Der Anaesthesist
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General cardiovascular properties of ketamine: "In vitro", ketamine has moderate negative inotropic effects. "In vivo", a significant central sympathomimetic action with consecutive hemodynamic effects is dominant. The sympathomimetic potency of ketamine is one of the most significant pharmacological features of the substance with direct clinical implications. Monoanaesthesia with S-(+)-ketamine: After application of racemic ketamine or S(+)-ketamine as well, identic and significant increases in plasma catecholamines, arterial pressure and heart rate are observed. This outstanding sympathomimetic action is beneficial in induction of patients with shock or asthmatic state. TIVA and analgosedation with S-(+)-ketamine and midazolam: The sympathomimetic effect of S(+)-ketamine, and racemic ketamine as well, is mitigated by midazolam. Nevertheless, significant increases in heart rate and arteriel pressure might be observed. Clinical use of the combination is common in short procedures like reposition maneuvers. Of greater importance is the use for analgosedation in patients with cardiovascular instability, particularly in patients with exogenous catecholamine demand. TIVA and analgosedation with S-(+)-ketamine and propofol: When S(+)-ketamine is combined with propofol, the sympatholytic effects of propofol are counteracted by S(+)-ketamine, and stable hemodynamic conditions are presented. This combination seems useful for TIVA in patients with hypotonic dysregulation or endocrine deficits like hypothyreosis and adrenal insufficiency. Furthermore, analgosedation with S(+)-ketamine and propofol is advantageous, when rapid recovery is necessary and negative circulatory effects should be avoided. ⋯ Sympathoadrenergic and hemodynamic effects of S(+)-ketamine and racemic ketamine are generally identical. The distinctest action is observed, when S(+)-ketamine is used as a monoanaesthetic. In combination with midazolam, a significant reduction is achieved. In combination with propofol, the sympatholytic effects of this hypnotic agent are compensated by S(+)-ketamine. With respect to sympathoadrenergic and hemodynamic reactions, the clinical position of S(+)-ketamine is unchanged. Nevertheless, a significant clinical progress can be expected due to improved recovery and reduced substance load, when racemic ketamine is replaced by S(+)-ketamine.
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The pharmacological profile of ketamine: Until recently, clinically available ketamine was a racemic mixture containing equal amounts of two enantiomers, (S)- and (R)-ketamine. The pharmacological profile of racemic ketamine is characterized by the so called dissociative anesthetic state and profound sympathomimetic properties. Among the different sites of action, N-methyl-D-aspartate (NMDA)-receptor antagonism is considered to be the most important neuropharmacological mechanism of ketamine. ⋯ In combination with midazolam and propofol, excellent control of analgosedation was found, making both combinations suitable for situations in which repeated neurological assessment of patients is necessary. In emergency and disaster medicine, (S)-ketamine is of outstanding importance because of its minimal logistic requirements, the chance for intramuscular administration and the broad range of use for analgesia, anaesthesia and analgosedation as well. Further perspectives of (S)-ketamine may be the treatment of chronic pain and the assumed neuroprotective action of the substance.
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The various components of commercial soda lime (sodium hydroxide, potassium hydroxide, calcium hydroxide, barium hydroxide) were studied in terms of their reactivity with sevoflurane at its boiling point (59 degrees C). A simple closed system, a reflux cooler, served as a model. Analyses were performed by GC/MS. ⋯ Calcium hydroxide and barium hydroxide showed little reaction with sevoflurane, whereas larger amounts of reaction products were observed with sodium hydroxide and potassium hydroxide. The alkali hydroxides of sodalime are presumably responsible for its reaction with halogenated inhalation anaesthetics. We therefore conclude that decomposing reactions of halogenated inhalation anesthetics with dry soda lime could be prevented by using a newly developed soda lime.
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All volatile anesthetics undergo chemical breakdown to multiple, partly identified degradation products in the presence of dry soda lime. These chemical reactions are highly exothermic, ranging from 100 degrees C for halothane to 120 degrees C for sevoflurane. The increase in temperature correlates with the moisture content of the soda lime, being maximal below 5%. ⋯ In conclusion, sevoflurane and isoflurane react with dry soda lime. These reactions are caused by the presence of two components of soda lime, sodium hydroxide and potassium hydroxide. A modification of soda lime to prevent its reaction with volatile anaesthetics is discussed.
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Case Reports
[Interactions of dry soda lime with enflurane and sevoflurane. Clinical report on two unusual anesthesias].
We report two cases of unexpected courses of inhalation anaesthesia with sevoflurane and enflurane which were caused by the presence dry soda lime. Case 1: During mask induction of a healthy 46-year-old female patient for elective hysterectomy it was noted that the vaporizer setting of 5% sevoflurane (in 50% O2, 50% N2O) did not result in the expected increase of inspiratory sevoflurane concentration. At the same time, the anaesthesiologist observed that the patient did not lose consciousness while the temperature of the soda lime canister increased sharply and the colour of the soda lime turned to blue with condensing water visible in the tubing. It was later determined that this anaesthesia machine had not been used for more than 2 weeks. Analysis of the soda lime showed a water content of <1%. Case 2: Following intravenous induction of a non-smoking 64-year-old male patient for elective gastrectomy, it was noted that the concomitant inhalation of enflurane was associated with a sharp rise in the temperature of the soda lime canister, a colour change of the soda lime to blue and a decrease in the measured inspiratory enflurane concentration despite an unchanged or even increased vaporizer setting. Arterial blood gas analysis revealed a CO-Hb concentration of 8.8% with otherwise normal acidity and partial gas pressures. Immediate change of the absorbant resulted in a decline in the CO-Hb concentration to 6.9% within 3 h. It was later determined that the anaesthesia machine had not been used for 34 h. Analysis of the soda lime showed a water content of 5.4%. ⋯ Both case reports were associated with a rise in temperature and a colour change to blue of the soda lime. Reactions of desflurane, enflurane or isoflurane with dry soda lime resulting in significant CO-Hb formation have been previously reported. Reactions of sevoflurane with dry soda lime have been observed but have so far not been published. Until further analysis of these phenomena is completed, it is mandatory for the patient's safety to guarantee that only soda lime with a sufficient water content be used for clinical anaesthesia.