Comparison of the Length and Shape of Various Preformed Nasotracheal Tubes

Abstract

Objective

We aimed to investigate the differences in the lengths and shapes of several preformed nasotracheal tubes (NTTs) among different manufacturers and compare our findings with a previous report.

Methods

Using reference points at the tube tip, the proximal edge of the cuff, and the flexion point, we measured tube lengths for NTTs with inner diameters of 6.5, 7.0, and 7.5 mm from 4 manufacturers: the Parker Preformed Cuffed Endotracheal Tube (Parker), the Medtronic Taper Guard RAE (RAE), the Rusch AGT Nasal Preformed Cuffed Endotracheal Tube, and the Portex Polar Preformed Tracheal Tube. Cuff lengths and shapes were also assessed. A historical comparison was then performed using a previous report from 2012.

Results

The effective lengths (distance between tube tip and flexion point) were largest for the Parker tubes (295-315 mm). The RAE and Rusch tubes had the shortest effective lengths (270-290 mm). Cuff lengths ranged from 30 to 39 mm, and cuff shapes were cylindrical, tapered, and oval. Comparison with the past data revealed substantial changes in tube lengths for Parker and RAE tubes, modest increases in cuff lengths, and a change in cuff shape from oval to tapered in RAE tubes.

Conclusion

Several changes in tube lengths and cuff lengths/shapes were noted among manufacturers relative to the historical data. These findings demonstrate that manufacturer specifications can change over time. In dentistry and oral surgery, Parker tubes may be more ideal due to their longer effective lengths because extension and/or rotation of the neck can decrease NTT insertion depth.

Preformed nasotracheal tubes (NTTs) are often used in general anesthesia for dentistry and oral surgery to secure the airway while allowing unfettered access to the surgical field. A preformed NTT is curved and flexed so that the connector faces cephalad and upward along the patient’s forehead to avoid interfering with visualization and surgery within the oral cavity. The part of the NTT between the flexion point and connector is typically not inserted into the nostril. Thus, the effective length of a preformed NTT can be defined as the distance from the NTT tip to the flexion point.

Anesthesiologists must understand the nuances of an endotracheal tube’s morphology to ensure safe tracheal intubation. Therefore, it is important to be aware of the effective lengths of each manufacturer’s preformed NTTs. There have been case reports in which the effective length was insufficient, so it is necessary to confirm any potential differences between manufacturers.^1,2 For example, if one manufacturer’s design has an effective length that is insufficient, it could cause the cuff to impinge upon the glottis when inflated. Although Soya et al³ reported in 2012 that the lengths of each part of the tube, including the effective length, differed among manufacturers, no reports have confirmed those findings since. More than 10 years have passed since that report was published, so manufacturer specifications in NTT designs may have changed.

The primary objective of this study was to compare the effective lengths, lengths of each NTT segment, and cuff shapes of current preformed NTTs among manufacturers. The secondary objective of this study was to compare the current findings with those reported over 10 years ago.

METHODS

We studied cuffed, preformed NTTs with inner diameters (IDs) of 6.5, 7.0, and 7.5 mm from 4 different manufacturers: (1) the Parker Preformed Cuffed Endotracheal Tube (MC Medical, Inc; Parker), (2) the Medtronic Taper Guard RAE (Covidien, Inc; RAE), (3) the Rusch AGT Nasal Preformed Cuffed Endotracheal Tube (Teleflex Medical Ltd; Rusch), and (4) the Portex Polar Preformed Tracheal Tube (Smiths Medical ASD, Inc; Polar).

Tube lengths were calculated based on measurements taken from each tube type and size. The effective length (A + B) was defined as the sum of the length between the tube tip and the proximal edge of the cuff (A) and the length between the proximal edge of the cuff and the flexion point (B) (Figure 1).

Figure 1.

Tube Length Measurements

Effective length (A + B) extended from the tube tip to the flexion point. A, Length between the tube tip and the proximal edge of the cuff; B, length between the proximal edge of the cuff and the flexion point.

To assess cuff length and morphology, each cuff was inflated with air to a pressure of 20 cm H₂O (Figure 2). Cuff length was measured from the distal and proximal cuff edges. Overall cuff shapes were also assessed.

Figure 2.

Cuff Length Measurements

Cuffs were inflated to a pressure of 20 cm of H₂O. Cuff length, length from the distal to the proximal cuff edges. Tube types: (a) Parker; (b) RAE; (c) Rusch; and (d) Polar.

We then performed a historical comparison by evaluating our findings on preformed NTT specifications (ie, effective length and cuff morphology) in light of the data from the 2012 report to assess for general changes in design. Changes in NTT lengths (A, B, and A + B) and cuff lengths were calculated by subtracting the 2012 measured lengths from our data. Cuff morphology changes were also assessed.

RESULTS

Effective Length

Table 1 shows the effective lengths for each of the 4 manufacturers. The effective lengths increased as NTT ID increased across all tube sizes for all manufacturers (270-315 mm). The Parker NTT designs had the longest effective lengths (295-315 mm), whereas the shortest effective lengths were found in the Rusch and RAE designs (270-290 mm). The Polar NTTs had effective lengths that were 5 mm shorter than those of the Parker NTTs, and the Rusch and RAE NTTs had effective lengths that were 25 mm shorter.

Table 1.

Preformed Nasotracheal Tube Length Measurements

ID, mm	Segment	Measurement, mm
		Parker	RAE	Rusch	Polar
6.5	A	57	65	50	50
	B	238	205	220	240
	Effective length	295	270	270	290
7.0	A	60	65	60	60
	B	245	215	220	240
	Effective length	305	280	280	300
7.5	A	60	65	60	65
	B	255	225	230	245
	Effective length	315	290	290	310

A, length between tube tip and proximal edge of cuff; B, length between proximal edge of cuff and flexion point; effective length, A + B (length between tube tip and flexion point); ID, inner diameter.

Length of Each Tube Section

Table 1 also shows the lengths of each NTT segment for each manufacturer. The Parker and Rusch tubes with ID of 7.0 and 7.5 mm had the same A values (60 mm). All 3 of the RAE tubes had the same A value (65 mm). The RAE tubes also had the longest A values and the shortest B values as compared with the other manufacturers. The Polar tubes had A values that increased as the tube ID increased.

Cuff Length and Morphology

Table 2 shows the cuff lengths and cuff shapes for each manufacturer. Polar had the shortest cuff lengths (30-35 mm) compared with the other manufacturers (33-39 mm). Polar tubes with ID of 7.0 and 7.5 mm had the same cuff lengths (35 mm), but the other manufacturers’ tubes all had cuff lengths that increased as the ID increased.

Table 2.

Cuff Length and Morphology

ID, mm	Cuff length, mm
	Parker	RAE	Rusch	Polar
6.5	33	34	34	30
7.0	34	35	36	35
7.5	39	37	38	35
Cuff shape	Cylindrical	Tapered	Cylindrical	Oval

Cuff length, length between proximal edge and distal edge of cuff; ID, inner diameter.

Both Parker and Rusch featured cuff shapes that were cylindrical. In comparison, RAE had tapered cuffs, and Polar had oval-shaped cuffs.

Historical Comparison

The comparison of our data with those from the 2012 report³ is shown in Tables 3 and 4. In comparison with the previous report, the Parker designs increased the effective lengths (A + B) by 25 mm or more for each tube size. These changes primarily consisted of increases of 27 mm or more in section B values, with minor adjustments (−2 to 2 mm) in section A values. The RAE designs decreased B values and increased A values by 10 to 20 mm, effectively bringing the cuff closer to the vocal cords. Although this did not change the effective length, it did alter the cuff position relative to the vocal cords. In contrast, the Rusch and Polar designs had very minimal changes.

Table 3.

Historical Comparison of Preformed Nasotracheal Tube Length Measurements

ID, mm		Measurements, mm
	Segment	Parker	RAE	Rusch	Polar
6.5	A	2	20	−5	0
	B	33	−20	5	3
	Effective length	34	0	0	3
7.0	A	−2	18	2	3
	B	27	−18	−2	−1
	Effective length	25	0	0	2
7.5	A	−2	10	0	8
	B	37	−10	0	−10
	Effective length	35	0	0	−2

A, length between tube tip and proximal edge of cuff; B, length between proximal edge of cuff and flexion point; effective length, A + B (length between tube tip and flexion point); ID, inner diameter. Measurements indicate a net change in tube lengths relative to 2012. Product names may vary from previous report.

Table 4.

Historical Comparison of Cuff Length and Morphology

ID, mm	Cuff length, mm
	Parker	RAE	Rusch	Polar
ID 6.5	5	12	5	5
ID 7.0	4	10	3	5
ID 7.5	9	10	3	5
Previous cuff shape	Cylindrical	Oval	Cylindrical	Oval
Current cuff shape	Cylindrical	Tapered	Cylindrical	Oval

A, length between tube tip and proximal edge of cuff; B, length between proximal edge of cuff and flexion point; effective length, A + B (length between tube tip and flexion point); ID, inner diameter. Measurements indicate a net change in cuff lengths relative to 2012. Product names may vary from previous report.

All manufacturers saw modest increases in cuff length (3-10 mm) across all 3 tube sizes. The RAE tubes saw the biggest increase (10-12 mm), whereas Rusch had the smallest (3-5 mm).

Cuff shape was unchanged for the Parker, Rusch, and Polar tubes, but the RAE tubes changed from oval to tapered cuffs.

DISCUSSION

Dental and oral surgery procedures are often performed under intubated general anesthesia,^4-7 and NTTs are often used to secure the airway and allow easy access to the surgical fields. Preformed NTTs are commonly used for nasotracheal intubation.

Incorrect placement of a cuffed tracheal tube can lead to serious complications, including glottic edema because of pressure from the inflated cuff. A series of anatomic dissections reported that the site of injury in such cases is likely the junction of the vocal process of the arytenoid cartilage and the membranous true vocal cord, approximately 6 to 10 mm below the level of the vocal cords.⁸ Thus, it is necessary to avoid positioning the NTT cuff within this likely site of injury.

Optimal endotracheal tube placement should ensure sufficient distance between the proximal cuff margin and the glottis. The patient’s head and neck may be rotated or extended during general anesthesia for dentistry or oral surgery, which can decrease the insertion depth of the tracheal tube by 2 to 2.5 cm. As such, the distance between the cuff proximal edge and the likely subglottic site of injury is recommended to be more than 2 to 2.5 cm.⁹ Therefore, the tube should be advanced at least 2.5 to 3.5 cm beyond the point where the cuff passes the glottis for patient safety and to avoid serious complications related to a malpositioned cuff, such as laryngeal nerve paralysis.

The effective length of a preformed NTT is from the tip to the flexion point. We reported previously that appropriate tube length can vary among patients of the same height.⁴ Therefore, the proper length from the patient’s external nostril to the tube tip will vary among patients. Cases in which the effective lengths of preformed NTTs were insufficient have been reported and involved tubes that were too short to enable proper intubation because the cuffs were positioned within the glottis.^1,2

In Parker tubes, a marker is added during the manufacturing process to serve as an index for positioning to ensure that the cuff is positioned below the glottis (Figure 3). This marker is designed to be used for determination of the tube insertion depth. It has been reported that Parker tubes should be inserted almost 1 cm deeper than indicated by the marker for dental and oral surgery cases.⁴ Polar tubes have a similar marker. However, the other 2 preformed NTTs that we assessed did not have a marker.

Figure 3.

Index Depth Markers

Parker and Polar have index depth markers to identify the cuff’s depth relative to the glottis. Parker tubes have 2 lines (double black arrows) and Polar tubes have 1 line (single black arrow). The other tubes have no index depth marker.

For proper or safe intubation, the distance of the tube tip relative to the carina and the distance of the cuff relative to the glottis should be used to determine ideal tube depth. For preformed NTTs, the maximum insertion depth is often limited by the tube’s flexion point. However, the bend in the preformed NTT can be straightened by force at the flexion point, allowing deeper insertion if needed. This may be possible for NTTs that are made of a soft material (eg, Polar tubes), but it may be more difficult for other NTTs made of harder materials. Forcing the tube to straighten may cause kinking of the tube, and it may also make the connector angulation less ideal. This application, straightening the NTT at the flexion point and inserting it deeper, should be considered only when necessary. As such, the effective length of preformed NTTs is generally considered to be from the tube tip to the flexion point.

Using preformed tubes with short effective lengths can be disadvantageous for patients who need the tube inserted deeper, because the flexion point is often the predetermining factor for maximum insertion depth. One case was reported in which the cuff of a RAE tube was caught on the glottis and caused air leakage, but the air leakage resolved after a switch to a Polar tube.¹ This report indicated that it was impossible to insert the tube deeper due to the flexion point, which may be characteristic of some preformed NTTs. It was reported that the distance between the external nostril and the glottis was long in the case of tall patients.^3,4 It was also reported that even in the same patient, a RAE tube (the old version) had no problems because the cuff position was closer to the tube tip and the A value was small, but a Parker tube (the old version) had problems due to its short effective length and large A value.³ In the current versions, RAE tubes may be problematic because of the increased A values and the decreased B values, which increase the cuff position relative to the tube tip, moving the cuff closer to the glottis. The newer Parker tubes are less likely to have problems because of their longer effective lengths due to increased B values and relatively unchanged A values, which reposition the cuff deeper relative to the glottis.

For safe and secure airway management, anesthesiologists should understand the specifications of each tube size and design when selecting an NTT. Soya et al³ reported that the NTT length differed among manufacturers, but no reports have since confirmed those findings. Interestingly, a recent report¹⁰ discussing the effective length of an NTT cited the 2012 report by Soya et al. However, more than 10 years have passed since that report, and because it is possible that specifications have changed, we set out to compare tube designs among manufacturers. Comparing the data from this study and the previous one from 2012, NTT specifications have changed significantly for Parker and RAE tubes. For Parker, the B value was increased to make the effective length longer. On the other hand, for RAE the A value was increased and the B value was decreased, but the effective length remained unchanged. In Parker tubes, increasing the B value should reduce the risk of the cuff compressing the glottis and traumatizing the vocal cords at the likely site of injury that was mentioned previously. Although it varied by tube size (ID), Parker generally had the longest B value compared with other tubes, whereas Polar had the next to the longest B values.

Looking at cuff length, all manufacturers saw increases in length compared with 2012. It was reported that high-volume/low-pressure cuffs created a self-sealing effect that maintained tracheal occlusion despite airway pressures exceeding cuff inflation pressures and that even when airway pressure increased, cuffs with a long tracheal contact length had smaller increases in cuff pressures.¹¹ Therefore, by increasing the cuff length of each tube, manufacturers helped to reduce pressure on the tracheal mucosa by increasing the contact area of the cuff.

Regarding cuff shape, Parker, Rusch, and Polar were unchanged; however, RAE changed from an oval to a tapered shape, which also increased the cuff length. The change to a tapered cuff was explained as a measure to prevent microaspiration, but it has also been reported that tapered-cuff tracheal tubes had no significant impact on microaspiration.^12,13 Further evaluation and study is needed to determine whether prevention of microaspiration and a reduction in postoperative pneumonia can be demonstrated when a tapered cuff is used.

Regarding the change in Parker’s effective length, the curved portion between the flexion point and the proximal edge of the cuff was elongated to increase the effective length according to the 2017 specification change notice published by the manufacturer. In that notice, the effective lengths before the specification change were 285, 295, and 300 mm for tubes with ID of 6.5, 7.0, and 7.5 mm, respectively. After the specification change, the effective lengths were described as 295, 305, and 315 mm. Because the effective lengths in the 2017 notice were longer than those reported by Soya et al³ in 2012, it is likely that the B values were increased even before the specification change notice to prevent intubation difficulties due to insufficient effective length. Even for NTTs with the same ID, different NTTs should be selected according to the patient’s body type because the specifications vary depending on the manufacturer’s specifications. Also, even for NTTs from the same manufacturer, the position of the cuff may change due to specification changes over time, so care must be taken when using NTTs of the same ID from the same manufacturer based on previous use in the patient’s history. In particular, this would seem most problematic for RAE tubes due to their shortened B value and increased A value.

In this study, RAE and Rusch had the shortest effective lengths (270-290 mm). In our previous study correlating patient height and accurate insertion depth for dental and oral surgery, linear regression analysis revealed a significant positive correlation between height and insertion depth (regression line of insertion depth, 13.84 + 0.086 64 × height).⁴ Applying the above formula, RAE and Rusch ID 6.5 tubes can be used only for patients whose height is 151 cm or less, ID 7.0 tubes can only be used for 163 cm or less, and ID 7.5 tubes can only be used for 174 cm or less. Although there is a correlation between height and accurate insertion length, there is a large variation, so even with the above heights, half of the cases will not have enough effective length. Therefore, RAE and Rusch tubes should be used only in patients with short body heights and short tracheal lengths. The correlation between patient height and accurate insertion depth has also been reported by other anesthesiologists.^14,15

The length of the tube and the position and shape of the cuff are different for each manufacturer, and product specifications often change frequently. Therefore, anesthesiologists should remain aware of product specifications so that they can select an appropriate tube when intubating a patient. During intubated general anesthetics for dentistry and oral surgery, we recommend Parker tubes due to their long effective lengths and long B values because extension and/or rotation of the neck can decrease the insertion depth of the NTT and lead to issues.

CONCLUSION

In this study, we assessed the tube lengths and cuff morphologies of preformed NTTs from 4 different manufacturers. We then compared our results with a previous report from 2012. In the preformed NTTs we assessed, Parker had the longest effective lengths, whereas RAE and Rusch had the shortest. All manufacturers had cuffs of similar lengths (30-39 mm). Parker and RAE tubes underwent the biggest changes in length compared with 2012. All 4 manufacturers saw modest changes in cuff length, but only RAE changed to a tapered cuff. NTTs with a longer effective length and a longer B value may be more ideal for cases where extension and/or rotation of the neck may occur. Anesthesia providers should select a tube likely to fit each patient individually as there is great variability among patients.

AUTHOR CONTRIBUTIONS

NN helped design and conduct the study, collect data, and write the manuscript. NK helped design and conduct the study and collect data. RO helped conduct the study. MM, Japanese Board of Dental Anesthesiologist (JBDA) helped conduct the study. TO, JBDA helped conduct the study. MN, JBDA, Board Certified Dental Anesthesiology Specialist (BCDAS) helped conduct the study. KO, JBDA, BCDAS helped design, conduct, and supervise the study and write the manuscript. All authors helpd critically reviewing the manuscript and, read and approved the nal manuscript.