Anesthesia and analgesia
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Anesthesia and analgesia · Sep 1997
Context-sensitive half-times and other decrement times of inhaled anesthetics.
The length of anesthetic administration influences the rate at which concentrations of anesthetics decrease after their discontinuation. This is true for both intravenous (I.V.) and inhaled anesthetics. This has been explored in detail for I.V. anesthetics using computer simulation to calculate context-sensitive half-times (the time needed for a 50% decrease in anesthetic concentration) and other decrement times (such as the times needed for 80% or 90% decreases in anesthetic concentration). However, decrement times have not been reported for inhaled anesthetics. In this report, published pharmacokinetic parameters and computer simulation were used to compare the context-sensitive half-times and the 80% and 90% decrement times of the expected central nervous system concentrations for enflurane, isoflurane, sevoflurane, and desflurane. The context-sensitive half-times for all four anesthetics are small (<5 min) and do not increase significantly with increasing duration of anesthesia. The 80% decrement times of both sevoflurane and desflurane are also small (<8 min) and do not increase significantly with duration of anesthesia. However, the 80% decrement times of isoflurane and enflurane increase significantly after approximately 60 min of anesthesia, reaching plateaus of approximately 30 and 35 min. The 90% decrement time of desflurane increased slightly from 5 min after 30 min of anesthesia to 14 min after 6 h of anesthesia. It remained significantly less than the 90% decrement times of sevoflurane, isoflurane, and enflurane, which reached values of 65 min, 86 min, and 100 min, respectively, after 6 h of anesthesia. ⋯ The major differences in the rates at which desflurane, sevoflurane, isoflurane, and enflurane are eliminated occur in the final 20% of the elimination process.
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Anesthesia and analgesia · Sep 1997
Randomized Controlled Trial Comparative Study Clinical TrialIntracranial pressure, middle cerebral artery flow velocity, and plasma inorganic fluoride concentrations in neurosurgical patients receiving sevoflurane or isoflurane.
This study examined the concentration-related effects of sevoflurane and isoflurane on cerebral physiology and plasma inorganic fluoride concentrations. Middle cerebral artery flow velocity (Vmca), intracranial pressure (ICP), electroencephalogram (EEG) activity, and jugular bulb venous oxygen saturation were measured, and cerebral perfusion pressure (CPP) and estimated cerebral vascular resistance (CVRe) were calculated at baseline and at 0.5, 1.0, and 1.5 minimum alveolar anesthetic concentration (MAC) sevoflurane (n = 8) or isoflurane (n = 6). Mannitol 0.5-0.75 g/kg was given before dural incision, and blood was sampled for plasma inorganic fluoride during surgery and for up to 72 h postoperatively. Both sevoflurane and isoflurane decreased Vmca (to 31 +/- 12 - 36 +/- 14 cm/s, mean +/- SD), did not significantly alter ICP (13 +/- 9 - 15 +/- 11 mm Hg), and did not cause epileptiform EEG activity. With sevoflurane, decreased Vmca was accompanied by decreased CPP and unchanged CVRe at 0.5 MAC, and unchanged CPP and increased CVRe at 1.0 and 1.5 MAC. Plasma inorganic fluoride was 39.0 +/- 12.9 microM at the end of anesthesia (3.2 +/- 2.0 MAC hours) with sevoflurane, similar to the value (36.2 +/- 3.9 microM) for 3.7 +/- 0.1 MAC hours sevoflurane in patients not receiving mannitol. Decreased Vmca during sevoflurane presumably results from decreased cerebral metabolic rate, with CVRe changing secondarily in accord with CPP. Plasma inorganic fluoride does not seem to be altered by mannitol-induced diuresis. ⋯ In neurosurgical patients, sevoflurane decreased middle cerebral artery flow velocity and caused no epileptiform electroencephalogram activity and no increase of intracranial pressure or plasma inorganic fluoride. These effects are suitable for neurosurgery. Two other possible effects of sevoflurane, i.e., increased cerebrospinal fluid volume and/or intracranial elastance, may not be suitable for neurosurgery and warrant further study.
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Anesthesia and analgesia · Sep 1997
Randomized Controlled Trial Comparative Study Clinical TrialPretreatment with topical 60% lidocaine tape reduces pain on injection of propofol.
We determined whether pretreatment with topical 60% lidocaine tape reduced the incidence of pain on injection of propofol compared with mixing intravenous lidocaine with propofol. In a randomized, double-blind trial, 90 patients were allocated to one of three groups: pretreatment with a bioocclusive dressing and administration of a premixed solution of propofol 180 mg and 2 mL of normal saline (Group A); pretreatment with 60% lidocaine tape and a premixed solution of propofol and normal saline (Group B); or pretreatment with a bioocclusive dressing and a premixed solution of propofol 180 mg and lidocaine 40 mg (Group C). The incidences of pain in Groups A, B, and C were 86.7%, 33.4%, and 20%, respectively. Group B and Group C had a significantly lower incidence of pain than Group A. There was no significant difference in the incidence of pain between Group B and Group C. There was no significant difference in the distribution of site of pain on injection of propofol among the three groups. Pretreatment with topical 60% lidocaine tape reduced the incidence of pain on injection of propofol similar to that of intravenous lidocaine mixed with propofol. ⋯ Pretreatment with topical 60% lidocaine tape reduces the pain associated with injection of propofol, a frequently used intravenous anesthetic. This approach should increase patient comfort during induction of anesthesia.
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Anesthesia and analgesia · Sep 1997
Randomized Controlled Trial Comparative Study Clinical TrialProphylaxis for vomiting by children after tonsillectomy: dexamethasone versus perphenazine.
The effects of dexamethasone and perphenazine on vomiting after tonsillectomy in children were compared in 226 healthy children aged 2-12 yr. The study was randomized, stratified, blocked, and double-blind. Anesthesia was induced intravenously (I.V.) with propofol or by inhalation with halothane and N2O. Dexamethasone 150 microg/kg or perphenazine 70 microg/kg was administered I.V. after the induction of anesthesia in a double-blind fashion. Perioperative management of emesis, pain, fluids, and patient discharge was all standardized. The groups had similar demographic characteristics. Perphenazine significantly reduced the incidence of in-hospital vomiting compared with dexamethasone (13% vs 36%, P < 0.001). The incidence of out-of-hospital vomiting was almost identical. Overall, the incidence was significantly different for perphenazine vs dexamethasone (33% vs 46%, P = 0.04) using logistic regression analysis. Of note, sex and induction technique were significant predictors of postoperative vomiting (P < 0.05) using logistic regression analysis, with male patients and those patients undergoing I.V. induction vomiting less. In conclusion, perphenazine more effectively decreases vomiting by children after tonsillectomy in an ambulatory hospital setting compared with dexamethasone. ⋯ Postoperative vomiting can have many debilitating effects, and children undergoing tonsillectomy are at particular risk. We compared the effects of dexamethasone and perphenazine on vomiting after tonsillectomy in 266 children. We found perphenazine more effective than dexamethasone before discharge from hospital but that the two drugs have similar effects after discharge.
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Anesthesia and analgesia · Sep 1997
Randomized Controlled Trial Comparative Study Clinical TrialThe laryngeal mask airway: a comparison between two insertion techniques.
The purpose of the study was to compare the ease of insertion of the laryngeal mask airway using the standard uninflated approach or with a fully inflated cuff. Two hundred consecutive patients undergoing anesthesia using a laryngeal mask airway were randomized to have the laryngeal mask inserted using either method. Successful insertion was judged primarily by the clinical function of the airway. The number of insertion attempts to achieve a satisfactory airway and whether an alternative technique was required for success were recorded. On removal of the laryngeal mask, a blind observer noted the presence or absence of blood. Just before leaving the recovery room, each patient was asked whether they had a sore throat. Insertion technique made no difference with regard to first attempt success. However, the presence of blood on the removed masks (P < 0.01) and sore throat (P < 0.01) were less frequent in the inflated cuff group. We conclude that the inflated cuff insertion technique is an acceptable alternative to the standard approach and has the advantage of reducing the incidence of minor pharyngeal mucosal trauma, as evidenced by mucosal bleeding and sore throat. ⋯ Insertion of the laryngeal mask airway with the cuff fully inflated is equally successful to the standard uninflated approach in experienced hands. The inflated technique was associated with less minor pharyngeal mucosal trauma and, consequently, a lower incidence of postoperative sore throat. This implies that the inflated technique would be acceptable to the general population of laryngeal mask users.