Australasian Anaesthesia 2011 - Australian and New Zealand ...

74 Australasian Anaesthesia 2011Trends in Paediatric Tracheal Tubes 75Khine et al. published the first randomised trial comparing the use of cuffed and uncuffed tubes in the paediatricanaesthetic setting in 1997. 7 In all 488 children were recruited with an average age of 3 years in each group. Agesranged from term neonates to 8 years. Outcome measures included the number of intubations required to achievean appropriately sized tube, need for fresh gas flows greater than 2 L/min indicating a significant leak, atmosphericpollution with nitrous oxide, and post-extubation croup. Khine’s study allocated a cuffed tube size according toformula Age/4 + 3, and an uncuffed tube by Age/4 + 4. For children less than 1 year of age, a cuffed size 3.0 oruncuffed 4.0 was used, although at the discretion of the anaesthetist a smaller tube was chosen for 15 of the 49children randomised to a 4.0 uncuffed tube. This suggests that in infants, a one size fits all approach to choosingan appropriate endotracheal tube is naive. Khine’s results demonstrated a correctly sized tube in 99% of patientsallocated to a cuffed tube but only 77% in the uncuffed group, necessitating reintubation with a better fitting tube.Atmospheric pollution of nitrous oxide exceeding 25 ppm occurred in 37% cases with an un-cuffed tube but in nocases where a cuffed tube was used. There was no difference in the number of patients with post-extubation stridor.From these results, Khine concludes that cuffed endotracheal tubes may be used routinely in term neonates throughto older children. There is, however, no breakdown of ages in Khine’s analysis so the reader is left wondering howapplicable the results are to a neonatal population where most controversy exists regarding cuffed tubes.Based on Khine’s publication, Murat reports a change in practice at a French Children’s Hospital. 8 After 1997,the institution changed to the use of cuffed endo-tracheal tubes exclusively. An audit conducted in 2000 showed,9845 anaesthetics, of which 55% were intubated. Over 3400 were under 8 years, and 900 were infants. There wasno morbidity attributable to the use of cuffed tracheal tubes and when data was compared to a similar auditconducted prior to the change in tube use there was considerable reduction in the operating theatre pollution withnitrous oxide.Another study by Newth et al in a paediatric intensive care setting reported outcomes from a 12 month periodfor children intubated with either cuffed or uncuffed tubes. Tube selection was at the discretion of the clinician andcuff pressure was regularly monitored to ensure a small leak at maximum inflation pressure. The outcome measuresused were the need for post-extubation adrenaline to treat stridor and the rate of failed extubation necessitatingreintubation. There was no significant difference in outcomes across 5 age sub-groups including neonates, howevernumbers in each group were not even with only 20% of neonates receiving a cuffed tube. 9 Despite this, Newthmakes the conclusion that traditional teaching of cuffed endotracheal tubes being contraindicated in children lessthan 8 years of age is “archaic”.MORBIDITYAll studies to date utilise surrogate outcome measures of laryngeal or tracheal morbidity when comparing cuffedand uncuffed endotracheal tubes. These outcomes include post-extubation stridor, need for adrenaline nebuliserspost-extubation, or need for reintubation. While these outcomes provide some measure by which comparison hasbeen made, they differ from the more meaningful outcome of subglottic stenosis. The early descriptions of prolongedintubation in children by McDonald and Stocks 2 , and Allen and Stevens 3 included cases of subglottic stenosis fromwhich recommendations were made. However, improved materials and care of intubated patients has madesubglottic stenosis an extremely rare outcome seen almost exclusively in small premature infants, intubated andventilated in the neonatal intensive care for longer periods. Josef Holzki publishes an alternate point of view, statingthat stridor is not necessarily present in spite of significant airway mucosal injury. 10 Holzki describes endoscopicfindings from children documented to have had airway trauma from intubation. Graphic pictures of airway morbidityare presented, many from children intubated with cuffed endotracheal tubes. One of his criticisms of cuffed tubesis the pressure that the ridges of an uninflated cuff can exert on the airway mucosa. Despite the compelling images,Holzki fails to produce the statistical evidence that cuffed endotracheal tubes are more likely to cause airway injury.What Holzki does raise is doubt that outcome measures used in studies are reflecting airway morbidity.In spite of these concerns editorial opinion was shifting towards a less dogmatic view of cuffed tubes in paediatrics.In 2001, Paediatric Anaesthesia published an editorial by James who examined the arguments for and againstcuffed tubes and in spite of a lack of evidence to support them being more dangerous, found there was not muchto be gained by using a cuffed tube. 11ADVANTAGES OF USING CUFFED TRACHEAL TUBESThere are, however, some instances where a cuffed endotracheal tube may be advantageous. The reduced numberof tube changes to achieve a satisfactory fitting tube has been demonstrated. 7,16 Reduced atmospheric pollution,reduced fresh gas flows 7 and improved capnography have also been shown with cuffed endotracheal tubes. James,in his editorial, raises another potential advantage. As the size of the cuffed endotracheal tube is generally one halfsize smaller than with an uncuffed tube, there is less potential for pressure from the round tube against the posteriorportions of the larynx and cricoid. The inflated cuff will therefore tend to help the tube sit centrally in the tracheafurther reducing pressure on the mucosa. 11Ventilatory mechanics are also altered by a leak around the endotracheal tube. Modern ventilators monitor leakby sensing the difference between the inspiratory and expiratory volumes. In the neonatal intensive care unit usinguncuffed tubes, tracheal tube leaks greater than 5% of tidal volume (VT) are present in 75% of all ventilatedneonates. 12 In over 40% of infants the leak was > 40% VT at some time during the period of ventilation. Sincemodern lung protective strategies rely on targeted tidal volumes, a significant leak makes instituting these strategiesimpossible. Furthermore, repetitive atelectasis and recruitment from loss of PEEP may result in mechanical stressand inflammation. Tracheal tube leak was most significant in infants with lower birth weight and smaller diametertubes placing the most vulnerable lungs at risk of errors in measuring VT. The authors make the comment that theuse of cuffed endotracheal tubes would enable better monitoring of VT and avoid the need for multiple intubationsin attempts to optimise tube size. However, since the smallest available cuffed tube is 3.0 mm internal diameterthere would not be that option in preterm and low birth-weight neonates.DISADVANTAGES OF USING CUFFED TRACHEAL TUBESDisadvantages of the use of cuffed tubes include increased cost, the need for a smaller internal diameter tubewhich has implications for suctioning and work of breathing in the spontaneously breathing child and the need tomonitor the pressure in the cuff. The ideal cuff pressure should provide a seal at inflation of the lungs but also permitperfusion of the tracheal mucosa. Mucosal perfusion pressure in small children is not well known but it has beenshown that the presence of a leak at 25 cmH2O reduces the incidence of post-extubation stridor with uncuffedtubes. 13 Cuff pressure needs to be monitored at regular intervals, if not continuously. In the presence of nitrousoxide, cuff pressures have been shown to increase above 25cmH2O within 12 minutes due to diffusion of nitrousoxide into the cuff. 14 Another disadvantage of cuffed endotracheal tubes is the small margin of error in depth ofinsertion. When the cuff of some brands of tube is placed below the level of the glottis the tube tip lies perilouslyclose to the carina. 15 Based on these findings, a new endotracheal tube (Microcuff) was developed with a shorter,low pressure-high volume cuff and a short distance from the cuff to tube tip. This design gives a wider margin ofsafety with respect to depth of insertion.The Microcuff endotracheal tube was compared to uncuffed tubes of several varieties in a large multi-centrerandomised controlled trial of over 2200 children across Europe. 16 The study included term neonates to childrenaged 5 years. Outcome measures were post-extubation stridor and the number of tube exchanges required to findan appropriately sized tube. The rate of post-operative stridor was around 4.5% for both cuffed and uncuffedgroups. When children were analysed in age groups 0 to