Ann Acad Med Singap
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The development of new preoperative fasting guidelines in paediatrics was reviewed in the light of present knowledge and some recent investigations. Although the proportion of healthy children with the potential risk of aspiration pneumonitis is relatively high (60-75%), the incidence of aspiration is low--1 to 8.6 in 10,000. In healthy children, there is no increase in the risk of aspiration by allowing them to drink clear fluids up to 2-3 hours before anaesthesia when compared with the conventional fasting regimen. ⋯ It is useful to have simple and explicit preoperative fasting instructions for parents to follow, especially in the day case setting. It is essential to note that the laryngeal mask airway (LMA) does not protect the patient's airway against the risk of regurgitation and aspiration of gastric contents in the same way as an endotracheal tube. Hence, constant vigilance is required when LMA is used in children.
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The anaesthetic machine used by most anaesthetists today closely resembles the anaesthetic machine of the late 1940s, with the addition of a multitude of devices and monitors necessary for the complexity of modern anaesthesia. Although modern anaesthesia boasts of a high level of safety, the ad hoc development of the anaesthetic machine has done little to enhance this safety record. Future improvements in patient safety will at least partially depend on improved ergonomics and human factor engineering in the design and arrangement of the anaesthetic workplace. Some innovative designs are now being seen both commercially and experimentally in which all monitoring is integrated and servo feedback control loops are used to deliver anaesthetic agents to the patient.
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The mechanism of anaesthesia is still a black box, although many investigators have been concerned about this theme since the 19th century. It is too complex to clarify the mode of anaesthetic action, as a variety of compounds have been adopted as anaesthetics. Hill coefficients calculated from the righting reflex dose-response curve in enflurane, isoflurane sevoflurane and halothane anaesthesia in a certain strain of mice were from 14 to 56. ⋯ It is suspected from Overton's experiment that the action site is not in the core of lipid bilayer but on the surface of membrane. It was demonstrated by 2 methodologies. Two-dimensional nuclear Overhauser effect spectrum in H1-NMR spectra of dipalmitoyl phosphatidylcholine (DPPC) vesicle membrane in the presence of methoxyflurane revealed from the existence of the cross-peak between the methoxy-proton and the choline methyl-proton that methoxyflurane molecule interacted only to the polar head of lipid membrane at lower temperatures.(ABSTRACT TRUNCATED AT 400 WORDS)
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The anaesthesia specialty has focused on the safety of the patient and examination of untoward outcomes. Serious injuries are now rare in medically advanced countries. Still, anaesthesia deaths and complications are important because the anaesthetic itself has no intended therapeutic effect. ⋯ Many efforts are believed to have contributed to improvements in the safety of anaesthesia: improved training of anaesthesia clinicians, new pharmaceuticals, new technologies for monitoring (especially pulse oximetry and capnography), standards for monitoring and other aspects of anaesthesia care, safety enhancements in anaesthesia equipment and the implementation of quality assurance and risk management programmes. The creation of the Anesthesia Patient Safety Foundation in the United States and a similar organization in Australia have helped to bring about awareness of safety issues and to support study of patient safety. Ultimately, the motto of the Anesthesia Patient Safety Foundation should be the goal of all anaesthesia professionals: "That no patient shall be harmed by anaesthesia".
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Desflurane is a new fluorinated ether with rapid onset of and recovery from anaesthesia. Recovery characteristics are comparable with or faster than after propofol infusion or isoflurane anaesthesia. The minimum alveolar concentration (MAC) varies with age from 9.4% (infants) to 6% (adults), and is reduced by opioids and sedative premedication. ⋯ Desflurane is a respiratory depressant, and enhances the action of neuromuscular blocking agents. Cerebrovascular autoregulation appears to be preserved, but intracranial pressure may still rise during desflurane anaesthesia. Delivery of vapour is using a new electrically heated vaporizer, the Tec 6, with internal monitoring circuitry and new safety features.