Journal of clinical monitoring最新文献

Objectives: The aim was to study the physiological effects of induced ventricular fibrillation and subsequent circulatory arrest for defibrillation threshold testing on the brain using the EEG, jugular bulb oxymetry and near-infrared spectroscopy.

Methods: Thirteen patients undergoing surgery for implantable cardioverter-defibrillator implantation or replacement under general anesthesia were included. We continuously monitored the jugular bulb oxygen saturation (SjO2), regional oxygen saturation (rSO2) and the EEG.

Results: 59 episodes of circulatory arrest were studied. In all cases the rSO2 fell instantly while the EEG changed within 12 +/- 4 seconds after induction. The EEG indicated ischemic changes, ranging from occurrence of rhythmic delta activity to cessation of all electrical activity. On successful defibrillation the rSO2 increased to values in excess of pre-arrest levels and restored towards baseline; the SjO2 initially fell followed by a similar overshoot. Recovery times increased in proportion to arrest duration.

Conclusion: Short lasting episodes of circulatory arrest have serious, but transient effects on brain function. The rSO2 is an effective non-invasive tool for monitoring cerebral oxygenation during DFT-testing.

Objective: To review, from a legal perspective the potential for using the Internet for inter-institutional transfer of patient medical records.

Methods: Basic issues and recent legislation that relate to protection of both medical data, and those transferring that data over public network systems is reviewed.

Results: Many laws already in existence can be applied to Internet transmission, but questions of jurisdiction remain. Providing signatures on requests for information, which are in essence contracts, is a problem. Signatures must both prove the identity of the participants and provide for non-repudiation of the agreement. Cryptographic digital signatures appear secure and effective, but their use is difficult to implement. Simpler methods are fraught with risks, yet are more easily accomplished. The patient's rights of privacy must be balanced against the need for access by government, physician, or healthcare institutions to confidential information. In general, information holders must put forth reasonable efforts to keep information confidential. The development of acknowledged standards will provide guidance. Multiple laws provide some deterrence and hence some reassurance to healthcare institutions, for example, by criminalizing acts of electronic interception of patient records in transit.

Conclusion: Some believe the expense of secure transfer of medical records by electronic means is a major obstacle; this is false: such transfers are now technologically quite easy. The greatest obstacle to electronic transfer of medical records at this point is the development of workable standards for signing agreements and protecting transmissions, but the perceived advantages will likely drive the necessary developments.

Objective: A novel algorithm to detect the dicrotic notch in arterial pressure signals is proposed. Its performance is evaluated using both aortic and radial artery pressure signals, and its robustness to variations in design parameters is investigated.

Methods: Most previously published dicrotic notch detection algorithms scan the arterial pressure waveform for the characteristic pressure change that is associated with the dicrotic notch. Aortic valves, however, are closed by the backwards motion of aortic blood volume. We developed an algorithm that uses arterial flow to detect the dicrotic notch in arterial pressure waveforms. Arterial flow is calculated from arterial pressure using simulation results with a three-element windkessel model. Aortic valve closure is detected after the systolic upstroke and at the minimum of the first negative dip in the calculated flow signal.

Results: In 7 dogs ejection times were derived from a calculated aortic flow signal and from simultaneously measured aortic flow probe data. A total of 86 beats was analyzed; the difference in ejection times was -0.6 +/- 5.4 ms (means +/- SD). The algorithm was further evaluated using 6 second epochs of radial artery pressure data measured in 50 patients. Model simulations were carried out using both a linear windkessel model and a pressure and age dependent nonlinear windkessel model. Visual inspection by an experienced clinician confirmed that the algorithm correctly identified the dicrotic notch in 98% (49 of 50) of the patients using the linear model, and 96% (48 of 50) of the patients using the nonlinear model. The position of the dicrotic notch appeared to be less sensitive to variations in algorithm's design parameters when a nonlinear windkessel model was used.

Conclusions: The detection of the dicrotic notch in arterial pressure signals is facilitated by first calculating the arterial flow waveform from arterial pressure and a model of arterial afterload. The method is robust and reduces the problem of detecting a dubious point in a decreasing pressure signal to the detection of a well-defined minimum in a derived signal.

To our knowledge, this is the first attempt at adapting an existing cardiovascular model to simulate the hemodynamics of a particular patient population. Despite attempts to define the physiologic alterations in advance, we discovered there were critical parameters not completely defined in the literature. These were discovered through the iterative process of testing, comparing resulting vital signs with targets, and literature review. A list of the parameters that should be sought for future modeling efforts is provided (Table 3), but this list is by no means exhaustive. As further work is performed in this area, additional independent and essential parameters will be identified (pressure characteristics of valvular anomalies, for example). To define a physiology that is less well described in the literature, empirical alterations and best-guess estimates of parameter changes will be required with significantly more iterations. Finally, we have described only modeling of cardiovascular physiology, modeling the respiratory system will require a similar process.

Current training methods in fiberoptic intubation entail a trial and error process in which trainees acquire skills by practicing this technique in mannequins or patients. These training methods are not efficient and may expose patients to unnecessary instrumentation. An interactive software program is described which uses Director, a commercially available multimedia authoring tool, to (1) familiarize trainees with video images of the upper airway, (2) permit operator controlled progress through a normal fiberoptic intubation, (3) simultaneously display (side by side) two-dimensional or three-dimensional computer tomographic images with a fiberscope in place and the corresponding endoscopic video images, and (4) demonstrate some of the obstacles which occur in clinical practice (e.g. "white-out" and saliva). The intent of this package is to simulate fiberoptic intubation techniques as well as help one create a mental image of the path a fiberscope takes within the lumen of the upper airway. The potential for improving operator immersion (virtual reality) by using a more sophisticated input device is discussed.