The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

THE USE OF A SLOW FLOW LOWER INFLECTION POINT MANEUVER TO SET PEEP LEVELS IN CARDIOVASCULAR POST-OPERATIVE PATIENTS


Brian Timon BS, RRT, Raymond Wolff RRT, Jennifer Ma BS, RRT, Ken Hargett RRT, The Methodist Hospital, Respiratory Care Services, Houston, TX.


Background:
Setting appropriate PEEP levels is important in preventing potential alveolar damage caused by recruitment / derecruitment. It has been proposed that the recruitment and subsequent collapse of alveoli on every mechanical breath induces lung injury. Recruiting alveoli and keeping them "open" for the duration of the breath should be a goal in PEEP therapy. For this reason, arbitrarily picking a PEEP level during mechanical ventilation may not be the best approach.

Method: Data was collected from performance of a standardized slow flow inflection maneuvers on 54 post-operative CVICU patients to find out the average critical opening pressure. The maneuvers were done on well-sedated patients in the absence of spontaneous breathing. The PEEP was turned to zero and the FIO2 was turned to 100% for two minutes prior to the maneuver. We used the Nellcor Puritan Bennett 840 Ventilator to perform the slow flow inflection maneuver using a strict protocol. Our therapists were trained to determine the critical opening pressure on the pressure-volume curve for that breath.

RESULTS:
The lower inflection points widely varied with a low of 3cmH2O and a high of 15 cmH2O. The mean critical opening pressure for these 54 patients was 6.52 cmH2O. Coronary Artery Bypass (CAB) surgery had a mean of 5.75 cmH2O and a high of 9.0 cmH2O. Atrial and Mitral Valve Replacement / Repair (AVR, MVR) surgery had a mean of 8.25 cmH2O and a high of 15 cmH2O. The results for each type of surgery are listed in the table below.

Surgery (n) Low (cmH2O) High (cmH2O) Mean (cmH2O)
CAB (27) 3 9 5.75
TAAA (6) 4 7.5 6.42
AVR and/or MVR (12) 3 15 8.25
Misc. Thoracotomy (9) 3 10 6.56
Total (54) 3 15 6.52


 
Conclusions:
Using a standard PEEP setting in mechanical ventilation (i.e. 5 cmH2O), may not be the best approach since the critical opening pressures vary widely from patient to patient and varies on the type of procedure performed. Using a bedside slow flow lower inflection point maneuver is a safe and reproducible method to determine post-operative PEEP requirements needed to avoid the potential injury caused from the inadequate recruitment or over-distention of alveoli. The use of a bedside inflection point maneuver allowed a consistent process to find the most appropriate PEEP for each individual patient and optimize its effects. Additional research is necessary to determine the long term clinical impact of this process.

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