Management of the Cardiac Surgery Patient

David B. S. Dyke

Richard L. Prager

Kim A. Eagle

THE EVOLUTION OF PROCEDURES. CARE SYSTEMS. TECHNOLOGY. AND EXPECTATIONS

The history of coronary artery revascularization dates back to the pre-World War I era. Alexis Carrel (1) developed a canine model of aortocoronary anastomosis, by using carotid arteries as conduit, work for which he was ultimately awarded the Nobel Prize. In an address to the American Surgical Association, Carrel spoke of some of the difficulties he encountered:

“In certain cases of angina pectoris, when the mouth of the coronary is calcified, it would be useful to establish a complementary circulation for the lower part of the arteries. I attempted to perform an indirect anastomosis between the descending aorta and the left coronary. It was, for many reasons, a difficult operation. On account of continuous motion of the heart, it was not easy to dissect and to suture the artery. In one case, I implanted one end of a long carotid artery, preserved in cold storage, on the descending aorta. The other end was passed through the pericardium and anastomosed to the peripheral end of the coronary, near the pulmonary artery. Unfortunately, the operation was too slow. Three minutes after the interruption of the circulation [by caval occlusion], fibrillatory contractions appeared, but the anastomosis took 5 minutes. By massage of the heart, the dog was kept alive. But he died less than 2 hours afterward. It shows that the anastomosis must be done in less than 3 minutes.”

It was not until the advent of cardiopulmonary bypass technology that this surgical technique could be applied to human heart surgery. Until that time, surgical techniques aimed at myocardial revascularization had met with only limited success. The Vineberg procedure (2), in which the internal mammary artery was implanted into the myocardium with subsequent collateralization, was one such technique.

The first successful use of full cardiopulmonary bypass occurred in 1953. Dr. John Gibbon (3) used this technology to close an atrial septal defect. The clinical use of this early “heart-lung machine” ushered in a new era in cardiac surgery. Soon to follow was the evolution of different types of conduits. Carotid arteries were quickly replaced, first by the use of internal mammary arteries, and later, by saphenous veins. Not until years later were the benefits of arterial over venous conduits recognized.

The advent of modern cardiac surgery led to a new paradigm for patient care. The physicians charged with such responsibility, the equivalent of the modern-day “intensivist,” developed techniques to deal with the multisystem issues that arose as a consequence of cardiopulmonary bypass and cardiac surgery. One of the most useful developments of this era, the intensive care unit, is now widely used across the various surgical and medical subspecialties.

The role of new technologies, such as off-pump and minimally invasive techniques, total arterial revascularization, and percutaneous and laser approaches to coronary
revascularization, continue to push the boundaries of cardiovascular medicine. Today, physicians have entered a true surgical and medical cardiac revascularization renaissance. Because of ever-increasing options, the process of determining which procedure or technique is correct for a patient is becoming increasingly more challenging. With this challenge, physicians find themselves in the process of relying on yet another tool: outcomes research.

The accumulation of large databases of information relating to medical and surgical treatment of coronary artery disease provides “benchmarks” with which new therapies can be compared. This allows us to determine rigorously which therapies hold promise and which therapies hold less appeal. The development of new technologies and therapies requires us to hold ourselves accountable, both medically and financially, for the direction that these technologies and therapies take us. Outcomes research allows us to do this with impressive results.

From a humanistic standpoint, outcomes research related to cardiovascular disease also allows us to understand better the limitations of our therapeutic options. It allows us to communicate our expectations accurately to patients and their families. This allows patients and families to compare their expectations with the reality of what the therapy and health care system can provide. This chapter was written with the benefit of data derived from meticulously performed outcomes research.

ROLE OF THE CARDIOLOGIST AND INTENSIVIST

The skill of the cardiothoracic surgeon is the cornerstone of successful outcomes for patients undergoing cardiac surgery, although it is becoming increasingly difficult for surgeons to provide the minute-to-minute bedside care required by these patients. Therefore a collaborative effort between cardiac surgeons and specialists with backgrounds across several disciplines is increasing. The team at our institution consists of the surgical staff, perfusionists, anesthesiologists, critical care physicians, cardiologists, and nurses with a specialization in cardiac care. Of all the physicians involved, the cardiologist has the unique privilege of observing the entire process: the initial referral, the diagnosis and workup phase, the surgical and recovery phase, and ultimately the return to and maintenance of health.

Cardiac surgical procedures create major physiologic challenges that are imposed on patients, many of whom have multiple underlying systems dysfunction. The understanding and anticipation of these alterations in physiology are imperative, and the time course required for return to baseline function should also be understood. With the evolution and expansion of off-pump techniques for operative revascularization, additional benefits and limitations of these techniques and the population best served by them are becoming better understood. At the present time, it remains more common to use full cardiopulmonary-bypass support for the majority of coronary artery surgical and all other intracardiac procedures. Therefore this chapter focuses on the management of patients undergoing fully supported cardiac surgery.

PHYSIOLOGY OF CARDIOPULMONARY BYPASS

Cardiopulmonary bypass allows continued systemic perfusion while the heart is arrested during the surgical procedure. It has been recognized as both a magnificent facilitator as well as a nonphysiologic and disruptive support system. It is well understood that systemic inflammatory responses are created by exposure to the extracorporeal circuits and nonpulsatile flow that define modern-day cardiopulmonary bypass. This response in and of itself alters clotting ability and membrane stability and creates the potential for fluid accumulation. Nonpulsatile flow further disrupts regulatory feedback loops found within certain organ systems, such as the kidneys and brain, which are responsive to normal pulsatile flow.

During the period of cardiopulmonary bypass, the body is subjected to an altered
hemodynamic milieu. Pulsatile blood flow is replaced by continuous blood flow at a mean pressure that is frequently lower than a normal mean arterial pressure. To tolerate this state of relative low-pressure circulation, the body is cooled to a temperature of approximately 28°C to 32°C. During certain procedures in which a cross-clamp cannot be applied to the aorta, exemplified by aortic arch repair, this process is taken to an extreme in which circulation, with the exception of retrograde venous cerebral perfusion, is completely arrested for short durations of time.

During the period of cardiopulmonary bypass, platelets are activated, and a general systemic inflammatory state ensues. This can result in lung injury, which in most cases is subtle but may lead to the acute respiratory distress syndrome. Renal injury is common, usually manifesting as a mild elevation in serum creatinine levels. Acute tubular necrosis, necessitating temporary or permanent renal replacement therapy, occurs uncommonly. Other consequences of cardiopulmonary bypass include relative transient gut ischemia that can manifest as temporarily altered motility. In severe cases, such as in patients with occult mesenteric vascular occlusive disease, altered gut perfusion can lead to effective loss of the mucosal barrier, which may allow transmigration of intestinal flora with resultant bacterial sepsis, but this is only rarely seen clinically. Neurologic injury may also occur. This topic is covered in more detail later in this chapter.

PREOPERATIVE EVALUATION

Estimation of Risk

A successful outcome in cardiac surgery is dependent on a thorough preoperative evaluation. Deciding whether long-term benefits will be achieved with an operative procedure, particularly in view of advances in medical therapy, as well as in percutaneous interventions, has become a difficult task. Integral in making a sound decision is the ability to consider all of the comorbid conditions particular to an individual patient that influence operative outcomes. Issues such as age, gender, obesity, and the presence of renal, pulmonary, neurologic, and other disease processes such as diabetes all factor into assessing the appropriateness, the predictive risks, and the expected benefits of cardiac surgery. Experience has enabled the development of predictive indices that improve the understanding of risk and allow individual estimation of perioperative risk.

Simple bedside tools, based on prediction models of these indices, make it easier for physicians, patients, and patients’ families to make clear, informed decisions when weighing all the possible therapeutic options. These tools also allow more-realistic expectations, particularly when questions of postoperative complications arise. A full discussion of this topic is beyond the scope of this chapter; however, several resources provide a comprehensive review of this subject. The American College of Cardiology/American Heart Association guidelines for coronary artery bypass graft surgery (4) contain many useful resources for preoperative risk prediction (Table 39.1). These resources are based on data derived from 14,971 patients who underwent cardiac surgery between 1999 and 2002. From these risk-prediction tools, the likelihood of mortality, cerebrovascular accident, and mediastinitis can be estimated with data encompassing basic demographics, ejection fraction, and the presence of chronic obstructive pulmonary disease, diabetes, peripheral vascular occlusive disease, renal dysfunction, and procedural urgency. The risk of postoperative renal dysfunction can similarly be predicted with basic preoperative data (Table 39.2).

An additional resource for preoperative estimation of risk is the Internet. Several web-based tools are now available for estimation of risk for patients being considered for cardiac surgical procedures. The Society of Thoracic Surgeons risk-assessment calculator can be accessed at the following website: http://66.89.112.110/STSWebRiskCalc/de.aspx The European system for cardiac operative risk evaluation (EuroSCORE) is a similar tool, derived from several different European countries, and can be accessed at the following website: http://www.euroscore.org/calc.html

TABLE 39.1. Preoperative estimation of risk of mortality, cerebrovascular accident, and mediastinitis

PATIENT OR DISEASE CHARACTERISTIC	MORTALITY SCORE		CVA SCORE	MEDIASTINITIS SCORE
For use only in isolated CABG surgery
Directions: Locate outcome of interest (e.g., mortality). Use the score in that column for each relevant preoperative variable, and then sum these scores to get the total score. Take the total score and look up the approximate preoperative risk in the table below.
Age 60-69	1.5		1.5	1
Age 70-79	2.5		2.5	1.5
Age ≥80	6.5		3	2
Female sex	2		1.5	—
Obesity (BMI 31-36)	—		—	2
Obesity (BMI ≥37)	—		—	4.5
EF <40%	2		1.5	1.5
Urgent surgery	2		1.5	2
Emergency surgery	5		3.5	2
MI ≤7 days	1.5		—	—
Prior CABG	2.5		—	—
Three-vessel disease	1.5		—	—
LM 50%-89%	1.5		—	—
LM ≥90%	2		—	—
WBC >12K	2.5		—	—
PVD	1.5		1.5	—
Diabetes	1		1.5	1.5
Dialysis	4		2	3
Creatinine ≥2	2		2	—
COPD	2		—	2
Total score
PERIOPERATIVE RISK
TOTAL SCORE	MORTALITY (%)		CVA (%)	MEDIASTINITIS (%)
0	0.2		0.4	0.3
1	0.2		—	0.3
2	0.3		0.6	0.4
3	0.3		0.9	0.5
4	0.5		1.3	0.7
5	0.7		1.4	0.9
6	1.0		2.0	1.3
7	1.3		2.7	1.7
8	1.8		3.4	2.5
9	2.3		4.2	3.2
10	3.0		5.9	4.2
11	4.0		7.6	5.6
12	5.3		≥10.0	≥7.3
13	6.9		—	—
14	8.8		—	—
15	11.5		—	—
16	14.1		—	—
17	18.7		—	—
18	≥23.0		—	—
Calculation of mortality risk: An 80-year-old woman with an EF <40% who is having elective CABG surgery has had no prior CABG surgery and has no other risk factors. Her total score = 6.5 (age ≥80) + 2 (female) + 2 (EF <40%) = 10.5. Because her total score = 10.5, round up to 11; her predicted risk of mortality = 4.0%.
Definitions:
EF <40% (left ventricular ejection fraction): the patient’s current EF is less than 40%.
Urgent: medical factors require patient to stay in hospital to have operation before discharge. The risk of immediate morbidity and death is believed to be low.
Emergency: patient’s cardiac disease dictates that surgery should be performed within hours to avoid unnecessary morbidity or death.
PVD (peripheral vascular disease): cerebrovascular disease, including prior CVA, prior TIA, prior carotid surgery, carotid stenosis shown by history or radiographic studies, or carotid bruit; lower-extremity disease, including claudication, amputation, prior lower-extremity bypass, absent pedal pulses, or lower-extremity ulcers.
Diabetes: currently treated with oral medications or insulin.
Dialysis: peritoneal or hemodialysis-dependent renal failure.
COPD (chronic obstructive pulmonary disease): treated with bronchodilators or steroids.
Obesity: Find the approximate height and weight in the table below to classify the person as obese or severely obese. Obesity, BMI 31-36; severe obesity, BMI ≥37.
WBC greater than 12K (white blood cells greater than 12,000): Use the patient’s last preoperative measurement of WBCs taken before the procedure.
	WEIGHT (LBS)			WEIGHT (LBS)
HEIGHT (FEET AND INCHES)	OBESITY BMI 31-36	SEVERE OBESITY BMI ≥37	HEIGHT (FEET AND INCHES)	OBESITY BMI 31-36	SEVERE OBESITY BMI ≥37
5′0″	158-186	≥187	5′8″	203-239	≥240
5′1″	164-192	≥193	5′9″	209-246	≥247
5′2″	169-199	≥200	5′10″	215-254	≥255
5′3″	175-205	≥206	5′11″	222-261	≥262
5′4″	180-212	≥213	6′0″	228-268	≥269
5′5″	186-219	≥220	6′1″	235-276	≥277
5′6″	191-225	≥226	6′2″	241-283	≥284
5′7″	198-232	≥233	6′3″	248-291	≥292
Data set and definitions for dependent variables:
The regression models that generated the scores for these prediction rules were based on 14,971 patients receiving isolated CABG surgery between 1999 and 2002. The dependent variables and observed event rates are as follows: In-hospital mortality, 2.5%; cerebrovascular accident, defined as a new focal neurologic event persisting at least 24 hours, 1.6%; and mediastinitis during the index admission, defined by positive deep culture and/or Gram stain and/or radiographic findings indicating infection and necessitating reoperation, 1.0%.
From: Northern New England Cardiovascular Disease Study Group, 4/03, with permission.

Prevention of Complications

Of every $10 spent on surgical treatment of coronary disease, $1 is related to complications (5). Because of the importance of preventing postoperative complications, it is imperative to be mindful of simple interventions that can improve outcomes. In the preoperative phase, several steps can be taken to minimize the likelihood of postoperative complications.

TABLE 39.2. Risk of postoperative renal dysfunction (PRD) after coronary artery bypass graft surgery

	COMBINATIONS OF PREOPERATIVE RISK FACTORS FOR PRD				RISK OF PRD IN VARIOUS CLINICAL STRATA DEPENDING ON RISK FACTORS AND AGE
NO. OF RISK FACTORS	CHF	REOP	DM	CREAT> 1.4 mg/dL	<70 YR	70-79 YR	≥80 YR
0	−	−	−	−	1.9% (n = 909)	7.0% (n = 330)	11.8% (n = 68)
1	−	−	−	+	5.0% (n = 80)	18.4% (n = 76)	12.5% (n = 16)
	−	−	+	−	5.9%(n = 68)	4.8% (n = 81)	*
	−	+	−	−	6.2% (n = 130)	14.3% (n = 56)	25.0% (n = 4)
	+	−	−	−	7.6% (n = 144)	12.3% (n = 73)	29.4% (n = 17)
2	−	−	+	+	22.2% (n = 9)	0% (n = 7)	*
	−	+	−	+	20.0% (n = 25)	30.8% (n = 13)	*
	−	+	+	−	37.6% (n = 8)	33.3% (n = 3)	*
	+	−	−	+	47.4% (n = 19)	7.7% (n = 26)	44.4% (n = 9)
	+	−	+	−	25.9% (n = 27)	18.2% (n = 11)	*
	+	+	−	31.6% (n = 19)	7.1% (n = 14)	*
3	−	+	+	+	100% (n = 1)	100% (n = 1)	*
	+	−	+	+	8.3% (n = 12)	25% (n = 4)	*
	+	+	−	+	*	33.3% (n = 9)	*
	+	+	+	−	33.3% (n = 3)	*	*
4	+	+	+	+	50.0% (n = 2)	*	*
CHD, prior congestive heart disease; Creat, preoperative serum creatinine level; DM, type I diabetes mellitus; PRD, postoperative renal dysfunction; Reop, repeat coronary bypass operation; −, risk factor absent; +, risk factor present.
From: Managano CM, Diamondstone LS, Ramsay JG, et al. Renal dysfunction after myocardial revascularization: risk factors, adverse outcomes, and hospital resource utilization: the Multicenter Study of Perioperative Ischemia Research Group. Ann Intern Med 1998;128:194-203, with permission.

Neurologic complications

Prevention of neurologic injury, primarily by reduction of atheroembolic episodes related to aortic manipulation, can be achieved by the use of epiaortic imaging. This technique allows a surgeon to select carefully the locations for cross-clamp application, aortic cannulation, and proximal conduit anastomosis. If extreme aortic disease is identified, no-clamp fibrillatory arrest and off-pump techniques may be used to avoid aortic manipulation.

From a medical perspective, adverse neurologic outcome can be minimized by identification of chronic atrial fibrillation that has not previously been treated with anticoagulation. Adequate anticoagulation for 3 to 4 weeks allows resolution or organization, or both, of left atrial clot. The same treatment should be considered for patients who have recently had an extensive anterior wall myocardial infarction, because these patients are at high risk for developing left ventricular mural thrombus.

Adverse neurologic outcomes may also be avoided by appropriate screening for cerebrovascular occlusive disease. Any patient with an audible cervical bruit or a history of left main disease, transient ischemic attack, or stroke should undergo noninvasive carotid imaging. The presence of significant disease (more than 75% stenosis in asymptomatic patients) may necessitate a staged procedure or combined carotid artery endarterectomy and coronary artery surgery.

In addition to these protective measures, appropriate management of diabetes-associated hyperglycemia may also help reduce the degree of cognitive neurologic injury that occurs during cardiac surgery (6).

Infections complications

Minimizing postoperative infection begins in the preoperative period. Guidelines for
standard clinical practice have been extensively reviewed in the American College of Cardiology/American Heart Association practice guidelines on coronary artery bypass graft (4). In general, preoperative antibiotics should be given routinely to any patient undergoing cardiac surgery. Antibiotics should be adequate at the tissue level during the entire procedure, which requires administration 30 to 60 minutes before skin incision. If the surgical duration exceeds 3 hours, antibiotics should be readministered appropriately. The cephalosporin class of antimicrobials is generally used unless a true penicillin allergy exists, in which case vancomycin can be substituted. Unless clinically indicated by the presence of infection, antibiotics should be continued for only 1 day postoperatively.

In addition to standard postoperative antibiotics, some centers advocate the use of chorhexidine gluconate oropharyngeal rinse and nasal ointment for preoperative decontamination, particularly of Staphylococcus aureus. Reduced rates of nosocomial infection as well as reduced length of stay have been observed with this type of selective decontamination (7). Another potential strategy for reducing postoperative complications is that of preoperative intensive inspiratory muscle training to prevent postoperative pulmonary complications (8). This can be accomplished by preoperative training and use of an incentive spirometer.

Atrial arrhythmias

Postoperative atrial fibrillation (see treatment of this entity later in this chapter) is a very common complication of cardiac surgery. A substantial body of literature has attempted to address this problem. Atrial arrhythmias can potentially be avoided by preoperative administration of either β-adrenergic blocking agents or amiodarone (9,10). Likewise, postoperative withdrawal of previously prescribed β-adrenergic blocking agents should be avoided, because this considerably increases the risk of postoperative atrial fibrillation. Other measures that may be helpful in reducing the risk of postoperative atrial arrhythmias include preoperative treatment with statins (11), n-3 polyunsaturated fatty acids (PUFAs) (12), steroids and nonsteroidal antiinflammatory agents; however, these have yet to be adopted by the AHA/ACC.

General risk-reduction opportunities

Finally, a good general physical examination and routine laboratory studies, including chest radiography, should be performed on all patients before they undergo cardiac surgery. Medical conditions such as hypertension, anemia, diabetes, thyroid dysfunction, and chronic obstructive pulmonary disease should be thoroughly evaluated and optimally treated, if feasible, before any cardiac surgical procedures.

THE EARLY POSTOPERATIVE PERIOD

Hemodynamic Monitoring

The physiologic changes that occur as a result of cardiac surgery include rapid fluid and electrolyte shifts, transient depression of myocardial function, and rapid fluctuations in vascular tone. Because of this dynamic process, hemodynamic monitoring is mandatory. Hemodynamic monitoring is used to ensure cardiovascular integrity and adequate oxygen delivery to the periphery. Oxygen delivery is determined by the following equation:

O₂ delivery	=	cardiac output
		X hemoglobin concentration
		X arterial oxygen saturation.

The typical method for accurate and continuous measurement of systemic blood pressure and O₂ delivery is by cannulation of the radial artery. The femoral or axillary artery can also be used. Arterial lines are useful for continuous blood pressure monitoring and for sampling of arterial blood for blood gas and electrolyte analysis.

Central hemodynamics are monitored with a pulmonary artery (Swan-Ganz) catheter. This device allows determination of intracardiac and central venous pressures, periodic or continuous cardiac output, and mixed-venous saturation. In this
patient population, the ability to interpret the data correctly is essential. Understanding potential inaccuracies and pitfalls in data interpretation also is essential. Various patterns of hemodynamic derangements that are encountered in the patient after cardiac surgery are discussed in more detail later.

Early removal of invasive lines, if the patient is stable enough for this to occur, is an important step in the recovery process because it decreases the risk of complications such as thrombosis and infection. Early removal also facilitates increased patient mobility.

A relatively new addition to the tools used in the post-cardiac surgery intensive care unit is transesophageal echocardiography. The placement of bandages, the location of chest tubes, and the presence of residual intrathoracic air frequently limits standard transthoracic echocardiography. Transesophageal echocardiography, albeit more invasive, is frequently more useful. Global and regional wall motion, valvular anatomy, and the presence of external compression of the heart by pericardial clot or blood are relatively easy to visualize with transesophageal echocardiography. This mode of cardiac imaging is frequently used intraoperatively; therefore its use in surgical intensive care units is a logical extension of this technology in selected patients with hemodynamic compromise.

Postoperative Hemodynamic Changes

Nearing the end of most cardiac surgical procedures, the process of rewarming begins. A frequent consequence of rewarming is systemic vasodilation, which leads to redistribution of blood volume to the periphery as well as to a decrease in systemic blood pressure. This process is usually complete after several hours; however, to maintain adequate mean arterial pressure during this time, vasoconstricting agents are frequently required. Standard vasopressors include dopamine, norepinephrine, epinephrine, phenylephrine, and, in extreme cases, arginine vasopressin.

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Aug 18, 2016 | Posted by drzezo in CARDIOLOGY | Comments Off

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