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A coma is a deep state of prolonged unconsciousness in which a person cannot be awakened, fails to Nociception to Pain, light, or sound, lacks a normal Circadian rhythm and does not initiate . (2025). 9780323022613, Mosby. ISBN 9780323022613 The person may experience respiratory and circulatory problems due to the body's inability to maintain normal bodily functions. People in a coma often require extensive medical care to maintain their health and prevent complications such as pneumonia or blood clots. Coma patients exhibit a complete absence of wakefulness and are unable to consciously feel, speak or move. Comas can be the result of natural causes, or can be Induced coma, for example, during general anesthesia.
Clinically, a coma can be defined as the consistent inability to follow a one-step command. (2025). 9781416032069 ISBN 9781416032069 For a patient to maintain consciousness, the components of wakefulness and awareness must be maintained. Wakefulness is a quantitative assessment of the degree of consciousness, whereas awareness is a qualitative assessment of the functions mediated by the cerebral cortex, including cognitive abilities such as attention, sensory perception, explicit memory, language, the execution of tasks, temporal and spatial orientation and reality judgment. (2025). 9780080450469 ISBN 9780080450469 Neuroscience, consciousness is maintained by the activation of the cerebral cortex—the gray matter that forms the brain's outermost layer—and by the reticular activating system (RAS), a structure in the brainstem.
The second most common cause of coma, which makes up about 25% of cases, is lack of oxygen, generally resulting from cardiac arrest. The central nervous system (CNS) requires a great deal of oxygen for its neurons. Oxygen deprivation in the Human brain, or cerebral hypoxia, causes sodium and calcium from outside of the to decrease and intracellular calcium to increase, which harms neuron communication. Lack of oxygen in the brain also causes ATP exhaustion and cellular breakdown from cytoskeleton damage and nitric oxide production.
Twenty percent of comatose states result from an ischemic stroke, brain hemorrhage, or brain tumor. During a stroke, blood flow to part of the brain is restricted or blocked. An ischemic stroke, brain hemorrhage, or brain tumor may cause restriction of blood flow. Lack of blood to cells in the brain prevents oxygen from getting to the neurons, and consequently causes cells to become disrupted and die. As brain cells die, brain tissue continues to deteriorate, which may affect the functioning of the ARAS, causing unconsciousness and coma.
Comatose cases can also result from traumatic brain injury, excessive blood loss, malnutrition, hypothermia, hyperthermia, hyperammonemia, abnormal glucose levels, and many other biological disorders. Furthermore, studies show that 1 out of 8 patients with traumatic brain injury experience a comatose state.
Heart-related causes of coma include cardiac arrest, ventricular fibrillation, ventricular tachycardia, atrial fibrillation, myocardial infarction, heart failure, arrhythmia when severe, cardiogenic shock, myocarditis, and pericarditis. Respiratory arrest is the only lung condition to cause coma, but many different lung conditions can cause decreased level of consciousness, but do not reach coma.
Other causes of coma include Epilepsy, kidney failure, liver failure, hyperglycemia, hypoglycemia, and infections involving the brain, like meningitis and encephalitis.
The cerebral cortex is the outer layer of neural tissue of the cerebrum of the brain. (2025). 9780073525600, McGraw-Hill. ISBN 9780073525600 The cerebral cortex is composed of Grey matter which consists of the nuclei of , whereas the inner portion of the cerebrum is composed of white matter and is composed of the of neuron. White matter is responsible for perception, relay of the sensory input via the thalamic pathway, and many other neurological functions, including complex thinking.
The RAS, on the other hand, is a more primitive structure in the brainstem which includes the reticular formation (RF). The RAS has two tracts, the ascending and descending tract. The ascending tract, or ascending reticular activating system (ARAS), is made up of a system of acetylcholine-producing neurons, and works to arouse and wake up the brain. (2025). 9780080453965 ISBN 9780080453965 Arousal of the brain begins from the RF, through the thalamus, and then finally to the cerebral cortex. Any impairment in ARAS functioning, a neuronal dysfunction, along the arousal pathway stated directly above, prevents the body from being aware of its surroundings. Without the arousal and consciousness centers, the body cannot awaken, remaining in a comatose state.
The severity and mode of onset of coma depends on the underlying cause. There are two main subdivisions of a coma: structural and diffuse neuronal. A structural cause, for example, is brought upon by a mechanical force that brings about cellular damage, such as physical pressure or a blockage in neural transmission. (2025). 9780323357753 ISBN 9780323357753 By contrast, a diffuse cause is limited to aberrations of cellular function which fall under a metabolic or toxic subgroup. Toxin-induced comas are caused by extrinsic substances, whereas metabolic-induced comas are caused by intrinsic processes, such as body thermoregulation or ionic imbalances (e.g. sodium). For instance, severe hypoglycemia (low blood sugar) or hypercapnia (increased carbon dioxide levels in the blood) are examples of a metabolic diffuse neuronal dysfunction. Hypoglycemia or hypercapnia initially cause mild agitation and confusion, but progress to obtundation, stupor, and finally, complete unconsciousness. (2025). 9780429158971 ISBN 9780429158971 In contrast, coma resulting from a severe traumatic brain injury or subarachnoid hemorrhage can be instantaneous. The mode of onset may therefore be indicative of the underlying cause.
Structural and diffuse causes of coma are not isolated from one another, as one can lead to the other in some situations. For instance, coma induced by a diffuse metabolic process, such as hypoglycemia, can result in a structural coma if it is not resolved. Another example is if cerebral edema, a diffuse dysfunction, leads to ischemia of the brainstem, a structural issue, due to the blockage of the circulation in the brain.
When an unconscious person enters a hospital, the hospital uses a series of diagnostic steps to identify the cause of unconsciousness. According to Young, the following steps should be taken when dealing with a patient possibly in a coma:
In those with deep unconsciousness, there is a risk of asphyxiation as the control over the muscles in the face and throat is diminished. As a result, those presenting to a hospital with coma are typically assessed for this risk ("airway management"). If the risk of asphyxiation is deemed high, doctors may use various devices (such as an oropharyngeal airway, nasopharyngeal airway or endotracheal tube) to safeguard the airway.
In the treatment of traumatic brain injury (TBI), there are four examination methods that have proved useful: skull x-ray, angiography, computed tomography (CT), and magnetic resonance imaging (MRI). The skull x-ray can detect linear fractures, impression fractures (expression fractures) and burst fractures. Angiography is used on rare occasions for TBIs i.e. when there is suspicion of an aneurysm, carotid sinus fistula, traumatic vascular occlusion, and vascular dissection. A CT can detect changes in density between the brain tissue and hemorrhages like subdural and intracerebral hemorrhages. MRIs are not the first choice in emergencies because of the long scanning times and because fractures cannot be detected as well as CT. MRIs are used for the imaging of soft tissues and lesions in the posterior fossa which cannot be found with the use of CT.
| Oculocephalic reflex | Oculocephalic reflex, also known as the doll's eye, is performed to assess the integrity of the brainstem.
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| Pupillary light reflex | Pupil reaction to light is important because it shows an intact retina, and cranial nerve number 2 (CN II)
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| Oculovestibular reflex (Cold Caloric Test) | Caloric reflex test also evaluates both cortical and brainstem function
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| Corneal reflex | The corneal reflex assesses the proper function of the trigeminal nerve (CN 5) and facial nerve (CN 7), and is present at infancy.
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| Gag reflex | The gag, or pharyngeal, reflex is centered in the medulla and consists of the reflexive motor response of pharyngeal elevation and constriction with tongue retraction in response to sensory stimulation of the pharyngeal wall, posterior tongue, , or faucial pillars.
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Assessment of posture and physique is the next step. It involves general observation about the patient's positioning. There are often two stereotypical postures seen in comatose patients. Decorticate posturing is a stereotypical posturing in which the patient has arms Flexion at the elbow, and arms adducted toward the body, with both legs extended. Decerebrate posturing is a stereotypical posturing in which the legs are similarly extended (stretched), but the arms are also stretched (extended at the elbow). The posturing is critical since it indicates where the damage is in the central nervous system. A decorticate posturing indicates a lesion (a point of damage) at or above the red nucleus, whereas a decerebrate posturing indicates a lesion at or below the red nucleus. In other words, a decorticate lesion is closer to the cortex, as opposed to a decerebrate posturing which indicates that the lesion is closer to the brainstem.
| Normal eye with two pupils equal in size and reactive to light. This means that the patient is probably not in a coma and is probably lethargic, under influence of a drug, or sleeping. |
| "Pinpoint" pupils indicate heroin or opiate overdose, which can be responsible for a patient's coma. The pinpoint pupils are still reactive to light (in both eyes, not just one). Another possibility is damage to the pons. |
| One pupil is dilated and unreactive, while the other is normal (in this case, the right eye is dilated, while the left eye is normal in size). This could mean damage to the oculomotor nerve (cranial nerve number 3, CN III) on the right side, or indicate the possibility of vascular involvement. |
| Both pupils are dilated and unreactive to light. This could be due to overdose of certain medications, hypothermia or severe anoxia (lack of oxygen). |
The Rancho Los Amigos Scale is a complex scale that has eight separate levels, and is often used in the first few weeks or months of coma while the patient is under closer observation, and when shifts between levels are more frequent.
Pneumonia is also common in coma patients due to their inability to swallow which can then lead to aspiration. A coma patient's lack of a gag reflex and use of a feeding tube can result in food, drink or other solid organic matter being lodged within their lower respiratory tract (from the trachea to the lungs). This trapping of matter in their lower respiratory tract can ultimately lead to infection, resulting in aspiration pneumonia.
Coma patients may also deal with restlessness or seizures. Soft cloth restraints may be used to prevent them from pulling on tubes or dressings and side rails on the bed should be kept up to prevent patients from falling.
Predicted chances of recovery will differ depending on which techniques were used to measure the patient's severity of neurological damage. Predictions of recovery are based on statistical rates, expressed as the level of chance the person has of recovering. Time is the best general predictor of a chance of recovery. For example, after four months of coma caused by brain damage, the chance of partial recovery is less than 15%, and the chance of full recovery is very low.
The outcome for coma and vegetative state depends on the cause, location, severity and extent of neurological damage. A deeper coma alone does not necessarily mean a slimmer chance of recovery; similarly, a milder coma does not indicate a higher chance of recovery. The most common cause of death for a person in a vegetative state is secondary infection such as pneumonia, which can occur in patients who lie still for extended periods.
There are reports of people coming out of a coma after long periods of time. After 19 years in a minimally conscious state, Terry Wallis spontaneously began speaking and regained awareness of his surroundings.
A man with brain damage and trapped in a coma-like state for six years was brought back to consciousness in 2003 by doctors who planted electrodes deep inside his brain. The method, called deep brain stimulation (DBS), successfully roused communication, complex movement and eating ability in the man with a traumatic brain injury. His injuries left him in a minimally conscious state, a condition akin to a coma but characterized by occasional, but brief, evidence of environmental and self-awareness that coma patients lack.
It has been argued that unawareness should be just as ethically relevant and important as a state of awareness and that there should be metaphysical support of unawareness as a state.
In the ethical discussions about disorders of consciousness (DOCs), two abilities are usually considered as central: experiencing well-being and having interest. Well-being can broadly be understood as the positive effect related to what makes life good (according to specific standards) for the individual in question. (2025). 9780190280307 ISBN 9780190280307 The only condition for well-being broadly considered is the ability to experience its 'positiveness'. That said, because experiencing positiveness is a basic emotional process with Phylogenetics roots, it is likely to occur at a completely unaware level and, therefore, introduces the idea of an unconscious well-being. Material was copied from this source, which is available under a Creative Commons Attribution 4.0 International License. As such, the ability of having interests is crucial for describing two abilities which those with comas are deficient in. Having an interest in a certain domain can be understood as having a stake in something that can affect what makes our life good in that domain. An interest is what directly and immediately improves life from a certain point of view or within a particular domain, or greatly increases the likelihood of life improvement enabling the subject to realize some good. That said, sensitivity to reward signals is a fundamental element in the learning process, both consciously and unconsciously. Moreover, the unconscious brain is able to interact with its surroundings in a meaningful way and to produce meaningful information processing of stimuli coming from the external environment, including other people. (2025). 9781317529590 ISBN 9781317529590
According to Hawkins, "1. A life is good if the subject is able to value, or more basically if the subject is able to care. Importantly, Hawkins stresses that caring has no need for cognitive commitment, i.e. for high-level cognitive activities: it requires being able to distinguish something, track it for a while, recognize it over time, and have certain emotional dispositions vis-à-vis something. 2. A life is good if the subject has the capacity for relationship with others, i.e. for meaningfully interacting with other people." This suggests that unawareness may (at least partly) fulfill both conditions identified by Hawkins for life to be good for a subject, thus making the unconscious ethically relevant.
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