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Efficacy of the Disposcope endoscope, a new video laryngoscope, for endotracheal intubation in patients with cervical spine immobilisation by semirigid neck collar: comparison with the Macintosh laryngoscope using a simulation study on a manikin
  1. Sang O Park1,
  2. Dong Hyuk Shin2,
  3. Kyeong Ryong Lee1,
  4. Dae Young Hong1,
  5. Eun Jung Kim3,
  6. Kwang Je Baek1
  1. 1Department of Emergency Medicine, Konkuk University Medical Center, Konkuk University School of Medicine, Seoul, Korea
  2. 2Department of Emergency Medicine, Kangbuk Samsung Hospital, Sungkyunkwan University School of Medicine, Seoul, Korea
  3. 3College of Nursing, Eulji University, Seongnam-Si, Gyeonggi-Do, Korea
  1. Correspondence to Professor Kwang Je Baek, Department of Emergency Medicine, Konkuk University Medical Center, Konkuk, University School of Medicine, 4-12 Hwayang-dong, Gwangjin-gu, Seoul 143-729, Korea; smc125{at}medimail.co.kr

Abstract

Objective To evaluate whether endotracheal intubation in patients with cervical spine immobilisation by a semirigid neck collar is easier using the Disposcope endoscope (DE), a new video laryngoscope, than with the Macintosh laryngoscope (ML).

Methods Sixty-eight medical interns who participated in a training programme for endotracheal intubation using the DE and ML were recruited to the randomised crossover trial 1 week after completing the training programme. In the trial, they used both the DE and the ML to perform intubation on a manikin wearing a semirigid neck collar. The time required to view the vocal cords and to complete intubation, successful endotracheal intubation, modified Cormack–Lehane classification (CL grade) and dental injury were recorded and analysed.

Results The mean (SD) time to view the vocal cords was significantly shorter with the DE than with the ML (10.0 (7.0) vs 20.8 (18.9) s; p<0.0001). There were higher rates of CL grades 1 and 2a (69.1% and 22.1%) using the DE than with the ML (10.3% and 14.7%). All 68 participants had a higher rate of successful endotracheal intubation using the DE than using the ML (68 (100%) vs 47 (69.1%); p<0.0001). It took less time to complete endotracheal intubation with the DE than with the ML (p<0.0001).

Conclusions In patients with cervical spine immobilisation by a semirigid neck collar, the DE may be a more effective device for endotracheal intubation than the ML.

  • Trauma
  • airway
  • RSI
  • spinal
  • respiratory
  • emergency care systems
  • emergency departments
  • resuscitation
  • training
  • chest
  • cardiac care
  • care systems
  • pre-hospital

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Introduction

Immobilisation of the neck with a semirigid neck collar is a basic emergency procedure in all patients with definite or suspected cervical spine injury.1 The application of a semirigid neck collar can prevent devastating neurological damage resulting from neck movement. When patients wearing a semirigid neck collar require advanced airway management, endotracheal intubation using the Macintosh laryngoscope (ML) may be difficult.2 ,3 Neck inline immobilisation and a collar may impede emergent endotracheal intubation because of restricted mouth opening and difficulty in viewing the glottis,

The Disposcope endoscope (DE) (Disposcope TAIWAN, Hsinchuang, Taiwan) is a recently introduced medical device for endotracheal intubation (figure 1). The DE consists of two parts. The first part is a ‘wire transmitter’, which is used for handling and for wireless connection to a portable 14.2 cm sized display screen. The second part is the ‘wire transfer (wire body)’, which includes a microcamera. The lens of the microcamera, located at the tip of the wire, enables visualization of the glottis more easily. The endotracheal tube can be placed over the wire transfer tube. Because this wire tube body is made of flexible memory metal, it can easily be substantially bent, which enables doctors to adjust it to optimum angles according to the patient and situation.

Figure 1

The Disposcope endoscope (Disposcope Taiwan, Hsinchuang, Taiwan) consists of a flexible ‘wire transfer (wire body),’ ‘wire transmitter’ and ‘portable screen’ (A). The Disposcope endoscope with endotracheal tube (B).

We hypothesised that this new device might allow faster intubation with a higher success rate than the conventional ML in patients with cervical spine immobilisation by neck collar. We therefore conducted a randomised crossover simulation study to compare the efficacy of the DE and the ML in performing endotracheal intubation on a manikin wearing a semirigid neck collar.

Methods

The study protocol was reviewed and approved by the Institutional Review Board for Human Research at Konkuk University Medical Center (approval number was KUH005126). After the study protocol was approved, participants were recruited from medical interns who attended routine airway training, and a test course was held at the clinical simulation centre of Konkuk University Medical Center.

The airway training course consisted of a 10 min standardised verbal introduction to endotracheal intubation using the ML or DE and a 50 min practice course of endotracheal intubation using the manikin trainers. In the normal airway scenario, participants practised endotracheal intubation with the two devices on SimMan (Laerdal, Stavanger, Norway) and RespiTrainer Advance with ETView (IngMar Medical, Pittsburgh, Pennsylvania, USA) airway trainer manikins.

When using the DE for endotracheal intubation, the operator first gripped the lower incisors and chin with the left thumb and fingers to open the mouth sufficiently wide. Then the operator grasped the distal third of the wire body, which was enclosed within the endotracheal tube, and held it parallel to, and above, the oral fissure. While viewing the video screen, the operator inserted the tube downward along the oropharyngeal curve and advanced the wire body within the endotracheal tube to the vocal cords. After confirming passage of the glottis, the operator pulled out the wire body at the same time as advancing the endotracheal tube. If participants were confident that they had attained sufficient skill, an intubation skill test was held with a normal airway scenario. They passed the test if they could perform three sequential successful endotracheal intubations within 30 s for each device in both airway training manikins. Participants who failed the test undertook repeated 10 min sessions of self-practice until they passed the intubation skill test.

One week after the end of the education course, participants revisited our simulation centre for the simulation trial (figure 2). After informed consent had been obtained from all participants, we presented a short introduction to endotracheal intubation using the ML or DE in patients with cervical immobilisation by neck collar, and an expert operator demonstrated the intubation (figure 3). Neck immobilisation was established by applying the Ambu Perfit ACE extrication collar (Ambu Inc., Maryland, USA) to a Laerdal airway management trainer (Laerdal, Stavanger, Norway) manikin. We randomised the groups by choosing the sealed envelope selection method. Thirty-four sealed envelopes containing ‘DE first’ labelled paper and the other 34 envelopes containing ‘ML first’ labelled paper were prepared. Each participants were assigned to either ‘DE-first group (n=34)’ or ‘ML first-group (n=34)’) (figure 2).

Figure 2

Flow diagram of the randomised controlled cross-over simulation study. DL, Disposcope endoscope; ML, Macintosh laryngoscope.

Figure 3

Endotracheal intubation using the Disposcope endoscope in simulator manikin with cervical immobilisation by neck collar: The operator grasped the distal third of the wire body, which was enclosed within the endotracheal tube (A), and held it parallel to and above the oral fissure (B). While viewing the video screen, the operator inserted the tube downward along the oropharyngeal curve (C), and advanced the wire body within the endotracheal tube into the vocal cord (D).

A cuffed endotracheal tube of 7.5 mm diameter (Mallinckrodt Medical, Athlone, Ireland) was used for all intubations. After participants used the ML or DE, a maximum of 2 min was allowed for endotracheal intubation, and operators declared the procedure completed after the conventional stylet or the wire body of the DE had been removed. Successful intubation was confirmed if we could observe visible lung expansion of the manikin during bagging with a bag-valve mask after the intubation. Failure of intubation was defined as either being unable to complete the intubation within the 2 min time limit or performing an oesophageal intubation. We used the modified Cormack−Lehane (CL) scale to classify the oropharyngeal airway view.4 CL scale was recorded by observing the video screen of DE during the intubation trial with the DE. In the intubation trial with ML, each operator reported the CL scale by review of the CL scale result at the end of the simulation trial.

The skill trainer manikin was designed to sound ‘ddal-kak’ when significant pressure was placed on the upper incisors. If ‘ddal-kak’ sounds were generated during the test, we recorded the presence of dental injury (‘yes’ or ‘no’). After the first test, participants were allowed sufficient rest (more than 1 h) before starting the crossover test. All procedures were recorded using a camcorder (Samsung Electrical, Seoul, Korea), and all the time variables were precisely recorded by review of the camcorder data.

The primary outcomes were overall success rate and time to complete intubation. The sample size was calculated according to time to completion of successful intubation. With reference to a prior manikin study,5 we predicted that it would take 20 s (SD was 10 s) to complete successful intubation using the ML and 15 s (SD was 10 s) to complete successful intubation using the DE. For an α error of 5% (two-sided) and a power of 80% in the randomised crossover between two groups, we estimated that a sample size of 64 was required, and so 68 subjects were enrolled. Because some time data included censored data (oesophageal intubation or uncompleted intubation), Kaplan–Meier analysis was used to compare the time to complete intubation between the two devices. The log-rank test was used to compare the cumulative success rate between the two devices. To compare the proportions of overall success, the presence of dental trauma and the grade of glottal view between the two groups, a χ2 test or Mann–Whitney rank sum test was used. Two-sided Student t tests were used to compare mean values. Two-sided p values <0.05 were considered statistically significant. Data were analysed using statistical software (SPSS V.17.0, SPSS Inc.).

Results

Sixty-eight participants enrolled in this study. The participants were between 26 and 35 years old (mean (SD) age 29.2 (2.5) years) and 37 were male (54.4%). Twenty-one participants had prior experience of intubation of real patients (all fewer than three cases), and 47 had no prior experience.

The mean (SD) time to view a vocal cord with the DE was significantly shorter than with the ML (10.0 (7.0) vs 20.8 (18.9) s; p<0.0001). Rates of CL grades 1 and 2a were higher (69.1% and 22.1%) using the DE than using the ML (10.3% and 14.7%) (table 1).

Table 1

Results of endotracheal intubation for each scenario

All 68 participants using the DE accomplished successful endotracheal intubation, but only 47 (69.1%) participants did so using the ML (p<0.0001). Three participants (4.4%) failed because they could not accomplish endotracheal intubation and 18 (26.5%) failed because they exceeded the time limit. Kaplan–Meier analysis of cumulative success rate related to time showed that it took less time to view a vocal cord and to complete endotracheal intubation with the DE than with the ML (all p<0.0001) (figure 4). There were more frequent dental injuries (16; 23.5%) in the group using the ML than in those using the DE (0; 0%) (table 1).

Figure 4

Kaplan–Meier analysis of cumulative success rate of the DE and ML relative to the time to view a vocal cord (A) and time to complete endotracheal intubation (B).

Discussion

This study showed that the DE had a higher success rate than the classical ML for endotracheal intubation by inexperienced operators under a simulated scenario of cervical immobilisation with a neck collar. Compared with the ML, the DE functioned better with respect to time required to see the vocal cords and to complete intubation.

According to adult trauma life support guidelines, endotracheal intubation with the ML using manual inline cervical stabilisation has generally been the standard method for airway management of patients with cervical spine injury.1 ,2 ,6 But the cervical neck collar is usually applied as the first step in trauma care, and careful removal of the neck collar may be necessary for urgent endotracheal intubation with manual inline cervical stabilisation. A device or method that could facilitate immediate endotracheal intubation without removal of the cervical neck collar would be likely to prevent delayed intubation or further cervical spine injuries by emergent removal of neck collar.

Endotracheal intubation on a patient wearing a semirigid neck collar can be a challenging procedure.2 ,3 Recently, with the development of fibre optic video technologies, portable video laryngoscopes such as the Pentax-AWS (Pentax Corporation, Tokyo, Japan) and the Glidescope (Saturn Biomedical System Inc, Burnaby, British Columbia, Canada) have been introduced to overcome this problem. Theoretically, a video laryngoscope can provide a better view of the glottis than the conventional ML, without alignment of the oral, pharyngeal and laryngeal axes. Previous studies have shown that both the Pentax-AWS and the Glidescope required a shorter time for intubation and had a higher success rate of intubation than the conventional ML in patients with cervical spine immobilisation.5 ,7–9

The DE, which was recently invented and manufactured, has obtained approval from the US Food and Drug Administration. Whereas the Pentax-AWS and Glidescope provide a view of the glottis from a microcamera embedded in the blade, the microcamera of the DE is located at the tip of the stylet-form body equipped with an endotracheal tube. This combination of video-embedded stylet-form body and surrounding endotracheal tube may have the advantage that an operator can advance the endotracheal tube more quickly on seeing the vocal cords. Another notable benefit of the DE is that the doctor can easily adjust it to achieve optimum angles in neck-immobilised patients. The wire of the DE is flexible and semirigid, allowing the operator to easily view the glottis opening by simply bending the end of the wire. Moreover, because the endotracheal tube is placed together with the wire, the operator can insert the tube immediately after view of a vocal cord.

Application of a neck collar can result in restricted mouth opening (20–30 mm), which is a major obstacle for endotracheal intubation.2 ,10 However, the DE can overcome this obstacle because the DE wire is enclosed in an endotracheal tube with an outer diameter of <10 mm. An additional benefit is that this device does not cause serious dental injury. The hard blade of the ML may cause dental injury during the procedure,11 and the likelihood of this is increased when mouth opening is restricted owing to neck immobilisation. In a simulation study using a manikin, operators may not be very concerned about damage to the teeth and therefore the incidence of dental injury may be higher than in real patients. However, we thought that some dental injuries might not be avoidable, and fear of causing dental injury can interfere with endotracheal intubation. Because the operator uses the DE without lifting the chin with the blade of a laryngoscope, the soft tube guided by the body of the DE could remove fears about causing dental injuries.

This study showed the higher possibility of successful intubation using the DE on a manikin wearing a semirigid neck collar, but it has some limitations. Because many patients who sustain cervical spinal injury have concurrent head or facial injuries, securing a view of the glottis may be hindered by blood, secretions and vomitus. In this situation, without proper suctioning, a poor view of the glottis may result in failed intubation. Securing a view of the vocal cords during endotracheal intubation using the DE without chin lift and tongue displacement may not be easy for novice operators. During the study period, we treated two patients with cervical-spine immobilised trauma in whom endotracheal intubation was attempted using the DE. One patient was successfully intubated by a well-trained emergency doctor and the other case was unsuccessful because of severe oral bleeding.

This study used a simulation setting, which has some limitations. First, a possible bias was introduced by the participants' varying levels of intubation skills. If our subjects had practised using both laryngoscopes simultaneously, then they might have acquired different degrees of skill for each type of laryngoscope. Second, our participants were not experienced doctors. Because successful intubation usually depends on the individual's skill levels, the results might differ from those of expert doctors. Third, this was a simulation design using a manikin. The manikin's model airway cannot precisely reproduce the varying conditions of real trauma patients such as bleeding, vomitus and secretions. Additionally, the emotional factors of operators in real trauma situations could not be reproduced.

To our knowledge, this is the first study to report the efficacy of this new device, and we found that the DE may be an effective device for intubation of trauma patients with cervical spine immobilisation by neck collar.

Conclusion

On a simulation manikin wearing a semirigid neck collar, the DE showed a higher success rate for endotracheal intubation, a better view of the glottis and a shorter time to complete intubation than the ML. The DE may be a promising device for performing endotracheal intubation in trauma patients wearing a semirigid neck collar.

Acknowledgments

The Disposcope endoscope was provided free of charge by Disposcope TAIWAN (Hsinchuang, Taiwan) for this simulation study.

References

Footnotes

  • Funding This work was supported by Konkuk University in 2011.

  • Competing interests None.

  • Patient consent Obtained.

  • Ethics approval Ethics approval was provided by the Institutional Review Board for Human Research at Konkuk University Medical Center (No: KUH005126).

  • Provenance and peer review Not commissioned; externally peer reviewed.

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