Pediatric Anesthesia in the Radiology Suite

Pediatric Anesthesia in Remote Locations

When working with children, the anesthesiologist needs to take into consideration the age-dependent physiology, psychological state, and pediatric comorbidities.

Preoperative Considerations

Children have distinctively different anesthetic requirements than adults. The preoperative considerations will be largely influenced by the child’s physiology and preexisting medical conditions. Neonates aged 0 to 28 days have a transitional physiology while adapting to extrauterine life. This period may be prolonged depending on the gestational age at delivery. The respiratory, circulatory, and metabolic systems are affected during this transitional phase. Because of an immature central nervous system, young infants are at risk for central apnea, as well as apnea in response to hypoxia and hypothermia. This risk is increased by anemia, younger gestational age at birth, and a history of apneic periods. In addition, administration of sedatives, opioids, or volatile anesthetics significantly increases the risk for postprocedural apneic episodes. Rather than an increase in respiration and sympathetic tone, hypoxia can lead to bradycardia and hemodynamic depression. Cardiac output in young infants is largely heart rate–dependent; thus a heart rate under 60 beats/min necessitates chest compression to maintain end-organ perfusion. Other differences to consider in the neonatal cardiovascular physiology include the presence of a patent foramen ovale and patent ductus arteriosus (PDA). Anesthesia induction generally decreases systemic vascular resistance. Because neonates have a higher pulmonary vascular resistance than older children and adults, which can further increase during a stressful induction, potential exists for reversal of the typically left-to-right to a right-to-left shunt. A shunt reversal should be considered in all cases of unexpected arterial oxygen desaturation. This is of particular interest in children who receive large amounts of intravenous fluids, because this can lead to a reopening of a functionally closed PDA within the first 2 weeks of life and lead to shunt reversal. Desaturations because of shunt reversal or inadequate oxygen supply are particularly pronounced in small children because of their high metabolic rate. Oxygen consumption is up to three times higher than in adults.

Another important factor in the anesthetic management of neonates is temperature control. Because of its large ratio of body surface area to volume, lack of subcutaneous fat, and poor temperature regulation, the neonate is prone to heat loss. Hypothermia again predisposes the neonate to apnea and bradycardia. Other side effects of hypothermia include shivering with increased oxygenation consumption, potential coagulation abnormalities, and increased discomfort during emergence. For these reasons, monitoring and maintenance of normal temperature remains important for all age groups.

As children’s physiology transitions from neonatal to adult state, their respiratory, cardiac, and central nervous systems mature. Some of the characteristics of the neonate may persist. For example, 50% of children 1 year of age have a probe patent foramen ovale and 30% of the adult population still has a probe patent foramen ovale. This necessitates meticulous avoidance of air bubbles in all intravenous lines to prevent a potentially dangerous paradoxical air embolus.

The normal vital signs in children will approach adult values over time, but vary significantly across age groups ( Table 18-1 ).

The most common medical conditions that one will encounter while taking care of children include respiratory infections, asthma, obstructive sleep apnea, and more common congenital diseases such as Down syndrome (trisomy 21) and sickle cell disease.

A child in daycare or school may have up to 14 upper respiratory tract infections (URIs) per year. A respiratory tract infection increases the perioperative risk for respiratory complications, such as laryngospasm, bronchospasm, thick airway secretions, mucous plugs, and croup. The risk may be increased by the choice of anesthetic (i.e., airway manipulation) and the age of the patient. Younger children are at higher risk, mainly because of the smaller airway diameter. All children with a URI develop an increased airway reactivity that can persist for 6 weeks after the initial symptoms. In cases of severe symptoms, an elective procedure probably should be postponed for 4 weeks.

Another risk group is the increasing number of children with preexisting reactive airway disease. Among patients with asthma, great variability exists in disease severity and compliance with medications. A thorough history concerning triggering agents and the frequency and severity of attacks should be obtained, and an elective procedure should potentially be postponed until optimal pulmonary status is achieved.

A third group at risk for airway complications is children with obstructive sleep apnea and/or upper airway obstruction secondary to airway hypotonia or adenotonsillar hypertrophy. These children are exquisitely sensitive to the respiratory depressant effects of sedatives, anesthetics, and opioids and are at risk for complete upper airway obstruction and respiratory arrest. They require a high level of vigilance, meticulous drug titration, and a low threshold for advanced airway management to ensure adequate ventilation and oxygenation. Children with developmental delays such as cerebral palsy may be at higher risk for airway obstruction because they are known to have up to a 40% decrease in their palatal width.

Among the commonly encountered congenital problems is Down syndrome. These children are prone to upper airway obstruction secondary to a small midface structure, a large tongue, and in some cases low baseline muscle tone. They also have a smaller-than-normal trachea, which requires downsizing the expected endotracheal tube size for age by 0.5 to 1. Another feature of the syndrome is a connective tissue abnormality that can make intravenous catheter placement a challenge and lead to atlantooccipital instability. The latter can place the child at risk for cord compression during intubation and should be evaluated after 1 year of age. In addition, children with Down syndrome may present with hypothyroidism and congenital heart defects. Even without a documented congenital heart defect, these patients have a high incidence of bradycardia with higher doses of anesthetics.

Another frequently encountered genetic problem is sickle cell disease. The tendency to develop vasoocclusive crisis with stress, hypothermia, anemia, hypercarbia, and hypoxia makes these patients a high-risk group. A thorough history concerning the severity and frequency of vasoocclusive crises should be obtained, and the transfusion thresholds should be discussed with the patient’s hematologist before the procedure. Preoperative determination of a hemoglobin level may be helpful. The anesthetic management needs to focus on keeping these children warm, well hydrated, comfortable, and well oxygenated.

An understanding of a child’s psyche and developmental age is imperative in planning an anesthetic. Reasoning with a child may not be possible, depending on the child’s age and general fear of the unknown. Parental influence will have a great impact on the overall experience as well as the anesthesiologist’s ability to interact with the child. Parental separation from the child can be a significant stressor to a young child. Children are able to feel the parent’s fear and anxiety, even if neither child nor parent is verbalizing it. The parent’s honest and appropriate preparation of the child for the procedure will allow the anesthesiologist more flexibility in choosing the anesthetic. Parental dishonesty about the procedure can cause unnecessary trauma and undermine the ability to form a trusting relationship with the treating physician. Patients who require multiple anesthetics, such as those undergoing radiation therapy, may develop a distrust that can complicate further treatments and patient care.

The stress of a traumatic anesthesia induction can lead to maladaptive behavior in more than half of the children who experience it. The anesthesiologist should employ comfort measures in light of the child’s potential anxiety. Measures may include parental presence, the use of a premedication, or walking the child through the procedure before the actual event. The appropriate comfort measure must be chosen to match the setting. For example, a parent who may become incapacitated or obstructive may not be suited to be present at induction. Premedication with oral midazolam has been shown superior to parental presence during induction but may lead to prolonged sedation after a short procedure. Even with a preoperative plan in place, the anesthesiologist must exhibit situational flexibility.

In planning the anesthetic, the anesthesiologist needs to know the procedure to be performed, the location of the procedure, and the age, physiology, and medical history of the patient. The anesthesia equipment necessary will largely depend on the location and type of procedure. There will be compatibility problems with the equipment in some locations. In other locations, problems of space availability due to the presence of other equipment may be an issue. Access to the patient may also be limited.

When preparing for the anesthetic, the age and weight of the patient will dictate the sizes of the equipment. Variability is greater in children than in adults in the sizes of airway equipment, intravenous setups, vascular access, fluid requirements, and drug dosages. The preparation of the endotracheal tube should include the availability of the calculated tube size and one size larger and smaller than calculated ( Table 18-2 ). When using a cuffed endotracheal tube, the calculated tube size should be decreased by 0.5. In cases of procedures with an unsecured airway, the appropriate-size airway equipment must still be present.

The availability and quality of the ventilators can significantly vary, depending on the institution and location. The anesthesiologist may be faced with older and less sophisticated equipment in contrast to the operating room. These ventilators may not be able to adequately accommodate the needs of the neonates or patients requiring special ventilation settings. For example, the requirement for a longer circuit may lead to rebreathing without using higher gas flows, inadequate tidal volume delivery, and erroneous end-tidal gas readings. High-frequency /oscillator ventilation may not be possible in many remote locations. Even if a ventilator is present, the appropriate size bag-valve-mask and oxygen source must always be available.

The intravenous catheter placement may be significantly more challenging in the pediatric patient secondary to lack of cooperation and smaller vasculature. Additional personnel will be necessary to hold the child, place, and secure the intravenous line. The parents may or may not be helpful. If the intravenous line is going to be placed awake, comfort measures in the form of local analgesics and distraction techniques should be used if possible. The available local anesthetics may include a eutectic cream, lidocaine applied via a needleless system, or an intradermal injection of lidocaine. Another option may be the use of a vapocoolant spray. One should have a variety of catheter sizes and the appropriate fluid setup ready before starting. At our institution, a large tertiary care children’s hospital, we use a buretrol intravenous line setup for children 5 years of age and under or weighing under 20 kg to prevent accidental overhydration. For children under 5 kg, the buretrol is initially filled with only 50 mL of crystalloid and in children over 5 kg it is filled with 100 mL.

The requirements of different age groups must be considered when choosing IV fluids. Most children will do well with a balanced salt solution such as 0.9 percent normal saline, lactated Ringer’s solution, or Plasmalyte. A good guideline for the calculation of the maintenance fluid is the 4-2-1 rule: 4 mL/kg for the first 10 kg, an additional 2 mL/kg for the second 10 kg, and an additional 1 mL/kg for each kilogram over 20 kg. The amount of fluid to be administered depends on the time of the last oral intake. The nil per os (NPO) guidelines for radiology procedures are the same as for operating room procedures ( Table 18-3 ), but parents may not adhere to these guidelines. Reasons for the noncompliance include a fear of the child suffering while NPO and the perception that radiology procedures are not equal to surgical procedures. A careful history of the patient’s last oral intake should be obtained. In cases of an NPO violation, the procedure should be postponed or the airway secured with an endotracheal tube. Some evidence in the literature indicates that hyperhydration with 20 mL/kg perioperatively may be beneficial in the prevention of postoperative nausea and vomiting.

Neonates are at risk for hypoglycemia because of their immature liver function and lack of glucose storage capability. Unless frequent glucose monitoring can be provided, neonates in the first week of life should receive D ₁₀ W at the maintenance rate (4 mL/kg/hr). After the first week, full-term babies who have been fed will tolerate a fast of several hours and will not require dextrose in their fluids. It is essential to avoid administering bolus doses of dextrose-containing fluids because of the risk of hyperglycemia. Children with metabolic disorders that lack gluconeogenesis, such as with acyl coenzyme A (CoA) dehydrogenase deficiency disorders and glycogen storage diseases, also may require supplemental glucose.

Drug dosages must be adjusted for the pediatric population. Factors that affect the dosage include weight, volume of distribution, and liver and kidney function. “Although children need higher doses by body weight than adults, they also react with respiratory depression and airway obstruction more quickly than adults do.” The medications and their indication may differ from those in adult practice.

Because of the higher incidence of laryngospasm and bradycardia in the pediatric patient, succinylcholine (2 mg/kg/dose intramuscularly or 0.5 to 2 mg/kg intravenously) and atropine (0.02 mg/kg intramuscularly or intravenously) must always be available. The first drug of choice during resuscitation is epinephrine. The resuscitation dose for pediatric patients is 10 mcg/kg. Most other vasoactive drugs are not commonly used in this population. The most frequently used medications for procedural sedation in radiology include chloral hydrate, midazolam, methohexital, pentobarbital, dexmedetomidine, fentanyl, and ketamine. A newer agent that is gaining popularity for imaging studies is dexmedetomidine. For a general anesthetic, inhalational agents or intravenous medications can be used. In certain locations outside the operating room, a total intravenous anesthetic (TIVA) with a hypnotic agent may be the only option. Common choices for TIVA include propofol, midazolam, and methohexital ( Table 18-4 ).

The intraoperative management and the choice of anesthetic depend on the procedure and the child. Factors that influence the choice between a general anesthetic and procedural sedation include the invasiveness, length, and level of stimulation of the procedure. Even though some procedures can be done with the patient awake or with sedation, a general anesthetic may still be required if a child cannot cooperate.

When inducing for a general anesthetic, we often choose an inhalational induction for pediatric patients to spare them the stress of an awake intravenous catheter placement. The exception is children who are at risk for aspiration or have preexisting conditions that preclude an inhalational induction. A mask induction has a higher risk for laryngospasm and other adverse respiratory events because of its slower transition through the stages of anesthesia.

Intraoperative monitoring should follow the ASA standard guidelines whenever possible. At a minimum, heart rate, oxygen saturation, end-tidal carbon dioxide, and blood pressure should be monitored routinely. During procedures with limited patient access, such as radiation therapy and magnetoencephalography (MEG) scans, it is necessary to ensure that the monitors are visible from outside the procedure room at all times. Efforts need to be made to protect the child and the anesthesiologist in locations with radiation exposure.

The patient recovering from a NORA procedure presents unique challenges. A dedicated area or personnel may not be available for the patient’s recovery. The nurses assisting the anesthesiologist during sedation or administration of an anesthetic often cannot stay with the recovering patient because they have to participate in the next scheduled procedure. Using the operating room postanesthesia care unit for recovery after a NORA procedure involves transporting the patient to that area during a vulnerable phase. Younger children are also at risk for emergence delirium. Although not always present, emergence delirium occurs most commonly between the ages of 2 and 5 years and is a state of significant agitation, inconsolability, and, frequently, unawareness of their surroundings. While not completely understood, emergence delirium has been linked to painful procedures, inhalational anesthetics, and shorter anesthesia times.

Adequate monitoring of the patient has to be ensured. The disposition of the patient after recovery needs to be discussed with the proceduralist and family of the patient before the procedure. Patients are discharged home after the majority of NORA procedures. The discharge criteria depend again on the procedure, the anesthetic, and the child. The risk for postoperative apnea and bradycardia will determine if the ex-premature infant can be discharged or has to be observed for 23 hours. In general, the younger the patient’s gestational and postconceptual ages, the greater the risk for postoperative apnea. Other patients who may require postoperative observation are those with obstructive sleep apnea or sickle cell disease and children who have undergone a procedure with increased risk for postoperative bleeding, such as liver biopsy or arterial angiography. (See Box 18-1 for a Preoperative Checklist.)