Author: Maritza Henriques Rodrigues
Date of first publication: 11.10.2024
The authors' point? Transpulmonary driving pressure is equivalent to airway driving pressure in terms of predicting outcomes. Their findings support the importance of limiting lung and airway driving pressure, while also maintaining positive end-expiratory PL in obese patients.
What is the relative importance of global and partitioned respiratory mechanics in predicting outcomes in ARDS patients, with a specific focus on the superiority of transpulmonary driving pressure (∆PL) compared to airway driving pressure (∆Paw), and the potential enhancement of predictive power by the oxygenation stretch index?
Prospective, observational, multicenter study (
| Inclusion criteria | Age greater than 18 years Diagnosis of ARDS as per the Berlin definition Receiving assist/control ventilation with sedation Within the first week of intubation |
| Exclusion criteria | Known esophageal pathology Active upper gastrointestinal bleeding or other contraindications to gastric tube insertion Severe hemodynamic instability defined as: - An increase > 30% in vasopressors in the previous 6 hours - Norepinephrine greater than 0.5 mcg/kg/min |
| Measurement aspect | Details |
|---|---|
| Respiratory mechanics | Semi-recumbent position No spontaneous breathing during measurements Deep sedation with or without neuromuscular blockade Ventilation settings: - Volume control (VC) - VT 6 ml/kg PBW - Constant inspiratory flow 50–60 l/min - 0.3-s end-inspiratory pause - PEEP set by the clinician |
| Esophaegeal catheter placement | Esophageal catheter inserted into the stomach then withdrawn to 40 cm Placement confirmed by cardiac artifacts, tidal change in esophageal pressure (Pes), and occlusion test Pes measured in moderate/severe ARDS with no spontaneous breathing effort |
| Mechanics and arterial blood gases | Measurements at clinical PEEP level Repeated 10 min after PEEP modification (±5 cmH2O) PEEP adjusted to maintain Pplat ≤ 35 cmH2O and hemodynamic stability Pplat limit only for measurement safety, not for clinical practice |
| Definitions in respiratory mechanics | Global mechanics (∆Paw) based on airway pressure ∆Paw calculated as plateau pressure (Pplat) minus total PEEP Lung and chest wall mechanics assessed using Pes and PL ∆Paw split into ∆PL and chest wall driving pressure (ΔPes during tidal breath) PL partitioned specific to ventral or dorsal lungs based on esophageal position: - Directly measured PL: Specifically reflects pressure across the dorsal lung - Elastance-derived PL: Specifically reflects pressure across the ventral lung |
| Calculated indices | Oxygenation stretch index [(PaO2/(FiO2 × ∆Paw)] Mechanical power calculated using a specified formula 0.098 × RR × [VT2 × [0.5 × Ers + RR × (1 + I:E)/(60 × I:E) × Rrs] + VT × PEEP] |
| Aspect | Findings |
|---|---|
| Measurements | Made within 2 days post-intubation Median clinical PEEP: 12 cmH2O Pes measured in 80% of the cohort (302 patients) |
| Characteristics | Non-survivors showed: Higher age, APACHE II at ICU admission, higher SOFA, and lower PaO2/FiO2 at enrollment |
| Respiratory mechanics | Non-survivors showed: - Higher Pplat, ∆Paw, ∆PL, elastance-derived plateau PL, and respiratory rate - Lower oxygenation stretch index There were no significant differences in responses to higher PEEP |
| Outcome association | ∆Paw and ∆PL were associated with a higher risk of death ∆Paw was a slightly better fit than ∆PL in adjusted models Chest wall driving pressure was correlated with non-pulmonary SOFA and associated with 60-day mortality in the unadjusted model Lower survival was shown for elevated ∆Paw, ∆PL, and elastance-derived plateau PL |
| Post-hoc analysis (obese patients) | Positive end-expiratory PL was associated with a higher survival probability at day 60 |
| Post-hoc analysis (mechanical power and ∆Paw × 4 + RR) | ∆Paw × 4 + RR had the best fit after adjusting for age and SOFA Mechanical power was only associated with 60-day mortality when normalized by respiratory system compliance |
| Oxygenation stretch index | Did not outperform ∆Paw in predicting mortality Higher values were associated with significantly lower 60-day mortality Association persisted after adjusting for age and non-pulmonary SOFA Dichotomizing stretch index < 10 mmHg/cmH2O showed higher survival for high values |
| Sensitivity analyses | No significant interaction between early measurement and mechanics for 60-day mortality The association between mechanics and mortaliy was maintained even when patients still ventilated at day 60 were excluded |
∆PL was equivalent to ∆Paw in terms of predicting outcome. The study supports the soundness of limiting lung and airway driving pressures during mechanical ventilation. Furthermore, maintaining positive end-expiratory PL may improve outcomes in obese patients.
The study highlights the importance of driving pressure (∆P) and esophageal pressure measurements in guiding mechanical ventilation strategies and ultimately improving patient outcomes. The technology in Hamilton ventilators can support clinicians in several ways.
| Driving pressure calculation | All Hamilton ventilators enable clinicians to calculate driving pressure in any ventilation mode, aligning with the study's emphasis on the significance of ∆P in ARDS management. |
| Esophageal pressure monitoring | HAMILTON-G5/S1 and HAMILTON-C6 ventilators feature an auxiliary port dedicated to connecting esophageal catheter pressure lines. Clinicians can monitor both esophageal and transpulmonary pressures to get a comprehensive view of respiratory mechanics. Ventilator settings can then be individualized in line with the study's recommendation. |
| Esophageal manometry with P/V Tool | Together with esophageal manometry, the P/V Tool offers a more in-depth assessment of lung mechanics. Assessing recruitment potential can help determine which recruitment strategy to apply, thereby helping to limit overdistension and prevent VILI. (P/V Tool available as a standard feature on the HAMILTON-S1 and optional on the HAMILTON-G5, HAMILTON-C3/C6.) |