Electrical impedance tomography in the clinical assessment of lung volumes following recruitment manoeuvres

Abstract

Background: Mechanical ventilation has dramatically improved outcomes in critically ill patients with respiratory failure. Minimizing volumes and higher positive end-expiratory pressures can further improve patient outcomes. Recruitment manoeuvres which can be used to individualize positive end-expiratory pressure may not improve outcome unless recruitable tissue is present. Existing methods of assessing if lung tissue is recruitable have a variety of limitations. Electrical impedance tomography (EIT) is a new technology that may be able to assess whether or not lung tissue is recruitable at the bedside.

Objectives: This review will assess the growing body of evidence that EIT is a promising technique which may help the clinician to optimize ventilation, while minimizing injury. We will review how the device works, the data supporting its use, and potential uses for the physical therapist in the critical care environment.

Major findings: EIT is a technique of injecting current through tissue, and measuring the difference between an array of electrodes. The difference relates to the changes of volume within the chest cavity – either blood or gas. It is reproducible, non-radiative, and real-time – allowing immediate and repeated imaging in the sickest of patients, who may require high levels of peep and recruitment manoeuvres.

Conclusions: This paper has demonstrated that with an understanding of the strengths and limitations of the device, EIT can be used successfully at the bedside by clinicians to guide recruitment and other clinical techniques.

Keywords:

• Electrical impedance tomography
• End expiratory lung volumes
• Functional residual capacity
• Lung volumes
• Recruitment