Prematurity

The preterm infant may present for many surgical procedures early in life. ROP, congenital cataracts, and glaucoma may require surgery even when the infant weighs less than 1000 g. The preterm infant may have significant systemic illnesses. Common complications of prematurity include acute and chronic pulmonary disease,¹⁰ respiratory failure and pulmonary hypertension, congenital heart disease (unrepaired or with a limited palliative repair), and intraventricular hemorrhage,¹¹ with or without obstructive hydrocephalus.

Acutely ill preterm infants and those younger than 1 year of age are at greater risk than older children and adults for perioperative complications.¹² Careful attention to airway management, assisted ventilation, and titration of oxygen therapy with specified goals are essential for success.¹³ In preterm infants whose airways are already intubated and whose lungs are ventilated mechanically, the anesthesiologist should confirm the position of the tube, transport the infant safely to the operating room, and limit the exposure to high concentrations of oxygen. Although institutional goals are not uniform regarding supplemental oxygen therapy,¹⁴ communication with the neonatal team is often helpful in gauging the infant’s previous oxygen requirement and current targeted goals (e.g., hemoglobin-oxygen saturation levels of 90% to 95%). Because most inhalational anesthetics impair hypoxic pulmonary vasoconstriction, a greater fraction of inspired oxygen (Fio₂) may be necessary to maintain the targeted hemoglobin saturation.

Hypercarbia and hypoxia may increase choroidal blood volume and increase IOP. Partial pressures of carbon dioxide (Pco₂) and oxygen (Po₂) should be controlled. Infants may be at greater risk for the OCR than older children and adults, and intravenous access should be obtained before the surgical procedure or any examination that may involve traction on the extraocular muscles or pressure on the globe.

Infants with extremely low birth weight require many weeks to grow and develop to a weight of approximately 1800 g and to maintain normothermia without special environmental control. These infants commonly have a history of short-term or intermediate-term assisted ventilation and may not require supplemental oxygen before an EUA or planned operative procedure for ROP.¹⁵ Many of these infants undergo ophthalmologic examinations while their lungs are ventilated in the neonatal intensive care unit.¹⁶ During surgical therapy (i.e., laser or cryosurgical stabilization) for ROP, these infants require anesthesia to provide optimal conditions (Fig. 32-1). Perioperative apnea may preclude tracheal extubation or require close postoperative monitoring after anesthesia.

FIGURE 32-1 A, Grade III retinopathy of prematurity with neovascularization of the retina requires surgical therapy to halt the growth of vessels. B, Retinal detachment caused by retinopathy of prematurity. This degree of damage results in permanent visual impairment. C, Appearance after cryotherapy. Cryotherapy causes a well-demarcated ridge of tissue scarring (arrow) that prevents further growth of the neovasculature (left to right in the middle).

Perioperative apnea in the preterm infant is widely described.^17,18 Whether the child is still hospitalized or presenting for elective surgery as an outpatient, the preoperative assessment should determine the pattern and frequency of apnea before the planned surgical procedure and anesthesia. If the child has been discharged, the current use of respiratory stimulants (i.e., caffeine or theophylline) and oxygen should be determined. Is an apnea monitor being used, or has it been discontinued? Guidelines have not been developed to manage some of the scenarios, but infants who continue to require supplemental oxygen, who are younger than 60 weeks postconceptional age, or who are monitored for apnea or bradycardia should have continuous cardiorespiratory and oxygen saturation monitoring postoperatively for at least 12 hours or until they are apnea free (see Chapter 4). The risk of apnea after general anesthesia and sedation decreases with advancing gestational age at birth and with advancing postnatal-postconceptual age. The risk of apnea is independent of opioid use; its multifactorial origins include the presence of general and neuraxial anesthetics and the immature central nervous system and respiratory center in the preterm infant. Flexible planning for possible postoperative ventilatory support is essential, and families should be informed of this possibility preoperatively.

The airway of the preterm infant who is younger than 52 to 60 weeks postconceptual age is usually intubated for ophthalmologic surgery (except for a very brief EUA) due to the immature respiratory drive, unpredictable respiratory response to anesthetic agents, and possible lag before recovery of respiratory drive after completion of the procedure and discontinuation of anesthetic agents. If the infant does not appear to have a stable respiratory drive and strength after anesthesia, assisted ventilation should be provided postoperatively and weaned during recovery. Planning for this contingency is vital. Ophthalmologic procedures may be brief and have a low risk of blood loss, but the risks of general anesthesia mandate full postoperative support. Intensive care resources for assisted ventilation in preterm and formerly preterm infants should be available before embarking on anesthesia.

Although chronic lung disease due to prematurity is prevalent, its intensity has been significantly reduced with the routine use of surfactant and advances in ventilator management strategies. Long-lasting respiratory effects from prematurity may include reactive airway disease, subglottic stenosis from prolonged intubation, and alveolar or interstitial disease with an oxygen requirement lasting weeks to years.¹⁰ Because many anesthetics impair hypoxic pulmonary vasoconstriction, an increased oxygen requirement in the perioperative period should be anticipated. Tracheal intubation, a light level of anesthesia, or topical use of β-adrenergic antagonists may exacerbate reactive airway disease, requiring further treatment to reduce air trapping and hypercarbia.

Along with assessing for airway and alveolar diseases, the anesthesiologist should determine whether pulmonary hypertension or right ventricular dysfunction is or was present.¹⁹ Some infants may be receiving continuing oxygen therapy as treatment for pulmonary hypertension and to reduce intermittent episodes of hypoxemia due to crying or while sleeping. If pulmonary hypertension was diagnosed previously, an updated evaluation is warranted. Because pulmonary hypertension is exacerbated by hypoxia and hypercarbia, tracheal intubation should be considered to ensure control of ventilation and oxygenation. At emergence, pulmonary hypertension may be exacerbated as hypercapnia develops, causing physiologic or anatomic shunting with systemic hemoglobin-oxygen desaturation. Immediate and continued evaluation of the airway is imperative to rule out an independent respiratory contribution to the systemic hypoxia.

Congenital cardiac disease may be diagnosed in the preterm neonate, infant, or child who presents for ophthalmologic procedures. A patent ductus arteriosus may not close spontaneously or after administration of cyclooxygenase inhibitors. This may lead to persistent congestive failure, reduced pulmonary compliance, and complications of fluid management. Congenital cardiac anomalies require assessment before elective surgery. The various complex congenital cardiac lesions have a wide spectrum of interactions with multiple anesthetic agents.²⁰ Many cardiac conditions require surgery or palliation (e.g., systemic-to-pulmonary shunts) before elective ophthalmologic procedures. Correction of congenital heart disease is limited by the difficulty of using cardiopulmonary bypass in infants weighing less than 2 kg. There may be an urgent need for ophthalmologic evaluation (e.g., congenital tumor, cataract, glaucoma) before repair of the congenital cardiac condition. Preoperative consultation with the infant’s pediatric cardiologist can provide useful information on the infant’s current ventricular function and the risk of dysrhythmias associated with cardiac defects. Medical management must be optimized before undertaking anesthesia and surgery.

Intraventricular hemorrhage is a major source of morbidity and mortality for preterm infants.¹¹ Obstructed hydrocephalus may occur and require cerebrospinal fluid diversion procedures to decompress the obstructed ventricular system and treat the associated increased intracranial pressure. Many of these infants require ophthalmologic surgery for repair of strabismus due to a neurologic insult. If a ventriculoperitoneal shunt is in place, its proper function should be determined by direct evaluation. The anesthesiologist should assess whether there is inappropriate macrocephaly or a bulging or tense fontanelle. Obstructed hydrocephalus may occur after the infant’s discharge from hospital, even though a ventriculoperitoneal shunt was not required previously. The preoperative assessment should include the child’s developmental and neurologic status at the time of surgery. Because intraventricular hemorrhage is associated with long-term morbidity, any history of seizures should be elicited, and the antiepileptic drugs being used should be documented.

Preterm and small infants rapidly lose heat when anesthetized. Prevention of hypothermia is essential in the perioperative environment. Hypothermia can decrease metabolism of most drugs and depresses respiratory drive in preterm infants (see Chapters 35 and 36).

Down Syndrome

Children with Down syndrome (i.e., trisomy 21) frequently present for ophthalmologic surgery because of associated pathologic processes such as neonatal cataracts, significant refractive errors (e.g., hypermetropia, astigmatism), strabismus, glaucoma, keratoconus, nasolacrimal duct obstruction, and nystagmus.^21–23 Infants with trisomy 21 should have an ophthalmologic evaluation in the neonatal period. If this requires an EUA, the anesthesiologist should be prepared for the extensive medical implications associated with trisomy 21.^24,25 Almost half of these infants are born with congenital heart disease, including septal defects, complete or partial atrioventricular canal, tetralogy of Fallot, transposition of the great arteries, and valvular insufficiency or stenosis. Any child with a left-to-right shunt may develop pulmonary hypertension, and children with trisomy 21 develop irreversible pulmonary hypertension at an earlier age. Bradycardia (25% to 60%) and hypotension (12% to 73%) have been reported during sevoflurane anesthesia in these children.^26,27 Complete understanding of the child’s cardiac defects is essential to planning anesthesia (see Chapters 14, 16, and 21).

Airway abnormalities such as narrowed nasopharyngeal passages, macroglossia, pharyngeal hypotonia, and subglottic stenosis are frequently observed in children with trisomy 21. These abnormalities may contribute to development of chronic intermittent hypoxia, further exacerbating pulmonary hypertension, and these children should be expected to demonstrate exacerbations of airway obstruction and hypoxia after general anesthesia.²⁸

Children with trisomy 21 have a wide spectrum of developmental delays. Cervical spine instability occurs, and occiput-C1 and C1-2 instabilities have been described.^29,30 Subluxation of the cervical spine has rarely been reported in these children during anesthesia. Nonetheless, the anesthesiologist and the surgeon should avoid extremes of neck flexion and extension and lateral rotation during head positioning for laryngoscopy and surgery. While the child is awake, the range of motion of the neck in flexion and extension should be assessed, along with complaints of numbness or tingling in the hands or feet in a particular position. Previous spine and neck investigations or operations should be reviewed. These infants and children may have ligamentous laxity of the cervical spine and other locations. No consensus exists for the radiologic workup of children who are asymptomatic for cervical disease, although many children have been evaluated radiologically before about 5 years of age.

Children with trisomy 21 may be born with congenital hypothyroidism, or it may develop at any time during their life span. They may develop junctional bradycardia during sevoflurane anesthesia.³¹ The bradycardia may be associated with or result from occult hypothyroidism. If the child is found to have a goiter on examination or has symptoms consistent with hypothyroidism (i.e., prolonged jaundice, hypothermia, constipation, dry skin, macroglossia, or relative bradycardia), thyroid function studies should be obtained before anesthesia for an elective procedure.

Alport Syndrome

Alport syndrome (i.e., progressive hereditary nephritis) is one of the disorders in a group of familial oculorenal syndromes. This classification includes Lowe (oculocerebral) syndrome and familial renal-retinal dystrophy. Alport syndrome involves sensorineural hearing loss, progressive renal disease, and multiple ophthalmologic disorders, including cataracts, retinal detachment, and keratoconus.^32,33 Development of myopathy and renal failure constitutes the major anesthesia concern. If the patient has myopathy, it is prudent to avoid succinylcholine and the risk of a hyperkalemic response. Renal insufficiency may alter the choice of pharmacologic agents to very-short-acting agents or agents that are not renally excreted.

Marfan Syndrome, Ehlers-Danlos Syndrome, and Homocystinuria

Marfan syndrome, Ehlers-Danlos syndrome, and homocystinuria are considered together only from the perspective of a general body phenotype. The metabolic and molecular causes of these syndromes are well described. They share problems with connective tissue development, possible joint laxity, and cardiovascular disorders.

Marfan syndrome is caused by a defect in the fibrillin 1 gene (FBN1), which affects elastic and nonelastic connective tissues. These children have an increased risk of retinal detachment, lens dislocation, glaucoma, and cataract formation (E-Fig. 32-1).³⁴ They may have significant pulmonary (scoliosis) and cardiovascular problems,³⁵ which may include aortic, mitral, or pulmonic valve insufficiency. Preoperative cardiovascular evaluation is indicated to determine the progression of cardiovascular abnormalities that inevitably occur. Blood pressure control is essential to prevent aortic dissection.

E-FIGURE 32-1 Patients with Marfan syndrome may present for surgical repair of ocular lens dislocation resulting from connective tissue defects. This photograph of a slit-lamp examination shows that the circular outer edge of the lens is displaced from its usual position. The capsule of the lens appears to be intact.

Homocystinuria has at least three forms and different inborn errors. Enzymatic deficiency of the metabolism of sulfur-containing amino acids causes the intermediate metabolite, homocysteine, to accumulate. These children suffer from cataracts, retinal degeneration, optic atrophy, glaucoma, and lens dislocation. The cardiovascular pathology includes coronary artery disease at a young age. Thromboembolic phenomena occur more frequently because the children may be hypercoagulable.³⁶ Nitrous oxide should be avoided because it inhibits methionine synthase, further limiting the conversion of homocysteine to methionine.

At least 10 forms of Ehlers-Danlos syndrome have been described. Not all forms express significant ocular pathology. From the anesthesiologist’s perspective, positioning is important to avoid trauma to the skin because these children develop hemorrhages with minor trauma and experience delayed wound healing. A thorough preoperative assessment should be performed for cardiac lesions. Hypertension should be avoided to reduce the risk of rupturing an aneurysm. The duration of effect of local anesthetics in patients with class III Ehlers-Danlos syndrome may be less than that in normal patients, and contingency plans should be in place to address these possibilities, including retrobulbar block or general anesthesia.³⁷

Mucopolysaccharidoses

The mucopolysaccharidoses are a group of disorders with enzyme defects that result in incomplete degradation of glycosaminoglycans. These children have various degrees of cognitive dysfunction, macroglossia, airway obstruction, cervical spine instability, and systemic involvement with deposition of mucopolysaccharide material. This leads to cardiac and respiratory dysfunction, airway obstruction, corneal opacities, and glaucoma.

The systemic complications of these disorders are sufficiently severe that even well-planned anesthesia management for ophthalmologic procedures may cause death.³⁸ Airway management can be extremely difficult with poor mask fit, dynamic airway obstruction with narrowed passages, a floppy epiglottis, and difficulty visualizing the larynx.³⁹ Infiltrative material may be deposited in the laryngeal inlet and pretracheal tissues; an LMA is particularly useful in maintaining a patent airway. Tracheal intubation may require the use of advanced airway management techniques, and the anesthesiologist should have several plans for airway management (see Chapter 12). Cardiac evaluation should be considered before an elective procedure to assess ventricular function and arrhythmias. Intravenous access may be difficult due to subcutaneous deposition of mucopolysaccharides.

Craniofacial Syndromes

Craniofacial syndromes may manifest as craniosynostosis or have only middle and lower facial structure involvement.⁴⁰ Apert and Crouzon syndromes are both disorders of craniofacial development, but syndactyly occurs only in the former (E-Fig. 32-2). They share the potential for many ocular disorders, including severe proptosis, and mask airway management may be difficult.⁴¹ Other mutations of the fibroblast growth factor receptor 2 gene (FGFR2) cause Antley-Bixler and Pfeiffer syndromes. These children may develop chronic airway obstruction, and some have complete tracheal rings. Tracheal narrowing should be anticipated, and smaller tracheal tube sizes should be used.

E-FIGURE 32-2 This child with Apert syndrome presented with hypertelorism, proptosis, and other pathologic ocular processes. Airway management and intravenous access in these cases are challenging for the anesthesiologist.

Children with asymmetry of facial and mandibular bone growth may present with limited mouth opening. Children with Goldenhar syndrome (i.e., hemifacial microsomia), Treacher Collins syndrome, and Pierre Robin sequence can be expected to present a challenge to airway management (see Chapters 12 and 33).⁴² Children with craniosynostosis have an increased risk of congenital heart disease, and a cardiac evaluation should be performed before anesthesia.⁴³ Neurologic morbidity and seizure disorders occur more frequently in this group of patients.

Phakomatoses

The phakomatoses are neurocutaneous syndromes with multiple ocular pathologic processes. These syndromes include neurofibromatosis,^44,45 encephalotrigeminal angiomatosis (i.e., Sturge-Weber syndrome),⁴⁶ tuberous sclerosis,^47,48 incontinentia pigmenti, and ataxia telangiectasia. Central nervous system involvement varies with each of these diseases. Patients may have developmental delay, seizures, and significant neurologic morbidity. Anticonvulsant drugs should be continued in the perioperative period. Electrolyte and hepatic function studies should be done, and plasma levels of antiepileptic agents should be evaluated preoperatively.

Intraocular Pressure

IOP is the pressure exerted by the internal components of the globe on the covering (i.e., sclera and conjunctiva). The normal IOP is 12 to 15 mm Hg. An IOP greater than 20 mm Hg is considered abnormal. Aqueous humor is a clear fluid that is secreted by the ciliary body and released into the anterior chamber of the globe. It traverses the anterior chamber and bathes the iris. It flows through the canal of Schlemm into the pores of Fontana and then drains into the episcleral veins (Fig. 32-2). The posterior chamber, which is larger than the anterior chamber, is composed of a gelatinous mix known as vitreous humor. The sclera and globe that encase the intraocular constituents are relatively noncompliant and are protected by the bony orbit. However, intraorbital masses may impinge on the globe and increase the relative IOP or alter the flow of aqueous humor, resulting in increased IOP. Any obstruction to the drainage of aqueous humor causes fluid to build up within the anterior chamber and increases IOP.⁴⁹ Increased central venous pressure (e.g., Trendelenburg position, coughing, Valsalva maneuver, straining, increased intrathoracic pressure) attenuates the drainage of aqueous humor from the eye. Arterial pressure does not directly effect changes in IOP. However, as arterial blood pressure increases beyond the normal range, approximately 30% of the increase in systolic blood pressure is reflected in IOP increases. Aqueous humor formation is described in the following equation:

FIGURE 32-2 Aqueous humor is synthesized in the ciliary process and then circulates around the iris, past the lens, and into the anterior chamber. After flowing through the trabecular meshwork, aqueous humor enters the canal of Schlemm (arrows), which drains into the episcleral venous system. Pathologic conditions that increase venous pressure, obstruct the canal of Schlemm, or increase aqueous humor production may increase intraocular pressure.

K is the coefficient of outflow, OP_aq is the osmotic pressure of aqueous humor, OP_pl is the osmotic pressure of plasma, and P_c is the capillary pressure. These variables allow calculation to intervene by increasing the plasma osmolality acutely with mannitol to lower the IOP. This increases the gradient of osmolality and draws water out of the aqueous humor, thereby reducing the IOP.

In the relatively noncompliant globe, any pharmacologic or metabolic process that increases choroidal blood volume (e.g., hypercapnia, coughing, increased central venous pressure) produces choroidal congestion and an increased IOP. Although well tolerated in the healthy eye, this congestion may lead to extrusion of contents if the globe is ruptured. The anesthesiologist should carefully control the child’s physiology during the induction and maintenance of anesthesia to minimize increases in IOP, regardless of whether there is a preoperative concern about increased IOP.

Congenital or trauma-induced glaucoma requires therapy to reduce the IOP. If the IOP remains elevated, blood flow in the retina will be impaired, possibly leading to loss of vision. Unfortunately, there are many causes of glaucoma in childhood. Hypercarbia, hypoxia, and drugs known or suspected to increase IOP (e.g., succinylcholine, ketamine) should be avoided or used with care. Reducing a child’s apprehension and crying and avoiding increases in central venous pressure are also important considerations.

The effect of succinylcholine on IOP is well documented.^50,51 Succinylcholine increases IOP 6 to 10 mm Hg, an effect that begins within 1 minute after administration and continues for up to 10 minutes, at which time the IOP returns to normal. This effect has been attributed to four possible mechanisms: