Comparison of aerosol box intubation with styletted endotracheal tube and intubation over bougie: A randomized controlled trial

Abstract

Background and Aims:

Severe acute respiratory syndrome coronavirus 2 (SARS CoV-2) is an infectious disease. The use of video laryngoscopes is recommended for intubation of patients with COVID-19. But in resource-poor countries, it is rare to have video laryngoscopes available. In this trial, we have compared the ease of oral intubation by direct laryngoscopy with styletted endotracheal tube and intubation over the bougie, with the use of the aerosol box. The secondary objectives were comparison of the incidence of airway loss, attempts taken to intubate, time for intubation and hemodynamic changes.

Material and Methods:

80 non-coronavirus infected patients coming for an elective procedure under general anesthesia were recruited in this randomized control trial. Participants were assigned into groups S and B using a computer-generated random sequence of numbers by closed envelope technique. In both groups, aerosol box was used. In Group S, participants were intubated by direct laryngoscopy with a styletted endotracheal tube and in group B, after direct laryngoscopy, the endotracheal tube was railroaded over the bougie.

Results:

Ease of endotracheal intubation was good (67.5%% vs. 45%), satisfactory (32.5%% vs. 37.5%), and poor (0% vs. 17.5%) in group S and B respectively (P < 0.011). The attempts required for intubation were similar in both groups. The time for intubation was significantly less in group S than B (23 vs. 55 s).

Conclusion:

The use of a styletted endotracheal tube made intubation easier and faster than tracheal intubation with bougie when the aerosol box was used in patients without known or predicted difficult airway and significant medical comorbidities.

Introduction

Severe acute respiratory syndrome coronavirus 2 (SARS CoV2) is infectious and spreads through aerosols and droplets.^[1] Many anesthesiologists use aerosol box along with WHO-recommended personal protective equipment (PPE) to prevent getting infected by SARS CoV2.^[2,3] Intubation through the aerosol box is challenging and it is not proven if it prevents aerosol and viral infection. But still many centers are continuing to use it. In a previous similar study, it was found that video laryngoscopic intubation was easier when an aerosol box was used.^[4] But in resource-poor countries, it is rare to have video laryngoscopes available for all intubations. Traditional direct laryngoscopy can be assisted by the use of the bougie or stylet.^[5] Hence in this study, ease of oral intubation by direct laryngoscopy with styletted endotracheal tube was compared with intubation over the bougie, when the aerosol box was used. We hypothesized that bougie would be better than stylet in improving the ease of intubation by direct laryngoscopy when the aerosol box was used. The secondary objectives included the comparison of the incidence of airway loss, attempts taken to intubate, time for intubation, and hemodynamic changes.

Material and Methods

This randomized control trial where the aerosol box was used during endotracheal intubation was done after obtaining written informed consent from patients, permission from the institutional ethical committee (IEC-AIMS-2020-ANES-093), and Clinical Trials Registry-India (CTRI/2020/07/026801). This study included 80 non-corona virus diseases (COVID-19) patients with an RT PCR negative report (within 48 h of surgery) belonging to the American Society of Anesthesiologists physical status I and II between age group 18-65 years presenting for the non-emergency procedure under general anesthesia requiring oral intubation [Figure 1]. This study was undertaken in a referral teaching hospital from August to December 2020. Patients with anticipated difficult airway like history of difficult airway, history of head and neck pathology, Mallampati class 3 and 4, <2 cm inter-incisor gap, prognathism, restricted neck movement, body mass index >30, raised intracranial or ocular pressure, hypertension, pregnancy, and heart disease were excluded in this study.

Figure 1.

Consort flow diagram

All patients were advised nil per oral for 6 h for solids and 2 h for clear fluids and were premedicated with alprazolam 0.25 mg and pantoprazole 40 mg orally on the night before surgery. On the day of the procedure after securing intravenous access, 5 lead electrocardiogram, saturation and blood pressure were noted. After informing the patient the aerosol box (a transparent box of dimensions 50 × 45 × 45 cm³) was placed. The box had openings, for introducing the anesthesiologist’s arms, a small opening for passing the bougie and one opening on the side for the assistant. The size of the opening for the arm of the anesthesiologist and assistant was 10 × 12 cm² each, and 3 × 4 cm² for passing the bougie. [Figure 2] Anesthesiologist draped in personal protective equipment (fitted N95 mask, face shield, disposable fluid resistant gown, hood, and boot cover) passes his/her arms through the elliptical openings in the aerosol box and pre oxygenates the patient for five minutes. Participants were then randomly assigned into groups S and B by computer-generated randomization and concealment was achieved with sequentially numbered, sealed, opaque envelopes. In Group S, patients were intubated by direct laryngoscopy with a styletted endotracheal tube and in group B, after direct laryngoscopy, a bougie was passed through the glottic opening into the trachea. The tracheal tube was then railroaded over the bougie.

Figure 2.

Aerosol box

To reduce aerosolization modified rapid sequence induction was performed and mask ventilation was avoided. Induction with intravenous fentanyl 2 mg/kg, propofol 2 mg/kg was followed by depolarizing muscle relaxant suxamethonium 1.5 mg/kg. All intubations were performed by a consultant anesthesiologist with more than 5 years of experience. Female patients were intubated with 7.5 mm and male patients with 8 mm cuffed endotracheal tube in classic sniffing position with Macintosh blade. In group S patients, a stylet (Rusch® Flexi-slip stylet) was used to aid intubation. In group B, after direct laryngoscopy, a bougie (PortexTM reusable bougie 14Fr, 70 cm long) was introduced through the glottic opening. The tracheal tube was then railroaded over the bougie. End-tidal capnography was used to confirm the correct placement of the tube. Patients were then mechanically ventilated and vitals were noted at induction (baseline), 1, 3, 5, and 15 min after intubation.

Coughing during intubation, injury to patient or health worker, airway loss during the procedure was noted. Airway loss was defined as any drop in saturation below 92% or requirement of more than two attempts to intubate. These patients were then removed from the study and the airway would be managed without the aerosol box. The ease of intubation was graded as good (Glottis visualized adequately and intubation accomplished easily), satisfactory (Glottis visualized adequately but required external manipulation over the larynx), and poor (Glottis visualized adequately but failed to intubate in the first attempt irrespective of external manipulation).^[4] If the glottis view was poor, but the intubating anesthesiologist without removing the laryngoscope blade, withdraws the bougie or tube and reintroduces it leading to successful intubation, attempts at intubation was counted as a single attempt but the ease of intubation was graded as poor. In case glottis was not visualized (Cormac Lehane grade 3 or 4), it was considered as a difficult airway and the aerosol box was removed and the patient was removed from the study and intubation was performed without the aerosol box. The intubation time was the time taken from the introduction of the Macintosh laryngoscope to the recording of the end-tidal carbon dioxide waveform. The ease of intubation, time for intubation, the number of attempts required was noted.

Since there are no similar studies in existing literature, a pilot study was conducted. Based on the proportion of ease of intubation of good in group B (50%) and group S (80%) obtained from the pilot study report performed with 10 patients in each group with a 95% confidence interval and 80% power the minimum sample size came to 38 per group. However, we enrolled 40 patients in each group to take care of any dropouts.

IBM SPSS 20.0 (SPSS, Chicago, Illinois) was used for statistical assessment. Continuous variables are given as mean ± SD and categorical variables as a percentage. For comparing the mean difference of numerical variables between groups, independent two-sample ‘t’ test was used. To find the association of categorical variables, Chi-square with Fisher’s exact test was used. A P value < 0.05 was considered as statistically significant.

Results

Eighty non-COVID patients participated in this study. They were randomly allocated into groups S and B [Figure 1]. The participants were comparable with respect to the mean age, weight, height, sex, Mallampati scores and ASA physical status [Table 1]. Ease of endotracheal intubation was good (67.5%% vs. 45%), satisfactory (32.5%% vs. 37.5%) and poor (0% vs. 17.5%) in group S and B respectively. This was found to be statistically significant with a P < 0.011. The attempts required for intubation was similar in both groups. All patients had either Cormac and Lehane grade 1 or 2. So no enrolled patients were excluded from the study. The time required for intubation was significantly less in group S than B (23 vs. 55 s) [Table 2]. There was no airway loss or intubation failure or pneumothorax in both groups. Blood pressure and heart rate were also comparable [Tables 3 and 4].

Table 1.

Demographic Data, ASA grade and Mallampati class

Variable	Group B n=40	Group S n=40	P
Age in years (Mean±SD)	45.65+10.053	45.83+9.367	0.936
weight in kg (Mean±SD)	64.85+8.6	63.03+8.396	0.342
Height in cm	155.13±7.035	154.20±7.871	0.581
BMI in kg/cm2	27.07±4.189	26.68±4.369	0.689
Sex n (%)
Male	13 (32.5%)	16 (40%)	0.485
Female	27 (67.5%)	24 (60%)
ASA Grade n (%)
1	25 (37.5%)	20 (50%)	0.260
2	15 (37.5%)	20 (50%)
MP Class n (%)
1	28 (70%)	23 (57.5%)	0.245
2	12 (30%)	17 (42.5%)

ASA - American Society of Anesthesiologists, MP - Mallampati class, SD - Standard deviation. Student’s t test and Chi-square test applied. P<0.05 is significant

Table 2.

Ease of intubation, number of attempts and intubation time

Variable and grading	Group B n=40	Group S n=40	P
Ease of Intubation Grade n (%)
Good	18 (45%)	27 (67.5%)	0.011
Satisfactory	15 (37.5%)	13 (32.5%)
Poor	7 (17.5%)	0 (0%)
Number of attempts n (%)
1	39 (97.5%)	39 (97.5%)	1.000
2	1 (2.5%)	1 (2.5%)
Intubation time in s (Mean±SD)	55±8.243	23.83±2.836	0.000

SD - Standard deviation. Student’s t-test and Chi-square test applied. P*<0.05 is significant

Table 3.

Comparison of mean arterial pressures between groups

MAP	Group B n=30 (Mean±SD)	Group S n=30 (Mean±SD)	P
Baseline	82.550±10.276	79.675±9.991	0.208
1 min	83.925±10.671	79.575±9.516	0.058
3 min	82.925±9.477	79.475±9.018	0.099
5 min	84.125±9.908	79.375±9.170	0.029
15 min	83.375±10.217	80.475±9.634	0.195

MAP - Mean arterial pressure, SD - Standard deviation. Student’s t test applied, P<0.05 is significant

Table 4.

Comparison of mean heart rate between groups

Mean HR	Group B n=30 (Mean±SD)	Group S n=30 (Mean±SD)	P
Baseline	77.825±12.438	77.850±10.650	0.992
1 min	77.575±11.598	78.625±11.399	0.684
3 min	77.700±12.043	79.650±12.071	0.472
5 min	78.650±10.309	78.225±12.029	0.866
15 min	79.000±10.612	77.825±11.703	0.639

HR - heart rate, SD - Standard deviation. Student’s t test applied, P<0.05 is significant

Discussion

In this study, ease of oral intubation by direct laryngoscopy with styletted endotracheal tube was compared with intubation over the bougie, when the aerosol box was used. Prolonged time at intubation, intubation failure and airway loss compel us to provide positive pressure ventilation with a mask and thereby increase aerosolization. During this pandemic, it is recommended to perform rapid sequence induction and avoid mask ventilation.^[6,7] In a previous similar study, we could establish that the use of video-laryngoscopes makes oral intubation easier compared to intubation with direct laryngoscopy.^[5] We planned this study, as Macintosh laryngoscope is the one which is available everywhere compared to video laryngoscope. If video laryngoscopes are not easily available, options are to use adjuncts like bougie or styletted endotracheal tubes.

Stylet is used to pre-shape, add rigidity to the endotracheal tube and to aid in its easy passage past the vocal cords. It helps to improve first-pass intubation success, reduce the duration of intubation and apnoea period in anticipated difficult airways and rapid sequence inductions. It is popular because it is cheap, easily available and portable. To aid in intubation, the tip of styletted endotracheal tube is bent into the shape of a hockey stick. The stylet is lubricated before inserting it into the endotracheal tube to minimize the resistance while removing it after intubation. Easy passage of the stylet in and out of the ETT should be confirmed by using water-based lubricant. Pulling the stylet out forcibly can result in slipping of the endotracheal tube and loss of airway. It is preferable to use stylet without sleeve. There have been case reports of the sleeve of the stylet slipping into the trachea during its removal. It is also recommended to check the stylet for any damage before and after its use. But we did not encounter any of these in our study group. In a styleto trial by Jaber et al. use of stylet for tracheal intubation in critically ill patients resulted in improved first attempt intubation without any incidence of severe adverse effects.^[8]

Bougie is an inexpensive introducer used to aid intubation in an unanticipated difficult airway. It has an angled tip to guide it into the larynx. We used 14 Fr, 70 cm long PortexTM reusable bougie in our study. The endotracheal tube is then railroaded over the bougie into the trachea. The bougie has a small diameter causing less obscuring of the operator’s view of the glottic inlet. In addition, when an incomplete view of the glottis is obtained at laryngoscopy, the tip of the bougie can be placed under the epiglottis to enter the glottic opening blindly. It also provides tactile feedback of proper tracheal placement by clicking on the tracheal rings.^[9] In a retrospective study by Driver and colleagues, the use of bougie was found to have higher first-pass success than conventional intubation.^[10] But the additional step of railroading results in prolonged intubation time. Bougie advanced past the carina can lead to airway trauma.^[11] Hence, the bougie should not be introduced beyond the mid tracheal level and an assistant should be instructed to hold it in place while the endotracheal tube is pushed into the trachea. Resistance encountered at arytenoid cartilage during railroading of endotracheal tube can be overcome by withdrawing the tube slightly or rotating the endotracheal tube by 90 degrees and then readvancing the tube.

COVID-19 pandemic and shortages of PPE have forced many anesthesiologists to use aerosol box or sheets to reduce exposure to droplets while performing aerosol-generating procedures such as intubation.^[12-15] Aerosol box was introduced in anesthetic practice by Dr Lai Hsien-yung.^[16] It is a transparent box to cover the patient’s shoulders and head and has holes for the anesthesiologist and assistant to pass arms for intubation. It may reduce operator exposure to infectious droplets and aerosol.^[17,18] Various modifications have been incorporated into the original design.^[3] In our institution, we use a transparent box made of acrylic with 4 circular openings-2 for passing the anesthetists arms, one for passing the bougie on the anterior surface of the box and one on the lateral side of the box for the assistant to give the endotracheal tube and laryngoscope [Figure 2]. All patients coming to the theatre should be considered as possible COVID positive and the anesthesiologist should be donned in WHO recommended PPE before intubation (a fit-tested N95 respirator, face shield, gown, boots and gloves).^[19] The use of an aerosol box may provide additional protection to the anesthesiologist involved in intubation.^[6,20] Bougie and stylet after use were initially cleaned with soap and water and then placed in glutaraldehyde solution for sterilization as they were reused.

Use of aerosol box has been questioned recently. It is suggested that use of boxes may not be appropriate especially as studies have shown less aerosolization during intubation than extubation when patient is given muscle relaxants. There are studies which showed increased intubation time, less first pass success and breaches in personal protective equipment with use of aerosol box. Hence some authors are worried that the use of aerosol box could expose patients to the risk of hypoxia especially if they are COVID-19 positive.^[18] Wakabayashi and colleagues studied the effect of an aerosol box on intubation difficulty and came to the conclusion that intubation difficulty caused by the aerosol box was not relevant for an experienced anesthesiologist.^[21] In a similar study, Turner and colleagues studied the effect of the aerosol box on intubation in difficult airways and opined that it affects the ease and increases the time to intubation in such airways. But in their study, residents with less experience had intubated.^[22] Whereas in our study, we did not encounter any loss of airway as intubations were performed by a consultant anesthesiologist and patients with an anticipated difficult airway were excluded. Hsu and colleagues recommended that during difficult intubation or in an emergency, the box should be removed to avoid any airway loss.^[12]

In a meta-analysis comparing the efficacy of bougie and stylets, Sheu and colleagues concluded that bougie was not superior to stylet and its selection should be made depending on personal preference and expertise.^[23] In this study, we found that the use of styletted endotracheal tube reduced the intubation time and ease compared to the use of a bougie. Hemodynamic response during intubation was similar in both groups. Even though intubation time was prolonged, there was no intubation response. Mean arterial pressure and heart rate remained almost the same as the basal values. This could be explained by the fact that all intubations were performed by experienced consultants and the increased time taken for intubation was because of the delay in transferring instruments and breathing circuit through the aerosol box. Also, there is a time delay for the appearance of the ETCO₂ waveform in the monitor.

There was no difference in the attempts taken to intubate between the two groups and none of the patients in both groups required more than 2 attempts at intubation. The intubation time required was considerably less in the stylet group compared to bougie. The bougie group had long intubation time as it was difficult to align the long bougie through the opening in the aerosol box up to the larynx and the endotracheal tube has to be railroaded through the bougie by an assistant. But we did not encounter any desaturation as all our patients were adequately pre oxygenated. There was no loss of airway in both groups.

This study has limitations. It is not a blinded study as it was impossible for the intubating anesthesiologist to be blinded to the technique used. Ease of intubation in difficult airways and ICU settings were also not assessed. Patients with difficult airway (Mallampati class 3 or 4 and Cormac Lehane grade 3 or 4) were excluded from the study. Another limitation is that, our group of patients were not COVID-19 positive and were less likely to desaturate. We used larger size tube for intubation, use of smaller size tube could have made intubation easier. At the time the study was started, it was our institutional protocol to use suxamethonium, if not contraindicated and avoid mask ventilation. We used a high dose of dose of intravenous suxamethonium to avoid coughing, but instead we could have used rocuronium.

Conclusion

The use of a styletted endotracheal tube made intubation easier and faster than tracheal intubation with bougie when the aerosol box was used in patients without known or predicted difficult airway and significant medical comorbidities.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.