Download A Smart Solution for Cannulation Bottlenecks in

vonsegesser_pap.qxd
9/10/03
17:00
Page 42
Cardiothoracic Surgery
A Smar t Solution for Cannulation Bottlenecks in Mini-invasive
Open Hear t Surger y
a report by
Dr Ludwig Karl von Segesser
Head, Department of Cardiovascular Surgery, Centre Hospitalier Universitaire Vaudois (CHUV)
Background
Dr Ludwig Karl von Segesser is
Head of the Department of
Cardiovascular Surgery in the Centre
Hospitalier Universitaire Vaudois
(CHUV), Lausanne, Switzerland. He is
a full clinical professor and has a
long-standing interest in research
into cardiopulmonary bypass,
surface modification and mechanical
circulatory support, as well as
paediatric and adult cardiovascular
surgery. He has published over 500
articles and is a member of more
than 30 scientific societies and 10
editorial boards, including Editor-inChief of the European Journal of
Cardio-thoracic Surgery and Founding
Editor of Interactive Cardiovascular
and Thoracic Surgery. Dr von Segesser
completed his cardiovascular surgery
training in Geneva, Houston and
Zurich prior to an academic
appointment at Zurich University
Hospital. He attended medical
school at the University of Basel,
Switzerland, and graduated prior to
training in general surgery
(Diplomat Swiss Board of Surgery).
About 50 years ago,1 the first successful open heart
operations were performed with cardiopulmonary
bypass. To allow for reliable intracardiac repair, a
man-made machine was responsible for the work of
the patient’s heart and lungs for a limited period of
time. Of course, the so-called pump oxygenator, a
device maintaining gas exchange (oxygenation and
CO2 removal) and blood pressure, was at the core. A
typical heart–lung machine used in the 1950s is
shown in Figure 1, and a lot of ancillary equipment
has been added since. However, the main basic
components, i.e. the artificial lung (at that time
excentric rotating drums) and the pump, can still be
found in modern machines that now rely on
disposable membranes for gas exchange.
Standard Cannulation
In order to fulfil its task, i.e. maintain gas exchange
and blood pressure while the heart is arrested for
surgical repair, the artificial blood path of the
heart–lung machine has to be connected somehow
to the blood circulation of the body. The traditional
method is to insert specifically designed cannulas
into the target vessels of the body, either centrally
(for example via vena cava and aorta), or
peripherally (for example via common femoral vein
and artery), and to connect them to the tubing
system of the heart–lung machine.
The original cannula designs, which were often
made from stainless steel and were reusable, have
been replaced since by disposable plastic models,
which nowadays are available in many sizes and
configurations. For a 70kg adult patient (target
pump oxygenator flow 4–5 litres/min), standard
cannulas measure 24 French (F) (= 8mm in
diameter) on the arterial side and up to 51F (17mm)
42
on the venous side if the inferior vena cave (see
Figure 2) is cannulated with a two-stage design
through the right atrium. If the right atrium is to be
opened, the two caval veins are usually cannulated
separately using two 28F (9mm) venous cannulas.
The latter allow for adequate venous drainage by
gravity,2 which is achieved as a result of the height
difference between the heart and the venous
reservoir of the heart–lung machine (typically
around 60cm).
Cannulation for Minimal Access
Cardiac Surgery
Major efforts have been made in recent years in
order to develop minimal access heart surgery.3
Sophisticated instruments, including videoendoscopic tools, telemanipulators and robots,
have been developed for this purpose. Due to the
very limited space for access, remote cannulation
is preferred for many of these procedures. Hence,
the heart–lung machine is usually connected to
the vessels in the groin using thin-walled
cannulas. There is a major issue for venous
cannulation here, where the diameter of the
access vessel (femoral vein in Figure 2 – typically
measuring 7–9mm for an adult patient)
determines the diameter of the traditional
cannulas at both levels, the access vessel and the
target vessel (the inferior vena cava measurements
in this example are around 20mm in diameter). A
femoral vein measuring 9mm in diameter is
typically cannulated by a device that is slightly
smaller, for example a 24F cannula (8mm). This
situation is depicted in Figure 3, where an 8mm
cannula is introduced through the femoral and the
iliac veins up into the inferior vena cava. At the
level of the right atrium, this cannula has exactly
the same diameter as at the level of insertion,
which is 8mm.
1. L K von Segesser, “From the magic mountain to rocket science”, Interactive Cardio-vascular and Thoracic Surgery, 2
(2003) (full text free at http://www.ICVTS.org).
2. Y Ni, B Leskosek, L Shi, Y Chen, L Qian, R Li, Z Tu and L K von Segesser, “Optimization of venous return tubing
diameter for cardiopulmonary bypass”, Eur. J. of Cardio-thoracic Surg., 20 (2001), pp. 614–620.
3. L K von Segesser, S Westaby, J Pomar, D Loisance, P Groscurth and M Turina, “Less invasive aortic valve surgery:
rationale and technique”, Eur. J. of Cardio-thoracic Surg., 15 (1999), pp. 781–785.
BUSINESS BRIEFING: GLOBAL SURGERY 2003
vonsegesser_pap.qxd
9/10/03
17:01
Page 43
A Smar t Solution for Cannulation Bottlenecks in Mini-invasive Open Hear t Surger y
The only way to achieve full blood flow through
such a long thin cannula with a cross-sectional area
representing only around 15% of the inferior vena
cava is to augment venous blood drainage, either
kinetically with a centrifugal pump, or with vacuum
applied to a hard shell venous reservoir.4 However,
although both techniques theoretically provide the
necessary pressure gradient in order to approach the
target blood flow required, the latter is not always
met in clinical practice.5
Advantages of Smart Central
Cannulation
The advantages of ‘collapsed insertion and expansion
in situ’, as described for the smartcanula™ in
Figure 1: A Melrose Pump Oxygenator Built in the 1950s at the Hammersmith
Hospital in London Exposing the Basic Principles of Function
The Smart Cannulation Concept
Rotating Excentric Drums
Inlet/Outlet
‘Collapsed insertion and expansion in situ’ is the basic
principle of the smart cannulation concept. The
smartcanula™ is designed from flexible material with
a memory effect in such a fashion that, prior to
insertion, it can be stretched over a mandrel and
collapsed. Some limitation of its diameter only occurs
within the theoretical smaller access vessel
(remaining short restriction). Removal of the
smartcanula™ is fairly easy, as gentle traction reduces
its diameter.
For peripheral cannulation (see Figure 4), it is
recommended that the smartcanula™ is slid in its
collapsed configuration over a guidewire, through
the femoral and iliac veins into the inferior vena
cava, where it is released. The mandrel and the
guidewire are removed and the cannula position is
secured. Due to its design, the smartcanula™
expands over the majority of its entire length to a
diameter well above the access vessel and much
closer to the diameter of the target vessel, thus
reducing the resistance to venous drainage.6
Pump
The blood is drained from the patient by gravity to the inlet of the rotating drums, which expose it on the inner surface as a
film to an atmosphere saturated with oxygen. The oxygenated blood collects on the lower situated left side, from where it is
pumped back to the patient. (Museum of the Department of Cardiovascular Surgery, CHUV, Lausanne, Switzerland).
Figure 2: Inferior Vena Cava and Main Peripheral
Affluent Veins Including, on Right and Left Sides,
Superficial and Deep Femoral Veins, Common
Femoral Veins, External and Internal Iliac Veins
Position
Mathematical calculations using computational fluid
dynamics predicted for the smartcanula™7 show a
drastic reduction of the cannula-induced pressure
drop and therefore increased blood flow. In vivo
evaluations have shown that the flow increased for
smartcanula™ in comparison with standard cannulas
by 34% for an access limited to 28F, 72% for an
access limited to 24F and 170% for an access limited
to 20F. Meanwhile, the superior venous drainage
capacity of the smartcanula™ has been demonstrated
clinically in nine patients participating in a
prospective study.
Diameter
Inferior vena cava
20mm
Common iliac vein
12mm
External iliac vein
10mm
Common femoral vein
9mm
Superficial femoral vein
7mm
Not shown are the renal and hepatic veins, which drain directly into the inferior
vena cava.
4. H Tevaearai, X Mueller, D Jegger, M Augstburger, F Stumpe and L K von Segesser, “Optimization of the pump driven
venous return for minimally invasive open heart surgery”, Int. J. Artif. Organs., 22 (1999), pp. 684–689.
5. L K von Segesser, “Cardiopulmonary support and extracorporeal membrane oxygenation for cardiac assist”, Ann. Thorac.
Surg., 68 (1999), pp. 672–677.
6. D Jegger, X Mueller, G Mucciolo, A Mucciolo, Y Boone, I Seigneul, J Horisberger and L K von Segesser, “A new
expandable cannula to increase venous return during peripheral access cardiopulmonary bypass surgery”, Int. J. Artif.
Organs., 25 (2002), pp. 135–140.
7. X Mueller, I Mallabiabarrena, G Mucciolo and L K von Segesser, “Optimized venous return with self-expanding cannula:
from computational fluid dynamics to clinical application”, Interactive Cardio-vascular and Thoracic Surgery, 1 (2002),
pp. 23–7 (full text free at http://www.ICVTS.org).
BUSINESS BRIEFING: GLOBAL SURGERY 2003
43
vonsegesser_pap.qxd
9/10/03
17:30
Page 44
Cardiothoracic Surgery
Figure 3: Peripheral Venous Cannulation
Position
Figure 4: smartcanula™
Cannula
Position
smartcanula
Inferior vena cava
8mm
Inferior vena cava
18mm
Common iliac vein
8mm
Common iliac vein
11mm
Common femoral vein
8mm
Common femoral vein
8mm
In addition to complex cardiac surgical procedures and unstable haemodynamic
situations, peripheral venous cannulation has gained renewed interest for minimally
invasive cardiac surgery using small access for exposure, endoscopic visualisation or
robotic instrumentation. However, the diameter of a traditional venous cannula
(standard and percutaneous) is determined over its entire length by the diameter of
the access vessel (e.g. the femoral vein): 8mm = 24F at the cannula inlet as well
as 8mm = 24F at the cannulation site.
Figure 5: smartcanula™ in Action
Although the access vein diameter is the same as in Figures 2 and 3, the
smartcanula™ expands over its entire length within the host vessel. As a matter of
fact, only a relatively short portion of the smartcanula™ (within the access vessel)
remains in partial expansion and thus the blood flow required for cardiopulmonary
bypass can be achieved easily by gravity drainage. Augmentation of venous return
by an additional pump or vacuum is no longer necessary.
memory effect of the smartcanula™ that limits the
possibility of the venous wall collapsing (resulting in
temporary interruption of the venous flow). The
latter is well known during cardiopulmonary bypass
with traditional cannulas and is known as ‘atrial
chatter’ – a quite disturbing phenomenon.
Snare
Outlook
A purse string suture (*-*-*-*) placed on the right atrium is snared and tied together with the cannula in optimal position. As
shown here, the smartcanula™can also be used for central cannulation. In contrast to standard right atrial two-stage
cannulas, which measure up to 51F, a smaller access orifice (around 24F or less than 50%) is sufficient for optimised venous
drainage and reduced atrial chatter.
44
peripheral cannulation, are also of interest for central
cannulation (see Figure 5). The most apparent
benefit, of course, is the fact that full blood flow can
be achieved through a relatively small access hole. As
a matter of fact, four-litre/min can be achieved with
a 20F orifice for access, which is a fraction of the
traditional orifice sizes for right atrial central
cannulation. Cannulation of a small right atrium, a
so-called ‘crowded’ right atrium and a previously
operated right atrium are just a few examples where
access orifice size matters. The self-expansion
capability is also an advantage during cardiac surgical
procedures requiring significant mobilisation of the
heart, where the smartcanula™ has proved to be
relatively kink-resistant for both the experimental
and the clinical set-up. It is the same material
Devices for venous cannulation have seen
significant progress over time. Until today, the
original, rigid steel cannulas have evolved towards
flexible plastic cannulas with wire support that
prevent kinking, very thin walled wire wound
cannulas allowing for percutaneous application and
all sorts of combinations. In contrast to all these
rectilinear venous cannula designs exposing the
same cross-sectional area over the entire
intravascular path, the smartcanula™ concept of
‘collapsed insertion and expansion in situ’ is the
logical next step for venous access combining
flexible cross-sectional area for optimised flow and
ease of use for both insertion and removal. Reduced
atrial chatter, kink resistance in situ and improved
blood drainage despite smaller access orifice size are
some of the most evident advantages of this new
device. The fact that flexible, self-expanding venous
cannulas of a given size cover various dimensions of
cannulas with traditional design will certainly
reduce the number of cannulas that have to be kept
in stock, and this will have an impact on warehouse
cost and thus reduce another bottleneck.
For the surgeon, however, the most intriguing aspect
of cannulation with the smartcanula™ device might
be the fact that this technology allows for intracardiac
surgery and a fully open right atrium without the
need to snare the vena cava – a totally new and very
promising perspective. ■
BUSINESS BRIEFING: GLOBAL SURGERY 2003