International journal of clinical monitoring and computing最新文献

Summary statement: Processed digitized Doppler signals abstracted from recordings during continuous air infusion in dogs were used to train a neural network to estimate air embolism infusion rates.

Background: Precordial Doppler is a sensitive technique for detecting venous air embolism during anesthesia, but it requires constant attentive listening. Since neural networks are particularly well suited to the task of pattern recognition, we sought to investigate this technology for detection and grading of air embolism.

Methods: Air was infused into peripheral veins of four anesthetized dogs at rates of 0.025, 0.05, 0.10, 0.25, 0.50 and 1.0 ml-1.kg-1.min-1 while digital recordings of the precordial Doppler ultrasound signal were collected. The frequency content of the recordings was determined by Fourier analysis. The output of the Fourier transform was the input to a neural network. The network was then trained to estimate the air infusion rate.

Results: The correlation coefficient between the size of the air embolism and the air infusion rate was greater than r2 = 0.93 for each of the four animals in the study when the network was trained using the data for all four dogs. When the data from a dog was withheld from the training set and used only for testing the correlation coefficients ranged from r2 = 0.75 to r2 = 0.27. For frequencies below 250 Hz, the acoustic energy tended to fall as the air infusion rate increased. The opposite occurred at frequencies above 325 Hz.

Conclusions: Neural network processing of the precordial Doppler signal provides a quantitative estimate of the size of an air embolism.

Hill's equation relating oxygen tension, saturation and P50 is used as the basis for a simple method to calculate P50 from a single blood sample. The effects of errors of measurement in oxygen tension and saturation are considered using the technique of sensitivity analysis. The method is illustrated using data published by Severinghaus.

Background: Double burst stimulation (DBS) was originally introduced for improved manual detection of residual neuromuscular blockade. Previous studies demonstrated a high correlation between mechanomyographical responses to DBS and train-of-four (TOF) stimulation during recovery from neuromuscular blockade. However, repeatability and bias analyses that are recommended when new monitoring devices are introduced into clinical practice [11] have not yet been performed.

Object: The object of the present study was to evaluate if DBS3,350/50 (3 stimuli at 50 Hz followed 0.750 sec later by 3 stimulations at 50 Hz) and TOF measurements are in so close agreement that they can be used interchangeably during spontaneous recovery from atracurium blockade.

Methods: The study comprised 20 women undergoing gynaecological laparotomy and anaesthetised with fentanyl, thiopentone, halothane, and nitrous oxide. The neuromuscular blockade was induced and maintained with atracurium. The ulnar nerve was stimulated using DBS or TOF stimulation. Neuromuscular transmission was monitored mechanomyographically. Alternating sequences of 4 DBS and 6 TOF stimulations were applied during the phase of spontaneous recovery. Repeatability, bias (accuracy) and limits of agreement were calculated as proposed by Bland and Altman [11].

Results: The repeatability coefficients before any neuromuscular blocking agent was given were 3.4 and 7.7% for T1 and D1, respectively (P < 0.05), and 3.8 and 3.5% for TOF ratio and DBS ratio, respectively (P > 0.05). The mean difference between duplicated DBS and TOF measurements during recovery (repeatability) differed from zero due to the ongoing recovery process. It was therefore not possible to calculate the repeatability coefficients. The DBS ratio bias decreased from 6.69 to 3.51% (P < 0.05) during recovery. The limits of agreement between the DBS and TOF ratios increased from -2.07 to 15.45%, to -11.93 to 18.95% during recovery, while the limits of agreement between the DBS and TOF twitch heights increased from -5.02 to 10.68%, to -21.02 to 25.26%.

Conclusion: The limits of agreement between DBS and TOF responses were so wide that DBS and TOF can not be used interchangeably.

Safety of closed-loop drug infusion systems is an issue often raised as a matter of concern. As a result, many closed-loop control systems are reported in the literature merely as computer simulation studies and few ever reach the stage of physical realisation and formal clinical evaluation. We address the safety issues involved with such systems by describing the development of a portable closed-loop control system for atracurium-induced muscle relaxation. This is a safety-critical system particularly when applied to brain and eye surgery where movement could have serious deleterious effects. The benefits of closed-loop muscle relaxation in providing stable surgical operating conditions over a wide range of patient sensitivities while infusing the minimum amount of drug makes this a worthwhile aim and serves to demonstrate safety issues which are generally applicable to other closed-loop drug infusion systems. It is hoped that the described methodology will facilitate and encourage the clinical application of closed-loop drug infusion systems so that clinical staff and patients may receive the benefits of closed-loop drug therapy.

The performance of an adaptive model-based controller for the administration of atracurium, mivacurium, rocuronium and vecuronium was compared in 159 adult surgical patients. The degree of neuromuscular block was set to 90% for atracurium, rocuronium and vecuronium and to 95% for mivacurium. Performance was assessed by calculating the median prediction error (bias), median absolute performance error (inaccuracy), divergence, wobble, the mean offset and the mean standard deviation from the setpoint. All indices of controller performance showed minimal deviation of the actual neuromuscular block from the setpoint. Although the controller appeared to be able to control rocuronium induced block at 90% and mivacurium induced block at 95% better than atracurium and vecuronium block at 90%, the differences in the controller performance between the four studied relaxants were small and have hardly any clinical significance. We conclude that a model-based adaptive controller is useful in the administration of atracurium, mivacurium, rocuronium or vecuronium.

Objectives: To compare charting of physiological parameters manually by nurses and automatically by computer and so decide whether this task could accurately be performed by computer.

Subjects/setting: 101 consecutive patients admitted for tertiary neonatal intensive care.

Design: Direct comparison of 48 hours of data collected by both methods. Computer data stored each second and the hourly median compared with the single hourly value noted by the nurse.

Methods: All patients were monitored by standard patient monitor and a computer. Four physiological parameters were compared between nurse and computer (both derived information from the standard patient monitor): heart rate, transcutaneous oxygen, mean blood pressure, central temperature. A random 51% of patients had the computer data displayed as trends at the cotside. Comparison of the hourly nurse observation and a computer hourly median value. Computer data was compared before and after the removal of artifact. In addition, the effects on nursing observations of either display or non display of the computer trend data was assessed.

Results: Nurse and computer observations were statistically significantly different (p < 0.001), though these were not clinically important. Nurses tended to note a higher figure than the computer median. The cotside display of computer data improved consistency between the nurse and computer observations. Artifact present in the data had little influence on the accuracy of the computer median value.

Conclusions: Computer systems can accurately chart physiological data, providing a more flexible record with a minimal risk to data reliability from artifact.

In critically ill patients haemodynamic parameters are being routinely monitored. All of the fluctuations in blood pressures cannot be visualised since on most monitors the time window is too short and trend curves do not have a sufficient time resolution. Therefore, frequency analysis was applied to an 800-second window. Systemic artery pressure, central venous pressure and pulmonary artery pressure curves of 6 patients were sampled with a frequency of 40 Hz. The signals were transformed into the frequency domain by the Fast Fourier Transform method. Bispectral analysis was applied to determine the origin of higher frequencies. There were three main frequencies present: heart stroke rate, respiratory frequency and a slow frequency (< 0.05 Hz), which was equal to the used infusion rate (2-10 ml/h) of vaso-active drugs. Continuous infusion of short-acting vaso-active drugs delivered by pulsatile diaphragm pumps to produce slow significant fluctuations in especially the arterial blood pressures (range: 5-40 mmHg). The periodicity of these slow fluctuations is not visualised during routine monitoring, so the observer may misinterpret the cause of changes in blood pressure and make inappropriate clinical decisions. A solution for detection of such slow waves is Fast Fourier Transform combined with bispectral analysis.

We designed a virtual device for a local area network observing, operating and connecting devices to a personal computer. To keep the widest field of application, we proceeded by using abstraction and specification rules of software engineering in the design and implementation of the hardware and software for the Infusion Monitor. We specially built a box of hardware to interface multiple medical instruments with different communication protocols to a PC via a single serial port. We called that box the Universal Device Communication Controller (UDCC). The use of the virtual device driver is illustrated by the Infusion Monitor implemented for the anaesthesia and intensive care workstation.

Invasive blood pressure measurement is used in patients with unstable haemodynamics. The demand of the accuracy of these measurements is high. The reliability of the reproduced signal strongly depends on the measurement system's dynamic characteristic-its resonance frequency and damping factor. These characteristics were examined with the frequency response method, which is valuable for second and higher order systems. Most of the pressure measuring systems in use in clinical practice have low damping factor (0.1-0.2), which causes high overshoot in systolic pressure values (up to 13%), since putting all the measuring components in a chain reduces the dynamic properties of a single component and the resonance frequency drops drastically from over 100 Hz to even below 10 Hz. One of the solutions to increase the damping ratio is to insert a damping device R.O.S.E. parallel to the tubing. The resonance frequency remains the same, the damping factor increases to around 0.5. Systems with higher damping factors (0.5-0.7) have lower overshoot (1-2%), therefore the blood pressure measurements are more accurate.