2005 OPEN FORUM Abstracts
THE MYTH OF "FEELING" COMPLIANCE DURING MANUAL VENTILATION:
John Salyer RRT, Don Foubare RRT. Respiratory Care Department. Children's Hospital and Regional Medical Center, Seattle WA.
Introduction: Self-inflating and flow-inflating resuscitation bags (SIB and FIB) have various relative merits. One suggested advantage of FIB is that they are made of softer material and thus allow the clinician to "feel" changes in lung compliance better than SIB. We sought to test this assumption. We hypothesized that ability to detect changes in compliance was unaffected by the type of manual resuscitation bag.
Methods: A pediatric test lung (Ingmar Adult-Pediatric) was modified to reflect compliance of 2 ml/cmH2O. The lung was an articulated, spring loaded bellows design, and compliance could be decreased by placing steel weights on top of the bellows, making it more difficult to inflate. The lung was encased in a cardboard box so that the test subjects could not see whether weight was added to the bellows or not. Test lung pressure was displayed for the test subjects on a pressure manometer mounted in the side of the box. A visual analog of movement of the bellows was created by attaching an 8 inch long piece of wood in such a fashion that one end of the piece of wood passed through a slit and could be seen outside the cardboard box and rose and fell with the movement of the bellows, thus mimicking chest wall motion. Test subjects were 13 neonatal-pediatric respiratory therapists. Years experience, mean = 7.3, standard deviation = 8.2, median = 3.6, range = 1.1 to 26.8 years. Each subject was asked to manually ventilate the test lung to PIP = 25 cmH2O, PEEP 5 cm H2O, f = 30/min, watching the manometer and chest rise analog. The investigator(s) then added or removed weights to the lung to simulate increases and decreases in compliance. Seven different changes were simulated; 1) â20%, 2) á20%, 3) â40%, 4) á40%, and three false changes, e.g. noise was made behind the cardboard to simulate adding or removing weights, but no actual change in compliance was made. The sequence of the changes is shown in the table at the left. Subjects were then asked if they could detect any changes in compliance. This process was repeated for 3 different resuscitators, Mercury disposable SIB (M), Vent Labs disposable SIB (V), Rusch non-disposable FIB (R).
Results: Overall, subjects were able to correctly identify compliance changes 65% of the time. Table one shows the correct percentage sorted by bag type. Differences between bag types were not statistically significant (Chi square P = 0.13).
Results: % correct compliance changes noted according to resuscitator type
Discussion: We have shown that a group of experienced RT's cannot distinguish changes in compliance better with FIB versus SIB. There are other compelling reasons to discourage the use of FIB, which have been shown to produce more variable ventilation, making careful control of tidal volume and PEEP more difficult (Respir Care 1999;44:1252 & 1999;44:1253). As the role of over-distention in lung injury has become clearer, the need to have more consistent VT during manual ventilation is becoming more recognized. Some clinicians have opposed replacing FIB with SIB, claiming that they can "feel" compliance changes better with a FIB. We have shown that this is not true. There are limitations to SIB, including the potential for staff to believe they are giving 100% O2 when they may not be. We believe these concerns are outweighed by well known ventilation variability produced with FIB. With proper training and attention to detail the SIB are safe, effective and preferred.