Influence of nitrous oxide on minimum alveolar concentration of sevoflurane for laryngeal mask insertion in children

BACKGROUND: Inhalational induction with sevoflurane and nitrous oxide is frequently used for Laryngeal Mask Airway (LMA; Laryngeal Mask Company, Henley-on-Thames, United Kingdom) insertion in children. The authors determined the influence of nitrous oxide on the minimum alveolar concentration (MAC) of sevoflurane for LMA insertion. METHODS: One hundred twenty unpremedicated children (age, 1-9 yr; American Society of Anesthesiologists physical status I) were randomly assigned to receive 1 of 15 end-tidal concentrations of nitrous oxide and sevoflurane for inhalational induction via a facemask: 0% nitrous oxide with 1.2, 1.4, 1.6, 1.8, or 2.0% sevoflurane; 33% nitrous oxide with 0.8, 1.0, 1.2, 1.4, or 1.6% sevoflurane; or 67% nitrous oxide with 0.4, 0.6, 0.8, 1.0, or 1.2% sevoflurane. The LMA was inserted after steady state end-tidal anesthetic concentrations had been maintained for 15 min. The response to insertion was recorded by three independent blinded observers. The interaction between nitrous oxide and sevoflurane was determined using logistic regression analysis. RESULTS: The MAC of sevoflurane for LMA insertion (95% confidence limit) was 1.57% (1.42-1.72%), and the concentration of sevoflurane required to prevent movement in 95% of children was 1.99% (1.81-2.57%). The addition of 33% and 67% nitrous oxide linearly decreased the MAC of sevoflurane for LMA insertion by 22% and 49%, respectively (P < 0.001). The interaction coefficient between nitrous oxide and sevoflurane did not differ from zero (P = 0.7843), indicating that the relation was additive. CONCLUSIONS: Nitrous oxide and sevoflurane suppress the responses to LMA insertion in a linear and additive fashion in children.     

Severity of airway hyperreactivity associated with laryngeal mask airway removal: correlation with volatile anesthetic choice and depth of anesthesia.

STUDY OBJECTIVE: To compare the influence of anesthetic depth and choice of volatile anesthetic drug on the incidence and severity of airway hyperreactivity associated with Laryngeal Mask Airway (LMA) removal. DESIGN: Randomized observer-blinded study. SETTING: Ambulatory Surgical Center at a University Medical Center. PATIENTS: 123 ASA physical status I and II children undergoing infraumbilical procedures. INTERVENTIONS: Patients were randomly assigned to one of four treatment groups: Group 1 = anesthetic induction with halothane, maintenance with isoflurane, nitrous oxide (N(2)O), and oxygen (O(2)), LMA removed when child awakened; Group 2 =anesthetic induction and maintenance as in Group 1, LMA removed while child anesthetized with age adjusted 2 minimum alveolar concentration (MAC) end-tidal concentration of isoflurane; Group 3 = anesthetic induction and maintenance with sevoflurane, N(2)O, and O(2), LMA removed when child awakened; Group 4 = anesthetic induction and maintenance as in Group 3, but LMA removed while child anesthetized with age-adjusted 2 MAC end-tidal concentration of sevoflurane. MEASUREMENTS AND MAIN RESULTS: Severity of airway hyperreactivity was graded as mild, moderate, or severe. A significant difference was not found amongst the four groups with respect to mild and moderate airway hyperreactivity. Severe airway hyperreactivity leading to a critical event [partial or complete laryngospasm with oxygen saturation (SPO(2)) < 85%] was only encountered in Group 1 patients (incidence 13%). Adverse airway events (SPO(2) < 90%, vomiting and bronchospasm) were also significantly higher in Group 1 (p < 0.05). Isoflurane use was independently associated with significantly higher airway hyperreactivity when compared with sevoflurane (p < 0.05). CONCLUSIONS: Depth of anesthesia during LMA removal does not appear to affect the incidence or severity of airway hyperreactivity when sevoflurane is the maintenance anesthetic. However, awake LMA removal during isoflurane anesthesia results in a higher incidence of adverse airway events and carries the risk of severe airway hyperreactivity.     

Additive contribution of nitrous oxide to sevoflurane minimum alveolar concentration for tracheal intubation in children.

BACKGROUND: To study the interaction between nitrous oxide and sevoflurane during trachea intubation, the authors determined the minimum alveolar concentration of sevoflurane for tracheal intubation (MAC(TI)) with and without nitrous oxide in children. METHODS: Seventy-two children aged 1-7 yr were assigned randomly to receive one of three end-tidal concentrations of nitrous oxide and one of four end-tidal concentrations of sevoflurane: 0% nitrous oxide with 2.0, 2.5, 3.0, or 3.5% sevoflurane: 33% nitrous oxide with 1.5, 2.0, 2.5, or 3.0% sevoflurane; or 66% nitrous oxide with 1.0, 1.5, 2.0, or 2.5% sevoflurane. After steady state end-tidal anesthetic concentrations were maintained for at least 10 min, laryngoscopy and intubation were attempted using a straight-blade laryngoscope and an uncuffed tracheal tube. The interaction between nitrous oxide and sevoflurane was investigated using logistic regression analysis of the responses to intubation. RESULTS: Logistic regression curves of the probability of no movement in response to intubation in the presence of sevoflurane and 0, 33, and 66% nitrous oxide were parallel. The interaction coefficient between nitrous oxide and sevoflurane did not differ significantly from zero (P = 0.89) and was removed from the logistic model. The MAC(TI) (+/- SE) of sevoflurane was 2.66+/-0.16%, and the concentration of sevoflurane required to prevent movement in 95% of children was 3.54+/-0.25%. Thirty-three percent and 66% nitrous oxide decreased the MAC(TI) of sevoflurane by 18% and 40% (P<0.001), respectively. CONCLUSIONS: We conclude that nitrous oxide and sevoflurane suppress the responses to tracheal intubation in a linear and additive fashion in children.     

The ED95 of end-tidal sevoflurane concentration for the smooth exchange of the tracheal tube for a laryngeal mask airway is 2.97%

PURPOSE: Exchanging the tracheal tube for the laryngeal mask airway (the TT/LMA exchange) while the patient is still anesthetized avoids coughing associated with tracheal extubation. This study was conducted to determine the end-tidal concentration of sevoflurane that prevented response to this exchange in 50% patients (MAC(TT/LMA)). METHODS: We studied 21 adult male patients, ASA I, aged 21-54 yr. Anesthesia was induced with thiamylal and sevoflurane, and the trachea was intubated following vecuronium neuromuscular blockade. Anesthesia was maintained with sevoflurane and nitrous oxide in oxygen. After surgery, a predetermined end-tidal sevoflurane concentration was achieved and a steady state was maintained for at least 20 min. The concentration at which the TT/LMA exchange was attempted was determined by a modification of Dixon's up-and-down method with 0.25% as the step size. At the time of the TT/LMA exchange, no residual nitrous oxide > 3% was detected, and the return to normal neuromuscular function was confirmed. When the TT/LMA exchange was accomplished without coughing, movement, or airway obstruction, it was considered a smooth exchange. RESULTS: Sevoflurane MAC(TT/LMA) determined using the up-and-down method was 2.63% +/- 0.14%. The 50% effective dose obtained using a probit analysis was similar [2.53% (95% confidence limits, 2.13-2.82%)]. CONCLUSION: Sevoflurane MAC(TT/LMA) in adult male patients was 2.63% (1.54 MAC) and may be useful for the smooth exchange of the tracheal tube for the LMA in a clinical setting.     

Similar haemodynamic, respiratory and metabolic changes with the use of sevoflurane or halothane in children breathing spontaneously via a laryngeal mask airway

BACKGROUND: In preschool children, short-lasting surgical procedures are often performed under combined inhalational and regional anaesthesia with the child breathing spontaneously via a laryngeal mask airway (LMA). Despite widespread use, only limited data are available on haemodynamic, respiratory and metabolic effects of sevoflurane and halothane during LMA anaesthesia. METHODS: In an open-label, randomised, controlled study, 49 children (aged 3-8 years) were allocated to receive either sevoflurane or halothane in 60% nitrous oxide. After insertion of the LMA, end-tidal concentrations of sevoflurane or halothane were maintained at 1 MAC with the child ventilating spontaneously throughout the entire procedure. Analgesia was provided by caudal block. Haemodynamic and respiratory parameters were recorded, and capillary blood-gas samples were obtained repeatedly. RESULTS: Changes in heart rate (HR) and systolic blood pressure were similar in both groups during all observed periods, apart from a significantly higher increase in HR during inhalational induction with sevoflurane (P<0.05). Regression slope analysis during anaesthesia revealed a decrease of the respiratory rate of 5 breaths h-1 (P<0.001) and an increase of end-tidal PCO2 and capillary PCO2 of about 0.25 kPa h-1 (P<0.001), with no significant difference between the two groups. Base excess, calculated in capillary blood gas samples, did not change over time (P>0.5) in either group. CONCLUSIONS: The use of approximately 1 MAC sevoflurane or halothane in 60% N2O in children breathing spontaneously via LMA resulted in comparable haemodynamic, respiratory and metabolic changes, and clinically relevant deteriorations did not occur during the 65-min study period.     

Effects of Sevoflurane with and without Nitrous Oxide on Human Cerebral Circulation: Transcranial Doppler Study

Background: This study was designed to evaluate the effects of sevoflurane with and without nitrous oxide on human middle cerebral artery (MCA) flow velocity, cerebrovascular carbon dioxide reactivity, and autoregulation compared with the awake state using transcranial Doppler ultrasonography.

Methods: In 14 patients, the time-mean middle cerebral artery flow velocity (Vmca) was measured when the end-tidal carbon dioxide level was approximately 30, 40, and 50 mmHg under the following conditions: (1) awake; (2) with 2% (1.2 MAC) sevoflurane; and (3) with 1.2 MAC sevoflurane-60% nitrous oxide. In six other patients, the cerebrovascular autoregulation during anesthesia was determined using intravenous phenylephrine to increase blood pressure.

Results: Sevoflurane (1.2 MAC) significantly decreased Vmca compared with the awake value at each level of end-tidal carbon dioxide, whereas 1.2 MAC sevoflurane-60% nitrous oxide did not exert significant influence. The Vmca in normocapnic patients decreased from 69 cm/s to 55 cm/s with 1.2 MAC sevoflurane and then increased to 70 cm/s when nitrous oxide was added. Sevoflurane (1.2 MAC) with and without 60% nitrous oxide had a negligible effect on cerebrovascular carbon dioxide reactivity. A phenylephrine-induced increase of mean arterial pressure did not influence Vmca during anesthesia.     

Anesthesia with 1.5 minimum alveolar concentration sevoflurane is not altered by physostigmine as measured by bispectral and clinical indices

STUDY OBJECTIVE: To evaluate the effect of physostigmine on 1.5% sevoflurane anesthesia and recovery. DESIGN: Prospective, randomized, double-blinded study. SETTING: Operating room of a university-affiliated, metropolitan hospital (Aretaieion Hospital and St Savas Hospital). PATIENTS: Forty female American Society of Anesthesiologists physical status I and II patients scheduled for breast biopsy. INTERVENTIONS: Patients were randomly assigned in physostigmine (PHYSO) and normal-saline (NS) group. Anesthesia was induced with sevoflurane 8% using a vital capacity breath technique, and rocuronium 0.6 mg/kg was given to facilitate Laryngeal Mask Airway (LMA) No. 4 insertion. Anesthesia was maintained with end-tidal sevoflurane 1.5 minimum alveolar concentration (MAC; 3% end-tidal concentration) throughout the procedure. MEASUREMENTS: After skin closure and under steady-state sevoflurane anesthesia 1.5 MAC, heart rate, blood pressure, and Bispectral Index (BIS) were recorded. Immediately after, the PHYSO group received intravenous 2 mg of physostigmine, whereas the NS group received equal volume of normal saline. Bispectral Index and hemodynamic measurements were recorded 5, 8, and 10 minutes after treatment. Anesthesia was then discontinued and the LMA was removed. Zero, 15, and 30 minutes after LMA removal, patients were evaluated for orientation, sedation, sitting ability, and the "picking up matches" test, as well as for nausea and vomiting. MAIN RESULTS: No difference was found in BIS (29 +/- 4, 32 +/- 6, 31 +/- 6, 30 +/- 7, 84 +/- 11 in the PHYSO group vs 29 +/- 6, 30 +/- 6, 30 +/- 5, 31 +/- 5, 86 +/- 7 in the NS group), hemodynamic parameters, or recovery parameters between the 2 groups at any time. No nausea or vomiting was observed in either group. CONCLUSIONS: Physostigmine did not influence BIS values or early recovery when administered to patients anesthetized with 1.5 MAC sevoflurane anesthesia.     

Oral clonidine premedication reduces minimum alveolar concentration of sevoflurane for laryngeal mask airway insertion in children

BACKGROUNDS: Sevoflurane is widely employed for inhalational induction in children. Clonidine deepens volatile anesthetics and reduces several types of MAC of sevoflurane. Laryngeal mask airway is a useful device for pediatric anesthesia. The aim of the current study was to determine whether oral clonidine premedication can reduce MAC of sevoflurane for an LMA insertion in children. METHODS: Fifty-six ASA physical status I patients (3-11 years) scheduled for general anesthesia were randomly divided into two groups of 28 patients each. One group (clonidine group) received clonidine 4 microg x kg(-1) approximately 100 min before anesthesia, and the other (control) group did not. Anesthesia was induced with sevoflurane. Each concentration of sevoflurane, at which an LMA insertion was attempted, was predetermined according to the modification of Dixon's up-and-down method with 0.25% as a step size and held constant for at least 20 min before the trial. All responses ('movement' or 'no movement') to an LMA insertion were assessed. RESULTS: Minimum alveolar concentration values of sevoflurane for an LMA insertion were lower in the clonidine group (1.31% +/- 0.18% [mean +/- sd]) than in the control group (2.00% +/- 0.16%). Logistic regression analysis revealed that sevoflurane EC95 values were 1.79% and 2.49% in the clonidine and control groups, respectively. CONCLUSIONS: Oral clonidine premedication reduced the MAC (EC50) and EC95 values of sevoflurane for LMA insertion by 38% and 28%, respectively.     

Success of Tracheal Intubation with Intubating Laryngeal Mask Airways: A Randomized Trial of the LMA Fastrach(TM) and LMA CTrach(TM)

Background: The LMA CTrach(TM) system (The Laryngeal Mask Company, Singapore) is a development of the LMA Fastrach(TM) system (The Laryngeal Mask Company, Singapore), with integrated fiberoptic bundles and a detachable liquid crystal display viewer. This randomized study of 271 patients compared tracheal intubation with these two systems.

Methods: In both groups, ventilation was optimized after insertion of the laryngeal mask conduit before proceeding further: intubation with the LMA Fastrach(TM), and optimizing the conduit placement and view and then intubation with the LMA CTrach(TM). The first-attempt and overall success rates of tracheal intubation, and the times required, were recorded.

Results: Tracheal intubation was successful on the first attempt in 93.3% of patients with the LMA CTrach(TM) and 67.9% of patients with the LMA Fastrach(TM) (P < 0.001). The success rates within three attempts were 100% with the LMA CTrach(TM) and 96.4% with the LMA Fastrach(TM) (P = 0.06). The median (interquartile range) time for the complete tracheal intubation process was 116 (82-156) s with the LMA CTrach(TM) and 100 (74-121) s with the LMA Fastrach(TM) (P = 0.002). There was no correlation between the grade of conventional laryngoscopy and success of intubation with either system.     

The minimum alveolar concentration (MAC) of sevoflurane in humans

Forty surgical patients were divided into two groups and anesthetized with either sevoflurane and oxygen or sevoflurane, oxygen, and nitrous oxide. The minimum alveolar concentration (MAC) for sevoflurane required to prevent movement in response to surgical incision in healthy patients was 1.71 +/- 0.07% (SE). The AD95 (anesthetic ED95) that prevented 95% of patients from moving was 2.07%. The addition of 63.5% end-tidal nitrous oxide allowed a reduction in the alveolar sevoflurane concentration to 0.66 +/- 0.06% (SE). The reduction in sevoflurane MAC was 61.4%. The AD95 for sevoflurane with 63.5% end-tidal nitrous oxide was 0.94%.     

Additive Contribution of Nitrous Oxide to Sevoflurane Minimum Alveolar Concentration for Tracheal Intubation in Children

Background: To study the interaction between nitrous oxide and sevoflurane during trachea intubation, the authors determined the minimum alveolar concentration of sevoflurane for tracheal intubation (MACTI) with and without nitrous oxide in children.

Methods: Seventy-two children aged 1-7 yr were assigned randomly to receive one of three end-tidal concentrations of nitrous oxide and one of four end-tidal concentrations of sevoflurane: 0% nitrous oxide with 2.0, 2.5, 3.0, or 3.5% sevoflurane; 33% nitrous oxide with 1.5, 2.0, 2.5, or 3.0% sevoflurane; or 66% nitrous oxide with 1.0, 1.5, 2.0, or 2.5% sevoflurane. After steady state end-tidal anesthetic concentrations were maintained for at least 10 min, laryngoscopy and intubation were attempted using a straight-blade laryngoscope and an uncuffed tracheal tube. The interaction between nitrous oxide and sevoflurane was investigated using logistic regression analysis of the responses to intubation.

Results: Logistic regression curves of the probability of no movement in response to intubation in the presence of sevoflurane and 0, 33, and 66% nitrous oxide were parallel. The interaction coefficient between nitrous oxide and sevoflurane did not differ significantly from zero (P = 0.89) and was removed from the logistic model. The MACTI (+/- SE) of sevoflurane was 2.66 +/- 0.16%, and the concentration of sevoflurane required to prevent movement in 95% of children was 3.54 +/- 0.25%. Thirty-three percent and 66% nitrous oxide decreased the MACTI of sevoflurane by 18% and 40% (P < 0.001), respectively.     

The effect of adding nitrous oxide on MAC of sevoflurane combined with two target-controlled concentrations of remifentanil in women

BACKGROUND AND OBJECTIVE: The aim of this prospective, randomized, double-blind study was to determine the effects of adding nitrous oxide on sevoflurane requirement for blunting sympathetic responses after surgical incision combined with two different target-controlled concentrations of remifentanil (1 and 3 ng mL(-1)) in female. METHODS: 102 female patients, aged 20-50 yr, ASA I, undergoing general anaesthesia for elective abdominal surgery were enrolled and randomly allocated to receive sevoflurane anaesthesia alone (Group A, n=53), or with the addition of 60% nitrous oxide (Group N, n=49). Patients of both groups were further assigned to receive a target-controlled remifentanil infusion with an effect-site concentration of either 1 ng mL(-1) (Group N1, n=27; Group A1, n=30), or 3 ng mL(-1) (Group N3, n=22; Group A3, n=23). Sympathetic responses to surgical incision were determined after a 20-min period of stable end-tidal sevoflurane and target-controlled remifentanil concentrations. Predetermined end-tidal sevoflurane concentrations and minimum alveolar concentration (MAC) for each group were determined using an up-and-down sequential allocation technique. RESULTS: The MAC of sevoflurane was 3.96% (95% confidence interval, CI95: 3.69-4.23%) in Group A1 and 1.2% (CI95: 0.9-1.3%) in Group N1 (P < 0.01), while in Groups A3 and N3 the MAC of sevoflurane was 0.36% (CI95: 0.24-0.47%) and 0.18% (CI95: 0.1-0.3%), respectively (P < 0.05). CONCLUSION: Adding 60% nitrous oxide reduces the MAC of sevoflurane by 70% when using a remifentanil concentration of 1 ng mL(-1) and 50% when using a remifentanil concentration of 3 ng mL(-1).     

七氟烷抑制全麻患儿喉罩通气道拔除反应的最低肺泡有效浓度

目的 确定七氟烷抑制全麻患儿喉罩通气道拔除反应的最低肺泡有效浓度(MAC).方法 择期全麻手术患儿25例,ASA Ⅰ或Ⅱ级,年龄3～8岁.吸人8%七氟烷麻醉诱导后置人喉罩,吸入3%七氟烷维持麻醉.术中均保留自主呼吸.术毕吸除口腔分泌物后维持预定七氟烷浓度10 min,采用序贯法调整七氟烷浓度,初始呼气末七氟烷浓度为1%,相邻浓度比值为1.2,喉罩通气道拔除反应阳性时,则下一例患儿升高1个浓度梯度;喉罩通气道拔除反应阴性时,则下一例患儿降低1个浓度梯度.拔除喉罩后1 min内患儿出现有目的性的肢体运动、屏气、喉痉挛和低氧血症(spO2<95%)为喉罩通气道拔除反应阳性,否则为阴性.将阳性反应到阴性反应的中点设为平衡点,计算所有平衡点七氟烷浓度的平均值,即为MAC.结果 七氟烷抑制喉罩通气道拔除反应的MAC为0.98%.结论 七氟烷抑制全麻患JL(3～8岁)喉罩通气道拔除反应的最低肺泡有效浓度为0.98%.     

Comparison of Mucosal Pressures Induced by Cuffs of Different Airway Devices

Background: High pressures exerted by balloons and cuffs of conventional endotracheal tubes, the Combitube(R) (Tyco Healthcare Nellcor Mallinckrodt, Pleasanton, CA), the EasyTube(R) (Teleflex Ruesch, Kernen, Germany), the Laryngeal Mask Airway (TM) (LMA North America, San Diego, CA), the Intubating Laryngeal Mask Airway (TM) (Fastrach(R); LMA North America), the ProSeal (TM) (LMA North America), and the Laryngeal Tube (LT; VBM Medizintechnik, Sulz, Germany) may traumatize the pharyngeal mucosa. The aim of this study was to compare pressures exerted on the pharyngeal, tracheal, and esophageal mucosa by different devices designed for securing the patient's airways.

Methods: Nineteen fresh cadavers were included. To measure mucosal pressures, microchip sensors were fixed on the anterior, lateral, and posterior surfaces of the proximal balloon and the distal cuff of the investigated devices. Depending on the respective airway device, the cuff volume was increased in 10-ml increments at the proximal balloon starting from 0 to a maximum of 100 ml, and in 2-ml increments at the distal cuff starting from 0 up to 12 ml.

Results: Tracheal mucosal pressures were significantly higher using the Combitube(R) compared with the endotracheal tube and the EasyTube(R). Maximal esophageal pressures were significantly higher using the EasyTube(R) compared with the Combitube(R). Using cuff volumes according to the manufacturers' guidelines, we found the highest pharyngeal pressures with the Intubating Laryngeal Mask Airway (TM) versus all other devices. At maximal volumes, the Laryngeal Mask Airway (TM), the Intubating Laryngeal Mask Airway (TM), and the ProSeal (TM) induced significantly higher pharyngeal pressures compared with all other devices. Using a pharyngeal cuff volume of 40 ml, the Intubating Laryngeal Mask Airway (TM) followed by the Laryngeal Mask Airway (TM) exerted significantly higher pressures compared with the other devices.     

Airway management in spontaneously breathing anaesthetized children: comparison of the Laryngeal Mask Airway with the cuffed oropharyngeal airway

BACKGROUND: The efficacy and safety of the smallest size of the cuffed oropharyngeal airway (COPA) for school age, spontaneously breathing children was investigated and compared with the Laryngeal Mask Airway (LMA). METHODS: Seventy children of school age (7-16 years) were divided into two groups: the COPA (n=35) and the LMA (n=35). Induction was with propofol i.v. or halothane, nitrous oxide, oxygen and fentanyl. After depression of laryngopharyngeal reflexes, a COPA size 8 cm or an LMA was inserted. Ventilation was manually assisted until spontaneous breathing was established. For maintenance, propofol i.v. and fentanyl or halothane with nitrous oxide were used. Local anaesthesia or peripheral blocks were also used. RESULTS: Both extratracheal airways had a highly successful insertion rate, but more positional manoeuvres to achieve a satisfactory airway were required with the COPA, 28.6% versus LMA 2.9%. The need to change the method of airway management was higher (8.6%) in the COPA group. After induction, the need for assisted ventilation was higher in the LMA group 54.3% versus 20% in the COPA group. Airway reaction to cuff inflation was higher in the LMA group 14.3% versus COPA 5.7%. Problems during surgery were similar, except continuous chin support to establish an effective airway was more frequent (11.4%) in the COPA group. In the postoperative period, blood on the device and incidence of sore throat were detected less in the COPA group. CONCLUSIONS: The COPA is a good extratracheal airway that provides new possibilities for airway management in school age children with an adequate and well sealed airway, during spontaneous breathing or during short-term assisted manual ventilation.     

Effect of nitrous oxide on the bispectral index during sevoflurane anesthesia

We studied the effects of nitrous oxide on the relationship between end-tidal sevoflurane concentration and bispectral index (BIS) in patients undergoing abdominal surgery. Anesthesia was maintained with combination of epidural and sevoflurane anesthesia in air (control group; n = 15) or with 67% nitrous oxide (nitrous oxide group; n = 15). The end-tidal sevoflurane concentration was increased by 0.5% every 15 min to 3% and BIS values were recorded at each step. In both groups, sevoflurane decreased BIS values in a dose-dependent manner and the decrease in BIS reached plateau at 2% of sevoflurane. Nitrous oxide with sevoflurane caused more reduction in BIS in comparison with sevoflurane alone. The sevoflurane concentration for BIS at 50 in the nitrous oxide group (0.9 +/- 0.4%) was significantly lower than that in the control group (1.2 +/- 0.4%). The results suggest that the hypnotic effect of sevoflurane was enhanced by the addition of nitrous oxide during abdominal surgery.     

The epileptogenic properties of the volatile anesthetics sevoflurane and isoflurane in patients with epilepsy

No study comparing epileptogenicity of sevoflurane to other volatile anesthetics has been performed. We compared the epileptogenic properties of sevoflurane to isoflurane in patients with epilepsy. In 24 mentally and/or physically disabled patients, 12 with epilepsy and 12 without epilepsy, electroencephalograms were recorded under anesthesia with 1.0 minimum alveolar anesthetic concentration (MAC), 1.5 MAC, and then 2.0 MAC sevoflurane or isoflurane under three ventilatory conditions: (A) 100% oxygen, and end-tidal CO(2) partial pressure (ETCO(2)) = 40 mm Hg, (B) 50% oxygen, 50% nitrous oxide, ETCO(2) = 40 mm Hg, and (C) 100% oxygen, ETCO(2) = 20 mm Hg. Spike activity was evaluated as a spike-and-wave index (% durations of spike and wave). The spike-and-wave index increased (P<0.05) from 1.99%+/-0.96% during 1.0 MAC sevoflurane to 6.14% +/- 4.45% during 2.0 MAC sevoflurane in (A) in the epilepsy group, while no spike activity was observed in the nonepilepsy group. Only a few spikes were observed under isoflurane anesthesia, 0.04% +/- 0.04% in (A), with no spikes in (B) and (C). Supplementation with 50% nitrous oxide or hyperventilation (P<0.05) suppressed the occurrence of spikes. Sevoflurane has a stronger epileptogenic property than isoflurane, but nitrous oxide or hyperventilation counteracts this specific epileptogenic property. Implications: The stronger epileptogenicity of sevoflurane than isoflurane was confirmed in a controlled study in patients with epilepsy. Hyperventilation and supplementation of nitrous oxide under sevoflurane anesthesia suppressed epileptogenicity. A combination of sevoflurane and nitrous oxide may be a safer method for seizure-prone patients than the use of sevoflurane alone.     

Laryngeal Resistance before and after Minor Surgery: Endotracheal Tube versus Laryngeal Mask Airway™

Background: The placement of an endotracheal tube (ETT) may promote laryngeal swelling, which is an important cause of upper airway obstruction after extubation. The authors hypothesized that laryngeal swelling after ETT placement increases laryngeal resistance and tested that hypothesis by comparing postoperative laryngeal patency between patients with ETT placement and those with a Laryngeal Mask Airway(TM) (LMA(TM)).

Methods: Fourteen adult patients who underwent elective minor surgeries were randomly allocated to two groups whose airway would be managed through ETTs (the ETT group) or LMAs(TM) (the LMA(TM) group) during the surgery. While maintaining at sevoflurane 1 minimum alveolar concentration, the authors measured laryngeal resistance before and after surgery, during both spontaneous breathing and mechanical ventilation under complete paralysis. In addition, they endoscopically measured the vocal cord angle under complete paralysis.

Results: In association with marked swelling of the vocal cords, the vocal cord angle significantly decreased after surgery in the ETT group, whereas the angle did not change in the LMA group. Laryngeal resistance during mechanical ventilation significantly increased only in the ETT group. Laryngeal resistance during spontaneous breathing significantly increased after surgeries in both groups.     

Propofol or sevoflurane for laryngeal mask airway insertion

PURPOSE: Sevoflurane is a volatile anesthetic agent, which combines rapid, smooth inhalational induction of anesthesia with rapid recovery, making it particularly suitable for day case anesthesia. The laryngeal mask airway is often also used in ambulatory anesthesia, with intravenous propofol being the agent of choice for its insertion. Our objective was to compare the conditions for laryngeal mask airway (LMA) insertion obtained by modified vital capacity breath sevoflurane inhalational induction of anesthesia with propofol intravenous induction. METHODS: Eighty-eight patients, aged 18-65 yr, ASA I-II, undergoing general anesthesia for elective surgery were randomized into two groups in a prospective, single-blind study. Patients in Group P (n=44) received 2.5 mg x kg(-1) propofol i.v. and in Group S (n=44) received sevoflurane 8% in nitrous oxide 50% and oxygen. Ventilation was not assisted. Laryngeal mask airway insertion was attempted at one minute intervals from loss of both verbal response and eyelash reflex, by an anesthesiologist unaware of the induction technique. Complications, such as coughing and head movement, were also noted at each attempt. RESULTS: Mean time to successful LMA insertion was 1.3 (1-3) min in P and 2.2 (1-3) min in S, P < 0.05. Eleven patients in Group P, (25%) required additional propofol compared with four (9%) in S, P < 0.05. Incidence of complications was similar in both groups and by 3 min, LMA was successfully inserted in all patients. CONCLUSION: Modified vital capacity breath inhalational induction with sevoflurane 8% is efficient for LMA insertion in most cases, but takes slightly longer than propofol.     

Remifentanil-sevoflurane anaesthesia for laparoscopic cholecystectomy: comparison of three dose regimens

The objective of this study was to determine a dosing regimen for remifentanil-sevoflurane anaesthesia that achieves an optimal balance between quality of anaesthesia and time to recovery. Patients undergoing elective laparoscopic cholecystectomy were randomly allocated to receive 0.4, 0.8 or 1.2 MAC (minimal alveolar concentration) of sevoflurane combined with remifentanil as required to maintain stable anaesthesia. For induction of anaesthesia, the remifentanil dose was 25 microg x kg(-1) x h(-1) and the mean propofol dose which was required to obtain loss of consciousness was 1.59 mg x kg(-1). During the maintenance phase, the mean remifentanil dose was 16.0, 14.1 and 13.0 microg x kg(-1) x h(-1) for the 0.4, 0.8 and 1.2 MAC groups, respectively. The mean sevoflurane maintenance dose was 0.91, 1.24 and 2.1% end-tidal for the 0.4, 0.8 and 1.2 MAC groups, respectively. The incidence of somatic responses was significantly higher in the 0.4 MAC sevoflurane group. Recovery times were significantly faster in the 0.4 compared to the 0.8 and 1.2 MAC groups and in the 0.8 compared to the 1.2 MAC group. The combination of 14 microg x kg(-1) x h(-1) remifentanil and 1.24% end-tidal sevoflurane achieved the optimal balance between the quality, and recovery from anaesthesia.