I Obstetric complications
From 1990 to 2005, the maternal mortality rate in the United States was 15 per 100,000 live births. The most common causes of maternal death include hemorrhage, embolic disorders, preeclampsia, infection, and cardiomyopathy.
1. Abnormal placental implantation
a) Introduction
(1) The placenta normally implants into the endometrium. A placenta implanted on or in the myometrium, the underlying muscular layer of the uterus, is termed placenta accreta (on the myometrium), placenta increta (into the myometrium), or placenta percreta (completely through the myometrium).
(2) Any of these abnormal placental implantations means that separation of the placenta from the uterine wall will be difficult and may be accompanied by severe bleeding.
(3) Placenta accreta, placenta increta, and placenta percreta are commonly associated with placenta previa and are more common in women who have had a previous C-section than in those who have not.
2. Blood loss
a) Introduction
(1) Blood loss is difficult to estimate in obstetric patients. Often, lost blood is hidden inside the patient’s body, soaked in laparotomy sponges, absorbed by drapes, or spilled onto the floor.
(2) In general, approximately 500 mL is lost during a spontaneous vaginal delivery and approximately 700 mL during a C-section with general anesthesia; 1500 mL or more is lost if a hysterectomy is performed during C-section.
(3) Because the term parturient has a 50% increase in blood volume, a great amount of blood can often be lost before the vital signs begin to change in response to the loss; 15% of the total blood volume may be lost without the occurrence of any compensatory tachycardia or vasoconstriction.
3. Breech presentation
a) Introduction
(1) Many obstetricians now choose to deliver fetuses in breech presentations by C-section. In this case, C-section usually is elective, and either a regional or a general anesthetic can be used.
(2) If the baby is to be delivered vaginally, an epidural anesthetic may be requested and is considered strongly indicated at some centers.
(3) The muscle relaxation that it provides is helpful, and analgesia is required, at least for the forceps delivery of the fetal head.
4. Cesarean hysterectomy
a) Introduction
(1) After delivery, when hemostasis is unobtainable despite the use of some combination of oxytocin, ergot alkaloids, and prostaglandin, the surgeon performs a hysterectomy to stop uterine bleeding.
(2) An atonic uterus, especially an incised uterus, can lose several liters of blood within a few minutes, outpacing the ability of even the most prepared anesthesia providers to replace intravascular volume.
(3) Anesthesia at this point becomes trauma anesthesia, the primary purpose of which is the maintenance of vital signs, vital organ perfusion, and oxygenation; maternal analgesia and amnesia are important but secondary concerns. Etomidate, ketamine, benzodiazepines, and opioids are useful because they cause minimal hemodynamic depression.
5. Disseminated intravascular coagulation
a) Introduction
(1) Disseminated intravascular coagulation (DIC) is frequently associated with three obstetric problems: retention of a dead fetus, placental abruption, and amniotic fluid embolism.
(2) Circulatory shock, which often accompanies DIC, worsens the problem by decreasing peripheral and hepatic blood flow and causing further cell damage. Renal failure may result from the deposit of fibrin and cellular debris in the filtration system.
b) Anesthetic technique
(1) Patients with DIC need fluid resuscitation, and they almost always are hemorrhaging. Increasing intravascular volume dilutes activated clotting factors and slows the clotting process. Increased peripheral and hepatic perfusion limits cellular damage and improves clearance of activated clotting factors.
(2) Because the patient is bleeding and many clotting factors are depleted, it appears as if repletion of clotting factors is necessary; however, administration of clotting factors fuels an already out-of-control coagulation process.
6. Embolism
a) Introduction
(1) Thromboembolism
(a) Thrombotic pulmonary embolism occurs in pregnant individuals fivefold more often than it does in nonpregnant individuals and is more likely to occur postpartum than antepartum.
(b) It is associated with prolonged inactivity, cesarean delivery, obesity, and increasing age and parity.
(c) Presentation varies from a few minor complaints to massive cardiovascular collapse. Pleuritic chest pain, dyspnea, hyperventilation, hypocapnia, coughing, hemoptysis, and distention of neck veins are associated with the disorder.
(2) Venous air embolism
(a) Venous air embolism can occur during labor, spontaneous vaginal delivery, and operative delivery and is frequently associated with placenta previa.
(b) The overall incidence of subclinical venous air embolism in parturients has been reported to be as high as 29% during general anesthesia; the incidence in the parturient may be as high as 97%.
(3) Amniotic fluid embolism
(a) Although rare, amniotic fluid embolism is almost uniformly fatal. It may occur during labor, vaginal delivery, or operative delivery and is associated with placental abruption.
(b) The pathogenesis is almost identical to that of venous air embolism except that patients who develop amniotic fluid embolism are prone to develop DIC if they survive the initial embolism.
(c) Signs and symptoms of amniotic fluid embolism include a chill, shivering, anxiety, cough, dyspnea, cyanosis, tachypnea, pulmonary edema, and cardiovascular collapse. O2 saturation has been reported to decrease quickly.
b) Anesthetic technique
(1) The incidence of postpartum thromboembolism can be affected by anesthetic interventions. C-sections performed with general anesthesia are associated with accelerated maternal coagulation compared with those performed with regional anesthesia, so the use of regional anesthesia may help reduce the incidence of postoperative thromboemboli.
(2) The anesthesia provider can help prevent prolonged inactivity in those who have had a C-section by providing analgesia sufficient to allow comfortable ambulation. Use of epidural opioid analgesia is often an appropriate solution to this problem. It may be specifically indicated in those at risk for thromboembolism even if it must be administered after a general anesthetic has been given.
(3) If embolism is suspected during spontaneous or operative delivery, the obstetrician should be informed immediately. The obstetrician can take steps to stop the entrainment of air or amniotic fluid, which include flooding the surgical field with saline, returning the uterus to within the abdomen, and stimulating uterine contractions.
(4) One hundred percent O2 should be administered by positive-pressure ventilation through a cuffed endotracheal tube.
(5) An arterial line may be needed for monitoring of oxygenation and blood pressure. IV fluids are administered as needed to bolster central venous pressure.
(6) A generous preload is necessary to enable the right side of the heart to pump volume forward against increased pulmonary vascular resistance.
(7) If the fetus has not been delivered, left uterine displacement improves uterine blood flow and facilitates venous return to the heart. Pharmacologic support of the cardiovascular system is likely to be needed.
(8) Patient position has been suggested to hinder the movement of the foreign substance into the pulmonary arteries. A slight anti-Trendelenburg (head-up) position with left lateral tilt of at least 15 degrees is designed to trap air in the right atrium, from which it can be aspirated via a central venous catheter. Unfortunately, it often is difficult to place the patient in this position and insert a central line in time to prevent pulmonary artery embolization.
(9) In the case of amniotic fluid embolism, prompt recognition and action are necessary to prevent maternal mortality. Immediate support of maternal circulation are necessary. Inotropic support should not be delayed (epinephrine, dopamine). Treatment for coagulopathy must also begin immediately and ideally with the consultation of a hematologist. Large-volume infusion devices may also be helpful for the resuscitation effort.
7. Multiple gestation
a) Introduction
(1) Multiple-gestation pregnancies carry higher risk for the both mother and fetuses than singleton pregnancies. Many of the risk factors affect anesthetic management.
(2) Multiple-gestation pregnancies, especially rare monoamniotic pregnancies, are associated with complications requiring emergent surgical intervention more often than singleton pregnancies.
(3) The anesthesia provider should constantly be prepared to provide anesthesia for an emergency C-section. The multiple fetuses are often small and premature.
(4) The large uterus compounds the problems of aortocaval compression; therefore left uterine displacement should be maintained at all times when the parturient is not lying on her side.
(5) If the fetuses are to be delivered vaginally, an epidural is valuable for maternal analgesia and neonatal safety. Because the neonate often is small and premature, a slow, controlled delivery through a well-relaxed birth canal makes birth trauma less likely.
(6) The epidural provides pelvic relaxation and reduces maternal discomfort, decreasing the likelihood that pain will induce a forceful reflexive expulsion of the fetus.
(7) Either regional or general anesthesia is appropriate for a C-section. After the babies have been delivered, the uterus may not contract well because it has been overstretched for many weeks.
(8) Larger-than-usual doses of oxytocin may be needed to induce the uterus to contract well and to stop bleeding. However, it is imperative that oxytocin administration not be started until after all the neonates have been delivered. Strong uterine contractions before the delivery of all neonates deprive any remaining fetuses of blood supply and oxygenation.
8. Placental abruption
a) Introduction
(1) Abruption occurs when the placenta begins to separate from the uterus before delivery; this allows bleeding behind the placenta and jeopardizes the fetal blood supply.
(2) Placental abruption results in bleeding (often hidden), uterine irritability (often hypertonic), abdominal pain, and fetal distress or death.
(3) Open venous sinuses in the uterine wall may allow products of hemostasis and amniotic fluid to enter the maternal circulation; this results in an incidence of DIC of up to 50%.
b) Anesthetic technique
(1) In cases of placental abruption without fetal distress, vaginal delivery may still be possible. Because fetal distress can occur without warning, the anesthesia provider should be prepared to administer anesthesia for an emergency C-section.
(2) Taking an anesthetic history as soon as the diagnosis of placental abruption becomes known and checking for adequate IV access is recommended. If the mother is unstable or if fetal distress is present, operative delivery is necessary.
(3) Regional anesthesia usually is not indicated because of the potential for coagulopathy and because of the uncertainty of uteroplacental blood flow and therefore of fetal oxygenation.
(4) Generous venous access should be established as soon as possible. Although placental abruption does not usually result in sudden blood loss, a large volume of blood may be lost.
(5) When abruption results in fetal death, the volume of lost maternal blood can be as great as 5 L, all of which may be concealed. Volume resuscitation should begin as soon as IV access has been secured. Large volumes of crystalloid and colloid solutions and of red blood cells may be needed.
(6) General anesthesia can be induced with ketamine, up to 1 mg/kg. If the uterus is hypertonic, another drug should be chosen because the use of ketamine may further increase uterine tone, decreasing fetal O2 supply.
(7) An alternate choice is etomidate, 0.3 mg/kg. If uterine tone is excessive, a volatile inhalation agent may be useful for maintenance of anesthesia and uterine relaxation.
9. Placenta previa
a) Introduction
(1) When the placenta has implanted on the lower uterine segment and either partially or completely covers the opening of the cervix, placenta previa is present.
(2) Placenta previa has an incidence of up to 1%, and the mortality rate for those with it approaches 1%.
(4) It most often results in painless vaginal bleeding before the onset of labor that may stop without intervention or hemodynamically significant blood loss. The potential exists, however, for sudden loss of large amounts of blood.
b) Anesthetic technique
(1) The diagnosis of placenta previa normally indicates an operative delivery. The anesthesia provider should prepare for heavy blood loss.
(2) The anesthesia provider may choose either a general or regional anesthetic technique, taking into consideration the parturient’s current volume status and the potential for blood loss.
10. Postpartum bleeding
a) Introduction
(1) Postpartum bleeding in moderate amounts is a normal event. Excessive bleeding may occur because of uterine atony (which accounts for 80% of all postpartum bleeding), placental retention, abnormalities of the uterus, lacerations of the delivery channel, uterine inversion, and abnormalities of coagulation.
(2) Uterine atony is associated with multiparity, prolonged infusions of oxytocin before delivery, polyhydramnios, and multiple gestation.
(3) A retained placenta or retained placental fragments must be removed manually to stop the bleeding. In the past, this has often required the administration of an inhalation agent for uterine relaxation.
(4) Nitroglycerin, a potent uterine relaxant with a relatively short duration of action, has been used successfully to provide uterine relaxation adequate for placental extraction. A dose of approximately 1 mcg/kg IV appears to be adequate.
(5) Sublingual nitroglycerin spray has also been used effectively and offers the added benefits of long shelf life and a ready-to-use preparation. Because nitroglycerin is a potent venodilator when given at low doses and is an arteriolar dilator when administered intravenously at a rate of 1 mcg/kg/min or higher, care should be taken to ensure that intravascular volume is adequate before this drug is administered.
b) Anesthetic technique
(1) When postpartum bleeding is excessive, the anesthesia provider performs fluid resuscitation while simultaneously working with the obstetrician to eliminate the cause of the bleeding. Fundal massage, IV oxytocin, IM methylergonovine maleate, or IM prostaglandin often is all that is needed. In some cases, anesthesia may be necessary for an additional procedure.
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