It frequently happens along with cardiac arrest, but not always. However, in the context of advanced cardiovascular life support, respiratory arrest is defined as a situation in which a patient ceases breathing but retains a pulse. Importantly, respiratory arrest can occur when breathing is inefficient, such as while suffering from agonal gasping. In this case, oxygen levels in blood drop to zero while carbon dioxide levels rise. This causes muscle tension and spasms, which may make it difficult or impossible for the patient to breathe. The patient's condition requires immediate attention because lack of oxygen will cause brain damage within minutes. Doctors use several techniques to ensure proper breathing during cardiopulmonary resuscitation (CPR). The first step is to check for a pulse. If it is not found, further examination should be conducted to locate the source of the problem. For example, doctors may want to know if the patient has been choking or has a blockage in their airway. If so, they will need to be cleared before CPR can continue. CPR involves using the arms and legs to pump the chest until healthy breaths are restored to the body. It is important not to delay any longer than necessary between checking for a pulse and starting CPR. The more time that passes without a pulse being found, the less likely it is that CPR will be able to restore it. After proper breathing has been established, additional measures can be taken to maintain oxygen levels in the blood and prevent further tissue damage.