Varying leaks: a challenge for modern ventilators?

Using patient-triggered ventilation, during which the patient is given the opportunity to trigger and cycle the ventilator, allows reducing the use of sedation,1 reduces ventilator-induced diaphragmatic dysfunction,2 facilitates weaning from mechanical ventilation,3 and improves patient comfort.4 To be efficient and comfortable, patient-triggered modes have to deliver pressurization in synchrony with the patient’s inspiratory efforts. Despite technological improvements, delays between delivered ventilator pressurization and the patient’s inspiratory effort can occur either at the beginning (triggering phase) or at the end of the inspiratory effort (cycling phase), resulting in patient-ventilator asynchrony.5 Severe asynchrony occurs in one fourth of invasively ventilated patients,6 and has been associated with increased respiratory muscles work load7 and prolonged mechanical ventilation.6 As ventilators use leaksensitive pneumatic signals to detect the start of a patient’s inspiratory effort and to manage the inspiration-expiration transition, patient-ventilator asynchrony dramatically increases in the presence of leaks,8 which can occur during invasive ventilation, related for example to a non-occlusive endotracheal tube cuff, the ventilator circuit, or bronchopleural fistula, and during noninvasive ventilation (NIV), because of the use of noninvasive interfaces. Therefore, in the presence of leaks the quality of delivered mechanical ventilation is tightly related to the ventilator’s performance. This is true both for ICU ventilators, originally designed to ventilate intubated patients without leaks, but now equipped with specific NIV algorithms,9 and for turbine-based NIV dedicated ventilators originally built to compensate for leaks. Choosing a “good” ventilator is crucial to deliver efficient ventilation in the presence of leaks, and underlines the need of having an extensive knowledge on how the various ventilators react to challenging clinical scenarios, for example, the occurrence of varying leaks. As patients and clinical scenarios cannot be standardized at the bedside, this requires the use of bench tests. By assessing 8 ventilators’ responses to varying amounts of increasing and decreasing leak, the study of Oto et al published in this issue of RESPIRATORY CARE, can be considered as a major contribution to current knowledge in the field.10 In this very interesting bench study, Oto et al simulated ARDS and COPD conditions and used a very realistic lung simulator and manikin setup, and elaborated increasing and decreasing leakage scenarios to assess the ability of 7 ICU ventilators and of 1 NIV-dedicated ventilator to prevent triggering and cycling asynchrony caused by varying leaks during both invasive and noninvasive ventilation. They also recorded the number of breaths required to obtain acceptable synchrony when leak was changed, which is a very original approach.