|Year : 2021 | Volume
| Issue : 2 | Page : 83-87
Comparison of confirmation of placement of laryngeal mask airway by fiberoptic laryngoscope and ultrasound examination: A feasibility study
Suvendu Panda, Chitra Chatterji, V Muralidhar, SK Rojalin Baby, Tulika Shrivastav
Department of Anaesthesia, Indraprastha Apollo Hospital, New Delhi, India
|Date of Submission||22-Sep-2020|
|Date of Decision||16-Nov-2020|
|Date of Acceptance||19-Nov-2020|
|Date of Web Publication||16-Apr-2021|
Dr. Suvendu Panda
Senior Resident, Department of Anaesthesia, Indraprastha Apollo Hospital, New Delhi
Source of Support: None, Conflict of Interest: None
Background: The laryngeal mask airway (LMA) is widely used as an effective and safe airway adjunct in the routine practice of anesthesia. There are various methods to assess the correct placement, the gold standard being fiberoptic visualization through the LMA. Ultrasound (USG) is a noninvasive, readily available diagnostic tool and has been used with increased frequency for airway examination. The aim of our study was comparison of fiberoptic and USG evaluation for the confirmation of placement of LMA. Patients and Methods: This was a cross-sectional observational study conducted on 250 patients of American Society of Anesthesiologists Grade 1 and 2, in the age group of 18–65 years undergoing elective surgery under general anesthesia with LMA. The position of the LMA cuff was confirmed by USG and reconfirmed with fiberoptic laryngoscopy (FOL). Results: We observed that the USG Grade 1 was seen in 76.8% of patients as compared to FOL Grade 1 seen in 81.6%. The frequency of LMA misplacement (i.e., Grades 2–4) noted with USG was 23.2% and with FOL was 18.4%. The Bland–Altman scatter plot showed insignificant differences between the two grading systems (near-zero mean: 0.05), with small limits of agreement (−0.509 to +0.609). Conclusion: USG can replace fiberoptic examination for confirmation of the correct placement of an LMA. USG can further give insight into the grading of LMA placement and the cause of airway and ventilation events, which can be corrected and prevented.
Keywords: Fiberoptic, laryngeal mask airway, ultrasound
|How to cite this article:|
Panda S, Chatterji C, Muralidhar V, Rojalin Baby S K, Shrivastav T. Comparison of confirmation of placement of laryngeal mask airway by fiberoptic laryngoscope and ultrasound examination: A feasibility study. Bali J Anaesthesiol 2021;5:83-7
|How to cite this URL:|
Panda S, Chatterji C, Muralidhar V, Rojalin Baby S K, Shrivastav T. Comparison of confirmation of placement of laryngeal mask airway by fiberoptic laryngoscope and ultrasound examination: A feasibility study. Bali J Anaesthesiol [serial online] 2021 [cited 2021 Jun 23];5:83-7. Available from: https://www.bjoaonline.com/text.asp?2021/5/2/83/313885
| Introduction|| |
The laryngeal mask airway (LMA) is a supraglottic airway device, which is widely used as an effective and safe airway adjunct in the routine practice of anesthesia. Main advantages of LMA being a relatively noninvasive airway adjunct, its ease of insertion when compared to endotracheal tube, downside is that it has a greater likelihood of malpositioning, leading to inadequate ventilation, high airway pressure, and partial gastric insufflation. To avoid these complications, it is essential to be able to identify the positioning of the LMA promptly and to be able to reinsert the LMA and ascertain its proper positioning quickly.
The various methods to assess the correct placement are mainly by clinical signs, auscultation, the leakage test, the bubble test, and fiberoptic examination. The leakage test is used most often and, under most circumstances, is good enough to judge LMA placement. However, the technique is not completely reliable, and an incorrect placement may not immediately be recognized until an adverse event has occurred. Fiberoptic examination at present is the most precise means of judging LMA position.
The gold standard for assessing placement of LMA cuff is by fiberoptic laryngoscope (FOL), and various grades have been given according to the structures seen., Ultrasound (USG) has also lately been used for airway visualization and confirming the placement of endotracheal tubes and LMA.
The present study therefore was designed with the primary objective to compare the two techniques, i.e., fiberoptic and USG for the conformation of grade placement of LMA following a classic blind technique. The secondary objectives were to assess the volume required for cuff inflation to prevent leakage and assess the cuff pressure simultaneously at that cuff volume and also to evaluate the postoperative complications such as nausea, vomiting, and sore throat.
| Patients and Methods|| |
After obtaining the Institutional Ethical Committee Approval No. 101-20120-142-202523 (October 6, 2018) and taking written informed consent, a cross-sectional observational study was conducted on 250 patients of American Society of Anesthesiologists Grade 1 and 2, in the age group of 18–65 years undergoing elective surgery under general anesthesia with LMA. Exclusion criteria included patient's refusal to participate, laparoscopic surgery, patients with full stomach, pregnant patients, patients with body mass index (BMI) >35 kg/m2, patients with previous upper airway surgery, and patients with uncontrolled cardiac or pulmonary disease.
In the operation theater, after securing peripheral venous access, standard monitoring, i.e., noninvasive blood pressure, electrocardiography, and pulse oximetry, were attached. A standard general anesthetic technique was used in all the patients. After 3 min of preoxygenation, patients were induced with fentanyl 2 mcg/kg and propofol 2 mg/kg. The muscle relaxation was achieved with atracurium 0.5 mg/kg.
An appropriate-sized Ambu® Aura40™ LMA 3 or 4 was selected depending on the body weight and placed using the classic, blind technique, i.e., with neck flexion, head extension, and full deflation of the cuff, and the use of index figure to press the LMA and advance it along the palatopharyngeal curve, until the resistance was sensed. Cuff was inflated with saline up to a maximum of 20 ml for side 3 and 30 ml saline for size 4 LMA, until the no more air-leak was heard by auscultation. At this time, the volume required to inflate the cuff and the pressure of the cuff were measured by cuff manometer. If still there was leak or patient could not be ventilated, then it was taken out and we re-applied the similar procedure for the second time. If a patient experienced two failures by the mentioned method, then the patient was discarded from the study and we proceeded with other airway devices.
Anesthesia was maintained with mixture of oxygen, air, isoflurane (set to FiO2 0.3 and MAC 1.0), and atracurium 0.1 mg/kg every 30 min. At the start of surgery, FOL and USG were carried out by two different investigators independently, not revealing the grade of placement to the other investigator for preventing bias. The position of the LMA cuff was confirmed by transverse neck USG, and the image of the USG was subsequently saved on pen drive and later graded by an ultrasonologist as per the grading in [Table 1] and [Figure 1]. FOL was done by the second investigator and grading was done as per Aoyama et al. and [Figure 2].
|Table 1: Proposed grading score of ultrasound confirmation of the laryngeal mask airway position|
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|Figure 1: Airway anatomy with ultrasound. *Thyroid cartilage. Ultrasound transducer position on the anterior neck, midline transverse view. AC: Arytenoid cartilages, SM: Strap muscle, VL: Vocal ligaments|
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|Figure 2: Structures seen with fibreoptic laryngoscopy through laryngeal mask airway|
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Transverse USG views of the LMA cuff was obtained with progressive transverse tilt of the wide band linear array probe (8–13 MHz). USG machine used was Venu 40 and FOL was done with Karl Storz Fiberscope. Ondansetron 4 mg was given 30 min before extubation. Reversal was done with injection neostigmine 0.05 mg/kg body weight and glycopyrrolate 0.01 mg/kg body weight. After taking out LMA, patients were shifted to the recovery room, and when completely awake, all the patients were asked about any complaints of sore throat, nausea, and vomiting.
Statistical analysis was conducted with the Statistical Package for the Social Science system version SPSS 25.0 (IBM Corp. Released 2017. IBM SPSS Statistics for Windows, Version 25.0. IBM Corp., Armonk, NY, USA). Continuous variables were presented as mean ± standard deviation or median (interquartile range) for unnormally distributed data. Categorical variables were expressed as frequencies and percentages. Nominal categorical data between the groups were compared using Chi-square test or Fisher's exact test as appropriate.For all statistical tests, a P < 0.05 was taken to indicate a significant difference. “Limits of agreement” with Bland–Altman plot was used to further compare the two methods (USG and FOL grading).
| Results|| |
[Table 2] depicts the distribution of various demographic parameters of the group under the study. It was observed that the mean age of distribution was 38.56 ± 11.45 years, the mean height of distribution was 165.92 ± 6.92 cm, the mean weight of distribution was 66.45 ± 12.84 kg, and the mean BMI of distribution was 24.07 ± 4.66 kg/m2.
[Table 3] portrays the comparison between USG grade frequency and fibreoptic bronchoscope (FOB) grade frequency of the group under the study. We observed that the USG Grade 1 was seen in 76.8% of patients as compared to FOL Grade 1 seen in 81.6%. The frequency of LMA misplacement (i.e., Grades 2– 4) noted with USG was 23.2% and with FOL was 18.4%.
We observed that the mean LMA cuff pressure was 36.18 ± 5.17 mmHg. The mean amount of saline to inflate LMA cuff was 16.8 ± 3.49 mL and median was 16.0 mL. We observed that postoperative nausea and vomiting (PONV) score 0 was seen in 56.8% of the subjects.
[Figure 3] shows the Bland–Altman scatter plot of the differences between the USG and FOB grading. It showed insignificant bias or difference between the two grades (near-zero mean = 0.05), with small limits of agreement (−0.509 to +0.609).
|Figure 3: Bland–Altman scatter plot for the differences in the ultrasound grade and fiberoptic grades of laryngeal mask airway position|
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| Discussion|| |
An appropriately placed LMA usually confirmed by several clinical tests, such as (1) meeting resistance on insertion of the LMA; (2) ventral movement of LMA upon cuff inflation; (3) and effective ventilation as evidenced by chest movement, EtCO2, and ratio of inspired to expired gas volume. The ability to effectively ventilate along with acceptable airway pressure showed a good correlation with correct LMA positioning.
However, several studies have demonstrated that the frequency of suboptimal LMA positioning was 12.8%–49% despite clinically successful ventilation. A suboptimally positioned LMA can maintain an airway to some extent, but the LMA may be at increased risk for further displacement during the operation. Therefore, ensuring optimal positioning of the LMA at the time of insertion becomes necessary.
In our study, LMA was found to be misplaced, i.e., Grade 2– 4, according to FOL in 19.1% of patients, whereas according to USG, it was seen in 24.1% of patients. Kim et al. found that the incidence of LMA malpositioning was higher with FOL as compared to USG, but the incidence of rotation was similar. Füllekrug et al. in their study with the use of fiberoptic found that LMA was in the central position in 59% of cases and malpositioned in 41% of cases with high airway pressure > 25 cmH2O. Ghai et al. compared fiberoptic assessment of LMA position in children using two LMA insertion techniques, i.e., standard and rotational. They found that th incidence of fiberoptic Grades 1 and 2 was 61.5% with standard technique and increased to 92.3% with rotational technique. In our study, the incidence of misplacement in comparison to others was less, and this may be due to a difference in various techniques used for LMA placement, the mean age of the study population taken, and the size and type of LMA used. Kim et al. and Ghai et al. conducted their study on pediatric population, with a mean age of distribution of 28.6 months and 4.35 years, respectively, whereas in our study, the mean age of distribution was 38.56 years. This might imply that pediatric population may have increased incidence of malpositioned LMA as compared to adults.
Gupta et al. in their study also found that USG grade of LMA position strongly correlated with the FOL grade of LMA position. Kim et al. in their study found that the incidence of LMA malposition was higher with FOL, but the incidence of rotation was similar by both the assessment techniques.
We found that in patients with misplaced LMA, there was significant increase in LMA cuff pressure and incidence of PONV and sore throat. Kim et al. found that patients with higher FOL grading had more incidence of PONV. Several studies using FOB, computed tomography, and magnetic resonance imaging have reported that a suboptimal LMA position can be clinically acceptable, but there were data to show that inappropriate positioning of an LMA was associated with airway complications.
In our study, we found that the mean volume of saline to inflate LMA to the point of no leak was 17.02 ± 3.42 ml and the mean LMA cuff pressure measured was 36.64 ± 5.25 mmHg. Increasing cuff volume to 25 ml and above does not improve seal pressure or fibreoptic view, commonly results in a deterioration in both, and may increase the risk of gastric insufflations. The soft low-volume cuff was better able to fit into the variable contours of the periglottic groove than the tensed, high-volume cuff. It was also likely that, at higher cuff volumes, the wedge-shaped tip was displaced from the wedged-shaped hypopharynx causing proximal displacement of the cuff, movement of the epiglottis into the bowl and exposing the oesophageal inlet. This would explain the deterioration in fiberoptic view and the greater gastric insufflations at greater cuff volumes.
The “gold standard” to detect LMA malposition is by FOL LMA grading. Some studies had questioned its accuracy since the grading of LMA placement by FOL depends upon the degree of exposure of various structures visualized. Kim et al. in their study mentioned that though rotation and malposition of the LMA could be easily diagnosed by FOL, the depth of LMA was difficult to know, whereas USG could detect rotation, malposition, as well as depth of LMA placement. Thus, in our study, we had examined the emerging role of USG in the context of bedside real-time airway evaluation of the LMA.
Limitation to this study was the use of only the transverse USG view and the location of probe was not standardized. Thus, the degree of LMA rotation on transverse image may reflect the degree of relative LMA position, but not the solid position within the hypopharynx.
| Conclusion|| |
USG examination can replace fiberoptic examination for confirmation of the correct placement of an LMA. It can further give insight into the grading of LMA placement and the cause of airway or ventilation events, which can be corrected and prevented.
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Conflicts of interest
There are no conflicts of interest.
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[Figure 1], [Figure 2], [Figure 3]
[Table 1], [Table 2], [Table 3]