Assessing Lung Inhomogeneity During Ventilation for Acute Hypoxemic Respiratory Failure

University Health Network, Toronto20 enrolled

Overview

Mechanical ventilation can cause damage by overstretching the lungs, especially when the lungs are collapsed or edematous. Raising ventilator pressures can reduce lung collapse and this can prevent overstretching from mechanical ventilation. It remains uncertain how much pressure (PEEP - positive end-expiratory pressure) should be used on the ventilator and how to identify patients who will benefit from higher ventilator pressures vs. lower ventilator pressures. The investigators are using a unique new imaging technology, electrical impedance tomography (EIT), to study this problem and to determine the safest and most effective ventilator pressure level. The results of this study will inform future trials of higher vs. lower PEEP strategies in mechanically ventilated patients.

Patients participating in this physiological cross-over randomized trial will undergo a series of PEEP maneuvers designed to assess lung recruitability, PEEP responsiveness, and optimal PEEP. EIT imaging and esophageal manometry will be employed throughout the protocol to quantify the effect of PEEP on lung function. Patients will be randomized to be ventilated at PEEP levels supplied by the ExPRESS strategy or by the EIT hyperdistention/collapse algorithm. The biological response will be assessed by measuring serum cytokines.

Study Type

INTERVENTIONAL

Allocation

RANDOMIZED

Purpose

TREATMENT

Masking

NONE

Enrollment

Conditions

Acute Respiratory Distress Syndrome

Interventions

Electrical Impedance TomographyDEVICE

Electrical impedance tomography (EIT) is a new technique that enables real-time visualization of the distribution of ventilation at the bedside. This technique allows clinicians and investigators to immediately determine how applying higher or lower PEEP levels affect stress and strain in the lung. The investigators propose to apply this new technique to test a strategy for finding the optimal level of PEEP that prevents lung injury and improves outcomes in critically ill patients.

ExPRESS-derived PEEP levelOTHER

The ExPRESS algorithm is a traditional approach to selecting PEEP based on respiratory mechanics.

Eligibility

Sex: ALLMin age: 18 Years

Medical Language ↔ Plain English

Inclusion Criteria: * Acute (≤7 days) hypoxemia with PaO2:FiO2 ratio less than or equal to 200 mm Hg * Oral endotracheal intubation and mechanical ventilation * Bilateral airspace opacities on chest radiograph or CT Exclusion Criteria: * Contraindication to EIT electrode placement (burns, chest wall bandaging limiting electrode placement) * Contraindication to esophageal catheter placement (recent upper GI surgery, actively bleeding esophageal varices) * Respiratory failure predominantly due to cardiogenic cause or fluid overload * Ongoing hemodynamic instability (requiring 2 vasopressor agents by continuous infusion AND rising vasopressor infusion rate requirements in the previous 8 hours) * Ongoing ventilatory instability (P/F \< 70 mm Hg, pH \< 7.2; ventilator driving pressures, PEEP, or FiO2 increasing by more than 25% in previous 30 minutes) * Intracranial hypertension (suspected or diagnosed by medical team) * Known or suspected pneumothorax recognized within previous 72 hours * Bronchopleural fistula * Bridge to lung transplant * Recent lung transplantation (within previous 6 weeks) * Attending physician deems the transient application of high airway pressures (\>40 cm H2O) to be unsafe

Outcomes

Primary Outcomes

Intratidal ventilation heterogeneity

A measure of variation in the distribution of ventilation throughout the lung as detected by electrical impedance tomography

Time frame: Assessed after completion of 3 hours on randomized strategy (EIT vs ExPRESS)

Secondary Outcomes

Difference in the optimal PEEP levels identified by several different PEEP titration strategies

Compare the relative degree of agreement or disparity between PEEP levels recommended by different PEEP titration strategies

Time frame: Assessed immediately after completion of decremental PEEP titration procedure

Change in ratio of partial pressure of oxygen (PaO2) to inspired fraction of oxygen (FiO2) ratio following a standardized increased in PEEP

Measurement of changes in oxygenation by PaO2/FiO2 ratio due to PEEP

Time frame: Assessed 10 minutes after step PEEP increase from 6-8 to 16-18 cm H2O

Respiratory mechanics (transpulmonary driving pressure)

The swing in transpulmonary pressure during inspiration, a measure of dynamic lung stress

Time frame: Assessed after completing 3 hours on the randomized PEEP strategy (EIT vs ExPRESS)