318 - Time Needed for Oxygen Adjustments During Resuscitation with T-piece Systems. Can dead-space and connectors explain differences?

Previous studies have recorded significant delays when adjusting the inhaled oxygen concentration in simulated positive pressure ventilation (PPV) with T-piece devices. The previous investigated factors include fresh gas flow, stepwise adjustments and leakage but not dead-space or oxygen sensor connector design.


Objective:

To investigate the time delay during oxygen adjustment related to dead space and sensor connector design.


Design/Methods:

The time between oxygen adjustment and delivery was measured in a mechanical lung model with a 50 mL Dräger test lung. PPV was delivered at PIP 24/PEEP 6 cm H2O with a respiratory rate of 60/min and a fresh gas flow of 10 LPM. The oxygen was adjusted from 30% to 60%. O2 was measured at 20Hz, using two chemical sensors (Teledyne, USA) at the Neopuff driver and at the Neopuff T-piece. At the T-piece, two connectors for the oxygen sensors were compared, a standard high volume and a 3D printed with reduced volume that diverts the flow to the sensor. Dead space was added using a 15 mm straight connector.


Results:

Time needed when increasing O2 was shorter with the reduced volume connector compared to the standard connector (51.9% vs 40.0% at 10 seconds and 57.5% vs 50.8% at 30 seconds, p< 0.05). Adding dead-space increased the time needed with approximately 20 seconds (Fig 1 and Table 1).


Conclusion(s):

The delay caused by the design of the oxygen sensor connector and when adding dead-space has previously not been reported. The delay may be clinically important when dead-space is added by a respiratory function monitor, a face mask or FiO2 measuring equipment. In previous studies, the time delay was similar or longer in simulations without leakage. The differences in reported times could be related to dead-space, titration protocols, PPV settings and equipment used.

Our results suggest that a low system volume reduce time needed after oxygen adjustments. Adding respiratory function monitoring systems and oxygen sensor connectors could lead to an increased delay. Resuscitation systems with lower dead-space and low volume interfaces (eg nasal prongs) should reduce the adjustment delay, if leakage remains unchanged. Replacing mainstream with sidestream monitors may be advantageous but was not investigated. 

In summary, the oxygen sensor connector design and amount of dead-space affect the time needed for adjustments of T-piece oxygen concentration. These findings are important when conducting bench tests. They may also be clinically important if dead space is added to the resuscitation system.