The most likely obstruction in an unconscious person is the tongue. The head tilt, chin lift manoeuvre (Figure 12.58), which prevents the tongue from occluding the oropharynx, is an effective method of opening an airway and relieving obstruction (Wittels [288]). If there is any suspicion of cervical spine injury, establish a clear upper airway by performing a jaw thrust (Figure 12.59) or chin lift with manual in‐line stabilization (Prasarn et al. [223]).

The rescuer should look in the mouth and remove any visible obstruction (leave well‐fitting dentures in place). A wide‐bore suction catheter, such as a Yankauer, should be used to remove blood, saliva or gastric contents from the upper airway. This is best done under direct vision during intubation but should not result in any delay in achieving a definitive airway (RCUK [232]). If tracheal suction is necessary, it should be as brief as possible, preceded and followed by ventilation with 100% oxygen.

Keeping the airway open, the rescuer should look, listen and feel for breathing (more than an occasional gasp or weak attempts at breathing) for up to 10 seconds. If the patient is breathing normally, they should be moved into the recovery position (Figure 12.60). If the patient is not breathing, an immediate call for the cardiac arrest team should be made. Normal breathing should not be confused with agonal respirations, which are infrequent, slow and noisy gaps, often seen within the first few minutes after cardiac arrest (RCUK [232], Riou et al. [234]). If there is any doubt as to whether breathing is normal, prepare to start CPR.

Circulation is assessed simultaneously with assessment of breathing. The rescuer should look for any signs of life, including movement, swallowing or breathing. If the rescuer is trained to do so, a pulse check should also be made by feeling the carotid pulse (Figure 12.61).

The above assessment should take less than 10 seconds to complete. The rapid assessment will indicate whether the patient is critically unwell and in need of immediate help. In the event of poor respiratory effort where no circulation is detected, cardiac compressions are used to maintain blood flow and ultimately oxygen delivery.

Mouth‐to‐mouth ventilation should be considered only if there are no immediate aids available. There have been isolated reports of infections such as tuberculosis and severe acute respiratory syndrome following mouth‐to‐mouth ventilation but none resulting in the transmission of HIV (RCUK [232]). There is no evidence to quantify the degree of risk to the rescuer that arises from performing mouth‐to‐mouth ventilation, but it is widely acknowledged that many people may be reluctant, especially if the victim is not known to the rescuer. If mouth‐to‐mouth ventilation is given, the recommended length of each breath is 1 second.

Pocket mask or mouth‐to‐face‐mask ventilation (Figure 12.63) can be used to avoid direct person‐to‐person contact. Some devices contain a filter that reduces the risk of cross‐infection between patient and rescuer (RCUK [232]). The patient should be in the supine position with the head in the ‘sniffing position’ (head tilt, chin lift). Apply the mask to the patient's face using the thumbs of both hands. Lift the jaw into the mask with the remaining fingers by exerting pressure behind the angles of the jaw (jaw thrust) (Figure 12.64). Blow through the inspiratory valve and watch the chest rise. Stop inflation and allow the chest to fall before blowing in the second breath. The mask directs the patient's exhaled air and any fluid away from the rescuer, and the oxygen port allows attachment of oxygen with enrichment of up to 45%.

An oropharyngeal airway is the recommended airway adjunct to be used in the event of a cardiac arrest (RCUK [232]). It is a curved plastic tube that is flanged and reinforced at the oral end, with a flattened shape to ensure that it fits neatly between the tongue and the hard palate. It is used to overcome backward tongue displacement in an unconscious patient (Wittels [288]). Oropharyngeal airways come in sizes 2, 3 and 4, for small, medium and large adults respectively. The right size is chosen by measuring the oropharyngeal airway against the patient's incisors to the angle of the jaw or mandible (see Procedure guideline 12.16: Insertion of an oropharyngeal airway, Action figure 12.70). The technique for inserting an oropharyngeal airway is outlined in Procedure guideline 12.16.

A bag valve mask (such as the Ambu bag) is the preferred means of delivering rescue breaths. When the device is attached to an oxygen supply, it can provide a patient with up to 85% oxygen. However, it should be emphasized that effective use of a bag valve mask requires two rescuers: one to hold the mask in place while maintaining an open airway, while the second rescuer gently squeezes the bag (RCUK [232]) (Figure 12.65; see also Figure 12.66).