Yuichi Yaguchi

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.

The awakening concentration of sevoflurane in children.

UNLABELLED Sevoflurane is frequently used as a rapidly acting drug for the induction of anesthesia. We investigated the awakening concentration (MAC-awake) of sevoflurane in ASA physical status I children (age range 2-10 yr). We also investigated the effects of two different doses of clonidine (2 and 4 microg/kg) on the MAC-awake of sevoflurane. Subjects were randomly divided into three groups and received placebo (n = 24), clonidine 2 microg/kg (n = 17), or clonidine 4 microg/kg (n = 22) orally, 100 min before the induction of anesthesia. Sedation scores were estimated, by using a five-point scale, after entry into the operating room, and anesthesia was induced and maintained with sevoflurane in oxygen and balanced nitrogen, without an additional anesthetic. After surgery, end-tidal sevoflurane was decreased stepwise by 0.2% at 15-min intervals, a standardized verbal command was played to the patients, and the MAC-awake was determined. The MAC-awake of sevoflurane alone was 0. 78% +/- 0.24% (mean +/- SD), which decreased to 0.36% +/- 0.09% and 0.36% +/- 0.16% (both P <0.0001, compared with the control group) after premedication with the small and large doses of clonidine, respectively. The lack of any dose-response relationship might be explained by a plateau effect. IMPLICATIONS The awakening concentration of sevoflurane in unpremedicated children was 0.78%. Oral clonidine premedication at a dose of 2 microg/kg reduced the awakening concentration to 0.36%. However, an additional decrease in this value was not observed after the administration of the larger dose of clonidine premedication (4 microg/kg).

The effects of clonidine premedication on sevoflurane requirements and anesthetic induction time

UNLABELLED We assessed the effects of oral clonidine preanesthetic medication (4.5 microg/kg) on the vital capacity rapid-inhalation anesthetic induction time (VCRII time) and minimum alveolar anesthetic concentration (MAC) to prevent a response to a verbal command in 50% of patients (MAC-Awake) by its hypnotic effect, and on MAC-Skin incision for the analgesic effect in patients anesthetized with sevoflurane. We studied 104 adult patients (control group: n = 52, clonidine group: n = 52) aged 30-48 yr scheduled to undergo general anesthesia. Fifty-two patients received oral clonidine 4.5 microg/kg 1.5 h before arrival in the operating room (clonidine group). The patients exhaled to residual volume and took three vital capacity breaths of 5% sevoflurane in oxygen. The VCRII time was defined as the time interval between the initiation of the VCRII and the disappearance of the response to verbal command. Anesthesia was maintained with sevoflurane in oxygen and air. The end-tidal (ET) sevoflurane concentration reached a predetermined value, then the ratio of predetermined ET to inspiratory concentration was maintained at > or =0.95 for at least 15 min before skin incision. After skin incision, the patients were observed for gross purposeful muscular movements. MAC was defined as the average of the cross-over midpoints in each cross-over. After maintaining the ET sevoflurane concentration for 15 min, patients were judged to be awake or asleep. Average times for VCRII using 5% sevoflurane were achieved in 44+/-11 s (mean +/- SD) and 27+/-6 s in the control and clonidine groups, respectively (P = 0.0001). MAC-Awake values of sevoflurane were 0.66%+/-0.03% and 0.35%+/-0.02% (P = 0.0001), and MAC-Skin incision values were 1.97%+/-0.19% and 1.29%+/-0.13% (P = 0.0001) in the control and clonidine groups, respectively. These results suggest that clonidine may have a more potent hypnotic effect than analgesic effect. IMPLICATIONS Oral clonidine preanesthetic medication (4.5 microg/kg) significantly reduces vital capacity rapid inhalation anesthetic induction time and minimum alveolar anesthetic concentration awake for sevoflurane.

A comparison of sex- and weight-based ProSeal laryngeal mask Size selection criteria: A randomized study of healthy anesthetized, paralyzed adult patients

Background:The authors compared the manufacturer’s weight-based formula (size 3 for weight < 50 kg, size 4 for weight 50–70 kg, and size 5 for weight > 70 kg) with a sex-based formula (size 4 for women and size 5 for men) for selecting the appropriate size of ProSeal™ laryngeal mask airway. Methods:Two hundred thirty-seven healthy, anesthetized, paralyzed adult patients (American Society of Anesthesiologists physical status I or II; age, 18–80 yr) were randomly allocated for weight- or sex-based size selection. An experienced user inserted the ProSeal™ laryngeal mask airway with the digital technique. The following were compared: ease of insertion, oropharyngeal leak pressure, ease of ventilation, gas exchange, location of gas leak, anatomic position, mucosal injury, and postoperative pharyngolaryngeal problems. Intraoperative and postoperative data collection were unblinded and blinded, respectively. Results:Ease of insertion, anatomic position, gas exchange, mucosal injury, and postoperative pharyngolaryngeal problems were similar between groups. For the sex-based group, larger ProSeal™ laryngeal mask airways were selected more frequently (P < 0.0001), oropharyngeal leak pressure (P = 0.02) was higher, leak volume (P = 0.004) and leak fraction (P = 0.007) were lower, and oropharyngeal leaks (P = 0.03) were detected less frequently. Conclusion:Size selection for the ProSeal™ laryngeal mask airway is equally effective using the manufacturer’s weight-based formula or the sex-based formula in healthy, anesthetized, paralyzed adult patients, but leakage of small volumes of air from the mouth occurs less frequently with the sex-based formula.

The reduction in minimum alveolar concentration for tracheal extubation after clonidine premedication in children

The effects of clonidine on minimum alveolar concentration for tracheal extubation (MAC-ex) have not been elucidated. Clonidine may lead to prolonged emergence from anesthesia. We investigated the effects of oral clonidine premedication on MAC-ex and examined the emergence properties of sevoflurane in children. Sixty ASA physical status I pediatric patients, aged from 2 to 9 yr, were randomly divided into one of three groups and received placebo, clonidine 2 &mgr;g/kg, or clonidine 4 &mgr;g/kg (n = 20 each) orally, 100 min before the induction of anesthesia. The induction of anesthesia, tracheal intubation, and maintenance of anesthesia were performed with sevoflurane in air and oxygen. MAC-ex was defined according to the modification of Dixon’s up-and-down method, with 0.25% as a step size. In addition, in the Control and 4 &mgr;g/kg groups, the time from tracheal extubation to spontaneous eye opening (eye-opening time) and the time from tracheal extubation to leaving the operating room (awakening time) were recorded. MAC-ex for sevoflurane (mean ± sd) was 1.63% ± 0.13%, 1.04% ± 0.26%, and 0.66% ± 0.09% respectively in the Control group, 2 &mgr;g/kg group, and 4 &mgr;g/kg group. Significant differences were observed among the three groups. The eye-opening times were 5.7 ± 3.5 min in the Control group and 5.1 ± 1.0 min in the 4 &mgr;g/kg group. The awakening times were 9.7 ± 3.7 min in the Control group and 9.2 ± 3.8 min in the 4 &mgr;g/kg group. No significant differences were observed among the groups.

Plasma lidocaine, monoethylglycinexylidide, and glycinexylidide concentrations after epidural administration in geriatric patients.

Background and Objectives: The purpose of this study was to evaluate the effect of age on the pharmacokinetics of lidocaine after epidural administration. Methods: Two percent lidocaine with epinephrine (5 μg/mL) was administered in two different age groups: an adult group (age 42 ± 6 years, n = 10) and an elderly group (age 77 ± 4 years, n = 10). Concentrations of lidocaine and its active metabolites, monoethylglycinexylidide (MEGX) and glycinexylidide (GX), were measured in plasma samples obtained after 15, 30, 45, 60, 90, 120, 150, and 180 minutes of administration using high‐performance liquid chromatography with ultraviolet detection. Results: No significant differences in plasma concentrations of lidocaine and its metabolites were observed between the two groups during the 3 hours of study. However, the elderly group showed significantly longer mean residence times (MRTs) and lower plasma clearance of lidocaine during the period compared with the adult group (P < .05). Plasma concentration ratios of MEGX/lidocaine were significantly lower in the elderly group after 2 hours of lidocaine administration (P < .05). Conclusions: The increase in plasma lidocaine concentration after epidural anesthesia in elderly patients was not as high as anticipated. However, the elderly patients showed longer MRTs, lower clearance, and lower ratios of MEGX/lidocaine than did the adult (middle‐age) patients.