A NOVEL ELECTROMECHANICAL DEVICE FOR NON-INVASIVE CONTINUOUS MONITORING OF THE INTRAABDOMINAL PRESSURE
Currently, IAP is measured invasively, manually, and only sporadically, causing side effects and, if not detected, potentially fatal abdominal conditions. Ideally, IAP is constantly monitored by dedicated equipment able to predict critical situations. With the IAP-CMM system, we aim to significantly reduce mortality through continuous and noninvasive assessment of the IAP. IAP-CMM will also lower operational costs since it requires much less work by
trained staff than current methods.
WHAT WE WANT TO DO
The project aims to develop and clinically test a multimodal sensor system to continuously and noninvasively monitor the intra-abdominal pressure (IAP) of intensive care patients (ICPs). Currently, IAP is measured only intermittently, so fatally high IAP, which occurs in about 20-40% of ICPs, may pass undetected. Current measurement methods are invasive, while the IAP Continuous Multimodal Monitoring System (IAP-CMM) relies on precise electromechanical measurements of the abdominal wall tension.
OUR GOALS
The goal of the project is to develop and test in clinical conditions a working prototype of a multimodal sensor system (the IAP-CMM system) for the continuous non-invasive monitoring of the IAP. The main result of the project is the IAP-CMM system, including its design and clinical validation. The IAP-CMM system will be composed of two measuring devices (the IAP-CMM devices) which are in contact with the skin of the patient's abdomen, and a processing unit which receives the signals from the IAP-CMM devices wirelessly and processes them to obtain the IAP in real-time. The algorithms on the processing unit will be based on preliminary results and findings during the project. They are the first goal of the project. The second goal is a simple interface which alerts and communicates with medical staff and other medical instruments. The third goal of the project is to develop the IAP CMM devices. These devices will unobtrusively and simultaneously collect three different types of body signals from the skin which contain information on the IAP. The three measured signals are the mechanical tension changes of the abdominal skin, electrical bio-impedance and body-surface potentials from the activity of abdominal muscles (surface electromyography, sEMG).
Reasons for measuring these signals:
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IAP changes induce tension changes of the abdominal skin.
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The electrical impedance of the abdominal wall varies as a result of the soft tissue deformation induced by IAP.
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The sEMG is measured to distinguish mechanical and impedance changes which are induced by abdominal muscle contraction/tension from changes which are induced by IAP changes.
Each of the 2 IAP-CMM devices (about 80mmx80mmx10mm) will have 4 dry electrodes, a mechanical muscle contraction sensor (MC-S), the necessary electronics for analogue-to-digital conversion of the signals and a module for wireless communication of the measured data.
In this project, an innovative new product (the IAP-CMM system) will be designed and prototyped. This device will allow TMG-BMC to have a unique solution in the market of IAP measurement. From the application point of view, the IAP-CMM system will be an improvement of the current IAP monitoring procedure. The added value of using the new IAP-CMM system will come from: Less side effects, reduced mortality rate of ICPs, reduced number of staff required for measuring the IAP, reduced costs and the possibility for data connectivity. The IAP-CMM system will be a breakthrough technology in ICP safety as it will allow continuous monitoring of IAP and will reduce the time until surgical intervention if Intraabdominal hypertension (IAH) occurs.
STATE-OF-THE -ART
The IAP is defined as the steady-state pressure in the abdominal cavity. The IAP oscillates with the respiratory phases and according to the abdominal wall resistance. An IAP level of up to 5 mmHg is considered physiological in adults; however, in obese patients, the IAP may range from 10 to 15 mmHg, while IAP values between 5 and 7 mmHg are expected in critically ill patients.
The World Society of the Abdominal Compartment Syndrome (WSACS) defines intra-abdominal hypertension (IAH) by an IAP>12 mmHg in 3 consecutive measurements taken at intervals of 4–6 hours. The IAP may gradually progress to abdominal compartment syndrome (ACS), with a sustained IAP above 20 mmHg and associated organ dysfunction. IAH is associated with significant morbidity and mortality in critically ill and injured patients. Among various techniques proposed for measuring the IAP by introducing catheters in the urinary bladder, in the stomach or in the inferior vena cava, the WSACS has set the intravesicular pressure measurement as the gold standard for diagnosing IAH/ACS. Today, commercial products require an existing Folley catheter to monitor IAP. ConvaTec offers 2 different IAP monitoring devices: UnoMeter™ Abdo-Pressure™ and AbViser™ AutoValve ™ IAP monitoring device. The first one works based on measuring the height of the fluid column. The latter includes a transducer which measures the pressure within the tubing. A similar product, the BARD® IAP monitoring device, also has a transducer.
Disadvantages of these solutions can be noted as:
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additional risks associated with needle stick injuries and exposure to blood and body fluids,
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increased risk of urinary tract infection or sepsis,
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impossibility of continuous measurements as they interfere with natural emiction,
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reduced repeatability due to the necessity of recalibration each time and dependence on the experience of
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the staff,
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high-labor costs, and
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dependence on the patient position.
WHY IS IT INOVATIVE?
The IAP-CMM system will assess the IAP non-invasively and continuously, in contrast to the current method, which is invasive and intermittent. The system measures three signals: mechanical tension changes in the abdominal skin, impedance changes in the abdominal wall, and the electrical activity of the abdominal muscles; simultaneous measurement of these three signals in one device has never been done before. The device will perform the measurements autonomously, meaning that after the fast installation and calibration process, the IAP-CMM device will not need further human attention, while the current method requires the manual work of typically two health professionals for every measurement. More so, the IAP-CMM allows rapid data acquisition over a prolonged period.
The real advantage of the IAP-CMM is, therefore, that it provides a fast, efficient, and reliable alternative to the time-consuming and error-prone invasive current method. Rather than obtaining isolated measurements, our system will have a user-friendly interface with a continuous graph of the IAP trend, which can be further analyzed with methods such as area under the curve (AUC) or time above threshold (TAT) to better predict clinical outcomes.
In contrast to the current method, the IAP-CMM records all data in digital format, facilitating the synchronization of the monitored IAP with other instruments and typical signals in the ICU and opening the possibility of data processing (extrapolation of critical parameters). The data collected by the IAP-CMM system and other ICU instruments will also be compatible with the future application of machine and deep learning as well as computational signal processing, allowing further improvements of preventative medical care.
Finally, we expect the IAM-CMM system will dramatically lower operational costs by reducing the necessary involvement of health professionals, even though some monitoring will still be necessary.
IAP is defined as the steady-state pressure in the abdominal cavity resulting from the interaction between the abdominal wall and viscera. The most obvious method is to directly measure the pressure inside the abdominal cavity. The WSACS rather recommends an indirect measurement however, namely the intra-vesical (urinary bladder) pressure measurement, as the reference standard. Therefore, we observe that experts in the domain favor a minimally-invasive indirect measurement even at the expense of a potential loss of accuracy when compared to invasive direct measurement. Our approach goes one step further since it is not only non-invasive, but also non-obtrusive. This greatly facilitates its acceptance in the ICU setting.
The accuracy of the intravesical pressure measurement, though accepted as the reference standard, is prone to degrade depending on the way it is exercised or due to the patient’s condition. For instance, putting the patient upright with the concomitant rise of the transducer may lead to an underestimated IAP, while putting the patient in the Trendelenburg position can lead to an overestimation. The WSACS has also set the amount of saline to be instilled to up to 25 ml. However, this liquid volume may not be adapted to patients with additional conditions such as the presence of intra-peritoneal adhesions, pelvic hematomas, pelvic fractures, or a neurogenic bladder. Although there have been improvements in the hardware such as close-loop systems to ensure sterility, the labour-intensive nature of the technique remains an obstacle towards the continuous measurement of IAP. Furthermore, it has to remain an intermittent technique as it interferes with urine output. All this puts a limitation on the early detection of acute IAH which can develop within hours.
Our approach provides at least a complementary solution rather than to completely replace the intravesical measurement as it will provide clinicians with the continuous trend of IAP, thus enabling early detection of acute IAH and providing the information that indicates when a reference measurement has to be done. Given the conditions of the patients in the ICU or even post-surgery, a Foley catheter is installed anyhow. Therefore, the intra-vesical method will still be possible and assisted by the continuous measurement with the proposed non-obtrusive approach. Instead of taking periodic measurements which do not necessarily align with the altering condition of the patient, it will be possible to identify the right moment for reference measurements. Furthermore, the time above a critical IAP threshold or the area under the curve above a threshold may be of greater clinical significance than the isolated IAP values, which do not even necessarily correspond to maximum points. On top of that, our approach provides the means for synchronizing the IAP measurements with additional physiological parameters that are already digitalized in an ICU setting, which is expected to facilitate the management of IAH and ACS as it provides a more complete picture of patient's condition.
Other indirect measurement methods, based on an idealized view of Pascal's law of transmission of fluid-pressure within the abdominal cavity, have also been proposed. However, till now these have not received clinical acceptance, nor commercial interest. For instance, an intra-gastric method employing a wireless motility capsule has been proposed, yet it suffered from limited monitoring duration, motion sensitivity, and it has been shown that it underestimates the IAP. Intra-vaginal measurements, on the other hand, have not found acceptance in IAP measurement due to their sex-specific nature and obtrusiveness.
Non-technical methods such as palpation of the abdomen have been ruled out since long for estimation of IAP and hence clinical management of IAH/ACS as they do not provide a quantifiable and accurate outcome.
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EUROSTARS PROJECT E114220 - IAP-CMM
