The Science Journal of the American Association for Respiratory Care

2009 OPEN FORUM Abstracts

IMPROVED SELECTION OF INITIAL TIDAL VOLUME FOR MECHANICAL VENTILATION BASED ON THE RADFORD NOMOGRAM

Shannon E. Cook, Robert L. Chatburn; Respiratory Institute, Cleveland Clinic, Cleveland, OH

BACKGROUND: General acceptance of ARDSnet guidelines have resulted in a standard of care for initial tidal volume for mechanical ventilation based on 6-8 mL/kg ideal body weight, originally an arbitrary “rule of thumb”. We have developed regression equations based on the Radford nomogram (J Appl Physiol. 1955;7(4):451) that incorporate both weight (W) and spontaneous breathing frequency (F) for a potentially more appropriate tidal volume prediction. The purpose of this study was to compare the predicted tidal volumes (Radford) to the currently accepted heuristic (ARDSnet). METHODS: Equations show V in mL, F in breaths/min and W in lb: Adults (80-250 lb, F = 8 - 18): -Male: V = 466.969 + (2.4 * W) - (26.342 * F), R2= 0.97. -Female: V = 456.408 + (1.794 * W) - (22.716 * F), R2= 0.97. Initial Vs for mechanical ventilation were generated using these equations and compared to conventional (6 mL/kg) for the set of W used to create the equations for weights from 80 to 250 lbs in 5 lb increments for frequencies from 8-18 breaths/min. Differences in volumes were calculated as Radford prediction minus ARDSnet prediction. Mean differences were evaluated with 1 sample t-test or Mann-Whitney Rank Sum Test. RESULTS: For both sexes and all weights, tidal volumes predicted using the Radford equation were 2% to 24% lower than the ARDSnet convention when spontaneous breathing frequency was at least 17/minute (P < 0.001). Tidal volume reduction was proportional to body weight and was higher for females (mean 7% vs 17%; P < 0.001). CONCLUSION: Current ARDSnet guidelines for selection of initial tidal volume during mechanical ventilation are based first on a linear regression equation for prediction of ideal body weight but then a simple rule of thumb for calculating the subsequent tidal volume. Substitution of the Radford equations, incorporating information about the patient’s pre-intubation breathing frequency, may offer additional advantage by reducing initial tidal volume to enhance lung protective ventilation strategies. Prediction equations may be programmed into bedside computers or mechanical ventilators. Sponsored Research - None

You are here: RCJournal.com » Past OPEN FORUM Abstracts » 2009 Abstracts » IMPROVED SELECTION OF INITIAL TIDAL VOLUME FOR MECHANICAL VENTILATION BASED ON THE RADFORD NOMOGRAM