The Science Journal of the American Association for Respiratory Care
BACKGROUND: HFOV is one option employed in the treatment of pediatric and adult patients with severe respiratory failure who fail conventional ventilation. Some difficulties in its application may be responsible for the lack of wider utilization. Specifically, endotracheal suctioning causes alveolar derecruitment, hypoxia, bradycardia, and hemodynamic instability. We sought a mechanism to reduce the occurrence of unneccessary suctioning.
METHOD: A SensorMedics 3100a ventilator was attached to a multiple balloon lung model. A mechanics monitor (Novametrix Cosmo+) was interfaced with a laptop computer and adapted to measure pressure changes distal to the end of an endotracheal tube (Camp). Pamp was read from the digital display of the 3100a ventilator and parameters were set as follows: Paw 35 cmH20; Hz 6; Power 6.0; bias flow rate 40 lpm and % 1 Time .33. Changes in Raw were created by varying endotracheal tube sizes (5,6,7,8,and 9). The lung model was positioned in a 50 gallon aquarium at depths of 0, 10, 20, and 30 cmH20 to simulate compliance changes. Camp was captured by measuring the pressure change between peak and trough of oscillations as recorded by the mechanics monitor and had a deviation of ± .7 cmH20.
Results: Increasing Raw (Smaller ETT diameter) resulted in an increasing Pamp and a decrease in Camp (P<0.001 for both - see figure). Decrease compliance also resulted in an increase in Pamp (P<0.001) and also a much smaller increase in Camp (P=0.03).
Conclusions: Monitoring the relationship between Camp and Pamp may help differentiate between compliance changes and increased Raw due to endotracheal tube secretions during HFOV. Pamp that changes inversely to Camp reflects Raw changes which may determine the appropriateness of endotracheal suctioning. Camp that remains unchanged or changes directly in relationship to Pamp indicates a change in compliance.
(See Original for Figure)