maybe this is a little vague, but how long would it take for a coma patient to die after their life support is withdrawn?
Very interesting question. It depends on what life support measures are being implemented, and how dependent on them the person is.
Life support is a range of different machines and therapies designed to keep a person alive. This ranges from something called ECMO, which effectively takes over for the heart and lungs for temporary periods, to simply a tube that goes from the nose to the stomach to deliver food and water to a person who cannot eat or drink.
As stated above, the most intensive life support is ECMO, which is essentially a machine that takes over the functions of the heart and lungs temporarily- oxygenating blood outside the body and circulating it. This is usually used in open heart surgery, though it can be used in some ICUs for longer periods of time. Assuming the person is entirely dependent on ECMO (as in, they do not have heart or lung function on their own), they would begin to die within minutes of ECMO being withdrawn.
Next down might be something like a ventilator. Ventilators have different modes that allow a person who has some respiratory function on their own to continue exercising it while being supported mechanically.
For example, someone may be on a ventilator only to provide extra pressure to overcome the resistance from a tube that goes from their mouth to their lungs to hold open their airway, and sometimes it adds pressure to make it easier for the person to pull in breaths. This person can probably breathe on their own for an indeterminate amount of time and would not necessarily die if the ventilator was withdrawn, though they may have trouble keeping their airway open or they may tire out easily trying to breathe.
Another vent setting involves the patient breathing as much as they can, and the ventilator serving as a backup. If the person doesn't take a breath in a set number of seconds, the ventilator gives them one. This person may survive for a while afterwards, but would likely eventually die due to high levels of carbon dioxide in their blood. It might be any time between an hour or less to several days before the person's death.
The highest setting on most vents still allows the patient to initiate breaths, but every breath they take is assisted to ensure it is a complete breath, and the machine also delivers a set number of breaths every minute. Someone who is dependent on this mode may pass within minutes of being taken off the vent and likely wouldn't live more than an hour or so, dying from lack of oxygen or buildup of carbon dioxide.
Another life support device is a cooling blanket. When certain parts of the brain are damaged (such as the parts that are damaged after a long period without oxygen), the person cannot control their own temperature, and they tend to get extremely overheated by their own metabolism. Temps can get into the 110's *F, which kills pretty quickly. Fever-reducing drugs are not effective. This would also be someone who could last anywhere from an hour or so to a couple of days, though their brain would quickly become more and more damaged during this time.
The least intensive form of life support would be the provision of food or water through an NG tube- a tube that goes from the nose to the stomach and allows medications and tube feed (water and basic nutrition) to be delivered to the stomach. If this is withdrawn and IV fluids are not provided, the person may live a week or more before dying of dehydration. If they are, for some reason, given IV fluids, they may live months.
Note that a person may be on a combination of modalities (like it would be weird for someone to be on a ventilator without an NG tube).
-Ross ( @macgyvermedical)
