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Biomedical subjects

L Versichelen

Publications and source records attributed to L Versichelen.

At least 19 recordsLinked to original sources
PubMed2002

Treatment of postoperative pain after ophthalmic surgery.

For ophthalmic surgery we have to deal with a wide range of different patient characteristics. We treat young healthy children, in some cases even neonates, but on the other hand we have debilitated aging patients with multiple concomitant diseases. Treatment of postoperative pain is imperative for inpatients, but is even more important for patients who are treated on an outpatient basis. There also is a wide range of different types of ophthalmic surgical procedures. The postoperative care after a cataract extraction is only seldom complicated by severe pain and is completely different of that after a vitrectomy with scleral buckling. More aggressive surgery as enucleation or evisceration of an eye often is a very stressful and painful procedure. We certainly have some excellent strategies to cope with postoperative pain. We can use topical anesthetics or non-steroidal anti-inflammatory medication. Regional anesthesia of the globe is extremely useful for anticipating on postoperative pain, especially when long-acting agents are used. We can administer analgesics by mouth or parenterally. Acetaminophen or paracetamol is widely used and can be supplemented with NSAIDs or opioids. Especially for children one has to use optimal doses of minor analgesics by an adequate route of administration in order to achieve a timely and efficient analgesia.

Acetaminophen↗
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↗
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

Methane influences infrared technique anesthetic agent monitors.

OBJECTIVE: During closed-circuit anesthesia, anesthetic vapor analysis by infrared absorption at 3.3 microm can be influenced by the concentration of accumulated methane, resulting in inaccurate readings of anesthetic concentrations. The current study examined the influence of different known methane concentrations on the analysis of halothane or isoflurane concentrations by the infrared absorption technique. METHODS: Three different gas mixtures containing 100, 500 and 1000 ppm methane were given through an experimental sampling bar. Four infrared technique anesthetic agent monitors were examined: (1) the Ultima (Datex), (2) the Andros analyzer (Cato anesthesia machine, Driger), (3) the anesthetic gas monitor 1304 (Brüel & Kjaer) and (4) the mainstream analyzer Irina (Drager). All devices, except the Brüel & Kjaer anesthetic gas monitor, function at 3.3 microm wavelength. The Brüel & Kjaer apparatus functions at 10.3-13 microm wavelength. The readings were recorded with and without addition of halothane (or isoflurane) at a halothane (or an isoflurane) dedicated sensitivity after application of methane. RESULTS: At the two highest methane concentrations (500 and 1000 ppm) all studied devices except the Brüel & Kjaer anesthetic gas monitor 1304 displayed inaccurate anesthetic concentrations. This was more pronounced at halothane than at isoflurane sensitivity. Introduction of halothane (0.8%) or isoflurane (0.8%) vapor into the experimental sampling bar resulted in values that were additive to the falsely recorded ones. CONCLUSIONS: In closed circuit or low-flow anesthesia, in which methane can accumulate, infrared measuring techniques for potent inhalation anesthetics that do not use the 3.3 microm wavelength appear to be preferable.

Anesthesia, Closed-Circuit↗
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

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↗
PubMed1997

Comparison of computer-controlled administration of propofol with two manually controlled infusion techniques.

Ninety women were studied in order to compare dose requirements and quality of anaesthesia between target-controlled infusion and two manually controlled infusion schemes for propofol administration: group I received target-controlled infusion for induction (4 micrograms.ml-1 target blood concentration, increased by 2 micrograms.ml-1 after 3 min of consciousness not lost), groups II and III received an induction bolus of propofol at infusion rates of 1200 or 600 ml.h-1, respectively, until loss of consciousness. Anaesthesia was maintained with propofol target-controlled infusion in group 1 or by constant rate infusion in the other two groups. Computer simulations were used to calculate blood and effect-site propofol concentrations. Mean induction times (SD) were 78 (65)s in group I versus 51 (10)s and 62 (12)s in groups II and III, respectively (p < 0.05 between groups II and III). Mean induction doses were: 1.31 (0.44), 2.74 (0.56) and 1.77 (0.43) mg.kg-1 and mean maintenance doses were 13.4 (3.55), 9.32 (1.72) and 9.97 (1.53) mg.kg-1 h-1 in groups I, II and III, respectively (p < 0.05 between all groups). There was a lower incidence of apnoea in group I than in groups II and III. There were no significant differences between the groups in other objective parameters of anaesthetic quality studied. Computer simulations showed an "overshoot' in propofol blood and effect-site concentration with manual induction and significantly higher maintenance levels with target-controlled infusion.

Adult↗
PubMed1996

Single dose i.v. tropisetron in the prevention of postoperative nausea and vomiting after gynaecological surgery.

In a prospective, randomized, multicentre, double-blind, placebo-controlled study, we have compared the efficacy of a single i.v. dose of tropisetron 0.5 mg, 2 mg and 5 mg in the prevention of postoperative nausea and vomiting (PONV). We studied 385 ASA class I and II female patients undergoing abdominal or vaginal gynaecological surgery, including laparoscopy. Tropisetron or placebo were administered before a standardized general anaesthetic. The frequency of vomiting in the 24-h period after entry into the recovery room was reduced from 44% after placebo to 31%, 26% and 30% after tropisetron 0.5 mg, 2 mg and 5 mg, respectively (P = 0.06, P = 0.009 and P = 0.043; unadjusted). Compared with placebo, nausea was reduced from 55% to 46%, 34% and 46% (P = 0.25, P = 0.003, P = 0.22), and need for rescue treatment from 39% to 29%, 23% and 35% (P = 0.13, P = 0.017 and P = 0.59) for the same groups. Tropisetron 2 mg appeared to be the optimal dose for prophylaxis against PONV with a side-effect profile similar to that of placebo.

Adult↗
PubMed1996

Accumulation of foreign gases during closed-system anaesthesia.

In a previous study, accumulation of methane was found at the end of closed-system ventilation. As on-line analysis of gas concentrations is now available, we examined the progressive increase in concentrations of methane, carbon monoxide and acetone during modern, closed-system conditions, and their influence on infrared halothane analysis, in 26 non-pregnant, gynaecological patients. A computer-controlled closed-system anaesthesia apparatus (PhysioFlex) was used for ventilation during total i.v. anaesthesia (excluding nitrous oxide or potent inhalation anaesthetics) for gynaecological laparoscopy. Methane, carbon monoxide and acetone concentrations were analysed every 15 min in a photoacoustic infrared monitor and halothane concentrations by built-in infrared spectrometry. Mean methane concentrations increased progressively after 105 min to 941 (SD 1094) ppm, but concentrations of carbon monoxide and acetone did not increase significantly. In 18 patients, the infrared measurement falsely indicated 0.79 (0.52)% "halothane" after 60 min, but no reading appeared in the other eight patients. We conclude that methane accumulated progressively under strict closed-system conditions in higher concentrations than reported previously. In two-thirds of patients it induced false "halothane" readings.

Acetone↗
PubMed1992

Propofol anaesthesia for ultrasound guided oocyte retrieval: accumulation of the anaesthetic agent in follicular fluid.

Propofol (2,6-diisopropylphenol, Diprivan, ICI-Pharmaceuticals, Manchester, UK) is widely used either as an adjunct in general anaesthesia or as sole anaesthetic agent by the continuous intravenous route and intermittent bolus injections for minor surgical interventions. For several years, we have been using this kind of anaesthesia in transvaginal oocyte retrieval for in-vitro fertilization (IVF), allowing a completely painless puncture on an out-patient basis. From in-vitro studies on mouse oocytes, it appeared that propofol could be deleterious for fertilization in a dose- and time-dependent manner. We therefore investigated the concentrations of propofol in follicular fluid during oocyte retrieval in women. We measured propofol levels in serum and follicular fluid of nine patients at fixed intervals during ultrasound guided oocyte retrieval. Serum levels fluctuated randomly, due to interference from top-off doses of propofol. In follicular fluid, however, we found a steady increase of propofol levels, which was proportional to the total dose of propofol administered. These data indicate that propofol accumulates in follicular fluid. Although it seems unlikely that propofol as used in the present protocol exerts a clinically significant unfavourable effect on IVF, we suggest that the oocyte retrieval procedure should be kept as short as possible, in order to limit the accumulation of the anaesthetic in follicular fluid.

Dose-Response Relationship, Drug↗