Therapeutic Considerations in the Management of Agitated or Delirious Critically 111 Patients

Agitation and delirium in the critical care unit are common problems that at times are difficult to treat. The difficulty stems from few placebo-controlled or even blinded trials evaluating various therapies. In addition, the literature in these areas is scattered through various journals in a variety of disciplines. Pharmacologic and nonpharmacologic techniques may achieve the therapeutic objective for these patients. Since no one drug will achieve the goals in every patient, therapy must be tailored to the characteristics and needs of each individual.     

Meet the challenge of high-pass filter and ST-segment requirements with a DC-coupled digital electrocardiogram amplifier

Background

The high-pass filter (HPF) in an electrocardiogram (ECG) amplifier can distort the ST segment required for ischemia interpretation. Therefore, the current standards and guidelines require −3 dB for monitoring and −0.9 dB for diagnostic purposes at 0.67 Hz. In addition, a minimal reaction to a rectangular pulse of 300 μV has to be proven. We raise the question of why the design of a DC-coupled digital ECG amplifier is reasonable when today the AC-coupled digital ECG amplifier including a 0.05-Hz HPF works so well, meets all required standards, and is already safe. We make the hypothesis that a digital DC-coupled ECG amplifier can as well meet the requirements and guarantee the same safety levels at the same time provide a higher degree of freedom for future improvements of the ECG signal quality.

Methods

Firstly, a historical research of the origin of the 0.05-Hz requirement has been made. Secondly, triangular pulses simulating unipolar QRS complexes have been passed through a digital filter to get qualitative results of the HPF response. And finally, to quantitatively describe the filter response, corresponding test requirement signals have been passed through a digital filter to simulate the HPF behavior, therefore understanding the reasons for the required tests.

Results

The oldest reference found to the 0.05-Hz filter dates from 1937. At that time, DC-coupled analogue ECG amplifiers were used. The simulation of the AC-coupled ECG amplifier with a first-order analogue HPF shows that the rectangular 300-μV pulse is a phase requirement and more restrictive than the frequency requirements. The phase requirement in fact corresponds to the requirement of a 0.05-Hz first-order analogue HPF (−3 dB) even if −0.9 dB at 0.67 Hz is required. The DC-coupled ECG amplifier (without an analogue HPF and during online and off-line acquisition) fulfils the phase and frequency requirements, just as the digital AC-coupled ECG amplifier does.

Conclusions

An AC-coupled ECG amplifier based on a first-order analogue HPF must have a maximum cutoff frequency of 0.05 Hz or requires a phase equalizer causing a delay of the acquired ECG. Because the desired delay during online acquisition should be short, the solution is practical but could be improved. Not the frequency cutoff of the HPF but the phase distortion of such a filter should be discussed. The DC-coupled ECG amplifier is as safe as the AC-coupled ECG amplifier; but it provides a higher degree of freedom for future filter designs certainly improving the ECG signal quality, while the safety can be guaranteed. Furthermore, the DC-coupled ECG amplifier allows investigation of the HPF, which is not easily possible when an AC-coupled ECG amplifier including the HPF is to be investigated.     

Development of a toolbox for electrocardiogram-based interpretation of atrial fibrillation

Background

Atrial fibrillation (AF) develops as a consequence of an underlying heart disease such as fibrosis, inflammation, hyperthyroidism, elevated intra-atrial pressures, and/or atrial dilatation. The arrhythmia is initiated by, or depends on, ectopic focal activity. Autonomic dysfunction may also play a role. However, in most patients, the actual cause of AF is difficult to establish, which hampers the selection of the optimal mode of treatment. This study aims to develop tools for assisting the physician's decision-making process.

Methods

Signal analytical methods have been developed for optimizing the assessment of the complexity of AF in all of the standard 12-lead signals. The development involved an evaluation of methods for reducing the signal components stemming from the electric activity of the ventricles (QRST suppression). The methods were tested on simulated recordings, on clinical recordings on patients in AF, and on patients exhibiting atrial flutter (AFL) and atrial tachycardia. The results have been published previously. Subsequently, the implementation of the algorithms in a commercially available electrocardiogram (ECG) recorder, an implementation referred to as its AF-Toolbox, has been carried out. The performance of this implementation was tested against those observed during the development stage. In addition, an improved visualization of the specific ECG components was implemented. This was enabled by providing a separate view on ventricular and atrial activity, which resulted from the steps implied in the QRST suppression. Furthermore, a search was initiated for identifying meaningful features in the cleaned up atrial signals.

Results

When testing the implementation of the previously developed methods in the Toolbox on simulated and clinical data, the suppression of ventricular activity in the ECG produced residuals down to the level of physiologic background noise, in agreement with those reported on previously. The QRST suppression resulted in a better visualization of the atrial signals in AF, atrial AFL, sinus rhythm in the presence of atrioventricular blocks, or ectopic beats. Classifiers for AF and AFL that have been defined so far include the distinct spectral components (multiple basic frequencies), exhibiting distinct dominance in specific leads. The annotations of ventricular and atrial activities, ventricular and atrial trigger, as well as ratio between atrial and ventricular rates were greatly facilitated. The time diagram of ventricular and atrial triggers provides an additional view on rhythm disturbances.

Conclusions

The AF-Toolbox that is currently developed for clinical applications has the potential of reliably detecting and classifying AF, as well as to correctly describe atrioventricular conduction, propagation blocks and/or ectopic beats. Based on the results obtained, a first industrial prototype has been built, which will be used to assess its performance in a routine clinical environment. The availability of this tool will facilitate the search for meaningful signal features for identifying the source of AF in individual patients.     

Challenges and Regulatory Considerations in the Acoustic Measurement of High‐Frequency (>20 MHz) Ultrasound

This article examines the challenges associated with making acoustic output measurements at high ultrasound frequencies (>20 MHz) in the context of regulatory considerations contained in the US Food and Drug Administration industry guidance document for diagnostic ultrasound devices. Error sources in the acoustic measurement, including hydrophone calibration and spatial averaging, nonlinear distortion, and mechanical alignment, are evaluated, and the limitations of currently available acoustic measurement instruments are discussed. An uncertainty analysis of acoustic intensity and power measurements is presented, and an example uncertainty calculation is done on a hypothetical 30‐MHz high‐frequency ultrasound system. This analysis concludes that the estimated measurement uncertainty of the acoustic intensity is +73%/?86%, and the uncertainty in the mechanical index is +37%/?43%. These values exceed the respective levels in the Food and Drug Administration guidance document of 30% and 15%, respectively, which are more representative of the measurement uncertainty associated with characterizing lower‐frequency ultrasound systems. Recommendations made for minimizing the measurement uncertainty include implementing a mechanical positioning system that has sufficient repeatability and precision, reconstructing the time‐pressure waveform via deconvolution using the hydrophone frequency response, and correcting for hydrophone spatial averaging.     

Friction and shear highly associated with pressure ulcers of residents in long‐term care – Classification Tree Analysis (CHAID) of Braden items

Aims Among various risk assessment scales for the development of pressure ulcers in long‐term care residents that have been published in the last three decades, the Braden scale is among the most tested and applied tools. The sum score of the scale implies that all items are equally important. The aim of this study is to show whether specific items are of greater significance than others and therefore have a higher clinical relevance. Design Data analysis of six pressure ulcer prevalence studies (2004–2009). Methods A total of 17 666 residents (response rate 79.6%) in 234 long‐term care facilities participated in 6 annual point prevalence studies that were conducted from 2004 to 2009 throughout Germany. For the classification of the sample regarding pressure ulcers as a dependent variable and the Braden items as predictor variables, Chi‐square Automatic Interaction Detector (CHAID) for modelling classification trees has been used. Results Pressure ulcer prevalence was 5.4% including pressure ulcer grade 1 and 3.4% for pressure ulcer grades 2–4. CHAID analysis for the classification tree provided the item ‘friction and shear’ as the most important predictor for pressure ulcer prevalence. On the second level, the strongest predictors were ‘nutrition’ and ‘activity’ and on the third level they were ‘moisture’ and ‘mobility’. Residents with problems regarding ‘friction and shear’ and poor nutritional status present with an 18.0 (14.8) pressure ulcer prevalence which is 3–4 times higher than average. Conclusion CHAID analyses have shown that all items of the Braden scale are not equally important. For residents in long‐term care facilities in Germany, the existence of ‘friction and shear’ as a potential and especially as a manifest problem has had the strongest association with pressure ulcer prevalence.