Abstract
Paediatric anaesthesia and airway management is in many ways similar to adult practice; however, deep understanding of the differences in anatomy, physiology and behavioural psychology is necessary, particularly in younger children and infants. This chapter aims to provide the anaesthetist with information on these differences and (re)introduce techniques and practical tips that may help practitioners with airway management in this population. The broad range of equipment sizes and drug doses are a challenge to memorise and guides are highly advised. While difficult airways are less frequent in children, their management can be challenging. Upper airway obstruction is a particularly frequent occurrence, and should be anticipated and prevented, focussing on basic, and much underappreciated, skills such as positioning, effective bag-mask ventilation and occasional careful use of adjuncts. Safe and non-traumatic practice is key. It is important to stress that modern devices such as videolaryngoscopes should be used carefully and under visual guidance at all times. Awake flexible optical bronchoscope (FOB)-guided intubation is the gold standard in adult difficult airway management. In paediatric practice, however, advanced airway procedures may need to be performed with prior general anaesthesia. We offer an introduction to some advanced techniques including paediatric emergency front of neck airway.
Introduction
This chapter aims to provide the anaesthetist with practical skills to be more comfortable during paediatric airway management. Incorporating some of the techniques described in this chapter may help with airway management but it should be remembered that anaesthetising infants and children with severe co-morbidity is associated with numerous potential complications and requires management by experts.
Anatomical and Physiological Differences
The child displays a number of unique anatomical and physiological properties that diminish over time and develop towards adult anatomy and physiology. Neonates are aged less than 1 month and infants less than 1 year. A child may variously be defined as less than 16 years or less than 18 years but in terms of airway management at age 8 years the child can generally be managed using adult techniques.
The protruding occiput of the neonate causes the neck to flex in the supine position. Use of padding under the shoulders during airway management helps prevent upper airway obstruction, which is caused partly by the relatively large tongue, narrow nasal cavity and cephalad larynx.
Reduced functional residual capacity, higher closing capacity and a relatively high baseline oxygen consumption result in rapid desaturation. High quality pre-oxygenation of the infant prevents desaturation for about 30 seconds in the healthy child, hence gentle positive pressure ventilation may be needed during rapid sequence induction. Hypoxaemia is the most common complication occurring during paediatric airway management and pre-oxygenation is warranted for all infants and small children. When hypoxia occurs severe bradycardia and cardiovascular collapse may occur early.
During laryngoscopy, the relatively large tongue and the long, floppy, omega-shaped epiglottis can hamper gaining a direct view of the glottis. The cephalad, and flexible larynx may be mobilised, to improve the view and facilitate intubation. The angled nature of the glottic opening can make tracheal tube insertion more difficult especially in passing the anterior commissure.
During intubation, resistance may be noticed distal to the vocal cords, as the elliptical aperture of the cricoid cartilage is reached. This non-distensible structure is functionally the narrowest site of the paediatric airway and choice of tube size is designed around avoiding trauma and oedema here. Neonates have a short and collapsible trachea of about 5 cm in length and accidental endobronchial intubation is a significant risk.
Oedema of the larynx and trachea, due to traumatic intubation, can have dramatic consequences. A small amount of airway swelling may have a critical impact on the calibre of the infant airway: a 1 mm circumferential oedema can reduce cross-sectional area by 75% and increase airway resistance 16-fold.
Basics of Paediatric Airway Management
Airway Assessment
History
Information on prior anaesthetics and adverse reactions is relevant. Are there any obvious signs of airway compromise at home – any snoring, wheezing or sleep apnoea? History of recent upper airway infection and/or passive smoking should be obtained as it increases risk of laryngospasm during anaesthesia.
Airway Examination
As small children are uncooperative, formal airway tests are impractical (and not validated) and it is necessary to rely on history and clinical impression. What is the global appearance of the child? Does the child look normal or do they have syndromic features? Older children (> 3–4 years old) can cooperate with a more formal airway assessment.
Incidence of Difficult Airway
Craniofacial syndromes are the most common reason for difficult airways in the paediatric population. Micrognathia is the most common physical finding associated with difficult laryngoscopy in an infant.
In children, the difficult airway is less common than in adults and is particularly uncommon in healthy children. Some studies show an incidence of difficult mask ventilation in children of 0.2% compared with 1.4% in adults. Difficult laryngoscopy in children may be 2- to 20-fold less common than in adults but infants are more likely to have a difficult laryngoscopy with around 5% having a Cormack and Lehane Grade 3 or 4.
Preparing for Anaesthesia
The Challenge of Different Sizes: Drugs and Equipment
Selecting the correct equipment and drug doses, especially in the emergency setting, is one of the core challenges of paediatric anaesthesia. Relevant paediatric anaesthesia practice guidelines should be available at all times and these include those based on height or weight. Using smartphones or tablets, entering the weight (or estimated weight) in various apps prompts age/weight-specific vital signs, equipment and drug dose recommendations (e.g. Copenhagen Paediatric Emergency App).
Preparing for Emergencies: Laryngospasm
Reflex spasm of the intrinsic muscles of the larynx is a common complication in paediatric anaesthesia. The overall incidence is less than 1%, but is more frequent in young children and during ENT anaesthesia. Knowledge of risk factors is paramount. Hypersensitivity of the airway (e.g. caused by passive smoking, current or recent upper airway infection or asthma) increases risk up to 10-fold. An inexperienced airway manager is also an independent risk factor, probably due to likelihood of ill-timed airway management.
Pre-drawn syringes with suxamethonium (gold standard) and/or propofol should be prepared and placed at a predefined location known to all anaesthesia team members.
Initial management strategies include 100% oxygen, jaw thrust and mask continuous positive airway pressure (CPAP; 5–15 cmH2O) followed by administration of propofol (1 mg kg−1) and/or suxamethonium IV (0.1–0.5 mg kg−1) or IM (4 mg kg−1).
Keeping the Airway Open
Positioning
Correct positioning of the patient, aligning the axes of the mouth, hypopharynx and trachea, is key to improving the chances of successful mask ventilation and intubation. Positioning of the patient differs based on the age:
Infant and child less than 2 years old: padding under shoulder to compensate for a large occiput
Young child (2–8 years old): lying flat on their back
Older child (> 8 years old): some level of head support to achieve ‘sniffing’ position
Practical Face Mask Ventilation
Select a mask of the correct size – the mask should enclose the nose and mouth but not cover the eyes (Figure 23.1). Using a uniform three-step technique enhances chances of successful face mask ventilation.
1. Open the patient’s mouth. This usually clears the tongue from resting on the palate – a classic cause of airway obstruction in small children.
2. Place the mask. Maintaining mouth opening, the mask is placed, base first, on the jaw then the mask apex is rested on the bridge of the nose.
3. Apply jaw thrust. Jaw thrust effectively moves the base of the tongue away from the posterior wall of the oropharynx.
Consider omitting chin lift as this may lead to pressure applied at the submental region causing partial or complete airway obstruction.
Other practical tips:
Supporting the weight of the anaesthesia circuit prevents traction on the face mask.
Occasionally a two-person technique is needed when maintaining a tight mask seal and jaw thrust. The assistant (or the ventilator) does the ‘bagging’.
Placing the child in the lateral position during mask ventilation can be helpful, especially in children with micrognathia.
Upper airway obstruction (e.g. hypertrophic tonsils) can usually be relieved by applying CPAP of 5–15 cmH2O. Splinting the airway in this way pushes soft tissue aside, and is a valuable and atraumatic strategy that should be used before insertion of airway adjuncts.
The Oropharyngeal Airway
The oropharyngeal airway is helpful in obtaining ‘tongue control’ in patients with no gag reflexes.
Sizing: the base of the oropharyngeal airway is positioned at the angle of the mouth; the tip should almost reach the angle of the jaw. If the oropharyngeal airway is too small, it will fail to ‘cup’ the base of the tongue and relieve the upper airway obstruction. If too large, it may cause hypopharyngeal trauma and/or laryngospasm.
Insertion: the standard technique is to use a tongue depressor, followed by ‘tip down’ atraumatic introduction. Alternatively, it can be inserted ‘tip up’ and rotated 180° on reaching the soft palate, before advancing into its final position.
The Nasopharyngeal Airway
The nasopharyngeal airway is a powerful tool in paediatric airway management during induction as well as recovery and readily overcomes supraglottic obstruction when correctly placed.
Commercial nasopharyngeal airways exist but soft uncuffed tracheal tubes (e.g. Portex Ivory) can be also be used for this purpose (see Figure 23.2).
Sizing: nasopharyngeal airway size should match the child’s tracheal tube size estimate. Insertion depth is estimated by the distance from the nares to the ipsilateral tragus of the ear.
Insertion: the lubricated nasopharyngeal airway can be inserted for immediate relief of upper airway obstruction, as it is much better tolerated by a child than the oropharyngeal airway. As target depth is approached, listening for breath sounds is advised. Gentle manipulation helps determine optimum positioning. Care must be taken to ensure a nasopharyngeal airway without a flange does not migrate inwards and get lost!
Laryngoscopy and Intubation
Basic Laryngoscopy
A selection of laryngoscope blades and handles exist, and for the healthy child most are effective. Introduction of the blade should be gentle and under direct vision at all times. Passing the base of the tongue, the rate of blade advancement should be reduced and finalised in small increments until optimum position is reached. Never use the laryngoscope as a fulcrum as gum and/or teeth damage can result.
One-person technique: hold the laryngoscope close to the hinge; this provides great control and makes your fifth finger available for external laryngeal manipulation in neonates, leaving the right hand available for tube insertion.
Two-person technique: sitting down, resting elbows on the operating table, the left hand supports the laryngoscope and the right hand can be used to manipulate the larynx. As direct vision of the glottis is established, the anaesthetist shifts the torso to one side, elbows still in place. An assistant confirms view of the cords and intubates the trachea.
Curved (Macintosh) blade laryngoscopy: this curved blade can be used in all age groups. The tip is placed in the vallecula and gentle ventral force is applied, to mobilise the epiglottis, facilitating direct vision of the cords and intubation. This technique can be challenging in neonatal airway management due to the high position of the larynx, and the long and floppy nature of the epiglottis. Failure to mobilise the epiglottis may necessitate gentle direct lifting of the epiglottis, if a straight Miller blade is not available.
Straight (Miller) blade laryngoscopy: the straight Miller blade is designed for airway management of the neonate and small child. The blade is advanced carefully over the body of the tongue, or in the right gutter of the mouth, aiming for the midline and the epiglottis. As the epiglottis is reached and lifted the glottis is exposed. The tracheal tube is either introduced ‘free hand’ or slid down the concave groove of the Miller blade and ‘railroaded’ into position.
The Tracheal Tube
These are classified according to internal diameter (ID) measured in millimetres. The smallest uncuffed tracheal tube measures 2.0 mm ID and the smallest cuffed equivalent is 3.0 mm ID, with both types increasing in size by 0.5 mm increments.
Importantly the outer diameter (OD) reflects the amount of space taken up by the tracheal tube once placed in the airway. The relation of ID and OD varies greatly depending on tracheal tube type. The OD of the uncuffed tracheal tube is only modestly greater than the ID whereas the cuffed tracheal tube has a thicker wall (housing the cuff inflation canal) and larger OD. A flexible tracheal tube has a wire-reinforced wall and correspondingly large OD.
In patients with airway pathology, it is advisable to specifically consider OD as part of the tube selection process.
The uncuffed tracheal tube: the uncuffed tracheal tube has traditionally been chosen in children younger than 8 years. High reintubation rates (as high as 30%) and risk of endothelial damage due to the snug fitting of the circular tracheal tube in the elliptical cricoid aperture are real drawbacks.
The cuffed tracheal tube: the cuffed tracheal tube has gained popularity in recent years for many reasons. Modern paediatric cuffed tubes have very soft high-volume low-pressure cuffs. It can be used in neonatal airway management, with minimal risk of post-extubation stridor, providing cuff pressure is kept low (preferably < 15 cmH2O, never above 30 cmH2O). The cuff provides a good seal protecting against aspiration, and enabling controlled ventilation in the presence of poor lung compliance or high airway resistance. A smaller tracheal tube (usually by 0.5–1.0 mm) than usual can be selected (see below).
Sizing
Diameter: a conservative approach to tube selection size should be taken to minimise the risk of airway trauma. Following these recommendations only 1% of patients need reintubation/change of initial tube.
Uncuffed tracheal tube size (ID in mm)
| Preterm 1000 g: | 2.5 |
| Preterm 1000–2500 g: | 3.0 |
| Neonate to 6 months: | 3.0–3.5 |
| 6 months to 1 year: | 3.5–4.0 |
| Children 1 to 2 years: | 4.0–5.0 |
| Children 2 to 8 years: | Age (year)/4 + 4 |
Cuffed tracheal tube size (ID in mm)
For preparation, it is advised to pick three tracheal tubes: one of the estimated size and one each of one size smaller and larger.
Insertion depth: the aim should be to stop advancing the tracheal tube as the cricoid is passed. Some tracheal tubes have insertion depth markers to aid insertion. In any case an insertion depth estimate is practical. Consider using the following equations:
Intubation insertion depth estimate (all ages)
| Oral Or (> 2 years): | uncuffed tracheal tube ID (mm) × 3 |
| Oral: | age (year)/2 + 12 |
| Nasal: | age (year)/2 + 15 |
Some preformed oral tracheal tubes such as the Ring–Adair–Elwyn tube have a bend-to-tip distance that may be critical. These may be used during tonsillectomy and there is a danger, particularly if a larger tube is used, that compression by the Boyle–Davis mouth gag (see Chapter 26) could advance the tube causing endobronchial intubation.
Fixation
Although many techniques exist, none is emphasised here. The key point is that securing the tracheal tube (to prevent displacement and advancement into the main bronchus) is vital, especially in difficult airway management. In any episode of perioperative desaturation, accidental tracheal tube displacement and endobronchial intubation should be considered.
The ‘DOPES’ Mnemonic
Due to the unique anatomy and physiology, the child is at particular risk of perioperative complications. DOPES is a mnemonic, aiding systematic assessment of perioperative desaturation and/or high airway pressure in the intubated child.
Displacement: tracheal tube displacement is critical and must be identified without delay. Extubation results in loss of capnography trace. Endobronchial intubation causes reduced tidal volume in pressure-controlled ventilation or elevated airway pressure during volume-controlled ventilation.
Obstruction: secretions must be cleared. The Boyle–Davis mouth gag may cause compression or obstruction by kinking. Kinking also may occur under a hot air warming device as the soft plastic of the tracheal tube warms and softens.
Pneumothorax: may complicate neonatal resuscitation and is infrequently seen in paediatric trauma. Early diagnosis (ultrasound assessment looking for lung sliding may be beneficial) and decompression is required as soon as possible.
Equipment: if anaesthesia apparatus failure is suspected, ventilation with auxiliary equipment must follow for immediate relief and safe problem solving.
Stomach: difficult bagging can cause massive accumulation of air in the stomach. Routine gastric decompression is advised. If forgotten difficult ventilation may ensue. Decompress immediately.
Supraglottic Airway Devices (SGAs)
The classic laryngeal mask airway, cLMA, was introduced for paediatric use in the late 1980s, as a downscaled version of the adult cLMAs. Second generation SGAs (i-gel, ProSeal LMA, LMA Supreme, Ambu AuraGain) are available with a wide array of specifications (Table 23.1). Use of an SGA as a conduit for intubation is more common in children than in adults. When using an SGA with an air-filled cuff a manometer should always be used to measure cuff pressure (never exceed 60 cmH2O). The appropriate size for a given age or weight is not standardised across different SGAs so it is important to consult manufacturer’s instructions for use when selecting a paediatric SGA. In the presence of airway leak during controlled ventilation with an SGA it is useful to consider ‘up-sizing’ the device.
Table 23.1 Supraglottic airways for use in the paediatric population
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