Special Characteristics of Pediatric Anesthesia

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CHAPTER 1 Special Characteristics of Pediatric Anesthesia

In the past few decades, new scientific knowledge of physiology and pharmacology in developing humans, as well as technologic advancements in equipment and monitoring, has markedly changed the practice of pediatric anesthesia. In addition, further emphasis on patient safety (e.g., correct side-site surgery, correct patient identification, correct procedure, appropriate prophylactic antibiotics) coupled with advances in minimally invasive pediatric surgery, have created a need for better pharmacologic approaches to infants and children, as well as improved skills in pediatric anesthetic management.

As a result of the advancements and emphasis on pediatric subspecialty training and practice, the American Board of Anesthesiology has now come to recognize the subspecialty of pediatric anesthesiology in its certification process.

Perioperative monitoring

In the 1940s and 1950s, the techniques of pediatric anesthesia, as well as the skills of those using and teaching them, evolved more as an art than as a science, as Dr. Robert Smith vividly and eloquently recollects through his firsthand experiences in his chapter on the history of pediatric anesthesia (see Chapter 41, History of Pediatric Anesthesia, as updated by Mark Rockoff). The anesthetic agents and methods available were limited, as was the scientific knowledge of developmental differences in organ-system function and anesthetic effect in infants and children. Monitoring pediatric patients was limited to inspection of chest movement and occasional palpation of the pulse until the late 1940s, when Smith introduced the first physiologic monitoring to pediatric anesthesia by using the precordial stethoscope for continuous auscultation of heartbeat and breath sounds (Smith, 1953; 1968.). Until the mid-1960s, many anesthesiologists monitored only the heart rate in infants and small children during anesthesia and surgery. Electrocardiographic and blood-pressure measurements were either too difficult or too extravagant and were thought to provide little or no useful information. Measurements of central venous pressure were thought to be inaccurate and too invasive even in major surgical procedures. The insertion of an indwelling urinary (Foley) catheter in infants was considered invasive and was resisted by surgeons.

Smith also added an additional physiologic monitoring: soft, latex blood-pressure cuffs suitable for newborn and older infants, which encouraged the use of blood pressure monitoring in children (Smith, 1968). The “Smith cuff ” (see Chapter 41, History of Pediatric Anesthesia, Fig. 41-4) remained the standard monitoring device in infants and children until the late 1970s, when it began to be replaced by automated blood pressure devices.

The introduction of pulse oximetry for routine clinical use in the early 1990s has been the single most important development in monitoring and patient safety, especially related to pediatric anesthesia, since the advent of the precordial stethoscope in the 1950s (see Chapters 10, Equipment; 11, Monitoring; and 40, Safety and Outcome) (Smith, 1956). Pulse oximetry is superior to clinical observation and other means of monitoring, such as capnography, for the detection of intraoperative hypoxemia (Coté et al., 1988, 1991). In addition, Spears and colleagues (1991) have indicated that experienced pediatric anesthesiologists may not have an “educated hand” or a “feel” adequate to detect changes in pulmonary compliance in infants. Pulse oximetry has revealed that postoperative hypoxemia occurs commonly among otherwise healthy infants and children undergoing simple surgical procedures, presumably as a result of significant reductions in functional residual capacity (FRC) and resultant airway closure and atelectasis (Motoyama and Glazener, 1986). Consequently, the use of supplemental oxygen in the postanesthesia care unit (PACU) has become a part of routine postanesthetic care (see Chapter 3, Respiratory Physiology).

Although pulse oximetry greatly improved patient monitoring, there were some limitations, namely motion artifact and inaccuracy in low-flow states, and in children with levels of low oxygen saturation (e.g., cyanotic congenital heart disease). Advances have been made in the new generation of pulse oximetry, most notably through the use of Masimo Signal Extraction Technology (SET). This device minimizes the effect of motion artifact, improves accuracy, and has been shown to have advantages over the existing system in low-flow states, mild hypothermia, and moving patients (Malviya et al., 2000; Hay et al., 2002; Irita et al., 2003).

Monitoring of cerebral function and blood flow, as well as infrared brain oximetry have advanced the anesthetic care and perioperative management of infants and children with congenital heart disease and traumatic brain injuries. Depth of anesthesia can be difficult to assess in children, and anesthetic overdose was a major cause of anesthesia-associated cardiac arrest and mortality. Depth-of-anesthesia monitors (bisectral index monitor [BIS], Patient State Index, Narcotrend) have been used in children and have been associated with the administration of less anesthetic agent and faster recovery from anesthesia. However, because these monitors use electroencephalography and a sophisticated algorithm to predict consciousness, the reliability of these monitors in children younger than 1 year old is limited.

In addition to advances in monitors for individual patients, hospital, patient, and outside-agency initiatives have focused on more global issues. Issues of patient safety, side-site markings, time outs, and proper patient identification together with the appropriate administration of prophylactic antibiotics have now become major priorities for health care systems. The World Health Organization (WHO) checklists have been positive initiatives that have ensured that the correct procedure is performed on the correct patient, as well as fostered better communication among health care workers. In anesthesia, patient safety continues to be a mantra for the specialty. Improved monitoring, better use of anesthetic agents, and the development of improved airway devices coupled with advancements in minimally invasive surgery, continue to advance the frontiers of pediatric anesthesia as a specialty medicine, as well as improve patient outcome and patient safety.

Anesthetic agents

More than a decade after the release of isoflurane for clinical use, two volatile anesthetics, desflurane and sevoflurane, became available in the 1990s in most industrialized countries. Although these two agents are dissimilar in many ways, they share common physiochemical and pharmacologic characteristics: very low blood-gas partition coefficients (0.4 and 0.6, respectively), which are close to those of nitrous oxide and are only fractions of those of halothane and isoflurane; rapid induction of and emergence from surgical anesthesia; and hemodynamic stability (see Chapters 7, Pharmacology; 13, Induction Maintenance and Recovery; and 34, Same-Day Surgical Procedures). In animal models, the use of inhaled anesthetic agents has been shown to attenuate the adverse effects of ischemia in the brain, heart, and kidneys.

Although these newer, less-soluble, inhaled agents allow for faster emergence from anesthesia, emergence excitation or delirium associated with their use has become a major concern to pediatric anesthesiologists (Davis et al., 1994; Sarner et al., 1995; Lerman et al., 1996; Welborn et al., 1996; Cravero et al., 2000; Kuratani and Oi, 2008). Adjuncts, such as opioids, analgesics, serotonin antagonists, and α1-adrenergic agonists, have been found to decrease the incidence of emergence agitation (Aono et al., 1999; Davis et al., 1999; Galinkin et al., 2000; Cohen et al., 2001; Ko et al., 2001; Kulka et al., 2001; Voepel-Lewis et al., 2003; Lankinen et al., 2006; Aouad et al., 2007; Tazeroualti et al., 2007; Erdil et al., 2009; Bryan et al., 2009; Kim et al., 2009).

Propofol has increasingly been used in pediatric anesthesia as an induction agent, for intravenous sedation, or as the primary agent of a total intravenous technique (Martin et al., 1992). Propofol has the advantage of aiding rapid emergence and causes less nausea and vomiting during the postoperative period, particularly in children with a high risk of vomiting. When administered as a single dose (1 mg/kg) at the end of surgery, propofol has also been shown to decrease the incidence of sevoflurane-associated emergence agitation (Aouad et al., 2007).

Remifentanil, a μ-receptor agonist, is metabolized by nonspecific plasma and tissue esterases. The organ-independent elimination of remifentanil, coupled with its clearance rate (highest in neonates and infants compared with older children), makes its kinetic profile different from that of any other opioids (Davis et al., 1999; Ross et al., 2001). In addition, its ability to provide hemodynamic stability, coupled with its kinetic profile of rapid elimination and nonaccumulation, makes it an attractive anesthetic option for infants and children. Numerous clinical studies have described its use for pediatric anesthesia (Wee et al., 1999; Chiaretti et al., 2000; Davis et al., 2000, 2001; German et al., 2000; Dönmez et al., 2001; Galinkin et al., 2001; Keidan et al., 2001; Chambers et al., 2002; Friesen et al., 2003). When combined, intravenous hypnotic agents (remifentanil and propofol) have been shown to be as effective and of similar duration as propofol and succinylcholine for tracheal intubation.

The development of more predictable, shorter-acting anesthetic agents (see Chapter 7, Pharmacology) has increased the opportunities for pediatric anesthesiologists to provide safe and stable anesthesia with less dependence on the use of neuromuscular blocking agents.

Airway devices and adjuncts

Significant changes in pediatric airway management that have patient-safety implications have emerged over the past few years. The laryngeal mask airway (LMA), in addition to other supraglottic airway devices (e.g., the King LT-D, the Cobra pharyngeal airway), has become an integral part of pediatric airway management. Although the LMA is not a substitute for the endotracheal tube, LMAs can be safely used for routine anesthesia in both spontaneously ventilated patients and patients requiring pressure-controlled support. The LMA can also be used in the patient with a difficult airway to aid in ventilation and to act as a conduit to endotracheal intubation both with and without a fiber optic bronchoscope.

In addition to supraglottic devices, advances in technology for visualizing the airway have also improved patient safety. Since the larynx could be visualized, at least 50 devices intended for laryngoscopy have been invented. The newer airway-visualization devices have combined better visualizations, video capabilities, and high resolution.

The development and refinement of airway visualization equipment such as the Glidescope, Shikani Seeing Stylet, and the Bullard laryngoscope have added more options to the management of the pediatric airway and literally give the laryngoscopist the ability to see around corners (see Chapters 10, Equipment; and 12, Airway Management).

The variety of pediatric endotracheal tubes (ETTs) has focused on improved materials and designs. ETTs are sized according to the internal diameter; however, the outer diameter (the parameter most likely involved with airway complications) varies according to the manufacturer (Table 1-1). Tube tips are both flat and beveled, and a Murphy eye may or may not be present. The position of the cuff varies with the manufacturer. The use of cuffed endotracheal tubes in pediatrics continues to be controversial. In a multicenter, randomized prospective study of 2246 children from birth to 5 years of age undergoing general anesthesia, Weiss and colleagues (2009) noted that cuffed ETTs compared with uncuffed ETTs did not increase the risk of postextubation stridor (4.4% vs. 4.7%) but did reduce the need for ETT exchanges (2.1% vs. 30.8%). However, the role of cuffed ETTs in neonates and infants who require prolonged ventilation has yet to be determined.

Intraoperative and postoperative analgesia in neonates

It has long been thought that newborn infants do not feel pain the way older children and adults do and therefore do not require anesthetic or analgesic agents (Lippman et al., 1976). Thus, in the past, neonates undergoing surgery were often not afforded the benefits of anesthesia. Later studies, however, indicated that pain experienced by neonates can affect behavioral development (Dixon et al., 1984; Taddio et al., 1995, 2005). Rats exposed to chronic pain without the benefit of anesthesia or analgesia showed varying degrees of neuroapoptosis (Anand et al., 2007). However, to add further controversy to the issue of adequate anesthesia for infants, concerns regarding the neurotoxic effects of both intravenous and inhalational anesthetic agents (GABAminergic and NMDA antagonists) have been raised. Postoperative cognitive dysfunction (POCD) has been noted in adult surgical patients (Johnson et al., 2002; Monk et al., 2008). In adults, POCD may also be a marker for 1-year survival after surgery. Although POCD is an adult phenomenon, animal studies by multiple investigators have raised concerns about anesthetic agents being toxic to the developing brains of infants and small children (Jevtovic-Todorovic et al., 2003, 2008; Mellon et al., 2007; Wang and Slikker, 2008). Early work by Uemura and others (1985) noted that synaptic density was decreased in rats exposed to halothane in utero. Further work with rodents, by multiple investigators, has shown evidence of apoptosis in multiple areas of the central nervous system during the rapid synaptogenesis period. This window of vulnerability appears to be a function of time, dose, and duration of anesthetic exposure. In addition to the histochemical changes of apoptosis, the exposed animals also demonstrated learning and behavioral deficits later in life.

In addition to apoptotic changes that occurred in rodents, Slikker and colleagues have demonstrated neuroapoptotic changes in nonhuman primates (rhesus monkeys) exposed to ketamine (an NMDA antagonist). As with the rodents, ketamine exposure in monkeys resulted in long-lasting deficits in brain function (Dr. Merle Poule, personal communication on the Safety of Key Inhaled and Intravenous Drugs in Pediatric Anesthesia [SAFEKIDS] Scientific Workshop, November 2009, White Oaks Campus Symposium). How these animal studies relate to human findings is unclear to date. However, three clinical studies have been reported, and all three studies are retrospective. Wilder et al. (2009) studied a cohort group of children from Rochester, Minnesota, and noted that children exposed to two or more anesthetics in the first 4 years of life were more likely to have learning disabilities, compared with children exposed to one anesthetic or none at all. Kalkman and others (2009) studied a group of children undergoing urologic surgery before age 6 years and reported that there was a tendency for parents to report more behavioral disturbances than those operated on at a later age. However, in a twin cohort study from the Netherlands, Bartels and coworkers (2009) reported no causal relationship between anesthesia and learning deficits in 1,143 monozygotic twin pairs.

In an effort to determine the impact of anesthetic agents or neurocognitive development, a collaborative partnership between the U.S. Food and Drug Administration (FDA) and the International Anesthesia Research Society has formed Safety of Key Inhaled and Intravenous Drugs in Pediatric Anesthesia (SAFEKIDS), a program designed to fund and promote research in this area.

Regional analgesia in infants and children

Although conduction analgesia has been used in infants and children since the beginning of the twentieth century, the controversy about whether anesthetic agents can be neurotoxic has caused a resurgence of interest in regional anesthesia (Abajian et al., 1984; Williams et al., 2006).

As newer local anesthetic agents with less systemic toxicity become available, their role in the anesthetic/analgesic management of children is increasing. Studies of levobupivacaine and ropivacaine have demonstrated safety and efficacy in children that is greater than that of bupivacaine, the standard regional anesthetic used in the 1990s (Ivani et al., 1998, 2002, 2003; Hansen et al., 2000, 2001; Lönnqvist et al., 2000; McCann et al., 2001; Karmakar et al., 2002). A single dose of local anesthetics through the caudal and epidural spaces is most often used for a variety of surgical procedures as part of general anesthesia and for postoperative analgesia. Insertion of an epidural catheter for continuous or repeated bolus injections of local anesthetics (often with opioids and other adjunct drugs) for postoperative analgesia has become a common practice in pediatric anesthesia. The addition of adjunct drugs, such as midazolam, neostigmine, tramadol, ketamine, and clonidine, to prolong the neuroaxial blockade from local anesthetic agents has become more popular, even though the safety of these agents on the neuroaxis has not been determined (see Chapters 15, Pain Management; and 16, Regional Anesthesia) (Ansermino et al., 2003; de Beer and Thomas, 2003).

In addition to neuroaxial blockade, specific nerve blocks that are performed with or without ultrasound guidance have become an integral part of pediatric anesthesia (see Chapter 16, Regional Anesthesia). The use of ultrasound has allowed for the administration of smaller volumes of local anesthetic and for more accurate placement of the local anesthetic (Ganesh et al., 2009; Gurnaney et al., 2007; Willschke et al., 2006). The use of catheters in peripheral nerve blocks has also changed the perioperative management for a number of pediatric surgical patients. Continuous peripheral nerve catheters with infusions are being used by pediatric patients at home after they have been discharged from the hospital (Ganesh et al., 2007). The use of these at-home catheters has allowed for shorter hospital stays. In addition, the use of regional techniques with ultrasound guidance, coupled with the natural interest in pain management, has allowed for pediatric anesthesiologists to spearhead pediatric acute and chronic pain management programs.

In addition to advances in anesthetic pharmacology and equipment, advances in the area of pediatric minimal invasive surgery have improved patient morbidity, shortened the length of hospital stays, and improved surgical outcomes (Fujimoto et al., 1999).

Although minimally invasive surgery (MIS) imposes physiologic challenges in the neonate and small infant, numerous neonatal surgical procedures can nevertheless be successfully approached with such methods, even in infants with single ventricle physiology (Georgeson, 2003; Ponsky and Rothenberg, 2008). The success of MIS has allowed for the evolution of robotic techniques, stealth surgery (scarless surgery), and Natural Orifice Transluminal Endoscopic Surgery (NOTES) (Dutta and Albanese, 2008; Dutta et al., 2008; Isaza et al., 2008).

Fundamental differences in infants and children

Regardless of all the advances in equipment, monitoring, and patient safety initiatives, pediatric anesthesia still requires a special understanding of anatomic, psychological, and physiologic development. The reason for undertaking a special study of pediatric anesthesia is that children, especially infants younger than a few months, differ markedly from adolescents and adults. Many of the important differences, however are not the most obvious. Although the most apparent difference is size, it is the physiologic differences related to general metabolism and immature function of the various organ systems (including the heart, lungs, kidneys, liver, blood, muscles, and central nervous system) that are of major importance to the anesthesiologist.

Psychological Differences

For a child’s normal psychological development, continuous support of a nurturing family is indispensable at all stages of development; serious social and emotional deprivation (including separation from the parents during hospitalization), especially during the first 2 years of development, may cause temporary or even lasting damage to psychosocial development (Forman et al., 1987). A young child who is hospitalized for surgery is forced to cope with separation from parents, to adapt to a new environment and strange people, and to experience the pain and discomfort associated with anesthesia and surgery (see Chapters 2, Behavioral Development; and 8, Psychological Aspects).

The most intense fear of an infant or a young child is created by separation from the parents, and it is often conceived as loss of love or abandonment. The sequence of reactions observed is often as follows: angry protest with panicky anxiety, depression and despair, and eventually apathy and detachment (Bowlby, 1973). Older children may be more concerned with painful procedures and the loss of self-control that is implicit with general anesthesia (Forman et al., 1987). Repeated hospitalizations for anesthesia and surgery may be associated with psychosocial disturbances in later childhood (Dombro, 1970

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