Chest Wall Influence on Respiratory System Mechanics in Morbidly Obese Patients

Study Overview
=================
Brief Summary
-----------------
The goal of this study is to describe the influence of the chest wall on the respiratory system mechanics in morbidly obese patients and in patients with high intra-abdominal pressure. The effects of increasing and decreasing positive end-expiratory pressure (PEEP) on chest wall and total respiratory system mechanics, lung volumes and gas exchange will be evaluated, both during controlled and assisted mechanical ventilation. Patients will be studied, first, during the acute phase of respiratory failure, when requiring intubation and controlled mechanical ventilation. Then, patients will be evaluated again during weaning from the ventilator to assess the influence of PEEP in assisted ventilation prior to extubation.

Detailed Description
-----------------
The goal of this study is to describe the influence of the chest wall on the respiratory system mechanics. Investigators want to describe how extreme obesity and Intra-Abdominal Hypertension (IAH) affect normal respiratory system behavior. The effects of increasing and decreasing positive end-expiratory pressure (PEEP) on respiratory system mechanics, lung volumes and gas exchange will be evaluated, both during controlled and assisted mechanical ventilation. Investigators will record and compare lung volumes, airway and transpulmonary pressure, gas exchange and hemodynamic changes caused by variations of PEEP. Patients will be studied, first, during the acute phase of respiratory failure, when requiring intubation and controlled mechanical ventilation. Patients will then again be evaluated during weaning from the ventilator to assess the influence of PEEP in assisted ventilation prior to extubation. Investigators believe that assessment of the transpulmonary pressure and lung volumes is essential to correctly evaluate respiratory system function in patients in which the relationship between the lung and chest wall is altered. Improper mechanical ventilation leads to lung damage. High ventilatory volume/pressure are associated with lung overdistension, while low volume/pressure leads to lung collapse and cyclic opening and closing of alveoli. All of these mechanisms have been associated with ventilator induced lung injury and poorer outcomes. Adequate PEEP and transpulmonary pressure are fundamental in preventing this vicious cycle.

Official Title
-----------------
Chest Wall Influence on Respiratory System Mechanics in Morbidly Obese Patients

Conditions
-----------------
Obesity, Intra-Abdominal Hypertension

Intervention / Treatment
-----------------
* Other: Respiratory mechanics assessment


Participation Criteria
=================
Eligibility Criteria
-----------------
Inclusion Criteria: 18 years or older Requiring intubation and mechanical ventilation BMI≥40 kg/m2 or IAP≥12 mmHg Exclusion Criteria: Known presence esophageal varices Recent esophageal trauma or surgery Severe thrombocytopenia (PTL≤10,000/mm3) Severe coagulopathy (INR≥2) Presence of pneumothorax Pregnancy Patients with diagnosed moderate to severe ARDS or with poor oxygenation index (PaO2/FiO2 < 200 mmHg)

Ages Eligible for Study
-----------------
Minimum Age: 18 Years

Sexes Eligible for Study
-----------------
All

Accepts Healthy Volunteers
-----------------
No

Study Plan
=================
How is the study designed?
-----------------

Arms and Interventions

| Participant Group/Arm | Intervention/Treatment |
| --- | --- |
| Obese<br>We will enroll patients with BMI≥40 kg/m2 to describe the impact of obesity on chest wall compliance and respiratory mechanics. Respiratory mechanics assessment: We will assess respiratory mechanics through different end expiratory pressure settings and recording airway and esophageal pressure tracings. | Other: Respiratory mechanics assessment<br>* Data collection on respiratory mechanics, end expiratory lung volumes, gas exchanges, work of breathing. Data will be obtained by setting different end expiratory pressures and recording esophageal and airways pressure tracings.<br>|
| Intraabdominal Hypertension<br>We will enroll patients with IAP≥12 mmHg to describe the impact of intraabdominal hypertension on chest wall compliance and respiratory mechanics. Respiratory mechanics assessment: We will assess respiratory mechanics through different end expiratory pressure settings and recording airway and esophageal pressure tracings. | Other: Respiratory mechanics assessment<br>* Data collection on respiratory mechanics, end expiratory lung volumes, gas exchanges, work of breathing. Data will be obtained by setting different end expiratory pressures and recording esophageal and airways pressure tracings.<br>|

What is the study measuring?
-----------------
Primary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| End Expiratory Lung Volumes | EELV variation at different levels of PEEP in mechanically ventilated and sedated morbidly obese patients and patients with intraabdominal hypertension | 2 hours | 

Secondary Outcome Measures

| Outcome Measure | Measure Description | Time Frame |
| --- | --- | --- |
| Respiratory mechanics | Evaluation of effects of PEEP level set by ICU staff on respiratory mechanics after 24 hours from enrollment Evaluation of PEEP level set by ICU staff | 24 hours | 
| Work of breathing | Evaluation of work of breathing variation at different level of PEEP during spontaneous breathing and ventilation weaning in morbidly obese patients | 20 minutes | 
| Respiratory mechanics | Respiratory mechanics variation at different levels of PEEP in mechanically ventilated and sedated morbidly obese patients and patients with intraabdominal hypertension | 2 hours | 
| Gas Exchange | Gas exchange variation at different levels of PEEP in mechanically ventilated and sedated morbidly obese patients and patients with intraabdominal hypertension | 2 hours | 
| Respiratory mechanics | Evaluation of respiratory mechanics at different level of PEEP during spontaneous breathing and ventilation weaning in morbidly obese patients | 20 minutes | 
| Gas exchange | Evaluation of gas exchange variation at different level of PEEP during spontaneous breathing and ventilation weaning in morbidly obese patients | 20 minutes | 
| End Expiratory Lung Volume | Evaluation of effects of PEEP level set by ICU staff on EELV after 24 hours from enrollment | 24 hours | 
| Gas Exchange | Evaluation of effects of PEEP level set by ICU staff on gas exchange after 24 hours from enrollment | 24 hours | 

 Terms related to the study
=================
Keywords Provided by Centre Hospitalier Valida
-----------------
Respiratory mechanics, Esophageal pressure, Functional residual capacity, positive end-expiratory pressure