Yet humans are rarely attacked by a shark, while millions of sharks are killed by humans. Some populations of shark species, such as the shortspine spurdog, may have dropped by 95 percent. The sharksâ population decline has a ripple effect â throwing entire marine ecosystems out of balance.
Quick Answer. A normal blood oxygen level during sleep is approximately 94 to 98 percent, according to Sleep Apnea Guide. Levels below 90 percent oxygen saturation are dangerous to the human body. The human brain can only survive four minutes without oxygen before cell death occurs.
Oxygen saturation sensing in a healthy child breathing room air will reveal a saturation rate between 96 and 98 percent. This is the normal range for a healthy adult as well. A disruption in oxygen metabolism can cause saturation levels to drop below 95 percent, at which point a physician might order intervention. Saturation levels that fall below 90 percent often require oxygen therapy, in which higher than normal amounts of oxygen are fed directly into the child's nose.