Among those who have been hardest hit by the stifling heat in their out-of-power residences are the elderly.

Hospitals across the region said their emergency rooms were treating elderly patients who live at home alone, without relatives in the area, and who use oxygen machines that rely on electricity.

At Suburban Hospital in Bethesda, the hospital set a record immediately after the storm for the most patients seen in a 48-hour period in its emergency department, spokeswoman Susan Laine said Thursday. Suburban treated about 150 patients each day between Saturday and Monday. A significant number of patients had symptoms of heat exhaustion.

Many were elderly. Some were from area nursing homes that had lost power. Others went to the hospital because the outages closed their primary care doctors’ offices.

By Tuesday and Wednesday, the numbers had dropped a bit, but the emergency department treated about 130 cases Tuesday and about 100 Wednesday, Laine said.

“They’ve just been slammed,” she said. On Thursday afternoon, about 20 people were in the emergency department waiting room, she added.

Since the weekend, about 50 percent of the cases at Suburban have been heat-related — mostly dehydration, shortness of breath and headaches, she said. But hospitals around the region also are seeing injuries from trips and falls, possibly from people cleaning up storm debris in their yards.

Six days after the storm, elderly patients who do not have power for their oxygen or other life-saving equipment were still showing up at Suburban’s emergency room, Laine said. The majority are from private residences, but hospital officials said there may still be nursing homes that do not have power.

A 78-year-old woman who neighbors said was suffering from dehydration was taken by ambulance to Suburban Hospital from the Old Farm neighborhood in Rockville. She was treated and released, a hospital spokeswoman said. Many homes in that neighborhood and nearby Tilden Woods, where trees have downed power lines and transformers, have been without electricity since the storm.

Suburban’s pediatrics emergency department also has had an increase in patients because parents have been unable to go to pediatricians’ offices to get asthma treatments for their children, she said.

Holy Cross Hospital in Silver Spring has had between 10 and 20 heat-related cases, a spokeswoman said.

At Inova Fairfax Hospital, the largest number of patients have been the elderly using oxygen, spokeswoman Joanna Fazio said.

The hospital set up a special process for such patients so they could be admitted directly to an observation unit where they could be comfortable, allowing the emergency department to be freed up for additional cases, she said. Most of the elderly did not arrive via ambulance but went to the hospital as a backup because of outages, Fazio said.

Inova Fairfax also has seen an uptick in trauma from car accidents and injuries incurred while cleaning up fallen trees.

At MedStar Georgetown University Hospital, the emergency department is continuing to see about a 20 percent bump in daily visits. Mostly, those coming in are dizzy, have fainted or feel like they are going to faint. Patients include residents with heat-related illnesses who had lost power, as well as some tourists, spokeswoman Marianne Worley said.

MedStar Washington Hospital Center, in northwest Washington, had a 15 to 30 percent increase in ER visits on Monday and Tuesday, but the number has fallen since. Many patients were without power, and the heat aggravated chronic conditions, spokesman Matt Brock said.

The hospital had to set aside public space for some patients who were ready to be discharged but couldn’t return home because of a lack of power. The hospital helped find them a cooling center or relatives who could care for them.

By Thursday, MedStar Washington reported that visits were back to normal — about 40 patients by mid-day.

At Howard University Hospital, one patient had been hospitalized with heat stroke, and the hospital also had treated a number of cases of heat exhaustion and dehydration. The numbers mirror those of last summer, when there was another stretch of high temperatures, spokesman Ron Harris said.