Hypoxia Health Dictionary

A procedure performed during a mother’s labour in which a blood sample is taken from a vein in the scalp of the FETUS. This enables tests to be performed that indicate whether the fetus is, for example, suffering from a shortage of oxygen (HYPOXIA). If so, the obstetrician will usually accelerate the baby’s birth.... fetal blood sampling

A colourless and odourless gas of molecular weight 32. It constitutes just less than 21 per cent of the earth’s atmosphere. As a medical gas, it is supplied in the UK compressed at high pressure (13,600 kilopascals (KPa)) in cylinders which are black with white shoulders. In hospitals, oxygen is often stored as a liquid in insulated tanks and controlled evaporation allows the gas to be supplied via a pipeline at a much lower pressure.

Oxygen is essential for life. It is absorbed via the lungs (see RESPIRATION) and is transported by HAEMOGLOBIN within the ERYTHROCYTES to the tissues. Within the individual cell it is involved in the production of adenosine triphosphate (ATP), a compound that stores chemical energy for muscle cells, by the oxidative metabolism of fats and carbohydrates. HYPOXIA causes anaerobic metabolism with a resulting build-up in LACTIC ACID, the result of muscle cell activity. If severe enough, the lack of ATP causes a breakdown in cellular function and the death of the individual.

When hypoxia occurs, it may be corrected by giving supplemental oxygen. This is usually given via a face mask or nasal prongs or, in severe cases, during ARTIFICIAL VENTILATION OF THE LUNGS. Some indications for oxygen therapy are high altitude, ventilatory failure, heart failure, ANAEMIA, PULMONARY HYPERTENSION, CARBON MONOXIDE (CO) poisoning, anaesthesia and post-operative recovery. In some conditions – e.g. severe infections with anaerobic bacteria and CO poisoning – hyperbaric oxygen therapy has been used.... oxygen

A complete absence of oxygen in a body tissue. Anoxia causes disruption of cell metabolism and cell death unless corrected within a few minutes. Anoxia occurs during cardiopulmonary arrest or asphyxiation and will cause permanent organ damage or even death if not corrected. (See also hypoxia.)... anoxia

In?ammation of the alveoli (see ALVEOLUS) of the lungs caused by an allergic reaction. When the in?ammation is caused by infection it is called PNEUMONIA, and when by a chemical or physical agent it is called pneumonitis. It may be associated with systemic sclerosis or RHEUMATOID ARTHRITIS.

Extrinsic allergic alveolitis is the condition induced by the lungs becoming allergic (see ALLERGY) to various factors or substances. It includes BAGASSOSIS, FARMER’S LUNG and BUDGERIGAR-FANCIER’S LUNG, and is characterised by the onset of shortness of breath, tightness of the chest, cough and fever. The onset may be sudden or gradual. Treatment consists of removal of the affected individual from the o?ending material to which he or she has become allergic. CORTICOSTEROIDS give temporary relief.

Fibrosing alveolitis In this disease there is di?use FIBROSIS of the walls of the alveoli of the lungs. This causes loss of lung volume with both forced expiratory volume and vital capacity affected, but the ratio between them remaining normal. The patient complains of cough and progressive DYSPNOEA. Typically the patient will be cyanosed (blue – see CYANOSIS), clubbed (see CLUBBING), and have crackles in the mid- and lower-lung ?elds. Blood gases will reveal HYPOXIA and, in early disease, hypocapnia (de?ciency of carbon dioxide in the blood due to hyperventilation). There is an association with RHEUMATOID ARTHRITIS (about one-eighth of cases), systemic lupus erythematosus (see under LUPUS), and systemic SCLEROSIS. Certain drugs – for example, bleomycin, busulphan and hexamethonium – may also cause this condition, as may high concentrations of oxygen, and inhalation of CADMIUM fumes.... alveolitis

A general term meaning the cessation of breathing. Apnoea is a medical emergency: death soon follows if breathing is not quickly restored (see APPENDIX 1: BASIC FIRST AID). Apnoea may be caused by an obstruction to the airway, for example by the tongue during general ANAESTHESIA, or by a disturbance of the mechanisms that control breathing. Rapid heavy breathing reduces the blood levels of carbon dioxide and can lead to a brief period of apnoea.

Neonatal apnoeic attacks may represent a serious emergency, being caused by prematurity, milk aspiration, heart failure, infection, HYPOXIA, HYPOGLYCAEMIA or HYPOCALCAEMIA. If stimulation of the baby does not immediately restore breathing, then bag-and-mask ventilation should be used.... apnoea

Rapidly alternating contractions and relaxations of the muscles, causing irregular movements of the limbs or body generally, usually accompanied by unconsciousness.

Causes The most common reason for convulsions is EPILEPSY, and the underlying cause of the latter often remains uncertain. In newborns, convulsions may be due to HYPOXIA following a di?cult labour, or to low levels of sugar or calcium in the blood (HYPOGLYCAEMIA; HYPOCALCAEMIA). A sudden rise of body temperature during infective illness may induce convulsions in an infant or young child.

Diseases of the brain, such as meningitis, encephalitis and tumours, or any disturbance of the brain due to bleeding, blockage of a blood vessel, or irritation of the brain by a fracture of the skull, may also be responsible for convulsions (see BRAIN, DISEASES OF).

Asphyxia, for example from choking, may also bring on convulsions.

Treatment Newborns with hypoglycaemia or hypocalcaemia are treated by replacing the missing compound. Infants with febrile convulsions may be sponged with tepid water and fever reduced with paracetamol.

In epilepsy, unless it is particularly severe, the movements seldom need to be restrained. If convulsions persist beyond a few minutes it may be necessary to give BENZODIAZEPINES, either intravenously or rectally. In the UK, paramedics are trained to do this; likewise many parents of epileptic children are capable of administering the necessary treatment. If however this fails to stop the convulsions immediately, hospital admission is needed for further treatment. Once ?ts are under control, the cause of the convulsions must be sought and the necessary long-term treatment given.... convulsions

Cyanide inhibits cellular RESPIRATION by binding rapidly and reversibly with the ENZYME, cytochrome oxidase. E?ects of poisoning are due to tissue HYPOXIA. Cyanide is toxic by inhalation, ingestion and prolonged skin contact, and acts extremely quickly once absorbed. Following inhalation of hydrogen cyanide gas, death can occur within minutes. Ingestion of inorganic cyanide salts may produce symptoms within 10 minutes, again proceeding rapidly to death. On a full stomach, effects may be delayed for an hour or more. Signs of cyanide poisoning are headache, dizziness, vomiting, weakness, ATAXIA, HYPERVENTILATION, DYSPNOEA, HYPOTENSION and collapse. Loss of vision and hearing may occur, then COMA and CONVULSIONS. Other features include cardiac ARRHYTHMIA and PULMONARY OEDEMA. Patients may have a lactic ACIDOSIS. Their arterial oxygen tension is likely to be normal, but their venous oxygen tension high and similar to that of arterial blood.

Treatment Administration of oxygen when available is the most important ?rst-aid management. Rescuers should be trained, must not put themselves at risk, and should use protective clothing and breathing apparatus. In unconscious victims, establish a clear airway and give 100 per cent oxygen. If breathing stops and oxygen is unavailable, initiate expired-air resuscitation. If cyanide salts were ingested, mouth-to-mouth contact must be avoided and a mask with a one-way valve employed instead. Some commercially available ?rst-aid kits contain AMYL NITRATE as an antidote which may be employed if oxygen is unavailable.

Once in hospital, or if a trained physician is on the scene, then antidotes may be administered. There are several di?erent intravenous antidotes that may be used either alone or in combination. In mild to moderate cases, sodium thiosulphate is usually given. In more severe cases either dicobalt edetate or sodium nitrite may be used, followed by sodium thio-sulphate. Some of these (e.g. dicobalt edetate) should be given only where diagnosis is certain, otherwise serious adverse reations or toxicity due to the antidotes may occur.... cyanide poisoning

An abnormally rapid resting respiratory rate (see RESPIRATION). If voluntarily induced, it causes lightheadedness and then unconsciousness by lowering the blood tension of carbon dioxide.

Hyperventilation is a manifestation of chest and heart diseases which raise carbon dioxide tension or cause HYPOXIA (e.g. severe CHRONIC OBSTRUCTIVE PULMONARY DISEASE (COPD) or PULMONARY OEDEMA). Mechanically ventilated patients may be hyperventilated to lower carbon dioxide tension in order to reduce INTRACRANIAL PRESSURE. (See also HYPOCAPNIA.)... hyperventilation

This is a colourless, odourless, tasteless, nonirritating gas formed on incomplete combustion of organic fuels. Exposure to CO is frequently due to defective gas, oil or solid-fuel heating appliances. CO is a component of car exhaust fumes and deliberate exposure to these is a common method of suicide. Victims of ?res often suffer from CO poisoning. CO combines reversibly with oxygen-carrying sites of HAEMOGLOBIN (Hb) molecules with an a?nity 200 to 300 times greater than oxygen itself. The carboxyhaemoglobin (COHb) formed becomes unavailable for oxygen transportation. In addition the partial saturation of the Hb molecule results in tighter oxygen binding, impairing delivery to the tissues. CO also binds to MYOGLOBIN and respiratory cytochrome enzymes. Exposure to CO at levels of 500 parts per million (ppm) would be expected to cause mild symptoms only and exposure to levels of 4,000 ppm would be rapidly fatal.

Each year around 50 people in the United Kingdom are reported as dying from carbon monoxide poisoning, and experts have suggested that as many as 25,000 people a year are exposed to its effects within the home, but most cases are unrecognised, unreported and untreated, even though victims may suffer from long-term effects. This is regrettable, given that Napoleon’s surgeon, Larrey, recognised in the 18th century that soldiers were being poisoned by carbon monoxide when billeted in huts heated by woodburning stoves. In the USA it is estimated that 40,000 people a year attend emergency departments suffering from carbon monoxide poisoning. So prevention is clearly an important element in dealing with what is sometimes termed the ‘silent killer’. Safer designs of houses and heating systems, as well as wider public education on the dangers of carbon monoxide and its sources, are important.

Clinical effects of acute exposure resemble those of atmospheric HYPOXIA. Tissues and organs with high oxygen consumption are affected to a great extent. Common effects include headaches, weakness, fatigue, ?ushing, nausea, vomiting, irritability, dizziness, drowsiness, disorientation, incoordination, visual disturbances, TACHYCARDIA and HYPERVENTILATION. In severe cases drowsiness may progress rapidly to COMA. There may also be metabolic ACIDOSIS, HYPOKALAEMIA, CONVULSIONS, HYPOTENSION, respiratory depression, ECG changes and cardiovascular collapse. Cerebral OEDEMA is common and will lead to severe brain damage and focal neurological signs. Signi?cant abnormalities on physical examination include impaired short-term memory, abnormal Rhomberg’s test (standing unsupported with eyes closed) and unsteadiness of gait including heel-toe walking. Any one of these signs would classify the episode as severe. Victims’ skin may be coloured pink, though this is very rarely seen even in severe incidents. The venous blood may look ‘arterial’. Patients recovering from acute CO poisoning may suffer neurological sequelae including TREMOR, personality changes, memory impairment, visual loss, inability to concentrate and PARKINSONISM. Chronic low-level exposures may result in nausea, fatigue, headache, confusion, VOMITING, DIARRHOEA, abdominal pain and general malaise. They are often misdiagnosed as in?uenza or food poisoning.

First-aid treatment is to remove the victim from the source of exposure, ensure an e?ective airway and give 100-per-cent oxygen by tight-?tting mask. In hospital, management is largely suppportive, with oxygen administration. A blood sample for COHb level determination should be taken as soon as practicable and, if possible, before oxygen is given. Ideally, oxygen therapy should continue until the COHb level falls below 5 per cent. Patients with any history of unconsciousness, a COHb level greater than 20 per cent on arrival, any neurological signs, any cardiac arrhythmias or anyone who is pregnant should be referred for an expert opinion about possible treatment with hyperbaric oxygen, though this remains a controversial therapy. Hyperbaric oxygen therapy shortens the half-life of COHb, increases plasma oxygen transport and reverses the clinical effects resulting from acute exposures. Carbon monoxide is also an environmental poison and a component of cigarette smoke. Normal body COHb levels due to ENDOGENOUS CO production are 0.4 to

0.7 per cent. Non-smokers in urban areas may have level of 1–2 per cent as a result of environmental exposure. Smokers may have a COHb level of 5 to 6 per cent.... carbon monoxide (co)

Linn.

Family: Ginkgoaceae.

Habitat: Native to China and Japan; cultivated in Indian gardens as an ornamental.

English: Maidenhair tree called Living Fossils (in India), Kew tree.

Action: Antagonizes bronchospasm, used as a circulatory stimulant, peripheral vasodilator.

Key application: Standardized dry extract—for symptomatic treatment of disturbed performance in organic brain syndrome within the regimen ofa therapeutic concept in cases of dementia syndromes— memory deficits, disturbance in concentration, depressive emotional conditions, dizziness, tinnitus and headache. (German Commission E, ESCOP, WHO.) As vasoactive and platelet aggregation inhibitor.

(The British Herbal Pharmacopoeia.) (For pharmocological studies in humans and clinical studies, see ESCOP.)

The majority of pharmacological studies and clinical trials have been conduced using a standardized extract which contains 24% flavonoid glyco- sides (Ginko flavone glycosides) and 6% terpenoids (ginkgolides and bilob- alide).

The extract increases tolerance to hypoxia and exhibits anti-ischaemic effect. It simultaneously improves the fluidity of blood, decreases platelet adhesion, decreases platelet and erythro- cyte aggregation and reduces plasma and blood viscosity. The extract protects erythrocytes from haemolysis. The extract also decreases the permeability of capillaries and protects the cell membrane by trapping deleterious free radicals.

The extract also increased cerebral blood flow in about 70% patients evaluated (patients between 30-50 year age had 20% increase from the base line, compared with 70% in those 50- to 70- year-olds).

A reversal of sexual dysfunction with concurrent use of ginkgo with antidepressant drugs has been reported. (Am J Psychiatry, 2000 157(5), 836837.)

The National Centre for Complementary and Alternative Medicine, USA, is conducting a 5-year study of 3000 people aged 75 and older to determine if ginkgo, 240 mg daily, prevents dementia or Alzheimer's disease.... ginkgo biloba

Shallow and/or slow breathing, often caused by the effects of injury or drugs on the respiratory centre. It causes HYPERCAPNIA and HYPOXIA.... hypoventilation

A derivative of HAEMOGLOBIN in which the iron has been oxidised from ferrous to ferric form. It does not combine with oxygen and therefore plays no part in oxygen transport. Normal concentration of methaemoglobin in red blood cells is less than 1 per cent of the total haemoglobin. When a large concentration of the haemoglobin is in the form of methaemoglobin, the patient will suffer from HYPOXIA and will be cyanosed (see CYANOSIS). Most cases of METHAEMOGLOBINAEMIA are due to chemical agents.... methaemoglobin

A core body temperature of less than 35 °C. As the temperature of the body falls, there is increasing dysfunction of all the organs, particularly the central nervous and cardiovascular systems. The patient becomes listless and confused, with onset of unconsciousness between 33–28 °C. Cardiac output at ?rst rises with shivering but then falls progressively, as do the oxygen requirements of the tissues. Below 17– 26 °C, cardiac output is insu?cient even to supply this reduced demand for oxygen by the tissues. The heart is susceptible to spontaneous ventricular FIBRILLATION below 28 °C. Metabolism is disturbed and the concentration of blood GLUCOSE and POTASSIUM rises as the temperature falls. Cooling of the kidneys produces a DIURESIS and further ?uid loss from the circulation to the tissues causes HYPOVOLAEMIA.

Severe hypothermia is sometimes complicated by gastric erosions and haemorrhage, as well as pancreatitis (see PANCREAS, DISORDERS OF). Infants and the elderly are less e?cient at regulating temperature and conserving heat than other age groups, and are therefore more at risk from accidental hypothermia during cold weather if their accommodation is not warm enough. Approximately half a million elderly people are at risk in Britain each winter from hypothermia. The other major cause of accidental hypothermia is near-drowning in icy water. Deliberate hypothermia is sometimes used to reduce metabolic rate so that prolonged periods of cardiac arrest may occur without tissue HYPOXIA developing. This technique is used for some cardiac and neurosurgical operations and is produced by immersion of the anaesthetised patient in iced water or by cooling an extracorporeal circulation.

Treatment of hypothermia is by warming the patient and treating any complications that arise. Passive warming is usual, with conservation of the patient’s own body heat with insulating blankets. If the core temperature is below 28 °C, then active rewarming should be instituted by means of warm peritoneal, gastric or bladder lavage or using an extracorporeal circulation. Care must be taken in moving hypothermic patients, as a sudden rush of cold peripheral blood to the heart can precipitate ventricular ?brillation. Prevention of hypothermia in the elderly is important. Special attention must be paid to diet, heating the home and adequate clothing in several layers to limit heat loss.... hypothermia

Perinatal mortality consists of deaths of the FETUS after the 28th week of pregnancy and deaths of the newborn child during the ?rst week of life. Today, more individuals die within a few hours of birth than during the following 40 years. It is therefore not surprising that the perinatal mortality rate, which is the number of such deaths per 1,000 total births, is a valuable indicator of the quality of care provided for the mother and her newborn baby. In 2002, the perinatal mortality rate was 7.87 in the United Kingdom compared with 11.4 in 1982 – and over 30 in the early 1960s.

The causes of perinatal mortality include extreme prematurity, intrapartum anoxia (that is, di?culty in the birth of the baby, resulting in lack of oxygen), congenital abnormalities of the baby, and antepartum anoxia (that is, conditions in the terminal stages of pregnancy preventing the fetus from getting su?cient oxygen).

The most common cause of perinatal death is some complication of placenta, cord or membranes. The next most common is congenital abnormality. Intrauterine hypoxia and birth asphyxia comprise the third most common cause.... perinatal mortality

Fluid in the small air sacs of the lungs, from inefficient pumping by the heart or leakage of fluid from the blood vessels in the lungs (possibly from envenomation). As it prevents air exchange in the lungs it causes hypoxia and may lead to death.... pulmonary oedema

Naturally produced in the LUNGS by cells called pneumocytes, this substance is a mixture of phospholipids (see PHOSPHOLIPID) and LIPOPROTEINS. Present in ?uid lining the alveoli (see ALVEOLUS) in the lungs, their action helps maintain their patency. Premature babies may have a de?ciency of surfactant, a disorder which causes severe breathing diffculties – RESPIRATORY DISTRESS SYNDROME or hyaline membrane disease – and HYPOXIA. They will need urgent respiratory support, which includes oxygen and the administration (via an endotracheal tube) of a specially prepared surfactant such as beractant (bovine lung extract) or edfosceril palmitate.... pulmonary surfactant

An appliance used in oxygen therapy that separates oxygen from the air and mixes it back in at a greater concentration. This oxygenenriched air is delivered through a tube for prolonged inhalation. The appliance is used by people who have persistent hypoxia due to severe chronic obstructive pulmonary disease (see pulmonary disease, chronic obstructive). (See also hyperbaric oxygen treatment.)... oxygen concentrator

The simplest form of intermittent positive-pressure ventilation is mouth-to-mouth resuscitation (see APPENDIX 1: BASIC FIRST AID) where an individual blows his or her own expired gases into the lungs of a non-breathing person via the mouth or nose. Similarly gas may be blown into the lungs via a face mask (or down an endotracheal tube) and a self-in?ating bag or an anaesthetic circuit containing a bag which is in?ated by the ?ow of fresh gas from an anaesthetic machine, gas cylinder, or piped supply. In all these examples expiration is passive.

For more prolonged arti?cial ventilation it is usual to use a specially designed machine or ventilator to perform the task. The ventilators used in operating theatres when patients are anaesthetised and paralysed are relatively simple devices.They often consist of bellows which ?ll with fresh gas and which are then mechanically emptied (by means of a weight, piston, or compressed gas) via a circuit or tubes attached to an endotracheal tube into the patient’s lungs. Adjustments can be made to the volume of fresh gas given with each breath and to the length of inspiration and expiration. Expiration is usually passive back to the atmosphere of the room via a scavenging system to avoid pollution.

In intensive-care units, where patients are not usually paralysed, the ventilators are more complex. They have electronic controls which allow the user to programme a variety of pressure waveforms for inspiration and expiration. There are also programmes that allow the patient to breathe between ventilated breaths or to trigger ventilated breaths, or inhibit ventilation when the patient is breathing.

Indications for arti?cial ventilation are when patients are unable to achieve adequate respiratory function even if they can still breathe on their own. This may be due to injury or disease of the central nervous, cardiovascular, or respiratory systems, or to drug overdose. Arti?cial ventilation is performed to allow time for healing and recovery. Sometimes the patient is able to breathe but it is considered advisable to control ventilation – for example, in severe head injury. Some operations require the patient to be paralysed for better or safer surgical access and this may require ventilation. With lung operations or very unwell patients, ventilation is also indicated.

Arti?cial ventilation usually bypasses the physiological mechanisms for humidi?cation of inspired air, so care must be taken to humidify inspired gases. It is important to monitor the e?cacy of ventilation – for example, by using blood gas measurement, pulse oximetry, and tidal carbon dioxide, and airways pressures.

Arti?cial ventilation is not without its hazards. The use of positive pressure raises the mean intrathoracic pressure. This can decrease venous return to the heart and cause a fall in CARDIAC OUTPUT and blood pressure. Positive-pressure ventilation may also cause PNEUMOTHORAX, but this is rare. While patients are ventilated, they are unable to breathe and so accidental disconnection from the ventilator may cause HYPOXIA and death.

Negative-pressure ventilation is seldom used nowadays. The chest or whole body, apart from the head, is placed inside an airtight box. A vacuum lowers the pressure within the box, causing the chest to expand. Air is drawn into the lungs through the mouth and nose. At the end of inspiration the vacuum is stopped, the pressure in the box returns to atmospheric, and the patient exhales passively. This is the principle of the ‘iron lung’ which saved many lives during the polio epidemics of the 1950s. These machines are cumbersome and make access to the patient di?cult. In addition, complex manipulation of ventilation is impossible.

Jet ventilation is a relatively modern form of ventilation which utilises very small tidal volumes (see LUNGS) from a high-pressure source at high frequencies (20–200/min). First developed by physiologists to produce low stable intrathoracic pressures whilst studying CAROTID BODY re?exes, it is sometimes now used in intensive-therapy units for patients who do not achieve adequate gas exchange with conventional ventilation. Its advantages are lower intrathoracic pressures (and therefore less risk of pneumothorax and impaired venous return) and better gas mixing within the lungs.... intermittent positive pressure (ipp)

PVS may occur in patients with severe brain damage from HYPOXIA or injury. Patients do not display any awareness of their surroundings, and are unable to communicate. Sleep alternates with apparent wakefulness, when some re?exes (see REFLEX ACTION) may be present: for example, patients’ eyes may re?exly follow or respond to sound, their limbs can re?exly withdraw from pain, and their hands can re?exly grope or grasp. Patients can breathe spontaneously, and retain normal heart and kidney function, although they are doubly incontinent (see INCONTINENCE).

For a diagnosis of PVS to be made, the state should have continued for more than a prede?ned period, usually one month. Half of patients die within 2–6 months, but some can survive for longer with arti?cial feeding. To assess a person’s level of consciousness, a numerical marking system rated according to various functions – eye opening, motor and verbal responses – has been established called the GLASGOW COMA SCALE.

The ETHICS of keeping patients alive with arti?cial support are controversial. In the UK, a legal ruling is usually needed for arti?cial support to be withdrawn after a diagnosis of PVS has been made. The chances of regaining consciousness after one year are slim and, even if patients do recover, they are usually left with severe neurological disability.

PVS must be distinguished from conditions which appear similar. These include the ‘LOCKED-IN SYNDROME’ which is the result of damage to the brain stem (see BRAIN). Patients with this syndrome are conscious but unable to speak or move except for certain eye movements and blinking. The psychiatric state of CATATONIA is another condition in which the patient retains consciousness and will usually recover.... persistent vegetative state (pvs)

The process of supplying a person with oxygen-enriched air to relieve severe hypoxia (inadequate oxygen in body tissues). The oxygen is usually delivered through a face-mask or a nasal cannula (a length of narrow plastic tubing with two prongs that are inserted into the nostrils). Piped oxygen is used in hospitals; oxygen in cylinders can be used at home for acute attacks of hypoxia, such as those occurring in severe asthma. Long-term therapy for people with persistent hypoxia may involve the use of an oxygen concentrator.

(See also hyperbaric oxygen treatment.)... oxygen therapy

A condition in which there is a buildup of carbon dioxide and a fall in the level of oxygen in the blood (see hypoxia). Causes include lung disorders, such as severe asthma, emphysema, or chronic bronchitis (see pulmonary disease, chronic obstructive), or damage to the respiratory centre in the brain due to, for example, an overdose of opioid drugs, a stroke, or serious head injury.

Treatment is with ventilation and oxygen for the underlying cause.... respiratory failure

The constriction of a passage or tube in the body that blocks the blood ?ow and disturbs the working of the affected organ. It is usually caused by compression or twisting. Strangulation customarily occurs when part of the INTESTINE herniates either inside the abdomen or outside as in an inguinal HERNIA. If a section of the intestine twists, this may strangulate and is known as a VOLVULUS.

Strangulation of a person’s neck, either with a ligature or with the hands, obstructs the jugular veins in the neck, preventing the normal out?ow of blood from the brain and head. The TRACHEA is also compressed, cutting o? the supply of air to the lungs. The combination of these effects leads to HYPOXIA and damage to the brain. If not quickly relieved, unconsciousness and death follow. Strangulation may be deliberate or accidental – the latter being a particular hazard for children, for example, when playing with a rope. Removal of the constriction, arti?cial respiration, and medical attention are urgently necessary.... strangulation

The BRAIN is the organ of the mind. Normal conscious alertness depends upon its continuous adequate supply with oxygen and glucose, both of which are essential for the brain cells to function normally. If either or both of these are interrupted, altered consciousness results. Interruption may be caused by three broad types of process affecting the brain stem: the reticular formation (a network of nerve pathways and nuclei-connecting sensory and motor nerves to and from the cerebrum, cerebellum, SPINAL CORD and cranial nerves) and the cerebral cortex. The three types are di?use brain dysfunction – for example, generalised metabolic disorders such as URAEMIA or toxic disorders such as SEPTICAEMIA; direct effects on the brain stem as a result of infective, cancerous or traumatic lesions; and indirect effects on the brain stem such as a tumour or OEDEMA in the cerebrum creating pressure within the skull. Within these three divisions are a large number of speci?c causes of unconsciousness.

Unconsciousness may be temporary, prolonged or inde?nite (see PERSISTENT VEGETATIVE STATE (PVS)), depending upon the severity of the initiating incident. The patient’s recovery depends upon the cause and success of treatment, where given. MEMORY may be affected, as may motor and sensory functions; but short periods of unconsciousness as a result, say, of trauma have little obvious e?ect on brain function. Repeated bouts of unconsciousness (which can happen in boxing) may, however, have a cumulatively damaging e?ect, as can be seen on CT (COMPUTED TOMOGRAPHY) scans of the brain.

POISONS such as CARBON MONOXIDE (CO), drug overdose, a fall in the oxygen content of blood (HYPOXIA) in lung or heart disease, or liver or kidney failure harm the normal chemical working or metabolism of nerve cells. Severe blood loss will cause ANOXIA of the brain. Any of these can result in altered brain function in which impairment of consciousness is a vital sign.

Sudden altered consciousness will also result from fainting attacks (syncope) in which the blood pressure falls and the circulation of oxygen is thereby reduced. Similarly an epileptic ?t causes partial or complete loss of consciousness by causing an abrupt but temporary disruption of the electrical activity in the nerve cells in the brain (see EPILEPSY).

In these events, as the brain’s function progressively fails, drowsiness, stupor and ?nally COMA ensue. If the cause is removed (or when the patient spontaneously recovers from a ?t or faint), normal consciousness is usually quickly regained. Strokes (see STROKE) are sometimes accompanied by a loss of consciousness; this may be immediate or come on slowly, depending upon the cause or site of the strokes.

Comatose patients are graded according to agreed test scales – for example, the GLASGOW COMA SCALE – in which the patient’s response to a series of tests indicate numerically the level of coma.

Treatment of unconscious patients depends upon the cause, and range from ?rst-aid care for someone who has fainted to hospital intensive-care treatment for a victim of a severe head injury or massive stroke.... unconsciousness

Formation of a blood clot within vessels of the brain. May be due to atheroma or embolism causing a blockage resulting in hypoxia (oxygen deficiency).

Alternatives. Teas. Lime flowers, Nettles, Horsetail, Ginkgo, Oats, Mistletoe, Yarrow.

Tea. Mix equal parts: Ginkgo, Hawthorn, Yarrow. One heaped teaspoon to each cup boiling water; infuse 5-10 minutes; 1 cup thrice daily.

Tablets/capsules. Ginkgo, Hawthorn, Prickly Ash.

Diet. See: DIET–HEART AND CIRCULATION.

Supplements. Daily: Vitamin E 1000mg; B6 50mg; B12 2mcg. Selenium 200mcg; Zinc 15mg. Strict bedrest; regulate bowels; avoid excessive physical and mental exertion. ... cerebral thrombosis

deterioration in renal function (of more than 25%) after administration of radiocontrast material. Development of this condition is more likely when there is pre-existing renal disease (the most important factor) or diabetes, vasoconstriction, simultaneous use of NSAIDs, and large amounts of radiocontrast are used. It is thought that the radiocontrast induces vasoconstriction in the vessels supplying the medulla of the kidney and aggravates hypoxia in this part of the kidney.... contrast nephropathy

soft fluffy spots in the retina resulting from accumulations of *axoplasm in the nerve-fibre layer of the retina. These may indicate diseases causing hypoxia (oxygen deficiency) in the nerve-fibre layer (e.g. diabetes, hypertension, connective-tissue disease, or AIDS).... cotton-wool spots

Degeneration or death of nerve cells and tracts within the brain that may be localized to a particular area of the brain or diffuse. Diffuse damage most commonly results from prolonged cerebral hypoxia (which may occur in a baby during a difficult birth), cardiac arrest, respiratory arrest, or causes such as poisoning or status epilepticus (prolonged convulsions). The damage may also occur gradually due to environmental pollutants such as lead or mercury compounds (see Minamata disease) or if nerve-cell poisons build up in the brain, as in untreated phenylketonuria. Other possible causes include brain infections such as encephalitis.

Localized brain damage may occur as a result of a head injury, stroke, brain tumour, or brain abscess. At birth, a raised blood level of bilirubin (in haemolytic disease of the newborn) causes local damage to the basal ganglia deep within the brain. This leads to a condition called kernicterus. Brain damage that occurs before, during, or after birth may result in cerebral palsy.

Damage to the brain may result in disabilities such as learning difficulties or disturbances of movement or speech.

Nerve cells and tracts in the brain and spinal cord cannot repair themselves once they have been damaged, but some return of function may be possible.... brain damage

Defects and disorders of the brain, which may have one of numerous causes including infection, injury, brain tumour, or a lack of blood or oxygen (hypoxia). Because the brain is encased in the skull, any space-occupying tumour, brain abscess, or haematoma creates raised pressure, which impairs the function of the whole brain. Brain disorders that are localized in a small region may affect a specific function such as speech (see aphasia). More often, damage is more diffuse and the symptoms can be varied and numerous. Some brain disorders are congenital due to genetic or chromosomal disorders, as in Down’s syndrome. Structural defects that arise during the development of the fetus in the womb include hydrocephalus and anencephaly.

Reduced oxygen supply may occur at birth, causing cerebral palsy. Later in life, cerebral hypoxia can result from choking or from arrest of breathing and heartbeat. From middle age onwards, cerebrovascular disease is the most important cause of brain disorder. If an artery within the brain becomes blocked or ruptures, leading to haemorrhage, the result is a stroke. The brain may also be damaged by a blow to the head see head injury).

Infection within the brain (encephalitis) may be due to viral infection. Infection of the membranes surrounding the brain (meningitis) is generally due to bacterial infection. Creutzfeldt–Jakob disease is a rare, fatal brain disease associated with an infective agent called a prion which, in some cases, has been linked with (bovine spongiform encephalopathy), a disease in cattle.

Multiple sclerosis is a progressive disease of the brain and spinal cord. Degenerative brain diseases include Alzheimer’s disease and Parkinson’s disease. Emotional or behavioural disorders are generally described as psychiatric illnesses; but the distinction between neurological and psychiatric disorders is now much less clear.... brain, disorders of

Death caused by suffocation and hypoxia (lack of oxygen) associated with immersion in a fluid. Most often, the person inhales liquid into the lungs; sometimes, no liquid enters the lungs, a condition called dry drowning (see drowning, dry). People who are resuscitated after prolonged immersion are said to be victims of “near drowning”.

Initially, automatic contraction of a muscle at the entrance to the windpipe, a mechanism called the laryngeal reflex, prevents water from entering the lungs; instead it enters the oesophagus and stomach.

However, the laryngeal reflex impairs breathing and can quickly lead to hypoxia and to loss of consciousness.

If the person is buoyant at this point and floats face-up, his or her chances of survival are reasonable because the laryngeal reflex begins to relax and normal breathing may resume.

An ambulance should be called and the person’s medical condition assessed.

If breathing and/or the pulse is absent, resuscitative measures should be started (see artificial respiration; cardiopulmonary resuscitation) and continued until an ambulance or doctor arrives.

Victims can sometimes be resuscitated, despite a long period immersed in very cold water (which reduces the body’s oxygen needs) and the initial appearance of being dead.

In all cases of successful resuscitation, the person should be sent to a hospital.... drowning

A condition in which deoxygenated blood flows directly back into the circulation rather than through the lungs, due to an abnormal connection between the left and right sides of the heart and pulmonary hypertension. The resultant hypoxia causes cyanosis, fainting, and breathing difficulty. The disorder most often occurs in people with certain congenital heart defects (see heart disease, congenital), such as ventricular septal defect, that have not been corrected.

The diagnosis is confirmed by cardiac catheterization.

Once Eisenmenger complex has developed, surgical correction of the original defect will not help.

Drug treatment may control symptoms.... eisenmenger complex

A condition in which increased production of red blood cells leads to an unusually large number of them in the blood. This condition is usually caused by another disorder or by hypoxia, and is called secondary polycythaemia. If it occurs for no apparent reason, it is called polycythaemia vera or primary polycythaemia.

Secondary polycythaemia occurs naturally at high altitudes due to the reduced oxygen level. It can also result from a disorder that impairs the oxygen supply to the blood, or can be secondary to liver cancer or some kidney disorders. Descending to sea level, or effective treatment of an underlying disorder, returns the blood to normal.Polycythaemia vera is a rare disorder that mainly affects people over 40. The large number of red blood cells causes increased volume and thickening of the blood, which may lead to headaches, blurred vision, and hypertension. There may also be flushed skin, dizziness, night sweats, and widespread itching. The

spleen is often enlarged. Possible complications include a tendency to bleed easily or to form blood clots; stroke; and myelofibrosis or acute leukaemia (see leukaemia, acute).

Diagnosis is made from a physical examination and blood tests and by ruling out other causes. Treatment is by venesection, sometimes in combination with anticancer drugs or with radioactive phosphorus. This enables most patients to survive for 10–15 years.... polycythaemia