Predicting outcomes in ARDS patients – Does partitioning respiratory mechanics help?

Статья

Автор: Maritza Henriques Rodrigues

Дата: 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.

Predicting outcomes in ARDS patients – Does partitioning respiratory mechanics help?

Clinical question

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?

Clinical background

Optimizing ventilatory strategies to minimize ventilator-induced lung injury (VILI) is crucial for improving patient outcomes in acute respiratory distress syndrome (ARDS).
Airway driving pressure has been found to show a strong association with outcomes in ventilated patients
VILI is linked to lung stretch, and transpulmonary driving pressure (∆PL) or tidal lung stress may be more accurate determinants of VILI than ∆Paw by eliminating the chest wall contribution to ∆Paw.
Calculated indices relating to transpulmonary pressures, particularly in the dorsal and ventral lung regions, may have varying implications for monitoring VILI.
Main study hypothesis: ∆PL is a superior predictor of outcome compared to ∆Paw.
Secondary hypothesis: The oxygenation stretch index, which is a composite variable using PaO2/FiO2 divided by ∆Paw, can enhance the predictive power of ∆Paw.

Design and setting

Prospective, observational, multicenter study (Chen L, Grieco DL, Beloncle F, et al. Partition of respiratory mechanics in patients with acute respiratory distress syndrome and association with outcome: a multicentre clinical study [published correction appears in Intensive Care Med. 2023 Mar;49(3):386. doi: 10.1007/s00134-023-06985-1]. Intensive Care Med. 2022;48(7):888-898. doi:10.1007/s00134-022-06724-y1)

Patients

Total number of enrolled patients: 385
Excluded from analysis: Eight patients where measurements were obtained in the prone position or under extracorporeal membrane oxygenation (ECMO)
Study cohort: 377 patients


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

Intervention

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]

Measurements and main results

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

Primary outcome

Mortality rate at day 60 was 37.7%.
Transpulmonary driving pressure did not correlate more strongly with outcomes than airway driving pressure.
The oxygenation stretch index as a combination of oxygenation and airway driving pressure did not outperform airway driving pressure alone.
Oxygenation lost its association with outcomes when adjusted for airway driving pressure.
Targeting a positive end-expiratory transpulmonary pressure appears relevant, particularly in obese patients.

Conclusions

∆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.

Food for thought

The study provides valuable insights for designing new ventilatory strategies based on respiratory mechanics.
A slightly improved goodness-of-fit was observed with ∆Paw in the adjusted models, highlighting the importance of considering not only lung-specific parameters but also chest wall mechanics when assessing the impact of driving pressures on patient outcomes.
The influence of chest wall driving pressure, linked to disease severity and outcomes, may explain the unexpected findings of this study.
Fixed balloon volumes were used for simplicity in measurements, which may impact on the accuracy of elastance-derived plateau pressure.
Almost one-third of ARDS patients experience complete airway closure, potentially affecting the precision of elastance measurements.
Data on key co-interventions for ARDS - such as prone positioning, neuromuscular blockade, steroids, and ECMO - were not collected, potentially influencing respiratory mechanics.

How can I incorporate these findings into my daily work with Hamilton Medical technology?

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.)

Сноски

Список литературы

1. Chen L, Grieco DL, Beloncle F, et al. Partition of respiratory mechanics in patients with acute respiratory distress syndrome and association with outcome: a multicentre clinical study [published correction appears in Intensive Care Med. 2023 Mar;49(3):386. doi: 10.1007/s00134-023-06985-1]. Intensive Care Med. 2022;48(7):888-898. doi:10.1007/s00134-022-06724-y

Partition of respiratory mechanics in patients with acute respiratory distress syndrome and association with outcome: a multicentre clinical study.

Chen L, Grieco DL, Beloncle F, et al. Partition of respiratory mechanics in patients with acute respiratory distress syndrome and association with outcome: a multicentre clinical study [published correction appears in Intensive Care Med. 2023 Mar;49(3):386. doi: 10.1007/s00134-023-06985-1]. Intensive Care Med. 2022;48(7):888-898. doi:10.1007/s00134-022-06724-y

Link to publication

PURPOSE

In acute respiratory distress syndrome (ARDS), physiological parameters associated with outcome may help defining targets for mechanical ventilation. This study aimed to address whether transpulmonary pressures (PL), including transpulmonary driving pressure (DPL), elastance-derived plateau PL, and directly-measured end-expiratory PL, are better associated with 60-day outcome than airway driving pressure (DPaw). We also tested the combination of oxygenation and stretch index [PaO2/(FiO2*DPaw)].

METHODS

Prospective, observational, multicentre registry of ARDS patients. Respiratory mechanics were measured early after intubation at 6 kg/ml tidal volume. We compared the predictive power of the parameters for mortality at day-60 through receiver operating characteristic (ROC) and assessed their association with 60-day mortality through unadjusted and adjusted Cox regressions. Finally, each parameter was dichotomized, and Kaplan-Meier survival curves were compared.

RESULTS

385 patients were enrolled 2 [1-4] days from intubation (esophageal pressure and arterial blood gases in 302 and 318 patients). As continuous variables, DPaw, DPL, and oxygenation stretch index were associated with 60-day mortality after adjustment for age and Sequential Organ Failure Assessment, whereas elastance-derived plateau PL was not. DPaw and DPL performed equally in ROC analysis (P = 0.0835). DPaw had the best-fit Cox regression model. When dichotomizing the variables, DPaw ≥ 15, DPL ≥ 12, plateau PL ≥ 24, and oxygenation stretch index < 10 exhibited lower 60-day survival probability. Directly measured end-expiratory PL ≥ 0 was associated with better outcome in obese patients.

CONCLUSION

DPL was equivalent predictor of outcome than DPaw. Our study supports the soundness of limiting lung and airway driving pressure and maintaining positive end-expiratory PL in obese patients.