for the used and uncleaned ETTs was equivalent to 275% of the R insp

Transcription

1 Anaesth Intensive Care 2013; 41: Effects of prolonged mechanical ventilation with a closed suction system on endotracheal tube resistance and its reversibility by a closed suction cleaning system N. A. Adi*, N. T. Tomer, G. B. Bergman, E. K. Kishinevsky, D. W. Wyncoll Intensive Care Unit, Kaplan Medical Center, Rehovot, Israel. Summary The study objective was to evaluate endotracheal tubes (ETT) from extubated adult patients and compare them to new, unused, size-matched control tubes for changes in inspiratory resistance ( ) and peak inspiratory pressure (PIP) before and immediately after suctioning with the Airway Medix Closed Suction System (AMCSS) (Biovo Technologies, 2013 Tel Aviv, Israel). Sixteen ETTs were recovered from predominantly medical patients who had required intubation and mechanical ventilation for more than 12 hours. ETTs were evaluated within 4.5 hours of extubation. Readings were taken during square wave flow, at rates of 40 and 60 l/minute. Cleaning of extubated ETTs using the AMCSS was able to restore them to almost original conditions in terms of and PIP. The examined ETTs included tubes of various sizes ranging from internal diameter (ID) 7 to 8.5 mm and intubation periods ranging from 12 hours to 21 days. The mean Ri nsp for the used and uncleaned ETTs was equivalent to 275% of the of sized-matched new and unused ETTs. For 8 mm ID ETTs this was comparable to a measured of a 5 mm tube. Following a single cleaning episode with the AMCSS, decreased, regaining an effective ETT ID of a 7.5 to 8 mm tube. A single suctioning episode with this device resulted in a significant reduction in, virtually restoring original flow variable values. The AMCSS represents a novel technology in closed suction systems, designed to achieve more effective inner lumen cleaning in prolonged mechanical ventilation. Key Words: endotracheal tubes, airway resistance, prolonged mechanical ventilation, closed suction cleaning system, airway medix Invasive positive pressure mechanical ventilation requires the placement of an endotracheal tube (ETT) in a patient s airway. ETT has the advantages of bypassing any potential upper airway obstruction and can facilitate tracheal toilet through suctioning of the ETT 1. However, ETTs can become markedly narrowed by the build-up of secretions and biofilm during the course of prolonged mechanical ventilation, thereby affecting key respiratory mechanics, including peak inspiratory pressure (PIP) and inspiratory resistance ( ) and work of spontaneous breathing. While ETT suctioning reduces the risk of ETT occlusion 2, progressive ETT narrowing leading to airflow obstruction remains a frequent problem as evidenced by measurements of ETT airflow obstr- * MD, Head of Department MD, Critical Care Specialist MD, Consultant, Department of Intensive Care Medicine, Guy's and St Thomas NHS Foundation Trust, London, UK Address for correspondence: Dr N. Adi, PO Box 1, Kaplan Medical Center, Rehovot 76100, Israel. nimrodad@gmail.com Accepted for publication on July 8, 2013 uction during mechanical ventilation 3 5 and examination of the ETT after extubation 6 9. According to Poiseuille s Law, resistance to flow in a tube is inversely proportional to the 4th power of its radius and directly proportional to the viscosity of the fluid within. As such, progressive accumulation of secretions inside the ETT lumen leads to a substantial increase in airway resistance and reduction in peak airflow accordingly. Complete occlusion of an ETT is a life-threatening emergency and partial ETT occlusion is associated with increased work of breathing and delayed weaning from mechanical ventilation 10,11. Furthermore, a partially blocked ETT may increase the retention of pulmonary secretions and risk of ventilator-associated pneumonia (VAP) 12. The endotracheal suctioning systems available today are divided into either an open suctioning system (OSS) or a closed suctioning system (CSS). Unlike OSS, CSS can remove secretions without disconnecting the ventilator circuit from the ETT, thereby maintaining positive pressure ventilation and positive end-expiratory pressure. A CSS is more

2 2 N. A. Adi, N. T. Tomer et al convenient and may theoretically improve infection control although whether this is really cost-effective and can improve healthcare worker and patient outcomes remains controversial and debatable The Airway Medix Closed Suction System (AMCSS) (Biovo Technologies, Tel Aviv, Israel) represents a novel technology in CSSs, designed to achieve more effective cleaning of ETTs in prolonged mech-anical ventilation. The AMCSS comprises four main parts: the machine end, the patient end, the catheter and the catheter sleeve (Figure 1). The machine end comprises the vacuum port for attachment to suction tubing, the thumb control valve to intermittently control the suction as required, the balloon inflation port with a one-way valve, allowing the balloon to remain inflated and the wetting fluid entry port where wetting fluid is instilled for supply to the wetting fluid ports in the catheter. The machine end also includes the International Organization for Standardization colour coding for the device, for immediate recognition of the catheter diameter (International Organization for Standardization 8836:1997). A wetting fluid syringe and balloon inflation syringe are not strictly part of the device, but are used to introduce a wetting fluid and inflate the balloon respectively. The patient end comprises the ventilation entry port for connection to the ventilation circuit and the tube adapter, where the device is attached to the endotracheal or tracheostomy tube. The catheter includes lateral suction ports around the patient end of the catheter, wetting fluid distribution ports, a cuff balloon and depth markings in centimetres that allow easy measurement of correct catheter insertion in the trachea. The catheter sleeve is a very thin, flexible plastic covering attaching the patient end to the machine end and encompassing the catheter when it is withdrawn from the patient. The AMCSS is incorporated into the ventilation circuit by attaching the suction tube to the vacuum port, the air supply to the ventilation entry port and the endotracheal tube to the tube adapter. The catheter is then fed into the endotracheal tube, the required amount of suction and wetting fluid (through the wetting fluid entry port) is applied and the balloon may be inflated as required (through the balloon inflation port). The injection of the wetting fluid may be facilitated using a syringe pump. After sufficient cleaning, the catheter is withdrawn with the balloon either in the inflated or deflated position as required. If inflated, the balloon will remove biofilm still attached to the inner wall of the endotracheal tube. Several methods have been used to assess the degree of ETT obstruction. The pressure drop from one end of the ETT to the other is a direct measure of the change along the entire tube 9. Others have used methods such as intraluminal catheters 3,7 or resistive work of breathing 16. The acoustic reflection methods correlate the ETT s intraluminal volume loss to intraluminal narrowing 4. The limitations of these studies include the introduction of confounding factors such as intraluminal catheters, the use of segments of tubes and small sample size. In this study, we evaluated ETTs from extubated adult patients who were mechanically ventilated for more than 12 hours and compared them to new, unused, size-matched control tubes for changes in and PIP before and after suctioning with the AMCSS. The extubated ETTs were connected to a test lung and measurements of PIP and before and after suctioning were recorded. MATERIALS AND METHODS Study location and patients This observational study took place at Kaplan Medical Center, Rehovot, Israel; a universityaffiliated teaching hospital. The study was approved by a local ethics review board who waived the need for patient consent (Approval No. KMC 0010/12). Study design All patients had similar ventilator circuits in place, which included the gas delivery tubing, CSS catheters (KimVent, Kimberley-Clark Healthcare, Roswell, GA, USA), water bath humidification system and small volume nebuliser. The in-line KimVent CSS catheters were replaced every 72 hours according to the manufacturer s instructions. Eleven of the ETTs were obtained after extubation in the intensive care unit and five ETTs were obtained after they were changed to a tracheostomy tube at the time of bedside percutaneous tracheostomy. Data collection The length of intubation was collected for all study patients. Resistance measurements Immediately after extubation, each ETT was placed in a biohazard bag with gauze wetted with 4 ml of 0.9% saline solution and sealed to avoid dehumidification during transportation to the laboratory. All studied ETTs were evaluated within 4.5 hours of extubation. A prefabricated plastic mould was used to cut the distal portion of the

3 Changes in ETT Resistance with use and cleaning 3 Figure 1: The AMCSS used during a bench study for the evaluation of changes in inspiratory resistance (Rinsp) and peak inspiratory pressure (PIP) before and after suctioning. AMCSS=Airway Medix Closed Suction System. Figure 2: The AMCSS tip of catheter showing spraying of fluid, inflated balloon and suction ports. AMCSS=Airway Medix Closed Suction System.

4 4 N. A. Adi, N. T. Tomer et al ETT (where the Murphy hole is located) to facilitate connection to a test lung (Hamilton Test Lung) via an ETT connector. Subsequently, the AMCSS catheter was attached to the ETT. The ventilator (Hamilton G5, Hamilton Medical, Reno, NV, USA) was set to volume-controlled mode at an inspired oxygen (FiO 2 ) of 40.0% and a positive end-expiratory pressure of 5 cmh 2 O. Readings were taken during square wave flow, at rates of 40 and 60 l/minute. The ventilator derives according to the least squares regression 17 and displays it in cmh 2 O/litre/ second. was recorded immediately before and after a suctioning episode with the AMCSS catheter. As all other components of the artificial airway described were the same for the pre and post-suctioned ETT, the difference in PIP and represents the change in resistance due to the AMCSS device. Statistical analysis Repeated measures analysis of variance (RM- ANOVA) was used to test for differences in both and PIP, with the ETT inner diameter and the condition of the tube as fixed factors. When statistically significant differences were found, Tukey s post hoc test was used to establish the direction of these differences. Data are reported as mean ± 1 standard deviation and null hypotheses were rejected at α=0.05. All statistical tests were performed by the program R (version , R & R of the Statistics Department of the University of Auckland, New Zealand). RESULTS Sixteen ETTs were recovered from predominantly medical patients who had required intubation and mechanical ventilation for more than 12 hours. Median time of intubation was 13 days (range between 12 hours and 26 days). Eleven ETTs with an internal diameter (ID) of 8 mm, three of 7.5 mm and one each with ID of 7 and 8.5 mm were com-pared to new, unused, size-matched control tubes. The changes in and PIP before and after suctioning with the AMCSS are presented in Table 1. before and following suctioning episode Flow 40 l/minute did not differ between conditions of the ETTs (RM-ANOVA: F 2,24 =3.26, P=0.06, Power=0.56). There was a trend towards having a lower resistance after the used ETTs were cleaned (9.14±2.35 cm H 2 O/l/s) compared to resistance of the used ETTs before cleaning (18.43±14.73 cmh 2 O/l/s), but both were having higher than the new ETT (6.50±0.76 cmh 2 O/l/s). \ Flow 60 l/minute was significantly affected by the condition of the ETTs (Figure 2; RM-ANOVA: F 2,24 =10.43, P<0.001, Power=0.98). Specifically, cleaning the used ETTs resulted in significantly lower resistance (11.57±2.79 cmh 2 O/l/s) compared to the used ETTs before cleaning (21.14±10.36 cmh 2 O/l/s; Tukey s post hoc test: P <0.001) and was not signifi- Table 1 Changes in and PIP before and after suctioning with the AMCSS Flow 40 l/min Flow 60 l/min Condition Sample size Diameter Resistance Pressure Resistance Pressure New Used Cleaned New ± ± ± ±0.50 Used ± ± ± ±4.58 Cleaned ± ± ± ±2.06 New ± ± ± ±1.03 Used ± ± ± ±19.00 Cleaned ± ± ± ±3.32 New Used Cleaned =inspiratory resistance, PIP=peak inspiratory pressure, AMCSS=Airway Medix Closed Suction System.

5 Changes in ETT Resistance with use and cleaning 5 cantly different from the resistance of new ETTs (7.57±0.76 cmh 2 O/l/s; Tukey s post hoc test: P=0.2). PIP before and following suctioning episode Flow 40 l/minute PIP did not differ between different conditions of the ETT (Figure 2; RM-ANOVA: F 2,24 =2.36, P=0.1, Power=0.43). The inner diameter of the ETT did not affect the (Figure 2; RM- ANOVA: F 1,12 =0.50, P=0.5, Power=0.10) and there was no dependency between the effect of cleaning the ETTs and the inner diameter (Figure 2; RM-ANOVA: F 2,24 =0.74, P=0.5, Power=0.16). Flow 60 l/minute PIP was significantly affected by the conditions of the ETTs (RM-ANOVA: F 2,24 =6.33, P=0.006, Power=0.86). Specifically, cleaning the ETTs resulted in lower PIP (40.79±2.99 cmh 2 O) compared to the PIP of used ETTs without cleaning (54.21±17.10 cmh 2 O; Tukey s post hoc test: P=0.003) and the PIP of the cleaned tube was not significantly different from the PIP of the new ETTs (36.57±1.02 cmh 2 O; Tukey s post hoc test: P=0.5). Estimating ETT obstruction The mean measured for extubated ETTs with an ID of 8 mm, with secretion build-up, was equal to the measured of a new tube with ID of 5 mm. After cleaning, the mean measured was equal to an ETT with ID of 7.5 to 8 mm (Figures 3 and 4). DISCUSSION Several devices designed to clean the ETT have already been studied in experimental animal and human protocols. The Mucus Shaver (MS) was previously tested in mechanically ventilated sheep. In an animal model it was found to be easy to use and effective in removing secretions from the ETT lumen 23. In a clinical model, the MS has proven to be effective in keeping the internal surface of a silver-based coated ETT clean, thus retaining the tube s full bactericidal effect 23. Despite promising clinical results, the MS is not commercially available. The Rescue Cath (Omneotech, Tavernier, FL, USA) is an alternative method of restoring airway patency of an ETT. It is an OSS for suctioning and removing secretions from the ETT lumen and Federal Drug Administration approved. The Rescue Cath consists of a stiff catheter with a mesh-encased cleaning balloon at the distal end, a depth calibrator, balloon inflation syringe, handle, irrigation port, stopcock valve and suction port. Only one report of three cases in a paper by Stone et al is available 22 and it appears to be safe and effective in removing mucus. However, this device is not intended for use on a regular basis in the daily care of intensive care unit patients. The endoclear device (endoclear LLC, Petoskey MI, USA) is another similar device being investigated by groups from different institutions in the United States. In a preliminary ex vivo study conducted at West Virginia University on seven ETTs removed from intensive care unit patients, Inspiratory resistance (cm H20/l/s) New Used Clean Inner diameter (mm) Figure 3: Mean inspiratory resistance (cmh 2 O/l/s) of ETT with different IDs (mm) at an inspiratory flow of 60 l/minute. Error bars are ± 1SD and numbers within bars denote number of ETTs tested. ETT=endotracheal tubes, ID=internal diameter, SD=standard deviation.

6 6 N. A. Adi, N. T. Tomer et al Inspiratory resistance (cm H20/l/s) New Used Clean Inner diameter (mm) Figure 4: Inspiratory resistance measurements of ETTs with different ID and different states. Inspiratory flow rate 40 l/minute. ETT=endotracheal tube, ID=internal diameter. data showed that the endoclear system was effective in restoring the function of the ETT airway to nominal 24. Currently this device is not available in Europe and is not embedded in a closed system, so ventilator disconnection is required to perform the cleaning manoeuvre. The Mucus Slurper is another device designed to keep the ETT and proximal trachea free of mucus. It should be used as an integral part of the tracheal tube to aspirate all mucus automatically at its distal tip. In studies in sheep lasting 24 hours the Mucus Slurper was safe and prevented all mucus accumulation within the ETT 25. The MS, endoclear and Mucus Slurper have a few clear disadvantages these are designed for single use only and should be discarded after a single use. They are also all OSSs which require the disconnection of the patient from the ventilator circuit before suction. In addition, the use of these devices has to be added to a standard, regular suction system. The AMCSS represents a novel CSS technology, designed to achieve more effective cleaning of ETTs in prolonged mechanical ventilation without the need to disconnect the ventilatory circuit. In this bench-top study, the cleaning of extubated ETTs using the AMCSS was able to restore the flow mechanics ( and PIP) of the used ETT similar to those measured in a new ETT. The examined ETTs included tubes of various sizes ranging from ID 7 to 8.5 mm and intubation periods ranging from 12 hours to 26 days. We found that the mean for used and uncleaned ETTs was equivalent to 275% of the of size-matched new and unused ETTs. For 8 mm ID ETTs this was comparable to a measured of a 5 mm ID tube. Following a single cleaning episode with the AMCSS, decreased, regaining an effective ETT ID of a 7.5 to 8 mm tube. Most of the used ETTs had been in place for prolonged periods of time before extubation (median time 13 days) and the secretion build-up was able to harden during the time between extubation and benchtesting. This may explain why a single cleaning episode could not fully restore the flow characteristics to that of a new one. In its intended use, the AMCSS is designed for daily use to prevent accumulation of secretions and build-up of biofilm. Therefore, it is plausible that by using the AM- CSS device while the patient is intubated and ventilated, the resistance to ventilation through the ETT may be significantly minimised. ETT narrowing and occlusion remain important causes of morbidity and potential mortality, in patients requiring prolonged intubation and venti-lation. Acute occlusion of the ETT is lifethreatening and requires immediate intervention, although it can be insidious and difficult to recognise. Gradual narrowing of the tube lumen is associated with increased work of breathing, may prolong mechanical ventilation and may lead to weaning failure 10,11. As secretion and biofilm buildup is not uniform along the length of the ETT, airflow is probably limited by segments of maximal accumulation, corresponding to a mean reduction in diameter of about 25 to 50% at the narrowest point, according to direct debris measurements 6. Compared to the AMCSS, all prior suctioning systems limit their action to a narrow cylinder created by the suction catheter, whose volume should not exceed half of the ETT lumen 18. Thus, intraluminal narrowing of the ETT and an increased due to secretion build-up remains a common occurrence in mechanically ventilated patients. The AMCSS represents a novel solution, through which the whole ETT ID volume is potentially subjected to more thorough cleaning. In the present study, the ETTs had been suctioned every three hours using a KIMVENT (Kimberly-Clark Health Care, Irving, TX, USA) in-line CSS catheter for the period of intubation. Although ETT suctioning is essential to mechanical ventilation, it is also associated with complications, and risks include bleeding, infection, cardiovascular instability and trauma to the tracheal mucosa 1. Thus, some authors recommend that suctioning should only be performed when clinically necessary or at a minimum frequency 1. It follows that efficient suctioning might not only minimise secretion build-up, but may also reduce the frequency of suctioning episodes. The AMCSS is designed to prevent secretion and microbial biofilm build-up on the intraluminal

7 Changes in ETT Resistance with use and cleaning 7 surface of the ETT. This biofilm may act as a reservoir of pathogens causing recurrent infection; biofilms are also increasingly being linked with the development of bacterial resistance 19. It is thought that fragments of biofilm detach spontaneously or become dislodged (by suctioning) and enter the lungs with the inspiratory gas flow. Moreover, deep suction with saline instillation may enhance active microbial biofilm dislodgement associated in the pathogenesis of VAP. It was demonstrated that 70% of patients with VAP had identical pathogens isolated from both their ETTs and lower respiratory tract 20. When using the AMCSS during suctioning and saline instillation, biofilm dislodgment into the distal bronchial tree is potentially reduced by the combined effect of the inflated occlusive balloon at the tip of the suctioning catheter and the efficient suctioning ports mounted between the occlusive balloon and the wetting ports. Our study has some limitations. First, the marked increase in compared to others is, in part, due to the selection of extubated ETTs with visible intraluminal secretions 21, (which were present, however, in most of the available ETTs). Indeed, this was reported by Alison et al 9, who found that 75% of randomly collected extubated ETTs exhibited a pressure drop >3 standard deviations of the normal range due to secretion build-up compared to size-matched control tubes. Although the median intubation time was 13 days, two of the ETTs with markedly increased were extubated from cardiac surgical patients just 12 hours after surgery. Second, intraluminal is a dynamic process affected by intraluminal movement of the sloughing airway secretions and other intraluminal materials through the ventilator cycle. The single point measurement of might be affected by the dynamic movement of the accumulated material. Third, we did not analyse the microbial biofilm and the occluding material that was extracted from the ETTs lumen by the AMCSS. Thus, the relationship between the adherent material and the development of VAP is currently unknown. Finally, this was a bench-top study and there was no patient-centred outcome. As such, whether using AMCSS can improve important clinical outcomes or reduce overall health costs for patients requiring prolonged mechanical ventilation remains uncertain, but this merits further study. CONCLUSION In conclusion, ETTs used for prolonged mechanical ventilation in critically ill patients had substantial increases in airflow resistance. Following a single suction and cleaning episode with the AMCSS device, decreased significantly to a level similar to an unused ETT. The effectiveness of the AMCSS in decreasing resistance due to secretion build-up has the potential to prevent ETT occlusion and narrowing. Further research is needed to show that the use of such a system might also help to reduce the incidence of VAP by preventing intraluminal biofilm formation. CONFLICTS OF INTEREST Nimrod Adi and Duncan Wyncoll are stock owners at Biovo Technologies (Tel Aviv, Israel). Biovo Technologies is the manufacturer of Airway Medix Closed Suction System. No funding was received from the company for this study. References 1. American Association for Respiratory Care. AARC Clinical Practice Guidelines. Endotracheal suctioning of mechanically ventilated patients with artificial airways Respir Care 2010; 55: Day T, Farnell S, Wilson-Barnett J. Suctioning: a review of current research recommendations. Intensive Crit Care Nurs 2002; 18: Jaber S, Pigeot J, Fodil R, Maggiore S, Harf A, Isabey D et al. Long-term effects of different humidification systems on endotracheal tube patency: evaluation by the acoustic reflection method. Anesthesiology 2004; 100: Lucchini A, Zanella A, Bellani G, Gariboldi R, Foti G, Pesenti A et al. Tracheal secretion management in the mechanically ventilated patient: comparison of standard assessment and an acoustic secretion detector. Respir Care 2011; 56: Villafane MC, Cinnella G, Lofaso F, Isabey D, Harf A, Lemaire F et al. Gradual reduction of endotracheal tube diameter during mechanical ventilation via different humidification devices. Anesthesiology 1996; 85: Boque MC, Gualis B, Sandiumenge A, Rello J. Endotracheal tube intraluminal diameter narrowing after mechanical ventilation: use of acoustic reflectometry. Intensive Care Med 2004; 30: Glass C, Grap MJ, Sessler CN. Endotracheal tube narrowing after closed-system suctioning: prevalence and risk factors. Am J Crit Care 1999; 8: Shah C, Kollef MH. Endotracheal tube intraluminal volume loss among mechanically ventilated patients. Crit Care Med 2004; 32: Wilson AM, Gray DM, Thomas JG. Increases in endotracheal tube resistance are unpredictable relative to duration of intubation. Chest 2009; 136: Adair CG, Gorman SP, Feron BM, Byers LM, Jones DS, Goldsmith CE et al. Implications of endotracheal tube biofilm for ventilator-associated pneumonia. Intensive Care Med 1999; 25: Rumbak MJ, Walsh FW, Anderson WM, Rolfe MW, Solomon DA. Significant tracheal obstruction causing failure to wean in patients requiring prolonged mechanical ventilation: a forgotten complication of long-term mechanical ventilation. Chest 1999; 115:

8 8 N. A. Adi, N. T. Tomer et al 12. Straus C, Louis B, Isabey D, Lemaire F, Harf A, Brochard L. Contribution of the endotracheal tube and the upper airway to breathing workload. Am J Respir Crit Care Med 1998; 157: Fernandez MdM, Piacentini E, Blanch L, Fernandez R. Changes in lung volume with three systems of endotracheal suctioning with and without pre-oxygenation in patients with mild-to-moderate lung failure. Intensive Care Med 2004; 30: Rabitsch W, Kostler WJ, Fiebiger W, Dielacher C, Losert H, Sherif C et al. Closed suctioning system reduces cross-contamination between bronchial system and gastric juices. Anesth Analg 2004; 99: Lorente L, Lecuona M, Jimenez A, Mora ML, Sierra A. Tracheal suction by closed system without daily change versus open system. Intensive Care Med 2006; 32: Lorente L, Lecuona M, Martin MM, Garcia C, Mora ML, Sierra A. Ventilator-associated pneumonia using a closed versus an open tracheal suction system. Crit Care Med 2005; 33: Diehl JL, El Atrous S, Touchard D, Lemaire F, Brochard L. Changes in the work of breathing induced by tracheotomy in ventilator-dependent patients. Am J Respir Crit Care Med 1999; 159: Jarreau PH, Louis B, Dassieu G, Desfrere L, Blanchard PW, Moriette G et al. Estimation of inspiratory pressure drop in neonatal and pediatric endotracheal tubes. J Appl Physiol 1999; 87: Peslin R, da Silva JF, Chabot F, Duvivier C. Respiratory mechanics studied by multiple linear regression in unsedated ventilated patients. Eur Respir J 1992; 5: Pedersen CM, Rosendahl-Nielsen M, Hjermind J, Egerod I. Endotracheal suctioning of the adult intubated patient what is the evidence? Intensive Crit Care Nurs 2009; 25: Feldman C, Kassel M, Cantrell J, Kaka S, Morar R, Goolam Mahomed A et al. The presence and sequence of endotracheal tube colonization in patients undergoing mechanical ventilation. Eur Respir J 1999; 13: Stone RH, Bricknell SS. Experience with a new device for clearing mucus from the endotracheal tube. Respir Care 2011; 56: Berra L, Coppadoro A, Bittner EA, Kolobow T, Laquerriere P, Pohlmann JR et al. A clinical assessment of the Mucus Shaver: a device to keep the endotracheal tube free from secretions. Crit Care Med 2012; 40: Macia I, Gossot D. Maintaining a clear vision during longlasting thoracoscopic procedures. Interact Cardiovasc Thorac Surg 2010; 11: Kolobow T, Li BG, Curto F, Zanella A. The Mucus Slurper: a novel tracheal tube that requires no tracheal tube suctioning. A preliminary report. Intensive Care Med 2006; 32: