The Science Journal of the American Association for Respiratory Care

2005 OPEN FORUM Abstracts

OTIS LAW OF LEAST WORK SELECTS LOW TIDAL VENTILATION IN A NON-COMPLIANT TEST LUNG

Francoise Boubert, BA, David Carney, MD, Joseph DiRocco, MD, Katy Hojnowski, Ryan LaFollette, Nils-Tomas McBride, Jillian Norton, Gary Nieman, BA. Department of Surgery, SUNY Upstate Medical University, Syracuse NY

Background: It is currently accepted that low tidal volume ventilation is protective in acute lung injury (ALI) and acute respiratory distress syndrome (ARDS). It may also be important to limit mechanical work of breathing as part of a lung protective strategy. To minimize the work of breathing, the Otis formula (OLW) proposes optimal settings for respiratory rate (RR), tidal volume (Vt) and inspiratory time (Ti) based on dynamic changes in lung compliance and resistance. In this study, we varied compliance and applied the OLW formula to evaluate its predicted ventilation strategy.

Methods: A test lung was ventilated with a Galileo GoldT with the following static settings: IBW: 70 kg, PEEP 5 cmH20, Ti 0.8 sec, resistance 5 cmH2O·s/L, Vt 9 cc/kg, minute ventilation 100 cc/kg/min. We varied compliance and recorded the OLW- proposed tidal volumes, respiratory rates, and inspiratory times. OLW-proposed settings were then applied and the resultant airway pressures recorded.

Results: The mean tidal volume for all compliances was 6.0 ± 0.4 cc/kg (Table). There was minimal decrease in OLW-proposed tidal volumes with decreasing compliance. Plateau pressures were < 32 cmH20.

Conclusions: Ventilation determined by the least work of breathing consistently selected a low tidal volume, irrespective of compliance. A method of ventilation that incorporates least amount of work of breathing may further reduce ventilator induced lung injury.

Table:

Compliance (mL/cmH2O) OLW-Proposed RR (min-1) OLW-Proposed Tidal Vol (cc/kg) OLW-Proposed Insp. Time (s) Peak Pressure (cmH2O) Plateau Pressure (cmH2O) Auto-PEEP (cmH2O)
60 16 6.4 1.88 14 13 0
30 17 5.9 1.73 20 19 0
15 18 5.7 1.70 32 31 0
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