Background The loss of pressures at the distal end of ET tube can be affected by the size and diameter of the ET tube and the flow rates.

Aim To study in vitro the pressure drop using varying sizes of ET tubes commonly used in preterm infants at different lengths, flow rates using different gases.

Methods We used Portex tubes for this in-vitro study. A water manometer (scale 0–300mm) was used to measure the pressure drop across ET tube. We used two different lengths (7 and 14cms); different sizes (2.5; 3.0; 3.5 and 4.0mm), different flow rates (4 to 11 litres/min) and two different gases (medical air and 100% oxygen) to assess the resistance across the ET tube. SPSS version 17® was used for statistical analysis. Data presented as mean(SD).

Results

1. There was no difference in the pressure drop at lengths of 7cms and 14cms respectively using air [120.6 (66.12) vs.127.3 (68.74)cms H₂O; p=0.297]; but with 100% Oxygen there was statistically significant increase at 14cm compared to 7cm length [146.73 (72.94) vs. 130.48 (72.94cms H₂O; p=0.015] at similar flow rates.

2. At all flow rates there was no difference in pressure drop at different tube diameters using air or 100% oxygen.

3. There was a statistically significant (p<0.05) increase in pressure drop at flow rates increasing from 4 to 11 litres/min.

Conclusion The results from this study could be utilised to optimise ventilation settings to achieve the desired pressure delivery using air or oxygen at different flow rates and with varying ETtube sizes.