The Association Between the Mechanical Ventilator Pressures and Outcomes in a Cohort of Patients with Acute Respiratory Failure

Background: Pressures measured during mechanical ventilation provide important information about the respiratory system mechanics and can help predict outcomes. Methods: The electronic medical records of patients hospitalized between 2010 and 2016 with sepsis who required mechanical ventilation were reviewed to collect demographic information, clinical information, management requirements, and outcomes, such as mortality, ICU length of stay, and hospital length of stay. Mechanical ventilation pressures were recorded on the second full day of hospitalization. Results: This study included 312 adult patients. The mean age is 59.1 ± 16.3 years; 57.4% were men. The mean BMI was 29.3 ± 10.7. Some patients had pulmonary infections (46.2%), and some patients had extrapulmonary infections (34.9%). The overall mortality was 42.6%. In a multi-variable model that included age, gender, number of comorbidities, APACHE 2 score, and PaO2/FiO2 ratio, peak pressure, plateau pressure, driving pressure, and PEEP all predicted mortality when entered into the model separately. There was an increase in peak pressure, plateau pressure, and driving pressure across BMI categories ranging from underweight to obese. Conclusions: This study demonstrates that ventilator pressure measurements made early during the management of patients with acute respiratory failure requiring mechanical ventilation provide prognostic information regarding outcomes, including mortality. Patients with high mechanical ventilator pressures during the early course of their acute respiratory failure require more attention to identify reversible disease processes when possible. In addition, increased BMIs are associated with increased ventilator pressures, and this increases the complexity of the clinical evaluation in the management of obese patients.

Physiological effects of alveolar, tracheal, and “standard” pressure supports

Pressure support (PS) is characterized by a pressure plateau, which is usually generated at the ventilator level (PSvent). We have built a PS device in which the pressure plateau can be obtained at the upper airway level (PSaw) or at the alveolar level (PSA). The effect of these different PS modes was evaluated in seven healthy men during air breathing and 5% CO2breathing. Minute ventilation during air breathing was higher with PSA than with PSaw and lower with PSvent (16 ± 3, 14 ± 3, and 11 ± 2 l/min, respectively). By contrast, there were no significant differences in minute ventilation during 5% CO2 breathing (25 ± 5, 27 ± 7, and 23 ± 5 l/min, respectively). The esophageal pressure-time product per minute was lower with PSA than with PSaw and PSvent during air breathing (29 ± 26, 44 ± 44, and 48 ± 30 cmH2O ⋅ s, respectively) and 5% CO2breathing (97 ± 40, 145 ± 62, and 220 ± 41 cmH2O ⋅ s, respectively). In conclusion, during PS, moving the inspiratory pressure plateau from the ventilator to the alveolar level reduces pressure output, particularly at high ventilation levels.