Nurses at Saint Vincent Hospital in Worcester allege that cost-saving measures are causing pervasive lapses in care, including two patients dying after failing to receive potentially life-saving dialysis. The new assertions come nearly three years after nurses there settled the longest nursing strike in state history with the hospital's for-profit owner, Tenet Healthcare, a battle waged in part over staffing levels. Now, they say, the situation has grown even more dangerous, with stretched-thin nurses often struggling to do their jobs right. The Massachusetts Nurses Association, the union that represents about 600 nurses at the hospital, alleged more than 70 concerning incidents between April and November, from preventable bedsores to unsafe rationing of limited supplies, in an 18-page complaint filed in December with federal and state officials and shared exclusively with the Globe. Perhaps the most incendiary allegation is that two female patients in the intensive care unit on Sept. 29 died because there weren't enough nurses to provide them with continuous dialysis, the preferred form of care for critically ill patients with acute kidney failure. Unlike traditional dialysis, which takes three or four hours, this treatment lasts 24 hours and requires constant bedside supervision. "That was probably the worst night of my life," said one nurse, who has many years of experience and spoke to the Globe on condition of anonymity. "And I've had some pretty bad nights." Because six nurses were overseeing 12 patients that night, the union alleges, one of the two patients received traditional dialysis, and it had to be cut short by 30 minutes. The other patient didn't receive dialysis at all. Both died in the intensive care unit. While both patients were very sick to begin with and might have died anyway, the nurses said, understaffing prevented the women from receiving the care doctors had ordered.