The use of ultrasound in the assessment of difficult laryngoscopy in children

Abstract

AimIn this study, we aimed to investigate whether ultrasound anatomic measurements of the airway prior to anesthetic administration could be used as a predictive standard for difficult intubation in children undergoing surgery under general anesthesia.MethodsThis observational study included 100 patients with an ASA I-III risk score between the ages of 0-6, whose operation was planned under general anesthesia. Age, height, body weight, Cormack-Lehane Classification and distance from skin to pre-epiglottic space (EPI), distance from skin to thyroid cartilage (TC), distance from skin to the anterior commissure (VCA) of vocal cord, distance from skin to posterior commissure (VCP) of the vocal cord and distance from skin to the hyoid bone (HYO) was recorded. These parameters were studied to examine the relationship between the classification of Cormack-Lehane.ResultsCormack Lehane classification Grade III and above were determined in 9 (9%) patients. There was a statistically significant relationship between intubation difficulty and distance from skin to the thyroid cartilage.ConclusionThe ultrasound parameters we studied, with the possible exception of TC, which was not compared to any other anatomical, radiological or surface anatomy measurement, are virtually useless in predicting intubation difficulty in 0 – 3 years.

Keywords

Introduction

In the pediatric population, ‘intubation time’ and ‘airway security’ are critical due to the anatomic and physiologic characteristics. In pediatrics, a smaller lung volume, and functional residual capacity in particular, considerably reduce apnea tolerance. Despite optimal preoxygenation of sufficient duration to prevent desaturation in children, no “safety period” can be established even for short-lasting apnea events.^1-2 Although measurement of anatomic structures and various scoring systems can be used, the Cormack–Lehane (CL) classification system has proven to be the best method for describing difficult intubation. CL classification has therefore become a standard for the investigational description of difficult laryngoscopy in anesthesia.^3-4-5 But although it is the standard for describing difficult intubation, it cannot be used in the preoperative evaluation as it is too invasive for a conscious patient.⁶
Airway assessment by ultrasound is an important non-invasive, cost-effective, and instructive method. Although it has not yet been established as a standard method for assessing the airway of patients, it has great potential in the prediction of difficult airway.⁷ However, there is a paucity of information focusing specifically on such methods in pediatric population where equipment, technique, and challenges are different.⁸ In the present study, the aim was to investigate whether ultrasound anatomic measurement of the airway prior to anesthetic administration could be used as a predictive standard for difficult intubation in children undergoing surgery under general anesthesia.

Materials and Methods

The study was conducted after obtaining written informed consent from the parents after the approval of the local ethics committee (2019/463) and in accordance with the ethical standards laid down in the 1964 Declaration of Helsinki revised in the year 2000.
A total of 100 patients who were aged 0–6 years, included in ASA (American Society of Anesthesiologists) classification groups I–III, and scheduled for endotracheal intubation under general anesthesia prior to elective surgery were included in the study. Patients without parental consent, with significant airway malformations, with head and neck deformities were excluded from the study. All tests and endotracheal intubation attempts in the study were performed by the same surgeon with four years of experience.
Demographic characteristics recorded in the preoperative evaluation were age, sex, body weight, weight percentile, height, and body mass index (BMI). For all patients whose difficult intubation was assessed with CL classification and ultrasound, the distances between the pre-epiglottic space and the skin (EPI), between the thyroid cartilage and the skin (TC), between the anterior commissure of the vocal cord and the skin (VCA), between the posterior commissure of the vocal cord and the skin (VCP), and between the hyoid bone and skin (HYO) were measured in centimeters. Ultrasound examinations were performed using a GE LOGIQ e (GE Healthcare, USA) ultrasound scanner.
Midazolam at a dose of 0.02 mg/kg was administered intravenously to all patients as premedication before surgery. After the patient was taken to the operating room, standard monitoring (ECG, pulse oximetry, non-invasive arterial blood pressure) was performed. During induction, bolus doses of 0.5–1 µg/kg of fentanyl and 1-2 mg/kg of propofol were administered intravenously. After establishing that the patient was able to be ventilated with an appropriate mask, rocuronium was administered intravenously at 0.6 mg/kg in order to induce muscle relaxation. Laryngoscopy was initiated 2–3 minutes after the administration of rocuronium.
Under ventilation with a mask, the neck was brought into extension for measurement. A hockey stick probe (8–16 MHz) placed transversely in the submandibular region of the patient was moved in the transverse plane from cranial to caudal without changing its position. Distances between the hyoid bone and the skin (HYO), between the pre-epiglottic space and the skin (EPI), between the thyroid cartilage and the skin (TC), between the anterior commissure of the vocal cord and the skin (VCA), and between the posterior commissure of the vocal cord and the skin (VCP) were measured in centimeters and recorded. Direct laryngoscopy was performed with Macintosh blades 0, 1, or 2. The condition of the vocal cords was assessed through their laryngoscopic appearance using CL classification. Patients were intubated and any complications during laryngoscopy were recorded.
In accordance with the CL classification system, if the glottis was completely visible, the patient was evaluated as grade I; if it was partially visible, they were evaluated as grade II; if only the epiglottis was visible, they were evaluated as grade III; and if even the epiglottis was not visible, they were evaluated as grade IV. Intubation was considered difficult if the CL test was grade III and IV despite appropriate head and neck position and the use of a laryngoscope blade.Ethical ApprovalThis study was approved by the Ethics Committee of Gaziantep University (Date: 15.01.2020, Decision No: 2019/463)Statistical AnalysisThe IBM SPSS Statistics 22 (IBM SPSS, Turkey) program was used for statistical analysis. The G Power program was used for power analysis. The conformity of numerical variables with the normal distribution was examined using the Shapiro-Wilk test. In the analysis of the study data, in addition to descriptive statistical methods (mean, standard deviation, median, frequency), the Student’s t-test was used to compare normally distributed parameters between two groups, while the MannWhitney U test was used to compare non-normally distributed parameters between two groups. When comparing three independent groups, an ANOVA test was used for normally distributed numeric variables, while the Kruskal-Wallis and Dunn’s tests were used for non-normally distributed variables. ROC analysis was performed to determine the threshold for significant levels. The MedCalc package program version 19.2.1 was used for ROC analysis. A p-value of less than 0.05 was accepted as significant.

Results

The study was conducted on 100 patients aged 0 to 6 years, including 68 (68%) boys and 32 (32%) girls. Of the patients with difficult intubation, seven (77.8%) were male and two (22.2%) were female. Sixty patients were classified as being ASA I (60%), 30 as ASA II (30%), and 10 as ASA III (10%). The C–L classification was grade I in 34 cases, grade II in 57 cases, and grade III in nine cases. There were no grade IV cases. As grades III and IV were considered difficult intubation, difficult intubation was noted in nine patients (9%), while there was no unsuccessful intubation.
The mean age of the patients was 2.1 ± 1.44 years, mean body weight was 11.72 ±4.56 kg, mean height was 86.62 ± 17.92 cm, and weight percentile was 41.96 ± 28.95. Two of the cases were in the 3% percentile (1.9%), 12 were in the 5% percentile (11.5%), 12 were in the 10% percentile (11.5%), four were in the 15% percentile (3.8%), 16 were in the 25% percentile (15.4%), 26 of them were in the 50% percentile (25%), 14 of them were in the 75% percentile (13.5%), 12 were in the 85% percentile (11.5%), and two were in the 90% percentile (1.9%).
In the study parameters of the cases, VCA was determined as 0.49 ± 0.06 cm, VCP as 1.41 ± 0.17 cm, HYO as 0.54 ± 0.11 cm, TC as 0.42 ± 0.09 cm, and EPI as 1.9 ± 0.22 cm, as the mean values of measurement. When we compared them, evaluated these parameters against one another in ratios, the mean value of VCA/VCP was 0.35 ± 0.05, EPI/VCA was 3.93 ± 0.46, and EPI/VCP was 1.36 ± 0.46 (Table 1).
The mean age of the patients with difficult intubation was 1.88 ± 1.22 years, the mean body weight was 10.83 ± 4.16 kg, the mean height was 83.22 ± 16.99 cm, and the weight percentile was 28.89 ± 17.09.
In accordance with their CL classification, the cases were divided into two groups: difficult and simple intubation. There was no statistically significant relationship between intubation difficulty and VCA, VCP, HYO, EPI, EPI/VCP ratio, and EPI/VCA ratio (p>0.05). There was a statistically significant relationship between intubation difficulty and TC (p<0.05). There was a statistically significant relationship between intubation difficulty and VCA/VCP ratio (p<0.05) (Table 2).
The statistical sensitivity of TC was 77.78%, its specificity was 72.53%, and its cut-off value was 0.38 cm. The statistical sensitivity of the VCA/VCP ratio was 66.67%, its specificity was 82.42%, and its cut-off value was 0.31 cm (Figure 1).

Discussion

The aim of the present study was to investigate whether ultrasound anatomic measurement of the airway prior to anesthetic administration could be used as a predictive standard for difficult intubation in children undergoing surgery under general anesthesia.
Skilled airway management is the cornerstone of high-quality anesthesia management. Airway complications remain a common cause of anesthesia-related complications in children because of their unique anatomy and physiology.⁹ In a retrospective study of 11,219 pediatric patients undergoing general anesthesia with endotracheal intubation, the rate of difficult direct laryngoscopy (CL grades III and IV) was 1.35%. The rate of direct difficult laryngoscopy was highest in children younger than 1 year old (0.7% in children older than 1 year vs. 4.7% in children younger than 1 year). Other predictors of difficult intubation were being classified as ASA III or IV, having a higher Mallampati score (if available), a lower body mass index, and a history of oromaxillofacial or cardiac surgery.¹⁰ Valois-Gomez et al. reported that the incidence of intubation difficulty was 1.2% in a sample of 484 children aged 0 to 8 years.¹¹ In a prospective multicentre study by Fiadjoe et al., difficult tracheal intubation occurred in 2–5 per 1000 pediatric anesthesia cases .¹²
Many different airway measurements have been used to predict difficult laryngoscopy in children. In a study on the airway of children younger than 5 years undergoing cardiac catheterization, it was concluded that body mass index, lower lip-to-chin distance (LCD), and thyromental distance (TMD) could be used to predict difficult laryngoscopic view. In the same study, the incidence of difficulty in viewing the larynx was 4%.¹³ However, our study found a higher rate than these studies, with an incidence of 9% for difficulty in viewing the larynx. It is critical to assess and recognize the potential for difficult airway prior to any procedure so that appropriate equipment and resources are available. For this reason, it has been emphasized that the relationship between various sonographic parameters and difficult airway should be investigated using point-of-care ultrasound (POCUS) for airway evaluation.¹⁴ Ultrasound has many advantages in upper airway imaging; it is safe, fast, portable, and accessible. It provides real-time static and dynamic images of various clinical indications of airway management.¹⁵
In a study on 130 adult patients, Parameswari et al.¹⁶ found that an ultrasonographically-measured distance between the epiglottis and the skin, based on CL classification, was the most sensitive (75% sensitivity) and the most specific (63.6% specificity) parameter in predicting difficult laryngoscopy. In a study on 301 patients, Falcetta et al.¹⁷ measured anterior cervical soft tissue thickness with ultrasound at two levels (thyrohyoid membrane.[epiglottic area] and vocal cords.[entry of the larynx]) on adult patients and found a high correlation between pre-epiglottic tissue thickness at the level of the thyrohyoid membrane and CL classification in predicting limited/difficult intubation. The fact that we have not come across any significant findings in the epiglottis region can be explained by the fact that our study was performed on pediatric patients.
In a pilot study conducted with 51 adult patients, Adhikari et al.¹⁸ demonstrated that sonographic measurements of anterior neck soft tissue thickness at the level of the hyoid bone and thyrohyoid membrane can be used to discriminate between difficult and easy laryngoscopy, by comparing the anterior neck soft tissue thickness measured at the level of the hyoid bone and thyrohyoid membrane against CL classification. The present study demonstrated a statistically significant correlation between the difficulty of intubation and the distance between the thyroid cartilage and the skin.
In their study on 72 patients, Gupta et al..¹⁹ found that the PES/EVC (pre-epiglottic space/distance between the epiglottis and the vocal cord) value was positively correlated with CL classification. In a study conducted with 100 patients, Reddy et al.³ showed that when measurements are taken using ultrasonography and based on CL classification, the PES/EVC value has a low-to-moderate predictive value in predicting difficult intubation. The sensitivity of the PES/EVC value was 1.2%, its specificity was 86.7%, its positive predictive value was 33.3, and its negative predictive value was 13.4%. There was a statistically significant relationship between intubation difficulty and the VCA/VCP ratio in this present study. However, we believe that there is room for more studies in this field as the results and anthropometric measurements of ultrasound studies are influenced by various parameters such as race and geography.

Conclusion

In this present study, TC and the VCA/VCP ratio were found to have a statistically significant relationship with CL classification. However, due to the multiple anatomic factors involved in difficult intubation and the lack of an ideal prediction test, an unexpectedly difficult airway should always be considered. Radiographic examination of the anatomy of the region, a method which has recently gained importance, can help predict difficult intubation during physical examination. The ultrasound parameters we studied, with the possible exception of TC, which was not compared to any other anatomical, radiological or surface anatomy measurement, are virtually useless in predicting intubation difficulty in 0 – 3 years.

References

1. Hsu G, von Ungern-Sternberg BS, Engelhardt T. Pediatric airway management. Curr Opin Anaesthesiol. 2021;34(3):276-283. doi:10.1097/aco.0000000000000993
   Article · PubMed · Google Scholar
2. Hardman JG, Wills JS. The development of hypoxaemia during apnea in children: a computational modelling investigation. Br J Anaesth. 2006;97(4):564-570. doi:10.1093/bja/ael178
   Article · PubMed · Google Scholar
3. Reddy PB, Punetha P, Chalam KS. Ultrasonography: a viable tool for airway assessment. Indian J Anaesth. 2016;60(11):807-813. doi:10.4103/0019-5049.193660
   Article · PubMed · Google Scholar
4. Cook TM. A new practical classification of laryngeal view. Anaesthesia. 2000;55(3):274-279. doi:10.1046/j.1365-2044.2000.01270.x
   Article · PubMed · Google Scholar
5. Law JA, Broemling N, Cooper RM, et al. The difficult airway with recommendations for management—part 2: the anticipated difficult airway. Can J Anaesth. 2013;60(11):1119-1138. doi:10.1007/s12630-013-0020-x
   Article · PubMed · Google Scholar
6. Ghatge S, Hagberg CA, eds. Does the airway examination predict difficult intubation? In: Hagberg CA, ed. Benumof and Hagberg’s Airway Management. Philadelphia, PA: WB Saunders; 2009:101-115. doi:10.1016/b978-1-4160-5996-7.00017-1
   Article · PubMed · Google Scholar
7. Daniel SJ, Bertolozio G, McHugh T. Airway ultrasound: point of care in children—the time is now. Paediatr Anaesth. 2020;30(3):347-352. doi:10.1111/pan.13823
   Article · PubMed · Google Scholar
8. Stafrace S, Engelhardt T, Teoh WH, Kristensen MS. Essential ultrasound techniques of the pediatric airway. Paediatr Anaesth. 2016;26(2):122-131. doi:10.1111/pan.12787
   Article · PubMed · Google Scholar
9. Habre W, Disma N, Virag K, et al. Incidence of severe critical events in paediatric anesthesia: APRICOT, a prospective multicentre observational study in 261 hospitals in Europe. Lancet Respir Med. 2017;5(5):412-425. doi:10.1016/s2213-2600(17)30116-9
   Article · PubMed · Google Scholar
10. Heinrich S, Birkholz T, Ihmsen H, Irouschek A, Ackermann A, Schmidt J. Incidence and predictors of difficult laryngoscopy in 11,219 pediatric anesthesia procedures. Paediatr Anaesth. 2012;22(8):729-736. doi:10.1111/j.1460-9592.2012.03813.x
    Article · PubMed · Google Scholar
11. Valois-Gomez T, Oofuvong M, Auer G, Coffin D, Loetwiriyakul W, Correa JA. Incidence of difficult bag-mask ventilation in children: a prospective observational study. Paediatr Anaesth. 2013;23(10):920-926.
    PubMed · Google Scholar
12. Fiadjoe JE, Nishisaki A, Jagannathan N, et al. Airway management complications in children with difficult tracheal intubation from the Pediatric Difficult Intubation Registry: a prospective cohort analysis. Lancet Respir Med. 2016;4(1):37-48. doi:10.1016/s2213-2600(15)00508-1
    Article · PubMed · Google Scholar
13. Maddali MM, Al-Zaabi HMA, Al-Aamri IS, Arora NR, Panchatcharam SM. Preoperative predictors of poor laryngoscope views in pediatric population undergoing cardiac catheterization. Ann Card Anaesth. 2018;21(4):376-381. doi:10.4103/aca.aca_47_18
    Article · PubMed · Google Scholar
14. Gottlieb M, Holladay D, Burns KM, Nakitende D, Bailitz J. Ultrasound for airway management: an evidence-based review for the emergency clinician. Am J Emerg Med. 2020;38(5):1007-1013. doi:10.1016/j.ajem.2019.12.019
    Article · PubMed · Google Scholar
15. You-Ten KE, Siddiqui N, Teoh WH, Kristensen MS. Point-of-care ultrasound of the upper airway. Can J Anaesth. 2018;65(4):473-484. doi:10.1007/s12630-018-1064-8
    Article · PubMed · Google Scholar
16. Parameswari A, Govind M, Vakamudi M. Correlation between preoperative ultrasonographic airway assessment and laryngoscopic view in adult patients: a prospective study. J Anaesthesiol Clin Pharmacol. 2017;33(3):353-358. doi:10.4103/joacp.joacp_166_17
    Article · PubMed · Google Scholar
17. Falcetta S, Cavallo S, Gabbanelli V, et al. Evaluation of two neck ultrasound measurements as predictors of difficult direct laryngoscopy: a prospective observational study. Eur J Anaesthesiol. 2018;35(8):605-612. doi:10.1097/eja.0000000000000832
    Article · PubMed · Google Scholar
18. Adhikari S, Zeger W, Schmier C, et al. Pilot study to determine the utility of point-of-care ultrasound in the assessment of difficult laryngoscopy. Acad Emerg Med. 2011;18(7):754-758. doi:10.1111/j.1553-2712.2011.01099.x
    Article · PubMed · Google Scholar
19. Gupta D, Srirajakalidindi A, Ittiara B, Apple L, Toshniwal G, Haber H. Ultrasonographic modification of Cormack Lehane classification for pre-anesthetic airway assessment. Middle East J Anaesthesiol. 2012;21(6):835-842.
    PubMed · Google Scholar

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