Sevoflurane 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 (MACEI) of sevoflurane in pediatric patients.The study group consisted of 36 ASA physical status 1 elective surgical patients, aged 1-9 yr. MACEI 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 MACEI 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.MACEI 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 MACEI/MAC ratio was 1.33.Sevoflurane appears to be suitable for use in pediatric patients as an induction agent, permitting tracheal intubation without neuromuscular relaxants.
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.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).Sevoflurane MACLMI was 2.00 +/- 0.28%. Sevoflurane MACTI was 2.83 +/- 0.34%, significantly greater than MACLMI.Laryngeal mask insertion can be performed at a lesser sevoflurane concentration than that required for tracheal intubation.
Positive or negative chronotropic effects of atropine and their magnitude are known to be determined primarily by patient's age, atropine dose, anesthetic agents or techniques, and preanesthetic medication. The aim of the present study is to investigate the effects of oral diazepam upon the hemodynamic responses to intravenous atropine in awake patients. Diazepam group (n = 26) received oral diazepam, 10 mg, whereas control group (n = 20) received no premedication. The direction and magnitude of heart rate and blood pressure responses to atropine were similar between the two groups. Heart rate significantly decreased from baseline values following atropine, 2.5 micrograms.kg-1, returned to baseline values following cumulative atropine doses, 5 micrograms.kg-1, then significantly increased from baseline values following cumulative atropine dose, 10 micrograms.kg-1 in both groups. Mean blood pressure significantly decreased from baseline values following cumulative atropine dose, 2.5 and 5 micrograms.kg-1, and returned to baseline following cumulative atropine dose, 10 micrograms.kg-1, in both groups. It is concluded that oral diazepam, 10 mg, as a premedicant does not alter the hemodynamic responses to intravenous atropine in humans.
The effects of nitrous oxide (75%) on the spinal dorsal born wide dynamic range (WDR) neuronal activity were studied in either spinal cord intact or spinal cord-transected cats. Extracellular activity was recorded in the dorsal horn from single WDR neurons responding to noxious and non-noxious stimuli applied to the cutaneous receptive fields on the left bind foot pads of intact or decerebrate, spinal cord-transected (L 1-2) cats. The experiment was divided into four sections as follows: (1) When 10 micrograms of bradykinin (BK) was injected into the femoral artery ipsilateral to the recording site as the noxious test stimulus in the spinal cord-transected cat, all of 6 WDR neurons gave excitatory responses which were not depressed by 75% nitrous oxide. (2) When the injection of 10 micrograms of BK into the femoral artery ipsilateral to the recording site was used in the spinal cord-intact cat, 6 of 15 WDR neurons (40%) gave excitatory responses, which were significantly depressed by 75% nitrous oxide, and 9 of 15 WDR neurons (60%) gave inhibitory responses, which were not affected by 75% nitrous oxide. (3) When 10 micrograms of bradykinin (BK) was injected into the femoral artery contralateral to the recording site as the noxious test stimulus in the spinal cord transected cat, 6 of 12 WDR neurons gave excitatory reasons, which were not depressed by 75% nitrous oxide. (4) When the injection of 10 micrograms of BK into the femoral artery contralateral to the recording site was used in the spinal cord-intact cat, 6 of 6 WDR neurons (100%) gave responses, which were affected by 75% nitrous oxide. We have observed that nitrous oxide reduces the excitation and inhibition of dorsal born WDR neuronal activities induced by BK injection in spinal cord-intact cats, but does not reduce the excitation of those in spinal cord-transected cats. This finding confirmed that the antinociceptive effect of nitrous oxide might be modulated by supraspinal descending inhibitory control systems. In addition our result showed that the supraspinal effect of nitrous oxide was mediated not only by an increase but also a decrease in a supraspinal descending inhibition.
The aim of this study was to evaluate the effect of age on the hemodynamic responses to intravenous (IV) ephedrine in pediatric patients anesthetized with halothane, nitrous oxide, and oxygen.One hundred ten pediatric patients, ranging in age from 0.1 to 15 yr, were assigned to receive 0.1 mg/kg (n = 55) or 0.2 mg/kg (n = 55) IV ephedrine. General anesthesia was maintained with 1.0 minimum alveolar anesthetic concentration (MAC) of halothane and 67% nitrous oxide in oxygen after tracheal intubation. Measurements of arterial blood pressure and heart rate were made at 1-min intervals for 10 min after ephedrine 0.1 or 0.2 mg/kg was injected IV as a bolus. Significant correlations were noted between age and changes in mean blood pressure (r = 0.37, P < 0.01 for the subjects receiving ephedrine 0.1 mg/kg; r = 0.63, P < 0.001 for the subjects receiving ephedrine 0.2 mg/kg), but not between age and changes in heart rate. The present results indicate that age correlates with the pressor but not the chronotropic effects of ephedrine in pediatric patients anesthetized with 1 MAC halothane and nitrous oxide. (Anesth Analg 1996;82:568-73)
Comment: Once again, we have confirmation that less anesthetic (in this case, sevoflurane) is required for insertion of the laryngeal mask airway (LMA) than for tracheal intubation. A secondary statement by the authors is perhaps more critical for the practicing anesthesiologist: the lower dose of anesthetic used for insertion of the LMA may be insufficient for the skin incision that follows.
The authors studied 30 patients undergoing general anesthesia in order to evaluate whether oral clonidine premedication could attenuate the hemodynamic changes associated with laryngoscopy and tracheal intubation. Patients were randomly assigned to one of two groups; clonidine group (n = 15) who received oral clonidine of approximately 5 micrograms.kg-1, or control group (n = 15) who received no clonidine. The magnitude of increases in mean blood pressure from baseline values following laryngoscopy and tracheal intubation in the clonidine group was significantly smaller as compared with that in the control group (20 +/- 12 vs. 31 +/- 14 mmHg, mean +/- SD, P less than 0.05). There was also a significant difference between the two groups in the incidence of systolic blood pressure increases above 180 mmHg following laryngoscopy and tracheal intubation (0% vs. 26%, P less than 0.05). However, no significant difference was noted between the two groups in the heart rate responses to laryngoscopy and tracheal intubation. It is concluded that oral clonidine of 5 micrograms.kg-1 as a preanesthetic medication could attenuate the pressor responses associated with laryngoscopy and tracheal intubation.
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.
