Table 2 Summary of laboratory studies

Dullenkopf, 2003 [8]

• 1 PU-cuffed ETT (MICROCUFF HVLP ICU; Microcuff GmbH, Heidelberg, Germany)

• 4 PVC-cuffed ETTs (Portex Profile Soft Seal, SIMS Portex Ltd., Hythe, UK; Rüschelit Super Safety Clear, Rüsch GmbH, Kernen, Germany; Mallinckrodt Hi-Lo, Mallinckrodt Medical, Athlone, Ireland; Sheridan/CF, Hudson Respiratory Care, Temecula, USA)

• ID all ETTs 7.5 mm

• Vertical PVC trachea model (ID 20 mm)

• Unlubricated and lubricated cuffs

• No ventilatory simulation

• 10, 15, 20, 25, 30, 60 cmH₂O

• Controlled by manometer

• Colored water (5 ml)

• Amount of leaked fluid passed through tube cuff within 5, 10, and 60 minutes

4 repetitions of 2 tubes of each brand

• Fluid leakage occurred in all PVC cuffs at P_cuff 10–60 cmH₂O. In the PU cuff, leakage was recorded only at P_cuff 10 cmH₂O (<5 minutes) and at P_cuff 15 cmH₂O (<60 minutes)

• PU cuffs sealed significantly better at conventional P_cuff (20–30 cmH₂O) than with all types of PVC cuffs; while no leak was observed in PU cuffs, >90 % of the test fluid (>4.5 ml) passed through cuff in all PVC cuffs

Lucangelo, 2008 [14]

• PU-cuffed ETT (Mallinckrodt SealGuard, Mallinckrodt Medical, Cornamady, Anthlone County, Ireland)

• PVC-cuffed ETT (Mallinckrodt Hi-Lo, Mallinckrodt Medical, Cornamady, Anthione County, Ireland)

• ID all ETTs 7.5 mm

• Room temperature

• Vertical Pyrex cylindertrachea model, ID 25 mm

• Unlubricated cuffs

• 5-, 7.5-, and 10-cm PEP randomly applied

• PEP removed after 30 minutes

• Experiment lasted 1 h

• 30 cmH₂O

• Controlled by aneroid manometer

• Evans blue (1 ml) diluted with normal saline (1 ml)

Triplicate experiments with new ETTs

• 10 minutes after PEP removal (40 minutes after Evans blue dye application on top of cuffs), all liquid had passed through PVC cuffs

• No leakage in PU cuffs

Dave, 2010 [24]

• PU-cuffed ETTs (standard SealGuard, Covidien, Athlone, Ireland; MICROCUFF, Kimberley Clark, Zaventem, Belgium)

• 3 PVC-cuffed ETT (Hi-Lo, Covidien, Athlone, Ireland; Portex Profile Soft Seal, SIMS Portex Ltd., Hythe, UK; Rüschelit Super Safety Clear, Rüsch GmbH, Kernen, Germany) ID all ETTs 7.5 mm

• Room temperature

• Artificial PVC trachea model with variable ID 16, 20, 22 mm

• Unlubricated cuffs

• No ventilatory simulation, no PEEP

• 25 cmH₂O

• Controlled by digital automated manometer

• Clear water (5 ml)

• Leakage measured at 5 minutes and 60 minutes

8 tubes tested of each ETT type

PVC cuffs leaked considerably more than PU cuffs

• At 5 minutes: - ID 16 and 20 mm: 0.03–1.62 ml (PU) vs. 4.27–4.67 ml (PVC) - ID 22 mm: 0–4.85 ml (PU) vs. 4.65–4.71 ml (PVC)

• At 60 minutes: - ID 16 and 20 mm: 0.90–4.58 ml (PU) vs. 4.61–4.69 ml (PVC) - ID 22 mm: 0–4.85 ml (PU) vs. 4.65–4.75 ml (PVC)

Dave, 2011 [13]

• PU-cuffed ETT (SealGuard, Covidien, Athlone, Ireland)

• PVC-cuffed ETT (Hi-Lo, Covidien, Athlone, Ireland) ID all ETTs 5 mm

• Vertical artificial PVC trachea model, ID 22 mm

• Unlubricated cuffs

• Test lung attached to trachea model

• Pressure-controlled ventilation with PIP 15, 20, 25 cmH₂O

• PEEP 5 and 10 cmH₂O

• Closed tracheal suction system attached with variable suction pressure (-20000 or -30000 Pa) during 5, 10, 15, and 20 seconds

• 25 and 50 cmH₂O

• Controlled by digital automated manometer

• Clear water (10 ml)

4 tubes tested of each ETT type

PU cuffs leaked less (range 0–0.12 ml) than PVC cuffs (range 0.05–6.28 ml) at all P_cuff levels (p < 0.001) and at all negative suction pressures tested (p < 0.001)

Kolobow, 2011 [27]

• 2 PU-cuffed ETTs (prototype tube with Lycra PU cuff, MICROCUFF, Kimberly-Clark, Kimberly-Clark Health Care, Roswell, Georgia, USA)

• PVC-cuffed ETT (Hi-Lo, Mallinckrodt/Covidien, Boulder, Colorado, USA) ID all ETTs 8 mm

• Vertical acrylic tube trachea model, ID 20 mm

• Cuffs not lubricated

• No ventilatory simulation, no PEEP

• 20 cmH₂O

• Controlled by aneroid manometer

• Methylene blue-colored water (15 ml)

• Leak time observation 24 h

• Leakage expressed as milliliters per hour

6 tubes tested of each ETT type

• No leakage in Lycra PU prototype ETT

• The other PU cuff (MICROCUFF) allowed less leakage (1.2 ± 0.4 ml/h) than PVC cuff (1.2 ± 1.3 ml/h) (p < 0.001)

Ouanes, 2011 [25]

• PU-cuffed ETTs (MICROCUFF, Kimberly-Clark, Zaventem, Belgium)

• PVC-cuffed ETT (Rüschelit Super Safety Murphy, Rüsch GmbH, Kernen, Germany) ID ETTs 7.5 and 8 mm

• Vertical artificial Plexiglas trachea model, ID 18 mm

• Cuffs not lubricated

• Ventilatory settings 10 cmH₂O PSV driven by active inspiration with trigger sensitivity at 2 L/minute and respiratory rate at 20 breaths/minute. Three effort intensities (occlusion pressure at 0.1 second): low = 2 cmH₂O, moderate = 5 cmH₂O, and high = 10 cmH₂O

• Experiments performed with PEEP 0 and 5 cmH₂O

• 30 cmH₂O

• Controlled by manual manometer every 3 h

• Methylene blue (1 ml) diluted with 4 ml normal saline

• Leak time observation 1 h

• Leakage expressed as milliliters per hour

3 tubes tested of each ETT type

At all inspiratory levels tested, significantly less leakage occurred with PU cuffs: mean 0.5 (SD 0.5) ml/h vs. 36.8 (SD 31.6) ml/h (p < 0.001)

Zanella, 2011 [15]

• PU-cuffed ETTs (MICROCUFF, Kimberly-Clark, GA, USA)

• 3 PVC-cuffed ETT (Mallinckrodt Hi-Lo, Mallinckrodt, NY, USA; Mallinckrodt High-Contour, Kimberly-Clark, Zaventem, Belgium; Portex Ivory, Smiths Medical, UK) ID all ETTs 8 mm

• Vertical PVC cylinder as trachea model, ID 20 mm

• Cuffs not lubricated

• Ventilatory settings: CPAP simulation with 4 levels of PEEP randomly applied (0, 5, 10, and 15 cmH₂O)

• 30 cmH₂O

• Continuously controlled by water seal valve providing continuous positive pressure into pilot balloon

• Methylene blue-dyed water added above the cuff to make water column 10 cm

• Leak time camera observation 24 h with picture taken every 60 seconds

• Leakage expressed as water column above cuff (cm)

• Leakage detected by blinded observer

5 tubes tested of each ETT type, at PEEP 5–15 cmH₂O

5 new ETTs tested at PEEP 0

Leakage observed after 24 h:

• PU cuff: - No leakage at PEEP levels 5, 10, and 15 cmH₂O - Minor leak without PEEP (about 2 cm)

• 3 types of PVC cuffs: -No leak at PEEP 15 cmH₂O - Minor leak at PEEP 10 cmH₂O (about 2 cm) - Major leak at PEEP 5 cmH2O (>8 cm) - Maximum leak without PEEP (10 cm)

Li Bassi, 2013 [11]

• 8 HVLP ETTs with various cuff characteristics, among which were: PU-cuffed ETT (Kimvent MICROCUFF, Kimberly-Clark Health Care, Roswell, GA, USA) PVC-cuffed ETTs (Rüschelit Safety Clear Plus, Teleflex, Limerick, PA, USA; Hi-Lo, Covidien-Nellcore and Puritan Bennett, Boulder, CO, USA)

• ID 7, 7.5, 8 mm

• Artificial trachea model (ID 18, 20, and 22 mm) oriented 30 degrees above horizontal

• Cuffs not lubricated

• No ventilatory simulation

• Short-term fluid sealing capacity (1 h): 3 ETT IDs at 4 P_cuff levels

• Long-term fluid sealing capacity (24 h) with 4 best-performing ETTs at 1 h; experiment performed with 7.5 mm ID ETTs and P_cuff 30 cmH₂O

• Measurement: multivariate analysis in which leakage rate was evaluated considering several other cuff characteristics: P_cuff, cuff OD, cuff length, PU cuff, taper-shaped cuff, ratio cuff OD/trachea model ID, ratio cuff OD/cuff length, cuff compliance, and trachea model ID

• 15, 20, 25, 30 cmH₂O

• Controlled by automated manometer

• Oropharyngeal secretion simulant (viscosity 3 cP at shear rate 75/second)

• Leakage recorded as milliliters per hour

• Leak time observation 1 h and 24 h

3 tubes tested of each ETT type

PU cuffs leaked substantially less than PVC cuffs:

• Short-term mean fluid leakage rates (1 h): - PU cuff (MICROCUFF): 0.09 ± 0.06 ml/h - PVC cuff (Rüschelit): 4.46 ± 3.47 ml/h - PVC cuff (Mallinckrodt Hi-Lo): 2.24 ± 1.93 ml/h

• Long-term mean fluid leakage rates (24 h): - PU cuff (MICROCUFF): 0.69 ± 0.36 ml/h - PVC cuff (Mallinckrodt Hi-Lo): 114.74 ± 16.79 ml/h

• In multivariate analysis (considering 8 types of ETTs with various cuff characteristics), internal P_cuff, cuff OD, and cuff length were independently associated with lower leakage rates; cuff material did not reach statistical significance in this model

Lau, 2014 [23]

• PU-cuffed ETTs (Kimvent MICROCUFF, Kimberly-Clark Health Care, US)

• PVC-cuffed ETT (Portex, Smiths Medical International Ltd., UK) ID all ETTs 8 mm

• Silicone cylinder trachea model (ID 20 mm) oriented 35 degrees above horizontal

• Cuffs not lubricated

• Ventilatory settings: 5 simulated mechanical ventilation scenarios, including different PEEP levels and disconnection with and without spontaneous breathing effort. Each scenario was tested under 3 P_cuff levels and then repeated with application of continuous suction force (−200 cmH₂O for 3 minutes)

• 10, 20, 30 cmH₂O

• Maintained by automated device

• Clear water (20 ml)

• Leakage observation time 20 minutes.

• Leakage was video-recorded and expressed as cumulative amount of leakage (ml)

2 ETTs of each type, and each ETT tested 4 times (8 measurements for each ETT per scenario and P_cuff)

PU cuffs consistently demonstrated best protection against fluid leakage; clinical situations associated with greater leakage were mechanical ventilation without PEEP, circuit disconnection with spontaneous breathing, application of suction, and low P_cuff (10 cmH₂O)

Li Bassi, 2015 [26]

• PU-cuffed ETTs (KimVent MICROCUFF, Halyard Health, USA)

• PVC-cuffed ETT (Rüschelit Safety Clear Plus, Teleflex Incorporated, Limerick, PA, USA) ID ETTs not reported

• Large White-Landrace pigs (37.3 ± 3.6 kg) randomized to be intubated with either of the test ETTs

• 5 pigs in PU group

• 4 pigs in PVC group

• Intubated, ventilated, and anesthetized for 76 h

• After 52 and 73 h, pigs were placed in prone, bed oriented 30 degrees above horizontal, and PEEP reduced to 0

• 28 cmH₂O

• Maintained by automated device

• Methylene blue (2 ml) and phosphate-buffered solution (3 ml) with 1.5 μl of 2.0-μm Invitrogen fluorescent microspheres (Life Technologies, Carlsbad, CA, USA)

• 1 h from instillation, leakage estimated by presence of methylene blue and quantification of microspheres in tracheal secretions quantified by calculating percentage of recovered microspheres per gram of tracheal secretions per total amount of instilled microspheres

1 ETT per animal

• Methylene blue was never found in tracheal secretions

• Percentage of aspirated microspheres was not significantly lower with PU cuffs (0.06 ± 0.05 %) than with PVC cuffs (0.12 ± 0.06 %)