1517CHAPTER 127 Airway Management Limited temporomandibular joint or cervical spine mobility may make laryngoscopy and tube placement difficult Midface insta bility or upper airway bleeding, edema, ai[.]
CHAPTER 127 Airway Management A 1517 B • Fig 127.4 Importance of inspecting the patient’s profile Child with significant micrognathia, not immediately apparent on frontal view (From Lipton JM, Ellis SR Diamond-Blackfan anemia: diagnosis, treatment, and molecular pathogenesis Hematol Oncol Clin North Am 2009;23:261–282, 2009.) Limited temporomandibular joint or cervical spine mobility may make laryngoscopy and tube placement difficult Midface instability or upper airway bleeding, edema, airway or neck masses, and foreign bodies are additional reasons for concern.45–50 Several assessment systems assist with recognition and classification of the adult patient with a difficult airway Although never validated in pediatrics, they provide a useful framework for assessing infants and children The Mallampati classification (Fig 127.5A) uses visibility of upper airway structures—particularly the uvula, soft palate, and faucial pillars—as a guide to the likely ease of intubation Mallampati class allows visualization of the uvula, soft palate, and faucial pillars In class 2, faucial pillars and soft palate are visualized, but the base of the tongue obstructs the uvula In class 3, only the soft palate is visualized In class 4, the soft palate is not seen Difficult intubation is more likely associated with classes and This scale can be used with cooperative children, and an approximate evaluation may be obtained by observing many crying infants and young children.51 The Cormack laryngeal view grade score is shown in Fig 127.5B The Cormack system requires an attempt to visualize the larynx; therefore, it is more valuable as a tool for describing difficulty once it has been encountered than for predicting it The Cormack score is grade 1, full view of vocal cords and glottis; grade 2, partial view of vocal cords and glottis; grade 3, only the epiglottis is seen; and grade 4, the glottis and epiglottis are not visualized Grades and predict difficult direct laryngoscopy Although these classification systems are helpful in a controlled environment, particularly the preoperative area of a hospital, they are recognized as having limited utility in the emergent situations often encountered in the ICU, and their ability to predict the degree of difficulty with intubation in children is not well established Ability to visualize the faucial pillars, soft palate, and uvula usually predicts an uncomplicated intubation, but visibility may be difficult to assess in a sick, uncooperative child.43 Children with severe hypoxia, severe hypovolemia, or other causes of hemodynamic instability, such as intracranial hypertension, a full stomach, or a combination of these conditions, present added difficulties that must be considered When airway problems are anticipated, the intensivist should approach intubation with a plan specific to the difficulty noted and with a backup strategy in mind.47–49 The option of relocating a patient with anticipated difficult airway to the operating room should be discussed, depending on the patient’s stability and availability of operating room personnel at the time of intubation Additional equipment should be on hand, including a variety of laryngoscope blades, forceps, ETT sizes, supraglottic airways, bronchoscopes, tracheostomy or cricothyrotomy trays, and additional skilled personnel as needed.49 Many institutions have developed difficult airway carts or packs and a team of highly skilled airway experts to assist when severe intubation challenges arise.51,52 When choosing the approach to sedation, agents that can be reversed pharmacologically are preferred and should be titrated slowly to the desired effect Fig 127.6 shows a modification of the difficult airway algorithm of the American Society of Anesthesiologists, which provides an approach to managing the difficult airway.53 A similar plan is necessary at the time of extubation Serious consideration should be given to extubating in the operating room or leaving an airway exchange catheter in place to facilitate reintubation if necessary 1518 S E C T I O N X I V Pediatric Critical Care: Anesthesia Principles in the Pediatric Intensive Care Unit Uvula Soft palate Hard palate Pillars A Class Class Vocal cords B Grade Class Class Epiglottis Grade Grade Grade • Fig 127.5 (A) Modified Mallampati classification Class 1: visualization of the faucial pillars, uvula, soft and hard palate Class 2: visualization of complete uvula and palate Class 3: visualization of only the base of the uvula and palate Class 4: visualization of only the hard palate (B) Cormack and Lehane classification of the laryngeal exposure Grade 1: most of the glottis is visible Grade 2: only the posterior portion of the glottis is visible Grade 3: only the epiglottis is visible Grade 4: not even the epiglottis is visible (From Amantéa SL, Piva JP, Zanella MI, et al Rapid airway access J Pediatr [Rio J] 2003;79[suppl 2]: S127–S138.) Process of Intubation All equipment for intubation must be available before the procedure (Fig 127.7) Many critical care units have implemented intubation checklists intended to decrease peri-intubation injury or adverse effects However, studies comparing the performance of a preprocedure checklist to usual care have yielded mixed results.54,55 A source of suction and appropriate catheters, oxygen and necessary tubing, ventilation bag, mask, laryngoscope and proper-sized blade with a well-functioning light, ETTs of the expected size plus larger and smaller ones, airway forceps, stylet, and a means of securing the ETT should be present at the head of the bed so that the intubator never needs to look away from the patient A functioning intravenous catheter for drug infusion is essential in all but the most extreme emergencies Prior to laryngoscopy, a decision should be made regarding use of video laryngoscopy or standard laryngoscopy Video laryngoscopy, as detailed later in this chapter, provides multiple benefits but must be weighed against immediacy of availability and potential disadvantages Laryngoscope handles are available in standard adult and pediatric sizes The smaller diameter of the pediatric handle makes it easier to manipulate, particularly when intubating infants and very young children Blades of many types are available The most important characteristic is length Inexperienced operators often select a blade that is too short, making visualization of the larynx difficult Excessively long blades make it difficult to avoid pressure on the upper lip and teeth Historically, straight blades have been recommended for intubating infants and young children, but recent evidence suggests that curved blades (e.g., Macintosh no or blades) are as likely to provide good visualization.56 The slightly curved tip of the Miller blade makes visualization of the larynx possible without actually lifting the epiglottis The broader blade and bore of the Wis-Hipple blade help displace soft tissues in the young infant’s oropharynx The Miller no blade is especially versatile in a broad age group (children ages to 10 years) In older children, use of a curved blade often works best If a cuffed ETT is to be used, a curved Macintosh no or blade is effective in most patients and may provide more room to manipulate a cuff in the oropharynx Operator experience is probably the most important factor that determines intubation success as well as willingness to try an alternative blade if one provides a poor view of the airway Selecting the proper tube size (diameter) is important for achieving effective mechanical ventilation and preventing tracheal injury A variety of formulas are in use, with the most common being the Cole formula: Tube size (inner diameter) (Age [years]/4) Cuffed tubes typically should be a half size smaller For infants, no formula is accurate Table 127.2 gives reasonable guidelines Individual differences require that the tube size be modified for each child so that the tube passes easily but fits snugly enough to allow delivery of adequate mechanical breaths at a given chest compliance Based on traditional teaching about airway anatomy, cuffed ETTs were viewed as unnecessary or inappropriate in young pediatric patients (,8 years) However, better recognition of the elliptical shape of the young child’s airway shows that a tube that permits a small leak around itself (as previously recommended) may still compress the lateral aspects of the tracheal mucosa (see Fig 127.1D) Cuffed tubes allow better occlusion of the airway CHAPTER 127 Airway Management 1519 Assess the likelihood and clinical impact of basic management problems: • Difficulty with patient coordination or consent • Difficult mask ventilation • Difficult supraglottic airway placement • Difficult laryngoscopy • Difficult intubation • Difficult surgical airway access Actively pursue opportunities to deliver supplemental oxygen throughout the process of difficult airway management Consider the relative merits and feasibility of basic management choices: • Awake intubation vs intubation after induction of general anesthesia • Non-invasive technique vs invasive techniques for the initial approach to intubation • Video-assisted laryngoscopy as an initial approach to intubation • Preservation vs ablation of spontaneous ventilation Develop primary and alternative strategies: Awake intubation Intubation after induction of general anesthesia Invasive airway access(b)* Airway approached by noninvasive intubation Initial intubation Initial intubation attempts unsuccessful From this point onwards consider: Calling for help Returning to spontaneous ventilation Awakening the patient Fail Succeed* Cancel case Consider feasibility of other options(a) Invasive airway access(b)* Face mask ventilation adequate Face mask ventilation not adequate Consider/attempt SGA SGA adequate* Nonemergency pathway Ventilation adequate, intubation unsuccessful Emergency pathway Ventilation not adequate, intubation unsuccessful If both face mask and SGA ventilation become inadequate Alternative approaches to intubation(c) Successful intubation* SGA not adequate or not feasible Call for help Emergency noninvasive airway ventilation(e) Fail after multiple attempts Fail Successful ventilation* Invasive airway access(b)* Consider feasibility of other options(a) Awaken patient(d) Emergency invasive airway access(b)* * Confirm ventilation, tracheal intubation, or SGA placement with exhaled CO2 a Other options include (but are not limited to): surgery utilizing face c Alternative difficult intubation approaches include (but are not limited mask or supraglottic airway (SGA) anesthesia (e.g., LMA, ILMA, to): video-assisted laryngoscopy, alternative laryngoscope blades, SGA laryngeal tube), local anesthesia infiltration or regional nerve blockade (e.g., LMA or ILMA) as an intubation conduit (with or without fiberoptic Pursuit of these options usually implies that mask ventilation will not be guidance), fiberoptic intubation, intubating stylet or tube changer, light problematic Therefore, these options may be of limited value if this step wand, and blind oral or nasal intubation in the algorithm has been reached via the emergency pathway d Consider re-preparation of the patient for awake intubation of canceling b Invasive airway access includes surgical or percutaneous airway, jet surgery ventilation, and retrograde intubation e Emergency non-invasive airway ventilation consists of a SGA • Fig 127.6 M odification of the American Society of Anesthesiologists difficult airway algorithm ENT, Otolaryngology (ear, nose, throat); ILMA, intubating laryngeal mask airway; LMA, laryngeal mask airway; NMB, neuromuscular blockade; OR, operating room (Modified from Committee on Standards and Practice Parameters, Jeffrey L Apfelbaum, Carin A Hagberg, Robert A Caplan, et al Practice guidelines for management of the difficult airway: an updated report by the American Society of Anesthesiologists Task Force on Management of the Difficult Airway Anesthesiology 2013;118[2]:251–270.) 1520 S E C T I O N X I V Pediatric Critical Care: Anesthesia Principles in the Pediatric Intensive Care Unit D E A C K F B J G I H L • Fig 127.7 Equipment for intubation A variety of sizes are available for pediatric patients (A) Nasopha- ryngeal airways (B) Oral airways (C) Masks (D) Anesthesia (Mapleson) bag (E) Laryngoscope handles (F) MacIntosh (curved) and Miller (straight) laryngoscope blades (G) Uncuffed and cuffed endotracheal tubes (H) Endotracheal tube stylets (I) Magill forceps (J) End-tidal carbon dioxide detectors (K) Yankauer suction (L) Tube changer TABLE Guidelines for Endotracheal Tube Diameter 127.2 in Infants and Children Age Premature Newborn 3–9 mo 9–18 mo 1.5–3 y 4–5 y 6–7 y 8–10 y 11–13 y 14–16 y Internal Diameter Orotracheal Length (cm) Nasotracheal Length (cm) 2–3 6–8 7–9 3–3.5 3.5–4 4–4.5 4.5–5 5–5.5 5.5–6 6–6.5a 6–7 a 7–7.5 a 9–10 10–11 11–12 11–13 12–13 14–15 12–4 16–17 14–16 18–19 16–18 19–20 17–19 21–23 18–21 22–25 20–22 24–25 Ideal tube size varies according to age, height, weight, specific airway anatomy, and ventilatory requirements of a child In general, an air leak around the tube at 15 to 30 cm H2O pressure is desirable a Cuffed tube cuffed tubes can be used in young children without higher incidence of airway complications.58–63 It appears that ideal tubes have clear depth markers along their length and an ultrathin, polyurethane, high-volume, low-pressure, spherical rather than elliptical cuff, positioned close enough to the tip of the tube to avoid inflation in the larynx.6 When a cuffed tube is used, great care should be taken to inflate it with the minimum occlusive volume, the minimum volume required to just seal the gas leak around the tube during mechanical inspiration and prevent mucosal ischemia and subsequent tracheal damage Our current best understanding is that pressure within the cuff should be maintained below 20 to 30 cm H2O There are inexpensive devices for measuring cuff pressure built into syringes used to fill the cuff In addition, a standard pressure transducer with air-filled tubing can be attached to the pilot balloon on the ETT and attached to a typical ICU monitor for continuous pressure measurements Cuffed tubes may be advantageous because they decrease the likelihood of needing multiple intubations to identify the correct size and not need to be changed in a critically unstable patient if lung disease worsens In addition, absence of a significant leak around the ETT may decrease the likelihood of flow-triggered ventilator autocycling The ability to occlude the leak also facilitates pulmonary function testing and indirect calorimetry Pharmacologic Agents to Facilitate Intubation and potentially place less pressure on the mucosa while offering better oxygenation and ventilation, more reliable end-tidal CO2 monitoring, and less risk of aspiration Routine use of cuffed tubes is increasing for patients of all ages as a greater variety enters the market.57 In addition, the greater elastic recoil of the lungs and chest wall of older patients may demand higher airway pressures for effective ventilation Cuffed tubes of all sizes are available and are especially useful in patients who require consistent minute ventilation (e.g., those with severely elevated ICP or reactive pulmonary vasculature) or relatively high airway pressures Increasing evidence indicates that With the exception of intubation during cardiopulmonary resuscitation, the physiologic and psychologic benefits of using analgosedation before intubation necessitate administration during almost all clinical scenarios.64,65 An analysis of data in the pediatric National Emergency Airway Registry shows that the intubation success rate is higher when both sedation and neuromuscular blockade are used.66 This finding is equally true in neonates, in whom sedation and neuromuscular blockade are still not used consistently.67 Most evidence in neonates indicates that use of neuromuscular blockade is associated with a lower risk of intracranial hemorrhage and pulmonary airleak.68 Excellent technical CHAPTER 127 Airway Management 1521 TABLE 127.3 Drugs That Facilitate Intubation Drug Dose Duration Comments Etomidate 0.3 mg/kg IV 3–5 Anesthesia, adrenal suppression (h mortality in sepsis?), minimal CV effect, apnea, g CMRO2, g CBF, g ICP Ketaminea 1–2 mg/kg IV; 4–6 mg/kg IM 10–15 Anesthesia, h systemic arterial pressure, h HR, h ICP, h IOP, hallucinations, laryngospasm, bronchodilation Propofol 1–3.5 mg/kg IV, then 0.05–0.3 mg/kg/min 10–15 g Systemic arterial pressure, g CMRO2, g CBF, g ICP, metabolic acidosis Fentanyla 2–5 m/kg IV 30–90 Analgesia, respiratory depression, CV stability, occasional bradycardia, or chest wall rigidity Remifentanil 1–3 mg/kg, then 0.25–1 mg/kg/min Morphinea 0.1–0.2 mg/kg IV 2–4 h Analgesia, respiratory depression, g systemic arterial and venous tone, g systemic blood pressure Midazolama 0.1–0.3 mg/kg IV 1–2 h Amnesia, sedation or euphoria, CV stability, occasional respiratory depression Lorazepam 0.1–0.3 mg/kg IV 2–4 h Sedation, anxiolysis, minimal CV effect Intravenous Anesthetics Sedatives/Analgesics Analgesia, respiratory depression, CV stability Neuromuscular Blocking Agents Rocuroniuma 0.6–1.2 mg/kg IV 15–45 Minimal cardiovascular effect, prolonged duration in liver failure a 0.1–0.3 mg/kg IV 30–75 Minimal cardiovascular effect, prolonged effect in hepatic failure 0.1 mg/kg, then 1–5 mg/kg/min 20–35 Metabolized by plasma hydrolysis, mild histamine release 0.5 mg/kg 30–40 Metabolized by plasma hydrolysis, mild histamine release 1–4 mg/kg IV 5–10 g HR, K1 release in neuromuscular disease, trauma or burns, masseter spasm, malignant hyperthermia, myoglobinuria Vecuronium Cis-atracurium Atracurium Succinylcholine a Duration of effect is only approximate and varies with age and physiologic state of the patient CBF, Cerebral blood flow; CMRO2, cerebral metabolic oxygen requirement; CV, cardiovascular; HR, heart rate; ICP, intracranial pressure; IM, intramuscular; IOP, intraocular pressure; IV, intravenous a Agents may be given intramuscularly but will have slower onset and more variable duration of effect airway skills are an absolute prerequisite, however, because losing control of the airway invites catastrophe Drugs that facilitate intubation are listed in Table 127.3 Anticholinergic Agents Anticholinergic agents decrease oral secretions and prevent bradycardia, particularly in young infants, although their use is not universally recommended.69,70 Atropine (0.02 mg/kg) and glycopyrrolate (0.01 mg/kg intravenously) are both immediately effective Glycopyrrolate does not cross the blood-brain barrier and may be useful in patients who have suspected traumatic brain injury with bradycardia and require monitoring by pupillary examination Scopolamine provides amnesia, decreases secretions, and prevents bradycardia but has a longer duration of onset The drying effect of all anticholinergics commonly requires approximately 15 to 30 minutes and is rarely achieved in emergency intubation Pediatric advanced life support guidelines (2011) recommend atropine for the following indications: (1) rapid-sequence intubation for infants under year of age, (2) patients to years of age receiving succinylcholine, (3) patients older than years receiving a second dose of succinylcholine, and (4) patients with bradycardia present before intubation These guidelines not provide information regarding patients older than year who are not receiving succinylcholine.71 Therefore, clinical judgment on a case-by-case basis is essential for determining when to use anticholinergics For example, a 3-year-old child with a heart rate of 60 beats/min may benefit from receiving atropine before intubation In contrast, a 10-month-old with a heart rate of 240 beats/ may not require administration prophylactically; instead, atropine should be readily available as needed Sedative and Analgesic Agents Most patients benefit from some degree of sedation for both comfort and facilitation of ideal intubating conditions Drugs commonly used include intravenous anesthetic agents, anxiolytic agents, and opioid analgesics The appropriate choice in a particular patient depends on the child’s hemodynamic status, level of anxiety, and underlying disease process One of three intravenous agents is usually appropriate to facilitate amnesia and ideal intubating conditions: etomidate, propofol, or ketamine Etomidate is a short-acting intravenous anesthetic that causes rapid loss of consciousness (at 0.3 mg/kg) and respiratory depression It also decreases cerebral oxygen consumption, cerebral blood flow (CBF), and ICP, without causing significant detrimental effects on cardiovascular function It causes less respiratory depression than thiopental—an agent widely used in the past but ... regarding use of video laryngoscopy or standard laryngoscopy Video laryngoscopy, as detailed later in this chapter, provides multiple benefits but must be weighed against immediacy of availability and... approached by noninvasive intubation Initial intubation Initial intubation attempts unsuccessful From this point onwards consider: Calling for help Returning to spontaneous ventilation Awakening the... intubating stylet or tube changer, light problematic Therefore, these options may be of limited value if this step wand, and blind oral or nasal intubation in the algorithm has been reached via the emergency