Comparison of the angle deviation of the nose line to the mentum and Mallampati test in predicting the difficult airway before anesthesia

ABSTRACT

Introduction:

A high percentage of dangerous events in anesthesia occur due to airway problems, and proper airway management is always one of the key points during anesthesia. Airway management in critically ill patients is one of the most stressful situations for primary care physicians and even for anesthesiologists. The aim of this study was to evaluate the anatomical features of patients’ airways, including the angle of deviation of the nasal line from the nasal to the mentum (NMLD), and perform a Mallampati test.

Method:

This cross-sectional study was performed on all patients admitted to Shohada Hospital in Tabriz, Iran, who were candidates for elective surgery for 1 year and 6 months, and underwent endotracheal intubation. Based on laryngeal observation, patients were classified into four groups. Then, all data related to individuals including type of surgery, age, sex, weight, height, body mass index (BMI), and nasal mentum line deviation (NMLD) were recorded. Then, all the collected data were analyzed using SPSS software version 19.

Results:

A total of 85 patients from 17 to 67 years with a mean age of 37.64 ± 12.89 were studied. There was a statistically significant relationship between laryngoscopy difficulty and Mallampati score (P = 0.001). The findings showed a statistically significant relationship between laryngoscopy difficulty and the mean NMLD (P = 0.01). A Mallampati of 85% indicates laryngoscopy difficulty. Also, NMLD can predict laryngoscopy difficulty by up to 66%.

Conclusion:

The present study demonstrated that both the Mallampati score variable and NMLD are related to the difficult airway problem. Furthermore, the Mallampati score has a higher predictive value for difficult intubation than the NMLD.

Introduction

Perhaps the most important task of an anesthesiologist is to manage the airway in patients, which is mainly done in emergency situations and non-emergency surgeries. As mentioned, rapid airway control in critically ill patients is one of the most stressful situations for primary care physicians and anesthesiologists.[1,2]

A high percentage of dangerous events in anesthesia occur due to airway problems, and proper airway management is one of the important and key points during anesthesia.[3] To manage the airway, obtaining a history, performing upper airway examinations (including head and neck, lower jaw), and opening the mouth help to estimate the possibility of difficulty in airway management and endotracheal intubation.[4,5] Airway anatomical assessments include observable items (such as mouth, teeth, tongue, and neck) and invisible items (e.g., the base of tongue, larynx, and epiglottis).[6] One of the contributing factors to difficult intubation is the nasal mentum line deviation (NMLD), which causes the NMLD to move backward or into the jaw, if the angle is less or more than normal, which in turn makes the intubation difficult. Consequently, to improve the quality of airway assessment, all the above factors should be considered simultaneously.[7,8] Inadequate ventilation, intraesophageal intubation, and endotracheal intubation are the most common mechanisms of severe respiratory consequences in anesthesia.[9] The incidence of difficult laryngoscopy, difficult intubation, and difficult ventilation with a mask is not well defined and has been reported to be 1.5–13%, 1.2–3.8%, and 0.01–0.5%, respectively, according to specialist opinions. There are various examinations to predict intubation before laryngoscopy, including the Mallampati classification, thyromental distance, and anatomical markers.[10] Various factors such as age, weight, race, and pregnancy can affect these indicators. For instance, in patients with acromegaly, the incidence of difficult intubation has been reported to be about 13–30%, which is higher than normal.[11]

According to the statements above, the purpose of this study was to evaluate the anatomical features of the patient’s airway, including the angle deviation of the nose line to the mentum and the Mallampati test in making the prediction of the difficult airway problem before airway surgery.

Materials and Methods

This cross-sectional study was performed on all patients admitted to Shohada Hospital in Tabriz, Iran, who were candidates for elective surgery for 1 year and 6 months, from September 2019 to April 1, 2020 and underwent endotracheal intubation. Patients with inclusion and exclusion criteria were included in the study.

Inclusion criteria include

Having informed consent and undergoing general anesthesia with oral intubation. Exclusion criteria included unwillingness to participate in the study, people with open mouth limitation, individuals with limited movements in the jaw and joints (temporomandibular joint), dental disorders, long mustache, and having a large beard and tongue.

Sample size

During 1 year and 6 months, 85 patients met the inclusion criteria.

Procedure

After obtaining informed and oral consent (for illiterate patients), information related to this study was extracted from patients’ medical records. Then, 1 day before the surgery, patients were referred to an anesthesiologist. The modified Mallampati test was performed for all individuals by the anesthesiologist and the data were recorded in specific forms. The modified Mallampati test was performed while the patient was sitting in a chair and then the patient was asked to open his/her mouth as wide as possible without making any noise or squeezing. Based on laryngeal observation, patients were classified into four groups. Then, all data related to individuals including the type of surgery, age, sex, weight, height, body mass index (BMI), and NMLD were recorded.

Anesthesia was performed on the day of surgery by a second specialist who was blind to previous assessments. Patients with Cormack and Lehane scores I or II were considered easy intubations, and patients with Cormack and Lehane grades III and IV were considered difficult intubations. All patients were evaluated after hospitalization for the following: distance between the upper and lower teeth, thyromental distance, neck movements, Mallampati classification, mandibular dislocation, prominent upper anterior teeth, chin or mandibular backward, intubation difficulty, and BMI.

Patients underwent general anesthesia after entering the operating room and performing the necessary monitoring including non-invasive blood pressure (NIBP), heart rate (HR), and saturation pressure oxygen (SPO₂) and stabilization of baseline values of hemodynamic variables. Ringer’s lactate serum infusion was performed at 5 mL/kg for patients. Induction of anesthesia was started with preoxygenation, and premedication was injected intravenously with midazolam (0.03 mg/kg) and fentanyl (1–2 mg/kg), followed by propofol injection at 2–2.5 mg/kg and atracurium at 0.5 mg/kg and ventilation with oxygen.

After determining the appropriate relaxation rate for intubation by peripheral neurotransmitter and using the TOF (Train of Four) method, intubations were performed by an anesthesiologist when the ratio of fourth response to first response was less than 30%, or disappeared, or its size was less than 30% relative to the base twitch response using twitch stimulation. The degree of laryngoscopy and intubation difficulties was determined using a laryngoscopic score and then recorded in a questionnaire.

Data analysis

Determination tests (sensitivity, specificity, and positive and negative predictive value) and a ROC curve were used to analyze the diagnostic value of the data. The studied quantitative variables were reported as mean standard deviation. Paired and unpaired Student t--tests were used to compare the means obtained in the study groups. All collected data were analyzed using the SPSS software version 19. A significance level of 0.05 was considered.

Ethical considerations

A written introduction letter and written consent were obtained from the officials of the selected research centers. The information of all patients was kept confidential by the project manager. We adhered to all Ethical Declarations of Helsinki and Ethics Research Committees of the University of Medical Sciences. The ethics code was IR.TBZMED.REC.1399.390.

Results

Finally, 85 patients were included in the study, of which 60 (70%) were male and 25 (30%) were female. Their mean age was 37.64 ± 12.89 years. The weight of the patients was 16.57 ± 83.17 kg in men and 13.06 ± 77.44 kg in women. Also, the mean total weight of the patients was 79.29 ± 11.96 kg [Table 1].

Table 1.

Demographic information

Variable	Low	High	Mean
Age	17	67	37.64±12.89
Male weight	65	135	83.17±16.57
Female weight			77.44±13.06
Height	162	185	172.81±5.6
BMI	19	49	26.05±3.7

Chart 1 shows the distribution of the degree of Mallampati and the mean Mallampati score of patients was found to be 1.88 ± 0.778.

Chart 1.

Mallampati score of patients

The distribution of laryngoscopic difficulty is shown in [Table 2], with a mean airway difficulty of 2.05 ± 1.01. Examination of the relationship between laryngoscopic difficulty and Mallampati score showed a statistically significant relationship between these two variables (P = 0.001).

Table 2.

Comparison of the degree of Mallampati and difficult laryngoscopy

Number
Patient’s numbers	Degree of Mallampati				Frequency
	4	3	2	1
32	11	1	7	2	1	Degree of laryngoscopy
26	02	2	19	5	2
18	0	6	12	0	3
9	2	6	1	0	4
85	2	15	39	29		Patient total

The mean angle deviation of the nose line to the mentum [Chart 2] was found to be 3.3 ± 2.04 mm. Examination of the relationship between difficult laryngoscopy and the mean angle of deviation of the nasal line to the mentum showed a statistically significant relationship between these two variables (P = 0.01).

Chart 2.

Nasal mentum line deviation (NMLD)

In [Chart 3], the amount of thyromental distance was examined. The mean distance of thyromental in patients was 5.49 ± 1.6 cm, which was in the range of 2 to 6 cm. The findings showed a statistically significant relationship between difficult laryngoscopy and thyromental distance (P = 0.001).

Chart 3.

Thyromental distance

Chart 4 shows the sensitivity and specificity of the Mallampati degree for the prediction of laryngoscopic difficulties, with an area under the Rock curve of 0.85, indicating that the Mallampati degree had the power to predict airway difficulty. A degree of 85% is a predictor of laryngoscopy difficulty.

Chart 4.

Sensitivity and specificity of Mallampati degree to predict laryngoscopy severity

The NMLD has the power to predict the difficulty of the airway. NMLD was also capable of predicting laryngoscopy difficulties by up to 66%. The area under the curve of both the Mallampati score and the NMLD was greater than 0.5, thus both variables have the power of predicting airway difficulty. The area under the ROC curve of Mallampati for predicting laryngoscopy difficulties was found to be greater than the area under the ROC curve of NMLD [Figure 1 and Chart 5].

Figure 1.

Nasal mentum line

Chart 5.

Sensitivity and specificity of the NMLD for prediction of laryngoscopy difficulties

Discussion

One of the most important causes of death in patients under general anesthesia is the failure to maintain a patent airway.[12]

Various studies have been conducted in this regard. In the study of Honarmand et al., the mean weight of patients was estimated to be 67.7 ± 3.2 kg, showing a strong correlation between weight gain and intubation difficulties, where obesity has increased the risk of intubation.[13] In the present study, the mean weight of patients was 79.29 ± 11.96 kg. Although this mean was found to be higher than the findings of the study,[14] the findings of our study showed a similar result where increasing body mass was associated with the possibility of intubation difficulties. Ezri et al.[15] also suggested that increasing the age increases the incidence of intubation difficulties in male patients with obesity (BMI ≥35). This finding is in line with the results of the present study. In this study, 64.7% of patients had grades 2 and 3 Mallampati, among which the increase in BMI indicated the relationship between obesity and intubation difficulty. In the study of Roh et al.[16] both the sensitivity and specificity of Mallampati were found to be 88%. These findings are very close to the results of the present study, where the sensitivity and specificity of Mallampati were 85%. However, Brodsky et al.[17] argue that the standard Mallampati class was not reliable for predicting intubation difficulty.

In the study of Rosenblatt et al.[18] the mean angle of extension of the neck, thyromental, and the mean distance of the upper and lower front teeth, which were considered as the criterion for intubation difficulties, were considered to be better than the mean. In this study, neck extension of at least 35 degrees, mouth opening (distance between upper and lower anterior teeth) by 4 cm, and thyromental space of 6 cm were considered as the minimum necessary criteria for successful intubation for neck extension angle study.

The results of this study were consistent with those of the present study, because in this study, like the other studies, the findings of the thyromental distance were evaluated based on a deviation of 6 cm and showed a statistically significant relationship between laryngoscopy difficulties and thyromental distance. Although none of the studies have determined the most sensitive and specific criteria for diagnosing intubation difficulties, the rate of opening of the mouth with 96.3% specificity was the highest criterion.[19] In the same study, the motility of the atlantoaxial joint and the distance from the thyroid cartilage to the chin were 89% and 87%, respectively, which was very close to the findings in this study because the Mallampati score sensitivity was found to be 85% for predicting intubation difficulties.

Therefore, it is not possible to compare these variables with confidence. Also, some of the differences may be related to differences in the method of implementation or different definitions of intubation difficulty.

In the present study, a clear relationship was found between a number of anatomical features such as the thyromental distance and the NMLD with laryngoscopy difficulties. Ambesh et al.[20] also suggested that the degree of Mallampati, neck movements, and thyromental distance are of little value in predicting the nose of intubation; this result is contrary to the findings in this study. Also, in this study, anatomical features such as the presence of prominent anterior teeth and backward movement of the mandible were not observed in patients, whereas the presence of dental problems was mentioned in all previous studies.[21] In this study, the degree of difficulty of intubation was higher in women, which is not consistent with previous studies. The reason for these differences may be due to the small sample size or differences in the definition of intubation difficulty or differences in the airway anatomy of these patients compared to previous studies.

Conclusion

The present study showed that both the Mallampati score variable and NMLD are related to the difficult airway problem. Furthermore, the Mallampati score has a higher predictive value for difficult intubation than the NMLD.

This article is taken from a Thesis

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Conflicts of interest

There are no conflicts of interest.