Inflammation and Distribution of Pulmonary Ventilation Before and After Tracheal Intubation in ARDS Patients

Prospective clinical protocol in patients admitted to the ICU of the Hospital Clínico UC-Christus, Santiago de Chile, with diagnosis of acute hypoxemic respiratory failure, but who are still ventilating spontaneously.

Clinical data:

After hospital admission, patients who meet inclusion/exclusion criteria will be asked to consent to participate in the study protocol. Patients will be monitored conventionally according with hospital protocols (continuous ECG, SpO2, invasive arterial pressure, and intermittent arterial blood gases).

EIT Monitoring:

An EIT belt will be installed around the patient thorax connected to Enlight impedance tomography monitor (Dixtal, São Paulo, Brazil). EIT data will be recorded during periods of 3 minutes for offline analysis. Regional distribution of ventilation will be analyzed by dividing the image in four ROIs, each covering 25% of the ventro-dorsal distance encompassing the whole lung area. In addition we will estimate recruitment-derecruitment, and overdistention, regionally. In addition, pendelluft phenomena, and spatial patterns of regional deformation will be assessed.

Study protocol:

After patient inclusion, the first EIT and physiological data acquisition will be recorded (hemodynamics, respiratory variables, arterial blood gases, plasma samples). The data acquisition will be repeated every 6 hours from enrollment until intubation, or upto 24 hours of follow up, after which the patient will only be followed for clinically relevant outcomes. If within 24 hours of inclusion the attending physician decides intubation and connection to MV, an extra assessment of EIT, clinical data and blood samples will be performed. After intubation these assessments will include MV data and will be repeated hourly for the first 6 hours, and then at 12, 18 and 24 hours thereafter.

Bronchoalveolar lavages:

Immediately after intubation and initial stabilization, a fiberoptic bronchoscope-guided distal-protected small volume bronchoalveolar lavage (FODP mini-BAL) will be performed. This early BAL will be used as representative of the previous period of spontaneous ventilation. After 48 hours of controlled MV a new BAL will be performed, at the same regions than the first BAL, to compare the changes in the pattern of regional inflammation. For each BAL one or two aliquots of 20 ml of warmed (37°C) sterile isotonic saline will be administered and subsequently recovered in dorsal (lateral inferior) and ventral segments (medial lobe or lingula). The first recovered aliquot will be discarded while the remaining BAL fluid will be rapidly filtered through a sterile gauze and spun at 4°C at 400 x g for 15 min. The supernatant will be centrifuged at 80,000 x g for 30 min at 4°C in order to remove the surfactant-rich fraction and then divided into aliquots and frozen at - 80 °C for subsequent cytokine and mechanotransduction markers determinations.

* BAL samples will only be collected if the attending physician determines that this procedure is clinically necessary.

Cytokine analysis in serum, BALF and tissue supernatants:

Quantification of TNF-α, IL-1β, IL-6, IL-8 and IL-10 levels in plasma at time to inclusion, intubation, and 24 and 48 hours after intubation. BALF will be analyzed to determine quantification of neutrophils, cytokines (TNF-α, IL-1β, IL-6, IL-8 and IL-10) and TGF-β (extracellular cytokine with mechanotransduction proprieties) at intubation time and 48 hours after intubation.

Gas Exchange, Hemodynamics, and Ventilatory Data:

At each time of physiological acquisition we will collect arterial and central venous blood gases (if central venous catheter is present). We will assess hemodynamics (arterial blood pressure, central venous pressure, central venous pressure inspiratory swings, heart rate), and ventilatory parameters. While patients remain in spontaneous ventilation we will assess respiratory rate, ventilatory pattern, and Borg dyspnea score. After intubation and connection to MV we will collect full ventilatory data from the pneumotach system for later analysis of flows, pressures and volumes.

Statistical Analysis:

For the clinical protocol we don´t have previous data about distribution of ventilation between dependent and non-dependent lung regions during spontaneous ventilation. Therefore, we calculated sample size based on an expected effect size of 0.5, with a standard deviation two times larger, between the period of spontaneous ventilation before intubation, and the period of controlled MV after intubation. For a power of 0.8 and a two-sided error of 0.05 the calculated sample size is 32. However, of the included patients, only a fraction will be intubated, so we calculated that 60 to 80 patients must be included during the 4-year period, to complete the required number of patients available for before-after analysis. We will express values as means - standard deviation (SD) or median - range where appropriate. The Shapiro-Wilk test will be used to test data for normality. Groups will be compared using Student's t-test or Mann-Whitney U-test, one-way (repeated-measures) analysis of variance (ANOVA) or Kruskal- Wallis test. Interactions between groups and time will be assessed with two-way repeated-measures ANOVA. The Bonferroni adjustment for multiple tests will be applied for post hoc comparisons. The statistical analyses will be conducted by SPSS v.20.0.0 software (SPSS, Inc, Chicago, IL, USA), and GraphPad Prism version 5.0 (GraphPad Software, San Diego, CA, USA).