Proportional modes of ventilation: technology to assist physiology
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NARRATIVE REVIEW
Proportional modes of ventilation: technology to assist physiology Annemijn H. Jonkman1,2,3, Michela Rauseo1,2, Guillaume Carteaux4,5,6, Irene Telias1,2, Michael C. Sklar1,2, Leo Heunks3 and Laurent J. Brochard1,2* © 2020 Springer-Verlag GmbH Germany, part of Springer Nature
Abstract Proportional modes of ventilation assist the patient by adapting to his/her effort, which contrasts with all other modes. The two proportional modes are referred to as neurally adjusted ventilatory assist (NAVA) and proportional assist ventilation with load-adjustable gain factors (PAV+): they deliver inspiratory assist in proportion to the patient’s effort, and hence directly respond to changes in ventilatory needs. Due to their working principles, NAVA and PAV+ have the ability to provide self-adjusted lung and diaphragm-protective ventilation. As these proportional modes differ from ‘classical’ modes such as pressure support ventilation (PSV), setting the inspiratory assist level is often puzzling for clinicians at the bedside as it is not based on usual parameters such as tidal volumes and P aCO2 targets. This paper provides an in-depth overview of the working principles of NAVA and PAV+ and the physiological differences with PSV. Understanding these differences is fundamental for applying any assisted mode at the bedside. We review different methods for setting inspiratory assist during NAVA and PAV+ , and (future) indices for monitoring of patient effort. Last, differences with automated modes are mentioned. Keywords: Mechanical ventilation, Proportional modes, Inspiratory assist, Respiratory effort Introduction Proportional modes of ventilation work by amplifying the effort of the patient’s respiratory muscle activity, providing the necessary support to improve the imbalance between capacity and demand and to reach the patient’s ventilation goal at the same time. Proportional modes have the potential to provide lung and respiratory muscle-protective ventilation by maintaining the patient’s control mechanisms against both lung overdistention and ventilator over-assistance, and avoiding the development of diaphragm disuse atrophy [1, 2]. Inspiratory assist is delivered in synchrony with patient effort during the total inspiratory cycle, and thus, by contrast with other modes, *Correspondence: [email protected] 1 Keenan Research Centre, Li Ka Shing Knowledge Institute, St. Michael’s Hospital, 209 Victoria Street, Room 4‑08, Toronto, ON M5B 1T8, Canada Full author information is available at the end of the article
directly responds to changes in ventilatory demands [3, 4]. This is fundamentally different from conventional partially supported modes of ventilation such as pressure support ventilation (PSV), where the same pressure is delivered by the ventilator for every breath and is independent of the metabolic needs and the magnitude of the patient’s effort and also, most often, of its timing. Hence, patient-ventilator asynchrony and ventilator over-assistance are common and often unnoticed in
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