Monitoring Lung Function with Electrical Impedance Tomography in the Intensive Care Unit

We monitor lung functioning with electro impedance tomography in the intensive care units. This technique translate variations in impedance over time in topograph images. This is helpful in a dynamic clinical environment where patient conditions can rapidly evolve.

Electro impedance tomograph, ultrasound, CT scan, esophageal manometer are currently being used to monitor aspects related to the lungs. The challenge is to correctly place the belt for obtaining high quality signal and interpret the data correctly. One needs to understand how the signal look like in each condition and then make a comprehensive interpretation.

We intend to understand heterogeneous lung disease, impact of patient positions to lung mechanics, evaluation of treatment effect, and personalized changes in mechanical ventilation parameters using EIT. EIT is a continuous, non-invasive, real-time, radiation-free monitor, and allows us to access regional ventilation and perfusion distribution. The other methods of lung monitoring could not provide the regional distribution information.

Nowadays, EIT is the only technique that allows us to access real-time regional distribution. To begin, instruct the patient to take the position for chest wall measurement. Using a tape, measure the thoracic perimeter between the fourth and fifth intercostal spaces and choose the appropriate belt among the different sizes.

Cover the electrode belt with disposable material and conductive gel. Place the belts on the fourth and fifth intercostal spaces of the patient's chest wall, ensuring no overlap with the electrodes. Connect the flow sensor to the ventilatory circuit close to the Y piece and position it with the sensor upwards to prevent fluid accumulation or signal interference.

Connect the belt to the EIT device. Next, connect the reference electrode to an electrocardiographic or ECG electrode. For both adult and pediatric patients, position the electrode on the abdomen or shoulder.

Turn on the electrical impedance tomography or EIT and enter patient demographic data. Then measure the anterior gap and fill in the results. Start monitoring in the absence of patient movements.

The EIT will generate two images, the dynamic image and the ventilation map. Then select the PEEP titration tool from the main screen icon and access the tool options. Set time intervals for PEEP changes during titration to stabilize ventilation in each condition.

Adjust the threshold value for automatic PEEP change detection. Press start on the PEEP titration screen to initiate the countdown based on the adjusted time for PEEP changes. When prompted, adjust the PEEP value on the ventilator according to the protocol.

The device will automatically detect the change and start a new countdown. Monitor the PEEP changes, and if automatic detection fails, manually stop and comment on the procedure. Optionally, provide comments or name the titration and obtain the PEEP titration graph.

First, ensure sufficient patient sedation and, if necessary, neuromuscular blockade, as any respiratory effort can disrupt the procedure. To start the procedure, click on the start icon within the EIT software. Switch to continuous positive airway pressure or pressure support ventilation mode with a pressure support of zero centimeters of water.

Quickly and consistently inject 10 milliliters of a 7.5%hypertonic saline solution through a central venous access catheter at the internal jugular or subclavian vein. Once the injection is complete, return to regular ventilation settings. Finally, obtain the reconstructed profusion image based on the first pass kinetics of the contrast flowing through the heart and lungs.

Dynamic imaging displays real-time air distribution changes during ventilation, using color variations from dark blue to white to show least to most ventilated areas, with gray indicating no change. EIT technology allows real-time monitoring of lung mechanics, presenting data on lung area responsiveness. EIT also extends to measuring pulmonary perfusion with the detection of changes in blood impedance, especially using intravenous hypertonic saline during specific maneuvers.

This helps to visualize and assess perfusion patterns alongside ventilation. This comprehensive evaluation aids in the early detection of lung pathologies such as atelectasis and reveals increased ventilation in the posterior lung, which increased from 23%to 43%in a patient.