Microcuff Pediatric Endotracheal Tubes: Evaluation of Cuff Sealing Pressure, Fiber-optic Assessment of Tube Tip, and Cuff Position by Ultrasonography.

BACKGROUND: Use of uncuffed tubes causes lots of morbidity, and there is a surge in the use of microcuff pediatric endotracheal tubes. These tubes are not evaluated in the Indian population. AIMS: The study aimed to evaluate the pediatric microcuff endotracheal tubes in terms of cuff sealing pressure, fiber-optic assessment of tube tip, and cuff position to assess postextubation airway morbidity. SETTINGS AND
DESIGN: Study design involves follow-up analytical study. SUBJECTS AND METHODS: Thirty-four children in the age group of 2-12 years were studied. Patients with leak pressure >20 cm H2O were exchanged with smaller size tube and excluded. Cuff pressure, fiber-optic assessment of tube tip to carina distance in neutral and flexion, ultrasound assessment of cuff position, and postextubation airway morbidity were assessed. STATISTICAL ANALYSIS USED: Parameters expressed as the median with the interquartile range. Nonparametric data were analyzed using the Wilcoxon signed-rank test.
RESULTS: The tracheal leak pressure was <20 cm H2O (median 14.5 cm H2O) in 30 children. Tube exchange was required in four patients. A complete seal was achieved in 30 patients with cuff pressures ranging from 6 to 8.25 cm of H2O (median 8 cm of H2O). The median caudal displacement is 0.8 cm (0.47-1.22 cm) with flexion. There was no airway-related morbidity in any of these patients.
CONCLUSIONS: The microcuff pediatric endotracheal tubes when used according to the age-based formula had a higher tube exchange rate in our study population. However, in children in whom the tube size was appropriate, the tubes provided good sealing without increasing airway morbidity. Further studies with a larger sample size might be required to confirm the findings. Copyright:

INTRODUCTION

The use of uncuffed pediatric endotracheal tubes is fraught with problems such as difficulty in ventilation due to leak around the tube, risk of aspiration, and inappropriate tube size leading to increased airway morbidity.[123] Hence, the need for cuffed endotracheal tubes arises. However, conventional cuffed tubes have inappropriate cuff positions and unreliable higher cuff pressures resulting in airway damage.[23456] This resulted in the introduction of microcuff endotracheal tubes in the pediatric population. The other advantages of microcuff pediatric endotracheal tubes are the presence of high volume, low-pressure cuffs which seals the trachea at pressures lower than the mucosal capillary perfusion pressure[78] and its anatomic design to avoid damage to the injury-prone subglottic region.[9] The anatomical design of the microcuff pediatric endotracheal tubes is based on the Western pediatric population. The appropriateness of tube size and its supremacy over uncuffed endotracheal tubes were studied extensively in the Western pediatric population.[78910] However, the airway anatomy of the Indian pediatric population is different from that of their Western counterparts.[11] Indian children are prone to risks such as inappropriately located cuff, endobronchial migration of the tube tip with neck movements, and subglottic injury due to cuff migration. There are not many studies evaluating the appropriateness of these tubes in the Indian pediatric population. Hence, the appropriateness of microcuff pediatric endotracheal tubes in the Indian pediatric population requires evaluation.

SUBJECTS AND METHODS

This study was registered with the Institute Research Committee (PGMRC/102/2013) and clinical trials registry of India (CTRI/2015/03/005604). This study was a prospective, single-center follow-up analytical study conducted in our institute between May 2014 and January 2015. A total of 34 American Society of Anesthesiologists physical status classes I and II children in the age group of 2–12 years, undergoing elective surgery under general anesthesia were recruited in the study after obtaining approval from the Institute Ethics Committee and written informed consent from the parents. Children with anticipated difficult airway, known airway anomalies, and surgery involving the airway, risk of aspiration, recent history of respiratory diseases, and those with leak pressures >20 cm H2O after intubation were excluded from the study. The included children were premedicated with oral midazolam 0.5 mg.kg-1 and 30 min before induction of anesthesia under standard monitoring.

In the operating room, standard monitors such as pulse oximetry, electrocardiogram, and noninvasive blood pressure were attached, and baseline recordings were obtained. A standard anesthetic protocol was followed, wherein anesthesia was induced with sevoflurane (4%–8%) in 100% oxygen in the absence of preexisting intravascular access before induction. Tracheal intubation was facilitated with fentanyl 2 μg.kg-1 and atracurium 0.5 mg.kg-1. In the presence of an intravascular access before induction, anesthesia was induced with intravenous fentanyl 2 μg.kg-1 and thiopentone 5 mg.kg-1 and paralyzed with atracurium 2 μg.kg-1. Tracheal intubation was performed using oral microcuff pediatric endotracheal tube with an inner diameter (mm) calculated according to the Motoyama formula (internal diameter = age/4 + 3.5).[12] The tracheal tube was placed with its intubation depth mark at the level of the vocal cords. Anesthesia was maintained as per the discretion of the attending anesthesiologist.

Tracheal leak pressure (airway pressure needed to establish an air leak around the tracheal tube with the cuff not inflated) was measured in manual mode on the Aestiva Anesthesia workstation with fresh gas flow of 3 L.min-1 and slowly closing the adjustable pressure limiting valve until a palpable leak appeared. In children with tracheal leak pressure of <20 cm H2O, the cuff was inflated with incremental volumes of 0.5 mL of air using a syringe until there was no palpable leak. The pressure at the point of disappearance of palpable leak was measured using cuff pressure manometer (Portex®) (sealing pressure), and the cuff pressure was measured every 15 min for 1 h. Children with tracheal leak pressure >20 cm H2O were excluded from the study. In such patients, the tracheal tube was exchanged with the next smaller size microcuff tube and surgery commenced.

The distance between the tube tip and carina was assessed with the patient supine and the head in the neutral position (the external auditory meatus and superior orbital margin in the vertical alignment) using flexible fiber-optic pediatric bronchoscope (Karl Storz [1130AB] outer diameter 2.8 mm, Tuttilingen, Germany). The bronchoscope was advanced endobronchially and then withdrawn until the crest of the tracheal carina was visualized. This length of the bronchoscope insertion cord was marked using a clip placed at the level of the tube connector. Then, the bronchoscope was further withdrawn until the tube tip was seen, and the length of the bronchoscope insertion cord was marked at the level of the tube connector as described above. The difference between the above two-mentioned distances gave the distance between the tube tip and carina in the neutral position. In addition, the distance between the tube tip and carina was reassessed with neck in flexion of 30° using a predecided template (by laying sheets under the head).

Cuff position was assessed by placing a 6–15 MHz linear ultrasound probe (Sonosite Fujifilm Corporation®) in the suprasternal region where the cross section of the cuff was identified after injection of air into the cuff [Figure 1]. The postextubation airway morbidities, such as cough, sore throat, stridor, and hoarseness (change of voice or character of cry), were assessed clinically for up to 6 h in the postanesthesia care unit.

Figure 1

Ultrasonographic view of the cuff: (a) Cuff deflated, (b) Cuff inflated with air

Statistical analysis

Sample size was calculated using convenient sampling technique. The patient characteristics (height, weight, and body mass index), leak pressure, and cuff pressures were expressed as the median with the interquartile range. Cuff pressure measured over time was analyzed using the Friedman's test. Tube tip to carina distance and the extent of tube tip displacement were analyzed using the Wilcoxon signed-rank test. All data were analyzed using the SPSS software version 20 (IBM Corp., Armonk, N.Y., USA). P < 0.05 was considered as statistically significant.

RESULTS

A total of 34 children (24 males and 10 females) between the age of 2 and 12 years (median 7.5 years) were enrolled in the study [Figure 2]. The patient characteristics are shown in Table 1. Out of them, four patients had tracheal leak pressure of >20 cm H2O. In these patients, the tubes were exchanged with a one size smaller microcuff tube, and these patients were excluded from the study. In the remaining 30 patients, the leak pressure was <20 cm H2O (median 14.5 cm H2O). A complete seal was achieved in all patients with median cuff pressure of 8 cm H2O (6–8.25 cm H2O). Median sealing pressure and tracheal leak pressure for each tube size are shown in Table 2. Maximum cuff pressure measured over 1 h was 10 cm of H2O which is well below the tracheal mucosal perfusion pressure, and there was no significant increase in cuff pressure over time.

Figure 2

Flowchart showing study design

Table 1

Patient characteristics

Age (years)	ETT size (ID mm)	Number of patients	Height* (m)	Weight* (kg)	BMI*
2-3	4	5	0.92 (0.83-0.95)	11.5 (10.2-14.65)	15.05 (12.98-17.44)
4-5	4.5	5	0.98 (0.915-1.01)	13 (13-17.5)	15.51 (13.26-18.4)
6-7	5	5	1.16 (1.05-1.26)	17 (15.6-23.5)	13.08 (12.53-16.21)
8-9	5.5	5	1.24 (1.17-1.29)	20 (18.5-25)	13.48 (11.96-16.53)
10-11	6	7	1.35 (1.28-1.38)	29 (23-31)	15.22 (12.62-16.21)
12	6.5	3	1.35 (1.28-1.35)	29 (26-29)	14.26 (13.79-14.26)
All patients (n=30)			1.23 (1-1.31)	20 (13.82-27.5)	14.15 (12.95-16.55)

*Data are median (interquartile range). BMI=Body mass index, ID=Internal diameter, ETT=Endotracheal tube

Table 2

Leak pressure and sealing pressure

Age group (years)	ID (mm)	Leak pressure (cm H2O)*	Sealing pressure (cm H2O)*
2-3	4	15 (13-16)	6 (4.5-7.5)
4-5	4.5	14 (11-15)	8 (7-9)
6-7	5	14 (9-17)	8 (6-9)
8-9	5.5	15 (11-18)	8 (7-9)
10-11	6	15 (12-18)	8 (7-10)
12	6.5	12 (6-12)	6
All patients (n=30)		14.5 (12-16.5)	8 (6-8.25)

*Data are median (interquartile range) n=30. ID=Internal diameter

The median tube tip to carina distance in neutral position was 2.65 cm (2.07–1.75 cm), and with flexion, the median tube tip to carina distance decreased to 1.75 cm (1.07–2.42 cm). There was 33% of reduction in tube tip to carina distance with flexion. However, there was no incidence of endobronchial intubation. The median caudal displacement was 0.8 cm (0.47–1.22 cm) which was statistically significant (P = 0.001). Tube tip to carina distance in neutral and flexion and maximum caudal displacement are shown in Table 3. Cuff position was assessed using ultrasonography in the suprasternal notch [Figure 1] which correlated with the tube position confirmed by flexible bronchoscope. Postextubation airway morbidity such as cough, stridor, and hoarseness (change of voice or character of cry) was assessed clinically, and none of the patients showed any airway-related morbidity.

Table 3

Measured tube tip to carina distance in neutral and flexion and measured maximum caudal displacement

Age (years)	ETT size (ID mm)	Tube tip to carina distance in neutral* (cm)	Tube tip to carina distance in flexion* (cm)	Maximum caudal displacement* (cm)	P
2-3	4	2 (1.35-2.2)	1.2 (1.2-1.5)	0.8 (0.4-0.8)	0.039†
4-5	4.5	3.5 (3.3-4.3)	2.2 (2-2.75)	1.2 (0.85-1.55)	0.042†
6-7	5	2.5 (1.9-3.05)	1.5 (1.1-2)	1 (0.65-1.2)	0.043†
8-9	5.5	3 (2.5-3.4)	2 (1.05-2.9)	1 (0.3-1.65)	0.043†
10-11	6	2.5 (2.1-4)	2 (0.7-4.5)	0.5 (0.3-0.8)	0.089
12	6.5	2.8 (2-2.8)	1.7 (0.8-1.7)	1.3 (0.3-1.3)	0.10
All patients (n=30)		2.65 (2.07-1.75)*	1.75 (1.07-2.42)*	0.8 (0.47-1.22)*	0.001

*Median (interquartile range), †P<0.05. ID=Internal diameter, ETT=Endotracheal tube

DISCUSSION

The salient findings observed in our study were the lower tracheal leak pressure (median 14.5 cm H2O) and sealing pressure (median 8 cm of H2O) in the 30 children to achieve an adequate seal. However, tube exchange was required in four patients, and they were excluded from the study. None of the patients had endobronchial intubation with the tube placement based on the depth marker.

The age-based formula (Motoyama formula)[12] used in this study for tracheal tube size allowed appropriate selection in 88% of our study population at the first attempt. Tube exchange was required in the remaining 12% of the patients. It has been found that the tube exchange rate was either low (2.1%) or none with the use of this age-related formula for tube size selection from the findings made by Weis et al.[1] and Mhamane et al.[13] The difference in this finding noted in our study can be due to the difference in patient characteristics. The four patients in whom the inappropriateness of tube selection noted was found to have height and weight below the 50th percentile of height and weight for age.

The present study demonstrated a lower sealing pressure (median 8 cm H2O) with the microcuff pediatric endotracheal tube. This finding is further corroborated by studies done by Weiss et al.[8] and Dullenkopf et al.[7] who observed a mean sealing pressure of 10.6 cm H2O and 9.7 cm H2O, respectively. This ability of the microcuff tracheal tube to provide adequate tracheal sealing at lower sealing pressure was due to the presence of ultrathin polyurethane cuff membrane which avoids the formation of longitudinal folds along the mucosal membrane. This characteristic feature provided uniform surface contact with the tracheal mucosal membrane which, in turn, allowed complete filling of the tracheal lumen and produced sealing pressure lower than the mucosal perfusion pressure. The upper safety limit of cuff pressure in adults is 25–30 cm H2O.[14] However, there are no data available regarding the tracheal mucosal perfusion pressure in children. The median cuff sealing pressure demonstrated in the present study was much lower than the recommended upper limit. Thus, there could be decreased risk of tracheal mucosal injury with the Microcuff® tracheal tubes when compared to the conventional cuffed tracheal tubes.

None of the patients in this study had endobronchial intubation. This suggested the appropriateness of the intubation depth marker which allowed adequate placement of the tracheal tube without risk of inadvertent endobronchial intubation. This finding correlated with the observations by Weiss et al.[9] Confirmation of tube position in this study was done by flexible pediatric bronchoscope. In addition, cuff position was assessed using ultrasonography which showed cuff in suprasternal position. This observation supported the use of ultrasound in confirming the tube position. The median distance between tube tip and carina in neutral position and flexion was 2.65 and 1.75 cm, respectively. Despite having a 33% reduction in tube tip to carina distance with head flexion, there was no incidence of endobronchial intubation. In this study, the caudal displacement of the tube was within the safe limits and in agreement with the observation by Weiss et al.[15]

Although the tube exchange rate was significantly high in this study (12%), in patients whom the tube selection was appropriate, the tube provided good sealing and no incidence of endobronchial intubation was there. This confirms the appropriateness of the design of the tube.

In this study, the maintenance of anesthesia was as per the discretion of attending anesthesiologists. In accordance with this statement, we observed that the use of nitrous oxide in 12 patients who demonstrated a median baseline cuff pressure of 7 cm H2O increased to 8 and 8.5 cm H2O at 30 and 60 min, respectively, following the onset of anesthesia. This increase in the cuff pressure was found to be statistically significant. However, it was not clinically relevant as the pressures were well below the upper safety limit of the cuff pressure.

In this study, no patient had cough, sore throat, stridor, or hoarseness of voice in the postextubation period. This finding was similar to the data provided by Dullenkopf et al.[7] and Al-Metwalli and Sadek[16] This confirmed the lower incidence of airway-related morbidity with the use of microcuff pediatric tracheal tube.

Limitations

In our study, we used the convenient sampling technique. A larger sample size would enable us to affirm the findings of the study.

CONCLUSIONS

The microcuff pediatric endotracheal tubes when used according to the Motoyama formula had a higher tube exchange rate in our study population. However, in children in whom the tube size was appropriate, the tubes provided good sealing without increasing airway morbidity. Further studies with a larger sample size might be required to confirm the findings.

Financial support and sponsorship

This study was financially supported by JIPMER institute research fund.

Conflicts of interest

There are no conflicts of interest.