Interact CardioVasc Thorac Surg 2006;5:540-543. doi:10.1510/icvts.2006.134676
© 2006 European Association of Cardio-Thoracic Surgery
ESCVS article - Cardiopulmonary bypass |
Small access (30F) clinical central venous smart cannulation: is it adequate?
Ludwig K. von Segesser*,a,
Piergiorgio Tozzi,
Enrico Riccardo Ferrari,
Christoph Huber,
Dominique Delay,
David Jegger and
Judith Horisberger
Department of Cardio-vascular Surgery, Centre Hospitalier Universitaire Vaudois, CHUV, CCV, BH 10-275, CH-1011, Lausanne, Switzerland
Received 9 April 2006;
received in revised form 12 July 2006;
accepted 13 July 2006
a Conflict of interest statement: The first author (LS) is founder and stock holder of Smartcanula LLC, Lausanne, Switzerland, the manufacturer of the smartcanula® 
 Presented at the 55th International Congress of the European Society for Cardiovascular Surgery, St Petersburg, Russian Federation, May 11–14, 2006.
*Corresponding author. Tel.: +41 21 314 22 79; fax: +41 21 314 29 78.
E-mail address: ludwig.von-segesser{at}chuv.ch (L.K. von Segessar).
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Abstract
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Objectives: To assess the performance of 45F vs. 36F smartcanula® in CPB with gravity drainage alone. Methods: Twenty patients were randomly assigned to two groups receiving for venous drainage a smartcanula® which is collapsed over a mandrel for trans-atrial insertion into the inferior vena cava and expanded in situ to either 45F or 36F. Results: Valve replacement/repair was realized in 7/10 and/or CABG in 6/10 for 36F (69±13 years) vs. 5/10 and 5/10, respectively, for 45F (63±11 years: NS). Body weight and surface area (BSA) were 83±9 kg (1.9±0.2 m2, max 2.2 m2) for 36F vs. 79±6 kg: NS (1.9±0.1 m2 (NS), max 2.1 m2) for 45F. Insertion and access orifice diameter (area) was 6 mm and 10 mm (78.5 mm2) for the 36F vs. 6 mm and 13 mm (132 mm2) for the 45F (+69%). Calculated target pump flow (2.4 l/min/m2) was 4.7±0.4 l/min for 36F vs. 4.5±0.3 l/min for 45F. Achieved pump flow accounted for 5.0±0.3 l/min for 36F (8% above target) vs. 4.8±0.3 l/min for 45F (8% above target): NS. The water balance during the pump run (clear volume added minus hemofilter and urine output) was 2.2±0.3 l for 36F vs. 2.0 l for 45F: NS. Conclusion: Due to its ‘open’ wall (the vena cava provides the seal), its reduced wall thickness (range: 0.0–0.4 mm), and its self-expanding design, the 36F smartcanula® requiring a 30F access orifice has sufficient drainage capacity by gravity alone for full CPB in adults with a BSA up to 2.2 mm2.
Key Words: Cannula; Venous drainage; Gravity drainage; Cardiopulmonary bypass; Augmentation; Perfusion; Small access; Minimal invasive
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1. Introduction
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Central cannulation, right atrium for venous drainage and aorta for arterial return, is the standard approach for cardiopulmonary bypass (CBP) in most cardiac operations for adult patients. There is little controversy about this statement for on-pump coronary bypass procedures as well as surgical procedures for repair or replacement of the aortic valve. As a matter of fact, the senior author of this paper prefers single right atrial cannulation for aortic valve replacement (including the Ross procedure [1,2]), and, among others, mitral valve replacement, as well as arterial switch procedures. However, because of inadequate venous drainage with remote cannulation in small access openheart surgery [3,4], we have introduced some time ago, the intelligent cannulation principle [5,6], which is based on the ‘collapsed cannula insertion and expansion in situ concept’. For this purpose we have developed specific cannulae (smartcanula®, Smartcanula LLC, Lausanne, Switzerland: Fig. 1). Superior drainage performance as compared to standard and percutaneous venous cannulae, was previously demonstrated in silico, in vitro, in vivo, and in the clinical setting [5,6]. In addition, we could also demonstrate, that full venous drainage can be achieved with the smartcanula® (V 3/8 36 630 S: collapsed dimension is <18F, expanded dimension is 36F) inserted through the femoral vein into the right atrium [7] without augmentation by a centrifugal pump or vacuum assistance. The present study was designed in order to find out whether central venous cannulation with a larger 45F smartcanula® would provide more blood drainage as compared to the previously established standard 36F design.
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Fig. 1. The smartcanula® principle is based on collapsed insertion and expansion in situ within the target vessel. This technology allows for achieving a relatively large mean cross-sectional area of the cannula body even if a short part of it, i.e. within the access aperture, remains smaller. Superior flow rates can be achieved [5–7,10].
Top: a mandrel is used for stretching and collapsing the smartcanula® prior to insertion.
Bottom: after insertion, the guide wire and the mandrel are removed and the smartcanula® re-expands spontaneously to a predetermined diameter or the vessel diameter, respectively.
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2. Patients and methods
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After approval of the protocol by the institutional review board, twenty adult patients undergoing on-pump cardiac surgery with central cannulation (right atrium for venous drainage, ascending aorta for arterial return) received for right atrial cannulation either (block randomization) a 36F smartcanula® connecting to a 3/8'' tubing (Smartcanula LLC, Lausanne, Switzerland; www.smartcanula.com: ordering number V 3/8 36 360 S) or a corresponding 45F smartcanula® connecting to a 1/2'' tubing.
The main differences between these two cannula configurations are displayed in Figs. 2, 3 and Table 1. Independently of the venous cannula selected, a standard perfusion set was used which includes a 1/2'' venous line, a hard shell venous reservoir, a hollow-fiber membrane oxygenator, a taperflex tubing (3/8''–1/2''–3/8'') in the roller pump raceway, a 3/8'' arterial line with an arterial filter, and a 24F arterial cannula. Perfusion was realized with our standard protocol including full systemic heparinization (heparin loading dose 300 IU/kg bodyweight, heparin priming dose 5000 IU/l priming volume, target activated coagulation time >480 s), a target pump flow of 2.4 l/min m2, moderate hypothermia (28–30 °C), blood cardioplegia, and a mixed venous oxygen saturation 60%.
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Fig. 2. Close-up view of the two test cannulae head to head with the connecting tubing (left), the covered braids (center), and the uncovered braids (right). The luminal diameter within the tubing is 9.5 mm for the 36F and 12.5 mm for 45F. The external cannula diameter at the level of the right atrial aperture (center) is 10 mm for 36F and 13 mm for 45F, respectively. The external diameter, at the level of the cannula body (right), which is also part of the drainage zone, accounts for 12 mm for 36F, and 15 mm for 45F.
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Fig. 3. Cross sectional area of the 36F and the 45F as a function of the cannula diameter: at (from the left to right) the level of the tubing (left in Fig. 2), the covered wall (center in Fig. 2), and the uncovered wall (right in Fig. 2).
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Continuous variables are expressed as mean±standard deviation (maximum where of interest) and compared with unpaired Student t-test. Fisher's exact test was used for comparison of non-parametric variables.
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3. Results
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The patients underwent valve replacement/repair in 7/10 and/or CABG in 6/10 (combined procedures in 3/10) for 36F (69±13 years) vs. 5/10 and 5/10, respectively, for 45F (63±11 years: NS). Body weight and surface area (BSA) were 83±9 kg (1.9+0.2 m2, max 2.2 m2) for 36F vs. 79±6 kg: NS (1.9±0.1 m2 (NS), max 2.1 m2) for 45F. Insertion and access orifice diameter (area) was 6 mm and 10 mm (78.5 mm2) for the 36F vs. 6 mm and 13 mm (132.7 mm2) for the 45F (+69%) whereas the cannula wall thickness at the site of insertion (at the drainage site) was the same for the 36F and the 45F cannula versions and varied between 0.1 (area of unsupported silicone) as compared to the areas with crossing wires 0.4 mm (0.0 open wall as compared to areas with crossing wires 0.36 mm). Calculated target pump flow (2.4 l/min/m2) was 4.7±0.4 l/min for 36F vs. 4.5±0.3 l/min for 45F (see also Fig. 4). Achieved pump flow accounted for 5.0±0.3 l/min for 36F (8% above target) vs. 4.8±0.3 l/min (NS) for 45F (8% above target: NS). The water balance during the pump run (clear volume added minus hemofilter and urine output) was 2.2±0.3 l for 36F vs. 2.0±0.4 l for 45F: NS. Packed red cells were transfused in 1/10 patients in each group and accounted for 28±50 ml for 36F as compared to 30±50 ml for 45F (NS).
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Fig. 4. Target flows and achieved flows±standard deviations for clinical perfusion with central canulation: no difference was observed with 36F vs. 45F smart cannula configuration.
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4. Discussion
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Due to its ‘open’ wall (the right atrium and the inferior vena cava provide the seal), its reduced wall thickness, and its self-expanding design, the 36F smartcanula® requiring a 30F access orifice (10 mm diameter) has sufficient drainage capacity by gravity alone for cardiopulmonary bypass applications with central venous cannulation in adults with a BSA up to 2.2 m2. There is no need for 1/2'' venous cannula and the corresponding larger (13 mm) atrial access aperture. As a matter of fact, there was no difference in venous drainage and consecutive pump flow which reached 108% of the target value for both, the 36F and the 48F smartcanula® versions. Likewise, there was no difference between groups with regard to the water balance (clear volume added minus hemofilter and urine output) as well as the need for blood products. These findings suggest, that for the vast majority of patients requiring CPB with central cannulation, venous drainage based on gravity alone, can be optimized up to a certain point which seems to be close to 10% above the target value of 2.4 l/m2 min.
Exactly these flows were achieved with the standard 36F smartcanula® configuration. The introduction of larger 45F smartcanulae® did not provide superior flow. As demonstrated, the pump flow achieved was exactly the same for both groups and equalled 108% of the target value. These findings are interesting because the 45F design requires not only a 30% larger cannula access aperture in the right atrial wall which translates in a 69% larger access area, but it has also a 25% larger expanded cannula diameter (Figs. 2 and 3), which translates in 56% larger expanded cannula cross-section (Table 1). It has to be mentioned here that 30% larger right atrial access diameter of the 45F smartcanula® is still well below most two stage cannulae diameters which are today's standard of care for most cases undergoing heart surgery with cardiopulmonary bypass, and which may exceed 17 mm in diameter, which turns out to require an access aperture to the right atrium representing 289% or more of the 36F smartcanula® design (227 mm2 for the former vs. 78.5 mm2 for the latter).
It comes as little surprise that the 36F smartcanula® design applied to central right atrial and inferior vena cava cannulation, in similar fashion as a central two stage venous cannula, provides sufficient drainage capacity in patients with a body surface area up to 2.2 m2, because we had previously shown [9] that similar flows (up to 110% of the target flow) can be achieved by trans-femoral cannulation of the right atrium with a long 36F smartcanula® (3/8 36F 630 S or 3/8 36F 530 S). In this previous study we had looked at a small series of patients undergoing mainly redo procedures on the ascending aorta and the aortic arch. Trans-femoral smart cannulation allowed for this setting a pump flow based on gravity drainage alone of 4.8±0.9 l/min for a calculated target flow of 4.4±0.6 l/min (109.5%). This finding was in agreement with our previous work in the experimental setting in silico, in vitro, and in vivo [6,7], where the superior performance of smart venous cannulation as compared to cannulation with standard cannula was demonstrated in various fashions.
There are a number of reasons that explain the superior performance of the self expanding smartcanula® as compared to standard cannulae. These include (A) the shape change in situ allowing to achieve a final intravascular cannula diameter, which is not only above the cannula diameter at the site of insertion, but also larger than the inner diameter of conventional cannulae, (B) the thinner cannula wall thickness, and (C) the open cannula wall design which allows for direct drainage of collaterals. In addition, (D) the total smartcanula® orifice area, i.e. the space available for the blood to enter the cannula, is at least one order of magnitude larger than typical for standard cannulae where the total orifice area is usually somewhat above the cross-sectional area of the cannula lumen.
Potential concern with the smartcanula® is related to the design of its covered wall, which is very thin and must be handled carefully and without sharps. In contrast, removal, of the smartcanula® is easy. As a matter of fact, axial tractions result in a reduction of its diameter, and therefore, potential friction is reduced. Reinsertion of the mandrel is not necessary for cannula removal, but it may be necessary for repositioning (deeper insertion). Minimal insertion is approximatively 1 cm of the covered part, in order to achieve sufficient seal at the access aperture.
With regard to flow, it had also been shown previously by Ni et al. [8], that a cross sectional area of 1 cm2 is sufficient for gravity drainage with a 2-m long venous line in both the experimental and the clinical setting. It appears that the venous line considered as optimal in his study is below 34F and therefore, it comes as no surprise that the 36F smartcanula® configuration provides adequate drainage capacity for the clinical applications studied. Concerning the bio-compatibility of the smartcanula®, it has been demonstrated previously that there is no additional blood trauma as compared to perfusion with traditional cannulae for both, the experimental [9], and the clinical setting [10].
Based on the arguments provided above, we conclude that a small access (30F) aperture to the right atrium is enough for clinical central venous smart cannulation of the inferior vena cava and allows for more than adequate venous drainage with gravity alone, provided the right cannulae are used.
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References
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Abstract
1. Introduction
