Introduction Bleeding during surgery is common. Increased bleeding may disturb procedure, induces haemodynamic instability and results in need for blood transfusion. Allogenic blood transfusions increase mortality and morbidity, especially risk of infections, pulmonary and renal complications, as well as thromboembolic events. Autotransfusion is in many cases a solution but forced suction may destroy or alter blood cells because of turbulences, shear forces and contact of the blood to extrinsic surfaces. The aim of the study was the analysis of turbulence profile and development of a new suction device reducing (or avoiding) turbulences.
Methods We registered turbulences with a microphone placed in different positions within the blood suction during surgery and analysed the spectrum. Then, we modified the circuit adding signals from optical sensors and pressure transducer to avoid air mixing and tight suction. Finally, we created the algorithm for the suction circuit regulating individualised suction modes.
Results We developed a new suction system based on a roller pump. We used a piezo sensor and registered the acoustic signals. The optimal position for this element was into the suction handle. After filtering the signal and further processing, we used it for regulation of the roller pump. Additionally, an optical sensor minimises air mixing due to further regulation of motor speed. Finally, a negative pressure transducer gives in case of tight suction information to the circuit stopping motor speed and equalising pressure by opening a valve before suctions starts again. The algorithm allows various suction modes in an individualised manner for specific situations in operating field.
Conclusions We developed a new blood suction device based on a roller pump. The system is turbulence-controlled and its algorithm allows several individualised suction modes. Additional features avoid tight suction and reduce air mixing.
- Blood Suction
- Blood Transfusion
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Bleeding during surgery is usual and disturbs unrestricted view of the operating field, and therefore, blood suction takes it out of the operating area. Severe bleeding leads to intravascular blood loss requiring transfusion of blood. In order to avoid blood transfusions, use of several blood processing systems increases. To achieve good treatment results, not only the washing procedure itself but also the condition of the blood collected from the surgical field is essential. For returning the patient’s own blood after suction from surgical field, blood must be of ‘good’ quality to avoid inflammatory reactions or intravascular coagulation activation.1 The intraoperative blood suction usually managed by vacuum leads to turbulences, to acceleration of sucked material at edges and to air mixture.2–7 The shear forces developed can exceed the resistance of biological membranes, resulting in increased destruction of cells.8 Additionally, blood cells get activated inducing leucocyte differentiation and activation of the coagulation cascade along with haemolysis and thrombocytopenia may result.1 9–14 Finally, the interaction of blood with foreign surfaces and air may lead to systemic inflammation reaction by activation of mediators (eg, cytokines and interleukins).
Another problem of suction is the contact of the suction tip to sensitive tissue with the risk of tissue damage.15 16 For reducing this risk, most suction heads have several secondary holes, but these side holes may cause severe turbulences. Suction at the blood/air borderline mixes air to the blood-forming foam, which leads to further cell reactions.17 As mentioned above, suction systems usually operate with vacuum, which is low cost and well established. However, roller pumps may achieve better negative pressure control and an optimised ratio of suction tube diameter and occlusion pressure may reduce haemolysis.18 19
The aim of the present study was to develop a novel suction system for improving the integrity of suction blood optimising several factors, such as turbulence, vacuum and air mixing with the goal of improving quality of blood before further processing and possible retransfusion.
We developed a novel suction system based on a roller pump-driven suction system. The circuit design is to avoid turbulences as far as possible. The core principle of the system is the registration and automatic analysis of acoustic turbulence signals.
Vibrations detected in the tip of suction were processed as an electrical voltage fluctuation, and these changes modified the control voltage of the roller pump motor.
In a first step, we recorded the frequency spectrum of a routine suction process during surgery. For this purpose, we placed a microphone (ECM8000, Ultra-Linear Measurement Condenser Microphone, Behringer-Music Group, Germany) 1 m away from the suction tip which is approximately equal to the distance from the suction tip to the surgeon’s ear. We recorded frequencies of different types of suction device and other sound sources (eg, speech, procedural noise) and extracted the acoustic signal using a steep-flank bandpass filter (Sequoia V13.1, Magix AG, Germany).
In a second step, we placed vibration sensors in different positions closer to the tip of a newly developed handle to find the ideal position improving the quality of the signal and eliminating interfering secondary noises. The signal recording was near to the source of turbulence but without direct blood contact. Four vibration sensors were tested: (a) a guitar pickup (AGX094, Fishman Acoustic Amplification, USA), (b) a violin pickup (V-100 violin/viola pickup, Fishman Acoustic Amplification), (c) a minimicrophone (Multicomp MCKPCM-60H27PC33-44DB-4623 Piezo, 900 HZ, 86 DB, Farnell, Germany) and (d) a piezo element (Piezo pressure transducer BiMorph CCCN 85365011, R&S, Germany).
The suction control system (figure 1) was constructed based on a roller pump (Polystan, Type Modular No. 1603, Vaerlose, Denmark) with ¼-inch tube system (HMT, Medizintechnik, Maisach, Germany). A negative pressure sensor (RTR-AL-20MA-RV1, −1 to 1 bar, B+B Thermo-Technik, Donauschingen, Germany) was additionally integrated and, finally, an optical element with two sensors (MRL601, Microeletronic Volkmann, Germany) with a distance of 7 cm was installed in order to detect interruptions of the sucked blood column by air bubbles. The negative pressure sensor detects critical pressure, and consequently, the system regulates the suction power ad hoc. The optical sensors recognise air.
All three sensor systems (vibration, negative pressure, optical density) were intend to regulate the suction power dynamically in real time, facilitating a sensible and safe suction process, sterilisable and reusable. This prototype was assessed for safety and used for 10 surgical procedures.
The acoustic signals were recorded in the tip of the suction device. In most cases, the signal was usable for the control system but it was still susceptible to interference by interspersing secondary noises from the operating area. Therefore, we filtered the control signal and developed a new suction handle. The acoustic signal initially registered was weak: 8–19 kHz and <1 mV. Therefore, a preamplifier in the handgrip (25 dB) trimmed the signal with a downstream bandpass filter (11–16 kHz) and suppressed all disturbing signals (eg, speech, noise from equipment, monitors or surgical instruments). The degree of influence of the turbulences (dB) on the control voltage of the motor was set with a gain control (amplification by preamplifier by 10 dB up to 60 dB). The signal indicative for the detection of the turbulence was directed into the control circuit (figure 2).
In addition, a gate filtered sudden artefacts (eg, nudge on the retractor) avoiding these signals to pass to the control circuit. Signals with a sufficiently long-lasting minimum intensity were processed. The processed signal adapted the real-time voltage of the roller pump motor (from 0 to 10 V) and subsequently regulated the motor speed (figures 1 and 3). This circuit limits the rotational speed of the roller pump below a specific level avoiding turbulences.
Figure 4 shows the relationship between pump flow, generated pressures and turbulences occurring during suction at the blood/air borderline. The suction control reduces highly significant turbulences (P<0.001) while the negative pressure corresponding to the pump flow is hardly influenced. If the tip of the suction is tight to the tissue, the vibration sensor detects no turbulences (figure 1) and the pump would normally increase the speed up to a maximum value. In order to avoid this condition, we interposed a pressure transducer between suction head and roller pump. The negative pressure limit is steeples adjustable up to 230 mm Hg. When a predefined negative pressure level was detected (or specific vacuum kinetics), the roller pump stops and a valve is briefly opened to a secondary pathway for pressure compensation. We found it advantageous to introduce fluids rather than air preventing foaming in the suction system. Subsequently, the valve closes again and the pump speed increases again slowly, resulting in a more effective suction process.
Finally, all elements installed correspond to the medical–technical regulations.
Air bubbles interrupt blood continuity in the suction tube (figure 5). The optical sensors detect these transported air bubbles. The following three states were registered:
State A: a continuous blood column without air bubbles is detected by both sensors.
State B: the blood column is interrupted by air bubbles.
State C: no blood, only air is detected.
The optical signals in the vacuum control system are additional competitive control variables to achieve reduction of air mixing. In state A, the rotation speed of the roller pump increases, in state B, the speed is reduced until a state A is reached again, and in state C, the rotation speed is reduced to a low stage until state A is detected again. Reaching later state speed increases up to the predefined turbulence or vacuum limit. With this algorithm, the air fraction is reduced up to 80% compared with a ‘standard’ suction.
Special situations in the operating field need different suction modes. The programmed modes receive information from the three sensor systems (turbulence, negative pressure and air in the system) and change the pump performance (speed). The basic mode is on medium sensitivity of all three sensors and is for standard suction in the operating field (‘preparation mode’). The ‘sensitive mode’ is suitable for non-manual automatic suction: the tip may be placed in the deepest point of the operating area (eg, peritoneal cavity, pericardium, the pleural cavity), resulting in continuous suction of blood from the operating field. This mode reduces significantly the contact time of blood to tissue. Activation of the ‘emergency mode’ leads to maximum power for 10 s. Then, the preselected mode resumes.
The developed prototype encodes the three modes; beside the basic mode, illuminated buttons (placed on the suction handle) activate the two additional modes.
The suction system with all components along with the algorithm is patented as the turbulence-controlled suction system (TCSS). Subsequently, aspirated blood is retransfused directly to the patient (via a heart–lung machine or a retransfusion system) or after further process (eg, cell-saver system). Finally, the destination of the sucked material can be defined; for example, flushing liquids may be directed into the waste and blood for further processing.
Use of the prototype during surgery was without any problem. Feedback of surgeons reported was positive due to very good effectiveness of suction resulting to ‘dry’ operating field during procedure with the sucker handle was placed at the lowest point of the pericardial space. Most surgeons found optical feedback comfortable. From a technical point of view, the device worked also without any problem; the pressure limitation worked as expected, and the optimal control points for each procedure remained stable without the need to change the parameters during procedure.
Surgical procedures can be associated with significant blood loss. The additional costs of treating bleeding complications lead to a high burden on the health system. Each year several billion euros (or dollars) are spent worldwide.20 21 Indication for blood transfusion is higher blood loss, but transfusions are associated with complications in short term and even in long term, leading to critical discussion.22–27 Therefore, several blood-saving concepts have been developed; for example, in some cases, especially in traumatology, vascular surgery, general surgery or cardiac surgery, cell-saver systems are used increasingly avoiding blood transfusions.18 19 23–25 27–32 A special situation is in cardiac surgery returning patient’s blood from the operating field using the heart–lung machine.
The synergistic interaction of the components of the described suction system reduces negative effects of forced suction. The turbulence control reduces the level of shear forces but also of air mixture. Air mixture disrupts blood surfaces and create foam, leading to cell activation. The optical sensors placed in the suction tube allow (semiquantitative) control of air within the blood column. The applied algorithm reduces automatically air mixture to a reasonable minimum.
Tight suction may lead to tissue injuries and can be avoided by controlling the achievable vacuum level.15 16 Usually uncontrolled suction systems reach a negative pressure up to 800 mm Hg until the suction tube collapses. When the presented suction system reaches a predefined negative pressure, the pump motor stops and a valve opens for pressure compensation, resulting in easy release of the suction tip from the tissue and avoiding tissue injuries.
The control features of the new suction system allow programming of the control unit in a specific and individualised manner. The surgical team has besides the unrestricted view of the operating field also an optical feedback of suction. In a further step, active direction of the suction material to processing or to waste is possible.
Surely, the TCSS will be more expensive than the standard method but now there is no cost calculation available. However, this device will reduce the need for blood transfusions and subsequently the risks associated with blood transfusion.
The next step in our investigation is to focus on the effects of the device on blood cells. Currently, we are performing in vitro experiments on erythrocyte concentrates and whole blood. Additionally, we have planned further studies with simulation of different surgical situations.
The presented suction system incorporates registration and control of turbulences, of negative pressure, and air mixture. The system shows practical advantages solving known problems. The demonstrated approach, even if complex, succeeds.
The authors thank Johannes Brand and Manfred Krukenberg. The newly developed suction handle is the result of unselfish cooperation with the highest technical know-how at Otto Bock HealthCare GmbH (Duderstadt, Germany). The TCSS is patented and the patent holder is the University Medical Center Göttingen (PCT/EP/2011/006330; US 9,402,937 B2; 2 August 2016).
Contributors MGF is responsible for the concept/design of SOTOS and the drafting of manuscript. PW is the medical technology engineer and was responsible for the technical implementation. TT is the senior author. SV carried out advanced tests of the TCSS. IB helped create the draft of this manuscript. MGF is the inventor of the TCSS and all included features. PW implemented the control ideas in several development steps into a composition of electronic components.
Funding This research received no specific grant from any funding agency in the public, commercial or not-for-profit sectors.
Disclaimer The authors alone are responsible for the content and writing of this report.
Competing interests None declared.
Provenance and peer review Not commissioned; externally peer reviewed.
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