Performance Increase in Venous Drainage for Mini-Invasive Heart Surgery: Superiority of Self-Expanding Cannulas

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.

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, 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.