Real-Time Effects of Disconnection of the Ventilator on Regional Lung Volumes and Ventilation Distribution

Introduction

Patients in ICUs are often temporarily disconnected from mechanical ventilators under various clinical circumstances, either with or without clamping the endotracheal tube (ETT). Reasons for disconnecting patients from the ventilatory circuit include aerosol treatments, intrahospital transportation, or need to change the ventilator or any part of the circuit. Opening passive patients’ airway to the atmosphere often leads to expiration as there is usually a degree of positive pressure in the circuit even at end expiration (PEEP). This may lead to atelectasis in dependent zones and worsen intrapulmonary shunt. Besides PEEP, dynamic hyperinflation may also be a possible explanation to prolonged expiration after disconnection.

Clamping the ETT during brief disconnections of a patient without inspiratory efforts could in theory prevent adverse physiological effects of circuit disconnection, but it remains a topic of discussion rather than an established practice. Yet, recently, ETT clamping was frequently performed in critically ill patients with COVID-19 to prevent the exposure of personnel to aerosols and secretions from the patients’ lungs.

Short-term physiological effects of circuit disconnection with or without tube clamping in a passive patient have not been directly measured. The aim of this prospective, randomized, crossover study was to evaluate the effect of ETT clamping—during periprocedural disconnections of the ventilator—on regional lung volumes and ventilation distribution using electrical impedance tomography (EIT)^1-4 and on intrapulmonary shunt using simultaneous arterial and central venous gas sampling.