According to a pre-print study by 2000 patients of the All India Institute of Medical Sciences (AIIMS)-Jhajjar nearly 40% of Covid-19 patients hospitalised had oxygen saturations below 94% at the time of admission. Of those who were admitted to hypoxia, 21.45 percent had no breathlessness, while 5.2 percent had no signs at all, according to the study.
The researchers said that hypoxia — a condition where the tissues and organs do not get enough oxygen — was one of the most important predictors of death in Covid-19 patients. The outcome was significantly worse in those with silent or happy hypoxia — patients who do not show symptoms like breathlessness and fatigue despite having low oxygen saturation.
The case fatality ratio (CFR) — the proportion of deaths — was as high as 45.4% among those with silent hypoxia and 40.03% among those who had shortness of breath along with hypoxia as per pulse oximeter.
“What the study shows is that hypoxia is not necessarily clinically evident in Covid-19 patients. Those with silent hypoxia continue working normally and by the time they reach hospital, it’s too late,” said Dr Sushma Bhatnagar, corresponding author of the paper and head of the department of onco-anaesthesia and palliative care at AIIMS.
She said, “You know people say that our patient walked into the hospital absolutely fine but they did not return; this is the reason. By the time they reach us, the oxygen saturation is already 70 or 80%.”
The normal oxygen saturation is between 95 and 100%, anything less than 94% is a cause for concern.
The study, which is being published in journal Chest, also shows that silent hypoxia is more common in women. Of those who reported silent hypoxia, 41% were men and 59% women, which is a statistically significant difference.
“We do not yet know why silent hypoxia was higher in women but it could be because women tend to ignore their health issues and hardly report a problem unless it gets too much,” said Dr Bhatnagar.
The study also shows that majority of those with silent hypoxia started experiencing it in the first week after getting infected when the virus multiplies. But hypoxia with symptoms such as shortness of breath was mostly reported during the second week of infection when the body’s overactive immune system starts damaging the organs.
The study also said that 65% of those with silent hypoxia came to the hospital in the first week of the infection, and 45.2% of those who had hypoxia with symptoms reached the hospital in the second week of infection.
“Almost half of the patients with dyspnea (shortness of breath) as a symptom along with hypoxia were brought to the hospital on oxygen. However, only 35% (60) of patients without dyspnea had their hypoxia diagnosed before reaching the hospital,” the study states.
With silent hypoxia significantly increasing the risk of death in Covid-19 patients, the researchers suggest that patients keep monitoring their oxygen saturation even when they are in home isolation.
“Whenever people start experiencing Covid-19-like symptoms, people should start monitoring their oxygen saturation,” said Dr Bhatnagar.