Coma

A coma is a profound state of prolonged unconsciousness where a person cannot be awakened and fails to respond to stimuli such as pain, light, or sound. They lack a normal wake-sleep cycle and do not initiate voluntary actions.

Comas can be caused naturally or medically induced. Patients in a coma often require extensive medical care to maintain health and prevent complications like pneumonia or blood clots.

Clinically, a coma can be defined by the consistent inability to follow a one-step command or a score of ≤ 8 on the Glasgow Coma Scale (GCS) lasting ≥ 6 hours.

Etymology

The term 'coma' comes from the Greek κῶμα (koma), meaning deep sleep. It was used historically by Hippocrates and Galen and reappeared in the medical literature during the 17th century.

Signs and Symptoms

Coma symptoms include the inability to voluntarily open the eyes, a non-existent sleep-wake cycle, lack of response to physical or verbal stimuli, depressed brainstem reflexes (e.g., pupils not responding to light), and abnormal or irregular breathing. Patients typically score between 3 and 8 on the Glasgow Coma Scale.

Causes

Comas can result from various conditions:

• Drug poisoning: This accounts for 40% of cases, where certain drugs impair synaptic functioning in the ascending reticular activating system (ARAS).
• Lack of oxygen: Making up about 25% of cases, typically due to cardiac arrest, causing brain cell damage from hypoxia.
• Stroke, brain haemorrhage, or brain tumour: Representing 20% of cases, these conditions restrict blood flow to the brain, leading to cell death and coma.
• Traumatic brain injury, excessive blood loss, malnutrition, hypothermia, hyperthermia, abnormal glucose levels, and other biological disorders: These can all lead to a comatose state.

Pathophysiology

Coma results from injury to the cerebral cortex or the reticular activating system (RAS). The cerebral cortex handles complex cognitive functions, while the RAS, located in the brainstem, arouses and wakes the brain. Structural causes of coma include mechanical damage, while diffuse causes involve metabolic or toxic dysfunctions.

Diagnosis

Diagnosing the cause of a coma involves a series of steps:

1. Perform a general examination and medical history check.
2. Ensure the patient is genuinely comatose, not experiencing locked-in syndrome or psychogenic unresponsiveness.
3. Locate the brain site causing the coma and assess severity with the Glasgow Coma Scale.
4. Conduct blood tests for drug involvement and metabolic imbalances.
5. Perform brain scans (CT, MRI) and monitor brain waves using EEGs.

Initial assessments often use the AVPU scale (alert, vocal stimuli, painful stimuli, unresponsive) and the Glasgow Coma Scale. Imaging tools like CT and MRI scans help identify specific causes, while EEGs monitor cortical activity.

Reflex tests (oculocephalic, pupillary light, oculovestibular, corneal, gag) assess brainstem and cortical function. Stereotypical postures (decorticate or decerebrate) indicate the lesion's location in the CNS.

Treatment

Treatment depends on the severity and cause:

• Initial Care: Coma patients are usually placed in an ICU. Respiratory and circulatory stability are maintained through intubation, ventilation, and intravenous fluids.
• Continued Care: Physical therapy, regular movement, and preventive measures against pneumonia and bedsores are essential.

Prognosis and Recovery

Comas can last from days to years. Outcomes vary: some patients recover, some progress to a vegetative or minimally conscious state, and others die. Recovery, often gradual, involves overcoming physical, intellectual, and psychological difficulties. For example, Terry Wallis began speaking after 19 years in a minimally conscious state, and deep brain stimulation has shown promise in some cases.

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Self-assessment MCQs (single best answer)

What is the primary characteristic of a coma?

Which of the following accounts for the highest percentage of coma cases?

A score of ≤8 on the Glasgow Coma Scale (GCS) lasting ≥6 hours defines:

The term 'coma' is derived from which language?

Which symptom is NOT typically associated with a coma?

Which diagnostic tool is used to measure cortical activity in a coma patient?

Which of the following is NOT a cause of coma?

Decorticate posturing indicates a lesion at or above which part of the brain?

What is a common initial care treatment for coma patients?

Which outcome is NOT a possible recovery scenario for coma patients?