AJA Asian Journal of Anesthesiology

Advancing, Capability, Improving lives

Research Paper
Volume 58, Issue 4, Pages 138-145
Sheng-Yu Chen 1 , Yi-Seng Tsai 2 , Yu-Hua Wu 1 , Shan-Tair Wang 3 , Ting-Wei Kang 1 , Chia-Chih Alex Tseng 1
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Abstract

Background: Betel-nut chewing (BC) causes oral submucous fi brosis (OSF), and this leads to diffi cult tracheal intubation (DI). Unanticipated DI was reported in chew with apparently normal preoperative airway evaluations (PAEs). This analysis aims to investig whether BC is an independent risk on DI besides the common DI risk prediction factors.

Methods: After the approval of Institutional Review Board and the written informed consent were obtained, 2,682 patients were enrolled in a cohort. PA intubation difficulty scale (IDS), intubation time, and perceived DI were recorded prospectively. All 805 m patients received classical intubation, 307 with BC and 498 without BC were analyzed. Data were analyzed Student’s t-test and chi-square test. Stepwise logistic regression was performed to identify effects on IDS adjusting for related factors with WEKA (Waikato Environment for Knowledge Analysis; Mach Learning Group at the University of Waikato, Hamilton, New Zealand).

Results: Fewer BC patients were Cormack–Lehane (CL) grade I (38.9% vs. 47.6%) or IDS degree “Easy” (24.8% vs. 33.5%). Compared with IDS degree “Easy”, patients in BC group had a signifi cantly higher odds ratio (OR) for “Slight + Moderate–Major” degree than in non-BC group (adjusted OR, 1.75; 95% CI, 1.15–2.68). Compared with CL grade I, patients with BC an independent risk for II (adjusted OR, 1.53; 95% CI, 1.02–2.32) and IV (adjusted OR, 3.25; 95% CI, 1.01–10.49). Otherwise, patient’s age ≥ 46 and the presence of teeth were also signifi cant risk fact for IDS degree “Slight + Moderate–Major”.

Conclusion: BC increased not only the tracheal intubation diffi culty in patients with apparent OSF but also in patients with PAEs. BC is an independent risk fac besides the commonly used DI prediction factors. We suggest physicians operating on BC patients to better prepared for DI.

Keywords

betel-nut chewing, Cormack–Lehane grade, diffi cult tracheal intubation, intubation diffi culty scale (IDS), Macintosh blade


Introduction

Unanticipated diffi cult intubation (DI) is one of the most serious problems in anesthesia.1-4 Betel-nut chewing (BC) is well recognized as being associated with the pathogenesis of oral submucous fibrosis (OSF),5-7 which may lead to trismus, resulting in DI.8 Alternative intubation methods like fiberoptic intubation are commonly used when physical appearance abnormalities are identified.8-10 Unfortunately, unanticipated DI has been reported even in BC patients without trismus.11,12 Few studies have been structured Unanticipated diffi cult intubation (DI) is one of the most serious problems in anesthesia.1-4 Betel-nut chewing (BC) is well recognized as being associated with the pathogenesis of oral submucous fibrosis (OSF),5-7 which may lead to trismus, resulting in DI.8 Alternative intubation methods like fiberoptic intubation are commonly used when physical appearance abnormalities are identified.8-10 Unfortunately, unanticipated DI has been reported even in BC patients without trismus.11,12 Few studies have been structured to clarify the effects and the prediction of BC on DI on patients with BC whose preoperative airway evaluations (PAEs) are appropriate for laryngoscopic intubation.13 The exact clinical effect of BC on DI on patients with normal physical appearance remains to be studied.

BC is common in South and Southeast Asia,5 China,7 and Taiwan,14 and has expanded to North America and Europe along with immigration from these regions.5,15,16 Besides the global expansion of BC, the number of younger betel-nut chewers and the use of commercial betel compounds are on the rise. Thus, an increase in the number of patients with BC undergoing intubation can be anticipated. A pilot study conducted by this team on BC and DI with 105 patients with long term BC found a tendency of higher Cormack–Lehane (CL) grade on BC patients (P = 0.10), though the results were statistically insignificant.13 The insignificant results were suspected to stem from the small patient number and the lack of analysis using a structured prediction model and the intubation difficulty scale (IDS).17

This study aims to clarify the effects of longterm BC on DI when PAEs is appropriate for classical laryngoscope intubation by measuring outcomes with IDS17 and intubation time in a clinical setting.

Methods

Patients enrolled in this study were participants in the prospective anesthesia-related outcomes longitudinal observation study. After approval from the Ethics Committee of Ditmanson Medical Foundation Chia-Yi Christian Hospital and the written informed consent from each patient were obtained (Ditmanson Medical Foundation Chia-Yi Christian Hospital Institutional Review Board: 097028; from January 2008 to December 2014), adult male patients that received tracheal intubation under direct laryngoscopy with a #3 Macintosh blade with or without BC were analyzed. The male patients were enrolled for analysis because the female patients with BC were few in our population. Patients, with a history of long-term BC (those who chewed betel-nut daily for over 5 years) were in BC group otherwise in non-BC (NBC) group. All patients were intubated after 5 attempts and 12 (1.5%) patients needed at least 3 attempts. No patients were impossible to intubate (IDS score = ∞).

Except the details of BC history, the commonly used PAEs parameters including gender, age, body mass index (BMI), and detailed airway physical examination with discrete data for cervical spine mobility, dentition, neck anatomy, thyromental distance, jaw protrusion, mouth opening, and Mallampati oropharyngeal classification (as modified by Samsoon and Young)18,19 were measured and recorded pre-operation by the research assistants as a routine but not talked to intubation doctors. Risk scores were defined as follows: “Limited thyromental distance”, thyromental distance < 6 cm; “Limited jaw protrusion”, maximal protrusion of the mandibular incisors or gums to extend past the maxillary incisors or gums < 0.1 mm; “Limited mouth opening”, maximum mouth opening (MMO) < 4 cm; “Neck thickness”, neck circumference ≥ 40 cm; “Limited neck extension”, Mallampati score ≥ 3; male gender, age ≥ 46 years old, and BMI ≥ 30 kg/m2 were also recorded as binary risk factors. A history of snoring was recorded as reported by the patients. The presence of much facial hair, teeth, previous neck radiation, or mass was recorded as well. The above risk factors each summation to yes = 1/ no = 0 were summed into a 12-point difficult airway management prediction score, and then transformed into a 5-grade risk index classification system (0–3 points, grade I; 4 points, grade II; 5 points, grade III; 6 points, grade IV; ≥ 7 points, grade V), which followed the report by Kheterpal et al.20

After the induction, the anesthetists reported the direct view score according to the CL grade (I– IV),21 the lifting force required (subjectively increased lifting force is necessary during laryngoscopy = 1), the necessity of external laryngeal pressure (if necessary = 1), and the position of the vocal cords (adduction = 1) and the research assistants recorded the number of supplementary attempts, the number of supplementary operators, and alternative techniques required for successful tracheal intubation. The data were used to calculate an IDS score as the primary outcome for each patient. Degree of IDS difficulty was clustered this score into 5-grade degrees which narrated below as IDS = 0 called “Easy”, IDS = 1–5 called “Slight difficulty”, IDS > 5 called “Moderate to major difficulty (Moderate–Major)”, and IDS = ∞ called impossible).17 The intubation time (seconds) and the perception of intubation difficulty were set as the secondary outcomes. In the meantime, a research assistant recorded the time (seconds) at each attempt and summed to the duration of successful intubation.

Continuous variables are presented by mean and standard deviation and categorical variables by count and percentage. Differences between group means were analyzed by Student’s t-test for continuous variables and associations between groups, and categorical variables were analyzed by chi-square test or Fisher’s exact test, as appropriate. We used logistic regression to build up a prediction model for IDS scores. BC (> 5 years), BMI, age, teeth (with or not), presence of facial hair (yes or no), neck circumference (cm), Thyroid mental distance raw score (cm), snore (yes or no), neck movement free (yes or no), smoking experience (yes or no), limited teeth protrusion (yes or no), history of previous neck radiation or mass (yes or no), unstable or limited neck (yes or no), and Mallampati score were considered as a pool of candidate predictors in the model building process (Table 1). Stepwise selection with entry and stay P values both set at 1.0 were applied for the search of predictors at each stage, and the Akaike information criterion (AIC) and Schwarz Bayesian Criterion (SBC) of the selected models at each stage were computed. All the successive selected models were compared, and the smaller AIC or SBC were, the better model fit the data. All statistical assessments were two-sided and evaluated at the 0.05 level of significance, and the analyses were performed with WEKA software (Waikato Environment for Knowledge Analysis; Machine Learning Group at the University of Waikato, Hamilton, New Zealand).

Table 1. Clinical Characteristics of Included Studies
Table 1.
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Results

A total of 809 male patients that received tracheal intubation under direct laryngoscopy with a #3 Macintosh blade were enrolled. Four patients without BC information had been excluded. Finally, 805 male adult patients were enrolled for analysis, with 307 in the BC group and 498 in the NBC group. The 12-risk-factors in the DI prediction score (Kheterpal score [K score] 0–12) which was reported by Kheterpal et al.20 were compared. This score clustered to 5 classes said class I, K score = 0–3; class II, K score = 4; class III, K score = 5; class IV, K score = 6; class V, K score = 7–12. Most of the individual risk factors as well as the total score were similar between the groups (Table 1), except for history of previous neck radiation or mass (P = 0.01), smoking experience (P < 0.001) which was significantly higher, and presence of teeth (P = 0.03) which was significantly lower in the BC group. More patients had unstable cervical spine or limited neck extension in the NBC group (P = 0.04). Although there was no significant difference in the 5-class risk index classification between the groups, fewer patients with class I (easy) in the BC group were found when comparing risk index class I with > 1 (K score 0–3 and > 3). Although 12 risk factors were identified, no patient in the dataset possessed all 12 risk factors. As a result, class V comprises patients with 7–10 risk factors.

No significant difference was found between the groups in the IDS score or its contributing factors except the CL grade (P = 0.005) and degree of IDS difficulty (P = 0.02). Patients in the BC group had higher CL grade II (44.1% vs. 32.7%), IV (3.3% vs. 2.0%). As to IDS degree, more patients in the BC group were more at IDS slight degree difficulty (73.9% vs. 64.7%) and less at easy than the NBC group. All patients were intubated after 5 attempts and 12 (1.5%) patients needed at least 3 attempts. No patients were impossible to intubate (IDS score = ∞). There was no significant difference in the number of attempts required for successful intubation (P = 0.61). The 12 patients that needed ≥ 3 attempts comprised 9 in the NBC group (1.8%) and 3 in the BC group (1.0%) (P = 0.61). 19.7% of patients had a perceived difficulty of intubation grade ≥ 3 on the 4-point scale (a total of 42 cases, with 13.7% in the BC group and 17.7% in the NBC group). The total time to successful intubation was also similar for the two groups (25.4 ± 21.6s vs. 27.4 ± 21.1s in the NBC and BC groups, respectively; P = 0.23) (Table 2).

Table 2. The IDS and Intubation Difficulty Measurements Between BC and NBCa
Table 1.
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The “Moderate–Major” degree of difficulty from IDS was 1.6% (n = 13), so we combined it with “Slight difficulty” as “Slight + Moderate–Major” degree. The univariate analysis showed that the degree of difficulty from IDS was significantly higher in “Slight + Moderate–Major” degree in the BC group than in the NBC group (75.2% vs. 66.5%, P = 0.008) (Table 2).

The logistic regression results show that the model with three predictor variables, BC, age > 46, and with teeth, had the lowest sum of AIC and SBC. The Cox Snell R square of this model was 0.046, the Hosmer and Lemeshow’s chi-square goodness of fit test was 7.8 (P = 0.456), and the area under receiver operating characteristics curve was 0.63 (95% confidence interval [CI], 0.58–0.68). Table 3 shows the odds ratios and associated 95% CI for this three predictor model.

Table 3. Results of the Multinomial Logistic Regression Analysis Between Long Term BC and IDS Degreea
Table 1.
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Discussion

Our data represents that there were fewer patients in the BC group with an IDS degree of “Easy” and CL grade I than in the NBC group (Table 2). This echoes the report by Narendra et al. those patients with BC may present with increased intubation difficulty.12 Furthermore, the multinomial logistic regression analysis showed long term BC is independently associated with IDS difficulty degree with an odds ratio of 1.15–2.68. This showed that long term BC is an independent risk factor for DI besides age and presence of teeth (Table 3). It may be necessary to take into consideration when patients over a long term used betel nut even though they are with normal PAEs.

Predicting the difficult airway management is not easy.22 Kheterpal et al. developed a 12 grades difficult mask ventilation combined with a difficult laryngoscopy prediction score from analysis of a 176,679 cases cohort.20 The Kheterpal score20 was higher in the BC group (P = 0.04, Table 1) in our analysis. More patients with long term BC had neck radiation or mass, unstable or limited neck movement, and lost teeth. The first two may be related to OSF. The prevalence of OSF in Taiwanese with BC has been reported to be as high as 14.3–24.4%.14 According to this ratio, there should be 44–75 cases in our BC group with OSF. However, only 4 (1.3%) of our patients with BC had “Moderate–Major” degree of IDS difficulty, and only 3 (1%) needed more than 3 attempts before successful intubation. That may because OSF can form in any location in the oral cavity, and it may be mild or in an area that does not cause trismus.5 Also, patients with limited MMO or oral cavity tumors were intubated with alternative intubation devices and were not included in this study.

The IDS with 7 contribution factors is believed to be a comprehensive DI measurement score. The degree of IDS difficulty was significantly higher in the BC group. However, the CL grade was the only factor higher in the BC group (Table 2). This suggests that CL grade may be a prominent factor for DI measurement in well-experienced anesthesiologist’s clinical practice.

A history of smoking has been suggested to be related to OSF and DI.23 Smoking patients had a significantly higher degree of DI. However, most patients with a history of smoking also had BC. Statistically, the smoking experience was significant in univariate analysis but was excluded as a covariate in multinomial logistic regression (Table 3). Though some previous reports suggested a synergistic effect of smoking20,23 and BC on DI, this was not identified in this analysis or other studies.14 However, few people in Taiwan chew tobacco along with betel nut. Patients with tobacco chewing receive direct tobacco stimulation on the mucosa, which may have a stronger effect than inhalation of tobacco smoke. The combined effect of BC and tobacco chewing on tracheal intubation requires further study.

DI is believed to be multi-factorials. Several existing models have been used to predict DI but most are limited in prediction power.22,24,25 The commonly used risk factors for quantitative prediction of DI were derived by Kheterpal et al.20 which was tested in this cohort but no significant difference was found between the groups either. Although there were significantly more patients with neck radiation or mass in the BC group, this was not an independent predictor of increased IDS score confirmed by multinomial logistic regression. That the risk factors used in difficult mask and DI risk predictors have less impact than long term BC in logistic regression analysis showing that the effects of BC on DI may be independent of the traditional factors, and more study is expected.

Our data have several limitations. This study is a prospective cohort design. Although the PAEs was done by the researchers who were independent of clinical practice and did not show the PAEs data to intubation doctors before intubation. We cannot exclude the possibility of the effects of PAEs characters on the subjective feeling of DI. But the subjective feeling DI scores were not higher in BC groups. In addition, because BC usually make teeth brown, it is difficult to be designed as double-blind design. Secondly, all the doctors were well-trained anesthesiologists—with at least 7 years of clinical anesthesia experience. As anesthesiologists in Taiwan practice an average of 1,500 anesthesia per year, 80% of which are intubated general anesthesia, most of our participating doctors may have more than 7,000 tracheal intubation experiences, and this may not be the case at all institutions. Third, our data focused on male patients only, since few females here were the long-term betel-nut chewers (14 patients, 1.1%). Thus, our data cannot be extended to the female betel-nut chewer. Differences in the demographics of BC should be taken into consideration when attempting to apply these findings to other populations. Finally, severe DI is not commonly encountered, and our cohort had only 13 patients with “Moderate–Major” airway (IDS score > 5), and none of the case with (IDS = ∞) which contributed to lack of power to discover the exacter effect of BC on severe DI.

In conclusion, BC is an independent risk increasing the IDS degree when patients’ PAEs apparent normal besides the commonly used prediction factors. Our results suggest that physicians operating tracheal intubation in patients with BC should be prepared for DI better.

Funding

This study was granted by Ditmanson Medical Foundation Chia-Yi Christian Hospital (CYCH097028). This study was partially granted by National Cheng Kung University Hospital (NCKUH- 10609010).


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References

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