Large airway obstruction in children

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Originally from Update in Anaesthesia | www.wfsahq.org/resources/update-in-anaesthesia

Large airway obstruction in children Reprinted with revisions from Update in Anaesthesia, (2004)18:44-49. Originally Royal College of Anaesthetists Newsletter 1999; Issue 47: 159-162, reused with permission. N S Morton Correspondence Email: neilmorton@mac.com part 1: caUSES and ASSESSment Opening and maintaining the airway is fundamental to the treatment of all emergency situations in paediatrics, as in adults. All resuscitation algorithms start with ABC (Airway, Breathing, Circulation) and must be qualified in trauma to include cervical spine control. The commonest cause of paediatric airway obstruction is still the child with depressed conscious level who is not positioned properly or whose airway is not opened adequately by Basic Life Support manoeuvres. Airway foreign bodies are also common and may need rapid intervention. The pattern of infective causes of airway obstruction has changed since the introduction of vaccination programmes against Haemophilus influenzae type B. There has been a marked reduction in the incidence of epiglottitis, with a relative predominance now of viral croup and bacterial tracheitis, usually caused by Staphylococcus aureus. Why are children at increased risk from airway obstruction? There are anatomical, physiological and developmental reasons for children to be particularly susceptible to airway obstruction. The nares, upper and lower airways are smaller in absolute terms in children. Resistance to air-flow (and thus the work of breathing) increases during quiet, laminar flow breathing in inverse proportion to the fourth power of the radius. A small decrease in radius of the airway increases markedly the resistance to breathing. This is even more noticeable during crying when air-flow is turbulent as resistance is then related to the fifth power of the radius. An example of this amplification effect in the upset child is to compare the increase in airway resistance when the airway narrows from 4mm to 2mm: in the quiet child the airway resistance increases 16-fold but when the child cries the increase is 32-fold. The infant has a relatively large tongue and the larynx is situated relatively high in the neck, with the epiglottis at the level of C1 at birth, C3 in the infant and C6 from puberty. The laryngeal inlet appears to lie more anteriorly because of its high position. In the infant, the epiglottis is long and omega shaped and angled away from the long axis of the trachea. The larynx is funnel shaped and is narrowest at the level of the cricoid ring compared with the cylindrical adult conformation, which is narrowest at the level of the vocal cords. The airway is more compressible as cartilage support components are less well developed. Thus, extrinsic pressure from haematomas, neoplasms, vessels or enlarged heart chambers may more readily compress the airway. The collapse of the laryngeal inlet during inspiration is a feature of laryngomalacia and the collapse of the trachea and/or bronchi during expiration occurs in tracheo-bronchomalacia. If the intrathoracic airways are narrowed from whatever cause, the extra work of inspiration and of expiration leads to large swings in intrathoracic pressure and the potential for gas trapping and hyperinflation behind the obstructed airway causing further compression of small airways. During forced expiration efforts, the intrathoracic airways may collapse down exacerbating the gas trapping effect. Hyperinflation and gas trapping also impair the function of the diaphragm which is unable to contract so efficiently from its optimal length. In infants the diaphragm has a smaller proportion of contractile elements and fewer fatigue resistant muscle fibres. The rib cage is cartilaginous and more compliant, so the diaphragm anchor points are more mobile, leading to wasted inspiratory work and the clinical sign of recession of the chest wall. The chest wall shape in cross-section is circular in the infant compared with the eliptical shape in the older child and the ribs are attached perpendicular to the vertebral column compared with the acute angle of attachment in the older child. This means that the contribution of the “bucket-handle” movement of the rib cage to inspiration is minimal in small infants and also the elastic recoil effect is much less during expiration. The intercostal muscles and accessory muscles of inspiration are also less well developed. Thus, the small infant is very reliant on the diaphragm’s contribution to inspiration and thus has few reserves when work of breathing has to increase. This is on top of the already high basal demands placed on the infant respiratory system by the higher rate of metabolism in early life. The small absolute size of airways in children means that secretions, small airway constriction, oedema or