A simple device to inject indicator gas for wash-out tests during mechanical ventilation

Abstract

Abstract.Objective: To evaluate a simple device which injects a constant fraction of indicator gas to the inspiratory mixture for performing multi-breath wash-out tests during controlled ventilation. Design: the technique in which the indicator gas is injected at the mouth of the patient (post-mix) is compared with the technique where the indicator gas is administered in the bellows of the ventilator (pre-mix). Setting." Surgical Intensive Care Unit of a University Hospital. Patients." 10 post-operative mechanically ventilated patients. Interventions: None. Measurements and results: 3 wash-out tests with the post-mix and 3 wash-out tests with the pre-mix method were performed within an hour on every patient. The calculated mean end expiratory lung volume (EEV) was 1.91 _+0.871 with the post-mix technique and 1.89_+0.881 with the premix technique. There was a good agreement with a mean difference of -1.9_+6.5% in the calculated EEV values by the two different techniques. Conclusion: The described injector is an affordable device, is easy to assemble and can be incorporated in most electronically regulated ventilators to perform multi-breath indicator gas wash-out tests for pulmonary monitoring at the bed side of ICU patients.

A modification of the Bohr method to determine airways deadspace for non-uniform inspired gas tensions

“…This was not always possible in the past due to the slow response and variable time delay of older-generation sensors and actuators. The proposed algorithm therefore can be used by other gas mixing techniques such as Gültuna et al (1992), Kirmse et al (1998) and Kanhai et al (2003).…”

“…In other techniques, the concentration of indicator in the inspired gas can be made to vary between breaths such as the sinusoidally varying inspired oxygen tensions employed by Williams et al (1997). These inspired gas variations may be achieved by pre-mixing the inspired gas breath by breath, or, in other cases by using devices that allow rapid injection of indicator gases (Gültuna et al 1992, Kirmse et al 1998, Kanhai et al 2003, Clifton et al 2012a into the inspired airflow in real time. In these circumstances, uniform inspired concentrations are difficult or impossible to achieve, which leads to inaccurate estimations of deadspace.…”

Assessment of ventilation inhomogeneity during mechanical ventilation using a rapid-response oxygen sensor-based oxygen washout method

“…Although inhomogeneity indexes are often used in pulmonary function labs and improve after application of positive end-expiratory pressure (PEEP) in paediatric anaesthesia, use in the intensive care unit (ICU) is limited by the need of specialized equipment and tracer gases [ 4 , 5 ]. Huygen et al [ 6 , 7 ] and Gültuna et al [ 8 ] worked on the development of inhomogeneity indexes and indicator gas injectors based on SF6 for critically ill patients, but implementation remained difficult due to the need of specialized equipment and gas containers at the bedside [ 6 , 7 ]. The availability of a routine method to quantify inhomogeneous alveolar ventilation at the bedside is expected to help to optimize ventilator settings in individual patients to achieve optimal gas exchange.…”