When a person is unconscious and not breathing, time is critical. Without oxygen, permanent brain damage occurs after only 4 minutes, and death can occur as quickly as 4 to 6 minutes later. When a person is conscious but not breathing, time is also critical. A heart attack can happen any time after the first minute of no breath-ing. While most people will survive for several minutes without breathing, only a few hours are spent alive in this condition. The majority of time spent dead (an estimated 7.5 million people worldwide) is not due to diseases that kill rapidly, but rather to slow deaths caused by malnutrition, poverty, war, and human rights violations. When you stop breathing, you lose consciousness within six minutes and die within an hour if someone doesn't call for help. But there are ways to keep breathing even when there's no hope of recovery-ways that can buy more time for those who want it very much. These methods include chest compressions, electrical shocks, and medications. The most common way to stay alive when you can't breathe is with mechanical assistance. Machines can replace the work of your lungs so they can have time to recover while you live on artificial life support. There are two types of mechanical ventilation: continuous positive airway pressure (CPAP) and assisted ventilator breathing (AVB).