebral ischaemia. A subset of these patients is believed to benefit from putative cerebroprotective effects of anaesthetic agents. Therefore, in this setting these drugs could have therapeutic modalities, besides their auxiliary functions to make surgery possible. However, both animal and especially human data are very disappointing. Only the barbiturates and isoflurane have an experimental record warranting further research to delineate proper indications for their use as neuroprotective agents in surgical patients.

Anesthetics↗
PubMed1999

Contractility in humans after coronary artery surgery.

BACKGROUND: Propofol's unique pharmacokinetic profile offers advantages for titration and rapid emergence in patients after coronary artery bypass graft (CABG) surgery, but concern for negative inotropic properties potentially limits its use in these patients. The current study analyzed the effect of various propofol plasma concentrations on left ventricular (LV) contractility by means of a single-beat contractile index based on LV maximal power (PWR(max)). METHODS: The study was conducted in 30 patients after CABG surgery. Immediately after admission to the intensive care unit (ICU), four different plasma concentrations of propofol 0.65, 1.30, 1.95, and 2.60 microg/ml were established. At each concentration level, the cardiac and vascular effects of propofol were studied by combining echocardiographic data with invasively derived aortic root pressure. Preload was characterized by LV end-diastolic dimensions. Afterload was indicated in terms of indexed systemic vascular resistance (SVRI), LV end-systolic meridional wall stress (LV-ESWS), and arterial elastance (Ea). Quantification of effects on contractility was achieved by preload-adjusted PWRmax. RESULTS: Myocardial contractility did not change during a fourfold increase in propofol plasma concentration. Preload-adjusted PWRmax amounted to 3.90+/-1.75 W x ml(-2) x 10(4), 3.98+/-1.69, 3.94+/-1.70, and 3.88+/-1.72, respectively (mean+/-SD). With respect to ventricular loading conditions, propofol caused a significant reduction in both pre- and afterload. CONCLUSIONS: The current results strongly suggest that propofol lacks direct cardiac depressant effects. Nevertheless, meaningful vascular actions of propofol could be demonstrated. Significant decreases in ventricular loading conditions accounted for a marked decrease in arterial blood pressure and supported the concept that propofol in clinically relevant concentration is a vasodilator.

Coronary Artery Bypass↗
PubMed1999

Influence of methane on infrared gas analysis of volatile anesthetics.

Contemporary multigas analyzers determine anesthetic gas concentrations using (near) infrared analysis at either 3.3 or 8-9 microns. Methane also absorbs infrared light at 3.3 microns, but not at 8-9 microns. Consequently, erroneous anesthetic agent readings may result when methane is present in the circuit (e.g. during closed circuit anesthesia), potentially compromising patient safety. We have analyzed in laboratory conditions the influence of different known methane concentrations (100, 500 and 1000 ppm) on the gas-analysis readings provided by some clinical monitoring devices that use infrared absorption for the measurement of inhalation anesthetic concentration. At 3.3 microns wavelength the influence on the measurement of halothane was important, whereas the influence on that of enflurane and isoflurane was less pronounced. For desflurane and sevoflurane measurements, the influence of methane at 3.3 microns wavelength proved to be minimal. At higher wavelengths (8-9 microns) no influence of methane could be demonstrated.

Anesthesia, Closed-Circuit↗
PubMed1998

Use of continuous bispectral EEG monitoring to assess depth of sedation in ICU patients.

Monitoring the depth of sedation in patients under intensive care is difficult. Clinical assessment by the different scoring systems produces insufficient information, especially once deeply sedated patients become unresponsive to any external stimulation. Recently, the bispectral index (BIS), the result of computerized bispectral electroencephalographic monitoring, was found to be the best predictor of depth of anaesthesia during surgical intervention. This report concerns BIS monitoring in 18 randomly selected, deeply sedated, surgical patients in the intensive care unit, who were unresponsive to standard clinical stimulation (Ramsay sedation score). A wide range of BIS was observed, with 15 of the patients having a BIS below 60, indicating a state of deep sedation (or possibly over-sedation). Therefore, further studies using BIS monitoring in patients under intensive care are needed to determine if this method can guide sedation and prevent oversedation in this context and, most importantly, to analyse its final cost-benefit ratio.

Analgesics, Opioid↗
PubMed1998

Closed-loop controlled administration of propofol using bispectral analysis.

Ten patients, undergoing elective orthopaedic surgery under spinal anaesthesia, were sedated with propofol using a closed-loop feedback control system. The bispectral index (BIS), a new processed EEG parameter, was used as control variable. Propofol administration was controlled by a patient individualised adaptive model-based controller incorporating target-controlled infusion technology combined with a pharmacokinetic-dynamic model. This feedback control system for propofol administration proved to be adequate and safe. BIS was found to be well suited as control variable.

Adolescent↗
PubMed1998

Influence of anaesthesia on defibrillation threshold.

Internal cardioverter-defibrillator implantation can be performed under local or general anaesthesia. Whether the technique of general anaesthesia influences the defibrillation threshold remains a matter of debate. We therefore compared, in a prospective, randomised clinical study, the effect of intravenous anaesthesia using propofol with inhalational anaesthesia using isoflurane on the defibrillation threshold in 68 patients scheduled for transvenous single-lead internal cardioverter-defibrillator implantation. Defibrillation threshold was measured at implantation and at device testing 1 week and 1 month after implantation. Patients acted as their own controls. Neither the anaesthetic technique nor the duration of anaesthesia was associated with significant changes in the defibrillation threshold. We conclude that in this group of high-risk patients, both types of anaesthesia are acceptable techniques for internal cardioverter-defibrillator implantation and testing.

Anesthesia, General↗
PubMed1998

Haemodynamic and electroencephalographic response to insertion of a cuffed oropharyngeal airway: comparison with the laryngeal mask airway.

We have compared the cuffed oropharyngeal airway (COPA), a modified Guedel airway device with a specially designed cuff at its distal end, with the laryngeal mask airway (LMA), on haemodynamic and electroencephalographic (EEG) responses to insertion. In addition, we examined the haemodynamic and EEG changes during initiation of the effect-compartment controlled infusion. We studied 35 female patients undergoing ambulatory gynaecological surgery allocated randomly to received an LMA or COPA to manage the airway. After premedication with midazolam 0.03 mg kg-1 i.v. and low-dose alfentanil (0.01 mg kg-1), anaesthesia was induced and maintained with propofol, using an effect-compartment controlled infusion set at an effect-site concentration of 4 micrograms ml-1. After intercompartmental equilibration, the LMA (group I) or COPA (group II) was inserted and haemodynamic (arterial pressure, heart rate) and EEG (bispectral index (BIS)) responses to insertion studied. The effect-compartment controlled infusion of propofol caused only mild haemodynamic changes during induction. Changes in arterial pressure and heart rate after insertion were similar in both groups and not significantly different from baseline values before insertion. Changes in BIS after insertion were minor and similar between groups.

Ambulatory Surgical Procedures↗
PubMed1998

Clinical usefulness of the bispectral index for titrating propofol target effect-site concentration.

The bispectral index, a new processed electroencephalographic parameter which may give information on depth of anaesthesia, was used in 58 patients undergoing outpatient gynaecological surgery in order to study if the addition of bispectral index monitoring to standard clinical monitoring could improve the titration of target propofol concentration when using effect-site target-controlled propofol infusion for sedation. In Group 1 (n = 30), the bispectral index was recorded but the anaesthetist was unaware of the readings and therefore only classical signs of depth of anaesthesia were used to guide the anaesthetist in controlling the effect-site concentration. In Group 2 (n = 28), bispectral index readings were available to the anaesthetist and effect-site concentration was adjusted to ensure that bispectral index was maintained between 40 and 60. Similar propofol induction and maintenance doses, blood and effect-site concentrations and mean bispectral index were found in the two groups. A greater percentage of bispectral index readings lying outside the target range (i.e. < 40 or > 60) and more movement at incision and during maintenance were found in Group 1. There was a trend towards more implicit awareness in patients in Group 1. Bispectral index was found to be useful for measuring depth of sedation when using propofol target-controlled infusion. Propofol dosage could not be decreased but a more consistent level of sedation could be maintained due to a more satisfactory titration of target effect-site concentration.

Adolescent↗
PubMed1998

Influence of pre-anaesthetic medication on target propofol concentration using a 'Diprifusor' TCI system during ambulatory surgery.

The effects of pre-anaesthetic medication on target propofol concentration, induction dose, time to induction, and discomfort on infusion were studied in 45 female patients undergoing ambulatory gynaecological procedures using 'Diprifusor' target controlled infusion of propofol. The patients were randomly allocated to receive either no premedication (group 1) or premedication with diazepam alone (group 2) or in combination with alfentanil (group 3). Induction was more successful in premedicated than unpremedicated patients with an initial target propofol concentration of 4 micrograms.ml-1 (87% in group 2 and 93% in group 3 vs. 38% in group 1, p < 0.01). Premedication was also associated with the requirement of a lower mean target concentration for induction, a lower induction dose and a shorter time to induction. There were no significant between-group differences in discomfort on infusion or target concentration during maintenance. For short ambulatory procedures, the recommended initial target concentration of propofol is 4 micrograms.ml-1 in premedicated and 6 micrograms.ml-1 in unpremedicated patients.

Adult↗
PubMed1998

Comparison of spontaneous frontal EMG, EEG power spectrum and bispectral index to monitor propofol drug effect and emergence.

BACKGROUND: The aim of this study was to investigate the accuracy of frontal spontaneous electromyography (SEMG) and EEG spectral edge frequency (SEF 95%), median frequency (MF), relative delta power (RDELTA) and bispectral index (BIS) in monitoring loss of and return of consciousness and hypnotic drug effect during propofol administration at different calculated plasma target concentrations. METHODS: Propofol was administered by using a target-controlled infusion at different propofol steady-state concentrations. All variables were measured simultaneously at specific calculated concentrations and endpoints. RESULTS: Loss of consciousness was accurately monitored by BIS, SEMG and SEF 95%, and propofol drug effect by BIS only. Return of consciousness was predicted by BIS, MF and SEF 95%. Due to the biphasic EEG pattern of propofol and the lack of reproducible data at specific propofol concentrations, the clinical usefulness of SEF 95%, MF and RDELTA was very limited. SEMG was useful to detect loss and return of consciousness, but without predictive value. CONCLUSIONS: The BIS might be an accurate measure to monitor depth of anaesthesia and hypnotic drug effect. Other neurophysiologic measures have limited value to monitor depth of anaesthesia and hypnotic drug effect.

Adult↗
PubMed1998

Jugular bulb oximetry: review on a cerebral monitoring technique.

Jugular bulb oximetry is the first available continuous monitoring method estimating the adequacy of cerebral perfusion. Despite its major technical as well as methodological shortcomings the information on the oxygen supply to demand balance of the brain seems most valuable. Especially the deleterious consequences of systemic variations (mainly concerning arterial blood pressure and CO2-tension) on the diseased brain are revealed by jugular bulb saturation values. The prevention and/or the early detection of these systemic secondary insults could have important implications as to final neurological outcome. Jugular bulb oximetry could also guide specific intracranial antihypertensive treatment, as it may reveal the pathophysiological mechanisms behind intracranial hypertension with regard to the status of cerebral perfusion (cerebral hyperemia or cerebral hypoperfusion). These insights might increase the efficacy of all treatments available for intracranial hypertension.

Antihypertensive Agents↗