[PLS2] What to consider when to set mechanical ventilation
Dr. Koh is a physician scientist working as a Professor of Department of Pulmonary and Critical Care Medicine, a Professor of Department of Medical Humanities & Social Sciences, and a critical care physician at Asan Medical Center, the University of Ulsan College of Medicine in Korea. His research interests include ARDS, mechanical ventilation, sepsis, and medical ethics. He has published more than 360 articles in peer review journals.
He had served medical academy societies as a President of Korean Society of Critical Care Medicine, and as a President of the Korean Society for Medical Ethics. He also had served as an organizing chairman of the 12th World Federation of Societies of Intensive and Critical Care Medicine (WFSICCM) Congress in 2015, as a council of the WFSICCM for 8 years, and as a chairman of the Asian Collaboration of Critical Care Trial Group. He has been contributing to enhance mechanical ventilation cares in Asia as ex-chairman of Asian Ventilation Forum.
The main goal of positive pressure ventilation (PPV) is to improve pulmonary gas exchange and to rest compromised respiratory muscles minimizing ventilator-associated lung injuries. Therefore, less invasive ventilatory support in optimal time is a key for better outcomes of patients with respiratory failure. PPV also alters heart-lung interaction, which can affect total oxygen delivery to tissues. Therefore, patient directed PPV setting should consider patient’s underlying lung pathophysiology, synchronization between the patient and mechanical ventilator, heart-lung interaction associated with PPV, and less invasive ventilation ways.
Two main causes of respiratory failure are oxygenation failure and respiratory pump failure. One major cause of the morbidity and mortality arising during PPV is prolonged excessive transpulmonary pressure application to achieve optimal gas exchange. The level of transpulmonary pressure for a tidal ventilation is determined by patient’s airway resistance and respiratory system elastance. The excessive transpulmonary pressure gradient frequently occurs in nonhomogeneous alveoli in acute respiratory distress syndrome (ARDS). Limiting transpulmonary pressure during PPV through low tidal volume under appropriate PEEP is a key of lung protective ventilation in ARDS. Another major cause of the morbidity and mortality arising during PPV in patients with chronic airflow obstruction is excessive dynamic pulmonary hyperinflation (DH) with auto-PEEP. The cornerstone to attenuate DH of lung is achieved by improving airflow resistance, limiting minute ventilation, maximizing time for expiration, and inducing synchronization between the patient and mechanical ventilator.
Adjunctive measures such as prone ventilation, a brief period of paralysis by using a neuromuscular blockade, and cautious use of sedatives analgesics should be considered to get beneficial outcome of patients with severe respiratory failures.
Two main causes of respiratory failure are oxygenation failure and respiratory pump failure. One major cause of the morbidity and mortality arising during PPV is prolonged excessive transpulmonary pressure application to achieve optimal gas exchange. The level of transpulmonary pressure for a tidal ventilation is determined by patient’s airway resistance and respiratory system elastance. The excessive transpulmonary pressure gradient frequently occurs in nonhomogeneous alveoli in acute respiratory distress syndrome (ARDS). Limiting transpulmonary pressure during PPV through low tidal volume under appropriate PEEP is a key of lung protective ventilation in ARDS. Another major cause of the morbidity and mortality arising during PPV in patients with chronic airflow obstruction is excessive dynamic pulmonary hyperinflation (DH) with auto-PEEP. The cornerstone to attenuate DH of lung is achieved by improving airflow resistance, limiting minute ventilation, maximizing time for expiration, and inducing synchronization between the patient and mechanical ventilator.
Adjunctive measures such as prone ventilation, a brief period of paralysis by using a neuromuscular blockade, and cautious use of sedatives analgesics should be considered to get beneficial outcome of patients with severe respiratory failures.