33 Plastic and Reconstructive Surgery
PEDIATRIC PLASTIC SURGERY is performed in children of all ages, even in utero.1 However, the majority of children who undergo plastic surgical and reconstructive procedures are between 2 and 9 years of age, with a median age of 5 years.2 A wide spectrum of associated craniofacial abnormalities, underlying medical conditions, and surgical procedures characterize this pediatric population. Consequently, a thorough preoperative assessment, consultation with medical and surgical teams, and anticipation and preparation for potential complications are of paramount importance to ensure a successful perioperative outcome. The incidence of major morbidity and mortality has been reduced over the last 30 years from 16.5% and 1.6% to less than 0.1% and 0.1%, respectively, in children undergoing major craniofacial surgeries.3
Cleft Lip and Palate
Cleft lip and palate are among the more common congenital malformations, occurring with an estimated incidence of approximately 1 in 700 births worldwide.4 More common in males than in females, this malformation likely results from both environmental and genetic causes. Parental occupation, in particular paternal farming, increases the risk of cleft lip or palate in the offspring, whereas the maternal occupation presents no additional risk.5 Folate metabolism disturbances and increased maternal homocysteine levels also may be contributory.6 Cleft lip with or without cleft palate has been linked to several loci on chromosomes 1, 2, 4, 6, 14, 17, and 19, suggesting a genetic basis for some of these anomalies.7–9
These disorders are associated with more than 400 syndromes; the more common syndromes are presented in Table 33-1. Cleft lip and palate begin as a defect in palatal growth in the first trimester of pregnancy. Fetal magnetic resonance imaging (MRI) provides a greater degree of resolution of defects in the posterior palate and lateral extent of cleft with greater diagnostic accuracy than ultrasound. MRI also enables early detection of potential syndromic conditions by providing a complete study of the fetal head and biometric development of the facial bones.10
TABLE 33-1 Syndromes Commonly Associated with Cleft Lip and Palate
Anesthetic Considerations
Surgical correction of cleft lip defect is usually performed at 3 months of age to allow sufficient time for maturation and associated abnormalities to become apparent. Preoperative assessment may reveal abnormalities such as mandibular hypoplasia in Pierre Robin sequence (Fig. 33-1 and E-Fig. 33-1) or restricted neck movement as in Klippel-Feil syndrome (E-Fig. 33-2).4 Pierre Robin sequence is defined as the triad of micrognathia, glossoptosis (caudally displaced insertion of the tongue), and respiratory distress in the first 24 to 48 hours after birth. The presence of other anomalies might warrant additional clinical or laboratory investigations. Cleft lip repair usually involves minimal blood loss, so for children with hematocrit values greater than 30%, homologous blood donation is unnecessary. Type and screen of donated blood is usually sufficient for a hematocrit value less than 30%.11
The frequency of difficult airways in children with cleft lip and palate varies from 4.7% to 8.4%.12–14 The incidence of difficult intubation in children with bilateral cleft is greater than that with unilateral cleft.14 Furthermore, micrognathia is an independent predictor of a difficult airway. The incidence of difficult laryngoscopy is approximately 50% in children with micrognathia but only about 4% in those without. In infants and young children, micrognathia may be subtle and not always easily detected. However, the presence of microtia, particularly bilateral microtia, which has a 42% incidence of difficult intubation with bilateral compared with 2% with unilateral microtia, should prompt a closer examination of the mandible for hypoplastic growth and raise the possibility of a hemifacial microsomia or Treacher Collins syndrome.15 Intubation difficulty with isolated micrognathia decreases with increasing age, with the greatest difficulty presenting in infants younger than 6 months. Tracheal intubation becomes easier with age in isolated micrognathia. This has been attributed to rapid growth of the mandible, which catches up to the maxilla, thereby aligning the two bones, by 2 years of age in most cases. A careful review of previous anesthetic records may forewarn of a difficult airway. In our experience, tracheal intubation is not particularly difficult in most infants and children with cleft lip or palate, unless concomitant defects such as micrognathia are present.
Induction of anesthesia via facemask is usually uncomplicated in infants with cleft lip and palate. Laryngoscopy should be performed using a straight blade via a right paraglossal approach (blade inserted into the pharyngeal gutter with tongue displaced to the opposite side)16 (or a left approach if a left-handed blade is available), taking care to avoid inserting the blade into the cleft (see also Fig. 12-28, A-C). If the mandible is hypoplastic, external laryngeal manipulation may be required to visualize the larynx. In some centers, the tongue is sutured to either the mandible or lower lip to preclude airway obstruction in infants with Pierre Robin sequence in the postnatal period. In such instances, the tongue cannot be displaced to the left to expose the larynx. To facilitate laryngoscopy in such cases, the tongue is first released from the lower lip using ketamine sedation. Direct laryngoscopy follows. If direct laryngoscopy fails to expose the larynx, then alternative airway maneuvers such as fiberoptic intubation through a laryngeal mask airway (LMA) may be used after an inhalational induction of anesthesia and release of the tongue (see Chapter 12 and Fig. 12-22, A-C).
A variety of tracheal tubes can be used to secure the airway for cleft lip and palate surgery, although the ideal tracheal tube is perhaps the oral Ring-Adair-Elwyn (RAE) tube, which can be fixed centrally to the chin to facilitate optimal surgical access. Reinforced tracheal tubes are suitable alternatives, but in both cases care must be taken to fix the tube at the correct depth to avoid endobronchial intubation. Throat packs usually impinge on the surgical field and are not normally required for cleft palate repair. The lungs are ventilated for the duration of the procedure, usually 1 to 2 hours. Inhalational or intravenous anesthetics combined with a short-acting opioid such as fentanyl (1 to 2 µg/kg) can be used for maintenance of anesthesia. Bilateral infraorbital nerve blocks may be used to provide postoperative analgesia for cleft lip repairs (see Fig. 41-11, A-C, and Chapter 41 videos)
. Such blocks reduce the need for opioids and antiemetics, improve the ability to feed,17 and increase parental satisfaction.18 A combination of infraorbital and external nasal nerve blocks for pain control after cleft lip repair is an alternative.19
During cleft palate surgery, the pharyngeal space is reduced dramatically (Fig. 33-2 and E-Fig. 33-3). The trachea is extubated after the upper airway reflexes have returned and the child is completely awake. These children are at particular risk for acute upper airway obstruction in the immediate postextubation period as a result of upper airway narrowing, edema, blood, and residual anesthetic effects.20–25 Accordingly, it is very important to extubate the trachea only when the child is completely awake. Late postoperative edema26 and severe subcutaneous emphysema are additional complications. Upper respiratory tract infections are common in this age group, and if these infections are present, they should weigh heavily in favor of delaying surgery until they are resolved. Antibiotics may reduce the incidence of postoperative respiratory complications.27
A nasopharyngeal airway may be inserted by the surgeon before extubation to ensure a patent airway after extubation and permit suctioning the airway without damaging the palatal repair (see Fig. 33-2). Arm restraints are used in many centers to prevent suture disruption. These children are monitored for signs of upper airway obstruction during the recovery period for approximately 48 hours.20 As soon as the child is awake, feeding with clear fluids is allowed. Postoperative pain is managed with a combination of opioids and acetaminophen. Sphenopalatine and infraorbital nerve blocks with a long-acting local anesthetic can be placed at the end of the procedure to prevent pain after cleft lip and palate repair.17 Palatal nerve block (nasopalatine, greater and lesser palatine)28 or a bilateral suprazygomatic maxillary nerve block reduce postoperative pain and favor early feeding.29
Craniosynostosis
Craniosynostosis, a congenital anomaly in which one or more cranial sutures closes prematurely, occurs in approximately 1 in 2000 births, and affects males more frequently than females. Embryologically, the cranial vault starts to ossify at 8 weeks after conception. Fusion of the parietal and frontal bones is usually completed by 7 months after conception. Postnatally, the anterolateral fontanelle closes by 3 months, the posterior fontanelle by 3 to 6 months, the anterior fontanelle by 9 to 18 months, and the posterolateral fontanelle by 2 years. Premature osseous obliteration of a bony suture might result from the absence of osteoinhibitory signals from the suture. Craniosynostosis may be categorized as simple (or nonsyndromic) (65% to 80% of cases), involving closure of one suture, or complex (or syndromic) (20% to 30%), involving closure of two or more sutures and often associated with a variety of clinical features and metabolic diseases (Table 33-2).30,31
TABLE 33-2 Classification of Craniosynostosis
In the child with craniosynostosis, the head may assume various shapes depending on the sutures involved (Fig. 33-3 and E-Fig. 33-4). The frequency of single suture closures varies with the specific suture: sagittal (50%), coronal (20%), and metopic (10%).30 The coronal suture is more commonly associated with syndromic craniosynostoses.
Although approximately 80% of premature suture closures are isolated defects, the remaining 20% involve multiple suture closures associated with more than 150 syndromes that present with a myriad of clinical features (see Table 33-2).30 Apert syndrome occurs in approximately 1 in 100,000 live births, usually as a sporadic mutation, although autosomal dominant inheritance patterns can occur. This syndrome phenotypically manifests as cloverleaf skull (craniosynostosis), hypertelorism, proptosis, midface hypoplasia, and syndactyly (upper or lower extremity). Development is often complicated by increased intracranial pressure (ICP) and obstructive sleep apnea (OSA).32,33 Whether children with Apert syndrome develop normal intelligence quotients (IQs) is unclear. One study reported that 32% of children with Apert syndrome had IQs greater than 70.34 Timing of cranial surgery may affect the child’s IQ; surgery in the first year of life was associated with an IQ greater than 70 in more than 50% of children in one study, whereas surgery after the first year of life was associated with an IQ greater than 70 in only 7%. Two other factors predicted improved IQ indices: absence of a defect in the septum pellucidum and noninstitutional residence (i.e., family home residence). Crouzon syndrome is phenotypically similar to Apert syndrome but has different ophthalmologic defects, specifically, optic atrophy occurring in up to 20%, and the absence of digital involvement.35 Fifty percent of Crouzon syndrome defects are sporadic mutations, and the remainder are familial. Pfeiffer syndrome occurs in approximately 1 in 25,000 live births. Most cases are familial with an autosomal dominant inheritance pattern, although many remain sporadic. The phenotype of Pfeiffer syndrome is similar to that of Apert syndrome but includes broad thumb, large first toe, and polydactyly. Children with Pfeiffer syndrome have normal intelligence. Carpenter syndrome is associated with craniosynostosis, syndactyly, cardiac defects, and obesity.36 Cognitive impairment is common.36 A relatively new but rare syndrome, Shprintzen-Goldberg, is characterized by craniosynostosis and a phenotype that resembles that of Marfan syndrome.
Indications for cranial vault reconstruction include increased ICP, severe exophthalmos, OSA, craniofacial deformity, and psychosocial reasons. If uncorrected, the deformed cranium may cause severe neurologic sequelae, including visual loss and developmental delay (see Chapter 23).37–49 Because rapid brain growth during infancy determines skull shape, surgical correction is undertaken within the first months of life to achieve the best cosmetic results.
Cranial vault reconstruction may involve the anterior or posterior aspect of the skull or both (total cranial vault reconstruction). Less invasive approaches to correct craniosynostosis are available and may be associated with reduced morbidity. Surgical correction may employ an extended strip craniectomy in which the cranial vault is split in multiple segments, allowing the skull to grow with the brain (Fig. 33-4 and E-Fig. 33-5). This technique is used in children younger than 6 months of age and is believed to be less invasive than total cranial vault reconstruction, although children are required to wear a protective helmet after surgery.50,51 Endoscopic strip craniectomy is increasingly being used in early infancy and has various benefits compared with the open procedures. Spring-assisted cranioplasty, a technique preferentially used in infants, involves performing a midline osteotomy along the fused sagittal suture and placing springs across the osteotomy to increase the biparietal dimension. Spring-assisted cranioplasty may be associated with reduced intraoperative blood loss, reduced transfusion requirement, and shorter duration of hospital stay.52 In a single-center study of 100 children with spring-assisted craniosynostosis, no child was transfused and none was admitted to the intensive care unit.53
E-FIGURE 33-5 Three-dimensional MRI of a child after extended strip craniectomy (see Fig. 33-4). This approach is commonly used in infants younger than 6 months of age. To protect the fragile skull bones, a protective helmet must be worn after surgery until cranial remodeling is complete.
Preoperative assessment of children with craniosynostosis should focus on airway management, eye protection, and ICP. An important consideration in children with midfacial hypoplasia and large tonsils is the presence of OSA. OSA may be present in 50% to 70% of children with syndromic craniosynostosis.33,54,55 Although some recommend preoperative adenotonsillectomy to treat OSA in children with craniosynostosis, neither airway dimensions nor airway collapse is improved. Midfacial advancement may be required to resolve OSA, and even then, residual airway obstruction may persist.33,54 Preoperative endoscopy has been recommended to assess the severity of midfacial hypoplasia and whether OSA is likely to persist after midface advancement. Careful titration of opioids in the perioperative period is indicated if the child exhibits severe nocturnal desaturation (i.e., if the Sao2 nadir is less than 85%) (see Chapter 31). Upper airway obstruction may also occur postoperatively in children who received opioids as a direct effect of opioids on the hypoglossal nucleus.56
Postoperative pain is generally not severe and is managed effectively with a combination of acetaminophen, nonsteroidal antiinflammatory drugs (NSAIDs), and intravenous opioids. Opioids remain the mainstay of pain management, but careful titration of reduced doses (approximately 50% less) must be considered if OSA is present. Given the small incidence of craniosynostosis and the large variability in the management of these patients, multicenter trials are required to determine the optimal management strategy for these children.57
Airway Management
Meticulous preoperative planning and evaluation of the airway is essential, particularly for OSA.54 A facemask may prove to be a challenge to seal on their flat faces and the nasal passages may be obstructed, together creating a difficult mask ventilation.58 External fixator devices on the face may also present challenges in managing the airway (E-Fig. 33-6).
Blood Loss, Coagulopathy, and Hyponatremia
Crystalloid solutions are commonly administered for minimal to moderate surgical blood loss and fluid shifts during craniosynostosis surgeries. Although lactated Ringer’s solution is most commonly used in North America, some advocate using normal saline because it may be less likely to induce hyponatremia and an acid-base disturbance than lactated Ringer’s solution. However, a recent study comparing the two solutions suggests that normal saline is more likely to induce (metabolic) acidosis than lactated Ringer’s solution in infants undergoing craniosynostosis.59 The explanation for this finding has been elusive, but it has been attributed to hyperchloremia, a dilutional acidosis, or both.
Surgery for craniosynostosis is associated with an increased incidence of cardiac arrest as a result of sudden massive blood loss.3,30,60,61 Although these procedures are extradural, significant blood loss from the scalp and cranium can occur. The blood loss can be so rapid during the surgery that the expression “trauma in progress” is applicable. The risk of massive blood loss and the need for invasive monitoring are determined in part by the specific suture involved, number of sutures scheduled for repair, type of surgery, and expertise of the surgeon.61 In children undergoing endoscopic strip craniectomy, weight less than 5 kg, those undergoing sagittal endoscopic craniectomy, those with syndromic craniosynostosis, and earlier date of surgery in the series were associated with blood transfusion.62 Some centers advocate commencing blood transfusions at the time of skin incision (particularly in infants) to prevent hemodynamic instability and the need for a rapid transfusion, but this must be tempered by whether the surgery is open or endoscopic (see later discussion).
To manage the large volume and rapidity of the blood loss, it is essential to establish large-bore peripheral venous access. Central venous access (see also Fig. 48-2), usually via the femoral route, can provide a useful estimate of the cardiac filling pressures but should not be used for rapid transfusion in small infants, because hyperkalemic cardiac arrests may occur with old blood infused rapidly into the right atrium and the lumens may limit the rate of blood infusion. Estimation of ongoing blood loss can be difficult because of the use of large volumes of irrigation fluid and blood loss onto surgical drapes and gowns.63 Invasive arterial blood pressure (BP) monitoring and serial blood gas sampling are indicated in this type of surgery (see Fig. 48-10, A-D). A urinary catheter should be inserted to monitor urine output.
Several blood conservation strategies have been proposed for this type of surgery, including preoperative recombinant human erythropoietin, directed blood donation (from the parents or siblings), acute normovolemic hemodilution, antifibrinolytics, and induced hypotension (see Chapter 10 for a more detailed discussion). These strategies should be combined with meticulous surgical technique and attention to hemostasis. Furthermore, bleeding from the scalp incision may be reduced by infiltration with a dilute (1 : 400,000) epinephrine-containing solution. The use of the reverse Trendelenburg position may help to decrease venous pressure and blood loss from osteotomy sites but also increases the risk of venous air embolism (which has been reported to be 5% to 80%; see later discussion). For this reason, the horizontal position is preferred.
Blood-conserving dual therapy with recombinant human erythropoietin (to optimize preoperative hematocrit) and use of a cell saver reduces transfusion in children undergoing craniosynostosis repair.64 Administration of preoperative recombinant human erythropoietin, in combination with elemental iron (6 mg/kg/day to a maximum of 200 mg/day for 6 weeks) increases the preoperative hematocrit value and decreases the need for autologous blood transfusion.65,66 If iron stores are at all compromised, iron therapy combined with oral vitamin C (to increase gastrointestinal absorption) should begin 3 weeks before erythropoietin therapy.67
Little evidence exists to suggest that autologous or directed blood donation decreases perioperative morbidity in craniosynostosis surgery, although it will decrease the number of blood unit exposures.68,69 Infants as young as 3 months have predonated, although the limited volume of predonated blood is unlikely to preclude all blood transfusions during craniosynostosis or repeat craniosynostosis surgery.68,69
Acute normovolemic hemodilution is a labor-intensive technique in which blood is collected from the child after induction of anesthesia but immediately before surgery and replaced with an equal volume of crystalloid or colloid, such as 5% albumin. Although acute normovolemic hemodilution may be beneficial in children with rare blood types, no evidence exists that it reduces either the incidence of homologous transfusion or the amount of homologous blood transfused in children undergoing craniosynostosis repair.70
The coagulation profile and clotting factors after fresh frozen plasma (FFP) or 5% albumin during craniofacial surgery have been compared in a nonrandomized study in infants younger than 12 months of age.71 The increases in activated partial thromboplastin time (aPTT) and decreases in the plasma concentration of factors XI and XIII and antithrombin 3 were less after intraoperative FFP than after 5% albumin. Fibrinogen concentrations remained stable in the FFP-treated group but decreased in the albumin-treated group. However, it should be emphasized that no clinical indication exists to administer FFP when the blood loss is less than 1 blood volume (Chapter 10). Recombinant factor VIIa has been used successfully for intractable hemorrhage during cranial vault reconstruction in an infant, although this is an isolated report.72
Antifibrinolytic therapy may decrease blood loss during craniosynostosis repair in children. Tranexamic acid (TXA) is a widely used agent, and several dosing regimens have been described: (1) A loading dose of 15 mg/kg TXA after induction of anesthesia, followed by an infusion of 10 mg/kg/hr until skin closure73; (2) 50 mg/kg TXA loading dose, followed by an infusion of 5 mg/kg/hr74 until skin closure; and (3) 15 mg/kg at induction of anesthesia, every 4 hours during surgery, and every 8 hours after surgery for 24 hours after surgery. Although dose-response data from a single study are lacking, two studies73,74 report that TXA reduces intraoperative and postoperative bleeding and transfusion requirements.75 Another antifibrinolytic, ε-aminocaproic acid (EACA), is effective in reducing bleeding in cardiac and spinal procedures, although its effectiveness in reducing blood loss during craniosynostosis has not been established. The dose that has been used for spinal surgery is 75 to 100 mg/kg loading dose intravenously over 15 to 20 minutes before skin incision, followed by 10 to 15 mg/kg/hr until skin closure.76
Induced hypotension defined as a 10% to 20% reduction in the mean arterial BP decreases intraoperative surgical blood loss and operating time,77 although studies demonstrating its efficacy during craniosynostosis surgery are lacking. A variety of pharmacologic agents have been used to induce hypotension, including inhalational agents, vasodilators, β-blockers, and remifentanil.77,78 Invasive arterial pressure monitoring is essential whenever hypotensive anesthesia is used. Induced hypotension should be used with caution in the presence of increased ICP because of the risk of compromising cerebral perfusion pressure (i.e., the difference between mean arterial pressure [MAP] and either ICP or central venous pressure, whichever is greater). Increases in ICP mandate invasive monitoring of MAP to ensure an adequate cerebral perfusion pressure. It is considered prudent to maintain normovolemia and normocapnia when induced hypotension is used (see Chapter 10 for a more detailed description of these techniques).
Whether used alone or in combination,79–81 the preceding techniques seldom obviate the need for all blood transfusions during craniofacial surgery. Therefore intravenous access with large-bore catheters remains essential and at least 2 units of packed red blood cells (PRBCs) should be crossmatched and available in the operating room at all times. All intravenous fluids should be administered via a fluid warmer to prevent hypothermia. Maintaining normothermia preserves normal coagulation indices and theoretically reduces bleeding and transfusion-related complications.82 A coagulopathy should always be anticipated once the blood loss exceeds 1 blood volume. Serial determinations of the international normalized ratio, partial thromboplastin time, platelet count, and fibrinogen concentration will identify an evolving coagulopathy and indicate which blood products, FFP, platelets, or cryoprecipitate, will best correct the abnormalities (see Chapter 10).
Endoscopic repair of craniosynostosis has become a rapidly growing surgical approach to reduce bleeding and decrease morbidity.83,84 Independent risk factors for bleeding during endoscopic strip craniectomy include low body weight (<5 kg), sagittal suture surgery (related to proximity to the sagittal vein), syndromic craniosynostosis, and earlier date of surgery.62
Hyponatremia and cerebral salt wasting syndrome are associated with craniosynostosis repair.85–89 Both intraoperative and postoperative hyponatremia have been described, with the latter occurring in approximately 30% of children. In a retrospective review of a cleft palate and craniofacial database, postoperative hyponatremia was significantly associated with preoperative increased ICP, blood loss, and female gender with normal preoperative ICP.89 The average reduction in sodium concentration was more pronounced in children who received hyponatremic (hypotonic) (5% dextrose and 0.2% or 0.5% NaCl) compared with normonatremic (isotonic) postoperative intravenous fluids.89 The perioperative use of balanced salt solutions is recommended to prevent hyponatremia (see Chapter 8 for a more in-depth discussion of new perioperative fluid management recommendations). In infants, the addition of 5% dextrose to the balanced salt solution may be required to avoid intraoperative or postoperative hypoglycemia.
Increased Intracranial Pressure
Early surgery for craniosynostosis is often indicated to prevent increases in ICP.31,32 One third of children with craniofacial dysostosis syndrome and 15% to 20% of children with single-suture craniosynostosis have increased ICP (>15 mm Hg).90 Approximately 40% to 50% of children with syndromic craniosynostosis have associated hydrocephalus, although differentiation from nonprogressive ventriculomegaly may be difficult.90–92 Timing of surgery may affect neurocognitive development and intelligence because these are adversely affected by sustained increased ICP. Associated OSA resulting in hypoxemia and hypercapnia may lead to an increase in cerebral blood volume and thereby exacerbate intracranial hypertension.93 Untreated intracranial hypertension may lead to optic atrophy and visual impairment.35,94 As a consequence, when increased ICP has been identified either preoperatively or postoperatively, placement of a ventriculoperitoneal shunt should be considered.92 This is more common an occurrence in Crouzon and Pfeiffer syndromes.92
For children who present with signs of intracranial hypertension, it is important to follow basic principles of neuroanesthesia to prevent further increases in ICP and decreases in cerebral perfusion pressure (see Chapter 24 for a more in-depth discussion). It may be prudent to use protective measures to attenuate the hypertensive response to laryngoscopy and intubation, including the administration of a short-acting opioid, a β-blocker, or topical local anesthesia to the upper airway. Intraoperatively, the anesthesiologist faces numerous challenges to control ICP. Mild to moderate hyperventilation (to an end-tidal carbon dioxide of 30 to 35 mm Hg), especially when signs of herniation are evident, avoidance of hypervolemia, and, where indicated, appropriate use of mannitol, furosemide, and dexamethasone may be employed to reduce ICP, reduce brain volume, and facilitate brain retraction. Although cranial vault reconstruction increases intracranial volume and reduces ICP,95 children remain at risk of increased ICP after surgery and require close ophthalmologic and clinical follow-up, even after a cosmetically successful cranial expansion.96,97
Venous Air Embolism
Venous air embolism (VAE) may occur during any operative procedure in which the operative site is above the level of the heart and noncollapsible veins are exposed to atmospheric pressure.98–105 The incidence of VAE in children undergoing craniectomy for craniosynostosis repair has been reported to be as great as 83%,105 although hemodynamically significant VAE is rare. The incidence associated with endoscopic craniectomy may be as small as 2%.62 Significant hypovolemia resulting from surgical blood loss can lead to a decrease in both systemic and central venous pressures and the development of a pressure gradient between the right atrium and the surgical site. This gradient increases the potential to entrain air via open dural sinuses or bony venous sinusoids.105,106 If the entrained volume of air is sufficiently large, right ventricular outflow obstruction may ensue, causing acute right-sided heart failure and cardiovascular collapse. Smaller volumes of air may cause a reduction in cardiac output, hypotension, and myocardial or cerebral ischemia.103 Transesophageal echocardiography (documenting the presence of air in the right ventricular outflow tract), precordial Doppler ultrasonography (continuous machinery mill murmur), end-tidal carbon dioxide (precipitous decrease in carbon dioxide tension), and nitrogen monitoring (sudden increase in nitrogen concentration in the exhaled breath) have been used to identify VAE with different sensitivities, well before cardiovascular collapse occurs (see Figure 24-6).103,107–110 Applying bone wax to the open edges of cut bone, reducing the degree of or avoiding the reverse Trendelenburg position, introducing positive-pressure ventilation with 5 cm of positive end-expiratory pressure, and maintaining normovolemia help to prevent VAE. Fluid resuscitation, vasopressors, and aspiration of air from the right side of the heart may prevent episodes of VAE from progressing to cardiovascular collapse.99,105,110
Prolonged Surgery
As with all surgeries that last several hours, preventing the complications associated with prolonged anesthesia is paramount.111 Nerve palsies, pressure necrosis of the skin, ophthalmic complications, hypothermia, and acidosis may occur. Careful positioning of the extremities, use of an egg-crate type mattress, and avoiding pressure to the eyes, particularly when the surgical procedure requires the prone position, will prevent the majority of these adverse outcomes. In children with proptosis, such as Crouzon syndrome, it is particularly essential to suture the eyelids closed after applying lubrication to prevent corneal abrasions. Anterior ischemic optic neuropathy that can cause transient or permanent postoperative blindness is a rare complication that occurs in the absence of external pressure to the eyes.112
Hypothermia is another major concern. Factors that predispose to hypothermia include the relatively large surface area exposed during surgery and the transfusion of large volumes of relatively cold intravenous fluids. Effective measures to prevent hypothermia include warming the operating room, insulating the child, and the use of forced air warmers and warming devices for blood and intravenous fluids. Preventing hypothermia and limiting blood loss and transfusion requirements are key factors in preventing the development of perioperative metabolic disturbance.113
Orbital Hypertelorism
The term orbital hypertelorism describes abnormally separated orbits. This deformity may occur in isolation or in association with other congenital abnormalities, such as facial clefts and Apert syndrome (Fig. 33-5). Surgical repair involves mobilization and repositioning of the orbit through either a subcranial approach, which leaves the roof of the orbit intact, or an intracranial approach via a frontal craniectomy. This procedure is performed in children older than 5 years who may have already undergone extensive surgical reconstruction. Surgical manipulation of the globe may elicit the oculocardiac reflex, resulting in bradyarrhythmias or asystole. Oculocardiac reflex may also occur during midface and orthognathic procedures (see also Fig. 32-3, A and B).114 These arrhythmias are prevented by administering a prophylactic anticholinergic such as atropine (10-20 µg/kg) or glycopyrrolate (5-10 µg/kg). Discontinuing the surgical stimulus almost always increases the heart rate.
