Background The use of cuffed endotracheal tubes (ETTs) in paediatric critical care has become widespread with the development of high volume – low pressure cuffs which require significantly lower sealing pressure than traditional ETTS. There remains a risk of over inflation which can impair tracheal capillary perfusion causing pressure necrosis of the surrounding fragile epithelium potentially resulting in permanent upper airway damage such as sub-glottic stenosis. Cuff pressure can vary over time therefore careful monitoring is vital to ensure the pressure remains within a safe range.
Objectives Connecting a manometer to the pilot balloon is one method to monitor cuff pressure. A prior study demonstrated that connecting a manometer caused a drop in pressure giving a falsely low readings. We hypothesised that pre-pressuring the manometer would result in accurate cuff pressure readings enabling detection of dangerously high pressures.
Methods An airway model was intubated with Halyard size 3.0 micro-cuff ETT. Using a commercially available manometer, a three way tap and syringe the cuff was inflated to a set pressure in increments of 1 cm H2O between 0 and 40 cm H2O. The manometer was then connected to the pilot balloon to check the pressure using 3 methods:
Control 1) Manometer connected directly to the pilot balloon (no tubing used therefore pressure in the system = 0 cm H2O)
Control 2) Manometer connected to the pilot balloon via extension tubing with 3 way tap and syringe in circuit (pressure in tubing and manometer system = 0 cm H2O)
Test 3) Manometer connected to the pilot balloon via extension cable with 3 way tap and syringe in circuit with the entire circuit pre-pressurised to 20 cmH2O before connecting
Set-up 2) was used as a control to show how the tubing and 3 way tap affected the readings. For each method three measurements were performed at every 1 cm H2O increment and the average reading was taken.
Results Using method 1 the average manometer reading was significantly lower than the pre-set cuff pressure for example pre-set pressures of 20 & 40 cm H2O read only 5.3 and 8 cm H2O respectively. Using method 2 the average readings dropped even further from the pre-set pressure. Using method 3 with the manometer pre-pressurised to 20 cm H2O the reading dropped if the cuff pressure was ≤19 cm H2O and increased if the cuff pressure was ≥21 cm H2O. A pre-set pressure of 0 gave a reading of 11 cm H2O, 10 read as 17.7 cm H2O, 30 read as 20 cm H2O and 40 read as 21.3 cm H2O.
Conclusions The results indicate that the intervention of connecting a manometer renders the reading inaccurate. This disparity is due to the dead space in the manometer and also the tubing as shown by the lower readings from method 2. The hypothesis of filling the dead space by pre-pressurising the manometer system did not result in more accurate readings as the pressure merely equalised across the system. Therefore the only way to ensure cuff pressures are not dangerously high is to deflate the cuff and use the 3-way tap system or cuff inflator to inflate to a safe pressure.
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