Shinichi Inomata

End-tidal Sevoflurane Concentration for Tracheal Intubation and Minimum Alveolar Concentration in Pediatric Patients

BackgroundSevoflurane is a new inhalational anesthetic agent having low solubility in blood and a relatively nonpungent odor. As such it should be useful as an inhalation induction in pediatric patients. The objectives of the study were to determine both the minimum alveolar concentration (MAC) and the concentration required for tracheal intubation (MACEL) of sevoflurane in pediatric patients. MethodsThe study group consisted of 36 ASA physical status 1 elective surgical patients, aged 1–9 yr. MACEl determination: After establishing and maintaining the end-tidal concentration for 15 min, tracheal intubation was attempted with an uncuffed tracheal tube without neuromuscular relaxants or other adjuvants. Each concentration at which tracheal intubation was attempted was predetermined according to the up-and-down method (with 0.5% as a step size). MAC determination: The patients examined were the same as those for MACEl determination except that for the exclusion of those to whom neuromuscular relaxants or other adjuvants drugs were administered. End-tidal sevoflurane concentration was determined according to the up-and-down method (with 0.5% as a step size) and held constant for at least 15 min before a skin incision. Result:MACEL of sevoflurane was 2.69% (95% fiducial limits: 2.23% and 3.37%); MAC of sevoflurane was 2.03% (95% fiducial limits: 1.51% and 2.53%); and the MACEL/MAC ratio was 1.33. ConclusionSevoflurane appears to be suitable for use in pediatric patients as an induction agent, permitting tracheal intubation without neuromuscular relaxants.

Determination of end-tidal sevoflurane concentration for tracheal intubation and minimum alveolar anesthetic concentration in adults.

The purpose of this study was to determine both the concentration of sevoflurane required for tracheal intubation (MACEI) and its minimum alveolar anesthetic concentration (MAC) in adults. The study group consisted of 86 elective surgical patients, ASA physical status I or II, aged 16–59 yr. There was no premedication administered. For MACEI determination, after establishing and maintaining the predetermined end-tidal concentration for 20 min, tracheal intubation was attempted using a cuffed tracheal tube without muscle relaxant or other adjuvants. Each concentration at which tracheal intubation was attempted was predetermined as follows: 2.5%, 3.0%, 3.5%, 4.0%, 4.5%, 5.0%, 5.5%, 6.0%, 6.5%, and 7.0%. For MAC determination, the patients examined were basically the same as those for MACEI determination, except for those who received muscle relaxant or other adjuvants because they were “not intubated smoothly.” After establishing and maintaining the predetermined end-tidal concentration at which skin incision was attempted was concentration at which skin incision was attempted was predetermined as follows: 0.5%, 1.0%, 1.5%, 2.0%, 2.5%, and 3.0%. The MACEI of sevoflurane was 4.52% (95% confidence limits, 3.91%-5.21%), and the ED95 for tracheal intubation was 8.07%. The MAC of sevoflurane was 1.58% (95% confidence limits, 1.14%-1.98%), and the AD95 (anesthetic ED95) was 2.96%. The MACEI/ MAC ratio was 2.86 (95% confidence limits, 2.63–3.43). Anesthesia induction followed by tracheal intubation can be accomplished in adults when sevoflurane is administered as a sole anesthetic, but in excess of 8% end-tidal concentration.

End-tidal Sevoflurane Concentrations for Laryngeal Mask Airway Insertion and for Tracheal Intubation in Children

BACKGROUND: Sevoflurane, a new inhalational anesthetic agent characterized by a low blood-gas partition coefficient and nonpungent odor, appears suitable as an induction agent for children. The laryngeal mask airway is a new device for maintaining airway patency during anesthesia. This study was conducted to determine the sevoflurane concentrations required for insertion of a laryngeal mask (MACLMI) and for tracheal intubation (MACTI) in children. METHODS: Forty-two patients, aged 1-9 yr, scheduled for surgery during general anesthesia were randomly assigned into two groups: MACLMI (n = 21) and MACTI (n = 21). After the predetermined end-tidal concentration had been established and maintained for 20 min, laryngeal mask insertion or tracheal intubation was attempted without neuromuscular relaxants or other adjuvants. Each concentration at which laryngeal mask insertion or tracheal intubation was attempted was predetermined by the up-and-down method (with 0.5% as a step size). RESULTS: Sevoflurane MACLMI was 2.00 +/- 0.28%. Sevoflurane MACTI was 2.83 +/- 0.34%, significantly greater than MACLMI. CONCLUSIONS: Laryngeal mask insertion can be performed at a lesser sevoflurane concentration than that required for tracheal intubation.

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.

Transient Bilateral Vocal Cord Paralysis after Insertion of a Laryngeal Mask Airway

A laryngeal mask airway (LMA) is used as an alternative to tracheal intubation *RF 1,2* and has been used safely in anesthetized adults and children during spontaneous breathing of controlled ventilation.[3–6] Compared with an endotracheal tube, airway related complications such as sore throat occur

CYP2C19 genotype affects diazepam pharmacokinetics and emergence from general anesthesia.

Diazepam is widely used to relieve preoperative anxiety in patients. The objective of this study was to investigate the effects of polymorphism in CYP2C19 and the effects of CYP3A4 messenger ribonucleic acid (mRNA) content in blood on recovery from general anesthesia and on diazepam pharmacokinetics.

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).

Determination of endtidal sevoflurane concentration for tracheal intubation in children with the rapid method

PurposeUsing the conventional method of determining the end-tidal concentration of inhalational anaesthetics for tracheal intubation, a constant end-tidal anaesthetic concentration is maintained for at least 15 min. As sevoflurane has a low tissue/gas partition coefficient, it seems possible in paediatric patients to determine end-tidal concentrations for tracheal intubation more rapidly by using a high inspired concentration. We determined ED50 and ED95 of sevoflurane for tracheal intubation, the end-tidal concentrations that prevented 50% and 95% of patients from coughing and gross purposeful muscular movements after intubation.MethodsTwenty-nine, ASA I, unpremedicated patients, aged two to eight years, were enrolled. Anaesthesia was induced using a mask and 5% sevoflurane, inspired, in oxygen. When end-tidal sevoflurane concentration attained a predetermined value, laryngoscopy and tracheal intubation were performed using an uncuffed tracheal tube without neuromuscular relaxants or adjuvants. Each concentration at which laryngoscopy and tracheal intubation were attempted was randomly predetermined (with 0.5% as a step size). When tracheal intubation was accomplished without gross purposeful muscular movements, it was considered a smooth tracheal intubation.ResultsThe ED50 end-tidal sevoflurane concentration for tracheal intubation was 3.10% (95% confidence limits: 2.43% and 3.78% ), and the ED95 was 4.68% (95% confidence limits: 3.91% and 12.74% ). The times to end-tidal sevoflurane concentrations of 3.0% and 4.5% were 149 ± 15 sec (mean ± SD) and 213 ± 23 sec.ConclusionIn paediatric patients, this method enabled determination of ED50 and ED95 end-tidal sevoflurane concentrations for tracheal intubation without obtaining a long stabilization period.RésuméObjectifA vec la méthode conventionnelle utilisée pour déterminer la concentration télé-expiratoire d’un agent inhalatoire pour l’intubation trachéale, une concentration télé-expiratoire constante est maintenue pendant au moins 15 min. Comme le sévoflurane a une coefficient partage tissus/gaz faible, il semble possible de déterminer chez des patients de pédiatric quelles concentrations télé-expiratoires sont suffisantes pour intuber la trachée plus rapidement en administrant des concentrations inspiratoires élevées. Nous avons déterminé l’ED50 et l’ED95 du sévoflurane nécessaires pour l’intubation, c.à.d. les concentration télé-expiratoires suffisantes pour prévenir la toux et les mouvements intentionnels incontrôlés après l’intubation.MéthodesVingt et un patients ASA I âgés de deux à huit ans faisaient partie de l’étude. L’anesthésie était induite au masque avec une concentration inspirée de sévoflurane 5% en oxygène. Après l’atteinte d’une concentration prédéterminée de sévoflurane, la laryngoscopie et l’intubation trachéale étaient tentées avec un canule trachéale sans ballonnet sans l’aide d’adjuvant ni de relaxant musculaire. La concentration correspondant à une tentative la laryngoscopie et d’intubation était prédéterminée aléatoirement (avec des échelons de 0,5%). L’intubation réalisée sans mouvements intentionnels désordonnés était considérée comme paisible.RésultatsL’ED50 télé-expiratoire du sévoflurane pour l’intubation trachéale était de 3,10% (limite de confiance 95%: 2,43% et 3,78%) et l’ED95 était de 4,68% (limite de confiance 95%: 3,91% et 12,74%). L’intervalle de temps requis pour atteindre une concentration télé-expiratoire de 3,0% et 4,5% était 149 ± 15 sec (moyenne ± ET) et 213 ± 23 sec.ConclusionChez les enfants, celte méthode a permis de déterminer l’ED50 et l’ED95 télé-expiratoires du sévoflurane pour l’intubation trachéale sans nécessiter une longue période de stabilisation.

Convulsions after ropivacaine 300 mg for brachial plexus block

A healthy 18-yr-old male (weight 60 kg, height 167 cm), with a history of febrile convulsions in childhood, developed a grand mal convulsion 10 min after the second of two injections of ropivacaine 150 mg, both given incrementally 15 min apart (total 300 mg), for combined axillary/interscalene brachial plexus block. Treatment was with oxygen, lung ventilation, and i.v. midazolam, and the patient made a complete recovery. Arterial plasma ropivacaine concentration 2 min after the onset of convulsions was only 2.13 mg litre(-1), suggesting that this patient was particularly susceptible to local anaesthetic toxicity. Whether sub-clinical EEG changes identified after operation were related to this sensitivity cannot be determined, but review illustrates wide variation in both the dose and the plasma concentration of local anaesthetics associated with systemic toxicity. The UK recommended dose of ropivacaine for brachial plexus block is 225-300 mg according to stature.

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.