Patients Requiring Ambulatory Surgery Under General Anesthesia Clinical Trial
Official title:
ED 50 of Propofol for Supreme LMA Insertion With and Without Remifentanil. A Randomized Trial
The aims of this study were to determine the clinically required concentration of propofol for LMA Supreme insertion, and to examine to what extent remifentanil reduces the dose of propofol and improves conditions for it's insertion.
The single-use Laryngeal Mask Airway SupremeTM (SLMA, Laryngeal Mask Company Limited,
Singapore) is a new single use supraglottic airway device introduced recently that present
combined features of the LMA ProSealTM (PLMA, Laryngeal Mask Company Limited) and the LMA
FastrachTM (FLMA, Laryngeal Mask Company Limited). The mask has an anatomically shaped
airway tube, elliptical in cross-section that facilitates easy insertion and minimizes
accidental rotation. The cuff bowl is designed to prevent airway kinking and offer higher
airway seal pressures around the laryngeal opening than the LMA ClassicTM (CLMA, Laryngeal
Mask Company Limited) It has a drain tube that provides functional separation of the
respiratory and digestive tracts to prevent gastric aspiration. Even though insertion of the
SLMA is associated with a higher initial success rate, fewer airway manipulations and a safe
and effective airway during anaesthesia, the anaesthetic techniques for its insertion were
not standardised. Most available data on the requirements of anaesthetic drugs and
co-induction agents used for insertion of SLMA originate from research involving other
assessments of the SLMA such as the seal with respiratory and gastrointestinal tract.We
tested for differences in the predicted concentration of propofol with and without
remifentanil for insertion of the SLMA.
Methods: 50 patients ASA class I or II aged 18-75 years undergoing ambulatory elective
surgery will be randomized to one of two groups: those who receive propofol + saline
(control group: n = 25) or propofol + remifentanil (propofol-remifentanil group: n=25). We
will use target-controled infusions (Alaris®PK) for both drugs: propofol (Marsh et al.´s
pharmacokinetic model) and remifentanil (Minto et al.´s pharmacokinetic model). The patients
wil be premedicated with midazolam 1 mg iv before surgery. The target concentration for each
patient was determined using the Dixon´s up-and-down method. Predetermined propofol and
remifentanil blood and effect site concentrations were held constant for at least 10 min.
After equilibration of plasma and effect site propofol concentrations, the SLMA will be
inserted, and secured according to the manufacture´s recommendations, without the use of
muscle relaxants. In control group, propofol concentrations will start at 4 μg ml-1, with
0,5 μg ml-1 as the step size, with the coadministration of saline. In propofol-remifentanil
group, propofol + remifentanil at a target-controlled infusion 5 ng/mL will be
coadministered. A single measurement will be obtained from each patient. If the patient
reacted with movement, the propofol concentration for the next patient was increased by 0.5
μg ml-1 ±1 ; if there was no movement, it was decreased by 0.5 μg ml-1 ±1 . Movement was
defined as bucking or gross purposeful muscular movement within 1 min of LMA insertion.
Values of Cp 50 wil be determined by calculating the midpoint concentration after at least
seven crossover points (movement/non movement) will be obtained in each group.
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Allocation: Randomized, Endpoint Classification: Safety/Efficacy Study, Intervention Model: Parallel Assignment, Masking: Double Blind (Subject, Investigator, Outcomes Assessor)