Optimal PEEP Titration Combining Transpulmonary Pressure Measurement and Electric Impedance Tomography

ARDS, Human

Diagnosis and treatment of the hypoxic respiratory failure induced by severe atelectasis with the background of acute lung injury is challenging for the intensive care physicians. Mechanical ventilation commenced with grave hypoxemia is one of the most common organ support therapies applied in the critically ill. However, respiratory therapy can improve gas exchange until the elimination of the damaging pathomechanism and the regeneration of the lung tissue, mechanical ventilation is a double edge sword. Mechanical ventilation induced volu- and barotrauma with the cyclic shearing forces can evoke further lung injury on its own. Computer tomography (CT) of the chest is still the gold standard in the diagnostic protocols of the hypoxemic respiratory failure. However, CT can reveal scans not just about the whole bilateral lung parenchyma but also about the mediastinal organs, it requires the transportation of the critically ill and exposes the patient to extra radiation. At the same time the reproducibility of the CT is poor and it offers just a snapshot about the ongoing progression of the disease. On the contrary electric impedance tomography (EIT) provides a real time, dynamic and easily reproducible information about one lung segment at the bed side. At the same time these picture imaging techniques are supplemented by the pressure parameters and lung mechanical properties assigned and displayed by the ventilator. The latter can be ameliorated by the measurement of the intrapleural pressure. Through with this extra information transpulmonary pressure can be estimated what directly effects the alveoli. Unfortunately, parameters measured by the respirator provide only a global status about the state of the lungs. On the contrary acute lung injury is characterized by focal injuries of the lung parenchyma where undamaged alveoli take part in the gas exchange next to the impaired ones. EIT can aim the identification of these lesions by the assessment of the focal mechanical properties when parameters measured by the ventilator are also involved. The latter one can not just take a role in the diagnosis but with the support of it the effectivity of the alveolar recruitment can be estimated and optimal ventilator parameters can be determined preventing further damage caused by the mechanical stress.

Following PEEP increment and decrement alveolar recruitment manoeuvre optimal PEEP would be assessed by transpulmonary pressure measurement to keep open up the lung. Physicians are lack of data at which pressure the most alveoli are recruited and if 40 cmH2O of pressure is really required for complete recruitment. By CT scan of chest and continuous EIT measurement rate of recruitment would be assessed.

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