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This study retrospectively examined the hemodynamic effects of passive leg raising (PLR) in mechanically ventilated patients during fluid removal before spontaneous breathing trials. In previous studies, we noticed varying cardiac responses after PLR completion, particularly in positive tests. Using a bioreactance monitor, we recorded and analyzed hemodynamic parameters, including stroke volume and cardiac index (CI), before and after PLR in post-acute ICU patients. We included 27 patients who underwent 60 PLR procedures. In preload-unresponsive patients, no significant CI changes were observed (CI_t-6 = 3.7 [2.6; 4.7] mL/min/m2 vs. CI_t9 = 3.3 [2.5; 3.4] mL/min/m2; p = 0.306), while in preload-responsive patients, two distinct CI response types to PLR were identified: a transient peak with immediate return to baseline (CI_t-6 = 2.7 [2.5; 3.1] mL/min/m2 vs. 3.3 [2.6; 3.8] L/min/m2; p = 0.119) and a sustained CI elevation lasting beyond the PLR maneuver (CI_t-6 = 2.8 [2.3; 2.9] L/min/m2 vs. 3.3 [2.8; 3.9] ml/min/m2; p = 0.034). The latter was particularly noted when ΔCI during PLR exceeded 25%. Our findings suggest that in certain preload-responsive patients, PLR can induce a more sustained increase in CI, indicating a possible persistent hemodynamic effect. This effect could be due to a combination of autotransfusion and sympathetic activation affecting venous return and vascular tone. Further research in larger cohorts and more comprehensive hemodynamic assessments are warranted to validate these observations and elucidate the possible underlying mechanisms.The Fluid unLoading On Weaning (FLOW) study was prospectively registered under the ID NCT04496583 on 2020-07-29 at ClinicalTrials.gov.

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A positive fluid balance may evolve to fluid overload and associate with organ dysfunctions, weaning difficulties, and increased mortality in ICU patients. We explored whether individualized fluid management, assessing fluid responsiveness via a passive leg-raising maneuver (PLR) before a spontaneous breathing trial (SBT), is associated with less extubation failure in ventilated patients with a high fluid balance admitted to the ICU after liver transplantation (LT). We recruited 15 LT patients in 2023. Their postoperative fluid balance was +4476 {3697, 5722} mL. PLR maneuvers were conducted upon ICU admission (T1) and pre SBT (T2). Cardiac index (CI) changes were recorded before and after each SBT (T3). Seven patients were fluid-responsive at T1, and twelve were responsive at T2. No significant differences occurred in hemodynamic, respiratory, and perfusion parameters between the fluid-responsive and fluid-unresponsive patients at any time. Fluid-responsive patients at T1 and T2 increased their CI during SBT from 3.1 {2.8, 3.7} to 3.7 {3.4, 4.1} mL/min/m2 (p = 0.045). All fluid-responsive patients at T2 were extubated after the SBTs and consolidated extubation. Two out of three of the fluid-unresponsive patients experienced weaning difficulties. We concluded that fluid-responsive patients post LT may start weaning earlier and achieve successful extubation despite a high postoperative fluid balance. This highlights the profound impact of personalized assessments of cardiovascular state on critical surgical patients.

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BACKGROUND: Current recommendations support guiding fluid resuscitation through the assessment of fluid responsiveness. Recently, the concept of fluid tolerance and the prevention of venous congestion (VC) have emerged as relevant aspects to be considered to avoid potentially deleterious side effects of fluid resuscitation. However, there is paucity of data on the relationship of fluid responsiveness and VC. This study aims to compare the prevalence of venous congestion in fluid responsive and fluid unresponsive critically ill patients after intensive care (ICU) admission. METHODS: Multicenter, prospective cross-sectional observational study conducted in three medical-surgical ICUs in Chile. Consecutive mechanically ventilated patients that required vasopressors and admitted < 24 h to ICU were included between November 2022 and June 2023. Patients were assessed simultaneously for fluid responsiveness and VC at a single timepoint. Fluid responsiveness status, VC signals such as central venous pressure, estimation of left ventricular filling pressures, lung, and abdominal ultrasound congestion indexes and relevant clinical data were collected. RESULTS: Ninety patients were included. Median age was 63 [45-71] years old, and median SOFA score was 9 [7-11]. Thirty-eight percent of the patients were fluid responsive (FR+), while 62% were fluid unresponsive (FR-). The most prevalent diagnosis was sepsis (41%) followed by respiratory failure (22%). The prevalence of at least one VC signal was not significantly different between FR+ and FR- groups (53% vs. 57%, p = 0.69), as well as the proportion of patients with 2 or 3 VC signals (15% vs. 21%, p = 0.4). We found no association between fluid balance, CRT status, or diagnostic group and the presence of VC signals. CONCLUSIONS: Venous congestion signals were prevalent in both fluid responsive and unresponsive critically ill patients. The presence of venous congestion was not associated with fluid balance or diagnostic group. Further studies should assess the clinical relevance of these results and their potential impact on resuscitation and monitoring practices.

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PURPOSE: The passive leg raising test (PLR) is a noninvasive method widely adopted to assess fluid responsiveness. We propose to explore if changes in the carotid flow assessed by echo-Doppler can predict fluid responsiveness after a PLR. METHODS: We conducted a performance diagnostic study in two intensive care units from Argentina between February and April 2022. We included patients with signs of tissular hypoperfusion that required fluid resuscitation. We labeled the patients as fluid responders when we measured, after a fluid bolus, an increase greater than 15% in the left ventricle outflow tract (LVOT) VTI in an apical 5-chamber view and we compared those results with the carotid flow (CF) velocity-time integral (VTI) from the left supraclavicular region in a semi-recumbent position and during the PLR. RESULTS: Of the 62 eligible patients, 50 patients (80.6%) were included. The area under the ROC curve for a change in CF VTI during the PLR test was 0.869 (95% CI 0.743-0.947). An increase of at least of 11% in the CF VTI with the PLR predicted fluid-responsiveness with a sensitivity of 77.3% (95% CI 54.6-92.2%) and specificity of 78.6% (95% CI 59-91.7%). The positive predictive value was 73.9% (95% CI 57.4-85.6%) and the negative predictive value was 81.5% (95% CI 66.5-90.7%). The positive likelihood ratio was 3.61 and the negative likelihood ratio was 0.29. CONCLUSION: An increase greater than 11% in CF VTI after a PLR may be useful to predict fluid responsiveness among critically ill patients.

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INTRODUCTION: Prediction of fluid responsiveness in acutely ill patients might be influenced by a number of clinical and technical factors. We aim to identify variables potentially modifying the operative performance of fluid responsiveness predictors commonly used in clinical practice. METHODS: A sensitive strategy was conducted in the Medline and Embase databases to search for prospective studies assessing the operative performance of pulse pressure variation, stroke volume variation, passive leg raising (PLR), end-expiratory occlusion test (EEOT), mini-fluid challenge, and tidal volume challenge to predict fluid responsiveness in critically ill and acutely ill surgical patients published between January 1999 and February 2023. Adjusted diagnostic odds ratios (DORs) were calculated by subgroup analyses (inverse variance method) and meta-regression (test of moderators). Variables potentially modifying the operative performance of such predictor tests were classified as technical and clinical. RESULTS: A total of 149 studies were included in the analysis. The volume used during fluid loading, the method used to assess variations in macrovascular flow (cardiac output, stroke volume, aortic blood flow, volume‒time integral, etc.) in response to PLR/EEOT, and the apneic time selected during the EEOT were identified as technical variables modifying the operative performance of such fluid responsiveness predictor tests (p < 0.05 for all adjusted vs. unadjusted DORs). In addition, the operative performance of fluid responsiveness predictors was also influenced by clinical variables such as the positive end-expiratory pressure (in the case of EEOT) and the dose of norepinephrine used during the fluid responsiveness assessment for PLR and EEOT (for all adjusted vs. unadjusted DORs). CONCLUSION: Prediction of fluid responsiveness in critically and acutely ill patients is strongly influenced by a number of technical and clinical aspects. Such factors should be considered for individual intervention decisions.

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BACKGROUND: Haemodynamic monitoring of patients after cardiac surgery using echocardiographic evaluation of fluid responsiveness is both challenging and increasingly popular. We evaluated fluid responsiveness in the first hours after surgery by determining the variability of the velocity-time integral of the left ventricular outflow tract (VTI-LVOT). METHODS: We conducted a cross-sectional study of 50 consecutive adult patients who underwent cardiac surgery and in whom it was possible to obtain VTI-LVOT measurements. We then determined the variability and correlations with our pulse pressure variation (PPV) measurements to predict fluid responsiveness. RESULTS: A strong positive correlation was seen between the VTI-LVOT variability index absolute values and PPV for predicting fluid responsiveness in the first hours after cardiac surgery. We also found that the VTI-LVOT variability index has high specificity and a high positive likelihood ratio compared with the gold standard using a cut-off point of ≥ 12%. CONCLUSIONS: The VTI-LVOT variability index is a valuable tool for determining fluid responsiveness during the first 6 postoperative hours in patients undergoing cardiac surgery.

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O choque circulatório é caracterizado por um estado de ineficiência da oferta de oxigênio tecidual e disfunção múltipla de órgãos. Necessita de diagnóstico e terapias rápidas e assertivas para redução de sua alta letalidade. O ecocardiograma já se estabeleceu como método fundamental no manejo do paciente com choque circulatório. Auxilia de forma crucial no diagnóstico etiológico, prognóstico, monitorização hemodinâmica e estimativa volêmica desses pacientes, tendo como potenciais vantagens a portabilidade, ausência de contraste ou radiação, baixo custo e avaliação em tempo real e de forma seriada. Em ambiente de UTI, demonstra alta correlação com formas invasivas (cateter de artéria pulmonar) e minimamente invasivas (termodiluição transpulmonar) de monitorização hemodinâmica. Atualmente, outras técnicas, como ultrassom pulmonar e VExUS score, têm se agregado à avaliação ecocardiográfica, tornando o método mais abrangente e acurado. Essas técnicas acrescentam dados relevantes na estimativa da volemia do paciente crítico, influenciando na decisão probabilística de fluidoresponsividade e agregando informações no raciocínio diagnóstico das causas do choque, otimizando o prognóstico desses pacientes. O point of care ultrasound (POCUS) tem como objetivo tornar mais acessível, ao médico não especialista em radiologia, habilidades para se obter informações a beira leito, por meio do ultrassom, que o ajudem na tomada de decisões. Esse artigo aborda as diversas aplicabilidades do ecocardiograma em pacientes com choque circulatório, incluindo avaliação prognóstica e diagnóstico etiológico por meio dos parâmetros encontrados nas principais causas de choque, além da monitorização hemodinâmica, avaliação de fluido-responsividade e utilização prática do ultrassom pulmonar.(AU)

Circulatory shock is characterized by a state of inefficient tissue oxygen supply and multiple organ dysfunction. Patients with circulatory shock require fast and assertive diagnosis and therapies to reduce its high lethality. Echocardiography has already been established as a fundamental method in managing patients with circulatory shock. It provides crucial assistance in etiological diagnosis, prognosis, hemodynamic monitoring, and volume estimation in these patients; its potential advantages include portability, absence of contrast or radiation, low cost, and real-time serial assessment. In the intensive care unit setting, it demonstrates a high correlation with invasive (pulmonary artery catheter) and minimally invasive (transpulmonary thermodilution) forms of hemodynamic monitoring. Currently, other techniques, such as pulmonary ultrasound and VExUS score, have been added to echocardiographic assessment, making the method more comprehensive and accurate. These techniques add relevant data to blood volume estimation in critical patients, influencing the probabilistic decision of fluid responsiveness and providing additional information in the diagnostic reasoning of the causes of shock, thus optimizing these patients' prognosis. Point of care ultrasound (POCUS) aims to make abilities to obtain information at the bedside more accessible to physicians who are not specialists in radiology, by means of ultrasound, which assists them in decision-making. This article addresses the diverse applications of echocardiography in patients with circulatory shock, including prognostic evaluation and etiological diagnosis by means of the parameters found in the main causes of shock, in addition to hemodynamic monitoring, evaluation of fluid responsiveness, and practical use of pulmonary ultrasound.(AU)

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BACKGROUND: The use of fluids is the most frequently used therapy for circulatory shock. Its inadequate use has adverse effects, requiring hemodynamic goals, highlighting the use of pulse pressure variation due to its high accuracy. One of the problems related to this method is the difficulties in measuring the pulse pressure variation (PPV) in most monitors for clinical use. We assessed the qualitative aspects of perceived usability of a smartphone application (app), which, based on a photograph of the patient's arterial pulse wave, can help measure PPV and help in the diagnosis and management of shock cases. METHODS: To assess the software perceived usability, we used the System Usability Scale (SUS) applied to 30 physicians in 2 tertiary hospitals in Brazil. The software accuracy was measured using a sequence of 3 images with different values ​​of pulse pressure variation, comparing the obtained values ​​ with the gold standard. The educational interface of the app was evaluated qualitativelyfrom the spontaneous testimonies of the selected test participants.The project was approved by the Research Ethics Committee of Centro Universitário Christus. RESULTS: The analysis showed an average SUS of 86.3 points on a scale of 1-100 (above 80.3 is considered the best in terms of interface). The assessment of the application's accuracy when evaluating pulse pressure variation showed that the average variation of the measurements taken by the participants was small, with a good measure of repeatability and reproducibility. The app's educational interface was qualitatively evaluated, being praised by the users. CONCLUSIONS: It can be concluded that the developed mobile application showed excellent qualitative aspects of perceived usability results. More studies with this app will be required to evaluate the potential to help professionals with hemodynamic evaluation in emergency and intensive care settings.

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Proper assessment of fluid responsiveness using accurate predictors is crucial to guide fluid therapy and avoid the serious adverse effects of fluid overload. The main objective of this study was to investigate the accuracy of respiratory variations in inferior vena cava diameter (∆IVC) to predict fluid responsiveness in mechanically ventilated children. This prospective single-center study included 32 children (median age and weight of 17 months and 10 kg, respectively) who received a fluid infusion of 10 ml kg-1 of crystalloid solutions over 10 min. ∆IVC and respiratory variation in aortic blood flow peak velocity (∆Vpeak) were determined over one controlled respiratory cycle before and after fluid loading. Thirteen (41%) participants were fluid-responders. ∆IVC, ∆Vpeak, stroke volume index, and cardiac index were found to be predictors of fluid responsiveness. However, the area under the ROC curve of ∆IVC was smaller when compared to ∆Vpeak (0.709 vs. 0.935, p < 0.012). The best cut-off values were 7.7% for ∆IVC (sensitivity, 69.2%; specificity 78.9%, positive predictive value, 69.2%; and negative predictive value, 78.9%) and 18.2% for ∆Vpeak (sensitivity, 84.6%; specificity, 89.5%; positive predictive value, 84.6%; negative predictive value, 89.5%). Changes in stroke volume were positively correlated with ∆IVC (ρ = 0.566, p < 0.001) and ∆Vpeak (ρ = 0.603, p < 0.001). A significant correlation was also found between changes in MAP and ∆Vpeak (ρ = 0.382; p = 0.031), but the same was not observed with ∆IVC (ρ = 0.011; p = 0.951). In conclusion, ∆IVC was found to have a moderate accuracy in predicting fluid responsiveness in mechanically ventilated children and is an inferior predictor when compared to ∆Vpeak.

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OBJECTIVE: To evaluate the use of the caudal vena cava collapsibility index (CVCCI) and the inspiratory/minimum and expiratory/maximum diameters of the vena cava to predict fluid responsiveness in hospitalized, critically ill cats with hemodynamic and tissue perfusion abnormalities. DESIGN: Diagnostic test study in a prospective cohort of hospitalized cats. SETTING: Private practice referral hospital. ANIMALS: Twenty-four hospitalized cats with spontaneous breathing and compromised hemodynamics and tissue hypoperfusion. INTERVENTIONS: Ultrasonographic examination before and after fluid expansion with 10 ml/kg of lactated Ringer's solution. MEASUREMENTS AND MAIN RESULTS: Fluid responsiveness was evaluated using the velocity-time integral (VTI) of the subaortic blood flow, by measuring it before and after a fluid load of 10 ml/kg of lactated Ringer's solution. The CVCCI was calculated using the following formula: (maximum diameter - minimum diameter / maximum diameter) × 100. Ten cats were fluid responders (42 %) and 14 were nonresponders (58 %). The area under the receiver operating characteristic curve (AUROC) with their 95% confidence interval for the predictors and the best cutoff values were as follows: CVCCI, AUROC = 0.83 (0.66-1.00) and cutoff = 31%; inspiratory/minimum diameter, AUROC = 0.86 (0.70-1.00) and cutoff = 0.24 cm; expiratory/maximum diameter, AUROC = 0.88 (0.74-1.00) and cutoff = 0.22 cm. A significant lineal correlation was observed between the percentage of increase in VTI after expansion and CVCCI (rs  = 0.68, P < 0.001), expiratory/maximum diameter (rs  = -0.72, P < 0.001), and inspiratory/minimum diameter (rs  = -0.71, P < 0.001). The intraobserver and interobserver variability was low for VTI, and the expiratory/maximum diameter and inspiratory/minimum diameter were high for CVCCI. CONCLUSIONS: Caudal vena cava measurements could be useful to predict the response to fluids in hospitalized cats with hemodynamic and tissue perfusion alterations. Additional studies are required to draw definitive conclusions about the role of these variables to guide fluid administration in cats.

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BACKGROUND: Point-of-care ultrasonography (POCUS) is proposed as a valuable method for hemodynamic monitoring and several ultrasound-based predictors of fluid responsiveness have been studied. The main objective of this study was to assess the accuracy of these predictors in children. METHODS: PubMed, Embase, Scopus, ClinicalTrials.gov, and Cochrane Library databases were searched for relevant publications through July 2022. Pediatric studies reporting accuracy estimates of ultrasonographic predictors of fluid responsiveness were included since they had used a standard definition of fluid responsiveness and had performed an adequate fluid challenge. RESULTS: Twenty-three studies involving 1028 fluid boluses were included, and 12 predictors were identified. A positive response to fluid infusion was observed in 59.7% of cases. The vast majority of participants were mechanically ventilated (93.4%). The respiratory variation in aortic blood flow peak velocity (∆Vpeak) was the most studied predictor, followed by the respiratory variation in inferior vena cava diameter (∆IVC). The pooled sensitivity and specificity of ∆Vpeak were 0.84 (95% CI, 0.76-0.90) and 0.82 (95% CI, 0.75-0.87), respectively, and the area under the summary receiver operating characteristic curve (AUSROC) was 0.89 (95% CI, 0.86-0.92). The ∆IVC presented a pooled sensitivity and specificity of 0.79 (95% CI, 0.62-0.90) and 0.70 (95% CI, 0.51-0.84), respectively, and an AUSROC of 0.81 (95% CI, 0.78-0.85). Significant heterogeneity in accuracy estimates across studies was observed. CONCLUSIONS: POCUS has the potential to accurately predict fluid responsiveness in children. However, only ∆Vpeak was found to be a reliable predictor. There is a lack of evidence supporting the use of POCUS to guide fluid therapy in spontaneously breathing children.

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Introducción. La variación de la velocidad máxima aórtica con la ventilación mecánica (ΔVpeakAo) ha demostrado ser el mejor predictor de respuesta a volumen en pediatría. Existe evidencia en adultos de que la variación de velocidad máxima de flujo carotídeo (ΔVpeakCar) es predictor de respuesta a fluidos. Al momento es escasa la información sobre este índice en pediatría. Su beneficio se basa en la no-invasividad, y que para su medición no es necesaria la ecocardiografía ni el acceso al tórax del paciente. Objetivo. El objetivo general de este trabajo fue estudiar la correlación y la concordancia de ΔVpeakCar con ΔVpeakAo en una población pediátrica bajo ventilación mecánica. Metodología. Se incluyeron pacientes de 0 a 12 años. Se registraron flujos aórtico y carotídeos máximos y mínimos y se calculó ΔVpeakCar y ΔVpeakAo. Para analizar correlación y concordancia entre las variables se utilizó el test de Pearson, análisis de Bland-Altman y análisis de los 4-cuadrantes. Resultados. Se estudiaron 58 pacientes, 13 lactantes (menores 12 meses), 21 preescolares (12-60 meses) y 24 escolares (mayores a 60 meses). Se observó una correlación significativa entre ΔVpeakAo y ΔVpeakCar (r=0,85; p<0,05) con un coeficiente de determinación de r2=0,72. El análisis de Bland-Altman mostró un sesgo del 0,15% (IC95%, -0.7-1.0) con un límite de concordancia del -6,1 a 6,2%. La concordancia fue 85%, con un sesgo angular de 4,5°±31°. El análisis por subgrupos mostró un r2 de 0.89 en escolares, 0.56 en preescolares y 0.45 en lactantes. La concordancia fue de 100% en escolares, 95% en prescolares y 93% en lactantes. Discusión y conclusiones. El registro de ΔVpeakCar fue viable. Al analizar la capacidad de ΔVpeakCar de sustituir a ΔVpeakAo en el total de la muestra, no es buena La correlación y concordancia son mejores en escolares. Es necesario continuar estudiando este nuevo índice.

Introduction. The variation in maximum aortic velocity with mechanical ventilation (ΔVpeakAo) has proven to be the most effective predictor of fluid response in pediatrics. While there is evidence in adults that the variation in maximum carotid flow velocity (ΔVpeakCar) predicts fluid response, information on this index in pediatrics remains limited. Its advantage lies in its non-invasive nature, eliminating the need for echocardiography or thoracic access for recording. Objective. This study aims to examine the correlation and concordance between ΔVpeakCar and ΔVpeakAo in a pediatric population. Methodology. The study included patients aged 0 to 12 years. Maximum and minimum aortic and carotid flows were recorded, and ΔVpeakCar and ΔVpeakAo were calculated. Correlation and agreement between variables were analyzed using the Pearson test, Bland Altman analysis, and 4-quadrant analysis. Results. A total of 58 patients were studied, comprising 13 infants (under 12 months), 21 preschoolers (12-60 months), and 24 school-aged children (over 60 months). A significant correlation was observed between ΔVpeakAo and ΔVpeakCar (r=0.85; p<0.05) with a coefficient of determination, r²=0.72. The Bland-Altman analysis revealed a bias of 0.15% (95% CI, -0.7-1.0) with an agreement limit of -6.1% to 6.2%. The concordance rate was 85%, with an angular bias of 4.5°±31°. Subgroup analysis showed r² values of 0.89 in school-aged children, 0.56 in preschoolers, and 0.45 in infants. Concordance rates were 100% in school-aged children, 95% in preschoolers, and 93% in infants. Discussion and Conclusions. The measurement of ΔVpeakCar proved feasible. However, when considering its ability to replace ΔVpeakAo, the results are suboptimal. Correlation and concordance are stronger in school-aged children. Further investigation into this new index is warranted.

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PURPOSE: The passive leg raising test (PLR) produces a reversible increase in venous return and, if the patient's ventricles are preload dependent, in the cardiac output. As this effect occurs in seconds, the transthoracic echocardiography is optimal for its real time assessment. The utility of the PLR for monitoring fluid responsiveness through the measurement of the left ventricle outflow tract velocity-time integral (LVOT VTI) in an apical 5-chamber view is well stablished. To achieve this view in critically ill patients is often challenging. The aim of this study is to explore the accuracy for predicting fluid responsiveness of the change in the right ventricle outflow tract velocity-time integral (RVOT VTI) from a subcostal view during a PLR. METHODS: This is a diagnostic accuracy study carried out in two centers in Argentina. We included patients admitted to the intensive care unit from January 2022 to April 2022, that required fluid expansion due to signs of tissular hypoperfusion. We measured the RVOT VTI from a subcostal view in a semi-recumbent position and during the PLR, and the LVOT VTI in an apical 5-chamber view before and after a fluid bolus. If the LVOT VTI increased by 15% after the fluid bolus, the patients were considered fluid responders. RESULTS: We included 43 patients. The area under the ROC curve for a change in the RVOT VTI during the PLR was 0.879 (95% CI 0.744-0.959). A change of 15.36% in the RVOT VTI with the PLR predicted fluid responsiveness with a sensitivity of 85.7% (95% CI 57.2%-98.2%) and specificity of 93.1% (95% CI 77.2-99.2). The positive predictive value was 85.7% (95% CI 60.8%-95.9%) and the negative predictive value was 93.1% (95% CI 78.8%-98%). The positive likelihood ratio was 12.43 and the negative predictive value was 0.15. CONCLUSION: The RVOT VTI change during a PLR is suitable for the prediction of fluid responsiveness in critically ill patients.

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Fluid resuscitation is a core component of emergency and critical care medicine. While the focus of clinicians has largely been on detecting patients who would respond to fluid therapy, relatively little work has been done on assessing patients' tolerance to this therapy. In this article we seek to review the concept of fluid tolerance, propose a working definition, and introduce relevant clinical signals by which physicians can assess fluid tolerance, hopefully becoming a starting point for further research.

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AIMS: The aim of this study was to investigate whether respiratory variations in carotid and aortic blood flows measured by Doppler ultrasonography could accurately predict fluid responsiveness in critically ill children. METHODS: This was a prospective single-center study including mechanically ventilated children who underwent fluid replacement at the discretion of the attending physician. Response to fluid load was defined by a stroke volume increase of more than 15%. Maximum and minimum values of velocity peaks were determined over one controlled respiratory cycle before and after volume expansion. Respiratory changes in velocity peak of the carotid (∆Vpeak_Ca) and aortic (∆Vpeak_Ao) blood flows were calculated as the difference between the maximum and minimum values divided by the mean of the two values and were expressed as a percentage. RESULTS: A total of 30 patients were included, of which twelve (40%) were fluid responders and 18 (60%) non-responders. Before volume expansion, both ∆Vpeak_Ca and ∆Vpeak_Ao were higher in responders than in non-responders (17.1% vs 4.4%; p < .001 and 22.8% vs 6.4%; p < .001, respectively). ∆Vpeak_Ca could effectively predict fluid responsiveness (AUC 1.00, 95% CI 0.88-1.00), as well as ∆Vpeak_Ao (AUC 0.94, 95% CI 0.80-0.99). The best cutoff values were 10.6% for ∆Vpeak_Ca (sensitivity, specificity, positive predictive value and negative predictive value of 100%) and 18.2% for ∆Vpeak_Ao (sensitivity, 91.7%; specificity, 88.9%; positive predictive value, 84.6%; negative predictive value, 94.1%). Volume expansion-induced changes in stroke volume correlated with the ∆Vpeak_Ca and ∆Vpeak_Ao before volume expansion (ρ of 0.70 and 0.61, respectively; p < .001 for both). CONCLUSIONS: Analysis of respiratory changes in carotid and aortic blood flows are accurate methods for predicting fluid responsiveness in children under invasive mechanical ventilation.

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AIMS: To evaluate the echocardiographic variable tricuspid annular plane systolic excursion normalised to body weight (TAPSEnorm) as a predictor of fluid responsiveness in hospitalised dogs with haemodynamic and tissue perfusion alterations and to investigate the association of left ventricular internal diameter in diastole normalised to body weight (LVIDdN) and aortic velocity time integral (VTIAo) with TAPSEnorm. METHODS: A single-centre, prospective study was carried out in a cohort of spontaneously breathing dogs, hospitalised for any reason, with severe haemodynamic and tissue perfusion alterations. The echocardiographic variables TAPSEnorm, LVIDdN, and VTIAO were measured. A bolus of 30 mL/kg of lactated Ringer's solution was administered and then VTIAo was subsequently remeasured. Patients were classified as fluid responsive if VTIAo increased by ≥15% after fluid expansion, or non-responsive if VTIAo increased by <15% after fluid expansion. The area under the receiver operating characteristic (AUROC) curve was generated to evaluate the ability of TAPSE to predict fluid responsiveness. Simple regression models were used to assess the linear relationship between TAPSEnorm and LVIDdN or VTIAO. RESULTS: TAPSEnorm was lower in fluid responsive dogs (mean 0.57 (95% CI = 0.50-0.64) cm/kg) compared to non-responsive dogs (mean 0.76 (95% CI = 0.62-0.90) cm/kg). The AUROC for TAPSEnorm was 0.827 (95% CI = 0.65-1.00). The optimal cut-off point was 0.76 with sensitivity of 80 (95% CI = 28.4-99.5)% and specificity of 86.7 (95% CI = 69.3-99.2)%, positive predictive value of 50 (95% CI = 15.7-84.3)% and negative predictive value of 96.3 (95% CI = 81-99.9)%. A monotonic linear relationship was observed between TAPSEnorm and LVIDdN (p<0.001) and between TAPSEnorm and VTIAo (p=0.001). CONCLUSIONS AND CLINICAL RELEVANCE: TAPSEnorm could be useful in determining those dogs that are likely to respond to a fluid bolus from those that are likely to be non-responsive. Additionally, a positive linear association between the LVIDdN and the TAPSEnorm suggests that TAPSEnorm decreases at lower preload values. The present study results suggest that TAPSEnorm could be a valuable tool for evaluating blood volume status and fluid responsiveness in hospitalised dogs.Abbreviations: AUROC: Area under the receiver operating characteristic; CO: Cardiac output; ICC: Intraclass correlation coefficient; LVIDd: Left ventricular internal diameter in diastole; LVIDdN: Left ventricular internal diameter in diastole normalised to body weight; TAPSE: Tricuspid annular plane systolic excursion; TAPSEnorm: Tricuspid annular plane systolic excursion normalised to body weight; VTIAo: Aortic velocity time integral.

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Resuscitative fluid therapy aims to increase stroke volume (SV) and cardiac output (CO) and restore/improve tissue oxygen delivery in patients with circulatory failure. In individualized goal-directed fluid therapy (GDFT), fluids are titrated based on the assessment of responsiveness status (i.e., the ability of an individual to increase SV and CO in response to volume expansion). Fluid administration may increase venous return, SV and CO, but these effects may not be predictable in the clinical setting. The fluid challenge (FC) approach, which consists on the intravenous administration of small aliquots of fluids, over a relatively short period of time, to test if a patient has a preload reserve (i.e., the relative position on the Frank-Starling curve), has been used to guide fluid administration in critically ill humans. In responders to volume expansion (defined as individuals where SV or CO increases ≥10-15% from pre FC values), FC administration is repeated until the individual no longer presents a preload reserve (i.e., until increases in SV or CO are <10-15% from values preceding each FC) or until other signs of shock are resolved (e.g., hypotension). Even with the most recent technological developments, reliable and practical measurement of the response variable (SV or CO changes induced by a FC) has posed a challenge in GDFT. Among the methods used to evaluate fluid responsiveness in the human medical field, measurement of aortic flow velocity time integral by point-of-care echocardiography has been implemented as a surrogate of SV changes induced by a FC and seems a promising non-invasive tool to guide FC administration in animals with signs of circulatory failure. This narrative review discusses the development of GDFT based on the FC approach and the response variables used to assess fluid responsiveness status in humans and animals, aiming to open new perspectives on the application of this concept to the veterinary field.

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INTRODUCTION: Dynamic predictors of fluid responsiveness have shown good performance in mechanically ventilated patients at tidal volumes (Vt) > 8 mL kg-1. Nevertheless, most critically ill conditions demand lower Vt. We sought to evaluate the operative performance of several predictors of fluid responsiveness at Vt ≤ 8 mL kg-1 by using meta-regression and subgroup analyses. METHODS: A sensitive search was conducted in the Embase and MEDLINE databases. We searched for studies prospectively assessing the operative performance of pulse pressure variation (PPV), stroke volume variation (SVV), end-expiratory occlusion test (EEOT), passive leg raising (PLR), inferior vena cava respiratory variability (Δ-IVC), mini-fluid challenge (m-FC), and tidal volume challenge (VtC), to predict fluid responsiveness in adult patients mechanically ventilated at Vt ≤ 8 ml kg-1, without respiratory effort and arrhythmias, published between 1999 and 2020. Operative performance was assessed using hierarchical and bivariate analyses, while subgroup analysis was used to evaluate variations in their operative performance and sources of heterogeneity. A sensitivity analysis based on the methodological quality of the studies included (QUADAS-2) was also performed. RESULTS: A total of 33 studies involving 1,352 patients were included for analysis. Areas under the curve (AUC) values for predictors of fluid responsiveness were: for PPV = 0.82, Δ-IVC = 0.86, SVV = 0.90, m-FC = 0.84, PLR = 0.84, EEOT = 0.92, and VtC = 0.92. According to subgroup analyses, variations in methods to measure cardiac output and in turn, to classify patients as responders or non-responders significantly influence the performance of PPV and SVV (p < 0.05). Operative performance of PPV was also significantly affected by the compliance of the respiratory system (p = 0.05), while type of patient (p < 0.01) and thresholds used to determine responsiveness significantly affected the predictability of SVV (p = 0.05). Similarly, volume of fluids infused to determine variation in cardiac output, significantly affected the performance of SVV (p = 0.01) and PLR (p < 0.01). Sensitivity analysis showed no variations in operative performance of PPV (p = 0.39), SVV (p = 0.23) and EEOT (p = 0.15). CONCLUSION: Most predictors of fluid responsiveness reliably predict the response of cardiac output to volume expansion in adult patients mechanically ventilated at tidal volumes ≤ 8 ml kg-1. Nevertheless, technical and clinical variables might clearly influence on their operative performance.

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OBJECTIVE: To evaluate the ability of transthoracic echocardiographic aortic flow measurements to discriminate response to a fluid challenge (FC) in healthy anesthetized dogs. STUDY DESIGN: Prospective experimental study. ANIMALS: A total of 48 isoflurane-anesthetized dogs (14.2-35.0 kg) undergoing elective surgery. METHODS: Fluid responsiveness was evaluated before surgery by FC (lactated Ringer's 10 mL kg-1 intravenously over 5 minutes). Percentage increases in transpulmonary thermodilution stroke volume (ΔSVTPTD) >15% from values recorded before FC defined responders to volume expansion. A group of 24 animals were assigned as nonresponders (ΔSVTPTD ≤15%). When ΔSVTPTD was >15% after the first FC, additional FC were administered until ΔSVTPTD was ≤15%. Final fluid responsiveness status was based on the response to the last FC. Percentage increases after FC in aortic flow indexes [velocity time integral (ΔVTIFC) and maximum acceleration (ΔVmaxFC)] and in mean arterial pressure (ΔMAPFC) were compared with ΔSVTPTD. RESULTS: After one FC, 24 animals were responders. For nonresponders, ΔSVTPTD was ≤15% after one, two and three FCs in eight/24, 15/24 and one/24 animals, respectively. The FC that defined responsiveness increased ΔSVTPTD by 29 (18-53)% in responders and by 8 (-3 to 15)% in nonresponders [mean (range)]. The area under the receiver operating characteristics curve (AUROC) of ΔVTIFC (0.901) was larger than the AUROCs of ΔVmaxFC (0.774, p = 0.041) and ΔMAPFC (0.519, p < 0.0001). ΔMAPFC did not predict responsiveness (p = 0.826). Best cut-off thresholds for discriminating responders, with respective zones of diagnostic uncertainty (gray zones) were >14.7 (10.8-17.6)% for ΔVTIFC and >8.6 (-0.3 to 14.7)% for ΔVmaxFC. Animals within the gray zone were 17% (ΔVTIFC) and 50% (ΔVmaxFC). CONCLUSIONS AND CLINICAL RELEVANCE: Changes in VTI induced by FC can determine responsiveness with reasonable accuracy in dogs and could play an important role in goal-directed fluid therapy.

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INTRODUCTION: Sepsis is a disease that is still associated with high mortality, in which timely interventions are related to better results. OBJECTIVE: To determine if there is a difference in in-hospital mortality, fluid balances, norepinephrine initiation and recovery time of blood pressure, when comparing the resuscitation of the patient who is admitted to the emergency room in septic shock by applying the ultrasound protocol (USER) versus the standard of care. PATIENTS AND METHODS: This is a prospective, cohort study conducted in the emergency room of a highly complex hospital of patients with septic shock. RESULTS: 83 patients recruited in total. The groups were comparable in demographics, mean baseline blood pressure, disease severity given by the SOFA value, and arterial lactate. A statistically significant difference was documented in the fluid balances at 4 hours, median 1325mL (IQR:451-2455mL) in Group C versus 900mL (IQR:440-1292) in Group U (p=0.048) and at 6 hours, median 1658mL (IQR:610-2925mL) versus 1107mL (IQR:600-1500mL), p=0.026, as well as in the total fluid balance of hospital stay, median 14,564mL (IQR:8660-18,705mL) versus 8660mL (IQR:5309-16,974mL), p=0.049. On the other hand, in the USER Group, the mean blood pressure ≥ 65mmHg was achieved in 97.4% of the patients 4 hours after the start of the protocol versus 50% in Group C (p=<0.001). Mortality with the use of the protocol compared with conventional therapy was (56.4% vs 61.36%, p=0.647). CONCLUSION: The use of the USER protocol in patients with septic shock in the emergency room showed lower fluid balances at 4 and 6 hours, and of the total hospital stay, as well as earlier initiation of norepinephrine and statistically significant faster improvement in blood pressure. Although a statistically significant difference was not found in the days of ICU stay, hospitalization and in-hospital mortality, a trend was observed in the reduction of these parameters.