October 2017 Paediatric Respiratory Workbook APCP RESPIRATORY COMMITTEE
This workbook is designed to introduce to you the difference between paediatric and adult anatomy and physiology. It will also give you an understanding of the normal function of the respiratory system and clinical implications when respiratory requirements change. It is designed for you to complete before the course to increase your knowledge and highlight areas that require further understanding, which can be discussed on the day. Further pre-reading into paediatric anatomy and physiology would be beneficial. Background Respiratory failure is the most common cause of cardiopulmonary arrest in children Children are more susceptible to acute airway compromise Goal of airway management to recognise respiratory compromise, provide support and stabilise Children are not just small adults! Paediatric airway is markedly different from adult this is most evident in the infant s airway and less important as the child grows Upper airways assume adult characteristics by approximately 8 years old 1
The Tongue & Nose Paediatric Respiratory Workbook The tongue is large in relation to amount of free space in oropharynx There is significant probability for airway occlusion as there is little room for swelling One of most common causes of upper airway obstruction in unconscious infants and children Neonates are nose breathers. They are able to suck simultaneously. They are able to breathe through the mouth by what age? They need to generate physiological PEEP due to the increased elastic recoil of their lungs and prevent atelectasis What does this do to the resistance of airflow? Narrow nostrils can account for nearly % of the total resistance of airways Can you think of what can narrow the nostrils? Increase in airway resistance contributes to retention of secretions and increased work of breathing Tonsils and adenoids are relatively large, further reducing airway space 2
The Epiglottis The epiglottis is larger, lies higher and more vertical than in adults The epiglottis is what shape? It is angled away from axis of the trachea During anaesthetic, what can cause respiratory obstruction? Anatomic descent of the epiglottis begins at 2 1/2 to 3 months of age The Pharynx The pharynx is almost completely soft tissue It is fragile, what is the significance of this? It is easily collapsed, the soft palate & epiglottis make contact with the posterior wall of the oropharynx and pharynx The lumen may collapse with negative pressure and airways structure muscles depressed or paralyzed 3
The Larynx This is situated between which two structures? and How is the larynx shaped and at what position in the neck? Paediatric shape Position Adult shape Position It is higher in neck in children, this high position allows the epiglottis to meet the soft palate and make a nasopharyngeal channel for nasal breathing during suckling There is a small cricoid cartilage, a complete ring. This is the narrowest part of airway and restricted in ability to freely expand. It is severely compromised with mucosal oedema Children with repeated tracheal intubation causes swelling and obstruction, risk of acquired subglottic stenosis Subglottic airway contains loosely attached connective tissue that can rapidly expand with inflammation and oedema 4
Trachea The paediatric trachea is shorter, smaller, more cartilaginous, softer and is subject to collapse and obstruction more than adults Neutral head position needed as it compromises airway as the trachea flops in which position? Airway diameter; Young baby trachea = 5mm Adult trachea = 14-15mm Vocal cords have an angled attachment to the trachea, in the adult it is more perpendicular 5
The Chest and Thorax Paediatric Respiratory Workbook The compliance of the chest wall in infants is very high due to what? If there is airway obstruction, active inspiration often results in what? The intercostal muscles are weak, the ribcage is very compliant, the ribs are horizontal thus not allowing the action, limiting inspiration The orientation of the ribs are horizontal in the infant; by 10 years of age, the orientation is in what position? The Diaphragm The diaphragm inserts more horizontally in infants compared to the oblique insertion found in adults, function can be compromised when the child is placed in what position? Children are almost totally reliant on the diaphragm which is deficient in what type of muscle cells? 6
These muscle cells are required for continuous, repeated exercise activities muscle cells fatigue easily 10% slow twitch (fatigue resistant) fibres in young infants Increasing to 30% in children Increasing to 50-60% in adults is mainly dependent on diaphragm, the intercostal muscles cannot lift chest wall sufficiently to maintain adequate ventilation The Lungs Maturation not complete until what age? Surfactant production begins at weeks gestation, but really increases between 30-34 weeks By 36 weeks, regular breathing movements of /min are noted Breathing movements begin in utero, to prepare for the big event Relatively small numbers of alveoli are developed and present at birth 20-50 million alveoli at birth in a term infant by the age of 8 years The increase in alveoli parallels the increase in alveolar surface area 2.8 m 2 at birth 32 m 2 at 8 years of age 75 m 2 by adulthood What is the period of most rapid growth?, tailing off by about 10 years Airways are much smaller in children; small amounts of sputum can decrease the airway radius, increase the airway resistance or block the airways completely, decreasing surface area and preventing gaseous exchange What immature structures contribute to poor secretion clearance? 7
The neonate has small amounts of collagen; the elastin-to-collagen ratio changes during the first months and years of life. How would this affect the physiology of the lungs? Lung recoil increases with age in children over 6 years of age (more elastin) Respiratory muscles in infants and young children lack tone, power and coordination, reducing respiratory efficiency The cough is often weak and inefficient at clearing secretions Collateral ventilation Not as established in infants as it is in adults (2-8 years) Collateral ventilation through the pores of Kohn and Lambert s canal are not well developed in the early years Collateral pathways may help prevent atelectasis, which is more common in children than in adults 8
Mucociliary Escalator Paediatric Respiratory Workbook Mucus is produced to dissolve or trap transport mucus to central airways Cleared by or swallowing The Heart The heart is larger in proportion to the lungs than the adult The heart has very little space within the thoracic cavity due to the smaller, softer ribcage The heart rate is faster and gradually reduces as the child grows A faster heart and respiratory rate produces a higher metabolic rate, which is needed for rapid growth The myocardium of babies has less contracture and more connective tissue, thus the baby is less able to increase, relying on a faster heart rate The heart occupies 2/3rds of the left of the thoracic cavity and 1/3 of the right, leaving less space for Presence of thymus gland on CXR up to one year old Presence of any thoracic mass can further decrease room for lung expansion 9
Respiratory requirements Paediatric Respiratory Workbook Functional residual capacity (FRC) is relatively close to an adult Oxygen consumption in an infant (6ml/kg/min) is twice that of an adult Greater oxygen consumption and high metabolic rate requires high Tidal volume is relatively fixed due to anatomical structures Excessive chest wall compliance requires the infant to perform more work than an adult chest to move a similar tidal volume What is minute alveolar ventilation? Minute alveolar ventilation is more dependent on increased respiratory rate than tidal volume What does this result in the infant having to perform? Effects of Positioning Infant oxygenation is preferentially distributed to the uppermost, non-dependant lung Compliant soft chest wall does not support the lungs as well as an adult therefore infants resting pleural pressure is closer to atmospheric pressure and airway closure occurs in more dependant regions Floppy chest wall in children causes closure of dependant alveoli, directing ventilation preferentially to where? The negative intra-pleural pressure on the dependant lung is virtually abolished and thus does not ventilate much with shallow respiration in what position? There is no loading effect of the abdominal contents on the already flat diaphragm This pattern predominates in the first 10 years of life, gradually reverses in the 2nd decade, & by age 18 has converted to the adult model 10
Effects of Oedema Clinical Implications Initially able to compensate to increase respiratory demands but then what happens? Work of breathing can account for up to 40% of the cardiac output Infants initially hyperventilate in response to hypoxia, but will not sustain this and begin to slow down their breathing Children decompensate quickly As they require more oxygen they become hypoxic rapidly Respiratory distress results when? Infants have an increased metabolic rate for oxygen consumption, therefore can develop rapidly 11
Hypoxic response Infants: (? due to myocardial hypoxia & acidosis ) Pulmonary vasoconstriction Adults: Tachycardia vasodilation Well done for completing the workbook. Please bring it with you on the training day. Quick reference guide of anatomy 12