Anaesthesia and intensive care
-
Anaesth Intensive Care · Aug 1994
ReviewControl of carbon dioxide levels during neuroanaesthesia: current practice and an appraisal of our reliance upon capnography.
With the widespread availability of capnography, many anaesthetists have swung away from formally verifying hypocapnia by intraoperative arterial blood gas analysis and, instead, have come to rely upon capnography as an acceptable and constant predictor of arterial CO2 tension (PaCO2) during neurosurgery. However, the nature of the arterial-end-tidal CO2 gradient is complex, and is frequently unexpectedly large, or even negative. The importance of close intraoperative CO2 control during neurosurgery--more specifically, routine hyperventilation, and our reliance upon capnography to guide intraoperative management--is reappraised. There is a growing appreciation of the adverse effects of hyperventilation and hypocarbia, especially upon abnormal or ischaemic brain, and it is clear that capnography alone cannot be used to confidently predict the true PaCO2 during neuroanaesthesia.
-
We present an automatic closed circuit anaesthesia ventilator designed for routine clinical use. The ventilator combines the benefits of high flow systems and true closed circuits, without their disadvantages. The system can be used with any FiO2, with air or nitrous oxide as carrier gas. ⋯ An automatic flush procedure prevents accumulation of unwanted gases. Operation is as easy as contemporary non-closed circuit ventilators. With this machine, closed circuit anaesthesia is possible from the beginning to the end of the procedure.
-
There are compelling reasons why the closed carbon dioxide filtration method for inhalation anaesthesia deserves serious reconsideration. Use of the closed absorption system today can provide all the benefits recognised by those who introduced it seventy to eighty years ago. A most important benefit is the increased opportunity of learning afforded the user, which leads either neophyte or senior clinician to improvement of both concept and clinical skills. The current resurgence of interest is fully appropriate for all physicians who aspire to be true specialists in the care of patients during clinical anaesthesia.
-
Anaesth Intensive Care · Aug 1994
Humidity of anaesthetic gases with respect to low flow anaesthesia.
It has been demonstrated in an experimental study in swine using the scanning electron microscope that a rebreathing technique utilising minimal fresh gas flowrates significantly improves climatization of anaesthetic gases. Consequently, effects of various anaesthetic techniques on airway climate must be assessed, which covers the need for suitable measuring devices. Basic principles and methods of humidity measurement in flowing anaesthetic gases include gravimetric hygrometry, dew point hygrometry, wet-dry bulb psychrometry, mass spectrometry, spectroscopic hygrometry and electrical hygrometry. ⋯ Humidity and temperature of inspired air obtained with fresh gas flowrates of 6.0 and 3.0 l/min were found to be inadequate for prolonged anaesthesia. Reducing the fresh gas flow to 1.5 l/min increases heat and moisture content in the respired gases, but conditions are still inadequate for prolonged anaesthesia. Sufficient moisture (> or 20 mg H2O/l) and temperature are obtained under minimal flow conditions after one hour.