- 1 Anoxia Definition
- 2 Anoxia vs. Hypoxia
- 3 Types of Anoxia and Hypoxia
- 4 Anoxia Symptoms
- 5 Anoxia Causes
- 6 Cardiac Anoxia
- 7 Cerebral Anoxia
- 8 Anoxia Treatment
- 9 Life After Anoxia
The word anoxia in its most general sense simply means the condition of being completely without oxygen and as such can be used in many different scenarios. Here however we are only considering the word’s meaning in a medical context where it refers to the condition where there is a complete absence of an oxygen supply to any organ, tissues or any part of the body. The word itself, like most medical terms, is new Latin but it is formed from three distinct parts with etymological roots being from the Greek. Ox or oximeans the presence of oxygen, the suffix –ia is added to indicate a state or condition and the prefix an- means not or without simply giving the word an opposite meaning. The medical term anoxia therefore means a condition where no oxygen is present. Perhaps a simpler definition of anoxia is oxygen starvation. Anoxia therefore is not a disease in its own right, nor is it a medical symptom but rather a condition brought about by various factors including disease and environmental events. In turn it gives rise to symptoms which can be extremely severe and in cases life-threatening.
Anoxia vs. Hypoxia
Although the term anoxia in its strictest definition refers to a complete absence of oxygen, this is a rare occurrence and in the past there has been a general tendency to incorrectly give this name to the more severe levels of hypoxia. This is the condition when when oxygen levels are lower than normal but there is not a total oxygen deprivation. In some instances, the terms anoxia and hypoxia have erroneously been regarded as being interchangeable. There are various other related terms which often give rise to confusion. The name anoxemia is often used to describe a condition where the blood circulates but has lower than normal oxygen levels. Just as above, this condition should, more correctly, be termed hypoxemia. Obviously, no patient could survive the condition of true anoxemia.
Types of Anoxia and Hypoxia
In considering the various different types of anoxia, it is necessary to also include the condition hypoxia as, in many cases, there is a substantial overlap between the two conditions along with even more confusing nomenclature. There are five basic types of anoxia as follows:
Anemia (anaemia) is a blood condition in which there is a decrease in hemoglobin (haemoglobin) or in the numbers of red blood cells which carry oxygen throughout the body. Parts of the body are therefore deprived of an adequate supply of oxygen. There are many causes of anemia including hemorrhage, iron deficiency and various autoimmune diseases which can seriously deplete red blood cell numbers.
This may sound like a contradiction in terms as we have already remarked that hypoexemia is a form of hypoxia affecting the blood rather than complete anoxia but in this condition, the blood’s hemoglobin is unable to become fully charged with oxygen resulting in a form of anemia but, unlike anemic anoxia above, the condition is not generally associated with low red blood cell numbers but is often due to external factors. Perhaps the best known example of hypoexemic anoxia is the condition known as altitude sickness. At high altitudes, the atmosphere has a lower concentration of oxygen but it is the decrease in atmospheric pressure that prevents the absorption of oxygen into the bloodstream. This is the reason why aircraft have pressurised cabins and mountaineers wear oxygen masks at high altitudes. Another form of hypoexemic anoxia results form carbon monoxide poisoning where the gas binds with the blood hemoglobin to form carboxyhemoglobin in place of the normal oxyhemoglobin.
This is another type of anoxia involving the circulatory system but, as its name implies, this condition arises due to the failure of the blood to flow properly rather than because of any problems with the oxygen carrying capabilities of the red blood cells. Heart disease commonly gives rise to such problems with cardiac arrest being a particularly severe cause but localised anoxia can also be due to problems in certain veins. In the condition known as Raynaud’s Phenomenon, the veins go into temporary spasms causing them to block cutting off the supply of oxygenated blood to the extremities, most commonly the fingers. Such episodes are usually fairly short-lived and seldom cause any serious problems.
Oxygen Affinity Anoxia
This form of anoxia is due to a blood disorder relating to the ability of the red blood cells to absorb and release appropriate levels of oxygen.
Although many cases of anoxia involve problems with the blood, there are cases where the circulatory system satisfactorily carries oxygen around the body but certain organs or tissues fail to utilise the oxygenated blood. This is usually due to the presence of toxins with cyanide poisoning typically showing such symptoms. Various narcotics, alcohols and solvents can also cause this effect and in intensive care units, conditions such as sepsis involve constant monitoring and possible organ support as necessary.
Anoxia is a very serious condition and the exclusion of oxygen from the body’s organs and tissues gives rise to a number of medical symptoms almost all of which signal a medical emergency. Anoxia (and hypoxia) can be either localised affecting a specific area, organ or part of an organ or generalised affecting the whole body. In some cases the causes of anoxia may be quite apparent but in other cases, the clinician may have to make a diagnosis based largely on symptoms along with blood tests. Although by definition, it is impossible to have a mild case of anoxia, its onset may reveal some tell-tale signs such as a bluish colouration to the lips and possibly the ends of the fingers including under the finger nails. The patient may also exhibit signs of confusion, dizziness and poor decision making. Dilated pupils may be noted. Neck stiffness and pain are common as are uncontrolled twitches (myoclonic jerks). Respiratory problems are usually evident such as tachypnea (rapid breathing), laboured breathing, coughing, choking or even not breathing. The symptoms often progress to include tremors, seizures, loss of consciousness and coma.
Anything which impedes the passage of atmospheric oxygen to the parts of the body where it is required may cause anoxia. These causes may be due to either physical/environmental events or a result of a disease process or abnormality.
Anoxia – Physical/Environmental Causes
The most easily understood causes of anoxia are due to the complete failure of the respiratory system to take oxygen into the body. Strangulation, choking and drowning are typical accidental events leading to the condition. Traumatic injuries involving tissue damage and hemorrhage may result in a sudden drop in blood pressure and anoxia. In severe cases, this may cause shock, organ failure and death. Various types of poisoning also give rise to anoxia. Carbon monoxide gas is particularly dangerous due to its ability to combine with hemoglobin forming carboxyhemoglobin in place of the normal oxyhemoglobin but whereas the latter readily reverts to hemoglobin, releasing its charge of oxygen in the process, carboxyhemoglobin does not, meaning that the red blood cells lose their oxygen carrying capabilities. Various other toxins cause histotoxic anoxia and anoxia can also occur as a complication arising from the use of some anesthetics.
Anoxia – Disease Causes
As anoxia is a result of oxygen not reaching parts of the body, it can clearly be seen than the whole of the respiratory and cardiovascular systems play a part in the process of oxygenation, along with several other systems. Any disease or condition impairing the correct functioning of these vital systems has the potential to cause, or contribute to, anoxia. There are literally hundreds of different diseases of the respiratory and cardiovascular systems and describing them all in detail would require a work of encyclopedic proportions but a few of the most commonly encountered are as follows:
Chronic obstructive pulmonary disease – This is a general term for conditions in which the airways of the lungs have become obstructed. It includes the diseases emphysema and chronic bronchitis. Heart disease – There are many heart conditions with the potential to cause anoxia or hypoxia. Cardiac arrest is obviously an immediate cause of anoxia but other conditions such as heart failure and myocardial infarction (heart attack) are also extremely serious with regard to causing anoxia. Respiratory failure is a term used to describe the body’s inability to adequately perform its gas exchange functions in the absorption and release of oxygen and the elimination of carbon dioxide from the body. This condition results in hypoxia possibly leading to anoxia and death. Severe asthma and allergies may also lead to hypoxia and anoxia. Strokes also result in the exclusion of oxygen from part of the brain causing brain cells to die.
Anoxia can be generalised, affecting the whole body, or localised affecting a specific part of the body, organ or part of an organ. As detailed above, heart problems can give rise to the generalised form of anoxia due to inadequate circulation but the heart organ itself may also be affected. The term cardiac anoxia however is rarely used as problems with the supply of oxygenated blood to the heart usually have more specific terms applied to them. Angina pectoris (commonly referred to simply as angina) is a condition where the supply of oxygenated blood serving the heart muscle is restricted.
The most usually cause being atherosclerosis which refers to problems with some of the arteries becoming hardened and narrowed, being lined with plaque. The symptoms usually include pain and a feeling of tightness in the chest which often spreads to the left arm, neck, jaw and possibly the back. Fortunately, the symptoms of an angina attack usually subside after a few minutes. Angina may be considered to be a form of hypoxia. A rather more severe form of oxygen deprivation to the heart occurs with acute myocardial infarction (heart attack). As with angina, the blood supply to the heart is interrupted, in this case usually due to a thrombus or embolus blocking a blood vessel. This results in anoxia and the subsequent death of part of the tissue of the heart. The symptoms are often similar to those experienced during an angina attack but much longer lasting and usually more intense. Needless to say, this constitutes a medical emergency.
Just as with the heart, the brain can be the subject of a specific localised form of anoxia but this condition is normally known by another name, that of course being a stroke. During a stroke, the blood supply to part of the brain is interrupted resulting in anoxia and death of the brain cells in that area. A stroke is caused either by a hemorrhage or by a blockage in one of the small blood vessels. A transient minor blockage is usually referred to as a mini-stroke. In the case of generalised anoxia or hypoxia, the brain is one of the organs most susceptible to serious damage. Although the brain only comprises of around 2% of the total human body weight, it consumes 25% of the body’s oxygen. Following an incident of anoxia, from any cause, the body’s first reaction is usually to increase the supply of blood to the brain in an attempt to restore brain function. This increase is limited to about double the normal rate of blood flow but may be sufficient to effect a remedy in very mild cases. In many cases however, there will have been some disturbance in brain function and symptoms are likely to appear as described above. Generalised anoxia can affect all parts of the brain but some parts appear to be more sensitive to damage than others especially the parietal and occipital lobes of the cerebral cortex and the hippocampus which is important in memory. The basal ganglia and cerebellum, both of which are important in the control of movement, are also particularly susceptible. In severe cases of anoxia, there may be damage to the hypothalmus and pituitary gland which regulates hormones throughout the body, resulting in many forms of hormone imbalance. In very severe cases of cerebral anoxia, brain swelling may occur with the potential for further damage as blood vessels become restricted due to the increased pressure. In some of these very severe cases, the patient may make the transition from unconsciousness to coma eventually passing into a persistent vegetative state (PVS). In some such cases, the decision is sometimes made not to resuscitate in the event of a major complication such as cardiac arrest.
Cerebral anoxia can occur at any time of life and is more common in older people and those with a predisposing condition but one of the most hazardous times of all is at the time of birth. Anoxia is a major cause of birth injury and is a particular risk for premature births where the lungs may not be sufficiently developed to take over the task of oxygenating the blood. Difficult deliveries such as those in which the umbilical cord may be kinked and obstructed pose dangers of anoxia and in some cases an emergency c-section may be required.
As anoxia is a condition rather than a disease, treatment options are rather limited and immediate assistance tends to focus on restoring high oxygen levels by using an oxygen mask or other forms of breathing assistance. The administration of fluids and medications may be advisable in order to stabilise the heart function, increase blood pressure levels where appropriate and to suppress seizures. In some cases, life support systems may be required. Later treatment will then concentrate on dealing with the underlying causes leading to the condition. Once this has been successfully addressed the chances of a recurrence are minimal. However the survival of an anoxic incident is only the first step and any prognosis must be guarded as there is certainly no guarantee of a rapid or complete recovery.
Life After Anoxia
Anoxia can be a life threatening condition and most forms of anoxia, especially cerebral anoxia, often referred to as a hypoxic-anoxic brain injury, or HAI, are a life changing experience. Complete recovery can occur but its pace and extent depend largely on the severity of the injury and on which parts of the brain have been damaged. All aspects of anoxia recovery are extremely unpredictable. In many cases it has a catastrophic impact on a person’s life and may lead to long-term disabilities. The post-anoxia problems can appear as cognitive (thought process) abnormalities or physical difficulties of movement. Short-term memory loss is common and a patient may exhibit poor judgement and decision making. Visual disturbances may result in a limited field of vision or colour recognition and in a rare form of cerebral blindness the patient may think that they are able to see perfectly but are unable to detect obstacles before them. There may be problems with speech and language use and difficulty selecting appropriate words. Weakness of the arms and legs (quadriparesis) is frequently to be seen and walking motion may exhibit a drunken gait known as ataxia. Spasticity and myoclonus disorders cause severe mobility problems with unintentional and uncontrolled movements. There may also be problems in completing a familiar sequence of movements (apraxia) such as bathing or brushing teeth. Mental confusion and agitation may also be observed possibly accompanied by delusions, hallucinations and personality and mood disorders. The road to recovery from HAI is therefore a long and arduous trail with many difficulties along the way both for the patient and those close by.
In some cases a full and complete recovery may follow but in others there may be lasting effects of varying severity. The brain has a way of adapting to its injured state but this takes time and in many cases many everyday tasks need to be completely relearned. The full extent of any recovery remains an unknown quantity but in many cases, the degree of recovery has been shown to bear some correlation to the length of time that the patient may have been in a comatose condition. In cases where the patient did not enter a coma or was in a coma for 12 hours or less, there was often a full and complete recovery. Of patients who had been in a coma for 4 weeks, the statistical chances of full recovery are reduced to around 20% and unfortunately for those who have passed from coma to PVS the outlook is rather more bleak and after a 3 month period in persistent vegetative state, there is very little chance of recovery. Of course there are always exceptions but it is wise to consider the statistical likelihood in such cases.
The most important thing to remember is that anoxia is an extremely serious and potentially life-threatening condition and in any instance where it is suspected, time is of the essence and emergency medical treatment must be obtained without delay.