23 – Anesthesia for Abdominal Wall Reconstruction Procedures




23 Anesthesia for Abdominal Wall Reconstruction Procedures


Ellen Choi and Samuel H. Wald



Gastroschisis/Omphalocele


The neonate with gastroschisis presents with the abdominal viscera herniated and exposed to air after delivery; this is usually an isolated lesion. Omphalocele is associated with other anomalies of cardiac, genetic, urologic, and/or metabolic (Beckwith–Wiedermann syndrome) origin, and the viscera are covered with a sac [1]. Specific considerations are directed at maintaining perfusion of the bowel, fluid resuscitation, and careful staged reduction with maintenance of pulmonary function. Surgical closure of the abdominal contents must be performed with close monitoring of changes in pulmonary compliance in order to prevent an abdominal compartment syndrome (Figure 23.1) [2,3].





Figure 23.1 Schematic of pulmonary compliance relative to increasing intra-abdominal pressure.


Source: [4]

Gastroschisis is a full-thickness defect in the anterior abdominal wall, usually located to the right of the umbilicus, leading to herniation of abdominal contents. The defect can be of variable size, but is generally less than 5 cm in diameter [5]. The etiology is uncertain, but various mechanisms have been proposed, including a failure of mesenchymal cells to cover the abdominal wall defect after normal return of the developing gastrointestinal tract to the embryologic abdominal cavity. Other theories include weakness in the abdominal wall leading to rupture and herniation of the rapidly growing gastrointestinal tract, defective involution of the right umbilical vein, and disruption of the right omphalomesenteric artery, leading to ischemia and atrophy or thinning of the anterior abdominal wall [6,7].


The herniated contents usually consist of small and/or large bowel, and may include solid organs such as liver if the defect is large. The gastrointestinal tract is not covered by the peritoneal sac, and is thereby fully exposed to amniotic fluid in utero and to the environment after birth. Blood supply to the abdominal viscera may be compromised, leading to ischemic or infarcted bowel. Often, the bowel may appear dilated, foreshortened and edematous, with areas of atresia from compromised blood flow in utero. The gut is functionally abnormal, even without atretic portions or other associated anomalies. A fibrinous “peel,” thought to come from gastrointestinal contents contacting amniotic fluid, may cover the exposed viscera, and is associated with a worse outcome [5,8].


The incidence of gastroschisis has been estimated to be approximately 1:3000–1:8000 live births, with recent increase in overall incidence worldwide [9,10]. One known risk factor is maternal age less than 20 years [11]. Serious associated congenital anomalies are uncommon, with most abnormalities affecting the gastrointestinal system, such as intestinal atresia [12]. Most cases are sporadic, but there has been an association with prematurity and low birth weight [13]. Complications of gastroschisis include sepsis, bowel infarction and perforation, and necrotizing enterocolitis, with patients also experiencing problems related to prematurity such as chronic lung disease and cardiac abnormalities. Gastrointestinal dysfunction may also lead to prolonged ileus, feeding delay or feeding intolerance and prolonged hospitalization [14]. Gastroschisis originally was associated with 100 percent mortality, but now with a staged closure has a 90 percent survival rate with specialist care. There is an overall good prognosis, although the risk of long-term disability associated with prematurity and gastrointestinal dysfunction exists [15]. A small cohort of over 60 neonates born with gastroschisis followed to 36 months had long-term problems with bowel motility, reflux, short gut syndrome and tube-feed or dependence on total parenteral nutrition [16].


Most cases of gastroschisis are diagnosed with prenatal ultrasound, and the diagnosis is supported with elevated maternal serum alpha-fetoprotein [17,18]. Once diagnosed, arrangements should be made for delivery at a facility capable of resuscitating the neonate with gastroschisis. The goals of resuscitation immediately after birth include airway protection, rapid assessment and support of adequate ventilation and oxygenation, protection of exposed bowel, and minimization of insensible fluid and heat losses [2]. The baby should be actively dried and warmed, with exposed bowel and the lower half of the body covered with a sterile transparent plastic bowel bag as a temporizing measure. The baby should be placed in the right lateral decubitus position to reduce the risk of compromised blood flow to the gastrointestinal tract while further assessment and resuscitation continues. A nasogastric tube for bowel decompression should be placed to reduce the risk of aspiration and regurgitation. Intravenous access should be established for targeted resuscitation with intravenous isotonic fluids and administration of broad-spectrum antibiotics. Catheterization of umbilical vessels is contraindicated in gastroschisis [1].


The high degree of third space losses with gastroschisis should not be underestimated. The neonate should be actively resuscitated with isotonic fluids, with regular assessment of volume status by exam, vital signs, urine output, and laboratory measurements of acid–base status [19]. Invasive monitoring with a peripheral arterial line should be considered. Care should be taken to keep the bowel covered with sterile plastic wrap to reduce the risk of profound hypothermia and dehydration, and the viscera should be physically supported to ensure that no twisting or impingement occurs at the herniation site leading to ischemia, particularly during times of transport [2,5].


Urgent reduction of abdominal contents is necessary due to the risk of ischemia and infection. The size of the abdominal wall defect determines surgical approach. Small defects may be managed with primary closure in the operating room or at bedside in the neonatal intensive care unit. Large defects may be managed in one of several ways, with many practitioners favoring a staged reduction using a preformed spring-loaded silo or a formal silastic silo, which is then suspended [20,21]. Gravity will allow the exposed bowel to gradually return to the abdominal cavity, with the silo concomitantly reduced in size daily. Physiologic neonatal diuresis will also lead to a decrease in bowel edema, enhancing reduction. The abdominal defect is closed in the operating room once the viscera have been completely reduced.


Preoperative preparation includes evaluation of volume status and adequacy of resuscitation, as well as screening for any comorbidities. These patients are at risk for infection, dehydration, hypothermia, acidosis, hypoproteinemia with decreased plasma oncotic pressure, and obstruction with vomiting and abdominal distention. The operating room should be warmed, with forced-air warming blankets, external heat lamps, heat-moisture exchangers and other devices to combat hypothermia [22,23]. Blood products should be cross-matched and available.


Prior to anesthetic induction, the nasogastric tube should be aspirated to drain gastric contents. A rapid-sequence or modified rapid-sequence induction is suggested after adequate preoxygenation. A difficult airway may necessitate advanced airway techniques including video laryngoscopy or fiberoptic intubation. Anesthesia may be maintained with volatile inhaled anesthetic, narcotic techniques, or supplemented with a caudal/epidural [24]. Neuraxial techniques are not contraindicated and can be particularly useful in cases of early extubation. Both ropivacaine 0.2 percent and chloroprocaine 3 percent infusions have been described and used successfully as adjuncts for major abdominal wall repair in the neonate [25]. Nitrous oxide should be avoided due to the propensity for bowel distention. Intravenous dextrose solution administration is recommended for maintenance of serum glucose, and additional intravenous isotonic fluids should be given to maintain euvolemia. A bladder catheter is often placed to monitor urine output. Standard monitors as well as arterial pressure monitoring may be necessary for larger defects. Both core and peripheral temperatures should be monitored. A central venous catheter may be placed for additional access or if total parenteral nutrition will be required postoperatively [23].


Intragastric or bladder pressures may also be monitored during primary closure of a large defect to assess for abdominal compartment syndrome [26]. Herniated viscera reduced into a relatively small abdominal cavity will raise intra-abdominal pressure, compressing the inferior vena cava, decreasing venous return and cardiac output [27]. In severe cases, this may lead to compromised renal and splanchnic circulation, leading to end-organ ischemia with resultant metabolic acidosis, renal failure, bowel perforation, and/or necrotizing enterocolitis. A tight closure may also lead to high wound tension and dehiscence, as well as compromised respiratory function, necessitating higher pulmonary inflation pressures. Peak inspiratory pressure prior to reduction should be noted to assist in evaluation of increased abdominal pressure [3,28]. Ventilation may become problematic with an endotracheal tube with a large leak after a tight reduction.


Omphalocele, or exomphalos, is a midline herniation of the gastrointestinal tract through the umbilical ring into the base of the umbilical cord, and can consist of any amount of intestine as well as liver, spleen, or other abdominal organs. The viscera are housed in a gelatinous-appearing membranous sac consisting of peritoneum, Wharton’s jelly, and amnion. The umbilical vessels themselves insert into the membrane, and the bowel is normal [7,29].


Most cases of omphalocele are sporadic. Unlike gastroschisis, the overall incidence has remained stable at approximately 1:5000 live births [30,31]. The exact mechanisms are unknown, but omphalocele is thought to result from the failure of the midgut to return to the developing abdominal cavity after the tenth week of gestation, with incomplete closure of the anterior abdominal wall at the umbilicus [32]. The size of the defect can be variable, ranging from 2–5 cm (small) in diameter to greater than 10 cm (large), with organ herniation and pulmonary hypoplasia from poorly developed abdominal and thoracic cavities. Greater than 60 percent of cases have associated congenital abnormalities, including cardiac (30–40 percent) defects such as Tetralogy of Fallot, chromosomal disorders (trisomy 13, 18, 21), cloacal or bladder extrophy, Beckwith–Wiedemann syndrome, congenital diaphragmatic hernia, malrotation of the gut, microcephaly, meningocele, and rarely, pentalogy of Cantrell (Table 23.1) [11]. Outcomes are affected by the severity of associated congenital defects, surgical complications, low birth weight, membrane rupture, bowel obstruction, and sepsis [33,34].




Table 23.1 Characteristics of omphalocele and gastroschisis
































Omphalocele Gastroschisis
Incidence 1:5000; stable 1:3000 – 1:8000; increasing worldwide
Position Midline Right of umbilicus
Size of defect Variable size, small (2–5 cm), large (>10 cm) Full thickness; variable, usually <5 cm
Presence of sac Yes, although sac may rupture No; bowel completely exposed pre- and postnatally
Associated defects Greater than 60 percent cases

   –  cardiac (30 – 40 percent), i.e., Tetralogy of Fallot

   –  chromosomal disorders, i.e., trisomy 13, 18, or 21

   –  urologic, i.e., bladder extrophy, cloacal defect

   –  metabolic, i.e., Beckwith–Wiedemann

   –  neurologic, i.e., microcephaly, meningocele

   –  congenital diaphragmatic hernia

   –  Pentalogy of Cantrell
Uncommon; usually isolated lesion

As with gastroschisis, most cases of omphalocele are detected on prenatal ultrasound, and associated with elevated levels of maternal serum alpha-fetoprotein, although values are generally not as high as with gastroschisis. Once omphalocele is suspected, amniocentesis and chorionic villus sampling should be pursued for karyotype analysis to screen for chromosomal abnormalities, along with fetal echocardiogram to evaluate for congenital heart disease [18,35]. There is associated high risk for intrauterine growth restriction, preterm labor and fetal demise [11]. Babies with a large omphalocele defect should be delivered by Cesarean section to decrease the risk of sac rupture [35]. The sac may rupture prior to, during or after delivery, leaving the bowel unprotected.


The goals of resuscitation immediately after birth include airway protection, rapid assessment and support of adequate ventilation and oxygenation, protection of exposed bowel and minimization of insensible fluid and heat losses [2]. Third-space losses, however, are not as profound as with gastroschisis, and there is less immediate urgency for surgical repair unless the sac has ruptured, although the risks of ischemia, bowel obstruction and sepsis are still present. A nasogastric tube for bowel decompression should be placed. The baby may be placed in the left lateral decubitus position to reduce the risk of compression of the inferior vena cava and compromised venous return. Intravenous access should be established for targeted resuscitation with intravenous isotonic fluids, administration of broad-spectrum antibiotics and dextrose solution. Catheterization of umbilical vessels is contraindicated [36]. Infants with Beckwith–Wiedemann syndrome have macroglossia so intubation may be difficult. Intraoperatively, they can develop hypoglycemia so a means of measuring serum glucose should be available.


Reduction of abdominal contents is necessary due to the risk of ischemia and infection. As with gastroschisis, care should be taken to keep the bowel covered with sterile wrap to reduce hypothermia and dehydration, and the viscera should be physically supported to ensure that no twisting or impingement occurs at the herniation site leading to ischemia, particularly during times of transport. Given the known association between omphalocele and other congenital defects, preoperative preparation should include a thorough medical screening, including chest radiograph, echocardiogram, renal ultrasound and laboratory panel [2].


Intraoperative management concerns are similar to those for gastroschisis repair, with the size of the abdominal wall defect determining the surgical approach. Primary closure may be used for small defects. Staged repair using a silo over days to weeks, mesh closure, and tissue expanders have all been described [20,21,37]. Large unruptured, stable defects may be allowed to epithelialize using escharotic topical agents (i.e., silver sulfadiazine), with later repair of the abdominal wall defect. If the liver is herniated, hepatic vein compression or damage to the liver itself during reduction may lead to hemodynamic instability.


Both term and premature neonates are thermogenically active. In order to maintain constant temperature, infants exposed to a cold environment increase their metabolic activity and heat production without shivering. This, however, has high energy and oxygen costs. Heat loss is favored due to the neonatal body habitus of reduced subcutaneous fat and large surface area to body ratio. Neonates have limited shivering and non-shivering thermogenesis (brown fat) and are at high risk for temperature losses in the perioperative period. Survival of premature neonates is directly related to ambient temperature. Perioperative goals of care should include maintenance of a neutral thermal environment. This is facilitated by use of heated transport, warmed solutions, warmed blood products, heated mattress, radiant warmer, and forced-air warmer [23].



Umbilical Hernia


Residual patency of the umbilical ring and the omphalomesenteric duct may lead to other, less severe forms of ventral abdominal wall defects, including umbilical hernia, Meckel’s diverticulum, umbilical polyp, or fistula [38].


All neonates have an umbilical defect for the umbilical vessels and cord. The umbilical ring closes naturally during the first few weeks of life, but in 10–30 percent of patients the ring fails to close. Certain ethnic groups have a higher incidence, with African Americans 6–10 times more likely than Caucasians to present with an umbilical hernia [39]. Those with low birth weight (less than 1200 g) are four times more likely to have umbilical ring defect than those with a birth weight greater than 2500 g. Other risk factors include trisomy 21 and Beckwith–Wiedemann syndrome [40]. Umbilical hernias are covered by skin and peritoneum. Most umbilical hernias will close spontaneously in the first few years of life, depending on the size of the defect and the age of the child at presentation. Most repairs are performed after three years of age. Incarceration is uncommon at less than 5 percent of cases, with a less than 2 percent rate of recurrence [41,42].


Preoperative preparation includes an assessment of any residual comorbidities of prematurity, associated syndromes, and evidence of incarceration or obstruction. Anesthetic techniques include general anesthesia supplemented with truncal (rectus sheath, paraumbilical) blocks [43] or caudal injection of local anesthetic, and regional anesthesia such as spinal or caudal injection of local anesthetic. Umbilical hernia repairs may be scheduled as ambulatory or day surgery cases for older patients that do not require postoperative apnea monitoring [44]. Recent studies have shown superior analgesia from ultrasound-guided rectus sheath blocks compared with peri-incisional infiltration of local anesthetic [45,46].



Inguinal Hernia


Indirect inguinal hernia results in a protrusion of intestine through a congenitally patent processus vaginalis, while a direct hernia is due to a defect in the transversalis fascia. The incidence is 0.8–4 percent of the population, and is approximately 5–10 times more common in boys than girls. It is quite common in premature infants and infants of low birth weight, affecting 10–30 percent of premature infants as opposed to 3–5 percent of term infants, with an incidence of 13 percent in babies born at less than 32 weeks’ gestation, and 30 percent in babies weighing less than 1000 g. It is found more commonly on the right (75 percent) than the left side (25 percent), reflecting the later descent of the right testicle in development. Bilateral hernias occur in 15–20 percent of cases, and risk factors for bilateral hernias include female gender, presentation with a left-sided hernia, prematurity, age less than one year and undescended testicle [47,48].


During development, the gonads descend from the urogenital ridge in the upper abdomen to the inguinal ring at three months’ gestation. The processus vaginalis develops from the peritoneal lining. At 6–7 months’ gestation, the testes descend through the inguinal canal, following the gubernaculum, and come to lie in the scrotum. The processus vaginalis is gradually obliterated, leaving behind the tunica vaginalis, with closure occurring earlier on the left than the right side during development [49]. There is greater likelihood of incomplete obliteration with decreasing age, and higher chance of indirect inguinal hernia formation. In females, the round ligament is analogous to the processus vaginalis, and inguinal hernias occur frequently at the canal of Nuck, anterior to the round ligament.


Hernias may be asymptomatic or minimally symptomatic, with intermittent presentation of a bulge at the internal or external inguinal ring. The bulge can disappear with rest or sleep, and may reappear with Valsalva maneuvers such as crying or straining. The differential diagnosis includes hydrocele, lymphadenopathy, neoplasm, torsion, and retractable testis. Ultrasound may reveal a patent processus vaginalis.


An easily reducible, asymptomatic hernia may be repaired electively. An incarcerated hernia is one that is not reducible, and may be associated with pain, tenderness, abdominal distention, emesis, and anorexia. Attempts should be made to reduce an incarcerated hernia at presentation, which may require the use of pain medication, sedation, or repositioning, with subsequent repair after reduction in 1–2 days to prevent recurrence of incarceration. If the hernia is irreducible or is causing obstruction, it should be repaired urgently due to the risk of strangulation. A strangulated hernia is an incarcerated hernia with compromised blood flow to the bowel or testes, and is a surgical emergency. Presentation includes emesis, pain, fever, leukocytosis, erythema, tachycardia, and history of a prolonged bulge. The patient may require a bowel resection for ischemic or infarcted bowel. Premature infants and those less than six months old are more likely to have incarceration [50,51].


Timing of inguinal hernia repair depends upon the age of the patient and existing comorbidities. The risk of incarceration is balanced with the risk of undergoing surgery, particularly amid evolving concerns about anesthetic neurotoxicity in the young and premature [52]. Factors affecting postoperative apnea and respiratory complications include young postconceptual age, existing lung disease, oxygen requirement, anemia, home apnea monitoring, and administration of sedatives, general anesthetics, and opioids [53]. The risk for postoperative apnea decreases with increasing postconceptual age, and many centers have in place institutional policies requiring postoperative admission for apnea monitoring for those patients whose postconceptual age is less than 52–60 weeks in the former premature infant and less than 45 weeks in the former term infant [44,54]. Hernia repair is often scheduled prior to planned discharge home for the former premature infant, or alternatively, the patient may be discharged home and scheduled to return for elective repair at a later time [55].


Inguinal hernia repair may be performed either open or laparoscopically, and opinion is divided regarding superiority of one approach over the other [56]. Surgical complications include infection, bleeding, infarction, and atrophy of the testis, injury to the vas deferens, bowel perforation, and hernia recurrence (less than 5 percent). Some practitioners will perform laparoscopic evaluation of the contralateral side for patent processus vaginalis and hernia, but whether to do so routinely remains controversial [57]. Fifty percent of children less than two years old will have a patent processus vaginalis on the contralateral side, but it is unclear how many of them will eventually present with hernia, with variable reported rates of 8–20 percent [50,58].


Preoperative preparation includes an assessment of residual comorbidities of prematurity, the nature of the hernia, and the planned surgical approach [53]. Administration of caffeine 10 mg kg–1 IV may be considered for those patients at risk of postoperative apnea [59]. Anesthetic techniques include general anesthesia supplemented with truncal (ilioinguinal, iliohypogastric, transversus abdominis plane) blocks [60,61] or caudal injection of local anesthetic, and regional anesthesia such as spinal or caudal injection of local anesthetic with or without placement of a caudal catheter [62]. The advantage of a spinal anesthetic is its quick onset, and the benefit of avoiding the effects of systemic sedation and postoperative apnea, but drawbacks include limited duration of action and variable reported failure rates [63]. Supplemental sedatives or opioids will eliminate the advantages of awake regional anesthesia on postoperative apnea [44]. Intraoperative restlessness can be soothed with a pacifier dipped in sucrose solution [64]. Caudal anesthesia may be more reliable but has a slower onset [65]. Large, bilateral, and complicated repairs may necessitate general anesthesia. Laparoscopic evaluation of the contralateral side for hernia is not an absolute contraindication for awake regional anesthesia, but can pose specific challenges during insufflation and pneumoperitoneum [63].



Hydrocele


Hydrocele is a fluid collection in the tunica vaginalis around the testicle. A communicating hydrocele is essentially a hernia, with a connection to the abdominal cavity via a patent processus vaginalis, whereas a noncommunicating hydrocele does not maintain such a connection [66].


During development, incomplete obliteration of the processus vaginalis will lead to either hernia or hydrocele. An open processus vaginalis with complete failure of obliteration leads to an inguinal or scrotal hernia. Distal obliteration of the processus vaginalis with a patent proximal portion will lead to inguinal hernia. Narrowing of the proximal processus creates a communicating hydrocele, and partial patency of the processus with obliteration of the proximal portion leads to a noncommunicating hydrocele [47].


Communicating hydroceles fluctuate in size during the day, enlarging especially in the dependent position, and are easily compressible. They are treated like inguinal hernias and generally require surgical repair [67]. Noncommunicating hydroceles do not fluctuate in size daily, but can gradually change in size over the course of weeks and are non-compressible. They are quite common after birth, with most resolving spontaneously by the first two years of life. If they have not resolved in the first 12–24 months of life, noncommunicating hydroceles should undergo surgical repair [50,68].


Like hernias, hydroceles are more common on the right than the left side. Those found at birth do not increase the chance of hernia later, although hydroceles that develop later in life imply the presence of a patent processus vaginalis with a chance of hernia formation. Repair is via an inguinal approach to evaluate for a patent processus [69]. A high ligation is performed, the distal sac is opened and the hydrocele is evacuated but is not completely excised due to potential risk of injury to the testicle.


Preoperative preparation includes screening for any residual comorbidities of prematurity or from the neonatal period, and the type of hydrocele and the surgical approach. Older infants and toddlers may benefit from premedication with an anxiolytic prior to parental separation and induction [70]. Anesthetic techniques include general anesthesia with or without caudal injection of a local anesthetic or ilioinguinal and iliohypogastric nerve blocks [71]. Either inhalational or intravenous induction may be performed. Regional anesthesia options include caudal or spinal anesthesia.




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