Off-Pump Coronary Artery Bypass Surgery
W. Brent Keeling
Michael E. Halkos
John D. Puskas
INTRODUCTION
Over the past decade, there has been increasing interest in performing coronary artery bypass grafting (CABG) without the use of cardiopulmonary bypass. The growth in off-pump coronary artery bypass surgery (OPCAB) has been largely driven by increasing recognition of the deleterious effects of cardiopulmonary bypass and the desire to avoid the diffuse inflammatory response, multiorgan dysfunction, and neurocognitive complications that may follow. Increasing clinical experience with OPCAB has allowed analysis of outcomes following the procedure and demonstrated improved clinical outcomes in both prospective and large, risk-adjusted, retrospective comparisons among various patient populations.
Approximately 20% of CABG cases performed annually in the United States are performed off-pump and some centers report a significantly higher percentage of OPCAB cases. Increasing technical proficiency has been facilitated in large part by continued improvements in exposure and retraction techniques and the development of specialized stabilizers and positioners, which allow experienced off-pump surgeons to conduct complex multivessel coronary revascularizations that were not previously feasible without the use of cardiopulmonary bypass. With current positioners and stabilizers, OPCAB can be performed in the vast majority of patients needing coronary revascularization.
Even among cardiovascular surgeons not routinely performing coronary revascularization off-pump, there are newly recognized clinical scenarios, such as patients with severe atherosclerosis of the ascending aorta, for whom the use of OPCAB techniques may be particularly beneficial. OPCAB continues to be a facilitating technology for surgeons developing and promoting minimally invasive approaches to coronary revascularization. OPCAB has, therefore, evolved into a component of the armamentarium of the modern cardiovascular surgeon.
PREOPERATIVE CONSIDERATIONS
Although OPCAB is now performed routinely in some clinical practices, the tendency to automatically or blindly assign patients to OPCAB should be resisted. Preoperative factors favoring OPCAB must be weighed carefully against relative or absolute contraindications for the procedure. Rational and systematic consideration of these factors maximizes the likelihood of a technically successful procedure while limiting the chance for adverse events.
SURGEON
The individual surgeon’s training, experience, and attitudes toward OPCAB are the starting point from which any preoperative decision making should begin. OPCAB presents a unique set of technical challenges to the cardiovascular surgeon, who otherwise would be operating in a motionless and bloodless field. It has been estimated that OPCAB is feasible in up to 95% of patients presenting for primary CABG.
Individual surgeon experience in OPCAB is an important determinant in patient selection for OPCAB. The unique technical challenges of OPCAB grafting and its relative unfamiliarity have raised concern that adoption of OPCAB may lead to poorer outcomes during each surgeon’s “learning curve.” With careful patient selection, OPCAB surgery can be gradually assimilated into clinical practice while preserving and ultimately improving clinical outcomes. Very early in a surgeon’s experience, it is reasonable to exclude patients with depressed left ventricular function, left main disease, and those requiring multiple lateral wall grafts. With experience, more complex and technically challenging cases can be performed safely off-pump. Over time, OPCAB can be applied to a broad spectrum of clinical settings, including patients with advanced age, multivessel disease, depressed left ventricular function, left main disease, and complete arterial revascularization. Gradual assimilation of OPCAB thereby develops surgeon familiarity and comfort with the technique, allowing its broader application to an increasing pool of patients who derive benefit from avoiding cardiopulmonary bypass.
Patient
Patients for whom OPCAB is inappropriate are those in cardiogenic shock, those suffering from recurrent ischemic arrhythmias, and those with thoracic anatomy that severely limits the ability to rotate the heart, for instance, those with pectus excavatum or previous left pneumonectomy (see Table 52.1). Relative contraindications include intramyocardial coronary arteries, and small or diffusely calcified distal target vessels. These targets may be safely bypassed off-pump only with the benefit of considerable experience. On the other hand, patients with left main coronary lesions and recent myocardial infarction can safely have coronary revascularization performed off-pump and should be considered candidates for the procedure.
The preoperative evaluation of the patient proceeds with a complete history and physical exam. If radial artery harvest is contemplated, patients with inconclusive Allen’s tests undergo radial and ulnar artery duplex examinations. Criteria for preoperative carotid duplex examination include left main disease, peripheral vascular disease, carotid bruits, history of CVA, history of heavy tobacco use, and age >65 years. If significant carotid disease is detected, further work-up is pursued and staged or concomitant carotid endarterectomy is performed.
The role of atherosclerotic lesions of the ascending aorta in perioperative stroke has become increasingly evident over the past decade, and it is in this group of patients where OPCAB may be of greatest benefit. OPCAB surgery combined with clampless proximal anastomosis techniques is a uniquely valuable alternative for patients with severe atherosclerosis of the ascending
aorta in which aortic clamping may pose a significant risk for atheroembolic stroke. Routine intraoperative use of epiaortic ultrasound is an invaluable tool for identifying patients with severe atherosclerosis of the ascending aorta so that their stroke risk can be effectively managed.
aorta in which aortic clamping may pose a significant risk for atheroembolic stroke. Routine intraoperative use of epiaortic ultrasound is an invaluable tool for identifying patients with severe atherosclerosis of the ascending aorta so that their stroke risk can be effectively managed.
Table 52.1 Contraindications to Off-Pump Coronary Artery Bypass | |||||||||||||||||||||||||||
|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|---|
| |||||||||||||||||||||||||||
INTRAOPERATIVE MANAGEMENT
The planned conduct of OPCAB introduces a number of new patient care issues to the staff of an operating room. An important underlying concept to ensuring patient safety and the smooth conduct of the procedure is communication between the surgeon, operating room staff, and anesthesiologists. Excellent communication between the surgeon and the anesthesia provider is paramount in order to ensure intraoperative hemodynamic stability and to coordinate any departure from the planned order of distal or proximal anastomoses.
ANESTHESIA
Several aspects of anesthetic management of patients during OPCAB are common to the management of patients having conventional CABG. All patients undergoing OPCAB require invasive monitoring. At a minimum, an arterial line and central venous line are required. Pulmonary artery catheters are used routinely. Monitoring of pulmonary artery pressures can be particularly useful during retraction of the heart for the construction of distal anastomoses, as pulmonary artery pressure elevations are frequently the first sign of hemodynamic compromise prior to ischemic arrhythmias or cardiovascular collapse. Transesophageal echocardiogram is utilized sparingly but may be of use in order to identify areas of hypokinesis or significant mitral regurgitation following periods of regional myocardial ischemia.
In addition to the routine monitoring and safe anesthetic induction desired in all CABG procedures, there are a number of anesthesia management issues that are specific to OPCAB. In contrast to conventional CABG procedures, maintenance of normothermia is critically important throughout the case, as the ability to actively rewarm the patient by cardiopulmonary bypass is forfeited. Significant hypothermia adversely affects coagulation, is arrhythmogenic, and delays postoperative extubation. Efforts to maintain normothermia should therefore begin prior to induction. At our institution, a convective air system cycles warm air continuously to warm the patient throughout the procedure (Bair Hugger; Arizant Healthcare, Eden Prairie, MN).
The major challenge in the intraoperative anesthetic management of patients undergoing OPCAB is maintenance of hemodynamic stability during the elevation and retraction of the heart necessary to obtain exposure of coronary targets. Significant alterations in blood pressure and cardiac output may occur if preparatory steps are not taken. This can occur with rightward retraction of the heart for lateral wall exposure. Acutely, this is typically related to decreases in preload and left ventricular filling that occur as the vena cavae, right atrium, right ventricular outflow tract, and pulmonary veins may be compressed with this maneuver. An effective first-line treatment for this response is the administration of intravenous fluids. An assessment of the patient’s intravascular volume status is made prior to manipulation of the heart and preload is subsequently optimized. In order to compensate for the acute changes in preload that occur during cardiac manipulation, placement of the patient in steep Trendelenburg and reverse Trendelenburg positions can rapidly alter preload conditions to favor different hemodynamic states. Patient positioning is particularly useful when moment-to-moment changes in blood pressure are desired, for instance when rightward displacement of the heart is anticipated (Trendelenburg position) or when moderate hypotension is desired prior to placement of a partial occluding vascular clamp on the ascending aorta (reverse Trendelenburg position). Often, significant pharmacologic manipulation of systemic blood pressure can be avoided with bed positioning alone. Releasing the right-sided pericardial traction sutures and elevating the right limb of the sternal retractor on rolled towels are routine and valuable maneuvers to facilitate exposure and hemodynamic stability. Opening the right pleural cavity or releasing pericardial attachments along the diaphragm can also prove useful during rightward displacement of the heart.
As experience with OPCAB continues to evolve, the use of inotropes and vasopressors to maintain hemodynamic stability has been liberalized. Early in our experience, adjustment of preload conditions with intravenous fluid was the primary means by which stable blood pressures were maintained. In order to limit the intravenous fluid load given to patients intraoperatively, low-to-moderate doses of alpha agents such as norepinephrine are now routinely used. This practice has led to more favorable volume status in the postoperative period and has not had untoward effects on myocardial protection. It is unusual for patients to have a significant inotrope or vasopressor requirement beyond the immediate perioperative period.
Familiarity with the OPCAB procedure on the part of the anesthesia team is critical to the safe conduct of the operation. Patient care issues specific to OPCAB are thereby anticipated and addressed before they adversely affect the outcome of the procedure. Communication between the anesthesia team and the surgeon prior to and during the operation is important, particularly when changes in the surgeon’s operative plan occur.
SURGERY
The surgeon should come to the operating room with an operative plan that optimizes the likelihood for a successful outcome but also should remain flexible enough to change the operation as intraoperative findings and events dictate. This is one area where OPCAB and conventional CABG procedures differ significantly. OPCAB procedures frequently require significant intraoperative decision making that may result in departure from the routine. The following describes how a typical OPCAB case is performed in a patient requiring multivessel bypass.
Preparation
All patients for whom OPCAB is planned receive an aspirin suppository following
induction of anesthesia and prior to being prepped for surgery. In our practice, we administer aspirin perioperatively and dual antiplatelet therapy (aspirin and clopidogrel) in the postoperative period for platelet inhibition. Clopidogrel is administered within 4 hours after surgery if chest tube output is <100 cm3/hour for 4 hours.
induction of anesthesia and prior to being prepped for surgery. In our practice, we administer aspirin perioperatively and dual antiplatelet therapy (aspirin and clopidogrel) in the postoperative period for platelet inhibition. Clopidogrel is administered within 4 hours after surgery if chest tube output is <100 cm3/hour for 4 hours.
The chest is opened in the usual manner through a midline sternotomy incision. Left and/or right internal mammary arteries (LIMA/RIMA) are harvested with the use of an upward-lifting retractor. Other radial artery or saphenous vein conduits are harvested simultaneously by endoscopic techniques as needed. Prior to vein or radial artery harvest, patients receive 5,000 units of heparin; this is important to avoid fibrin strands in endoscopically harvested conduits. Prior to division of IMA conduits from the chest wall, heparin is given (180 units/kg) to achieve a target activated clotting time of >350 seconds. Heparin is re-dosed every 30 minutes to maintain this level of anticoagulation. A sternal retractor (OctoBase; Medtronic, Inc., Minneapolis, MN) designed to act as a platform for OPCAB stabilizers and positioners (Octopus Evolution AS and Starfish EVO, Medtronic, Inc.; ACROBAT and EXPOSE, Maquet, Inc., Wayne, NJ) is placed in the chest. A wide inverted “T”-shaped pericardiotomy is performed, dividing the pericardium along the diaphragm. The phrenic nerves should be identified and protected during pericardiotomy. It is important to divide the pericardium to the apex to facilitate cardiac displacement. The left pleural space is opened widely; opening the right pleural space will facilitate cardiac displacement, but has been less necessary since the introduction of cardiac positioning devices and is infrequently performed in the absence of RIMA harvest. Care is taken during the dissection to clip any large vessels encountered and to avoid the phrenic nerves. It is also important to divide the diaphragmatic muscle slips, which insert on the right side of the xyphoid in order to allow elevation of the right sternal border, creating space for rightward cardiac displacement. Placement of two rolled towels under the right limb of the retractor elevates the right sternal edge, allowing the heart to be positioned toward the right without compression against the sternum or retractor.
The most important traction suture is a deep posterior pericardial suture placed approximately two-third of the way between the inferior vena cava and left pulmonary vein at the point where the pericardium reflects over the left atrium. Care should be taken with superficial placement of this suture to avoid the underlying descending thoracic aorta, esophagus, left lung, and pulmonary veins. The suture is covered with a soft rubber catheter to prevent laceration of the epicardial surface of the heart. The purpose of this deep traction suture is to elevate the heart up and out of the pericardial well to facilitate exposure of the coronary targets. When this suture is retracted toward the patient’s left hip, it elevates the base of the heart toward the ceiling and points the apex vertically with remarkably little change in hemodynamics. When the deep pericardial traction suture is retracted toward the left shoulder, the heart rotates from left to right. This exposure can occasionally be obtained without the deep stitch by placing a warm laparotomy pad underneath the heart.
Stay updated, free articles. Join our Telegram channel
Full access? Get Clinical Tree
