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What are the Causes of Decreased Consciousness?

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What are the Causes of Decreased Consciousness?

Consciousness is decreased by conditions that directly affect the brain or those that affect the entire body.


Causes of decreased levels of consciousness are listed below:

Conditions that decrease oxygen, glucose or cofactors supply to the brain: Conditions that deprive the brain of its requirements to function properly result in an altered level of consciousness. These include:

  • Alterations in glucose levels: High blood sugar levels can lead to diabetic coma. On the other hand, low glucose levels can lead to hypoglycemic coma. An altered level of consciousness in a diabetic should raise the suspicion of a problem in blood sugar level.
  • Cardiac causes: A cardiac arrest results in a reduced supply of oxygen-rich blood to the brain. Other heart conditions like heart failure could cause similar problems. These conditions may be diagnosed with an ECG or other cardiac tests. Low blood pressure could also result in decreased blood supply to the brain.
  • Lung diseases: Severe lung conditions like chronic obstructive pulmonary disease, pulmonary edema (fluid in the lungs), pulmonary embolism (a clot in the lungs), and severe and long-lasting asthma attacks can reduce oxygen content of the blood and thereby the supply to the brain and result in brain damage. A difficulty with breathing is usually obvious in these patients.
  • Deficiency of B group of vitamins: A person with severe deficiency of vitamin B1 or thiamine suffers from beriberi, which sometimes causes confusion and delusions. Deficiency of the vitamin B3 or niacin results in pellagra, which is also associated with confusional states. In addition, the patient shows digestive problems and skin inflammation.

Metabolic, Hormonal and Other General Conditions: Metabolic conditions result in the accumulation of excessive or toxic substances in the blood resulting in decreased consciousness: Some of these conditions are listed below:

  • Liver failure: Liver failure results in the accumulation of toxic substances in the body, which affect the brain and reduce consciousness, even leading to hepatic encephalopathy and coma. Other signs of liver failure may be present like accumulation of fluid in the abdomen and jaundice.
  • Kidney failure: Kidney failure results in high levels of urea in the body, which could affect the level of consciousness. Other features of kidney failure may be present in these patients.
  • Hypothyroidism: Very low or very high thyroid levels are associated with altered consciousness. Very low levels could result in a type of coma called myxedema coma.
  • Hypothermia or hyperthermia: A change in temperature can affect the brain resulting in damage. High temperatures tend to affect the brain more as compared to lower temperatures.
  • Abnormal sodium levels: High sodium levels in the blood, which is often a consequence of dehydration, can reduce consciousness. On the other hand, hyponatremia or low sodium levels could result in accumulation of fluid in the brain, again affecting the level of consciousness.

Drugs, Alcohol and Poisons: Consciousness could be affected by substances that act on the brain. A history of intake of these substances may be obtained from the patientís relatives. Some of these are:

  • Drugs: Drugs are often the cause of an altered level of consciousness in older individuals. This is especially in the case of drugs that act on the brain like sedatives and opioids. Older people are more sensitive to medications and often take multiple medications. Dosages if not reduced in these individuals can result in decreased consciousness. People who take drugs that could possibly reduce their level of consciousness are advised to avoid using machinery or drive to avoid accidents. They are also advised to avoid alcohol due to the additive effect in reducing brain function.
  • Alcohol: Alcohol affects the brain in multiple ways. It can directly affect the brain cells causing them to function slowly. In addition, it can affect lung function and reduce the oxygen supply to the brain.
  • Poisoning: Poisoning with carbon monoxide results in reduced oxygen-rich blood to the brain.

Conditions affecting the brain: Conditions that directly affect either both the cerebral halves of the brain or the reticular activating system of the brainstem (which is responsible for arousal) can result in reduced levels of consciousness. These conditions are diagnosed based on a detailed neurological examination and tests like CT scan and MRI. These conditions include:

  • Stroke: A stroke can affect consciousness in a number of ways. It decreases blood supply to the areas of the brain involved in maintaining consciousness like the brainstem and the cerebrum. A bleed within or just outside the brain can exert pressure on the brain or result in irritation.
  • Brain tumors / abscess: A brain tumor or abscess can occupy space within the skull and exert pressure on a part of the brain. In some cases, it can press on the brain excessively damaging it and even pushing it through some of the openings at the base of the skull. This situation is referred to as herniation of the brain, which can worsen the patientís condition. The tumor may also directly affect the areas of the brain controlling consciousness. Breathing may be altered in these patients. Examination of the eyes helps in the diagnosis of these conditions.
  • Aneurysms in the brain: An aneurysm is a swelling of a blood vessel of the brain. It could affect consciousness by exerting pressure on the brain or resulting in a bleed.
  • Head injury: Head injury may damage the brain and cause loss of consciousness, sometimes even leading to coma. In some cases, the head injury results in a bleed within the skull. The bleed puts pressure on a part of the brain and can result in decreased consciousness.
  • Seizures: Following a seizure, the patient sometimes goes into a deep sleep. This is referred to as the post-ictal stage.
  • Infections: Infections of the brain called encephalitis, or the covering of the brain called meningitis can result in altered levels of consciousness. The neck of the patient may be rigid in cases of meningitis. Besides, sepsis may also affect the brain, altering the consciousness levels.

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