This study compared the leakage characteristics of different types of dual-cannula fenestrated tracheostomy tubes during positive pressure ventilation. Fenestrated Portex® Blue Line Ultra®, TRACOE® twist, or Rüsch® Traceofix® tracheostomy tubes equipped with nonfenestrated inner cannulas were tested in a tracheostomy-lung simulator. Transfenestration pressures and transfenestration leakage rates were measured during positive pressure ventilation. The impact of different ventilation modes, airway pressures, temperatures, and simulated static lung compliance settings on leakage characteristics was assessed. We observed substantial differences in transfenestration pressures and transfenestration leakage rates. The leakage rates of the best performing tubes were <3.5% of the delivered minute volume. At body temperature, the leakage rates of these tracheostomy tubes were <1%. The tracheal tube design was the main factor that determined the leakage characteristics. Careful tracheostomy tube selection permits the use of fenestrated tracheostomy tubes in patients receiving positive pressure ventilation immediately after stoma formation and minimises the risk of complications caused by transfenestration gas leakage, for example, subcutaneous emphysema.
Percutaneous dilatational tracheostomy (PDT) is frequently performed in the intensive care unit [
As soon as the need for high-level respiratory support subsides, trials of spontaneous breathing are usually introduced. During the rehabilitation phase the initial configuration of a tightly sealed tracheostomy tube during positive pressure ventilation is changed to cuff deflation during episodes of spontaneous breathing [
Following the publication of reports of subcutaneous emphysema and pneumothorax developing in connection with the use of dual-cannula fenestrated tracheostomy tubes for PDT, many authors advised against the use of these types of tubes in patients who require positive pressure ventilation [
We hypothesised that the risk of surgical emphysema formation is related to the degree of air leakage through the fenestrations. We therefore performed a bench study to quantify and compare the leakage characteristics of different types of commonly used dual-cannula fenestrated tracheostomy tubes under varying conditions. A pseudotrachea was used to study ex vivo the performance of tracheostomy tubes. Our aim was to derive recommendations regarding the safe use of fenestrated tracheostomy tubes immediately after tracheostomy formation.
We built a tracheostomy simulator comprising a polyethylene tube that represented the trachea (length, 20 cm; internal diameter, 25 mm). A 10 mm side hole was fashioned at one-third the length of the tubing; it represented the tracheostomy (Figure
Types and specifications of tracheostomy tubes tested.
Type | Manufacturer | Size | Inner cannula |
Outer cannula |
---|---|---|---|---|
Portex Blue Line Ultra | Smith Medical, Grasbrunn, Germany | 8 | 6.5 mm | 11.9 mm |
TRACOE twist | Tracoe Medical, Nieder-Olm, Germany | 8 | 8.0 mm | 11.4 mm |
Rüsch Traceofix | Teleflex, Kernen, Germany | 8.5 | 7.0 mm | 10.3 mm |
Schematic drawing of tracheostomy simulator with a fenestrated tracheostomy tube sited. TFLR: transfenestration leakage rate; TFP: transfenestration pressure.
A tracheostomy tube to be tested was inserted through the tracheostomy, and the cuff was inflated. A seal was fashioned around the tracheostomy insertion site using rubber washers and putty. Leak testing was performed prior to each experiment to ascertain the leak tightness of both the tracheostomy tube cuff within the trachea and the insertion site of the tracheostomy tube. The trachea simulator was then placed upright into a laboratory stand. The lower (“bronchial”) portion of the artificial trachea was connected to a single compartment lung simulator (LS-122; Medishield, Harlow, Essex, UK), and the upper (“pharyngeal”) portion of the artificial trachea was connected to a 2.3-l anaesthesia breathing bag so that any gas escaping through the fenestrations of the tracheostomy tube could be collected. Polyvinylchloride fittings and nonexpandable polyethylene tubing were used for all connections. A SERVO-i® ventilator (Maquet, Rastatt, Germany) was connected to the tracheostomy tube. The ventilator and lung simulator compliance settings were varied as described in Table
Ventilator and lung simulator compliance settings.
Variable | Settings |
---|---|
Ventilation mode | Volume-controlled |
Ventilator rate (breaths·min−1) | 15 |
Tidal volume (mL) | 450 ± 5% |
Inspiration : expiration ratio | 1 : 2 |
Positive end-expiratory pressure (mbar) | 3, 6, 9, 12 |
Lung simulator compliance (mL·mbar−1) | 20, 50 |
Lung simulator resistance (mbar·mL−1·sec−1) | 5 |
Experiments were run at either 21°
Two types of measurements were obtained for each combination of ventilator and lung simulator settings and temperatures. The first measurement was the transfenestration pressure (TFP): the pharyngeal end of the trachea was occluded by clamping the connecting tubing, and the build-up of pressure in the space above the tracheostomy tube was measured with a digital manometer (PCE-P01; PCE Instruments, Meschede, Germany) until a steady state was reached. The second measurement was the transfenestration leak rate (TFLR) (minute ventilation fraction). Prior to each experimental run, the anaesthesia bag was thoroughly emptied and gas escaping through the fenestrations of the tracheostomy tube was collected into the anaesthesia breathing bag for 1–3 min, depending on the magnitude of the leakage. The volume of the collected gas was measured using the water displacement method. To distinguish between the amount of gas leaking through the fenestration and the amount of gas leaking through the connection site of the inner and outer cannula, the difference between the inspiratory and expiratory minute volumes measured by the ventilator and the TFLR was calculated. All experiments were run in duplicate. Measurements were repeated if corresponding pressure measurements differed by >5% or volume measurements differed by >5% and >10 mL·min−1.
Statistical analysis was performed using the StatPlus® 8 software package (AnalystSoft Inc., Alexandria, VA, USA). Data are presented as individual measurements. The Mann-Whitney test was used for comparisons of nonnormally distributed continuous data, and the Wilcoxon matched-pairs test was used for comparisons of nonnormally distributed paired data. Spearman’s rank order correlation coefficient was used to assess the relationships between continuous variables. All tests of statistical significance were two-sided.
The reliability of the experimental setup as assessed by the Bland-Altman method is depicted in Figures
Bland-Altman plot of paired transfenestration leakage rates of Portex Blue Line Ultra (+), TRACOE twist (×), or Rüsch Traceofix (
Differences in TFLR and TFP were observed between different types of tracheostomy tubes exposed to identical experimental conditions. Additionally, variations in TFLR and TFP were observed for each tracheostomy tube as the experimental conditions were modified.
TFLR ranged from 0.2% to 67.6% of minute ventilation, and TFP ranged from 1 to 16 mbar across the entire range of investigated combinations of types of tracheostomy tubes, temperatures, ventilation modes, and compliance settings.
Figures
Transfenestration leakage rates of Portex Blue Line Ultra (+), TRACOE twist (×), or Rüsch Traceofix (
Because tracheostomy tube’s performance at body temperature is relevant to clinical practice, the following results refer to experiments that were performed at
Figure
Transfenestration pressures of Portex Blue Line Ultra (+), TRACOE twist (×), or Rüsch Traceofix (
Figure
Transfenestration leakage rates of Portex Blue Line Ultra (+), TRACOE twist (×), or Rüsch Traceofix (
By comparing the ratio of TFLR to the difference in the inspiratory and expiratory minute volume as measured by the ventilator, an additional source of leakage at the interface of the inner and outer cannulas was identified in the TRACOE twist tube (Figure
Loss of delivered minute volume of Portex Blue Line Ultra (+), TRACOE twist (×), or Rüsch Traceofix (
Switching from the volume-controlled ventilation mode to the pressure-controlled ventilation mode resulted in no statistically significant variation in TFP or TFLR for any make of tracheostomy tube.
Changes in static compliance did not significantly alter TFP or TFLR for any make of tracheostomy tube.
In this study, the sources and degree of leakage of different types of tracheostomy tubes during positive pressure ventilation, the impact of the tube design, and the variability of tracheostomy tube’s performance at different temperatures were investigated for the first time.
We found substantial variations in TFLR and TFP for different types of fenestrated tracheostomy tubes when used in combination with nonfenestrated inner cannulas. The leakage rates of the best performing tubes did not exceed 3.5% of the delivered minute volume. When tested at body temperature, the leakage rates of these tracheostomy tubes dropped even further to <1%. The tracheal tube design was the main factor that determined the leakage characteristics. Two features of the cannula design were found to be associated with the lowest TFLR and TFP: connection of the ventilator catheter mount to the inner cannula and a tightly sealed interface of the inner and outer cannulas. The Blue Line Ultra tracheostomy tube is designed to connect to the ventilator catheter mount via the outer cannula; it yielded the highest TFLR and TFP. The TRACOE twist tube had low TFLR but a significant degree of leakage at the interface of the inner and outer cannulas. The Rüsch Traceofix tracheostomy tube had low TFLR and TFP and a tight seal at the cannula interface. The ventilation mode and lung compliance had little impact on the leakage characteristics.
The cause of subcutaneous emphysema after PDT and insertion of dual-cannula fenestrated tracheostomy tubes is the tracking of air between the nonfenestrated inner cannula and the fenestrated outer cannula with subsequent leakage through the fenestrations [
Mostert and Stuart [
Fikkers et al. [
Orme and Welham [
In 2008, the UK Intensive Care Society [
Weaning from mechanical ventilation and from the tracheostomy itself is a challenging, often drawn out task, particularly after long-term ventilator support. The ability to communicate verbally is an important step towards reestablishing patient autonomy and quality of life [
During spontaneous breathing through a tracheostomy tube, airflow resistance should be decreased to minimise the work of breathing [
Abandoning the use of fenestrated tracheostomy tubes reduces both the speed and the efficiency of the rehabilitation process, because the advantages of these types of tubes will be unavailable until a change of tracheostomy tube. This can only be safely performed several days after the initial procedure; it requires resources and carries certain risks [
Our work provides insight into the benefits of using particular types of fenestrated tracheostomy tubes and can be used in the selection of a suitable tracheostomy tube. In devising a pseudotrachea we built on the experience reported by Hussey and Bishop of the use of a model trachea to study tracheostomy tube’s performance [
Our study could be criticised for not including the entire range of commercially available tracheostomy tubes. Because we aimed to explore not only the implication of the tube design but also the impact of temperature, ventilator settings, and lung compliance, we made a conscious decision to limit the scope of the study to a selection of widely used tracheostomy tubes.
The thermal behaviour of plastic materials provides a possible explanation for our observation of a significant improvement in leakage rates when tracheostomy tubes were tested at body temperature. Tracheostomy tubes are made from polyvinylchloride or polyurethane, and inner tubes are made from polypropylene. These materials are thermoplastics: they expand and become more pliable as temperature rises [
Little is known about the impact of the thermoplastic characteristics of the various plastic materials used on tracheostomy tube performance [
Transfenestration gas leakage of fenestrated tracheostomy tubes is highly variable when these tubes are used in combination with nonfenestrated inner cannulas and exposed to positive pressure ventilation. In vitro leakage testing enables the identification of fenestrated tracheostomy tubes that are suitable for immediate use after stoma formation in patients expected to benefit from early trials of spontaneous breathing and rehabilitation of swallowing, communication, and mobilisation.
The authors declare that there are no competing interests regarding the publication of this paper.
The authors are indebted to Professor Jukka Takala, chairman of the Department of Intensive Care Medicine at Inselspital, for providing the opportunity to conduct this investigational project.