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From the Department of Anesthesiology (Clinical Track), Emory University School of Medicine, Atlanta, Georgia, USA.
Address correspondence to: Dr. James Ramsay, Department of Anesthesiology, Room B343, Emory University Hospital, 1364 Clifton Road, Atlanta, GA 30322 USA. Phone: 404-712-7021; Fax: 404-778-5194; E-mail: james_ramsay{at}emory.org
CORONARY artery surgery developed into the standard of care for severe coronary artery disease aided by the development of cardiopulmonary bypass (CPB), and the ability to stop the heart safely (cardioplegia) to provide a motionless field. In recent years interventional cardiology has approached the efficacy of surgical revascularization, dramatically influencing the number and type of patients presenting for surgery. Cardiac surgeons have responded by attempting to provide less invasive approaches to revascularization, the most popular of which is currently off-pump surgery through a standard sternotomy incision, or OPCAB. Reports from less industrialized countries lacking the resources for routine CPB indicated that off-pump surgery to anterior vessels (left anterior descending or LAD, and diagonal branches) was possible, and was associated with less complications than the same procedure done with CPB.1,2 The procedure has been refined by the use of specific surgical techniques and epicardial stabilizers to permit access to all regions of the myocardium. Some surgeons now perform all revascularizations without CPB.
Is OPCAB "better" than on-pump CABG?
A central issue is the quality of the left internal mammary artery (LIMA) to LAD graft, as well as other grafts. Long-term follow-up of LIMA to LAD grafts done on pump show an excellent patency (>95% at ten years),3 while early reports of patency with OPCAB were not nearly as good.4 Recent reports suggest early patency of this graft is now approaching what can be achieved on pump.5 Long-term patency results will require years of follow-up.
While there is a widely held perception that avoidance of great vessel cannulation and CPB should reduce complications and adverse outcomes after CABG, there is little objective evidence for this belief. Initial reports where partial heparinization was used indicated a reduction in the need for blood products, as well as a shortened length of stay.6–8 This may not be true for multi-vessel bypass with full heparinization. The non-randomized reports that are published do not indicate a statistically significant reduction in the incidence of peri-operative myocardial infarction (PMI), renal failure, or stroke, although there are definitely "trends" to a lower overall incidence of adverse outcome. Currently, reports from only one randomized clinical trial comparing on-pump CABG to OPCAB have been published.9–11 Surgical techniques were not standardized, and anesthetic and anticoagulation regimens were not given; the reports suggest a reduction in the need for blood products and hospital costs, but no significant changes in morbidity or mortality. At least two randomized trials are under way in the United States at the current time, and these should provide more definitive information regarding possible benefits of OPCAB as practiced currently.
Anesthetic technique
Specific anesthetic and post-operative analgesic techniques for OPCAB do not differ importantly from those used for on-pump CABG. Both types of surgery are done through a sternotomy incision, and early awakening/extubation is the current standard of care. Concern regarding neuraxial analgesic techniques in patients who will be fully heparinized applies to both approaches.
Several aspects of intra-operative management of patients for OPCAB differ significantly from that for CABG done on the pump. The principal differences are (a) performing grafts on a beating heart requires acute interventions to mitigate the effects of abnormal cardiac position and ischemia; (b) intense observation and monitoring may be desired for brief intra-operative periods, but the expected post-operative course is benign; (c) maintenance of normothermia is important in order to facilitate early recovery; and (d) anticoagulation management may be altered.
Acute interventions
Unlike on-pump CABG where specific coronary anatomy is not usually relevant to the anesthetic management, in OPCAB the effect of coronary occlusion (in order to perform the distal anastomosis) may be minimal or extreme. Occlusion of a tightly stenosed, distal vessel may cause minimal or no hemodynamic disturbance, while occlusion of a more proximal, lesser stenosis may cause acute ventricular failure. Where there is extensive collateral circulation the sequence of grafting may be critical. The anesthesiologist must review the coronary anatomy, attempt to predict the consequences of vessel occlusion and, most importantly, discuss the surgical plan including sequence of vessel grafting with the surgeon. Various surgical strategies can reduce the impact of vessel occlusion, including the use of intra-coronary shunts, performance of proximal anastomoses first, or the use of perfusion assistance (perfusion assisted direct coronary artery bypass, or PADCAB).12
Compression of the heart (especially the right ventricle), torsion of the great veins, and coronary occlusion all contribute to hemodynamic compromise. Use of the head-down or Trendelenberg position,13 as well as volume loading helps reduce this problem. Some patients require hemodynamic support with inotropic/vasopressor medications; those with reduced ventricular function may even warrant the use of a "prophylactic" intra-aortic balloon pump.
Monitoring
Publications describing anesthetic management of OPCAB suggest the use of either or both transesophageal echocardiography (TEE) and the pulmonary artery (PA) catheter.14,15 While arguments can be made for these monitors, no amount of monitoring can make up for lack of vigilance on the part of the anesthesiologist. Adequate central access for drug and volume administration, an arterial cannula for blood pressure monitoring, and close observation/communication with the surgeon are all that is needed for many OPCAB procedures. In patients with poor ventricular function, extensive collateral circulation, and undergoing multi-vessel grafting, intra-operative TEE may provide useful information about remote effects of vessel occlusion (e.g., ventricular dilatation, mitral regurgitation). Information from a PA catheter may be useful to guide therapy in the post-operative period.
Hypothermia
Unlike on-pump CABG where prevention of hypothermia in the pre-bypass period is largely irrelevant, for OPCAB there is no heat exchanger to rewarm the patient. Hypothermia in the post-operative period interferes with early recovery and can complicate hemodynamic and ventilatory control as well as contribute to coagulopathy. In order to deliver normothermic patients to the post-operative intensive care unit the anesthesiologist must intervene early to prevent heat loss. Patients should be kept covered maximally for as long as possible, and the operating room heated to the highest degree tolerated by the surgical team. Heating devices such as mattress warmers, warmed-air circulating devices, and iv fluid warmers should be employed.
Anticoagulation
In early reports of one- or two-vessel OPCAB, "partial" heparinization (e.g., half of usual doses used for cardiopulmonary bypass) was used. Today most surgeons are requesting full heparinization, which is certainly required when PADCAB is employed. While cardiopulmonary bypass induces a multi-factorial coagulopathy well known to cardiac anesthesiologists, a concern about OPCAB is that the post-pump coagulopathy is replaced by the hypercoagulable state associated with other major surgeries.16 This presents the cardiac surgeon with concerns similar to the interventional cardiologist: early graft occlusion due to thrombosis. While it seems as least as likely that early graft occlusion is due to problems with the anastomosis, some surgeons have become advocates of "partial reversal" of heparinization, and early use of antiplatelet drugs in the post-operative period. Post-operative bleeding then becomes an issue, and as alluded to above, it may be that the current practice of full heparinization, partial reversal and early antiplatelet drugs results in similar transfusion requirements after OPCAB as for on-pump CABG.
The future
Early attempts to reduce the invasiveness of cardiac surgery focussed on the incisions (Heartport®, MIDCAB, etc.). However, the surgical community has recognized that great vessel cannulation and cardiopulmonary bypass are probably more "invasive" than the incision. That being said, there is still tremendous interest in reducing surgical trauma. While angioplasty provides inferior long-term results when compared to surgical bypass,17 the risks and morbidity of surgery give angioplasty a clear margin of preference in the minds of most patients. Developments in laparoscopic techniques and robotic instrumentation are now making robotic heart surgery through port incisions a reality.18 There can be little doubt that the techniques developed for operating on the beating heart will continue to be adapted to robotic instruments, with the potential that robotic, port-access OPCAB will become a standard approach for coronary bypass surgery. This will give rise to a whole new series of considerations for the anesthesiologist, including the probable need for one-lung anesthesia, lack of direct access to the heart (e.g., for defibrillation or pacing), and a variety of position and access issues.
References
1
Benetti FJ, Naselli G, Wood M, Geffner L. Direct myocardial revascularization without extracorporeal circulation. Experience in 700 patients. Chest 1991; 100: 312–6.
2
Buffolo E, de Andrade JCS, Branco JNR, et al. Coronary artery bypass grafting without cardiopulmonary bypass. Ann Thorac Surg 1996; 61: 63–6.
3 Cooper GJ, Underwood MJ, Deverall PB. Arterial and venous conduits for coronary artery bypass: a current review. Eur J Cardiothorac Surg 1996; 10: 129–40.[Abstract]
4
Subramanian VA, McCabe JC, Geller CM. Minimally invasive direct coronary artery bypass grafting: two- year clinical experience. Ann Thorac Surg 1997; 64: 1648–55.
5
Puskas JD, Wright CE, Ronson RS, et al. Off-pump multivessel coronary bypass via sternotomy is safe and effective. Ann Thorac Surg 1998; 66: 1068–72.
6
Kshettry VR, Flavin TF, Emery RW, et al. Does multivessel off-pump coronary artery bypass reduce postoperative morbidity? Ann Thorac Surg 2000; 69: 1725–31.
7
Arom KV, Flavin TF, Emery RW, et al. Safety and efficacy of off-pump coronary artery bypass grafting. Ann Thorac Surg 2000; 69: 704–10.
8
Cartier R, Brann S, Dagneais F, et al. Systematic off-pump coronary artery revascularization in multivessel disease: experience of three hundred cases. J Thorac Cardiovasc Surg 2000; 119: 221–9.
9
Ascione R, Lloyd CT, Underwood MJ, et al. On-pump vs off-pump revascularization: evaluation of renal function. Ann Thorac Surg 1999; 68: 493–8.
10
Cox MC, Ascione R, Cohen AM, et al. Effect of cardiopulmonary bypass on pulmonary gas exchange: a prospective, randomized study. Ann Thorac Surg 1999; 69: 140–5.
11
Ascione R, Lloyd CT, Underwood MJ, et al. Economic outcome of off-pump coronary artery bypass surgery: a prospective randomized study. Ann Thorac Surg 1999; 68: 2237–42.
12
Guyton RA, Thourani VH, Puskas JD, et al. Perfusion-assisted direct coronary artery bypass: selective graft perfusion in off-pump cases. Ann Thorac Surg 2000; 69: 171–5.
13
Grundeman PF, Borst C, van Herwaarden JA, et al. Vertical displacement of the beating heart by the octopus tissue stabilizer: influence on coronary flow. Ann Thorac Surg 1998; 65: 1348–52.
14 Resano FG, Stamou SC, Lowery RC, Corso PJ. Complete myocardial revascularization on the beating heart with epicardial stabilization: anesthetic considerations. J Cardiothorac Vasc Anesth 2000; 14: 534–9.[Medline]
15 Moises VA, Mesquita CB, Campos O, et al. Importance of intraoperative transesophageal echocardiography during coronary surgery without cardiopulmonary bypass. J Am Soc Echocardiogr 1998; 11: 1139–44.[Medline]
16
Mariani MA, Gu J, Boonstra P, et al. Procoagulant activity after off-pump coronary operation: is the current anticoagulation adequate? Ann Thorac Surg 1999; 67: 1370–5.
17
Hannan EL, Racz MJ, McCallister BD, et al. A comparison of three-year survival after coronary artery bypass graft surgery and percutaneous transluminal coronary angioplasty. J Am Coll Cardiol 1999; 33: 63–72.
18
Louimet D, Carpentier A, d'Attellis N, et al. Endoscopic coronary artery bypass grafting with the aid of robotic assisted instruments. J Thorac Cardiovasc Surg 1999; 118: 4–10.
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