1995 OPEN FORUM Abstracts
PREDICTIVE EQUATIONS FOR DETERMINATION PEAK AIRWAY PRESSURE.
Daniel J. Reily BS. RRT, William Clark AS. RRT. University of Pennsylvania Medical Center, 3400 Spruce Street, Philadelphia, PA 19104-4283.
Introduction: When patients are mechanically ventilated many variables can effect peak airway pressure (Paw) such as lung compliance, flow rate (FR), flow pattern (FP) and endotracheal tube (ETT) size. A clinician would find it helpful to be able to predict PAW before a change in FR, FP, EET size is made. This could prevent undesired high PAW or discern what changes are necessary to reduce PAW. The study was undertaken to develop equations that predict Paw with various FP, FR, and ETT size.
Methods: A Purtian-Bennett 7200ae ventilator was used without humidifier. A silicone ventilator circuit was attached to a Marquest swivel adaptor (SA). Each ETT was attached to the SA. The volume breaths were discharged through the ETT to the atmosphere. The resulting Paws for each ETT and selected FP (square and ramp) were recorded at FRs from 20 L/m to 120 L/m in increments of 5 L/m. Five Paw measurements were recorded on each size ETT with each FP and FR, then averaged. To insure tidal volume (VT) was taken into account the same procedure was used for VTs of 0.6L, 0.7L, 0.8L, 0.9L and 1.0L. In all 25 data points were collected and averaged for each ETT at each FR on each FP. Results/Equations: Using linear regression six equations were developed to predict Paw when ETT size, FR and FP are known.
Size 6 EET Square FP Size 6 EET Ramp FP
Paw=45.14 + 1.002 (FR-70) Paw=21.3 + 0.414 (FR-70)
Size 7 EET Square FP Size 7 EET Ramp FP
Paw=24.82 + 0.582 (FR-70) Paw=13.3 + 0.266 (FR-70)
Size 8 EET Square FP Size 8 EET Ramp FP
Paw=14.71 + 0.346 (FR-70) Paw=8.87 + 0.178 (FR-70)
Conclusions: The equations enable the clinician to discriminate between increases in Paw due to patient induced changes verses changes in selection of PF, FP or ETT size. A pilot study is underway to validate the accuracy and clinical benefit of the equations.