Der Anaesthesist
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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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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.