BJA Advance Access published online on December 14, 2007
British Journal of Anaesthesia, doi:10.1093/bja/aem350
Pathways through the nose for nasal intubation: a comparison of three endotracheal tubes
1 Department of Anaesthesia, University Hospital Birmingham, Birmingham B15 2TH, UK
2 Academic Department of Military Anaesthesia, Royal Centre for Defence Medicine, Birmingham B15 2SQ, UK
* Corresponding author: Selly Oak Hospital, University Hospital Birmingham, Raddlebarn Road, Birmingham B29 6JD, UK. E-mail: j.e.smith{at}bham.ac.uk
Accepted for publication November 11, 2007.
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Abstract |
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Background: In nasotracheal intubation, there are two main pathways in the nostril through which the endotracheal tube may pass. The lower pathway lies along the floor of the nose underneath the inferior turbinate. The upper pathway lies above the inferior turbinate, just below the middle turbinate. The lower pathway may be considered to be the safer route as it is located away from the middle turbinate and cribiform plate.
Methods: We conducted a randomized controlled trial comparing the frequency with which preformed, reinforced, and thermosoftened preformed tubes pass through upper and lower pathways. Ninety-two maxillofacial patients requiring nasotracheal intubation as part of their anaesthetic management were studied. Two patients were excluded from the study at endoscopy because of atypical nasal anatomy. After the induction of general anaesthesia, a standardized traditional nasal intubation was performed with a Macintosh laryngoscope, the operators endeavouring to direct the tube along the floor of the nose. Fibreoptic nasendoscopy was then performed by passing the tip of the fibrescope 2–3 cm into the nasal cavity above and below the tube, to identify the pathway taken.
Results: Data were analysed on 30 patients in each group. Five (16.7%) preformed tubes, 17 (56.7%) reinforced tubes, and 6 (20%) thermosoftened preformed tubes passed through the lower pathway. Significantly more reinforced tubes took the preferred pathway (P=0.001). Tubes passing through the upper pathway caused significantly more epistaxis than tubes passing through the lower pathway (P=0.003).
Conclusions: Endotracheal tubes, particularly preformed tubes, frequently take the less favourable pathway during nasotracheal intubation, in spite of specific attempts to avoid this.
Keywords: anaesthetic techniques, fibreoptic; anatomy, airway; complications, intubation nasotracheal; equipment, tubes tracheal
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Introduction |
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In nasotracheal intubation, there are two main anatomical pathways in the nostril through which the endotracheal tube may pass1 (Fig. 1). The lower pathway lies along the floor of the nose, underneath the inferior turbinate. The upper pathway lies above the inferior turbinate, just below the middle turbinate. When the tube is established in one pathway, it is likely that migration of the tube to the other pathway is usually prevented by the medial border of the inferior turbinate, which approximates to the nasal septum. The middle turbinate is part of the ethmoid bone. It is a vascular structure that is attached by a thin lamella to the cribiform plate, which, in turn, forms part of the base of the cranium. Thus, trauma to the middle turbinate may lead to avulsion and massive epistaxis.2–5 Damage to the cribiform plate may result in cerebrospinal fluid rhinorrhoea or olfactory nerve injury. This is especially likely in the presence of middle turbinate hypertrophy and anatomical variations such as concha bullosa.6 Therefore, the lower pathway may be considered to be the safer route as it is located away from the middle turbinate and cribiform plate.
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Traditional teaching emphasizes the importance of not advancing the nasotracheal tube in a cephalad direction, but rather advancing it in the lower part of the nostril, along the floor of the nose, in order to minimize the risk of trauma to the middle turbinate and cribiform plate.7–10 However, the frequency with which commonly used endotracheal tubes actually pass through the lower pathway is not known. The aim of this prospective randomized study was to compare the frequency with which preformed, reinforced, and thermosoftened preformed polyvinyl tubes pass through the upper and lower nasal pathways in traditional nasotracheal intubation.
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Methods |
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After local research ethics committee approval and informed written consent, 92 ASA I and II adult patients, undergoing elective maxillofacial surgery requiring nasotracheal intubation as part of their anaesthetic management, were recruited. Exclusion criteria included morbid obesity (BMI>35), a history of nasal trauma, surgery, or obstruction, gastrooesophageal reflux, bleeding diathesis, and anticipated difficulties with tracheal intubation. All patients were asked if they had any difficulty with nasal breathing and only asymptomatic patients, who were able to breathe easily through both nostrils, were invited to participate in the study.
Two sprays of xylometazoline 0.1% (0.09 mg per spray) were applied to the nasal mucosa of each nostril approximately 30 min and then again 5 min before the induction of anaesthesia. The ECG, non-invasive arterial pressure, oxygen saturation, and end-tidal carbon dioxide were monitored. After preoxygenation with oxygen 100% for 3 min, anaesthesia was induced with glycopyrrolate 0.004 mg kg–1, fentanyl 1.5 µg kg–1, and propofol 2.5 mg kg–1, followed by atracurium 0.5 mg kg–1. Anaesthesia was maintained with isoflurane in oxygen using a face mask attached to a circle system until neuromuscular block was complete. Patients were randomly allocated to receive either a preformed (MallinckrodtTM Preformed Nasal RAETM), reinforced (MallinckrodtTM Reinforced tube), or thermosoftened preformed tube by opening opaque sealed envelopes.
The endoscopies and intubations were shared equally between the three investigators. Each nostril, in turn, was examined with an Olympus GP fibreoptic laryngoscope (diameter 4 mm) attached to an endoscopic video camera system and a videotape recorder. Videotape recordings of the endoscopies were made for later review. We followed the General Medical Council guidelines on Making and Using Visual and Audio Recordings of Patients.11 After anterior rhinoscopy, the lower and upper nasal pathways were examined systematically by passing the fibrescope underneath the inferior turbinate and then above the inferior turbinate, below the middle turbinate, in both nostrils. The presence of any intranasal abnormality was documented and the most patent nostril was selected for the intubation. If the nostrils were considered to be equally patent, a random selection was made.
Standardized traditional nasotracheal intubation was then performed using the Macintosh laryngoscope. Size 7 and 6 mm tubes were used for male and female patients, respectively. Thermosoftening of the preformed tubes was performed by immersing the tubes in sterile saline 0.9% maintained at 37 (SD 0.5)°C in a warming cabinet. All tubes were lubricated with sterile, water-soluble jelly, and McGill forceps was used to assist the intubations, as necessary. All tubes were oriented in a standard manner with the concavity of the tube facing infero-posteriorly, the tip of the tube to the right and the bevel facing left. The selected tube was introduced into the selected nostril and with the proximal part of the tube pulled cephalad, the tip was directed along the floor of the nose (Manipulation 1), in an attempt to advance it along the lower pathway. If undue resistance was encountered, the tube was redirected slightly more caudally in the nasal cavity (Manipulation 2). If resistance was still encountered, the tube was redirected slightly more cephalad (Manipulation 3), in an attempt to intubate the pathway offering the least resistance. The number of manipulations required was recorded. The resistance offered to the passage of the tube was graded as slight resistance or moderate resistance. If no clear pathway could be found, then an attempt was made to intubate the other nostril, in the same way. Ventilation was re-established with oxygen, air, and isoflurane, and an independent anaesthetist, who had not witnessed the intubation, inspected the pharynx with a Macintosh laryngoscope and recorded the presence or absence of epistaxis. Blood staining, pooling, clotting, or trickling into the oropharynx was considered to be evidence of epistaxis. The pathway taken by the tube was identified and documented by passing the fibrescope above and below the tube in the nostril, to a distance of 2–3 cm. Videotape recordings of the post-intubation endoscopies were again made for later review. If any difficulty was encountered in determining the pathway, the procedure was abandoned and the patient was withdrawn from the study.
Statistics
A pilot study indicated that more than 75% of preformed tubes took the upper pathway. We performed a sample size calculation based on the assumption that a clinically relevant difference between the groups was a 50% reduction in the tubes traversing the upper pathway. On the basis of this assumption, we calculated that a sample size of 30 participants in each group would be required for an alpha error of 0.05 and a power of 0.8. 
2 and Fisher’s exact tests with Bonferroni corrections were used to compare the pathways taken by the tubes, the number of manipulations, the estimates of resistance, and the incidence of epistaxis. ANOVA was used to compare age and weight, and 2 test was used to analyse gender. A P-value of <0.05 was considered statistically significant. Statistical analysis was performed using SigmaStat 2.03 (SPSS Inc., Chicago, IL, USA).
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Results |
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All tubes were successfully passed through the first nostril attempted. Fifty-five patients were considered to have one nostril more patent than the other and 37 patients were considered to have equally patent nostrils. In 90 patients, the tube was found to occupy either the upper or lower pathway. In two patients with capacious nasal cavities, the tubes were found to lie alongside the lower border of the inferior turbinate, in which location they were well separated from both the floor of the nose and the middle turbinate. These tubes were considered to be lying between the two pathways, and the data from these patients were excluded from the statistical analysis.
The three groups were similar in respect of age, weight, and gender (Table 1).
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Through the lower pathway, 16.7% of the preformed tubes (PT), 56.7% of the reinforced tubes (RT), and 20% of the thermosoftened preformed tubes (TPT) were passed. The clinical observations were subsequently confirmed by reviewing the videotape recordings. Compared with the preformed and thermosoftened preformed tubes, significantly more reinforced tubes passed through the lower pathway (P=0.001) (Table 1).
The number of manipulations required to pass tubes through the nose was not significantly related to the type of tube (Table 1). Although more than one manipulation was required more frequently when inserting PTs and TPTs, this difference did not achieve statistical significance. The proportion of tubes entering the lower pathway after one manipulation (21 out of 51) was significantly greater than the proportion entering after two or more manipulations (7 out of 39) (P=0.022).
It was estimated that 46% of all tubes encountered slight resistance and that 54% encountered moderate resistance. There was no difference between the proportions of slight and moderate resistance estimates between the three types of tube (Table 1). There was no significant association between the estimated resistance and the proportions of the three types of tubes entering the upper and lower pathways; however, nasal passages offering moderate resistance were associated with significantly more frequent epistaxes (28 out of 49) than those offering slight resistance (13 out of 41) (P=0.020).
Epistaxis was caused by 45.5% of all intubations. RT and TPT caused less epistaxis than PT, but this did not achieve statistical significance (Table 1). Tubes passing through the upper pathway caused significantly more epistaxis than tubes passing through the lower pathway (P=0.003) (Table 2). Table 2 also illustrates that when reinforced tubes passed through the upper pathway, significantly more epistaxis was produced than when the tubes passed through the lower pathway (P=0.008). However, the proportions of PT and TPT causing epistaxis when passing though upper and lower pathways did not achieve statistical significance.
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Reinforced tubes passing through the upper pathway caused significantly more epistaxis than when the tubes passed through the lower pathway (P=0.008)Forty-one tubes were passed through the left nostril and 49 tubes were passed through the right nostril. There was no significant relationship between the nostril used and the pathway taken by the tube (in the left nostril, 12 out of 41, and in the right nostril, 16 out of 49, took the lower pathway). There was also no significant difference between the number of epistaxes associated with left nostril and right nostril intubations (Table 2).
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Discussion |
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This investigation has shown that the great majority (97.8%) of nasotracheal tubes passed along one of the two anatomical nasal pathways1 (Figs 1 and 2). The lower pathway lies along the floor of the nose, usually at the base of the septum, underneath the inferior turbinate. The upper pathway lies above the inferior turbinate, below the middle turbinate. It is likely that migration of tubes between pathways is usually prevented by the medial border of the inferior turbinate, which approximates to the nasal septum (Fig. 2A and B). However, in a small minority of patients with capacious nostrils, the tubes were not constrained within a pathway and lay freely alongside the inferior turbinate. Nasotracheal intubation is a potentially traumatic process and standard teaching advocates that the tube is passed through the lower part to the nasal cavity in order to avoid impacting with structures associated with the ethmoid bone in the roof of the nose.7–9 The investigators thus endeavoured to pass tubes through the lower pathway by following the standardized insertion technique described. Seventeen per cent preformed tubes, 57% reinforced tubes, and 20% thermosoftened preformed tubes took the lower pathway. Significantly more reinforced tubes took the intended pathway (P=0.001). In this investigation, tubes with internal diameters of 7 and 6 mm for males and females, respectively, were used. However, the thicknesses of the two types of tube differ, the external diameter of reinforced tubes being slightly greater than that of preformed tubes. This may be considered an important determinant of the route taken by the tube. A possible explanation for the better performance of reinforced tubes is that although they are of slightly greater external diameter, they have the flexibility required to enter narrow pathways more readily, whereas preformed tubes are relatively firm and inflexible. Immersing preformed tubes in saline at 37°C certainly softened them, and resulted in less epistaxis, but thermosoftening appeared less effective in increasing their flexibility.
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The middle turbinate is an integral part of the ethmoid bone.12 It is the free, convoluted margin of a thin lamella which descends from the under surface of the cribiform plate; posteriorly, it is loosely anchored to the posterior ethmoid air cells,2 and the body of the turbinate is pneumatized in continuity with the ethmoid air cell system. The middle turbinate is associated with many functions of the nasal cavity, including olfaction, humidification, lubrication of the upper airways, regulation of airflow and temperature, and filtration.13 The olfactory nerves originate from the mucosa covering the superior and middle turbinates and run superiorly through the cribiform plate. The mucous membrane covering the turbinate is thick and vascular, its blood supply being derived from the anterior ethmoidal artery which traverses the ethmoid air cells. In addition, the lamina propria of the mucous membrane contains a plexus of large veins or cavernous sinusoids. The middle turbinate may thus be vulnerable to traumatic avulsion, of which there have been many reports in the anaesthetic literature,2–5 and this may be associated with massive epistaxis, particularly as vessels become entrapped in tight osseous canals and fail to retract.3 The application of excessive force to the turbinate may cause olfactory nerve injury13 or fracture of the cribiform plate which may be associated with cerebrospinal fluid rhinorrhoea.14
The inferior turbinate is a larger structure,15 a bone in its own right, firmly tethered to the lateral wall by the following articulations (from anterior to posterior): the conchal crest of the maxilla, the descending process of the lacrimal bone, the frontal process of the maxilla, the uncinate process of the ethmoid, and the conchal crest of the palatine bone. Despite these attachments, avulsion has occurred during nasotracheal intubation; an amputated inferior turbinate has completely occluded a nasotracheal tube16 and has also been deposited into a main bronchus.17
Anaesthetists should be aware that it is difficult to direct the nasal tubes, particularly preformed tubes, along the floor of the nose. There is a strong tendency for tubes to advance in a cephalad direction, and take the upper pathway, in spite of specific attempts to avoid this. On the first attempt at intubation, 57% tubes passed successfully through the nose and 41% of these took the lower pathway. Forty-three per cent tubes met undue resistance and one or more extra manipulations were required, since excessive force should never be used. Although the lower pathway may be considered the safer route, in the sense that it is located away from the middle turbinate and cribiform plate of the ethmoid complex, it is vital to remember that the ultimate test of suitability is still based on the feeling of ‘give’ as nasal structures accommodate the nasal tube. Further manipulations of these 43% tubes were successful in finding a route with minimal resistance, but only 18% of these tubes took the lower pathway. It appears that the lower pathway is not able to accommodate many tubes that the upper pathway can. It is not known whether narrower tubes would be more successful in cannulating the preferred pathway. Reinforced tubes are significantly more successful in this respect, although the use of these tubes has financial implications.
There were no turbinectomies in this series of patients, but 45.5% patients had epistaxes. There were significantly more epistaxes in upper pathway compared with lower pathway cannulations (P=0.003). On endoscopy, the endotracheal tube could be seen in contact with or compressing the mucosa of the middle turbinate in 90% patients (Fig. 2C), when it traversed the upper pathway. It is plausible that this is an indication of the vulnerability of the middle turbinate mucosa. The two nostrils had a similar incidence of epistaxis, confirming the findings of other studies.18 In this investigation, the tube was oriented with the bevel facing the turbinates in the left nostril and with the bevel facing the septum in the right nostril, but it was found that the two nostrils had a similar number of upper and lower pathway cannulations. This observation conflicts with those who advise that the lower pathway is more easily cannulated when the bevel of the tube faces the turbinates.19
A weakness of this type of study, which compared three types of tube, is that anaesthetist and endoscopist could not be blinded to the type of tube being used. It was also not possible to blind the epistaxis observer to the type of tube, although the observer was blinded to the number of manipulations and the ease of navigation of the tube. It is important to remember that the study was limited to patients with normal nasal airway function who had no history of nasal trauma or surgery. All the intubations were performed by experienced anaesthetists in anesthetized and paralysed patients. We can only hypothesize about whether the results of the study are applicable when spontaneous ventilation is preserved in patients undergoing nasal intubation.
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