Anesthesia for coronary artery bypass grafting surgery

INTRODUCTION — Coronary artery bypass grafting (CABG) is the most commonly performed cardiac surgical procedure in the United States [1]. Anesthetic planning depends partially on the expected surgical approach to revascularization. CABG is typically performed via a midline sternotomy incision with the aid of cardiopulmonary bypass (CPB). In selected patients, off-pump coronary artery bypass (OPCAB) without CPB may be accomplished via either a full sternotomy or a small anterior left thoracotomy incision, termed a minimally invasive direct coronary artery bypass (MIDCAB) approach.

This topic will discuss anesthetic management of patients undergoing on-pump or off-pump CABG surgery.

General considerations during the perioperative period for patients undergoing cardiac surgical procedures and cardiopulmonary bypass are also reviewed separately:

●Preoperative considerations (See "Preoperative evaluation for anesthesia for cardiac surgery".)

●Prebypass considerations

•(See "Anesthesia for cardiac surgery: General principles", section on 'Monitoring'.)

•(See "Anesthesia for cardiac surgery: General principles", section on 'Induction of general anesthesia'.)

•(See "Anesthesia for cardiac surgery: General principles", section on 'Maintenance of general anesthesia'.)

•(See "Anesthesia for cardiac surgery: General principles", section on 'Preparations for cardiopulmonary bypass'.)

●Cardiopulmonary bypass

•(See "Initiation of cardiopulmonary bypass".)

•(See "Management of cardiopulmonary bypass".)

•(See "Weaning from cardiopulmonary bypass".)

●Postbypass considerations

•(See "Anesthesia for cardiac surgery: General principles", section on 'Management during the postbypass period'.)

•(See "Intraoperative problems after cardiopulmonary bypass".)

PREBYPASS PERIOD — The key steps that must be completed in the prebypass period are listed in the table and are discussed in a separate topic (table 1). (See "Anesthesia for cardiac surgery: General principles".)

The following sections note specific management considerations during the prebypass period for patients undergoing coronary revascularization.

Avoidance and treatment of ischemia — It is particularly important to detect, prevent, and treat myocardial ischemia throughout the prebypass period.

Monitoring for ischemia — We simultaneously and continuously monitor the electrocardiogram (ECG) to detect ST-segment depression or elevation and the transesophageal echocardiogram (TEE) to detect new regional wall motion abnormalities (RWMAs) (eg, hypokinesis or akinesis). Also, elevations in right or left ventricular (LV) filling pressures (eg, the central venous pressure [CVP] or the pulmonary artery wedge pressure [PAWP]) may indicate ischemia. These commonly employed monitoring modalities to detect ischemia have varying degrees of sensitivity and specificity [2]. (See "Anesthesia for cardiac surgery: General principles", section on 'Monitoring'.)

We conduct an initial comprehensive prebypass TEE examination , followed by continuous use of the TEE to monitor for ischemia, as well as monitoring ventricular function and volume [3-5]. Regional wall motion abnormalities indicating ischemia (figure 1 and figure 2), as well as global left and right ventricular function are assessed. Details are described in a separate topic. (See "Anesthesia for cardiac surgery: General principles", section on 'Monitoring with transesophageal echocardiography' and "Anesthesia for cardiac surgery: General principles", section on 'Initial transesophageal echocardiography examination'.)  

Maintaining hemodynamic goals — Myocardial oxygen (O₂) supply is determined by the oxygen content in the blood (hemoglobin level and saturation) and by coronary blood flow. Myocardial O₂ demand is determined by factors that influence myocardial work (heart rate, myocardial wall stress, and contractility). (See "Approach to the patient with suspected angina pectoris", section on 'Pathophysiology'.)

Hemodynamic and physiologic goals are prevention of ischemia by providing optimal myocardial O₂ supply and minimizing demand (table 2). (See "Anesthesia for noncardiac surgery in patients with ischemic heart disease", section on 'Prevention of ischemia' and "Anesthesia for noncardiac surgery in patients with ischemic heart disease", section on 'Treatment of ischemia'.)

Specific hemodynamic goals include:

●Blood pressure (BP) is maintained within 20 percent of baseline (typically, a mean arterial BP 75 to 95 mmHg and/or diastolic BP 65 to 85 mmHg).

●A low to normal heart rate (HR) (eg, 50 to 80 beats per minute [bpm]) is maintained. Tachycardia compromises both oxygen supply and demand (figure 3).

●Tachycardia with hypotension is typically treated by administering bolus doses of a pure alpha-1 agonist agent (eg, phenylephrine 50 to 100 mcg boluses or a phenylephrine infusion (table 3)) to restore normal blood pressure.

●Tachycardia with hypertension is treated by increasing anesthetic depth (eg, administering a bolus dose of a rapid-acting opioid such as fentanyl 50 to 250 mcg or propofol 10 to 50 mg, or increasing the concentration of a volatile anesthetic agent) if the likely cause is pain or inadequate anesthesia. If anesthetic agents are not effective, small boluses of a beta blocker (eg, esmolol, metoprolol, or labetalol) or an infusion of nitroglycerin are typically administered (table 4).

●Fluid administration is restricted, which helps to avoid fluid overload with resultant LV distention and increased wall stress. (See "Anesthesia for cardiac surgery: General principles", section on 'Prebypass fluid management'.)

Induction and maintenance of general anesthesia — The goals of general anesthetic induction and maintenance are to produce and maintain unconsciousness, attenuate the hemodynamic responses to endotracheal intubation and surgical stimulation, and prevent or treat hemodynamic changes that lead to myocardial oxygen imbalance and ischemia. Hemodynamic manipulation is typically required in patients with ischemic heart disease to achieve a simultaneous state of unconsciousness while maintaining a favorable myocardial oxygen balance. Severe pain and endogenous catecholamine release during initial incision and subsequent sternotomy necessitate adequate depth of general anesthesia to prevent tachycardia and hypertension. Subsequently, it is appropriate to reduce anesthetic doses to avoid hypotension during the periods of reduced surgical stimulation that typically follow sternotomy. (See "Anesthesia for cardiac surgery: General principles", section on 'Induction of general anesthesia' and "Anesthesia for cardiac surgery: General principles", section on 'Maintenance techniques'.)

Positioning — After sternotomy, placement of a sternal retractor is necessary for harvesting the internal thoracic or internal mammary artery (IMA) (see 'Incision, sternotomy, and harvesting of venous and arterial grafts' below). Retractor positioning is closely observed since the steel post attaching it to the operating table may compress the upper arm causing radial nerve injury, and may also be associated with brachial plexus injury [6-8]. In addition, when the retractor lifts the sternum, the patient's head may be lifted off the supporting head cushion, particularly in an older patient who has cervical spine arthritis. If this occurs, the retractor should be adjusted or the patient's head should be repositioned with additional pillow support.

Other positioning considerations are discussed in a separate topic. (See "Anesthesia for cardiac surgery: General principles", section on 'Patient positioning'.)

Incision, sternotomy, and harvesting of venous and arterial grafts — Incision, sternotomy, harvesting of peripheral vein(s) and/or a peripheral artery, dissection to free the IMA from the chest wall, and exposure of the heart and great vessels are the fundamental surgical steps that precede aortic and venous cannulation.

CARDIOPULMONARY BYPASS — Initiation, management, and weaning from cardiopulmonary bypass (CPB) are discussed in separate topics:

●(See "Initiation of cardiopulmonary bypass".)

●(See "Management of cardiopulmonary bypass".)

●(See "Weaning from cardiopulmonary bypass".)

POSTBYPASS PERIOD — Key steps for any cardiac surgical procedure in the period immediately after cardiopulmonary bypass (CPB) include venous and arterial decannulation, reversal of anticoagulation with protamine administration, insertion of temporary or backup epicardial pacing wires, and reinfusion of pump blood (table 1).

Hemodynamic stability must be maintained after weaning from CPB. Cardiovascular problems that result in hypotension are identified and treated (table 5 and table 3). (See "Intraoperative problems after cardiopulmonary bypass", section on 'Cardiovascular problems'.)

Recognition and management of other intraoperative problems that may occur during the postbypass period are discussed separately. (See "Intraoperative problems after cardiopulmonary bypass".)

Postbypass transesophageal echocardiography — Transesophageal echocardiography (TEE) examination immediately after coronary artery bypass grafting (CABG) surgery emphasizes the following aspects [3,4,9]:

●Global left ventricular (LV) and right ventricular (RV) function are evaluated.

●LV regional wall motion abnormalities (RWMAs) are documented as part of the overall assessment of the adequacy of revascularization in territories of myocardium perfused by each of the major coronary arteries supplying the LV (figure 1 and figure 2).

Previously ischemic or hibernating myocardium may show improved function in the early postbypass period. However, myocardial stunning is common and consequently, myocardial segments that had abnormal contraction in the prebypass period may remain impaired even after adequate coronary blood flow has been restored.

Significant deterioration of regional wall motion in previously normal myocardial segments may indicate a technical problem with a coronary graft (eg, poor quality of a bypass graft anastomosis, kinking, vasospasm, or embolization of air or microparticulate debris into the graft) (movie 1). Poor graft flow can be confirmed by a Doppler flow probe applied to the graft. ST-segment changes on the electrocardiogram (ECG) or hypotension with low cardiac output may also be noted. Detection of such problems allows surgical correction prior to leaving the operating room. (See "Intraoperative problems after cardiopulmonary bypass", section on 'Surgical or technical problems'.)

In patients who require ventricular pacing after CPB, a distinct septal motion abnormality termed "septal bounce" is often observed; this occurs due to the abnormal pattern of ventricular depolarization that accompanies RV epicardial pacing (movie 2). Septal bounce can be distinguished from a true RWMA because septal thickening persists during ventricular pacing but is absent when the septum is ischemic. If this is difficult to discern visually, a brief pause in ventricular pacing may be helpful.

New or worsening mitral regurgitation (MR) in the postbypass period should prompt a thorough evaluation for LV RWMAs indicating an ischemic cause of the MR.

●LV and RV chamber sizes are assessed to determine intravascular volume status (movie 3). This is important because CVP and PAP measurements are poor predictors of intravascular volume and fluid responsiveness [10]. (See "Intraoperative transesophageal echocardiography for noncardiac surgery", section on 'Volume status'.)

●Hypotension after myocardial revascularization may occasionally be caused by dynamic left ventricular outflow tract (LVOT) obstruction with systolic anterior motion (SAM) of the mitral valve anterior leaflet [11].

●If aortic dissection is suspected following decannulation (eg, in a patient with a calcific or diffusely atheromatous ascending aorta, or one who develops postbypass hypotension that is unresponsive to treatment), the ascending aorta is evaluated to identify this potentially fatal complication (image 1).

●Adequacy of any additional surgical repair (eg, repair or replacement of a cardiac valve) is assessed.

Additional considerations for the postbypass TEE examination are discussed separately. (See "Anesthesia for cardiac surgery: General principles", section on 'Postbypass transesophageal echocardiography'.)

TEE is also used for continuous monitoring throughout the postbypass period to assess ventricular volume and function, and to detect development of hypovolemia, hypervolemia, or low systemic vascular resistance [4]. (See "Anesthesia for cardiac surgery: General principles", section on 'Monitoring with transesophageal echocardiography'.)

Transport and handoff in the intensive care unit — Preparations, transport, and handoff in the intensive care unit are addressed separately. (See "Handoffs of surgical patients", section on 'Operating room to intensive care unit' and "Anesthesia for cardiac surgery: General principles", section on 'Transport and handoff in the intensive care unit'.)

Further details regarding postoperative complications after on-pump or off-pump CABG surgery are addressed in the following topics [12]:

●(See "Early cardiac complications of coronary artery bypass graft surgery".)

●(See "Early noncardiac complications of coronary artery bypass graft surgery".)

●(See "Off-pump and minimally invasive direct coronary artery bypass graft surgery: Clinical use".)

OFF-PUMP CORONARY ARTERY BYPASS SURGERY

General considerations — Off-pump coronary artery bypass graft surgery (OPCAB) refers to coronary artery bypass grafting (CABG) without the use of cardiopulmonary bypass (CPB). This technique avoids potential morbidity associated with aortic cannulation and cross-clamping (eg, embolism of aortic plaque with consequent stroke), and with use of CPB (eg, systemic inflammatory response, platelet activation, fibrinolysis, bleeding, vasodilatory shock). (See "Intraoperative problems after cardiopulmonary bypass".)

Outcomes such as death, cardiovascular events, and need for revascularization are no better and may be worse in many patients undergoing OPCAB compared to on-pump CABG [13-15] (see "Off-pump and minimally invasive direct coronary artery bypass graft surgery: Clinical use", section on 'Outcomes'). However, OPCAB is often selected for patients at high risk for stroke due to extensive atheromatous involvement of the ascending aorta. (See "Off-pump and minimally invasive direct coronary artery bypass graft surgery: Clinical use", section on 'Patient selection'.)

OPCAB is usually accomplished via a standard midline sternotomy incision. In some cases, a small left anterior thoracotomy incision (termed minimally invasive direct coronary artery bypass [MIDCAB]) is suitable to approach an anterior coronary vessel, typically the left anterior descending artery [16]. (See "Minimally invasive coronary artery bypass graft surgery: Definitions and technical issues".)

Details regarding patient selection, surgical techniques, advantages, disadvantages, and outcomes for OPCAB and MIDCAB are available in other topics. (See "Minimally invasive coronary artery bypass graft surgery: Definitions and technical issues" and "Off-pump and minimally invasive direct coronary artery bypass graft surgery: Clinical use".)

Anesthetic management — Anesthetic management for OPCAB differs from management for on-pump CABG in the following ways:

●Less systemic anticoagulation is required (typically 100 to 200 units/kg of intravenous [IV] heparin, approximately one-third of the dose employed for CPB). Activated whole blood clotting time (ACT) is checked before partial clamping of the aorta or other vessels (eg, the internal mammary artery [IMA]). An ACT value of 250 to 300 seconds is targeted in most institutions, although evidence defining optimal ACT for OPCAB is lacking. This level of anticoagulation balances ischemic and hemorrhagic complications, particularly in patients recently receiving antiplatelet agents.

●We do not routinely administer an antifibrinolytic agent (eg, epsilon-aminocaproic acid [EACA] or tranexamic acid [TXA]) after systemic heparinization for OPCAB surgery. TXA reduces exposure to allogeneic RBC in OPCAB, but an optimal dosing regimen has not been established. In addition, its impact on clinically relevant outcomes in this setting is unknown [17,18].  

●Fluid loading (typically 15 to 20 mL/kg) to provide optimal preload is employed to maintain hemodynamic stability during coronary artery grafting and manipulation, rotation, and lifting of the heart required during OPCAB [19]. This is in contrast to the fluid restriction employed during the prebypass period for patients undergoing CABG surgery with CPB. (See "Anesthesia for cardiac surgery: General principles", section on 'Prebypass fluid management'.)

The Trendelenburg (head down tilt) position is also frequently used to improve preload during off-pump manipulation of the heart [20]. (See "Patient positioning for surgery and anesthesia in adults", section on 'Trendelenburg'.)

●Vasoactive infusions (eg, phenylephrine and/or norepinephrine (table 3)) are typically necessary to maintain hemodynamic stability during off-pump periods of manipulation of the heart [19]. In particular, marked hemodynamic instability is noted with displacement of the heart during mobilization for posterior coronary targets [19,21]. Constant communication between the surgical and anesthesiology teams is necessary to recognize and aggressively treat instability (eg, with adjustments in the positioning of the heart and vasoactive infusion management) [19].

●Atrial pacing is used as a means of enhancing arterial blood pressure and cardiac output, especially when preoperative beta blockade-induced bradycardia is present [22].

●Transesophageal echocardiography is particularly helpful to differentiate between hemodynamic instability due to myocardial ischemia (presenting as regional wall motion abnormalities [RWMAs] in the distribution of the coronary artery undergoing revascularization) compared with restricted chamber filling resulting from external compression of the heart [19,23].

●There may be increased risk for myocardial ischemia after revascularization during the intraoperative and early postoperative periods since the heart was not protected from ischemia with CPB and administration of cardioplegia. Thus, close continuous monitoring of the electrocardiogram (ECG) and TEE images (while the TEE probe remains in place) for ischemic changes is necessary [19].

●Normothermia should be maintained during the intraoperative period. In one study of 1714 patients undergoing OPCAB, moderate-to severe hypothermia (<35.5°C) at the time of admission to the postoperative intensive care unit was associated with a higher mortality risk compared with those who were normothermic (adjusted hazard ratio [HR] 2.03, 95% CI 1.41-2.93) [24].

●In some patients, it may be necessary to convert an OPCAB procedure to on-pump CABG with CPB due to intractable hemodynamic instability, malignant arrhythmias, global ventricular ischemia, and/or technical difficulty with adequate exposure and mobilization of target coronary vessels [19,25].

SOCIETY GUIDELINE LINKS — Links to society and government-sponsored guidelines from selected countries and regions around the world are provided separately. (See "Society guideline links: Coronary artery bypass graft surgery".)

SUMMARY AND RECOMMENDATIONS

●Induction and maintenance of anesthesia – Goals of general anesthetic induction and maintenance during coronary artery bypass grafting (CABG) surgery are to produce and maintain unconsciousness, attenuate the hemodynamic responses to endotracheal intubation and surgical stimulation, and prevent or treat hemodynamic changes that lead to myocardial oxygen imbalance and ischemia. Severe pain and endogenous catecholamine release during initial incision and subsequent sternotomy necessitate adequate depth of general anesthesia to prevent tachycardia. Subsequently, it is appropriate to reduce anesthetic doses to avoid hypotension during the periods of reduced surgical stimulation that typically follow sternotomy. (See 'Induction and maintenance of general anesthesia' above.)

●Avoidance and treatment of ischemia – It is particularly important to detect, prevent, and treat myocardial ischemia throughout the prebypass period. Specific hemodynamic and physiologic goals maintain optimal myocardial oxygen supply and minimize demand during induction and the prebypass periods (table 2). (See 'Avoidance and treatment of ischemia' above.)

●Use of transesophageal echocardiography (TEE) – TEE is typically used for patients undergoing CABG to:

•Conduct an initial comprehensive prebypass TEE examination, and a focused postbypass examination. (See 'Postbypass transesophageal echocardiography' above and "Anesthesia for cardiac surgery: General principles", section on 'Initial transesophageal echocardiography examination'.)

•Continuously monitor for regional wall motion abnormalities (RWMAs) that may indicate ischemia (figure 1 and figure 2 and movie 1), as well as for monitoring global ventricular function and volume status throughout the prebypass and postbypass periods. (See "Anesthesia for cardiac surgery: General principles", section on 'Monitoring with transesophageal echocardiography'.)

●Off-pump coronary artery bypass graft (OPCAB) surgery – Off-pump coronary artery bypass graft surgery (OPCAB) refers to CABG without the use of CPB. Anesthetic management differs from management for on-pump CABG in the following ways (see 'Off-pump coronary artery bypass surgery' above):

•Less systemic anticoagulation is required.

•Antifibrinolytics are not administered.

•Fluid loading (typically 15 to 20 mL/kg), Trendelenburg positioning, and vasoactive infusions (eg, phenylephrine and/or norepinephrine (table 3)) are typically employed to maintain hemodynamic stability during surgical manipulation of the heart.

ACKNOWLEDGMENT — The editorial staff at UpToDate acknowledge Ryan Konoske, MD, who contributed to an earlier version of this topic review.