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Labor and Delivery
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LABOR AND DELIVERY
Yaakov Beilin, MD
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27-year-old woman presents to the delivery suite in labor after an uncomplicated pregnancy. A lumbar epidural catheter is placed at the L4–L5 interspace to facilitate analgesia. After an adequate trial of labor, the obstetricians elect to perform a cesarean section for cephalopelvic disproportion. A T4 level of anesthesia is achieved via the epidural catheter and the cesarean section is initiated. Immediately after delivery of the baby, maternal hemorrhage becomes severe.
QUESTIONS 1. What options are available to the mother for labor analgesia? 2. Explain the advantages and disadvantages of various regional anesthetic techniques for labor and delivery. 3. What is a “walking epidural”? 4. Describe the regional anesthetic techniques that can be employed for cesarean section. 5. Outline the treatment for postdural puncture headache. 6. What are the advantages and disadvantages of general anesthesia for cesarean section? 7. Describe the elements of placental drug transfer. 8. What techniques can be used for post-cesarean pain relief?
9. Outline the differential diagnosis of postpartum hemorrhage. 10. Explain the risk factors, presentation, and treatment of uterine atony. 11. Describe the presentation and treatment of retained placenta.
1. What options are available to the mother for labor analgesia? Many techniques have been utilized to reduce the perception of pain during labor. In addition to systemic medications, inhalation agents, and regional anesthesia, hypnosis, psychoprophylaxis, acupuncture, and transcutaneous electrical nerve stimulation (TENS) have been used. Systemic opioids can be used to attenuate labor pains; however, low-dose opioids do not completely eliminate the pain. Meperidine is the most frequently used opioid for labor analgesia. Intravenous meperidine peaks in about 10 minutes and lasts approximately 3–4 hours. Neonates born within 2 hours of maternal administration of meperidine are at risk for respiratory depression. Morphine is rarely used during labor because neonates are extremely sensitive to its respiratory depressant effect. Remifentanil can be used as part of patient-controlled analgesia (PCA) during labor. The advantage of remifentanil is that its onset and duration of action are shorter than those of meperidine. However, it is also more potent and close maternal respiratory monitoring is required, preferably with pulse oximetry. 347
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The goal of inhalation analgesia during labor is to achieve analgesia without depressing airway reflexes. Typically, at the beginning of each contraction the mother, using a hand-held device, self-administers the anesthetic agents. The most commonly used vapors are nitrous oxide and enflurane. Although this technique provides moderately good analgesia, it is not commonly used because of the risk of maternal aspiration with deep levels of anesthesia. Regional anesthesia, epidural or combined spinalepidural, have become popular modalities for labor analgesia because of their safety and efficacy profile.
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2. Explain the advantages and disadvantages of various regional anesthetic techniques for labor and delivery. Rational use of regional anesthesia necessitates an understanding of the pain pathways involved during labor. Labor is traditionally divided into three distinct stages: ■
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First stage: begins with the onset of regular contractions and ends with complete cervical dilation. Second stage: begins when the cervix is completely dilated and ends with delivery of the fetus. Third stage: begins after delivery of the fetus and concludes with delivery of the placenta.
The first stage of labor is associated with uterine and cervical pain mediated by spinal segments T10–L1 (Fig. 59.1). Local anesthetics administered to the epidural, spinal, or caudal spaces readily anesthetize these pain pathways. In addition, subarachnoid opioids and paracervical blocks can be used for pain relief during the first stage of labor. Caudal anesthesia is rarely used because of the risk of inadvertent fetal scalp penetration and the associated high fetal levels of local anesthetic. The second stage of labor is associated with perineal and vaginal distention mediated by spinal segments S2–S4. Epidural, spinal, and caudal anesthetics are also effective during the second stage of labor. In addition, pudendal nerve blocks can be used for second-stage analgesia. Epidural analgesia is the most popular technique for the relief of labor pain. Its popularity is first and foremost related to its efficacy. Women can obtain almost complete relief from the pain of labor. From the anesthesiologist’s perspective, because a catheter is threaded into the epidural space, it is also a versatile technique. During the earlier stages of labor, dilute solutions of local anesthetic can be used to achieve analgesia. As labor progresses, a more concentrated solution of local anesthetic may be necessary or an adjunct, such as an opioid, may be needed. Additionally, the epidural catheter can be utilized to maintain a low dermatomal level of anesthesia for labor (T10–L1) and, when needed, the dermatomal level can be raised to T4 for cesarean section.
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FIGURE 59.1 Schematic drawing of parturition pain pathways. First-stage labor pain is due to uterine contraction and cervical dilatation. Afferent pain fibers from the uterus and cervix accompany sympathetic fibers and enter the spinal cord from T10 to L1. Second-stage labor pain originates from the vagina and perineum. Afferent pain fibers from the vagina and perineum course with the pudendal nerves, S2–S4. (From Stoelting RK, Miller RD: Basics of Anesthesia, 3rd edition. Churchill Livingston, New York, 1994, p. 364, with permission.)
Patient-controlled epidural analgesia (PCEA) is a technique that allows the patient to self-medicate, thereby controlling her own analgesia. Compared with continuous infusion or intermittent bolus techniques, PCEA is associated with a lower total dose of local anesthetic, less motor blockade, and fewer interventions by anesthesiologists. Although maternal satisfaction may be greater with PCEA, the above-stated advantages have not been documented in all studies. Therefore, this technique is not routinely offered. A commonly used PCEA regimen is bupivacaine 0.0625% with fentanyl 2 μg/mL with the following PCEA settings: basal rate of 10 mL/hr, bolus dose of 5 mL,
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10 minute lockout, and a 30 mL/hr maximum limit. A basal rate is not always used because it may be associated with a greater total milligram dose of local anesthetic when compared with the total milligram dose when a basal rate is used. Theoretical risks of PCEA, such as high dermatomal levels or overdose, have been described in the general surgical patient. Overdose occurs because of catheter migration into the subarachnoid space or from excessive administration by the patient or a helpful family member. To date, these complications have not been reported in the parturient during labor. There are a number of disadvantages with labor epidural analgesia that have prompted the search for alternative techniques. One disadvantage is the time it takes to provide analgesia to the patient. The time from epidural catheter placement until the patient is comfortable is variable, but depending on the local anesthetic used can take up to 30 minutes. Other disadvantages of labor epidural analgesia include: maternal hypotension, inadequate analgesia (15–20% of cases), and motor blockade, even with the very dilute local anesthetic solutions. Subarachnoid opioids offer rapid, intense analgesia with minimal changes in blood pressure or motor function. Most patients can, if desired, ambulate with this technique. The opioid is usually administered as part of a combined spinal-epidural (CSE) technique where a spinal and an epidural are performed at the same time. After locating the epidural space in the usual manner, a long small-gauge spinal needle is inserted through the epidural needle into the subarachnoid space. An opioid (usually fentanyl 25 μg or sufentanil 5 μg), either alone or in combination with a local anesthetic, is administered through the spinal needle. The spinal needle is removed and an epidural catheter is
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inserted for future use. Analgesia begins within 3–5 minutes and lasts 1–1.5 hours. There are several advantages to the CSE technique. The primary advantage is the rapid (3–5 min) onset of analgesia. There is also less motor blockade. Because of these advantages there is greater satisfaction by women who receive a CSE than those who receive the “standard” epidural technique of bupivacaine 0.25%. There are some concerns about CSE, most of which are only theoretical but have not been documented. There is no increased risk of subarachnoid catheter migration of the epidural catheter. Metallic particles are not produced as a result of passing one needle through another. The incidence of postdural puncture headache is not increased by the intentional dural puncture. Fetal bradycardia in association with a hypertonic uterus may occur immediately or shortly after induction of either epidural or subarachnoid labor analgesia. There does not appear to be any difference in the incidence of fetal heart rate decelerations or emergent cesarean section following labor epidural or spinal anesthesia. One proposed theory for increased uterine tone after CSE is related to the rapid decrease in maternal catecholamines associated with the rapid onset of pain relief. The decrease in circulating β-adrenergic agonists results in a predominance of α activity, which causes uterine contractions. If this should occur, treatment is with subcutaneous terbutaline or intravenous nitroglycerin. 3. What is a “walking epidural”? The term “walking epidural” has become popular, especially in the lay community. The term refers to any epidural
Stages of Labor Begins
Ends
Innervation
Anesthesia
First
Regular contractions
Complete cervical dilation
T10–L1
E, S, C Subarachnoid opioids Paracervical block
Second
Complete cervical dilation
Delivery of the fetus
S2–S4
E, S, C Pudendal block
Third
Delivery of the fetus
Delivery of the placenta
Note: caudal analgesia is rarely used. E, epidural; S, spinal; C, caudal.
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or spinal technique that allows the parturient to ambulate. Some initial retrospective data had suggested that ambulating or the upright position is associated with a shorter first stage of labor, less pain in early labor, and decreased analgesia requirements. However, prospective and randomized studies have not been able to document any medical benefit of ambulating, in terms of either duration of labor or mode of delivery. Although few patients really want to ambulate, using a technique that produces minimal motor blockade will improve maternal satisfaction. Both epidural analgesia using dilute local anesthetic/opioid solutions or a CSE technique can achieve this goal. However, several precautions should be taken before allowing a parturient to walk after receiving epidural or CSE analgesia. First, it should be determined whether she is a candidate for intermittent fetal heart rate monitoring. Blood pressure and fetal heart rate should be monitored for 30–60 minutes after induction of analgesia and reassessed at least every 30 minutes thereafter. Because even small doses of subarachnoid and epidural local anesthetics can produce motor deficits, motor function should be assessed. This is accomplished by asking the parturient to perform a modified deep knee bend or step up and down on a stool. She must have an escort at all times. 4. Describe the regional anesthetic techniques that can be employed for cesarean section. Regional anesthetic techniques include spinal and epidural anesthesia. During regional anesthesia the mother remains awake during the delivery, thereby significantly decreasing the risk of maternal aspiration associated with general anesthesia. Regional anesthesia also minimizes the potential for depression of the neonate from maternal drug
Regional Anesthesia for Cesarean Section Advantages Decreased risk of maternal aspiration Minimizes neonatal depression from maternal drug administration Absolute contraindications Infection at site Severe hypovolemia Increased intracranial pressure Patient refusal Coagulation abnormalities Relative contraindications Neurologic disease (e.g., multiple sclerosis) History of back surgery History of back pain Systemic infection
administration. Because regional anesthesia is safer than general anesthesia for both the mother and the fetus, it should be used for all elective cesarean deliveries. Relatively few absolute contraindications exist to regional anesthesia. These include infection at the injection site, severe hypovolemia, raised intracranial pressure, patient refusal, and coagulation abnormalities. Relative contraindications include neurologic disease such as multiple sclerosis, history of back surgery or back pain, and systemic infection.
Spinal Versus Epidural Anesthesia Spinal
Epidural
Advantages
Reliable and rapid onset
Better control of spread Mitigates precipitous drop in blood pressure Unlimited duration
Disadvantages
Potential for hypotension Inability to control spread Limited duration PDPH
Time to achieve adequate surgical anesthesia Local anesthetic toxicity
PDPH, postdural puncture headache.
LABOR
A Suggested Technique for Performing Regional Anesthesia for Cesarean Section 1. Check the anesthesia machine. Prepare resuscitative equipment and drugs including endotracheal tubes of different sizes, laryngoscopes, airways, suction, thiobarbiturate, succinylcholine, ephedrine or phenylephrine. 2. Transport to the operating room with left uterine displacement. 3. Administer a nonparticulate antacid by mouth. 4. Rapidly prehydrate with 1000–1500 mL of a crystalloid solution. 5. Place routine monitors including blood pressure cuff, electrocardiogram, and pulse oximeter. Administer oxygen via nasal cannula or facemask. 6. Epidural: After placing an epidural catheter, administer 3 cc of 2% lidocaine as a test dose. Wait 5 minutes, observing for signs of either intravascular or subarachnoid injection. After confirming catheter position, inject 2% lidocaine with epinephrine 1:200,000, 3% chloroprocaine, or 0.5% bupivacaine in aliquots of 5 mL no more frequently than every 5 minutes until a T4 level of anesthesia is achieved. Spinal: Use a small-gauge pencil-point spinal needle. Administer 1.5–2.0 mL of 0.75% hyperbaric bupivacaine. 7. Monitor vital signs every 2 minutes for the first 20 minutes, and then every 5 minutes thereafter, if stable. 8. If hypotension occurs, administer 250–500 mL boluses of crystalloid and ephedrine in 5 mg or phenylephrine in 50 μg increments, until the blood pressure returns to normal.
Spinal anesthesia provides reliable and rapid anesthesia. In certain urgent situations, spinal anesthesia can even be used in place of general anesthesia. Disadvantages of spinal anesthesia include a potential for hypotension, inability to
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control the spread of anesthesia, limited duration and possibility of postdural puncture headache. Continuous epidural anesthesia allows for multiple repeat doses of local anesthetic, which offers better control over anesthetic spread, mitigates against precipitous drops in blood pressure, and allows almost unlimited duration of anesthesia. Epidural anesthesia can be used for both labor and cesarean delivery. Compared with spinal anesthesia, the major disadvantages of epidural anesthesia are the time required to place a needle or catheter and the potential for local anesthetic toxicity. 5. Outline the treatment for postdural puncture headache. Postdural puncture headache (PDPH) can occur any time the dura is punctured. Persistent cerebrospinal fluid (CSF) leak decreases the amount of fluid available to cushion the brain. In the absence of an adequate fluid buffer, the brain shifts within the calvarium, placing tension on pain-sensitive blood vessels. Risk factors for PDPH include increasing size of needle, type of needle (lower with pencilpoint needles), bevel perpendicular to dural fibers (for non-pencil-point needles), female gender, pregnancy, and increasing number of attempts. The headache is classically located over the occipital or frontal regions. It is frequently accompanied by neck tension, tinnitus, diplopia, photophobia, nausea, and vomiting. The most diagnostic feature of PDPH is that it changes with position. The symptoms improve in the supine position and are exacerbated in the erect position (sitting or standing). Treatment is divided into noninvasive and invasive measures. Noninvasive therapy includes analgesics, hydration, and caffeine. Invasive therapy involves placing an epidural blood patch. This is accomplished by sterilely injecting 20 mL of autologous blood into the epidural space. The success rate is 70–75%. A second blood patch is needed occasionally. Prophylactic blood patching or prophylactic epidural saline infusions to reduce the incidence of PDPH are controversial. 6. What are the advantages and disadvantages of general anesthesia for cesarean section? The major advantages of general anesthesia over regional anesthesia are the shorter preoperative preparatory time and the freedom from sympathectomy. The disadvantages of general anesthesia include maternal aspiration and neonatal depression. In addition, general anesthesia precludes immediate maternal bonding. Aspiration pneumonia is a leading cause of morbidity and mortality in the parturient undergoing general anesthesia, thus general anesthesia should be reserved for the
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emergent situation. Before induction of general anesthesia, a careful evaluation of the airway should be performed and a nonparticulate antacid administered. Antacids increase gastric pH resulting in a decreased incidence and severity of pneumonitis should aspiration occur. Defasciculating doses of nondepolarizing muscle relaxants are avoided prior to induction because they may produce profound weakness predisposing to aspiration and may delay the onset time of succinylcholine. After preoxygenation, induction of anesthesia can proceed with essentially any of the available induction agents and application of cricoid pressure. There are some data indicating that Apgar scores and neurobehavioral scores are depressed when propofol is used, but these are controversial. A thiobarbiturate is often chosen for patients who are hemodynamically stable, whereas ketamine is frequently selected when there is hemodynamic instability or severe bronchospasm. Although thiamylal crosses the placenta, doses less than 7 mg/kg do not adversely affect the fetus. This is because the small amount of drug reaching the fetus is diluted by fetal blood returning from the lower half of the body before it reaches the central nervous system. Muscle relaxation for endotracheal intubation is achieved with succinylcholine because it provides the most rapid onset amongst relaxants currently available. Succinylcholine’s duration of action may be prolonged, due to abnormally low levels of pseudocholinesterase, when compared with the nonpregnant state. The extended duration of action generally does not exceed 15 minutes and is, therefore, clinically insignificant. Muscle relaxants do not cross the placenta because they are highly ionized and have a large molecular weight. Anesthesia is maintained with 50% nitrous oxide (N2O) in O2 and either isoflurane 0.3–0.5% or enflurane 0.5–0.7%. N2O does cross the placenta but due to fetal tissue uptake it does not cause significant fetal depression if the induction to delivery time is less than 20 minutes. Sub-MAC concentrations of the potent inhaled anesthetic agents administered prior to delivery protect from maternal recall without causing fetal depression or uterine relaxation. After delivery of the fetus, N2O concentrations are increased and opioids administered to supplement the anesthetic. Extubation of the trachea follows classic full stomach precautions. The residual muscle relaxation is antagonized with an anticholinesterase and vagolytic agents and the patient must be fully awake.
A Suggested Method of Performing General Anesthesia for Cesarean Section 1. Check the anesthesia machine. Prepare resuscitative equipment and drugs including endotracheal tubes of different sizes, laryngoscopes, airways, suction, thiamylal, succinylcholine, ephedrine or phenylephrine. 2. Transport to the operating room with left uterine displacement. 3. Administer a nonparticulate antacid by mouth. 4. Prehydrate with 1000–1500 mL of crystalloid. 5. Place routine monitors including blood pressure cuff, electrocardiogram, and pulse oximeter. Administer oxygen by facemask or nasal cannula. 6. After denitrogenation with 100% oxygen for 3–5 minutes, induce anesthesia with thiamylal 4 mg/kg or ketamine 1–2 mg/kg followed by succinylcholine 100 mg and apply cricoid pressure. Do NOT use a defasciculating dose of a nondepolarizing agent. 7. Maintain anesthesia with 50% N2O/O2, and isoflurane 0.3–0.5% or enflurane 0.5–0.7% until the baby is delivered. 8. After delivery of the baby, administer fentanyl 100 μg and increase the N2O concentration to 70%. Keep the concentration of the halogenated agent below 0.5 MAC to avoid uterine relaxation. 9. At completion of the procedure, administer neostigmine 0.07 mg/kg and glycopyrrolate 0.01 mg/kg to antagonize residual neuromuscular blockade. 10. Extubate the trachea when the patient is fully awake.
7. Describe the elements of placental drug transfer. Placental drug transfer occurs by diffusion. Fick’s equation describes the factors governing the transfer of drugs across the placenta. Qd = Kd × A × [Pd(m) − Pd(f )]/b
where: Qd = quantity of drug transferred per unit time Kd = diffusion constant for the drug A = surface area of the placenta
LABOR
Pd(m) = mean drug concentration of maternal blood in the intervillous space Pd(f) = mean drug concentration of fetal blood in the intervillous space b = thickness of the placenta. Factors over which the anesthesiologist has control are limited to the specific drug administered and the amount used. Other factors, such as the surface area and thickness of the placenta, are clearly not under our control. In order to minimize the amount of drug reaching the placenta, the quantity of maternally administered drug needs to be reduced. Diffusion constants, which vary from one drug to another, are determined by four main properties: molecular weight, lipid solubility, protein binding, and electrical charge. Placental transfer of drug is facilitated by a molecular weight of less than 500, high lipid solubility, minimal maternal protein binding, and a low degree of ionization. Thus, fentanyl, a non-ionized, highly lipid-soluble molecule with a low molecular weight, crosses the placenta easily. In contrast, succinylcholine, a highly ionized molecule, does not cross the placenta readily. 8. What techniques can be used for post-cesarean pain relief? Intravenous (IV), intramuscular (IM), and neuraxial opioids can be administered for post-cesarean pain relief. Women who receive epidural morphine sulfate complain of less pain than women who receive IV or IM morphine sulfate. Morphine sulfate in either the subarachnoid or epidural space provides analgesia for up to 24 hours. The dose of epidural morphine is 3–4 mg and of subarachnoid morphine is 0.1–0.25 mg. 9. Outline the differential diagnosis of postpartum hemorrhage. The most common cause of postpartum hemorrhage is uterine atony, which occurs in 2–5% of all deliveries. Other causes of postpartum hemorrhage include retained placenta, placenta accreta, cervical and vaginal lacerations, inverted uterus, and conditions associated with coagulopathy such as amniotic fluid embolism and preeclampsia. Treatment of postpartum hemorrhage is etiology-specific. Coagulopathies often respond to therapy for their specific cause.
Any condition associated with overdistention of the uterus, such as multiple births, polyhydramnios, or a large baby, is a risk factor for uterine atony. Other risk factors
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include multiparity, retained placenta, prolonged labor, previous tocolysis, β-agonists, prolonged general anesthesia with potent inhaled anesthetic agents, ruptured uterus, and chorioamnionitis. Uterine atony presents as continued painless vaginal bleeding after delivery. The noncontracting uterus appears boggy and large. Obstetric management is aimed at increasing myometrial tone. Massaging the uterus through the abdominal wall or directly via the vagina is initially attempted to induce contractions. If massaging does not work, oxytocin and ergot derivatives are administered intravenously as well as prostaglandin F2α directly into the uterus to induce contractions. Anesthetic management is initially aimed at maternal resuscitation. Intravascular volume is restored with crystalloid, colloid, and/or blood. Massive blood loss may lead to shock. Coagulation factor replacement may be required. Vaginal examination and suturing in attempts to stop the bleeding require anesthesia; however, conduction techniques are hazardous in the face of hypovolemia. Intravenous sedation with small amounts of fentanyl, ketamine, and/or midazolam generally suffices. If sedation is inadequate, a rapid sequence induction of general anesthesia with endotracheal intubation is required to reduce the risk of maternal aspiration. Continued hemorrhage may require hypogastric artery ligation or hysterectomy, which necessitate general anesthesia. Anesthetic management for these procedures is the same as for placenta previa. Pelvic artery embolization, usually performed in the radiology suite, can sometimes reduce the bleeding and prevent the need for a hysterectomy. Although general anesthesia is not required, maternal fluid resuscitation must be continued during embolization.
Differential Diagnosis of Postpartum Bleeding Uterine atony Retained products of conception Placenta accreta Cervical and vaginal lacerations Inverted uterus
10. Explain the risk factors, presentation, and treatment of uterine atony.
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Coagulopathy Preeclampsia Amniotic fluid embolus
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Frequent vital sign monitoring is required and resuscitative equipment must be available. Successful intraoperative cell salvage (cell saver) have been reported in obstetrics. The major concern with its usage is that the amniotic fluid will not be completely removed during the centrifuging and cleansing process leading to iatrogenic amniotic fluid embolism. Recommendations for its use include discarding all surgical field fluids before collecting blood with the cell saver device. Use of this technique should be reserved for situations where there is no other blood available or the patient refuses autologous blood transfusion (Jehovah’s witness).
evacuation of the uterus. Hysterectomy or hypogastric artery ligation requires general anesthesia, the management of which is similar to that described above.
SUGGESTED READINGS Ackerman WE, Colclough GW: Prophylactic epidural blood patch: the controversy continues. Anesth Analg 66:913–917, 1987 Finster M, Mark LC, Morishima HO, et al.: Plasma thiopental concentrations in the newborn following delivery under thiopental–nitrous oxide anesthesia. Am J Obstet Gynecol 95:621–629, 1966
11. Describe the presentation and treatment of retained placenta.
Heubert WN, Cefalo RC. Management of postpartum hemorrhage. Clin Obstet Gynecol 27:139–150, 1984
Retained placenta occurs in about 1 in 300 deliveries and is characterized by painless vaginal bleeding following delivery. Treatment goals focus on manually removing the placenta, which prevents uterine contractions. Dilatation and curettage may be required to evacuate the uterus. Abnormal implantation in the uterus, such as placenta accreta, placenta increta, or placenta percreta, may make removal of the placenta impossible. Hysterectomy, hypogastric artery ligation, or arterial embolization may be lifesaving maneuvers. For the anesthesiologist, maternal resuscitation is the first priority. Intravenous sedation usually suffices for
Marx GF, Joshi CW, Louis RO: Placental transmission of nitrous oxide. Anesthesiology 32:429–432, 1970 Nageotte MP, Larson D, Rumney PJ, et al.: Epidural analgesia compared with combined spinal-epidural analgesia during labor in nulliparous women. N Engl J Med 337:1715–1719, 1997 Pais SO, Glickman M, Schwartz P, et al.: Embolization of pelvic arteries for control of postpartum hemorrhage. Obstet Gynecol 55:754–758, 1980 Reisnner LS, Lin D: Anesthesia for cesarean section. pp. 465–492. In Chestnut DH (ed): Obstetric Anesthesia, Principles and Practice, 2nd edition. Mosby, St. Louis, 1999
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LABOR AND DELIVERY
Yaakov Beilin, MD
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27-year-old woman presents to the delivery suite in labor after an uncomplicated pregnancy. A lumbar epidural catheter is placed at the L4–L5 interspace to facilitate analgesia. After an adequate trial of labor, the obstetricians elect to perform a cesarean section for cephalopelvic disproportion. A T4 level of anesthesia is achieved via the epidural catheter and the cesarean section is initiated. Immediately after delivery of the baby, maternal hemorrhage becomes severe.
QUESTIONS 1. What options are available to the mother for labor analgesia? 2. Explain the advantages and disadvantages of various regional anesthetic techniques for labor and delivery. 3. What is a “walking epidural”? 4. Describe the regional anesthetic techniques that can be employed for cesarean section. 5. Outline the treatment for postdural puncture headache. 6. What are the advantages and disadvantages of general anesthesia for cesarean section? 7. Describe the elements of placental drug transfer. 8. What techniques can be used for post-cesarean pain relief?
9. Outline the differential diagnosis of postpartum hemorrhage. 10. Explain the risk factors, presentation, and treatment of uterine atony. 11. Describe the presentation and treatment of retained placenta.
1. What options are available to the mother for labor analgesia? Many techniques have been utilized to reduce the perception of pain during labor. In addition to systemic medications, inhalation agents, and regional anesthesia, hypnosis, psychoprophylaxis, acupuncture, and transcutaneous electrical nerve stimulation (TENS) have been used. Systemic opioids can be used to attenuate labor pains; however, low-dose opioids do not completely eliminate the pain. Meperidine is the most frequently used opioid for labor analgesia. Intravenous meperidine peaks in about 10 minutes and lasts approximately 3–4 hours. Neonates born within 2 hours of maternal administration of meperidine are at risk for respiratory depression. Morphine is rarely used during labor because neonates are extremely sensitive to its respiratory depressant effect. Remifentanil can be used as part of patient-controlled analgesia (PCA) during labor. The advantage of remifentanil is that its onset and duration of action are shorter than those of meperidine. However, it is also more potent and close maternal respiratory monitoring is required, preferably with pulse oximetry. 347
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The goal of inhalation analgesia during labor is to achieve analgesia without depressing airway reflexes. Typically, at the beginning of each contraction the mother, using a hand-held device, self-administers the anesthetic agents. The most commonly used vapors are nitrous oxide and enflurane. Although this technique provides moderately good analgesia, it is not commonly used because of the risk of maternal aspiration with deep levels of anesthesia. Regional anesthesia, epidural or combined spinalepidural, have become popular modalities for labor analgesia because of their safety and efficacy profile.
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2. Explain the advantages and disadvantages of various regional anesthetic techniques for labor and delivery. Rational use of regional anesthesia necessitates an understanding of the pain pathways involved during labor. Labor is traditionally divided into three distinct stages: ■
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First stage: begins with the onset of regular contractions and ends with complete cervical dilation. Second stage: begins when the cervix is completely dilated and ends with delivery of the fetus. Third stage: begins after delivery of the fetus and concludes with delivery of the placenta.
The first stage of labor is associated with uterine and cervical pain mediated by spinal segments T10–L1 (Fig. 59.1). Local anesthetics administered to the epidural, spinal, or caudal spaces readily anesthetize these pain pathways. In addition, subarachnoid opioids and paracervical blocks can be used for pain relief during the first stage of labor. Caudal anesthesia is rarely used because of the risk of inadvertent fetal scalp penetration and the associated high fetal levels of local anesthetic. The second stage of labor is associated with perineal and vaginal distention mediated by spinal segments S2–S4. Epidural, spinal, and caudal anesthetics are also effective during the second stage of labor. In addition, pudendal nerve blocks can be used for second-stage analgesia. Epidural analgesia is the most popular technique for the relief of labor pain. Its popularity is first and foremost related to its efficacy. Women can obtain almost complete relief from the pain of labor. From the anesthesiologist’s perspective, because a catheter is threaded into the epidural space, it is also a versatile technique. During the earlier stages of labor, dilute solutions of local anesthetic can be used to achieve analgesia. As labor progresses, a more concentrated solution of local anesthetic may be necessary or an adjunct, such as an opioid, may be needed. Additionally, the epidural catheter can be utilized to maintain a low dermatomal level of anesthesia for labor (T10–L1) and, when needed, the dermatomal level can be raised to T4 for cesarean section.
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FIGURE 59.1 Schematic drawing of parturition pain pathways. First-stage labor pain is due to uterine contraction and cervical dilatation. Afferent pain fibers from the uterus and cervix accompany sympathetic fibers and enter the spinal cord from T10 to L1. Second-stage labor pain originates from the vagina and perineum. Afferent pain fibers from the vagina and perineum course with the pudendal nerves, S2–S4. (From Stoelting RK, Miller RD: Basics of Anesthesia, 3rd edition. Churchill Livingston, New York, 1994, p. 364, with permission.)
Patient-controlled epidural analgesia (PCEA) is a technique that allows the patient to self-medicate, thereby controlling her own analgesia. Compared with continuous infusion or intermittent bolus techniques, PCEA is associated with a lower total dose of local anesthetic, less motor blockade, and fewer interventions by anesthesiologists. Although maternal satisfaction may be greater with PCEA, the above-stated advantages have not been documented in all studies. Therefore, this technique is not routinely offered. A commonly used PCEA regimen is bupivacaine 0.0625% with fentanyl 2 μg/mL with the following PCEA settings: basal rate of 10 mL/hr, bolus dose of 5 mL,
LABOR
10 minute lockout, and a 30 mL/hr maximum limit. A basal rate is not always used because it may be associated with a greater total milligram dose of local anesthetic when compared with the total milligram dose when a basal rate is used. Theoretical risks of PCEA, such as high dermatomal levels or overdose, have been described in the general surgical patient. Overdose occurs because of catheter migration into the subarachnoid space or from excessive administration by the patient or a helpful family member. To date, these complications have not been reported in the parturient during labor. There are a number of disadvantages with labor epidural analgesia that have prompted the search for alternative techniques. One disadvantage is the time it takes to provide analgesia to the patient. The time from epidural catheter placement until the patient is comfortable is variable, but depending on the local anesthetic used can take up to 30 minutes. Other disadvantages of labor epidural analgesia include: maternal hypotension, inadequate analgesia (15–20% of cases), and motor blockade, even with the very dilute local anesthetic solutions. Subarachnoid opioids offer rapid, intense analgesia with minimal changes in blood pressure or motor function. Most patients can, if desired, ambulate with this technique. The opioid is usually administered as part of a combined spinal-epidural (CSE) technique where a spinal and an epidural are performed at the same time. After locating the epidural space in the usual manner, a long small-gauge spinal needle is inserted through the epidural needle into the subarachnoid space. An opioid (usually fentanyl 25 μg or sufentanil 5 μg), either alone or in combination with a local anesthetic, is administered through the spinal needle. The spinal needle is removed and an epidural catheter is
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inserted for future use. Analgesia begins within 3–5 minutes and lasts 1–1.5 hours. There are several advantages to the CSE technique. The primary advantage is the rapid (3–5 min) onset of analgesia. There is also less motor blockade. Because of these advantages there is greater satisfaction by women who receive a CSE than those who receive the “standard” epidural technique of bupivacaine 0.25%. There are some concerns about CSE, most of which are only theoretical but have not been documented. There is no increased risk of subarachnoid catheter migration of the epidural catheter. Metallic particles are not produced as a result of passing one needle through another. The incidence of postdural puncture headache is not increased by the intentional dural puncture. Fetal bradycardia in association with a hypertonic uterus may occur immediately or shortly after induction of either epidural or subarachnoid labor analgesia. There does not appear to be any difference in the incidence of fetal heart rate decelerations or emergent cesarean section following labor epidural or spinal anesthesia. One proposed theory for increased uterine tone after CSE is related to the rapid decrease in maternal catecholamines associated with the rapid onset of pain relief. The decrease in circulating β-adrenergic agonists results in a predominance of α activity, which causes uterine contractions. If this should occur, treatment is with subcutaneous terbutaline or intravenous nitroglycerin. 3. What is a “walking epidural”? The term “walking epidural” has become popular, especially in the lay community. The term refers to any epidural
Stages of Labor Begins
Ends
Innervation
Anesthesia
First
Regular contractions
Complete cervical dilation
T10–L1
E, S, C Subarachnoid opioids Paracervical block
Second
Complete cervical dilation
Delivery of the fetus
S2–S4
E, S, C Pudendal block
Third
Delivery of the fetus
Delivery of the placenta
Note: caudal analgesia is rarely used. E, epidural; S, spinal; C, caudal.
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or spinal technique that allows the parturient to ambulate. Some initial retrospective data had suggested that ambulating or the upright position is associated with a shorter first stage of labor, less pain in early labor, and decreased analgesia requirements. However, prospective and randomized studies have not been able to document any medical benefit of ambulating, in terms of either duration of labor or mode of delivery. Although few patients really want to ambulate, using a technique that produces minimal motor blockade will improve maternal satisfaction. Both epidural analgesia using dilute local anesthetic/opioid solutions or a CSE technique can achieve this goal. However, several precautions should be taken before allowing a parturient to walk after receiving epidural or CSE analgesia. First, it should be determined whether she is a candidate for intermittent fetal heart rate monitoring. Blood pressure and fetal heart rate should be monitored for 30–60 minutes after induction of analgesia and reassessed at least every 30 minutes thereafter. Because even small doses of subarachnoid and epidural local anesthetics can produce motor deficits, motor function should be assessed. This is accomplished by asking the parturient to perform a modified deep knee bend or step up and down on a stool. She must have an escort at all times. 4. Describe the regional anesthetic techniques that can be employed for cesarean section. Regional anesthetic techniques include spinal and epidural anesthesia. During regional anesthesia the mother remains awake during the delivery, thereby significantly decreasing the risk of maternal aspiration associated with general anesthesia. Regional anesthesia also minimizes the potential for depression of the neonate from maternal drug
Regional Anesthesia for Cesarean Section Advantages Decreased risk of maternal aspiration Minimizes neonatal depression from maternal drug administration Absolute contraindications Infection at site Severe hypovolemia Increased intracranial pressure Patient refusal Coagulation abnormalities Relative contraindications Neurologic disease (e.g., multiple sclerosis) History of back surgery History of back pain Systemic infection
administration. Because regional anesthesia is safer than general anesthesia for both the mother and the fetus, it should be used for all elective cesarean deliveries. Relatively few absolute contraindications exist to regional anesthesia. These include infection at the injection site, severe hypovolemia, raised intracranial pressure, patient refusal, and coagulation abnormalities. Relative contraindications include neurologic disease such as multiple sclerosis, history of back surgery or back pain, and systemic infection.
Spinal Versus Epidural Anesthesia Spinal
Epidural
Advantages
Reliable and rapid onset
Better control of spread Mitigates precipitous drop in blood pressure Unlimited duration
Disadvantages
Potential for hypotension Inability to control spread Limited duration PDPH
Time to achieve adequate surgical anesthesia Local anesthetic toxicity
PDPH, postdural puncture headache.
LABOR
A Suggested Technique for Performing Regional Anesthesia for Cesarean Section 1. Check the anesthesia machine. Prepare resuscitative equipment and drugs including endotracheal tubes of different sizes, laryngoscopes, airways, suction, thiobarbiturate, succinylcholine, ephedrine or phenylephrine. 2. Transport to the operating room with left uterine displacement. 3. Administer a nonparticulate antacid by mouth. 4. Rapidly prehydrate with 1000–1500 mL of a crystalloid solution. 5. Place routine monitors including blood pressure cuff, electrocardiogram, and pulse oximeter. Administer oxygen via nasal cannula or facemask. 6. Epidural: After placing an epidural catheter, administer 3 cc of 2% lidocaine as a test dose. Wait 5 minutes, observing for signs of either intravascular or subarachnoid injection. After confirming catheter position, inject 2% lidocaine with epinephrine 1:200,000, 3% chloroprocaine, or 0.5% bupivacaine in aliquots of 5 mL no more frequently than every 5 minutes until a T4 level of anesthesia is achieved. Spinal: Use a small-gauge pencil-point spinal needle. Administer 1.5–2.0 mL of 0.75% hyperbaric bupivacaine. 7. Monitor vital signs every 2 minutes for the first 20 minutes, and then every 5 minutes thereafter, if stable. 8. If hypotension occurs, administer 250–500 mL boluses of crystalloid and ephedrine in 5 mg or phenylephrine in 50 μg increments, until the blood pressure returns to normal.
Spinal anesthesia provides reliable and rapid anesthesia. In certain urgent situations, spinal anesthesia can even be used in place of general anesthesia. Disadvantages of spinal anesthesia include a potential for hypotension, inability to
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control the spread of anesthesia, limited duration and possibility of postdural puncture headache. Continuous epidural anesthesia allows for multiple repeat doses of local anesthetic, which offers better control over anesthetic spread, mitigates against precipitous drops in blood pressure, and allows almost unlimited duration of anesthesia. Epidural anesthesia can be used for both labor and cesarean delivery. Compared with spinal anesthesia, the major disadvantages of epidural anesthesia are the time required to place a needle or catheter and the potential for local anesthetic toxicity. 5. Outline the treatment for postdural puncture headache. Postdural puncture headache (PDPH) can occur any time the dura is punctured. Persistent cerebrospinal fluid (CSF) leak decreases the amount of fluid available to cushion the brain. In the absence of an adequate fluid buffer, the brain shifts within the calvarium, placing tension on pain-sensitive blood vessels. Risk factors for PDPH include increasing size of needle, type of needle (lower with pencilpoint needles), bevel perpendicular to dural fibers (for non-pencil-point needles), female gender, pregnancy, and increasing number of attempts. The headache is classically located over the occipital or frontal regions. It is frequently accompanied by neck tension, tinnitus, diplopia, photophobia, nausea, and vomiting. The most diagnostic feature of PDPH is that it changes with position. The symptoms improve in the supine position and are exacerbated in the erect position (sitting or standing). Treatment is divided into noninvasive and invasive measures. Noninvasive therapy includes analgesics, hydration, and caffeine. Invasive therapy involves placing an epidural blood patch. This is accomplished by sterilely injecting 20 mL of autologous blood into the epidural space. The success rate is 70–75%. A second blood patch is needed occasionally. Prophylactic blood patching or prophylactic epidural saline infusions to reduce the incidence of PDPH are controversial. 6. What are the advantages and disadvantages of general anesthesia for cesarean section? The major advantages of general anesthesia over regional anesthesia are the shorter preoperative preparatory time and the freedom from sympathectomy. The disadvantages of general anesthesia include maternal aspiration and neonatal depression. In addition, general anesthesia precludes immediate maternal bonding. Aspiration pneumonia is a leading cause of morbidity and mortality in the parturient undergoing general anesthesia, thus general anesthesia should be reserved for the
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emergent situation. Before induction of general anesthesia, a careful evaluation of the airway should be performed and a nonparticulate antacid administered. Antacids increase gastric pH resulting in a decreased incidence and severity of pneumonitis should aspiration occur. Defasciculating doses of nondepolarizing muscle relaxants are avoided prior to induction because they may produce profound weakness predisposing to aspiration and may delay the onset time of succinylcholine. After preoxygenation, induction of anesthesia can proceed with essentially any of the available induction agents and application of cricoid pressure. There are some data indicating that Apgar scores and neurobehavioral scores are depressed when propofol is used, but these are controversial. A thiobarbiturate is often chosen for patients who are hemodynamically stable, whereas ketamine is frequently selected when there is hemodynamic instability or severe bronchospasm. Although thiamylal crosses the placenta, doses less than 7 mg/kg do not adversely affect the fetus. This is because the small amount of drug reaching the fetus is diluted by fetal blood returning from the lower half of the body before it reaches the central nervous system. Muscle relaxation for endotracheal intubation is achieved with succinylcholine because it provides the most rapid onset amongst relaxants currently available. Succinylcholine’s duration of action may be prolonged, due to abnormally low levels of pseudocholinesterase, when compared with the nonpregnant state. The extended duration of action generally does not exceed 15 minutes and is, therefore, clinically insignificant. Muscle relaxants do not cross the placenta because they are highly ionized and have a large molecular weight. Anesthesia is maintained with 50% nitrous oxide (N2O) in O2 and either isoflurane 0.3–0.5% or enflurane 0.5–0.7%. N2O does cross the placenta but due to fetal tissue uptake it does not cause significant fetal depression if the induction to delivery time is less than 20 minutes. Sub-MAC concentrations of the potent inhaled anesthetic agents administered prior to delivery protect from maternal recall without causing fetal depression or uterine relaxation. After delivery of the fetus, N2O concentrations are increased and opioids administered to supplement the anesthetic. Extubation of the trachea follows classic full stomach precautions. The residual muscle relaxation is antagonized with an anticholinesterase and vagolytic agents and the patient must be fully awake.
A Suggested Method of Performing General Anesthesia for Cesarean Section 1. Check the anesthesia machine. Prepare resuscitative equipment and drugs including endotracheal tubes of different sizes, laryngoscopes, airways, suction, thiamylal, succinylcholine, ephedrine or phenylephrine. 2. Transport to the operating room with left uterine displacement. 3. Administer a nonparticulate antacid by mouth. 4. Prehydrate with 1000–1500 mL of crystalloid. 5. Place routine monitors including blood pressure cuff, electrocardiogram, and pulse oximeter. Administer oxygen by facemask or nasal cannula. 6. After denitrogenation with 100% oxygen for 3–5 minutes, induce anesthesia with thiamylal 4 mg/kg or ketamine 1–2 mg/kg followed by succinylcholine 100 mg and apply cricoid pressure. Do NOT use a defasciculating dose of a nondepolarizing agent. 7. Maintain anesthesia with 50% N2O/O2, and isoflurane 0.3–0.5% or enflurane 0.5–0.7% until the baby is delivered. 8. After delivery of the baby, administer fentanyl 100 μg and increase the N2O concentration to 70%. Keep the concentration of the halogenated agent below 0.5 MAC to avoid uterine relaxation. 9. At completion of the procedure, administer neostigmine 0.07 mg/kg and glycopyrrolate 0.01 mg/kg to antagonize residual neuromuscular blockade. 10. Extubate the trachea when the patient is fully awake.
7. Describe the elements of placental drug transfer. Placental drug transfer occurs by diffusion. Fick’s equation describes the factors governing the transfer of drugs across the placenta. Qd = Kd × A × [Pd(m) − Pd(f )]/b
where: Qd = quantity of drug transferred per unit time Kd = diffusion constant for the drug A = surface area of the placenta
LABOR
Pd(m) = mean drug concentration of maternal blood in the intervillous space Pd(f) = mean drug concentration of fetal blood in the intervillous space b = thickness of the placenta. Factors over which the anesthesiologist has control are limited to the specific drug administered and the amount used. Other factors, such as the surface area and thickness of the placenta, are clearly not under our control. In order to minimize the amount of drug reaching the placenta, the quantity of maternally administered drug needs to be reduced. Diffusion constants, which vary from one drug to another, are determined by four main properties: molecular weight, lipid solubility, protein binding, and electrical charge. Placental transfer of drug is facilitated by a molecular weight of less than 500, high lipid solubility, minimal maternal protein binding, and a low degree of ionization. Thus, fentanyl, a non-ionized, highly lipid-soluble molecule with a low molecular weight, crosses the placenta easily. In contrast, succinylcholine, a highly ionized molecule, does not cross the placenta readily. 8. What techniques can be used for post-cesarean pain relief? Intravenous (IV), intramuscular (IM), and neuraxial opioids can be administered for post-cesarean pain relief. Women who receive epidural morphine sulfate complain of less pain than women who receive IV or IM morphine sulfate. Morphine sulfate in either the subarachnoid or epidural space provides analgesia for up to 24 hours. The dose of epidural morphine is 3–4 mg and of subarachnoid morphine is 0.1–0.25 mg. 9. Outline the differential diagnosis of postpartum hemorrhage. The most common cause of postpartum hemorrhage is uterine atony, which occurs in 2–5% of all deliveries. Other causes of postpartum hemorrhage include retained placenta, placenta accreta, cervical and vaginal lacerations, inverted uterus, and conditions associated with coagulopathy such as amniotic fluid embolism and preeclampsia. Treatment of postpartum hemorrhage is etiology-specific. Coagulopathies often respond to therapy for their specific cause.
Any condition associated with overdistention of the uterus, such as multiple births, polyhydramnios, or a large baby, is a risk factor for uterine atony. Other risk factors
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include multiparity, retained placenta, prolonged labor, previous tocolysis, β-agonists, prolonged general anesthesia with potent inhaled anesthetic agents, ruptured uterus, and chorioamnionitis. Uterine atony presents as continued painless vaginal bleeding after delivery. The noncontracting uterus appears boggy and large. Obstetric management is aimed at increasing myometrial tone. Massaging the uterus through the abdominal wall or directly via the vagina is initially attempted to induce contractions. If massaging does not work, oxytocin and ergot derivatives are administered intravenously as well as prostaglandin F2α directly into the uterus to induce contractions. Anesthetic management is initially aimed at maternal resuscitation. Intravascular volume is restored with crystalloid, colloid, and/or blood. Massive blood loss may lead to shock. Coagulation factor replacement may be required. Vaginal examination and suturing in attempts to stop the bleeding require anesthesia; however, conduction techniques are hazardous in the face of hypovolemia. Intravenous sedation with small amounts of fentanyl, ketamine, and/or midazolam generally suffices. If sedation is inadequate, a rapid sequence induction of general anesthesia with endotracheal intubation is required to reduce the risk of maternal aspiration. Continued hemorrhage may require hypogastric artery ligation or hysterectomy, which necessitate general anesthesia. Anesthetic management for these procedures is the same as for placenta previa. Pelvic artery embolization, usually performed in the radiology suite, can sometimes reduce the bleeding and prevent the need for a hysterectomy. Although general anesthesia is not required, maternal fluid resuscitation must be continued during embolization.
Differential Diagnosis of Postpartum Bleeding Uterine atony Retained products of conception Placenta accreta Cervical and vaginal lacerations Inverted uterus
10. Explain the risk factors, presentation, and treatment of uterine atony.
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Coagulopathy Preeclampsia Amniotic fluid embolus
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Frequent vital sign monitoring is required and resuscitative equipment must be available. Successful intraoperative cell salvage (cell saver) have been reported in obstetrics. The major concern with its usage is that the amniotic fluid will not be completely removed during the centrifuging and cleansing process leading to iatrogenic amniotic fluid embolism. Recommendations for its use include discarding all surgical field fluids before collecting blood with the cell saver device. Use of this technique should be reserved for situations where there is no other blood available or the patient refuses autologous blood transfusion (Jehovah’s witness).
evacuation of the uterus. Hysterectomy or hypogastric artery ligation requires general anesthesia, the management of which is similar to that described above.
SUGGESTED READINGS Ackerman WE, Colclough GW: Prophylactic epidural blood patch: the controversy continues. Anesth Analg 66:913–917, 1987 Finster M, Mark LC, Morishima HO, et al.: Plasma thiopental concentrations in the newborn following delivery under thiopental–nitrous oxide anesthesia. Am J Obstet Gynecol 95:621–629, 1966
11. Describe the presentation and treatment of retained placenta.
Heubert WN, Cefalo RC. Management of postpartum hemorrhage. Clin Obstet Gynecol 27:139–150, 1984
Retained placenta occurs in about 1 in 300 deliveries and is characterized by painless vaginal bleeding following delivery. Treatment goals focus on manually removing the placenta, which prevents uterine contractions. Dilatation and curettage may be required to evacuate the uterus. Abnormal implantation in the uterus, such as placenta accreta, placenta increta, or placenta percreta, may make removal of the placenta impossible. Hysterectomy, hypogastric artery ligation, or arterial embolization may be lifesaving maneuvers. For the anesthesiologist, maternal resuscitation is the first priority. Intravenous sedation usually suffices for
Marx GF, Joshi CW, Louis RO: Placental transmission of nitrous oxide. Anesthesiology 32:429–432, 1970 Nageotte MP, Larson D, Rumney PJ, et al.: Epidural analgesia compared with combined spinal-epidural analgesia during labor in nulliparous women. N Engl J Med 337:1715–1719, 1997 Pais SO, Glickman M, Schwartz P, et al.: Embolization of pelvic arteries for control of postpartum hemorrhage. Obstet Gynecol 55:754–758, 1980 Reisnner LS, Lin D: Anesthesia for cesarean section. pp. 465–492. In Chestnut DH (ed): Obstetric Anesthesia, Principles and Practice, 2nd edition. Mosby, St. Louis, 1999