Effects of Large Tidal Volumes Despite Minimal Inspiratory Support in Spontaneously Ventilated Intubated Resuscitation Patients. Pathophysiological Exploratory Study.

Overview

Some ICU ventilated patients might present with large tidal volume despite very low or inexistant presser support. Patient-Self Inflicted Lung Injury (P-SILI) might appear related with large alveolar stretch an distension. Two clinical presentations are observed: patients with or without respiratory distress signs such as supra-clavicular depression and thoracic-abdominal asynchronies. The aim of this study is to compare the pulmonary physio(-patho)logical parameters of these two types of patients (eupneic or with respiratory distress signs), and presenting important TV in spite of a minimal adjustment of the ventilatory support, except for Acute Respiratory Distress Syndrome (ARDS).

The use of invasive mechanical ventilation is one of the most frequent therapies in the intensive care unit. There are several types of indication, depending on the failure: mainly neurological, hemodynamic or respiratory. In recent years, the concept of Ventilator Induced Lung Injury (VILI) has led to changes in ventilator settings in both intensive care units and operative rooms. Thus, tidal volume (TV) reduction to 6-8 mL.kg-1 of predicted body weight, the use of an individualized positive end-expiratory pressure (PEEP) and the possible use of therapies to optimize pulmonary aeration (alveolar recruitment maneuvers, prone positioning sessions...) have become mandatory. More recently, some authors have described the existence of Patient-Self Inflicted Lung Injury (P-SILI). In certain situations (delirium, encephalopathies, pulmonary receptor stimulation, metabolic acidosis...), some patients may present, in spite of an "optimized" ventilator setting, very important VT, which may exceed 10 mL.kg-1 of theoretical ideal weight. Two circumstances of observation of these large VT needs despite low pressure supports can be observed. The first corresponds to a patient with signs of respiratory distress (signs of respiratory distress: supra-clavicular, thoraco-abdominal asynchronies...) who presents with significant inspiratory efforts. The second is a patient with no sign of respiratory distress (eupnea). In both cases, the "trigger" comes from a (hyper)-stimulation (drive) of respiratory brainstem centers. It is currently uncertain whether these two types of patients are comparable in terms of P-SILI. It is possible that in the second case, lesions are non-existent (or minimal) due to low trans-pulmonary pressure (stress) and low levels of pulmonary alveolar distension (strain). Indeed, the most likely determinant of alveolar injury is trans-pulmonary pressure, defined as the difference between upper airway pressure and pleural pressure (Ptp = Paw - Ppl). Thus, in case of a negative pathophysiological parameter, it would be preferable to sedate the patient more deeply and to temporarily consider controlled mechanical ventilation to limit the alveolar stretch and lesions. However, we know that excessive sedation of resuscitation patients increases their morbidity and mortality, by exposing them to increased duration of mechanical ventilation, and thus to the risk of pneumonia acquired under mechanical ventilation. In this context, daily sedation release tests are recommended. Physicians must therefore find the right balance between an optimal level of sedation compatible with the least deleterious ventilatory support possible. The aim of this study is to compare the pulmonary physio(-patho)logical parameters of these two types of patients (eupneic or with respiratory distress signs), and presenting important TV in spite of a minimal adjustment of the ventilatory support, except for Acute Respiratory Distress Syndrome (ARDS).