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October 19, 2009
2:00 PM - 4:00 PM
Room Area M
Battery Duration of a Simplified Automated Ventilator in High and Low Pulmonary Compliance
  **   Michael K. Tiger, B.S., Jameson Voss, B.S., Dale F. Szpisjak, M.D., M.P.H., Richard R. Kyle, M.S.
Anesthesiology, Uniformed Services University of the Health Sciences, Bethesda, Maryland
Introduction: The Simplified Automated Ventilator (SAVe)® (AutoMedx Inc., Germantown, MD) is a compact ventilation system, designed for austere environments, that delivers ambient air at a fixed tidal volume (V T ) of 600 mL and a fixed respiratory rate (RR) of 10 bpm. The SAVe can be powered from an AC outlet or, per the manufacturer, for up to 5.5 hours by a self-contained battery. Knowledge of ventilator performance as the battery discharges affects patient safety, especially in the pre-hospital transport phase of respiratory care. The goal of this study was to determine battery duration and ventilator performance in mechanical lung models with high (HC) and low (LC) pulmonary compliance.

Methods: The ventilator was connected to the VentAid TTL® calibrated test lung (Michigan Instruments, Grand Rapids, MI) via a 1 m long, 15 mm diameter tubing that included a flow control valve. The model 3700 linear pneumotach (Hans Rudolph, Kansas City, MO) was connected between this tubing and the TTL. Respiratory data were recorded with the RSS 100HR Pneumotach after calibration with a 3-L calibration syringe. The battery was charged overnight before data collection. Two lung compliances were tested: HC = 100 mL/cm H 2 O and LC = 20 mL/cm H 2 O. Control limits were determined by collecting data for 5 hours on AC power for each lung compliance and the mean V E ± 1 SD arbitrarily defined the control limits.(1) There were 4 runs for each compliance setting. Each run lasted 6 hours. RR and mean V T were recorded every minute, and V E was calculated from this data. Battery duration was defined as the time when the first of 5 consecutive V E data points were below the lower control limit. Between-group comparisons were analyzed with the independent samples t -test. P < 0.05 accepted as significant.

Results: Battery duration was less in the LC group (figure 1) compared with the HC group (figure 2) [296.8 (± 1.5) v. 309.0 (± 3.4) min, 95%CI =- 16.8 to -7.7 min, P = 0.006].[figure1][figure2]On battery power, the HC V T and V E were larger than the LC V T and V E [640 (± 27) v. 537 (± 17) mL and 5976 (± 464) v. 5656 (± 562) mL/min respectively for time < 270 minutes, P < 0.0001], whereas the HC RR was smaller than the LC RR [9.3 (± 0.7) v. 10.5 (±1.1), P < 0.0001].

Conclusion: Battery duration in the LC lung model was approximately 297 minutes and was 12 minutes less than in the HC lung model. Limiting the clinical use of this transport ventilator (starting with a fully charged battery) to 4.5 hours provides the patient a safety factor of > 25 minutes in both HC and LC lungs.

Reference: 1. Albright SA, Winston W, Zappe CJ. Statistical Process Control. In: Data analysis and decision making with Microsoft excel. Pacific Grove: Brooks/Cole 1999:499-550.

From Proceedings of the 2009 Annual Meeting of the American Society Anesthesiologists.
Figure 1

Figure 2