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Critical care of a patient after CABG surgery

Mullen-Fortino, Margaret RN, MSN; O'Brien, Noreen RN, MSN; Jones, Maryann RN, MSN

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doi: 10.1097/01.CCN.0000357491.92428.71
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In Brief

Figure
Figure

In a previous article (January's Nursing2009 Critical Care), we described the basics of caring for a patient after coronary artery bypass graft (CABG) surgery. In this article, we'll take a closer look at your role in postoperative hemodynamic monitoring, mechanical ventilation, controlling postoperative bleeding, and maintaining tight glycemic control.

As you know, CABG can be performed with the patient on cardiopulmonary bypass or off. A meta-analysis of randomized clinical trials found that patients who'd had off-pump CABG had reduced rates of atrial fibrillation (AF) and respiratory infections, and less need for red blood cell transfusions and inotropes than patients who'd had on-pump CABG. However, rates of myocardial infarction (MI), stroke, renal dysfunction, and death, weren't significantly different between the two groups.1 No studies recommend one method of CABG over another, but the postoperative course and patient care is the same.

The greatest risk of dying after CABG is associated with the urgency of the surgery, age over 80, and a previous history of cardiac surgery. Other risk factors include impaired left ventricular function, number of major coronary arteries with significant stenoses, female sex, percent of stenosis of left main coronary artery, and diabetes.2

The urgency of surgery is determined by the severity of the patient's signs and symptoms, including the degree of hemodynamic instability and the area of at-risk myocardium. CABG surgery poses the greatest risk to patients with unstable or post-infarct angina, or those who've had an MI within the last week, compared to patients with stable angina.3

Preparing for your patient

About half an hour before your patient arrives in the specialized recovery area after surgery, you'll receive a report from the anesthesia provider. Report will include information such as the type of CABG procedure performed, the patient's postoperative diagnosis, anesthesia agents administered, past medical and surgical histories, prehospitalization medications, vital signs, cardiac rate and rhythm, pertinent lab results, allergies, vascular access devices, drains and catheters, such as pulmonary artery (PA) catheter and chest tubes, estimated blood loss and blood products administered, pacemaker type and settings, mechanical ventilator settings, types and amounts of I.V. fluids administered, and current medication infusions. The patient's antibiotic administration times also will be reviewed so that you can maintain proper scheduling postoperatively.

Prepare the patient's room with the necessary equipment, including monitoring cables, infusion pumps, a forced-air warming device, and suction. Enter his height and weight into the continuous cardiac output (CO) monitor. Notify respiratory therapy so that the mechanical ventilator is ready for the patient's arrival. Label the necessary paperwork, including a flow sheet, patient profile, and lab slips, and place them at the bedside.

The patient arrives

The anesthesia provider will usually accompany the patient as he's transported from the OR to the ICU. The patient's cardiac rhythm and BP are continuously monitored during transport and the patient is manually ventilated via the endotracheal (ET) tube. Once the patient arrives in the ICU, cardiac monitoring and arterial, central venous, and PA pressure monitoring are transferred to the appropriate bedside monitors. Assess the patient for hemodynamic stability and, as ordered, begin fluid resuscitation if he's hypotensive. If hypotension persists, institute epicardial pacing at a rate of 90 to 100 beats/minute with the addition of vasoactive medications as ordered.

The patient is placed on a volume-cycled bedside ventilator and continuous pulse oximetry monitoring is initiated. Your initial assessment includes auscultation of breath sounds. Connect the patient's chest tubes to suction and note the initial output: An output greater than 200 mL in 15 minutes may indicate active bleeding.

Obtain a 12-lead ECG, portable chest X-ray, and blood work, as ordered, including complete blood cell (CBC) count, basic metabolic panel, coagulation studies, and an arterial blood gas (ABG) analysis. To reduce postoperative hypothermia, use a forced-air warming device. The target temperature for rewarming the patient is between 36° C and 37° C (96.8° F to 98.6° F).

When the patient has been stabilized, the family can visit for a short time. Before they come into the ICU, provide explanations about the patient's appearance, including the ET tube and mechanical ventilator, as well as the fact that the patient won't be fully awake due to the effects of anesthesia. Explain that the greatest progression in recovery will take place in the next 24 to 48 hours.

Managing hemodynamics

Most patients who undergo CABG have a PA catheter, which is placed preoperatively and lets the anesthesia provider monitor the patient during surgery. After surgery, the PA catheter helps you manage the patient's hemodynamic status. Occasionally, a patient may have a central venous pressure (CVP) catheter instead, which provides information about preload. Follow the trends for the parameters in Hemodynamics: Monitoring indicators of cardiac function so that you can anticipate problems and intervene promptly.

Let's look at some common hemodynamic problems in patients after CABG surgery:

  • Dysrhythmias, most often tachydysrhythmias, are common; AF occurs in 15% to 40% of patients after CABG. Patients at increased risk for AF include those with older age, mitral valve disease, previous history of AF, chronic obstructive pulmonary disease, and those who haven't been treated with a beta-blocker or angiotensin-converting enzyme inhibitor or who have been withdrawn from previous treatment with either of these drugs. Patients with hypokalemia and hypomagnesemia may be more prone to AF.

Administering beta-blockers before surgery or in the early postoperative period to reduce the risk of AF after CABG is standard therapy.4 For patients who have contraindications to beta-blockers, amiodarone is appropriate prophylactic therapy.

If AF or atrial flutter occur, they're most likely to start on postoperative day 2 or 3. A rapid ventricular response and loss of atrial kick can decrease diastolic filling time and CO and cause myocardial ischemia and systemic hypotension. Rate control is best achieved with beta-blockers, although calcium channel blockers and digoxin can be used if beta-blockers are contraindicated.

Table
Table:
Hemodynamics: Monitoring indicators of cardiac function12

AF greatly increases a patient's risk for stroke, so if AF persists for more than 24 hours, patients should start warfarin therapy, with a target international normalized ratio (INR) of 2.5.4,5 Because of the bleeding risk associated with heparin, warfarin therapy may be started without heparin. In high-risk patients, such as those with history of stroke or transient ischemic attack, heparin can be used a bridging therapy until the INR is therapeutic.6

Ventricular dyshrythmias can occur anytime after surgery but are more common in the early postoperative period. If bradydysrhythmias occur, they usually resolve several hours after surgery.

  • Low CO. Maintaining an adequate CO and BP to ensure adequate perfusion to the vital organs is key to your patient's recovery. Low CO is defined as less than 4 L/minute (the normal range is 5 to 8 L/minute). The causes of low CO occur with alterations in the four determinants of CO: decreased preload, increased afterload, reduced contractility, and changes in heart rate. Acute changes in rhythm may also affect CO and should be managed accordingly.

Preload reflects the patient's volume status and is measured by the CVP or the PA wedge pressure. A major cause of decreased preload is hypovolemia from bleeding or fluid shifts caused by the systemic inflammatory response. Treatment goals are directed at increasing the circulating volume with blood products, 0.9% sodium chloride solution, or lactated Ringer's solution.

Afterload is the resistance the ventricle has to overcome during systole. Low CO due to increased afterload occurs as a result of vasoconstriction caused by hypothermia during surgery. You'll see increased afterload reflected by an increase in the patient's systemic vascular resistance.

If the patient is hypothermic, use forced-air warming devices and overhead heating lamps to warm him. Meperidine also may be used to relax the smooth muscles and dilate the vessels.7 A patient who's normothermic with increased afterload may need a vasoactive medication such as nitroglycerin or nitroprusside to decrease afterload and increase CO. Another cause of vasoconstriction, no matter what the patient's temperature, is sympathetic nervous system stimulation from pain. Administering opioids (usually morphine) as prescribed can control pain and reduce sympathetic nervous system stimulation.

Hypoxia, acidosis, and electrolyte imbalances may contribute to the development of dysrhythmias and low CO. Intraoperative myocardial ischemia and MI also contribute to dysrhythmias. Monitor the patient's ECG closely to promptly recognize dysrhythmias and intervene to restore CO. Treatment generally consists of correcting the underlying electrolyte imbalances and managing respiratory function to correct acidosis.

Pharmacologic inotropic support may be needed to improve myocardial contractility. However, positive inotropes should be used cautiously because they increase myocardial oxygen demand. See How some cardiac drugs affect hemodynamics for details.

Because the patient's heart rate may need support after CABG, temporary atrial and ventricular epicardial pacing is used. If the heart rate falls below 60 beats/minute, and the patient is hypotensive, the pacemaker rate may be used to assist with CO.

  • Suspect cardiac tamponade, a life-threatening emergency, if your patient has a low cardiac index. Bleeding into the pericardial cavity puts pressure on the heart, reducing diastolic filling of the heart and resulting in decreased CO. The end result is inadequate oxygenation of the vital organs and circulatory collapse.

Signs and symptoms of cardiac tamponade include a sudden drop in chest tube output, muffled heart sounds, distended jugular veins, hypotension, and a decreased response to inotropic support. You'll also note pulsus paradoxus, a hallmark of cardiac tamponade, in which the patient's arterial BP during expiration exceeds arterial pressure during inspiration by more than 10 mm Hg.8 A bedside echocardiogram may be ordered to confirm the diagnosis.

Once the diagnosis of tamponade is confirmed, prepare the patient to return to the OR for evacuation of the clot and repair of the bleeding site. If the patient's clinical condition deteriorates to the point where cardiac arrest is imminent, the physician may perform an emergency bedside reexploration sternotomy.

Postoperative bleeding

Bleeding after CABG surgery is considered excessive if the patient's chest tube output exceeds 200 mL every 15 minutes in the first hour. When bleeding is this brisk, the usual cause is surgical, such as bleeding at the anastomosis site. The patient may need to return to the OR to correct the problem.

Table
Table:
How some cardiac drugs affect hemodynamics18

Additional positive end-expiratory pressure (PEEP) may be delivered through the ventilator to help control bleeding by decreasing venous return and increasing pressure in the mediastinum. This increased pressure functions as a tourniquet to the bleeding vessels.9

Protamine may be prescribed to reverse the effects of heparin, and desmopressin may be indicated if the bleeding is severe. Desmopressin is a synthetic form of vasopressin that increases plasma levels of Factor VIII and von Willebrand factor. Aprotinin, a protease inhibitor that modulates the inflammatory effects of cardiopulmonary bypass, is no longer used to control post-CABG bleeding, because it may increase the patient's risk of renal failure, MI, heart failure, and stroke.10

Monitor the patient's coagulation studies and CBC results. If his clotting factors are abnormal and he's bleeding, administer blood products as ordered. For example:

  • Red blood cells are indicated for patients with a hematocrit value of less than 26% and who are actively bleeding. The risks of this therapy include acute lung injury, prolonged mechanical ventilation, infection, sepsis, renal dysfunction, and increased mortality.11
  • Platelets are indicated for patients with a platelet count less than 100 × 103/mm3 or platelet dysfunction secondary to cardiopulmonary bypass or preoperative administration of antiplatelet medications (aspirin, clopidogrel, or glycoprotein IIb/IIIa receptor inhibitors).
  • Fresh frozen plasma is indicated for patients who need multiple coagulation factors replaced.
  • Cryoprecipitate is indicated for patients who need replacement of factors VIII, XIII, von Willebrand factor, or fibrinogen.

Mechanical ventilation

The primary goals of mechanical ventilation are to improve arterial oxygenation and alveolar ventilation. Follow your facility's policy to obtain serial ABG analyses, and use these results to make necessary adjustments to the ventilator settings in order to keep the patient's acid-base balance in normal range. Continuously monitor the patient's SpO2 and keep it above 92%.

The patient will remain mechanically ventilated and sedated until he's hemodynamically stable and his core temperature is above 36.5° C (97.7° F). At this point, you can assess the patient for readiness to wean from mechanical ventilation. Follow your standard orders and weaning protocol and place him on continuous positive airway pressure mode for 30 minutes. During this time, monitor his weaning parameters and obtain repeat ABGs as indicated. (See Is your patient ready to be extubated? for more details.)

If the patient becomes agitated, diaphoretic, hemodynamically unstable, or has dysrhythmias during the weaning trial, he'll need to return to the support of mechanical ventilation. Other indications of unreadiness to wean include somnolence, a respiratory rate of greater than 35 breaths/minute, and a heart rate of greater than 120 beats/minute.12

After the patient is extubated, administer humidified oxygen at 40% via face mask as per protocol. Gradually wean the percentage of oxygen to room air (21%) as long as the patient maintains an SpO2 above 92%. Monitor the patient for respiratory compromise, which is characterized by shortness of breath and decreased oxygen saturation via pulse oximetry. Pulmonary dysfunction and hypoxemia may occur in 30% to 60% of patients after CABG, usually as a result of residual fluid volume overload, poor inspiratory effort, and atelectasis from chest wall splinting.13 A history of heart failure, chronic obstructive pulmonary disease, smoking, diabetes, age over 65, and increased length of intubation may increase postoperative pulmonary complications.14

Atelectasis, a common postoperative complication, can be related to cardiopulmonary bypass (which suppresses surfactant production) and effects of general anesthesia. Frequently assess the patient's respirations and breath sounds, SpO2, and ABG results, and encourage him to perform incentive spirometry every hour while he's awake. Also institute early and aggressive ambulation and coughing and deep breathing, which can help prevent postoperative pulmonary complications.5,15 If he has copious secretions or bronchospasm, he may need chest physiotherapy or nebulized bronchodilators.

Neurologic issues

Neurologic dysfunction after CABG surgery can be caused by hypoxia, decreased cerebral perfusion, embolism, hemorrhage, or metabolic abnormalities. Signs and symptoms may range from subtle cognitive deficits such as memory loss and diminished attention span to signs of acute stroke, such as facial droop, arm drift, or abnormal speech.4 Neurological deficits resulting from intraoperative events are usually evident within 24 to 48 hours after surgery.

Most postoperative strokes are embolic. Patients at risk for postoperative acute ischemic stroke include those with advanced age, history of a neurologic event such as a transient ischemic attack or previous stroke, diabetes, COPD, peripheral vascular disease, and use of cardiopulmonary bypass.16

Cognitive dysfunction and delirium, common after CABG, occur most often in patients with hypertension, a history of alcohol abuse, and advanced age.16 Medication overdose, including analgesics and sedatives, also may contribute to cognitive impairment.

Before surgery, assess the patient's neurological function, perform medication reconciliation, and identify any recent history of substance abuse. Because metabolic disturbances can cause acute mental status changes, after surgery review the patient's lab data, including ABGs, serum electrolytes, blood urea nitrogen, serum creatinine, magnesium, and calcium.

Maintaining glycemic control

Tight glycemic control can improve patient outcomes and reduce the incidence of sternal wound infections after CABG surgery.17 Monitor the patient's blood glucose levels and follow the protocol to titrate the insulin infusion based on hourly glucose results. Remember that the patient's insulin requirements will decrease as his dose of epinephrine is decreased (because of epinephrine-induced hyperglycemia), so he may need more frequent monitoring.

Continuous insulin infusions of greater than 6 units/hour may alter the patient's potassium results. Administering potassium in this case may cause the patient to become hyperkalemic as the insulin infusion decreases. Because insulin drives potassium into cells, lower potassium levels are acceptable. Once the insulin doses decrease, potassium returns to the bloodstream and potassium levels return to more normal levels.

Beyond the ICU

Most patients are transferred to a step-down unit or cardiac surgical floor on postoperative day 1. Prepare the patient for transfer by talking to him and his family about the anticipated recovery phase. Provide a detailed report to the receiving nurse, including the patient's pre- and postoperative history, current lab values, medications, and an assessment of discharge needs.

Accompany the patient during the transfer. He'll be on a portable cardiac monitor and telemetry. Once he's settled into his room, he'll be weighed and his cardiac rhythm monitored by telemetry. Review with the receiving nurse any additional interventions or assessments. By anticipating possible complications, you'll be able to help the healthcare team provide appropriate treatment and ensure the best possible postoperative outcome.

Is your patient ready to be extubated?19,20

Your patient is ready for extubation if he initiates spontaneous inspiratory efforts, can open and close his eyes on command, can lift his head off the pillow on command, and meets the following hemodynamic parameters:

  • SpO2 greater than 92%
  • PEEP less than 8 cm H2O
  • FIO2 less than 0.5
  • Heart rate between 50 and 100 beats/minute
  • Systolic BP between 90 and 140 mm Hg
  • Minute ventilation between 10 and 15 L/minute
  • Negative inspiratory force of −20 to −30 cm H2O

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