The Smartcanula: a new tool for remote access perfusion in limited access cardiac surgery

Virtually Wall-Less versus Standard Thin-Wall Venous Cannula in the Minimally Invasive Mitral Valve Surgery: Single-Center Experience

Background and Objectives: Minimally invasive cardiac surgery (MICS) has been developing since 1996. Peripheral cannulation is required to perform MICS, and good venous drainage and a bloodless field are crucial for the success of this procedure. We assessed the benefits of using a virtually wall-less cannula in comparison with the standard thin-wall cannula in clinical practice. Materials and Methods: Between January 2021 and December 2022, we evaluated 65 elective patients, who underwent isolated minimally invasive mitral valve surgery. Both the virtually wall-less and the thin-wall cannulas were placed through a surgical cut-down. Patients' characteristics at baseline were similar in the two groups, except for the body surface area (BSA), which was greater in the virtually wall-less group compared to the thin-wall one. In the standard group, the size of the cannula was chosen depending on the patient's BSA, and the choice of the Smartcannula was based on their height. Results: There were no significant differences between the two groups in terms of negative pressure applied, target flow achieved, hemolysis, the need for blood transfusion, and the post-operative increases in liver and renal enzymes. However, in all the patients, the estimated target flow was achieved, thereby showing the better hemodynamic performance of the virtually wall-less cannula, since, in this group, the patients' BSA was significantly greater compared to the thin-wall group. Ultimately, the mean cross-clamp time, as an indirect index of the effectiveness of the venous drainage, is shorter in the virtually wall-less group compared with the thin-wall group. Conclusions: The virtually wall-less cannula should be preferred in minimally invasive mitral valve surgery due to its superior performance in terms of venous drainage compared with the standard thin-wall cannula.

Usefulness of Self-Expanding Drainage Cannula in Venovenous Extracorporeal Membrane Oxygenation: Tips, Tricks, and Results of an Early Experience

Inadequate venous drainage decreases the efficiency of extracorporeal membrane oxygenation (ECMO). Pump augmentation may even make it worse due to collapse of the venous system under negative pressures. Furthermore, recirculation is a phenomenon that occurs when oxygenated blood supplied through the infusion cannula is withdrawn directly through the drainage cannula without contributing to the oxygenation of the patient and also compromises the efficacy of the therapy. Large drainage cannulas allow for similar flow rates at lower pump speed. But percutaneous insertion of these larger cannulas could be challenging. When using a self-expandable cannula, the diameter of the cannula for the insertion can be reduced, and once inserted, its intravascular diameter maximized, resulting in a large venous cannula due to in situ expansion after mandrel removal (up to 36F). We present a retrospective series of selfexpanding venous cannula 430 or 530 mm in length in six consecutive patients undergoing venovenous (VV) ECMO. No vascular or cardiac iatrogenic injury was caused during implantation. Target flows were reached, and no clinically significant recirculation was described in any case. The use of selfexpanding drainage cannulas was safe, and efficient drainage was achieved with easy and definitive unique positioning during cannulation.

Clinical Experience in Minimally Invasive Cardiac Surgery With Virtually Wall-Less Venous Cannulas

OBJECTIVE

Inadequate peripheral venous drainage during minimally invasive cardiac surgery (MICS) is a challenge and cannot always be solved with increased vacuum or increased centrifugal pump speed. The present study was designed to assess the benefit of virtually wall-less transfemoral venous cannulas during MICS.

METHODS

Transfemoral venous cannulation with virtually wall-less cannulas (3/8″ 24F 530-630-mm ST) was performed in 10 consecutive patients (59 ± 10 years, 8 males, 2 females) undergoing MICS for mitral (6), aortic (3), and other (4) procedures (combinations possible). Before transfemoral insertion of wall-less cannulas, a guidewire was positioned in the superior vena cava under echocardiographic control. The wall-less cannula was then fed over the wire and connected to a minimal extracorporeal system. Vacuum assist was used to reach a target flow of 2.4 l/min per m with augmented venous drainage at less than -80 mm Hg.

RESULTS

Wall-less venous cannulas measuring either 630 mm (n = 8) in length or 530 mm (n = 2) were successfully implanted in all patients. For a body size of 173 ± 11 cm and a body weight of 78 ± 26 kg, the calculated body surface area was 1.94 ± 0.32 m. As a result, the estimated target flow was 4.66 ± 0.78 l/min, whereas the achieved flow accounted for 4.98 ± 0.69 l/min (107% of target) at a vacuum level of 21.3 ± 16.4 mm Hg. Excellent exposure and "dry" intracardiac surgical field resulted.

CONCLUSIONS

The performance of virtually wall-less venous cannulas designed for augmented peripheral venous drainage was tested in MICS and provided excellent flows at minimal vacuum levels, confirming an increased performance over traditional thin wall cannulas. Superior results can be expected for routine use.

New, Virtually Wall-Less Cannulas Designed for Augmented Venous Drainage in Minimally Invasive Cardiac Surgery

Objective

Inadequate venous drainage during minimally invasive cardiac surgery becomes most evident when the blood trapped in the pulmonary circulation floods the surgical field. The present study was designed to assess the in vivo performance of new, thinner, virtually wall-less, venous cannulas designed for augmented venous drainage in comparison to traditional thin-wall cannulas.

Methods

Remote cannulation was realized in 5 bovine experiments (74.0 ± 2.4 kg) with percutaneous venous access over the wire, serial dilation up to 18 F and insertion of either traditional 19 F thin wall, wire-wound cannulas, or through the same access channel, new, thinner, virtually wall-less, braided cannulas designed for augmented venous drainage. A standard minimal extracorporeal circuit set with a centrifugal pump and a hollow fiber membrane oxygenator, but no inline reservoir was used. One hundred fifty pairs of pump-flow and required pump inlet pressure values were recorded with calibrated pressure transducers and a flowmeter calibrated by a volumetric tank and timer at increasing pump speed from 1500 RPM to 3500 RPM (500-RPM increments).

Results

Pump flow accounted for 1.73 ± 0.85 l/min for wall-less versus 1.17 ± 0.45 l/min for thin wall at 1500 RPM, 3.91 ± 0.86 versus 3.23 ± 0.66 at 2500 RPM, 5.82 ± 1.05 versus 4.96 ± 0.81 at 3500 RPM. Pump inlet pressure accounted for 9.6 ± 9.7 mm Hg versus 4.2 ± 18.8 mm Hg for 1500 RPM, −42.4 ± 26.7 versus −123 ± 51.1 at 2500 RPM, and −126.7 ± 55.3 versus −313 ±116.7 for 3500 RPM.

Conclusions

At the well-accepted pump inlet pressure of −80 mm Hg, the new, thinner, virtually wall-less, braided cannulas provide unmatched venous drainage in vivo. Early clinical analyses have confirmed these findings.

New Dual Lumen Self-Expanding Catheter Design Requiring Less Suction

Contribution of venovenous extracorporeal membrane oxygenation (v-v ECMO) to gas transfer is flow dependent. Catheter design is a key factor for optimal pressure/flow rate relationship. This study was designed for the assessment of a new self-expanding dual lumen catheter design versus the current standard. Outlet pressure/flow rate and inlet pressure/flow rate for a new Smart catheter with self-expanding dual lumen design constricted to 27 F with 5 mm long constrictor corresponding to the percutaneous path versus Avalon 27 F catheter (control) were compared on a flow bench with a Biomedicus centrifugal pump. Flow, pump inlet pressure and outlet pressure were determined at 500, 1,000, 1,500, 2,000, and 2,500 revolutions per minute (RPM). At 500 RPM and with a 5 mm long constrictor (1,000; 1,500; 2,000; and 2,500 RPM), catheter outlet pressure values were -0.13 ± 0.07 mm Hg (-2.55 ± 0.06; -7.38 ± 0.14; -15.03 ± 0.44; -26.46 ± 0.39) for self-expanding versus -2.93 ± 0.23* (-10.60 ± 0.14; -22.74 ± 0.34; -38.43 ± 0.41; -58.25 ± 0.40)*: p < 0.0001* for control. The flow values were 0.61 ± 0.01 L/min (1.64 ± 0.03, 2.78 ± 0.02; 4.07 ± 0.04; 5.37 ± 0.02) for self-expanding versus 1.13 ± 0.06*; (2.19 ± 0.04; 3.30 ± 0.03; 4.30 ± 0.03; 5.30 ± 0.03)*: p < 0.0001* for control. The corresponding catheter inlet flow rates of the self-expanding catheter were slightly more than that of the control. For the given setup, our evaluation demonstrated that the new dual lumen self-expanding catheter requires lower catheter outlet pressures for higher flows as compared to the current standard.

How to prevent venous cannula orifice obstruction during extracorporeal circulation

Venous cannula orifice obstruction is an underestimated problem during augmented cardiopulmonary bypass (CPB), which can potentially be reduced with redesigned, virtually wall-less cannula designs versus traditional percutaneous control venous cannulas. A bench model, allowing for simulation of the vena cava with various affluent orifices, venous collapse and a worst case scenario with regard to cannula position, was developed. Flow (Q) was measured sequentially for right atrial + hepatic + renal + iliac drainage scenarios, using a centrifugal pump and an experimental bench set-up (afterload 60 mmHg). At 1500, 2000 and 2500 RPM and atrial position, the Q values were 3.4, 6.03 and 8.01 versus 0.77*, 0.43* and 0.58* l/min: p<0.05* for wall-less and the Biomedicus® cannula, respectively. The corresponding pressure values were -15.18, -31.62 and -74.53 versus -46.0*, -119.94* and -228.13* mmHg. At the hepatic position, the Q values were 3.34, 6.67 and 9.26 versus 2.3*, 0.42* and 0.18* l/min; and the pressure values were -10.32, -20.25 and -42.83 versus -23.35*, -119.09* and -239.38* mmHg. At the renal position, the Q values were 3.43, 6.56 and 8.64 versus 2.48*, 0.41* and 0.22* l/min and the pressure values were -9.64, -20.98 and -63.41 versus -20.87 -127.68* and -239* mmHg, respectively.

At the iliac position, the Q values were 3.43, 6.01 and 9.25 versus 1.62*, 0.55* and 0.58* l/min; the pressure values were -9.36, -33.57 and -44.18 versus -30.6*, -120.27* and -228* mmHg, respectivly. Our experimental evaluation demonstrates that the redesigned, virtually wall-less cannulas, allowing for direct venous drainage at practically all intra-venous orifices, outperform the commercially available control cannula, with superior flow at reduced suction levels for all scenarios tested.

Peripheral cannulation for cardiopulmonary bypass

Peripheral cannulation is the historical route for connecting the pump-oxygenator to the vasculature of the patient in order to establish partial or complete cardiopulmonary bypass. Although most open heart procedures are nowadays realized with central cannulation, there is renewed interest in remote cannulation through the femoral, iliac, axillary, subclavian and jugular vessels. Remote cannulation is not only of interest in hemodynamically unstable patients who can be put on cardiopulmonary bypass in local anesthesia, and stabilized prior to intubation, but also for complex procedures like replacement of the thoracoabdominal aorta, acute type A aortic dissections, complex redo open heart surgery, extracorporeal membrane oxygenation, and more recently, small access open heart surgery, robotic surgery, and others. In the following shall be described femoral arterial cannulation with standard cannulas, femoral arterial cannulation with percutaneous cannulas, femoral venous cannulation using standard cannulas, femoral venous cannulation using percutaneous cannulas, as well as optimized venous cannulation relying on more advanced cannula designs.

Prevention of caval collapse during venous drainage for CPB

A new plastic self-expanding Smartcanula (Smartcanula LLC, Lausanne, Switzerland) is designed for central insertion and prevention of caval collapse. The objective of our work is to assess the influence of the new design on atrial chatter. Caval collapse over the entire caval axis, right atrial, hepatic, renal vein, and iliac vein is realized in drainage tubes with holes at 5 cm distance intervals. Smartcanulas with various lengths (26 cm [= right atrial], 34 cm [= hepatic], 43 cm [= renal], and 53 cm [= iliac]) versus two-stage cannulas are compared. Pressure drop (ΔP) is measured using Millar pressure-transducers. Flow rate (Q) is measured using an ultrasonic flow meter. Cannula resistance is defined as the ΔP/Q ratio. Data display and recording are controlled using LabView virtual instruments. At an 88 cm height differential, Q values are 8.69 and 6.8 l/min, and ΔP/Q ratios are 0.63 and 1.28 for the 26-cm Smartcanula and the reference cannula, respectively. The 34-cm Smartcanula showed 8.89 l/min and 0.6 ΔP/Q ratio vs. 7.59 l/min and 0.9 for the control cannula (P < 0.05). The 43-cm and 53-cm Smartcanulas showed Q values of 9.04 and 8.81 l/min, respectively, and ΔP/Q2 ratio of 0.6. The Smartcanula outperforms the two-stage cannula, and direct cannula insertion without guide wire is effective.

Superior venous drainage in the "LifeBox": a portable extracorporeal oxygenator with a self-expanding venous cannula

BACKGROUND

In an experimental setting, the performance of the LifeBox, a new portable extracorporeal membrane oxygenator (ECMO) system suitable for patient transport, is presented. Standard rectilinear percutaneous cannulae are normally employed for this purpose, but have limited flow and pressure delivery due to their rigid structure. Therefore, we aimed to determine the potential for flow increase by using self-expanding venous cannulae.

METHODS

Veno-arterial bypass was established in three pigs (40.6+/-5.1 kg). The venous line of the cardiopulmonary bypass was established by cannulation of the external jugular vein. The arterial side of the circulation was secured by cannulation of the common carotid artery. Two different venous cannulae (SmartCanula 18/36F 430mm and Biomedicus 19F) were examined for their functional integrity when used in conjunction with the centrifugal pump (500-3000 RPM) of the LifeBox system.

RESULTS

At 1500, 2000, 2500, and 3000 RPM, the blood flow increased steadily for each cannula, but remained higher in the self-expanding cannula. That is, the 19F rectilinear cannula achieved a blood flow of 0.93+/-0.14, 1.47+/-0.37, 1.9+/-0.68, and 1.5+/-0.9 l/min, respectively, and the 18/36F self-expanding cannula achieved 1.1+/-0.1, 1.9+/-0.33, 2.8+/-0.39 and 3.66+/-0.52 l/min. However, when tested for venous line pressure, the standard venous cannula achieved -29+/-10.7mmHg while the self-expanding cannula achieved -13.6 +/-4.3mmHg at 1500 RMP. As the RPM increased from 2500 to 3000, the venous line pressure accounted for -141.9+/-20 and -98+/-7.3mmHg for the 19F rectilinear cannula and -30.6+/-6.4 and -45+/-11.6mmHg for the self-expanding cannula.

CONCLUSION

The self-expanding cannula exhibited superior venous drainage ability when compared to the performance of the standard rectilinear cannula with the use of the LifeBox. The flow rate achieved was approximately 40% greater than the standard drainage device, with a maximal pump flow recorded at 4.3l/min.

Using computational fluid dynamics to evaluate a novel venous cannula (Smart canula) for use in cardiopulmonary bypass operating procedures

Peripheral access cardiopulmonary bypass (CPB) is initiated with percutaneous cannulae (CTRL) and venous drainage is often impeded due to smaller vessel and cannula size. A new cannula (Smartcanula, SC) was developed which can change shape in situ and, therefore, may improve venous drainage. Its performance was evaluated using a 2-D computational fluid dynamics (CFD) model. The Navier-Stokes equations could be simplified due to the fact that we use a steady state and a 2-dimensional system while the equation of continuity (p constant) was also simplified. We compared the results of the SC to the CTRL using CFDRC (Version 6.6, CFDRC research corporation, Huntsville, USA) at two preloads (300 and 700 Pa). The SC's mass flow rate outperformed the CTRL by 12.1% and 12.2% at a pressures of 300 and 700 Pa, respectively. At 700 Pa, a pressure gradient of 50% was measured for the CTRL and 11% for the SC. The mean velocity at the 700 Pa for the CTRL was 1.0 m.s(-1) at exit while the SC showed an exit velocity of 1.3 m.s(-1). Shear rates inside the cannulae were similar between the two cannulae. In conclusion, the prototype shows greater mass flow rates compared to the classic cannula; thus, it is more efficient. This is also advocated by a better pressure gradient and higher average velocities. By reducing cannula-tip surface area or increasing hole surface area, greater flow rates are achieved.

Perfusion techniques during surgery of the thoracic and thoraco-abdominal aorta: the veno-arterial bypass

Open repair of the descending thoracic aorta and the thoraco-abdominal aorta remains a challenging procedure. On the proximal side, pressure overload in the supra-aortic territories and pump failure are just two examples for undesirable effects of descending thoracic aortic cross-clamping which may end with a disaster. On the distal side, potential problems include among others, paraplegia, renal failure, visceral and peripheral ischemia. Finally, there are per-procedural issues like hypoxia due to single lung ventilation, uncontrollable inflow or backflow, excessive blood loss, unrealistic time constraints for systematic revascularization of intercostals arteries etc. Partial (femoro-femoral) cardiopulmonary bypass provides answers to many of the issues raised above. In addition, perfusion with heparin coated equipment allowing for significant reduction of anticoagulation has been shown to be useful for maintaining the hemostatic potential of the patient and limiting blood loss. Our current approach to perfusion for descending thoracic and thoraco-abdominal aneurysm repair has evolved into a versatile cardiopulmonary bypass strategy allowing for rapid conversion from partial cardiopulmonary bypass with peripheral cannulation to full, and if necessary, central, cardiopulmonary bypass, and all sorts of combinations including deep hypothermic circulatory arrest.