Cerebral palsy and seizure disorders are very common in the pediatric population, thus anesthesia providers should be familiar with their clinical characteristics and the pharmacologic agents used for their treatment. Although less common, myopathies are associated with significant morbidity in children, and are noteworthy because of their potential association with malignant hyperthermia and the potentially catastrophic hyperkalemic response to administration of succinylcholine (and in some cases, volatile anesthetics).
Cerebral Palsy
Cerebral palsy (CP) is a static motor encephalopathy that affects tone, coordination, and movement of the musculoskeletal system. It is a collection of motor system disorders caused by perinatal or early childhood neurologic insult. The cumulative incidence rate of CP at the age of 5 to 7 years is 2.4 cases per 1000 live births. The contribution of very low birth weight infants to this population of children is significant: about 52,000 very low birth weight infants (<1500 g) are born annually. These infants make up more than 25% of children diagnosed with CP.
Children with CP exhibit a wide variety of clinical manifestations that range from mild (e.g., slight lower extremity spasticity and normal cognitive function) to severe (e.g., spastic quadriplegia and marked intellectual disability). Respiratory system dysfunction usually parallels the overall severity of the disease. Bulbar motor dysfunction causes a loss of airway protective mechanisms (impaired cough, gag, etc.) and leads to chronic pulmonary aspiration, recurrent pneumonia, reactive airway disease, and parenchymal lung damage. Other airway considerations include abnormal dentition, temporomandibular joint dysfunction, and positioning difficulties. Gastrostomy tubes are often placed during infancy to optimize nutritional status.
Prematurely born infants may develop areas of brain ischemia secondary to cerebral hemorrhages in the early newborn period. The area of infarction is termed periventricular leukomalacia (white matter atrophy surrounding the ventricles) and is associated with development of varying degrees of limb spasticity ( Fig. 5.1 ).
Chronic absence of motor input results in progressive development of limb contractures during childhood that worsen with age. Baclofen, a gamma-aminobutyric acid (GABA) agonist, reduces pain associated with muscle spasms and slows development of contractures. Side effects are common with oral baclofen, thus intrathecal baclofen has become popular for children of any age. This requires surgical intervention for catheter placement and implantation of the baclofen pump in the anterior abdominal wall. Side effects of baclofen include urinary retention and lower extremity weakness, which usually abate when the dose is reduced. Abrupt withdrawal from oral or intrathecal baclofen may cause seizures, hallucinations, disorientation, and dyskinesias, and when severe may be fatal. If intrathecal baclofen is discontinued because of infection of local structures or cerebrospinal fluid (CSF), close observation of the patient for withdrawal symptoms is necessary. On occasion, when withdrawal is severe enough, a temporary intrathecal catheter may be placed to provide baclofen. Two case reports highlight the successful use of dexmedetomidine to manage acute, severe withdrawal in two patients.
Children with CP may undergo various surgical interventions during childhood. Orthopedic procedures are the most common and include scoliosis repair and a variety of limb procedures to improve range of motion and decrease progression of contractures. Dorsal rhizotomy may be required to control painful lower limb spasticity. Nissen fundoplication is performed to control chronic gastroesophageal reflux and may include a feeding gastrostomy, which is increasingly performed by laparoscopy.
Surgical complications are relatively common. In a review of 19 children with CP undergoing scoliosis surgery, 9 had at least one major complication, most commonly blood loss or the need for postoperative mechanical ventilation. Risk factors included the presence of two or more comorbidities and thoracotomy.
Preoperative assessment includes defining and optimizing all systemic medical illnesses. Concurrent upper respiratory infections are poorly tolerated and will exacerbate preexisting respiratory disease. Preoperative anxiolysis should be administered to children when appropriate, although some children with CP are prone to upper airway obstruction with mild sedation and should be closely monitored. Administration of an anticholinergic agent may decrease pooling of oropharyngeal secretions, but this is not evidence-based. Routine preoperative echocardiography for cardiovascular evaluation in the absence of signs or symptoms suggestive of cardiac dysfunction is not necessary.
There are no special considerations when choosing an agent for induction or maintenance of general anesthesia because children with CP usually tolerate all anesthetic agents well. If a gastrostomy tube is present, suctioning or leaving it open before induction of general anesthesia may help decompress the stomach. Because of possible malformation of facial structures, mask ventilation may be difficult, but endotracheal intubation should be straightforward in most cases. Presence of gastroesophageal reflux and increased oropharyngeal secretions may encourage the anesthesia provider to secure intravenous (IV) access earlier during induction of anesthesia and secure the airway using IV induction agents.
Children with CP demonstrate increased sensitivity to succinylcholine ; approximately 30% of children with CP have abnormal distribution of acetylcholine receptors. Succinylcholine-induced hyperkalemia in CP has not been studied to the extent that is required to capture such a rare event. We are aware of a child with CP that experienced cardiac arrest upon receiving succinylcholine; therefore, succinylcholine should be used only to treat life-threatening airway emergencies in CP patients. Nondepolarizing muscle relaxants are less potent and have a relatively shorter duration of action in children with CP. This may be related to chronic anticonvulsant administration or underlying spasticity.
Sevoflurane is relatively more potent (i.e., lower minimum alveolar concentration) in children with CP. Increased opioid sensitivity should be assumed in all but mild forms of CP. Doses should be reduced, and greater vigilance at the time of extubation is necessary to ensure the child’s ability to maintain a patent upper airway. Hypothermia is a common intraoperative problem in children with CP. Impaired temperature regulation is caused by hypothalamic dysfunction and the relative absence of muscle and subcutaneous fat. A child with spastic quadriplegic CP may have an esophageal temperature of 34°C to 35°C within a few minutes of induction of anesthesia. Therefore the ambient temperature should be 21°C to 24°C (70°F–75°F) in the operating room while the patient is relatively exposed during induction and line placement. Line placement will also become increasingly more difficult as the child becomes increasingly hypothermic. Forced-air warming is effective and should be used starting in the preoperative holding area, if possible.
Regional analgesia may benefit children with CP who have difficulty communicating the severity of their pain. Epidural catheter placement via lumbar or caudal approach is commonly used for lower extremity orthopedic procedures. Addition of epidural clonidine to local anesthesia may help reduce postoperative lower limb spasticity, which can be a significant component of their postoperative discomfort. Oral diazepam may help alleviate muscles spasms.
Seizures are present in about 30% of patients with cerebral palsy. Anticonvulsants should be continued until the morning of surgery and reinstituted as quickly as possible during the postoperative period. When it is not feasible to continue enterally administered anticonvulsants, some can be administrated rectally (phenytoin, valproic acid, carbamazepine, levetiracetam) and some intravenously (phenytoin, valproic acid, phenobarbital, levetiracetam). If the surgical procedure causes significant blood loss, anticonvulsant levels should be checked postoperatively, and doses should be adjusted to reestablish optimal levels.
Seizure Disorders
Seizures are clinical manifestations of a variety of disorders. Febrile seizures are the most common type, affecting 5% of children. Idiopathic epilepsy, primarily seen in older children, is less common with an estimated incidence of 0.6% of the population. Trauma, hypoxia, and infection are the primary pathologic causes of seizures in infants. Additional causes include metabolic disease, hypoglycemia, electrolyte abnormalities, toxic ingestions, and congenital or developmental defects. However, in about 50% of children, the etiology of the seizure is unknown.
The currently accepted international classification of epileptic seizures divides these disorders into three etiologic categories and three types of seizures ( Table 5.1 ). Etiologic categories include genetic, structural/metabolic, and unknown. Seizure types are divided by onset location: focal, generalized, or unknown.
| Focal Onset Seizures |
|
| Generalized Onset Seizures |
|
| Unknown Onset Seizures |
|
Focal onset seizures are akin to partial seizures, in which the initial clinical and electroencephalogram (EEG) changes indicate activation of a system of neurons limited to part of one cerebral hemisphere. Focal seizures may or may not have impaired awareness. Focal seizures can be subdivided by clinical presentation and EEG characteristics into motor, sensory, autonomic, or higher cortical/aura symptoms. There may not be a postictal state. Focal onset seizures may spread bilaterally and progress to a “focal to bilateral” tonic-conic seizure.
Generalized onset seizures involve bilateral cerebral hemispheres with clinical and EEG changes from the onset and accompanied with impaired awareness. Motor manifestations, if present, are also bilateral. Generalized seizures may be convulsive or nonconvulsive.Generalized tonic-clonic seizures consist of an initial tonic contraction phase, during which it is common for patients to become apneic and cyanotic from the tonic rigidity of the thoracic cavity. This is followed by the clonic, repetitive twitching phase, where breathing resumes but can be shallow and irregular.
Nonmotor “absence” seizures are nonconvulsive generalized seizures. They are further subdivided into typical (staring spells during which the patient is not responsive, and last a few seconds), atypical (less abrupt onset/offset, some loss of muscle tone), myoclonic, or eyelid myoclonia.
Motor seizures are subdivided by the presence or absence of three characteristics:
- 1.
Tone
- 2.
Clonus (regular and rhythmic twitch)
- 3.
Myoclonus (irregular, arhythmic)
Generalized motor seizures range from atonic (where atonia is the only prominent feature) to myoclonic-tonic-clonic (where all three abnormalities are alternatively present).
- 1.
Epileptic spasms, which include infantile spasms, are of poorly understood origin and classified as “unknown.”
Infantile spasms (West syndrome) consist of the triad of unique salaam-like seizure movements, arrest of psychomotor development, and a characteristic EEG pattern called hypsarrhythmia . The onset peaks between 4 and 7 months of age and almost always occurs before 12 months. It can be associated with a known underlying neurologic disorder, or it can be idiopathic and associated with a poor neurodevelopmental outcome. Lennox-Gastaut syndrome consists of different types of seizures that occur frequently and are difficult to control. It manifests itself in the 3- to 5-year age group and is associated with severe intellectual disability. Both infantile spasms and Lennox-Gastaut syndrome are difficult to control with anticonvulsant agents.
Anesthetic concerns for children with seizure disorders depend on coexisting morbidities and are individualized depending on the mental status of the child. If necessary, children who require strict pharmacologic control of their seizure disorder should have their oral anticonvulsants converted to the IV forms (or equivalent medications if IV forms are not available) during the preanesthetic fasting interval and during the postoperative period if oral intake is not possible. In most cases, preanesthetic anticonvulsant levels are not necessary. Anesthesiologists should be aware of the most common side effects of anticonvulsants.
Most anesthetic and analgesic agents can be safely administered to children with seizure disorders. A possible exception is multiple doses of meperidine. Its metabolite, normeperidine, possesses proconvulsant properties. Nitrous oxide, sevoflurane, etomidate, propofol, and all opioids have been anecdotally associated with seizure-like movements or lowering of the seizure threshold in both healthy and epileptic patients, without serious sequelae. In most of these cases these movements were a benign form of myoclonus. Virtually all general anesthetic agents except ketamine have anticonvulsant properties in doses associated with loss of consciousness but lower doses have been associated with an increase in EEG spike activity. Higher doses and shorter dosing intervals of neuromuscular blockers are required in patients taking anticonvulsants. The precise mechanism of this is unknown. However, this resistance is not as prominent for neuromuscular blockers that are metabolized in the plasma (i.e., atracurium), so it may be related to a pharmacokinetic effect based in the liver. Levetiracetam may prolong neuromuscular blockade. Anticonvulsants may also cause some resistance to opioids. Although definitive data are lacking, it does not appear that general anesthesia impacts the postoperatively subsequent frequency or severity of seizures.
Neuromuscular Diseases
Neuromuscular diseases can be broadly divided into disorders of the muscle or of neuromuscular transmission ( Table 5.2 ). Muscle diseases can be further categorized into developmental myopathies, muscular dystrophies, and metabolic myopathies. Disorders of neuromuscular transmission can be further categorized into diseases of the neuromuscular junction and diseases of anterior horn cells. This list is extensive and only the most common and most important in pediatric anesthesia will be reviewed here.
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