The Science Journal of the American Association for Respiratory Care

2004 OPEN FORUM Abstracts

The use of a slow flow inflation manuever to reduce differences in left and right lung critical opening pressures in post-operative TAAA patients

Raymond Wolff Jr. RRT, Brian Timon BS, RRT, Ken Hargett BS RRT The Methodist Hospital, Respiratory Care Department, Houston, TX.

Background: The Thoracotomy Abdominal Aortic Aneurysm (TAAA) Repair presents a unique population of patients. Post operative respiratory complications are reported as high as 35%. These patients have substantial acute unilateral lung injury as a result of the extreme manipulation to the left lung during the TAAA repair surgery. Previous data collected at our institution revealed a large variation in the right and left lung critical opening pressure. This results in the complicated task of protecting one lung from hyperinflation and preventing the opposite lung from experiencing severe refractory atelectasis during post-op mechanical ventilation. Critical opening pressure is used at our institution to set PEEP and differences between lungs makes selecting the correct PEEP difficult. Minimizing the difference in left and right lung critical opening pressures has become a goal in this patient population. We investigated a process of implementing a series of recruitment maneuvers immediately post-op to improve the left lung compliance.

Method:
Data was collected by performing slow flow inflection maneuvers on 10 post-operative TAAA patients to separately determine the critical opening pressure of each lung. The Nellcor Puritan Bennett 840 Ventilator was used to perform the inflection maneuver using a strict protocol and therapists were trained to identify the critical opening pressure on the pressure-volume curve produced by the maneuver. All patients had a double-lumen endotracheal tube inserted pre-operatively which allowed for isolation of left and right lungs. The maneuvers were done on heavily sedated patients in the absence of spontaneous breathing. After identifying the critical opening pressure of the left lung, a recruitment maneuver series was performed to only the left lung. On the final maneuver of the series a critical opening pressure was recorded for the left lung.

Results:
The mean results of pre and post recruitment maneuver critical opening pressure from the 10 patients are listed in the table below.

  Both Pre Right Pre Left Pre Diff Post Right Post Left Post Diff
Average 6.15 6.10 11.75 5.65 5.10 7.95 2.85

There was initially a significant difference between right and left lung critical opening pressure and when both lungs were measured together the critical opening pressure reflected the right lung only. After performing one recruitment maneuver series the left lung, critical opening pressure average decreased to 7.9 cmH2O. The left and right lung critical opening pressure difference was reduced to an average of 2.8 cmH20.

Conclusions:
Using the inflection maneuver allows you to identify the potentially dramatic difference in the right to left lung critical opening pressure within the TAAA population. Our data indicates that differences in critical opening pressure can be reduced through selective slow flow recruitment maneuvers immediately post-op in this patient population. Additional trials are necessary to determine if these maneuvers reduce post-op respiratory complications.

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