The Moment of Death

I'VE NEVER DIED BEFORE,'' ONE OF Dr. Kathleen Foley's cancer patients at New York's Memorial Sloan-Kettering Cancer Center told her. ""What will it be like?''

The moment of death is as individual as the decades of life, yet in more and more cases doctors can answer Foley's patient. Some of what they know comes straight out of medical textbooks. When the kidneys fail, impurities such as potassium build up in the blood, often producing cardiac arrhythmias; the chaotically beating heart stops supplying blood to the brain and the brain shuts down, one region at a time, like the floors of an office building going dark. And some of what physicians know, especially about the subjective experience of dying, comes from people who have been wrested back from death. Dr. Sherwin Nuland, author of the 1994 best seller ""How We Die,'' tells the story of a patient who had a heart attack while playing tennis. The man felt darkness closing in on him, in slow motion. Neurologists know why: as the brain runs out of oxygen, it closes down noncritical functions first. Sight, hearing and consciousness fade out, as though by the gradual twist of a dimmer switch. Pain vanishes.

In some ways, the many ways to die bring different last moments. Scarlet fever produces delirium and fevers. Meningitis brings unbearable headaches and convulsions. People who bleed to death first hyperventilate: the body automatically tries to make up for the plummeting volume of blood by short, fast breaths, as if that will bring it more oxygen. Heart rate surges. But, short of blood and hence oxygen, the heart and then brain slow. A flood of natural opiates called endorphins washes over the brain, bringing on both tranquillity and hallucinations, says Nuland. These are the ""near-death experiences,'' the visions of light and sense of floating, reported by people wrested back from death.

But in the end, the very end, no matter what official cause of death is printed on the death certificate, a person dies because too little oxygen reached his brain. This fact is reflected in the legal definition of death, the permanent cessation of brain function. The disease differs but the dying is the same. Some examples:

Heart disease: Blood contains the protein hemoglobin, a little ferry of a chemical whose sole cargo is an oxygen molecule. Hemoglobin picks up oxygen at the lungs, carrying it first to the left side of the heart and then out the aorta to the rest of the body. When fatty deposits narrow the arteries, too little blood reaches the heart, depriving its cells of oxygen. A crushing pain squeezes the chest, radiating down the left arm. In more than half of all people with heart disease, death follows within an hour of an attack, as the heart stops pumping blood, and hence oxygen, to the brain. But chronic congestive heart failure brings a slower, more painful death. When the weakened heart cannot pump out all the blood inside it, the blood backs up into veins and leaks through small blood vessels; tissues swell painfully. The heart beats faster; the patient huffs and puffs in a futile attempt to get oxygen; the kidneys and liver fail. And, starved of oxygen, so does the brain.

Liver failure: Stricken by cancer or hepatitis, the liver can no longer clear toxic chemicals from the body. A poisonous metabolite of ammonia builds up in the blood, explains Dr. Robert Glick, chief of emergency services at Oroville Hospital in California. When the toxic compound reaches the brain, it kills neurons in the brain stem, which controls heartbeat and respiration. The patient lapses into a coma. Consciousness fades away. There is neither pain nor other sensation. Death follows, usually within hours.

Cancer: ""Very few people die of the primary tumor''--the cancer they are said to ""have,'' explains cancer surgeon Dr. Murray Brennan of Sloan-Kettering. It is metastasis that kills. If cancer cells invade the lungs, they can induce fatal pneumonia, as the lungs can no longer absorb oxygen from inhaled air. A common cause of death in cancer patients is cachexia, the weakness and wasting that make the disease so horrific. The tumor monopolizes nutrients. The body consumes its own muscles, including the heart. Organs fail.

Does dying hurt? Half of all patients who die conscious and in a hospital, a 1995 study found, suffered moderate to severe pain. But there is no excuse for that, says Sloan-Kettering's Foley. Doctors have a whole arsenal of weapons to ease the final days: pain medication, anti-depressants, anti-nausea and anti-constipation drugs, appetite stimulants. Their use is not as widespread as it should be, due largely to the ignorance of many physicians. However death comes, when it finally arrives the patient's pupils widen, for the last time, into still, black circles. The skin takes on a grayish pallor. One by one, cells cease all biological activity. Life flickers out. The dying is over.