Tomografía de impedancia eléctrica: fundamentos de hardware y aplicaciones médicas

Introduction: The following article shows a systematic review of publications on hardware topologies used to capture and process electrical signals used in Electrical Impedance Tomography (EIT) in medical applications, as well topicality of the EIT in the field of biomedicine. This work is the product of the research project “Electrical impedance tomography based on mixed signal devices”, which took place at the University of Cauca during the period 2017-2019. Objective: This review describes the operation, topicality and clinical use of Electrical Impedance Tomography systems. Methodology: A systematic review was carried out in the IEEE-Xplore, ScienceDirect and Scopus databases. After the classification, 106 relevant articles were obtained on scientific studies of EIT systems; applications dedicated to the analysis of medical images. Conclusions: Impedance-based methods have a variety of medical applications as they allow for the reconstruction of a body region, by estimating the conductivity distribution inside the human body; this is without exposing the patient to the damaging effects of radiation and contrast elements. Impedance-based methods are therefore a very useful and versatile tool in the treatment of diseases such as: monitoring blood pressure, detection of atherosclerosis, localization of intracranial hemorrhages, determining bone density, among others. Originality: It describes the necessary components to design an EIT system, as well as the design characteristics depending on the pathology to be visualized.  Introducción: En el siguiente artículo se muestra una revisión sistemática de publicaciones sobre topologías hardware utilizadas para capturar y procesar señales eléctricas utilizadas en tomografía por impedancia eléctrica (TIE) en aplicaciones médicas, así como la actualidad del TIE en el campo de la biomedicina. Este trabajo es producto del proyecto de investigación “Tomografía de impedancia eléctrica basada en dispositivo de señal mixta”, que tiene lugar en la Universidad del Cauca durante el período 2017-2019.   Objetivo: Esta revisión describe la estructura hardware de los sistemas de TIE, además de sus características, como frecuencia y magnitud de señales de corriente, patrones de inyección y medición de señales y número de electrodos orientado a, uso clínico.   Metodología: Se realizó una revisión sistemática, en las bases de datos IEEE-Xplore, ScienceDirect y Scopus. Tras la clasificación se obtuvo 106 artículos relevantes sobre estudios científicos de sistemas, aplicaciones dedicadas al análisis de imágenes médicas.   Conclusión: Los métodos basados en impedancia, tienen una variedad de aplicaciones médicas, puesto que permite la reconstrucción de una región corporal, mediante la estimación de la distribución de conductividad al interior del cuerpo humano, sin radiación y elementos de contraste, tan perjudiciales para la salud de los pacientes; convirtiéndola en una herramienta muy útil y versátil en el tratamiento de enfermedades como: monitorear la presión arterial, detección de arterosclerosis, localización de hemorragias intracraneales, determinar la densidad ósea, entre otras.     &nbsp

ELECTRICAL IMPEDANCE TOMOGRAPHY – CASE REPORT WITH SHORT REVIEW OF TECHNOLOGY AND CLINICAL APPLICATION SCENARIOS

Električna impedancijska tomografi ja (EIT) je neinvazivna metoda praćenja koja se u prvom redu koristi za procjenu regionalne distribucije ventilacije u plućima, ali je dokumentirana i druga uporaba (kao što je procjena distribucije perfuzije). Temelji se na fi zikalnom principu razlike u impedancijama različitih tkiva ili razlika u prozračenosti plućnog tkiva. Tomogram se zatim dinamički generira pomoću računalnog softvera i slikovno prikazuje. Klinički je prihvatljiva korelacija između EIT i kompjuterizirane tomografi je (engl. computed tomography - CT) za procjenu reverzibilnog alveolarnog kolapsa, što čini EIT vrijednim dijagnostičkim sredstvom za prilagođivanje postavki mehaničke ventilacije i regrutiranje alveola kod bolesnika s akutnim respiratornim distres sindromom (engl. acute respiratory distress syndrome – ARDS). Prikazujemo bolesnika primljenog u jedinicu intenzivne medicine (JIM) zbog ARDS-a koji je izazvan intraoperacijskom aspiracijom želučanog sadržaja. Nakon započinjanja mehaničke ventilacije i bronhoskopske lavaže, uz pomoć EIT provedeno je određivanje razine pozitivnog tlaka na kraju ekspirija (engl. positive end expiratory pressure – PEEP) potrebne da se izbjegne alveolarna predistendiranost ili kolaps. PEEP vrijednost od 14 mbara utvrđena je kao najniža razina PEEP iznad alveolarnog kolapsa. Plinske analize arterijske krvi nakon određivanja navedene razine PEEP pokazale su značajno poboljšanje u odnosu na početne vrijednosti, pa je pacijent sljedeći dan ekstubiran, otpušten iz JIM-a nakon dva dana i iz bolnice 4 dana kasnije bez ikakvih respiratornih komplikacija.Electrical impedance tomography (EIT) is a noninvasive monitoring method which is primarily used to assess regional distribution of ventilation in the lungs, but other uses (such as perfusion mapping) have been documented as well. It works on the physical principle of varying impedance of various tissues or differences in aeration of lung tissue. A tomogram is then dynamically generated by computer software to show regional distribution of ventilation. Clinically agreeable correlation was found between EIT and computed tomography (CT) assessment of recruitable alveolar collapse, which makes EIT a valuable bedside diagnostic tool to aid recruitment maneuvers in patients with acute respiratory distress syndrome (ARDS). We present a patient with ARDS induced by intraoperative aspiration of gastric contents, who was admitted to the intensive care unit (ICU). After initiation of mechanical ventilation and bronchoscopy guided alveolar lavage, stepwise positive end expiratory pressure (PEEP) trial was performed using EIT to detect alveolar overdistension or collapse. PEEP value of 14 mbar was established as the lowest level of PEEP above alveolar collapse. Arterial blood gas tests after the trial showed marked improvement over baseline values, the patient was extubated on the next day, discharged from the ICU two days later, and discharged from the hospital 4 days later without any respiratory complications

Emergency Cardiology

This fully revised and updated second edition offers practical advice on the diagnosis and management of acute cardiac conditions. Throughout the book, the authors employ an evidence-based approach to clinical practice and provide detailed guidance for day-to-day practice in a wider variety of settings-from the emergency department to intensive care and the cardiac ward. Authored by four cardiologists with extensive experience in the emergency setting, it includes the results of the most groundbreaking clinical trials. Topics include arrhythmias, acute aortic syndromes, pericarditis, and cardiac trauma

Emergency Cardiology

This fully revised and updated second edition offers practical advice on the diagnosis and management of acute cardiac conditions. Throughout the book, the authors employ an evidence-based approach to clinical practice and provide detailed guidance for day-to-day practice in a wider variety of settings-from the emergency department to intensive care and the cardiac ward. Authored by four cardiologists with extensive experience in the emergency setting, it includes the results of the most groundbreaking clinical trials. Topics include arrhythmias, acute aortic syndromes, pericarditis, and cardiac trauma

The conditioning of medical gases with hot water humidifiers

During invasive mechanical ventilation due to the dryness of medical gases is necessary to provide an adequate level of conditioning. The hot water humidifiers (HWH) heat the water, thus allowing the water vapor to heat and humidify the medical gases. In the common HWH there is a contact between the medical gases and the sterile water, thus increasing the risk of patient’s colonization and infection. Recently to avoid the condensation in the inspiratory limb of the ventilator circuit, new heated ventilator circuits have been developed. In this in vitro study we evaluated the efficiency (absolute/relative humidity) of three HWH: (1) a common HWH without a heated ventilator circuit (MR 730, Fisher&Paykel, New Zeland), (2) the same HWH with a heated ventilator circuit (Mallinckrodt Dar, Italy) and (3) a new HWH (DAR HC 2000, Mallinkckrodt Dar, Italy) with a heated ventilator circuit in which the water vapor reaches the medical gases through a gorotex membrane, avoiding any direct contact between the water and gases. At a temperature of 35°C and 37°C the HWH and heated tube were evaluated. The absolute humidity (AH) and relative humidity (RH) were measured by a psychometric method. The minute ventilation, tidal volume respiratory rate and oxygen fraction were: 5.8 ± 0.1 l/min, 740 ± 258 ml, 7.5 ± 2.6 bpm and 100%, respectively. Ventilator P2 Use of a bougie during percutaneous tracheostom

An investigation into the effects of commencing haemodialysis in the critically ill

<b>Introduction:</b> We have aimed to describe haemodynamic changes when haemodialysis is instituted in the critically ill. 3 hypotheses are tested: 1)The initial session is associated with cardiovascular instability, 2)The initial session is associated with more cardiovascular instability compared to subsequent sessions, and 3)Looking at unstable sessions alone, there will be a greater proportion of potentially harmful changes in the initial sessions compared to subsequent ones. <b>Methods:</b> Data was collected for 209 patients, identifying 1605 dialysis sessions. Analysis was performed on hourly records, classifying sessions as stable/unstable by a cutoff of >+/-20% change in baseline physiology (HR/MAP). Data from 3 hours prior, and 4 hours after dialysis was included, and average and minimum values derived. 3 time comparisons were made (pre-HD:during, during HD:post, pre-HD:post). Initial sessions were analysed separately from subsequent sessions to derive 2 groups. If a session was identified as being unstable, then the nature of instability was examined by recording whether changes crossed defined physiological ranges. The changes seen in unstable sessions could be described as to their effects: being harmful/potentially harmful, or beneficial/potentially beneficial. <b>Results:</b> Discarding incomplete data, 181 initial and 1382 subsequent sessions were analysed. A session was deemed to be stable if there was no significant change (>+/-20%) in the time-averaged or minimum MAP/HR across time comparisons. By this definition 85/181 initial sessions were unstable (47%, 95% CI SEM 39.8-54.2). Therefore Hypothesis 1 is accepted. This compares to 44% of subsequent sessions (95% CI 41.1-46.3). Comparing these proportions and their respective CI gives a 95% CI for the standard error of the difference of -4% to 10%. Therefore Hypothesis 2 is rejected. In initial sessions there were 92/1020 harmful changes. This gives a proportion of 9.0% (95% CI SEM 7.4-10.9). In the subsequent sessions there were 712/7248 harmful changes. This gives a proportion of 9.8% (95% CI SEM 9.1-10.5). Comparing the two unpaired proportions gives a difference of -0.08% with a 95% CI of the SE of the difference of -2.5 to +1.2. Hypothesis 3 is rejected. Fisher’s exact test gives a result of p=0.68, reinforcing the lack of significant variance. <b>Conclusions:</b> Our results reject the claims that using haemodialysis is an inherently unstable choice of therapy. Although proportionally more of the initial sessions are classed as unstable, the majority of MAP and HR changes are beneficial in nature