| |
October 2001
Volume 65 |
Number 10
|
| |
|
| Recent
Advances in Anesthesia for Congenital Heart Disease |
Dean B. Andropoulos,
M.D.
Stephen A. Stayer, M.D.
Anesthesia for patients with congenital heart disease is a rapidly
evolving field with a number of significant recent developments.
Providing care for these patients stretches the boundaries of
both the pediatric anesthesiologist and the cardiac anesthesiologist
and has given rise to the developing subspecialty of pediatric
cardiac anesthesia. We will review some of the major advances
of the past decade.
The Patient
The number of patients undergoing surgery for congenital heart
disease is expanding at both ends of the age spectrum. In many
centers, few, if any, patients are denied surgery because of extremes
of age or size. Today, full-term newborns undergo corrective surgeries
such as the arterial switch operation for transposition of the
great vessels with near zero mortality. This and other procedures
such as the Norwood procedure for hypoplastic left heart syndrome
are now routinely performed on small, even premature, newborns
down to weights of 2 kg or less and at gestational ages down to
32 weeks.1
These very small, fragile infants present unique challenges to
the anesthesiologist related to vascular access and management
of cardiopulmonary bypass. Their immature organ systems are susceptible
to the sequelae of prematurity, including retinopathy of prematurity,
intracranial hemorrhage and bronchopulmonary dysplasia. Despite
these obstacles, the outcome of these tiny patients has been encouraging,
with a survival rate of 83 percent for infants 700-2,500g.1
Moving up the age spectrum, teenagers and adults are presenting
for cardiac surgery with increasing frequency. There are an estimated
800,000 patients in the United States with congenital heart disease,
many of whom had previous corrective or palliative surgeries.
Patients who have had previous palliative surgeries or were never
repaired may have developed severe sequelae such as ventricular
failure, dysrhythmias, pulmonary hypertension (e.g., Eisenmenger’s
syndrome) and longstanding cyanosis. These patients now present
for revision of previous surgical repairs such as conversion to
modern versions of the Fontan procedure; or they may present for
further palliation or first-time complete corrective surgeries
such as Tetralogy of Fallot repair.
We recently reviewed our experience with 85 such older patients,
comparing them to patients under age 5 with the same diagnosis.
The older patients had a higher incidence of dysrythmias and much
longer anesthetic, surgical, bypass and aortic crossclamp times.
In addition, they were the only patients to experience massive
bleeding during sternotomy or to require femoral bypass or cardiopulmonary
resuscitation in the operating room. Despite these intraoperative
problems for the anesthesiologist, the mortality rate remained
low (4 percent), and there was no major morbidity in the survivors.
2
Cardiopulmonary Bypass
Several changes in cardiopulmonary bypass techniques deserve discussion.
The first is the miniaturization of the oxygenator-heat exchanger
and other components of the bypass circuit, which reduces the
priming volume to as little as 150-200 ml for small infants. This
compares with former priming volumes of 500-700 ml and has the
advantage of less severe hemodilution and decreased dilution of
coagulation factors, less surface area for activation of coagulation
and inflammatory cascades, and less exposure to fewer blood donors.
Evidence is accumulating that pH stat management of bypass (temperature-correcting
blood gas values to achieve normocarbia and normal pH during cooling)
leads to improved cerebral perfusion and oxygenation and improved
neurologic outcome. 3 Hemofiltration or ultrafiltration,
either while on bypass during the rewarming phase or immediately
after bypass, has been demonstrated to remove inflammatory mediators
and reduce the need for inotropic and ventilatory support. 4
Deep hypothermic circulatory arrest (DHCA), usually at temperatures
of 17-18 degrees celsius, is used for complex intracardiac and
aortic repairs. DHCA can be utilized for approximately 45 minutes,
after which the incidence of neurologic complications increases
significantly. Surgical techniques have thus been altered to minimize
the exposure to DHCA.
One such technique is regional low-flow cerebral perfusion (RLFP)
5 in which only the brain is perfused via cannulation
of the right innominate artery during complex aortic reconstruction,
thereby providing perfusion to the brain throughout surgery. Neurophysiologic
monitoring (see below) is crucial for determining the appropriate
level of flow and pressure for each individual patient. Finally,
the use of ventricular assist devices and extracorporeal membrane
oxygenation for cardiac and pulmonary support both preoperatively
and postoperatively has increased, and anesthesiologists are involved
in the development and implementation of these techniques.
A notable result of these increasingly complex perfusion protocols
is that in many centers, the anesthesiologist is now much more
actively involved in managing cardiopulmonary bypass.
Monitoring Techniques
Transesophageal echocardiography (TEE) has been demonstrated to
reduce the number of patients leaving the operating room with
residual, uncorrected cardiac defects, reducing morbidity and
mortality. 6 Knowledge and skill in TEE is an
essential tool for the congenital cardiac anesthesiologist. This
tool has traditionally been used to assess preoperative and postoperative
anatomy. Anesthesiologists also use TEE, however, to assess ventricular
function and filling or regional wall motion abnormalities, to
aid the surgeon during de-airing maneuvers and to guide correct
placement of central venous catheters. Miniaturization of the
technology has provided multiplane transducers for pediatric patients,
allowing the advantages of this modality in infants as small as
2-3 kg. Real-time, three-dimensional TEE will become a reality
in the near future and will be particularly useful in assessing
the complex anatomy of congenital heart disease.
Neurophysiologic monitoring has gained more widespread use as
evidence accumulates that these monitors add information for the
anesthesiologist to direct anesthetic and bypass management more
precisely and that this may improve outcome. 7
Bispectral index has been studied during cardiopulmonary bypass
in children and appears to correlate with depth of anesthesia
and induced hypothermia. 8 Near-infrared spectroscopy
(NIRS) provides an estimate of cerebral oxygen saturation and
is now available commercially for pediatric patients. NIRS is
a particularly important guide during special bypass techniques,
such as DHCA, RFLP or low-flow bypass. Transcranial Doppler ultrasound
to measure cerebral blood flow also is easily utilized for congenital
heart surgery and, in combination with NIRS, can be used to adjust
bypass flow, pressure and carbon dioxide in order to optimize
oxygen delivery to the brain. The interpretation of mutimodality
neurologic monitoring requires increased participation of the
anesthesiologist in the management of cardiopulmonary bypass.
Regional Anesthesia, Pain Control and Early Extubation
Regional anesthesia, using opioids and/or local anesthetics, is
administered via the caudal, lumbar, thoracic epidural or intrathecal
route using single-shot or catheter techniques and has been described
for pediatric cardiac surgery. 9 These techniques
appear to facilitate early extubation and provide excellent pain
control for selected patients. Despite the theoretical risk of
epidural bleeding with systemic heparinization, this complication
has not been reported in this population to date. Many practitioners
feel that single-shot intrathecal techniques provide optimal postoperative
analgesia and minimize the risk from an epidural hematoma. Infusions
of short-acting agents such as remifentanil and propofol postbypass
are also used to facilitate early extubation in the intensive
care unit for selected patients.
Nitric Oxide
Nitric oxide (NO) can be continuously delivered through the anesthesia
circuit to treat pulmonary hypertension and has become an important
tool in the armamentarium of the congenital cardiac anesthesiologist.10
It is frequently very effective at decreasing pulmonary vascular
resistance, thus allowing better systemic oxygen delivery in the
early postoperative period and often leads to a shorter intensive
care unit stay with lower morbidity. Indeed, some operations would
not have been considered in the past in patients with pulmonary
hypertension, but they are undertaken today with the availability
of NO.
Cardiac Catheterization, Noncardiac Surgery and Cardiac MRI
Procedures performed in the cardiac catheterization laboratory
have become more invasive and provide new therapeutic options
for patients with congenital heart disease. Atrial septal defects
are closed using an umbrella-like device loaded in a catheter,
and a patent ductus arteriosus can be occluded with coils. Electrophysiological
procedures such as mapping and radiofrequency ablation of arrhythmogenic
foci and transvenous pacemaker implantation are performed on smaller
children with increasing frequency. Many of these procedures require
an anesthesiologist to provide either general anesthesia or monitored
anesthesia care, and the procedures themselves may be quite lengthy
and involve significant hemodynamic instability.
As patients with all forms of congenital heart disease (but especially
single-ventricle patients) show improved survival, their needs
for noncardiac surgery increase. The unique pathophysiology of
the single-ventricle patient makes it particularly important that
the anesthesiologist thoroughly understand the hemodynamic effects
of anesthetics and of positive-pressure ventilation for these
patients.
Cardiac magnetic resonance imaging (MRI) may supplement or replace
other imaging modalities such as cardiac catheterization and echocardiography
for many cardiac lesions, particularly abnormalities of the aorta
and pulmonary arteries. Providing sedation or general anesthesia
for these patients, with their pathophysiologic considerations,
is challenging with less reserve in case of anesthetic problems
such as airway obstruction or relative overdose of an anesthetic
agent.
All of these changes make anesthesia for congenital heart disease
an exciting, challenging, intense and rapidly changing field.
The complexity of the discipline, along with an explosion in the
volume of information specific to this field, has led to the emergence
of a subspecialty of anesthesia for patients with congenital heart
disease, with dedicated divisions and training programs organized
to meet the unique needs of these patients.
References:
1. Reddy VM, McElinney DB, Sagrado T, et al. Results
of 102 cases of complete repair of congential heart defects in
patients weighing 700-2500 grams. J Thorac Cardiovasc Surg. 1999;
117:324-330.
2. Andropoulos DB, Stayer SA, Bent ST, et al.
Anesthetic and perioperative outcome of teenagers and adults with
congenital heart disease. Anesthesiology. 2001; 95:A146.
3. Kurth CD, O’Rourke MM, et al. Comparison
of pH-stat and alpha-stat cardiopulmonary bypass on cerebral oxygenation
and blood flow in relation to hypothermic circulatory arrest in
piglets. Anesthesiology. 1998; 89: 110-118.
4. Journois D, Israel-Biet D, et al. High-volume,
zero-balanced hemofiltration to reduce delayed inflammatory response
to cardiopulmonary bypass in children. Anesthesiology. 1996; 85:965-976.
5. Pigula FA, Nemoto EM, Griffith BP, et al. Regional
low-flow perfusion provides cerebral circulatory support during
neonatal aortic arch reconstruction. J Thorac Cardiovasc Surg.
2000; 119:331-339.
6. Russell IA, Miller-Hance WC, Silverman NH.
Intraoperative transesophageal echocardiography for pediatric
patients with congenital heart disease. Anesth Analg. 1998; 87:1058-1076.
7. Austin EH, Edmonds HL, Auden SM, et al. Benefit
of neurophysiologic monitoring for pediatric cardiac surgery.
J Thorac Cardiovasc Surg. 1997; 114:707-717.
8. Laussen PC, McGowan FX, Sullivan LJ, et al.
Bispectral index monitoring in children during mild hypothermic
cardiopulmonary bypass. Anesthesiology. 1998; 89A:A925.
9. Peterson KL, De Campli WM, Pike NA, et al.
A report of 220 cases of regional anesthesia in pediatric cardiac
surgery. Anesth Analg. 2000; 90:1014-1019.
10. Russell IA, Zwass MS, et al. The effects
of inhaled nitric oxide on postoperative pulmonary hypertension
in infants and children undergoing surgical repair of congenital
heart disease. Anesth Analg. 1998; 87:46-51.
| |
|
Dean B. Andropoulos,
M.D., is Director, Pediatric Cardiovascular Anesthesiology,
Texas Children’s Hospital, and Associate Professor, Anesthesiology
and Pediatrics, Baylor College of Medicine, Houston, Texas. |
|
| |
|
Stephen A. Stayer,
M.D., is Attending Pediatric Cardiovascular Anesthesiologist,
Texas Children’s Hospital, and Associate Professor, Anesthesiology
and Pediatrics, Baylor College of Medicine, Houston, Texas. |
|
return to top
|