Preoperative Assessment

A careful assessment of the child must be made at the time of the preoperative visit. Although many children are healthy, some have diseases with significant implications for the anesthesiologist. A thorough history is obtained from the child’s chart and the parents. Review the systems and search for special problems that may complicate anesthesia ( Table 4-1 ). When a significant history is obtained, it is important to establish the current status of the disease; this may require consultation with the pediatrician, the surgeon or radiologist, and other physicians. Although most children take no medications, some may be taking medications that have implications for management during the perioperative period. Document all medications, neutraceuticals, and drug allergies. Common medications for children and their significance to anesthetic management are detailed in Table 4-2 ; ( N.B. Some herbal preparations may have anesthetic implications [ Table 4-3 ]). Throughout the preoperative interview, strive to gain the confidence of the child and the parents; always invite questions from both the parents and the child so as to help establish rapport and confidence.

Preoperative Feeding Orders

Infants and children should not be subjected to prolonged preoperative fasting. Excessive fluid restriction rapidly leads to dehydration and hypovolemia because of their high metabolic rate; hypotension in infants during induction of anesthesia has been shown to be directly related to the duration of fasting. In addition, excessive fasting may precipitate hypoglycemia and/or metabolic acidosis, particularly in young infants. Studies have shown that healthy children may safely be given unlimited clear fluids up to 2 hours before induction of general anesthesia. The volume and acidity of the gastric contents are not increased when this regimen is used. Indeed, clear fluids 2 hours before anesthesia may reduce gastric contents at induction, possibly by stimulating gastric emptying. Furthermore, this practice reduces hunger and thirst and makes for a happier child! Fasting guidelines are presented in the Table 4-4 .

Children who are scheduled for afternoon surgery may have a light breakfast (dry toast and black tea) early in the morning. These rules must, of course, be modified in special cases (e.g., for diabetics). Children who require emergency surgery, those with gastrointestinal disease, and any others at increased risk for vomiting during induction should receive intravenous fluids and a rapid sequence induction. When evaluating injured children, the interval between last food or fluid and the injury is the best predictor of the likely stomach contents. Children for whom any period of fluid deprivation might pose a risk (e.g., those with cyanotic heart disease) should have an intravenous infusion established at the commencement of any prolonged period of restricted oral intake.

Prophylaxis Against Hemorrhage for Infants

Ensure that the neonate undergoing surgery has been given vitamin K ₁ to prevent Vitamin K deficiency bleeding (VKDB). Aqueous vitamin K ₁ (1 mg IM or IV) corrects the deficiency within a few hours and therefore should be given as early as possible. Late onset VKDB may occur in breast-fed infants who were never given vitamin K; check the history.

Basic Laboratory Tests

Preoperative laboratory tests are considered unnecessary for most children; however, in some regions, these tests are legislated requirements. Preoperative urinalysis has not been found useful in detecting significant diseases or in routine screening of children. However, because a history is unreliable, urine (or blood) for pregnancy testing has become mandatory in many centers for all females who have reached menses. Hemoglobin (Hb) determination is likewise of little value in otherwise healthy children. Mild degrees of anemia have not been shown to increase the risk of anesthesia and do not alter the anesthesia technique selected. Most authorities now recommend that these tests may be omitted in healthy children undergoing minor surgery. All small infants, especially those who were born preterm, should have a preoperative Hb determination to exclude anemia, which is more common in such infants and may increase the risk of complications. Older children with systemic diseases, those with a history of anemia, and those who may lose significant amounts of blood intraoperatively should also have a preoperative Hb determination. A sickle cell test is now performed routinely in neonates immediately after birth in many regions. Older infants and children whose sickle status is unknown should be tested with a Sickledex and if that is positive, a hemoglobin electrophoresis should be performed.

Premedication

Drugs may be given preoperatively to block unwanted autonomic reflex (vagal) responses, produce preoperative sedation and tranquility, facilitate separation from parents if necessary, and smooth the induction of anesthesia.

Special Considerations

• 1.
  

  Neurosurgical patients who may have increased ICP should not receive any sedative premedication.

  
  
• 2.
  

  Children with a suspected difficult airway or OSA should be sedated with caution because it could lead to respiratory depression or airway obstruction.

  
  
• 3.
  

  Atropine should not be given intramuscularly to children with a fever because it may exacerbate the fever by abolishing sweating. If needed, it may be given intravenously at the time of induction.

  
  
• 4.
  

  Some children undergoing correction of strabismus are assessed by the ophthalmologist immediately before the operation and should not be premedicated with atropine. They may receive atropine (0.02 mg/kg intravenously) at induction to block the oculocardiac reflex.

Mask Anesthesia

• 1.
  

  During mask anesthesia, always have age and size appropriate equipment for endotracheal intubation immediately at hand:

  
  
  
  
  • a.
    

    A selection of suitably sized tracheal tubes with connectors in place ( Table 4-6 )

    
    
    
    

    TABLE 4-6

    
    

    Approximate Diameter of Pediatric Endotracheal Tubes * and Insertion Depth

    
    

    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    
    

    Age of Child (yr)	Internal Diameter (ID) (mm) †	Approximate depth of insertion (cm) to mid- trachea* from:
    		Teeth	Nares
    Premature	2.5 (for infants <1500 g) to 3.0 (for infants >1500 g)	6-9	8-11
    Neonate	3.5	9-10	12
    1	4.0	11	13
    2	4.5	12	14
    4	5.0	14	16
    6	5.5	15	17
    8	6.0	16	18
    10	6.5	17	19
    12	7.0	18	20
    14	7.5	19	21
    16	8.0	20	22

     
    

    * See also page 97 .

    
    

    † Formula: (age of child (≥2 yr) in years ÷ 4) + 4.0 = size of tube ID in millimeters. The tube diameters listed are given only as a guide. Always prepare a selection of tubes, and use the one with the best fit (see text).

    
    
    
    
  • b.
    

    Two properly functioning laryngoscope handles with several suitable blades

    
    
  • c.
    

    Labeled syringes containing atropine, succinylcholine, and induction agent (propofol, thiopental, ketamine, etomidate)

  
  
  
  
• 2.
  

  Select a mask that fits the contours of the child’s face and minimizes the dead space if possible. The Rendell Baker mask is ideal for infants and small children; however, the anesthesiologist may find it easier to achieve a good seal with a cushion-type mask.

  
  
• 3.
  

  The relatively large tongue in infants and adenoid or tonsillar hypertrophy in older children may cause airway obstruction. If obstruction occurs, insert an oropharyngeal or nasopharyngeal airway of suitable size. Alternatively, sublux the temporomandibular joint by applying digital pressure to the apex of the ascending rami (behind the pinna) directing the force towards the frontal hairline. This maneuver translocates the mandible anteriorly and rotates the joint, thereby lifting the tongue and intraoral tissues off the posterior pharyngeal wall and opens the airway and the mouth.

  
  
• 4.
  

  Infants have soft laryngeal cartilages and tracheal rings. Therefore the anesthesiologist should avoid applying pressure over the airway in the neck during mask anesthesia. Monitor breath sounds, EtCO ₂ , and the movement of the reservoir bag continuously.

Laryngospasm

Laryngospasm occurs most commonly during induction of anesthesia, but also during emergence and occasionally during maintenance of anesthesia if the child is stimulated while lightly anesthetized. It occurs more commonly in infants (compared with older children), in preterm infants, children with recent URIs, children with reactive airways disease, after airway surgery and in those exposed to second-hand smoke. The clinical hallmarks of laryngospasm include high-pitched sounds with inspiratory stridor that may progress to silence as the glottic aperture closes. Suprasternal and supraclavicular retractions occur with paradoxical chest wall motion, increased diaphragmatic excursions and if the spasm persists, hemoglobin desaturation and bradycardia/asystole. As soon as laryngospasm is suspected, the precipitating event (such as secretions, blood, or other foreign material) should be cleared. Initial treatment should include the application of a facemask to deliver 100% oxygen with positive end-expiratory pressure (maximum pressure of 10 to 15 cm H ₂ O) ( Figure 4-1 ). If laryngospasm continues, the mandible should be displaced by transiently applying pressure to the superior end of the ascending ramus of the mandible (i.e., the condyles) using a single digit behind each pinna (see previous discussion). Although subluxing the mandible, the thumbs should seal the facemask to the face. Oral airways must be used with great caution in these circumstances as short oral airways may push the tongue into the glottic opening and long airways may push the epiglottis into the opening, in both instances obstructing rather than helping the airway. An additional benefit from pressing on the ascending ramus of the mandible is that the stimulation incurred increases respiratory effort. However, if these measures fail and the oxygen saturation and heart rate continue to decrease, early treatment should include IV atropine (0.02 mg/kg) followed by IV propofol (1 to 2 mg/kg) and/or succinylcholine (1 to 2 mg/kg IV or 4 to 5 mg/kg IM) and intubation. If the child is in extremis (i.e., bradycardia and hypoxic) from laryngospasm, then intubate the trachea immediately, and ventilate the lungs with 100% oxygen.

Laryngospasm algorithm.

(From Hampson-Evans D, Morgan P, Farrar M: Pediatric laryngospasm. Pediatr Anesth 18:303-307, 2008.)

Postobstructive Pulmonary Edema

Postobstructive pulmonary edema is a complication that may occur after relief of acute (laryngospasm) or chronic upper airway obstruction (tonsillectomy). The mechanism of this pulmonary edema appears to be the generation of extreme negative intrathoracic pressure against a closed glottis and its sudden release causing a dramatic increase in pulmonary blood flow resulting in low pressure, noncardiogenic pulmonary edema. This complication should be suspected when pink frothy sputum appears in the tracheal tube and oxygen desaturation continues unabated. Treatment is to continue positive pressure ventilation and IV lasix as needed.

Postintubation Croup

Postintubation croup or subglottic edema is associated with traumatic intubation, tight-fitting endotracheal tubes, coughing on the tube, a change in the child’s position, prolonged intubation, surgery of the head and neck, and a history of croup. Treatment includes the inhalation of cool mist, steroids, and racemic epinephrine. Inhalation of racemic epinephrine (0.5 ml in 3 ml normal saline over 10 minutes) is usually effective although its effects are temporary and its use may be followed by rebound edema. Prolonged observation or overnight admission may be required.

Laryngoscopy

• 1.
  

  Ensure that the head is correctly positioned and supported.

  
  
  
  
  • a.
    

    For infants and children younger than 6 years of age, the head should be on the level of the table and supported in a low head ring. At this age, the larynx is positioned high in the neck and there is no advantage to anterior displacement of the cervical spine because the relatively large head accomplishes this naturally. Extension of the neck at the atlanto-occipital joint aligns the oral, pharyngeal, and tracheal axis for optimal visualization. External pressure (so called optimal external laryngeal manipulation [OELM]) applied to the thyroid cartilage region of the anterior aspect of the neck (applied most effectively by the anesthesiologist using their second hand, in a posterior and cephalad direction) may further improve the view of the glottic aperture.

    
    
  • b.
    

    For older children and adolescents, place a folded sheet or blanket under the head as a pillow to cause anterior displacement of the cervical spine and improve the alignment of the airway and the view of the glottis as in adults.

    
    
  • c.
    

    Beware of conditions that may be associated with an unstable cervical spine (e.g., Down syndrome, Marfan syndrome). In such cases, note the range of spontaneous motion of the neck when the child is awake and inquire about the presence of neurologic symptoms preoperatively (wide based gait, urinary or fecal/urinary incontinence). There is no evidence that cervical spine films are helpful in ruling out unstable cervical vertebra; however, we advise extreme care be taken to limit neck movement during intubation or surgical positioning.

  
  
  
  
• 2.
  

  Examine the teeth carefully; many young children have loose deciduous teeth. The teeth must be kept in view throughout laryngoscopy: retract the lip with your thumb and exert no pressure on the teeth during laryngoscopy. If loose teeth are present, it should be noted preoperatively and the parents should be informed that it may be safer to remove them once the child is anesthetized. If teeth are removed, they should be retained and given to the parents after the anesthetic. A plastic tooth guard may be applied to the maxillary teeth and is particularly useful for older children and adolescents when a Macintosh (curved) blade is used.

  
  
• 3.
  

  In infants and children, the anesthesiologist’s view of the glottis may be obscured by the epiglottis unless it is raised with the tip of the straight blade. (This is why we advocate the use of a straight blade in this age group.) In small infants, it is sometimes a problem to lift the epiglottis without it slipping off the laryngoscope blade. If this happens, advance the blade into the hypopharynx (with the entire tongue to the left of the blade) and slowly withdraw it until the glottis slips off the blade and the base of the epiglottis is firmly held. Alternatively, a straight blade may be used as would a curved blade and slowly advanced along the surface of the tongue. As the tip of the blade enters the vallecula, lift the base of the tongue to avoid trauma to other laryngeal structures.

  
  
• 4.
  

  Insufflation of oxygen into the pharynx during laryngoscopy (especially in infants or those with a difficult airway) improves oxygenation during attempts at intubation. Specially designed blades with an oxygen port are available (Oxyscope, Anesthesia Medical Specialties, Santa Fe Springs, Calif.), or an oxygen catheter may be taped to the side of any blade so as to deliver approximately 2 L/min of oxygen.

Tracheal Intubation

• 1.
  

  The optimal size of the tube is the largest one that passes easily through the glottis and subglottic regions without incurring resistance. The presence of a leak around an uncuffed tube at 20 cm H ₂ O positive pressure depends on a number of factors (including head position and muscle relaxation). A leak should be tested and achieved between 20 and 30 cm H ₂ O peak inflation pressure. If the leak is too large, the next half size larger tube may be inserted. If there is no leak at 30 cm H ₂ O, then a smaller diameter tube should be considered. In deciding that the tube size is appropriate, many clinicians depend more on the absence of any resistance when the tube passes through the cricoid region than on the presence of an audible leak. There is increasing use of cuffed tracheal tubes in children in the operating room (OR) and PICU but these tubes should also have a leak when the cuff is deflated (see later discussion).

  
  
• 2.
  

  Clear, thin-walled polyvinyl chloride (PVC) tubes (Z79-approved) are preferred.

  
  
• 3.
  

  Cuffed tubes may be preferred for major surgery in children whose lungs may be difficult to ventilate and who may be at increased risk for regurgitation of gastric contents. Even in infants and young children, the use of an appropriately sized cuffed tracheal tube does not increase postoperative morbidity. The use of a cuffed tube reduces the need to change tubes, reduces OR pollution, and may reduce the risk of aspiration. It also obviates the need to have a close fit in the subglottic region to ensure effective ventilation. For this reason it may be preferable, in children with a known tendency to subglottic stenosis (e.g., Down syndrome), to use a tube of smaller diameter together with a cuff to seal the airway. Small-sized cuffed tubes are now available with a wall thickness similar to that of uncuffed tubes. In infants and small children when a cuffed tube is used, the cuff may not require inflation to achieve an adequate seal for ventilation. However, positioning the cuff below the cords places the tip of the tube much closer to the carina in small infants and may increase the risk of an endobronchial intubation. The new MicroCuff tubes have addressed these shortcomings by designing a high compliance, better shaped cuff that is more distally attached to the tube.

  
  
• 4.
  

  Endotracheal connectors must have a lumen at least equal to the internal diameter (ID) of the tube and must be firmly inserted. Tracheal tube connectors (particularly in small diameter tubes) should be removed, moistened with an alcohol swab, and reinserted into the tube up to the shoulder.

  
  
• 5.
  

  The correct positioning of the tracheal tube should be immediately confirmed by observation of the chest excursion, the presence of humidity within the lumen of the tube, the capnograph trace, and chest auscultation. Ventilation should be auscultated in both axillae. The length of the trachea of the infant and young child is short, only 5 cm in the neonate. The tip must be accurately placed at midtracheal level to minimize the risk of an endobronchial intubation or accidental extubation. Note carefully the length of tube that is passed through the cords, and check the tube length marking at the teeth. An easy method of determining the correct depth of insertion of the tracheal tube when it is even with the teeth or alveolar ridge is 10 cm in a neonate, 11 for a 1-year-old and 12 for a 2-year-old ( N.B. The second digit is the child’s age in years.); beyond 2 years, halve the child’s age and add 12 cm (see Table 4-6 ). Tubes must be firmly taped in place, preferably near the middle of the mouth, where they are less likely to kink. When cuffed tubes are used, the cuff should be positioned just past the vocal cords; check for bilateral ventilation and secure the tube carefully. As previously mentioned, the margin of safety before the tip passes into the bronchus is shorter with cuffed tubes.

  
  
• 6.
  

  Avoid pressure by anesthetic hoses and other equipment on the child’s face or head by the use of suitable padding. Facial nerve palsy has been reported after anesthesia because of pressure of anesthesia equipment.

  
  
• 7.
  

  The anesthesia circuit and tube must be carefully positioned and supported to prevent any traction on the tube that might cause it to kink or become dislodged. Endotracheal tubes used in children kink very easily, and this is a potential cause of disastrous accidents.

  
  
• 8.
  

  Remember that extension of the neck withdraws the tip of the tube proximally in the trachea and flexion advances the tube; 1 to 3 cm of movement may occur between full flexion and full extension in infants. Position the tube carefully and consider the effects of changing the head position. Always reassess bilateral ventilation after repositioning the child.

  
  
• 9.
  

  Be aware that some neonates and infants have a congenitally short trachea, which increases the danger of endobronchial intubation (e.g., DiGeorge syndrome).

Nasotracheal Intubation

If the nasal route is chosen, the child should be prepared as outlined earlier. When performing nasotracheal intubation it is not unusual to cause some bleeding from the nose. As a result, several strategies have been developed to reduce this risk. Although warming the tip of the tube softens it, this has not been shown to be effective in reducing nose bleeding. Two effective strategies are application of a vasoconstrictor (e.g., oxymetazoline) to the nares and/or telescoping the tip of the tube into the flange end of a smooth red rubber catheter. With the latter, the catheter tip should be lubricated and passed along the floor of the (preferably left) nostril followed by the tube. (The left nostril aligns the tip of the tube [bevel on the left] directly with the glottic opening and aligns the bevel of the tube on the turbinate side.) The catheter is then advanced into the oropharynx where it is visualized in the hypopharynx and pulled off the endotracheal tube with McGill forceps. The tube is then directed using McGill forceps into the trachea.

A Note on Awake Intubation in the Neonate. It was common practice to intubate the neonate awake; however, it is now usual to induce anesthesia first. Intubation is more likely to be successful and less desaturation to occur if the neonate is first anesthetized. Awake intubation might be considered in neonates who are hemodynamically unstable, have micrognathia or a difficult airway, or who are extremely premature. To perform an awake intubation, pretreat the neonate with oxygen and atropine, have a styletted tube available, and have an assistant position the neonate’s arms fully abducted against the head to stabilize the neonate’s head. With the laryngoscope in one hand and the tube in the second, remove the facemask and intubate the trachea rapidly. Awake intubation increases blood pressure and intracranial pressure to a similar extent as crying and coughing. There has been a concern raised regarding an increased risk of IVH in preterm infants whose tracheas were intubated awake; however, this risk has never been confirmed. If awake intubation is deemed to be necessary, a local anesthetic solution (diluted, with upper limits predetermined) may be applied to the oropharynx and palate to reduce the infant’s distress and struggling. Small doses of fentanyl (0.5-1 µg/kg) and midazolam (0.05-0.1 mg/kg) may also facilitate the process. The use of a laryngeal mask airway (LMA) to establish the airway before anesthesia may also be considered (see later discussion).

Rapid Sequence Induction (RSI)

RSI is an intravenous induction technique used to rapidly and safely secure the airway with a tracheal tube when there is a risk of vomiting or regurgitation and aspiration. Careful preparation for a RSI is essential and requires the following:

• 1.
  

  Equipment; anesthesia machine, age appropriate laryngoscopes and tracheal tubes, functioning suction.

  
  
• 2.
  

  Predetermined drugs in weight-appropriate doses.

  
  
• 3.
  

  Skilled anesthesiologist and skilled assistant.

The equipment must include all standard monitors and the necessary airway instruments and supplies. The airway equipment should include two functioning laryngoscope blades and handles, two sets of suction tubing, cuffed tracheal tubes of age appropriate size (plus a half-size larger and smaller diameters) and a stylet. Predetermined drugs include 100% oxygen to be given before the sequence begins, an intravenous induction agent (propofol 3 to 4 mg/kg, ketamine 1 to 2 mg/kg, or etomidate 0.2 to 0.3 mg/kg) in predetermined doses according to weight and physical status ( N.B. Severity of dehydration and sepsis, etc.), atropine (0.02 mg/kg), and a muscle relaxant (succinylcholine 2 mg/kg or rocuronium 1.2 mg/kg). The child’s head is optimally positioned during preoxygenation and as anesthesia is induced, cricoid pressure (see below) is applied by the assistant. (Before commencing, ensure that your assistant is instructed in the effective application of cricoid pressure.) Once paralyzed, the trachea is intubated without delay and the cuff inflated. In the modified RSI technique, the lungs may be ventilated manually with 100% oxygen while maintaining cricoid pressure (see later discussion).

Cricoid Pressure

Cricoid pressure (Sellick maneuver) should be applied to the cricoid ring with thumb and long finger as anesthesia is induced and should be maintained until tracheal position is confirmed. Cricoid pressure has been popularized as an adjunct to the RSI to prevent passive regurgitation of gastric contents during induction of anesthesia. The use of this technique is widely advocated. However, evidence has not been forthcoming to support the effectiveness of cricoid pressure to either occlude the lumen of the esophagus or prevent passive regurgitation of gastric contents. MRI evidence indicates that the lumen of the esophagus is lateral to the cricoid ring in 50% of patients and is laterally displaced with cricoid pressure in 90%. Moreover, studies of the force required to occlude the lumen in adults report that inadequate force is applied in the majority of patients. Surveys indicated that cricoid pressure is used in only half of those children in whom it is indicated. In adults, 30 to 40 Newton (3 to 4 kg of force) must be applied to the esophagus; there are no comparable data in children. Cricoid pressure is known to relax lower esophageal sphincter tone. If mask ventilation is ever necessary in a child with a full stomach, it is probably prudent to continue to apply cricoid pressure to prevent gastric inflation and maintain small peak inflation pressures. Contraindications to cricoid pressure should be recognized ( Table 4-7 ). Excessive cricoid pressure may increase the difficulty of laryngeal visualization; OELM combined with cricoid pressure may be needed.

The Laryngeal Mask Airway

The LMA is an oropharyngeal tube provided with an anatomically conforming elliptical inflated rim designed to encircle the laryngeal inlet. If correctly inserted, the mask tip lies against the upper esophageal sphincter, the sides against the pyriform fossa, and the upper border against the base of the tongue. It was primarily designed as a substitute for mask anesthesia in spontaneously ventilating adults, but more recently its use has been extended to some children whose lungs were ventilated. In children, controlled ventilation without distention of the stomach may be possible if peak airway pressures are maintained at approximately 15 cm H ₂ O. The LMA does not protect the airway should vomiting or regurgitation occur. LMAs are sized according to the child’s weight ( Table 4-8 ).

Insertion of the LMA is performed after induction of adequate anesthesia by inhalation or by an intravenous injection of propofol (3 to 4 mg/kg for children). The cuff should be checked before it is inserted. After the cuff has been completely deflated and the mask well lubricated, it is inserted blindly along the curve of the palate into the pharynx, with the aperture positioned anteriorly, until resistance is felt. If the LMA becomes “hung up” on the posterior pharyngeal wall, a finger should be inserted into the mouth to lift the tip of the LMA and continue insertion. The LMA is then advanced using gentle pressure. When the cuff is inflated, the LMA should rise slightly out of the mouth. The adequacy of ventilation and fit are checked. Generally, a leak will become obvious at approximately 15 cm H ₂ O peak inflation pressure. An alternative method of insertion in children has also been suggested: with the cuff partly inflated, the LMA is inserted with the mask facing posteriorly and then rotated 180° as it enters the pharynx. In either case, a black guideline on the proximal visible tube should lie against the central incisors when the LMA is in place and correctly oriented. Coughing and laryngospasm may occur if insertion is attempted at too light a level of anesthesia; such complications may be more common in infants and small children than in adults.

Studies have shown that, when the LMA is in position, the tip of the tube lies in the hypopharynx but the relationship of the cuff to the epiglottis and laryngeal aperture may vary somewhat despite an apparently good airway.

Some difficulty with insertion may be encountered in up to 25% of children; this is more likely in the smaller child having a size 1 or size 1.5 LMA inserted. In a very small percentage of children, it may be impossible to place the LMA correctly.

When correctly positioned, the LMA provides a good airway with less resistance than an endotracheal tube. It avoids instrumentation through the glottis and frees the anesthesiologist from holding a facemask. It is particularly useful during imaging procedures, radiotherapy, and for other short procedures where mask anesthesia with spontaneous ventilation might be used. Somewhat surprisingly, some have found the LMA to be useful during adenotonsillectomy, and it has been suggested that less aspiration of blood occurs with the LMA than with an uncuffed endotracheal tube. (We, and most ENT surgeons prefer to intubate the trachea). A special application of the LMA is to use it as a guide to assist management of the child with a difficult airway, where it may be used as a prelude to fiberoptic endoscopy and intubation. The LMA can be inserted in awake infants (e.g., with Pierre Robin syndrome) after inhalation of nebulized lidocaine, and used to provide an airway to induce and deepen anesthesia before fiberoptic intubation. The LMA is useful when difficulty with ventilation occurs in a child during attempts at intubation. The LMA may also be advantageous in infants with tracheal stenosis, in whom passage of an endotracheal tube would severely reduce an already compromised airway diameter. It must be remembered that the LMA does not guarantee the airway as does an endotracheal tube, and it does not protect against aspiration. The ProSeal LMA provides a better seal (average leak at ~25 cm H ₂ O peak inflation pressure) and a means for venting the stomach; this device may be optimal for management of the difficult airway in a situation where the child has a full stomach.

At the end of the procedure, the LMA may be left in place until protective reflexes have returned, or it may be removed while the child is still deeply anesthetized. Removal while the child is anesthetized results in fewer airway complications and less desaturation, but a facemask should be applied until the child is able to maintain a safe airway. The incidence of postoperative sore throat is similar whether an LMA or an endotracheal tube is used. Other supraglottic devices are available and each practitioner should decide which is best in their hands.

“Difficult Tracheal Intubation”

Management Strategies

It is most important to be prepared for every option when facing a difficult airway in a child. Confirm that all the equipment you may require is readily available. It is essential to keep all the “difficult pediatric airway” supplies on a special cart that is located centrally and can be wheeled into any room where it is required. It is always advantageous to have expert assistance on hand. If there are other members of the department with special skills, do not hesitate to enlist their aid, even if their initial role is simply to stand by, provide moral support, and be ready to intervene.

Preoperative administration of an anticholinergic drug may be advantageous to decrease secretions in the mouth and pharynx and minimize the possibility of laryngeal spasm. No heavy sedation should be administered; small doses of anxiolytics might be administered when necessary, using suitable caution and appropriate monitoring. Children who cannot be fasted and require emergency surgery may be prepared with the use of histamine ₂ -blocking drugs and intravenous metoclopramide.

A recommended sequence to follow is outlined in the Pediatric Difficult Airway Algorithm ( Figure 4-2 ).

Difficult airway algorithm.

The choice of anesthetized versus awake intubation is quite simple: children, unlike adults, almost always require general anesthesia. Children are very easily upset and will not cooperate during attempts at an awake intubation (even after local anesthesia is applied to the airway). Small infants may be severely stressed by attempts at awake intubation and are more easily and rapidly intubated when they are anesthetized. An exception is advised for certain small infants (i.e., those with Pierre Robin syndrome), in whom intubation may be very difficult and who may be more safely managed by topical anesthesia of the mouth and insertion of a well-lubricated LMA while the infant is awake. The LMA can then be used as a route to induce anesthesia and, if necessary, as a conduit for fiberoptic intubation (see Table 4-8 ).

Extubation of the Trachea

• 1.
  

  Children are prone to laryngeal spasm during extubation, especially if extubated during a light plane of anesthesia. Therefore,

  
  
  
  
  • a.
    

    Before extubation, ensure that all airway equipment to ventilate with oxygen and to reintubate if necessary are available.

    
    
  • b.
    

    Extubate when the child is fully awake (or, if indicated, deeply anesthetized).

    
    
  • c.
    

    Some children should not cough or strain with the endotracheal tube in situ during emergence (e.g., those having neurosurgery or intraocular surgery). This may be achieved with a planned “deep” extubation, preceded by careful suctioning of the stomach and pharynx. Lidocaine, 1 to 2 mg/kg IV administered slowly before extubation, also decreases the risk of coughing and breath holding. After the tracheal tube is removed, a facemask should be applied, the airway maintained, and oxygen administered until the child is awake. Studies suggest that oxygen saturation (Sa o ₂ ) levels are better maintained if extubation is performed while the child is still anesthetized and oxygen is then given by mask until the child is fully awake.

    
    
  • d.
    

    When judging whether the child is “awake” enough for awake extubation, wait until the eyes and mouth open spontaneously, all limbs are moving, and the child resumes regular spontaneous ventilation after coughing.

    
    
  • e.
    

    Do not disturb the child unnecessarily during the awaking stage, so as to minimize coughing and bucking on the tube before the child is fully awake. A “No touch” technique while waiting to extubate awake is very successful in many children.

    
    
  • f.
    

    All monitors should be left in place until successful extubation is complete.

  
  
  
  
• 2.
  

  Severe laryngospasm upon extubation may be followed by pulmonary edema as the laryngospasm is relieved. If this occurs, it should be treated by continued positive pressure ventilation, a diuretic (e.g., Lasix) and morphine.

  
  
• 3.
  

  The following children should be fully awake before extubation:

  
  
  
  
  • a.
    

    All those in whom tracheal intubation was difficult.

    
    
  • b.
    

    All those having emergency surgery; these children may vomit gastric contents during emergence from anesthesia.

    
    
  • c.
    

    All infants.

  
  
  
  
• 4.
  

  Children who have had a mouth gag with tongue blade inserted by the surgeon (e.g., for cleft palate repair) are at risk for postoperative swelling of the tongue; always inspect the mouth before extubation.

Extubation of the Difficult Pediatric Airway

Extubation should be performed as a well-planned exercise, with the necessary equipment and personnel to reintubate the child readily available. In selected children a trial extubation, leaving an airway exchange catheter in situ, may be indicated.

All children with difficult airways should be extubated or have the LMA removed only after they have fully regained consciousness and when all danger of swelling in the region of the airway has passed. Corticosteroids (dexamethasone) have been used before extubation to decrease the likelihood of stridor, and all children should be given humidified oxygen after the tracheal tube is removed.

The golden rule: If there is any doubt about the airway, leave the trachea intubated.

Pediatric Anesthetic Circuits

The ideal anesthetic circuit for children should be lightweight; with low resistance and dead space; with low compliance; adaptable to spontaneous, assisted, or controlled ventilation; and readily humidified and scavenged. These conditions are most nearly met by the T-piece systems; however, modified circle systems are now extensively used for children.

Humidification of Anesthetic Gases

Humidification of inspired gases during anesthesia in the past was recommended to prevent damage to the respiratory tract by dry gases and to minimize heat loss via the respiratory tract and thereby assist in maintaining normothermia. Dry gases inhibit ciliary activity and lead to the accumulation of inspissated secretions, which may, in the extreme, progress to obstruct the endotracheal tube. Degenerative changes in cells exfoliated from the trachea after exposure to dry gas have been described, but an increased incidence of postoperative morbidity from pulmonary complications remains unproved. However, the use of circle systems, particularly with low flows has reduced the need for a humidifier. Gases should be humidified during very prolonged surgery and in the intensive care unit to reduce the risk of tube blockage from inspissated secretions.

Humidified anesthetic gases significantly reduce heat loss during surgery, particularly in neonates and infants. However, heated humidifiers are not as easily incorporated into circle circuits and accumulated water may plug capnogram tubing. Humidifiers are less frequently used in pediatric anesthesia since other effective means for maintaining body temperature are now available. An alternative means of humidification for older children is the use of a heat and moisture exchanger (HME) inserted at the connection of the endotracheal tube to the circuit. The HME conserves approximately 50% of the water normally lost via the respiratory tract and thus prevents a corresponding heat loss. The HME is most efficient with smaller tidal volumes and greater respiratory frequency, so it is quite useful in pediatric cases. These normally are very low resistance, but if blocked by secretions will significantly increase airway resistance; always monitor ventilation carefully when an HME is used.

Controlled Ventilation During Anesthesia

During anesthesia, ventilation may be controlled using manual or mechanical ventilation.

Mechanical Ventilation

Mechanical ventilators have the advantage of maintaining a relatively constant level of ventilation while freeing the anesthesiologist to perform other functions. Remember that in small children the compression volume of the anesthesia circuit may exceed the tidal volume that is delivered to the lungs. Therefore the volume readings on the ventilator may be meaningless. The adequacy of ventilation must be judged by auscultation of the chest and observation of chest movement, along with EtCO ₂ or arterial carbon dioxide levels.

Controlled ventilation with the circle system permits the use of extremely small fresh gas flows while monitoring the adequacy of ventilation by capnography. Several strategies for mechanical ventilation have been introduced into clinical anesthesia.

• 1.
  

  Volume cycled ventilation. In this mode, the ventilator delivers the prescribed tidal volume (unless it reaches the pressure relief limit—usually 40 mm Hg). Therefore during surgeries in which the compliance of the chest/abdomen changes, the delivered tidal volume remains relatively constant. (Tidal volume may decrease slightly because of the large volume of gas compressed in the anesthesia circuit as compliance decreases).

  
  
• 2.
  

  Pressure cycled ventilation. In this mode, the ventilator delivers a volume until the preset pressure is reached (usually 20 to 40 mm Hg). In this mode, if the pressure is reached before a desired tidal volume is delivered, the ventilator switches into expiration. During surgeries in which the compliance of the chest/abdomen changes, the delivered tidal volume varies from breath to breath as compliance changes. Hence, without an accurate capnogram, tidal volume delivered cannot be estimated. We find this mode only acceptable during minor peripheral surgery.

  
  
• 3.
  

  Pressure assisted ventilation—new ventilators incorporate the potential for various modes of ventilation. The place of these in pediatric anesthesia is undetermined at the present time.

Monitoring During Anesthesia

Cannulation Techniques