INVOLUTION OF THE REPRODUCTIVE TRACT
Birth Canal
Return to the nonpregnant state begins soon after delivery. The vagina and its outlet gradually diminish in size but rarely regain their nulliparous dimensions. Rugae begin to reappear by the third week but are less prominent than before. The hymen is represented by several small tags of tissue, which scar to form the myrtiform caruncles. Vaginal epithelium begins to proliferate by 4 to 6 weeks, usually coincidental with resumed ovarian estrogen production. Lacerations or stretching of the perineum during delivery may result in vaginal outlet relaxation. Some damage to the pelvic floor may be inevitable, and parturition predisposes to urinary incontinence and pelvic organ prolapse. This is discussed in detail in Chapter 27 (p. 536).
Uterus
The massively increased uterine blood flow necessary to maintain pregnancy is made possible by significant hypertrophy and remodeling of pelvic vessels. After delivery, their caliber gradually diminishes to approximately that of of the prepregnant state. Within the puerperal uterus, larger blood vessels become obliterated by hyaline changes, are gradually resorbed, and are replaced by smaller ones. Minor vestiges of the larger vessels, however, may persist for years. During labor, the margin of the dilated cervix, which corresponds to the external os, may be lacerated. The cervical opening contracts slowly and for a few days immediately after labor, readily admits two fingers. By the end of the first week, this opening narrows, the cervix thickens, and the endocervical canal reforms. The external os does not completely resume its pregravid appearance. It remains somewhat wider, and typically, ectocervical depressions at the site of lacerations become permanent. These changes are characteristic of a parous cervix (Fig. 36-1). The markedly attenuated lower uterine segment contracts and retracts, but not as forcefully as the uterine corpus. During the next few weeks, the lower segment is converted from a clearly distinct substructure large enough to accommodate the fetal head to a barely discernible uterine isthmus located between the corpus and internal os. FIGURE 36-1 Common appearance of nulliparous (A) and parous (B) cervices. Cervical epithelium also undergoes considerable remodeling, and this actually may be salutary. Ahdoot and associates (1998) found that approximately half of women showed regression of high-grade dysplasia following vaginal delivery. Kaneshiro and coworkers (2005) found similar regression—about 60 percent overall—regardless of delivery mode. Postpartum, the fundus of the contracted uterus lies slightly below the umbilicus. It consists mostly of myometrium covered by serosa and internally lined by basal decidua. The anterior and posterior walls, which lie in close apposition, are each 4 to 5 cm thick (Buhimschi, 2003). At this time, the uterus weighs approximately 1000 g. Because blood vessels are compressed by the contracted myometrium, the uterus on section appears ischemic compared with the reddish-purple hyperemic pregnant organ. Myometrial involution is a truly remarkable tour de force of destruction or deconstruction that begins as soon as 2 days after delivery as shown in Figure 36-2. As emphasized by Hytten (1995), studies that describe the degree of decreasing uterine weight postpartum are poor quality. Best estimates are that by 1 week, the uterus weighs approximately 500 g; by 2 weeks, about 300 g; and at 4 weeks, involution is complete and the uterus weighs approximately 100 g. After each successive delivery, the uterus is usually slightly larger than before the most recent pregnancy. The total number of myocytes does not decrease appreciably—rather, their size decreases markedly. FIGURE 36-2 Cross sections of uteri made at the level of the involuting placental site at varying times after delivery. p.p. = postpartum. (Redrawn from Williams, 1931.) Sonographic Findings Uterine size dissipates rapidly in the first week (Fig. 36-3). And the uterus and endometrium return to pregravid size by 8 weeks after delivery (Belachew, 2012; Steinkeler, 2012). In a study of 42 normal women postpartum, Tekay and Jouppila (1993) identified fluid in the endometrial cavity in 78 percent at 2 weeks, 52 percent at 3 weeks, 30 percent at 4 weeks, and 10 percent at 5 weeks. Demonstrable uterine cavity contents are seen for up to 2 months following delivery. Belachew and colleagues (2012) used 3-dimensional sonography and visualized intracavitary tissue matter in a third on day 1, 95 percent on day 7, 87 percent on day 14, and 28 percent on day 28. By day 56, the small cavity was empty. Sohn and associates (1988) described Doppler ultrasound results showing continuously increasing uterine artery vascular resistance during the first 5 days postpartum.
Decidua and Endometrial Regeneration Because separation of the placenta and membranes involves the spongy layer, the decidua basalis is not sloughed. The remaining decidua has striking variations in thickness, it has an irregular jagged appearance, and it is infiltrated with blood, especially at the placental site (see Fig. 36-2). Within 2 or 3 days after delivery, the remaining decidua becomes differentiated into two layers. The superficial layer becomes necrotic and is sloughed in the lochia. The basal layer adjacent to the myometrium remains intact and is the source of new endometrium. This arises from proliferation of the endometrial glandular remnants and the stroma of the interglandular connective tissue. Endometrial regeneration is rapid, except at the placental site. Within a week or so, the free surface becomes covered by epithelium, and Sharman (1953) identified fully restored endometrium in all biopsy specimens obtained from the 16th day onward. Histological endometritis is part of the normal reparative process. Moreover, microscopic inflammatory changes characteristic of acute salpingitis are seen in almost half of women between 5 and 15 days, but these findings do not reflect infection (Andrews, 1951). Clinical Aspects Afterpains. In primiparous women, the uterus tends to remain tonically contracted following delivery. In multiparas, however, it often contracts vigorously at intervals and gives rise to afterpains, which are similar to but milder than labor contractions. These are more pronounced as parity increases and worsen when the infant suckles, likely because of oxytocin release (Holdcroft, 2003). Usually, afterpains decrease in intensity and become mild by the third day. We have encountered unusually severe and persistent afterpains in women with postpartum uterine infections. Lochia. Early in the puerperium, sloughing of decidual tissue results in a vaginal discharge of variable quantity. The discharge is termed lochia and contains erythrocytes, shredded decidua, epithelial cells, and bacteria. For the first few days after delivery, there is blood sufficient to color it red—lochia rubra. After 3 or 4 days, lochia becomes progressively pale in color—lochia serosa. After approximately the 10th day, because of an admixture of leukocytes and reduced fluid content, lochia assumes a white or yellow-white color—lochia alba. The average duration of lochial discharge ranges from 24 to 36 days (Fletcher, 2012).
Thứ Bảy, 11 tháng 10, 2014
NEWBORN
INITIATION OF AIR BREATHING
Immediately following birth, the infant must promptly convert to air breathing as the fluid-filled alveoli expand with air and pulmonary perfusion is established. The newborn begins to breathe and cry almost immediately after birth, which indicates establishment of active respiration. Some factors that appear to influence the first breath include: • Physical stimulation—examples include handling the neonate during delivery. • Oxygen deprivation and carbon dioxide accumulation—these serve to increase the frequency and magnitude of breathing movements both before and after birth (Dawes, 1974). • Thoracic compression—this occurs during pelvic descent, following which vaginal birth forces fluid from the respiratory tract in volume equivalent to approximately a fourth of the ultimate functional residual capacity (Saunders, 1978). • Aeration of the newborn lung does not involve the inflation of a collapsed structure, but instead, the rapid replacement of bronchial and alveolar fluid by air. After delivery, the residual alveolar fluid is cleared through the pulmonary circulation and to a lesser degree, through the pulmonary lymphatics (Chernick, 1978). Delay in fluid removal from the alveoli probably contributes to the syndrome of transient tachypnea of the newborn (TTN) (Guglani, 2008). As fluid is replaced by air, compression of the pulmonary vasculature is reduced considerably, and in turn, resistance to blood flow is lowered. With the fall in pulmonary arterial blood pressure, the ductus arteriosus normally closes (Fig. 7-8, p. 136). High negative intrathoracic pressures are required to bring about the initial entry of air into the fluid-filled alveoli. Normally, from the first breath after birth, progressively more residual air accumulates in the lung, and with each successive breath, lower pulmonary opening pressure is required. In the normal mature newborn, by approximately the fifth breath, pressure-volume changes achieved with each respiration are very similar to those of the adult. Thus, the breathing pattern shifts from the shallow episodic inspirations characteristic of the fetus to regular, deeper inhalations (Chap. 17, p. 337). Surfactant, which is synthesized by type II pneumocytes and already present in the alveoli, lowers alveolar surface tension and thereby prevents lung collapse. Insufficient surfactant, common in preterm infants, leads promptly to respiratory distress syndrome, which is described in Chapter 34 (p. 653).
CARE IN THE DELIVERY ROOM
Personnel designated for infant support are responsible for immediate care and for acute resuscitation initiation if needed.
Immediate Care
Before and during delivery, careful consideration must be given to several determinants of neonatal well-being including: (1) maternal health status; (2) prenatal complications, including any suspected fetal malformations; (3) gestational age; (4) labor complications; (5) duration of labor and ruptured membranes; (6) type and duration of anesthesia; (7) difficulty with delivery; and (8) medications given during labor and their dosages, administration routes, and timing relative to delivery.
Newborn Resuscitation
The International Liaison Committee on Resuscitation (ILCOR) updated its guidelines for neonatal resuscitation that are sanctioned by the American Academy of Pediatrics and the American Heart Association (Biban, 2011; Perlman, 2010). These substantially revised guidelines are incorporated into the following sections. Approximately 10 percent of newborns require some degree of active resuscitation to stimulate breathing, and 1 percent require extensive resuscitation. It is perhaps not coincidental that there is a two- to threefold risk of death for newborns delivered at home compared with those delivered in hospitals (American College of Obstetricians and Gynecologists, 2013b). When deprived of oxygen, either before or after birth, neonates demonstrate a well-defined sequence of events leading to apnea (Fig. 32-1). With oxygen deprivation, there is a transient period of rapid breathing, and if it persists, breathing stops, which is termed primary apnea. This stage is accompanied by a fall in heart rate and loss of neuromuscular tone. Simple stimulation and exposure to oxygen will usually reverse primary apnea. If oxygen deprivation and asphyxia persist, however, the newborn will develop deep gasping respirations, followed by secondary apnea. This latter stage is associated with a further decline in heart rate, falling blood pressure, and loss of neuromuscular tone. Neonates in secondary apnea will not respond to stimulation and will not spontaneously resume respiratory efforts. Unless ventilation is assisted, death follows. Clinically, primary and secondary apneas are indistinguishable. Thus, secondary apnea must be assumed and resuscitation of the apneic newborn must be started immediately.
Resuscitation Protocol
The updated algorithm for newborn resuscitation recommended by ILCOR and the International Consensus on Cardiopulmonary Resuscitation is shown in Figure 32-2. Many of its tenets follow below.
Basic Measures
The vigorous newborn is first placed in a warm environment to minimize heat loss, the airway is cleared, and the infant dried. Routine gastric aspiration has been shown to be nonbeneficial and even harmful (Kiremitci, 2011). And although previously recommended, there is no evidence that bulb suctioning for clear or meconium-stained fluid is beneficial, even if the newborn is depressed (Chap. 33, p. 638). With stimulation, the healthy newborn will take a breath within a few seconds of birth and cry within half a minute, after which routine supportive care is provided.
Assessment at 30 Seconds of Life. Apnea, gasping respirations, or heart rate < 100 bpm beyond 30 seconds after delivery should prompt administration of positive-pressure ventilation with room air (Fig. 32-3). Assisted ventilation rates of 30 to 60 breaths per minute are commonly employed, and the percent of oxygen saturation is monitored by pulse oximetry. At this point, supplemental oxygen can be given in graduated increasing percentages to maintain oxygen saturation (Spo2) values within a normal range (Vento, 2011). Adequate ventilation is indicated by improved heart rate. ventilation. The head should be in a sniffing position with the tip of the nose pointing to the ceiling. The neck should not be hyperextended. Assessment at 60 Seconds of Life. If the heart rate remains < 100 bpm, then ventilation is inadequate. The head position should be checked as shown in Figure 32-3, secretions cleared, and if necessary, inflation pressure increased. If the heart rate persists below 100 bpm beyond 60 seconds, tracheal intubation is considered. A number of conditions may be the cause of inadequate response, including the following: • Hypoxemia or acidosis from any cause • Drugs administered to the mother before delivery • Immaturity • Upper airway obstruction • Pneumothorax • Lung abnormalities • Meconium aspiration • Central nervous system developmental abnormality • Sepsis syndrome. Tracheal Intubation If bag-and-mask ventilation is ineffective or prolonged, tracheal intubation is then performed. Other indications include the need for chest compressions or tracheal administration of medications, or special circumstances such as extremely low birthweight or a congenital diaphragmatic hernia. A laryngoscope with a straight blade—size 0 for a preterm infant and size 1 for a term neonate—is introduced at the side of the mouth and then directed posteriorly toward the oropharynx as shown in Figure 32-4. The laryngoscope is next moved gently into the vallecula—the space between the base of the tongue and the epiglottis. Gentle elevation of the laryngoscope tip will raise the epiglottis and expose the glottis and the vocal cords. The tube is then introduced through the vocal cords. Gentle cricoid pressure may be useful. Tube sizes vary from 3.5 to 4.0 mm for term infants down to 2.5 mm for those < 28 weeks or < 1000 g.
Immediately following birth, the infant must promptly convert to air breathing as the fluid-filled alveoli expand with air and pulmonary perfusion is established. The newborn begins to breathe and cry almost immediately after birth, which indicates establishment of active respiration. Some factors that appear to influence the first breath include: • Physical stimulation—examples include handling the neonate during delivery. • Oxygen deprivation and carbon dioxide accumulation—these serve to increase the frequency and magnitude of breathing movements both before and after birth (Dawes, 1974). • Thoracic compression—this occurs during pelvic descent, following which vaginal birth forces fluid from the respiratory tract in volume equivalent to approximately a fourth of the ultimate functional residual capacity (Saunders, 1978). • Aeration of the newborn lung does not involve the inflation of a collapsed structure, but instead, the rapid replacement of bronchial and alveolar fluid by air. After delivery, the residual alveolar fluid is cleared through the pulmonary circulation and to a lesser degree, through the pulmonary lymphatics (Chernick, 1978). Delay in fluid removal from the alveoli probably contributes to the syndrome of transient tachypnea of the newborn (TTN) (Guglani, 2008). As fluid is replaced by air, compression of the pulmonary vasculature is reduced considerably, and in turn, resistance to blood flow is lowered. With the fall in pulmonary arterial blood pressure, the ductus arteriosus normally closes (Fig. 7-8, p. 136). High negative intrathoracic pressures are required to bring about the initial entry of air into the fluid-filled alveoli. Normally, from the first breath after birth, progressively more residual air accumulates in the lung, and with each successive breath, lower pulmonary opening pressure is required. In the normal mature newborn, by approximately the fifth breath, pressure-volume changes achieved with each respiration are very similar to those of the adult. Thus, the breathing pattern shifts from the shallow episodic inspirations characteristic of the fetus to regular, deeper inhalations (Chap. 17, p. 337). Surfactant, which is synthesized by type II pneumocytes and already present in the alveoli, lowers alveolar surface tension and thereby prevents lung collapse. Insufficient surfactant, common in preterm infants, leads promptly to respiratory distress syndrome, which is described in Chapter 34 (p. 653).
CARE IN THE DELIVERY ROOM
Personnel designated for infant support are responsible for immediate care and for acute resuscitation initiation if needed.
Immediate Care
Before and during delivery, careful consideration must be given to several determinants of neonatal well-being including: (1) maternal health status; (2) prenatal complications, including any suspected fetal malformations; (3) gestational age; (4) labor complications; (5) duration of labor and ruptured membranes; (6) type and duration of anesthesia; (7) difficulty with delivery; and (8) medications given during labor and their dosages, administration routes, and timing relative to delivery.
Newborn Resuscitation
The International Liaison Committee on Resuscitation (ILCOR) updated its guidelines for neonatal resuscitation that are sanctioned by the American Academy of Pediatrics and the American Heart Association (Biban, 2011; Perlman, 2010). These substantially revised guidelines are incorporated into the following sections. Approximately 10 percent of newborns require some degree of active resuscitation to stimulate breathing, and 1 percent require extensive resuscitation. It is perhaps not coincidental that there is a two- to threefold risk of death for newborns delivered at home compared with those delivered in hospitals (American College of Obstetricians and Gynecologists, 2013b). When deprived of oxygen, either before or after birth, neonates demonstrate a well-defined sequence of events leading to apnea (Fig. 32-1). With oxygen deprivation, there is a transient period of rapid breathing, and if it persists, breathing stops, which is termed primary apnea. This stage is accompanied by a fall in heart rate and loss of neuromuscular tone. Simple stimulation and exposure to oxygen will usually reverse primary apnea. If oxygen deprivation and asphyxia persist, however, the newborn will develop deep gasping respirations, followed by secondary apnea. This latter stage is associated with a further decline in heart rate, falling blood pressure, and loss of neuromuscular tone. Neonates in secondary apnea will not respond to stimulation and will not spontaneously resume respiratory efforts. Unless ventilation is assisted, death follows. Clinically, primary and secondary apneas are indistinguishable. Thus, secondary apnea must be assumed and resuscitation of the apneic newborn must be started immediately.
Resuscitation Protocol
The updated algorithm for newborn resuscitation recommended by ILCOR and the International Consensus on Cardiopulmonary Resuscitation is shown in Figure 32-2. Many of its tenets follow below.
Basic Measures
The vigorous newborn is first placed in a warm environment to minimize heat loss, the airway is cleared, and the infant dried. Routine gastric aspiration has been shown to be nonbeneficial and even harmful (Kiremitci, 2011). And although previously recommended, there is no evidence that bulb suctioning for clear or meconium-stained fluid is beneficial, even if the newborn is depressed (Chap. 33, p. 638). With stimulation, the healthy newborn will take a breath within a few seconds of birth and cry within half a minute, after which routine supportive care is provided.
Assessment at 30 Seconds of Life. Apnea, gasping respirations, or heart rate < 100 bpm beyond 30 seconds after delivery should prompt administration of positive-pressure ventilation with room air (Fig. 32-3). Assisted ventilation rates of 30 to 60 breaths per minute are commonly employed, and the percent of oxygen saturation is monitored by pulse oximetry. At this point, supplemental oxygen can be given in graduated increasing percentages to maintain oxygen saturation (Spo2) values within a normal range (Vento, 2011). Adequate ventilation is indicated by improved heart rate. ventilation. The head should be in a sniffing position with the tip of the nose pointing to the ceiling. The neck should not be hyperextended. Assessment at 60 Seconds of Life. If the heart rate remains < 100 bpm, then ventilation is inadequate. The head position should be checked as shown in Figure 32-3, secretions cleared, and if necessary, inflation pressure increased. If the heart rate persists below 100 bpm beyond 60 seconds, tracheal intubation is considered. A number of conditions may be the cause of inadequate response, including the following: • Hypoxemia or acidosis from any cause • Drugs administered to the mother before delivery • Immaturity • Upper airway obstruction • Pneumothorax • Lung abnormalities • Meconium aspiration • Central nervous system developmental abnormality • Sepsis syndrome. Tracheal Intubation If bag-and-mask ventilation is ineffective or prolonged, tracheal intubation is then performed. Other indications include the need for chest compressions or tracheal administration of medications, or special circumstances such as extremely low birthweight or a congenital diaphragmatic hernia. A laryngoscope with a straight blade—size 0 for a preterm infant and size 1 for a term neonate—is introduced at the side of the mouth and then directed posteriorly toward the oropharynx as shown in Figure 32-4. The laryngoscope is next moved gently into the vallecula—the space between the base of the tongue and the epiglottis. Gentle elevation of the laryngoscope tip will raise the epiglottis and expose the glottis and the vocal cords. The tube is then introduced through the vocal cords. Gentle cricoid pressure may be useful. Tube sizes vary from 3.5 to 4.0 mm for term infants down to 2.5 mm for those < 28 weeks or < 1000 g.
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