Transpulmonary pressure monitoring in critically ill patients: pros and cons.

The use of transpulmonary pressure monitoring based on measurement of esophageal pressure has contributed importantly to the personalization of mechanical ventilation based on respiratory pathophysiology in critically ill patients. However, esophageal pressure monitoring is still underused in the clinical practice. This technique allows partitioning of the respiratory mechanics between the lungs and the chest wall, provides information on lung recruitment and risk of barotrauma, and helps titrating mechanical ventilation settings in patients with respiratory failure. In assisted ventilation modes and during non-invasive respiratory support, esophageal pressure monitoring provides important information on the inspiratory effort and work of breathing. Nonetheless, several controversies persist on technical aspects, interpretation and clinical decision-making based on values derived from this monitoring technique. The aim of this review is to summarize the physiological bases of esophageal pressure monitoring, discussing the pros and cons of its clinical applications and different interpretations in critically ill patients undergoing invasive and non-invasive respiratory support.

Estimation of the transpulmonary pressure from the central venous pressure in mechanically ventilated patients.

Transpulmonary pressure (PL) calculation requires esophageal pressure (PES) as a surrogate of pleural pressure (Ppl), but its calibration is a cumbersome technique. Central venous pressure (CVP) swings may reflect tidal variations in Ppl and could be used instead of PES, but the interpretation of CVP waveforms could be difficult due to superposition of heartbeat-induced pressure changes. Thus, we developed a digital filter able to remove the cardiac noise to obtain a filtered CVP (f-CVP). The aim of the study was to evaluate the accuracy of CVP and filtered CVP swings (ΔCVP and Δf-CVP, respectively) in estimating esophageal respiratory swings (ΔPES) and compare PL calculated with CVP, f-CVP and PES; then we tested the diagnostic accuracy of the f-CVP method to identify unsafe high PL levels, defined as PL>10 cmH2O. Twenty patients with acute respiratory failure (defined as PaO2/FiO2 ratio below 200 mmHg) treated with invasive mechanical ventilation and monitored with an esophageal balloon and central venous catheter were enrolled prospectively. For each patient a recording session at baseline was performed, repeated if a modification in ventilatory settings occurred. PES, CVP and airway pressure during an end-inspiratory and -expiratory pause were simultaneously recorded; CVP, f-CVP and PES waveforms were analyzed off-line and used to calculate transpulmonary pressure (PLCVP, PLf-CVP, PLPES, respectively). Δf-CVP correlated better than ΔCVP with ΔPES (r = 0.8, p = 0.001 vs. r = 0.08, p = 0.73), with a lower bias in Bland Altman analysis in favor of PLf-CVP (mean bias - 0.16, Limits of Agreement (LoA) -1.31, 0.98 cmH2O vs. mean bias - 0.79, LoA - 3.14, 1.55 cmH2O). Both PLf-CVP and PLCVP correlated well with PLPES (r = 0.98, p < 0.001 vs. r = 0.94, p < 0.001), again with a lower bias in Bland Altman analysis in favor of PLf-CVP (0.15, LoA - 0.95, 1.26 cmH2O vs. 0.80, LoA - 1.51, 3.12, cmH2O). PLf-CVP discriminated high PL value with an area under the receiver operating characteristic curve 0.99 (standard deviation, SD, 0.02) (AUC difference = 0.01 [-0.024; 0.05], p = 0.48). In mechanically ventilated patients with acute respiratory failure, the digital filtered CVP estimated ΔPES and PL obtained from digital filtered CVP represented a reliable value of standard PL measured with the esophageal method and could identify patients with non-protective ventilation settings.

Differential Effects of Intra-Abdominal Hypertension and ARDS on Respiratory Mechanics in a Porcine Model.

Background and Objectives: Intra-abdominal hypertension (IAH) and acute respiratory distress syndrome (ARDS) are common concerns in intensive care unit patients with acute respiratory failure (ARF). Although both conditions lead to impairment of global respiratory parameters, their underlying mechanisms differ substantially. Therefore, a separate assessment of the different respiratory compartments should reveal differences in respiratory mechanics. Materials and Methods: We prospectively investigated alterations in lung and chest wall mechanics in 18 mechanically ventilated pigs exposed to varying levels of intra-abdominal pressures (IAP) and ARDS. The animals were divided into three groups: group A (IAP 10 mmHg, no ARDS), B (IAP 20 mmHg, no ARDS), and C (IAP 10 mmHg, with ARDS). Following induction of IAP (by inflating an intra-abdominal balloon) and ARDS (by saline lung lavage and injurious ventilation), respiratory mechanics were monitored for six hours. Statistical analysis was performed using one-way ANOVA to compare the alterations within each group. Results: After six hours of ventilation, end-expiratory lung volume (EELV) decreased across all groups, while airway and thoracic pressures increased. Significant differences were noted between group (B) and (C) regarding alterations in transpulmonary pressure (TPP) (2.7 ± 0.6 vs. 11.3 ± 2.1 cmH2O, p < 0.001), elastance of the lung (EL) (8.9 ± 1.9 vs. 29.9 ± 5.9 cmH2O/mL, p = 0.003), and elastance of the chest wall (ECW) (32.8 ± 3.2 vs. 4.4 ± 1.8 cmH2O/mL, p < 0.001). However, global respiratory parameters such as EELV/kg bodyweight (-6.1 ± 1.3 vs. -11.0 ± 2.5 mL/kg), driving pressure (12.5 ± 0.9 vs. 13.2 ± 2.3 cmH2O), and compliance of the respiratory system (-21.7 ± 2.8 vs. -19.5 ± 3.4 mL/cmH2O) did not show significant differences among the groups. Conclusions: Separate measurements of lung and chest wall mechanics in pigs with IAH or ARDS reveals significant differences in TPP, EL, and ECW, whereas global respiratory parameters do not differ significantly. Therefore, assessing the compartments of the respiratory system separately could aid in identifying the underlying cause of ARF.

Physiological effects of lung-protective ventilation in patients with lung fibrosis and usual interstitial pneumonia pattern versus primary ARDS: a matched-control study.

BACKGROUND: Although patients with interstitial pneumonia pattern (ILD-UIP) and acute exacerbation (AE) leading to severe acute respiratory failure may require invasive mechanical ventilation (MV), physiological data on lung mechanics during MV are lacking. We aimed at describing the physiological effect of lung-protective ventilation in patients with AE-ILD-UIP compared with primary ARDS. METHODS: Partitioned lung and chest wall mechanics were assessed in a series of AE-ILD-UIP patients matched 1:1 with primary ARDS as controls (based on BMI and PaO2/FiO2 ratio). Three PEEP levels (zero = ZEEP, 4-8 cmH2O = PEEPLOW, and titrated to achieve positive end-expiratory transpulmonary pressure PL,EE = PEEPTITRATED) were used for measurements. RESULTS: Ten AE-ILD-UIP patients and 10 matched ARDS were included. In AE-ILD-UIP median PL,EE at ZEEP was - 4.3 [- 7.6- - 2.3] cmH2O and lung elastance (EL) 44 [40-51] cmH2O/L. At PEEPLOW, PL,EE remained negative and EL did not change (p = 0.995) versus ZEEP. At PEEPTITRATED, PL,EE increased to 0.8 [0.3-1.5] cmH2O and EL to 49 [43-59] (p = 0.004 and p < 0.001 compared to ZEEP and PEEPLOW, respectively). ΔPL decreased at PEEPLOW (p = 0.018) and increased at PEEPTITRATED (p = 0.003). In matched ARDS control PEEP titration to obtain a positive PL,EE did not result in significant changes in EL and ΔPL. CONCLUSIONS: In mechanically ventilated AE-ILD-UIP patients, differently than in patients with primary ARDS, PEEP titrated to obtain a positive PL,EE significantly worsened lung mechanics.

Neurological and respiratory effects of lung protective ventilation in acute brain injury patients without lung injury: brain vent, a single centre randomized interventional study.

INTRODUCTION: Lung protective ventilation (LPV) comprising low tidal volume (VT) and high positive end-expiratory pressure (PEEP) may compromise cerebral perfusion in acute brain injury (ABI). In patients with ABI, we investigated whether LPV is associated with increased intracranial pressure (ICP) and/or deranged cerebral autoregulation (CA), brain compensatory reserve and oxygenation. METHODS: In a prospective, crossover study, 30 intubated ABI patients with normal ICP and no lung injury were randomly assigned to receive low VT [6 ml/kg/predicted (pbw)]/at either low (5 cmH2O) or high PEEP (12 cmH2O). Between each intervention, baseline ventilation (VT 9 ml/kg/pbw and PEEP 5 cmH2O) were resumed. The safety limit for interruption of the intervention was ICP above 22 mmHg for more than 5 min. Airway and transpulmonary pressures were continuously monitored to assess respiratory mechanics. We recorded ICP by using external ventricular drainage or a parenchymal probe. CA and brain compensatory reserve were derived from ICP waveform analysis. RESULTS: We included 27 patients (intracerebral haemorrhage, traumatic brain injury, subarachnoid haemorrhage), of whom 6 reached the safety limit, which required interruption of at least one intervention. For those without intervention interruption, the ICP change from baseline to "low VT/low PEEP" and "low VT/high PEEP" were 2.2 mmHg and 2.3 mmHg, respectively, and considered clinically non-relevant. None of the interventions affected CA or oxygenation significantly. Interrupted events were associated with high baseline ICP (p < 0.001), low brain compensatory reserve (p < 0.01) and mechanical power (p < 0.05). The transpulmonary driving pressure was 5 ± 2 cmH2O in both interventions. Partial arterial pressure of carbon dioxide was kept in the range 34-36 mmHg by adjusting the respiratory rate, hence, changes in carbon dioxide were not associated with the increase in ICP. CONCLUSIONS: The present study found that most patients did not experience any adverse effects of LPV, neither on ICP nor CA. However, in almost a quarter of patients, the ICP rose above the safety limit for interrupting the interventions. Baseline ICP, brain compensatory reserve, and mechanical power can predict a potentially deleterious effect of LPV and can be used to personalize ventilator settings. Trial registration NCT03278769 . Registered September 12, 2017.

Effects of different positive end-expiratory pressure titration strategies during prone positioning in patients with acute respiratory distress syndrome: a prospective interventional study.

BACKGROUND: Prone positioning in combination with the application of low tidal volume and adequate positive end-expiratory pressure (PEEP) improves survival in patients with moderate to severe acute respiratory distress syndrome (ARDS). However, the effects of PEEP on end-expiratory transpulmonary pressure (Ptpexp) during prone positioning require clarification. For this purpose, the effects of three different PEEP titration strategies on Ptpexp, respiratory mechanics, mechanical power, gas exchange, and hemodynamics were evaluated comparing supine and prone positioning. METHODS: In forty consecutive patients with moderate to severe ARDS protective ventilation with PEEP titrated according to three different titration strategies was evaluated during supine and prone positioning: (A) ARDS Network recommendations (PEEPARDSNetwork), (B) the lowest static elastance of the respiratory system (PEEPEstat,RS), and (C) targeting a positive Ptpexp (PEEPPtpexp). The primary endpoint was to analyze whether Ptpexp differed significantly according to PEEP titration strategy during supine and prone positioning. RESULTS: Ptpexp increased progressively with prone positioning compared with supine positioning as well as with PEEPEstat,RS and PEEPPtpexp compared with PEEPARDSNetwork (positioning effect p < 0.001, PEEP strategy effect p < 0.001). PEEP was lower during prone positioning with PEEPEstat,RS and PEEPPtpexp (positioning effect p < 0.001, PEEP strategy effect p < 0.001). During supine positioning, mechanical power increased progressively with PEEPEstat,RS and PEEPPtpexp compared with PEEPARDSNetwork, and prone positioning attenuated this effect (positioning effect p < 0.001, PEEP strategy effect p < 0.001). Prone compared with supine positioning significantly improved oxygenation (positioning effect p < 0.001, PEEP strategy effect p < 0.001) while hemodynamics remained stable in both positions. CONCLUSIONS: Prone positioning increased transpulmonary pressures while improving oxygenation and hemodynamics in patients with moderate to severe ARDS when PEEP was titrated according to the ARDS Network lower PEEP table. This PEEP titration strategy minimized parameters associated with ventilator-induced lung injury induction, such as transpulmonary driving pressure and mechanical power. We propose that a lower PEEP strategy (PEEPARDSNetwork) in combination with prone positioning may be part of a lung protective ventilation strategy in patients with moderate to severe ARDS. TRIAL REGISTRATION: German Clinical Trials Register ( DRKS00017449 ). Registered June 27, 2019. https://www.drks.de/drks_web/navigate.do?navigationId=trial.HTML&TRIAL_ID=DRKS00017449.

Positive End-Expiratory Pressure, Pleural Pressure, and Regional Compliance during Pronation: An Experimental Study.

Rationale: The physiological basis of lung protection and the impact of positive end-expiratory pressure (PEEP) during pronation in acute respiratory distress syndrome are not fully elucidated. Objectives: To compare pleural pressure (Ppl) gradient, ventilation distribution, and regional compliance between dependent and nondependent lungs, and investigate the effect of PEEP during supination and pronation. Methods: We used a two-hit model of lung injury (saline lavage and high-volume ventilation) in 14 mechanically ventilated pigs and studied supine and prone positions. Global and regional lung mechanics including Ppl and distribution of ventilation (electrical impedance tomography) were analyzed across PEEP steps from 20 to 3 cm H2O. Two pigs underwent computed tomography scans: tidal recruitment and hyperinflation were calculated. Measurements and Main Results: Pronation improved oxygenation, increased Ppl, thus decreasing transpulmonary pressure for any PEEP, and reduced the dorsal-ventral pleural pressure gradient at PEEP < 10 cm H2O. The distribution of ventilation was homogenized between dependent and nondependent while prone and was less dependent on the PEEP level than while supine. The highest regional compliance was achieved at different PEEP levels in dependent and nondependent regions in supine position (15 and 8 cm H2O), but for similar values in prone position (13 and 12 cm H2O). Tidal recruitment was more evenly distributed (dependent and nondependent), hyperinflation lower, and lungs cephalocaudally longer in the prone position. Conclusions: In this lung injury model, pronation reduces the vertical pleural pressure gradient and homogenizes regional ventilation and compliance between the dependent and nondependent regions. Homogenization is much less dependent on the PEEP level in prone than in supine positon.

Assessment of different computing methods of inspiratory transpulmonary pressure in patients with multiple mechanical problems.

While plateau airway pressure alone is an unreliable estimate of lung overdistension inspiratory transpulmonary pressure (PL) is an important parameter to reflect it in patients with ARDS and there is no concensus about which computation method should be used to calculate it. Recent studies suggest that different formulas may lead to different tidal volume and PEEP settings. The aim of this study is to compare 3 different inspiratory PL measurement method; direct measurement (PLD), elastance derived (PLE) and release derived (PLR) methods in patients with multiple mechanical abnormalities. 34 patients were included in this prospective observational study. Measurements were obtained during volume controlled mechanical ventilation in sedated and paralyzed patients. During the study day airway and eosephageal pressures, flow, tidal volume were measured and elastance, inspiratory PLE, PLD and PLR were calculated. Mean age of the patients was 67 ± 15 years and APACHE II score was 27 ± 7. Most frequent diagnosis of the patients were pneumonia (71%), COPD exacerbation(56%), pleural effusion (55%) and heart failure(50%). Mean plateau pressure of the patients was 22 ± 5 cmH2O and mean respiratory system elastance was 36.7 ± 13 cmH2O/L. EL/ERS% was 0.75 ± 0.35%. Mean expiratory transpulmonary pressure was 0.54 ± 7.7 cmH2O (min: - 21, max: 12). Mean PLE (18 ± 9 H2O) was significantly higher than PLD (13 ± 9 cmH2O) and PLR methods (11 ± 9 cmH2O). There was a good aggreement and there was no bias between the measurements in Bland-Altman analysis. The estimated bias was similar between the PLD and PLE (- 3.12 ± 11 cmH2O) and PLE and PLR (3.9 ± 10.9 cmH2O) measurements. Our results suggest that standardization of calculation method of inspiratory PL is necessary before using it routinely to estimate alveolar overdistension.

Oesophageal balloon positioning by echocardiography to guide positive pressure ventilation.

Understanding the respiratory mechanics of ARDS patients is crucial to avoid ventilator-induced lung injury (VILI), and this is much more challenging if not only lung compliance is altered but the whole compliance of the respiratory system is abnormal, as in obese patients. We face this problem daily in the ICU, and to optimize ventilation, we estimate respiratory mechanics using an oesophageal balloon. The balloon position is crucial to assess reliable values. In the present technical note, we describe the use of echocardiography to confirm the correct position of this instrument.

Personalized mechanical ventilation in acute respiratory distress syndrome.

A personalized mechanical ventilation approach for patients with adult respiratory distress syndrome (ARDS) based on lung physiology and morphology, ARDS etiology, lung imaging, and biological phenotypes may improve ventilation practice and outcome. However, additional research is warranted before personalized mechanical ventilation strategies can be applied at the bedside. Ventilatory parameters should be titrated based on close monitoring of targeted physiologic variables and individualized goals. Although low tidal volume (VT) is a standard of care, further individualization of VT may necessitate the evaluation of lung volume reserve (e.g., inspiratory capacity). Low driving pressures provide a target for clinicians to adjust VT and possibly to optimize positive end-expiratory pressure (PEEP), while maintaining plateau pressures below safety thresholds. Esophageal pressure monitoring allows estimation of transpulmonary pressure, but its use requires technical skill and correct physiologic interpretation for clinical application at the bedside. Mechanical power considers ventilatory parameters as a whole in the optimization of ventilation setting, but further studies are necessary to assess its clinical relevance. The identification of recruitability in patients with ARDS is essential to titrate and individualize PEEP. To define gas-exchange targets for individual patients, clinicians should consider issues related to oxygen transport and dead space. In this review, we discuss the rationale for personalized approaches to mechanical ventilation for patients with ARDS, the role of lung imaging, phenotype identification, physiologically based individualized approaches to ventilation, and a future research agenda.

Early Inspiratory Effort Assessment by Esophageal Manometry Predicts Noninvasive Ventilation Outcome in De Novo Respiratory Failure. A Pilot Study.

Rationale: The role of inspiratory effort still has to be determined as a potential predictor of noninvasive mechanical ventilation (NIV) failure in acute hypoxic de novo respiratory failure.Objectives: To explore the hypothesis that inspiratory effort might be a major determinant of NIV failure in these patients.Methods: Thirty consecutive patients with acute hypoxic de novo respiratory failure admitted to a single center and candidates for a 24-hour NIV trial were enrolled. Clinical features, tidal change in esophageal pressure (ΔPes), tidal change in dynamic transpulmonary pressure (ΔPl), expiratory Vt, and respiratory rate were recorded on admission and 2-4 to 12-24 hours after NIV start and were tested for correlation with outcomes.Measurements and Main Results: ΔPes and ΔPes/ΔPl ratio were significantly lower 2 hours after NIV start in patients who successfully completed the NIV trial (n = 18) compared with those who needed endotracheal intubation (n = 12) (median [interquartile range], 11 [8-15] cm H2O vs. 31.5 [30-36] cm H2O; P < 0.0001), whereas other variables differed later. ΔPes was not related to other predictors of NIV failure at baseline. NIV-induced reduction in ΔPes of 10 cm H2O or more after 2 hours of treatment was strongly associated with avoidance of intubation and represented the most accurate predictor of treatment success (odds ratio, 15; 95% confidence interval, 2.8-110; P = 0.001 and area under the curve, 0.97; 95% confidence interval, 0.91-1; P < 0.0001).Conclusions: The magnitude of inspiratory effort relief as assessed by ΔPes variation within the first 2 hours of NIV was an early and accurate predictor of NIV outcome at 24 hours.Clinical trial registered with www.clinicaltrials.gov (NCT03826797).

Transpulmonary driving pressure during mechanical ventilation-validation of a non-invasive measurement method.

BACKGROUND: Transpulmonary driving pressure plays an important role in today's understanding of ventilator induced lung injury. We have previously validated a novel non-invasive method based on stepwise increments of PEEP to assess transpulmonary driving pressure in anaesthetised patients with healthy lungs. The aim of this study was to validate the method in patients who were mechanically ventilated for different diagnoses requiring intensive care. METHODS: We measured transpulmonary pressure (Ptp) and calculated transpulmonary driving pressure (ΔPtp) in 31 patients undergoing mechanical ventilation in an intensive care unit. Parallel triplicate measurements were performed with the PEEP step method (PtpPSM) and the conventional oesophageal balloon method (Ptpconv). Their agreement was compared using the intraclass correlation coefficient (ICC) and the Bland Altman plot. RESULT: The coefficient of variation for the repeated measurements was 4,3 for ΔPtpPSM and 9,2 for ΔPtpconv. The ICC of 0,864 and the Bland Altman plot indicate good agreement between the two methods. CONCLUSION: The non-invasive method can be applied in mechanically ventilated patients to measure transpulmonary driving pressure with good repeatability and accuracy comparable to the traditional oesophageal balloon method.

A novel method for transpulmonary pressure estimation using fluctuation of central venous pressure.

The objective of the study is to develop a correction method for estimating the change in pleural pressure (ΔPpl) and plateau transpulmonary pressure (PL) by using the change in central venous pressure (ΔCVP). Seven children (aged < 15 years) with acute respiratory failure (PaO2/FIO2 < 300 mmHg), who were paralyzed and mechanically ventilated with a PEEP of < 10 cmH2O and had central venous catheters and esophageal balloon catheters placed for clinical purposes, were enrolled prospectively. We compared change in esophageal pressure (ΔPes), ΔCVP, and ΔPpl calculated using a corrected ΔCVP (cΔCVP-derived ΔPpl). cΔCVP-derived ΔPpl was calculated as κ × ΔCVP, where κ was the ratio of the change in airway pressure (ΔPaw) to ΔCVP during the occlusion test. cΔCVP-derived ΔPpl correlated better than ΔCVP with ΔPes (R2 = 0.48, p = 0.08 vs. R2 = 0.14, p = 0.4) with lesser bias and precision in Bland-Altman analysis. The plateau PL calculated using the cΔCVP-derived ΔPpl (17.6 ± 2.6 cmH2O) correlated well with the ΔPes-derived plateau PL (18.1 ± 2.3 cmH2O) (R2 = 0.90, p = 0.001). Our correction method can estimate ΔPpl and plateau PL from ΔCVP with a reasonable accuracy in paralyzed and mechanically ventilated pediatric patients with respiratory failure.

Effect of transpulmonary pressure-guided positive end-expiratory pressure titration on lung injury in pigs with acute respiratory distress syndrome.

To investigate the effect of positive end-expiratory pressure (PEEP) guided by transpulmonary pressure or with maximum oxygenation-directed PEEP on lung injury in a porcine model of acute respiratory distress syndrome (ARDS). The porcine model of ARDS was induced in 12 standard pigs by intratracheal infusion with normal saline. The pigs were then randomly divided into two groups who were ventilated with the lung-protective strategy of low tidal volume (VT) (6 ml/kg), using different methods to titrate PEEP level: transpulmonary pressure (TP group; n = 6) or maximum oxygenation (MO group; n = 6). Gas exchange, pulmonary mechanics, and hemodynamics were determined and pulmonary inflammatory response indices were measured after 4 h of ventilation. The titrated PEEP level in the TP group (6.12 ± 0.89 cmH2O) was significantly lower than that in the MO group (11.33 ± 2.07 cmH2O) (P < 0.05). The PaO2/FiO2 (P/F) after PEEP titration both improved in the TP and MO groups as compared with that at T0 (when the criteria for ARDS were obtained). The P/F in the TP group did not differ significantly from that in the MO group during the 4 h of ventilation (P > 0.05). Respiratory system compliance and lung compliance were significantly improved in the TP group compared to the MO group (P < 0.05). The VD/VT in the TP group was significantly lower than that in the MO group after 4 h of ventilation (P < 0.05). Central venous pressure increased and the cardiac index decreased significantly in the MO group as compared with the TP group (P < 0.05), whereas oxygen delivery did not differ significantly between the groups (P > 0.05). The pulmonary vascular permeability index and the extravascular lung water index in the TP group were significantly lower than those in the MO group (P < 0.05). The TP group had a lower lung wet to dry weight ratio, lung injury score, and MPO, TNF-, and IL-8 concentrations than the MO group (P < 0.05). In summary, in a pig model of ARDS, ventilation with low VT and transpulmonary pressure-guided PEEP adjustment was associated with improved compliance, reduced dead space ventilation, increased cardiac output, and relieved lung injury, as compared to maximum oxygenation-guide PEEP adjustment.

Esophageal Manometry and Regional Transpulmonary Pressure in Lung Injury.

RATIONALE: Esophageal manometry is the clinically available method to estimate pleural pressure, thus enabling calculation of transpulmonary pressure (Pl). However, many concerns make it uncertain in which lung region esophageal manometry reflects local Pl. OBJECTIVES: To determine the accuracy of esophageal pressure (Pes) and in which regions esophageal manometry reflects pleural pressure (Ppl) and Pl; to assess whether lung stress in nondependent regions can be estimated at end-inspiration from Pl. METHODS: In lung-injured pigs (n = 6) and human cadavers (n = 3), Pes was measured across a range of positive end-expiratory pressure, together with directly measured Ppl in nondependent and dependent pleural regions. All measurements were obtained with minimal nonstressed volumes in the pleural sensors and esophageal balloons. Expiratory and inspiratory Pl was calculated by subtracting local Ppl or Pes from airway pressure; inspiratory Pl was also estimated by subtracting Ppl (calculated from chest wall and respiratory system elastance) from the airway plateau pressure. MEASUREMENTS AND MAIN RESULTS: In pigs and human cadavers, expiratory and inspiratory Pl using Pes closely reflected values in dependent to middle lung (adjacent to the esophagus). Inspiratory Pl estimated from elastance ratio reflected the directly measured nondependent values. CONCLUSIONS: These data support the use of esophageal manometry in acute respiratory distress syndrome. Assuming correct calibration, expiratory Pl derived from Pes reflects Pl in dependent to middle lung, where atelectasis usually predominates; inspiratory Pl estimated from elastance ratio may indicate the highest level of lung stress in nondependent "baby" lung, where it is vulnerable to ventilator-induced lung injury.

High-frequency oscillatory ventilation guided by transpulmonary pressure in acute respiratory syndrome: an experimental study in pigs.

BACKGROUND: Recent clinical studies have not shown an overall benefit of high-frequency oscillatory ventilation (HFOV), possibly due to injurious or non-individualized HFOV settings. We compared conventional HFOV (HFOVcon) settings with HFOV settings based on mean transpulmonary pressures (PLmean) in an animal model of experimental acute respiratory distress syndrome (ARDS). METHODS: ARDS was induced in eight pigs by intrabronchial installation of hydrochloric acid (0.1 N, pH 1.1; 2.5 ml/kg body weight). The animals were initially ventilated in volume-controlled mode with low tidal volumes (6 ml kg- 1) at three positive end-expiratory pressure (PEEP) levels (5, 10, 20 cmH2O) followed by HFOVcon and then HFOV PLmean each at PEEP 10 and 20. The continuous distending pressure (CDP) during HFOVcon was set at mean airway pressure plus 5 cmH2O. For HFOV PLmean it was set at mean PL plus 5 cmH2O. Baseline measurements were obtained before and after induction of ARDS under volume controlled ventilation with PEEP 5. The same measurements and computer tomography of the thorax were then performed under all ventilatory regimens at PEEP 10 and 20. RESULTS: Cardiac output, stroke volume, mean arterial pressure and intrathoracic blood volume index were significantly higher during HFOV PLmean than during HFOVcon at PEEP 20. Lung density, total lung volume, and normally and poorly aerated lung areas were significantly greater during HFOVcon, while there was less over-aerated lung tissue in HFOV PLmean. The groups did not differ in oxygenation or extravascular lung water index. CONCLUSION: HFOV PLmean is associated with less hemodynamic compromise and less pulmonary overdistension than HFOVcon. Despite the increase in non-ventilated lung areas, oxygenation improved with both regimens. An individualized approach with HFOV settings based on transpulmonary pressure could be a useful ventilatory strategy in patients with ARDS. Providing alveolar stabilization with HFOV while avoiding harmful distending pressures and pulmonary overdistension might be a key in the context of ventilator-induced lung injury.

Fifty Years of Research in ARDS. Respiratory Mechanics in Acute Respiratory Distress Syndrome.

Acute respiratory distress syndrome is a multifactorial lung injury that continues to be associated with high levels of morbidity and mortality. Mechanical ventilation, although lifesaving, is associated with new iatrogenic injury. Current best practice involves the use of small Vt, low plateau and driving pressures, and high levels of positive end-expiratory pressure. Collectively, these interventions are termed "lung-protective ventilation." Recent investigations suggest that individualized measurements of pulmonary mechanical variables rather than population-based ventilation prescriptions may be used to set the ventilator with the potential to improve outcomes beyond those achieved with standard lung protective ventilation. This review outlines the measurement and application of clinically applicable pulmonary mechanical concepts, such as plateau pressures, driving pressure, transpulmonary pressures, stress index, and measurement of strain. In addition, the concept of the "baby lung" and the utility of dynamic in addition to static measures of pulmonary mechanical variables are discussed.

Esophageal pressure balloon and transpulmonary pressure monitoring in airway pressure release ventilation: a different approach.

This is a case of Acute Respiratory Distress Syndrome managed using esophageal balloon catheter to adjust inspiratory pressure and positive end expiratory pressure according to the inspiratory and expiratory transpulmonary pressures. There are no studies that examine the transpulmonary pressures in airway pressure release ventilation (APRV). We aimed to test the feasibility of using the esophageal balloon in the nonconventional mode of APRV. All pressures were observed when switching the mode from a pressure-controlled mode to APRV using the same inspiratory pressure and using various incremental release times (TLow)to calculate the expiratory transpulmonary pressure. At all TLow levels the transpulmonary pressure at end exhalation was in the negative value indicating alveolar collapse. A larger study is needed to confirm our findings and to help guide setting APRV.

Cardiopulmonary exercise test predicts right heart catheterization.

BACKGROUND: Right heart catheterization (RHC) is usually required to confirm the diagnosis of pulmonary artery hypertension (PAH). As an invasive test, RHC may be associated with possible complications, so noninvasive parameters able to predict PAH at RHC would be extremely useful. AIM: To ascertain possible correlations between cardiopulmonary exercise testing (CPET) and hemodynamic parameters at RHC indicative of pulmonary hypertension (PH). METHODS: Thirty-six consecutive outpatients with suspect of PAH underwent CPET and RHC; the intercept of ventilation (VEint) on the VE vs carbon dioxide production (VE/VCO2 ) and VE/VCO2 slope at CPET and diastolic pressure gradient (DPG), trans-pulmonary pressure gradient (TPG), mean pulmonary artery pressure (mPAP) and pulmonary vascular resistance (PVR) at RHC were assessed and compared. RESULTS: Ventilation VCO2 slope was directly related to DPG (r: .41, P: .019), TPG (r: .45, P: .01), mean pulmonary arterial pressure (mPAP, r: .36, P: .031), PVR (r: .41, P: .029), VEint and VE/VCO2 slope inversely related to DPG (r: -.63, P < .001), TPG (r: -.67, P < .001), mPAP (r: -.68, P < .001) and PVR (r: -.5, P < .001). CONCLUSION: In patients with suspected PAH, VEint during exercise and the VE/VCO2 slope might provide useful information to predict results of RHC. Their correlations with PVR and with DPG may be helpful in discriminating patients with isolated postcapillary PH from those with combined postcapillary and precapillary.