Coronary Artery Bypass Grafting Periprocedural Care

Updated: Oct 30, 2017
  • Author: Rohit Shahani, MD, MS, MCh; Chief Editor: Karlheinz Peter, MD, PhD  more...
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Periprocedural Care

Preprocedural Evaluation

Before performing coronary artery bypass grafting (CABG), clinicians should carefully examine the patient’s medical history for factors that might predispose to complications, such as the following:

  • Recent myocardial infarction (MI)
  • Previous cardiac surgery or chest radiation
  • Conditions predisposing to bleeding
  • Renal dysfunction
  • Cerebrovascular disease including carotid bruits and transient ischemic attack (TIA)
  • Electrolyte disturbances that might predispose the patient to dysrhythmias
  • Infection including urinary tract infection, skin infections, and dental abscesses
  • Respiratory function including the presence of chronic obstructive pulmonary disease or infection [3]

The Euroscore is one of several scoring systems used to predict CABG mortality. Results can be rendered logistically or as a simple score, which can be calculated by using the Euroscore interactive calculator. [4]

Routine preoperative investigations include the following [3] :

  • Full blood count (abnormalities corrected)
  • Clotting screen
  • Creatinine and electrolyte levels (abnormalities corrected and discussed with the anesthetist)
  • Liver function tests
  • Screening for methicillin-resistant Staphylococcus aureus
  • Chest radiography
  • Electrocardiography (ECG)
  • Echocardiography or ventriculography (to assess left ventricular [LV] function)
  • Coronary angiography (to define the extent and location of coronary artery disease [CAD])

A raised white blood cell (WBC) count should prompt a careful examination for any cause of infection. If possible, CABG should be postponed until infection has been excluded or treated. If the patient’s demographic characteristics (eg, age or smoking) indicate an increased risk of cancer, a gastrointestinal or urinary tract malignancy should be excluded.

The initial CABGs in the 1960s were performed “off pump” (OPCABG) because of the lack of cardiopulmonary bypass technology. [44] With the subsequent development of safe and effective cardiopulmonary bypass, most CABGs are now performed “on pump” (ONCABG). However, the off-pump approach has been reintroduced, with varying degrees of popularity, in an effort to reduce the complications associated with cardiopulmonary bypass. The surgical experience of the operating surgeons performing the OPCABG is critical to the outcome of the procedure. In a Cochrane review that analyzed 86 randomized trials involving 10,716 patients, Moller and colleagues reported that OPCABG resulted in increased all-cause mortality compared to ONCABG (3.7% vs 3.1%; P = 0.04), but there were no significant differences in MI, stroke, renal insufficiency, or coronary artery reintervention between the two techniques other than that OPCABG resulted in fever distal anastomoses. [45]

Elderly patients who have major comorbid conditions (eg, previous stroke or TIA; peripheral vascular disease [PVD]; bleeding disorders; or current respiratory, liver, or renal disease) may benefit from an off-pump approach. The off-pump approach may also be preferred in patients with a heavily calcified or atheromatous aorta, where cannulation is associated with a high risk of stroke. [46]

Assessment of Risk

Risk models to predict 30-day mortality following isolated CABG is an active area of research. Risk models such as the Euroscore system, [4] and the Society of Thoracic Surgeons (STS) Cardiac Surgery Risk Model, [5]  are the most commonly used predictors in cardiac surgery. Shared variables in these two impressive models include age, previous MI, PVD, renal failure, hemodynamic state, and ejection fraction (EF). In the STS model, 78% of the variance is explained by eight of the most important variables, which include age, surgical acuity, reoperative status, creatinine level, dialysis, shock, chronic lung disease, and EF.

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Patient Preparation

Premedication

The aims of premedication are to minimize myocardial oxygen demands by reducing heart rate and systemic arterial pressure and to improve myocardial blood flow with vasodilators.

Before the advent of coronary artery bypass grafting (CABG), the majority of patients with coronary artery disease (CAD) received beta-adrenoceptor blocking drugs and calcium channel antagonists or nitrates. These drugs were continued until the point of surgery because sudden withdrawal of the medications could cause tachycardia, rebound hypertension, and a loss of coronary vasodilatation.

Administration of temazepam immediately before CABG can decrease the risk of tachycardia and hypertension resulting from anxiety regarding the procedure. In the operating room, intravenous (IV) administration of a small dose of midazolam before arterial line insertion can also reduce anxiety, tachycardia, and hypertension.

In patients referred for CABG, aspirin should be continued up to the time of surgery, especially in those who present with an acute coronary syndrome (ACS). In patients receiving a thienopyridine (eg, clopidogrel or prasugrel) in whom elective CABG is planned, the drug should be withheld if possible for either 5 days (for clopidogrel) or 7 days (for prasugrel) before the procedure.

Each patient should be cross-matched with 2 units of blood (for simple cases) or 6 units of blood, fresh frozen plasma, and platelets (for complex cases). [3, 6, 7] Tranexamic acid (1-g bolus before surgical incision followed by an infusion of 400 mg/hr during surgery) may be considered to reduce the amount of postoperative mediastinal bleeding and the quantity of blood products used (ie, red blood cell and fresh frozen plasma) [8]

Antidepressant treatment for 2-3 weeks before undergoing CABG and continued for 6 months afterward may foster a faster postoperative mental health recovery and have a beneficial effect on postoperative pain. [47, 48]

Anesthesia

After standard monitoring equipment is attached and peripheral venous access is achieved but before the arterial line is inserted, the midazolam dose is administered. Before placement of the arterial line, ensure that a radial artery graft will not be used for CABG.

During induction and tracheal intubation, it is important to maintain a steady heart rate and blood pressure. Thus, patients should be preoxygenated. Induction of anesthesia is accomplished with high doses of an opioid (usually fentanyl or remifentanil) to minimize the dose of propofol, etomidate, or thiopental, and thereby maximize cardiovascular stability. Although etomidate usually does not cause changes in blood pressure, it may induce hypotension in cardiac patients.

A number of agents may be used for muscle relaxation. However, they each have their own associated complications, as follows:

  • Pancuronium increases myocardial oxygen demand
  • Vecuronium may cause bradycardia in association with opioids
  • Rocuronium can cause tachycardia
  • Atracurium (which is not considered suitable for operations of long duration) can cause hypotension secondary to histamine release

The trachea should be intubated orally because nasal intubation may cause significant bleeding once heparin is administered. A double-lumen endotracheal tube is required if CABG is being performed via a left thoracotomy.

Central venous access should be obtained, as it is not uncommon for the patient to become hypotensive. To ensure that there is sufficient diastolic pressure to maintain coronary perfusion, hypotension should be treated with IV fluids or with an alpha agonist if left ventricular function is depressed.

Typically, maintenance of anesthesia is accomplished with an opioid infusion (fentanyl, alfentanil, sufentanil, or remifentanil) combined with either a propofol infusion (total IV anesthesia) or a volatile agent. Volatile agents are generally carried in an air-oxygen mixture because the use of nitrous oxide as a carrier is controversial. Isoflurane may have a myocardial protective effect and is therefore especially useful in off-pump surgery.

Positioning

For a standard sternotomy, the anterior thorax is exposed with the patient in a supine position. A roll is placed in the interscapular region to improve access to the sternum by extending the neck and elevating the sternal notch. Usually the sterile field extends from the chin to the toes to include the sternotomy incision as well as access to the saphenous veins for harvesting as a conduit. If the radial artery is being used as a conduit, the appropriate arm is also prepped into the sterile field.

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Monitoring and Follow-up

In addition to the standard anesthetic monitoring (electrocardiography [ECG], pulse oximetry, nasopharyngeal temperature, urine output, and gas analysis), there are a number of specific monitoring requirements for cardiac surgery, including the following:

  • Invasive blood pressure
  • Central venous access
  • Transesophageal echocardiography (TEE)
  • Neurologic monitoring
  • Pulmonary artery pressure monitoring with a Swan-Ganz catheter
  • Cerebral oxygen saturation monitors bilaterally

Accurate and rapidly updated blood pressure measurements are required during cardiac anesthesia. Generally, the radial artery of the nondominant hand is cannulated, although the right radial artery should be used if the patient requires additional aortic surgery or insertion of an intra-aortic balloon pump (IABP). Care should be taken to ensure that radial grafts will not be used for bypass conduits in the procedure.

Central venous access is required for administering vasoactive drugs, inserting a transverse pacing wire (if indicated), monitoring central venous pressure, and passing a pulmonary artery catheter.

TEE is often useful during coronary artery bypass grafting (CABG) to assess left ventricular (LV) function, determine the presence of mitral valve insufficiency, and evaluate the patient who is difficult to wean from cardiopulmonary bypass. TEE is now almost universally accepted as a standard of care for major intraoperative monitoring.

Neurologic monitoring is regularly used in CABG, but no monitoring device enables accurate and easy identification of potential neurologic damage (a complication in 1-3% of patients). Available monitors include electroencephalography (EEG), transcranial Doppler ultrasonography, jugular venous bulb oxygen saturation, and near-infrared spectroscopy for monitoring cerebral oxygen saturation.

After CABG, transport the patient to a dedicated cardiac surgery intensive care unit (SICU). If the patient’s condition is uncomplicated, basic management and progress assessment include the following:

  • During the first 6-12 hours after CABG, there is usually a decline in myocardial function secondary to a number of factors, including myocardial edema and ischemia-reperfusion injury. If this occurs, the patient may require increased inotropic support or pacing. However, most patients can be weaned from inotropic support within 24 hours after the operation, and the temporary epicardial pacing wires can be removed at around 3 days.
  • In the early postoperative period, a continuous infusion of nitroglycerin should be administered if a radial graft has been used, because such grafts are prone to spasm in the period immediately following the operation, resulting in myocardial ischemia.
  • Although many patients can be extubated in the first 6 hours following CABG, the majority are not extubated until postoperative day 1.
  • The patient’s temperature should be carefully regulated. Some patients may have peripheral vasodilation and hypotension secondary to an elevated body temperature arising from difficulties in central thermoregulation. This hypotension is associated with a worse neurologic outcome.
  • There is usually a 1 mL/kg/h diuresis immediately after CABG as a consequence of the amount of fluid administered intraoperatively. The urinary catheter can be removed once the patient is mobile. Oral furosemide can be used postoperatively, if needed. If LV function is preserved and the patient’s weight has returned to baseline, diuretic therapy can usually be discontinued late in the first postoperative week.
  • Drainage from the mediastinum should gradually decrease over the first 6 hours after CABG. The mediastinal drains often can be removed on postoperative day 1 when there has been no drainage for 3 consecutive hours. After their removal, a chest radiograph should be taken.
  • Ideally, patients should be sitting in a chair on postoperative day 1 and should be mobilized as soon as possible.

Also note the following:

  • In the first 6 hours after CABG, many patients require increased insulin. Lactulose and senna can be used as a laxative from day 1. Patients are encouraged to drink fluids and ingest an advancing diet after extubation and confirmation of normal mental status. Shortly thereafter, insulin sliding scales can be stopped and normal antihyperglycemic drugs started.
  • A prophylactic dose of 75 mg of aspirin once daily by mouth should be commenced in the first 6 hours after the procedure. Statins should be started on postoperative day 1. Low-molecular-weight heparin and antiembolism stockings should be used for prophylaxis of deep vein thrombosis; the stockings have the added benefit of reducing edema in the saphenous donor leg. [49]
  • In the absence of epidural analgesia, patient-controlled analgesia should be used for pain relief once the patient has been extubated. It is usually required for only 2-3 days postoperatively, by which time orally administered analgesia typically provides sufficient pain relief.
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