Continous lung function analysis using Electrical Impedance Tomography for monitoring of lung collapse and perfusion during general anesthesia.

Abstract

Lung collapse (atelectasis) usually occurs during general anesthesia with mechanical ventilation what could cause hypoxemia and postoperative complications (infection and acute lung injury). The use of low fraction of inspired oxygen (FIO2) and PEEP (Positive End Expiratory Pressure) may reduce the amount of lung collapsed. Currently, there is no device that allows continuous evaluation of lung collapse during general anesthesia and helps setting the ventilator to reduce the amount of lung collapsed. The kinetics of the development of atelectasis in the intraoperative period in different adjustments of FIO2 and PEEP is also not well known, as well as, the associate changes in lung perfusion. Thoracic Electrical Impedance Tomography (EIT) allows continuous and non-invasive analysis of pulmonary function, as well as the amount of lung collapsed and also lung perfusion. The objectives of this study are: (a) to identify, using EIT, in healthy animals (pigs) submitted to general anesthesia and mechanical ventilation the value of PEEP that prevents lung collapse; and (b) analyze in those animals the magnitude and kinetics of formation of lung collapse with two values of FIO2 (0.4 and 1) and two values of PEEP (3 cmH2O and a value identified by EIT which avoids the lung collapse); c) to compare the values of collapsed lung obtained by EIT and Thoracic Computed Tomography (CT); d) to evaluate the temporal changes of perfusion, quantified by EIT and Thoracic CT. Our hypotheses are: a) the formation of lung collapse will be slower with the use of FIO2 of 0.4; b) the value of PEEP identified by EIT will prevent the formation of a lung collapse in the studied period; and c) the degree of hypoxic vasoconstriction will be correlated with the amount of lung collapse. (AU)