A signal processing tool for extracting features from arterial blood pressure and photoplethysmography waveforms.

Arterial blood pressure (ABP) and photoplethysmography (PPG) waveforms contain valuable clinical information and play a crucial role in cardiovascular health monitoring, medical research, and managing medical conditions. The features extracted from PPG waveforms have various clinical applications ranging from blood pressure monitoring to nociception monitoring, while features from ABP waveforms can be used to calculate cardiac output and predict hypertension or hypotension. In recent years, many machine learning models have been proposed to utilize both PPG and ABP waveform features for these healthcare applications. However, the lack of standardized tools for extracting features from these waveforms could potentially affect their clinical effectiveness. In this paper, we propose an automatic signal processing tool for extracting features from ABP and PPG waveforms. Additionally, we generated a PPG feature library from a large perioperative dataset comprising 17,327 patients using the proposed tool. This PPG feature library can be used to explore the potential of these extracted features to develop machine learning models for non-invasive blood pressure estimation.

Accuracy and precision of non-invasive cardiac output monitoring devices in perioperative medicine: a systematic review and meta-analysis†.

Cardiac output (CO) measurement is crucial for the guidance of therapeutic decisions in critically ill and high-risk surgical patients. Newly developed completely non-invasive CO technologies are commercially available; however, their accuracy and precision have not recently been evaluated in a meta-analysis. We conducted a systematic search using PubMed, Cochrane Library of Clinical Trials, Scopus, and Web of Science to review published data comparing CO measured by bolus thermodilution with commercially available non-invasive technologies including pulse wave transit time, non-invasive pulse contour analysis, thoracic electrical bioimpedance/bioreactance, and CO2 rebreathing. The non-invasive CO technology was considered acceptable if the pooled estimate of percentage error was <30%, as previously recommended. Using a random-effects model, sd, pooled mean bias, and mean percentage error were calculated. An I2 statistic was also used to evaluate the inter-study heterogeneity. A total of 37 studies (1543 patients) were included. Mean CO of both methods was 4.78 litres min−1. Bias was presented as the reference method minus the tested methods in 15 studies. Only six studies assessed the random error (repeatability) of the tested device. The overall random-effects pooled bias (limits of agreement) and the percentage error were −0,13 [−2.38 , 2.12] litres min−1 and 47%, respectively. Inter-study sensitivity heterogeneity was high (I2=83%, P<0.001). With a wide percentage error, completely non-invasive CO devices are not interchangeable with bolus thermodilution. Additional studies are warranted to demonstrate their role in improving the quality of care.

Perioperative goal directed therapy: Evidence and compliance are two sides of the same coin / Tratamiento perioperatorio enfocado hacia los objetivos: las pruebas y el cumplimiento son las dos caras de una misma moneda

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Goal-Directed fluid therapy with closed-loop assistance during moderate risk surgery using noninvasive cardiac output monitoring: A pilot study.

BACKGROUND: Goal directed fluid therapy (GDFT) has been shown to improve outcomes in moderate to high-risk surgery. However, most of the present GDFT protocols based on cardiac output optimization use invasive devices and the protocols may require significant practitioner attention and intervention to apply them accurately. The aim of this prospective pilot study was to evaluate the clinical feasibility of GDFT using a closed-loop fluid administration system with a non-invasive cardiac output monitoring device (Nexfin™, BMEYE, Amsterdam, Netherlands). METHODS: Patients scheduled for elective moderate risk surgery under general anaesthesia were enrolled. The primary anaesthesia team managing the case selected GDFT targets using the controller interface and all patients received a baseline 3 ml kg(-1) h(-1) crystalloid infusion. Colloid solutions were delivered by the closed-loop system for intravascular volume expansion using data from the Nexfin™ monitor. Compliance with GDFT management was defined as acceptable when a patient spent more than 85% of the surgery time in a preload independent state (defined as pulse pressure variation <13%) or when average cardiac index during surgery was >2.5 litre min(-1) m(-2). RESULTS: A total of 13 patients were included in the study group. All patients met the established criteria for delivery of GDFT for greater than 85% of case time. The median length of stay in the hospital was 5 [3-6] days. CONCLUSION: In this pilot study, GDFT management using the closed-loop fluid administration system with a non-invasive CO monitoring device was feasible and maintained a high rate of protocol compliance. CLINICAL TRIAL REGISTRATION: NCT02020863.

Variability in practice and factors predictive of total crystalloid administration during abdominal surgery: retrospective two-centre analysis.

BACKGROUND: Variation in clinical practice in the perioperative environment and intensive care unit is a major challenge facing modern medicine. The objective of the present study was to analyse intraoperative crystalloid administration practices at two academic medical centres in the USA. METHODS: We extracted clinical data from patients undergoing intra-abdominal procedures performed at UC Irvine (UCI) and Vanderbilt University (VU) Medical Centres. Limiting data to uncomplicated elective surgery with minimal blood loss, we quantified variability in fluid administration within individual providers, between providers, and between types of procedures using a corrected coefficient of variation (cCOV). Regression was performed using a general linear model to determine factors most predictive of fluid administration. RESULTS: For provider analysis and model building, 1327 UCI and 4585 VU patients were used. The average corrected crystalloid infusion rate across all providers at both institutions was 7.1 (sd 4.9) ml kg(-1) h(-1), an overall cCOV of 70%. Individual providers ranged from 2.3 (sd 3.7) to 14 (sd 10) ml kg(-1) h(-1). The final regression model strongly favoured personnel as predictors over other patient predictors. CONCLUSIONS: Wide variability in crystalloid administration was observed both within and between individual anaesthesia providers, which might contribute to variability in surgical outcomes.

First closed-loop goal directed fluid therapy during surgery: a pilot study.

OBJECTIVE: Intraoperative haemodynamic optimization based on fluid management and stroke volume optimization (Goal Directed Fluid Therapy [GDFT]) can improve patients' postoperative outcome. We have described a closed-loop fluid management system based on stroke volume variation and stroke volume monitoring. The goal of this system is to apply GDFT protocols automatically. After conducting simulation, engineering, and animal studies the present report describes the first use of this system in the clinical setting. STUDY DESIGN: Prospective pilot study. PATIENTS: Patients undergoing major surgery. METHODS: Twelve patients at two institutions had intraoperative GDFT delivered by closed-loop controller under the direction of an anaesthesiologist. Compliance with GDFT management was defined as acceptable when a patient spent more than 85% of the surgery time in a preload independent state (defined as stroke volume variation<13%), or when average cardiac index during the case was superior or equal to 2.5l/min/m(2). RESULTS: Closed-loop GDFT was completed in 12 patients. Median surgery time was 447 [309-483] min and blood loss was 200 [100-1000] ml. Average cardiac index was 3.2±0.8l/min/m(2) and on average patients spent 91% (76 to 100%) of the surgery time in a preload independent state. Twelve of 12 patients met the criteria for compliance with intraoperative GDFT management. CONCLUSION: Intraoperative GDFT delivered by closed-loop system under anaesthesiologist guidance allowed to obtain targeted objectives in 91% of surgery time. This approach may provide a way to ensure consistent high-quality delivery of fluid administration and compliance with perioperative goal directed therapy.

Effect of phenylephrine and ephedrine bolus treatment on cerebral oxygenation in anaesthetized patients.

BACKGROUND: How phenylephrine and ephedrine treatments affect global and regional haemodynamics is of major clinical relevance. Cerebral tissue oxygen saturation (Sct(O2) )-guided management may improve postoperative outcome. The physiological variables responsible for Sct(O2) changes induced by phenylephrine and ephedrine bolus treatment in anaesthetized patients need to be defined. METHODS: A randomized two-treatment cross-over trial was conducted: one bolus dose of phenylephrine (100-200 µg) and one bolus dose of ephedrine (5-20 mg) were given to 29 ASA I-III patients anaesthetized with propofol and remifentanil. , mean arterial pressure (MAP), cardiac output (CO), and other physiological variables were recorded before and after treatments. The associations of changes were analysed using linear-mixed models. RESULTS: The CO decreased significantly after phenylephrine treatment [▵CO = -2.1 (1.4) litre min(-1), P<0.001], but was preserved after ephedrine treatment [▵CO = 0.5 (1.4) litre min(-1), P>0.05]. The was significantly decreased after phenylephrine treatment [▵ = -3.2 (3.0)%, P<0.01] but preserved after ephedrine treatment [▵ = 0.04 (1.9)%, P>0.05]. CO was identified to have the most significant association with (P<0.001). After taking CO into consideration, the other physiological variables, including MAP, were not significantly associated with (P>0.05). CONCLUSIONS: Associated with changes in CO, decreased after phenylephrine treatment, but remained unchanged after ephedrine treatment. The significant correlation between CO and implies a cause-effect relationship between global and regional haemodynamics.

Influence of the site of measurement on the ability of plethysmographic variability index to predict fluid responsiveness.

BACKGROUND: Plethysmographic variability index (PVI) is an accurate predictor of fluid responsiveness in mechanically ventilated patients. However, the site of measurement of the plethysmographic waveform impacts its morphology and its respiratory variation. The goal of this study was to investigate the ability of PVI to predict fluid responsiveness at three sites of measurement (the forehead, ear, and finger) in mechanically ventilated patients under general anaesthesia. METHODS: We studied 28 subjects after induction of general anaesthesia. Subjects were monitored with a pulmonary artery catheter and three pulse oximeter sensors (the finger, ear, and forehead). Pulse pressure variation, central venous pressure, cardiac index (CI), and PVI measured at the forehead, ear, and finger (PVI(forehead), PVI(ear), and PVI(finger)) were recorded before and after fluid loading (FL). Subjects were responders to volume expansion if CI increased >15% after FL. RESULTS: Areas under the receiver-operating curves to predict fluid responsiveness were 0.906, 0.880, and 0.836 for PVI(forehead), PVI(ear), and PVI(finger), respectively (P<0.05). PVI(forehead), PVI(ear), and PVI(finger) had a threshold value to predict fluid responsiveness of 15%, 16%, and 12% with sensitivities of 89%, 74%, and 74% and specificities of 78%, 74%, and 67%, respectively. CONCLUSIONS: PVI can predict fluid responsiveness in anaesthetized and ventilated subjects at all three sites of measurement. However, the threshold values for predicting fluid responsiveness differ with the site of measurement. These results support the use of this plethysmographic dynamic index in the cephalic region when the finger is inaccessible or during states of low peripheral perfusion.

Predicting fluid responsiveness in mechanically ventilated children under general anaesthesia using dynamic parameters and transthoracic echocardiography.

BACKGROUND: Dynamic variables are accurate predictors of fluid responsiveness in adults undergoing mechanical ventilation. They can be determined using respiratory variation in aortic flow peak velocity (▵Vpeak), arterial pulse pressure [▵PP and pulse pressure variation (PPV)], or plethysmographic waveform amplitude [▵POP and pleth variability index (PVI)]. These indices have not been validated in children. We studied the ability of these variables to predict fluid responsiveness in mechanically ventilated children. METHODS: All results are expressed as median [median absolute deviation (MAD)]. Thirty mechanically ventilated children were studied after undergoing general anaesthesia. Mechanical ventilation was maintained with a tidal volume of 10 ml kg(-1) of body weight. ▵PP, PPV, ▵POP, PVI, ▵Vpeak, and aortic velocity-time integral were recorded before and after volume expansion (VE). Patients were considered to be responders to VE when the aortic velocity-time integral increased more than 15% after VE. RESULTS: VE induced significant changes in ▵PP [13 (MAD 4) to 9 (5)%], PPV [15 (5) to 9 (5)%], ▵POP [15 (10) to 10 (6)%], PVI [13 (6) to 8 (5)%], and ▵Vpeak [16 (9) to 8 (3)%] (P<0.05 for all). Differences in ▵PP, ▵POP, PPV, and PVI did not reach statistical significance. Only ▵Vpeak was significantly different between responders (R) and non-responders (NR) to VE [22 (3) vs 7 (1)%, respectively; P<0.001]. The threshold ▵Vpeak value of 10% allowed discrimination between R and NR. CONCLUSIONS: In this study, ▵Vpeak was the most appropriate variable to predict fluid responsiveness.

Impact of biventricular and left ventricular pacing on hemodynamics and left ventricular dyssynchrony compared with right ventricular pacing in the early postoperative period following cardiac surgery.

OBJECTIVES: The aims of this study were to test the hypotheses that in the postoperative period following corrective surgery for congenital heart defects: (i) atrio-right ventricular (RA-RV) pacing decreases cardiac output (CO) compared with right atrial (RA) pacing, (ii) atrio-biventricular (RA-BiV) and left ventricular (RA-LV) pacing improves CO compared with RA-RV pacing. STUDY DESIGN: Prospective observational study. PATIENTS: Children 0-2years of age referred for surgery of congenital heart defects were studied during intrinsic rhythm and atrial, atrio-right ventricular, atrio-left ventricular and atrio-biventricular pacing. CO, extrapolated from mean systolic aortic velocity (MSAV), and left ventricular dyssynchrony were assessed using transthoracic echocardiography. RESULTS: RA-RV pacing induced a significant decrease in CO (MSAV 0.52±0.19m/s to 0.46±0.16m/s, p=0.01) and a significant increase in LV dyssynchrony (8.7±7.9ms to 33±21ms, p=0.001). RA-BiV pacing induced a significant increase in CO (MSAV 0.46±0.16m/s to 0.52±0.18m/s, p=0.01) and a significant decrease in LV dyssynchrony (33±21ms to 7±4ms, p=0.0003) compared with RA-RV pacing. RA-LV pacing induced a significant decrease in LV dyssynchrony (33±21ms to 9±7ms, p=0.0007) without a significant improvement of CO compared with RA-RV pacing. CONCLUSIONS: RA-BiV pacing improves CO compared with RA-RV pacing in the early postoperative period following pediatric cardiac surgery. This improvement is related to a reduction in left ventricular dyssynchrony.

[Activity and the available human resources working in 66 French Southern intensive care units]. / Quelle activité et quels personnels soignants dans 66 unités de réanimation du sud de la France?

BACKGROUND: The aim of the study was to determine the activity and the available human resources working in 66 intensive care unit (ICU). METHODS: One-day audit performed between January 2009 and May 2009 by trained residents. RESULTS: Among 710 beds, 695 (98%) beds were available for 626 patients (occupation rate=90%). The two most frequent causes of admission were shock and pneumonia. On admission, the median SAPS II was 46. More than 75% of patients had at least two organ dysfunctions within their ICU stay (respiratory failure=80%, circulatory failure=67%). At the moment of the audit, the median SOFA score was 3, and 549 (88%) patients had required a billing procedure with an admission SAPS II greater or equal to 15. Twenty seven percent of ICUs had a ratio patients/nurses or patients/aid nurse greater than 2.5 and 4, respectively whereas 58% ICUs had a ratio open beds/nurse greater than 2.5 or open beds/aid nurse greater than 4. CONCLUSION: In this study, more than 75% patients had at least two organ dysfunctions within their ICU stay and 88% required a billing procedure and had an admission SAPS II greater or equal to 15. Nevertheless, the staff resource remained below the 2002 decree in 27% ICUs.

[Automatic and continuous monitoring of preload dependence in the perioperative period: Interests and limits]. / Monitorage continu et automatisé de la précharge dépendance en anesthésie et en réanimation : intérêts et limites.

OBJECTIVES: To describe preload dependence monitoring tools currently available as well as their limits and potential applications in the anaesthesiology setting. DATA SOURCE: References were obtained from PubMed data bank (http://www.ncbi.nlm.nih.gov/entrez/query.fcgi) using the following keywords: fluid responsiveness, cardiopulmonary interactions, preload dependence, hypovolemia, cardiac output. DATA SYNTHESIS: When measured in optimal conditions, dynamic parameters are the best predictors of fluid responsiveness as compared to static indicators in patients under general anaesthesia and mechanical ventilation. These dynamic parameters rely on cardiopulmonary interactions and allow evaluating preload dependence and the ability of the heart to transform an increase in preload into an increase in cardiac output. Recently, it is possible to monitor these dynamic parameters either invasively (from the arterial pressure waveform) or noninvasively (from the plethysmographic waveform). These tools have intrinsic limitations. However, they have potential to be used for fluid optimization during anaesthesia.

[Comparison of ICG thoracic bioimpedance cardiac output monitoring system in patients undergoing cardiac surgery with pulmonary artery cardiac output measurements]. / Comparaison des valeurs de débit cardiaque obtenues à l'aide d'un nouveau système d'impédancemétrie thoracique avec les données du cathéter artériel pulmonaire en postopératoire de chirurgie cardiaque.

OBJECTIVE: Thoracic bioimpedance has been proposed for cardiac output (CO) determination and monitoring without calibration or thermodilution (ICG Monitor 862146, Philips Medical System, Philips, Suresnes, France). The accuracy and clinical applicability of this technology has not been fully evaluated in the cardiac surgery setting. We designed this prospective study to compare the accuracy of the ICG Monitor (CO(ICG)) versus pulmonary artery catheter standard bolus thermodilution (CO(PAC)) in patients after cardiac surgery or having benefited from cardiac surgery. STUDY DESIGN: Prospective, monocentric. MATERIAL AND METHODS: We studied 13 patients in the postoperative period. CO(ICG) and CO(PAC) were determined at the arrival in the intensive care unit and every four hours. Bland-Altman and Critchley and Critchley's analysis were used to assess the agreement between CO(ICG) and CO(PAC). RESULTS: CO(PAC) ranged from 2.6 to 11.0 l/min and CO(ICG) ranged from 1.8 to 11.7 l/min. There was a significant relationship between CO(PAC) and CO(ICG) (r=0.61 ; p<0.001). Agreement between CO(PAC) and CO(ICG) was -0.5+/-1.3 l/min (Bland-Altman analysis). Percentage error between the two methods was 49% (Critchley and Critchley's analysis). CONCLUSION: We found clinically unacceptable agreement between CO(ICG) and CO(PAC) in this setting. Despite its non invasiveness, this device cannot be recommended for CO monitoring in the postoperative period following cardiac surgery.

[Clinical usefulness of new-generation pulse oximetry in the paediatric cardiac surgery setting]. / Utilisation clinique d'un oxymètre de pouls de nouvelle génération dans le cadre de la chirurgie cardiaque pédiatrique.

OBJECTIVES: Arterial oxygen saturation (SaO(2)) monitoring using pulse oximeter (SpO(2)) is mandatory in the intensive care unit. The aim was to assess bias and precision of new (SpO(2)ng) and old (SpO(2)og) pulse oximeter technologies in the postoperative period following pediatric cardiac surgery in cyanotic children. STUDY DESIGN: Prospective, monocentric. PATIENTS AND METHODS: Ten patients (7 days to 53 months old) were studied in the postoperative period following palliative cardiac surgery. SaO(2), SpO(2)og, and SpO(2)ng were obtained every 4 hours. SaO(2) of arterial blood sample was obtained from an intra-arterial catheter located in the radial artery, on the same side as the oximeters. Bias and precision were assessed using Bland-Altman analysis. RESULTS: We obtained 136 SaO(2) determinations. Mean SaO(2) was 76+/-15%. SpO(2)og was significantly different from SaO(2), while SpO(2)ng was not different from SaO(2). In 21 (15%) cases, SpO(2)og was not available whereas SpO(2)ng was available in 136 (100%) cases. In the remaining 115 cases, SpO(2)ng's precision was significantly better than SpO(2)og's precision. DISCUSSION: SpO(2)ng is more accurate and more reliable than SpO(2)og for SaO(2) monitoring in the postoperative period following pediatric cardiac surgery in cyanotic children.

Pleth variability index to monitor the respiratory variations in the pulse oximeter plethysmographic waveform amplitude and predict fluid responsiveness in the operating theatre.

BACKGROUND: Respiratory variations in pulse oximetry plethysmographic waveform amplitude (DeltaPOP) can predict fluid responsiveness in mechanically ventilated patients but cannot be easily assessed at the bedside. Pleth variability index (PVI) is a new algorithm allowing for automated and continuous monitoring of DeltaPOP. We hypothesized that PVI can predict fluid responsiveness in mechanically ventilated patients under general anaesthesia. METHODS: Twenty-five patients were studied after induction of general anaesthesia. Haemodynamic data [cardiac index (CI), respiratory variations in arterial pulse pressure (DeltaPP), DeltaPOP, and PVI] were recorded before and after volume expansion (500 ml of hetastarch 6%). Fluid responsiveness was defined as an increase in CI > or =15%. RESULTS: Volume expansion induced changes in CI [2.0 (sd 0.9) to 2.5 (1.2) litre min(-1) m(-2); P<0.01], DeltaPOP [15 (7)% to 8 (3)%; P<0.01], and PVI [14 (7)% to 9 (3)%; P<0.01]. DeltaPOP and PVI were higher in responders than in non-responders [19 (9)% vs 9 (4)% and 18 (6)% vs 8 (4)%, respectively; P<0.01 for both]. A PVI >14% before volume expansion discriminated between responders and non-responders with 81% sensitivity and 100% specificity. There was a significant relationship between PVI before volume expansion and change in CI after volume expansion (r=0.67; P<0.01). CONCLUSIONS: PVI, an automatic and continuous monitor of DeltaPOP, can predict fluid responsiveness non-invasively in mechanically ventilated patients during general anaesthesia. This index has potential clinical applications.