Flow Index: a novel, non-invasive, continuous, quantitative method to evaluate patient inspiratory effort during pressure support ventilation.
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ABSTRACT: Background
The evaluation of patient effort is pivotal during pressure support ventilation, but a non-invasive, continuous, quantitative method to assess patient inspiratory effort is still lacking. We hypothesized that the concavity of the inspiratory flow-time waveform could be useful to estimate patient's inspiratory effort. The purpose of this study was to assess whether the shape of the inspiratory flow, as quantified by a numeric indicator, could be associated with inspiratory effort during pressure support ventilation.Methods
Twenty-four patients in pressure support ventilation were enrolled. A mathematical relationship describing the decay pattern of the inspiratory flow profile was developed. The parameter hypothesized to estimate effort was named Flow Index. Esophageal pressure, airway pressure, airflow, and volume waveforms were recorded at three support levels (maximum, minimum and baseline). The association between Flow Index and reference measures of patient effort (pressure time product and pressure generated by respiratory muscles) was evaluated using linear mixed effects models adjusted for tidal volume, respiratory rate and respiratory rate/tidal volume.Results
Flow Index was different at the three pressure support levels and all group comparisons were statistically significant. In all tested models, Flow Index was independently associated with patient effort (p < 0.001). Flow Index prediction of inspiratory effort agreed with esophageal pressure-based methods.Conclusions
Flow Index is associated with patient inspiratory effort during pressure support ventilation, and may provide potentially useful information for setting inspiratory support and monitoring patient-ventilator interactions.
SUBMITTER: Albani F
PROVIDER: S-EPMC8182360 | biostudies-literature |
REPOSITORIES: biostudies-literature
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Project description:BackgroundBedside assessment of low levels of inspiratory effort, which are probably insufficient to prevent muscle atrophy, is challenging. The flow index, which is derived from the analysis of the inspiratory portion of the flow-time waveform, has been recently introduced as a non-invasive parameter to evaluate the inspiratory effort. The primary objective of the present study was to provide an external validation of the flow index to detect low inspiratory effort.MethodsDatasets containing flow, airway pressure, and esophageal pressure (Pes)-time waveforms were obtained from a previously published study in 100 acute brain-injured patients undergoing pressure support ventilation. Waveforms data were analyzed offline. A low inspiratory effort was defined by one of the following criteria, work of breathing (WOB) less than 0.3 J/L, Pes-time product (PTPes) per minute less than 50 cmH2O•s/min, or inspiratory muscle pressure (Pmus) less than 5 cmH2O, adding "or occurrence of ineffective effort more than 10%" for all criteria. The flow index was calculated according to previously reported method. The association of flow index with Pes-derived parameters of effort was investigated. The diagnostic accuracy of the flow index to detect low effort was analyzed.ResultsModerate correlations were found between flow index and WOB, Pmus, and PTPes per breath and per minute (Pearson's correlation coefficients ranged from 0.546 to 0.634, P < 0.001). The incidence of low inspiratory effort was 62%, 51%, and 55% using the definition of WOB, PTPes per minute, and Pmus, respectively. The area under the receiver operating characteristic curve for flow index to diagnose low effort was 0.88, 0.81, and 0.88, for the three respective definition. By using the cutoff value of flow index less than 2.1, the diagnostic performance for the three definitions showed sensitivity of 0.95-0.96, specificity of 0.57-0.71, positive predictive value of 0.70-0.84, and negative predictive value of 0.90-0.93.ConclusionsThe flow index is associated with Pes-based inspiratory effort measurements. Flow index can be used as a valid instrument to screen low inspiratory effort with a high probability to exclude cases without the condition.
| S-EPMC9510081 | biostudies-literature
Project description:BackgroundFlow Index, a numerical expression of the shape of the inspiratory flow-time waveform recorded during pressure support ventilation, is associated with patient inspiratory effort. The aim of this study was to assess the accuracy of Flow Index in detecting high or low inspiratory effort during pressure support ventilation and to establish cutoff values for the Flow index to identify these conditions. The secondary aim was to compare the performance of Flow index,of breathing pattern parameters and of airway occlusion pressure (P0.1) in detecting high or low inspiratory effort during pressure support ventilation.MethodsData from 24 subjects was included in the analysis, accounting for a total of 702 breaths. Breaths with high inspiratory effort were defined by a pressure developed by inspiratory muscles (Pmusc) greater than 10 cmH2O while breaths with low inspiratory effort were defined by a Pmusc lower than 5 cmH2O. The areas under the receiver operating characteristic curves of Flow Index and respiratory rate, tidal volume,respiratory rate over tidal volume and P0.1 were analyzed and compared to identify breaths with low or high inspiratory effort.ResultsPmusc, P0.1, Pressure Time Product and Flow Index differed between breaths with high, low and intermediate inspiratory effort, while RR, RR/VT and VT/kg of IBW did not differ in a statistically significant way. A Flow index higher than 4.5 identified breaths with high inspiratory effort [AUC 0.89 (CI 95% 0.85-0.93)], a Flow Index lower than 2.6 identified breaths with low inspiratory effort [AUC 0.80 (CI 95% 0.76-0.83)].ConclusionsFlow Index is accurate in detecting high and low spontaneous inspiratory effort during pressure support ventilation.
| S-EPMC8672539 | biostudies-literature
Project description:BACKGROUND:In pressure-controlled (PC) ventilation, tidal volume (V T) and transpulmonary pressure (P L ) result from the addition of ventilator pressure and the patient's inspiratory effort. PC modes can be classified into fully, partially, and non-synchronized modes, and the degree of synchronization may result in different V T and P L despite identical ventilator settings. This study assessed the effects of three PC modes on V T, P L , inspiratory effort (esophageal pressure-time product, PTPes), and airway occlusion pressure, P 0.1. We also assessed whether P 0.1 can be used for evaluating patient effort. METHODS:Prospective, randomized, crossover physiologic study performed in 14 spontaneously breathing mechanically ventilated patients recovering from acute respiratory failure (1 subsequently withdrew). PC modes were fully (PC-CMV), partially (PC-SIMV), and non-synchronized (PC-IMV using airway pressure release ventilation) and were applied randomly; driving pressure, inspiratory time, and set respiratory rate being similar for all modes. Airway, esophageal pressure, P 0.1, airflow, gas exchange, and hemodynamics were recorded. RESULTS:V T was significantly lower during PC-IMV as compared with PC-SIMV and PC-CMV (387 ± 105 vs 458 ± 134 vs 482 ± 108 mL, respectively; p < 0.05). Maximal P L was also significantly lower (13.3 ± 4.9 vs 15.3 ± 5.7 vs 15.5 ± 5.2 cmH2O, respectively; p < 0.05), but PTPes was significantly higher in PC-IMV (215.6 ± 154.3 vs 150.0 ± 102.4 vs 130.9 ± 101.8 cmH2O × s × min-1, respectively; p < 0.05), with no differences in gas exchange and hemodynamic variables. PTPes increased by more than 15% in 10 patients and by more than 50% in 5 patients. An increased P 0.1 could identify high levels of PTPes. CONCLUSIONS:Non-synchronized PC mode lowers V T and P L in comparison with more synchronized modes in spontaneously breathing patients but can increase patient effort and may need specific adjustments. Clinical Trial Registration Clinicaltrial.gov # NCT02071277.
| S-EPMC5630544 | biostudies-literature
Project description:BackgroundAssessment of the patient's respiratory effort is essential during assisted ventilation. We aimed to evaluate the accuracy of airway pressure (Paw)-based indices to detect potential injurious inspiratory effort during pressure support (PS) ventilation.MethodsIn this prospective diagnostic accuracy study conducted in four ICUs in two academic hospitals, 28 adult acute respiratory failure patients undergoing PS ventilation were enrolled. A downward PS titration was conducted from 20 cmH2O to 2 cmH2O at a 2 cmH2O interval. By performing an end-expiratory airway occlusion maneuver, the negative Paw generated during the first 100 ms (P0.1) and the maximal negative swing of Paw (∆Pocc) were measured. After an end-inspiratory airway occlusion, Paw reached a plateau, and the magnitude of change in plateau from peak Paw was measured as pressure muscle index (PMI). Esophageal pressure was monitored and inspiratory muscle pressure (Pmus) and Pmus-time product per minute (PTPmus/min) were used as the reference standard for the patient's effort. High and low effort was defined as Pmus > 10 and < 5 cmH2O, or PTPmus/min > 200 and < 50 cmH2O s min-1, respectively.ResultsA total of 246 levels of PS were tested. The low inspiratory effort was diagnosed in 145 (59.0%) and 136 (55.3%) PS levels using respective Pmus and PTPmus/min criterion. The receiver operating characteristic area of the three Paw-based indices by the respective two criteria ranged from 0.87 to 0.95, and balanced sensitivity (0.83-0.96), specificity (0.74-0.88), and positive (0.80-0.91) and negative predictive values (0.78-0.94) were obtained. The high effort was diagnosed in 34 (13.8%) and 17 (6.9%) support levels using Pmus and PTPmus/min criterion, respectively. High receiver operating characteristic areas of the three Paw-based indices by the two criteria were found (0.93-0.95). A high sensitivity (0.80-1.00) and negative predictive value (0.97-1.00) were found with a low positive predictive value (0.23-0.64).ConclusionsBy performing simple airway occlusion maneuvers, the Paw-based indices could be reliably used to detect low inspiratory efforts. Non-invasive and easily accessible characteristics support their potential bedside use for avoiding over-assistance. More evaluation of their performance is required in cohorts with high effort.
| S-EPMC10643759 | biostudies-literature
Project description:PurposeThe COVID-19-related shortage of ICU beds magnified the need of tools to properly titrate the ventilator assistance. We investigated whether bedside-available indices such as the ultrasonographic changes in diaphragm thickening ratio (TR) and the tidal swing in central venous pressure (ΔCVP) are reliable estimates of inspiratory effort, assessed as the tidal swing in esophageal pressure (ΔPes).MethodsProspective, observational clinical investigation in the intensive care unit of a tertiary care Hospital. Fourteen critically-ill patients were enrolled (age 64 ± 7 years, BMI 29 ± 4 kg/m2), after 6 [3; 9] days from onset of assisted ventilation. A three-level pressure support trial was performed, at 10 (PS10), 5 (PS5) and 0 cmH2O (PS0). In each step, the esophageal and central venous pressure tidal swing were recorded, as well as diaphragm ultrasound.ResultsThe reduction of pressure support was associated with an increased respiratory rate and a reduced tidal volume, while minute ventilation was unchanged. ΔPes significantly increased with reducing support (5 [3; 8] vs. 8 [14; 13] vs. 12 [6; 16] cmH2O, p < 0.0001), as did the diaphragm TR (9.2 ± 6.1 vs. 17.6 ± 7.2 vs. 28.0 ± 10.0%, p < 0.0001) and the ΔCVP (4 [3; 7] vs. 8 [5; 9] vs. 10 [7; 11] cmH2O, p < 0.0001). ΔCVP was significantly associated with ΔPes (R2 = 0.810, p < 0.001), as was diaphragm TR, albeit with a lower coefficient of determination (R2 = 0.399, p < 0.001).ConclusionsIn patients with COVID-19-associated respiratory failure undergoing assisted mechanical ventilation, ΔCVP is a better estimate of inspiratory effort than diaphragm ultrasound.
| S-EPMC7908005 | biostudies-literature
Project description:BackgroundWhether respiratory efforts and their timing can be reliably detected during pressure support ventilation using standard ventilator waveforms is unclear. This would give the opportunity to assess and improve patient-ventilator interaction without the need of special equipment.MethodsIn 16 patients under invasive pressure support ventilation, flow and pressure waveforms were obtained from proximal sensors and analyzed by three trained physicians and one resident to assess patient's spontaneous activity. A systematic method (the waveform method) based on explicit rules was adopted. Esophageal pressure tracings were analyzed independently and used as reference. Breaths were classified as assisted or auto-triggered, double-triggered or ineffective. For assisted breaths, trigger delay, early and late cycling (minor asynchronies) were diagnosed. The percentage of breaths with major asynchronies (asynchrony index) and total asynchrony time were computed.ResultsOut of 4426 analyzed breaths, 94.1% (70.4-99.4) were assisted, 0.0% (0.0-0.2) auto-triggered and 5.8% (0.4-29.6) ineffective. Asynchrony index was 5.9% (0.6-29.6). Total asynchrony time represented 22.4% (16.3-30.1) of recording time and was mainly due to minor asynchronies. Applying the waveform method resulted in an inter-operator agreement of 0.99 (0.98-0.99); 99.5% of efforts were detected on waveforms and agreement with the reference in detecting major asynchronies was 0.99 (0.98-0.99). Timing of respiratory efforts was accurately detected on waveforms: AUC for trigger delay, cycling delay and early cycling was 0.865 (0.853-0.876), 0.903 (0.892-0.914) and 0.983 (0.970-0.991), respectively.ConclusionsVentilator waveforms can be used alone to reliably assess patient's spontaneous activity and patient-ventilator interaction provided that a systematic method is adopted.
| S-EPMC8802480 | biostudies-literature
Project description:There is a clinical need for monitoring inspiratory effort to prevent lung- and diaphragm injury in patients who receive supportive mechanical ventilation in an Intensive Care Unit. Different pressure-based techniques are available to estimate this inspiratory effort at the bedside, but the accuracy of their effort estimation is uncertain since they are all based on a simplified linear model of the respiratory system, which omits gas compressibility of air, and the viscoelasticity and nonlinearities of the respiratory system. The aim of this in-silico study was to provide an overview of the pressure-based estimation techniques and to evaluate their accuracy using a more sophisticated model of the respiratory system and ventilator. The influence of the following parameters on the accuracy of the pressure-based estimation techniques was evaluated using the in-silico model: 1) the patient's respiratory mechanics 2) PEEP and the inspiratory pressure of the ventilator 3) gas compressibility of air 4) viscoelasticity of the respiratory system 5) the strength of the inspiratory effort. The best-performing technique in terms of accuracy was the whole breath occlusion. The average error and maximum error were the lowest for all patient archetypes. We found that the error was related to the expansion of gas in the breathing set and lungs and respiratory compliance. However, concerns exist that other factors not included in the model, such as a changed muscle-force relation during an occlusion, might influence the true accuracy. The estimation techniques based on the esophageal pressure showed an error related to the viscoelastic element in the model which leads to a higher error than the occlusion. The error of the esophageal pressure-based techniques is therefore highly dependent on the pathology of the patient and the settings of the ventilator and might change over time while a patient recovers or becomes more ill.
| S-EPMC9958297 | biostudies-literature
Project description:ObjectivesAcute respiratory distress syndrome guidelines suggest limiting plateau pressures to 28-30 cm H2O. Plateau pressure is most accurately measured in square-flow modes, such as volume control. In children, decelerating-flow modes, such as pressure-regulated volume control and pressure control, are more common. Consequently, plateau pressures are rarely obtained, and pressure limits are instead provided for peak inspiratory pressure. The degree to which peak inspiratory pressure in decelerating-flow overestimates plateau pressure is unknown. Therefore, we assessed the correlation and accuracy of peak inspiratory pressure in decelerating-flow ventilation for approximating plateau pressure during square-flow ventilation.DesignProspective, observational study.SettingTertiary, academic PICU.PatientsFifty-two intubated children with acute respiratory distress syndrome enrolled between January 2020 and May 2021.InterventionsMeasurement of peak inspiratory pressure in decelerating-flow ventilation and plateau pressure after transition to square-flow ventilation.Measurements and main resultsPeak inspiratory pressure in decelerating-flow was highly correlated (r2 = 0.99; p < 0.001) with plateau pressure in square-flow. Peak inspiratory pressure was 1.0 ± 0.6 cm H2O higher than plateau pressure, with 96% of values within 2 cm H2O. The single outlier had coexistent asthma and inspiratory flows that did not reach zero.ConclusionsPeak inspiratory pressure measured during decelerating-flow ventilation may be an adequate surrogate of plateau pressure in pediatric acute respiratory distress syndrome when inspiratory flow approaches zero. Practitioners should be aware that peak inspiratory pressures in decelerating-flow may not be substantially higher than plateau pressures.
| S-EPMC8897219 | biostudies-literature
Project description:ObjectivesLung- and diaphragm-protective ventilation is a novel concept that aims to limit the detrimental effects of mechanical ventilation on the diaphragm while remaining within limits of lung-protective ventilation. The premise is that low breathing effort under mechanical ventilation causes diaphragm atrophy, whereas excessive breathing effort induces diaphragm and lung injury. In a proof-of-concept study, we aimed to assess whether titration of inspiratory support based on diaphragm effort increases the time that patients have effort in a predefined "diaphragm-protective" range, without compromising lung-protective ventilation.DesignRandomized clinical trial.SettingMixed medical-surgical ICU in a tertiary academic hospital in the Netherlands.PatientsPatients (n = 40) with respiratory failure ventilated in a partially-supported mode.InterventionsIn the intervention group, inspiratory support was titrated hourly to obtain transdiaphragmatic pressure swings in the predefined "diaphragm-protective" range (3-12 cm H2O). The control group received standard-of-care.Measurements and main resultsTransdiaphragmatic pressure, transpulmonary pressure, and tidal volume were monitored continuously for 24 hours in both groups. In the intervention group, more breaths were within "diaphragm-protective" range compared with the control group (median 81%; interquartile range [64-86%] vs 35% [16-60%], respectively; p < 0.001). Dynamic transpulmonary pressures (20.5 ± 7.1 vs 18.5 ± 7.0 cm H2O; p = 0.321) and tidal volumes (7.56 ± 1.47 vs 7.54 ± 1.22 mL/kg; p = 0.961) were not different in the intervention and control group, respectively.ConclusionsTitration of inspiratory support based on patient breathing effort greatly increased the time that patients had diaphragm effort in the predefined "diaphragm-protective" range without compromising tidal volumes and transpulmonary pressures. This study provides a strong rationale for further studies powered on patient-centered outcomes.
| S-EPMC8797006 | biostudies-literature
Project description:BackgroundThe driving pressure of the respiratory system is a valuable indicator of global lung stress during passive mechanical ventilation. Monitoring lung stress in assisted ventilation is indispensable, but achieving passive conditions in spontaneously breathing patients to measure driving pressure is challenging. The accuracy of the morphology of airway pressure (Paw) during end-inspiratory occlusion to assure passive conditions during pressure support ventilation has not been examined.MethodsRetrospective analysis of end-inspiratory occlusions obtained from critically ill patients during pressure support ventilation. Flow, airway, esophageal, gastric, and transdiaphragmatic pressures were analyzed. The rise of gastric pressure during occlusion with a constant/decreasing transdiaphragmatic pressure was used to identify and quantify the expiratory muscle activity. The Paw during occlusion was classified in three patterns, based on the differences at three pre-defined points after occlusion (0.3, 1, and 2 s): a "passive-like" decrease followed by plateau, a pattern with "clear plateau," and an "irregular rise" pattern, which included all cases of late or continuous increase, with or without plateau.ResultsData from 40 patients and 227 occlusions were analyzed. Expiratory muscle activity during occlusion was identified in 79% of occlusions, and at all levels of assist. After classifying occlusions according to Paw pattern, expiratory muscle activity was identified in 52%, 67%, and 100% of cases of Paw of passive-like, clear plateau, or irregular rise pattern, respectively. The driving pressure was evaluated in the 133 occlusions having a passive-like or clear plateau pattern in Paw. An increase in gastric pressure was present in 46%, 62%, and 64% of cases at 0.3, 1, and 2 s, respectively, and it was greater than 2 cmH2O, in 10%, 20%, and 15% of cases at 0.3, 1, and 2 s, respectively.ConclusionsThe pattern of Paw during an end-inspiratory occlusion in pressure support cannot assure the absence of expiratory muscle activity and accurate measurement of driving pressure. Yet, because driving pressure can only be overestimated due to expiratory muscle contraction, in everyday practice, a low driving pressure indicates an absence of global lung over-stretch. A measurement of high driving pressure should prompt further diagnostic workup, such as a measurement of esophageal pressure.
| S-EPMC7385937 | biostudies-literature