1522 SECTION XIV Pediatric Critical Care Anesthesia Principles in the Pediatric Intensive Care Unit no longer readily available in the United States These character istics have led to the common use o[.]
1522 S E C T I O N X I V Pediatric Critical Care: Anesthesia Principles in the Pediatric Intensive Care Unit no longer readily available in the United States These characteristics have led to the common use of etomidate for emergency intubation.72,73 It is important to note that etomidate has no analgesic properties and is not titratable; however, intubation doses of etomidate are amnestic and induce a state of general anesthesia Adverse effects include vomiting, myoclonus, and lowering of the seizure threshold Etomidate can cause adrenal insufficiency, making it inappropriate for long-term use in the ICU.74 Growing evidence suggests that it may suppress adrenal function even after a single dose, particularly in patients with sepsis and shock, raising questions about its use in these settings.75–87 However, the favorable hemodynamic profile of etomidate may outweigh the risk of adrenal insufficiency, which can be followed and treated with corticosteroids as needed The hemodynamic stability is particularly relevant in cases of septic shock or catecholamine depletion Ketamine is another potent nonnarcotic analgesic and anesthetic that has been used safely in children in the critical care setting.88,89 It is an especially useful sedative agent when maintenance of spontaneous ventilation is desired, as ketamine is associated with a low risk of apnea when used in isolation Ketamine increases heart rate, systemic blood pressure, and cardiac output and is a fairly potent bronchodilator However, myocardial depression may be apparent after administration to patients with catecholamine depletion In a multicenter, prospective observational cohort study, ketamine use in patients with unstable hemodynamics was not associated with a lower prevalence of new hypotension.90 Ketamine may be of particular value in patients with status asthmaticus or other reasons for bronchospasm and may have a beneficial effect in sepsis Although spontaneous ventilation is preserved in most patients, laryngospasm may occur.91 Given the risk of laryngospasm, it is important to note that ketamine is a sialogogue Anticholinergic agents, such as glycopyrrolate and atropine, can be used to prevent/reduce the hypersalivation caused by ketamine In the past, ketamine was considered inappropriate for patients with intracranial hypertension because of evidence that it increases cerebral metabolic rate, blood flow, and ICP More recent studies indicate that it may be used safely in these patients, but no clear consensus has emerged.92–94 Emergence delirium and hallucinations occur frequently and may be prolonged and recurrent, particularly in adolescents and young adults Ketamine has been used successfully for a variety of procedures in children, with few reported neuropsychiatric complications, but follow-up in most studies has been short and superficial.95–100 Whereas most patients not suffer severe disturbances, those who may have severe and prolonged distress Benzodiazepines or barbiturates may decrease the incidence and severity of such adverse effects and the incidence of vomiting, although the data in children are limited and conflicting.79,85,95,97,101,102 Propofol is an ultra–short-acting agent with rapid onset and offset unless given by continuous infusion It causes respiratory depression, desaturation, and systemic hypotension secondary to its negative inotropic effects and peripheral venous and arterial vasodilation Its role in airway management of critically ill children is limited because of these effects It has gained widespread acceptance as an anesthetic agent in children, however, and has been used extensively for procedural sedation.103,104 Use in the ICU for more than approximately hours is not recommended because of its association with metabolic acidosis, cardiovascular collapse and death, and propofol infusion syndrome among pediatric ICU patients.104–107 Current labeling warns against its use for prolonged sedation in children The benzodiazepines—including diazepam and midazolam— relieve anxiety, produce sedation in most children, and provide amnesia for noxious procedures They not relieve pain Benzodiazepines have relatively little hemodynamic effect in most patients (except for those with myocardial depression) and rarely interfere with spontaneous breathing at therapeutic doses when used in isolation Benzodiazepines decrease cerebral oxygen consumption modestly and, when used for intubation, are best combined with an opioid analgesic to decrease the discomfort and pain associated with laryngoscopy and passage of the tube Opioids commonly used for intensive care include morphine, fentanyl, and some of the ultra–short-acting agents, such as remifentanil They cause respiratory depression in a dose-dependent fashion and increase intracranial blood flow in proportion to the increase in partial pressure of arterial carbon dioxide (Paco2) If hypercarbia is prevented, opioids decrease cerebral metabolic rate and blood flow In the setting of altered cerebral autoregulation, they may not protect the patient from alterations of CBF.108,109 Morphine may lead to histamine release with peripheral vasodilation and may precipitate systemic hypotension Fentanyl is approximately 100 times more potent than morphine but does not cause histamine release and has little hemodynamic effect, even at anesthetic doses However, large doses given rapidly can cause bradycardia or chest wall rigidity; therefore, the ready availability of a short-acting NMBA is critical Remifentanil is a rapid-onset, ultra-short-acting opiate that is even more potent than fentanyl and may have potential benefit during intubation for procedures In some patients with severe hemodynamic instability, a titrated opioid-only approach may be appropriate Neuromuscular Blocking Agents Whether to use neuromuscular blockade and which NMBA to use are important considerations for the pediatric intensivist preparing to intubate a critically ill child NMBAs cause reversible paralysis that facilitates visualization of the airway and insertion of the ETT in an atraumatic fashion NMBAs are divided into two major categories: depolarizing and nondepolarizing agents Nondepolarizing NMBAs are the most commonly used by pediatric intensivists Differences between specific agents are primarily in their hemodynamic effects, metabolism, and excretion.110,111 Among nondepolarizing NMBAs, the aminosteroid agent rocuronium is most commonly used for facilitation of intubation in critically ill patients Rocuronium rapidly provides ideal intubating conditions nearly as rapidly as succinylcholine (in ,45–90 s)112–114 without the adverse effects Its duration is longer, lasting 15 to 45 minutes (and longer in infants).115–117 Rocuronium has minimal hemodynamic effect, is metabolized by the liver, and is largely excreted in bile (with a small amount excreted by the kidneys) Similar to rocuronium, vecuronium has virtually no hemodynamic effect Its duration of action varies depending on the patient’s age, approximately 70 minutes in infants and 35 minutes in older children Vecuronium is metabolized exclusively by the liver Atracurium and cis-atracurium, both benzylquinolinium agents, also have minimal hemodynamic effects in most patients but may cause histamine release and hypotension in some Metabolism occurs by spontaneous plasma hydrolysis; thus, neither renal nor hepatic function is necessary for elimination Duration of action is short at about 15 to 20 minutes The only depolarizing NMBA in clinical use is succinylcholine Its only advantage is its rapid onset of action (45–60 s) and brief duration of action (5–10 min) Muscle fasciculations occur at the onset of action in patients older than years and may CHAPTER 127 Airway Management increase intracranial, intraocular, and intragastric pressure Defasciculating doses of a nondepolarizing neuromuscular blocker prior to succinylcholine administration minimize such effects Massive hyperkalemia may occur after its use in patients with spinal cord injury, severe burns, crush injuries, or neuromuscular disease More recently, the spread of acetylcholine receptors outside of the neuromuscular junction, the mechanism presumed to underlie the massive hyperkalemic response, has been recognized to occur in many forms of critical illness associated with immobility, placing many critically ill patients at risk.118 Succinylcholine is a known trigger for malignant hyperthermia, even in the absence of volatile anesthetic exposure, and is a particular risk to patients with previously undiagnosed myopathies, often associated with abnormality in the ryanodine receptor type gene (RYR1).119 It frequently causes myoglobinuria in otherwise healthy children The US Food and Drug Administration has issued a warning against succinylcholine use for routine intubation in children because of these complications Although it is frequently used for emergency intubations and is widely recommended,66,120,121 the difference in time to conditions for intubation between succinylcholine and rocuronium is small (,30 s), rarely of clinical significance, and inadequate to justify the added risk in most cases The time to critical hemoglobin desaturation in the case of a failed airway is shorter than its duration of action, especially in children Therefore, its shorter duration of action does not provide a meaningful advantage over nondepolarizing blockers.122 In the past, scenarios that required rapid onset of neuromuscular blockade but short duration (e.g., the unanticipated difficult or critical airway) often called exclusively for succinylcholine However, sugammadex, a unique neuromuscular blockade reversal agent for aminosteroid nondepolarizing blockers, is now available for immediate reversal of deep neuromuscular blockade Sugammadex, unlike neostigmine, does not inhibit acetylcholinesterase; thus, it does not have to be coadministered with antimuscarinic agents (glycopyrrolate or atropine) Sugammadex works by binding up the relaxant agent; it has a greater affinity for rocuronium than for vecuronium, though it can be used to reverse both In published studies, sugammadex was 10.22 minutes (6.6 times) faster than neostigmine in reversing moderate induced paralysis and 45.78 minutes (16.8 times) faster than neostigmine in reversing deep induced paralysis.123 A more extensive discussion of anesthetic agents and their use is given in Chapters 130 and 131 1523 peripheral capillary oxygen saturation reaches 90%, can be extended up to almost 10 minutes after minutes of classic preoxygenation.126 Some ICUs are starting to use noninvasive ventilation (BiPAP and continuous positive airway pressure [CPAP]) for preoxygenation before intubation It is important to note, however, that a large multicenter randomized controlled trial of 20001 adult patients in France did not show a reduction in the risk of severe hypoxemia in patients with acute hypoxemic respiratory failure when preoxygenation was used with noninvasive ventilation during intubation.127 Orotracheal Intubation When all equipment is ready, an assistant is assigned to monitor the child’s color, heart rate, blood pressure, and oxygen saturation and to administer drugs when ordered The child is placed supine with the head in the “sniffing” position The infant’s large occipitofrontal diameter naturally results in good position most of the time, but a small pad under the shoulders may be helpful In older children, a thin pad under the occiput helps establish slight neck flexion (Fig 127.8) The head is extended to align the oral, pharyngeal, and laryngeal axes as much as possible Applying cricoid O P P L O L A O P L B D O P L E P O L L P O Preoxygenation Spontaneous or manual ventilation with supplemental oxygen is maintained as drugs to facilitate intubation are given Many patients who require emergency intubation have severely impaired gas exchange and may need to breathe 100% oxygen for several minutes, often with positive inspiratory and end-expiratory pressure.124 An integrative literature review identified 14 studies that showed benefits of passive apneic oxygenation during emergency intubations.125 During the apneic phase of emergency intubations, passive oxygenation via nasal cannula oxygen (standard or heated high flow) may prevent hypoxia or improve oxygen saturation, allowing for safe extension of apnea time and improved first-pass attempt success rate.125 Three minutes of spontaneous breathing at 100% FiO2 allows denitrogenation with alveolar oxygen fraction close to 95% in patients with normal lung function.126 Tolerable apnea time, defined as the delay until the C F • Fig 127.8 (A) Positioning of the young child and infant for laryngoscopy and tracheal intubation (B) Placing the child’s head on a thin pad flexes the neck slightly and helps align the pharyngeal and laryngeal axes (C) Extension of the atlanto-occipital joint (into the sniffing position) further aligns the oral axis with the pharyngeal and laryngeal axes (D) Before the age of approximately years, the child’s large frontal occipital diameter makes the pad beneath the head unnecessary, but a small pad under the shoulders (E) may improve alignment of the pharyngeal and laryngeal axes (F) As with the older child, head extension improves alignment of the oral, pharyngeal, and laryngeal axes L, Laryngeal axis; O, oral axis; P, pharyngeal axis (From McAllister JD, Gnauck KA Rapid sequence intubation of the pediatric patient: fundamentals of practice Emerg Med 1999;46:1249–1284.) 1524 S E C T I O N X I V Pediatric Critical Care: Anesthesia Principles in the Pediatric Intensive Care Unit pressure during manual ventilation helps to minimize gastric distention by air (Fig 127.9).128 After the medications take effect, the pharynx is suctioned and stomach contents are aspirated The patient is again briefly oxygenated, and the mask is removed In a fully relaxed patient in good position, the mouth falls open It can be opened more widely with caudad pressure on the chin by the intubator’s left fifth finger as the laryngoscope is introduced into the right corner of the mouth If the patient is not sedated or the mouth opens abnormally, it may be necessary to open the jaw with the often-recommended scissor-like use of the right thumb and forefinger The laryngoscope is gently advanced into the pharynx and leftward, sweeping the tongue out of the way Holding the handle at a 45-degree angle to the bed and lifting along the line of the handle to avoid pressure on the lips, teeth, or alveolar ridge, the intubator displaces the mandible until the vocal cords are in view (Fig 127.10) Application of gentle cricoid pressure by an assistant may be helpful Once the larynx is clearly visible, the tube is advanced from the right corner of the mouth into the larynx (not through or along the blade itself ) An appropriately sized tube usually passes easily The nearly universal tendency to plumb the depths of the child’s airway with extra centimeters of tube results in mainstem intubation Unfortunately, the recommendation to use three times the ETT size for appropriate depth of tube placement Cricoid cartilage for a child results in malposition in 15% to 25% of patients.129 Placement is likely to be better if the intubator is careful to place the appropriate markings near the tip of the ETT at the level of the cords If such markings are absent, careful attention to advancing the tip of the tube only a few centimeters (2–4 cm) beyond the cords prevents mainstem intubation With the tube in place, the child again receives manual ventilation with oxygen Typically, a small air leak around the tube is present Assuming use of a cuffed tube, the cuff is inflated to less than 20 to 30 cm H2O or the lowest pressure that occludes the leak Correct tracheal placement of the tube is suggested by observation of moisture condensing in the tube, good chest excursion, symmetric breath sounds, and effective oxygenation The most reliable means of ensuring proper placement, after clear visualization of the tube passing between the vocal cords, is documentation of CO2 in expired gas (by capnometry or a disposable CO2 detector) Only in the settings of full cardiac arrest or extremely low pulmonary blood flow can the ETT be in the airway without detection of expired CO2 Under other conditions, malposition of the tube, most commonly in the esophagus or a mainstem intubation, must be assumed It is important to remember that capnometry does not ensure correct positioning within the airway CO2 will be detected if the tube is situated anywhere from a bronchus to above the vocal cords Documenting location of the tip of the tube between the thoracic inlet and T4 on chest radiograph, with the head in a neutral position, is important The tip will descend deeper into the trachea with neck flexion and move cephalad with neck extension.130,131 With the ETT in good position, an inflated cuff often can be palpated at the sternal notch when quick pressure is applied to the sentinel balloon When securing the tube, the intubator should avoid placing pressure on the lips, particularly at the angle of the mouth, and keep the vermilion border of the lip free of tape Nasotracheal Intubation Esophagus • Fig 127.9 Sellick maneuver Pressure on the cricoid cartilage occludes the esophagus or hypopharynx Nasotracheal intubation is rarely performed in emergent situations Contraindications to nasotracheal intubation include coagulopathy, maxillofacial trauma, CSF leak, and basilar skull fracture If nasotracheal intubation is preferred, it should generally follow orotracheal intubation so that an assistant can ventilate the child while the somewhat more difficult intubation is accomplished A topical vasoconstricting agent, such as phenylephrine Base of the tongue Vestibular fold Epiglottis Larynx Vocal cords Arytenoids Esophagus • Fig 127.10 Glottic area view via laryngoscopy CHAPTER 127 Airway Management 0.25% or oxymetazoline 0.05%, sprayed into the nasal fossa minimizes the risk of bleeding In most children, a tube of the same diameter as the oral tube can be gently advanced along the floor of the nasal cavity, essentially directly posteriorly, into the nasopharynx with firm, but not aggressive, pressure With the oral tube in the left corner of the mouth, the laryngoscope is again advanced into the pharynx until the oral tube is visualized passing through the cords and the tip of the nasal tube is seen in the nasopharynx The nasal tube is advanced until it lies directly above the cords, anterior to the oral tube Use of Magill forceps may facilitate this maneuver When the nasal tube is in good position to enter the larynx, the assistant removes the oral tube and helps advance the nasal tube Difficulty advancing the tube after it has passed the vocal cords may be overcome by rotating the tube or flexing the neck The tube then is secured; pressure on the septum or anterior rim of the nares should be avoided Although an orotracheal tube usually is placed more rapidly in emergencies, nasotracheal intubation has some potential advantages Orotracheal tubes often stimulate gagging, make mouth care difficult, and are easily kinked or bitten Anchoring the tube may be difficult because of saliva, and tongue movement may contribute to palatal or tracheal erosion and increase the likelihood of accidental extubation Trauma to lips, teeth, tongue, and other oropharyngeal structures also may occur Nasotracheal intubation is more comfortable for most conscious patients, causes less stimulation of the gag reflex, is more easily secured, and prevents the problem of biting in patients with seizures, decerebrate rigidity, or extreme agitation Infants with nasotracheal tubes may benefit from the ability to exercise their natural suck reflex, including pacifier use However, bleeding; adenoid injury; sinusitis; and trauma to the nasal turbinates, septum, or nares may occur with nasotracheal intubation In addition, the risk of sinusitis is greater than with orotracheal tubes.132,133 1525 A Adjunctive Airway Approaches Laryngeal Mask Airway The laryngeal mask airway (LMA) can be a safe means of securing a difficult-to-manage airway in an infant or child.134–136 It was designed as a supraglottic airway device that would offer the benefit of noninvasive ventilation LMA use rapidly gained acceptance in anesthesiology and has been incorporated into the American Academy of Anesthesiology difficult airway algorithm.53 The LMA consists of a small mask with an inflatable rim and a tube with a universal adaptor, which permits attachment to a resuscitation or anesthesia bag or ventilator (Fig 127.11) The original LMA consists of a wide-bore tube designed to sit in the hypopharynx The tube is attached to an inflatable bowl-shaped base that bypasses the tongue, sits around the epiglottis, conforms to the shape of the larynx, and provides a low-pressure seal around the supraglottic area.137 The LMA is available in a wide range of sizes, allowing use in very small infants to very large adolescents and adults Choice of LMA size is weight based.138,139 Since the initial development of the LMA, several other types have been designed, including the flexible LMA, intubating LMA, disposable LMA, and ProSeal LMA.140 The LMA insertion technique can be learned quickly by physicians and other providers, including emergency transport personnel, often more quickly than endotracheal intubation Once in place, the LMA can serve as a means of ventilating the patient until the desired definitive airway can be established LMAs can B • Fig 127.11 Laryngeal mask airway (LMA) (A) Mask portion of the airway with the rim deflated for insertion (left) and inflated (right) (B) LMA in position, with the rim inflated around the laryngeal inlet (From Efrat R, Kadari A, Katz S The laryngeal mask airway in pediatric anesthesia: experience with 120 patients undergoing elective groin surgery J Pediatr Surg 1994;29:206.) facilitate subsequent tracheal intubation, if desired, either with blind technique or via fiberoptic bronchoscopy through an intubating LMA In fact, the intubating LMA is preferred for use in the pediatric critical care setting, as it does not need to be removed for definitive airway placement and facilitates continuous oxygenation and ventilation Insertion of the LMA does not require muscle relaxation or use of a laryngoscope; therefore, it is considered a blind technique With the rim deflated or partially inflated, the LMA is advanced along the posterior pharyngeal wall with the dorsum of the mask facing the palate until resistance of the upper esophageal sphincter is encountered The cuff is then inflated, forming a seal around 1526 S E C T I O N X I V Pediatric Critical Care: Anesthesia Principles in the Pediatric Intensive Care Unit A B C D • Fig 127.12 Inserting the laryngeal mask airway (LMA) Preoxygenate the patient as necessary Insert the LMA into the mouth and advance, following the palate and posterior pharyngeal wall until resistance is met (Modified from Ramachandran SK, Kumar AM Supraglottic airway devices Respir Care 2014;59[6]: 920–932.) the laryngeal outlet, and the attached tube is connected to a source of oxygen and positive pressure (Fig 127.12) Proper placement and seating is essential but very challenging in infants, most likely because the margin of error for placement in the small pharynx is so small In general, the risk of downfolding the epiglottis—thus, occluding the trachea—is greater in children than in adults Nevertheless, LMAs have been successful in the neonatal delivery room and shown to be effective in premature infants as early as 29 weeks.141,142 Successful placement depends on the shape and tone of the pharynx; adequate matching of the cuff; palatopharyngeal curve and shape of the posterior pharynx; extent to which anterior structures (such as tonsils) obliterate the curve; position of the head and neck; efficacy of digital manipulation; and the depth of anesthesia/sedation, muscle relaxation, or loss of airway reflexes.137 Tissue trauma is uncommon, and the need to manipulate the cervical spine during placement is minimal In most patients, the autonomic response to placement is less pronounced than with laryngoscopy and intubation On the other hand, the device does not fully protect against aspiration if the patient has a full stomach In addition, it may not be effective in patients with glottic or subglottic pathology Although its primary use is in the operating room, growing experience has shown that the LMA can be lifesaving in a variety of other settings when no other nonsurgical means of maintaining an airway is successful, particularly in patients with anatomically abnormal airways.143 LMAs are used to successfully oxygenate, ventilate, and assist in intubating patients with a variety of challenging airway scenarios, both anticipated and unanticipated, including those with Pierre Robin, Treacher Collins, and Goldenhar syndromes Their value for managing such patients in the operating room has now translated to emergency settings such as the emergency department or ICU The ease and rapidity of insertion and decreased gastric air insufflation during resuscitation make the LMA an invaluable tool when intubation fails during adult resuscitation.144 Pediatric advanced life support incorporates the LMA as an effective alternative to intubation during resuscitation when inserted by trained providers, but ideal airway management during pediatric cardiopulmonary resuscitation is still being debated.145,146 In neonatal resuscitation, when face mask ventilation or intubation is not successful, the LMA provides a means of rapidly improving oxygenation and heart rate However, it is not effective for aspirating meconium and may be inadequate for infants with severely noncompliant lungs Use by prehospital personnel has been effective for critically ill adults, but experience with children in the field has not been as widely successful In fact, results are worse than those obtained with continued bagmask ventilation when that technique is possible.147–150 Patients with intact protective reflexes poorly tolerate the LMA Thus, its use is largely limited to those with severely depressed levels of consciousness, heavy sedation, or anesthesia A disadvantage of the LMA is the inability to use airway pressures greater than approximately 20 mm Hg to prevent air leaking ... volatile anesthetic exposure, and is a particular risk to patients with previously undiagnosed myopathies, often associated with abnormality in the ryanodine receptor type gene (RYR1).119 It frequently... position most of the time, but a small pad under the shoulders may be helpful In older children, a thin pad under the occiput helps establish slight neck flexion (Fig 127.8) The head is extended... of apnea time and improved first-pass attempt success rate.125 Three minutes of spontaneous breathing at 100% FiO2 allows denitrogenation with alveolar oxygen fraction close to 95% in patients