An induced comaalso known as a medically induced coma (MIC), barbiturate-induced coma, or drug-induced comais a temporary

coma A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to respond normally to painful stimuli, light, or sound, lacks a normal wake-sleep cycle and does not initiate voluntary actions. Coma patients exhi ...

(a deep state of

unconsciousness Unconsciousness is a state in which a living individual exhibits a complete, or near-complete, inability to maintain an consciousness, awareness of self and environment or to respond to any human or environmental Stimulus (physiology), stimulus. ...

) brought on by a controlled dose of an anesthetic drug, often a

barbiturate Barbiturates are a class of depressant drugs that are chemically derived from barbituric acid. They are effective when used medically as anxiolytics, hypnotics, and anticonvulsants, but have physical and psychological addiction potential as we ...

such as pentobarbital or

thiopental Sodium thiopental, also known as Sodium Pentothal (a trademark of Abbott Laboratories), thiopental, thiopentone, or Trapanal (also a trademark), is a rapid-onset short-acting barbiturate general anesthetic. It is the thiobarbiturate analog of pe ...

. Barbiturate comas are used to protect the

brain A brain is an organ that serves as the center of the nervous system in all vertebrate and most invertebrate animals. It is located in the head, usually close to the sensory organs for senses such as vision. It is the most complex organ in a v ...

during major

neurosurgery Neurosurgery or neurological surgery, known in common parlance as brain surgery, is the medical specialty concerned with the surgical treatment of disorders which affect any portion of the nervous system including the brain, spinal cord and peri ...

, as a last line of treatment in certain cases of

status epilepticus Status epilepticus (SE), or status seizure, is a single seizure lasting more than 5 minutes or 2 or more seizures within a 5-minute period without the person returning to normal between them. Previous definitions used a 30-minute time limit. The s ...

that have not responded to other treatments, and in

refractory In materials science, a refractory material or refractory is a material that is resistant to decomposition by heat, pressure, or chemical attack, and retains strength and form at high temperatures. Refractories are polycrystalline, polyphase, ...

intracranial hypertension following traumatic brain injury. Induced coma usually results in significant systemic adverse effects. The patient is likely to completely lose respiratory drive and require

mechanical ventilation Mechanical ventilation, assisted ventilation or intermittent mandatory ventilation (IMV), is the medical term for using a machine called a ventilator to fully or partially provide artificial ventilation. Mechanical ventilation helps move air ...

; gut motility is reduced;

hypotension Hypotension is low blood pressure. Blood pressure is the force of blood pushing against the walls of the arteries as the heart pumps out blood. Blood pressure is indicated by two numbers, the systolic blood pressure (the top number) and the dias ...

can complicate efforts to maintain

cerebral perfusion pressure Cerebral perfusion pressure, or CPP, is the net pressure gradient causing cerebral blood flow to the brain (brain perfusion). It must be maintained within narrow limits because too little pressure could cause brain tissue to become ischemic (having ...

and often requires the use of vasopressor drugs. Hypokalemia often results. The completely immobile patient is at increased risk of bed sores as well as infection from catheters. Induced coma is a feature of the

Milwaukee protocol Rabies is a viral disease that causes encephalitis in humans and other mammals. Early symptoms can include fever and tingling at the site of exposure. These symptoms are followed by one or more of the following symptoms: nausea, vomiting, vio ...

, a controversial method that is promoted as a means of treating

rabies Rabies is a viral disease that causes encephalitis in humans and other mammals. Early symptoms can include fever and tingling at the site of exposure. These symptoms are followed by one or more of the following symptoms: nausea, vomiting, vi ...

infection in people. __TOC__

Theory

Barbiturates reduce the metabolic rate of brain tissue, as well as the

cerebral blood flow Cerebral circulation is the movement of blood through a network of cerebral arteries and veins supplying the brain. The rate of cerebral blood flow in an adult human is typically 750 milliliters per minute, or about 15% of cardiac output. Arterie ...

. With these reductions, the

blood vessel The blood vessels are the components of the circulatory system that transport blood throughout the human body. These vessels transport blood cells, nutrients, and oxygen to the tissues of the body. They also take waste and carbon dioxide away ...

s in the brain narrow, resulting in a shrunken brain, and hence lower

intracranial pressure Intracranial pressure (ICP) is the pressure exerted by fluids such as cerebrospinal fluid (CSF) inside the skull and on the brain tissue. ICP is measured in millimeters of mercury (mmHg) and at rest, is normally 7–15 Millimeter of mercury, mmHg ...

. The hope is that, with the swelling relieved, the pressure decreases and some or all

brain damage Neurotrauma, brain damage or brain injury (BI) is the destruction or degeneration of brain cells. Brain injuries occur due to a wide range of internal and external factors. In general, brain damage refers to significant, undiscriminating t ...

may be averted. Several studies have supported this theory by showing reduced mortality when treating refractory intracranial hypertension with a barbiturate coma. About 60% of the glucose and oxygen used by the brain is meant for its electrical activity and the rest for all other activities such as metabolism. When barbiturates are given to brain injured patients for induced coma, they act by reducing the electrical activity of the brain, which reduces the metabolic and oxygen demand. The infusion dose rate of barbiturates is increased under monitoring by

electroencephalography Electroencephalography (EEG) is a method to record an electrogram of the spontaneous electrical activity of the brain. The biosignals detected by EEG have been shown to represent the postsynaptic potentials of pyramidal neurons in the neocortex ...

until burst suppression or cortical electrical silence (isoelectric "flatline") is attained. Once there is improvement in the patient's general condition, the barbiturates are withdrawn gradually and the patient regains consciousness. Controversy exists over the benefits of using barbiturates to control intracranial hypertension. Some studies have found that barbiturate-induced coma can reduce intracranial hypertension but does not necessarily prevent brain damage. Furthermore, the reduction in intracranial hypertension may not be sustained. Some

randomized trial In science, randomized experiments are the experiments that allow the greatest reliability and validity of statistical estimates of treatment effects. Randomization-based inference is especially important in experimental design and in survey sampl ...

s have failed to demonstrate any survival or morbidity benefit of induced coma in diverse conditions such as neurosurgical operations, head trauma, intracranial aneurysm rupture,

intracranial hemorrhage Intracranial hemorrhage (ICH), also known as intracranial bleed, is bleeding within the skull. Subtypes are intracerebral bleeds ( intraventricular bleeds and intraparenchymal bleeds), subarachnoid bleeds, epidural bleeds, and subdural bleeds. ...

, ischemic

stroke A stroke is a medical condition in which poor blood flow to the brain causes cell death. There are two main types of stroke: ischemic, due to lack of blood flow, and hemorrhagic, due to bleeding. Both cause parts of the brain to stop functionin ...

, and

. If the patient survives, cognitive impairment may also follow recovery from the coma.

References

{{Authority control Neurology procedures Intensive care medicine Coma

Theory

See also

References