NEW YORK ( MainStreet) — When 50-year-old Denise Karnes discovered that her brother Chad had charged $10,000 on their 82-year-old mother's credit cards, she called the police and filed a complaint with the state attorney.

"He hasn't paid off the debt," said Karnes, a former casino worker in Las Vegas. "He was always irresponsible, but this is too much." Chad Karnes, 53, subsequently moved out of their mother's house and left his younger sister holding the bag.

"I had to abandon my career and move back to Alabama to take care of Mom," Karnes said. "My brother has disappeared."

Accidental caregiving is a harsh reality for nearly 40% of Americans who find themselves caring for a sick or elderly relative or friend without warning, according to Michael Bloom, author of The Accidental Caregiver's Survival Guide (Bloom Coaching & Performance, 2013).

"When duty calls, the caregiver selflessly jumps in to support a loved one in need without hesitation and puts other parts of their life on hold or on the back burner," Bloom said.

Caring.com's Caregiver Survey found that more than a quarter of those providing care for a loved one say their family relationships have been negatively impacted since becoming a caregiver.

"Cooperative sibling dialogue is sadly rare. Siblings are divided, divisive, argumentative or bitter and often hold the parent hostage with their ridiculous disagreements that have everything to do with childhood and nothing to do with the issue at hand," said Elaine Pereira, certified dementia practitioner and caregiver and author of I Will Never Forget (iUniverse 2012).

Once thrust into the role, caregivers find themselves committing more and more time, money and energy. Sibling rivalry doesn't help.

"Adult siblings often bring longstanding and heart felt bias to the discussions surrounding their aging parents," said Sheri Samotin, author of the forthcoming Facing the Finish: A Road Map for Aging Parents and Adult Children (Itasca, 2014). "Unless these realities are acknowledged openly, they can quickly interfere with effective communication and decision-making that can benefit the parent,"

Although one sibling tends to do the majority of the care giving work, Karnes could have availed herself of emerging resources to cope with her eldest brother's flight.

"Having an objective third party run a family meeting is one way to handle it," said Samotin, who is a certified guardian and professional daily money manager.

"If the sibling still refuses, then I work with my client and their attorney to create the legal structure to allow for decision making without the difficult sibling and then coach them to learn to accept and work around the barrier."

A legal structure might include guardianship or durable power of attorney but even engaging a geriatric care manager or daily money manager can be helpful.