Care of the adult cardiac surgery patient: part I

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Introduction

The field of cardiac surgery had its beginning at the dawn of the 20th century. Ludwig Rehn was the first to successfully suture a penetrating wound of the heart in 1896.1 Subsequently, closed cardiac procedures evolved in the first half of the 20th century, notably patent ductus arteriosus (PDA) ligation, Blalock-Taussig shunts, removal of foreign bodies from the heart, and closed approaches to the mitral valve.2 Cardiac operations utilizing cardiopulmonary bypass (CPB) dominated the second half of the 20th century, after a brief period when operations utilized systemic hypothermia3 and cross circulation approaches.4 The number of operations utilizing CPB has grown to a present annual rate of almost 800,000 cases in the United States, with the majority being coronary artery bypass grafting5 (CABG) (Table 1).

Increased knowledge and experience, coupled with improved clinical processes, and technical advances, have made open heart surgery safer and more readily available, with decreased morbidity and mortality rates and lower costs. The raw operative mortality rate for cardiac operations in the United States is less than 5%, with an operative mortality rate for isolated CABG of less than 3%.6 Representative institutional experiences are summarized in TABLE 2, TABLE 3 . Morbidity, however, is noted in 25% to 40% of patients after cardiac surgery with individual incidences of specific complications in the 2% to 4% range (TABLE 4, TABLE 5 ). This has remained stable despite changing demographics (i.e., age, sex, and body surface area), complex cardiac conditions with decreased left ventricular (LV) function, and increasing associated comorbidities8 (Table 6). Preoperative patient selection and preparation, sophisticated operative approaches and technique, and advances in the intensive care unit (ICU) have contributed to this continued success. The ICU has emerged as the dominant area where the fragile transition from the operating room to sophisticated care occurs.

The evolution from the first dedicated ICU at Johns Hopkins Hospital in 1923 through the establishment of a specialized coronary care unit in 1962 to the present multispecialized and subspecialized units of today has been nothing short of dramatic.12 The care in the cardiac surgery ICU in many medical centers has become a cooperative and collaborative effort involving the cardiac surgery team, the cardiac anesthesiologists, the critical care team, a sophisticated group of medical consultants, and allied health personnel, particularly critical care nurses and respiratory therapists. Diagnostic support, increasing electronic interface, bedside computerized nursing, and point of care testing have become integral components of the critical care pathway. The present review gives an overview of the care of the adult cardiac surgical patient with particular emphasis on the early postoperative phase in the ICU utilizing a subsystem approach.

Cardiac surgery has made significant advances over the past 50 years. Despite increasing patient age and comorbidity the results continue to improve. This is due principally to the specific areas of improvement and experience in preoperative patient selection and preparation; database and risk analysis; operative advances, especially in monitoring, anesthesia, surgical techniques, and perfusion; and postoperative care, particularly in the ICU. A 2-part review is presented to give the reader an overview of the care of the adult cardiac surgery patient. Part I focuses on general clinical information and the subsystem approach to perioperative care. Part II continues this subsystem approach to critical care.

There has been an increasing focus on open heart surgery in terms of access, cost, and results. This has occurred in the setting of a more sophisticated public that desires more information regarding both surgeon-specific and institutional outcomes, data that are now readily available on the Internet (Table 7). Several scoring systems utilizing univariate and multivariate regression models have emerged to help the cardiologist and cardiac surgeon better counsel the patient and family regarding surgical risk.13 They are essential tools for risk assessment, cost analysis, and to study the benefit of operation for the patient. Operative mortality rates can be recorded as raw, unadjusted, and expected, and may be defined as deaths within 30 days of operation or as “in-hospital” mortality (i.e., the patient does not survive to discharge). The major determinants of perioperative morbidity and mortality rates remain demographics (e.g., age, sex, and body surface area), acuity of the operation (e.g., elective, urgent, and emergency), associated comorbidities (especially smoking, diabetes, obesity, renal dysfunction, hypertension, stroke, chronic obstructive pulmonary disease [COPD], and peripheral vascular disease); and the degree of cardiac dysfunction (Table 8). Univariate analysis is used to correlate a particular risk factor with a specific outcome, which is the methodology utilized in the Society of Thoracic Surgeons (STS) database. This calculation is difficult to assess when multiple factors are involved. In multivariate regression analysis, only those variables found significant in univariate analysis are used to assess the independent association of these variables with specific outcome or results. Several multivariate risk models allow for bedside calculation of operative risk. The Cleveland Clinic (CCF in Table 8) severity scoring system is practical in that the score is directly correlated with the predicted mortality22 (Table 9 and Fig 1). The risk of advanced age will become even more important and relevant in terms of access to care, cost, and outcome. At present, 3% of Americans are octogenarians, and by 2010 there is projected to be an increase to 4.3%, representing 12 million people.28 Between 1987 and 1990 there was a 67% increase in the number of cardiac operations in octogenarians.29 Mortality rates and quality of life are the prime indicators of success in all age groups. Operative mortality rates between 7.9% and 13.5% have been reported in octogenarians, with 1 study reporting a 5-year median survival rate of 55%, compared with 69% in the age group 70 to 79 years, and 81% for the age group 60 to 69 years.29 Utilizing the Standard Form 36 Health Questionnaire (SF-36 form) and the Seattle Angina Questionnaire, 83.7% of surgical octogenarian patients were living at home with 74.8% enjoying good or excellent health.30 Women remain at higher risk for myocardial revascularization. Two recent studies show a 2- to 3-fold increase in mortality rates for women versus men.31, 32

Interestingly none of the risk scores for myocardial revascularization include either hospital- or surgeon-specific case volumes as specific risk factors for mortality or adverse outcome. At least 10 large studies have addressed the notion that hospitals performing small numbers of coronary artery bypass grafting (CABG) operations have higher operative mortality rates. Seven of these 10 studies found increased operative mortality rates in low volume providers.33, 34, 35, 36, 37, 38, 39 In 3 other large studies there was no such association.40, 41, 42 Interestingly, in the 3 studies performed more recently (since 1996) there was no clear relationship between outcome and volume. The Institute of Medicine summarized the relationship between higher case volume and better outcome (http://www.nap.edu/catalog/1005.html) and concluded that procedure or patient volume is an imprecise indicator of quality even though a majority of the studies reviewed showed some association of higher volume and better outcome.43 The dilemma is that some low volume providers have excellent outcomes and some high volume providers have poor outcomes. These observations on operator volume and outcome prompted some authorities to suggest “regionalization” to refer nonemergency CABG patients to large volume centers.38, 44, 45 A role for “selective regionalization” was advocated by Nallamothu and colleagues,42 since they found that low risk patients fared equally well in high volume or low volume hospitals. These investigations suggest regional referral for elective high risk patients to high volume institutions. Crawford and colleagues46 pointed out that a policy of regionalized referrals for CABG might have several adverse effects on health care, including increased cost, decreased patient satisfaction, and reduced availability of surgical services in remote or rural locations.

Risk is stratified for the overall cardiac surgery experience, including early outcomes for the operative procedure based on preoperative risk factors. The APACHE III score (Acute Physiologic And Chronic Health Evaluation) is commonly used for noncardiac surgery patients based on clinical presentation on arrival in the ICU. Because application of the Apache III scale to cardiac surgery patients is difficult, a refined APACHE III was developed for patients undergoing CABG. Independent predictors of survival were acute physiology score, age, emergency operation, reoperation, number of grafts performed, and gender.47 Higgins and colleagues48 reported an ICU admission score for predicting morbidity and mortality rates (Table 10). This allowed sequential assessment of prognosis and improved stratification because of continuously updated data. For example, the use of intra-aortic balloon counterpulsation (IABP) signified a worsening prognosis likely due to degree of cardiac pathology, poor myocardial protection, or technical events in the operating room. This applied to extended CPB times as well.

Outcomes after hospitalization have become increasingly important in terms of quality of life. The SF-36 form is a short questionnaire with 8 multi-item variables49. Lindsay and colleagues50 reported on 214 patients undergoing CABG in whom SF-36 was used before and after operation. At a mean of 16.4 months postoperatively, the SF-36 score showed that high levels of social support were associated with improved health status and quality of life. Simchen and colleagues,51 in a study from Israel, reported on 1270 patients 1 year after CABG. One third of respondents reported their quality of life as “not good,” particularly women and those of lower socioeconomic status. Rehabilitation programs were targeted as a means of improvement. Quality of life measures following CABG will undoubtedly become more important as the population ages.

The number of Medicare patients has risen to over 40 million. At the same time, the number of uninsured individuals in the United States is also rising. Access to care and rising costs continue to challenge health care providers. The Health Care Financing Administration [HCFA: now called Centers for Medicare and Medicaid Services (CMS)] budget has risen from $21.5 billion in 1977 to $214.6 billion in 199752; treatment for coronary artery disease (CAD) accounted for more than $80 billion of that cost in 1997, yet CAD continued to be the leading cause of death and morbidity in the United States. At the same time, expensive medical technology continues to grow and develop. With the escalating costs of cardiac surgery, attempts have been made to find effective ways to reduce these costs while maintaining good outcomes. Beginning in the last decade, individual cardiac surgeon and institutional results in New York State were made available to the media and public, causing outcries both within the medical establishment and the general public.53 HCFA has mandated progressively lowered reimbursements, utilizing DRGs for cardiac surgical procedures, in a further attempt to control the continuing growth of operations and cost. The reimbursement for cardiothoracic surgery from Medicare decreased 9.3% from 1991 to 1997.52 With a rising population and the influx of the baby boomers into the patient mix, financial issues will become even more important.

The specific cost of CABG has been studied extensively, with particular attention given to preoperative risk factors and complications that increase the hospital length of stay (LOS). Taylor and colleagues54 prospectively studied 500 patients undergoing CABG and found a charge of $11,900 ± $12,700. No preoperative clinical features were significant predictors of cost, whereas postoperative sternal wound infection, respiratory failure, and LV failure were. Ferraris and colleagues55 studied hospital charges in 938 patients undergoing CABG. They found that risk factors for postoperative morbidity are different than those for postoperative mortality. Their findings suggested that older patients with preoperative anemia and low blood volume who also have other comorbidities [congestive heart failure (CHF), stroke, COPD, or hypertension] are at increased risk for postoperative complications and increased hospital costs. The most costly outcome in their study was perioperative death. Cohen and colleagues56 analyzed hospital cost (not charges) for 89 elective CABG patients with an average postoperative LOS of 9.3 days, and found the total costs averaged $17,420, $19,153, and $21,828 for the 25th, 50th, and 75th percentiles, respectively. Williams and colleagues57 found increased cost to be correlated with higher average risk (utilizing the Parsonnet equation) and increased LOS in 2589 CABG patients. Shahian and colleagues,58 however, showed no correlation between hospital size, volume of surgery, and cost.

Strategies to decrease cost, include operating on lower risk patients, more expedient surgery (i.e., during the same admission as diagnostic catheterization), same-day admissions, shortening ICU and restricting hospital stays, improved home care, and greater use of chronic care facilities and rehabilitation centers. Shorter LOS in the acute care hospital, however, has led to increased readmission rates, and more frequent discharges to chronic facilities, along with increasing utilization of home health services. Lazar and colleagues59 demonstrated a distinct change from 1990 to 1998, with discharge-to-home-with-services increasing from 14.75% to 46.7%, and transfer to rehabilitation units increasing from 2.9% to 13.7%. Reported readmission rates following cardiac surgery range from 5.3% to 20.9%.59, 60, 61, 62, 63 Preoperative risk factors associated with increased readmission rates include female sex, diabetes, chronic lung disease, and preoperative atrial fibrillation.62, 63 Common readmission diagnoses include atrial fibrillation, angina, CHF, ventricular tachycardia, wound problems, pneumonia, and gastrointestinal complaints.60

Simply put, evidence is the link between what we know and what we do in medicine. Evidence-based medicine (EBM) is designed to achieve optimal management of clinical problems or challenges. Practice management guidelines, paradigms, and algorithms can then be developed. The ultimate goal of risk stratification and outcome assessment is to account for differences in patient risk factors so that patient outcomes can be used as an indicator of quality of care. A major problem arises in achieving this goal because uniform definitions of quality of care are not available. This is particularly true of cardiovascular disease. For example, there are substantial geographic differences in the rates at which patients with cardiovascular disease undergo diagnostic procedures and, incidentally, there is little, if any, evidence that these variations are related to survival or improved outcome.64, 65, 66, 67 In 1 study, coronary angiography was performed in 45% of patients after acute myocardial infarction for patients in Texas compared with 30% for patients in New York State (P < 0.001 for comparison between states).65 In these patient populations the rate of coronary revascularization was similar, and the survival rate in these patients was not related to the type of treatment of diagnostic procedures. Regional variations of this sort suggest that a rigorous definition of the “correct” treatment of acute myocardial infarction, as in other cardiovascular disease states, is elusive and the definition of quality of care for such patients in imperfect. Similar imperfections exist for nearly all outcomes in patients with cardiothoracic disorders. Risk adjustment methodologies can isolate patient risk factors that are associated with poor outcome, but what to do about these risk factors and how to improve outcomes based on risk stratification is uncertain. More work is required to define optimal outcomes and treatment standards based on risk profile.

Recognizing the difficulties in defining “best practices” for a given illness, professional organizations have opted to promote practice guidelines or “suggested therapy” for a given disease68, 69 (Tables 11). These guidelines or recommendations represent a compilation of available published evidence, including randomized trials and risk-adjusted observational studies, as well as consensus among panels of experts proficient at treating patients with the given disease.69 For example, the practice guideline for coronary artery bypass grafting is available on the Internet (http://www.acc.org/clinical/guidelines/bypass/ExecIndex.htm) for both practitioners and the lay public. These guidelines were developed using a summation of available randomized controlled trials, risk-adjusted observational studies, and expert consensus. They are meant to provide clinicians with accepted standards of care that most would agree on, with an ultimate goal of limiting deviations from accepted standards. Guideline development represents a work in progress. The methodology for developing guidelines for disease treatment is evolving. Many published guidelines do not adhere to accepted standards for developing guidelines.70 The area where greatest improvement is needed is in the identification, evaluation, and synthesis of the scientific evidence.

In summarizing available medical evidence on a given subject, information retrieval is paramount. Nowhere is this more evident than in the Cochrane Collection of available randomized trials on various medical subjects. For example, a recent Cochrane review (http://www.update-software.com/abstracts/ab002138.htm) found 17 trials that evaluated postoperative neurological deficits in patients having hypothermic CPB compared with normothermic CPB.71 This compares to a recently published meta-analysis on a similar topic that only found 11 trials on which to perform a similar analysis.72 Few current EBM recommendations are available related to perioperative care of the cardiac surgery patient. It is difficult to assess evidence in critical care. As an example, Scheinkestel and colleagues73 point out that multiple interventions in a cohort of patients without informed consent are difficult to study in a randomized prospective way. Such issues as the use of pulmonary artery catheters, colloid fluid resuscitation, target hemoglobin level, choice of inotropic agents, and the degree and route of nutritional support remain unsettled and controversial.

Section snippets

Anesthesia

Advances in cardiac anesthesiology techniques have been attributed to increased experience, safer and improved pharmacologic agents, predictable and proven anesthetic techniques, and technological advances in hemodynamic monitoring. The anesthesiologist, certified registered nurse anesthetist (CRNA), and anesthesia technician continue to play expanding roles in the preoperative, operative, and postoperative phases of cardiac surgery, particularly with the increasing use of off-pump coronary

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