Pregnancy in any woman is a physiological challenge, but in women with congenital heart disease (CHD) it may pose considerable risks to both mother and fetus. Cardiac disease remains the most common cause of indirect maternal death in the United Kingdom, with mortality rates significantly higher in the latest report of the Confidential Enquiries into Maternal Deaths than those in the 1980s (RR: 2.22, 95% CI: 1.36 to 3.61, p = .001). It was noted that, although many cardiac deaths may not have been preventable, there was often a lack of prepregnancy counseling, involvement of cardiologists, and communication between specialists—including anesthetists and intensivists.
Anesthetic (and to a lesser extent, analgesic) techniques may superimpose alterations in cardiovascular function on to an already critical, or near-critical, pathophysiological state in such patients. In this chapter we outline the important physiological changes in pregnancy that are particularly relevant for anesthesia and analgesia and some practical aspects of anesthetic techniques that are used.
Physiological Changes in Pregnancy
Major cardiovascular changes are seen from 6 weeks of gestation. By 20 weeks of gestation, cardiac output increases by 40% and blood volume increases by 45%. A reduction in systemic vascular resistance (SVR) can encourage right-to-left shunt in certain conditions. Blood pressure falls by 20% by 20 weeks of gestation then returns to preconception levels during the third trimester. Pulmonary blood flow increases, but a reduction in pulmonary vascular resistance (PVR) ensures that pulmonary arterial pressure (PAP) does not increase. In women with pulmonary hypertension the normal reduction in PVR during pregnancy may not occur, leading to a further rise in PAP. Structural remodeling of the myocardium occurs and takes up to a year to regress after pregnancy. Some women with CHD are left with permanent deterioration in ventricular function. In labor, cardiac output is further increased by up to 40% during contractions. Immediately after delivery there is an autotransfusion of approximately 500 mL blood from the contracted uterus, although bleeding offsets this to a variable degree. There is a physiological anemia in pregnancy caused by a greater increase in plasma than red blood cell volume. Thromboembolic risk is increased sixfold during pregnancy and 11-fold in the puerperium.
In a parturient with CHD these physiological changes can lead to cardiovascular compromise from early pregnancy.
Planning
A successful outcome for mother and baby demands early risk assessment, meticulous and frequent antenatal care, and multidisciplinary consultation for planning of delivery and postnatal care. The importance of prepregnancy counseling, at which the particular risks posed by the patient’s condition can be discussed and prepregnancy optimization planned, cannot be overstated. Some patients will be advised to avoid pregnancy altogether.
Anesthetic or analgesic intervention during labor is usually necessary for patients with CHD, except those with the lowest risk. Traditional management used to favor elective cesarean section under general anesthesia. However, spontaneous vaginal delivery (SVD) is now preferred for the majority of women with CHD because cesarean section incurs increased risks of hemorrhage, infection, and thromboembolism and leads to more dramatic fluid shifts. Thus in most cases, cesarean section should be undertaken for obstetric indications or for particularly high risk cardiac lesions only, such as unstable aortic lesions with risk of dissection. It must be remembered that, despite aiming for a SVD, a proportion of deliveries will culminate in emergency surgical procedures with the hazards this entails. Emergency cesarean section should also be discussed and planned for in the antenatal period. Appropriate cardiovascular monitoring during labor should be considered in the antepartum period, with noninvasive blood pressure measurement, continuous oxygen saturation, and electrocardiogram monitoring used for all patients. Invasive blood pressure monitoring can be usefully added for patients at higher risk with minimal risks aside from maternal discomfort and restriction of movement. Consideration should be given to the most suitable location for delivery and whether cardiothoracic surgeons and cardiac anesthetists should be on site. A high dependency unit should always be available.
Analgesia for Labor
Effective regional analgesia is the main reason that vaginal delivery has become the preferred option for the majority of women with CHD because it reduces the pain-related cardiovascular stress of labor. Therefore it should be recommended to most women unless there are contraindications. Unlike alternative methods of pain relief, epidural analgesia can abolish pain and its associated cardiovascular effects and allows controlled management of the second stage (delivery of the baby) without, or with minimal, active pushing from the mother, avoiding the associated prolonged major Valsalva maneuver. The lower concentrations of local anesthetic used for modern epidural analgesia cause minimal hypotension and, with careful titration and monitoring, are safe and effective for most patients with CHD.
Regional analgesia may be contraindicated (eg, concurrent anticoagulation therapy or patient choice). Other analgesic techniques are available but provide less effective pain relief and may be less suitable. Nitrous oxide in a 50:50 mix with oxygen (Entonox) may be helpful in up to 50% to 70% of women. It commonly causes nausea and vomiting. Intramuscular pethidine and diamorphine are commonly used because midwives are able to prescribe and administer them, although they provide only modest reductions in labor pain. More recently, the short-acting opioid remifentanil, given intravenously via a patient-controlled pump, has become established as an alternative. This affords improved analgesia over pethidine and nitrous oxide but does not produce the same quality of analgesia and therefore cardiovascular benefit as regional analgesia. In addition, there have been case reports of profound respiratory depression and collapse if monitoring is not scrupulously applied.
Vaginal Delivery
The second stage of delivery (from full dilatation to birth of baby) should be planned before labor. This will usually involve a specified time of pushing (if allowed) with or without instrumental assistance. Management of the third stage (delivery of the placenta) and control of uterine bleeding need to be considered because the side effects of uterotonic drugs must be weighed against the risk of postpartum hemorrhage. In women without cardiac disease, Syntocinon is routinely given as a slow initial bolus, with an infusion commenced for those at risk of uterine atony and hemorrhage. Even in these healthy patients, Syntocinon causes vasodilation and decreases mean arterial pressure by 30% and SVR by 50%. Cardiac output increases by 50% to compensate for this through an increase in heart rate and stroke volume. In cardiac patients this degree of vasodilation and tachycardia can be dangerous. Options include giving a reduced dose initially, omitting the initial dose and using an infusion only, or using a lower dose infusion. A case-by-case decision is required, but standard care for women with CHD at the authors’ institution involves a lower-dose infusion only.
Other available uterotonics include carbetocin, ergometrine, carboprost, and misoprostol. Carbetocin is a long-acting synthetic oxytocin analogue with a similar side-effect profile to Syntocinon. Ergometrine leads to systemic and pulmonary vasoconstriction; it may be appropriate to use intramuscularly (or very cautiously, intravenously) in selected cases, such as aortic stenosis. It is usually avoided in women with hypertensive disease and should not be given in patients with pulmonary hypertension. Carboprost is associated with gastrointestinal upset, bronchospasm and, rarely, hypertension, cardiovascular collapse, and pulmonary edema; it is usually avoided in cardiac patients. Misoprostol can lead to pyrexia and shivering; there has been limited study of its use in cardiac patients, although its side effects do not cause immediate concerns. Nonpharmaceutical methods of hemorrhage control should also be considered in advance, such as intrauterine balloon tamponade and/or compression sutures.
Anesthesia for Cesarean Section and Other Procedures
The majority of cesarean sections in the United Kingdom are performed using regional anesthesia (in our institution, 99% of elective cases and 93% of emergencies). It is generally accepted that maternal mortality is reduced by avoiding the use of general anesthesia, in particular the risk of a difficult airway or aspiration of gastric contents. The advantages and disadvantages of regional and general anesthesia are summarized in Table 23.1 .
| Regional Anesthesia | General Anesthesia | |
|---|---|---|
| Advantages | Mother awake for delivery of baby Partner may be present Avoids risks of general anesthesia Allows slow titration of drugs against response Better analgesia postoperatively Less nausea/vomiting postoperatively Less blood loss | Avoids maternal intraoperative anxiety Not affected by anticoagulation issues Can give 100% oxygen if required Invasive monitoring easier to site Can apply DC cardioversion easily if necessary Avoids risk of inadequate/high block Allows tracheobronchial suction Easy transition to postoperative ventilation if required |
| Disadvantages | Maternal intraoperative anxiety may have deleterious cardiovascular effects Lying flat may be difficult to tolerate Anticoagulation issues Risk of headache Risk of inadequate block Risk of high block with impaired coughing/breathing and risk of aspiration Marked decrease in systemic vascular resistance; risk of severe hypotension (especially in patients with fixed cardiac output) or worsening hypoxemia (in patients with right-to-left shunts) Inability to give 100% oxygen Discomfort if operative time is long | Failed/difficult tracheal intubation Aspiration of gastric contents Cardiovascular stress from tracheal intubation/extubation Cardiac depressant effect of anesthetic agents Risk of awareness Propensity for nitrous oxide to expand air bubbles (important in patients with right-to-left shunts, who are at risk from systemic air embolism) Volatile anesthetic agents may relax the uterus Fetal and maternal opioid-induced respiratory depression Increased risk of postoperative atelectasis Increased risk of postoperative venous thromboembolism More pain/nausea/vomiting postoperatively Greater blood loss |
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