Michael Schumacher, Formula One driver, remains in a medically induced coma more than a week after his skiing accident. Here's more about induced comas.
What is medically induced coma?
Sometimes doctors use controlled amounts of drugs to deliberately put a patient into a deep yet temporary state of unconsciousness. This is called a medically-induced, or drug-induced, coma. The drugs usually used are barbiturates, which act by slowing down the brain's metabolism and reducing blood flow to the tissue.
Dr Andrew Rose-Innes, a neurologist in private practice in Portand, Oregon, and expert consultant to Health24, explains: "The patient needs to be intubated and ventilated (i.e. linked up to a machine that 'breathes for you'), because all brain function can be shut down in the deepest levels of sedation."
The aim of the procedure is to reduce swelling of the brain tissue, which is common with head injuries, and during brain surgery. Swelling of the brain can cause it to press against the skull, leading to brain damage.
Why brain swelling is so serious
Rose-Innes explains that raised pressure is such an issue with brain injury because, "The swollen brain has nowhere to go – the skull is a largely closed box, and so the brain tissue can get squashed or squeezed through partitions within the skull or jammed into the hole at the bottom of the skull – so-called brain herniation."
Easing the swollen brain: other methods
Rose-Innes points out that, "There are several ways to try to reduce intracranial pressure (pressure within the skull) – hyperventilation (i.e. making the ventilator "over-breathe" and so dropping the level of carbon dioxide; using diuretics or salty (hypertonic) intravenous solutions to relatively dehydrate the brain; removing part of the skull – this is called a decompressive craniectomy, which allows the brain to expand outside its usual bony confines.
"Other options include draining the cerebrospinal fluid with a ventricular drain if this is appropriate; and induced hypothermia – cooling the patient down to slow down metabolism and cellular damage.
"All these methods, including medically induced coma, need to be done carefully in an intensive care setting."
A high-risk procedure
Usually a coma is only induced when other methods have failed, as it carries serious risks. Potential complications associated with barbiturate-induced coma include impaired immune response and infection, blood clots, cardiac arrest and depression of brain activity. The latter makes it difficult to gauge brain function.
"One of the problems with inducing coma is that one cannot judge how bad the neurological injury is with bedside examination, and one is dependent on such measures as pressure readings and EEG (the induced coma may be judged deep enough when suppression of the normal electroencephalographic rhythms occurs)," says Rose-Innes.
A deeply vulnerable state
"An 'induced coma' sounds exotic, but in fact an induced coma is not too different to what every general anaesthetic is. We make use of the same kind of procedure to stop seizures that won't stop on their own, and don't respond to other medications – so-called 'status epilepticus' which is fatal if not treated.
"An illicit drug overdose that produces unconsciousness is an accidental 'induced coma'.
"A person in a coma from any cause is very vulnerable – they can't cough, can't breathe, can't move, they are unaware of internal or external stimuli, and the body can't control blood pressure or pulse rate very well."
(Olivia Rose-Innes, Health24, April 2009, updated January 2014)
(Information sources: Health24, Channel News Asia)