What is the usual safe duration limit for deep hypothermic circulatory arrest at temperatures of 18-20 degrees Celsius?

The safe duration limit for deep hypothermic circulatory arrest typically ranges around 45 minutes at temperatures between 18-20 degrees Celsius. This time frame is established based on the physiological responses and metabolic demands of the human body when subjected to such low temperatures.

When body temperature drops, metabolic processes slow down significantly, reducing the brain's demand for oxygen and glucose. This allows for a longer duration of circulatory arrest without causing irreversible damage. The threshold of about 45 minutes balances the need for safety with surgical practicalities during procedures requiring deep hypothermia, such as certain cardiac surgeries.

While durations beyond 45 minutes may be possible in specific cases with optimal conditions or advances in protective measures, 45 minutes generally represents a conservative and well-accepted guideline aiming to minimize the risk of neurological impairment and other complications associated with prolonged circulatory arrest at low temperatures.