Physicians practicing medicine at the start of
the 21st century are recognizing a patient population that is living longer
and has an increase in the number and severity of comorbid illnesses. As a
result, clinicians are often asked to evaluate the perioperative risk status
of their patients.
The cardiovascular systems of patients who undergo general anesthesia and
noncardiac surgical procedures are subject to multiple stresses and
complications. A previously stable patient may decompensate postoperatively,
leading to significant morbidity and mortality. A substantial number of all
deaths among patients undergoing noncardiac surgery result from
cardiovascular complications.
Each year, approximately 30 million individuals in the United States
undergo noncardiac surgery. Approximately one third have cardiac disease or
major cardiac risk factors. Current estimated rates of serious perioperative
cardiac morbidity vary from 1-10%. The incidence of perioperative myocardial
infarction (MI) has increased 10- to 50-fold in patients who have had
previous coronary events.
Cardiac risk stratification allows clinicians to group patients into
various risk categories; therefore, low-risk patients can be spared further
testing, whereas intermediate- and high-risk patients may undergo necessary
investigations and treatment to reduce overall cardiac perioperative
morbidity and mortality.
Cardiac effects of
general anesthesia
The cardiovascular effects of general anesthesia include changes in the
arterial and central venous pressures, cardiac output, and varying heart
rhythms, which occur by the following mechanisms: decreased systemic
vascular resistance, decreased myocardial contractility, decreased stroke
volume, and increased myocardial irritability.
Induction of general anesthesia lowers systemic arterial pressures by
20-30%, tracheal intubation increases the blood pressure by 20-30 mm Hg, and
agents such as nitrous oxide lower cardiac output by 15%.
The use of fentanyl, sufentanil, or alfentanil results in less myocardial
depression compared to inhaled anesthetics. Yet, these intravenous agents
still cause venodilation, thus reducing preload and hence, depressing
cardiac output. Patients with congestive heart failure (CHF) are
particularly sensitive to these changes. By increasing the preoperative
volume status and applying the Frank-Starling principle, one can offset this
decrease in cardiac output. Additionally, inhalational and intravenous
anesthetics along with muscle relaxants can be detrimental by sensitizing
the myocardium to circulating catecholamines. As a result of the stress of
the surgical procedure, circulating catecholamine levels are elevated,
thereby increasing the risk of ventricular ectopy.
Cardiac effects of regional anesthesia
Both epidural and spinal anesthetics cause arteriodilation and
venodilation by blocking sympathetic outflow, decreasing preload, and,
ultimately, reducing cardiac output. To offset this deleterious effect, the
clinician may volume load the patient preoperatively. However, this
intervention increases the risk of postoperative CHF by 10-15%.
Although many clinicians believe that regional anesthesia is safer than
general anesthesia, randomized studies comparing the 2 modalities have shown
no difference in mortality or cardiopulmonary complications. Combined
epidural and general anesthesia with analgesia for pain control may
attenuate sympathetic hyperactivity, reduce the need for additional
parenteral analgesia postoperatively, improve postoperative pulmonary
function, and reduce the duration of stay in the intensive care unit
following surgery.
PATIENT- AND
PROCEDURE-RELATED FACTORS
Patient-related factors
Hypertension
Approximately 40% of patients who are aware they have hypertension are
either not treated or inadequately treated with pharmacological therapy.
In the perioperative period, poorly controlled hypertension is associated
with an increased incidence of ischemia, MI, left ventricular dysfunction,
arrhythmia, and stroke. Patients with hypertension are at a higher risk for
labile blood pressure and for hypertensive emergencies during surgery and
immediately following extubation. Patients should continue taking
antihypertensive medications throughout the perioperative period. The
clinician should aim for a diastolic blood pressure lower than 100 mm Hg
before proceeding with elective surgery. Intravenous esmolol, labetalol, or
nitroprusside may be used for acute episodes of hypertension, whereas
calcium channel blockers or angiotensin-converting enzyme (ACE) inhibitors
may be used in less acute situations.
Congestive heart failure
The mortality rate following noncardiac surgery increases with worsening
cardiac class and with the presence of pulmonary congestion. The
perioperative mortality rate appears to be more dependent on the patient's
condition at the time of surgery rather than on the myocardial depressant
effects of the anesthesia. CHF should be aggressively and adequately treated
before the patient undergoes major elective surgery. Therapy is aimed at
reducing ventricular filling pressures in addition to improving cardiac
output. Medications proven to show both a morbidity and mortality benefit
include ACE inhibitors, beta-blockers, and spironolactone. Digoxin and
diuretics have been shown to improve morbidity rates without reducing
mortality rates. Detsky et al suggest that patients with decompensated CHF
should be stabilized for at least one week before undergoing elective
surgery.
Ischemic heart disease
Ischemic heart disease (IHD) is a major determinant of perioperative
morbidity and mortality. During the 1970s, several studies reported a 30%
risk of reinfarction or cardiac death for patients undergoing surgery within
3 months of an MI, 15% when surgery was performed 3-6 months after an
infarction, and 5% when the operation was performed 6 months later.
True lifesaving procedures should be performed regardless of cardiac
risk, but consideration should be given to performing elective surgery 6
months following an MI. In patients requiring semiurgent surgery, the
patient's risk should be evaluated with prognostic studies (see
