1995 OPEN FORUM Abstracts
DYNAMIC MEASUREMENTS OF INTRINSIC PEEP DO NOT REPRESENT THE LOWEST INTRINSIC PEEP.
Yuhji Fujino, MD, Masaji Nishimuri, MD, Dean Hess, PhD, RRT, Robert M. Kacmarek, PhD, RRT. Osaka University Hospital, Hyogo College of Medicine, Japan and Massachusetts General Hospital, Boston, MA.
Although intrinsic positive end-expiratory pressure (PEEPi) has been described primarily in patients with COPD, it is also common during mechanical ventilation of patients with acute respiratory failure. PEEPi is usually measured using static conditions by occluding the airway opening at end-exhalation (PEEPi-stat). Dynamic PEEPi (PEEPi-dyn) is the airway pressure required to overcome expiratory flow and has been considered to represent the lowest regional PEEPi. There has been little data to validate this assumption. The purpose of this study was to compare PEEPi-dyn with PEEPi-stat.
Methods: Measurements were performed in 5 adult white rabbits who were anesthetized, tracheotomized, and intubated with uncuffed endotracheal tubes (2.0, 2.5, 3.0, or 3.5 mm ID). The trachea was tied to prevent air leak. The animals were ventilated (Servo 900C) using a low compliance circuit. Airway pressure was measured at the proximal endotracheal tube with a pressure transducer and flow was measured simultaneously at the proximal endotracheal tube with a hot wire anemometer. Pressure and flow signals were amplified, digitized, and recorded (CODAS, Dataq). The animals were paralyzed and ventilated in the supine position. Baseline ventilator settings were a rate of 50/min, I:E ratio of 2:1, and minute ventilation manipulated to create 3 or 5 cm H_2O PEEPi-stat. PEEPi-Stat was measured using the expiratory hold button of the ventilator. PEEPi-dyn was measured from 5 respiratory cycles immediately prior to measurement of PEEPi-stat. The measurements were repeated 3 times for each ventilator setting and each endotracheal tube size.
Results: PEEPi-dyn showed large variations with ventilator settings at the same PEEPi-stat level (Pɘ.05). Differences between PEEPi-dyn and PEEPi-stat increased with increased minute ventilation (Pɘ.05).
endotrachealtarget PEEPi-stat of 3 cm H_2O target PEEPi-stat of 5 cm H_2O
tube size PEEPi-stat PEEPi-dyn PEEPi-stat PEEPi-dyn
2.02.64 ± 0.58 4.06 ± 0.89 5.30 ± 0.18 7.70 ± 0.67
2.53.05 ± 0.16 4.45 ± 0.37 4.86 ± 0.08 7.49 ± 0.70
3.03.19 ± 0.23 5.08 ± 0.53 4.96 ± 0.70 8.54 ± 0.91
3.53.00 ± 0.33 5.07 ± 0.51 5.12 ± 0.37 9.71 ± 0.94
Conclusions: In this animal model with normal lung function, PEEPi-dyn exhibited large variation with ventilator settings and minute ventilation. The fact that PEEPi-dyn was greater than PEEPi-stat strongly suggests that PEEPi-dyn does not reflect the lowest regional PEEPi.