From the Guidelines

Agonal breathing, even with normal vital signs, is a significant indicator of impending death or cardiac arrest.

Agonal breathing is characterized by slow, irregular gasping respirations that are ineffective for ventilation 1.
The presence of agonal breathing is a common reason for lay rescuers to misdiagnose a patient as not being in cardiac arrest, highlighting its importance as an indicator of cardiac arrest 1.
Lay rescuers should be trained to recognize agonal breathing as a sign of cardiac arrest and initiate CPR promptly 1.
Emergency dispatchers should also be educated to identify agonal gasps and abnormal breathing, as these are critical factors in recognizing cardiac arrest 1.
The identification of agonal breathing or gasps is crucial for the initiation of CPR, and training in this area can increase the rate of dispatcher-guided CPR 1.
Normal vital signs do not rule out the possibility of cardiac arrest or impending death in the presence of agonal breathing, as the breathing pattern itself is a significant indicator of distress 1.

From the Research

Agonal breathing is a type of abnormal breathing that can occur in individuals who are near death or experiencing cardiac arrest 2, 3, 4.
Studies have shown that agonal breathing can be present in up to 40% of out-of-hospital cardiac arrests and is often mistaken for normal breathing or a sign of circulation 2, 4.
The presence of agonal respirations has been associated with increased survival rates, with one study finding that 27% of patients with agonal respirations were discharged alive compared to 9% without them 4.

Changes in vital signs, such as decreases in blood pressure and oxygen saturation, can be indicators of impending death in non-cancer patients 5.
A study found that systolic blood pressure, diastolic blood pressure, and oxygen saturation significantly decreased from day -3 to death in non-cancer patients, whereas no significant changes were noted in any vital sign in days -7 to -4 5.
Another study found that respiration with mandibular movement, also known as agonal breathing, was a consistent finding before death in ill elderly patients, along with loss of oral intake and consciousness impairment 6.

There is limited research on agonal breathing with normal vital signs as an indicator of impending death.
However, studies suggest that agonal breathing can occur in individuals with normal vital signs, and its presence can be a sign of cardiac arrest or impending death 2, 3, 4.
Further research is needed to fully understand the relationship between agonal breathing, vital signs, and impending death 5, 6.