61: High-Risk Obstetrics

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CHAPTER 61 High-Risk Obstetrics

Brenda A. Bucklin, MD

1 What is a high-risk pregnancy?

High-risk pregnancies include but are not limited to women with:

image Medical complications (e.g., preeclampsia, diabetes mellitus)
image Fetal complications (e.g., prematurity, intrauterine growth restriction, multiple gestations)
image Intrapartum complications (e.g., maternal fever, abnormal vaginal bleeding)

2 Describe the hypertensive disorders of pregnancy

Hypertensive disorders occur in approximately 5% to 10% of all pregnancies. Preeclampsia, chronic hypertension, preeclampsia superimposed on chronic hypertension, and gestational hypertension are terms used to describe the hypertensive disorders of pregnancy. The term pregnancy-induced hypertension (PIH) is no longer used (Table 61-1).

TABLE 61-1 Hypertensive Disorders of Pregnancy*

image

3 What causes preeclampsia?

Preeclampsia is a disorder of unknown etiology. It is a systemic disorder with heterogeneous causes that are linked to maternal, paternal, fetal, and placental factors. In the first stage of the disease process abnormal placentation occurs in which the spiral arteries fail to dilate with or without atherosis. This results in reduced placental perfusion and release of vasoactive substances.

4 What clinical findings are present in preeclampsia?

The principal features of preeclampsia include hypertension and proteinuria. Edema can be physiologic or pathologic and should not be used in the diagnosis of preeclampsia (see Table 61-1).

5 What conditions contribute to maternal and perinatal mortality in preeclampsia?

Complications result from cerebrovascular hemorrhage, stroke, renal or hepatic failures, liver hemorrhage, disseminated intravascular coagulation, abruptio placentae, and pulmonary edema. These complications occur more frequently in women who develop preeclampsia before 32 weeks’ gestation and in those with preexisting medical comorbidities. Perinatal mortality most often results from prematurity.

6 What is HELLP syndrome?

HELLP syndrome (hemolysis, elevated liver enzymes, and low platelet count) is a complication of preeclampsia. Patients develop a microangiopathic hemolytic anemia associated with thrombocytopenia and elevated liver enzymes. Ten to twenty percent of these patients will have normal blood pressure, making the diagnosis sometimes difficult. Although HELLP syndrome is not an indication itself for immediate cesarean delivery, delivery is the only definite treatment for preeclampsia. Patients who develop laboratory evidence of disseminated intravascular coagulation are delivered immediately, regardless of gestational age.

7 How is preeclampsia managed?

Magnesium sulfate is the drug of choice for seizure prophylaxis. Although magnesium has no substantial effect on blood pressure after a bolus dose and the mechanism for the anticonvulsant activity of magnesium is unknown, it attenuates the vascular responses to endogenous and exogenous pressor substances. It also dilates the vascular beds. Other anticonvulsants (e.g., phenytoin, diazepam) have been evaluated, but magnesium sulfate therapy is more effective in preventing recurrent seizures than either phenytoin or diazepam. The benefit of magnesium sulfate administration in women with mild disease is unclear. However, women with severe disease should received magnesium sulfate prophylaxis during labor and after delivery. Acute severe hypertension should be treated to prevent cerebrovascular and cardiovascular complications. Blood pressures should not be normalized. However, blood pressures of at least 160/105 mm Hg should be treated with antihypertensive medications. Because uteroplacental perfusion is proportionate to blood pressure, precipitous decreases in blood pressure can cause fetal compromise.

Antihypertensive agents should be titrated. Although hydralazine is the most commonly administered agent, it was recently compared to intravenous labetalol or oral nifedipine in a metaanalysis of trials. In the systematic review labetalol or nifedipine therapies were as effective as hydralazine in controlling blood pressure with fewer side effects. Labetalol is representative of a class of drugs that act as competitive antagonists at both α- and β-adrenergic receptors. Although systemic vascular resistance is reduced, cardiac output is maintained. Labetalol has also been shown to preserve uteroplacental perfusion. Hydralazine, an arteriolar vasodilator, remains a popular drug for patients with preeclampsia because it increases renal and uterine artery blood flow. The onset and duration are often unpredictable. Side effects include reflex tachycardia and ventricular dysrhythmias. Nifedipine is a calcium channel blocker that prevents the release of calcium, resulting in smooth muscle relaxation. Sodium nitroprusside is another alternative antihypertensive most often administered to patients with refractory hypertension and severe hypertension. Sodium nitroprusside administration requires placement of an arterial catheter to facilitate continuous assessment of maternal blood pressure. Advantages include a fast onset and short duration. It also preserves uteroplacental perfusion. Side effects include reflex tachycardia, cerebral vasodilation, and potential cyanide toxicity.

8 What are the indications for invasive monitoring?

In severe preeclampsia there is no proven benefit of invasive hemodynamic monitoring. Although the indications for invasive central monitoring remain controversial, most agree that the accepted indications include:

image Refractory hypertension.
image Pulmonary edema.
image Refractory oliguria unresponsive to fluid challenge.
image Severe cardiopulmonary disease (Table 61-2).

TABLE 61-2 Indications for Invasive Monitoring in Preeclampsia

Refractory pulmonary edema
Pulmonary edema
Refractory oliguria unresponsive to fluid challenge
Severe cardiopulmonary disease

9 What potential problems may occur in patients receiving magnesium sulfate?

The therapeutic range of magnesium sulfate is 4 to 8 mEq/L. As plasma concentrations increase, patients develop electrocardiogram changes with widening of the QRS complex and prolonged QT interval. Deep tendon reflexes are absent at 10 mEq/L; sinoatrial block and respiratory paralysis occur when concentrations are 15 mEq/L; cardiac arrest occurs at 25 mEq/L. In therapeutic doses magnesium sulfate increases sensitivity to muscle relaxants, especially nondepolarizing muscle relaxants. Because magnesium sulfate also crosses the placenta, newborns may demonstrate decreased muscle tone, respiratory depression, and apnea. Magnesium toxicity is treated with intravenous calcium.

10 What are the anesthetic considerations in patients with preeclampsia?

Before initiation of neuraxial anesthesia, evaluation of coagulation status is recommended. Because thrombocytopenia is the most common coagulopathy in preeclampsia, a screening platelet count is recommended. Although an arbitrary platelet count of 100,000 is often suggested, the actual platelet count safe for spinal or epidural placement is unknown.

Spinal anesthesia has been controversial in patients with severe preeclampsia because of the potential risk of sudden hypotension with rapid onset of sympathetic blockade, but there is growing support for its administration for cesarean delivery. It may be preferable to general anesthesia when the patient does not have an existing epidural catheter or there is insufficient time because of nonreassuring fetal heart rate tracing.

11 What is eclampsia?

Eclampsia is defined as peripartum convulsions and/or coma not caused by coincident neurologic disease. Eclampsia is usually preceded by preeclampsia. Symptoms of headache, visual disturbance, and epigastric pain often precede seizure activity. Seizure activity often begins with facial twitching and generalized tonic-clonic seizures developing within seconds.

12 How are eclamptic seizures treated?

Intrauterine resuscitation and maternal airway management are of overriding importance. The initial management of seizure activity includes:

image Supplemental oxygen
image Airway support vs. intubation
image Lateral positioning
image Sodium thiopental 50 to100 mg (terminates seizure activity)
image Supplemental magnesium sulfate
image Intrauterine resuscitation

13 Discuss preterm labor

Infants delivered between 20 and 37 weeks after the first day of the last menstrual period are defined as preterm. In the United States preterm delivery accounts for 69% to 83% of neonatal deaths. Preterm labor is associated with placental abruption, uterine abnormalities, multiple gestations, premature rupture of the membranes, urinary tract, systemic, or gynecologic infection.

14 What is the treatment of preterm labor?

Calcium channel blockers, magnesium sulfate, cyclooxygenase inhibitors and β-mimetic tocolytics have all been used to treat preterm labor. Nifedipine is being used more frequently because of its low incidence of significant maternal and fetal side effects and ease of administration.

15 Discuss antepartum hemorrhage

Placenta previa, placental abruption, uterine rupture, and vasa previa are all causes of antepartum hemorrhage. Placental abruption is a separation of the placenta most often accompanied by vaginal bleeding, uterine tenderness, and increased uterine activity. Uterine rupture is a defect in the uterine wall that results in fetal distress and/or maternal hemorrhage. Vasa previa is of no threat to the mother; however, there is a velamentous insertion of the cord where the fetal vessels traverse the fetal membranes ahead of the presenting part. Rupture of these vessels can cause fetal exsanguination. Patients with antepartum hemorrhage are also at risk for postpartum hemorrhage. Underestimation of blood loss is a frequent problem in such cases.

16 What is placenta previa?

Placenta previa occurs when the placenta implants before the presenting part. Classification depends on the relationship between the cervical os and placenta. Several factors are associated with placenta previa: uterine trauma, multiparity, prior cesarean delivery or other uterine surgery, advanced maternal age, and a prior history of placenta previa. Painless vaginal bleeding occurs in the second or third trimester and is not related to any particular event. A lack of abdominal pain and no change in uterine activity differentiate it from placental abruption. The first episode of bleeding rarely causes shock or fetal compromise.

17 What is postpartum uterine atony? How is it managed?

Uterine atony is a failure of contraction and involution of the uterus. It can result in severe hemorrhage. It is frequently associated with the following conditions:

image Multiple gestations
image Macrosomia
image Polyhydramnios
image High parity
image Prolonged labor
image Chorioamnionitis
image Precipitous labor
image Augmented labor
image Tocolytic agents

Obstetric management includes bimanual compression, uterine massage, and uterotonics. Oxytocin is the first-line therapy. It is a synthetic hormone that is administered intravenously (20 to 50 units/1000 ml crystalloid). Bolus administration (5 to 10 units intravenously) produces vasodilation that can result in hypotension in hypovolemic patients. Methylergonovine is an ergot alkaloid preparation and is administered intramuscularly in a dose of 0.2 mg. It is contraindicated in hypertensive disorders, peripheral vascular disease, and ischemic heart disease. 15-Methylprostaglandin F2α is administered intramyometrially or intramuscularly (250 mcg) for the treatment of refractory uterine atony. Side effects include bronchospasm, disturbed ventilation-perfusion ratios, increased intrapulmonary shunt fraction, and hypoxemia. Uterine atony refractory to these agents may require surgical ligation of arteries, embolization of arteries supplying the uterus, and hysterectomy.

18 Discuss diabetes and its anesthetic considerations

Pregnant patients with diabetes are at risk for preeclampsia, polyhydramnios, fetal macrosomia, fetal malformations, and cesarean delivery. Pregestational diabetes is associated with preterm labor and delivery. Glycemic control and treatment of hypotension with nonglucose-containing crystalloids and ephedrine or phenylephrine are helpful in preserving fetal acid-base status during neuraxial anesthesia for labor and delivery.

19 What causes disseminated intravascular coagulation in obstetric patients?

Disseminated intravascular coagulation results from abnormal activation of the coagulation cascade with formation of large amounts of thrombin, depletion of coagulation factors, activation of the fibrinolytic system, and hemorrhage. In obstetrics, the most frequent causes are preeclampsia, sepsis, fetal demise, abruptio placentae, sepsis, and amniotic fluid embolism.

20 What types of renal diseases are most frequently seen in obstetric patients?

Two groups of disorders occur: glomerulopathies (nephritic and nephrotic syndromes) and tubulointerstitial diseases. Nephritic syndromes are disorders that involve necrotizing or inflammatory lesions. Nephrotic syndromes involve abnormal permeability to proteins. Tubulointerstitial disease is characterized by abnormal tubular function, resulting in abnormal urine composition and concentration.

21 How is anesthetic management affected in patients with renal disease?

Management is dependent on the extent of renal disease and severity of hypertension. Patients with mild-to-moderate disease, well-controlled hypertension, and stable renal function require minimal-to-no special considerations. However, patients with end-stage disease require careful monitoring of volume and cardiac status. In addition, these patients are at risk for hyperkalemia, hypoalbuminemia, hypertension, anemia, metabolic acidosis, hypocalcemia, and hyperphosphatemia.

22 Which cardiac disease most commonly complicates pregnancy?

Congenital heart disease is the most common cardiac disease in pregnant women in the United States. It accounts for approximately 60% to 80% of cardiac disease during pregnancy.

23 How is congenital heart disease managed during pregnancy?

Pulmonary artery catheterization is rarely required for most patients with congenital heart disease. Intrathecal opioid injections are good choices for labor analgesia when patients will not tolerate decreased systemic vascular resistance and decreased venous return. Epidural anesthesia is contraindicated in few, if any cardiac lesions, provided that the induction of anesthesia is slow and hemodynamic changes are treated promptly. Single-injection spinals for cesarean delivery are contraindicated in many patients with congenital heart disease.

KEY POINTS: High-Risk Obstetrics image

1. Maternal morbidity and/or mortality from hypertensive disorders most often results from cerebrovascular and cardiovascular complications.
2. In preeclampsia hypertension should be treated, but blood pressure should not be normalized.
3. Indications for invasive central monitoring in preeclamptic patients include: (1) refractory hypertension, (2) pulmonary edema, (3) refractory oliguria unresponsive to fluid challenge, and (4) severe cardiopulmonary disease.
4. Uterine atony is the most common cause of postpartum hemorrhage and often results in substantial blood loss.

Website image

Society for Obstetric Anesthesia and Perinatology

http://www.soap.org

SUGGESTED READINGS

1. Beilin Y., Reid R.W. Renal disease. In: Chestnut D.H., Polley L.S., Tsen L.C., Wong C.A., editors. Obstetric anesthesia: principles and practice. ed 4. Philadelphia: Elsevier Mosby; 2009:1095-1107.

2. Harnett M., Tsen L.C. Cardiovascular disease. In: Chestnut D.H., Polley L.S., Tsen L.C., Wong C.A., editors. Obstetric anesthesia principles and practice. ed 4. Philadelphia: Elsevier Mosby; 2009:881-912.

3. Mayer D.C., Smith K.A. Antepartum and postpartum hemorrhage. In: Chestnut D.H., Polley L.S., Tsen L.C., Wong C.A., editors. Obstetric anesthesia principles and practice. ed 4. Philadelphia: Elsevier Mosby; 2009:811-836.

4. Polley L.S. Hypertensive disorders. In: Chestnut D.H., Polley L.S., Tsen L.C., Wong C.A., editors. Obstetric anesthesia principles and practice. ed 4. Philadelphia: Elsevier Mosby; 2009:975-1007.

5. Practice Guidelines for obstetric anesthesia: An updated report by the American Society of Anesthesiologists Task Force on Obstetric Anesthesia. Anesthesiology, 106. 2007:843-863.

6. Practice Guidelines for pulmonary artery catheterization: an updated report by the American Society of Anesthesiologists Task Force on Pulmonary Artery Catheterization. Anesthesiology, 99. 2003:988-1014.

7. Sibai B.M. Hypertension. In: Gabbe S.G., Niebyl J.R., Simpson J.L., editors. Obstetrics: normal and problem pregnancies. ed 5. Philadelphia: Churchill Livingstone; 2007:864-912.

8. Visalyaputra S., Rodanant O., Somboonviboon W., et al. Spinal versus epidural anesthesia for cesarean delivery in severe preeclampsia: a prospective randomized, multicenter study. Anesth Analg. 2005;101:862-868.

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