Special characteristics of pediatric anesthesia

Introduction

In the past few decades, new scientific knowledge of physiology and pharmacology in developing humans and technologic advancements in equipment and monitoring have 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 and 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, and the first subspecialty board examination was administered in 2013.

Perioperative monitoring

In the 1940s and 1950s, the techniques of pediatric anesthesia, and the skills of those using and teaching them, evolved more as an art than as a science, as Dr. Robert Smith (now deceased) vividly and eloquently recollected through his firsthand experiences in his chapter on the history of pediatric anesthesia (see Chapter 61 : History of Pediatric Anesthesia, updated by Mark A. Rockoff and David Neville Levine). 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 ( ). 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 surgeons resisted its use.

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 ( ). The Smith cuff (see Chapter 61 : History of Pediatric Anesthesia; Fig. 61.7 ) remained the standard monitoring device for infants and children until the late 1970s, when automated blood pressure devices began to replace them.

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 Chapter 17 : Equipment; Chapter 18 : Monitoring). Pulse oximetry is superior to clinical observation and other means of monitoring, such as capnography, for the detection of intraoperative hypoxemia ( ). In addition, 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 ( ). 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 ( ; ; ).

Trending of hemoglobin (Hgb) can also be performed with oximetry. Noninvasive pulse cooximetry (SpHb) has been used in both children and neonates to measure SpHb. Pulse cooximetry uses pulse oximeter technology that involves sensors with light emitting diodes of many wavelengths. demonstrated in children undergoing major surgical procedures with anticipated substantial blood loss that SpHb followed the trend in invasively measured Hgb with respect to bias and precision and that the trend accuracy was better than the absolute accuracy. In both term and preterm neonates who weighed less than 3000 g at birth, noted a good agreement between the noninvasive SpHb and the invasive Hgb. In a study of adults and children, noted that the difference between lab-measured Hgb and SpHb was less in children than in adults.

Monitoring of cerebral function and blood flow, as well as infrared brain oximetry, has 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 of age is limited.

More recently, interest has developed in the use of noninvasive monitors to assess fluid responsiveness. Static variables (central venous pressure, pulmonary artery wedge pressure, and left ventricle area) are not reliable predictors of fluid responsiveness. Dynamic indicators that are based on cardiopulmonary interactions in mechanically ventilated patients, such as aortic peak velocity, systolic blood pressure variation (SPV), pulse pressure variation (PPV), and pleth variability index (PVI), have been shown to be predictive in adults. In children, the results of studies involving dynamic variables have been mixed, but it appears that aortic peak velocity is a reliable indicator of fluid responsiveness ( ; ; ; ; ; ).

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 appropriate administration of prophylactic antibiotics, have now become major priorities for healthcare systems. World Health Organization (WHO) checklists are positive initiatives that have ensured that the correct procedure is performed on the correct patient and have fostered better communication among healthcare 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 and improve patient outcomes 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 Chapter 10 : Inhaled Anesthetic Agents; Chapter 21 : Induction, Maintenance, and Recovery). 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, whereas other studies have raised concerns regarding the anesthetic agents causing neurotoxicity in infants and children. (See Chapter 2 : Behavioral Development.)

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 ( ; ; ; ; ; ). Adjuncts, such as opioids, analgesics, serotonin antagonists, and α ₁ -adrenergic agonists, have been found to decrease the incidence of emergence agitation ( ; ; ; ; ; ; ; ; ; ; ; ; ; ).

Propofol has increasingly been used in pediatric anesthesia as an induction agent, for intravenous sedation, or as the primary agent of a total intravenous anesthetic technique ( ). 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 for 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 ( ).

Dexmedetomidine is an α ₁ -adrenergic agonist approved for use as a sedation agent for adult ICU patients ( ). In pediatrics, off-label use of dexmedetomidine is common and has been used in the settings of procedural sedation and ICU sedation. It also has been administered as an adjunct to general anesthesia in order to decrease both opioid and inhalational anesthetic requirements. It has been used to treat supraventricular tachycardia and junctional ectopic tachycardia in pediatric cardiac patients and has been used successfully for both prophylaxis and treatment of emergence agitation in postoperative surgical patients ( ; ; ; ). In order to attenuate the biphasic hemodynamic response of dexmedetomidine, the package insert recommends infusing the drug over 10 minutes. However, studies involving rapid bolus administration (less than 3 seconds) of dexmedetomidine in both healthy children and children who had received a heart transplant demonstrated minimal clinical significance ( ; ; ).

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 opioid ( ; ). 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 ( ; ; ; ; ; ; ; ; ). 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 Part II: Pharmacology) has increased the opportunities for pediatric anesthesiologists to provide safe and stable anesthesia with less dependence on the use of neuromuscular blocking agents. Remimazolam is a new benzodiazepine that is metabolized by tissue carboxylesterases to an inactive metabolite. In adult volunteers it is rapidly metabolized with fast onset and recovery times and has moderate hemodynamic effect ( ; ).

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, it 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 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 McGrath, C-MAC, and Glidescope have added more options to the management of the pediatric airway and literally give the laryngoscopist the ability to see around corners (see Chapter 17 : Equipment; Chapter 19 : Normal and Difficult Airway Management). The importance of these advanced airway devices cannot be overstated, as evidenced by their use in the algorithms for the difficult pediatric airway ( ; ; ).

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, noted that cuffed ETTs compared with uncuffed ETTs did not increase the risk for postextubation stridor (4.4% vs. 4.7%) but did reduce the need for ETT exchanges (2.1% vs. 30.8%), thereby reducing the possibility of additional trauma from multiple intubation attempts.

There has been a recent gradual but steady trend toward the routine and exclusive use of cuffed ETTs in pediatric anesthesia, including in infants ( ; ; ; ). was the first to propose the use of cuffed ETTs exclusively for children of all ages with the record of no complications without using uncuffed ETTs for a 3-year span in a major children’s hospital in Paris. The change in practice of not using uncuffed ETT is due to the recognition that the shape of the glottic opening at the cricoid ring, the narrowest fixed diameter in the upper airways, is more elliptic in shape than circular, with a larger anteroposterior (AP) diameter and a narrower transverse diameter ( ; ). These findings mean that the most appropriately sized uncuffed ETT (<20 cm H ₂ O leak pressure) would compress the lateral wall mucosa of the cricoid, causing ischemia even when there are enough anteroposterior spaces left for air leaks ( ). A recently developed thin-walled (with smaller outer diameter), cuffed endotracheal tube specifically designed for pediatric anesthesia (Microcuff by Kimberly-Clark) has two major modifications: the cuff is made of ultrathin polyurethane, allowing a more effective tracheal seal at a much lower pressure than the pressure known to cause tracheal mucosal necrosis, and the short cuff is located more distally near the tip of the endotracheal tube shaft, allowing more reliable placement of the cuff below the nondistensible cricoid ring and reducing the chance of endobronchial intubation ( ; ). Whether the new, more costly endotracheal tube actually reduces the incidence of intubation-related airway injury is being investigated.

A main concern with cuffed endotracheal tubes relates to excessive pressure in the cuff. The exact pressure a cuff needs to exert against the wall of the tracheal mucosae to induce ischemia is not known; recommendations range from 20 to 30 cm H ₂ O. In an observational trial of 200 pediatric patients, noted that when cuff pressures were measured, 23.5% of the patients had pressures greater than 30. Various devices have been prepared to monitor intracuff pressure ( ; ; ; ). Although the role of cuffed ETTs in neonates and infants who require prolonged ventilation has yet to be determined ( ), it is clear that in neonates undergoing minimally invasive surgery, cuffed endotracheal tubes allow for more effective ventilation and more reliable end-tidal gas monitoring while likely maintaining safety ( ; ).

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 ( ). 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 ( ; ; ). Rats exposed to chronic pain without the benefit of anesthesia or analgesia showed varying degrees of neuroapoptosis ( ). However, to add further controversy to the issue of adequate anesthesia for infants, concerns have been raised regarding the neurotoxic effects of both intravenous and inhalational anesthetic agents (GABAergic and NMDA antagonists) (see Chapter 2 : Behavioral Development).

Although postoperative cognitive dysfunction (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 ( ; ; ; ; ). Early work by 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. The potential neurotoxic risk of anesthetic agents is less clear in human pediatric patients. Studies performed on this population have helped to clarify this risk, and it appears that a single short anesthetic in early infancy has no adverse effects on IQ at 2 and 5 years of age. See Chapter 2 (Behavioral Development) for a more in-depth discussion.

Point of care ultrasound

Ultrasound has advanced the care of many medical specialties, including pediatric anesthesiology. This technology has diagnostic and therapeutic applications in pediatric patients of all ages. In addition to its widely accepted role in regional anesthesia and vascular access, ultrasonography can facilitate diagnostic procedures including airway management, pulmonary pathology like pneumothorax, fluid management, and nasogastric tube positioning. (See Chapter 20 : Point of Care Ultrasonography.)

Regional analgesia in infants and children

Although conduction analgesia has been used in infants and children since the beginning of the 20th century, the controversy about whether anesthetic agents can be neurotoxic has caused a resurgence of interest in regional anesthesia ( ; ).

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 are greater than that of bupivacaine, the standard regional anesthetic used in the 1990s ( ; ; ; ; ). 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 medications, 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 also Part IV: Pain Management).

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 24 : 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 ( ; ; ). 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 ( ; ; ). The use of these at-home catheters has allowed for shorter hospital stays.

As pediatric regional anesthesia becomes more prevalent, the ability to collect data, audit practice patterns, and report on complications in infants and children undergoing regional anesthesia becomes essential to improving care for children. In this context, the Pediatric Regional Anesthesia Network (PRAN) was formed ( ; ; ; ). reported on over 100,000 blocks in children from the PRAN registry and noted that there was no added risk of placing a block in the anesthetized child. The risk of transient neurologic deficit was 2.4:10,000 patients and severe local anesthetic systemic toxicity was 0.76:10,000 patients.

In addition to advances in anesthetic pharmacology and equipment, advances in the area of pediatric minimally invasive surgery (MIS) have improved patient morbidity, shortened the length of hospital stays, and improved surgical outcomes ( ). Although 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 ( ; ). The success of MIS has allowed for the evolution of robotic techniques, stealth surgery (scarless surgery), and Natural Orifice Transluminal Endoscopic Surgery (NOTES) ( ; ; ).