The Science Journal of the American Association for Respiratory Care

2008 OPEN FORUM Abstracts

MEASUREMENT OF RESPIRATORY MECHANICS BY ICU VENTILATORS

Daniel W. Chipman1, Andrew D. Marchese1, Robert M. Kacmarek1



Background: Current generation of ICU ventilators display respiratory mechanics. We questioned if these displayed values were accurate.

Methods: Using the Ingmar ASL 5000 Lung Simulator in passive mode we set 8 different conditions: resistance (R) 100 cm H2O/l/sec-compliance (C) 3 ml/cm H2O, R 100 cm H2O/l/sec-C 6 ml/cm H2O, R 50 cm H2O/l/sec-C 3 ml/cm H2O and R 50 cm H2O/l/sec-C 6 ml/cm H2O to represent pediatric respiratory mechanics and R 10 cm H2O/l/sec-C 30 ml/cm H2O, R 10 cm H2O/l/sec-C 60 ml/cm H2O, R 5 cm H2O/l/sec-C30 ml/cm H2O and R 5 cm H2O/l/sec-C 60 ml/cm H2O to represent adult respiratory mechanics. The lung model was ventilated with a Maquet Servoi and a Puritan Bennett 840 ventilator in the volume assist control mode. Pediatric, tidal volume (VT) 50 ml-flow 5 l/min, VT 50 ml-flow 6 l/min, VT 125 ml-flow 10 l/min and VT 125 ml-flow 15 l/min were set. Adult, VT 500 ml-flow 30 l/min, VT 500 ml-flow 60 l/min, VT 750 ml-flow 30 l/min and VT 750 ml-flow 60 l/min were set. All scenarios were delivered with 5, 10, and 15 cm H2O PEEP, all flows square wave and rate was set at10/minute. Values for R and C displayed by the ventilator were recorded, as were the values for peak inspiratory pressure (PIP), plateau pressure (Pplat) and exhaled tidal volume (VTexp). The inspiratory R and C were then calculated as follows: R = (PIP-Pplat)/ flow, C = VTexp / (Pplat-PEEP). Pplat was derived by performing an inspiratory hold and an end expiratory hold maneuver as recommended by the manufacturer and recording the value displayed by the ventilator. Exhaled tidal volume was that value displayed at end-exhalation for the Pplat breath. Important differences were where p < 0.05 and mean difference >10%.

Results: Mean R and C displayed on the ventilator (Rv and Cv) and mean calculated R and C (Rc and Cc) were evaluated. In the pediatric mode, all displayed and calculated values differed from set values. In the adult mode 21 out of the 32 displayed and calculated values differed from set values. In pediatric mode there were more instances of displayed values differing from calculated values than in the adult mode. In the pediatric mode there were fewer differences between the PB840 and Servoi than in the adult mode. In both modes, changes in flow, PEEP, and VT, did not affect Rv, Rc, Cv, and Cc.

Conclusion: Values for R and C on the Maquet Servoi and Puritan Bennett 840 ventilators and set values for R and C on the Ingmar ASL 5000 Lung Simulator must be questioned!