The Effect of Halothane and Enflurane on the Aorta Contracted with Phenylephrine in Rabbits / 대한마취과학회지

BACKGROUND: Inhalation anesthetics have been known as vasodilators, but there are several reports that halothane and enflurane have different effects on vascular smooth muscles. Vasodilatation and vasoconstriction were observed in different vessels in the same animal. We tried to observe the effect of halothane and enflurane on the contraction of the aorta in rabbits. METHODS: Isolated tracheal preparations of rabbits were used. Halothane (1.4%) and enflurane (1.4%, 2.8% and 5%) were administered after contractions induced by phenylephrine (10(-7) M), and verapamil (10(-7), 10(-6), 10(-5), 10(-4), and 10(-3) M) was administered. In the verapamil pretreated group, after a phenylephrine (10(-7) M) induced contraction, verapamil (10(-7) M) and enflurane (2.8% and 5%) were administered. The percentile contraction to the contraction induced by phenylephrine was evaluated. RESULTS: The potentiation of the contration by phenypephrine was observed by halothane and enflurane administration and these potentiations disappeared with the adminstration of verapamil. With prior administration of verapamil, there was no potentiation of the contraction by enflurane. CONCLUSIONS: Halothane and enflurane potentiates the contraction induced by phenylephrine in rabbit aortas. In addition, the influx of extracellular calcium seems to play a role in this potentiation of the contraction.

The Effect of Inhaled Concentration of N2O (Nitrous Oxide) during Emergenceon Awakening Time after Propofol-N2O-O2 Anesthesia / 대한마취과학회지

BACKGROUND: N2O has a unique analgesic effect and reduces the amount of hypnotics for preventing surgical stimuli during maintenance of anesthesia. Also, it was reported that high concentrations of N2O affect level of consciousness. The aim of this study was to evaluate the effect of inhaled concentrations of N2O during emergence on awakening time after propofol-N2O-O2 anesthesia. METHODS: Sixty ASA class I or II patients scheduled for lower extremity surgery were randomly allocated to one of three groups according to inhaled concentration of N2O during emergence. Group 1: 0% N2O (n = 20), group 2: 33% N2O (n = 20) and group 3: 50% N2O (n = 20). Anesthesia was induced and maintained with propofol (Ct: 3.5 6 microgram/ml)-67% N2O-33% O2 and the target concentration of propofol was kept at 4 microgram/ml at least 30 min before the end of infusion of propofol using TCI. At the time of skin closure, we discontinued the propofol, maintained the allocated concentration of N2O and continuously checked vital signs, current/effect concentration of propofol, bispectral index (BIS), and elapsed time until eye opening to verbal contact (awakening time). RESULTS: Awakening time and bispectral index significantly increased as the inhaled concentration of N2O was higher. At awakening time, The predicted current/effect site concentrations of propofol significantly decreased as the inhaled concentrations of N2O were increased. CONCLUSIONS: Continuous inhalation of N2O after discontinuation of propofol infusion significantly delayed the awakening time after propofol-N2O-O2 anesthesia using TCI.

The Effect of Concentration of Nitrous Oxide on Bispectral Index and Sedation Score / 대한마취과학회지

BACKGROUND: Bispectral index (BIS) has been designed to measure objectively the degree of sedation and hypnosis for several anesthetics. It is predicted that sedation and hypnosis during nitrous oxide inhalation affect BIS in an unusual manner due to a different mechanism compared to usual hypnotics. The aim of this study was to evaluate the effect of different concentration of nitrous oxide inhalation on BIS and sedation score. METHODS: Forty unpremedicated ASA physical status I or II patients scheduled for lower extremity surgery were studied. After performing epidural anesthesia, patients inhaled gradually increasing concentrations of nitrous oxide from 0 to 67% (15 minutes for each concentration) via a tightly sealed face mask. At the end of each inhalation, BIS and OAA/S scale (Observers's Assessment of Alertness/ Sedation scale) were assessed. RESULTS: The increasing concentrations of inhaled nitrous oxide resulted in significant reduction of the OAA/S scale but in no change of BIS. Concentrations of nitrous oxide exceeding 50% affected behavior or emotion of the patients. CONCLUSIONS: Following increasing concentrations of inhaled nitrous oxide, sedation score was reduced significantly but BIS was not affected.

Hypercarbia Due to Mistaken Supply of Carbon Dioxide Originating from Nitrous Oxide Gas Tank: A case report / 대한마취과학회지

A 49 year-old male was scheduled for a cholecystectomy, thereafter a 37 year-old female scheduled for removal of a epidural hematoma in the same operating room. Both of them had no specific medical problems and past medical histories for anesthesia. For those reasons, anesthesia was induced with thiopental sodium and succinylcholine with endotracheal intubation. After induction, vital signs including body temperatures were stable. But moisture dew in the unidirectional valves and corrugated tubes, and color changes of soda lime were discovered. At that time, severe hypercarbia was recognized by arterial blood gas analysis in both cases. In both cases, there were no malfunctions in unidirectional valves, expiratory valves, corrugation tubes, soda lime, ventilators and there connection parts in the anesthetic machines. Also there were no abnormalities of blood pressures, electrocardiograms, pulse oxymeters, temperatures and the pulse in the patient monitoring systems except capnography. At first, we thought that medical signs revealed malignant hyperthermias. But vital signs, air way pressures and functions of all kinds of anesthetic machine components including ventilators were normal. After discontinuing N2O gas deliveries in the operation room, hypercarbias disappeared. Thus, anesthetic gas delivery systems via central piping systems were checked and it was discovered that CO2 gas was in the N2O gas tank instead of N2O.

The Cardiovascular Effects of Epinephrine Used for Hemostasis under Enflurane-N2O Anesthesia during Tonsillectomy / 대한마취과학회지

BACKGROUND: Exogenously administered epinephrine under enflurane anesthesia was known to have mild myocardial sensitizing effect. And N2O activates the sympathetic nervous system mildly. We planed this study to confirm cadiovascular effects of clinically administered epinephrine for hemostasis under the enflurane-N2O anesthesia during tonsillectomy. METHODS: Eighty children scheduled to have tonsillectomy were selected randomly and divided into 2 groups as follows; Group E: 1:100,000 epinephrine 2ug/kg and Group EL: 1:100,000 epinephrine containing 1% lidocaine 2 g/kg. Blood pressure, heart rate, and the occurrence of arrhythmia were evaluated before injection, at injection, 1 min, 2 min, 3 min, 5 min and 10 min after injection and 1 min after operation start. RESULTS: In both groups, systolic and diastolic blood pressure and heart rate are increased. But there are no significant statistical differences in each group and between groups. One min after operation, there are significant increases in systolic and diastolic blood pressure and heart rate in both groups (p<0.05), but there is no significant difference between groups. CONCLUSION: Under the enflurane-N2O anesthesia of children, 1:100,000 epinephrine 2ug/kg used for hemostasis could be used comparatively safe without any significant hemodynamic changes. But because there is always the possibility of myocardial sensitization, careful observation is necessary during epinephrine injection under the enflurane-N2O anesthesia.

Comparison of Propofol-N2O and Propofol-fentanyl Anesthesia for Outpatient Surgery / 대한마취과학회지

BACKGROUND: The choice of anesthetic agents and adjuvants during outpatient surgery is of critical importance. Propofol is widely used for the induction and maintenance of outpatient anesthesia. Because propofol lacks analgesic properties, very high concentrations may be required when propofol is used as the sole anesthetic drug. Propofol is used with adjuvants such as nitrous oxide or opioid. This study was designed to evaluate the intraoperative hemodynamic response, recovery characteristics and side effects of propofol-fentanyl anesthesia compared with propofol-N2O anesthesia for outpatient surgery. METHODS: Twenty six healthy and unpremedicated patients scheduled for outpatient surgery were randomly allocated to receive either propofol-N2O anesthesia (N-group) or propofol-fentanyl anesthsia (F-group). The patients in N-group were ventilated with nitrous oxide 60~70% in oxygen and the patients in F-group were ventilated with oxygen 40% in nitrogen via laryngeal mask airway (LMA). RESULTS: There was no significant difference in blood pressure during anesthesia, recovery time and side effects between two group. There was significant decrease of heart rate in F-group. CONCLUSION: We concluded that nitrous oxide and fentanyl are reasonable adjuvants of propofol anesthesia in outpatient anesthesia.

The Effects of Nitrous Oxide on Volume and Pressure of Endotracheal Tube Cuffs during General Inhalation Anesthesia / 대한마취과학회지

BACKGROUND: Many studies have demonstrated that nitrous oxide diffuses into the cuffs of endotracheal tubes and increases cuff volumes and pressures. Such increments of cuff pressure maybe result in damage to the trachea. We evaluated the increase of intracuff pressure, volume and the statistical significance was analyzed with personal computer. METHODS: Fourty-nine patients ranging in age 37+/-15 years, in ASA physical status class 1~2 , they were 26 males and 23 females. They divided into two groups, group I(n=25) were anesthesia with nitrous oxide : oxygen (2 L/min : 2 L/min), group II were(n=24) anesthesia with nitrous oxide : oxygen (4 L/min : 2 L/min). The cuff pressure was measured every 30 minutes and compared with each others and group I and II. RESULTS: Our results suggest that a significant intracuff volume and pressure changes developed between two groups (p<0.05), more significant intracuff pressure changes occured at group II than group I (p=0.001) and significant increment changes according to time and different concentration of nitrous oxide between two groups (p<0.05). CONCLUSIONS: This study was conducted to determine the degree of intracuff pressure and volume changes during general inhalation anesthesia with different concentration of nitrous oxide. These results suggest that a nitrous oxide significantly increases cuff pressure and volume in a concentration and time related fashion.