The Science Journal of the American Association for Respiratory Care

2009 OPEN FORUM Abstracts

MID FREQUENCY VENTILATION: OPTIMUM SETTINGS FOR NEONATES

Robert L. Chatburn1, Eduardo Mireles-Cabodevila2; 1Respiratory Institute, Cleveland Clinic, Cleveland, OH; 2Pulmonary and Critical Care Medicine, University of Arkansas for Medical Sciences, Little Rock, AR

We previously described Mid Frequency Ventilation (MFV) as a means for optimizing alveolar ventilation while minimizing the inspiratory pressure change during pressure controlled ventilation of adults with acute respiratory failure (Respir Care 2008;53:1669 –1677). This study expands the earlier study to include ventilation of neonates with respiratory distress syndrome (RDS). The purpose of the study was to compare the performance of actual ventilators with the mathematical model of MFV. Our specific hypothesis was that modern ventilators are capable of delivering the relatively higher frequencies suggested by MFV than those used conventionally. METHODS:We first developed an algorithm that seeks the optimum frequency using a required alveolar minute ventilation (AMV) prediction. The prediction was based a patient weight of 1.0 kg (J Clin Mon Comput 2009;23:93). The algorithm increases frequency and decreases tidal volume iteratively until AMV can no longer be sustained. The MFV mathematical model was set to resistance = 125 cm H2O/L/s and compliance = 0. 5 mL/H2O, dead space fraction = 0.45. The model performance was then compared to actual ventilators (Maquet Servo i and Puritan Bennett 840) using the same algorithm. The ventilators were connected to a lung simulator (ASL 5000, IngMar Medical Inc.) set to the same parameters as the math model, with no simulated patient effort. RESULTS: The ability of the model and the ventilators to maintain a target AMV of 0.16 L/min is shown in the Figure. The math model predicted an optimum frequency of 95 breaths/min and tidal volume of 4.4 mL. Both ventilators were able to sustain the target AMV at a setting of 100 breaths/min, due to a slight overshoot in the airway pressure waveform at the start of inspiration. Tidal volumes at this frequency were 4.6 mL (PB 840) and 4.7 mL (Servo i). CONCLUSIONS: This study shows that MFV offers theoretical advantages, based on patients’ lung mechanics, compared to current practice. The optimum frequency in this study was higher and optimum tidal volume lower than the upper limit (6 mL/kg) of current recommendations for neonates with RDS (60/min and 6 mL/kg respectively; Semin Perinatol 30:192-199:192). Optimum tidal volume during MFV was much lower than actual values reported (8.4 mL) in a recent study (Pediatrics International 2007; 49:631–636). Furthermore, current generation ICU ventilators are capable of delivering MFV at the theoretical optimum values. Sponsored Research - None

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