PAEDIATRIC AIRWAY

Dr. Gunjan Badwaik

Professor, Department of Anaesthesia
Datta Meghe Medical College, Nagpur.

Introduction:

 The pediatric patients have significant anatomical and physiological differences compared with adults. Furthermore, there are a number of pathological processes, typically seen in the pediatric population, which present unique anatomical or functional difficulties in airway management. Paediatric patients tend to desaturate very fast compared to adults. Hence assessment and prediction of difficult airway is very important. Many instruments and devices are currently available which have been designed to aid in paediatric airway management and one should master in few of them.

Airway Anatomy:

 The airway of the pediatric patient differs in many ways. Predictably, these differences are most pronounced at birth and the most unfamiliar airway is encountered in neonates and infants under 1 year of age.[1] The head of a pediatric patient is larger relative to body size, with a prominent occiput. This predisposes to airway obstruction in asleep children, because the neck is in flexed when they lie on a flat surface. A folded towel or shoulder roll is best to achieve a neutral position of the neck and open up the airway and aligns the oral, laryngeal, and tracheal axes.[2]

The tongue is larger and the mandible shorter. In infancy, the child is an obligate nasal breather until 5 months of age. Prominent adenoids and tonsils are common in preschool children.[3] These factors contribute to loss of upper airway space which can lead to difficulty with mask ventilation, obstruction during spontaneous ventilation, and can make laryngoscopy more difficult. In addition, sedatives, hypnotic, and anaesthetic drugs cause loss of tone of upper airway muscles which can result in potential upper airway obstruction.[4]

The larynx is relatively anterior in neck. The cricoid ring is located approximately at the level of the C4 vertebrae at birth, C5 at age 6, and C6 as adult.[5] Vocal cords are not typically found at a right angle (90°) to the trachea as in adults. They are angled in an anterior-inferior to posterior-superior fashion.[2] It can make insertion of the endotracheal tube more challenging or more traumatic and will have a higher tendency to collide with the anterior commissure of the vocal folds.

The epiglottis in children is more “U” shaped (compared to flat in adults).[5] This feature makes many anaesthesiologists prefer semi-straight laryngoscope blades such as a Miller which are designed to directly lift the epiglottis out of view. The hyoid bone is the first airway structure to ossify. The flexible cartilaginous rings of the trachea can predispose to dynamic obstruction with negative pressure ventilation, especially when any partial airway obstruction exists. [5,6]

In adult airway, the narrowest portion is the glottis and the airway is cylindrical whereas the pediatric airway is funnel-shaped with the narrowest portion of the airway is at the level of the cricoid. Hence endotracheal tube passes easily though the vocal cords but may not pass through the cricoid ring. The cricoid ring in an infant is elliptical, not circular, being of larger diameter in the Antero-posterior dimension.[7] This affects the seal of cuffed and uncuffed endotracheal tubes.

Physiology:

 The pediatric patient has a number of physiological challenges which can predispose them to hypoxemia. Oxygen consumption of an infant is 6 mL/kg/min whereas in adults, it is 3 mL/kg/min.[6] This combined with lower functional residual capacity can lead to rapid desaturation during apnoea, such as during laryngoscopy. CO₂ production is likewise increased around100-150 mL/kg/min compared to the 60 mL/kg/min of an adult. Since the tidal volume (per kg body weight) is relatively consistent with that of an adult, the respiratory rate in children is higher to achieve this need for higher minute ventilation to eliminate the CO₂.[8] According to Poiseuille’s law (R =8ƞL/πr⁴ ) a small amount of narrowing (due to oedema, inflammation, intubation trauma etc.) in the already small pediatric airway could have severe consequences on respiratory function.

Airway Assessment:

The airway assessment starts with a good history from parents. Questions are directed toward eliciting indications of a potentially difficult airway. This would include any complications of birth or delivery, any history of prior trauma or surgery to the airway or adjacent structures, or of prior anaesthesia exposure. One should enquire about current or recent symptoms suggesting upper respiratory infection (URI), difficulty in breathing or feeding, hoarseness, and noisy breathing. Many syndromes are associated with potentially difficult airway management like Pierre Robin, Goldenhar, Treacher Collins, Edwards, Apert, Down Syndrome etc.

Limited head extension, reduced mandibular space, and increased tongue thickness have been the most reliable predictors of difficult intubation.[9] Some series of cases have demonstrated a relationship between mandible length and lip to chin distance being associated with Cormack and Lehane view classification.[10] In one large case series the rate of difficult laryngoscopy, as defined as Cormack and Lehane grade III or IV, was found to be 1.35%. Some factors that increased likelihood of difficult visualization included age <1year, cardiac surgery, ASA status III and IV, Mallampati III or IV, and low or high body mass index.[1]

Airway Management: Tools and Techniques

Upper airway obstruction during mask ventilation is often relieved by head tilt, chin lift, jaw thrust and the application of continuous positive airway pressure. Lateral position also improves airway patency especially in postoperative period. . The appropriate size of airway can be assessed by the distance from the anterior gum line to the angle of the mandible.[8] Nasopharyngeal airways may also be used to relive upper airway obstruction during mask ventilation.

The supraglottic airway hold advantages over endotracheal intubation for anaesthesia in children with recent URI. In one randomized trial comparing LMA to endotracheal tube, the LMA group had significantly fewer respiratory complications compared to the endotracheal tube group.[11] Two of the most popular supraglottic devices, the classic laryngeal mask airway (LMA) and proseal LMA have good data in the pediatric population to support their safety and efficacy. Once a supraglottic airway has been inserted, it is recommended that the inflation pressure be kept to less than 40 cm H₂O. This improves the oropharyngeal leak pressure and reduce the incidence of throat pain postoperatively.[8]

In younger children the epiglottis in a more anterior-posterior plane and elevating the epiglottis may be less effective. Therefore, many anaesthesiologists prefer the use of a straight or semi-curved blade designed to directly elevate the epiglottis in patients under the age of 4 or 5 years.[6] Whereas historically uncuffed endotracheal tubes were used in paediatric population to minimize pressure trauma to the subglottis, it is now believed that cuffed tubes can provide better ventilating conditions and also minimizing trauma to the delicate airway of pediatric patients. Additionally, the use of uncuffed endotracheal tubes may be associated with a higher incidence of laryngospasm.[12]

An audible air leak is usually heard at airway pressure of less than 20 cm H₂O. In one observational study median cuff pressures were found to be 40-60 cm H₂O, exceeding the commonly accepted limit of 20-30 cm H₂O.[13] So monitoring of cuff pressure is vital in safe paediatric anaesthesia practice.

There are many newer devices designed to aid laryngoscopy. These include pediatric sizes of Glidescope, Karl-Storz video laryngoscope on essentially a Miller 1 blade, Airtraq optical laryngoscope etc. Anaesthesiologist should master in one or more such devices in case of difficult laryngoscopy and intubation.

In “cannot ventilate, cannot intubate” situation needle cricothyroidotomy in preferred choice. But in the pediatric population, this may be more challenging owing to the flexible and compressible nature of the cricoid and trachea. Direct surgical approach to cricothyroidotomy is likely to be more successful.[14] The neonatal cricothyroid membrane is small, measuring only 3 mm wide and 2.6 mm tall. The hyoid bone overlaps the usually prominent thyroid cartilage, thereby making identification of crucial anatomy more difficult. Some experts have, therefore, suggested that in these youngest patients the preferred approach may be direct puncture of the trachea below the level of the cricoid.[15]

Conclusion:

The airway of the pediatric patient has a number of significant differences when compared to the adult airway and presents some unique challenges. Awareness of anatomical and physiological differences, important pathological conditions affecting children, and a knowledge of the available airway techniques and tools will allow the anaesthesiologist to formulate and execute safe and effective management of the pediatric airway.

References:

1. Heinrich S, Birkholz T, Ihmsen H, Irouschek A, Ackermann A, Schmidt J. Incidence and predictors of difficult laryngoscopy in 11,219 pediatric anesthesia procedures. Paediatr Anaesth. 2012;22:729–36. doi: 10.1111/j.1460-9592.2012.03813.
2. Carr RJ, Beebe DS, Belani KG. The difficult pediatric airway. Sem Anesth Perioper Med Pain. 2001;20:219–27.
3. Sunder RA, Haile DT, Farrell PT, Sharma A. Pediatric airway management: Current practices and future directions. Paediatr Anaesth. 2012;22:1008–15. doi: 10.1111/pan.12013. 
4. Litman RS, McDonough JM, Marcus CL, Schwartz AR, Ward DS. Upper airway collapsibility in anesthetized children. Anesth Analg. 2006;102:750–4. doi: 10.1213/01.ane.0000197695.24281.df. 
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7. Sims C, von Ungern-Sternberg BS. The normal and the challenging pediatric airway. Paediatr Anaesth. 2012;22:521–6. doi: 10.1111/j.1460-9592.2012.03858.
8. Brambrink AM, Braun U. Airway management in infants and children. Best Pract Res Clin Anaesthesiol. 2005;19:675–97. doi: 10.1016/j.bpa.2005.07.002. 
9. Frei FJ, Ummenhofer W. Difficult intubation in paediatrics. Paediatr Anaesth. 1996;6:251–63. doi: 10.1111/j.1460-9592.1996.tb00447.
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11. Tait AR, Pandit UA, Voepel-Lewis T, Munro HM, Malviya S. Use of the laryngeal mask airway in children with upper respiratory tract infections: A comparison with endotracheal intubation. Anesth Analg. 1998;86:706–11. doi: 10.1097/00000539-199804000-00006.
12. von Ungern-Sternberg BS, Boda K, Chambers NA, Rebmann C, Johnson C, Sly PD, et al. Risk assessment for respiratory complications in paediatric anaesthesia: A prospective cohort study. Lancet. 2010;376:773–83. doi: 10.1016/S0140-6736(10)61193-2.
13. Ong M, Chambers NA, Hullet B, Erb TO, von Ungern-Sternberg BS. Laryngeal mask airway and tracheal tube cuff pressures in children: Are clinical endpoints valuable for guiding inflation? Anaesthesia. 2008;63:738–44. doi: 10.1111/j.1365-2044.2008.05486.
14. Weiss M, Engelhardt T. Proposal for the management of the unexpected difficult pediatric airway. Paediatr Anaesth. 2010;20:454–64. doi: 10.1111/j.1460-9592.2010.03284.
15. Coté CJ, Hartnick CJ. Pediatric transtracheal and cricothyrotomy airway devices for emergency use: Which are appropriate for infants and children? Paediatr Anaesth. 2009;19(Suppl 1):66–76. doi: 10.1111/j.1460-9592.2009.02996.