Respiratory depression: another term for hypoventilation, meaning that ventilation of the lungs is inadequate to perform needed gas exchange. Sometimes a respiratory rate of fewer than 12 breaths per minute is used as a definition of respiratory depression. Hypoventilation leads to an increased concentration of carbon dioxide in the blood (hypercapnia) and respiratory acidosis (a decrease in blood pH). Respiratory depression can result from a number of different disease processes. It can also be a side effect of medications, such as opioid pain medications and sedatives.
Kasper, D., et al., eds. "Harrison's Principles of Internal Medicine, 19th Ed." United States: McGraw-Hill Professional, 2015.