To evaluate the equipment used for nasal insufflation of oxygen and determine its
Oxygen delivery assemblies consisting of a flowmeter, bubble humidifier, oxygen delivery
tubing and nasal insufflation catheters were assembled. Single and double catheter
assemblies were made for four sizes of nasogastric feeding tubes (3.5 Fr, 5.0 Fr,
8.0 Fr and 10.0 Fr) resulting in 64 individual assemblies. A gas flow analyzer measured
oxygen flow at the tip of the nasal catheter assemblies and from the pressure relief
valve (PRV) of the bubble humidifiers. Statistical analyses were conducted to assess
the functionality of assemblies. For functional assemblies, the accuracy of oxygen
flow relative to the prescribed flow settings was determined.
Catheter size was significantly associated with the functionality of assemblies. Probability
(95% confidence interval) of 3.5 Fr, 5.0 Fr and 8.0 Fr assemblies being functional
was estimated at 0.53 (0.14, 0.89), 0.83 (0.36, 0.98) and 0.98 (0.76, 0.99), respectively.
All 10.0 Fr assemblies were functional. Functional assemblies, in general, consistently
under-delivered the prescribed flow because a large portion of set flow was diverted
through the bubble humidifier PRV.
Leaks through the PRV cause significant diversion of oxygen prior to it reaching the
catheter tips. Smaller patients are particularly susceptible, as small catheters limit
oxygen delivery creating proportionally greater leaks through the PRV.
It was not possible to accurately deliver oxygen because of leaks through the PRV.
Targeting a specific outcome (e.g., oxyhemoglobin saturation > 94%, PaO2 80–120 mmHg; 11–16 kPa) and avoiding unnecessarily high fractions of inspired oxygen
cannot be done if flow delivery cannot be accurately assured. One possible solution
would be to use a bubble humidifier with a 6 psi PRV that does not leak prior to reaching
the opening pressure.