Journal of clinical monitoring and computing
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J Clin Monit Comput · Apr 2012
Comparative StudyContinuous minimally invasive peri-operative monitoring of cardiac output by pulmonary capnotracking: comparison with thermodilution and transesophageal echocardiography.
A number of technologies are available for minimally-invasive cardiac output measurement in patients during surgery but remain little used. A system has been developed based on CO(2) elimination (VCO(2)) by the lungs for use in ventilated patients, which can be fully integrated into a modern anesthesia/monitoring platform, and provides semi-automated, continuous breath-by-breath cardiac output monitoring. A prototype measurement system was constructed to measure VCO(2) and end-tidal CO(2) concentration with each breath. ⋯ The method followed sudden changes in cardiac output due to arrythmias and run onto cardiopulmonary bypass in real time. The accuracy and precision were comparable to other clinical techniques. The method is relatively seamless and largely automated and has potential for continuous, cardiac output monitoring in ventilated patients during anesthesia and critical care.
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The authors evaluated an analyser for the determination of propofol concentrations in whole blood. The Pelorus 1000 (Sphere Medical) measures propofol concentrations in around 5 min without the requirement for sample preparation. The performance of the analyser was characterised with respect to linearity, precision in control solutions and whole blood and method comparison to an HPLC based reference method. ⋯ The only cross interference of note is to a highly elevated level of conjugated bilirubin, while low haematocrit levels lead to a 0.13 μg/ml under reading with respect to the HPLC reference. The system fulfils the requirements for measurement of propofol concentrations in whole blood samples with precision and accuracy suitable for elucidating propofol pharmacokinetics at clinically relevant concentrations. With no requirement for sample preparation and a fast time to results, the analyser opens up the possibility of studies to measure and respond to blood propofol concentrations in patients in close to real time.
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J Clin Monit Comput · Feb 2012
Respiratory and non-respiratory sinus arrhythmia: implications for heart rate variability.
The quantity of blood arriving at the left side of the heart oscillates throughout the breathing cycle due to the mechanics of breathing. Neurally regulated fluctuations in the length of the heart period act to dampen oscillations of the left ventricular stroke volume entering the aorta. We have reported that stroke volume oscillations but not spectral frequency variability stroke volume measures can be used to estimate the breathing frequency. ⋯ Both respiratory and non-respiratory sinus arrhythmia was observed amongst healthy adults. This observation at least partly explains why heart period parameters and heart rate variability parameters are not reliable estimators of breathing frequency. In determining the validity of spectral heart rate variability measurements we suggest that it is the position of the spectral peaks and not the breathing frequency that should be the basis of decision making.
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Many of the complications related to prolonged ventilation are related to inappropriate handling of endotracheal tube (ETT) cuff. This article reviews the possible complications associated with the ETT cuff, and the landmark development made in that field. The article challenges the present paradigm of cuff use and reviews the current clinical practice in that area.