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Year : 2021  |  Volume : 10  |  Issue : 3  |  Page : 370-371

COVID-19 pandemic: It is time to think for micro-electro-mechanical system-based bidirectional flow sensor

1 Department of Trauma and Emergency, AIIMS, Patna, Bihar, India
2 Department of Anaesthesiology, AIIMS, Patna, Bihar, India

Date of Submission12-Jul-2021
Date of Decision15-Jul-2021
Date of Acceptance02-Aug-2021
Date of Web Publication13-Sep-2021

Correspondence Address:
Dr. Neeraj Kumar
Department of Trauma and Emergency, AIIMS, Room No. 503, 5th Floor, New OT Complex, B Block, Patna - 801 505, Bihar
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Source of Support: None, Conflict of Interest: None

DOI: 10.4103/ijrc.ijrc_95_21

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How to cite this article:
Kumar N, Kumar A, Kumar A. COVID-19 pandemic: It is time to think for micro-electro-mechanical system-based bidirectional flow sensor. Indian J Respir Care 2021;10:370-1

How to cite this URL:
Kumar N, Kumar A, Kumar A. COVID-19 pandemic: It is time to think for micro-electro-mechanical system-based bidirectional flow sensor. Indian J Respir Care [serial online] 2021 [cited 2021 Dec 2];10:370-1. Available from: http://www.ijrc.in/text.asp?2021/10/3/370/325894


Pulmonary protective ventilation with careful control of pressure and volume is required when ventilating patients with complex acute respiratory distress syndrome (ARDS) like pneumonia associated with COVID-19. These are evidence-based interventions for mechanical ventilation in patients with ARDS for improving outcomes.[1] Modern intensive care unit (ICU) ventilators provide complex control and intricate feedback loops for a wide variety of respiratory parameters and ventilation modalities. However, many commercially available ventilators that were built specifically for emergency use in large number of COVID-19 patients have only one mode of assisted ventilation (i.e., mandatory breaths not synchronised to patient's inspiratory effort).[2] These do not have the capability of sensing flow of gases reliably and therefore cannot control pressure and volume delivery in response to changing characteristics of the COVID-19 lungs. There is increased risk of barotrauma and further deterioration of lung injury.

There are various types of flow sensors. Differential pressure flow sensors or hot wire anemometers are commonly used in modern ventilators. The flow sensors have a thin membrane within a hollow plastic tube used to measure the amount of gases delivered to patients and measure the flow signal. This helps provide feedback to adjust the desired amount of gas to be delivered during mechanical ventilation. Precise volume, flow, and pressure data allow better assessment of the patient's lung condition. These flow sensors are very sensitive and can detect a flow rate as low as 200 ml/min during the initiation of respiratory effort to support breaths in spontaneously breathing patients or to trigger a synchronized assisted breath. They are helpful to constantly monitor the volume delivered by the mechanical ventilator and act as a safety check by giving an alarm if exhaled tidal volume significantly varies with preset settings.

Malfunction of flow sensors may be due to several known factors such as a leak from flow sensor, use of inappropriate size flow sensor, disconnection, wrong fitting of flow sensors, trapping of water, and presence of water vapor in flow sensor pressure tubing. However, reverse placement of flow sensors resulting in loss of ventilatory parameters and flow graphics is not reported. We report a very unusual situation following reverse placement of proximal flow sensor during the use of a mechanical ventilator (CV 200, Bharat Electronic Ltd, Licensed under Skanray Technologies Pvt. Ltd., Mysore, India) in our ICU for the ventilatory management of an adult patient with type 1 respiratory failure due to COVID-19 infection.

[Figure 1] shows the loss of ventilatory patient parameters and flow graphics following reverse placement of flow sensor on ventilator display. The proximal flow sensor, a centerpiece of all CV 200 Medical ventilators, is available as single-use or multiple-use, autoclavable for use in adults, pediatrics, and neonates.[3] If inspiratory or expiratory check valves accidentally remain open due to valve sticking, it may result in a bidirectional flow.[4] Kumar et al. reported unwanted ventilator alarms due to the use of the different sizes of proximal flow sensors in Hamilton C-3 ventilator.[5]
Figure 1: Loss of ventilatory patient parameter no flow graphic on ventilator display following reverse connection of flow sensor

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The sensor measurement technology-based flow sensors are a type of modern flow sensors. Hotwire anemometer Sensirion is a next-generation CMOSens® Technology-based modern flow sensor. It has differential pressure flow sensors which are based on a micro-electro-mechanical system. The advantages of these modern flow sensors are that they are simple, easy to use, fully digitally calibrated, with the temperature-compensated output signal. These sensors allow measurement of airflow symmetrically in both directions and are used in challenging emergency ventilation.[6]

If any problem is encountered while operating the mechanical ventilator, a systematic approach is required (i.e., all ventilator-related problems must be differentiated from patient-related problems). When in doubt, a test lung can be used to determine whether the issue is related to the patient or is due to ventilator malfunction. Inability to generate enough tidal volume may show a ventilator-related problem. If generated tidal volume (VT) is not reaching the patient, or the VT reaching the patient is not being properly measured, it may suggest a patient-related problem or a flow sensor-related problem.

In our case, improper placement of proximal flow sensor resulted in the loss of ventilatory parameters and flow graphics. In this current COVID-19 pandemic situation, the process of medical device design requires consideration and, if possible, mitigation of patient and user risk. To ensure safety and to avoid malfunction, it is time to develop a bidirectional flow sensor that can work in both directions for use with the indigenous ventilator.

Declaration of patient consent

The authors certify that they have obtained all appropriate patient consent forms. In the form the patient(s) has/have given his/her/their consent for his/her/their images and other clinical information to be reported in the journal. The patients understand that their names and initials will not be published and due efforts will be made to conceal their identity, but anonymity cannot be guaranteed.

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Conflicts of interest

There are no conflicts of interest.

  References Top

Fan E, Brodie D, Slutsky AS. Acute respiratory distress syndrome: Advances in diagnosis and treatment. JAMA 2018;319:698-710.  Back to cited text no. 1
Knorr JM, Sheehan MM, Santana DC, Samorezov S, Sammour I, Deblock M, et al. Design and performance testing of a novel emergency ventilator for in-hospital use. Can J Respir Ther 2020;56:42-51.  Back to cited text no. 2
CV 200 ventilator. Skanray Technologies Pvt. Ltd, 2020 Mysore India. Available from: https://www.skanray.com/?q=content/ventilators. [Last accessed on 2021 Jul 28].  Back to cited text no. 3
Tham R, Oberle. How do flow sensors work. APSF Newsletter 2008;23:11-3 Available from: https://www.apsf.org/article/how-do-flow-sensors-work/. [Last accessed on 2021 Aug 01].  Back to cited text no. 4
Kumar A, Kumar N, Kumar A, Dubey PK. Unwanted ventilatory alarm: Be careful about flow sensors size. J Clin Anesth 2018;46:23-4.  Back to cited text no. 5
Alt A. Sensirion AG. Flow Sensor Solutions in Modern Medical Ventilators. Available from: https://www.sensirion.com/en/about-us/newsroom/sensirion-specialist-articles/flow-sensor-solutions-in-modern-medical-ventilators. [Last accessed on 2021 Jul 31].  Back to cited text no. 6


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