Concentration-Dependence of Halothane Metabolism in Rabbits

Effect of end-expiratory halothane concentration on its aerobic and anaerobic metabolism was studied in 20 male rabbits. Biliary excretion of trifluoroacetic acid (TF AA), an aerobic metabolite of halothane, and the pulmonary excretion of CF2CHCl (CDFF) and CF3CH2Cl (CTFE), anaerobic metabolites of halothane, were measured simultaneously during 5 hr of inhalation at various concentrations of halothane (0.02-1.5%). The total amount of biliary TF AA excreted for 5 hr remained unchanged (38.4μmol- 44.lμmol) at each concentration except 0.02%. However, the total amount of CDFE and CTFE excreted for 5 hr increased in a concentration-dependent manner up to 0.5% end-expiratory halothane, and remained unchanged (47.2μmol-64.7μmol) at more than 0.5%. Total biliary excretion of TF AA reached its maximum at a 0.05%. These results suggest that the primary route of halothane metabolism at a subanesthetic concentration is the aerobic pathway which produces TF AA. However, at anesthetic concentration exceeding 0.5%, the anaerobic route which produces volatile CDFE and CTFE plays a role also as an aerobic route.This study was supported in part by Science Research Grants from the Ministry of Education, Science and Culture of Japa

Use of the Laryngeal Mask Airway in Combination with Regional Anesthesia Facilitates Induction and Emergence from General Anesthesia in Patients Undergoing Colorectal Surgery

The laryngeal mask airway (LMA) is selected as an alternative to the endotracheal tube (ETT) when rapid recovery from general anesthesia is considered. However, the clinical significance of this airway for abdominal surgery is unclear. Thus, we evaluated whether the LMA, in combination with regional anesthesia, facilitates the induction of and emergence from general anesthesia in patients undergoing elective colorectal surgery. Anesthesia-controlled time in a ETT/Epidural Anesthesia (EA) group [n = 11; general anesthesia, combined with epidural anesthesia, was maintained by sevoflurane (< 3%) supplemented with a fixed rate of propofol (3 mg/kg/h) under controlled ventilation using the ETT] was compared with that in a LMA/Combined Spinal-Epidural Anesthesia (CSEA) group [n = 10; in combination with spinalepidural anesthesia, general anesthesia was maintained as the same protocol as the ETT/EA under spontaneous ventilation using the LMA]. Time for airway placement in the LMA/CSEA group was significantly shorter than that in the ETT/EA group. Intervals from the end of surgery until the removal of the airway or the decision to exit the operating room in the LMA/CSEA group were shorter than those in the ETT/EA group. No practical sign of aspiration pneunomia and/or atelectasis was found in patients in either group. Under the circumstance of regional anesthesia being requested for post-surgical pain management, we concluded that the LMA facilitated the emergence from as well as the induction of anesthesia without any practical complication when used for patients in colorectal surgery

Comparative Benefit of Preemptively Applied Thiopental for Propofol Injection Pain : the advantage over lidocaine

Propofol is one of the most frequently applied intravenous anesthetics for the induction of general anesthesia. However, pain on injection of this agent is a considerable problem in daily anesthesia practice because of its severity. Administration of lidocaine prior to propofol injection is a standard technique for reducing the pain on injection. However, this method provides insufficient pain relief. To evaluate whether pretreatment with an ultra-short acting barbiturate, thiopental, is more effective than with lidocaine, a randomized and single-blinded trial was conducted. Patients (20-65 years old, n=137) were allocated into six groups, and applied with physiological saline, thiopental (25, 50, 75, or 100mg), or lidocaine (40mg) at 30 second prior to propofol injection (1mg/kg, 1200ml/h). The patient was interviewed about the degree of pain just after propofol was totally injected. Both thiopental (≧25mg) and lidocaine decreased the severity of pain in comparison with physiological saline as evaluated by a six-graded pain score. Lidocaine failed to influence the incidence of pain (from 86% to 55%), although thiopental significantly decreased it to 40% (25mg), 21% (50mg), 12% (50mg), and 0% (100mg), respectively. Thiopental (≧50mg) decreased both the severity and incidence of pain more effectively than lidocaine. A Hill plot analysis of these data, after rearrangement by patient's body weight, estimated that the half-effective dose (ED_) and the ED_ of this drug to block pain on injection of propofol were 0.6 and 1.4mg/kg, respectively

A Prospective Multicenter Trial to Determine the Incidence of Transient Neurologic Symptoms after Spinal Anesthesia with Phenylephrine Added to 0.5% Tetracaine

The addition of vasoconstrictors for spinal anesthesia is controversial, since an increase in the incidence of transient neurologic symptoms (TNS) has been reported. A multicenter, randomized, double-blind study was conducted to assess the effectiveness of spinal anesthesia with phenylephrine in addition to tetracaine as well as the incidence of neurological complications. We studied 64 patients with comparable demographic characteristics who were scheduled for elective surgery for a lower limb, or a gynecological or urological procedure. The patients were allocated randomly into 2 groups. Group P (n = 34) received 0.5% tetracaine in 10% glucose with 0.025% phenylephrine, while group C (n = 30) received 0.5% tetracaine in 10% glucose.　　 Our results showed that only 2 patients (6.7%) in group C experienced TNS, and their symptoms disappeared within 72 hr after anesthesia, while none of the patients (0%) in group P complained of symptoms. The incidence of TNS was thus not significantly different between the two groups. Six hours after the sensory block, group P patients demonstrated sensory disturbance, with the median spinal dermatome corresponding to the L1 segment. Moreover, systolic blood pressure in group P was significantly higher than that in group C, 5 min, 15 min, and 20 min after injection.　　 The incidence of TNS in the present study does not seem to be greater after surgery with spinal anesthesia using 0.5% hyperbaric tetracaine and 0.5 mg phenylephrine than without phenylephrine. Randomized, double-blind, cross-over trials with a larger sample size would be required in the future to obtain more reliable results