J Thorac Cardiovasc Surg 2005;130:684-686
© 2005 The American Association for Thoracic Surgery
Cardiopulmonary Support and Physiology |
A femoral artery cannula that allows distal blood flow
James A. Magovern, MD
a
,
*
,
James D. Fonger, MD
b
,
David H.J. Wang, PhD
c
,
Dennis Kopilec, PhD
c
,
Dennis R. Trumble, MS
a
,
Douglas E. Smith, PhD
c
a Department of Cardiac Surgery Research, Allegheny General Hospital, Pittsburgh, Pa
b Department of Surgery, Lenox Hill Hospital, New York, NY
c CardiacAssist, Inc, Pittsburgh, Pa.
Received for publication December 6, 2004; revisions received February 28, 2005; accepted for publication March 14, 2005.
* Address for reprints: James A. Magovern, MD, Department of Cardiovascular and Thoracic Surgery, Allegheny General Hospital, 320 E North Ave, 14ST, Pittsburgh, PA 15212. (Email: jmagovern{at}wpahs.org).
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Abstract
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OBJECTIVE: A femoral artery cannula is used for certain types of circulatory support but can cause ischemia, especially during prolonged perfusion. This study tests the function of a femoral cannula designed to allow proximal and distal blood flow.
METHODS: Five pigs were used in the study. In each animal a distal-flow cannula was implanted in the femoral artery of one leg, and the same-sized standard cannula was implanted in the other. Blood was drained from the left atrium and delivered to the femoral artery through the distal-flow cannula or standard cannula by using a centrifugal pump. An ultrasonic flow probe and microspheres were used to quantify flow and perfusion distal to the cannula.
RESULTS: Distal femoral flow and tissue perfusion were present in all animals (5/5) with the distal-flow cannula but only in 1 of 5 animals with the standard cannula (P < .048). Distal flow did not change with pump flow. Mean distal flow at each level of pump flow was higher with the distal-flow cannula (P < .05). Tissue perfusion was also higher with the distal-flow cannula (0.052 ± 0.028 vs 0.010 ± 0.022 mL·min–1
·g–1, P < .03).
CONCLUSIONS: In the swine model the distal-flow cannula allowed greater and more consistent distal flow than the standard cannula. The use of a distal-flow cannula for circulatory support might reduce the risk of distal limb ischemia.
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Introduction
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There are circumstances in which femoral cannulation is used during cardiopulmonary bypass or mechanical circulatory support. Problems can occur with this approach when the cannula occludes the femoral artery, resulting in significant leg ischemia.
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If this problem develops, blood can be diverted from the arterial line and delivered to the distal vessel by means of an additional cannula.
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This provides adequate distal flow but requires extra hardware and a second puncture. A need exists for a single arterial cannula that allows both proximal and distal blood flow. A distal-flow cannula (DFC) was proposed by Matsuura and colleagues
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but was never commercialized. This report presents experimental data on the functional performance of a new DFC cannula design.
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Materials and Methods
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This study was approved by the Institutional Animal Care and Use Committee of Allegheny-Singer Research Institute. All procedures were performed in compliance with the "Guide for the Care and Use of Laboratory Animals" prepared by the National Academy of Sciences and published by National Academy Press (1996). Farm pigs (n = 5) weighing 120 to 136 lbs were used in the studies. The DFC is shown in Figure 1. This design incorporates a diverting side hole, with 2 supporting rails next to the side hole that lift the cannula away from the vessel wall, allowing blood to flow past the cannula. A 2-stage obturator is used to ensure the proper placement of the DFC. The tip of the obturator is larger in diameter than the proximal shaft and occludes the section of the cannula from the tip to the side hole. The proximal shaft end has a smaller diameter that leaves a hollow passage between the cannula wall and the obturator. The resulting space is dubbed the "flash chamber" because it allows blood to "flash back" when the diverting side hole enters the vessel. The proximal end of the DFC wall is transparent for the purpose of visualizing the flash-back effect. During DFC percutaneous insertion, the flash-back feature informs the operator when the diverting hole enters the femoral artery, which helps proper placement of the DFC.
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Figure 1. The important features of the DFC are shown. The end of the cannula has an end hole and multiple side holes. The distal flow port has 2 rails surrounding a side hole. The rails keep the cannula away from the vessel wall, allowing blood to flow past the cannula.
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The common femoral arteries were exposed by surgical means, and lidocaine was applied to prevent vessel spasm. The vessel's outer diameter was measured with a caliper. A left thoracotomy was performed to expose the left atrium. Activated clotting time was measured and adjusted to around 400 seconds by administering heparin. A 24F venous return cannula (DLP Single Stage Venous Cannula; Medtronic, Grand Rapids, Mich) was placed in the left atrial appendage. The Seldinger technique was then used to cannulate the femoral artery, rather than an arteriotomy, to avoid bleeding around the cannula. No pursestring suture, ligature around the artery, or occlusion of the distal vessel was done in either group of animals. A TandemHeart percutaneous ventricular assist device (CardiacAssist, Inc, Pittsburgh, Pa) was used to pump the blood from the left atrium to the femoral artery at a flow of 1.0 to 3.5 L/min. A Transonic flow probe (5SB Perivascular Flowprobe; Transonic Systems, Inc, Ithaca, NY) was placed around the femoral artery distal to the cannula insertion site. The performance of the DFC was compared with that of a standard cannula (SC) in 2 sequential experiments, which were identical except for the order in which the cannulas were tested. First, either the DFC or the SC was inserted, tested, and removed. Then the other cannula was inserted, tested, and removed. The order for inserting the cannulas was randomized. The cannulas were each secured to the skin with sutures to prevent movement during the experiments.
Distal leg tissue perfusion was quantified with a neutron-activated microsphere technique.
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For each leg, a 5-mL volume of microspheres (BioPhysics Assay Laboratory, Inc, Worcester, Mass) was injected at a speed of 5 mL over 30 seconds through the side port of the cannula at a pump flow rate of 3.50 L/min. Microspheres of different intensity were used for each infusion. After the experiment, calf muscles from each leg were excised to yield 2 replicate samples weighing about 1 g each. The samples were dried and sent to BioPal for microsphere concentration quantification and calculation of tissue perfusion. Each animal experiment took approximately 3 hours, 1 hour for surgical exposure and instrumentation and 2 hours for the cannula studies (1 hour for each).
A section of femoral artery around the cannula insertion site was excised for explant analysis. The vessels were opened longitudinally on the side opposite to the puncture hole. Samples were examined with a microscope for intimal tears or tears at the puncture site.
The data were analyzed by using 2 statistical tests. The presence or absence of flow and perfusion was compared with a 2-tailed Fisher's exact test. The magnitude of flow and tissue perfusion for the 2 groups were compared with paired t tests.
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Results
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The mean arterial diameter for vessels in which the DFC and SC were used was 0.60 ± 0.17 and 0.59 ± 0.11 cm, respectively. Mean baseline femoral flow in the vessels in which the DFC and SC were used was 99 ± 44 mL/min and 100 ± 46 mL/min, respectively. Distal femoral artery flow after cannulation is listed in Table 1. Distal femoral flow did not change with increased pump flow. Flow was present in 5 of 5 animals with the DFC but in only 1 of 5 animals with the SC (P < .024, 2-tailed Fisher's exact test). The one animal with distal flow with the SC had the largest baseline vessel size (0.76 cm). Paired t tests showed higher flow using the DFC than the SC at each level of flow (P < .05).
The tissue perfusion results are presented in Table 2. Perfusion was measured at a pump flow of 3.5 L/min. Distal leg perfusion was higher with the DFC than the SC (P < .03). Evidence of tissue perfusion was found in 5 of 5 animals with the DFC but only in 1 of 5 animals with the SC (P < .024).
The insertion of the DFC was no different than that of the SC, except for positioning of the diverting hole with the flash-back feature. Good flash-back visualizations were observed during all DFC placement procedures. The same length of cannula was inserted into the femoral artery for the DFC and the SC. There was no difficulty in removing the DFC. Explant analyses showed no intimal tears or thrombus with either cannula.
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Discussion
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This study shows that the DFC allowed significant blood flow distal to the cannulation site, whereas the same size SC did not. In addition, distal blood was a consistent feature of the DFC, which was measured in all animals, whereas the SC showed no flow in most animals. The average distal flow was approximately two thirds of baseline value. The microsphere data confirmed this finding, showing no tissue perfusion in most animals with the SC and consistent perfusion with the DFC. These data support the hypothesis that the SC frequently caused mechanical obstruction of the vessel, which was alleviated by the design of the DFC.
This was an experimental study that evaluated the concept of a DFC, but the ultimate goal is a commercial product for use by cardiac surgeons. Possible clinical indications include extracorporeal membrane oxygenation, percutaneous left heart assistance, complex aortic arch operations, and difficult redo sternotomy procedures.
There are limitations to the current study that warrant consideration. All the animals had normal blood vessels, whereas the patient population for this device might have peripheral vascular disease, which could influence the performance of the cannula. Therefore this study serves as preliminary evidence, and further studies will be needed in diseased vessels. Also, the duration of the experiments did not exceed 4 hours. Studies of much longer duration will be necessary to investigate the performance of the DFC in the clinical setting. Despite these limitations, the current study clearly demonstrates that the DFC provides greater distal flow than an SC of the same size, providing a rationale for development of a clinical DFC cannula.
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Acknowledgments
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We acknowledge the technical contributions made to this work by Deborah Scalise, Katherine O'Callaghan, Tom Will, and the staff of animal facility at Allegheny-Singer Research Institute, Pittsburgh, Pa.
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References
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- Hendrickson SC, Glower DD. A method for perfusion of the leg during cardiopulmonary bypass via femoral cannulation. Ann Thorac Surg. 1998;65:1807-1808.[Abstract/Free Full Text]
- Serry C, Najafi H, Dye WS, Javid H, Hunter JA, Goldin MD. Superiority of aortic over femoral cannulation for cardiopulmonary bypass, with specific attention to lower extremity neuropathy. J Cardiovasc Surg. 1978;19:277-279.[Medline]
- Yoshimura N, Ataka K, Nakagiri K, Azami T, Yoshida M, Yamashita C, et al. A simple technique for the prevention of lower limb ischemia during femoral veno-arterial cardiopulmonary support. J Cardiovasc Surg. 1996;37:557-559.[Medline]
- Greason KL, Hemp JR, Maxwell JM, Fetter JE, Moreno-Cabral RJ. Prevention of distal limb ischemia during cardiopulmonary support via femoral cannulation. Ann Thorac Surg. 1995;60:209-210.[Abstract/Free Full Text]
- Matsuura H, Yang XM, Fonger JD, et al. Percutaneous bidirectional femoral cannulation for extended extracorporeal circulatory support. In: Chang JB, editor. Modern vascular surgery. Berlin: Springer-Verlag; 1994.
- Reinhardt CP, Dalhberg S, Tries MA, Marcel R, Leppo JA. Stable labeled microspheres to measure perfusion. validation of a neutron activation assay technique. Am J Physiol Heart Circ Physiol. 2001;280:H108-H116.[Abstract/Free Full Text]
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Abstract
Introduction
