International journal of clinical monitoring and computing最新文献

Background: Arterial and venous pressure is commonly measured using fluid filled catheters. To avoid obstruction they are continuously spilled by a flush-device. The accuracy of the flowrate has not been investigated previously.

Methods: The accuracy of 5 different flush-devices available in Switzerland was checked for flowrate when factory new, after a single sterilization with ethylen-oxide, in a long-term test over 96 hours, after repeated handling of the integrated bypass and under application of a pulsing counter-pressure.

Results: Flow is linearly related to differential-pressure and is constant over time. The flow of each flush-device at 200 mmHg differential-pressure was below the indicated 3 ml per hour (1.69 - 2.49 ml/h). Sterilization in two types produced a significant but not relevant difference in flowrate. Longtime-use, bypass actuation and pulsing pressure did not alter the flowrate significantly (p <0.05). In two factory-new flush-devices and 4 re-used ones a plugged capillary induced cessation of flow.

Conclusions: Flowrate in flush-devices is accurate under sterilization, longtime use, bypass-actuation and pulsing counter pressure. A plugged capillary occurred in a few new and reused flush-devices, which can be the explanation for clotted catheters in clinical use.

It is possible to link a Laser-Doppler to a DOS-compatible personal computer in order to monitor microcirculation of the free flap after plastic surgery. We connected such a system to a second computer by telephone modems, in order to control the Laser-Doppler via the telephone line from a distant location using only commercially available hardware and software. The aim was to develop a low-cost system which would not require the purchase or construction of any specialised equipment. Using this system, it was possible to show the Laser-Doppler waveforms to colleagues who were not at the patient site, for their (more experienced) opinions without any further delays. Preliminary tests on five cases showed that it was indeed possible to transfer recorded information about the blood flow rate of free skin flaps from one computer to a remote one, without any loss of information. In these cases, the measured blood flow and clinical surveillance of the blood supply were adequate, thus making revision of the tissues not necessary. This preliminary study suggests that standard 'off-the-shelf' personal computer tools may be useful in improving the monitoring of microcirculation after plastic surgery.

Considering the heart as a physical pump cardiac efficiency is calculated from the ratio of cardiac work performed to the maximum level of energy of the heart. The aim of the study was to compare cardiac efficiency with cardiac output and right ventricular ejection fraction. Nine patients scheduled for coronary artery bypass grafting were investigated. A femoral arterial and a right ventricular ejection fraction pulmonary artery catheter were placed in the awake state. Anaesthesia was induced with eltanolone and fentanyl. Cardiac output, pulmonary artery and central venous pressures, and right ventricular ejection fraction were measured in the awake state (baseline), 2 min after induction of anaesthesia and 1 and 5 min after intubation. Cardiac efficiency was calculated by dividing the stroke work by the maximum energy of the heart as calculated from the pressure volume diagram. An analysis of variance was carried out for cardiac efficiency, cardiac output and right ventricular ejection fraction. Cardiac efficiency was significantly (p < 0.05) reduced 1 min after intubation from 28 +/- 11 to 14 +/- 5%. In contrast the right ventricular ejection fraction (from 48 +/- 10 to 35 +/- 13%) and cardiac output (from 6.5 +/- 1.5 to 5.3 +/- 1.2 L/min) did not change significantly during the induction of anaesthesia. Cardiac efficiency was found to be a more sensitive parameter to describe changes in the right ventricular function than the ejection fraction and cardiac output during induction of anaesthesia with eltanolone and fentanyl which was used as a model to vary cardiac performance and afterload.

Background: The location of epidural space for local anaesthetic injection can be difficult. The aim of this study was to define the mathematical function of the pressure changes in the syringe during puncture of the epidural space. Knowledge of pressure changes might be of help to the anesthetist who attempts to ascertain the location of the needle, and it is essential to the design of a device with which to locate epidural space.

Methods: Epidural punctures were performed in 20 patients, using an 18-Tuohy needle connected to a 10 ml syringe. The epidural space was located by the loss of resistance technique. Pressure variations within the injection system during epidural puncture were measured and digitized at 250 Hz. Pressure curves were analyzed for amplitude and rate of a decay after entry of the needle into the epidural space.

Results: Pressure increased as the needle passed through skin, subcutaneous fat and muscle. The maximal pressure was observed when the needle perforated the ligamentum flavum (689 +/- 124 cm H2O). When the needle entered the epidural space, an exponential decrease in pressure was observed in all patients (R2 = 0.99; tau = 2.1 +/- 0.9 seconds). End-residual pressure was 22 +/- 12 cm H2O. The change in pressure observed when the needle entered the epidural space fitted a negative exponential function (y = e-x/2.08).

Conclusions: Pressures within the injection system for epidural puncture can reach 1100 cm H2O. Location of the epidural space is characterized by an exponential decay to and end-residual pressure below 50 cm H2O, with a constant time of approximately 2 seconds.

We have studied day-time vigilance in 31 patients (median age 49 years) with suspected sleep disorders using a new visual reaction time and performance test. The findings in the day-time vigilance test were compared with the number of desaturation events and movement arousals measured with a sensitive movement detector in the night-time. In our statistical model the high number of desaturations correlated with a high dispersion in reaction-times. The squared multiple r was 0.465 in a model where the dispersion of reaction times was the dependent variable and the number of desaturations, duration of quiet sleep and the mode of oxygen saturation were independent variables. A high amount of body movements (movement arousals, duration less than 5 seconds) correlated with gradual deterioration in the performance test. The squared multiple r was 0.447 in a model where the regression coefficient of reaction times was the dependent variable and active sleep and number of body movements less than 5 seconds in duration were the independent variables. Frequent arousals in apnoeic patients are observed in hyper-excitable responders and are known to cause sleep deprivation and hypersomnia. Our findings in desaturating patients indicate that in those with a low chemoreceptor response to hypoxia the failure in day-time regulation of vigilance may differ from the failure associated with sleep-deprivation.

We wished to assess the accuracy of a modified form of Trigg's Tracking Variable (TTV) at detecting the onset of changes in systolic blood pressure. A computer model generated systolic blood pressures which changed to a new value after period of stability. A separate algorithm based on TTV indicated when a 'significant' change had been detected. This signal occurred when TTV had exceeded a set limit (0.8-0.99) a predetermined number of times (1-10). Five anaesthetists were shown 40 sets of data generated by same the computer model and asked to indicate the onset of changes. The greatest number of changes (94.1%) were correctly identified when TTV exceeded 0.92 on 4 consecutive determinations. The onset of the trend was detected after an average delay of 140 s. The anaesthetists correctly detected 85% of the changes after an average delay of 162 s. There was no statistically significant difference between the anaesthetists and the algorithm, although only one anaesthetist performed better than the modified TTV. The modified TTV detected changes in simulated invasive systolic blood pressures faster and more accurately than four of a group of five anaesthetists. Such simple trend detection systems may be useful as 'advisory' alarms.

The mechanical respiration of intubated patients is a process which is influenced by many parameters and, through its many interactions, is extremely complex. Taken by itself the logical analysis of this complexity is extraordinarily difficult and leads very often to false conclusions. For that reason computer simulation of complex systems by means of the computer is an important tool in the analysis of these processes. Required is a model which describes the actual behavior of the system. However, it should not be overlooked that a model always describes only a portion of reality. Models having exclusively to do with ventilation mechanics or with gas exchange cannot simulate the interactions between the two. To accomplish this purpose, an improved model is necessary, including both partial processes and thereby capturing the complexity of the system. Accordingly, both ventilation mechanics and gas exchange have been integrated equally into the newly developed model for the simulation program Simu Vent. The core of the program builds a functional multicompartment model of the lungs and considers the partial processes ventilation mechanics, gas transport, gas mixing and gas exchange. Further considered are the respirator, blood circulation and peripheral compartments. The program runs under a graphical user interface, allowing its easy use. Responsible for this ease is the user's ability to interact with the program while simulation is in progress and the specially designed graphic screen mask. Comparing measured with simulated values demonstrated that the measured curve can be simulated with minimal error. Furthermore, the multicompartment model describes disruptions in distribution. Simu Vent's application is especially well advised in the description and analysis of the theoretical fundamentals of mechanical respiration. This aspect is meaningful above all in education and research, rendering these two the model's main areas of use.

Computerised physiological data contains artifact that needs to be identified and possibly removed. Whilst computers may eventually satisfactorily perform this function, at present only manual removal is possible for the majority of intensive care computer groups. We assessed the effects of artifact and its removal on the physiological data of 3 patients. Artifact was manually removed from 7 days of data in 4 parameters (heart rate, respiratory rate, systolic blood pressure [sbp] and transcutaneous oxygen [tcpO2]) by 3 independent observers. Six hour time periods were analysed. Median and mean values before and after the manual removal of artifact were compared. Overall 6.5% of data was removed as artifact. This was greatest for tcpO2 (9.9%) and sbp (10.6%), with smaller amounts for respiratory rate (2.8%) and heart rate (2.4%). Sbp showed a marked difference in the amount of data removed between patients, whereas tcpO2 data contained quite large volumes of artifact, but this was fairly consistent between patients. Removal of artifact affected mean values more than median values. One observer considered that both physiological and non-physiological artifact should be removed, whereas the other two observers removed only non-physiological artifact. Agreement in results between the latter was good. Our results suggest that inter-observer variability should have a minimal effect on values, once rules identifying the type of artifact to be removed are agreed. Removal of artifact did not have a clinically significant effect on results, but may be an important consideration in the statistical analysis of computerised physiological data.