Non-invasive indirect monitoring of intra-abdominal pressure using microwave reflectometry: system design and proof-of-c
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ORIGINAL RESEARCH
Non‑invasive indirect monitoring of intra‑abdominal pressure using microwave reflectometry: system design and proof‑of‑concept clinical trial Marcelo David1 · Aviad Raviv1 · Ariel Guttel1 · Valentina García Reyes2 · Franco Simini3 · Francisco Pracca2 Received: 22 June 2020 / Accepted: 5 October 2020 © Springer Nature B.V. 2020
Abstract Monitoring intra-abdominal pressure (IAP) has become a standard in intensive care units. Correlation between the abdominal wall’s thickness (AWTh) and IAP has been reported previously. The abdominal wall can be modeled as a compound of parallel dielectric slabs; changes in their width have a direct effect on the reflection coefficient of the abdominal wall at microwave frequencies. This work describes the design of a reflectometry system and its proof-of-concept trial on five patients during laparoscopic surgery. The system complies with IEEE Std. C95.1-2005 concerning exposure of humans to microwave electromagnetic fields in controlled environments. The results putatively show an inverse correlation between IAP and the reflection coefficient, and a strong dependence on the body mass index. A better understanding of the dynamics in the changes of the AWTh (during intra-abdominal hypertension) will allow further development of a microwave-based technique for the continuous non-invasive indirect monitoring of IAP in critical patients. Keywords Intra-abdominal pressure · Microwave reflectometry · Non-invasive
1 Introduction Intra-abdominal pressure (IAP) is the steady-state pressure concealed within the abdominal cavity [1]. The monitoring of IAP has become a standard in intensive care units (ICUs) as intra-abdominal hypertension (IAH) is directly associated with increased morbidity and mortality [2]. This relies on the fact that IAH (i.e. IAP over 12 mmHg) entails a negative impact in abdominal organ perfusion which could lead to organ dysfunction [2]. The most feared consequence of IAH, known as abdominal compartment syndrome (ACS), is defined as a sustained IAP > 20 mmHg, associated with severe organ dysfunction [2–5]. By monitoring IAP, our ultimate goal is to guarantee an adequate organ blood flow * Marcelo David [email protected] 1
Department of Electrical Engineering, Jerusalem College of Technology – Lev Academic Center, Jerusalem, Israel
2
Department of Intensive Medicine, Hospital de Clínicas, Universidad de la República, Montevideo, Uruguay
3
Núcleo de Ingeniería Biomédica, Universidad de la República, Montevideo, Uruguay
and, consequently, to reduce the risk of organ dysfunction, employing corresponding treatments [6]. Since IAH affects about 54–59% of critical patients [1, 7], monitoring IAP is usually indicated in ICUs [2, 8]. Diverse techniques are used in intensive care for monitoring IAP [9, 10]. Continuous monitoring of IAP has been researched by several groups in the past years [2, 3, 11–13], but no feasible or easy-to-use non-invasive method has reached clinical use yet [3]. In 2017, David et al. [14] proposed a generic numeric
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