Wednesday, March 25, 2009

Improving Oxygenation: APRV optimization of settings.

Improving Oxygenation: titrating t-Low

To improve oxygenation one of the first goals when utilizing APRV is to maximize end-expiratory lung volume.
To do this assess the T-PEFR; if the T-PEFR is less than 50% decrease the release time until a T-PEFR of 75% is obtained. 

*the above image shows a measured PEFR of 50%, even if the calculated value is 50% or greater the operator can still adjust the t-Low setting to obtain a T-PEFR of up to 75% to maximize lung recruitment. 

Improving Oxygenation: increasing p-High or p-High & t-High

Another way to improve oxygenation during APRV is to increase mean airway pressure. 
One way is to increase p-High to recruit aveoli by achieving threshold opening pressure, p-High should be adjusted at only 2-5 cmH2O increments while monitoring the patients hemodynamic status. 
Furthermore, t-High can be lengthened, this increases gas mixing & recruits alveoli with longer time constants.

note- always assess hemodynamics if increasing p-High or t-High. 
If increasing settings is limited due to decreased cardiac output or hypotension, consider therapeutics which increase cardiac output & blood pressure.