[Endocrine reactions following S-(+)-ketamine]

ANAESTHETICS, ENDOCRINE SYSTEM, AND STRESS: The effects of anaesthetics on the nervous system are invariably associated with endocrine reactions, which are of great importance for the general characterization of anaesthetics or anaesthetic regimens. In this context, the endocrine stress response is mainly represented by adrenaline (A), noradrenaline (NA), antidiuretic hormone/vasopressin (ADH), adrenocorticotropic hormone (ACTH), and cortisol. PHARMACOLOGICAL PROFILE AND ANAESTHETIC ACTION OF KETAMINE: The pharmacological profile of ketamine is characterized by the term "dissociative anaesthesia." At the present time, the anaesthetic action of ketamine cannot be explained by a single mechanism. Its overall action might be due to different central and peripheral factors, and stereospecific effects are obvious. ENDOCRINE RESPONSES TO RACEMIC KETAMINE AND S(+)-KETAMINE: In contrast to stereospecific differences in the anaesthetic action of racemic ketamine and S-(+)-ketamine, the endocrine reactions to the S-(+) isomer and the racemic mixture are very similar. When S(+)-ketamine is used as the sole anaesthetic, significant activation of the sympathoadrenergic system with increases in plasma levels of A and NA can be observed. This effect is mitigated by midazolam. In combination with propofol, sympathoadrenergic responsiveness is preserved without overwhelming effects. In contrast to monoanaesthesia with S(+)-ketamine, during combination with midazolam and propofol significant increases in plasma ADH levels are observed, which might be due to suppressed sympathoadrenergic reactivity. In addition, surgical stress activates the pituitary-adrenocortical system with increases in ACTH and cortisol. Effects of midazolam and propofol on this effect are similar. SYNOPSIS AND CLINICAL ASPECTS: S-(+)-ketamine as a monoanaesthetic has significant sympathomimetic properties, which are beneficial during induction of patients in shock and patients with asthma. The combination of S-(+)-ketamine and midazolam has weaker sympathomimetic and general endocrine-stimulating properties, and can be used for analgosedation in patients with cardiovascular instability and exogenous catecholamine requirements. In combination with propofol, the sympathomimetic and general endocrine-stimulating effects of S-(+)-ketamine are less pronounced because of contrasting properties of both drugs. This combination might be useful in patients with endocrine deficits and for analgosedation, when rapid recovery is necessary and negative circulatory effects should be avoided.