- Paediatric airway anatomical differences to adult and how to overcome them
- Airway assessment
- Preoperative considerations, planning and emergency preparation
- Induction of anaesthesia in a patient with a potentially difficult airway
- Congenital syndromes that have specific airway considerations
- Calculations and formulas for airway devices
Paediatric airway differences to adult and how to overcome them
If you were explaining this in the viva, I think I would structure it anatomically from head to lungs:
|Paediatric airway compared to adult||Adaptations for paeds|
|Head||Large head compared to body size||Head in neutral position (instead of sniffing the morning air) to visualise the glottis. Tips: blankets/pillows under the trunk lowers the occiput in relation to the back|
|Short neck||Would be difficult to perform a tracheostomy|
|Nose||Neonates preferentially nose breathe|
|Narrow nasal passages easily blocked and high resistance||Careful sizing of ETT and NGT and suction from nostrils: ETT size = age/4 + 4 (age > 1 years) or Broselow measurement or approximate size of little finger (-1 if cuffed tube).|
|Mouth||Large tongue||LMA sizes: |
1: up to 5kg
|Teeth||More likely to have loose teeth|
|Epiglottis||Long and stiff and U shaped, flopping posteriorly|
|Larynx||Higher than adults|
|Funnel shaped (adults cylindrical) and narrowest at level of cricoid cartilage (adults vocal cords) and has anterior angulation||Straight Miller blade instead of curved Macintosh for neonates and infants. |
Size 0 if <4kg
Curved blade after child is 6-10kg
|Fragile mucosa and tendency to swell and form oedema. 1mm oedema can narrow a baby’s airway by 60%||Uncuffed ETT with appropriately calculated size until 8-10 y of age, or a special micro cuff tube (high volume low pressure). |
If using uncuffed, an appropriate leak should be present (too small risks oedema, too large risks ventilation problems)
|Trachea||Short, in line with right bronchus||Tube length should be calculated, always auscultate to check for endobronchial intubation, tape and secure carefully to prevent migration of tube. |
Depth from lower lip (cm) = age/2 + 12 (oral intubation).
OR Internal diameter x 3 for an oral ETT and add 2cm for a nasal tube is easier to remember.
Depth from nares (cm) = age/2 + 15 (nasal intubation)
Tip: Secure ETT with elastoplast and at least one fixed point is on the less mobile maxilla. Recheck tube length when taping.
|Highly compliant trachea||Risk of tracheomalacia|
|Lungs||Chest wall significantly more compliant, FRC relatively low compared to adults. FRC decreases with apnoea and anaesthesia, and closing volume > FRC until 6-8y of age, causing lung collapse and airway closure at end respiration||IPPV for neonates and infants during anaesthesia, with PEEP and higher respiratory rates. CPAP during spontaneous ventilation improves oxygenation and decreases work of breathing. |
RR = 24 – age/2
Spont TV = 6-8ml/kg
IPPV TV = 7-10ml/kg
|Minute ventilation is rate dependent as there is little means to increase tidal volume due to horizontal ribs preventing bucket handle action. Main ventilatory muscle is diaphragm so bulky abdo organs or stomach filled with gas can splint the diaphragm and reduce the ability to ventilate adequately||Decompress stomach to improve ventilation|
|Work of respiration may be 15% oxygen consumption and in infants <1y, muscles of ventilation are easily subject to fatigue from lower percentage of type 1 muscle fibres in the diaphragm||Lower threshold for ventilation management|
|Alveoli thick walled at birth and 10% of total number of alveoli found in adults|
|Apnoeas are common post operatively in premature infants – significant if >15 seconds and associated with desaturation or bradycardia||Caffeine 10-20mg/kg oral or IV preoperatively may be useful, ensure post operative apnoea monitoring|
|Physiological dead space = 30% and increased by anaesthetic equipment||Paediatric circuits and T piece if <25kg, ensure your machine spirometry is programmed using paediatric circuit otherwise your tidal volumes will be wrong|
Routine preoperative assessment AND
Special features in history:
- Previous airway attempts, NICU stay, duration of invasive ventilation
- Congenital syndromes that are related to airway anomalies (see section below)
- Other comorbidities eg. respiratory, seizures, congenital cardiac lesions, neuromuscular disorders and susceptibility to malignant hyperthermia
Signs and symptoms of an easily obstructed airway:
- OSA: history of apnoea episodes, day time somnolence, snoring
- Stridor and increased work of breathing
Special features of clinical examination:
- Dentition – loose teeth
- Chin – Overbite, recessive
- Mouth opening
- Head and neck mobility
- Facial anomalies (micro/retrognathia, mid-face hypoplasia)
- Anomalies of palate and mandibular floor
- Assessment of thyromental distance
The COPUR index below may be useful.
What to tell the patient’s parents and patients if appropriate:
- I often describe the set up of the anaesthetic room and mention that there will be a few people there and what their roles might be
- Explain the issues if any, and if applicable, the possibility of having a surgical airway.
- Discuss premedication if needed, and procedure of an inhalational/intravenous induction.
- It is important to highlight that once the patient is asleep, that the parent has to leave the anaesthetic room with the paediatric nurse or play specialist or escort immediately. I usually tell them during the pre-operative visit that the reason for this is to allow us to concentrate on looking after their child and keep their child safe. I recheck that they understand the plan when they come to the anaesthetic room and confirm with the nurse/play specialist/escort that they also understand that when we give the signal they have to leave with the parent. Hopefully doing this removes one piece of your cognitive burden when anaesthetising children with potentially difficult airways (or just any child in general!).
Planning for induction
- ENT surgeons (may need to scrub)
- ODPs (specialist ODPs with paeds/airway experience are invaluable if looking after particularly high risk children)
- Theatre staff
- Other anaesthetists (paediatric specialist anaesthetists, PICU, or airway specialists are all worth their weight in gold if you anticipate problems with the airway)
- Ward staff and play specialists
- Recovery or PICU/PHDU nursing staff
Theatre? ED? PICU? NICU? ENT specific theatre?
Consider staff familiarity with the location.
- Premed plan
- Induction plan (IV/inhalational)
- Cannula plan (US guided/central line/IO)
- Mask ventilation plan, which may include HFNO
- Airway plan (in DAS format, plan ABCD)
- Maintenance plan (TIVA/inhalational)
- Analgesia plan which may include regional
- Post op plan which may include planning a PICU/PHDU admission
- Preparation for emergencies (see below)
- Muscle relaxation
Equipment: A lot may be available on the paeds difficult airway trolley but always check it anyway!
Monitoring: BP, sats, ECG, capnography, temperature, glucose, invasive blood pressure, CVP, urine output
Checklists: Intubation checklists, difficult airway algorithms, AAGBI quick reference handbook
Airway: oropharyngeal, nasopharyngeal devices, LMAs, iGels, different sized tubes, laryngoscopes (miller/mac), video laryngoscopes (including hyperangulated), bougie/stylets of the correct size (may need shaping beforehand), syringe for cuff inflation, fibreoptic scopes, suction, NG tubes and syringes, elastoplast, eye protection, optilube, gauze, pillows and shoulder rolls for positioning
Breathing: Face masks, paediatric circuit (circle) or T piece with Jackson Rees modification (ensure you also have the little white connector for T piece to oxygen cylinder), correct settings on anaesthetic machine and ventilator, capnography, STETHOSCOPE
Cannula: US machine, different sizes of cannula, flushes, dressings, intraosseous box, infrared vein finders, fluids (may need Burette)
Sedation: TIVA, volatile, N2O if using
Analgesia: US machine, caudal equipment or regional equipment if using, nerve stimulator if using, nurse controlled analgesia pumps
Temperature control: Underbody or overbody bairhugger and temp probes and fluid warmers if needed, blankets and head wrap
Glucose control: BM machine and glucose solution in cupboard
Possible emergencies and key things to prepare:
Laryngospasm – Propofol, suxamethonium IV and IM with blue needle in tray with doses written down based on weight
Difficult face mask ventilation – DAS guidelines for difficult face mask ventilation in paeds, supraglottic device, mask, circuit, NGT
Difficult intubation – DAS guidelines for unanticipated difficult intubation in paeds, and equipment as above
Can’t intubate, can’t oxygenate – DAS guidelines for CICV in paeds, jet ventilation and ENT equipment based on surgical preference. Important to consider having either a manual jet system (manujet) or automatic jet system (eg. typhoon) ready if this might be required because it will take a long time to set up and acquire in an emergency. Sugammadex with dose calculated should be available. Cannula for cricothyroidotomy techniques if needed with site marked if this is a concern before induction.
Regurgitation – Suction
Vagal responses and bradycardia – atropine and glycopyrrolate drawn up with doses written down based on weight
Haemodynamic instability – paediatric crash trolley available, fluids calculated and prepared in a burette
Anaphylaxis – box ready
Induction of anaesthesia in a child with a potentially difficult airway
Difficult airway = difficulty establishing intubation/ventilation by a suitably trained practitioner with adequate airway experience
|Inhalational induction||IV induction|
|Advantages||Maintains spontaneous ventilation|
Less distressing than IV especially if no topical LA available
|Safer as all emergency drugs could be administered IV in a titratable manner|
|Disadvantages||Airway has to be held open while IV access gained – 2 person technique|
If laryngospasm, difficult to administer emergency drugs and may take longer to work
|Unpleasant for child especially if difficult to cannulate|
Inhalational: ‘Blow up balloon’, ‘scuba diver mask’, ‘guess the fruit’, sitting on parents’ lap with clear +/- sweet smelling mask held tightly to the face, start with 1-2% sevo then up to 8% with or without N2O (eg. 6 L O2, 4L N2O, 8% sevo). Once asleep, assistant holds airway open and applies CPAP via T piece open ended bag if necessary and monitors capnography trace. IV access gained and flushed. At this point, some practitioners give muscle relaxant -> intubate; or some will also give some fentanyl or propofol with muscle relaxant -> intubate. If using the latter technique, many practitioners will dial down the N2O and sevo to target MAC 1.4-1.6 for intubation. Some even turn off N2O at this point.
Intravenous: If difficult airway anticipated, or history of OSA, propofol is best used as a sole agent for induction + muscle relaxant before intubation, and inhalational or TIVA maintenance depending on familiarity with TIVA. Fentanyl’s effect on respiratory drive may lead to difficulties establishing spontaneous ventilation again if difficult intubation/ventilation or after waking up in recovery. You have to titrate these risks against the hypertensive response and risk of laryngospasm if fentanyl (or another opioid) is not used.
Antisialogogues: Glycopyrrolate 4 µg kg−1 given i.m. an hour before intubation can help with salivation but for it to work you do have to wait the time.
Topicalisation: For patients with very difficult airways, spontaneous ventilation is preferred with topicalisation of the airway for intubation. Use a MADgic device (photo below) for topicalisation, it gives all the following benefits shown in the photo. Lidocaine dose 3mg/kg but doses up to 9mg/kg have been used.
Bag mask ventilation:
Dr Arnie Choi from OUH does a brilliant talk for Oxford trainees available here with password protection.
- Oxygenation is a priority.
- Triple airway manoeuvre: Head tilt (shoulder roll), jaw thrust, open mouth (make sure to move the tongue away from palate)
- Consider oropharyngeal/nasopharyngeal airway.
- Ensure mask is well fitting.
- Nasogastric tube should be available to decompress later
Video laryngoscopy is a learning curve – 3 common problems:
- Depth of view – too close to the cords. Solution – pull back and realign sagittal axis.
- Tube going off to the side – Solution – can rotate the handle of your laryngoscope clockwise or anticlockwise in the coronal axis
- Anterior impingement (despite good view) – Solution: retract stylet/bougie/tube slowly and rotate it anticlockwise.
- Check for a leak before extubation
- Have all the airway devices used at the beginning ready in case this is needed
- Surgeons should stay in theatre for high risk extubations
- Consider deep switch to LMA for a smoother extubation
- Nil by mouth for 2 hours post topicalisation of vocal cords (stickers on anaesthetic charts/recovery handover sheets)
- Suction available
- Emergency drugs available
- Higher dependency monitoring or a ward where post op apnoea monitoring is available after extubation
Congenital syndromes with airway considerations
These are the syndromes mentioned in the CEACCP article, but there are many many more conditions that may lead to difficult airways.
- Trisomy 21
- Beckwith-Wiedemann syndrome
- Pierre Robin sequence
- Treacher Collins syndrome
- Goldenhar syndrome
- Apert’s syndrome
- Klippel-Feil syndrome
Definition: Genetic disorder caused by presence of all or part of a 3rd copy of chromosome 21, most common chromosomal abnormality (1:600-800 live births)
Airway problems: Short neck, relative macroglossia, microdontia, mid facial and mandibular hypoplasia, atlantoaxial instability with vertebral ligamentous abnormalities, high incidence of congenital subglottic/tracheal stenosis, tonsillar and adenoidal hypertrophy and OSA
Practicalities: Laryngoscopy is usually straightforward. Use an ETT 0.5-1mm smaller than calculated size as trachea can be narrow subglottically. May need C spine precautions if concern about atlantoaxial problems (may need radiological investigation pre op) and a soft C spine collar.
Common non-airway problems to look out for: Learning difficulties (99%), separation of abdo muscles (80%), flexible ligaments and hypotonia (80%), congenital heart disease (45%) of which AVSD 40% and VSD 35%, haematological malignancies (ALL/AML), hypothyroidism, Hirschsprung’s disease risk, hearing impairment
Definition: Sporadic or autosomal dominant mutations in chromosome 11. Clinical syndrome of macroglossia, omphalocoele or umbilical hernia, and visceromegaly/gigantism. 1:14000 live births
Airway problems: Maxillary hypoplasia and macroglossia -> upper airway obstruction and difficult laryngoscopy. OSA may be present +/- pulmonary hypertension and cor pulmonale. Visceromegaly of abdominal organs may shift diaphragm upwards and reduce FRC and shorten distance from teeth to carina resulting in increased risk of end-bronchial intubation.
Practicalities: Prone or lateral positioning may help relieve upper airway obstruction to ventilate. May need assistant to pull tongue away from view with forceps to improve laryngoscopy view. Tracheal diameter may be larger than calculated so use micro cuff. Have fiberoptic bronchoscopy available.
Common non-airway problems: Cardiac anomalies, skeletal anomalies, hypothyroidism, tumours eg Wilm’s
Pierre Robin sequence
Definition: Presence of clinical triad of micrognathia, glossoptosis and a U or V shaped cleft palate. 1:8500 live births. Associated with other syndromes.
Airway problems: Hypoplasia of mandible prevents palatal shelf from fusion – resulting in retrognathia and glossoptosis and variable airway obstruction.
Practicalities: Prone positioning, nasopharyngeal airways, temporary LMA and tracheal intubation may be required in early life as risk of severe respiratory or feeding problems requiring surgical intervention eg tracheostomy, mandibular distraction or glossopexy. Degree of airway obstruction depends on how the tongue relates to the posterior pharynx. Direct laryngoscopy is very difficult, fibreoptic intubation gold standard. Laryngoscopy becomes easier with age and mandibular growth.
Treacher Collins syndrome
Definition: Disorder of neural crest formation of the 1st and 2nd branchial arches from genetic mutation of chromosome 5. 1:10000 live births.
Airway problems: Maxillary, mandibular and zygomatic hypoplasia; a high arched cleft palate, small oral aperture, abnormalities of temporal mandibular joint.
Practicalities: (opposite to Pierre Robin) – Airway management more difficult with increasing age due to decreased mandibular growth. If LMA can be inserted patients are easy to ventilate.
Common non-airway problems: Conductive hearing loss and malformed or absent ears
Definition: Hemifacial microsomia – oculoauriculovertebral syndrome
Airway problems: Facial asymmetry, asymmetrical mandibular hypoplasia, hemifacial microsomia, tracheal deviation to one side, craniovertebral abnormalities eg C1-2 subluxation and limited neck mobility.
Practicalities: Taping the side of the face mask with gauze can help improve mask seal. May need radiological evaluation before intervention. Fiberoptic is gold standard
Common non airway problems: Scoliosis, hearing loss, underdeveloped or absent internal organs
Definition: Autosomal dominant single gene defect in chromosome 10 affecting first branchial arch
Airway issues: Hypertelorism, mid face hypoplasia with narrow nasopharyngeal passages and variable choanal stenosis, a high arched palate with excessive soft tissue. Progresses with age and makes airway management more difficult. Fused cervical vertebrae in 2/3 patients usually at C5-6. Bamboo trachea from fused rings and narrowed tracheal lumen.
Practicalities: Use smaller tube than anticipated, check for tracheomalacia, bronchodilators and increasing depth of anaesthesia may be required if respiratory distress. optimise airway secretions and infections.
Common non airway problems: Limb anomalies
Definition: Sporadic triad of short neck, low posterior hairline, limited neck mobility caused by absence of fusion of cervical vertebrae.
Airway problems: Severely limited neck motion, micrognathia and mandibular anomalies. Risk of spinal cord injury during laryngoscopy, intubation and positioning. Sudden rotatory head movements induce syncope from compromised blood supply from vascular anomalies. Difficulties increase with age.
Practicalities: Careful neck movement and positioning, fiberoptic assisted intubation
Common non airway problems: Scoliosis (60%), cardiac anomalies, genitourinary abnormalities
Definition: Lysosomal storage disorder. Hurler’s syndrome is most severe and best known.
Airway problems: Difficult mask ventilation and intubation from coarse facial features (gargoylism), macroglossia,thickened nasal oral and pharyngeal mucosa, hypertrophy of adenoids and tonsils, hypo plastic mandible, reduced TMJ mobility, narrowed trachea and short, immobile and potentially unstable neck. Odontoid hyypoplasia and atlantoaxial subluxation can occur which may lead to anterior dislocation and spinal cord compression.
Practicalities: Enzyme replacement therapy (ERT) and haemopoietic stem cell transplantation (HSCT) treatment can help with airway obstruction and pulmonary complications in Hurler syndrome.
Common non airway problems: Multisystem deposition of glycosaminoglycans in bone, skeleton, connective tissues and organs. Cardiomyopathy, OSA, hepatosplenomegaly, hydrocephalus and learning difficulties
Calculations and formulas for airway devices:
Dr Choi’s talk demonstrates the airway matrix created by him and Dr Maria Rivero-Bosch for Oxford University Hospitals where they have a grid for age and equipment used for advanced paediatric airway intervention.
Weight: (Age + 4) x2
- Neonates <5kg – Mac 1/Miller 0
- Infant 5-10kg Mac 1/Miller 1
- 1-5 years 10-20kg Mac 2
- 5-8y 20-30kg Mac 2/3
- 9-16y 30-50kg Mac 3
- <5kg – size 1
- 5-10kg – size 1.5
- 10-20kg – size 2
- 20-30kg – size 2.5
- 30-50kg – size 3
ETT formula = (Age / 4 ) + 4 for uncuffed, (Age/ 4) + 3.5 for microcuff
ETT length at lips = (Age / 2) + 12
ETT length at nostril = (Age / 2) + 15
Stylets: 2mm for <5y, 4mm <16y
Bougies: 5 Ch for <5kg child, 10 Ch for up to 8y then adult 15 Ch for >9 y