Ashley Lasbury, 64, of Portland, listens to Evelyn Olson, a clinical pharmacist at Trellis Health, a membership-based model for primary care launched by MaineHealth. (Derek Davis/Staff Photographer)MaineHealth is expanding a membership-based system of primary care that has the potential to change the way many people access their doctors. Dr. Andy Mueller, MaineHealth’s CEO, told the Portland Press Herald in a recent interview that this new primary care network won’t replace the system’s traditional primary care options but it will offer more direct care. Mueller said this new system of care should reduce the burden on other parts of the health care system, such as emergency room visits and specialists. Mara McDermott, CEO of Accountable for Health, a national advocacy group for health care payment reform said, “when you’re transforming a trillion dollar health care system, it takes patience.