Der Anaesthesist
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As the mechanism of action of ketamine, particularly its non-competitive antagonism at the N-methyl-D-aspartate receptor (NMDA), has become better understood, the use of the drug as a neuroprotective agent has received increasing interest. Although the potential prometabolic effects of ketamine might be counterproductive to neuroprotection, the increase in intracranial pressure it has repeatedly been reported to produce does not appear to be relevant clinically under certain conditions, e.g. in patients with normocapnia and a stable blood pressure. Also, the drug has been shown to be anticonvulsant in clinically applied doses rather than epileptogenic, as was previously assumed. ⋯ But as both in vitro and in vivo studies are inconclusive, the benefits of the drug are still controversial. In addition, the potential neurotoxicity attributed to extremely high ketamine doses is poorly understood. Consequently, well controlled animal experiments and studies in humans would be necessary to establish the role of ketamine and its more potent enantiomer S-(+)-ketamine in combination with other neuroprotective measures and to shed light on its true neuroprotective potential and its possible neuroregenerative effects.
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Although ketamine has been in clinical use for 3 decades, the neuropharmacological basis of its analgesic, anaesthetic, sympathomimetic, and psychotomimetic effects is still a subject of controversial discussion and intensive investigational efforts. In recent years, however, new experimental approaches to its effects on the cellular and molecular level and the availability of pure ketamine enantiomers contributed substantially to the understanding of its complex neuropharmacology. ⋯ In contrast to the uncertainty surrounding the potential role of opioid receptors, there is now considerable evidence that NMDA antagonism is a central mechanism that contributes to the amnesic, analgesic, anaesthetic, and psychotomimetic as well as the neuroprotective actions of ketamine. Moreover, the involvement of non-NMDA glutamate receptors, muscarinic and nicotinic cholinergic transmission, interactions with 5-HT receptors, and L-Type Ca2+ channels may account for some of its anaesthetic and neuroprotective properties.
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Thermoregulation and its impairment by anaesthesia and surgery has recently been brought back into focus by researchers and clinicians. All volatile and IV anaesthetics, opioids, as well as spinal and epidural anaesthesia increase the inter-threshold range of thermoregulation from 0.2 degree C to 4 degrees C between vasodilation and vasoconstriction. Thermoregulatory vasoconstriction and shivering occurs in anaesthetized patients at lower core temperatures than in awake subjects. ⋯ These hypothermia-related morbidities therefore have consequences reaching fare into the postoperative period. Prevention of inadvertent hypothermia is always indicated. Forced-air warming is the most effective and safest method to prevent perioperative hypothermia.
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In a recently published German multicenter study, 25% of the patients with witnessed cardiac arrest outside the hospital were resuscitated successfully and discharged from the hospital. Approximately 100,000 people suffer a fatal cardiac arrest in Germany annually, which is approximately tenfold the number of deaths from motor vehicle accidents. Cardiopulmonary resuscitation (CPR) performed by bystanders is an important part of the chain of survival to minimize the time interval without artificial circulation and ventilation in a cardiac arrest victim. ⋯ This strategy would decrease the inspiratory flow rate and, therefore, peak airway inflation pressure, which is associated with stomach inflation. Animal models indicate that lower esophageal sphincter pressure may decrease rapidly to 5 cm H2O during cardiac arrest, which may further increase the importance of a low peak airway pressure during ventilation with an unprotected airway. Gastric inflation may cause, besides regurgitation, aspiration, and pneumonia, an increased intragastric pressure, which may push up the diaphragm, decrease lung compliance, and induce a vicious circle of hypoventilation and stomach inflation.(ABSTRACT TRUNCATED)