Anaesthesia
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Comparative Study Clinical Trial Controlled Clinical Trial
The peri-operative use of the oesophageal Doppler monitor in patients undergoing coronary artery revascularisation. A comparison with the continuous cardiac output monitor.
This study was carried out to evaluate the ease of use and reliability of cardiac output estimations performed by an oesophageal Doppler monitor and to compare its use with that of a continuous cardiac output pulmonary flotation catheter. Measurements were made during and after surgery in 16 patients scheduled to undergo coronary revascularisation. Both devices suffered significant intra-operative problems which led us to question their suitability as operating theatre monitors. After surgery the continuous cardiac output monitor provided stable results while the oesophageal Doppler monitor required the continuous presence of an experienced anaesthetist to ensure comparable cardiac output estimations.
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Clinical Trial
A noninvasive method for evaluating the effect of thoracotomy on shunt and ventilation perfusion inequality.
A new noninvasive method was used to evaluate gas exchange in 12 patients undergoing thoracotomy for a variety of surgical procedures. A plot of inspired oxygen partial pressure versus oxygen saturation was analysed to calculate the independent contribution of shunt and intermediate ventilation/perfusion ratio which occurs during general anaesthesia for thoracotomy. A model based on the inspired to arterial oxygen difference involving the shunt equation was used to show how the relationship between inspired oxygen partial pressure and oxygen saturation could be used to derive two parameters of oxygen exchange, the virtual shunt and an index of low ventilation/perfusion ratio. ⋯ Thoracotomy caused a mean increase in shunt from 13.8% to 20.8% and a worsening ventilation/perfusion ratio from 0.5 to 0.2, the magnitude of which depended on the underlying pathology. In two patients, the ventilation/perfusion ratio decreased to less than 0.1. The method enables the prediction of oxygen saturation at different inspired oxygen partial pressures and allows the two components of gas exchange to be isolated using simple routine measurements of inspired oxygen and pulse oximetry.
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When volatile anaesthetics are used in a closed breathing system it is usually assumed that inflow of anaesthetic to the system matches uptake by the patient. Early laboratory reports on the interactions between sevoflurane and soda lime cast doubt on that assumption. We have measured the loss of sevoflurane, desflurane and isoflurane from a closed breathing system and found no differences of consequences.
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The Oxyvent is an anaesthetic machine designed specifically for use in the developing world and difficult situations. It is made up of four components, each of which has, in its own right, already proved to be of great value in difficult situations. These are the drawover system, the Penlon Manley Multivent Ventilator, the DeVilbiss Oxygen Concentrator and the air compressor. ⋯ The Oxyvent can be used to provide anaesthesia in the absence of electricity or oxygen or both. It is simple, robust and easily serviceable. It is versatile and can be used both as an anaesthetic machine in the operating theatre and as a ventilator in an intensive care unit.