WASHINGTON (AP) — For many of the growing millions who depend on home medical equipment, a power outage goes way beyond the inconvenience most of us feel. It could be deadly.

It's an issue that snuck up on emergency officials as better medical treatments over the past decade have helped more critically ill people not only survive but move out of nursing homes.

The Associated Press found emergency planners around the country struggling to find new ways to identify people at risk before the lights go out, to ensure they will have the aid they need to survive small outages or big ones.

How serious is the problem?

When ice downed electric lines in Epping, N.H., last month, police found 60-year-old Richard Lapoint dead, hooked to his powerless oxygen machine. The town's rescue workers hadn't known he was power-dependent.

A generator and stack of batteries couldn't keep up with Gatlan Graham's ventilator and other life-supporting equipment when Hurricane Ike knocked out power to his Houston home for 14 days in September. The family fled in search of electricity, spending more than $1,500 to keep the 17-year-old alive.

When Hurricane Gustav hit Louisiana, dozens of people with home oxygen machines in tow evacuated to government medical shelters, where surprised officials had to scramble to find enough old-fashioned oxygen tanks when back-up generators in Baton Rouge failed.

Utilities in every state operate "medical priority lists" designed to track who depends on power for life. But an AP survey found huge state-to-state variations that suggest only a fraction of patients know they could sign up. Illinois' biggest utilities together report 10,000 patients on critical-care lists, for example. Neighboring Indiana's biggest list carries just 2,000 names.

Even if patients did sign up, in large outages companies don't have the ability to restore power to one home before another down the street. The lists may offer false hope.

"The power companies don't get on the phone and dial 911 for their customers," said Dr. David Prezant, chief medical officer for the New York City Fire Department, who is pushing for medical registries of the power-dependent. "When there's a blackout, citywide, nationwide, we are really unprepared with any structured database, knowledge of who these people are and where they are."

Registries are starting to form. A pilot project in northwest Ohio is giving cards to life-support users to hang in their windows during a flood or tornado, signaling to rescuers if they need help or are OK.

San Diego Gas & Electric says it recently met with each of its 700 known power-dependent customers to discuss emergency plans for outages, and it offers advance warning when wildfires trigger rolling blackouts.

In contrast, this is the advice from Idaho's Public Utilities Commission: "If someone has a power requirement for life and health, the individual is responsible for coming up with their own back-up plans."

To help people prepare, the Food and Drug Administration this spring plans to issue the first checklist for device recipients to receive when leaving the hospital.

Emergency workers feel the clock ticking.

"It's incumbent upon us over the next 41âÑ2 months, before we get into hurricane season again, to have a better plan than we had going into Ike," said Terry Moore, Houston's deputy emergency management coordinator.

Under consideration are mobile "charging stations" that could rotate through Houston neighborhoods for patients to recharge depleted batteries, or perhaps evacuating the power-dependent.

"This is a huge vulnerability," added Dr. Lewis Rubinson of the University of Washington, who advises the government on disaster preparations and separately is preparing guidelines for emergency oxygen supplies. "This is something that patients should demand."

It's a growing population. Roughly 2 million people use home oxygen machines, mostly "concentrators" that make oxygen on the spot as long as electricity flows. Just a few years ago, oxygen-gas tanks that don't require home electricity were the norm.

At least another 10,000 people breathe with home ventilators, and thousands more have implanted heart pumps called VADs, or ventricular assist devices.

Millions more use other at-home equipment: dialysis machines, nebulizers, IV and nutrition pumps, CPAP breathing masks. But power failures bring the most immediate risk for users of ventilators, heart pumps and oxygen.

No one knows how often a power outage means death for such patients. Typically, death certificates note just the underlying disease, said disabilities specialist Lex Frieden of the University of Texas at Houston, who tried to track down the power-dependent during Ike's prolonged outage to see who needed help.

Back-ups sometimes fail even in short outages.

Last summer, 15-year-old Fernando Vargas died when a Boston power outage silenced his ventilator early one morning.

But long outages are the big threat because batteries don't last and oxygen tanks need repeated refills.

Whatever a family's back-up plan, Rubinson and Prezant stress that local emergency officials must know how many power-dependent patients they might have to rescue, and getting utilities and home-care companies to share customer lists is a good start.