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.

Single-Center Experience With a Self-Expandable Venous Cannula During Minimally Invasive Cardiac Surgery

OBJECTIVE

Venous drainage is often problematic in minimally invasive cardiac surgery (MICS). Here, we describe our experience with a self-expandable stent cannula designed to optimize venous drainage.

METHODS

The smart canula^® was used in 58 consecutive patients undergoing MICS for mitral valve disease (n = 40), left atrial myxoma (n = 3), left ventricular outflow tract obstruction (n = 1), and aortic valve replacement via a right anterior minithoracotomy (n = 14) procedures. The venous cannula was placed under transesophageal echocardiography guidance to reach the superior vena cava. Vacuum-assisted venous drainage (between -20 and -35 mm Hg) was used to reach a target flow index of 2.2 L/min/m² at a core temperature of 34 °C using a goal-directed perfusion strategy aimed at a minimum DO₂ of 272 mL/min/m². Cardiopulmonary bypass (CPB) parameters were recorded, and hemolysis-related parameters were analyzed on postoperative days 1 to 7.

RESULTS

Mean body surface area and median body mass index were 1.9 ± 0.2 m² and 25.2 (23.4, 30.2) kg/m². Mean CPB and median cross-clamping times were 107.7 ± 24.4 min and 64.5 (53, 75.8) min, and median CPB flow during cardioplegic arrest was 4 (3.6, 4.2) L/min (median cardiac index 2.1 [2, 2.2] L/min/m²). Venous drainage was considered sufficient by the surgeon in all cases, and insertion and removal were uncomplicated. Mean SvO₂ during CPB was 80.2% ± 5.5%, and median peak lactate was 10 (8, 14) mg/dL, indicating sufficient perfusion. Mean venous negative drainage pressure during cross-clamping was 27.2 ± 12.3 mm Hg. Platelets dropped by 73.6 ± 37.5 K/µL, lactate dehydrogenase rose by 81.5 (44.3, 140.8) U/L, and leukocytes rose by 3.4 (2.2, 7.2) K/µL on postoperative day 1.

CONCLUSIONS

The venous smart canula^® allows for optimal venous drainage at low negative drainage pressures, facilitating sufficient perfusion in MICS.

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.

Effect of blood viscosity on the performance of virtually wall-less venous cannulas

AIM

This study was designed to quantify the influence of blood as test medium compared to water in cannula bench performance assessment.

METHODS

An in vitro circuit was set-up with silicone tubing between two reservoirs. The test medium was pumped from the lower reservoir by centrifugal pump to the upper reservoir. The test-cannula was inserted in a silicone tube connected between the lower reservoir and the centrifugal pump. Flow rate and pump inlet-pressure were measured for wall-less versus thin-wall cannula using a centrifugal pump in a dynamic bench-test for an afterload of 40-60 mmHg using two media: blood 10 g/dL and 5.6 g/dL and water 0 g/dL.

RESULTS

The wall-less cannula showed significantly higher flows rates as compared to the thin-wall cannula (control), with both hemoglobin concentrations and water. Indeed, for a target volume of 200-250 mL of blood (Hg 10 g/dL) in the upper reservoir, the cannula outlet pressure (P) was -14 ± 14 mmHg versus -18 ± 11 mmHg for the wall-less and control respectively; the cannula outlet flow rate (Q) was 3.91 ± 0.41 versus 3.67 ± 0.45 L/min, respectively. At the same target volume but with a Hg of 5.7 g/dL, P was -16 ± 12 mmHg versus -19 ± 12 mmHg and Q was 4 ± 0.1 versus 4 ± 0.4 L/min for the wall-less cannula and control respectively. Likewise, P and Q values with water were -1 mmHg versus -0.67 ± 0.58 mmHg and 4.17 ± 0.45 L/min versus 4.08 ± 0.47 L/min for the wall-less and control respectively.

CONCLUSION

Walls-less cannula showed 5.6% less pump inlet-pressure differences calculated between blood and water, as compared to that of thin-wall cannula (-21 times). Flow differences were 6% and 10% for the walls-less and thin-wall cannula respectively. We conclude that testing the cannula performance with water is a good scenario and can overestimate the flow by a 10%. However, superiority for wall-less is preserved with both water and blood.

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, optimized, dual-lumen cannula for veno-venous ECMO

Objective:

The present study was designed to assess in vivo a new, optimized, virtually wall-less, dual-lumen, bi-caval cannula for veno-venous ECMO in comparison to a commercially available cannula.

Methods:

Veno-venous extracorporeal membrane oxygenation (ECMO) was carried out in a bovine study (n=5, bodyweight 75±5kg). Following systemic heparinization, ECMO was established in a trans-jugular fashion through a calibrated 23F orifice, using a new, optimized, virtually wall-less, dual-lumen, bi-caval 24F cannula (Smartcanula LLC, Lausanne, Switzerland) versus a commercially available 23F bi-caval, dual-lumen control cannula (Avalon Elite®, Maquet, Rastatt, Germany) in a veno-venous ECMO setup. Veno-venous ECMO was initiated at 500 revolutions per minute (RPM) and increased by incremental steps of 500 RPM up to 2500 RPM. Catheter outlet pressure, catheter inlet pressure, oxygen saturation and pump flow were recorded at each stage.

Results:

Mean flow accounted for 0.37±0.04 L/min for wall-less versus 0.29± 0.07 L/min for control at 500 RPM, 0.97±0.12 versus 0.67±0.06 at 1000 RPM, 1.60±0.14 versus 1.16±0.08 at 1500 RPM, 2.31±0.13 versus 1.52±0.13 for 2000 RPM and 3.02±0.5 versus 2.11±0.18 (p<0.004). The mean venous suction required was 19±8 mmHg for wall-less versus 20±3 mmHg for control at 500 RPM, 7±3 versus 9±4 for 1000 RPM, -11±10 versus -12±8 at 1500 RPM, -39±15 versus -49±10 for 2000 RPM and -60±28 versus -94±7 for 2500 RPM. The mean venous injection pressure accounted for 29±7 mmHg for wall-less versus 27±5 mmHg for control at 500 RPM, 50±6 versus 61±7 at 1000 RPM, 89±10 versus 99±17 for 1500 RPM, 142±14 versus 161±9 at 2000 RPM and 211±41 versus 252 ±3 for 2500 RPM.

Conclusion:

Compared to the commercially available control cannula, the new, optimized, virtually wall-less, dual-lumen, bi-caval 24F cannula allows for significantly higher blood flows, requires less suction and results in lower injection pressures in vivo.

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.

Use of self-expanding venous cannula in tricuspid reoperation

Significant tricuspid regurgitation requiring surgical correction is associated with poor survival in patients undergoing tricuspid valve reoperations. Right chamber dilatation increases the risk of injury during resternotomy. The novel technique of peripheral cannulation using an expandable venous cannula for cardiopulmonary bypass can help to reduce the risk of complications and associated morbidity, thus enhancing the short-term outcomes.

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.

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.

How to improve flow during cardiopulmonary bypass in an acardia experimental model

OBJECTIVES In extreme scenarios, such as hyperacute rejection of heart transplant, an urgent heart explantation might be necessary. The aim of this experimental study was to determine the feasibility and to improve the haemodynamics of a venoarterial cardiopulmonary bypass after cardiectomy. METHODS A venoarterial cardiopulmonary bypass was established in seven calves (56.4 ± 7 kg) by the transjugular insertion to the caval axis of a self-expanding cannula, with a carotid artery return. After baseline measurements (A), ventricular fibrillation was induced (B), great arteries were clamped (C), the heart was excised and the right and left atria remnants, containing the pulmonary veins, were sutured together leaving an atrial septal defect over the cannula in the caval axis (D). Measurements were taken with the pulmonary artery clamped and declamped. RESULTS Initial pump flow was 4.16 ± 0.75 l/min dropping to 2.9 ± 0.63 l/min (P(AB )< 0.001) 10 min after induction of ventricular fibrillation. After cardiectomy with the pulmonary artery clamped, the pump flow increased non-significantly to 3.20 ± 0.78 l/min. After declamping, the flow significantly increased close to baseline levels (3.61 ± 0.73 l/min, P(DB )= 0.009, P(DC )= 0.017), supporting the notion that full cardiopulmonary bypass in acardia is feasible only if adequate drainage of pulmonary circulation is assured to avoid pulmonary congestion and loss of volume from the left-to-right shunt of bronchial vessels.