![]() ![]() Furthermore, in order to solve the synchronization problems about gas flow and concentration measurements, P ETCO 2 is used to calculate V T-alv. Previous studies showed that an increase in V D-alv that is induced by PEEP leads to impaired V̇ CO 2 in both healthy and injured lungs, 17– 19 which can cause an underestimation of V T-alv and EELV. 13 Alveolar tidal volume (V T-alv) is an important variable to calculate the volume of nitrogen in this method, and is computed according to the Bohr formula: According to the algorithm of the method, the volume of nitrogen wash-out/wash-in is not measured directly but is calculated by determining oxygen consumption (V̇ O 2), carbon dioxide elimination (V̇ CO 2), and inspiratory and end-tidal concentrations of oxygen and carbon dioxide (P ETCO 2). 16Īlthough the EELV-N 2 technique is now commercially available and can be performed easily, a potential problem in using this method is alveolar dead space (V D-alv), which can affect the accuracy. Previous studies demonstrated that the EELV-N 2 method is highly accurate in patients with acute respiratory failure, 13, 14 ventilated pediatric patients, 15 and in an animal model of unilateral pleural effusion. Recently, multiple breath wash-out methods, such as the modified nitrogen wash-out/wash-in technique (EELV-N 2), 13 have enabled EELV determination in ventilated patients without the need to interrupt mechanical ventilation. 12 However, the repeated measurements of EELV by pulmonary CT are obviously impractical because of radiation exposure, arduous analysis process, and the unavailability of the CT scan at the bedside. Quantitative analysis of pulmonary computed tomography (CT) at end-expiration is the gold standard for EELV measurement. 11ĭespite its critical role in the management of critically ill patients, EELV measurement is not without difficulties, especially in ventilated patients. Determination of end-expiratory lung volume (EELV) can help to monitor severity of acute lung injury 1 to assess respiratory mechanics, such as specific lung compliance, 2 lung strain, 3, 4 and alveolar recruitment 5– 7 to guide lung-protective ventilation 8– 10 and to identify patients who profit from recruitment maneuver after endotracheal suctioning. ![]()
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