Friday, March 20, 2009

t-Low: APRV initial settings

Initial t-Low settings are 0.2-0.8 seconds in adult & pediatric patients, and 0.2-0.4 seconds in neonates. 
This short time interval is needed to minimize lung de-recruitment, a longer release phase may interfere with oxygenation. 

note- this cannot be accomplished when using Bi-level on the PB 840 ventilator, where t-Low is not directly set. However, one can manipulate the frequency & "TH" settings to set a t-Low. 

Since atelectasis can develop rapidly when peak airway pressure drops below the opening pressure of the injured lung, t-Low should always be titrated based on analyzing the 'Peak Expiratory Flow Rate' (PEFR) and the 'Peak Expiratory Flow Rate Termination' (T-PEFR) point, utilizing the flow waveform pattern. 

*The above image identifies the PEFR & the T-PEFR in the flow waveform pattern (purple). 

Titration of t-Low

t-Low should be titrated to obtain a T-PEFR at 50-75 percent of measured PEFR.

Example: the above image shows a measured PEFR of -1050 milliliters/second (blue arrow) and a T-PEFR of -350 milliliters/second (yellow arrow). 
This equals 33% of the PEFR
In this example the t-Low would have to be set lower (shorter time) to achieve the 50-75% range to allow for optimal paCO2 removal and maintain enough expiratory lung volume to prevent alveolar de-recruitment.

Observation of the flow waveform should be paired with patient ventilator assessments to identify any need for t-Low adjustments. Changes in pulmonary dynamics result in the need to adjust t-Low settings.