Changes In End-expiratory Lung Volume Research Articles

Capnodynamic end-expiratory lung volume assessment in anesthetized healthy children.

Capnodynamic lung function monitoring generates variables that may be useful for pediatric perioperative ventilation. Establish normal values for end-expiratory lung volume CO2 in healthy children undergoing anesthesia and to compare these values to previously published values obtained with alternative end-expiratory lung volume methods. The secondary aim was to investigate the ability of end-expiratory lung volume CO2 to react to positive end-expiratory pressure-induced changes in end-expiratory lung volume. In addition, normal values for associated volumetric capnography lung function variables were examined. Fifteen pediatric patients with healthy lungs (median age 8 months, range 1-36 months) undergoing general anesthesia were examined before start of surgery. Tested variables were recorded at baseline positive end-expiratory pressure 3 cmH2 O, 1 and 3 min after positive end-expiratory pressure 10 cmH2 O and 3 min after returning to baseline positive end-expiratory pressure 3 cmH2 O. Baseline end-expiratory lung volume CO2 was 32 mL kg-1 (95% CI 29-34 mL kg-1 ) which increased to 39 mL kg-1 (95% CI 35-43 mL kg-1 , p < .0001) and 37 mL kg-1 (95% CI 34-41 mL kg-1 , p = .0003) 1 and 3 min after positive end-expiratory pressure 10 cmH2 O, respectively. End-expiratory lung volume CO2 returned to baseline, 33 mL kg-1 (95% CI 29-37 mL kg-1 , p = .72) 3 min after re-establishing positive end-expiratory pressure 3 cmH2 O. Airway dead space increased from 1.1 mL kg-1 (95% CI 0.9-1.4 mL kg-1 ) to 1.4 (95% CI 1.1-1.8 mL kg-1 , p = .003) and 1.5 (95% CI 1.1-1.8 mL kg-1 , p < .0001) 1 and 3 min after positive end-expiratory pressure 10 cmH2 O, respectively, and 1.2 mL kg-1 (95% CI 0.9-1.4 mL kg-1 , p = .08) after 3 min of positive end-expiratory pressure 3 cmH2 O. Additional volumetric capnography and lung function variables showed no major changes in response to positive end-expiratory pressure variations. Capnodynamic noninvasive and continuous end-expiratory lung volume CO2 values assessed during anesthesia in children were in close agreement with previously reported end-expiratory lung volume values generated by alternative methods. Furthermore, positive end-expiratory pressure changes resulted in physiologically expected end-expiratory lung volume CO2 responses in a timely manner, suggesting that it can be used to trend end-expiratory lung volume changes during anesthesia.

Mechanical ventilation decreases tidal volume heterogeneity but increases heterogeneity in end-expiratory volumes.

How the heterogeneous distribution of lung volumes changes in response to different mechanical ventilation (MV) strategies is unclear. Using our well-developed four-dimensional computed tomography (4DCT) high-resolution imaging technique, we aimed to assess the effect of different MV strategies on the distribution and heterogeneity of regional lung volumes. Healthy adult female BALB/c mice received either 2 h of "injurious" MV [n = 6, mechanical ventilation at high PIP with zero PEEP (HPZP)] with a peak inspiratory pressure (PIP) of 20 cmH2O and zero positive end-expiratory pressure (PEEP), or 2 h of "protective" MV [n = 8, mechanical ventilation at low PIP with PEEP (LPP)] with PIP = 12 cmH2O and PEEP = 2 cmH2O. 4DCT images were obtained at baseline (0 h) and after 2 h of MV. Tidal volume (Vt) and end-expiratory lung volume (EEV) were measured throughout the whole lung on a voxel-by-voxel basis. Heterogeneity of ventilation was determined by the coefficient of variation (COV) of Vt and EEV. Our data showed that MV had minimal impact on global Vt but decreased EEV in the HPZP group (P < 0.05). Both ventilation modes decreased the COV of Vt (39.4% for HPZP and 9.7% for LPP) but increased the COV in EEV (36.4% for HPZP and 29.2% for LPP). This was consistent with the redistribution index, which was significantly higher in the HVZP group than in the LPP group (P < 0.001). We concluded that regional assessment of the change in EEV showed different patterns in progression between LPP and HPZP strategies. Both ventilation strategies decreased heterogeneity in Vt after 2 h of MV but increased heterogeneity in EEV. Further work is required to determine the link between these effects and ventilator-induced lung injury.NEW & NOTEWORTHY Tidal volume heterogeneity decreases over time in response to mechanical ventilation, in contrast to end-expiratory volume heterogeneity which increases.

Effect of modified high-flow oxygen therapy on positive end-expiratory pressure and end-expiratory lung volume based on simulated lung platform

ObjectiveThe aim of this study was to assess the effect of modified high-flow oxygen therapy on end-expiratory lung volume (EELV) and positive end-expiratory pressure (PEEP) in tracheotomized patients with normal pulmonary, acute hypoxic respiratory failure (AHRF) or chronic obstructive pulmonary disease (COPD). MethodsA ventilator and an artificial lung model were used to simulate the normal or strong inspiratory effort state of normal lung, AHRF and COPD patients. The traditional high-flow respiratory humidification therapy device connected with a standard interface (group A), and the modified therapy device added two types of resistance valves (group B, inner diameter 7.7 mm, length 24.0 mm; group C, inner diameter 7.7 mm, length 34.0 mm) to the exhalation end of the standard interface. The changes of end-expiratory lung volume (ΔEELV) and PEEP with the increase of flow rate (10 L/min, 20 L/min, 30 L/min, 40 L/min, 50 L/min, 60 L/min) in the three groups was recorded. ResultsUnder simulated conditions of normal lung, AHRF and COPD, as the flow rate increased by using the modified therapy device, the PEEP values in all groups showed an exponential increasing trend, and the ΔEELV also increased accordingly. In addition, under the same flow rate level, the PEEP values of the two modified high-flow oxygen therapies (Group B and Group C) were significantly higher than those of the standard high-flow oxygen therapy (Group A) (p < 0.05). In the normal lung model with normal or strong inspiratory effort, and in the AHRF or COPD model with strong inspiratory effort, when the flow rate was higher than 30 L/min, the PEEP levels of Group B were significantly lower than those of Group C (p < 0.05). In the AHRF model with normal inspiratory effort, when the flow rate was between 10 L/min and 60 L/min, the PEEP levels of Group B were significantly lower than those of Group C (p < 0.05). Moreover, in the COPD model with normal inspiratory effort, the PEEP levels of Group B were significantly lower than that of Group C only when the flow rate was 60 L/min (p < 0.05). ConclusionThe addition of different types of resistance valves to the high-flow exhalation end may be a feasible solution to improve the clinical efficacy of tracheotomized high-flow oxygen therapy.

Comparison of the effects of open and closed aspiration on end-expiratory lung volume in acute respiratory distress syndrome.

Alveoli tend to collapse in patients with acute respiratory distress syndrome (ARDS). Endotracheal aspiration may increase alveolar collapse due to the loss of end-expiratory lung volume (EELV). We aimed to compare the loss of EELV after open and closed suction in patients with ARDS. This randomized crossover study included 20 patients receiving invasive mechanical ventilation for ARDS. Open and closed suction were applied in a random order. Lung impedance was measured using electric impedance tomography. The change in end-expiratory lung impedance end of suction and at 1, 10, 20, and 30 min after suction, was used to represent the change in EELV. Arterial blood gas analyses and ventilatory parameters such as the plateau pressure (Pplat), driving pressure (Pdrive), and compliance of the respiratory system (CRS) were also recorded. Less volume loss was noted after closed suction than after open suction (mean ΔEELI: -2661 ± 1937 vs. -4415 ± 2363; mean difference: -1753; 95% CI [-2662, -844]; P = 0.001). EELI returned to baseline 10 min after closed suction but did not return to baseline even 30 min after open suction. After closed suction, the Pplat and Pdrive decreased while the CRS increased. Conversely, the Pplat and Pdrive increased while the CRS decreased after open suction. Endotracheal aspiration may result in alveolar collapse due to loss of EELV. Given that closed suction is associated with less volume loss at end-expiration without worsening ventilatory parameters, it should be chosen over open suction in patients with ARDS.

Lack of Association between Diaphragm Thickening Fraction and Transdiaphragmatic Pressure Swing in COVID-19 Pneumonia during Helmet Continuous Positive Airway Pressure: Research Letter.

Recently, evaluation of the diaphragm by means of ultrasound has become popular.1 The increase in diaphragm thickness during inspiration (thickening fraction) has been proposed as a noninvasive bedside measure of diaphragm function,2,3 although previous studies have reported wide variability between thickening, inspiratory effort, and transdiaphragmatic pressure.4–6 We hypothesized that the force-length and force-generating relationship in the diaphragm is altered by different positive end-expiratory pressure (PEEP) levels in patients with SARS-CoV-2.7We investigated the relationship between diaphragm thickening fraction and transdiaphragmatic pressure swing during noninvasive helmet continuous positive airway pressure. From March to December 2021, a total of 26 consecutive patients with laboratory-confirmed SARS-CoV-2 infection admitted to the intensive care unit of Santa Chiara Hospital (Trento, Italy) were prospectively enrolled. The study was approved by the ethics committee (Rep. Int. 282/2022), and written informed consent was obtained. At intensive care unit admission, according to the local protocol, noninvasive respiratory assistance with helmet continuous positive airway pressure was started, and a nasogastric tube provided with two balloons for registering the esophageal and gastric pressures was inserted.8 Intragastric positioning of the tube was checked with standard methods; both balloons were inflated with manufacturer- recommended volume. Intragastric position of the lower balloon was confirmed by positive pressure deflections during gentle abdominal compressions; the mid-lower third esophageal position of the proximal balloon was confirmed by inspiratory negative deflections and the presence of cardiac artifacts. In vivo calibration of the filling volume was performed. Patients underwent a trial with three increasing levels of PEEP, lasting 30 min each. The first level was set at 0 cm H2O. PEEP was then increased to 5 and 10 cm H2O; fractional expired oxygen tension was left unchanged. An average of three measurements was made, with careful attention to select the same breaths for the diaphragm ultrasound and for esophageal/gastric pressure measurements. During the last 5 min of each step, esophageal and transdiaphragmatic pressure swing and diaphragmatic ultrasound were recorded. The right hemidiaphragm was identified in the zone of apposition as a three-layered structure by B-mode ultrasonography, with the probe at the mid-axillary line at the 10th intercostal space.1 Thickness was measured from frozen M-mode images as the distance from the pleural to the peritoneal line. All the examinations were performed by the same expert physician and recorded for a subsequent offline analysis.The study population had a median age of 67.5 [62.3–72.5 interquartile range] yr, 16 (61.5%) were male, body mass index was 27 [24–33 interquartile range] kg/m2, and Pao2/fractional expired oxygen tension ratio and Paco2 at admission were 122 [103–139 interquartile range] and 39 [37–44 interquartile range] mmHg, respectively. No association was found between diaphragm thickening fraction and transdiaphragmatic pressure swings or esophageal pressure swings, at 0 cm H2O, 5 cm H2O, and 10 cm H2O (fig. 1).In a previous investigation, Steinberg et al.9 found that neither thickening fraction nor diaphragmatic excursion was able to estimate esophageal pressure swings in patients with SARS-CoV-2. We sought to extend these findings by investigating the relationship between diaphragm ultrasound and the transdiaphragmatic pressure swing, which should be more representative of the contribution of the diaphragm to the total inspiratory effort. Similar to other authors,4 we confirm the lack of association between diaphragm thickening and the transdiaphragmatic pressure. Despite that it may lie on the nonlinear pressure–volume relationship of the diaphragm, during a single breath, the diaphragm inspiratory thickening and the transdiaphragmatic pressure generated depend on the specific pattern of thoracoabdominal motion (i.e., a descent of the diaphragm rather than expansion of the rib cage). The application of PEEP also causes changes in the diaphragm geometry also modifying the force generated by the diaphragm that may not be uniform across the muscle.The different position of the diaphragm muscle over its force or length relationship is likely explained by changes in end-expiratory lung volume during the PEEP trial. Although not directly measured, diaphragm dysfunction can also be a contributing factor; COVID-19 is associated with a viral myositis,10 which might have affected diaphragm force-generating capacity.However, the impact of the small sample size on any statistical inference must be considered, and the lack of Gilbert index and pressure-time product of diaphragmatic pressure calculation reduces the interpretation of our results.In summary, despite being promising for its feasibility and noninvasive characteristics, the assessment of diaphragm thickening should not be used as a surrogate for inspiratory effort. In SARS-CoV-2 patients during helmet continuous positive airway pressure in the acute setting, an increase in inspiratory effort, as measured by transdiaphragmatic pressure swings, is not related to diaphragm thickening fraction. We suggest caution against using this tool to inform clinical choices about respiratory support, at least until more robust data will be available.Support was provided solely from institutional and/or departmental sources.The authors declare no competing interests.

Effect of prone positioning on end-expiratory lung volume, strain and oxygenation change over time in COVID-19 acute respiratory distress syndrome: A prospective physiological study.

Prone position (PP) is a recommended intervention in severe classical acute respiratory distress syndrome (ARDS). Changes in lung resting volume, respiratory mechanics and gas exchange during a 16-h cycle of PP in COVID-19 ARDS has not been yet elucidated. Patients with severe COVID-19 ARDS were enrolled between May and September 2021 in a prospective cohort study in a University Teaching Hospital. Lung resting volume was quantitatively assessed by multiple breath nitrogen wash-in/wash-out technique to measure the end-expiratory lung volume (EELV). Timepoints included the following: Baseline, Supine Position (S1); start of PP (P0), and every 4-h (P4; P8; P12) until the end of PP (P16); and Supine Position (S2). Respiratory mechanics and gas exchange were assessed at each timepoint. 40 mechanically ventilated patients were included. EELV/predicted body weight (PBW) increased significantly over time. The highest increase was observed at P4. The highest absolute EELV/PBW values were observed at the end of the PP (P16 vs S1; median 33.5 ml/kg [InterQuartileRange, 28.2-38.7] vs 23.4 ml/kg [18.5-26.4], p < 0.001). Strain decreased immediately after PP and remained stable between P4 and P16. PaO2/FiO2 increased during PP reaching the highest level at P12 (P12 vs S1; 163 [138-217] vs 81 [65-97], p < 0.001). EELV/PBW, strain and PaO2/FiO2 decreased at S2 although EELV/PBW and PaO2/FiO2 were still significantly higher as compared to S1. Both absolute values over time and changes of strain and PaO2/FiO2 at P16 and S2 versus S1 were strongly associated with EELV/PBW levels. In severe COVID-19 ARDS, EELV steadily increased over a 16-h cycle of PP peaking at P16. Strain gradually decreased, and oxygenation improved over time. Changes in strain and oxygenation at the end of PP and back to SP were strongly associated with changes in EELV/PBW. Whether the change in EELV and oxygenation during PP may play a role on outcomes in COVID-ARDS deserves further investigation. [www.ClinicalTrials.gov], identifier [NCT04818164].

Inspiratory and end-expiratory effects of lung recruitment in the prone position on dorsal lung aeration - new physiological insights in a secondary analysis of a randomised controlled study in post-cardiac surgery patients.

Cardiac surgery produces dorso-basal atelectasis and ventilation/perfusion mismatch, associated with infection and prolonged intensive care. A postoperative lung volume recruitment manoeuvre to decrease the degree of atelectasis is routine. In patients with severe respiratory failure, prone positioning and recruitment manoeuvres may increase survival, oxygenation, or both. We compared the effects of lung recruitment in prone vs supine positions on dorsal inspiratory and end-expiratory lung aeration. In a prospective RCT, 30 post-cardiac surgery patients were randomly allocated to recruitment manoeuvres in the prone (n=15) or supine position (n=15). The primary endpoints were late dorsal inspiratory volume (arbitrary units [a.u.]) and left/right dorsal end-expiratory lung volume change (a.u.), prone vs supine after extubation, measured using electrical impedance tomography. Secondary outcomes included left/right dorsal inspiratory volumes (a.u.) and left/right dorsal end-expiratory lung volume change (a.u.) after prone recruitment and extubation. The last part of dorsal end-inspiratory volume after extubation was higher after prone (49.1 a.u.; 95% confidence interval [CI], 37.4-60.6) vs supine recruitment (24.2 a.u.; 95% CI, 18.4-29.6; P=0.024). Improvement in left dorsal end-expiratory lung volume after extubation was higher after prone (382 a.u.; 95% CI, 261-502) vs supine recruitment (-71 a.u., 95% CI, -140 to -2; n=15; P<0.001). After prone recruitment, left vs right predominant end-expiratory dorsal lung volume change disappeared after extubation. However, both left and right end-expiratory volumes were higher in the prone group, after extubation. Recruitment in the prone position improves dorsal inspiratory and end-expiratory lung volumes after cardiac surgery. NCT03009331.

Gas distribution by EIT during PEEP inflation: PEEP response and optimal PEEP with lowest trans-pulmonary driving pressure can be determined without esophageal pressure during a rapid PEEP trial in patients with acute respiratory failure

Objective. Protective ventilation should be based on lung mechanics and transpulmonary driving pressure (ΔPTP), as this ‘hits’ the lung directly. Approach. The change in end-expiratory lung volume (ΔEELV) is determined by the size of the PEEP step and the elastic properties of the lung (EL), ΔEELV/ΔPEEP. Consequently, EL can be determined as ΔPEEP/ΔEELV. By calibration of tidal inspiratory impedance change with ventilator inspiratory tidal volume, end-expiratory lung impedance changes were converted to volume changes and lung P/V curves were obtained during a PEEP trial in ten patients with acute respiratory failure. The PEEP level where ΔPTP was lowest (optimal PEEP) was determined as the steepest point of the lung P/V curve. Main results. Over-all EL ranged between 7.0–23.2 cmH2O/L. Optimal PEEP was 12.9 cmH2O (10–16) with ΔPTP of 4.1 cmH2O (2.8–7.6). Patients with highest EL were PEEP non-responders, where EL increased in non-dependent and dependent lung at high PEEP, indicating over-distension in all lung. Patients with lower EL were PEEP responders with decreasing EL in dependent lung when increasing PEEP. Significance. PEEP non-responders could be identified by regional lung P/V curves derived from ventilator calibrated EIT. Optimal PEEP could be determined from the equation for the lung P/V curve.

Capnodynamic monitoring of lung volume and blood flow in response to increased positive end-expiratory pressure in moderate to severe COVID-19 pneumonia: an observational study

BackgroundThe optimal level of positive end-expiratory pressure (PEEP) during mechanical ventilation for COVID-19 pneumonia remains debated and should ideally be guided by responses in both lung volume and perfusion. Capnodynamic monitoring allows both end-expiratory lung volume ({text{EELV}}_{{{text{CO}}_{2} }}) and effective pulmonary blood flow (EPBF) to be determined at the bedside with ongoing ventilation.MethodsPatients with COVID-19-related moderate to severe respiratory failure underwent capnodynamic monitoring of {text{EELV}}_{{{text{CO}}_{2} }} and EPBF during a step increase in PEEP by 50% above the baseline (PEEPlow to PEEPhigh). The primary outcome was a > 20 mm Hg increase in arterial oxygen tension to inspired fraction of oxygen (P/F) ratio to define responders versus non-responders. Secondary outcomes included changes in physiological dead space and correlations with independently determined recruited lung volume and the recruitment-to-inflation ratio at an instantaneous, single breath decrease in PEEP. Mixed factor ANOVA for group mean differences and correlations by Pearson’s correlation coefficient are reported including their 95% confidence intervals.ResultsOf 27 patients studied, 15 responders increased the P/F ratio by 55 [24–86] mm Hg compared to 12 non-responders (p < 0.01) as PEEPlow (11 ± 2.7 cm H2O) was increased to PEEPhigh (18 ± 3.0 cm H2O). The {text{EELV}}_{{{text{CO}}_{2} }} was 461 [82–839] ml less in responders at PEEPlow (p = 0.02) but not statistically different between groups at PEEPhigh. Responders increased both {text{EELV}}_{{{text{CO}}_{2} }} and EPBF at PEEPhigh (r = 0.56 [0.18–0.83], p = 0.03). In contrast, non-responders demonstrated a negative correlation (r = − 0.65 [− 0.12 to − 0.89], p = 0.02) with increased lung volume associated with decreased pulmonary perfusion. Decreased (− 0.06 [− 0.02 to − 0.09] %, p < 0.01) dead space was observed in responders. The change in {text{EELV}}_{{{text{CO}}_{2} }} correlated with both the recruited lung volume (r = 0.85 [0.69–0.93], p < 0.01) and the recruitment-to-inflation ratio (r = 0.87 [0.74–0.94], p < 0.01).ConclusionsIn mechanically ventilated patients with moderate to severe COVID-19 respiratory failure, improved oxygenation in response to increased PEEP was associated with increased end-expiratory lung volume and pulmonary perfusion. The change in end-expiratory lung volume was positively correlated with the lung volume recruited and the recruitment-to-inflation ratio. This study demonstrates the feasibility of capnodynamic monitoring to assess physiological responses to PEEP at the bedside to facilitate an individualised setting of PEEP.Trial registration: NCT05082168 (18th October 2021).

Global and Regional Tidal Volume Distribution in Spontaneously Breathing Mechanically Ventilated Children.

Allowing the ventilated adult patient to breathe spontaneously may improve tidal volume (VT) distribution toward the dependent lung regions, reduce shunt fraction, and decrease dead space. It has not been studied if these effects under various levels of ventilatory support also occur in children. We sought to explore the effect of level of ventilatory support on VT distribution and end-expiratory lung volume (EELV) in spontaneously breathing ventilated children in the recovery phase of their acute respiratory failure. This is a secondary analysis of data from a prospective clinical trial comparing 2 different ventilator modes during weaning in mechanically ventilated children < 5 y: CPAP + pressure support ventilation (PSV) and pressure control (PC)/intermittent mandatory ventilation (IMV) + PSV with the mandatory breath rate set at 25% of baseline. Using electrical impedance tomography (EIT), we assessed VT distribution by calculating the center of ventilation. Polynomial functions of the second degree were plotted to evaluate regional lung filling characteristics. Changes in end-expiratory impedance were calculated to assess changes in EELV. Baseline measurements were compared with measurements during CPAP/PSV, PC/IMV + PSV, and during a downward titration of the level of pressure support. Thirty-five subjects with a median age 4.5 (2.1-12.9) months and a median ventilation time of 4.9 (3.3-6.9) d were studied. The overall median coefficient of variation was 50.1% and not different between CPAP/PSV or PC/synchronized IMV + PSV. Regional filling characteristics of the lung identified a homogeneous VT distribution under all study conditions. Downtapering of the level of PSV resulted in a significant shift of the coefficient of variation toward the dependent lung regions. Our data showed that allowing ventilated children in the recovery phase of respiratory failure to breathe spontaneously in a continuous spontaneous ventilation mode did not negatively affect VT distribution or EELV.

Prolonged Continuous Monitoring of Regional Lung Function in Infants with Respiratory Failure.

Rationale: Electrical impedance tomography (EIT) allows instantaneous and continuous visualization of regional ventilation and changes in end-expiratory lung volume at the bedside. There is particular interest in using EIT for monitoring in critically ill neonates and young children with respiratory failure. Previous studies have focused only on short-term monitoring in small populations. The feasibility and safety of prolonged monitoring with EIT in neonates and young children have not been demonstrated yet. Objectives: To evaluate the feasibility and safety of long-term EIT monitoring in a routine clinical setting and to describe changes in ventilation distribution and homogeneity over time and with positioning in a multicenter cohort of neonates and young children with respiratory failure. Methods: At four European University hospitals, we conducted an observational study (NCT02962505) on 200 patients with postmenstrual ages (PMA) between 25 weeks and 36 months, at risk for or suffering from respiratory failure. Continuous EIT data were obtained using a novel textile 32-electrode interface and recorded at 48 images/s for up to 72 hours. Clinicians were blinded to EIT images during the recording. EIT parameters and the effects of body position on ventilation distribution were analyzed offline. Results: The average duration of EIT measurements was 53 ± 20 hours. Skin contact impedance was sufficient to allow image reconstruction for valid ventilation analysis during a median of 92% (interquartile range, 77-98%) of examination time. EIT examinations were well tolerated, with minor skin irritations (temporary redness or imprint) occurring in 10% of patients and no moderate or severe adverse events. Higher ventilation amplitude was found in the dorsal and right lung areas when compared with the ventral and left regions, respectively. Prone positioning resulted in an increase in the ventilation-related EIT signal in the dorsal hemithorax, indicating increased ventilation of the dorsal lung areas. Lateral positioning led to a redistribution of ventilation toward the dependent lung in preterm infants and to the nondependent lung in patients with PMA > 37 weeks. Conclusions: EIT allows continuous long-term monitoring of regional lung function in neonates and young children for up to 72 hours with minimal adverse effects. Our study confirmed the presence of posture-dependent changes in ventilation distribution and their dependency on PMA in a large patient cohort. Clinical trial registered with www.clinicaltrials.gov (NCT02962505).

Control of the expiratory flow in a lung model and in healthy volunteers with an adjustable flow regulator: a combined bench and randomized crossover study

BackgroundPursed-lips breathing (PLB) is a technique to attenuate small airway collapse by regulating the expiratory flow. During mandatory ventilation, flow-controlled expiration (FLEX), which mimics the expiratory flow course of PLB utilizing a digital system for measurement and control, was shown to exert lung protective effects. However, PLB requires a patient’s participation and coordinated muscular effort and FLEX requires a complex technical setup. Here, we present an adjustable flow regulator to mimic PLB and FLEX, respectively, without the need of a patient’s participation, or a complex technical device.MethodsOur study consisted of two parts: First, in a lung model which was ventilated with standard settings (tidal volume 500 ml, respiratory rate 12 min−1, positive end-expiratory pressure (PEEP) 5 cmH2O), the possible reduction of the maximal expiratory flow by utilizing the flow regulator was assessed. Second, with spontaneously breathing healthy volunteers, the short-term effects of medium and strong expiratory flow reduction on airway pressure, the change of end-expiratory lung volume (EELV), and breathing discomfort was investigated.ResultsIn the lung model experiments, expiratory flow could be reduced from − 899 ± 9 ml·s−1 down to − 328 ± 25 ml·s−1. Thereby, inspiratory variables and PEEP were unaffected. In the volunteers, the maximal expiratory flow of − 574 ± 131 ml·s−1 under baseline conditions was reduced to − 395 ± 71 ml·s−1 for medium flow regulation and to − 266 ± 58 ml·s−1 for strong flow regulation, respectively (p < 0.001). Accordingly, mean airway pressure increased from 0.6 ± 0.1 cmH2O to 2.9 ± 0.4 cmH2O with medium flow regulation and to 5.4 ± 2.4 cmH2O with strong flow regulation, respectively (p < 0.001). The EELV increased from baseline by 31 ± 458 ml for medium flow regulation and 320 ± 681 ml for strong flow regulation (p = 0.033). The participants rated breathing with the flow regulator as moderately uncomfortable, but none rated breathing with the flow regulator as intolerable.ConclusionsThe flow regulator represents an adjustable device for application of a self-regulated expiratory resistive load, representing an alternative for PLB and FLEX. Future applications in spontaneously breathing patients and patients with mandatory ventilation alike may reveal potential benefits.Trial registration: DRKS00015296, registered on 20th August, 2018; URL: https://www.drks.de/drks_web/setLocale_EN.do.

End-Expiratory Lung Volumes During Spontaneous Breathing Trials in Tracheostomized Subjects on Prolonged Mechanical Ventilation.

The role of end-expiratory lung volume (EELV) during a spontaneous breathing trial (SBT) in patients who were tracheostomized and on prolonged mechanical ventilation is unclear. This study aimed to assess EELV during a 60-min SBT and its correlation with weaning success. Enrolled subjects admitted to a weaning unit were measured for EELV and relevant parameters before and after the SBT. Of the 44 enrolled subjects, 29 (66%) were successfully liberated, defined as not needing mechanical ventilation for 5 d. The success group had fewer subjects with chronic kidney disease (41% vs 73%, P = .044), stronger mean ± SD maximum inspiratory pressure (41.6 ± 10.4 vs 34.1 ± 7.1 cm H2O; P = .02) and mean ± SD maximum expiratory pressure (46.9 ± 11.7 vs 35.3 ± 16.9 cm H2O; P = .01) versus the failure group. Toward the end of the SBT, the success group had a significant increase in the mean ± SD EELV (before vs after: 1,278 ± 744 vs 1,493 ± 867 mL; P = .040) and a decrease in the mean ± SD rapid shallow breathing index (83.8 ± 39.4 vs 66.3 ± 29.4; P = .02), whereas there were no significant changes in these 2 parameters in the failure group. The Cox regression analysis showed that, at the beginning of SBT, a greater difference between EELV with a PEEP of 0 cm H2O and with a PEEP of 5 cm H2O was significantly correlated to a higher likelihood of weaning success. Toward the end of the SBT, a greater EELV level at a PEEP of 0 cm H2O was also correlated with weaning success. Also, the greater difference of EELV at a PEEP of 0 cm H2O between the beginning and the end of the SBT was also correlated with a shorter duration to weaning success. The change in EELV during a 60-min SBT may be of prognostic value for liberation from prolonged mechanical ventilation in patients who had a tracheostomy. Our findings suggest a model to understand the underlying mechanism of failure of liberation from mechanical ventilation in these patients.

Extubation generates lung volume inhomogeneity in preterm infants

ObjectiveTo evaluate the feasibility of electrical impedance tomography (EIT) to describe the regional tidal ventilation (VT) and change in end-expiratory lung volume (EELV) patterns in preterm infants during the process...

Normal saline and lung recruitment with paediatric endotracheal suction (NARES): A pilot, factorial, randomised controlled trial

Background/objectiveEndotracheal suction is one of the most common and harmful procuedres performed on mechanically ventilated children. The aim of the study was to establish the feasibility of a randomised controlled trial (RCT) examining the effectiveness of normal saline instillation (NSI) and a positive end-expiratory pressure recruitment manoeuvre (RM) with endotracheal suction in the paediatric intensive care unit. MethodsPilot 2 × 2 factorial RCT.The study was conducted at a 36-bed tertiary paediatric intensive care unit in Australia.Fifty-eight children aged less than 16 years undergoing tracheal intubation and invasive mechanical ventilation.(i) NSI or no NSI and (ii) RM or no RM with endotracheal suction . The primary outcome was feasibility; secondary outcomes were ventilator-associated pneumonia (VAP), change in end-expiratory lung volume assessed by electrical impedance tomography, dynamic compliance, and oxygen saturation-to-fraction of inspired oxygen (SpO2/FiO2) ratio. Results/FindingsRecruitment, retention, and missing data feasibility criteria were achieved. Eligibility and protocol adherence criteria were not achieved, with 818 patients eligible and 58 enrolled; cardiac surgery was the primary reason for exclusion. Approximately 30% of patients had at least one episode of nonadherence. Children who received NSI had a reduced incidence of VAP; however, this did not reach statistical significance (incidence rate ratio = 0.12, 95% confidence interval = 0.01–1.10; p = 0.06). NSI was associated with a significantly reduced SpO2/FiO2 ratio up to 10 min after suction. RMs were not associated with a reduced VAP incidence (incidence rate ratio = 0.31, 95% confidence interval = 0.05–1.88), but did significantly improve end-expiratory lung volume at 2 and 5 min after suction, dynamic compliance, and SpO2/FiO2 ratio. ConclusionRMs provided short-term improvements in end-expiratory lung volume and oxygenation. NSI with suction led to a reduced incidence of VAP; however, a definitive RCT is needed to test statistical differences. A RCT of study interventions is worthwhile and may be feasible with protocol modifications including the widening of participant eligibility.

COMPARISON OF END-EXPIRATORY LUNG VOLUME MEASUREMENT BY ELECTRICAL IMPEDANCE TOMOGRAPHY AND NITROGEN WASHOUT METHOD IN PIGS

End-expiratory lung volume (EELV) can be determined using several methods that allow clinically accurate measurements, but it is difficult to apply these methods to the patient's bedside. Electrical impedance tomography (EIT) is offered as another method for measuring EELV. The aim of the study is to compare changes in EELV measured by nitrogen washout method with changes of EELV calculated from the change in end-expiratory lung impedance (EELI) measured by EIT and to determine whether changes in EELV calculated from changes in chest impedance can be used as one of the parameters for EIT data analysis and description. The prospective interventional animal study was performed on ten pigs. The animals received total intravenous anesthesia with muscle relaxation. Mechanical lung ventilation was conducted in the volume-controlled mode. 16-electrode EIT system was used for data acquisition. End-expiratory lung volume was measured by a modified nitrogen wash-in/wash-out technique developed by Olegard et al. The study protocol consisted of the baseline phase, two incremental PEEP steps, two decremental PEEP steps and from normal saline i. v. administration. For each animal, a reference frame (baseline frame) was selected from the initial baseline phase and was used for the reconstruction of EIT images and impedance waveforms. For each breath cycle, tidal variation image was calculated as a difference between the end-inspiratory and the previous end-expiratory EIT image. An equivalent end-expiratory volume change (ΔEELVequiv) was calculated from EELI. The values of ΔEELVequiv were compared with reference EELV data measured by a modified nitrogen wash-in/wash-out technique (ΔEELVmeas). The measured and the estimated changes in EELV were statistically compared and correlation between ΔEELVequiv and ΔEELVmeas was calculated. Statistically significant difference between ΔEELVequiv and ΔEELVmeas was observed only in administration of normal saline bolus. Pearson’s correlation coefficients were 0.29 for increase in PEEP, 0.45 for decrease in PEEP and -0.1 during administration of normal saline bolus. The study showed that during changes in PEEP in the porcine model, there was no linear relationship between ΔEELVequiv and ΔEELVmeas. Although there was no linear relationship between ΔEELVequiv and ΔEELVmeas with changes in PEEP, no statistically significant difference was demonstrated between these two methods, which justifies the use of ΔEELVequiv as a parameter suitable for description and evaluation of EIT data.

Lung Volume Measurement and Ventilation Distribution During Invasive Mechanical Ventilation.

Lung volume measurement performed during invasive mechanical ventilation can be used to determine functional residual capacity, changes in end-expiratory lung volume with the application of PEEP, and lung strain. However, many bedside measurements provide useful information without the use of specialized equipment. Ventilation distribution through the lung has traditionally been assessed with computed tomography, but more recently electrical impedance tomography has brought the ability to monitor this at the bedside, and without exposure to radiation. This review will describe techniques to measure lung volumes in the ICU and the relationship between lung strain, stress, and other measurements. This review will also discuss monitoring ventilation distribution at the bedside and the clinical assessment of regional compliance that this technology provides.

End-expiratory lung volume assessment using helium and carbon dioxide in an experimental model of pediatric capnoperitoneum.

Capnoperitoneum during laparoscopy leads to cranial shift of the diaphragm, loss in lung volume, and risk of impaired gas exchange. Infants are susceptible to these changes and bedside assessment of lung volume during laparoscopy might assist with optimizing the ventilation. Thus, the primary aim was to investigate the monitoring value of a continuous end-expiratory lung volume (EELV) assessment method based on CO2 dynamics ( ) in a pediatric capnoperitoneum model by evaluating the correlation and trending ability against helium washout (EELVHe ). Intra-abdominal pressure (IAP) was randomly varied between 0, 6, and 12mmHg with CO2 insufflation, while positive end-expiratory pressure (PEEP) levels of 3, 6, and 9cm H2 O were randomly applied in eight anesthetized and mechanically ventilated chinchilla rabbits. Concomitant and EELVHe and lung clearance index (LCI) were obtained under each experimental condition. Significant correlations were found between and EELVHe before capnoperitoneum (r=.85, P<.001), although increased IAP distorted this relationship. The negative influence of IAP was counteracted by the application of PEEP 9, which restored the correlation between and EELVHe and resulted in 100% concordance rate between the methods regarding changes in lung volume. EELVHe and LCI showed a curvilinear relationship, and an EELVHe of approximately 20mLkg-1 , determined with a receiver operating characteristic curve, was associated with near-normal LCI values. In this animal model of pediatric capnoperitoneum, reliable assessment of changes in EELV based on requires an open lung strategy, defined as EELV above approximately 20mLkg-1 .

Flow-controlled ventilation (FCV) improves regional ventilation in obese patients \u2013 a randomized controlled crossover trial

BackgroundIn obese patients, high closing capacity and low functional residual capacity increase the risk for expiratory alveolar collapse. Constant expiratory flow, as provided by the new flow-controlled ventilation (FCV) mode, was shown to improve lung recruitment. We hypothesized that lung aeration and respiratory mechanics improve in obese patients during FCV.MethodsWe compared FCV and volume-controlled (VCV) ventilation in 23 obese patients in a randomized crossover setting. Starting with baseline measurements, ventilation settings were kept identical except for the ventilation mode related differences (VCV: inspiration to expiration ratio 1:2 with passive expiration, FCV: inspiration to expiration ratio 1:1 with active, linearized expiration). Primary endpoint of the study was the change of end-expiratory lung volume compared to baseline ventilation. Secondary endpoints were the change of mean lung volume, respiratory mechanics and hemodynamic variables.ResultsThe loss of end-expiratory lung volume and mean lung volume compared to baseline was lower during FCV compared to VCV (end-expiratory lung volume: FCV, − 126 ± 207 ml; VCV, − 316 ± 254 ml; p < 0.001, mean lung volume: FCV, − 108.2 ± 198.6 ml; VCV, − 315.8 ± 252.1 ml; p < 0.001) and at comparable plateau pressure (baseline, 19.6 ± 3.7; VCV, 20.2 ± 3.4; FCV, 20.2 ± 3.8 cmH2O; p = 0.441), mean tracheal pressure was higher (baseline, 13.1 ± 1.1; VCV, 12.9 ± 1.2; FCV, 14.8 ± 2.2 cmH2O; p < 0.001). All other respiratory and hemodynamic variables were comparable between the ventilation modes.ConclusionsThis study demonstrates that, compared to VCV, FCV improves regional ventilation distribution of the lung at comparable PEEP, tidal volume, PPlat and ventilation frequency. The increase in end-expiratory lung volume during FCV was probably caused by the increased mean tracheal pressure which can be attributed to the linearized expiratory pressure decline.Trial registrationGerman Clinical Trials Register: DRKS00014925. Registered 12 July 2018.

Integrated EIT system for functional lung ventilation imaging

BackgroundElectrical impedance tomography (EIT) has been used for functional lung imaging of regional air distributions during mechanical ventilation in intensive care units (ICU). From numerous clinical and animal studies focusing on specific lung functions, a consensus about how to use the EIT technique has been formed lately. We present an integrated EIT system implementing the functions proposed in the consensus. The integrated EIT system could improve the usefulness when monitoring of mechanical ventilation for lung protection so that it could facilitate the clinical acceptance of this new technique.MethodsUsing a custom-designed 16-channel EIT system with 50 frames/s temporal resolution, the integrated EIT system software was developed to implement five functional images and six EIT measures that can be observed in real-time screen view and analysis screen view mode, respectively. We evaluated the performance of the integrated EIT system with ten mechanically ventilated porcine subjects in normal and disease models.ResultsQuantitative and simultaneous imaging of tidal volume (TV), end-expiratory lung volume change (triangleEELV), compliance, ventilation delay, and overdistension/collapse images were performed. Clinically useful parameters were successfully extracted including anterior/posterior ventilation ratio (A/P ratio), center of ventilation ({mathrm{CoV}}_{{x}}, {mathrm{CoV}}_{{y}}), global inhomogeneity (GI), coefficient of variation (CV), ventilation delay and percentile of overdistension/collapse. The integrated EIT system was demonstrated to suggest an optimal positive end-expiratory pressure (PEEP) for lung protective ventilation in normal and in the disease model of an acute injury. Optimal PEEP for normal and disease model was 2.3 and 7.9 , {mathrm{cmH}}_{2}mathrm{O}, respectively.ConclusionsThe proposed integrated approach for functional lung ventilation imaging could facilitate clinical acceptance of the bedside EIT imaging method in ICU. Future clinical studies of applying the proposed methods to human subjects are needed to show the clinical significance of the method for lung protective mechanical ventilation and mechanical ventilator weaning in ICU.