Cardiac Physiology

The transition from fetal to neonatal circulation is characterized by a change from parallel circulation (cardiac output contributes to both pulmonary and systemic perfusion, simultaneously allowing mixing of oxygenated and deoxygenated blood) to one that occurs in series (cardiac output contributes to either pulmonary or systemic perfusion with minimal admixture). High pulmonary vascular resistance (PVR) and relatively low systemic vascular resistance (SVR) also characterize fetal circulation. In utero, oxygenated blood from the placenta is transported to the fetus via the umbilical vein ( Fig. 21-1 ). Blood from the gastrointestinal (GI) tract combines with the umbilical vein to become the ductus venosus, which drains into the inferior vena cava (IVC). Blood from the IVC enters the right atrium and preferentially crosses the foramen ovale to the left atrium and left ventricle, thereby providing slightly more oxygenated blood for cerebral circulation. The superior vena cava (SVC) drains into the right atrium and is pumped primarily to the systemic circulation via the ductus arteriosus. Less than 10% of combined ventricular output contributes to pulmonary flow. A series of events occur at birth that change fetal (parallel) circulation into neonatal circulation (series).

Course of fetal circulation in late gestation.

Note the selective blood flow patterns across the foramen ovale and the ductus arteriosus.

(From Greeley WJ, Steven JM, Nicolson SC: Anesthesia for pediatric cardiac surgery. In Miller RD, editor: Miller’s anesthesia, ed 6, Philadelphia, 2005, Churchill Livingstone, p 2007.)

During delivery, PVR decreases and SVR increases, allowing for a significant increase in pulmonary blood flow. The increase in SVR occurs secondary to separation from the placenta. The decrease in PVR occurs for several reasons. With the onset of lung ventilation, there is a decrease in the mechanical compression of the alveoli and an increase in oxygen tension (P o ₂ ). At birth, the mechanical distention of the alveoli coupled with the increased P o ₂ results in a precipitous decrease in PVR. The changes in PVR are mediated by biochemical factors, including nitric oxide and prostaglandin. In the newborn period, the pulmonary vessels exhibit a highly reactive tone. Maintenance of an elevated PVR is lethal to the neonate. Pulmonary vasoconstriction with right-to-left shunting in response to hypoxia, hypercarbia, sepsis, and acidosis can cause severe hypoxemia and death.

With a decrease in PVR, pulmonary blood flow and venous return to the left atrium increase. The increase in left atrial pressure and flow closes the foramen ovale. Over the next few months of life, PVR decreases even further. Hypoxemia and acidosis are two important factors that affect PVR. An increase in PVR can lead to right-to-left shunting across the foramen ovale and ductus arteriosus. This persistence of an elevated PVR can lead to further hypoxemia and tissue acidosis. Thus, hypoxemia and acidosis can lead to a vicious cycle of increased PVR, increased right-to-left shunting, increased hypoxemia, increased tissue acidosis, and further increase in PVR and shunting.

The neonatal myocardium is immature and continues its development after birth. Many functional differences between the neonatal and adult myocardium are directly related to the immaturity of the neonatal tissue components. At delivery and extending into the neonatal period, fewer contractile elements and less elastin are present in the newborn’s myocardium, resulting in a decreased contractile capacity and decreased ventricular compliance, respectively. Fetal myocardium has limited ability to generate the equivalent contractile force as the adult myocardium throughout the entire range of the length-tension curve. The consequence is a reduced capacity to adapt to increases in preload or afterload. This does not mean the stroke volume is fixed. Echocardiographic evidence indicates that the immature heart, while limited, is able to increase stroke volume. Because of this immaturity, the neonatal heart has a diminished capacity to handle significant volume loads and more easily develops ventricular overload and failure.

Respiratory Physiology

A significant difference between neonatal and adult respiration is oxygen consumption. Neonatal O ₂ consumption is two to three times greater than that of the adult (5-8 vs. 2-3 mL/kg/min). This contributes to the rapid O ₂ desaturation observed in infants during periods of apnea or hypoventilation.

The neonatal/infant lung is less compliant than the adult lung. The immature lung in the pediatric patient is characterized by small, poorly developed alveoli with thickened walls and decreased elastin. The amount of elastin in the lung continues to increase until late adolescence. Before and after late adolescence, pulmonary elastin is decreased. Elastin provides elasticity to the lung, without which there is airway collapse. Because they have less elastin, infants and older adults are prone to alveolar collapse. The closing capacity, the lung volume at which there is airway collapse, occurs at a larger lung volume in the very young and the very old populations ( Fig. 21-2 ). In the infant, airway closure can occur before end exhalation, resulting in atelectasis and right-to-left transpulmonary shunting. In contrast to the pediatric lung, the pediatric chest wall is more compliant than the adult chest wall, because of the increased amount of cartilage in pediatric ribs. This increased chest wall compliance may help contribute to airway collapse because negative intrathoracic pressure can result in chest wall collapse.

Closing capacity in relation to age.

The difference between functional residual capacity (FRC) and closing capacity is charted against age. Note that closing capacity is greater than FRC in children younger than 5 years and adults older than 45.

(From Mansell A, Bryan C, Levison H: J Appl Physiol 33: 771-774, 1972.)

Temperature Regulation

Neonates and infants are at increased risk of thermoregulatory instability because they are more prone to heat loss and they have a decreased ability to produce heat. They are at increased risk of heat loss because of their large surface area/volume ratio. They also have decreased ability to restrict heat loss secondary to limited vasoconstriction compared with adults. The primary method of heat production in the neonate and infant consists of nonshivering thermogenesis, which compensates poorly for heat loss. Nonshivering thermogenesis occurs primarily in brown fat, which may be decreased in premature neonates. This mechanism can also be inhibited by inhalational agents. Nonshivering thermogenesis is mediated by norepinephrine, a potent pulmonary vasoconstrictor. Consequently, cold stresses can cause elevations to PVR and provide a mechanism for right-to-left shunting. Shivering thermogenesis assumes a less significant role in infants. Temperature stability can be ensured by using neonatal warming lights, forced warm air blankets, intravenous fluid warmers (if large amounts of fluids or blood products are given) increasing the ambient temperature of the operating room and keeping the infant covered.

Renal Physiology

In the first few days of life, a major physiologic priority of the neonate is to lose weight as a result of a reduction in extracellular body water. This physiologic weight loss usually is a function of an isotonic contraction of body fluids. Perturbations of this process can affect infant morbidity and mortality. The neonatal kidney develops its full complement of nephrons by 36 weeks’ gestation. The glomerular filtration rate is lower in the neonate (~25% of adult value) and achieves adult values within the first few years of life. Tubular function in the neonate is also limited; consequently, a glomerular/tubular imbalance is present in the first few years of life as well.

Neonates have limited capacity to concentrate their urine. When challenged, term infants can concentrate to 800 mOsm/kg of plasma water, whereas preterm infants can concentrate to 600 mOsm/kg of plasma water. Neonates have diminished end-organ responsiveness to vasopressin, whereas fluid-challenged term infants and premature infants can dilute their urine to 50 and 70 mOsm/kg of plasma water, respectively. Thus, excessive fluid restriction and overhydration can result in dehydration and intravascular volume overload. Renal sodium losses are inversely related to gestational age and disease states (hypoxia, respiratory distress, acute tubular necrosis, and hyperbilirubinemia can exacerbate these losses).

Pain and Perioperative Stress Response

Pain and stress can induce significant physiologic and behavioral consequences. Newborns and infants are capable of mounting a hormonal response to the stress of their illness. A better understanding of the causes, mechanisms, and treatment of pain during development has provided clinicians with a wide array of techniques to manage procedural and postoperative pain safely.

The nervous system at birth displays hypersensitivity to sensory stimuli compared with the nervous system of the mature adult. In neonates, thresholds of response to mechanical and thermal stimulation are reduced, and further sensitization can occur with sustained or repetitive stimulation, which is different from the mature nervous system. Structural and functional changes in the peripheral and central nervous systems that take place in the postnatal period involve alterations in expression, distribution, and function of receptors, ion channels, and neurotransmittors. These changes can profoundly affect the character of nociceptive responses at different stages of development. Perinatal brain plasticity is affected by this sensitization and increases the vulnerability of the neonatal brain to early adverse experiences, leading to abnormal neurologic development and behavior.

A multimodal approach to pediatric pain management is necessary and may involve pharmacologic and nonpharmacologic methods. The use of nonopioid analgesics (acetaminophen, nonsteroidal anti-inflammatory drugs), opioids, local anesthetics, and regional techniques provides a balanced analgesic approach to pain management.

Congenital Laryngeal Webs and Atresia

Congenital laryngeal webs are uncommon and have an estimated incidence of 1 in 10,000 births. Most laryngeal webs are glottic with extension into the subglottic area. The laryngeal web is a result of a failure to recanalize the laryngeal inlet at about 10 weeks’ gestation. The symptoms vary according to the location of the web and the degree of involvement ( Fig. 21-4 and Box 21-1 ). Symptoms are related to vocal cord dysfunction ranging from mild hoarseness to aphonia. Most webs involve the anterior glottis and are generally thin and associated with mild hoarseness and minimal airway obstruction. With laryngoscopy the vocal folds are visible. Subglottic webs are infrequent, and supraglottic webs are rare. Complete congenital laryngeal atresia is incompatible with life unless an emergency tracheotomy is carried out in the delivery room. Complete congenital atresia is associated with tracheal and esophageal anomalies ( Fig. 21-5 ). Signs and symptoms of infants with congenital laryngeal webs include disorders of phonation, stridor, and airway obstruction; Box 21-2 lists disorders mimicking these laryngeal web symptoms.

Congenital laryngeal web.

Medium-sized, thicker, anterior glottic web.

(Courtesy Charles Bluestone, MD.)

Laryngeal atresia.

(Courtesy Charles Bluestone, MD.)

Thin anterior webs and laryngeal webs in the glottic area may require incision and dilation. If the web involves the subglottic larynx, the anterior cricoid plate is usually abnormal. In these patients, treatment requires an external approach with division of the web and the cricoid plate and the use of cartilage grafting. Fibrosis and scarring of the vocal cords tend to occur with the laryngotracheal reconstruction techniques. Recently, the combination of minimally invasive endoscopic approaches with carbon dioxide (CO ₂ ) laser scar transection, mitomycin C application, and antiproliferation agents effectively reduced scar tissue.

Choanal Atresia

Choanal atresia occurs in approximately 1 in 7000 live births. About 90% of the atresias are bony, and 10% are membranous. Abnormal embryogenesis of neuroectodermal cell lines may explain choanal atresia. The primitive face develops from five facial prominences ( Fig. 21-6 ). The frontonasal prominence is responsible for nasal development from weeks 3 to 10 of gestation. Migrating neural crest cells form the nasal (or olfactory) placode, a convex thickening on the frontonasal prominence. The primitive nasal pit is formed from a central depression in these placodes. Mesenchymal proliferation around the nasal placode allows horseshoe-shaped medial and lateral prominences to develop and fuse to form the nostril. The nasal pits grow backward.

Facial embryogenesis.

A, Five facial prominences: frontonasal process, paired mandibular processes, and paired maxillary processes. B, Fusion of medial and lateral nasal processes.

(From Losee JE, Kirschner RE, Whitaker LA, Bartlett SP: Plast Reconstr Surg 113:676-689, 2004.)

Choanal atresia is thought to result from the persistence of bucconasal and buccopharyngeal membranes or an insufficient excavation of the nasal pits. Postnasal cavity outlet obstruction is more common. Half of patients with choanal atresia have other congenital anomalies. Choanal atresia may be partial or one of a constellation of congenital abnormalities known as the CHARGE association (coloboma, heart disease, atresia [choanal], retarded growth, genital abnormalities, ear deformity). Choanal atresia can be unilateral or bilateral. Because neonates are obligate nose breathers, bilateral choanal atresia frequently presents as immediate onset of respiratory distress. Obstruction of the nasal cavity can present with apneic episodes and “cyclic” cyanosis, which are exacerbated by feeding and improved with crying.

The initial presentation of the newborn with bilateral choanal atresia is the immediate onset of respiratory distress. The relationship between the neonatal tongue and the palate perpetuates this obstruction. The use of an oral airway or McGovern nipple (modified nipple with enlarged perforations at tip) acts as an alternative, temporary airway. Unilateral choanal atresia is usually asymptomatic, except for unilateral mucoid discharges.

Diagnosis

Inability to pass a 6-Fr catheter through the nasal cavity to more than 32 mm, coupled with an endoscopic examination, verifies the suspected diagnosis. Axial computed tomography (CT) remains the study of choice to delineate the type of atresia and aid with operative planning (transpalatal vs. transnasal approach). Adequate preparation of the patient before scanning by aspirating secretions and the use of decongestant drops helps ensure the best-quality radiographic result. Box 21-4 lists associated craniofacial syndromes.

Box 21-4

Choanal Atresia: Craniofacial Associations

Data from Papay FA, McCarthy VP, Eliachar I, et al: Laryngotracheal anomalies in children with craniofacial syndromes, J Craniofac Surg 13:351-364, 2002.

• 
  

  CHARGE association: Coloboma, heart defects, atresia of choanae, retarded CNS growth or development, GU abnormalities, ear anomalies/deafness

  
  
• 
  

  Apert’s syndrome (acrocephalosyndactyly, type I): Craniosynostosis, syndactylism, difficult airway

  
  
• 
  

  Fraser’s syndrome (cryptophthalmos syndrome) : Laryngeal/tracheal stenosis, congenital heart disease, GU anomalies, renal agenesis/hypoplasia

CNS, Central nervous system; GU, genitourinary.

Treatment

About 90% of patients with choanal atresia have bony involvement, whereas in 10% the obstruction is membranous. For bilateral choanal atresia, surgical correction occurs in the neonatal period and involves a transnasal correction using CO ₂ or neodymium:yttrium-aluminum-garnet (Nd:YAG) lasers. The nasal passage is stented open for 3 to 5 weeks to improve airway patency. The surgical technique generally involves an endoscopic approach in which a vertical mucosal incision is made in the posterior bony septum and a perforation created in the atresia plate ( Fig. 21-7 ). This perforation is then amenable to serial dilation.

Choanal atresia.

A, Choanal atresia in neonate. Atresia plate on the right side has just been perforated. B, The situation after opening in atresia plate has been enlarged.

(Courtesy Charles Bluestone, MD.)

A transpalatal approach has also been used for bony and bilateral atresia. However, the disadvantages of the transpalatal approach are long operative time and large blood loss. Additionally, malocclusion occurs in 50% of patients, and oronasal fistulas can occur. In patients with unilateral choanal atresia, surgery is usually performed at any time during childhood; the approach can be transnasal or transpalatal.

Cystic Hygroma

Cystic hygroma is a congenital lymphatic malformation caused by dysplasia of lymphatics, but it may also result from hamartoma or true neoplasm. The lesion is uncommon, occurring in 1 in 12,000 live births. Clinically, a cystic hygroma occurs most often (60%-70%) in the neck ( Fig. 21-8 ). Typically, the neck mass develops in the posterior triangle. If it develops higher in the neck (suprahyoid), it can occupy the anterior triangle and may be associated with intraoral lesions. Suprahyoid lymphangiomas are more likely to involve the mouth and cause feeding problems and airway obstruction. Infection or hemorrhage into the cyst can also cause acute airway compromise. About 20% of cystic hygromas occur below the clavicles in the axillae or the mediastinum. Mediastinal extension can cause respiratory symptoms. Usually, cystic hygromas are diagnosed at birth; however, many are diagnosed during prenatal ultrasound.

Neonate with large neck mass consistent with cystic hygroma.

(From Zitelli BJ, Davis HW: Atlas of pediatric physical diagnosis, ed 4, St Louis, 2002, Mosby, p 560.)

Anesthetic management

During the preoperative evaluation, infants with feeding difficulties should be suspected of having intraoral lesions. Those with respiratory symptoms or coughing should be evaluated for mediastinal involvement with a chest radiograph or CT. Delay in the evaluation should be minimized because the lesions can grow rapidly. The primary anesthetic concern during induction is airway management. Inhalational induction can be performed, but difficulty with both ventilation and intubation has been described. A nasopharyngeal airway may help open the airway and restore ventilation. If preoperative examination suggests difficulty with both ventilation and intubation, consideration should be given to performing an awake or a sedated fiberoptic nasal intubation. Other options include sedated placement of a laryngeal mask airway (LMA) with subsequent fiberoptic intubation, blind nasotracheal intubation, or a sedated tracheostomy.

The surgical resection of a cystic hygroma can be associated with significant blood loss. Intraoperative management should focus on maintaining normovolemia and normothermia. Intravascular access with two large IV catheters and an arterial catheter may be required to manage the resuscitation. Central venous access from the neck or chest may not be possible depending on the location of the lymphangioma. Femoral venous cannulation should be considered as an alternative. Fluid shifts and third-space fluid losses may be significant. Maintenance of body temperature can be achieved with warming lights, fluid warmers, and forced-warm-air blankets. Surgical resection may involve manipulation of the vagal nerve, which can result in bradycardia. Evaluation at the end of surgery will determine the feasibility of early extubation. Infants with difficult intubation, significant fluid shifts, or hemodynamic instability should remain intubated and undergo recovery in the intensive care unit (ICU). Vocal cord dysfunction can result from nerve injury from the surgical dissection and should be considered if acute airway obstruction occurs after extubation.

Management of prenatally diagnosed cystic hygromas may involve delivery through the ex utero intrapartum treatment (EXIT) procedure. During EXIT the head and torso of the fetus are delivered and the airway is secured while uteroplacental support is maintained. Intubation can be achieved with direct laryngoscopy. If the anatomy makes this impossible, rigid bronchoscopy or tracheostomy can be performed ( Fig. 21-9 ). Tracheostomy may be difficult if the mass repositions or covers the trachea.

Rigid bronchoscopy performed during the EXIT procedure on neonate with cystic hygroma.

(Courtesy Laura Myers, MD.)

Clefts: Treacher Collins Syndrome

Craniofacial clefts involve a defect of the underlying cranial and/or facial skeleton. This group of deformities has been best classified by Tessier, who uses the orbit as the center of the defect from which the clefts radiate like the spokes of a wheel ( Fig. 21-10 ). Cleft lip and palate are the more commonly recognized examples of craniofacial clefts.

Tessier classification of rare craniofacial clefts.

Using orbit as center of reference, clefts are oriented like spokes of wheel, with those caudad to the orbit considered facial and those cephalad considered cranial. For descriptive purposes, clefts involving two regions are designated by two numbers (e.g., 4, 10), the sum of which is typically 14. Bony clefts (B) are usually reflected in soft tissue (A).

(From Whitaker LA, Bartlett SP: Craniofacial anomalies. In Jurkiewicz J, Krizek T, Mathes S, Ariyan S, editors: Plastic surgery: principles and practice, St Louis, 1990, Mosby, p 109.)

Treacher Collins syndrome, also known as the incomplete form of mandibulofacial dysostosis, is an example of a craniofacial cleft that involves clefts 6, 7, and 8. Treacher Collins syndrome was first described in 1846 by Thompson and was further elaborated by Treacher Collins. This is a rare syndrome of facial clefting and is transmitted in an autosomal dominant pattern. The syndrome is characterized by poorly developed supraorbital ridges, aplastic/hypoplastic zygomas, ear deformities, cleft palate (in one third), and mandibular and midface hypoplasia ( Fig. 21-11 ). From birth, issues of airway adequacy take priority. The hypoplastic maxillae and mandible along with choanal atresia and glossoptosis all contribute to varying degrees of airway obstruction. Tracheostomy may be required during infancy for those at highest risk of obstructive sleep apnea and sudden infant death syndrome (SIDS). Aside from cleft lip and palate repair, the timing of major reconstruction typically occurs during childhood or adolescence when the cranio-orbital-zygomatic bony development is almost complete. Infants and children with Treacher Collins syndrome can have congenital cardiac defects.

Child with Treacher Collins syndrome.

(From Losee JE, Bartlett SP: Treacher Collins syndrome. In Lin KY, Ogle RC, Jane JA, editors: Craniofacial surgery: science and surgical technique, Philadelphia, 2001, Saunders.)

Craniosynostosis

Craniosynostosis is defined as a premature closure of one or more of the cranial sutures. This results in abnormalities in the size and shape of the calvarium, cranial base, and orbits and constitutes a diverse group of deformities. The craniosynostoses not only affect cosmetic appearance but also can affect brain growth, intracranial pressure (ICP), and vision, resulting in developmental delay, increased ICP, and visual loss. The synostoses are classified based on head shape, not the involved suture ( Fig. 21-12 ).

Craniosynostosis.

Typical patterns of associated craniofacial morphology: A, Turribrachycephaly; B, plagiocephaly; C, trigonocephaly; D, scaphocephaly.

(From Whitaker LA, Bartlett SP: Craniofacial anomalies. In Jurkiewicz J, Krizek T, Mathes S, Ariyan S, editors: Plastic surgery: principles and practice, St Louis, 1990, Mosby, p 119.)

Craniosynostosis can occur alone (simple) or as a major component of a syndrome (complex or syndromic). Six syndromes are associated with craniosynostosis: Apert’s, Pfeiffer’s, Saethre-Chotzen, Carpenter’s, Meunke’s, and Crouzon’s. Table 21-2 lists the various syndromes and their associated anomalies and anesthetic concerns. Four of the five are categorized as acrocephalosyndactylies because they involve deformities of the head (cephalo) and extremities (syndactyly). Crouzon’s disease does not have musculoskeletal anomalies as part of the syndrome. Infants and children with synostosis present to the OR for cranial vault remodeling to reduce ICP, prevent brain injury, and enhance appearance. Repair of syndromic craniosynostosis may be more complicated and appears to be associated with increased blood loss. The etiology of the increased bleeding is unclear but may be related to the length of surgery.

Apert’s syndrome is an acrocephalosyndactyly with an autosomal dominant pattern of inheritance. The etiology is a mutation within the fibroblast growth factor receptor-2 gene (FGFR2). The characteristic features of Apert’s syndrome include turribrachycephaly (high steep flat forehead and occiput), midface hypoplasia, and orbital hypertelorism ( Fig. 21-13 ). Cleft palate occurs in approximately 30% of Apert’s patients. Choanal atresia and occasionally tracheal stenosis are reported and can cause airway obstruction. Congenital cardiac disease is one of the more common associated visceral anomalies, occurring in approximately 10%. Genitourinary (GU) anomalies (hydronephrosis, cryptorchidism) also occur in 10% of patients with Apert’s syndrome. Severe synostosis can result in increased ICP and, if uncorrected, developmental delay. Syndactyly of the hands and feet often present as the fusion of digits 2 to 4, which can make IV access difficult. Cervical spine fusion has been reported in Apert’s patients and may make endotracheal intubation even more challenging if there is decreased neck mobility. Many children with Apert’s syndrome have been intubated uneventfully. However, suboptimal laryngoscopic views secondary to abnormal anatomy may require flexible fiberoptic intubation. The LMA may also be a reasonable adjunct in patients difficult to ventilate or intubate, although to date there are no reported cases of its use in infants or children with Apert’s syndrome. The clinical features and the anesthetic implications of Apert’ syndrome and the other acrocephalosyndactylies are outlined in Table 21-2 . Unlike Apert’s syndrome, the other acrocephalosyndactylies are not typically associated with difficult airways. However, midface hypoplasia is common in these infants and may cause significant upper airway obstruction intraoperatively and postoperatively.

Child with Apert’s syndrome.

(From Buchman SR, Muraszko KM: Syndromic craniosynostosis. In Lin KY, Ogle RC, Jane JA, editors: Craniofacial surgery: science and surgical technique, Philadelphia, 2001, Saunders.)

Crouzon’s disease, also known as craniofacial dysostosis, is also part of the syndromic craniosynostoses. These infants present with craniofacial anomalies without visceral or extremity involvement. The anomalies can result in significant airway obstruction that may require early tracheostomy. Crouzon’s disease results from a mutation in FGFR2, the same gene that causes Apert’s syndrome. Table 21-2 outlines the main clinical features and anesthetic issues. During infancy these patients may present to the OR for tracheostomy and cranial vault remodeling.

Hypoplasia

Hypoplasia of the craniofacial skeleton is a category of craniofacial anomalies characterized by hypoplasia or atrophy of a portion of the craniofacial soft tissue and skeleton. Pierre Robin sequence and hemifacial microsomia (including Goldenhar’s syndrome) are examples of these anomalies.

Pierre Robin sequence is characterized by retrognathia, glossoptosis (tongue falling to the back of the throat), and airway obstruction and probably occurs secondary to a fixed fetal position in utero that inhibits mandibular growth. Management of this sequence depends on the severity of respiratory distress and airway obstruction. Infants with mild obstruction and minimal respiratory distress who can continue to feed may require only prone positioning or no intervention. For more severe respiratory distress, the tongue can be surgically attached to the lower lip (tongue-lip adhesion) to decrease airway obstruction and allow the mandible to grow.

Airway management in the infant with Pierre Robin sequence can be challenging because of difficulty with mask ventilation and intubation. The LMA has been successfully used to ventilate and to assist in the intubation of these patients. Nasal intubation with the flexible fiberoptic scope has also been described. In infants who present with significant difficulty with ventilation or intubation, aside from oropharyngeal and oronasal airways, a suture (0-silk) can be placed at the base of the tongue to displace the tongue anteriorly to assist with ventilation or intubation.

Hemifacial microsomia is characterized by unilateral or asymmetric development of the facial bones and muscles and frequently involves the ear. This manifests as hypoplasia of the malar-maxillary-mandibular region and usually involves the temporomandibular joint. The defect occurs from an anomaly of the first and second branchial arches and is believed to be secondary to a fetal vascular accident. Goldenhar’s syndrome is a subset of hemifacial microsomia and is composed of hemifacial microsomia, epibulbar dermoid, and rib or vertebral anomalies. The vertebral pathology can involve the cervical vertebrae and can significantly reduce range of motion. Other associated anomalies of hemifacial microsomia include cardiac (ventricular septal defect, tetralogy of Fallot, coarctation), renal, and neurologic (hydrocephalus) defects. Patients with hemifacial microsomia can have significant upper airway obstruction and obstructive sleep apnea.

Airway management is a major concern in hemifacial microsomic patients. Mask ventilation may be difficult because of the facial asymmetry. Intubation is more challenging because of micrognathia, asymmetric mandibular hypoplasia, and potentially from decreased cervical range of motion. This difficulty may decrease with age but may increase after surgical reconstruction. Successful ventilation and intubation of an infant with Goldenhar’s syndrome has been reported with an LMA and flexible fiberoptic scope. Successful intubation has also been described with the glidescope in this population.

Surgical Correction

Craniofacial anomalies are surgically corrected to improve form and function and to minimize disability. Airway obstruction, increased ICP, developmental delay, and visual loss are some of the pathologic processes that may be corrected or prevented with appropriate surgical intervention. Procedures to correct these deformities include strip craniectomy (endoscopic or open), cranial vault remodeling, frontal-orbital advancement, midface advancement (Le Fort I, Le Fort III, monoblock advancement), and distraction osteogenesis. Craniectomy, remodeling, and advancement are surgical approaches to correct craniosynostosis. The goal is to release the synostotic sutures and open up the cranium to allow brain growth and development. The endoscopic strip craniectomy involves less blood loss but because of premature refusion, is usually reserved for patients with sagittal synostosis. The surgical approach for the open strip craniectomy, cranial vault remodeling, and frontal-orbital advancement is through a bicoronal incision. Subperiosteal dissection allows access to the upper facial skeleton for surgical manipulation ( Fig. 21-14 ). These procedures are performed during the first year of life. Blood loss can be significant, and preparations to ensure patient safety include adequate IV access and availability of blood products.

Bicoronal incision (A) with extensive subperiosteal dissection (B) provides access for surgical manipulation of upper facial skeleton.

(From Whitaker LA, Bartlett SP: Craniofacial anomalies. In Jurkiewicz J, Krizek T, Mathes S, Ariyan S, editors: Plastic surgery: principles and practice, St Louis, 1990, Mosby, p 107.)

Mandibular advancement procedures are frequently performed to correct appearance, malocclusion, and airway obstruction. These can be performed with distraction osteogenesis and during infancy.

Distraction osteogenesis was developed to elongate bone by creating a bone cut (osteotomy) and distracting the two ends. first used by orthopedic surgeons but not for craniofacial surgery until 1992, McCarthy et al. described distraction osteogenesis to lengthen the human mandible. This technique has now been used in many children to distract the mandible and midface, used to correct appearance and upper airway obstruction ( Fig. 21-15 ). Airway obstruction has been corrected using distraction osteogenesis in infants as young as 14 weeks.

Mandibular distractor in infant with Pierre Robin sequence.

(Courtesy Joseph E. Losee.)

Anesthetic management

The anesthetic management of infants with craniofacial anomalies begins with a complete preoperative evaluation. The history should define the anomaly and identify if there is an associated syndrome. Infants and children with syndromes may have more difficult airways, other organ involvement, and more complicated surgical repair with more bleeding. Associated anomalies that can present a challenge to the anesthesiologist include facial and airway features that make mask ventilation and intubation difficult. Airway pathology can also cause obstruction, and some of these children have obstructive sleep apnea. History of fatigue or sweating with feedings, cyanosis, and syncope suggests an underlying cardiac anomaly. Cardiac pathology is associated with some of the syndromes (e.g., Treacher Collins, Apert’s, Pfeiffer’s, Carpenter’s, hemifacial microsomia). Some of these infants and children may have increased ICP, manifesting as headaches, vomiting, and somnolence.

A thorough airway examination may be difficult to perform on an infant. Features that may predict difficulty with mask ventilation include midface hypoplasia and enlarged tongues. In addition, a small mandibular space, decreased jaw opening and translocation, and decreased neck flexion and extension predict difficult intubation. Identifying a heart murmur may uncover an underlying congenital cardiac defect. In infants with syndactyly, identifying potential IV and arterial access sites is critical. For reconstructions that involve significant blood loss, a preoperative hematocrit and type and crossmatch should be performed. Former premature infants and infants younger than 1 month should have their glucose level monitored. Premedication can be performed for most children older than 1 year but is rarely necessary in those younger than 10 months. Children with evidence of airway obstruction or acutely elevated ICP should not receive a premedicant. Endocarditis prophylaxis is not typically required in patients with congenital heart disease having craniofacial surgery.

Airway management in these patients may be very challenging. As previously stated, the difficulty may present during attempts at ventilation, intubation, or both. Although difficult airways are not common, the incidence is higher in patients with congenital syndromes and in those with previous reconstruction. Many techniques have been successfully described in infants (e.g., Bullard laryngoscope, LMA, flexible fiberoptic scope, glidescope, retrograde intubation). A combination of techniques may be required to secure the airway. For example, the LMA has been used to facilitate the passage of the fiberoptic scope and endotracheal tube (ETT). Some infants with craniofacial anomalies require tracheostomy because of significant upper airway obstruction. Adequate preparation entails having all the necessary equipment available and experienced personnel, perhaps also with a pediatric otorhinolaryngologist immediately available.

Several intraoperative considerations exist when managing the anesthetic for craniofacial repairs. Often these procedures are long and expose infants to the risks of hypovolemia, hypothermia, blood loss, and venous air emboli. The craniofacial procedures performed during the first year of life include cranial vault remodeling, fronto-orbital advancement, strip craniectomy, and distraction osteogenesis. The cranial-based procedures can involve significant blood loss because of the duration of the procedure and also because of complications such as entering the sagittal sinus. In some centers 90% to 100% of the infants undergoing these procedures will require a blood transfusion. However, some centers have significantly reduced blood transfusions through a perioperative blood conservation program, including cell salvage and preoperative epogen. Even the endoscopic strip craniectomy, which is typically performed to correct sagittal synostosis and results in less blood loss, can still produce significant hemorrhage. Infants are particularly at risk of being exposed to transfusions because they can present to the OR at the nadir of their physiologic anemia (2-3 months). Preparation for these procedures requires a baseline hematocrit and a type and crossmatch. Adequate IV access needs to be obtained for resuscitation. In an infant, at least two large-bore (22- to 18-gauge) peripheral IV catheters should provide adequate access. Arterial pressure monitoring is recommended for beat-to-beat analysis of blood pressure and intravascular volume status, as well as for arterial blood gas (ABG) monitoring.

Techniques to minimize blood loss have been proposed and include preoperative recombinant erythropoietin, acute normovolemic hemodilution, induced hypotension, electrocautery, aprotinin, and use of a cell saver. Preoperatively, recombinant erythropoietin may decrease the transfusion requirements in infants having craniosynostosis repair. The reported dose of erythropoietin is 300 to 600 units/kg subcutaneously one to three times weekly, along with oral iron supplementation. Erythropoietin is started 3 weeks before surgery. A prospective study of once-weekly dosing decreased the incidence of transfusion in infants having craniosynostosis repair from 93% to 57%.

Antifibrinolytics can reduce the transfusion requirements in infants having cranial vault reconstructions. Two prospective blinded studies demonstrated a reduction in allogeneic blood exposure in infants having craniofacial surgery for craniosynostosis. A 50-mg/kg loading dose of tranexamic acid was followed by 5 mg/kg/hr.

In the past, the use of cell saver has been reported as being impractical for small pediatric patients because of the size of the receptacle. Recently, the cell-saver reservoirs are available in sizes as small as 55 mL. This technology may reduce the rate of autogenous blood transfusion in infants having craniofacial surgery. In a prospective analysis evaluating the use of cell saver with a 55-mL pediatric bowl in patients pretreated with erythropoietin, only 30% of those infants having cranial vault remodeling required allogeneic blood.

Venous air embolism (VAE) is a potential complication of craniofacial and neurosurgical procedures. It can present as hemodynamic instability and can result in death. VAE can occur frequently in pediatric patients having cranial-based procedures. A prospective study using a precordial Doppler detected VAE in 82% of infants and children having craniosynostosis repair; 31% developed hypotension secondary to VAE, but none developed cardiovascular collapse. This is higher than the previously reported incidence of 66%. Infants may be at increased risk of VAE because they can hemorrhage significantly during cranial vault remodeling, resulting in low central venous pressure (CVP). In addition, the relatively large size of the infant head may raise the surgical site above the level of the heart, thereby increasing the pressure gradient for air entrainment. Some advocate the placement of central venous catheters to monitor the CVP trend and minimize the risk of air embolism. However, no data suggest that CVP monitoring decreases the risk of VAE. Management of VAE begins with preventing hypovolemic states by providing adequate volume resuscitation and using a precordial Doppler for early detection of VAE. Lowering the head of the bed, flooding the surgical field with saline, applying bone wax, discontinuing nitrous oxide, and providing inotropic support are all measures used to manage VAE acutely.

Craniofacial procedures can last several hours. Complications resulting from long surgical procedures include skin breakdown, neuropathic injury, and hypothermia. Attention must be paid to the initial setup to ensure adequate positioning and padding to minimize these intraoperative injuries. Infants having cranial vault remodeling may be positioned prone, and attention to protecting the face and eyes is important. Patients with syndromes that alter the architecture of the midface may present a challenge when placed prone because adequately protecting the face and eyes may be more difficult; Figure 21-16 shows an example of the initial setup. The infant is placed on a full access Bair hugger to minimize hypothermia, and the surgical site (head) is then isolated from the body using plastic drapes. This not only minimizes convective and radiant heat losses, but also prevents conductive heat loss to a wet bed from irrigation and blood. Blood products should be warmed through a fluid warmer before administration (except for platelets).

Operating room setup for posterior cranial vault remodeling.

Note application of forced-warm-air plastic sheets to isolate the head from the body. This creates a barrier to fluids (blood, prep solution, irrigation). Special attention to avoid ocular pressure is essential.

(Courtesy Joseph E. Losee.)

Postoperative Management

The postoperative management of infants having craniofacial surgery depends on coexisting morbidities and the procedure performed. Infants who have had distractors placed may have a more difficult airway after extubation because of location of the device. Mask ventilation can be difficult with mandibular distractors. Airway equipment, including appropriately sized LMAs, should be available after extubation. External maxillary distractors are not typically placed in infants. However, their use in older children can make access to the airway more challenging, and personnel and equipment to remove part of the device are important in the OR. Infants having cranial vault remodeling and frontal-orbital advancement can experience significant blood loss intraoperatively. Providing these patients are adequately resuscitated and are hemodynamically stable, they can often be extubated in the OR. Infants with difficult airway, significant airway obstruction, or who have experienced intraoperative complications may benefit from delayed extubation in the ICU/OR after their condition has stabilized. Ongoing blood loss is common after major craniofacial surgery, and infants may require repeat transfusions in the immediate postoperative setting. Other complications include cerebral edema, visual changes, CSF leak, infection, electrolyte abnormalities (hyponatremia), metabolic acidosis, and transfusion reactions.