Reduction of CPR artifacts in the ventricular fibrillation ECG by coherent line removal.

BACKGROUND: Interruption of cardiopulmonary resuscitation (CPR) impairs the perfusion of the fibrillating heart, worsening the chance for successful defibrillation. Therefore ECG-analysis during ongoing chest compression could provide a considerable progress in comparison with standard analysis techniques working only during "hands-off" intervals. METHODS: For the reduction of CPR-related artifacts in ventricular fibrillation ECG we use a localized version of the coherent line removal algorithm developed by Sintes and Schutz. This method can be used for removal of periodic signals with sufficiently coupled harmonics, and can be adapted to specific situations by optimal choice of its parameters (e.g., the number of harmonics considered for analysis and reconstruction). Our testing was done with 14 different human ventricular fibrillation (VF) ECGs, whose fibrillation band lies in a frequency range of [1 Hz, 5 Hz]. The VF-ECGs were mixed with 12 different ECG-CPR-artifacts recorded in an animal experiment during asystole. The length of each of the ECG-data was chosen to be 20 sec, and testing was done for all 168 = 14 x 12 pairs of data. VF-to-CPR ratio was chosen as -20 dB, -15 dB, -10 dB, -5 dB, 0 dB, 5 dB and 10 dB. Here -20 dB corresponds to the highest level of CPR-artifacts. RESULTS: For non-optimized coherent line removal based on signals with a VF-to-CPR ratio of -20 dB, -15 dB, -10 dB, -5 dB and 0 dB, the signal-to-noise gains (SNR-gains) were 9.3 +/- 2.4 dB, 9.4 +/- 2.4 dB, 9.5 +/- 2.5 dB, 9.3 +/- 2.5 dB and 8.0 +/- 2.7 (mean +/- std, n = 168), respectively. Characteristically, an original VF-to-CPR ratio of -10 dB, corresponds to a variance ratio var(VF):var(CPR) = 1:10. An improvement by 9.5 dB results in a restored VF-to-CPR ratio of -0.5 dB, corresponding to a variance ratio var(VF):var(CPR) = 1:1.1, the variance of the CPR in the signal being reduced by a factor of 8.9. DISCUSSION: The localized coherent line removal algorithm uses the information of a single ECG channel. In contrast to multi-channel algorithms, no additional information such as thorax impedance, blood pressure, or pressure exerted on the sternum during CPR is required. Predictors of defibrillation success such as mean and median frequency of VF-ECGs containing CPR-artifacts are prone to being governed by the harmonics of the artifacts. Reduction of CPR-artifacts is therefore necessary for determining reliable values for estimators of defibrillation success. CONCLUSIONS: The localized coherent line removal algorithm reduces CPR-artifacts in VF-ECG, but does not eliminate them. Our SNR-improvements are in the same range as offered by multichannel methods of Rheinberger et al., Husoy et al. and Aase et al. The latter two authors dealt with different ventricular rhythms (VF and VT), whereas here we dealt with VF, only. Additional developments are necessary before the algorithm can be tested in real CPR situations.

Role of disinfection as infection prophylaxis over the course of time - anesthesia, intensive care and emergency medicine, pain therapy.

It is alarming that anesthetists, just as in earlier years, have been shown to be the specialists with the poorest rate of compliance with simple, basis everyday rules of hygiene. Unfortunately, infection prophylaxis is something to which the physician ascribes importance only when he sees the consequences of his actions, that is to say when he has to diagnose and treat infections in "his" patient as a result of his "failure" to adhere to infection control regulations. That infection control measures have not been taken at the bedside highlights the need for enlightenment and education of staff and serves as the basis for their involvement. Such measures can be taken much less easily in emergency medicine. The emergency physician / anesthetist is rarely confronted with the patient's outcome. Any errors in infection prophylaxis have no perceptible consequences. "The threat posed to vital functions does not allow any time," said the emergency doctor. "During the time elapsing from first administering the anesthetic until full narcosis is reached or in the case of intrasurgical bleeding, I'm feeling stressed and then have no time for hygiene" admits the anesthetist in the OR. To improve this situation, the root cause of ignorance and thoughtlessness as regards hygiene must be addressed. Apart from general training and continuing education for correct conductance of hygienic measures and regarding the consequences of failure to observe the guidelines, today the individual aspect of motivation must be addressed. Each professional administering treatment makes a difference for the patient through his individual approach to hygiene. Each head physician and medical director makes a difference to the behavior of future anesthetists by acting as a role model. And within the hospital system the factors "overburdened personnel and time pressure" as the cause of inappropriate infection control must be clarified. Today hygiene does not merely denote "clean working practices" and reduced patient morbidity. Today reduced infection rates mean reduced costs in the healthcare sector and hence reserves for the future care of the population. Today we know that hygienic practices when attending to the patient are not an onerous burden but that they pay off. We must "only" get around to implementing them.

The prediction of defibrillation outcome using a new combination of mean frequency and amplitude in porcine models of cardiac arrest.

UNLABELLED: We estimated the predictive power with respect to defibrillation outcome of ventricular fibrillation (VF) mean frequency (FREQ), mean peak-to-trough amplitude (AMPL), and their combination. We examined VF electrocardiogram signals of 64 pigs from 4 different cardiac arrest models with different durations of untreated VF, different durations of cardiopulmonary resuscitation, and use of different drugs (epinephrine, vasopressin, N-nitro-L-arginine methyl ester, or saline placebo). The frequency domain was restricted to the range from 4.33 to 30 Hz. In the 10-s epoch between 20 and 10 s before the first defibrillation shock, FREQ and AMPL were estimated. We introduced the survival index (SI; 0.68 Hz(-1). FREQ + 12.69 mV(-1). AMPL) by use of multiple logistic regression. Kruskal-Wallis nonparametric one-way analysis was used to analyze the different porcine models for significant difference. The variables FREQ, AMPL, and SI were compared with defibrillation outcome by means of univariate logistic regression and receiver operating characteristic curves. SI increased predictive power compared with AMPL or FREQ alone, resulting in 89% sensitivity and 86% specificity. The probabilities of predicting defibrillation outcome for FREQ, AMPL, and SI were 0.85, 0.89 and 0.90, respectively. FREQ, AMPL, and SI values were not sensitive in regard to the four different cardiac arrest models but were significantly different for vasopressin and epinephrine animals. IMPLICATIONS: We present a retrospective data analysis to evaluate the predictive power of different ventricular fibrillation electrocardiogram variables in pigs with respect to defibrillation outcome. We showed that our combination of variables leads to an improved forecast, which may help to reduce harmful unsuccessful defibrillation attempts.

Routine handling of propofol prevents contamination as effectively as does strict adherence to the manufacturer's recommendations.

PURPOSE: Propofol is a potential vector of infection, because it contains no preservative. Thus, the manufacturer's specific recommendations for preparing injections or infusions go beyond the guidelines commonly used in our operating rooms for preparing other iv drugs. The purpose of the present study was to determine whether in the daily routine of an operating theatre a modified propofol handling technique can prevent contamination as effectively as do the manufacturer's handling recommendations. METHODS: A total of 160 consecutive neurosurgical patients were allocated to either Group I (manufacturer's handling recommendations: i.e., 1) disinfecting propofol vials and ampoules before filling syringes; 2) replacing empty syringes; 3) discarding all material at the end of surgery); or Group II (modified propofol handling protocol: i.e., 1) refilling empty syringes; 2) renewing only the infusion line to the patient). RESULTS: Total contamination rates were comparable in both groups (Group I: 14/160 (8.75%), Group II: 13/160 (8.13%) (chi2= 0.074; P=0.96). Frequency of contamination was not different between groups; either in sample 1 taken at the beginning of the procedure, (Group I: 5/80 (6.25%) vs Group II: 6/80 (7.5%); chi2=0.098; P=0.76) or in sample 2, taken at the end, (Group I: 9/80 (11.25%) vs Group II: 7/80 (8.75%); chi2=0.278; P=0.598). CONCLUSION: We conclude that in the daily routine of the operating theatre following a modified propofol handling protocol prevents contamination of propofol syringes as effectively as does adhering to the manufacturer's specific handling recommendations. However, neither of the tested guidelines completely prevented contamination.