Obstetric anesthetic management of women with acquired or congenital heart disease
INTRODUCTION —
Anesthetic management of the pregnant woman with acquired heart disease (AHD) or congenital heart disease (CHD) is best achieved by a multidisciplinary team of providers (cardiologists, obstetricians, and anesthesiologists) .
HEMODYNAMIC CHANGES DURING PREGNANCY--
An understanding of these hemodynamic changes of pregnancy allows the clinician to anticipate which cardiac conditions are likely to decompensate antepartum and peripartum.
As an example, women with stenotic valvular lesions are typically at higher risk of pregnancy-related heart failure than those with regurgitant valvular lesions.
The physiology of aortic stenosis requires adequate afterload for coronary perfusion to supply the thickened myocardium, whereas mitral stenosis physiology gains no benefit from decreased afterload.
In aortic insufficiency, however, the decreased afterload lessens the regurgitant volume improving hemodynamics.
Likewise, in mitral insufficiency, the lesser systemic pressure may reduce the degree of valvular regurgitation and improve functional cardiac output.
The following synopses describe hemodynamic changes in normal pregnancy and selected pregnancy complications.
Antepartum —
Significant hemodynamic changes begin as early as the fourth week of gestation and persist for several months postpartum. Systemic vascular tone falls, inducing a compensatory 30 percent increase in cardiac output by the end of the first trimester.
Cardiac output plateaus around week 26 at a level about 40 percent above its prepregnancy baseline, and then gradually falls by about 10 percent until by term it is about 30 percent above baseline.
Both systolic and diastolic blood pressure decrease (by about 10 mmHg and 5 mmHg, respectively) until 30 weeks of gestation due to decreased vascular tone.
Maternal heart rate increases (by about 15 beats per minute), peripheral and pulmonary vascular resistance decrease, colloid osmotic pressure decreases, and a dilutional anemia occurs (due to a disproportionate increase in red cell volume [1500 mL to 1800 mL] compared to plasma volume [2500 mL to 3800 mL]).
Intrapartum —
Cardiac output increases progressively during the first stage of labor, sometimes reaching an additional 50 percent by the late second stage.
Immediately postpartum, autotransfusion of uteroplacental blood to the intravascular space significantly increases cardiac output; within the first 10 minutes following a term vaginal delivery, the cardiac output and stroke volume increase by 59 and 71 percent, respectively . At one hour postpartum, both the cardiac output and stroke volume remain increased (by 49 and 67 percent, respectively) while the heart rate decreases by 15 percent; blood pressure remains relatively unchanged.
These hemodynamic changes resolve slowly over the ensuing weeks, with typical return to nongravid status by six months postpartum.
Cesarean delivery —
During cesarean delivery, if neuraxial anesthesia is performed, initial hypotension and/or bradycardia can result from the local anesthetic-induced sympathectomy. This is typically treated with bolus intravenous hydration and vasopressor therapy, if required.
At the time of cesarean delivery, cardiac index increases by 47 percent, stroke volume index decreases by 39 percent and mean arterial pressure remains stable. These acute changes occur within two minutes of delivery and persist for about 10 minutes postpartum .
Multiple gestation —
In patients with multiple gestations, maternal blood volume expansion occurs earlier in gestation and reaches a peak volume that is 40 percent greater than in singleton gestations. Anemia can be more profound and blood loss at delivery is typically greater, and can be twice that associated with a singleton birth .
Venous thromboembolism, pulmonary edema, gestational hypertension and preeclampsia also occur more frequently.
Preeclampsia —
Cardiac patients with preeclampsia and eclampsia are exquisitely sensitive to sympathetic stimulation due to impaired endothelial function. Cerebral vascular accidents from malignant hypertension must be avoided with adequate antihypertensive therapy, a deep induction prior to laryngoscopy, adequate anesthesia throughout surgery, and careful titration of sympathomimetic agents.
These patients can also exhibit abnormal coagulation studies, which can complicate or preclude regional anesthesia.
RISK STRATIFICATION —
In practice, anesthesiologists do not follow one specific risk stratification system as a formula for management.
The American College of Cardiology/American Heart Association (ACC/AHA) and the European Society of Cardiology (ESC) guidelines on the management of valvular heart disease consider women with one of the following valve lesions to be at high maternal and/or fetal risk during pregnancy :
- Severe aortic stenosis with or without symptoms
- Symptomatic mitral stenosis (NYHA class II to IV)
- Aortic or mitral regurgitation with NYHA class III to IV symptoms
- Aortic and/or mitral valve disease with severe left ventricular dysfunction (defined as a left ventricular ejection fraction less than 40 percent) or severe pulmonary hypertension (defined as pulmonary artery pressure >75 percent of systemic pressure)
- Marfan syndrome with or without aortic regurgitation
OBSTETRICAL MANAGEMENT — Women with cardiac disease that are considered to be at high maternal or fetal risk should receive prenatal care and deliver at a tertiary care center .
The health care team should have a thorough understanding of the management of potential complications of AHD and CHD in the intrapartum and peripartum periods, and the tertiary center should have appropriate facilities for evaluation, monitoring, and treatment of potential complications of heart disease.
If possible, delivery should be planned (scheduled induction or cesarean delivery) to enable all members of the healthcare team to be present.
Indications for cesarean delivery — Cesarean delivery is rarely performed solely for a maternal cardiac indication. Exceptions include aortopathy with a dilated root >4 cm or progressive enlargement noted with advancing gestation, aortic dissection, or aortic aneurysm, because intrapartum increases in cardiac output related to contractions may significantly increase the risk of a cardiac event .
Maternal warfarin treatment within two weeks of delivery is another possible indication for cesarean delivery because of risk of transplacental anticoagulation leading to fetal intracranial hemorrhage during vaginal birth.
Vaginal delivery — There is no consensus regarding absolute contraindications to vaginal delivery, as this decision is usually dependent on maternal status at time of delivery, her anticipated cardiopulmonary tolerance to the increased hemodynamic demands of labor, and concurrent fetal condition. Given the unpredictability of time of delivery, care should be taken to confirm availability of all necessary support personnel throughout the labor process.
A left lateral decubitus position will enhance venous return, and supplemental oxygen should be given if pulse oximetry indicates decreased oxygenation.
A dense epidural anesthesia early in labor can be used to allow the patient to labor comfortably, since pain and anxiety have multiple potentially deleterious hemodynamic effects . The epidural anesthetic must provide deep sacral coverage so the mother does not feel either pain or a strong reflexive urge to push.
Fetal descent during the majority of the second stage can be accomplished exclusively by uterine contractions without the aid of maternal expulsive efforts. When the fetal head reaches the pelvic floor, a low or outlet operative vaginal delivery (either forceps or vacuum extraction) can be performed to avoid the physiologic changes associated with maternal Valsalva maneuvers (pushing): increased intrathoracic pressure —> decreased venous return —> decreased preload —> decreased cardiac output.
While most obstetricians would likely not permit a prolonged second stage of labor in a patient with a dilated aortic root, a patient with well-compensated moderate aortic stenosis may remain asymptomatic despite repeated Valsalva maneuvers.
Induction of labor, if required, is usually performed in a conventional manner. Particular attention to volume status is important if oxytocin infusion is prolonged. If cervical ripening is performed, misoprostol or mechanical methods, including balloon catheter or cervical dilators (laminaria), are effective. Cardiovascular side effects of misoprostol are rare. With mechanical methods, vagal stimulation can occur if there is forcible cervical dilation. Amniotomy is an option for patients with favorable cervical status.
ANESTHETIC MANAGEMENT
Preoperative evaluation —
The obstetric anesthesiology team should obtain a thorough cardiac, obstetric, medical, and anesthetic history; consultation should occur well in advance of delivery if possible.
In particular, it is important to ascertain for the presence of intracardiac shunting, cyanosis, prior arrhythmias, current pacemaker, left heart obstruction, poor functional status, prior episodes of heart failure, and left and right heart function. Documentation of the patient's acquired or congenital heart lesion and all palliative or reparative procedures should be reviewed. Any pertinent recent cardiac testing, including echocardiograms, should be reviewed.
The managing obstetrician should discuss with the anesthesiologist the likelihood of successful vaginal versus cesarean delivery and potential complications.
Factors such as abnormal placentation, multiple prior cesarean deliveries, or prior postpartum hemorrhage may prompt additional intravascular access, while multiple gestation or preeclampsia may prompt more judicious use of fluids.
The patient with heart disease may not have adequate cardiac reserve to withstand complications of childbirth. Thus, the anesthetic management should include contingency plans for complications such as peripartum arrhythmias, pulmonary edema, postpartum hemorrhage, or need for emergent cesarean delivery.
In patients at high risk for cardiac morbidity or mortality, a direct conversation with the cardiologist to discuss pertinent concerns should occur.
If maternal condition is tenuous or terminal, consideration should be given to discussing her resuscitative wishes in the event of cardiopulmonary arrest.
Labor analgesia —
Excellent labor analgesia is of paramount importance in laboring women with cardiac lesions. Pain and anxiety during labor and delivery provoke catecholamine surges, resulting in tachycardia, hypertension, increased cardiac output, and increased systemic ventricular stress. This can be catastrophic for the patient with heart disease, who may develop arrhythmias, ischemia, or heart failure.
Either an epidural or a combined spinal-epidural (CSE) anesthetic can be performed safely for most patients with cardiac disease.
If a rapid decrease in preload and afterload are likely to compromise cardiac status, then we eliminate local anesthetics from the intrathecal portion of the CSE, and only administer intrathecal opioids. In such patients, the epidural should be dosed slowly with local anesthetics to maintain stable hemodynamics and adequate uteroplacental blood flow. This technique carries the risk of a potential delay in discovery of a poorly placed epidural catheter after a CSE; however, epidural catheters placed during a CSE are less likely to fail .
An epidural-only technique is an alternative option. Either a CSE or an epidural is a reasonable approach since both provide excellent analgesia with local anesthetic dosing.
We suggest using the loss of resistance technique with saline rather than air in order to avoid paradoxical air embolism if the epidural needle is inadvertently placed into an epidural vein. Women with intracardiac shunts are at risk for paradoxical air embolus.
The risks and benefits of test dosing with an epinephrine solution need to be considered on a case-by-case basis, as even a small dose of epinephrine in these patients could result in tachyarrhythmias and increased systemic ventricular stress.
Conversely, bupivacaine toxicity from intravascular injection or a total spinal from intrathecal injection could be catastrophic for any patient, especially those with heart disease.
If neuraxial analgesia is not an option for a high-risk cardiac patient, then the advisability of vaginal delivery may need to be reconsidered. Although patient-controlled analgesia (PCA) via intravascular opioid infusion with remifentanil or fentanyl is performed in many patients, this may not be a good alternative for the cardiac patient. Pain control is typically suboptimal, leading to increased catecholamine release.
Furthermore, to achieve even moderately effective analgesia, the dose of opioid required could suppress ventilation. The resultant carbon dioxide retention can cause respiratory acidosis, further catecholamine release, and increased pulmonary hypertension leading to arrhythmias, ischemia, or heart failure in the high risk cardiac patient.
Monitoring during labor —
Standard labor monitoring, including noninvasive blood pressure measurement, tocodynamometry, and fetal heart rate monitoring should be employed, with consideration of five-lead telemetry and continuous pulse oximetry.
We suggest telemetry during labor for patients at increased risk of developing arrhythmias and pulse oximetry for patients with cyanotic CHD or right-to-left vascular shunting.
The addition of more invasive monitors during labor, such as arterial blood pressure and central venous pressure monitoring, depends upon the stability of the patient.
As an example, if the woman develops progressive dyspnea, arterial and perhaps central venous pressure monitoring may better characterize the effects of uterine contractions and maternal expulsive efforts on overall hemodynamics, and guide obstetric and anesthetic interventions.
Surgical anesthesia — The decision regarding the type of anesthesia for cesarean delivery in a pregnant woman with a cardiac lesion is very important. The paramount decision is whether to perform general or neuraxial anesthesia.
With CHD, maintenance of spontaneous respirations with a neuraxial approach may result in fewer cardiopulmonary complications because many congenital heart lesions affect lung mechanics and alveolar gas exchange. Alternatively, if there is a high probability of intraoperative complications requiring emergent induction and establishment of an airway, some anesthesiologists recommend planned general anesthesia.
In some cases, the choice of regional versus general anesthesia is clearly dictated by obstetric or anesthetic indications. As an example, a history of a difficult airway or a family history of malignant hyperthermia favors a regional anesthetic, while an emergent obstetric situation or a significant coagulopathy necessitates general anesthesia as the safer choice.
Specific cardiac indications for general versus regional are few; most anesthesiologists would agree with Dobb and Yentis, who state: "the care with which each technique is used, rather than the technique itself, is most important" .
A summary of factors that should be taken into account when weighing the cardiac considerations of regional versus general techniques .
If regional anesthesia is chosen, then the anesthesiologist must decide between a single-shot spinal, an epidural, a combined spinal-epidural (CSE), or a continuous spinal technique.
The rapid decrease in preload and afterload associated with a single shot spinal may be contraindicated in some cardiac lesions (eg, mitral stenosis, aortic stenosis, aortic coarctation, or right-to-left shunting).
An epidural dosed slowly with appropriate monitoring and vigilance is likely to result in the least cardiovascular disruption.
Addition of an opioid when dosing the neuraxial anesthetic will reduce the amount of local anesthetic required while improving both intraoperative and postoperative analgesia.
The elimination of epinephrine from the epidural dose will eliminate the possible deleterious effects of systemic epinephrine.
An excellent alternative to a single-shot spinal or epidural technique is a low-dose CSE technique. In one report where this approach was used in four high-risk cardiac patients, CSE was performed with an intrathecal dose of 4 to 5 mg of heavy bupivacaine along with 20 to 25 mcg fentanyl, followed by slow loading of the epidural local anesthetic to achieve a T4 surgical level .
The benefits of the low-dose CSE technique include slow-onset of the neuraxial block, which allows the anesthesiologist to maintain preload and afterload during the onset, while still achieving the greater block reliability of intrathecal local anesthetic administration.
The anesthesiologist must remain vigilant during the onset of neuraxial surgical anesthesia. Maintaining uterine blood flow is important for fetal well-being and, in patients with intravascular shunting, maintaining systemic vascular resistance is important for preventing worsening cyanosis.
Cautious intravenous hydration and/or gentle titration of phenylephrine or ephedrine are options to counteract the hemodynamic effects of surgical neuraxial block.
If symptomatic hypotension occurs, the choice of vasoactive drugs depends upon multiple factors. As an example, phenylephrine to treat hypotension in the presence of tachycardia would also be expected to reduce the heart rate, while ephedrine would increase the heart rate when used to treat hypotension in the presence of bradycardia. Phenylephrine in the presence of an intracardiac shunt would increase pulmonary blood flow.
Intraoperative monitoring — In addition to the American Society of Anesthesiology (ASA) recommendations for standard operating room monitors , arterial blood pressure and central venous pressure monitoring may be helpful in fluid management, especially in the event of intraoperative hemorrhage or heart failure.
As an example, in peripartum cardiomyopathy, if the patient has pulmonary edema and decreased ejection fraction, fluid management can be difficult. Central venous pressure monitoring can help with titration of fluids or vasopressor agents.
If an arterial line and/or central venous catheter are planned, we recommend placement prior to administration of regional anesthesia. A unique aspect of placing invasive monitors for a cesarean delivery is that the patient is usually awake during the procedure. Should a general anesthetic be planned, placement of lines prior to induction will minimize fetal anesthetic exposure prior to delivery.
The American Society of Anesthesiologists (ASA) practice advisory for perioperative management addresses use of automated implanted cardiac defibrillators (AICD) and pacemakers . They recommend that the anesthesiologist determine the type of pacemaker and/or AICD, the patient's dependency on it, and its current function through interrogation of the device. After consulting with the cardiology team in complex cases, it may be appropriate to reprogram the pacemaking device to an asynchronous mode and/or turn the AICD off for surgical cases that involve unipolar cautery. This prevents electromechanical interference. The placement of external defibrillation pads on the patient and the rapid availability of a cardiac defibrillator are recommended when an AICD is inactivated.
Filters should be placed on all intravenous lines to prevent paradoxical air embolism in patients with intracardiac shunts.
Echocardiography may be useful in the setting of cardiovascular compromise, and transesophageal imaging can be performed intraoperatively.
Pulmonary arterial (PA) catheter monitoring is rarely indicated. The risk of complications from these catheters may be increased in this population because of conduction and anatomic abnormalities inherent to the patient's heart lesion. The merits of direct monitoring should be carefully weighed against the risks of arrhythmia and infections on an individual basis.
ENDOCARDITIS PROPHYLAXIS — American College of Cardiology/American Heart Association Task Force on Practice Guidelines: endorsed by the Society of Cardiovascular Anesthesiologists, Society for Cardiovascular Angiography and Interventions, and Society of Thoracic Surgeons state vaginal or cesarean delivery is not an indication for routine antibiotic prophylaxis since the rate of bacteremia with these procedures is low . However, antibiotic prophylaxis may be considered in some particularly high risk circumstances.
MEDICAL MANAGEMENT OF POSTPARTUM HEMORRHAGE —
The medical management of postpartum hemorrhage in a woman with cardiac disease needs to consider the patient's cardiac status, medical history, and side effects of the various uterotonic drugs.
The following medications are listed in the order we consider their use for treatment of uterine atony in women with heart disease and postpartum hemorrhage.
First-line therapy — We suggest oxytocin (Pitocin®) for prevention and initial medical therapy of postpartum hemorrhage.
Generally administered as a continuous infusion of 10 to 40 units oxytocin diluted in 500 to 1000 mL crystalloid. Side effects include decrease in mean arterial pressure , decrease in total peripheral vascular resistance decreases , and possibly a slight increase in pulmonary artery pressure . Side effects occur more frequently with intravenous bolus administration.
Oxytocin has a short half-life; cardiovascular changes typically last less than 10 minutes after the infusion is discontinued.
Second-line therapy — Misoprostol (Cytotec®) is a prostaglandin E1 analogue.
Administered as a rectal suppository (600 to 1000 mcg) or placed in the patient's cheek for transbuccal absorption. The patient should be instructed not to swallow these pills because gastrointestinal upset and diarrhea can occur.
Maternal cardiac function remains unchanged even with high doses . Cardiovascular adverse drug reactions have been noted in fewer than 2 percent of patients, but causality has not been established.
Administered as an intramuscular injection of 250 mcg.
Contraindicated in patients with reactive airway disease. Side effects include bronchospasm and altered ventilation/perfusion ratio resulting in increased intrapulmonary shunt fraction and possibly hypoxemia . These side effects can lead to worsening cyanosis in patients with an intracardiac shunt.
May induce hypertension at high doses, possibly because of vascular smooth muscle contraction.
Fourth-line therapy — Methergonivine (Methergine®), which most likely exerts its uterotonic effect via alpha-1 receptor stimulation.
Administered as a 0.2 mg intramuscular injection (intravascular injection should be avoided)
Relatively contraindicated in patients with heart disease, especially those with hypertension or preeclampsia. Side effects, which are more significant with bolus intravenous injection, include:
- Vasoconstriction leading to sudden, systemic hypertension. This could cause stroke or seizure , especially in patients with baseline hypertension.
POSTPARTUM CARE — The intensity of postpartum monitoring is determined by the status of the patient's heart disease and any obstetric or cardiac events that occurred during labor and delivery.
In general, hemodynamics do not return to prepregnancy values until 6 to 12 weeks following delivery. Cardiac death during this period has been reported, especially in women with pulmonary hypertension, so careful monitoring for cardiac symptoms is important .
SUMMARY AND RECOMMENDATIONS
Major hemodynamic changes occur during pregnancy.
Cardiac lesions can be stratified according to their risk of death or severe morbidity during pregnancy .
Cesarean delivery is rarely performed solely for a maternal cardiac indication. Exceptions include some types of aortic disease and fetal anticoagulation.
A "cardiac" vaginal delivery refers to modifications of the usual management of labor and delivery to accommodate the hemodynamic limitations of the patient with heart disease. It involves early, deep regional anesthesia and avoidance of maternal Valsalva efforts.
Epidural or a combined spinal-epidural (CSE) are preferred for most patients with cardiac disease. For women undergoing cesarean delivery, factors that should be taken into account when weighing the cardiac considerations of regional versus general techniques are shown in the table.
We suggest telemetry during labor for patients at increased risk of developing arrhythmias, and pulse oximetry for patients with cyanotic heart disease or those with right-to-left vascular shunting. The addition of more invasive monitors for labor, such as arterial blood pressure and central venous pressure monitoring, depends upon the stability of the patient.
For treatment of postpartum hemorrhage, we suggest oxytocin (Pitocin®) as a first-line agent and misoprostol (Cytotec®) as a second-line agent, given they are associated with fewer cardiorespiratory effects than 15-Methyl prostaglandin F2 alpha (Hemabate®) and Methergonivine (Methergine®) (Grade 2C).
Notice the intrathecal opioids used in maintaining more stable hemodynamics in pregnant cardiac patients under regional anesthesia & analgesia.
This is a new trend in anesthetic practice.
|关于我们|业务合作|手机版|新青年麻醉论坛
( 浙ICP备19050841号-1 )
发表于 2009-12-8 23:41:46
QQ好友和群
收藏
淘帖
鲜花
鸡蛋
提升卡
置顶卡
变色卡
楼主
发表于 2009-12-9 17:51:33
