|Year : 2020 | Volume
| Issue : 1 | Page : 4-12
Anatomy of infant larynx and cuffed endotracheal tubes
Department of Pediatrics, University of Liége Faculty of Medicine, Liége; Department of Pediatrics, Central Hospital of Liége, Chenée, Belgium
|Date of Submission||28-Apr-2020|
|Date of Acceptance||29-Apr-2020|
|Date of Web Publication||30-May-2020|
Dr. Josef Holzki
Beienburger Street 45, D-51503 Roesrath
Source of Support: None, Conflict of Interest: None
The anatomy of the infant larynx has been discussed since 1897. Mainly, anatomists have described the particulars of the paediatric airway and have laid the base for tube selection for safe intubation of infants. The findings were similar to what anaesthesiologists, paediatric ENT-surgeons and airway endoscopists encountered in daily practice. However, since 2003, radiologists challenged the findings of anatomists, paediatric ENT-surgeons and airway endoscopists by using radiologic modalities (such as computed tomographic scans and magnetic resonance imaging) to propose quite different anatomical forms of the infant larynx. They thought that the outlet of the cricoid ring was oval shaped and that the funnel shape of the larynx had its narrowest part at the glottic level. This can be found neither in endoscopic investigations nor in fresh autopsies, the most realistic approach to the anatomy of the infant larynx. These aspects will be thoroughly discussed in this article.
Keywords: Anatomy of infant larynx, cuffed endotracheal tubes, uncuffed endotracheal tubes
|How to cite this article:|
Holzki J. Anatomy of infant larynx and cuffed endotracheal tubes. Airway 2020;3:4-12
| Introduction|| |
This article will describe and discuss the anatomy of the paediatric larynx described in literature and by recent anatomical investigations. It will further discuss the endotracheal tubes (ETTs) available for infants and children and their safety.
| Anatomy of Infant Larynx|| |
The first scientifically valid anatomical investigation of the paediatric larynx was carried out by the anatomist Bayeux in 1897. This study provided evidence of the special characteristics of the paediatric larynx. It consists of two distinct anatomical zones – the pliable, wide, distensible glottis and subglottis; and the rigid, circular/near-circular outlet of the cricoid ring (the cricoid outlet being the narrowest part) [Figure 1]a and [Figure 1]b. Several decades later, anatomist Peter confirmed Bayeux's findings in 1936. His measurements focused particularly on the dimensions of the cricoid outlet. The transverse diameter of the cricoid outlet was moderately wider than the anteroposterior diameter (ratio of anteroposterior to transverse diameter being 1:1.15). These measurements remain almost constant from newborns till about the age of 8 years. He described the lamina of the cricoid as leaning backwards in all specimens investigated, as an integral part of the funnel shape of the paediatric larynx for this age group [Figure 1]b and [Figure 2]a. He also observed that the funnel shape of the larynx can persist until the 17th year of age. However, from the 8th year of age, the glottis gradually becomes the narrowest part of upper airway. The findings of both these authors are valid even until today. These observations formed the basis for the selection of ETTs in children.
|Figure 1: Anatomical description of the paediatric larynx by Bayeux. (a) Frontal view of the paediatric larynx with a measuring rod in the lumen of the larynx and trachea. The rod could pass the glottis comfortably but not the cricoid outlet until the cricoid arch was split, permitting the passage of the rod into the upper trachea. This finding proves, in a three-dimensional way, that the outlet of the cricoid ring is unquestionably the narrowest part of the paediatric larynx. (b) Anteroposterior transection through a paediatric larynx (soot print by Bayeux) showing that the outlet of the cricoid ring is the narrowest part|
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|Figure 2: Anatomical description of the paediatric larynx by Peter. (a) Drawing of anteroposterior transection of a newborn larynx. The relief aspect of the mucosa depicts the distensible part of larynx (glottis, arytenoid cartilage and subglottic mucosal folds) outlined in red. The closely distally positioned rigid cricoid ring outlined in blue documents the outlet as the narrowest part of the paediatric upper airway [Figure 1b]. The cricoid angle between the arch and lamina demonstrates the funnel shape of the cricoid cartilage itself. (b) Endoscopic picture of infant glottis and subglottis during inspiration under inhalation anaesthesia. The cricothyroid membrane narrows the subglottic opening from anterior and the slanting lamina from posterior, ending in the far narrower outlet of the cricoid which is circular. The interarytenoid distance during inspiration is larger than that of the cricoid outlet, documenting the glottic and immediate subglottic space as wider during inspiration than the cricoid outlet. Every professional laryngoscopy can demonstrate this (adapted from lecture series by B Benjamin of the American Academy of Otolaryngology)|
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For the first time,in vivo laryngoscopic observations of the paediatric larynx were made by anaesthesiologist Eckenhoff. He reported that the glottic opening is triangular and the posterior glottis is widely distensible and measurable, tapering down to the narrower, circular cricoid outlet. He coined the term ‘funnel shape’ with the narrowest part at the outlet of the cricoid ring. The introduction of the landmark ‘interarytenoid distance', very important for evaluating the lumen of the larynx correctly [Figure 2]b, occurred later but is always visible during laryngoscopy, confirming Eckenhoff's observation.
Fayoux et al. prospectively studied the larynx and trachea of foetuses and infants from 150 postmortem examinations. They demonstrated that the larynx of prematures has a certain degree of elasticity up to 37 weeks of gestation. In the premature population, injury risks predominate in the posterior part of the glottis. This elasticity disappears around 37 weeks of gestation, with the injury risk now predominating in the subglottic region.
In 2003, Litman et al. revisited the laryngeal dimensions in nonparalysed, sedated children. They used magnetic resonance imaging (MRI) of the larynx, measuring transverse dimensions of glottis and subglottis in coronal sections. The larynx was described as a static, rigid structure. They asserted that the vocal cord level is the narrowest part of the paediatric larynx in deeply sedated children [Figure 3]a.
|Figure 3: Schematic coronal section through paediatric larynx and anteroposterior radiological image of the same. (a) Schematic coronal section through paediatric larynx (adapted from Körner/Steurer, 1944) showing the glottic level as a narrow lumen in the anteroposterior view, caused by the closed anterior commissure of the vocal cords and the collapsed subglottic space, which expands in this perspective to a wider transverse diameter towards the cricoid outlet. The widely distensible proximal part of the larynx is indicated within the red square. The nondistensible, cartilaginous ring, the narrowest part of the larynx and paediatric upper airway, is marked in blue. Coronal sections cannot demonstrate the path which tracheal tubes take into the trachea. Only wax moulds and calibrations, endoluminal measurements and modern video-sequences can visualise this. (b) Anteroposterior radiological image of a normal paediatric larynx and upper trachea showing a similar narrowing of the glottic level as in the coronal autopsy specimen, anteroposterior computed tomography scans and magnetic resonance imaging. The glottic level and the immediate subglottic space appear seemingly narrow. This is however caused by the anterior commissure and the collapsed, distensible subglottic space. A coronal section alone cannot depict the real lumen of the larynx because the cartilaginous structures of the cricoid ring are not visible in conventional X-rays, computed tomography scans or magnetic resonance imaging|
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This was completely in contrast to what was known for over a 100 years and led to considerable confusion. This confusion was compounded by contradictory statements by the authors who described the glottic opening as the narrowest portion of the larynx while at the same time asserting that the rigid cricoid ring is functionally the narrowest portion of the larynx. This assertion came about because the authors misinterpreted a common radiological artefact that is well known to radiologists. Deep sedation simulates a narrowness of the subglottic region in every patient undergoing anteroposterior X-ray investigations, regardless of age, showing the seemingly narrowest part of the larynx at the vocal cord level [Figure 3]b.
Dalal et al. added videobronchoscopy to MRI investigations in 2009. The authors investigated 128 anaesthetised and paralysed patients from 6 months to 13 years of age. They obtained static pictures by attaching distance holders to a Hopkins lens in order to photograph the glottic level and the lumen of the cricoid ring ‘at the level of the superior aspect’ with the same distance and calculated and compared both surface areas in mm2 [Figure 4]a. The endoscopic picture in their article does not show the cricoid outlet directly but from a rather large distance. The conclusion of the authors that cross-sectional areas of the glottic level under anaesthesia and neuromuscular blockade are smaller than the ‘superior aspect of the cricoid ring', however, cannot be found in their image.
|Figure 4: Normal paediatric larynx as seen through the Hopkins lens. (a) Proximal aspect of a normal paediatric larynx (Hopkins lens, adaptation of image by Dalal et al.) under anaesthesia and neuromuscular blockade with suction catheter attached to the lens as a distance holder. The left vocal cord is visible, as also the cricothyroid membrane and the superior aspect of the cricoid arch and posterior leaning lamina, documenting the level of illumination as clearly above the cricoid outlet. The transverse diameter of the cricoid inlet is definitely larger than the cricoid outlet. (b) Endoscopic in vivo findings of Dalal et al. pasted on an anteroposterior transection of an autopsy specimen, showing the area of interest of the investigators about 5 mm above the cricoid outlet. The light source is positioned at the vocal cord level as shown in Figure 4a. The light beam reaches the region of interest in the middle of the larynx ‘at the level of the superior aspect of the cricoid ring’ (outlined in blue), which is obviously above the cricoid outlet. The superior aspect of the cricoid cartilage is oval shaped and steeply slanting towards the lower, narrower circular outlet of the cricoid cartilage [Figure 5a]. Technically, there is evidence that the subglottic space is larger than the cricoid outlet. Autopsy specimen courtesy Rothschild|
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To explain [Figure 4]a in a more precise way, the landmarks were plotted on an anteroposterior-transected fresh autopsy specimen. It shows the structure of the paediatric cricoid cartilage with the anterior leaning arch and the backward tilting lamina [Figure 4]b, delineating the frame of the cricoid ring with a distinct cricoid angle as a funnel with a steeply slanting, oval-shaped entrance and a distal, circular, narrower rigid outlet. One of the reasons why discussions about the anatomy of the paediatric larynx often end in disagreement is the often inaccurate presentation of the details of the cricoid cartilage in literature.
Liu et al. reviewed the cervical computed tomography (CT) scan of patients aged 1–20 years. After performing multiplanar reconstruction and correcting the slant, they measured the transverse and anteroposterior internal diameters of the inlet and outlet of the cricoid cartilage. They concluded that the transverse inner diameter of the inlet, not of the outlet, is the smallest diameter of the cricoid cartilage. The ‘funnel shape’ of the cricoid cartilage remains unchanged during development. They recommended that the outer diameter should be considered when selecting an ETT.
The most realistic descriptions of the paediatric larynx are provided by investigating autopsy specimens. [Figure 5]a shows the steeply slanting, oval-shaped entrance of a freshly prepared cricoid ‘ring’ of an infant. The true ring part lies between the cricoid arch and the distal lamina. [Figure 5]b documents the proximal cuff of a Microcuff® tube within the outlet of the cricoid ring, whereas the oval-shaped entrance of the ring is visibly larger than the outlet when viewing the entrance of the cricoid cartilage from above [Figure 2]b and [Figure 4]a, [Figure 4]b, observing the cricoid angle [Figure 2]a and [Figure 4]b. Not understanding this unique structure is apparently one of the causes for the ongoing controversy between the circular and oval-shaped structure of the larynx because it depends on which plane of the cricoid cartilage was reconstructed in CT or MRI. A single, adequate photograph via a Hopkins lens can easily solve this controversy [Figure 2]b and [Figure 4]a.
|Figure 5: (a) Freshly prepared cricoid cartilage, showing the low cricoid arch, the four times higher lamina as posterior wall of the larynx., The entrance is oval shaped and steeply slanting towards the proximal cricoid arch. An imitation of a light source is placed ‘at the superior aspect of the cricoid ring’ as shown in Figure 4A, showing the difficulty to create comparable, horizontal transections through an infant cricoid cartilage. However, the only true circular part of the larynx, the distal cricoid outlet, is not distensible and has a height of 2.5–3.0 mm in infants (autopsy specimen courtesy M Rothschild). (b) A 3.5 mm ID Microcuff® tube positioned on anteroposterior transection through the larynx of a 2-year-old child. As indicated, the distance from the vocal cords to cricoid outlet is 15.1 mm and the cuff-free distance between the vocal cord marker and the proximal part of the cuff is 10 mm. This brings the folds of the proximal, uninflated cuff several millimetres into the cricoid outlet, exposing the mucosa to damage by the wrinkles of the cuff, particularly when the neck of the patient is moving (autopsy specimen courtesy M Rothschild. Drawings on pictures JH)|
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The importance of airway endoscopy with simple instruments is too often underestimated. The infant Hopkins lens [Figure 6] is easily available, provides pictures without pixels (glass lenses) and has a steep learning curve for its clinical use.
|Figure 6: Hopkin's lens. Battery-powered Hopkins lens with instantaneous pictures of glottis and subglottis (a) View of glottis, cricothyroid membrane, cricoid outlet and proximal trachea in the background. (b) View of subglottic space from the left vocal cord to the cricoid outlet which is clearly circular and narrower than the proximal subglottis. (c) View into the upper trachea with distal obstruction. (d) View of the injury at the cricoid outlet|
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| Endotracheal Tubes for Infants|| |
Since the early 1950s, uncuffed ETTs have been used in infants and children. This practice proved to be successful because it was easy to choose an appropriate size uncuffed tube with two basic rules:
- Never try to overcome a resistance while advancing a tube. Placement of a too large bore tube must be avoided
- Intubation should be followed by a leak test.
Millions of children have been intubated with uncuffed tubes with small numbers of complications., Movements of adequately sized, uncuffed tubes do not traumatise the mucosa. Too large tubes are the main source of injury when uncuffed tubes are used, and this is something that can be practically prevented.
The early available cuffed tubes for children were smaller versions of adult cuffed tubes without any standardisation in terms of size, shape, volume, pressure and position of the cuff. Hence, it was difficult to make a standard recommendation for selection of this tube. In addition, the cuff of most of these tubes was sitting at the cricoid ring when the tip of the tube was placed at the mid-tracheal level. Observing the pitfalls of the currently available cuffed tubes, anaesthesiologists at Children´s Hospital Zurich, led by Marcus Weiss and Andreas Gerber, promoted a low-pressure, soft (polyurethane), cuffed ETT called the ‘Microcuff® paediatric endotracheal tube (PET)'.
In recent years, use of cuffed ETTs in children has become more popular even in infants. A cuffed tube is supposed to provide a sealed airway, preventing leakage of gases and vapour, thereby decreasing theatre pollution and supposedly the cost. It also allows correct spirometry and measurement of end-tidal carbon dioxide. But what about laryngotracheal injury? Can the cuffed tube be used in infants and younger children without causing any trauma to the larynx and trachea? Let us examine the scientific evidence available as to the safety of the Microcuff® tube in infants and children.
To the present day, the properties and effects of Microcuff® tubes in relation to direct airway damage are inadequately investigated and described in detail. Industrial advertisement claims the advantages of Microcuff® PET tubes over other brands. In easily performed desktop experiments, it can be observed that the very wide cuffs are always densely wrinkled within the paediatric larynx and trachea and allow continuous aspiration of fluids even when high cuff pressures are applied [Figure 7]. It is surprising that this important reality was only hinted at in literature, testing large tubes of 7.5 mm ID. In Microcuff® PET tubes, this is quite different with significant fluid passage despite high cuff pressures [Figure 7].
|Figure 7: Comparison of 3.5 mm ID Microcuff® tracheal tubes under experimental conditions to images from industrial advertisement. (a) Cuff in artificial infant trachea with cuff inflated to an intracuff pressure of 38 cm H2O permitting tinted fluid to pass freely between the folds of cuff into the trachea independent of cuff pressure. The cuffs can never unfold to a lean surface because they are by far too large. Inspiratory phase during mechanical ventilation cannot disperse the fluid into the pharynx due to strong adhesion pressures between the folds. (b) Comparison between advertised cuff in trachea and real size of cuff which can enter the trachea only when squeezed together. The cuff can never unfold to a lean surface. (c) Deflated cuff in normal size artificial infant trachea. The wrinkles of the cuff fill the trachea tightly, always impinging on the mucosa despite an intracuff pressure of 0 cm H2O. The advertisement shows an incorrect dimension of the deflated cuff. Microcuff® paediatric endotracheal tubes cannot seal the paediatric airway. The ultrathin cuff membrane is of no advantage because the folds have to be squeezed through the larynx into the trachea and impinge constantly on the mucosa|
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The cuff-free distance on the shaft of the Microcuff® tube, although described as allowing safe placement of the tracheal tube with a cuff-free laryngeal zone, is definitely too short with the result that the proximal part of the cuff of Microcuff® tubes is always very close to or within the cricoid outlet [Figure 5]b. The question whether low-volume normal pressure cuffs (20 cm H2O) might be less traumatic to the mucosa because they are positioned at a safe distance from the cricoid outlet and form a lean surface [Figure 8] is yet to be investigated on a larger scale.
|Figure 8: 3.5 mm ID and 3.0 mm ID Microcuff® paediatric endotracheal tube, and low-volume to low-pressure cuffs placed on a demonstration board. The level of the glottis and cricoid outlet of infants 0–10 months of age is indicated. The proximal part of cuffs of Microcuff® tubes 3.0 mm ID and 3.5 mm ID is always too close or within the cricoid outlet [Figures 4b and 5b]. The cuffs are too large for the cricoid outlet and upper trachea both in the inflated and the deflated states (inserted endoscopic pictures). They can be advanced into the trachea only against the resistance of the folds of the cuffs [Figure 9]. The low-volume cuffs are not only better adapted to the airway anatomy with a longer cuff-free distance but they can achieve a lean surface within the trachea when carefully inflated. However, scientific studies with these tubes have not been carried out yet, but they are frequently used in tonsillectomies|
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If Microcuff® tubes with a purportedly safe intubation depth marking have to be checked for adequate position at the cricoid outlet/upper trachea, radiologic controls are apparently not sufficient. Figures 5b and 8 show the proximal cuff within the cricoid cartilage despite a correct placement of the depth marking at the vocal cord level. Only the proof in autopsies can show that practically all proximal cuffs of Microcuff® tubes remain within or very near the cricoid outlet, damaging the mucosa by impinging, particularly when head and neck movements are allowed.,
The details and conclusions drawn from several studies on cuffed versus uncuffed tubes as well as on cuffed tubes are enumerated in [Table 1].,,,,
|Table 1: Summary of studies on Microcuff® and uncuffed endotracheal tube|
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The frequently quoted references 14 to 18 listed in [Table 1] have deficiencies which limit the scientific validity of their conclusions. Endoscopic visualisation of the paediatric airway gives definite answers about the incidence and severity of airway injury and has been recommended since 1954. However, none of the studies have attempted endoscopic assessment of direct injury caused by cuffs. They used the entirely unreliable symptom of stridor as outcome measure in their studies. Many invasive injuries which did not show the symptom of stridor have been documented.,, Wiel et al. described that only one out of five children with postanaesthesia subglottic stenosis presented with the symptom of stridor postoperatively. The cuff-free distances of the tube shafts have not been measured directly but calculated only from the position of tube tips within the trachea. The outer diameters of deflated cuffs, the real cause of airway damage, were never reported in relation to airway damage [Figure 8].
| Trauma to the Larynx by Intubation|| |
The assertion that the narrowest part of the paediatric larynx lies at the level of the vocal cords would mean that the ETT should seal the airway at the glottic level. It has been attempted with extremely deleterious results [Figure 9]a. A cuffed tube is needed only when the easily distensible glottis is anatomically narrower than the rigid cricoid outlet, which is never the case in infancy or the preschool age. All injuries depicted in children <4 years of age [Figure 9]a could have been avoided by using adequately sized uncuffed tubes.
|Figure 9: (a) Injuries by cuffed tubes in glottis and trachea. Only glottic injury in this figure produced the symptom of stridor, not the following injuries. (b) Microcuff® tubes too large for infant airways (1) Smallest Microcuff® tube cuff being advanced with considerable force to pass the equivalent of an infant cricoid outlet. (2) 3.5 mm ID Microcuff® tube in the cricoid outlet of a 16-month-old child. The wrinkles of the cuff fold upon themselves, compressing the mucosa of the larynx. (3) 3.5 mm ID Microcuff® tube uninflated in animal trachea with an internal diameter of approximately 6.5 mm. The wrinkles of the cuff distend the trachea to a certain extent, resulting in mucosal compression. (4) Same sized animal trachea with 3.5 mm ID tube in place is now split open. The folds of the uninflated cuff protrude from the tracheal incision, impinging on the mucosa when the tube is forwarded|
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Reproducing the structure of the cricoid outlet with plastic rings with identical diameters like the cricoid outlets in infants 0 to 12 months of age, it can be observed that the grossly overdimensioned cuffs of Microcuff® tubes [Figure 9]b need always to be pushed with considerable force through the cricoid ring [b1] and fill the scarcely wider trachea tightly [b2] because high-volume to low-pressure cuffs have the tendency to fold on themselves and wrinkle also in the tracheal specimen of infant-sized animals [b3] and can cause points of extremely high pressure. While splitting such a trachea with a 3.0 mm ID Microcuff® tube in place, the folds of the cuff pop out, showing their continuous pressure on the tracheal wall [b3, b4].
Kutter et al. performed a randomised study in piglets, ventilating them for 4 h with Microcuff® tracheal tubes. One group had a cuff pressure sufficient to seal the trachea at 12 to 18 cm H2O (mean of 14 cm H2O) and the second at 20 cm H2O. The animals were sacrificed after the experiment, and scanning electron microscopy of the tracheal mucosa under the cuff was performed. The mucosa under the cuff was damaged in 85% in the lower pressure group and in 79% in the higher pressure group. In 25% of the damaged mucosa, the cilia were completely lost; in an additional 25%, the entire basement membrane was destroyed. The very high incidence of airway injury under the cuff with inflation pressure up to 20 cm H2O was reported for the first time, but found no echo in the scientific literature thereafter.
In an earlier study by Sanada et al., 18 dogs (6 of them controls) were intubated with high-volume low-pressure cuffed tubes for 4 h with live observation for 2 weeks. The average cuff pressure was set at 20 cm H2O. Outcome measures were biopsies, mucociliary tantalum clearance and scanning electron microscopy of the mucosa under the cuff. Light micrographs revealed inflammatory changes in the tracheal wall for 3 days; scanning electron microscopy showed marked ciliary injury in large areas with fragmentation of the remaining cilia. Light micrographs showed disappearance of the basement membrane at the 3rd day, remaining till the 7th day in five dogs. Appreciable amounts of tantalum dust remained in the trachea till the 3rd day. Tantalum clearance was normal after 3–5 h in normal dogs. All injuries appeared normal only after 14 days.
These outcome measures reveal how intense and long-lasting mucosal injuries by the folds of low-pressure cuffs can be. It also highlights the point that the symptom of postoperative stridor regularly misses significant airway injury., Unfortunately, two exceptional studies, are not quoted in literature recommending cuffed intubation even in neonates, but they indicate that the aspect of mucosal injuries by cuffed tubes needs more urgent scientific investigation.
Thomas et al. did a retrospective cohort study on babies weighing <3 kg admitted to the neonatal intensive care unit (NICU), wherein they compared the use of cuffed and uncuffed tubes. They observed no difference in adverse outcomes and concluded that Microcuff® tube might be safe in neonates <3 kg. No airway trauma was checked after extubation. They looked for stridor, strange but true! The NICU policy of intubating premature babies of 35 to 37 weeks gestational age (with a cricoid internal diameter of 3.7–4.2 mm) with Microcuff® PET tube whose outer diameter is 4.3 mm with deflated cuff 6.1 mm defies scientific reasoning. The cricoid ring of premature babies should never be overdistended because of actual airway damage. [Figure 9]b, [Figure 10]
|Figure 10: Smallest Microcuff® tube showing the interaction of laryngeal size and deflated cuff. (a) Deflated cuff under extubation movement. The folds of the cuff have to overcome marked resistance within the cricoid outlet. (b) Advancement of cuff through glottis of infant model with an internal diameter of approximately 6.0 mm. The folds of the cuff can pass only with considerable force. (c) The folds of the cuff getting stuck within the glottis. Note the sharp edges of the cuff attachments|
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| Conclusion|| |
The conclusion may be left to the judgment of the readers from the following paragraphs, two Editorials and a Cochrane Review.
Lönnqvist in an editorial in the British Journal of Anaesthesia and Litman et al. in an editorial in Anesthesiology on cuffed or uncuffed tracheal tubes during anaesthesia in infants and small children have subtitles ‘time to put the eternal discussion to rest?’ and ‘the debate should finally end'. Because many questions raised regarding the incidence and severity of airway injury in infants and small children by cuffs have not yet been satisfactorily answered, this statement calling for an end to a debate in such a vital field of paediatric anaesthesia seems to be an affront to science.
In a Cochrane review, De Orange et al. drew path-breaking conclusions from comparing numerous studies qualifying for review under the title Cuffed versus uncuffed endotracheal tubes for general anaesthesia in children aged eight years and under. The reviewers were unable to draw definitive conclusions from comparison of the effects of cuffed or noncuffed ETTs in children undergoing general anaesthesia because their confidence is limited by risks of bias, imprecision and indirectness in the available studies reviewed. The quality of evidence as to the lower requirement for exchange of tubes with cuffed ETTs and postextubation stridor was very low. The requirement for less medical gas used and consequent lower cost was low quality evidence since the higher cost of the cuffed tubes may be offset by the savings made with anaesthetic gases. No clear evidence emerged to suggest any difference between cuffed and uncuffed tubes for outcomes such as the need to treat postextubation stridor with tracheal reintubation, adrenaline or corticosteroid, or need for intensive care unit admission to treat postextubation stridor. The quality of evidence was very low for all these criteria.
The Cochrane reviewers suggested that large randomised controlled trials of high methodological quality should be conducted to help clarify the risks and benefits of cuffed ETTs for children. Such trials should not only investigate the capacity to deliver appropriate tidal volume but also address cost-effectiveness and respiratory complications. Such studies should correlate the age of the child with the duration of intubation, and with possible complications. Studies should also be conducted on newborn babies. Future research should be conducted to compare the effects of the different types or brands of cuffed tubes used worldwide. Finally, trials should be designed to perform more accurate assessments and to diagnose the complications encountered with cuffed as compared to uncuffed tracheal tubes.
This recommendation by the Cochrane Library cannot be expressed in a more concise and scientific way. It supports the message of this article to apply direct visualisation (endoscopy) to detect airway injury such as deep ulcers which are not accompanied by the symptom of stridor but later by subglottic stenosis.,
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Conflicts of interest
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[Figure 1], [Figure 2], [Figure 3], [Figure 4], [Figure 5], [Figure 6], [Figure 7], [Figure 8], [Figure 9], [Figure 10]