British journal of anaesthesia
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Comparative Study
Static v. dynamic tests in the in vitro diagnosis of malignant hyperthermia susceptibility.
In vitro contracture tests, in which muscle specimens are exposed to halothane or caffeine are, at present, the only generally accepted screening methods for the diagnosis of susceptibility to malignant hyperthermia (MHS). Static tests (performed with the muscle held at constant length) are used more commonly although, in addition, some MH investigation units use dynamic tests, in which the length of the specimen is varied. ⋯ The dynamic halothane test was more sensitive in discriminating between MHS and MH negative (MHN) individuals than the static halothane test. However, the dynamic caffeine test was less sensitive at discriminating between MHS and MHN individuals, and nothing is to be gained by including it in the investigation.
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This report describes the management of a poor risk Nepalese patient (active pulmonary tuberculosis, haemoglobin concentration 4.6 g dl-1, weight 28.5 kg) requiring emergency Caesarean section for fetal distress. Subarachnoid blockade (0.5% bupivacaine plain 3.5 ml) was satisfactory; blood loss was around 400 ml and was replaced with Haemaccel and lactated Ringer's solution (blood was not available). Although unresponsive at birth, the child had an Apgar score of 10 at 15 min.
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An artificial patient capable of spontaneous and artificial ventilation has been used for bench testing of the Ohmeda CPU-1. This ventilator has an extensive capacity for interaction with the spontaneous breathing of the patient, and provides a wide variety of operating modes. These include spontaneous breathing with or without continuous positive pressure, volume-cycled and pressure-cycled artificial ventilation, with or without positive end-expiratory pressure or synchronization. ⋯ The synchronization permits adaptation of the ventilator to spontaneous respiration according to a wide range of harmonics. In any mode, artificial ventilation is initiated if spontaneous respiration is inadequate. The mandatory minute volume mode is based on a complicated program of a cautious nature which reacts instantly to inadequate spontaneous breathing, but is slow to discontinue artificial ventilation.
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Conventional anaesthetic breathing systems are not designed to control end-tidal gas concentrations, nor can they be used to measure accurately the uptake of oxygen or of anaesthetic agent. We built and tested a leak-tight closed-loop anaesthetic breathing system with low solubility to volatile anaesthetic agents and with efficient gas mixing. The system included a water-sealed spirometer, a small carbon dioxide absorber, a coaxial tube to the patient, a circulating pump and feedback controllers for system volume and anaesthetic concentration. ⋯ Stability was maintained with +/- 50% changes in alveolar ventilation and cardiac output. During subsequent investigations in an animal model, arterial, mixed venous and cerebral venous blood halothane concentrations were measured to show that the feedback-controlled halothane induction was optimized. We conclude that feedback control appears to be clinically applicable for adjusting the end-tidal halothane concentration and system volume to provide a rapid and optimized induction of anaesthesia.
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Conventional anaesthetic techniques do not allow for the automatic control of end-tidal halothane concentration and, therefore, brain concentration cannot be predicted. In this study, eight dogs were ventilated with halothane in oxygen using a new closed-loop anaesthetic breathing system which provided a constant end-tidal concentration. During the first 60 min the end-tidal concentration was maintained at 0.87 vol% (1 MAC). ⋯ Measured uptake differed from theoretically calculated uptake by 18.3-57.6%, depending on the model used. Measured arterial and cerebral venous concentrations differed from theoretically calculated values by 7% and 17.5%, respectively. It was shown that the required end-tidal concentrations can be obtained rapidly and accurately, and that brain tissue concentrations can be predicted within certain limits.