The Science Journal of the American Association for Respiratory Care

2003 OPEN FORUM Abstracts

Using Compliance to determine appropriateness of the low tidal volume ventilation STRATEGY

John H. Boynton Jr. RRT, Kenneth Hawkins RRT, Dean Holland, RRT, Parkland Health and Hospital System Dallas, Texas

BACKGROUND: In the most complete study of ARDS/ALI to date, the ARDS Network provided convincing evidence that patients who were ventilated at plateau pressures of 30 cm/H2O or less had improved outcomes. However recently we noted that a sub-group of these patients did not tolerate the low tidal volume strategy of management. We have been able to identify this subgroup by isolating those patients within the ARDS Net population who present with static compliance (Cst ) of >50 cm/H2O. We designed a ventilatory management method specifically to address the needs of this "high compliance" sub-group. For the purposes of this protocol initial PEEP levels are set using a PEEP inflection curve. Initial tidal volume settings are adjusted within the 8-12ml/kg ideal body weight range to optimize O2 saturation. 

METHOD: We evaluated the efficacy of our protocol in five patients in our SICU who presented with Cst of 50 cm/H2O or higher and who otherwise met criteria for low tidal volume ventilation as outlined in ARDS Net. These patients served as their own controls. All patients were initially managed using ARDS Net guidelines. Each patient's ventilatory settings were modified to our protocol based management in response to decreased compliance, falling O2 saturation, and/or the onset of hemodynamic instability.

RESULTS: The table below illustrates the impact on measured parameters in patients with static compliance (Cst ) of >50 cm/H2O following initiation of protocol.

 O2 SATURATION  Increased
MAP  Decreased or same
CST   Increased or same

Our preliminary data suggests that patients who have Cst > 50cm/H2O and who require FIO2 > 60% and <10 cmH2O PEEP to maintain a P/F of 200 should be managed using tidal volumes adjusted within the 8-12ml/kg ideal body weight range to optimize Osaturation rather than by ARDS net guidelines. Given the recent work on low tidal volume ventilation we think it is prudent to note that a subset of patients that may appear to be candidates for a low tidal volume strategy, yet upon further inspection are not. ARDS Net depends on chest x-rays and P/F ratios to identify the ARDS population yet each parameter lacks sensitivity. We believe that in spite of the well documented limitations associated with compliance measurements, they are useful in helping clinicians identify those patients who will not benefit from the low volume strategy. In addition, ARDS Net ties PEEP levels to FIO2 rather than incorporating mechanics into the equation. Our experience suggests that PEEP initiated based on PEEP inflection curves resulted in application of less PEEP in our study population without deleterious effects. We recognize that much work remains to refine the management of our sickest patients. We suggest that areas of study should include efforts to establish the value of compliance in ventilator management as an independent entity in or when indexed to a volume or weight (specific compliance). Questions persist regarding application of the PEEP inflection curve. Beyond the questions that remain, we present this abstract to convey that application of the ARDS net study should be limited to those patients with low compliance.



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