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The Shikani Optical Stylet as an Alternative to Awake Fiberoptic Intubation in Patients at Risk of Secondary Cervical Spine Injury

A Randomized Controlled Trial

Mahrous, Rabab S.S., MD; Ahmed, Aly M.M., MD

Journal of Neurosurgical Anesthesiology: October 2018 - Volume 30 - Issue 4 - p 354–358
doi: 10.1097/ANA.0000000000000454
Clinical Report

Background: Conventional intubation of the trachea and consequent prone positioning of anesthetized patients with cervical spine instability may result in secondary neurological injury. Historically, flexible fiberoptics used to be the chief choice for patients presenting with cervical spine instability surgery with difficult airway. Recently, the rigid optical stylets have shown promise in assisting difficult intubations.

Purpose: The aim of the present study was to compare the efficacy of Shikani optical stylet (SOS) with the flexible fiberscope for awake intubation in patients with cervical spine instability.

Patients and Methods: In total, 60 adult patients diagnosed with cervical instability or at risk of secondary cervical injury, who were planned for awake intubation and/or self-positioning prone, were registered in this study and were randomly categorized into 2 equal groups (30 patients each), a fiberoptic group and an SOS group, followed by assessment of coughing and gagging during intubation, time to successful intubation, number of attempts for successful intubation, and hemodynamic parameters.

Results: As regards time to successful intubation, statistically significant differences were detected between the 2 studied groups, with the fiberoptic group having significantly longer intubation time than the Shikani group, whereas no statistically significant differences were recorded between the 2 groups with regard to the first-attempt success, the mean heart rate value, the mean arterial blood pressure, coughing, and occurrence of complications.

Conclusion: This study validates the efficacy of both SOS and flexible fiberoptic bronchoscope for awake oral intubation in patients with cervical spine instability. SOS has been found to be more effective in reducing time to intubation.

Department of Anaesthesia and Surgical Intensive Care, Faculty of Medicine, Alexandria University, Alexandria, Egypt

The authors have no funding or conflicts of interest to disclose.

Address correspondence to: Rabab S.S. Mahrous, MD, 33 Bahaa Eldin Elghatwary St., Smouha, Alexandria 21648, Egypt (e-mail: roba98@hotmail.com).

Received February 28, 2017

Accepted July 10, 2017

Surgery on the cervical spine is usually indicated for decompression of the spinal cord or a nerve root and to stabilize the spine in cases of traumatic or pathologic cervical instability.1 The conventional intubation of the trachea and the prone positioning of anesthetized patients carry a high risk of secondary neurological injury as a result of extension, hyperflexion, and/or rotation of the head and neck.2

Anesthesiologists caring for patients with a potentially unstable cervical spine need to secure the airway before the cervical spine has been surgically stabilized. Besides, these patients will typically have their cervical spine immobilized in the neutral position using a rigid cervical collar. These combinations have been shown to produce the greatest restriction in mouth opening and cervical spine motility.3 Therefore, airway management of these patients is a complicated scenario and is not without a risk of secondary neurological injury.4

Awake intubation allows a postintubation neurological examination to confirm that no secondary neurological injury occurred during the intubation procedure.5 Moreover, self-positioning prone before inducing general anesthesia is not only a safer option in these patients but also offers neurological revaluation after positioning.2

Historically, the flexible fiberoptic bronchoscope (FOB), first described in the late 1960s has been the main choice for patients scheduled for cervical spine instability surgery either with normal, anticipated difficult airway or even unanticipated difficult airway. In trauma patients, the success rate of flexible FOB has been reported to be around 83%.5,6 Nonconventional intubation aids include bladed laryngoscopes (videolaryngoscopes) and optical stylets, which integrate flexible fiberoptic imaging features in a rigid intubating stylet, are now available.7,8

One of the most commonly used intubating fiberoptic stylets is the Shikani optical stylet (SOS) (Clarus Medical, Minneapolis, MN). SOS has the advantage of being a portable and reusable scope with a shapeable (malleable) stainless-steel stylet, adjustable tube stop, oxygen insufflation port, high-resolution eyepiece, and light source. The eyepiece can be used alone, or combined with a camera or a monitor. The adult SOS is designed to accommodate any size of endotracheal intubation (ETT) above 5.5 mm ID. There is also a pediatric version, which can accommodate size 2.5 mm ID ETT.9,10

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AIM OF THE WORK

The aim of this study was to compare the efficacy of SOS with the flexible fiberoptic bronchoscope (Five) (Karl Storz, Tuttlingen, Germany) for awake oral intubation in patients with cervical spine instability.

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PATIENTS AND METHODS

This prospective, randomized study was approved by the local ethical committee of Alexandria Main University Hospital. Written informed consent was obtained from all the participants. In total, 60 patients aged 18 to 65 years with American Society of Anesthesiologists physical status I to III were enrolled in this study. These patients were diagnosed by the neurosurgeon as having cervical instability or at risk of secondary cervical injury and were scheduled for awake oral intubation and/or self-positioning prone for elective neurosurgical intervention. Patients with increased risk of pulmonary aspiration, requirement for rapid sequence induction, or associated head injury precluding adequate clinical neurological examination were excluded from the study. All patients had their cervical spine immobilized in the neutral position using a rigid cervical collar (Philadelphia collar). Data collected from each patient included demographic data, level of cervical spine pathology, and the neurological status by asking the patients to move their hands (wrist dorsiflexion) and legs (ankle planter flexion).

An assistant not directly involved in the study got numbered opaque presealed envelopes containing the randomized group allocations after every patient was enrolled into the study. Patients were randomly assigned into either a fiberoptic group (FOB, n=30) or a Shikani group (SOS, n=30) utilizing a sealed-envelope technique.

Anesthesiologists concerned within the study had expertise with both devices and were skilled in using the devices in a difficult airway situation. Routine preanesthetic assessments were performed, in addition to a standard airway assessment, recording the presence of any oropharyngeal injury before surgery. Noninvasive monitoring was used before intubation comprising pulse oximetry, blood pressure, and electrocardiography. Before starting topical anesthesia, all patients were given atropine 0.4 mg as an antisialagogue agent, midazolam 2 mg, and increments of fentanyl 25 μg intravenously till the patient was calm and sedated but maintaining his airway.

Topical anesthesia of the oral cavity was performed with lidocaine 10% spray. Anesthesia of the larynx just above the vocal cords, vocal cords, and the upper trachea was achieved with superior laryngeal nerve block using 4 mL of 2% lidocaine (2 mL on each side), at the lateral ends of the thyrohyoid membrane just beneath the greater cornu of the hyoid bone. The recurrent laryngeal nerve block (transtracheal injection) was performed using a 20-G plastic catheter, with 4 mL of 2% lidocaine injected through the cricothyroid membrane at the end of inspiration.

Tracheal intubation was then executed with either the flexible fiberoptic bronchoscope (Five) (Karl Storz) or the SOS (Clarus Medical, Minneapolis, MN), according to the randomized allocation. The SOS was bent to the same bend as a Macintosh laryngoscope blade, lubricated, and a 7 mm ID armored endotracheal tube (Flexicare, UK) was mounted on it. The tube was settled to the stylet by the “adjustable tube stop” so that the tip of the stylet did not project beyond the end of the tube (Fig. 1). The anesthesiologist held and elevated the mandible using the left hand; the patient was asked to protrude his tongue if applicable, and the stylet was introduced from the right side of the mouth. Thereafter, under direct vision, the tip was inserted between the vocal cords, the “tube stop” was released, and the tube was unmounted into the trachea; the stylet was removed. Once tracheal intubation was accomplished, confirmation of the position of the endotracheal tube was accomplished by capnography and chest auscultation. If intubation was unsuccessful (takes >180 s or if desaturation was noted; SpO2<93%), the intubation attempt was stopped and the lungs ventilated with oxygen for 3 minutes, followed by a second attempt. First attempt of using SOS failed in 3 patients with a successful second attempt in the 3 patients. It was planned to consider 3 failed attempts of insertion as failure of intubation, with a ready C-MAC D-Blade videolaryngoscope (Karl Storz, Tuttlingen, Germany) to be used for intubation in these patients.

FIGURE 1

FIGURE 1

In total, 23 of 30 patients in the SOS group and 25 of 30 in the FOB group were planned for posterior cervical spine approach, and these patients were asked to move to the prone position on the bolsters after intubation. The anesthesia provider guarded the head and tube during the move, and neurological examination was repeated by asking the patient to move his hands (wrist dorsiflexion) and legs (ankle planter flexion). Once the position was settled, the presence of end-tidal carbon dioxide was confirmed and general anesthesia was set up.

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Measurements

Measurements were made of coughing and gagging during and after intubation using a scale of 1 to 4 (1, none; 2, <3 times [slight coughing and gagging comparable with “clearing one’s throat”]; 3, >2 times [mild coughing or gagging lasting <1 min]; 4, persistent coughing or gagging). The interval from once the device was introduced into the mouth to once the endotracheal tube crosses the glottic opening was recorded as time to successful intubation. Number of attempts for successful intubation were recorded, and the time of the second successful attempt in the 3 patients with failed first attempt was recorded as the time to intubation in these cases. We also recorded the hemodynamic parameters including heart rate, systolic and diastolic and mean blood pressures during the intubation process with readings taken in baseline, immediately after intubation and at 3 and 5 minutes after intubation. After intubation, careful examination of the oropharynx was performed to diagnose any lip or mucosal trauma. The patient was asked to move his hands (wrist dorsiflexion) and legs (ankle planter flexion) to reassess the motor function after tracheal intubation and after the prone positioning.

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Statistical Analysis

Data were analyzed by using SPSS software (Statistical package for social science for personal computers). Qualitative data were described using number and percentage (%) and were compared using the χ2 test, and the Fisher exact test was used for testing associations between categorical variables, whereas normally quantitative data were expressed in mean±SD and were compared using the independent t test for 2 independent groups and the paired t test for paired samples. The P-value was considered statistically significant if P<0.05.

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RESULTS

Demographic data in both groups are presented in Table 1. The demographic results did not show any significant difference between the 2 studied SOS and FOB groups as regards age, sex, and weight with a P-value of 0.555, 1.000, and 0.204, respectively.

TABLE 1

TABLE 1

On comparing the mean time to intubation between both groups, a statistically significant shorter time of intubation using SOS than when using FOB was recorded (53.20±7.14 and 102.57±10.98 s, respectively) with a P<0.001. However, there were no statistically significant differences among the 2 studied groups with regard to the first-attempt success (90% and 100%, respectively) and the cough and gag scale (2 each) with a P-value of 0.237 and 1.000, respectively (Table 2).

TABLE 2

TABLE 2

As regards complications, no neurological deterioration could be detected in both groups. Although sore throat was detected in 4 patients (13.3%) in the SOS group, none complained of sore throat in the FOB group. This difference was proved to be statistically insignificant with a P-value of 0.112 (Table 3).

TABLE 3

TABLE 3

On comparing the fluctuation in mean heart rate (HR) values among the 2 studied groups in baseline, immediately after intubation and at 3 and 5 minutes after intubation, no statistically significant differences were recorded (Fig. 2). Similar results were recorded with regard to the mean arterial blood pressure (MAP) values in baseline, immediately after intubation and at 3 and 5 minutes after intubation, with no statistically significant differences between the 2 studied groups (Fig. 3).

FIGURE 2

FIGURE 2

FIGURE 3

FIGURE 3

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DISCUSSION

The success in preventing secondary neurological insult to patients with cervical spine injury is considered as the most crucial step in managing such patients. Anesthesiologists are directly committed to this, aiming at the safety of tracheal intubation. The safety of awake fiberoptic intubation in patients with cervical spine disorders is well known, with a success rate of 83%.5,6 The SOS is a reusable intubating stylet, produced in adult and pediatric versions. It has the advantage of being a light wand besides possessing the features of an FOB.9,10

To our knowledge, there are no similar studies in the English literature comparing SOS with FOB in awake oral ETT. In addition, we believe that this study is the first study assessing SOS for awake ETT in patients with cervical instability.

The present study has achieved its aim by comparing the efficacy of SOS and FOB for awake oral intubation in patients with cervical spine instability and showed that both were 100% successful without a statistically significant difference in the first-attempt success rate but with a statistically significant less time to intubation in the SOS group.

On reviewing the literature we found that few authors reported on comparing SOS with GlideScope videolaryngoscope or Macintosh laryngoscope, but there have been no studies comparing SOS and FOB intubation in patients with a difficult airway.

The present study demonstrated that there were no statistically significant differences with regard to demographic data including age, sex, and weight. Moreover, there were also no statistically significant differences between the 2 studied groups with regard to the hemodynamic parameters including HR and MAP. However, there was a statistically significant difference between the baseline and postintubation values in each group.

HR was elevated from a baseline value of 66.8±12.2 to 74.4±11.7 beats/min immediately after intubation, whereas MAP increased from 78.1±11.6 to 88.6±11.8 mm Hg. These results agree with the results of Yao et al12 who used SOS by means of the left molar approach without locally anesthetizing the airway; they found a significant difference in HR between the baseline value and that immediately after intubation (79±11 and 86±15 beats/min, respectively). Liu et al10 also demonstrated significant HR changes in the SOS group from 74.2±8.8 beats/min before intubation to 76.4±9.2 beats/min 1 minute after intubation, whereas MAP raised from 12.1±0.9 kPa (90.8 mm Hg) before intubation to 12.9±1.1 kPa (96.8 mm Hg) 1 minute after intubation.

The present study showed a statistically significant shorter time of intubation using SOS than when using FOB (53.20±7.14 and 102.57±10.98 s, respectively). However, Turkstra et al13 recorded a much shorter time to intubation with SOS than the present study (28±17 and 53.20±7.14 s, respectively) while evaluating cervical spine movement during tracheal intubation in patients subjected to both Macintosh and Shikani laryngoscopy with manual inline stabilization following induction of anesthesia. This difference in time may be due to the use of a different end point of intubation, as positioning the SOS tip between the vocal cords was accepted by Turkstra and colleagues as successful placement, whereas in this study the time of intubation was not recorded until the crossing of the ETT through the glottic opening.

This is comparable with Liu et al10 who demonstrated that the time to intubate using SOS as a substitute to the glidescope and direct laryngoscopy in thyroid tumor patients with a difficult airway was 42.4±24.1 seconds. In addition, Phua et al9 found that the time to intubate using SOS as an alternative to the glidescope in simulated difficult intubations (rigid neck collar applied to simulate difficulty) was 58±26 seconds.

There was no statistically significant difference between the 2 studied groups as regards the first-attempt success rate, which was 90% in the SOS group compared with 100% success rate in the FOB group. The 3 cases who were not intubated in the first attempt, were successfully intubated in the second attempt. On the basis of the assumption that a 30% reduction in the success of the first attempt between the 2 studied groups would be of clinical relevance, the power of the current study to detect such a difference is 85%. This came in agreement with Liu et al10 who demonstrated that the first-attempt success rate of SOS was 90%. Likewise, Yao et al12 and Xu et al14 succeeded in completing the ETT using SOS at the first attempt. Yao and colleagues reported no difference in intubation time in all the patients recruited in their series, and Xu and colleagues explained their 100% first-attempt success rate because of the anesthesiologist’s extensive experience.

In contrast, Turkstra et al13 encountered 2 failures of visualization of the glottic opening of 23 patients using the SOS, making intubation improbable. However, they considered this attempt as a failure without trying a second attempt and intubation was reverted to the conventional Macintosh intubation technique. They concluded that SOS may be beneficial in reducing cervical spine movement during tracheal intubation (55% less in comparison with Macintosh) but at the expense of a higher failure rate and longer duration, which must be taken into consideration while choosing the intubation technique.

With regard to the cough and gag assessment during and after intubation, no statistically significant difference between the 2 groups was recorded. A difference of 1 in the gag scale between the 2 groups was considered clinically relevant, and the power of the current study to detect such difference is 100%. Malcharek et al2 found that 50% of the patients (7/14) showed slight coughing or gagging during intubation using FOB. The lower incidence of gag and cough in this study may be due to the combination of oropharyngeal spray of lidocaine with a transtracheal injection of lidocaine, whereas Malcharek and colleagues performed either local spray or transtracheal injection without combining them together.

No neurological deterioration was reported among the studied groups, whereas 4 patients (13.3%) in the SOS group and none in the FOB group complained of postoperative sore throat. Despite this obvious difference between the 2 groups, no statistically significant difference was detected; this may represent a type II error in the statistical hypothesis testing. Moreover, we did not monitor the cuff pressure of the endotracleal tube during prone position; hence, we could not ignore its role in causing postoperative sore throat. Phua et al9 and Liu et al10 did not report mucosal injury in patients intubated using the SOS. Although in the series conducted by Liu et al10 10 of 40 patients had developed postoperative sore throat, these patients were intubated under general anesthesia without using airway block.

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CONCLUSIONS

This study validates the efficacy of both SOS and flexible FOB for awake oral intubation in patients with cervical spine instability. SOS has been found to be more effective in reducing time to intubation with nonsignificant differences with regard to demographic data, coughing and gag assessment, first-attempt success, failure rate, hemodynamic changes, and occurrence of complications.

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REFERENCES

1. Kumar R, Taylor C. Cervical spine disease and anaesthesia. Anaesth Intensive Care Med. 2014;15:257–259.
2. Malcharek MJ, Rogos B, Watzlawek S, et al. Awake fiberoptic intubation and self-positioning in patients at risk of secondary cervical injury: a pilot study. J Neurosurg Anesthesiol. 2012;24:217–221.
3. Robitaille A. Airway management in the patient with potential cervical spine instability: continuing professional development. Can J Anesth. 2011;58:1125–1139.
4. Martini RP, Larson DM. Clinical evaluation and airway management for adults with cervical spine instability. Anesthesiology Clin. 2015;33:315–327.
5. Diedrich DA, Rose PS, Brown DR. Airway management in cervical spine injury. Curr Anesthesiol Rep. 2013;3:197–204.
6. Collins SR, Blank RS. Fiberoptic intubation: an overview and update. Respir Care. 2014;59:866–880.
7. Mihai R, Blair E, Kay H, et al. A quantitative review and meta-analysis of performance of non-standard laryngoscopes and rigid fiberoptic intubation aids. Anaesthesia. 2008;63:745–760.
8. Liem EB, Bjoraker DG, Gravenstein D. New options for airway management: intubating fiberoptic stylets. Br J Anaesth. 2003;91:408–418.
9. Phua DS, Mah CL, Wang CF. The Shikani optical stylet as an alternative to the GlideScope videolaryngoscope in simulated difficult intubations. Anaesthesia. 2012;67:402–406.
10. Liu L, Yue H, Li J. Comparison of three tracheal intubation techniques in thyroid tumor patients with a difficult airway: a randomized controlled trial. Med Princ Pract. 2014;23:448–452.
11. Finucane BT, Tsui BCH, Santora AH. Advanced Airway Devices: Optical Stylets. Principles of Airway Management, 4th ed. New York, NY: Springer Science+Business; 2011:272–278.
    12. Yao YT, Nai JIA, Chang LI, et al. Comparison of endotracheal intubation with the Shikani optical stylet using left molar approach and direct laryngoscopy. Chin Med J. 2008;121:1324–1327.
    13. Turkstra TP, Pelz DM, Shaikh AA, et al. Cervical spine motion: a fluoroscopic comparison of Shikani optical stylet vs Macintosh laryngoscope. Can J Anaesth. 2007;54:441–447.
    14. Xu M, Li XX, Guo XY, et al. Shikani optical stylet versus Macintosh laryngoscope for intubation in patients undergoing surgery for cervical spondylosis: a randomized controlled trial. Chin Med J. 2017;130:297–302.
    Keywords:

    Shikani optical stylet; rigid optical stylets; awake; fiberoptic intubation; cervical spine injury

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