Evaluation of tracheal cuff pressure variation in spontaneously breathing patients.

BACKGROUND: Most of the studies referring cuff tubes' issues were conducted on intubated patients. Not much is known about the cuff pressure performance in chronically tracheostomized patients disconnected from mechanical ventilation.
OBJECTIVE: To evaluate cuff pressure (CP) variation in tracheostomized, spontaneously breathing patients in a weaning rehabilitation center.
MATERIALS AND METHODS: Experimental setup to test instruments in vitro, in which the gauge (TRACOE) performance at different pressure levels was evaluated in six tracheostomy tubes, and a clinical setupin which CP variation over 24 h, every 4 h, and for 6 days was measured in 35 chronically tracheostomized clinically stable, patients who had been disconnected from mechanical ventilation for at least 72 h. The following data were recorded: Tube brand, type, and size; date of the tube placed; the patient's body position; the position of the head; axillary temperature; pulse and respiration rates; blood pressure; and pulse oximetry.
RESULTS: In vitro difference between the initial pressure (IP) and measured pressure (MP) was statistically significant (P < 0.05). The difference between the IP and MP was significant when selecting for various tube brands (P < 0.05). In the clinical set-up, 207 measurements were performed and the CP was >30 cm H2O in 6.28% of the recordings, 20-30 cm H2O in 42.0% of the recordings, and <20 cm H2O in 51.69% of the recordings.
CONCLUSION: The systematic CP measurement in chronically tracheostomized, spontaneously breathing patients showed high variability, which was independent of tube brand, size, type, or time of placement. Consequently, measurements should be made more frequently.

INTRODUCTION

Microaspiration of oropharyngeal contents caused by underinflation of the tracheal cuff in intubated patients can lead to ventilator-associated pneumonia (VAP) causing morbidity and mortality in intubated, mechanically ventilated, and tracheostomized spontaneously breathing patients. It is recommended that cuff pressure (CP) levels be kept at 20-30 cm H2O.[12345] When the CP falls to <20 cm H2O, the risk of VAP increases four-fold; in comparison, at >30 cm H2O, the cuff may damage the tracheal tissue.[45678910] Despite the control of CP, underinflation and overinflation occur frequently in the intensive care unit (ICU). Most guidelines regarding the control and regulation of CP are based on surveys and they vary considerably, suggesting checks every 2-12 h.[11121314]

Several factors influence CP, including changes in tracheal muscle tone, body temperature, anesthetic gas diffusion inside the cuff, endotracheal tube (ETT) position, respiratory system impedance, level of consciousness, and the position of the body, head, and neck.[15161718] Although continuous CP control monitors variation throughout the day in mechanically ventilated patients with an ETT, allowing for pressure regulation, the incidence of VAP does not decrease.[6192021] There is no agreement on the best CP monitoring method; however, the most commonly used method is direct control with a pressure gauge.[222324252627]

Most studies of variation and regulation of CP have been performed using intubated and mechanically ventilated patients, but studies on CP in tracheostomized patients are scarce. Our aim was to evaluate CP variation in tracheostomized, spontaneously breathing patients in a weaning rehabilitation center.

MATERIALS AND METHODS

This two-part study was carried out at a weaning center in Buenos Aires, Argentina, from March 1 to May 31, 2010. It consisted of an experimental setup to test instruments in vitro and a clinical set-up, in which CP variation was measured in tracheostomized patients.

To monitor the pressure, we used a TRACOE Cuff Pressure Monitor (Medical, Frankfurt, Germany), Rüsch Safety Clear tracheostomy tubes (numbers 8, 9, and 10); a Portex Blue Line Ultra Suctionaid Tracheostomy Tube Kit (number 8); Mallinckrodt Tracheosoft Evac ETT (numbers 8 and 10); and a 10 cm × 28 mm rigid plastic cylinder.

Experimental setup

Using the in vitro setup, we evaluated the gauge performance at different pressure levels in six tracheostomy tubes (APPENDIX 1).

A plastic cylinder was used to simulate the trachea; a tracheostomy tube was inserted and the cuff was inflated to the initial pressure (IP) level with a TRACOE pressure gauge. The gauge was removed, reattached, and measured pressure (MP) was recorded in an Excel spreadsheet. If necessary, the pressure was corrected to the initial value. This sequence was repeated ten times, with different IPs each time, starting at 40 cm H2O and decreasing by 2 cm H2O for each measurement to reach 10 cm H2O on the last measurement. This process was repeated for all six tracheostomy tubes.

Clinical setup

The aim of the first part of this study was to evaluate CP variations over 24 h in 35 patients aged >18 years, who were chronically tracheostomized, clinically stable, and who had been disconnected from mechanical ventilation for at least 72 h. The patients were excluded if they required tube replacement, mechanical ventilation, transfer to another center, or discharge during the study period. The tube brands used were the Mallinckrodt Tracheosoft Evac in 20 patients; Portex Blue Line Ultra Suctionaid in 3 patients; and Rüsch Safety Clear in 12 patients. The patients were randomly allocated to three groups. Each patient was then randomly assigned to a preset measurement scheme for 6 days [Table 1]. All assignments were made via sealed envelopes. According to this scheme, all patients had their CP calibrated to 30 cm H2O (IP) at 8:00 AM. Then, for the following 6 days, each patient's CP was measured and calibrated only once every day at a pre-set time, which differed for each patient daily. In this way, the CP was monitored over 24 h, every 4 h, and for 6 days. This scheme was designed by our team to avoid lapses in the recorded data and pressure loss resulting from consecutive measurements.

Table 1

Daily cuff pressure measurements for each patient

The following data were recorded using forms and an Excel spreadsheet: Tracheostomy tube brand, type, and size; date the tube was placed; the patient's body position (dorsal decubitus, lateral decubitus, or seated); the position of the head (neutral or rotated); axillary temperature; pulse and respiration rates; blood pressure; and pulse oximetry [Table 2].

Table 2

Description of the studied population

Categorical variables are presented as frequencies (%). Continuous variables are described as the mean ± SD. Normality was tested using Shapiro–Wilks and Kolmogorov–Smirnov testsAnalysis of variance (ANOVA) for repeated measurements and multiple linear regression were used to analyze the data. P ≤ 0.05 was considered significant. SPSS v. 19 (IBM, Armonk, NY, USA) was used for all statistical analyses.

RESULTS

A total of measurements were performed in vitro [Table 3]. The difference between the IP and MP was statistically significant (P < 0.05). Moreover, the difference between the IP and MP was significant when selecting for various tube brands (P < 0.05). The Table in APPENDIX 1 details our laboratory measurements.

Table 3

In vitro cuff pressure measurements (experimental setup: 960 measurements)

A total of 207 measurements were performed. The CP was >30 cm H2O in 6.28% of the recordings, 20-30 cm H2O in 42.0% of the recordings, and <20 cm H2O in 51.69% of the recordings. Figure 1 shows significant variation in the CP. The mean time between intubation and the first CP measurement was 69.9 days (range, 7-209 days). The time between tube placement and first measurement, which was divided into three categories (0-2, 2-4, and 4-6 months), showed a mean CP of 24.22, 18.37, and 17.85 cm H2O, respectively.

Figure 1

CP variation in 1 day. CI (confidential interval) 95% P > 0.05

A multiple linear regression model showed no significant difference in CP depending on the tube brand, size, and time of placement. The variation in CP for the various tube brands is shown in Figure 2. No significant difference was found in CP for the different body and head positions: Dorsal decubitus/neutral head was at 21.87 (±11.44) cm H2O; dorsal decubitus/rotated head was at 20.23 (±9.52) cm H2O; lateral decubitus/neutral head was at 20.03 (±6.44) cm H2O; lateral decubitus/rotated head was at 17.45 (±5.53) cm H2O; seated/neutral head was at 17.6 (±4.82) cm H2O; and seated/rotated head was at 19.25 (±8.54) cm H2O. The CP tended to be lower in the lateral decubitus/rotated head and seated/neutral head positions.

Figure 2

CP variation over 1 day for each of the tracheostomy tube brands. CI 95% P > 0.05

DISCUSSION

We assessed the variation in CP in spontaneously breathing, chronically tracheostomized patients for 24 h and then the CP variation when it was controlled every 4 h, and we suggest that measurements should be taken at least every 4 h.

In the experiment, we found that the mean CP decrease for each tracheostomy tube brand was very similar at every IP level. This might be explained by the characteristic pressure loss at the time of measurement in each tube, and the losses might be caused by leaks in the cuff pilot valve when the pressure gauge was inserted or removed; however, they were not caused by the compressible volume of the equipment. This concurs with Blanch et al., who found that the compressible volume of four brands of pressure gauge was not significant.

Although we found no significant differences in the pressures according to the age of the tube, the pressure loss tended to be greater in older tubes. A larger sample might have allowed us to confirm this tendency. Clinically, Portex tubes had the most recordings >30 cm H2O [Figure 2]. These tubes showed stable performance in terms of pressure loss in the experiment.

Controlling the CP every 4 h in the same tube for 24 h would have led to large pressure loss within the period studied, affecting the true determination of CP variation. Using a correction table in the experiment, we noted that the pressure loss resulting from consecutive measurements produced values below the minimum recommended values.

The continuous measurement technique is the most reliable technique for describing the CP variation.[1920] However, it is very difficult to apply this method in clinical practice. Published studies using continuous measurement did not assess the CP variation over 24 h, indicating that the CP variation was not controlled during the night. On analyzing the data, we found that the CP variation at night was similar to that recorded during the day. The studies based on autoregulation systems do not describe the CP variation, but they manage to keep it constant.[620]

We found that 51.69% of the CP measurements were <20 cm H2O, while 6.28% were >30 cm H2O, and 42.52% were normal, within the range of 20-30 cm H2O. In a study of continuous measurement in ETT patients ventilated mechanically, Sole et al., reported that, in 54% of the measurements, the CP varied from 20 to 30 cm H2O, while it was >30 cm H2O 16% of the time and <20 cm H2O 30% of the time.[21] They reported a mean 24.6 cm H2O for 12 h of continuous measurement, while our mean CP was 19.75 ± 9.08 cm H2O over 24 h.

Unlike the study by de Godoy et al., we did not find significant CP changes with body position.[17] We described the patient's position at the time of measurement, while de Godoy assessed the CP after a change in the patient's position, which might have affected the CP. We did not observe any influence of the position of the head and neck at the time of measurement on the CP. Inoue et al., described the pressure changes in patients with head extension or flexion, and they associated the variation with ETT movement.[18] Although we found no significant difference in our population, the CP tended to be lower in the lateral decubitus or seated position versus dorsal decubitus.

Inoue et al., and de Godoy et al., analyzed the CP in relation to the ETT. The ETT length and the traction of the head/neck movement on the ETT might have more influence on the ETT CP than on a tracheostomy tube cuff, probably because the ETT parallels the cervical spine, while tracheotomy tubes are inserted at lower cervical level.

The limitations of our study is that it was not a randomized control trial, as that would have allowed us to compare the pressure control method and the standard control every 8 h. Another serious limitation was that the tubes used in the clinical setup were those that the patients already had when we started the study; brand new tubes in all patients may have shown different results.

CONCLUSION

The systematic CP measurement in chronically tracheostomized, spontaneously breathing patients showed high variability, independent of tube brand, size, type, or time of placement. Therefore, values above or below the recommended values may be found at any measurement time, even after daily calibration. Consequently, measurements should be made more frequently. Nevertheless, measurements taken every 4 h are associated with a progressive reduction in CP, which might be associated with micro-aspiration. Therefore, we suggest checking the CP daily, or at least every 4 h, and maintaining the CP at the upper limit (30 cm H2O) to avoid CP decrements below the lower limit. Patients hospitalized in rehabilitation centers are generally active and perform activities out of bed. To our knowledge, this is the first study of tube performance and CP variation in such a population. Further research is needed to assess the clinical impact CP variation during the measurement process.

APPENDIX

Using the in vitro setup, we evaluated the gauge performance at different pressure levels in six tracheostomy tubes. A total of measurements were performed in vitro (960 measurements were performed). The difference between the IP and MP was statistically significant (P < 0.05). Moreover, the difference between the IP and MP was significant when selecting for various tube brands (P < 0.05).