Cardiac Physiology Changes During Pregnancy
During pregnancy, the heart adapts to excess fluid volume levels. Pregnancy entails a 50% increase in intravascular volume, with the largest volume burden during the third trimester of pregnancy. Excess volume results in dilutional anemia without a change in mean corpuscular volume. Platelet counts also fall during pregnancy due to this excess volume. Pregnancy is a hypercoagulable state predisposing mothers to venous thrombosis, especially deep vein thrombosis, placing expectant mothers at increased risk of pulmonary embolism. There is a significant increase in clotting factors VIII, IX, and X. Fibrinogen levels rise by approximately 50% compared to pre-pregnancy levels with a balanced reduction in fibrinolytic activity.
Cardiac changes happen early in pregnancy, with cardiac output increasing by 20% at 8 weeks gestation. Cardiac output primarily increases via vasodilation; a reduction in vascular resistance allows for an increase in stroke volume with each heartbeat. Most vasodilation is precipitated by endothelium-dependent factors such as vasodilatory prostaglandins (i.e., PGI2) and an increase in nitric oxide synthesis. Peripheral vasodilation reduces systemic vascular resistance by up to 30% resulting in an increase in cardiac output by a maximum of 40% over the course of pregnancy.
The heart itself also undergoes significant changes over the course of pregnancy. Ventricular wall mass and end-diastolic volumes increase without an increase in end-diastolic pressure. The heart develops a "dilated cardiomyopathy-like" picture with accompanying increases in contractility. Echocardiography can be a valuable tool early in pregnancy to establish a baseline with which to compare later in pregnancy. Heart rate typically increases by 10 to 20 beats per minute.
The gravid uterus has a profound effect on hemodynamics. A pregnant mother lying in the supine position may reduce up to 25% in cardiac output simply from the uterus compressing the inferior vena cava and inhibiting venous return to the heart. If a mother is experiencing hypotension or if there is suspected compromised blood flow to the uterus, it is not uncommon for the mother to be asked to lie in a left lateral position to take pressure off the inferior vena cava and improve preload to the heart. Poor cardiac output is equivocal to poor uterine blood flow and, by association, poor blood flow to the fetus.
Labor is particularly taxing on the heart and can have significant consequences for those with cardiovascular disease. Cardiac output increases by about 15% during the first stage of labor and 50% during the second stage of labor. Uterine contractions are associated with an auto-transfusion of up to 500 mL of blood back into the bloodstream and a resulting increase in systolic blood pressure of up to 20%. Patients sensitive to volume overload, such as those with mitral stenosis, can have rapid declines in cardiopulmonary function from this phenomenon. After relieving the inferior vena cava obstruction from the gravid uterus in the post-partum period, cardiac output increases 60 to 80% compared to pre-pregnancy levels, and there is a massive transfer of fluids from the extravascular space to the intravascular space. Women with cardiovascular issues are at the greatest risk of pulmonary edema in the second stage of labor and during the postpartum period.
Issues of Concern
Methods of Labor Anesthesia
The two main methods of neuraxial anesthesia during labor and delivery are epidural anesthesia and combined spinal-epidural anesthesia. Epidural anesthesia generally has a slower onset to peak effectiveness at 15 to 20 minutes and provides greater sacral dermatomal coverage with more uniformity in the sensory blockade. Combined spinal-epidural is preferred for initiation of analgesia in cases of advanced labor due to its expediated onset in 2 to 5 minutes. Some practices are performing dural puncture epidural anesthesia in place of combined spinal-epidural.
Modern labor analgesia regimens for epidurals typically consist of a combination of a dilute local anesthetic with a low-dose opioid (i.e., bupivacaine and fentanyl). The combination of two low-dose analgesics reduces the risk of local anesthetic systemic toxicity and a high or total spinal anesthetic (encountered with unintentional intrathecal injection). Hemodynamic effects and placental transfer is minimized via this technique. Dilute local anesthetics helps to mitigate the risk of motor block, which would necessitate the need for instrumental delivery due to compromised ability to push. Initiation of epidural anesthesia involves a bolus of an amide local anesthetic (i.e., bupivacaine or ropivacaine) with a lipid-soluble opioid (i.e., fentanyl or hydromorphone).
After an initial bolus, maintenance of epidural anesthesia can be obtained through various combinations of techniques, including continuous infusion, intermittent bolus, and/or patient-controlled bolus. An opioid-only intrathecal dose such as 25 micrograms of fentanyl provides excellent analgesia for the first and second stage of labor while maintaining hemodynamic stability. Still, it is associated with a high incidence of pruritis.
Systemic opioids are an excellent choice for patients who cannot obtain neuraxial anesthesia due to various contraindications, including therapeutic anticoagulation and difficult spinal anatomy. A common approach includes patient-controlled analgesia with 25 micrograms of intravenous fentanyl administered every 10 to 15 minutes with a maximum of 100 micrograms per hour. Remifentanil for patient-controlled analgesia has gained popularity due to its short half-life, metabolism by plasma-esterases, and very low risk of significant transfer across the placenta. However, maternal sedation and risk of respiratory depression are higher for patients receiving remifentanil versus fentanyl alone for patient-controlled analgesia.
The downside of administering opioids is the side effect of pruritis. Pruritis can be managed with low doses of naloxone without comprising pain control. Interestingly, pain control quality with systemic opioids has been shown in some studies to be similar to pain control with nitrous oxide alone, albeit at the cost of the environment and for a much shorter duration of action.
Outside of the United States, nitrous oxide has been successfully incorporated into labor analgesia for years but is not wholely embraced in the United States. Nitrous oxide has a large margin of safety. Some countries will even allow patients to self-administer nitrous oxide via a face mask during labor; mixtures are 50% nitrous oxide and 50% oxygen to avoid a hypoxic gas mixture. The analgesia provided by nitrous oxide is inferior to that provided by neuraxial techniques but can be a suitable adjunct when epidurals do not work as intended.
Nitrous oxide has the benefit of having a fast onset and offset while producing minimal hemodynamic changes, which can be advantageous in the cardiac disease patient. Nitrous oxide also has the added benefit of no effect on labor progression. Maternal side effects include nausea, vomiting, and dizziness. More rigorous study is required to more clearly delineate if adverse neonatal effects are higher in mothers receiving nitrous oxide during labor and delivery. Some experimental models have shown higher incidents of neonatal neurotoxicity, although the gas has been used safely for many years.
Conversion of Epidural Analgesia to Surgical Anesthesia
Epidural analgesia with a combined low dose local anesthetic and an opioid infusion is generally inadequate to provide surgical anesthesia for a Cesarean section. When a vaginal delivery is converted to a Cesarean section, a dense block with either 15 to 20mL of 2% lidocaine with 1 to 200,000 epinephrine or 15 to 20 mL of 3% 2-chloroprocaine is preferred. Chloroprocaine has the advantage of slightly faster onset and metabolism by plasma esterases, so accidental intrathecal injection is relatively inconsequential. Successful conversion to segmental anesthesia is essential in patients with cardiac disease who may not be able to tolerate general anesthesia.
Hypotension During Labor and Delivery
Spinal anesthesia is associated with hypotension due to decreases in systemic vascular resistance. Uterine blood flow does not have autoregulation like the brain during pregnancy, as the vessels are already maximally dilated as a consequence of massive increases in circulating volume. Placental blood flow is entirely dependent on uterine perfusion pressure and is sensitive to changes in uterine vascular resistance. Multiple trials have compared ephedrine to phenylephrine in gravid patients and found phenylephrine to be the superior vasopressor. Ephedrine is associated with greater fetal acidosis, while phenylephrine has the added benefit of less maternal nausea and vomiting.
Current evidence supports the initiation of prophylactic phenylephrine infusions at 25 to 100 micrograms per minute to preemptively combat hypotension associated with neuraxial anesthesia. More recent studies suggest that norepinephrine may also be a reasonable vasopressor choice. Norepinephrine has the advantage of weak beta-1 agonist activity in addition to a strong alpha-1 activity which is advantageous in patients with a low resting heart rate. Norepinephrine will increase heart rate and improve cardiac output in patients who need this effect, in addition to improving afterload. Phenylephrine causes a dose-dependent reduction in heart rate. In patients with cardiac disease, norepinephrine may be a better choice depending on the circumstances.
Anesthetic Goals by Cardiac Condition
Coronary Artery Disease
Coronary artery disease is relatively uncommon in females of childbearing age. Approximately 1 in 10,000 gravidae have a previous history of coronary disease, and only 13% of gravidae who suffer a myocardial infarction during pregnancy had a previous history of coronary disease. When myocardial infarction occurs during pregnancy, the effects are devastating, with a 37 to 45% mortality rate. Therefore, it is essential to reduce myocardial oxygen demand with bed rest and nitroglycerin in patients with significant disease. Decreased systemic vascular resistance in pregnancy reduces diastolic pressure, which subsequently reduces coronary perfusion pressures. Decreased systemic vascular resistance accompanied by the increased heart rate associated with labor can reduce coronary filling time resulting in myocardial ischemia.
Coronary Perfusion Pressure (CPP) = Aortic Diastolic Pressure – Left Ventricular end-diastolic Pressure (LVEDP)
Patients with coronary artery disease should be maintained at a normal heart rate via excellent analgesia control and avoidance of beta-agonists that may precipitate an increase in heart rate. Epidural anesthesia is the mainstay of pain control in this population. A local anesthetic bolus through an epidural can significantly decrease systemic vascular resistance, potentially precipitating tachycardia; thus, slow titration is preferred. Beta-blockers should be continued throughout the labor and delivery process. Early institution of epidural anesthesia with a maintenance infusion reduces both preload and afterload, which subsequently reduces myocardial oxygen demand in these patients sensitive to ischemia. Intraarterial pressure monitoring should be considered, and phenylephrine is the vasopressor of choice given pregnancy's reduction of systemic vascular resistance. Cardiac delivery is preferred for vaginal deliveries as the force of uterine contraction is the main factor causing fetal descent as opposed to a Valsalva maneuver. Valsalva maneuvers may result in intolerable hemodynamic changes in high-risk patients.
Ideally, if a Cesarean section is performed, the epidural should have sufficient time to be titrated slowly to a surgical level of blockade with hypotension managed with judicious fluid administration. Spinal anesthesia is less desirable due to immediate sympathetic blockade, which could trigger sudden hypotension and reflexive tachycardia. If general anesthesia is warranted, the anesthesiologist should be cognizant of the stimulus of tracheal intubation and attempt to maintain normal hemodynamic parameters during laryngoscopy and tracheal intubation.
Primary pulmonary hypertension, although rare, usually affects women of childbearing age. Secondary causes of pulmonary hypertension are typically cardiac or pulmonary in nature. The disease process involves a reduction in both nitric oxide and prostacyclin synthesis and prolific increases in endothelin and thromboxane production. On pathology slides, medial thickening and intimal fibrosis can be observed. Pulmonary artery hypertension is diagnosed via right heart catheterization and is defined as a mean pulmonary artery pressure of greater than 25 mmHg at rest. Primary pulmonary hypertension has perinatal mortality as high as 30%, whereas secondary pulmonary hypertension has a mortality rate as high as 60%. The mortality risk with pulmonary hypertension is so high in the pregnant population due to the immense increase in volume during pregnancy and the inability of the right ventricle to adapt to an increased load.
The primary treatment modality for pulmonary hypertension is pulmonary vasodilators. Fixed pulmonary vasculature is problematic for the increased cardiac output associated with pregnancy. Increased pulmonary vascular resistance can lead to right-sided heart failure. Calcium channel blockers such as nifedipine and phosphodiesterase inhibitors like sildenafil are commonly used in the outpatient setting.
During analgesia and anesthesia of these patients, the principal goal is to avoid increases in pulmonary vascular resistance and optimization of right ventricular function. The main precipitants of increased pulmonary vascular resistance include hypercarbia, hypoxia, acidosis, and high ventilation pressures for those who are intubated—vasopressors such as epinephrine and norepinephrine increase not only systemic vascular resistance but also pulmonary vascular resistance. Vasopressin is a potential option for raising systemic vascular resistance without significantly affecting pulmonary vascular resistance since there are few receptors in the pulmonary vasculature.
The recommended mode of delivery is vaginal delivery with epidural anesthesia. Epidural anesthesia reduces pain which therefore reduces oxygen consumption and hemodynamic variability. An emphasis should be placed on minimizing increases in pulmonary vasculature resistance. Supplemental oxygen should be utilized throughout labor and delivery to prevent hypoxic pulmonary vasoconstriction. This patient population could also benefit from intrathecal opiates due to their hemodynamic stability and enhanced ability to reduce pain.
Oxytocin should be used with caution as it can decrease systemic vascular resistance while also elevating pulmonary vascular resistance; this results in decreased cardiac output due to decreased left ventricular filling. Cesarean section in this patient population is associated with increased maternal mortality. Although a dense neuraxial blockade may seem ideal, it may reduce right ventricular afterload too much, resulting in right ventricular failure. General anesthesia with an opioid-based technique may allow better control over pulmonary pressures, especially in accompaniment with a pulmonary artery catheter. Nitrous oxide is ill-advised since it increases pulmonary vascular resistance. Post-partum, the patient should be monitored for signs of right-sided heart failure.
Unstable Arrhythmia History
Pregnancy, labor, as well as delivery predispose patients to tachyarrhythmias. Cardiac dysrhythmias discovered during pregnancy are usually benign. Cardioversion can be performed in pregnancy without harming the fetus; fetal distress is a good indicator of the need for cardioversion. The ventricular rate can be safely controlled with verapamil and beta-blocking agents. For hemodynamically stable supraventricular tachycardia, intravenous adenosine can be employed (3 to 12 mg).
Patients should be evaluated for a pacemaker and an automatic implantable cardioverter-defibrillator (AICD). The pacemaker and AICD should be kept functioning during labor for a vaginal delivery, but a contingency plan should be in place in case of conversion to cesarean section; electrocautery interference can disrupt the function of the device. A magnet can usually convert devices to asynchronous mode (VOO). Epidural anesthesia is associated with a decreased risk of mothers in the peripartum period developing a dysrhythmia making it an ideal modality for pain control.
Patients with Marfan's syndrome are at an increased risk for aortic rupture and dissection during pregnancy, labor, and delivery. Those without Marfan's may have an increase in dilation of their aortic root over the course of pregnancy and delivery. Approximately 50% of all aortic dissections in women under the age of 40 years old happen in the pregnant population. Mothers present with severe chest and/or interscapular pain with signs of end-organ damage. Aortic wall tension should be minimized as much as possible through avoidance of Valsalva as well as the continuation of beta-blockade during pregnancy and delivery.
Cardiac delivery allows the fetus to descend with each uterine contraction; this is a reasonable approach if the patient is hemodynamically stable. If the patient has a suspected dissection, labetalol can be an excellent adjunct to prevent the hemodynamic changes with labor and delivery and reduce the shearing forces of the dissection. Patients should be monitored post-partum for signs of aortic dissection or rupture.
Mechanical Prosthetic Valve
Anti-coagulation cannot be stopped during pregnancy for extended periods of time for patients with mechanical valves. The mainstay of anticoagulation for non-pregnant patients involves using vitamin K antagonist agents (warfarin), which are teratogenic. This can result in alternative anticoagulation regimens during pregnancy which may be suboptimal. These patients are typically placed on low-molecular-weight heparin (enoxaparin) while outpatient and possibly unfractionated heparin while inpatient. Heparin is preferred for anticoagulation as the molecule is too large to cross the placenta and affect the fetus. The combination of a hypercoagulable state during pregnancy with potentially suboptimal anticoagulation regimens places patients at increased risk of valvular thrombosis.
Risks of anticoagulation with an anesthetic technique should be carefully weighed. Anticoagulation significantly increases the risk of epidural hematoma when using neuraxial anesthesia. Regional anesthetic techniques should not be attempted unless anticoagulation has been discontinued for at least 12 to 24 hours. One method for patients at significant risk of thrombosis is to continue heparinization throughout labor and delivery whilst using systemic analgesia with an opiate such as fentanyl for labor and then switching to general anesthesia for delivery. General anesthesia should be used for Cesarean section patients who are therapeutically anticoagulated. Anticoagulation significantly increases the risk of peripartum and postpartum bleeding, so the potential for hemorrhage should be anticipated, and blood products made readily available. Postpartum, patients should be evaluated for evidence of valvular clotting and obstetric bleeding.
Mitral stenosis is one of the most difficult valvulopathies to manage during pregnancy. Approximately 90% of rheumatic heart lesions managed during pregnancy are mitral stenosis. Twenty-five percent of patients with mitral stenosis develop symptoms for the first time during the third trimester. This valvulopathy is characterized by decreased valve area resulting in fixed preload filling of the left ventricle, potentially resulting in pulmonary edema if the patient becomes too volume overloaded. Tachycardia can prevent the adequate filling of the left ventricle; thus should be avoided when administering anesthesia. Cardiac output is fixed secondary to the belabored filling of the left ventricle. Decreases in oncotic pressure can further exacerbate pulmonary edema. Another consequence of mitral stenosis is dilation of the left atrium, predisposing patients to atrial fibrillation. Atrial fibrillation can be particularly dangerous in mitral stenosis as patients rely on atrial systole to maintain sufficient left ventricular filling.
Beta-blockade should be continued throughout labor and delivery. Beta-agonists such as terbutaline should be avoided for fear of precipitating tachycardia. Atrial fibrillation should be avoided if possible and cardioversion considered early. If cardioversion is unsuccessful, rate control should be instituted immediately. Much like patients with pulmonary hypertension, this subset of patients is sensitive to volume status, so euvolemia should be maintained. Infusion of too much volume can quickly compromise oxygenation through pulmonary edema, whereas hypovolemic patients are susceptible to hypotension from inadequate cardiac output. Mitral stenosis management involves walking a fine line between hyper and hypovolemia. If pulmonary edema develops, consideration of diuresis is reasonable to minimize or prevent pulmonary edema.
A key axiom in management includes excellent labor analgesia to prevent tachycardic responses to pain. This is best accomplished with a segmental lumbar epidural. Neuraxial anesthesia minimizes catecholamine-induced increases in heart rate. If a cardiac delivery is attempted, epidural anesthesia is ideal, allowing for both pain control and fetal descent without significant hemodynamic changes. If an epidural is unable to be obtained, a low spinal with opiates is the next best option as it can help curb unfavorable hemodynamic responses. When neuraxial anesthesia is contraindicated, a pudendal nerve block or systemic analgesia with opiates can be considered a last resort.
Cesarean section should also be approached similarly to vaginal delivery. Epidural anesthesia is preferred as the primary means of anesthesia. The prudent anesthesiologist must be cognizant of added dangers of operative delivery such as fluid shifts secondary to anesthesia, operative blood loss, and fluid mobilization associated with the post-partum period. Ephedrine should be avoided as it may produce tachycardia. Low-dose phenylephrine is the vasopressor of choice.
When general anesthesia is necessary, the biggest concerns involve direct laryngoscopy and extubation, as both of these events are associated with potential tachycardia. General anesthesia is best maintained with generous opiates, adequate neuromuscular blockade, and potentially nitrous oxide due to its hemodynamic stability.
Significant aortic stenosis is infrequently encountered in pregnant patients due to the natural progression of the disease. Rheumatic heart disease generally needs several decades to produce clinically significant disease. However, patients with congenital bicuspid or monocuspid valves may have severe aortic stenosis during childbearing years. Severe aortic stenosis is defined as an aortic valve area of fewer than 1 cm and a transvalvular gradient of greater than 50 mmHg. When present in its severe form, there is a high mortality rate for both the mother and fetus. Transvavular gradient pressures increase over the course of pregnancy due to increased blood volume and decreased systemic vascular resistance. Increased transvalvular gradient pressures may be characterized clinically by chest pain, syncope, angina, and poor fetal oxygenation.
Pregnancy decreases systemic vascular resistance, and when combined with aortic stenosis, this can result in decreased diastolic pressures, which may not produce coronary perfusion pressures adequate to meet the increased myocardial oxygen demand from a thickened left ventricular wall. Left ventricular diastolic dysfunction during pregnancy predisposes this subset of patients to left ventricular heart failure and pulmonary edema in the setting of increased circulating volumes.
The most important aspect of anesthetic management of patients with aortic stenosis is maintaining afterload. Phenylephrine is the vasopressor of choice as it is a pure alpha agonist. Intravenous fluids can be used to augment preload, but judicious use is advised as volume overload can result in pulmonary edema. Decreased systemic vascular resistance associated with neuraxial anesthesia should be expected and managed with phenylephrine to increase afterload. Tachycardia should be avoided to ensure adequate left ventricular filling. If aortic stenosis is quite severe, aortic valve area less than 0.3cm, balloon valvuloplasty has been utilized in the past with good outcomes. For patients with a transvalvular gradient greater than 50 mmHg, a pulmonary artery catheter should be utilized.
Segmental epidural anesthesia is the anesthetic of choice but should be pursued with caution as decreases in preload and afterload may not be tolerated in this population. Slow titration of epidural anesthesia is ideal. Another option for the patient population is subarachnoid or intrathecal opioids. Spinal opioids have no cardiovascular effects as they preserve myocardial contractility, preload, and systemic vascular resistance. If general anesthesia is utilized, it should be approached with the same diligence as mitral stenosis patients, avoiding myocardial depression with volatile anesthetics. An opioid-based induction is beneficial when left ventricle function is not ideal.
Compared to stenotic valvulopathy, the regurgitant valvular disease is generally well tolerated during pregnancy; the combination of increased plasma volume with diminished systemic vascular resistance improves cardiac output. Therefore, mitral and aortic regurgitation can actually improve during pregnancy. Unlike aortic stenosis, emphasis is placed on avoiding significant increases in systemic vascular resistance. Neuraxial anesthesia is an excellent choice amongst this population due to further reductions in afterload. Bradycardia should be avoided as it can worsen regurgitation.
Mitral valve insufficiency is the second most common valvular lesion encountered during pregnancy. The pathophysiology of this valvulopathy involves an incompetent mitral valve producing chronic volume overload and dilation of the left ventricle. The decrease in systemic vascular resistance improves flow across the aortic valve. Labor pain, contractions, and surgical stimulation produce increases in vascular resistance, which worsen regurgitation; the feared complication is left ventricular failure. Thus, adequate labor analgesia is the mainstay to combat against increases in afterload.
Aortic regurgitation can be congenital or acquired. Aortic regurgitation results in chronic overloading of the left ventricle resulting in subsequent hypertrophy and dilation with elevated compliance. Hypertrophy results in increased myocardial oxygen demand, which is further worsened by diminished coronary perfusion pressures since diastolic pressure is reduced in aortic insufficiency. Much like mitral regurgitation, the main anesthetic goal is to avoid pain-related catecholamine-induced increases in systemic vascular resistance. Neuraxial anesthesia is desirable in this subset of patients due to diminished afterload associated with the anesthetic.
Right to Left Cardiac Shunt
Cardiac right to left shunt can be seen in uncorrected Tetralogy of Fallot and Eisenmenger syndrome. Eisenmenger's syndrome is a complication of uncorrected left to right intracardiac shunting resulting in increased pulmonary pressures. The increased pressure in the preceding right ventricle reverses the direction of blood flow through the shunt. This condition is often accompanied by persistent arterial hypoxemia. Cardiac right to left shunting is typically associated with congenital heart disease in pregnant patients. In general, this patient population should be considered very high risk, and a cardiac anesthesiologist at a specialized center should be involved in the care of these patients. There is a high mortality rate associated with pregnancy, labor, and delivery, with a mortality rate estimated at 30 to 50%.
Decreases in systemic vascular resistance will increase right to left shunting and result in hypoxia with possible cyanosis. Afterload should be maintained with phenylephrine to reduce shunting. Intraarterial pressure monitoring should be strongly considered. Caution should be executed when titrating oxytocin. Much like in pulmonary hypertension, pulmonary vascular resistance should be minimized with supplemental oxygen and avoidance of oversedation. Paradoxical embolism may occur with an introduction of air via intravenous lines or while placing an epidural utilizing a loss of resistance technique with air; loss of resistance with saline should be utilized to not potentially introduce air into the circulation.
The main anesthetic goal for this patient population is to avoid any decrease in systemic vascular resistance and myocardial depression. Hypotension from any etiology may result in inadequate right ventricular preload that is unable to combat the increased pulmonary artery pressures, thus not allowing proper perfusion of the pulmonary arterial beds. This can result in sudden death from the inability to oxygenate. Anesthesia for labor and delivery is best accomplished through more hemodynamically stable options such as systemic opioid therapy or the administration of sub-arachnoid opioids. For the second stage of labor, caudal epidurals are preferred over lumbar epidurals as caudal epidurals produce less sympathetic blockade. Cesarean section delivery is most safely performed with general anesthetic techniques, emphasizing maintaining systemic vascular resistance and avoiding tachycardia.
Left to Right Cardiac Shunt
The most common cardiac conditions resulting in left to right shunt include atrial and ventricular septal defects. The decreased systemic vascular resistance in pregnancy can actually decrease left to right shunting. Women without pulmonary hypertension and left to right shunt generally tolerate pregnancy well. The increase in blood volume may precipitate heart failure as the patient is in a state of compensatory hypervolemia. Therefore, a strong emphasis on maintaining euvolemia is prudent. Abrupt increases in afterload should be avoided in fear of increasing shunting. This subset of patients is also susceptible to paradoxical air embolism, so filters should be placed on intravenous lines, and loss of resistance with saline rather than air should be used when placing an epidural.
The main emphasis of anesthetic management of this subset of patients is minimizing unnecessary increases in vascular resistance. Increases in either systemic or pulmonary vascular resistance can increase strain on the right ventricle and potentially lead to ventricular failure. Increases in pulmonary vascular resistance specifically can reverse the shunt to a right to left shunt and result in unintended hypoxemia. Anesthesia for labor and delivery is best accomplished with lumbar epidural therapy with slow titration of local anesthetics to prevent sudden changes in vascular resistance. Cesarean section can be safely performed with either epidural or general anesthesia with the same attention to detail.
Multidisciplinary coordination amongst all specialists involved (i.e., obstetricians, anesthesiologists, cardiologists, etc.) is highly advisable. In general, vaginal delivery is usually the safest option without obstetrical indications for cesarean section. Vaginal delivery has a multitude of advantages, such as less blood loss, reduced thrombotic risk, and lower rates of infection. For vaginal deliveries, neuraxial anesthesia is the preferred method of analgesia/anesthesia. It is associated with lower risks of death, cardiac arrest, and anesthetic complications. However, general anesthesia may be a better option in select patients who may not tolerate or may be unable to receive neuraxial anesthesia.
Cesarean section is preferred in all patients suffering from Ehlers-Danlos Type IV, Marfan, or Loeys-Dietz syndrome with a measured aortic diameter >4.5 cm and patients with concurrent bicuspid aortic valve and an aortic diameter >5.0 cm. Mothers with intractable heart failure typically do not tolerate labor well and should be evaluated for cesarean section. Mothers who are on therapeutic anticoagulation and are unable to receive neuraxial anesthesia should receive general anesthesia for Cesarean sections. Otherwise, a properly placed epidural catheter or combined spinal-epidural approach is recommended in most cases.
Another option is a "cardiac vaginal delivery." Utilizing this method involves waiting until complete cervical dilation is attained, then allowing the uterus to "labor down" the fetus instead of instructing the mother to push. Forceps or a vacuum assist device can then be utilized to complete the delivery once the head becomes low enough. Avoidance of the Valsalva maneuver is thought to be hemodynamically favorable in patients with cardiac conditions to avoid reductions in preload and increases in afterload.