The support of respiration (breathing) with devices is known as mechanical ventilation . Mechanical ventilation, provided by ventilators, is used routinely when persons have general anesthesia (unconsciousness) for operations, for critically ill individuals who are in intensive care units (ICUs), and on an outpatient basis for some persons who cannot breathe on their own. The amount of oxygen (up to a maximum of 100% oxygen) can be adjusted to the patient's needs. The volume of respiration per breath (tidal volume ) and number of respirations per minute can also be regulated. Chest x-rays, arterial blood gases (blood samples that measure the content of oxygen and carbon dioxide), and continual observation (including listening to the lungs and feeling the pulses) of the patient help to guide doctors and nurses in caring for individuals who need mechanical ventilation. To provide mechanical ventilation, an endotracheal tube must be inserted into a patient's trachea from the mouth or the nose. The procedure, known as intubation , is most often done after giving sedative medications, or, in the case of general anesthesia, after medications are given to produce unconsciousness to ensure the patient's comfort. In emergency situations (such as cardiac arrest or during cardiopulmonary resuscitation [CPR]), intubation may be necessary as part of life support measures. The March 3, 2010, issue of JAMA includes an article about mechanical ventilation.