What the Anesthesiologist Should Know before the Operative Procedure
In the United States, surgical coronary revascularization is performed utilizing cardiopulmonary bypass (on-pump coronary artery bypass, [ONCAB]) in >80% of patients and without CPB (off-pump coronary artery bypass [OPCAB]) in ≈10-20%. The reported deleterious effects of cardiopulmonary bypass (CPB) and the application of aortic cross-clamp, and increased comorbidities in an aging population make OPCAB an appealing alternative to ONCAB. The skill and preference of the surgeon and patient factors determine when to perform CABG as ONCAB or OPCAB. Contraindications to OPCAB or conditions that make OPCAB suboptimal include: intramyocardial or severely calcified coronary arteries, physiologic intolerance to cardiac manipulation, and requirement for intracardiac (e.g., valve replacement) surgery. Preoperative or intraoperative profound hemodynamic instability or ischemia-induced arrhythmias can rarely be dealt with OPCAB.
Most OPCAB procedures are currently performed via median sternotomy although other approaches are occasionally utilized (i.e., limited left anterolateral thoracotomy [minimally invasive direct coronary artery bypass or MIDCAB], robotic via thoracic ports). Many of the management issues of MIDCAB are similar to OPCAB via median sternotomy. Differences include decreased number of vessels anastomosed (i.e., LIMA to LAD), use of one-lung ventilation, limited access to epicardial surface if pacing becomes necessary, and management of thoracotomy rather than median sternotomy incisional pain. OPCAB through a standard left lateral thoracotomy for grafting the posterior circulation, especially after a previous CABG surgery is another approach.
Important differences between OPCAB (median sternotomy) and ONCAB include:
A patient with coronary artery disease, preserved LV function, significant atherosclerosis of the ascending aorta and good distal coronary artery targets may be an ideal candidate for OPCAB
OPCAB may be especially beneficial in the elderly high-risk patient with high-grade aortic atherosclerosis
Increased intensity of anesthetic care including:
Requirement for excellent communication between surgeon and anesthesiologist before and throughout procedure
Increased importance of understanding coronary lesions and planned approach/order of revascularization
Frequent hemodynamic instability during cardiac manipulation requiring vasopressors and/or inotrope administration to maintain perfusion pressure and cardiac output
Management of myocardial ischemia during coronary occlusion
Importance of maintaining normothermia
Possible need for immediate/emergent conversion to on-pump
Anesthetic care that allows “Fast Tracking” in most patients
Both on- and off-pump CABG surgery have an excellent safety profile and low morbidity and mortality (Table 1).
1. What is the urgency of the surgery?
Although OPCAB may be performed emergently, the presence of hemodynamic instability, arrhythmias, and intramyocardial or severely calcified coronary arteries is a relative contraindication.
Emergent: Data on truly emergent OPCAB are scarce. Emergency coronary revascularization is associated with increased operative mortality but can be performed off-pump. OPCAB may have some benefit over ONCAB in patients with STEMI who undergo surgery within 6 hours of onset of symptoms. If myocardial ischemia is associated with hemodynamic instability or ischemia-induced arrhythmias, CPB is frequently utilized. Extended phases of hypotension and decreased cardiac output often associated with cardiac positioning (especially during revascularization of the circumflex territory) during OPCAB may lead to cardiac decompensation and emergent conversion to CPB (≈2.5-12%). If conversion from planned OPCAB to ONCAB becomes necessary, it is associated with increased morbidity (i.e., stroke) and mortality (2-6 times)
Urgent: If hemodynamic instability or ischemia-induced arrhythmias present, CPB is frequently utilized rather than attempted OPCAB. Delaying procedure for further testing is rarely warranted and could result in further myocardial injury.
Elective: When coronary revascularization is needed but not emergently/urgently, time should be utilized to optimize the patient for surgery. This may include: (1) Cardiovascular; blood pressure control, beta blockade, ASA, diuresis, (2) pulmonary; smoking cessation, pulmonary function tests (spirometry), bronchodilators, antibiotics if infection, preoperative teaching (incentive spirometer), (3) endocrine; glucose control in diabetic, (4) hematologic; restoring RBC volume. Planned surgical approach should be reviewed in detail with the surgeon.
2. Preoperative evaluation
Common medical conditions other than coronary artery disease include congestive heart failure, cerebrovascular disease, renal insufficiency, diabetes, and hypertension. Cardiac anesthesiologist, cardiologist, and cardiac surgeon participation in care make medical consultation by other specialists unnecessary in most cases. The occasional patient with GI bleeding, stroke/TIA, or rare endocrine abnormalities may necessitate further workup.
Medically unstable conditions warranting further evaluation include cerebrovascular disease (e.g., TIA, stroke), unstable arrhythmias, COPD exacerbation, GI bleeding, diabetic ketoacidosis, infection (pneumonia), symptomatic congestive heart failure, malignant hypertension, and acute kidney injury. Although not necessarily medically unstable, the presence of an intra-cardiac lesion that would require cardiac surgery with CPB to repair (i.e., atrial septal defect, cardiac valve abnormality, LV aneurysm), should be thoroughly investigated and deemed not necessary to intervene before attempted OPCAB.
Delaying surgery may be indicated if unstable medical conditions are present in a patient scheduled for urgent or elective surgery. Recent TIA/stroke, malignant hypertension, active GI bleeding (patient will be anticoagulated during surgery), acute hepatitis, incompletely diagnosed coagulation disorders, acute renal insufficiency, severe anemia, exacerbation of COPD, and infection (e.g., UTI, pneumonia). These are examples of conditions that may warrant further assessment, consultation, workup, and stabilization.
3. What are the implications of co-existing disease on perioperative care?
Common coexisting diseases include hypertension, diabetes, peripheral vascular disease, chronic obstructive pulmonary disease, and cigarette smoking. The implications of these on perioperative care is similar to patients undergoing on-pump CABG. However, patients with severe pulmonary disease, severe aortic atheromatous disease, and possibly severe renal disease may be preferentially selected for OPCAB and avoidance of CPB. Obesity and COPD with associated large lung volumes may make surgical exposure more difficult. Dysrhythmias with associated irregular or fast heart rate can make coronary anastomosis more difficult on the beating heart although mechanical stabilization has obviated much of this problem.
b. Cardiovascular system (also see Chapter on On-Pump CABG])
(1) Clinical history and physical exam focused on angina symptoms, functional status, previous coronary interventions [PCI, CABG], symptoms of TIA/stroke, presence of peripheral vascular disease, blood pressure control, diabetic control, and evidence of heart failure.
(2) Tests: Review coronary angiogram results noting vessels involved, precise location (proximal versus distal) and degree of stenosis, vessels involved that are more difficult to revascularize with OPCAB (i.e. left main, obtuse marginals, distal RCA or its branches), and presence or absence of collateral vessels. Proximal surgical occlusion during OPCAB of a coronary artery with high-grade distal disease may not be tolerated as well as severe proximal disease with collateralization. Intramyocardial and/or heavily calcified coronary arteries make OPCAB more difficult. Although left main disease is not an absolute contraindication to OPCAB, it is associated with relatively high conversion to CPB. There is a preferential selection of patients needing more bypass grafts to ONCAB. Previous PCI is not a predictor of early morbidity or mortality in patients undergoing OPCAB. Review the echocardiogram especially noting LV and RV size and function, presence of regional wall motion abnormalities (RWMAs), presence and significance of coexisting valvular heart disease, pulmonary hypertension, and aortic atheromatous disease. Review the ECG. Presence of ischemia-induced dysrhythmias may necessitate ONCAB. Atrial fibrillation is associated with increased age, low LVEF, and is a frequent postoperative complication.
Perioperative CV Risk Reduction
(1) Understand and communicate coronary anatomy, planned surgical procedure, sequence of revascularization, cardiac stabilization methods (mechanical stabilizer), and physiologic perturbations likely during cardiac positioning.
(2) Identify factors present that are associated with more difficult OPCAB; coronary anatomy (i.e., intramyocardial, heavily calcified, circumflex distribution, RCA, lack of collateralization), and systolic dysfunction. Be prepared for immediate and early conversion to CPB if it becomes necessary.
(3) Most cardiac medications including beta-blockers, statins, and ASA should be continued perioperatively. If a patient is not taking ASA, it is likely to be started before OPCAB. Attempted prophylaxis strategies against postoperative atrial fibrillation are not usually utilized.
(4) Preinduction arterial line and intraoperative hemodynamic monitoring including CVP or PAC and TEE.
(5) Maintain or restore adequate myocardial oxygen supply ratio avoiding myocardial ischemia. Low heart rate (i.e., 60-80 bpm), maintain diastolic blood pressure, optimize hemoglobin, contractility, afterload, and preload.
(6) Preparation for likely hypotension during cardiac positioning including available in-line vasopressors/inotropes, ability to give warmed fluids rapidly, and full dose of heparin drawn and ready if urgent/emergent CPB becomes necessary.
(7) Clopidogrel is frequently added postoperatively to ASA for dual antiplatelet therapy in attempt to reduce graft thrombosis in OPCAB patients.
(1) Patients with pulmonary disease undergoing CABG may especially benefit from avoiding CPB. The hyper-inflated lungs associated with COPD may make surgical exposure during OPCAB more difficult.
(2) Clinical history including history of disease process, current medications, smoking history, and review of available studies (e.g., CXR, spirometry, ABG).
Perioperative Risk Reduction
(1) Decreased rates of postoperative respiratory infection and ventilation time have been associated with OPCAB vs ONCAB.
(2) Continue pulmonary medications including bronchodilators. Steroid therapy if appropriate (severe obstructive pulmonary disease).
(3) Pneumonia or acute exacerbation of COPD should be weighed against cardiac risk and likely prompt delay of surgery for treatment.
(4) Smoking cessation prior to and after surgery should be encouraged. Cessation days prior to surgery will increase oxygen carrying capacity (decrease carboxyhemoglobin levels), decrease nicotine (sympathetic stimulant), but is not likely to effect postoperative pulmonary complications, PFTs, or decrease mucous production. Long term smoking cessation (>2 months) decreases postoperative pulmonary complications.
Patients are often diabetic, aged, and recently received intravenous contrast prior to OPCAB. Acute renal failure (ARF) requiring dialysis after ONCAB is associated with increased mortality. GI complications such as GI bleeding and intestinal ischemia occur in 0.6-4.1% after CABG.
(1) The presence of diabetes, dehydration, recent contrast administration, and preoperative renal dysfunction should be investigated by history and laboratory testing.
(2) Prior history of GI bleeding, old age, and advanced arteriosclerosis are associated with perioperative GI complications.
(3) If surgery is emergent, patient may not have been NPO.
Perioperative Risk Reduction
(1) Risk factors for postoperative acute renal dysfunction include: preoperative renal dysfunction, age, diabetes, duration of CPB (if utilized), exposure to contrast, and perioperative hemodynamic instability.
(2) Preoperative renal dysfunction secondary to recent contrast studies must be weighed against cardiac risk when determining whether to delay surgery. There is some evidence that delaying surgery at least one day and ideally five days, especially if there is an acute increase in creatinine or the patient received a high dose of contrast, reduces the risk of postoperative ARF.
(3) Mild preoperative renal dysfunction is an independent predictor of adverse outcomes in both the short term and long term after CABG.
(4) Attempts to control patients’ hemodynamics and hydration, optimization of perfusion pressure, and use of drugs such as mannitol, furosemide, and dopamine have not been shown to reduce postoperative renal dysfunction.
(5) The effect of OPCAB on postoperative renal dysfunction is controversial and should not be the deciding factor when determining whether or not a patient with normal or impaired renal function undergoes CABG surgery as OPCAB vs ONCAB.
(6) Confirm NPO status and make preparations to reduce risk of pulmonary aspiration; gastric acid reducing, gastric volume reducing, and antacid medications as appropriate. Consider need for RSI.
(7) Incidence rates of GI complications are quite similar OPCAB vs ONCAB.
(8) Utilize postoperative GI prophylaxis
While stroke (≈3%) and cognitive dysfunction (>50% of patients at discharge) following ONCAB have been associated with cannulation, pump time, inflammation, and microembolization, they also occur following OPCAB. Coronary atherosclerosis increases the likelihood of coexisting carotid artery disease.
(1) Elderly and those with peripheral vascular disease should have evaluation of their aorta and carotid arteries. The presence of high-grade aortic atherosclerosis (TTE) and/or high-grade carotid artery disease (carotid US) may alter surgical management.
(2) Preoperative transthoracic echo for evaluation of ascending aorta in high-risk patients. Intraoperative, pre-incision TEE evaluation of ascending and descending aorta with epiaortic scanning of the ascending aorta if significant atherosclerosis is found on TEE or suspected by palpation of the ascending aorta by the surgeon prior to aortic manipulation.
(3) Symptoms of cerebrovascular disease (i.e., TIA, stroke), elderly patients, presence of left main coronary artery disease, PVD, carotid bruit, and smoking history should prompt investigation of possible carotid artery disease with noninvasive (US) or invasive (arteriography) testing.
Perioperative Risk Reduction
(1) High grade ascending aortic atheromatous disease/calcification; Risk of stroke is quite high and patient may benefit from OPCAB vs ONCAB. OPCAB, with avoiding application of an aortic crossclamp (“no touch” technique) reduces embolization. However, if intraoperative conversion from planned OPCAB to ONCAB is required, it is associated with a high stroke rate.
(2) Carotid endarterectomy (CEA) is frequently performed in a combined (CABG + CEA, one-stage) procedure in symptomatic patients with carotid artery disease to reduce risk of perioperative stroke.
(3) Cognition among people with heart disease declines over time, regardless of whether they undergo bypass surgery or receive alternative forms of treatment. A similar pattern of early decline and late recovery of cognitive function is seen with both OPCAB and ONCAB. No specific risk reduction strategy for cognitive decline after surgery can be recommended.
(4) Postoperative beta blockade may decrease risk of atrial fibrillation which has been associated with stroke.
(1) Diabetes is a risk factor for CAD. OPCAB is feasible in poorly controlled diabetics. Preoperative evaluation should focus on glucose control, insulin requirements, and presence or absence of ketoacidosis.
(2) Metabolic syndrome (dyslipidemia, hypertension, and increased plasma glucose levels) is present in ≈1/4 of patients undergoing CABG surgery and a risk factor for acute kidney injury and infections after OPCAB.
Perioperative Risk Reduction
(1) If ketoacidosis is present, cardiac risk must be weighed against the preferred plan of delaying surgery and instituting more rigorous glucose control and investigating possible causes of poor control (infection).
(2) American College of Physician guidelines (2011) for glycemic control in surgical intensive care patients with or without diabetes mellitus recommend not using intensive insulin therapy (target glucose 80-110 mg/dL). Intensive insulin therapy to achieved targeted normoglycemia is not associated with improved health outcomes and increases the risk of hypoglycemia. However, poorly controlled hyperglycemia is associated with morbidity and mortality. Evidence is not sufficient to give a precise range of glucose control but a target value of 140-200 mg/dL is a reasonable option.
(3) Targeted control of lipids, blood pressure, and glucose seem appropriate but evidence supporting appropriate levels of each and outcomes that might be improved is lacking.
g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (eg. musculoskeletal in orthopedic procedures, hematologic in a cancer patient)
Hematologic: Hematocrit/hemoglobin and correct preoperative anemia if possible. Platelet count to detect thrombocytopenia and possible HIT.
4. What are the patient's medications and how should they be managed in the perioperative period?
Common medications include beta blockers, statins, ASA, insulin oral hypoglycemic agents, antihypertensives (i.e. renin-angiotensin system [RAS] inhibitors), heparin and other anticoagulants, and diuretics. Most should be continued preoperatively.
i. What should be recommended with regard to continuation of medications taken chronically?
Cardiac: Most cardiac medications should be continued including beta-blockers and statins. RAS inhibitors may be continued and do not have a negative effect on postoperative renal function, but intraoperative hypotension is a potential side effect. Aspirin does not appear to significantly influence operative outcome (bleeding) and should be continued prior to surgery.
Pulmonary: Recommend continuing medications to control obstructive lung disease including inhaled beta agonists, and anticholinergics, leukotriene inhibitors, inhaled and oral steroid therapy.
Renal: Diuretics should be held in the preoperative period unless patient is using for management of CHF.
Neurologic: Antiepileptic and Parkinson’s medications should be continued preoperatively.
Antiplatelet: There is evidence that coronary revascularization by OPCAB results in a more pro-thrombotic postoperative state than after ONCAB. Many patients are already on ASA and this should be continued.
Psychiatric (antidepressants, benzodiazepines):The selective serotonin-reuptake inhibitors (SSRIs) can cause platelet dysfunction by inhibiting dense granule release and ultimately platelet aggregation. However, SSRI use is not associated with increased adverse events after ONCAB including any bleeding complications and can be continued. Tricyclic antidepressants have alpha-blocking activity and block reuptake of norepinephrine. It is generally recommended to continue tricyclic antidepressants. The most significant concern regarding discontinuation of benzodiazepines in the perioperative period is the development of withdrawal symptoms (e.g., headache, anxiety, tremor, psychoses, seizures). Anesthetic care for OPCAB frequently involves perioperative administration of benzodiazepines so this is rarely a problem. If chronic alprazolam use documented, it is frequently re-started in the ICU following extubation. Monoamine oxidase inhibitor (MAOIs) management should be discussed with the patient’s psychiatrist. It is widely considered unnecessary to discontinue before elective surgery but interactions with meperidine and indirect sympathomimetics (i.e. ephedrine) have been described.
j. How To modify care for patients with known allergies –
k. Latex allergy
Latex is a common trigger of anaphylaxis in the perioperative period. Preoperatively determine if the patient has sensitivity to latex (i.e. rash from gloves) versus history of anaphylactic reaction. Prepare the operating room with latex-free products.
l. Does the patient have any antibiotic allergies
If beta-lactam allergy, replace cefazolin with clindamycin for preoperative prophylaxis.
m. Does the patient have a history of allergy to anesthesia?
One of the most common triggers of anaphylaxis in the perioperative period is neuromuscular blocking agents and it is extremely rare for a patient to know this preoperatively.
Malignant Hyperthermia (MH): If significant family history or personal history of MH, avoid all triggering agents such as succinylcholine and inhalational agents. Ensure that dantrolene is immediately available and in adequate dose. If OPCAB requires conversion to hypothermic CPB (ONCAB), rapid rewarming should be avoided.
5. What laboratory tests should be obtained and has everything been reviewed?
Hemoglobin level: A large amount of blood can be lost in the groin following coronary catheterization and hemoglobin should be measured. Although hemodilution from pump prime will be avoided (OPCAB) with attendant drop in hematocrit, baseline hemoglobin is required prior to the considerable blood loss that can occur during OPCAB surgery, possible need for CPB, and requirement for maintaining myocardial oxygen supply.
Electrolytes: Obtain and review sodium, potassium, BUN, and creatinine.
Coagulation panel: Obtain and review PT, PTT, and platelet count. A baseline activated coagulation time (ACT) is obtained before administration of heparin. In some institutions a baseline TEG may be obtained.
Imaging: (1) Echocardiogram; review and especially note LV and RV function, presence of regional wall motion abnormalities, intracardiac lesions (i.e., severe aortic and mitral valve disease, patent foramen ovale that might change plan of OPCAB and necessitate the use of CPB), and presence of aortic atheromatous disease. (2) Coronary angiogram; review coronary anatomy and pathology and note measurement of LVEDP and left ventriculogram with estimate of LV function if performed. (3) CXR; obtain and review.
Other tests: Type and crossmatch. As indicated; pulmonary function tests (spirometry), carotid US.
Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?
The possible benefit of regional for cardiac surgery is controversial and the risk of neuraxial bleeding increased in anticoagulated patients.
a. Regional anesthesia
Although controversial, the addition of thoracic epidural analgesia to general anesthesia may be associated with reduced hospital stay, improved pain control, and quality of recovery in patients undergoing OPCAB. Consider thoracic epidural for postoperative pain management especially if thoracotomy approach is used (i.e., MIDCAB).
b. General Anesthesia
General anesthesia (inhalational anesthesia with supplemental opioids) without neuraxial analgesia is commonly chosen.
c. Monitored Anesthesia Care
6. What is the author's preferred method of anesthesia technique and why?
General anesthesia without neuraxial analgesia. Most cardiac medications including beta-blockers, statins, and ASA are continued preoperatively and preinduction sedation provided with midazolam (<5 mg IV). Long acting benzodiazepines are avoided. Aspirin is administered preoperatively to decrease the chance of postoperative graft occlusion. The patient is transported to a warm operating room and positioned on a warming blanket. A forced air warmer is used as possible and fluids warmed. The CPB machine is on standby (primed vs unprimed) with perfusionist present for rapid conversion to ONCAB if severe hemodynamic compromise, severe dysrhythmias, unsuitable distal target, and/or inability to expose difficult target vessels (lateral, posterior) without severe hemodynamic compromise ensues during attempted OPCAB.
Following placement of an arterial catheter, general anesthesia is induced with a variety of techniques that often include etomidate, midazolam, opioid (fentany, sufentanil) and intermediate acting neuromuscular blocking agent (vecuronium rocuronium). Maintenance of anesthesia is with inhaled anesthesia (isoflurane) and opioid (fentanyl, sufentanil) as bolus and/or infusion. When fentanyl is used and “fast tracking” planned, the dose of fentanyl is usually limited to <15 mcg/kg. Volatile anesthetics may have ischemic conditioning protective effects, are easily titrated (BIS, hemodynamics), and allow rapid awakening. Bispectral index guided anesthesia reduces the anesthetic requirements for OPCAB. Fentanyl and sufentanil are less expensive then remifentanil and in appropriate doses still allow “fast tracking.”
Central access is obtained via the right internal jugular vein (consider ultrasound guidance) and a pulmonary artery catheter with continuous cardiac output and mixed venous oxygenation placed. A decrease in CO and/or SVO2 during cardiac positioning and coronary occlusion during OPCAB may provide an early warning for intervention. However, thermodilution cardiac output and other methods of monitoring CO such as pulse contour analysis show large discrepancies between each other during OPCAB surgery and clinically acceptable agreement seen only for trends in CO during hemodynamically stable periods.
Arterial pressure waveform based CO does not provide an accurate basis for therapeutic decisions for patient safety during OPCAB. Baseline intraoperative TEE examination focuses on LV and RV function, regional wall motion abnormalities, the ascending and descending aorta (atheroma and calcification), and intracardiac pathology that might necessitate the use of CPB (severe valvular disease). Identification of significant atherosclerosis in the ascending or descending aorta suggests need for epiaortic echo scanning of the ascending aorta which may lead to altered surgical management.
New regional wall motion abnormalities identified during coronary revascularization may necessitate placement of shunt, revision of anastomoses or if severe hemodynamic compromise, conversion to ONCAB. Baseline mitral regurgitation is identified since increasing mitral regurgitation during OPCAB may indicate worsening myocardial ischemia or need for changing the cardiac position/mechanical stabilizer.
Warmed intravenous saline is administered usually in volumes less than required during ONCAB. High molecular weight first generation hetastarch may increase postoperative bleeding in ONCAB and OPCAB and is usually avoided. Preparation is made for possible rapid administration of warmed fluids during hypotension associated with cardiac manipulation/positioning especially during revascularization of posterior and lateral lesions.
Since CPB is not used, we do not routinely administer antifibrinolytics (e.g., Amicar). Following median sternotomy and before surgical coronary artery occlusion, intravenous heparin (150-200 units/kg) is administered to maintain ACT 300 seconds or longer. Full dose heparin (300-400 units/kg, ACT >400 seconds) is immediately available if conversion to CPB becomes necessary. Some surgeons will insert temporary epicardial pacing wires, which should be connected to an external pacemaker, to manage bradycardia or heart block if it occurs.
Management of hemodynamics during cardiac positioning and occlusion of the target coronary artery is discussed later. Following completion of proximal and distal coronary artery anastomoses, a TEE examination is performed to rule out any new RWMA which could indicate problems with the grafting, and if satisfactory, a reduced dose of protamine (1 mg/kg, usually aimed to reduce the ACT to about 150-180 seconds) is administered. More protamine may be given if persistent bleeding is present.
A propofol infusion (10-30 mcg/kg/min) or occasionally dexmedetomidine is used for sedation on transfer to the ICU and during rapid weaning from mechanical ventilation.
What prophylactic antibiotics should be administered?
Intravenous cefazolin within 1 hour prior to incision. If beta-lactam allergy, clindamycin or vancomycin. (Surgical Care Improvement Project [SCIP]). Antibiotics discontinued within 48 hours after anesthesia end time.
What do I need to know about the surgical technique to optimize my anesthetic care?
Technically more difficult than ONCAB-Surgery on the beating heart with displacement and temporary coronary occlusion is technically more difficult for the surgeon and anesthesiologist than ONCAB. Increased surgeon and institutional experience with OPCAB is associated with improved outcome. If OPCAB planned when previous bypass grafting has been performed (re-do CABG), adequacy of vascular access for transfusion, availability of blood, and ability to externally defibrillate should be considered.
There are two critical steps in the conduct of OPCAB; (1) application of immobilizer and positioning of the heart, and (2) occlusion of the target coronary artery for performing the distal anastomosis and these two steps may be repeated for each distal anastomosis. Each may be associated with hemodynamic instability and/or dysrhythmias (Table 2).
Application of the immobilizer and positioning of the heart; The hemodynamic changes (systemic hypotension, increased PCWP and CVP, decreased CO, aggravation of mitral regurgitation) that occur with displacement and stabilization of the heart do so within seconds of positioning and tend to stabilize within 5 minutes although systemic pressure may continue to decrease from ischemia during distal coronary anastomosis. OPCAB is consistently associated with decreased systemic pressure and increase in pulmonary artery pressures. Pulmonary capillary wedge pressures and central venous pressures also increase although TEE has demonstrated smaller ventricular volumes especially on the right side.
A rise in right atrial pressure above the PCWP in the presence or a PFO or ASD may result in right to left shunting and hypoxemia. The fall in CO and systemic pressure is most likely caused by RV compression. Access to anterior wall (LAD, diagonals) requires only mild repositioning such as a laparotomy pad under the cardiac apex and has minimal impact on cardiac function. Access to the RCA or left circumflex coronary artery marginal branches requires twisting of the heart often accomplished with a suction apparatus on the heart apex. This may cause hemodynamic compromise often the result of right ventricular compression. Dissection of the right pericardium and pleura may provide more room for the RV to fill during positioning required for anastomosis of circumflex artery vessel distribution surgery and improve hemodynamics.
Causes: It is multifactorial including compression of the ventricles, especially the right ventricle, induction of mitral regurgitation, and myocardial ischemia.
Monitoring: MAP, CVP, PAP and PAOP, SvO2, CO, TEE (especially for MR and new regional wall motion abnormalities associated with ischemia)
Management: The patient is positioned in Trendelenberg with slight right lateral tilt. Initial hypotension, common during cardiac manipulation and placement of mechanical stabilization devices, is treated with time (tends to resolve), reduction in the amount of retraction and distortion by the surgeon, administration of warmed fluids, and phenylephrine or norepinephrine since RV and LV filling may be impaired. If intravenous nitroglycerin (0.2-2.0 mcg/kg/min) potentiates the hypotension associated with heart positioning, it is discontinued. Extreme hemodynamic instability related to positioning and/or myocardial ischemia may require inotropic support (epinephrine), placement of IABP, institution of femoral-femoral bypass, use of a temporary coronary artery perfusion catheter (coronary shunt) or conversion to traditional CABG with CPB. Remember to give adequate heparin before initiating partial or full CPB.
Occlusion of the target coronary artery, making an incision in the coronary artery, and performance of the distal anastomosis; This may have two consequences; myocardial ischemia and bleeding out of the vessel, the latter makes visualization of the surgical field by the surgeon difficult and may contribute to ischemia by a coronary steal. Ischemia is more common if the proximal stenosis is less severe (≈70%) with poor development of collaterals, while bleeding out of of the target vessel is more common if the proximal stenosis is severe or total (due to collateral flow into the target artery).
Manifestations and monitoring: This may present as hypotension, fall in cardiac output, rise in filling pressure, hypoxemia, increased mitral regurgitation and bradycardia. When the right coronary artery is occluded this may cause bradycardia due to atrial asystole, nodal rhythm, or complete heart block. Traditional monitors of myocardial ischemia, the ECG and TEE, may not be as useful due to distortion of the heart.
Management: Maintaining an adequate diastolic arterial pressure and keeping heart rate slow (60-80 with an esmolol infusion) will minimize ischemia. It may be tolerated if the occlusion time can be limited (about 5 minutes). The surgeon may insert a temporary internal coronary shunt within the coronary vessel running proximal to distal through the open coronary artery. Some surgeons use shunts routinely, but they are not risk free.
Excessive bleeding out of the target coronary
Management: Often this is managed by use of a “blower” which blows a mixture of saline and carbon dioxide onto the site to wash the blood away. However, this can result in retrograde gas embolization into the aortic root. Insertion of a temporary internal coronary shunt is another approach.
Grafting Sequence/Order-Coronary artery grafting sequence varies with patient pathology and surgeon preference and significantly effects anesthetic management. If endoscopic vein harvest used, some of the insufflated carbon dioxide may be absorbed and cause the PaCO2 and PETCO2 to increase if minute ventilation is unchanged. One revascularization sequence is: (1) proximal coronary anastomoses performed first with side partial occlusion clamp on the proximal aorta in a single application and up to four hand-sewn anastomoses, (2) patient placed in Trendelenberg position before crossclamp removed to allow de-airing of the aorta through the grafts, (3) distal grafting of collateralized vessels before grafting poorly collateralized (Note: It is safer to graft a totally occluded or highly stenotic vessel with collaterals than one that provides collateral flow to another totally occluded one), (4) and the LIMA to LAD last to avoid significant manipulation of the graft (possible spasm) or the heart once it is performed.
However, may surgeons prefer placing the LIMA into the LAD first since this is often the most critical vessel to revascularize, and can be accomplished with the least manipulation of the heart, and will provide additional coronary blood flow immediately. When the ascending aorta is severely atheromatous/calcified, a “no touch” technique may be used where the LIMA provides blood flow to all of the other grafts which are anastomosed proximally to the LIMA.
What can I do intraoperatively to assist the surgeon and optimize patient care?
Have advanced knowledge of the operative plan and maintain excellent communication during procedure
TEE assessment of ascending aorta and other cardiac pathology with report to surgeon prior to incision
Avoid hypothermia; keep patient warm preoperatively, warm room, minimize exposure, use fluid warmers for high volume intravenous infusions, use low total fresh gas flows, and utilize warming adjuncts (heated mattress, forced air warmers)
Optimize surgical exposure; may need to decrease tidal volume especially during lateral and posterior exposure, adjust OR table position.
Trendelenberg and right tilt position, fluid administration prior to positioning of mechanical stabilizer, vasopressors (norepinephrine, phenylephrine) as needed.
Avoid hypertension during application of partial occluding clamp on the proximal aorta
Provide a slow heart rate and treat dysrhythmias. May need to slow heart rate or provide short period of pharmacologic induced cardiac standstill with adenosine during difficult coronary artery anastomosis.
Avoid tachycardia and hypertension; increases myocardial oxygen requirements.
Monitor for consequences of coronary occlusion; hypotension, decreased CO and SVO2, increased PAP, increased mitral regurgitation, and presence of new regional wall motion abnormality. Epicardial pacing may be required for ischemia-induced bradycardia (RCA anastomosis). TEE monitoring is more difficult but still possible during heart displacement.
Communicate presence of hemodynamic instability, especially if inability to correct, as not to delay conversion to CPB.
Use shorter acting anesthetic agents: “Fast tracking” if appropriate
What are the most common intraoperative complications and how can they be avoided/treated?
Hemodynamic perturbations during heart displacement secondary to limitations of LV filling, obstruction of RV outflow tract, and RV ventricular compression
Trendelenberg position prior to heart displacement helps normalize LV filling but the right ventricle may still remain compressed.
Rapid administration of warmed fluids
Temporary use of vasopressors or inotropes
Dissection of the right pericardium and pleura if right ventricle compressed and needs room to expand
Conversion to CPB
Temporary myocardial ischemia
Orderly planned sequence of revascularization; collateralized vessels before collateralizing vessels.
Ischemia during planned coronary occlusion may lead to regional LV and/or RV dysfunction, arrhythmias, and hemodynamic compromise. Right coronary lesions predispose to bradycardia, heart block, and atrial dysrhythmias. The ability to pace the heart (epicardial) and perform cardioversion should be immediately available. Left-sided coronary lesions may cause hemodynamic collapse (ischemia) and malignant ventricular dysrhythmias.
Treatment: Restoration of coronary blood flow, temporary coronary perfusion catheter (shunt), or conversion to CPB.
Conversion to CPB
Inability to manage hypotension and decreased cardiac output associated with cardiac manipulation and myocardial ischemia is the most frequent cause of intraoperative conversion to CPB and occurs in ≈2-15% of cases.
Keep patient warm preoperatively, warm room, warm fluids, and use warming mattress and forced air warmer if possible. Use low FGF.
b. If the patient is intubated, are there any special criteria for extubation?
Although patients are occasionally extubated in the operating room there is little evidence this is of benefit (including economic benefit). Tracheal extubation within 2-4 hours after OPCAB is a reasonable goal for most patients. Early extubation is avoided in the setting of hypothermia, persistent myocardial ischemia, significant mediastinal bleeding, severe global myocardial dysfunction, and severe pulmonary disease. Propofol sedation is discontinued before extubation while dexmedetomidine can be continued through extubation.
c. Postoperative management
What analgesic modalities can I implement?
Initial IV opioid (morphine/fentanyl) first 18-24 hours followed by PO Percocet or oxycodone with PRN IV morphine for breakthrough pain. Patient controlled analgesia (PCA) is rarely required. Thoracic epidural is occasionally used and may be associated with improved pain scores and quality of recovery in OPCAB but with no relevant benefit on the frequency of major complications after elective ONCAB.
What level bed acuity is appropriate?
Cardiothoracic Intensive care with telemetry and hemodynamic monitoring for first 12-24 hours or longer. Weaning from mechanical ventilation and extubation should usually be possible within four hours. invasive lines should be removed as soon as possible and getting out of bed, ambulating and resuming oral intake begun promptly.
What are common postoperative complications, and ways to prevent and treat them?
Hypothermia: It is important to maintain normal postsurgical core temperatures. Significant predictors of hypothermia include older age, lower body surface area, and CHF. Hypothermia is associated with adverse outcomes. Forced air warming measures are very effective in re-warming.
Atrial fibrillation (AF): Risk may be decreased with OPCAB as compared with ONCAB. Increased age and possibly increased transfusion requirement is associated with an increased incidence postoperatively. Atrial fibrillation is a risk for other morbidities including stroke, CHF, MI, renal insufficiency, and mortality. Preoperative AF prophylaxis is not indicated. Treatment: If AF occurs with hemodynamic instability, cardioversion is indicated. If AF present with stable hemodynamics, rate control (diltiazem, beta blocker) or chemical cardioversion (amiodarone).
Low systemic vascular resistance state: Often seen following ONCAB and attributed to the systemic inflammatory response induced by CPB. Low SVR state also seen after OPCAB. Tx: Vasopressors (i.e. phenylephrine, norepinephrine, vasopressin, methylene blue).
Cerebral injury and stroke: Stroke rate may be decreased but most studies show no significant difference in the incidence of postoperative long-term neurocognitive decline between OPCAB and ONCAB. Tx: Neurology/neurosurgical consult, cerebral imaging, stroke protocol, supportive care.
Pulmonary insufficiency/respiratory failure: is associated with increased mortality, development of multi-organ failure and sepsis. Risk factors for prolonged mechanical ventilation include; age, smoking LV dysfunction, and CHF among others. Early ambulation which begins with preoperative orientation and teaching is important. Tx: Mechanical ventilation (lung protection strategies)
Reoperation for bleeding: OPCAB may have less postoperative bleeding but can be associated with significant bleeding resulting in hypovolemia and tamponade with hypotension and low cardiac output. Beware of hidden blood loss in the mediastinum and pleural cavities in the absence of significant chest tube drainage. Tx: Volume replacement, transfusion, and after correcting coagulation abnormalities, may need reexploration.
Myocardial ischemia/infarction: ECG changes with myocardial ischemia and new regional wall motion abnormalities suggesting the coronary involved (e.g., marginal branch and lateral wall) and troponin elevation should prompt immediate investigation of graft patency by echocardiography, if not already done, and/or by coronary angiography. Tx: May require re-exploration for graft thrombosis or kinking. Quality of revascularization and graft patency rate is considered by some to be a limitation of OPCAB.
Acute kidney injury: No consensus as to the role of OPCAB vs ONCAB in prevention of postoperative renal injury. Risk factors for acute kidney injury include preoperative renal dysfunction, aging, and postoperative myocardial dysfunction. Tx: Ensure adequate volume, optimize cardiac output and systemic pressure, and renal replacement therapy as needed.
Prothrombotic state: Thromboembolic prophylaxis and antiplatelet therapy may need to be more aggressive after OPCAB. Cardiopulmonary bypass is associated with platelet dysfunction and fibrinolysis. OPCAB may cause hypercoagulability. Aspirin is usually resumed in early postoperative period to avoid graft thrombosis. Many add several months of clopidogrel therapy to ASA, similar to that used in intracoronary stent patients.
Mediastinal infection: Prophylactic antibiotics should be administered within 1 hour before incision and discontinued within 48 hours after surgery.
Anemia: Blood loss is the usual etiology. Tx: Transfusion to keep hematocrit between ≈28-30.
GI complications: Incidence of GI complications appears to be about the same as with ONCAB, although incidence of intestinal ischemia may be less but incidence of GI bleeding may be greater.
What's the Evidence?
Kuss, O, von Salviati, B, Borgermann, J. “Off-pump versus on-pump coronary artery bypass grafting: a systematic review and meta-analysis of propensity score analyses”. J Thorac Cardiovasc Surg. vol. 140. 2010. pp. 829-835. (Meta-analysis comparison of outcomes of OPCAB vs ONCAB in more than 123,000 patients.)
Huffmyer, J, Raphael, J. “The current status of off-pump coronary bypass surgery”. Curr Opin Anaesthesiol. vol. 24. 2011. pp. 64-69. (Recent review of OPCAB vs ONCAB short term and long term outcomes.)
Shroyer, AL, Grover, FL, Hattler, B. “On-pump versus off-pump coronary artery bypass surgery”. N Engl J Med. vol. 361. 2009. pp. 1827-1837. (OPCAB associated with higher 1-year mortality and lower graft patency in this large, prospective multicenter randomized trial.)
Hoff, SJ. “Off-pump coronary artery bypass: Techniques, pitfalls, and results”. Semin Thorac Cardiovasc Surg. vol. 21. 2009. pp. 213-223. (Review of the technical aspects of OPCAB and assessment of current results.)
Chu, D, Bakaeen, FG, Dao, TK. “On-pump versus off-pump coronary artery bypass grafting in a cohort of 63,000 patients”. Ann Thorac Surg. vol. 87. 2009. pp. 1820-7. (Similar mortality and stroke rates. OPCAB actually cost more.)
Hueb, W, Lopes, NH, Pereira, AC. “Five-year follow-up of a randomized comparison between off-pump and on-pump stable multivessel coronary artery bypass grafting. The MASS III Trial”. Circulation. vol. 122. 2010. pp. S48-S52. (At in-hospital and 5 year follow-up no difference in cardiac outcomes or the incidence of composite end point between patients with multi-vessel disease and preserved ventricular function who underwent ONCAB vs OPCAB.)
Bainbridge, D, Cheng, DCH. “Minimally invasive direct coronary artery bypass and off-pump coronary artery bypass surgery: Anesthetic considerations”. Anesthesiology Clin. vol. 26. 2008. pp. 437-452. (Thorough review of anesthetic considerations for OPCAB.)
Couture, P, Denault, A, Limoges, P. “Mechanisms of hemodynamic changes during off-pump coronary artery bypass surgery”. Can J Anaesth. vol. 49. 2002. pp. 835-49. (Review of common hemodynamic changes associated with OPCAB.)
Gurbuz, AT, Hecht, ML, Arslan, AH. “Intraoperative transesophageal echocardiography modifies strategy in off-pump coronary artery bypass grafting”. Ann Thorac Surg. vol. 83. 2007. pp. 1035-40. (Routine use of TEE during OPCAB resulted in a major change in planned operative strategy in 16% of patients.)
Caputo, M, Alwair, H, Rogers, CA. “Thoracic epidural anesthesia improves early outcome in patients undergoing off-pump coronary artery bypass surgery. A prospective, randomized, controlled trial”. Anesthesiology. vol. 114. 2011. pp. 380-90. (In a randomized trial of more than 200 patients undergoing off-pump CABG, the addition of thoracic epidural analgesia to general anesthesia was associated with reduced hospital stay, improved pain control and quality of recovery, and reduced incidence of dysrhythmias.)
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- What the Anesthesiologist Should Know before the Operative Procedure
- 1. What is the urgency of the surgery?
- 2. Preoperative evaluation
- 3. What are the implications of co-existing disease on perioperative care?
- b. Cardiovascular system (also see Chapter on On-Pump CABG])
- c. Pulmonary
- d. Renal-GI:
- e. Neurologic:
- f. Endocrine:
- g. Additional systems/conditions which may be of concern in a patient undergoing this procedure and are relevant for the anesthetic plan (eg. musculoskeletal in orthopedic procedures, hematologic in a cancer patient)
- 4. What are the patient's medications and how should they be managed in the perioperative period?
- i. What should be recommended with regard to continuation of medications taken chronically?
- j. How To modify care for patients with known allergies -
- k. Latex allergy
- l. Does the patient have any antibiotic allergies
- m. Does the patient have a history of allergy to anesthesia?
- 5. What laboratory tests should be obtained and has everything been reviewed?
- Intraoperative Management: What are the options for anesthetic management and how to determine the best technique?
- 6. What is the author's preferred method of anesthesia technique and why?
- What prophylactic antibiotics should be administered?
- What do I need to know about the surgical technique to optimize my anesthetic care?
- What can I do intraoperatively to assist the surgeon and optimize patient care?
- What are the most common intraoperative complications and how can they be avoided/treated?
- b. If the patient is intubated, are there any special criteria for extubation?
- c. Postoperative management