Research ArticleClinical Studies
Open Access

Evaluation of Factors Affecting Illumination Intensity in Lightwand Endotracheal Intubation

KWAN YOUNG HONG, JA EUN LEE, HYUN JI HWANG, WOO SEOG SIM, HUE JUNG PARK and JIN YOUNG LEE
In Vivo January 2024, 38 (1) 490-495; DOI: https://doi.org/10.21873/invivo.13464

Abstract

Background/Aim: A lightwand is a stylet with a light bulb at its tip that can be used to guide intubation by confirming the illumination through the anterior neck. We aimed to determine the factors affecting the illumination intensity during lightwand endotracheal intubation. Patients and Methods: We retrospectively collected data from 180 patients who underwent lightwand endotracheal intubation. We recorded illumination intensity on a 5-point scale. The patients were categorized into weak (score <3) and bright (score ≥3) groups based on the illumination intensity scale score. Results: A total of 176 patients were analyzed, of whom 125 (71.1%) were enrolled in the bright group, and 51 (29.0%) were enrolled in the weak group. Multivariable logistic regression analysis revealed that an increased body mass index (BMI) and mask ventilation grade were associated with light intensity. For mask ventilation, moderate vs. easy (p=0.010) and difficult vs. easy (p=0.008) were associated with the weak group. Receiver operating characteristic curve analysis showed that BMI ≥24.6 kg/m2 was correlated with the weak group. Conclusion: BMI ≥24.6 kg/m2 or mask ventilation grade above moderate indicates increased odds of weak illumination intensity in lightwand intubation. Pre-intubation examination of these factors helps increase the chances of successful intubation.

Key Words:

Successful intubation is of great importance for airway management during general anesthesia. Although intubation techniques and tools have rapidly developed, the lightwand, which has long been used in airway management, still has benefits. Lightwand intubation is a technique in which a light-bulb stylet is introduced into the endotracheal tube and the tube tip is directed into the trachea by transillumination through the anterior neck tissue (1). The lightwand has been recommended for difficult airway management by the American Society of Anesthesiologists (ASA) (2). When mask ventilation is adequate, but intubation is unsuccessful, alternative non-invasive approaches can be attempted using a lightwand, laryngeal mask airway, or different laryngoscope blades (non-emergency pathways) (1, 2). In 2022, the ASA updated their recommendations concerning the suggested equipment for the management of difficult airways (3). In particular, they suggested non-invasive and invasive alternatives by emphasizing awareness of the passage of time and limiting the number of attempts using different devices and techniques (3). Non-invasive devices include lighted or optical stylets, videolaryngoscopes, flexible intubation scopes, and adjuncts (3). In anticipated difficult airway management, if a non-invasive approach is selected, they recommend identifying a preferred sequence of non-invasive devices (3). The lightwand is easy to carry and prepare, inexpensive, and easy for physicians to learn (4). A lightwand can be a valuable disposable intubation tool for difficult intubation (5), particularly during the COVID-19 pandemic. After the COVID-19 pandemic was declared by the World Health Organization (WHO) in March 2020, single-use intubation tools were introduced to achieve efficacies similar to those of videolaryngoscopy at a lower cost. A new disposable laryngoscope with a straight, transparent, and illuminated blade showed a 91% successful first-pass rate in normal and difficult airways but required a longer time for intubation and ventilation (6). The lightwand is beneficial in cases of cervical immobilization, limited mouth opening, or intubation difficulty during video-assisted intubation (7, 8). In cases of poor visualization during intubation, repeated conventional laryngoscopy with multiple blades can injure the soft tissues of the airway, thereby increasing the difficulty of intubation. A lightwand can be inserted into the trachea without visualization by confirming the transillumination. In the traditional intubation technique using a lightwand, the physician holds the wand in a manner similar to that used with a pencil, stands directly behind the patient’s head, inserts the lightwand into the side of the mouth, and sweeps the tip to the midline (9). To successfully intubate with a lightwand, confirmation of the illumination through the anterior neck is vital. Sui et al. reported that laterally deviated transillumination and/or dim transillumination through the neck leads to failure of lightwand intubation (10). However, the factors affecting the illumination intensity have not yet been evaluated. This study aimed to evaluate the factors affecting the illumination intensity in patients undergoing lightwand endotracheal intubation.

Patients and Methods

Patients. We retrospectively reviewed the electronic medical records of patients who underwent lightwand endotracheal intubation for general anesthesia from May to July 2020 at a single tertiary care hospital. In this study, we enrolled patients with normal airways to minimize bias affecting the illumination intensity. Therefore, we excluded patients with ASA class IV, congenital or acquired abnormalities in the upper airway, history of airway-related surgery, upper respiratory tract infections, previous difficult intubation history, pre-existing sore throat, nasogastric tube insertion, limited cervical spine mobility, altered neck anatomy, and intubation requiring ≥3 attempts. Enrolled patients were aged 19-88 years. This retrospective study was approved by our departmental ethics committee (SMC 2020-11-111) and was registered with the Clinical Research Information Service of the Korea National Institute of Health (http://cris.nih.go.kr/cris/index.jsp, ref: KCT00005672). The requirement for obtaining patient consent was waived owing to the retrospective nature of this study, which involved a review of the medical records.

Anesthesia. All procedures were performed by experienced anesthesiologists. Patients were not preoperatively medicated. The intraoperative anesthetic management was standardized. Standard monitoring (IntelliVue MP70, Philips Healthcare, Best, the Netherlands) was performed and included oxygen saturation, electrocardiography, end-tidal carbon dioxide, pulse oximetry, bispectral index (BIS), and non-invasive blood pressure measurements. Anesthesia was induced intravenously with 40 mg of 2% lidocaine, 2 mg/kg of 2% propofol, 0.5-1 μg/kg of fentanyl, and 0.6-0.8 mg/kg rocuronium. After approximately 3-5 min of mask ventilation and loss of all four twitches by train-of-four stimulation of the ulnar nerve, endotracheal intubation was performed using a lightwand (Light Way®, Luminous stylet; Ace Medical, Seoul, Republic of Korea). Under ambient light conditions, the patient’s head and neck were placed in a neutral position and jaw thrust was applied. The lightwand was introduced in the endotracheal tube, and the proximal end of the tube was bent to a 90-degree angle. When central transillumination was observed on the cricothyroid membrane, the lightwand was withdrawn and the endotracheal tube was advanced (10). The position of the endotracheal tube was confirmed by capnography and bilateral lung sounds. After intubation, anesthesia was maintained with 1.5-3.0 vol% sevoflurane and a bolus injection of 0.5-1 μg/kg fentanyl to maintain hemodynamic parameters within 20% of baseline values and a BIS value between 40 and 60. The lungs were then ventilated with 50% oxygen. This was adjusted to maintain an end-tidal carbon dioxide level of 30-40 mmHg. At the end of surgery, patients were intravenously administered 0.25 mg/kg of pyridostigmine and 0.005 mg/kg of glycopyrrolate. After extubation, the patients were moved to the postoperative anesthesia care unit (PACU). At PCAU, sore throat was measured using a 10-point numerical rating scale (NRS; 0=no pain to 10=intolerable pain). During lightwand intubation, the illumination intensity was recorded using a 5-point scale, where 1=very weak, 2=weak, 3=moderate, 4=bright, and 5=very bright. The mask ventilation grade was categorized as easy, moderate, or difficult.

Bright vs. weak groups. Patients who scored ≥3 and <3 on the illumination intensity scale were included in the bright and weak illumination groups, respectively.

Statistical analysis. All data were analyzed using SAS 9.4 (SAS Institute, Cary, NC, USA). Data are expressed as mean±standard deviation (SD) or numbers (percentages), as appropriate. Demographic data of the two groups were compared using the chi-squared test, t-test, or Fisher’s exact test. Logistic regression was used to determine whether significant variables from the demographic and clinical data were independently associated with the weak group. Confounders were selected for inclusion in the multivariable models. Statistical significance was set at p<0.05.

Results

Of the 180 patients assessed for eligibility, four were excluded because they met the exclusion criteria. Thus, 176 patients were included in the analysis. The demographic and clinical data are summarized in Table I. Age, ASA class, thyromental distance, and mouth opening did not differ significantly between the groups. Sex, body mass index (BMI), neck circumference, Mallampati class, mask ventilation grade, and number of attempts differed between the groups. The incidence of successful intubation on the first attempt was significantly higher in the bright group than in the weak group (p<0.001). Anesthetic data and sore throat intensities are described in Table II. No differences were observed between the groups. The results of the univariate logistic regression analysis are summarized in Table III. Male sex, BMI, neck circumference, Mallampati class (II and III), and mask ventilation grade (moderate or difficult) were associated with illumination intensity. The illumination intensity differed with mask ventilation grade (p=0.026) and BMI [odds ratio (OR)=1.231, 95% confidence interval (CI)=1.016-1.491, p=0.034] (Table IV), between moderate vs. easy mask ventilation grade (OR=4.244, 95%CI=1.418-12.699, p=0.010) and between difficult vs. easy mask ventilation grade (OR=20.656, 95%CI=2.189-194.873, p=0.008). Receiver operating characteristic curve analysis showed that BMI ≥24.6 kg/m2 (area under the curve 0.777, 95%CI=0.700-0.853, sensitivity 73%, specificity 74%) was correlated with the weak group. There was one case of failed intubation after two attempts using the lightwand. The patient was successfully intubated using a video-laryngoscope. None of the patients in the study experienced intubation failure or intubation-related complications (vocal cord paralysis, hoarseness, pain during speaking, bleeding, aspiration, dental injury, or pharyngeal injury).

View this table:
Table I.

Demographic and clinical characteristics of the patients.

View this table:
Table II.

Anesthetic data and sore throat.

View this table:
Table III.

Univariate logistic regression analysis for variables and illumination intensity.

View this table:
Table IV.

Multivariable logistic regression analysis for variables and illumination intensity.

Discussion

In this study, we demonstrated that when the BMI was ≥24.6 kg/m2 or the mask ventilation grade was above moderate, the odds of weak illumination intensity for lightwand intubation increased. Therefore, BMI should be considered as a factor for safe airway management. In the obstetric population, BMI >25 kg/m2 was a risk factor for difficult intubation, which was a non-obstetric factor in nature (11). Patients with morbid obesity present with excess fatty tissue in the breast, neck, thoracic wall, mouth, and pharynx (12). These excess tissues can impede access to the upper airway (12), thus leading to dim light during lightwand intubation. The mask ventilation grade can be affected by a small thyromental distance, limited jaw thrust, limited mouth opening, altered neck anatomy, or limited cervical spine mobility (11). During intubation, limited jaw thrust can cause impaired displacement of the tongue into the submental space and impaired movement of the mandible into the submental space (13). In our study, thyromental distance and mouth opening did not differ between the groups. We suspect that moderate or difficult mask ventilation resulting from limited jaw thrust had a decisive effect on illumination intensity by disturbing the entry route into the trachea. Yang et al. reported that the two-handed jaw thrust in lightwand intubation resulted in a shorter time for intubation and a lower number of intubation attempts compared to the single-handed chin lift, as it secures sufficient oropharyngeal space (14). In patients with cervical immobilization due to cervical myelopathy or an unstable cervical spine, maintaining the cervical alignment during intubation is needed. Lightwand intubation does not require anterior displacement of the tongue and epiglottis. Kim et al. reported that laryngoscope-assisted lightwand intubation resulted in a higher incidence of successful intubation on the first attempt than intubation with only a lightwand, by improving the maintenance of midline alignment in the hypopharynx and allowing free movement of the lightwand in the oral cavity (15).

A difficult airway is defined as a clinical situation in which anticipated or unanticipated difficulty or failure is experienced by a physician trained in anesthesia care due to difficult face mask ventilation (inadequate mask seal, excessive gas leak, or excessive resistance to the ingress or egress of gas), difficult laryngoscopy (not possible to visualize any portion of the vocal cords after multiple attempts at laryngoscopy), difficult supraglottic airway ventilation, difficult or failed tracheal intubation and extubation, and inadequate ventilation (3). Lightwands have been used in difficult laryngoscopy situations because of limited mouth opening and/or neck extension, loose teeth, or facial trauma. In a comparative study of lighted stylet and direct laryngoscopic intubation in patients with Mallampati class III, the lighted stylet showed a higher success rate on the first intubation attempt and shorter intubation time than direct laryngoscopy (16).

For confident intubation, direct visualization of the airway has been recommended with direct laryngoscopy (17). After failed intubation with direct laryngoscopy, the most frequently chosen rescue technique was videolaryngoscopy, with a higher success rate (92%) than those of other techniques, such as a supraglottic airway conduit (78%), flexible bronchoscopy (78%), a lighted stylet (77%), and an optical stylet (67%) (18). Lightwands have a more flexible structure than that of direct laryngoscopes. The illumination intensity determines the accuracy of a target point. Therefore, successful intubation using a lightwand is based on clear illumination. In our study, a weak illumination intensity was related to a higher BMI and mask ventilation grade. Physicians should prepare proper intubation tools after airway examination considering these factors.

For lightwand intubation, the effective dose of muscle relaxants has not been sufficiently evaluated. In difficult mask ventilation and difficult intubation, ASA guidelines recommend an anesthetic technique without muscle relaxation, allowing rapid return to spontaneous ventilation if ventilation becomes inadequate (1, 2). In our study, we enrolled patients with a normal airway and used a standard dose (0.6-0.8 mg/kg) of rocuronium. Massó et al. reported that lightwand intubation with 0.6 mg/kg rocuronium showed a lower failure rate, decreased intubation time, and fewer attempts compared to that in patients who did not receive rocuronium in the normal airway (1). Park et al. described the optimal doses of rocuronium in lightwand intubation for short surgical procedures or outpatient surgery. The 50% and 95% clinical effective doses of rocuronium were 0.2 mg/kg and 0.35 mg/kg, respectively, which were lower than those for direct laryngoscopy intubation because rapid return to spontaneous ventilation is needed for day-care surgery (19). Few studies have reported clinical factors affecting successful lightwand intubation (4). A high Mallampati class and BMI ≥30 kg/m2 interfered with the ease and success of lightwand intubation, because adequate transillumination could not be easily achieved (4). A long epiglottis prolongs intubation time with a lightwand by preventing free advancement of the tube into the trachea even with jaw lift (20). In our study, increased BMI was correlated with the weak group because of inadequate light passage through the neck tissue. Inversely, lean patients may have bright intensity even in cases of esophageal insertion due to thin neck tissue. Further studies are needed to evaluate lower cut-off values of BMI related to the brightness of the lightwand.

This study had some limitations. First, we categorized the patients using a subjective scale of illumination intensity. Second, we did not measure the insertion distance of the lightwand. In our study, we stopped at the brightest point during lightwand insertion. Cho et al. reported that 1 cm below the vocal cords was an effective glow point for the lightwand tip to avoid deep or shallow insertions (21). They showed a 93.5% success rate at the first attempt, which was similar to our results. Third, we did not have data regarding jaw thrust, including the two-handed or single-handed technique (13). Fourth, the lightwand technique is based on no visualization of the airway with a lighted stylet, which may increase the risk of mechanical vocal cord damage during intubation. Mechanical laryngeal injury, such as arytenoid dislocation or subluxation, may occur in patients who received endotracheal intubation, with a 0.01% incidence rate (22). The reported risk factors include endotracheal intubation using excessive force, loosening of the cricoarytenoid joint capsule, nasogastric tube placement, and prolonged operative time (22). Physicians should exercise caution during intubation in patients with these factors by considering the use of visualization intubation tools. Finally, the sample size of this study was small.

Conclusion

This study demonstrated that a weak illumination intensity was associated with increased BMI and mask ventilation grade. Pre-intubation examination of these factors is necessary to increase the possibility of successful intubation.

Footnotes

  • Authors’ Contributions

    KYH and JYL performed conceptualization, data curation, formal analysis, investigation, methodology, writing, and editing. HJP and WSS performed review and editing. JEL and HJH performed data curation and formal analysis. All authors have read and approved the manuscript.

  • Conflicts of Interest

    The Authors declare that they have no conflicts of interest in relation to this study.

  • Received August 23, 2023.
  • Revision received October 12, 2023.
  • Accepted October 19, 2023.

This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY-NC-ND) 4.0 international license (https://creativecommons.org/licenses/by-nc-nd/4.0).

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Evaluation of Factors Affecting Illumination Intensity in Lightwand Endotracheal Intubation
KWAN YOUNG HONG, JA EUN LEE, HYUN JI HWANG, WOO SEOG SIM, HUE JUNG PARK, JIN YOUNG LEE
In Vivo Jan 2024, 38 (1) 490-495; DOI: 10.21873/invivo.13464
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