Lung elastance and PEEP level with lowest transpulmonary driving pressure can be determined by a rapid PEEP step procedure without esophageal pressure measurements.
Lung elastance and PEEP level with lowest transpulmonary driving pressure can be determined by a rapid PEEP step procedure without esophageal pressure measurements.
Project description:Uncertainty remains about the best level of intraoperative positive end-expiratory pressure (PEEP). An ongoing RCT ('DESIGNATION') compares an 'individualized high PEEP' strategy ('iPEEP')-titrated to the lowest driving pressure (ΔP) with recruitment maneuvers (RM), with a 'standard low PEEP' strategy ('low PEEP')-using 5 cm H2O without RMs with respect to the incidence of postoperative pulmonary complications. This report is an interim analysis of safety and feasibility. From September 2018 to July 2022, we enrolled 743 patients. Data of 698 patients were available for this analysis. Hypotension occurred more often in 'iPEEP' vs. 'low PEEP' (54.7 vs. 44.1%; RR, 1.24 (95% CI 1.07 to 1.44); p < 0.01). Investigators were compliant with the study protocol 285/344 patients (82.8%) in 'iPEEP', and 345/354 patients (97.5%) in 'low PEEP' (p < 0.01). Most frequent protocol violation was missing the final RM at the end of anesthesia before extubation; PEEP titration was performed in 99.4 vs. 0%; PEEP was set correctly in 89.8 vs. 98.9%. Compared to 'low PEEP', the 'iPEEP' group was ventilated with higher PEEP (10.0 (8.0-12.0) vs. 5.0 (5.0-5.0) cm H2O; p < 0.01). Thus, in patients undergoing general anesthesia for open abdominal surgery, an individualized high PEEP ventilation strategy is associated with hypotension. The protocol is feasible and results in clear contrast in PEEP. DESIGNATION is expected to finish in late 2023.
Project description:Pneumothorax is a potentially fatal complication in patients with acute respiratory distress syndrome (ARDS), presenting challenges in determining the optimal positive end-expiratory pressure (PEEP) level to prevent atelectasis without exacerbating the pneumothorax. This case report describes the successful application of transpulmonary pressure and electrical impedance tomography (EIT) at the bedside to guide PEEP selection in a patient with ARDS complicated by pneumothorax due to methicillin-resistant Staphylococcus aureus infection. By using minimal PEEP to maintain positive end-expiratory transpulmonary pressure and visualizing lung reopening with EIT, the optimal PEEP level was reaffirmed, even if traditionally considered high. The patient's condition improved, and successful weaning from the ventilator was achieved, leading to a transfer out of the intensive care unit. Clinical trial registration: https://clinicaltrials.gov/show/NCT04081142, identifier NCT04081142.
Project description:BackgroundMechanical ventilation is applied to unload the respiratory muscles, but knowledge about transpulmonary driving pressure (ΔPL) is important to minimize lung injury. We propose a method to estimate ΔPL during neurally synchronized assisted ventilation, with a simple intervention of lowering the assist for one breath ("lower assist maneuver", LAM).MethodsIn 24 rabbits breathing spontaneously with imposed loads, titrations of increasing assist were performed, with two neurally synchronized modes: neurally adjusted ventilatory assist (NAVA) and neurally triggered pressure support (NPS). Two single LAM breaths (not sequentially, but independently) were performed at each level of assist by acutely setting the assist to zero cm H2O (NPS) or NAVA level 0 cm H2O/uV (NAVA) for one breath. NPS and NAVA titrations were followed by titrations in controlled-modes (volume control, VC and pressure control, PC), under neuro-muscular blockade. Breaths from the NAVA/NPS titrations were matched (for flow and volume) to VC or PC. Throughout all runs, we measured diaphragm electrical activity (Edi) and esophageal pressure (PES). We measured ΔPL during the spontaneous modes (PL_PES) and controlled mechanical ventilation (CMV) modes (PL_CMV) with the esophageal balloon. From the LAMs, we derived an estimation of ΔPL ("PL_LAM") using a correction factor (ratio of volume during the LAM and volume during assist) and compared it to measured ΔPL during passive (VC or PC) and spontaneous breathing (NAVA or NPS). A requirement for the LAM was similar Edi to the assisted breath.ResultsAll animals successfully underwent titrations and LAMs for NPS/NAVA. One thousand seven-hundred ninety-two (1792) breaths were matched to passive ventilation titrations (matched Vt, r = 0.99). PL_LAM demonstrated strong correlation with PL_CMV (r = 0.83), and PL_PES (r = 0.77). Bland-Altman analysis revealed little difference between the predicted PL_LAM and measured PL_CMV (Bias = 0.49 cm H2O and 1.96SD = 3.09 cm H2O). For PL_PES, the bias was 2.2 cm H2O and 1.96SD was 3.4 cm H2O. Analysis of Edi and PES at peak Edi showed progressively increasing uncoupling with increasing assist.ConclusionDuring synchronized mechanical ventilation, a LAM breath allows for estimations of transpulmonary driving pressure, without measuring PES, and follows a mathematical transfer function to describe respiratory muscle unloading during synchronized assist.
Project description:Transpulmonary pressure (PL) is computed as the difference between airway pressure and pleural pressure and separates the pressure delivered to the lung from the one acting on chest wall and abdomen. Pleural pressure is measured as esophageal pressure (PES) through dedicated catheters provided with esophageal balloons. We discuss the role of PL in assessing the effects of mechanical ventilation in patients with acute respiratory distress syndrome (ARDS). In the supine position, directly measured PL represents the pressure acting on the alveoli and airways. Because there is a pressure gradient in the pleural space from the non-dependent to the dependent zones, the pressure in the esophagus probably represents the pressure at a mid-level between sternal and vertebral regions. For this reason, it has been proposed to set the end-expiratory pressure in order to get a positive value of PL. This improves oxygenation and compliance. PL can also be estimated from airway pressure plateau and the ratio of lung to respiratory elastance (elastance-derived method). Some data suggest that this latter calculation may better estimate PL in the nondependent lung zones, at risk for hyperinflation. Elastance-derived PL at end-inspiration (PLend-insp) may be a good surrogate of end-inspiratory lung stress for the "baby lung", at least in non-obese patients. Limiting end-inspiratory PL to 20-25 cmH2O appears physiologically sound to mitigate ventilator-induced lung injury (VILI). Last, lung driving pressure (∆PL) reflects the tidal distending pressure. Changes in PL may also be assessed during assisted breathing to take into account the additive effects of spontaneous breathing and mechanical breaths on lung distension. In summary, despite limitations, assessment of PL allows a deeper understanding of the risk of VILI and may potentially help tailor ventilator settings.
Project description:BACKGROUND:Excessive respiratory muscle effort during mechanical ventilation may cause patient self-inflicted lung injury and load-induced diaphragm myotrauma, but there are no non-invasive methods to reliably detect elevated transpulmonary driving pressure and elevated respiratory muscle effort during assisted ventilation. We hypothesized that the swing in airway pressure generated by respiratory muscle effort under assisted ventilation when the airway is briefly occluded (ΔPocc) could be used as a highly feasible non-invasive technique to screen for these conditions. METHODS:Respiratory muscle pressure (Pmus), dynamic transpulmonary driving pressure (ΔPL,dyn, the difference between peak and end-expiratory transpulmonary pressure), and ΔPocc were measured daily in mechanically ventilated patients in two ICUs in Toronto, Canada. A conversion factor to predict ΔPL,dyn and Pmus from ΔPocc was derived and validated using cross-validation. External validity was assessed in an independent cohort (Nanjing, China). RESULTS:Fifty-two daily recordings were collected in 16 patients. In this sample, Pmus and ΔPL were frequently excessively high: Pmus exceeded 10 cm H2O on 84% of study days and ΔPL,dyn exceeded 15 cm H2O on 53% of study days. ΔPocc measurements accurately detected Pmus > 10 cm H2O (AUROC 0.92, 95% CI 0.83-0.97) and ΔPL,dyn > 15 cm H2O (AUROC 0.93, 95% CI 0.86-0.99). In the external validation cohort (n = 12), estimating Pmus and ΔPL,dyn from ΔPocc measurements detected excessively high Pmus and ΔPL,dyn with similar accuracy (AUROC ≥ 0.94). CONCLUSIONS:Measuring ΔPocc enables accurate non-invasive detection of elevated respiratory muscle pressure and transpulmonary driving pressure. Excessive respiratory effort and transpulmonary driving pressure may be frequent in spontaneously breathing ventilated patients.
Project description:BackgroundMechanical ventilation increases the risk of lung injury (VILI). Some authors propose that the way to reduce VILI is to find the threshold of driving pressure below which VILI is minimized. In this study, we propose a method to titrate the driving pressure to pulmonary elastance in an acute respiratory distress syndrome model using Young's modulus and its consequences on ventilatory-induced lung injury.Material and methods20 Wistar Han male rats were used. After generating an acute respiratory distress syndrome, two groups were studied: (a) standard protective mechanical ventilation: 10 rats received 150 min of mechanical ventilation with driving pressure = 14 cm H2O, tidal volume < 6 mL/kg) and (b) individualized mechanical ventilation: 10 rats received 150 min of mechanical ventilation with an individualized driving pressure according to their Young's modulus. In both groups, an individualized PEEP was programmed in the same manner. We analyzed the concentration of IL-6, TNF-α, and IL-1ß in BAL and the acute lung injury score in lung tissue postmortem.ResultsGlobal driving pressure was different between the groups (14 vs 11 cm H2O, p = 0.03). The individualized mechanical ventilation group had lower concentrations in bronchoalveolar lavage of IL-6 (270 pg/mL vs 155 pg/mL, p = 0.02), TNF-α (292 pg/mL vs 139 pg/mL, p < 0.01) and IL-1ß (563 pg/mL vs 131 pg/mL, p = 0.05). They presented lower proportion of lymphocytes (96% vs 79%, p = 0.05) as well as lower lung injury score (6.0 points vs 2.0 points, p = 0.02).ConclusionIn our model, individualization of DP to pulmonary elastance through Young's modulus decreases lung inflammation and structural lung injury without a significant impact on oxygenation.