Development of a Fluid Management System for Surgical Operations in Microgravity

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"Time, money, and resources will be saved by giving crewmembers access to medical treatment without needing to return to Earth. This will increase the overall safety of space-based missions and boost confidence in long-distance space travel from Earth."

- Christopher Higginson, University of Louisville

The Challenge:
Today, patients who require surgical treatment while in space would need to return to Earth for that surgery. To move closer to a future where physicians can operate in space, an experiment must be designed and deployed on an unmanned suborbital flight to investigate fluidic manipulation for a custom surgical isolation dome with leak-free trocar ports that hermetically isolate a simulated wound site.

The Solution:
With the I/O flexibility and convenient form factor of NI RIO hardware, participants in our research partnership between the University of Louisville and Cardiovascular Innovation Institute automatically triggered the initiation of a zero-gravity experiment and used LabVIEW and Ultiboard to develop control and automation of a fluid management system (FMS) and multifunctional surgical wand (MFSW).

Author(s):
Christopher Higginson - University of Louisville

 

The current NASA-supported project seeks to solve the problem of performing surgical operations in a microgravity environment. Thankfully, in the history of space flight, there has never been a surgical procedure performed nor an accident requiring immediate surgical treatment in space. Despite the technological advances that allow humans to live for extended stretches of time just outside Earth’s atmosphere, if a medical emergency does arise, the patient would need an emergency capsule to travel back to Earth for treatment. With plans for sending manned missions back to the Moon, then to Mars, and eventually beyond, medical complications are an absolute certainty, and appropriate treatment at the time of injury will be critical. This has led to the conceptualization and development of a surgical isolation dome (Figure 1), which requires a fluid management system (FMS) and multifunctional surgical wand (MFSW) to contain and control the site of surgery and function in the absence of gravity.

 

Figure 1. Surgical Isolation Dome With Surgical Instruments Inserted Into Leak-Free Trocars

 

The dome concept prevents further contamination of the spacecraft with blood and tissue debris (a significant problem in reduced gravity), reduces intraoperative blood loss, provides a sterile microenvironment, and maintains visualization of the operative field. The hemispherical shape was designed to be placed securely over a wound site and allow saline solution to be pumped in until the dome is full. Multiple studies with the surgical dome have led to the development of a flight-ready surgical FMS that is designed to operate both on the ground and under reduced gravitational conditions. The system manages and controls suction, irrigation, pressurization, and the purging/emptying of fluid in the dome with the aid of a custom MFSW (Figure 2) that provides manual control of these functions, including illumination, and cautery in an ergonomically designed surgical wand.

 

Figure 2. Prototype 3 of the MFSW

 

Early Development

During the early stages of development, we manually manipulated fluids with an approach to control and contain the surgical site in reduced gravity. We used a push-button technique for the simple filling and emptying of the dome (Figure 3). A second-generation prototype provided semiautomatic (timed) and sensor-based control. In the early versions, we used a printed circuit board (PCB) with an integrated microcontroller (Atmega328) running a custom embedded control program to activate the pumps and valves of the FMS flow loop. This ensured that we could implement events such as fluid initiation, completion, and emptying/purging in the dome with the press of a specific button. An optical fluid/air interface sensor was used to automatically stop the filling step by detecting the end of the fill step, which was sensed by the microcontroller.


We developed the MFSW as a companion device for the second-generation FMS to provide additional features such as dispensing a blood simulant, clearing the visual field (incomplete dome emptying), and irrigating with mild pressure increases inside the dome (fluidic tamponade).

The FMS was successfully tested in simulated zero gravity on a C130, the famed Vomit Comet.

 

Figure 3. First-Generation FMS Control PCB (left); Manual Control Interface (right)

 

NI myRIO Interfacing for System Automation

The grant provides support for an experiment on SpaceShipTwo (Virgin Galactic) in fall 2018, which is an unmanned flight campaign. Therefore, we needed to develop a fully automated system to support the FMS and MFSW components. To achieve the additional features necessary for this more challenging scenario, we replaced the original microcontroller with a real-time controller, the myRIO-1900. Besides compatibility with the rapid development provided by the LabVIEW programming environment, myRIO has several built-in hardware features (accelerometer, differential analog inputs, industry-standard pin connectors) that enabled us to develop a mature and feature-rich experimental setup in a relatively short time. For example, to further help with system automation, we incorporated a pressure sensor at the inlet of the surgical isolation dome to constantly monitor the equilibrium pressure during the experiment.

The FMS and MFSW were designed to run in concert with an automated control configuration programmed to remove the need for manual button presses and to sequence the experiment based on the prescribed timing for each of the flow steps. We also developed a virtual manual control interface (Figure 4) to take advantage of the built-in Wi-Fi module. Data from the onboard accelerometer of the myRIO was used to initiate the automated evaluation protocol upon the detection of microgravity (<0.02 G). We performed validation testing of this sensor by developing software to trigger high-resolution data capture upon entering microgravity. We used the NASA Glenn Research Center’s 2.2-second drop tower to validate the software trigger. The myRIO loaded into an experimental drag shield system and raised to 24 m (79 ft) before being dropped. Nine total experiments were performed, and the trigger was successful in detecting the zero-gravity condition in each case. Results also showed single bits above absolute zero G from the accelerometer when in the zero-G condition, matching the specification of the 3.9 mGrms reported in the datasheet (±8 Gs/212). Additionally, the z-axis reported higher Gs than the maximum 8 Gs reported in the datasheet (~14 Gs reported on impact after the zero-G condition; ~300 Hz sample rate).

 

Figure 4. Virtualized Manual Control Interface

 

 

Integration of a Full-Configuration PCB With myRIO

Both the myRIO-1900 MXP 34-pin connectors were used to connect to a custom PCB designed using NI Multisim and Ultiboard (V 11.1) software (Figure 5). The PCB containing the control circuitry plugs directly into the myRIO-1900. We used the myRIO dual MXP daughterboard template as a starting point since it provided a prepopulated configuration for I/O connectivity. This template helped us appropriately place the female MXP connectors on the PCB with correct spacing and dimensions as well as allowed us to appropriately assign the pins on the subcircuits for I/O connectivity. Electronic components that support the FMS and MFSW (pumps, valves, flow meter, flow sensor, pressure sensor) were equipped with individual headers on the perimeter of the PCB, and similar components were combined into one header (button control from the MFSW).

 

Figure 5. Ultiboard 3D Rendition of the Custom Control PCB

 

After designing the PCB, a circuit prototype was constructed on an NI Educational Laboratory Virtual Instrumentation Suite (NI ELVIS) prototyping board to confirm the functionality of the circuit design. We used LEDs at this stage to simulate the fluidic components of the system and confirm that all components of the system were functional.

 

Benefits of the FMS and MFSW to NASA and Beyond

A fully functional FMS and collection of appropriately sized surgical domes will provide a compact, efficient technique to perform minimal surgical operations during space travel. The FMS will manage the infusion of all necessary fluids and increase overall system reliability, With the companion MFSW, it will act as a helping hand for the limited number of personnel who will populate an extended flight spacecraft (approximately four to six crew members). Time, money, and other resources will be saved by giving crewmembers access to medical treatment without needing to return to Earth. This will increase the overall safety of space-based missions and boost confidence in long-distance space travel from Earth. The FMS not only facilitates space-based surgery but also offers the potential for fluid management in ground-based surgery while eliminating certain medical devices and extra personnel from the operating room during laparoscopic procedures.

 

What’s Next

Work is under way to prepare the FMS and MFSW for flight readiness deployment on a suborbital flight evaluation onboard the Virgin Galactic SpaceShipTwo in fall 2018. In spring 2018, we sent the PCB into production, fabricated a custom circuit enclosure, completed the design of the MFSW, and finalized the fluidic component placement on the experiment board (Figure 6). Extensive ground-based testing will ensure that the circuitry and LabVIEW control program successfully operate the FMS and MFSW. These validation tests are critical considering the experiment ultimately will be performed in near-zero gravity (approximately two minutes of zero G conditions) and the entire experiment must be triggered automatically because the flight is unmanned.

 

Figure 6. This SolidWorks rendition of the FMS shows all the components including the high-speed peristaltic pumps and surgical dome (white). The tubing and dome ports are not shown for clarity. The PCB and myRIO are located below the fluidic components.

 

Author Information:
Christopher Higginson
University of Louisville

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