Abstract

Background

High cuff pressure of tracheal tube (TT) may cause tracheal damage. Maintaining an optimal cuff pressure is important in tracheal intubation. This study aimed to examine whether inexperienced anesthetists or airway care providers, after training and practice, demonstrate more expertise in the determination of optimal cuff pressure by feeling the pilot balloon with their fingers.

Methods

One hundred participants were asked to inflate the TT cuff with an air volume that they believe to be correct based on their previous experience. The cuff pressure after inflation was measured by a manometer. Then, the cuff of a standard adult TT was inflated with air until the pressure reached 25 cm H₂O, and each participant was instructed to palpate the pilot balloon to feel the pressure, until s/he became accustomed to the feeling. After training, the same procedure was performed immediately, and repeated 1 week and 1 month later. We compared the pre-training data with the post-training data, and the differences between seniority of employment and age.

Results

A total of 98 examinees completed the study. Before training, the mean cuff pressure they determined to be correct was actually 29.3 ± 19.49 cmH₂O; 32.7% of the examinees had over-inflated the cuff. The cuff pressures they inflated immediately, 1 week and 1 month after training were significantly different from those found before training (p = 0.009, p = 0.038 and p = 0.045, respectively). Before training, the performance of the participants who were of middle seniority (5–10 years of experience) and middle age (30–45 years old) was significantly better than that of the less experienced (< 5 years of experience; p = 0.007) and younger participants (< 30 years old; p = 0.002).

Conclusion

The anesthesia trainers in this study are capable of teaching TT cuff inflation correctly. After practical training, the airway care providers, irrespective of seniority or age, can roughly determine an optimal TT cuff pressure non-instrumentally.

Keywords

patient simulation; pressure, cuff; teaching; tracheal tube;

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1. Introduction

The cuff of a tracheal tube (TT) has two functions: (1) it ensures air-tightness to maintain the efficiency of ventilation support; (2) it protects the lower airway from aspiration of secretions and blood. Insufficient cuff pressure can compromise these functions, but excessive cuff pressure can induce tracheal damage.¹ Tracheal mucosa is a very delicate structure; high cuff pressure-induced tracheal injuries, such as trachea rupture,^2,3 stenosis,⁴ and fistula formation have been reported.⁵ Even maintaining a slightly higher TT cuff pressure for only 2 hours may produce serious tracheal ciliary damage that takes at least 3 days to recover from.⁶ In addition, post-intubation sore throat is a common side effect of intubation that bears much relation to excessive TT cuff pressure.^7,8 Hence, maintaining an optimal TT cuff pressure is very important in patients with tracheal intubation. Avoidance of TT cuff pressure exceeding 30 cmH2O has been suggested.⁹

Although direct measurement of TT cuff pressure by a manometer has been suggested,¹⁰ this practice does not appear to have been adopted as standard clinical practice. Fingertip palpation of the pilot balloon is a common way of determining TT cuff pressure. However, this technique has been reported to be unreliable for determining an appropriate TT cuff pressure because it is experiential without scientific guidance for maturing.¹¹ In this study, by using a special training device, we sought to examine airway care providers’ judgment of the inflating pressure used to inflate the TT cuff, with the volume pressure they deemed to be optimal, and then trained them to become accustomed to the feel of the correct pressure at the pilot balloon of the TT cuff by repeat fingertip palpation.

2. Methods

With the approval of the Institutional Review Board of Tri-Service General Hospital and exemption from obtaining informed consent from the participants (due to there being no medical ethics-related issues in this study), 100 airway care providers who had some prior experience in taking care of intubated patients enrolled in this study of their own free will. We excluded staff without any exposure to the use of cuffed endotracheal tubes and those with fewer than 6 months of related professional experience.

The training device comprised five basic components (Figure 1):

1. two 10-mL plastic syringes;

2. a three-way stopcock;

3. a TT with high-volume and low-pressure cuff, with a pilot balloon attached at the proximal end of the air conduit (ID: 6.5 mm; Mallinckrodt Medical, Dublin, Ireland);

4. a hand-held portable manometer (Cuff Pres sure Gauge, VBM Medizintechnik, Sula, Germany);

5. an extension tube.

A syringe and a TT was put in a bag for concealment (Figure 2). At the beginning of the study, participants were asked to inflate the TT cuff to a pressure they deemed to be correct according to the feel of the pilot balloon based on their past experience. The cuff pressure as registered on the manometer was recorded. Then, participants were immediately trained to exercise fingertip palpation of the pilot balloon that was already inflated with an optimal cuff pressure of 25 cmH₂O as indicated by the manometer. Each participant was allowed, without time limit, to become accustomed to the feeling of the pilot balloon by fingertip palpation, until s/he was confident of being able to recognize the pressure on subsequent tries. On getting hold of the essentials, the participants were again asked to inflate the TT cuff to a pressure they deemed to be correct according to the feel of the pilot balloon. This test was carried out thrice, i.e. immediately after training, and 1 week and 1 month after training.

The TT was disposed of after every test and a new TT was used for each test to avoid any elasticity change in the TT cuff biasing the outcome. It was ensured that when the trainees were being tested, only the evaluator could see the pressure reading on the manometer.

Data were assessed by generalized estimating equation (SAS version 9.1.3; SAS Institute Inc., Cary, NC, USA). We compared the data between pre- and post-training, seniority of employment (junior, < 5 years of experience; middle, 5−10 years of experience; senior, > 10 years of experience) and age (young, < 30 years old; middle-aged, 30−45 years old; elder, > 45 years old). Data were expressed as mean ± standard deviation and analyzed by oneway analysis of variance with post hoc comparison by t test to detect the differences between groups. A p value < 0.05 was considered to be statistically significant.

3. Results

A total of 98 participants (age range, 23−60 years) finished the study, of whom 46 were certified registered nurse anesthetists, 10 were anesthesia residents, and 42 were intensive care nurses (Table 1). Two did not complete the study because they resigned from their jobs. The length of experience of taking care of intubated patients ranged from 1 to 36 years.

Before training, the mean cuff pressure deemed to be correct by the participants was 29.3 ± 19.49 cmH₂O (range, 12−118 cmH₂O); 32.7% of the trainees over-inflated the cuff, with pressure exceeding 30 cmH₂O. Figure 3 shows the cuff pressures in the different groups of trainees before training, and immediately, 1 week and 1 month after training. The cuff pressures that were registered immediately, 1 week and 1 month after training differed significantly from those obtained before training (p= 0.009, p= 0.038 and p= 0.045, respectively). Figures 4 and 5 show the cuff pressures of individual groups according to seniority and age. With the optimal cuff pressure defined as 25 cmH₂O before training, participants of middle seniority (5−10 years of experience, n= 35) performed the inflation significantly better than did the juniors (< 5 years of experience, n= 41; p= 0.007). The performance of the middle-aged group (30−45 years old, n= 39) was significantly better than that of the young group (< 30 years old, n= 49; p= 0.002). There were no other significant differences among groups.

4. Discussion

This study showed that the cuff pressure applied by the participants varied widely before training, with up to 32.7% of participants over-inflating. These results are consistent with those of previous studies.^10,12 However, training with this new device led to significant improvement in the performance of trainees, and the effect may last at least up to 1 month.

Excessive cuff pressure-induced severe tracheal complications are well documented and notoriously refractory to treatment. Tracheal ischemia, inflammation, ulceration, granulation, and stenosis at the site of the injured tracheal wall may develop after suboptimal tracheal intubation.¹³ Ensuring that an optimal cuff pressure is applied is crucial if these complications are to be avoided. Of the TTs currently in use, the intracuff pressure is almost equal to the pressure it exerts on tracheal mucosa. As to what actually constitutes optimal cuff pressure in practice, there is no consensus on what is an appropriate standard. Ranges from 25 to 40 cmH₂O have been suggested.^9,13,14 A cuff pressure greater than 34 cmH₂O can result in decreased perfusion of the tracheal wall, whereas total obstruction of blood flow to the tracheal wall can occur at a compression pressure of 50 cmH₂O.¹⁴ In fact, cuff pressure of 27 cmH₂O may reduce blood flow to the cuff site by 75%.¹³ A minimal cuff pressure of 20 cmH₂O has been recommended for positive-pressure ventilation and aspiration prevention.¹⁵ Accordingly, we designated a cuff pressure of 25 cmH₂O as optimal in this study.

A prospective study assessing the risk factors for tracheal stenosis in patients subjected to prolonged tracheal intubation (> 8 hours in duration) concluded that strict scrutiny of the cuff pressure thrice a day might help to prevent ischemic lesions and tracheal stenosis.¹⁶ Vyas et al¹⁷ also suggested that TT cuff pressure should be regularly checked in intubated patients in intensive care units. Cuff pressure monitoring is equally important in patients receiving intubational general anesthesia. But how should this be done? Direct measurement with a manometer has been suggested.^10,12 However, using manometers to measure cuff pressure is costly and time-consuming. From the results of this study, it would appear that training on fingertip palpation of the inflated pilot balloon of the TT is a feasible and effective method to help airway care providers apply the desired optimal TT cuff pressure. Furthermore, this method of learning through the sense of touch may make the experience unforgettable and vivid in the mind of the trained professionals. In this study, we performed follow-up evaluation 1 month after training to see if the skill was retained for at least this length of time. The results showed that there was a tendency to increase the exercise of feeling the determined cuff pressure after training. To determine the time when a retraining course should be provided, further study with a longer observation period is warranted.

The pre-training data indicate that both seniority and age of the trained airway care providers have an influence on TT cuff pressure. More clinical experience aided assessment of what constituted an appropriate TT cuff pressure. However, post-training data showed that seniority and age no longer had an influence. During the course of training, we were surprised to discover that some of the participants were ignorant of the fact that high cuff pressure can induce tracheal complications—they were only aware of the fact that the inflated cuff is able to prevent aspiration. Therefore, through this training program, airway care providers can be taught to understand the importance of applying an optimal pressure to the TT cuff in intubated patients.

Fernandez et al¹¹ reported that feeling the pilot balloon to estimate correct TT cuff pressure may be unreliable because of the different volumes and shapes of the pilot balloons from different manufacturers. However, in most hospitals, TTs are usually purchased from one manufacturer only. Thus, the unreliability of finger-feel assessment can be minimized by using just a single brand of TT.

In conclusion, the device we designed for use in this study is a useful tool for training airway care providers on how to apply optimal TT cuff pressure by finger palpation of the pilot balloon. Through such training courses, airway care providers can learn how to appropriately inflate the TT cuff and become more aware of the importance of applying appropriate cuff pressure to avoid complications related to tracheal intubation.