Electrical Impedance Tomography for Assessing the Impact of Inhaled Nitric Oxide on Pulmonary Artery Pressure

A 43-yr-old woman experienced acute respiratory failure with right ventricular dysfunction following a complex left pneumonectomy (fig. 1A) with cardiopulmonary bypass. She was intubated and mechanically ventilated.Electrical impedance tomography was employed to assess ventilation distribution and pulmonary perfusion. The ventilation distribution was determined by detecting tidal changes in impedance throughout the respiratory cycle, whereas the pulmonary perfusion assessment was performed through a breath-hold maneuver with a 10-ml injection of 7.5% saline solution, inducing impedance alterations.1,2 The amplitude and slope of curves after saline injection were calculated and used as surrogates of pulmonary blood volume and flow, respectively.3 Last, ventilation and perfusion impedance signals were integrated into an electrical impedance tomography ventilation/perfusion match map. The ventilation/perfusion match map defines regions of even match between the mostly ventilated and mostly perfused regions.Subsequently, inhaled nitric oxide at 20 ppm was administered. The pulmonary perfusion curves demonstrated a 25% increase in amplitude and a 17% steeper slope after inhaled nitric oxide treatment (fig. 1B), indicating a reduction of right heart afterload. The calculated pulmonary systolic arterial pressure by transthoracic echocardiogram reduced from 57 to 49 mmHg after 1 h of inhaled nitric oxide treatment, whereas the heart rate, systemic blood pressure, and estimated left ventricular ejection fraction remained unchanged. The improvement in pulmonary perfusion was attributed to the selective pulmonary vasorelaxation properties of inhaled nitric oxide. Interestingly, despite an increase in pulmonary perfusion, ventilation/perfusion match (fig. 1C) and arterial blood oxygen saturation remained unchanged. The patient was successfully weaned off from the inhaled nitric oxide the following day and extubated 3 days later. The case elucidates that the potential of electrical impedance tomography as a real-time monitoring tool can be utilized to optimize patient care in complex respiratory scenarios.Dr. Santiago received an honorarium from the Society of Critical Care Medicine (Mount Prospect, Illinois) for delivering a lecture unrelated to the content of this article; the content of the lecture does not overlap with the subject matter presented here. Dr. Victor received consulting fees from Timpel (São Paulo, Brazil), which manufactures a device used in this study. The other authors declare no competing interests.