19 декабря 2001 00:00 |
Technical Tips and Pitfalls in OPCAB Surgery: The Buffalo
ABSTRACT
The Center for Minimally Invasive and Robotic Heart Surgery has
performed more than 1,500 off-pump coronary artery bypass (OPCAB)
procedures since 1995. The operation has changed significantly based
on experience and development of new tools. These improvements have
made the operations safer and applicable to more patients. No
patients are presently scheduled for on-pump bypass surgery in our
center. The purpose of this paper is to describe some of the
problems and pitfalls we have experienced and how to avoid them.
INTRODUCTION
The technique for OPCAB has been significantly modified since 1995,
but at present a relatively standard procedure has emerged. We are
also fully aware that OPCAB per se was developed years ago and that
successful off-pump coronary surgery has been performed by pioneers
in South America [Benetti 1991] long before the re-invention of the
procedure in North America. Of course, the learning experience
continues and there has been constant improvement in the tools
utilized. Many of the modifications have occurred to overcome
technical problems that were not anticipated. The purpose of this
presentation is to help others steepen their learning curve and
thereby avoid some of the most common mistakes. We have divided this
brief paper in what we believe are the most important steps in OPCAB
surgery.
Selection
In our center, all coronary artery bypass grafting (CABG) patients
are scheduled for OPCAB. We do get a significant percentage of
high-risk patients and our cardiologists often refer patients who
have been turned down for standard CABG [D'Ancona 1999a]. Although
the «highest risk patient gets the most benefits» we recommend
avoiding this potential «trap» in the start up phase for new
programs. The margin is less in high-risk cases and it is easy to
get into trouble. Although OPCAB is starting to become «mainstream»,
there is still skepticism and the procedure may be blamed in cases
of an unfavorable result. In our opinion, all patients benefit from
OPCAB vs. standard CABG. It is recommended to start an OPCAB program
by selecting favorable patients who should do very well and then
expand to the more challenging and high-risk cases.
«Ideal» patients for OPCAB
1. Good distal vessels.
2. Good left ventricular function.
3. No ongoing ischemia.
4. No critical left main disease.
We also recommend the «novice» OPCAB surgeon be careful with
patients with only one target when the other vessels are ungraftable
and totally occluded. This situation can rapidly turn into a very
difficult management situation with severe ischemia and unstable
hemodynamics. Also, do not hesitate to go on pump in case of
trouble. This is not a defeat and should not cause major problems
when the patient is converted in a controlled fashion.
Medical management
The patient should be well controlled at the time of surgery if at
all possible. Patients with acute and ongoing ischemia are difficult
to manage intra-operatively. Although some of the most aggressive
OPCAB surgeons in South America are tackling patients in full
cardiac arrest with OPCAB techniques, we certainly do not advocate
this approach. Patients should be medically stable on calcium
channel, beta-blocking agents, nitrates and other drugs as needed.
With modern pharmacological therapy, almost all patients with
coronary artery disease can be successfully stabilized. We routinely
give aspirin and Plavix preoperatively to interfere with
platelet-function. Since there is no cardiopulmonary bypass (CPB) to
cause platelet dysfunction and a fibrinolytic stage, we believe it
is important to interfere with platelet function to improve graft
patency. Although we have no hard data, there is increasing evidence
and concern about the so-called hypercoagulable state in OPCAB
surgery [Mariani 1999].
In very unstable patients with ongoing ischemia we occasionally use
intra aortic balloon pumping (IABP) preoperatively. IABP can make
the unstable patient nonischemic and make OPCAB a nice
hemodynamically simple experience in the most severe cases.
Anesthesia
An informed and interested anesthesiologist is crucial for success.
The following pitfalls can make OPCAB an extremely challenging and
frustrating experience. The experienced cardiac anesthesiologist or
nurse anesthetist will anticipate and treat hemodynamic changes
ahead of time, thereby making the whole procedure smooth with few
peaks of valleys in the blood pressure. A two-way communication
between anesthesiologist and surgeon must take place on a continuous
basis. Specific issues are summarized below:
1. Volume management. This is an important issue and will cause
major problems if not handled properly. The OPCAB patient does not
get a big fluid load through the pump-prime and fluid added into the
pump and is therefore frequently given inadequate amounts of fluids.
Relative hypovolemia will make it virtually impossible to position
the heart. The reaction of the inexperienced will be to give higher
doses of inotropes or vasoconstrictors. Such drugs in high doses
will cause ischemia, arrhytmias and possibly end organ damage.
2. Blood loss. Although it has been shown that OPCAB may save
blood-products in coronary surgery, there are several pitfalls. The
management of bleeding, shed blood, and volume infusion requires
careful attention. Otherwise severe anemia and bleeding diathesis
may result. This is especially important when multiple grafts are
done and if meticulous hemostasis is not observed during harvesting
of arterial conduits. Excellent hemostasis should be assured before
administration of heparin. The shed blood is in general saved and
washed by the «Cellsaver», which will remove the clotting factors
and platelets. If four, five or six grafts are done, loss of blood
can become a major issue and the patient occasionally requires
packed red cells and even components. This can in most cases be
avoided by the precise and compulsive surgeon.
3. Blood pressure and hemodynamic management. Although we have
demonstrated only relatively minor hemodynamic changes during heart
positioning when the «single stitch» technique is utilized [D'Ancona
2000a], there is frequently a need for pharmacological intervention
to stabilize the blood pressure. We prefer to use vasoconstrictors
and nitroglycerin to decrease it. Beta-blockers are used to reduce
the heart rate but are seldom needed. Calcium-channel blockers are
used routinely to reduce spasm in arterial grafts.
Monitoring
1. Arterial line and central venous pressure (CVP) are mandatory. We
have occasionally performed OPCAB without monitoring any invasive
pressures but this is quite nerve wrecking for the surgeon and is
not recommended.
2. Pulmonary artery catheter is helpful in unstable patients and
patients with low ejection fraction or mitral regurgitation. Some
centers use pulmonary artery catheters routinely while we have tried
to use them selectively. When significant volume infusions and the
use of vasoconstrictors and inotropes are anticipated, pulmonary
artery pressure monitoring may be very useful in prevention and
management of ischemia.
3. Transesophageal echo is seldom utilized in our center in OPCAB
operations, but may help in the evaluation of the aorta and the left
ventricular function as well as regional wall motion abnormalities.
4. Electro-encephalography and continuous svO2 monitoring has been
used extensively by the Tampa-group [Novitzky 2000] and may have an
important role in the prevention of adverse CNS-events secondary to
hypotension. We do not have experience with this methodology but are
planning to initiate such monitoring for our cardiac patients.
Incisions
In the term OPCAB, we include all off-pump CABG. Although the
majority of the cases are done through a median sternotomy, there is
an important role for alternate incisions. In primary cases the
incision may be limited to obtain a truly minimally invasive
procedure and a superior cosmetic result. In reoperations the choice
of incision may have major influence on overall outcomes and
complications [Miyaji 1999, D'Ancona 2000b]. The planning of such
operations is crucial since the exposure is limited and the purpose,
especially in the reoperative minimally invasive procedure, is to
limit dissection and minimize positioning, which can cause tension
and embolization of old grafts.
obviously has to be present and the left anterior descending artery
(LAD) must be of reasonable quality and not intramuscular.
Minimally invasive procedures to the right coronary artery (RCA)
using the gastroepiploic artery [GrandJean 1996] require careful
evaluation of the abdominal status.
Positioning
In the standard OPCAB with multi-vessel bypasses, we use the
«LIMA-stitch» (after Ricardo Lima, Recife, Brazil). This stitch has
been well described [Karamanoukian 1999] and is also called deep
pericardial stitch by some. In our modification, a gauze pack is
fixed to the posterior pericardium. By pulling on the gauze the
heart is lifted. The heart rests on the gauze-pad. All vessels may
be exposed using this technique [Karamanoukian 1999].
The potential dangers of this positioning technique are:
1. Damage to the left pulmonary veins may cause bleeding.
2. The gauze pack may cause compression of the circumflex or its
branches if too much traction is utilized. In a patient dependent on
the circumflex (relatively uncommon in our experience) we perform
grafting of LAD first. In very unstable or critical circumstances,
we perform the LAD-anastomosis with minimal elevation of the heart.
Other groups are solving this problem by doing circumflex first,
basing the perfusion on the native LAD. We believe that it is more
dangerous to do major elevation of the heart prior to LAD grafting,
especially if the lesion in LAD or left main is severe.
Alternative positioning technique
We previously utilized the positioning technique described by Dr.
Gerard Guardion to perform ablation of aberrant atrioventricular
connection of the posterior heart. Dr. Antonio Calafiore modified
this technique and included gauze tapes passed through the
transverse sinus and under the vena cava. These tapes were then used
for heart positioning. The major danger of this method was the
potential of exerting direct pressure on the left main coronary with
severe ischemic and hemodynamic collapse.
Positioning must always be performed in close cooperation with the
anesthesiologist. If the desired position is not tolerated, the
heart should be placed back in its normal position and the situation
reassessed. Anesthesia should then be given time to volume load the
patient or pharmacologically improve the hemodynamic state. Usually
the second time will be better with the same or slightly different
position. The key element is to be patient especially early on
during the teams learning curve.
Stabilization
We have mainly used pressure stabilization and have been satisfied
with this method. There are certain important pitfalls with this
type of stabilization, however.
1. Perforation of the heart with the stabilizing fork. Although we
have not had this complication, it is a definite danger. It is very
important that the surgeon and the assistant perform the placement
and removal of the stabilizer foot together; one person should be
holding the heart and the second handling the stabilizer.
2. Removing the device can cause avulsion of the graft. This is a
real danger especially when the stabilizer bar is placed cephalad.
If the stabilizer bar is placed caudal, the danger of graft avulsion
is less but the stabilization may be less satisfactory. When great
care is taken on removing the device after grafting, this
complication is usually avoided.
3. If too little pressure is applied, there may be motion between
the stabilizer foot and the heart. This will cause a «sawing action»
and damage to the epicardium and to cardiac veins.
4. If too much pressure is applied, cardiac output may potentially
be impaired. We have studied this and found it to be uncommon.
Remember more pressure does not necessarily improve stabilization.
5. Another more common pitfall is obstruction of another vessel
during grafting. This is most common if the diagonal branch of LAD
is stabilized. The stabilizer can easily occlude the LAD itself,
causing ischemia and hemodynamic problems. The best way to avoid
this is to graft LAD first with a different conduit (usually the
mammary artery). This potential problem is the main reason we are
reluctant to graft diagonal and LAD with sequential LIMA-grafts. A
T-configuration is in general much safer.
Preparing for grafting
When the heart is positioned and the conduits ready, grafting must
be performed in a relaxed controlled atmosphere or the case will
quickly get out of hand. A proximal snare is placed to obstruct the
vessel. The heart and hemodynamics are now observed for two to three
minutes to evaluate if the patient will tolerate obstruction of the
vessel to be grafted. After such «pre-conditioning» the actual
grafting may proceed.
Everything must now be prepared: blower, shunts, and suction. An
open vessel bleeding is siphoning the distal vessel and may thereby
be causing ischemia. It is therefore much better to shunt, distally
snare, or use a simple intraluminal obstructor, than leaving the
distal vessel open. This concern is especially important for the
right coronary artery.
Tools utilized during grafting
1. Blower. This is an essential tool of great value but dangerous if
used incorrectly. The gas flow must be misted with saline. The flow
of gas must not be too high since damage to the endothelium may
occur. If unmisted air is used damage to the vessel is obvious. An
experienced assistant must still do the blowing. There is a great
easier and safer part of the operation.
2. Snares. We always use a proximal snare and have continued to use
4−0 polypropylene, compressed pledgets, and rubber tourniquets to
accomplish obstruction. This snare must be placed far enough
«upstream» to create enough space for the anastomosis. If possible,
avoid heavily diseased vessel areas for the snare to avoid vessel
cracking or incomplete obstruction. Occasionally the suture may
damage a septal perforator. In such case the snare is removed and a
new one placed in another location. A distal snare is occasionally
used but we prefer to use a shunt or obstructor.
3. Shunts. There are in principle two types of shunts local- and
aortocoronary-shunts which both have their advantages and pitfalls.
diameter and, since they are shunting from an area that is distal to
the coronary obstruction, the flow in such shunts can be questioned.
The limited studies that have been done on such shunts (personal
communication) have shown that the flow in such shunts is indeed
very low. Our own personal experience is that such shunts do prevent
severe ischemia when they are used properly. In heavily diseased
vessels, shunts can cause dissection and serious intimal damage and
may be better avoided.
of a large bore catheter in the aorta, IV tubing, and an olive
tipped plastic cannula for coronary insertion. Although this system
provides a higher-pressure head at the distal coronary level, there
is still no control of the flow. When blood pressure decreases, flow
in the shunt will also decrease. In general, however, these shunts
work very well. We have usually applied them during RCA grafting.
Grafting
This is obviously the crucial point of the operation and why the
procedure is done in the first place. The surgeon must be in a
relaxed comfortable state with a stable patient. Positioning should
be excellent and the heart rates should neither be too slow or too
fast; 70 to 80 are ideal. We use to slow the heart to make it easier
to suture, but with modern stabilizers this is not necessary.
Actually a large stroke volume and slow heart rate is not
advantageous since motion is increased.
The stabilizer is applied and the vessel opened and controlled. The
most important aspects of suturing are listed below:
1. Steady hands. Rest them on the patient but don't rest anything on
the heart.
2. Needle position in the needle holder is crucial. The needle must
always be positioned to take a gentle non-traumatic curve through
the vessel walls.
3. The curve of the needle must be followed to avoid a larger then
necessary hole in the intima. Lifting of tissues with the needle is
unacceptable, since this will make a big hole or even a tear in the
vessel increasing the chance of thrombosis. The positioning of the
needle is one of the most important points of the OPCAB procedure,
but often not emphasized in discussions. Surgeons who are starting
OPCAB often do not realize that suturing is not the same as on-pump.
In an arrested heart the vessel can usually be presented to the
surgeon in a favorable plane. In OPCAB, the plane of presentation
may be quite unusual.
4. Manipulation of the needleholder. We recommend that a Castro-type
needle holder is moved by finger-motion primarily and not the wrist.
This is an important detail in the prevention of intimal damage.
Graft verification
Graft verification is a must in OPCAB as in all CABG [D'Ancona
1999b]. The initiation of a new graft-technique certainly makes it
even more important to have a quality assurance tool available. We
have found transit-time flowmetry to be a simple reliable method for
assessment of graft patency. Although the method is very simple and
does not require calibration certain technical details must be
emphasized.
1. Flow must be measured with and without proximal occlusion. A
graft obstructed at the toe may show perfectly normal flow if there
is a significant perfusion in proximal direction.
2. Don't rely on mean flow alone. The graft may be compromised with
relatively high mean flow. A graft can also be normal with low mean
flow. Therefore the diastolic flow pattern must be evaluated.
3. When in doubt an intraoperative «stress-test» may be performed,
analyzing flow and curves at higher blood-pressure and/or with
injection of vasodilators such as nitroglycerin, papaverine or
adenosine.
4. Beware of air bubbles. Presence of air in the graft may simulate
organic obstruction. If this is suspected the graft should be milked
and the measurement repeated.
5. When a malfunctioning graft is diagnosed, it should be
immediately revised to prevent ischemia and hemodynamic problems
during the remaining procedure.
6. A graft that is functioning well in the heparinized state may
occlude after administration of protamine. Measurement of graft flow
should therefore be repeated after heparin reversal.
7. Final graft verification should be done just before chest-closure
since grafts that are too short or too long may kink on
chest-closure.
Using these principles early, graft patency can be assured and
adverse cardiac events during the post-operative phase avoided.
Cardiopulmonary bypass
There is no shame in using the heart-lung machine. CPB is an
extremely valuable tool and should be utilized whenever necessary.
We do convert in a few cases and have shown that this is not a major
detriment in most cases [Soltoski 1998]. It is important to be
prepared for this possibility. We always have a non-primed heart
lung machine available and a perfusionist present in the room or
nearby. When we use CPB we commonly continue to work on the beating
heart, just utilizing the hemodynamic support. This makes it very
easy and fast to go on pump. Crossclamping and cardioplegia is
seldom utilized.
It is very important to avoid the so-called «crashing on pump» that
frequently results in major complications from the cannulation or
other aspects of the CPB. We also are very afraid of what we call
the «double conversion». This occurs when a case originally planned
other strong contraindications to CPB. When such a patient needs to
be converted again to on-pump, chances of major adverse events are
very high. In this situation, careful assessment and compromise in
the completeness of revascularization should be considered.
CONCLUSION
OPCAB is an old procedure antedating traditional on-pump CABG.
Technology was not available at that time, making off-pump CABG
difficult and unpredictable in all but the most skillful hands.
There has been rapid improvement in technology for OPCAB over the
last five years. Stabilization, shunting and graft verification have
become simpler and more effective.
We believe the need for CPB in coronary surgery will be more or less
eliminated during the next several years and that coronary
intervention will be performed on a beating heart in the cath.lab or
in the operating room with only occasional use of pumps or other
AUTHOR/ARTICLE INFORMATION
Presented at the Minimally Invasive Cardiac Surgery (MICS)
Symposium, Key West, Florida, May 28, 2000.
Address correspondence and reprint requests to: Jacob Bergsland, MD,
Buffalo General Hospital, 100 High Street, Buffalo, New York 14203,
Phone: (716) 859−2248, Fax: (716) 859−4697, Email: nielsb@aol.com
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