Q. I have a grandfather who has worsening dementia and feeding difficulties. He never wanted a feeding tube. My question is, how long can a person live without drinking, and is death from dehydration painful?

- JT

A.

Death by dehydration times vary widely depending on the circumstances, from two hours to two weeks. Age, exposure to temperature extremes, exertion, and presence of edema (fluid overload) all affect survival.

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A baby left in a hot car, or a marathon runner not drinking enough in the heat, can each die of dehydration in a matter of hours.

For the average healthy individual in a survival scenario, severe symptoms kick in by the second day and can become life-threatening by the third. Thirst, fatigue, rapid heart rate, muscle spasms, and confusion occur.

At the other extreme, patients in persistent vegetative states can generally survive 12 days or so without fluids. Why so long? With no exertion, temperature variation, weather exposure, or other significant diseases to contend with, their metabolism and fluid losses are minimal.

Patients with dementia and dehydration are in between these extremes, generally succumbing in less than a week. If the dehydration is expected, the patient can be treated with oral wetting agents to eliminate thirst, muscle relaxants to relieve cramping, and anti-anxiety medicines if needed. But generally, in the chronically ill elderly, dehydration is fairly quick and non-dramatic.

Sodium levels rise, affecting the brain. Lethargy and confusion set in and quickly progress to stupor, a sleep-like state of reduced consciousness. If not reversed with intravenous fluids or tube feeding, the patient slips deeper into a coma. Eventually, either the heartbeat or the respiratory drive stops. Dehydration is a mode of death as old as mankind, and with the benefit of modern medicines, should be completely without pain or anxiety.

Gary Payinda MD is an emergency medicine consultant in Whangarei.

Have a science, health topic or question you'd like addressed? Email: drpayinda@gmail.com

(This column provides general information and is not a substitute for the medical advice of your personal doctor.)