All three are being treated at the National Hospital of Tropical Diseases, with information of the third patient, a Vietnamese, not revealed.

Doctors have had to perform blood filtration on the three patients and put them on a life support machine called Extracorporeal membrane oxygenation (ECMO) to allow their lungs and hearts to improve and function properly, the Health Ministry said Tuesday.

The Vietnamese woman, 64, was suffering from vestibular disorder as an underlying condition. She experienced breathing difficulties that escalated into respiratory failure on March 15.

Doctors had inserted a breathing tube and used a ventilator, among other measures, to help stabilize her. She was later transfered to the ICU.

However, she continued to experience respiratory failure the following day. Her lungs were heavily damaged and her blood had to be filtered continuously.

Blood filtration is a standard treatment for people in critical condition including those who suffer from septic shock, multiple organ failure, and metabolic disorders.

Two days later, doctors decided to use the ECMO on her.

The British patient, 69, had several underlying conditions, including diabetes and hypertension.

Since March 15, he has been put on a ventilator and had his blood filtered. Two other people at the same hospital have also been put on ventilators.

The Vietnamese woman is the aunt of 26-year-old Nguyen Hong Nhung, Hanoi's first Covid-19 patient who had landed March 2 in Hanoi on Vietnam Airlines flight VN54 that flew in from London. She was confirmed infected on March 7, a day after Nhung, while the British man, who was among several patients from that flight, was confirmed infected on March 8.

The National Hospital of Tropical Diseases in Hanoi is currently treating 46 Covid-19 patients out of the 106 active cases in Vietnam. Of the 46, 34 are Vietnamese, while the remaining are foreigners. Starting Tuesday, it has transfered less serious cases to other hospitals in the city to reduce the work load.

The critical cases were discussed at a meeting on Monday attended by Deputy Minister of Health Nguyen Truong Son, Director of Medical Examination Department Luong Ngoc Khue and infectious disease experts.

WHO’s updated Covid-19 diagnostic and treatment guidelines and that of other countries were brought up at the meeting. While some drugs are being clinically tested, there is no specific medication which cures Covid-19 and all current drugs are used to treat the symptoms, experts said at the meeting.

The country has confirmed 123 infection cases. Of these, 17 have been discharged from the hospitals. Of the currently active cases, 14 have tested negative either once or twice.

Many of the active cases are Vietnamese nationals returning from Europe and the U.S. and foreigners visiting from the same regions.

Most patients are in stable condition with no symptoms of fever, severe cough or breathing difficulties. X-ray images of their lungs show that they are normal. However, some are being treated for lung infections.