Handbook of Clinical Anesthesia

Chapter 43

Obstetrical Anesthesia

During pregnancy, alterations occur in nearly every maternal organ system, with associated implications for anesthesiologists (Table 43-1) (Braveman FR, Scavone BM, Wong CA, Santos AC: Obstetrical anesthesia. In Clinical Anesthesia. Edited by Barash PG, Cullen BF, Stoelting RK, Cahalan MK, Stock MC. Philadelphia: Lippincott Williams & Wilkins, 2009, pp 1137–1170).

  1. Physiologic Changes of Pregnancy
  2. Increased alveolar ventilation along with decreased functional residual capacity enhances maternal uptake and elimination of inhaled anesthetics.
  3. Decreased functional residual capacity and increased basal metabolic rate may predispose the parturient to arterial hypoxemia during periods of apnea, as associated with endotracheal intubation.
  4. Vascular engorgement of the airway may predispose the patient to bleeding on insertion of nasopharyngeal airways, nasogastric tubes, or endotracheal tubes.
  5. Controversy exists as to when a pregnant woman becomes at risk for aspiration. Earlier studies showing delayed emptying in the first trimester may have been a result of subjects' pain, anxiety, or opioid administration.
  6. Placental Transfer and Fetal Exposure to Anesthetic Drugs
  7. Most drugs (opioids, local anesthetics, inhaled anesthetics) readily cross the placenta.
  8. Placental transfer depends on several factors (Table 43-2).
  9. Rapid transfer of inhalational agents results in detectable arterial and venous concentrations after 1 minute.

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Table 43-1 Physiologic Changes of Pregnancy

Hematologic Alterations Increased total blood volume (25%–40%)
Increased plasma volume (40%–50%)
Increased fibrinogen (100%)
Decreased cholinesterase activity (20%–30%)
Cardiovascular Changes
Increased cardiac output (30%–50%)
Aortocaval compression (supine hypotensive syndromeoccurs in about 50% of parturients)
Ventilatory Changes
Increased minute ventilation (50%)
Increased alveolar ventilation (70%)
Decreased functional residual capacity (20%)
Increased oxygen consumption (20%)
Decreased PaCO2 (10 mm Hg)
Increased PaO2 (10 mm Hg)
Airway edema
Gastrointestinal Changes
Delayed gastric emptying
Decreased lower esophageal sphincter tone (heartburn)
Altered Drug Responses
Decreased requirements (32%–40%) for inhaled anesthetics (MAC) by 8–12 weeks (parallels increased progesterone levels)
Decreased local anesthetic requirements (engorgement of veins resulting in decreased volume of the epidural and subarachnoid space versus progesterone-induced increased sensitivity of nerves to local anesthetics)

MAC = minimum alveolar concentration.

Table 43-2 Determinants of Drug Passage Across the Placenta

Physical and Chemical Characteristics of the Drug
Molecular weight (<500)
Lipid solubility
Non-ionized vs ionized
Concentration Gradient
Dose administered
Timing of IV administration relative to uterine contraction
Use of vasoconstrictors
Hemodynamic Factors
Aortocaval compression
Hypotension from regional blockade

IV = intravenous.

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Table 43-3 Characteristics of Fetal Circulation That Delay Drug Equilibration

The fetal liver is the first organ perfused by the umbilical vein
Dilution of umbilical vein blood by fetal venous blood from the gastrointestinal tract, head, and extremities (this explains why thiopental [4 mg/kg IV] administered to the mother does not produce significant depressant effects in the fetus)

  1. Fetus and Newborn.Several characteristics of the fetal circulation delay equilibration between fetal arterial and venous blood and thus delay the onset or magnitude of depressant effects of anesthetic drugs (Table 43-3).
  2. Neurobehavioral studies in neonates born in the presence of epidural anesthesia may reveal subtle changes in newborn neurologic and adaptive function. (These changes are minor and transient, lasting only 24 to 48 hours.)

III. Anesthesia for Labor and Vaginal Delivery

Whereas analgesia for the first stage of labor (pain caused by uterine contractions) is provided by block of T10–L1, analgesia for the second stage of labor (pain caused by distention of the perineum) is provided by block of S2–S4.

  1. Nonpharmacologic methods of labor analgesia(massage, aromatherapy, hydrotherapy, biofeedback, transcutaneous electrical nerve stimulation, acupuncture, hypnosis) remain unproven for efficacy.
  2. Systemic Medication.The time and method of administration must be chosen carefully to avoid maternal and neonatal depression.
  3. Opioids
  4. Meperidineappears to produce less neonatal ventilatory depression than does morphine. Meperidine administered intravenously (IV) (analgesia in 5–10 minutes) or intramuscularly (peak effect in 40–50 minutes) rapidly crosses the placenta.
  5. Fentanyl(1 µg/kg IV) provides prompt pain relief (during forceps application) without severe neonatal depression. For more analgesia, fentanyl

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or remifentanil may be administered with patient-controlled delivery devices.

  1. Naloxone(10 µg/kg IV) may be administered directly to newborns to reverse excessive opioid depression.
  2. Ketamine(0.2–0.4 mg/kg IV) provides adequate analgesia without producing neonatal depression.
  3. Regional Anesthesia.Regional techniques (central neuraxial blockade [spinal, epidural, combined spinal–epidural]) provide excellent analgesia with minimal depressant effects in the mother and fetus. Hypotension resulting from sympathectomy is the most frequent complication that occurs with central neuraxial blockade. (Maternal systemic blood pressure is typically monitored every 2 to 5 minutes for about 15 to 20 minutes after the initiation of the block and at regular intervals thereafter.) Regional analgesia may be contraindicated in the presence of coagulopathy, acute hypovolemia, or infection at the needle insertion site. (Chorioamnionitis without frank sepsis is not a contraindication.)
  4. Epidural analgesiamay be used for pain relief during labor and vaginal delivery and may be converted to anesthesia for cesarean delivery if required.
  5. Effective analgesia during the first stage of labor may be achieved by blocking the T10–L1 dermatomes with dilute concentrations of local anesthetic with or without the use of opioids that have their effect at the opioid receptors in the dorsal horn of the spinal cord (Table 43-4). For the second stage of labor and delivery, because of pain from vaginal distention and perineal pressure, the block should be extended to include the S2–S4 segments.

Table 43-4 Tests to Rule Out Intrathecal or Intravascular Placement of a Lumbar Epidural Catheter

Aspiration (may not be diagnostic)
Local anesthetic (7.5 mg of bupivacaine or 45 mg of lidocaine)
Epinephrine (15 µg; a false-positive reaction may be seen with uterine contractions; may decrease uteroplacental perfusion)

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  2. The first stage of labor may be slightly prolonged by epidural analgesia, but this is not clinically significant provided aortocaval compression is avoided. Epidural analgesia initiated during the latent phase of labor (2–4 cm cervical dilation) does not result in a higher incidence of dystocia or cesarean section.
  3. Prolongation of the second stage of labor by epidural analgesia (presumably related to loss of the urge to push by the patient) may be minimized by the use of an ultra-dilute concentration of local anesthetic in combination with an opioid.
  4. Analgesia for the first stage of labor may be achieved with 5 to 10 mL of bupivacaine, ropivacaine, or levobupivacaine (0.125%–0.25%) followed by continuous infusion (8–12 mL/hr) of 0.0625% bupivacaine or levobupivacaine or 0.1% ropivacaine. The addition of 1 to 2 µg/mL of fentanyl (or 0.3–0.5 µg/l mL of sufentanil) permits a more dilute local anesthetic solution to be administered. During delivery, the sacral dermatomes may be blocked with 10 mL of 0.5% bupivacaine or 1% lidocaine or if a rapid effect is needed, 2% chloroprocaine may be administered in the semirecumbent position.
  5. Patient-controlled epidural analgesia is an alternative to bolus or infusion techniques.
  6. Spinal Analgesia
  7. A single subarachnoid injection for labor analgesia has the advantages of a reliable and rapid onset of neuraxial blockade.
  8. Spinal analgesia with 10 µg of fentanyl or 2 to 5 µg of sufentanil alone or in combination with 1 mL of isobaric bupivacaine 0.25% may be appropriate in multiparous patients whose anticipated course of labor does not warrant a catheter technique.
  9. Spinal anesthesia (“saddle block”) is a safe and effective alternative to general anesthesia for instrumental delivery.
  10. There is a risk of postdural puncture headache, and the motor block may be undesirable.
  11. Combined Spinal–Epidural Analgesia
  12. Combined spinal–epidural analgesia is an ideal analgesic technique for use during labor because

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it combines the rapid onset of profound analgesia (spinal injection) with the flexibility and longer duration of epidural techniques.

  1. After identification of the epidural space, a long pencil-point spinal needle is advanced into the subarachnoid space through the epidural needle. After intrathecal injection (10–20 µg of fentanyl or 2.5–5 µg of sufentanil alone or in combination with 1 mL of bupivacaine 0.25% produces profound analgesia lasting 90 to 120 minutes with minimal motor block), an epidural infusion of bupivacaine 0.03% to 0.625% with added opioid is started.
  2. Women with hemodynamic stability and preserved motor function who do not require continuous fetal monitoring may ambulate with assistance. (Walking has little effect on the course of labor.)
  3. The most common side effects of intrathecal opioids are pruritus, nausea, vomiting, and urinary retention. The risk of postdural puncture headache does not seem to be increased. Fetal bradycardia may occur.
  4. The potential exists for epidurally administered drug to leak into the subarachnoid space after dural puncture, particularly if large volumes of drug are rapidly injected.
  5. This technique should be used with caution in women who may require an urgent cesarean section and women who are at most increased risk (morbidly obese, difficult airway).
  6. A paracervical blockinterrupts transmission of nerve impulses from the uterus and cervix during the first stage of labor.
  7. A pudendal nerve blockmay provide anesthesia for outlet forceps delivery and episiotomy repair.
  8. Anesthesia for Cesarean Delivery

The choice of anesthesia is often influenced by the urgency of the operative procedure and the condition of the fetus. Most patients undergoing cesarean delivery in the United States do so under spinal or epidural anesthesia.

  1. Neuraxial anesthesiaoffers the advantages of decreased risk of pulmonary aspiration of gastric

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contents, avoidance of depressant drugs, and fulfillment of the mother's wishes to remain awake. The risk of hypotension is greater than during vaginal delivery because the block must extend to at least the T4 dermatome. Proper positioning and prehydration with up to 20 mL/kg of crystalloid solution is recommended. If hypotension occurs despite these measures, left uterine displacement is increased, the rate of IV infusion is augmented, and 10 to 15 mg of ephedrine or 20 to 50 µg of phenylephrine is injected IV.

  1. Spinal anesthesiais provided most often with 1.6 to 1.8 mL of hyperbaric bupivacaine 0.75% lasting approximately 120 to 180 minutes. Improved perioperative analgesia can be provided by addition of fentanyl (6.25 µg) or preservative-free morphine (100 µg) to the local anesthetic solution. It is probably not necessary to adjust the dose of local anesthetic based on the parturient's height.
  2. Despite a block extending to T4, parturients often experience visceral discomfort, particularly with exteriorization of the uterus and traction on abdominal viscera (25 µg of fentanyl IV may be useful).
  3. Oxygen should be routinely administered by face mask to optimize maternal and fetal oxygenation.
  4. Lumbar Epidural Anesthesia.Compared with spinal anesthesia, lumbar epidural anesthesia requires more time and drug to establish an adequate sensory level, but there is a lower risk of postdural puncture headache, and the level of anesthesia can be adjusted by titration of local anesthetic solution injected through the indwelling catheter.
  5. Adequate anesthesia is usually achieved with injection through the lumbar epidural catheter of 15 to 25 mL of local anesthetic solution (Table 43-5).

Table 43-5 Epidural Anesthesia for Cesarean Section

2-Chloroprocaine 3%
Lidocaine 2% with epinephrine 1:200,000
0.5% Bupivacaine, ropivacaine, or levobupivacaine

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  2. Addition of morphine (3–5 mg) to the local anesthetic solution provides postoperative analgesia.
  3. Combined spinal–epidural anesthesiafor cesarean delivery provides a rapid onset of a dense block with a low anesthetic dose and the ability to extend the duration of anesthesia and perhaps to provide continuous postoperative analgesia.
  4. General anesthesiamay be necessary when contraindications exist to regional anesthesia or when time precludes central neuraxial blockade. Situations in which uterine relaxation facilitates delivery (multiple gestations, breech position) are most often managed with general anesthesia (Table 43-6).

Table 43-6 General Anesthesia for Cesarean Section

Preoperative evaluation of the airway (inability to intubate is the leading cause of maternal death related to anesthesia)
Premedication with 15–30 mL of a nonparticulate antacid within 30 minutes of induction
The parturient should be maintained in the left uterine displacement position while on the operating table
Preoxygenation
A defasciculating dose of nondepolarizing muscle relaxant is not necessary
4 mg/kg IV of thiopental (2 mg/kg of propofol or 0.5 mg/kg IV of ketamine), plus 1–1.5 mg/kg IV of succinylcholine should be used during cricoid pressure (drugs should be injected at the onset of contraction if the patient is in labor)
Skin incision should be done after confirmation of tracheal tube placement
Rocuronium (0.6 mg/kg IV) is an acceptable alternative when succinylcholine is contraindicated
An LMA should be considered if tracheal intubation cannot be accomplished
Maintenance in the predelivery interval with 50% nitrous oxide and 0.5 MAC of a volatile anesthetic (temporarily increased to 2 MAC a few minutes before delivery if uterine relaxation is needed to facilitate delivery; alternatively, nitroglycerin relaxes the uterus)
Extreme hyperventilation of the lungs should be avoided because it may reduce uterine blood flow
Oxytocin is added to the infusion after delivery, and anesthesia is deepened (possibly with opioids)
The trachea is extubated when the patient awakens

IV = intravenous; LMA = laryngeal mask airway; MAC = minimum alveolar concentration.

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  2. A newborn's condition after cesarean section with general anesthesia is comparable to that when regional techniques are used. The uterine incision to delivery time (<180 seconds) is more important to fetal outcome than is the anesthetic technique.
  3. The usual amount of blood loss during cesarean section is 750 to 1000 mL, and transfusion is rarely necessary.
  4. When tracheal intubation is unexpectedly difficult, it may be prudent to permit the parturient to awaken and then to pursue alternative approaches (awake fiberoptic tracheal intubation, regional anesthesia) rather than to persist with repeated unsuccessful and traumatic attempts at tracheal intubation (Fig. 43-1).
 

Figure 43-1. Management of the difficult airway in pregnancy. ASA = American Society of Anesthesiologists.

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  1. Anesthetic Complications

(Table 43-7)

  1. Management of High-Risk Parturients
  2. Preeclampsia and Eclampsia.Preeclampsia (pregnancy-induced hypertension) and eclampsia (seizures) are characterized by hypertension, proteinuria, and edema that may progress to oliguria, congestive heart failure, and seizures (eclampsia) (Table 43-8).

Table 43-7 Anesthetic Complications in Obstetric Patients

Maternal Mortality
Most often related to arterial hypoxemia during airway management difficulties
Pregnancy-induced anatomic changes (decreased functional residual capacity, increased oxygen consumption, or oropharyngeal edema may expose the parturient to an increased risk of arterial oxygen desaturation during periods of apnea and hypoventilation)
Pulmonary Aspiration
Hypotension
Regional anesthesia (related to the degree and rapidity of local anesthetic-induced sympatholysis)
Prehydration (<20 mL/kg of lactated Ringer's solution) before initiation of regional anesthesia and avoidance of aortocaval compression may decrease the incidence of hypotension
Treatment is increased displacement of the uterus, rapid IV fluid infusion, titration of ephedrine (5–10 mg) or phenylephrine (20–50 µg), oxygen administration, and placement in the Trendelenburg position
Total Spinal Anesthesia
Local Anesthetic-Induced Seizures
Treatment is with IV administration of thiopental (50–100 mg) or diazepam (5–10 mg)
Postdural Puncture Headache
The incidence is lower with pencil-point needles (Whitacre or Sprotte) compared with diamond-shaped (Quincke) cutting needles
Treatment of a severe headache is with a blood patch (10–15 mL of the patient's blood is injected into the epidural space close to the site of dural puncture)
Nerve Injury
The possible role of compression of the maternal lumbosacral trunk by the fetus should be considered

IV = intravenous.

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Table 43-8 Symptoms of Severe Preeclampsia

Systolic blood pressure >160 mm Hg
Diastolic blood pressure >110 mm Hg
Proteinuria >5 g/24 hours
Evidence of end organ damage
   Oliguria (<400 mL/24 hours)
   Cerebral or visual disturbances
   Pulmonary edema
   Epigastric pain
   Intrauterine growth retardation
Thrombocytopenia (steroids may prevent)

  1. Many of the symptoms associated with preeclampsia may result from an imbalance between the placental production of prostacyclin and thromboxane.
  2. The HEELP syndrome is a form of severe preeclampsia characterized by hemolysis, elevated liver enzymes, and low platelet count. In contrast to preeclampsia, elevations in blood pressure and proteinuria may be mild.
  3. General Management(Table 43-9)
  4. Anesthetic Management
  5. Epidural anesthesia or combined spinal–epidural analgesia for labor and delivery is acceptable provided no clotting abnormality or plasma volume deficit is present. In volume-repleted parturients positioned with left uterine displacement, the institution of epidural anesthesia does not typically cause an unacceptable decrease in blood pressure and may result in significant improvements in placental blood flow.

Table 43-9 Considerations in the Management of Parturients with Preeclampsia or Eclampsia

Prevent or control seizures (magnesium sulfate potentiates muscle relaxants and may increase the severity of hypotension under regional anesthesia).
Restore intravascular fluid volume (central venous or pulmonary capillary wedge pressure, 5–10 mm Hg; urine output, 0.5–1 mL/kg/hr).
Normalize blood pressure (hydralazine, nitroprusside).
Correct coagulation abnormalities.

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  2. Spinal anesthesia may produce severe alterations in cardiovascular dynamics resulting from sudden sympathetic nervous system blockade.
  3. General anesthesia is often chosen for acute emergencies, but the practitioner should keep in mind the probable exaggerated blood pressure responses to induction of anesthesia and intubation of the trachea and possible interactions of muscle relaxants with magnesium sulfate therapy.
  4. Decreased doses of ephedrine are recommended to treat patients with hypotension because parturients with preeclampsia or eclampsia may exhibit increased sensitivity to vasopressors.
  5. Obstetric Hemorrhage.Life-threatening massive hemorrhage occurs in approximately one in 1000 deliveries.
  6. Placenta previa (painless, bright red bleeding after the seventh month of pregnancy) is the most common cause of postpartum hemorrhage.
  7. Abruptio placentae typically manifests as uterine hypertonia and tenderness with dark red vaginal bleeding. Maternal and fetal mortality rates are increased.
  8. General anesthesia (often with ketamine [0.75 mg/kg IV] induction of anesthesia) is used in view of the increased risk of hemorrhage and clotting disorders.
  9. Heart Disease.Cardiac decompensation and death occur most commonly at the time of maximum hemodynamic stress. For example, cardiac output increases during labor, with the greatest increase immediately after delivery of the placenta. These changes in cardiac output are blunted by regional anesthesia.
  10. Congenital Heart Disease(Table 43-10)
  11. Valvular Heart Disease(Table 43-11)

Table 43-10 Congenital Heart Disease and the Parturient

Prior successful surgical repair (asymptomatic)
Uncorrected or partially corrected (may experience cardiac decompensation with pregnancy)
Eisenmenger's syndrome (pulmonary hypertension reverses flow to a right-to-left shunt; general anesthesia is often selected)

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Table 43-11 Hemodynamic Goals with Valvular Lesions

Lesion

Goal

Aortic stenosis

Sinus rhythm

Maintain HR
Avoid decreased SVR
Maintain venous return

Aortic insufficiency

Mild increase in HR
Avoid increased SVR

Mitral stenosis

Sinus rhythm
Decrease HR
Maintain SVR
Maintain venous return

Mitral insufficiency

Sinus rhythm
Mild increase in HR
Avoid increased SVR
Avoid increased venous return

HR = heart rate; SVR = systemic vascular resistance.

  1. Coarctation of the aortais similar to aortic stenosis and may manifest as left ventricular failure during labor and delivery.
  2. Primary pulmonary hypertensionis seen predominantly in young parturients, and pain during labor and delivery may further increase pulmonary vascular resistance. (Neuraxial analgesia is useful.)
  3. Peripartum cardiomyopathyis a diagnosis of exclusion, and the prognosis is good if cardiac function returns to normal within 6 months of delivery.
  4. Coronary artery disease and myocardial infarctionare rare but are associated with high maternal and infant mortality.
  5. Diabetes Mellitus.Gestational diabetes mellitus or glucose intolerance is first diagnosed during pregnancy (there is an increasing incidence with obesity).
  6. Obesityis associated with antenatal comorbidities (hypertension, diabetes, preeclampsia) and an increasing need for cesarean delivery. Despite technical challenges, continuous neuraxial analgesia provides excellent pain relief during labor and delivery.
  7. Advanced maternal age(older than 35 years of age) is associated with poorer outcomes and a higher incidence of maternal morbidities

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(gestational diabetes, preeclampsia, placental abruption, cesarean delivery) and chronic medical conditions.

Table 43-12 Problems Associated with Prematurity

Respiratory distress syndrome (glucocorticoids administered to the mother for 24–48 hours may enhance fetal lung maturity)
Intracranial hemorrhage
Hypoglycemia
Hypocalcemia
Hyperbilirubinemia

VII. Preterm Delivery

Preterm labor and delivery is defined as birth before the 37th week or term weight of the infant as more than two standard deviations below the mean (small for gestational age). Such infants account for 8% to 10% of all births and nearly 80% of early neonatal deaths in the U.S.

  1. Several problems are likely to develop in preterm infants (Table 43-12).
  2. β2-Agonists (ritodrine, terbutaline) used to inhibit labor may interact with anesthetic drugs or produce undesirable changes before induction of anesthesia (Table 43-13).
  3. Delay of anesthesia for at least 3 hours after the cessation of tocolysis allows β-mimetic effects of β2-agonists to dissipate; potassium supplementation is not necessary.
  4. Preterm infants are more sensitive to the depressant effects of anesthetic drugs. Regardless of the technique or drugs selected, the most important goal is prevention of asphyxia of the fetus.

Table 43-13 Side Effects of β2-Agonists Administered to Stop Premature Labor

Hypokalemia (cardiac dysrhythmias)
Hypotension (accentuated by regional anesthesia)
Tachycardia (atropine and pancuronium should be avoided)
Pulmonary edema (cautious prehydration)

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Table 43-14 Substance Abuse Among Women of Childbearing Age

Tobacco abuse (intrauterine growth retardation, preterm delivery, sudden infant death syndrome)
Alcohol (fetal alcohol syndrome)
Opioids (withdrawal symptoms)
Marijuana (intrauterine growth retardation, preterm delivery)
Cocaine
Amphetamines (fetal anomalies)

VIII. HIV and AIDS

  1. Prevention of viral transmission to the fetus is based on antiretroviral therapy to decrease maternal viral load and elective cesarean delivery before rupture of membranes or labor.
  2. Spread of HIV to the central nervous system occurs rapidly after initial infection, and there is no evidence linking the use of regional anesthesia to progression of the disease.
  3. Using a blood patch to treat postdural puncture headache does not seem to accelerate HIV symptoms.
  4. Substance Abuse

Nearly 90% of women with substance abuse are of childbearing age (Table 43-14). Cocaine abuse has the greatest implications for anesthetic management (Table 43-15).

Table 43-15 Anesthetic Considerations Associated with Cocaine or Amphetamine Abuse

Uncontrolled hypertension
Cardiac arrhythmias (ventricular tachycardia or fibrillation)
Myocardial ischemia
Ephedrine-resistant hypotension with neuraxial blockade (a direct-acting drug should be used)
Acute use may increase the MAC of volatile drugs
Chronic use may decrease the dosage of anesthetic drugs
The patient may exhibit increased sensitivity to the arrhythmogenic effects of volatile drugs

MAC = minimum alveolar concentration.

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Table 43-16 Biophysical Monitoring of the Fetus

Baseline heart rate (normal, 120–160 bpm)
Beat-to-beat variability (reflects variations in autonomic nervous system tone; disappears with fetal distress, opioids, local anesthetics)
Fetal heart rate deceleration

  1. Fetal and Maternal Monitoring
  2. Biophysical Monitoring.Ultrasonographic cardiography and measurement of uterine activity with a tocodynamometer provide noninvasive monitoring of fetal well-being (Table 43-16 and Fig. 43-2). Prolonged

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deceleration is present when fetal heart rate decreases below baseline for more than 2 but less than 10 minutes. All decelerations should be quantified based on the deviation from baseline and the duration.

 

Figure 43-2. Relationship and significance of fetal heart rate (FHR) changes in association with uterine contractions (UCs).

Table 43-17 Events Associated with Neonatal Depression at Birth

Prematurity (80% <1500 g need resuscitation)
Drugs used during labor or delivery
Trauma or precipitated labor
Birth asphyxia (reflects interference with placental perfusion)
Tight umbilical cord
Prolapsed cord
Premature separation of placenta
Uterine hyperactivity
Maternal hypotension

  1. Fetal pulse oximetryis an adjunct to fetal heart rate monitoring as a reflection of intrapartum fetal oxygenation.
  2. Fetal oxygen saturation between 30% and 70% is considered normal.
  3. Saturation readings consistently below 30% for 10 to 15 minutes are suggestive of fetal acidemia.
  4. Newborn Resuscitation in the Delivery Room

Several factors contribute to the likelihood of depression at birth and require neonatal resuscitation (Table 43-17).

  1. Resuscitation.Every delivery room must be equipped with appropriate resuscitation equipment and drugs for newborn and maternal resuscitation (Fig. 43-3).
  2. Initial Treatment and Evaluation of All Infants.The pharynx is suctioned, heart rate is quantified, and ventilation is assessed. The scoring system introduced by Dr. Virginia Apgar, an anesthesiologist, is a useful method of clinically evaluating newborns (Table 43-18).
  3. Meconium staining is treated by oropharyngeal suctioning at the time of delivery; tracheal intubation and airway suctioning are probably only necessary in the presence of a low Apgar score and evidence of mechanical airway obstruction.
  4. Use of cardiac massage(chest compressions of the middle third of the sternum) should be provided if

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heart rate is below 60 bpm despite adequate ventilation for 30 seconds. The ratio of chest compression to ventilation should be approximately 3:1 or 100 compressions to 30 breaths/min (Table 43-19).

 

Figure 43-3. Algorithm for neonatal resuscitation. HR = heart rate.

  1. Rapid Correction of Acidosis.Sodium bicarbonate is not recommended during brief cardiopulmonary resuscitation because hyperosmolarity and carbon dioxide generation may be detrimental to cardiac

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and cerebral function. After ensuring adequate ventilation and perfusion, severe acidosis (pH <7.0) may need to be corrected promptly by infusion of sodium bicarbonate into the umbilical vein.

Table 43-18 Calculation of the Apgar Score

 

0

1

2

Heart rate

Absent

<100 bpm

>100 bpm

Respiratory effort

Absent

Slow and irregular

Crying

Muscle tone

Limp

Some flexion of extremities

Moving

Reflex irritability

No response

Grimace

Crying, cough

Color

Pale; blue

Body pink; extremities blue

Pink

  1. Other Drugs and Fluids(Table 43-20)
  2. Diagnostic Procedures.After the neonate is successfully resuscitated and stabilized, diagnostic procedures are indicated to rule out choanal atresia (occlusion of the nostrils to confirm absence of obstruction) and esophageal atresia (aspiration of gastric contents).
  3. EXIT procedure(ex utero intrapartum treatment) maintains uteroplacental support for a time period

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after delivery of the fetus (large neck masses, clips placed for diaphragmatic hernia). Often two anesthesia teams are needed—one for the mother and one for the fetus or newborn).

Table 43-19 Therapeutic Guidelines for Neonatal Resuscitation

Drug or Volume Expander

Concentration

Dosage

Route/Rate

Epinephrine

1:10,000

0.01–0.03 mg/kg

IV or IT

Volume expanders

Packed red blood cells
Normal saline
Lactated Ringer's solution

10 mL/kg

Give over 5–10 minutes

Naloxone

 

0.1 mg/kg

IV, IM, SC, or IT given rapidly

IM = intramuscular; IT = intratracheal; IV = intravenous; SC = subcutaneous.

Table 43-20 Other Drugs and Fluids Used in Neonatal Resuscitation

Naloxone (should be avoided in infants born to opioid-addicted mothers)
Epinephrine (used to treat asystole or persistent bradycardia; administered IV or by tracheal tube)
Lactated Ringer's solution (10 mL/kg IV)
Type O-negative blood (10 mL/kg IV)

IV = intravenous.

XII. Anesthesia for Non-Obstetric Surgery in Pregnant Women (Fig. 43-4)

  1. When the necessity for surgery in a pregnant patient arises, anesthetic considerations are related to multiple factors (Table 43-21).
 

Figure 43-4. Recommendations for management of parturients and surgical procedures.

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Table 43-21 Considerations in the Management of Anesthesia for Non-obstetric Surgery in Pregnant Women

Physiologic changes of pregnancy
Decreased requirements for local and inhaled anesthetics
Low functional residual capacity
High basal metabolic rate
Slowed gastric emptying
Aortocaval compression
Teratogenicity of anesthetic drugs (period of organogenesis is 15–56 days; single exposure seems unlikely to cause abnormalities)
Adequacy of uteroplacental circulation
Initiation of premature labor

  1. Only emergency surgery should be performed during pregnancy, especially in the first trimester. It is logical to select drugs with a long history of safety (opioids, muscle relaxants, thiopental, nitrous oxide). The fetal heart rate should be monitored after the 16th week.

Editors: Barash, Paul G.; Cullen, Bruce F.; Stoelting, Robert K.; Cahalan, Michael K.; Stock, M. Christine

Title: Handbook of Clinical Anesthesia, 6th Edition

Copyright ©2009 Lippincott Williams & Wilkins

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