Diagnosis requires clinical evaluation, as detailed below. Initial assessment After determining the scene is safe, approach the patient and attempt to converse with him or her. If the patient responds verbally, you have established that there is at least a partially patent airway and that the patient is breathing (therefore not currently in<unk> . If the patient is unresponsive, look for chest rise, which is an indicator of active breathing. A sternal rub is sometimes used to further assess for responsiveness. Initial assessment also involves checking for a pulse, by placing two fingers against the carotid artery, radial artery, or femoral artery to ensure this is purely<unk>  and not cardiopulmonary<unk> . Checking a pulse after encountering an unresponsive patient is no longer recommended for non-medically trained personnel. Once one has determined that the patient is in<unk> , the steps below can help to further identify the cause of the<unk> . Clearing and opening the upper airway The first step to determining the cause of<unk>  is to clear and open the upper airway with correct head and neck positioning. The practitioner must lengthen and elevate the patient's neck until the external auditory meatus is in the same plane as the sternum. The face should be facing the ceiling. The mandible should be positioned upwards by lifting the lower jaw and pushing the mandible upward. These steps are known as head tilt, chin lift, and jaw thrust, respectively. If a neck or spinal injury is suspected, the provider should avoid performing this maneuver as further nervous system damage may occur. The cervical spine should be stabilized, if possible, by using either manual stabilization of the head and neck by a provider or applying a C-collar. The C-collar can make ventilatory support more challenging and can increase intracranial pressure, therefore is less preferable than manual stabilization. If a foreign body can be detected, the practitioner may remove it with a finger sweep of the oropharynx and suction. It is important that the practitioner does not cause the foreign body to be lodged even deeper into the patient's body. Foreign bodies that are deeper into the patient's body can be removed with Magill forceps or by suction. A Heimlick maneuver can also be used to dislodge the foreign body. The Heimlick maneuver consists of manual thrusts to the upper abdomen until the airway is clear. In conscious adults, the practitioner will stand behind the patient with arms around the patient's midsection. One fist will be in a clenched formation while the other hand grabs the fist. Together, both hands will thrust inward and upward by pulling up with both arms.
Respiratory arrest
Cardiac arrest
Sleep paralysis
Syncope 
Expiratory apnea
Spinal shock
Permissive hypotension
Inert gas asphyxiation