The use of life-saving measures of mouth-tomouth resuscitation and external cardiac compression massage in a person who has collapsed with CARDIAC ARREST. Speedy restoration of the circulation of oxygenated blood to the brain is essential to prevent damage to brain tissues from oxygen starvation. The brain is irreversibly damaged if it is starved of oxygen for more than 4–5 minutes. Someone whose heart has stopped will be very pale or blue-grey (in particular, round the lips) and unresponsive; he or she will not be breathing and will have no pulse. It is important to determine that the collapsed person has not simply fainted before starting CPR. The procedure is described under car-diac/respiratory arrest in APPENDIX 1: BASIC FIRST AID. In hospital, or when paramedical sta? are attending an emergency, CPR may include the use of a DEFIBRILLATOR to apply a controlled electric shock to the heart via the chest wall.