Loss Of Consciousness

When talking about possible causes of unconsciousness, we touch an extremely broad issue. By loosing consciousness the organism reacts to many situations. Generally, the point is that for some reason there is a temporary or permanent loss of brain function due to brain disorders, circulatory system problems or due to a significant distortion of internal environment. In this short text I will name only the most common or most important causative factors.

We can distinguish between long-term and short-term losses of consciousness. A short and transient episode of unconsciousness is marked as syncope.


Brain disorders

There are many pathological conditions disorders that manifest as impaired or totally lost consciousness. A classic example is brain concussion and other head and brain injuries. Unconsciousness can also emerge by a stroke, encephalitis and meningitis. Unconscious can be people during epileptic seizures and in cases when there is an increase in intracranial pressure and by cerebral edema (brain swelling) occurrence. This can happen by subdural or epidural hematoma, by brain tumors, by brain metastases, etc.).

Cardiovascular disorders

Consciousness is impaired in situations where circulatory system is unable to transport enough oxygen to brain. Typical situations are low blood pressure, narrowing of certain vessels (both carotid arteries narrowing), heart failure and certain dangerous arrhythmias (like ventricular fibrillation). Severe disruption to circulatory system often leading to coma is connected with shock conditions.

Respiratory disorders

They are closely related to circulatory causes. If human lungs are unable to oxygenate blood, brain is always affected. The cause of this condition may be virtually any factor causing severe shortness of breath (severe forms of pneumonias, COPD, asthma attack, pulmonary embolism, etc).

Metabolic causes

Many cases of internal environment disorders influence brain activity and can lead to unconsciousness. This includes hypoglycemic and hyperglycemic conditions (complications of diabetes), changes in pH, disorders in concentrations of minerals, hormonal disorders (for example increased or decreased thyroid function), changes of body temperature and accumulation of waste products by major organs failure (mainly liver failure, acute kidney failure and untreated last stages of chronic kidney failure).

Psychological causes

Various forms of consciousness disorders may be part of the manifestations of psychiatric disorders, hysterical seizures, etc.


A number of drugs and medicines in overdose cause loosing of consciousness. Probably such the most common substance is alcohol.


Note: The most common and essentially banal reason for short-term loss of consciousness is called vasovagal response (vagovagal syncope). Some people, especially women, are prone to this condition. It is caused by fact that inner nerves in body that control blood vessels dilation and blood pressure maintenance don’t work properly and can not prevent a sudden drop in blood pressure in certain circumstances. Such risky circumstances are prolonged standing, dehydration, rapid change of position from lying to sitting. Such sudden drop in blood pressure is followed by a short and transient loss of consciousness (syncope). Unconsciousness does not come quite suddenly, but is usually preceded by a feeling of weakness, dizziness, sweating, seeing stars, etc. First aid is to carefully put the affected person down on the ground and lift his or her lower extremities up. This increases blood flow into brain and causes rapid restoration of consciousness.

Diagnostic approach

It is necessary to make sure that an unconscious patient is in stable condition; at least a basal medical history can be often obtained from relatives. Information about circumstances of falling unconscious is especially important. Physical examination must be done carefully; the depth of coma is assessed using the so-called Glasgow Coma Scale (GCS). GCS is evaluated by numbers according to patient’s non-verbal and verbal reactions to external stimuli A healthy fully conscious person has GCS 15, the deepest coma reaches a minimum value of GCS 3.


If we look for the cause of consciousness disturbance, we must proceed systematically. It is important to perform a neurological examination, blood tests (blood glucose level, renal parameters, liver tests, minerals, CRP, blood count, thyroid hormones, etc.), ECG and usually a computed tomography of brain. Heart function can be evaluated by echocardiography. The flow rate through cervical arteries is investigated by an ultrasound. If there is a suspicion on paroxysmal heart arrhythmia presence, it is appropriate to evaluate the patient using the so-called Holter monitor. Further approach is managed according to outcome of previously named examination methods.

Jiri Stefanek, MD  Author of texts: Jiri Stefanek, MD
 Contact: jiri.stefanek@seznam.cz
 Sources: basic text sources