Semi-invasive measurement of cardiac output based on pulse contour: a review and analysis.

PURPOSE: The aim of this review was to provide a meta-analysis of all five of the most popular systems for arterial pulse contour analysis compared with pulmonary artery thermodilution, the established reference method for measuring cardiac output (CO). The five investigated systems are FloTrac/Vigileo(®), PiCCO(®), LiDCO/PulseCO(®), PRAM/MostCare(®), and Modelflow. SOURCE: In a comprehensive literature search through MEDLINE(®), Web of Knowledge (v.5.11), and Google Scholar, we identified prospective studies and reviews that compared the pulse contour approach with the reference method (n = 316). Data extracted from the 93 selected studies included range and mean cardiac output, bias, percentage error, software versions, and study population. We performed a pooled weighted analysis of their precision in determining CO in various patient groups and clinical settings. PRINCIPAL FINDINGS: Results of the majority of studies indicate that the five investigated systems show acceptable accuracy during hemodynamically stable conditions. Forty-three studies provided adequate data for a pooled weighted analysis and resulted in a mean (SD) total pooled bias of -0.28 (1.25) L·min(-1), percentage error of 40%, and a correlation coefficient of r = 0.71. In hemodynamically unstable patients (n = 8), we found a higher percentage error (45%) and bias of -0.54 (1.64) L·min(-1). CONCLUSION: During hemodynamic instability, CO measurement based on continuous arterial pulse contour analysis shows only limited agreement with intermittent bolus thermodilution. The calibrated systems seem to deliver more accurate measurements than the auto-calibrated or the non-calibrated systems. For reliable use of these semi-invasive systems, especially for critical therapeutic decisions during hemodynamic disorders, both a strategy for hemodynamic optimization and further technological improvements are necessary.

The efficacy of spontaneous and controlled ventilation with various cricothyrotomy devices: a quantitative in vitro assessment in a model lung.

BACKGROUND: Guidelines for the management of a difficult airway recommend performing a cricothyrotomy in a "can't intubate/can't ventilate" situation. We investigated the tidal volumes delivered by controlled and spontaneous ventilation by seven commercially available cricothyrotomy sets (cuffed: Quicktrach II, Portex Cricothyroidotomy Kit, and Melker cuffed cannula and uncuffed: Airfree, 4.0-mm ID Quicktrach, 6.0-mm inner diameter Melker, and 13-gauge Ravussin cannula) and two improvised devices (14-gauge intravenous cannula and spike and drip chamber device). METHODS: A LS800 model lung, set at different values for compliance and resistance and modified with different upper airway diameter, was ventilated via the respective cricothyrotomy device mechanically and using a self-inflating bag. With the 13-gauge Ravussin cannula and the 14-gauge intravenous cannula, a Manujet injector was used for jet ventilation. Spontaneous ventilation was simulated with a Michigan 560i lung. RESULTS: During controlled or manual ventilation, all cuffed cricothyrotomy devices yielded adequate tidal volumes. Uncuffed devices provided tidal volumes≥300 mL only with an upper airway diameter of ≤3 mm. With a Manujet injector, adequate tidal volumes required an upper airway diameter between 3 mm and 5 mm. A spike and drip chamber device does not provide suitable emergency airway access. Spontaneous ventilation at adequate inspiratory pressure levels required a device inner diameter of at least 4 mm. CONCLUSION: As expected, cuffed cricothyrotomy devices yield the best results during controlled, manual, and spontaneous ventilation. With uncuffed cricothyrotomy devices, ventilation becomes ineffective when the upper airway obstruction allows for an upper airway diameter>3 mm.

Use of independent component analysis for reducing CPR artefacts in human emergency ECGs.

AIM: We applied independent component analysis (ICA) to cardiopulmonary resuscitation (CPR)-corrupted human multichannel emergency ECGs with the aim of reconstructing the original ECGs. MATERIALS: Two ICA algorithms (EFICA and JADE) were selected. Data for ICA were acquired by simultaneously recording eight ECG channels during CPR on a porcine model. The algorithms' reconstruction performance was assessed by the Spearman correlation coefficient (SCC) and the shock advice algorithm of an AED. We then compared the performance of EFICA with the established second-channel adaptive matching pursuit method (AF). RESULTS: ICA was applied to 918 corrupted ECG multichannel signals. The sensitivity of the AED's shock/no-shock decision increased from 93.5% (corrupted signal) to 99.5/99.8% (JADE/EFICA) in the selected independent component; specificity increased from 50.5% to 78.9/83.2% (JADE/EFICA). The SCCs comparing the reconstructed with the original signal (JADE: 0.75±0.15; EFICA: 0.76±0.15, n=918) were significantly higher than for the corrupted signal vs. the original (0.52±0.22). The SCC is significantly higher (p<0.01) using EFICA than AF (EFICA: 0.75±0.16; AF: 0.72±0.19, n=718). For all signals at all SNR levels, specificity did not differ significantly between EFICA (83.6%) and AF (80.2%). EFICA proved to be superior especially at low corruption levels (SNR<-5dB). Sensitivity was above 99.5% for both algorithms. CONCLUSION: We have demonstrated that CPR artefacts in the emergency ECG can be reduced using ICA. EFICA and JADE are at least as successful in this regard as are other published algorithms. In particular, non-shockable signals with low SNRs (<-5dB) are reconstructed significantly better (p=0.01) with EFICA than with AF.

Strong corruption of electrocardiograms caused by cardiopulmonary resuscitation reduces efficiency of two-channel methods for removing motion artefacts in non-shockable rhythms.

AIM: Cardiopulmonary resuscitation (CPR) artefact removal methods provide satisfactory results when the rhythm is shockable but fail on non-shockable rhythms. We investigated the influence of the corruption level on the performance of four different two-channel methods for CPR artefact removal. MATERIALS AND METHODS: 395 artefact-free ECGs and 13 pure CPR artefacts with corresponding blood pressure readings as a reference channel were selected. Using a simplified additive data model we generated CPR-corrupted signals at different signal-to-noise ratio (SNR) levels from -10 to +10 dB. The algorithms were optimized on learning data with respect to SNR improvement and then applied to testing data. Sensitivity and specificity were derived from the shock/no-shock advice of an automated external defibrillator before CPR corruption and after artefact removal. RESULTS: Sensitivity for the filtered data (>95%) was significantly superior to that for the unfiltered data (76%), p<0.001. However, specificity was similar for the filtered and unfiltered data (<90% vs 89.3%). For large artefacts (-10 dB) specificity decreased below 70%. No important difference in the performance of the four algorithms was found. CONCLUSION: Using a simplified data model we showed that, when the ECG rhythm is non-shockable, two-channel methods could not reduce CPR artefacts without affecting the rhythm analysis for shock recommendation. The reason could be poor reconstruction when the artefacts are large. However, poor reconstruction was not a hindrance to re-identifying shockable rhythms. Future investigations should both include the refinement of filter methods and also focus on reducing motion artefacts already at the recording stage.

CPR artifact removal in ventricular fibrillation ECG signals using Gabor multipliers.

BACKGROUND AND OBJECTIVE: We present an algorithm for discarding cardiopulmonary resuscitation (CPR) components from ventricular fibrillation ECG (VF ECG) signals and establish a method for comparing CPR attenuation on a common dataset. Removing motion artifacts in ECG allows for uninterrupted rhythm analysis and reduces "hands-off" time during resuscitation. METHODS AND RESULTS: The current approach assumes a multichannel setting where the information of the corrupted ECG is combined with an additional pressure signal in order to estimate the motion artifacts. The underlying algorithm relies on a localized time-frequency transformation, the Gabor transform, that reveals the perturbation components, which, in turn, can be attenuated. The performance of the method is evaluated on a small set of test signals in the form of error analysis and compared to two well-established CPR removal algorithms that use an adaptive filtering system and a state-space model, respectively. CONCLUSION: We primarily point out the potential of the algorithm for successful artifact removal; however, on account of the limited set of human VF and animal asystole CPR signals, we refrain from a statistical analysis of the efficiency of CPR attenuation. The results encourage further investigations in both the theoretical and the clinical setup.

The color change in CO2 absorbents on drying: an in vitro study using moisture analysis.

UNLABELLED: Alkali hydroxide-free absorbents change color markedly when they dry, whereas absorbents containing alkali hydroxides do not. We investigated whether this observation can be explained by the weaker hygroscopic properties of pure calcium hydroxide compared with alkali hydroxides. Samples of the alkali hydroxide-free absorbents Amsorb or Superia and samples of these two absorbents with 1% or 3% NaOH or 3% KOH added were dried in a moisture analyzer at 105 degrees C to determine their moisture content and to assess the color of the samples during drying (each group, n = 5). Additionally, we repeated the experiments with pulverized samples of Baralyme and Spherasorb, which contain approximately 4% KOH and 1% NaOH, respectively. Amsorb and Superia changed color long before they were dry. After the addition of 1% NaOH, and as with the Spherasorb samples, the drying time required for a color change was longer, and the intensity of the resulting violet was less. This effect was even stronger when 3% NaOH was added. The samples with added KOH and the Baralyme did not change color at all on drying. We conclude that the differences in color change on drying in absorbents with varying NaOH or KOH content cannot be explained by larger water retention because of the hygroscopic properties of the alkali hydroxides. IMPLICATIONS: In an in vitro study, the moisture content and color change on drying were determined in samples of Amsorb or Superia and in the same absorbents with added NaOH or KOH. With increasing concentrations of alkali hydroxide, a delay in the color change upon drying was observed. However, the moisture content did not change.

Several interacting genes influence the malignant hyperthermia phenotype.

Malignant hyperthermia (MH), a potentially lethal disorder of skeletal muscle calcium homeostasis, manifests only on exposure to certain anaesthetic drugs. The mode of inheritance appears to be autosomal dominant with both locus and allelic heterogeneity having been reported. Association analysis of eight MH candidate loci in UK families has indicated that several genes influence susceptibility in individual families, rather than MH simply being a major gene defect. In support of this hypothesis, we present data on a replica analysis of an independent sample of European MH families.

Small carbon monoxide formation in absorbents does not correlate with small carbon dioxide absorption.

UNLABELLED: In this study we sought to determine whether an absorbent in which little carbon monoxide (CO) forms has a correspondingly small capacity to absorb carbon dioxide (CO(2)). Completely dried samples (600 g) of Baralyme (A), Drägersorb 800 (B), Drägersorb 800 Plus (C), Intersorb (D), Spherasorb (E), LoFloSorb (F), Superia (G), and Amsorb (H) were exposed to a flow of 0.5% (A-H; n = 4-5) and 4% isoflurane (F-H; n = 3) in pure oxygen at 5 L/min for 60 min. Downstream CO concentration, temperature, and isoflurane concentration were recorded every 60 s to calculate CO formation and isoflurane loss. The CO(2) absorption capacity of each brand was determined by passing 5.1% CO(2) in oxygen (flow, 250 mL/min) through untreated samples (30 g; n = 5) until the outlet CO(2) concentration reached 0.5%. CO formation was largest in absorbents containing potassium hydroxide (A and B) and negligible in absorbents not containing any alkali hydroxide (F-H). The outlet temperature correlated with CO formation, but the isoflurane loss did not. The duration of CO(2) absorption also did not correlate with CO formation. We conclude that absorbents that allow only very little CO formation are not necessarily poor CO(2) absorbents. IMPLICATIONS: In an in vitro study, carbon dioxide (CO(2)) absorption capacity and possible carbon monoxide (CO) formation were tested in different absorbent brands. Absorbents with very small CO formation are not necessarily poor CO(2) absorbents.

Using amsorb to detect dehydration of CO2 absorbents containing strong base.

BACKGROUND: Because Amsorb changes color when it dries, the authors investigated whether Amsorb combined with different strong base-containing carbon dioxide absorbents signals dehydration of such absorbents. METHODS: Five different carbon dioxide absorbents (1,330 g) each topped with 70 g of Amsorb were dried in an anesthesia machine (Modulus CD, Datex-Ohmeda, Madison, WI) with oxygen (Amsorb layer at the fresh gas inflow site). As soon as a color change was detected in the Amsorb, the authors tested the samples for a change in weight and carbon monoxide formation from 7.5% desflurane or 4% isoflurane. In a different experiment with the five absorbents, Amsorb was layered at the drying gas outflow site. In further experiments, the authors tested for a color change in Amsorb from drying and rehydrating and from drying with nitrogen. Finally, they dried a mixture of Amsorb and 1% NaOH and examined it for color change. RESULTS: In the experiments with Amsorb layered at the inflow, the Amsorb changed color when the water content of the samples was only marginally reduced (to a mean 13.6%), and no carbon monoxide formed. With Amsorb layered at the outflow, it changed color when the mean water content of the samples was reduced to 8.8%, and carbon monoxide formation was detected to varying degrees. The color change was independent of the drying gas and could be reversed by rehydrating. Adding NaOH to Amsorb prevented a color change. CONCLUSIONS: Dehydration in strong base-containing absorbents can reliably be indicated before carbon monoxide is formed when Amsorb is layered at the fresh gas inflow. The authors assume that the indicator dye in Amsorb changes color on drying because of the absence of strong base in this absorbent.