Electrical impedance tomography: a future item on the “Christmas Wish List” of the intensivist?

Excerpt

Sir: The principal objective of the invasive ventilatory management of patients with acute respiratory distress syndrome (ARDS) is the maintenance of acceptable gas exchange without inflicting additional lung damage [1]. The key elements of such a lung protective approach are to limit lung distension and to maintain sufficient end-expiratory lung volume to prevent alveolar collapse, thus avoiding re-recruitment with each ventilatory cycle [2]. ARDS was first described more than 30 years ago for the first time by Ashbaugh et al. [3]. Since then, little has changed in the development of routine bedside tools to contribute to the assessment of the severity of the disease. Conventional respiratory measures, such as dynamic compliance and airway resistance, can describe the global mechanical characteristics but do not assess regional differences in lung mechanics. Inert tracer gas washout techniques have been used in the past to measure end-expiratory level and ventilation maldistribution, but they have had little impact on ventilatory management [4]. It has been appreciated that the description of global lung behavior is not accurate enough to allow optimal protective ventilation for all lung regions. The ideal lung function test would therefore consist of an imaging technique that additionally provides information on regional lung mechanics. Computer tomography (CT) of the lung has emerged in several clinical trials as an ideal tool to assess whether regional ventilation distribution inequalities do exist and whether potential lung recruitment can be performed resulting in higher effective alveolar ventilation [5]. The CT analysis has shown that significant regional ventilation inequalities exist in ARDS with regions experiencing tidal hyperinflation, regions normally aerated, regions with cyclic collapse and poorly aerated, and regions non-aerated [6]. There are, however, limitations to using CT as a diagnostic tool, and these include the following: (a) only static images are captured; (b) the patient is exposed to potential harmful radiation; and (c) it is not suitable for continuous monitoring of ventilation distribution. …