Uremia

Uremia, presence in the bloodstream of too many chemical wastes such as urea, a nitrogen-rich waste product attributable to extra protein in the diet. As chemical wastes build up in the body they produce a toxic effect, possibly resulting in drowsiness, irritability, nausea, vomiting, breathlessness, headaches, and muscle cramps. In extreme cases, uremia may cause convulsions, coma, or death.

The kidneys normally filter chemical wastes from the blood and send them to the urinary system for elimination from the body.

Uremia most commonly develops when the kidneys fail to function properly. In some cases, however, uremia occurs when blood flow to the kidneys is reduced due to severe bleeding, serious burns, or heart attack, or when more wastes are formed in the bloodstream as a result of traumatic injuries or large surgical incisions than can be removed by the kidneys. A kidney stone, a tumor in the urinary tract, or a severely enlarged prostate in males may also cause uremia.

Victims of uremia due to kidney failure undergo kidney dialysis, a medical procedure that removes wastes from the blood. Transplantation of kidneys from healthy donors to uremic patients has also proven effective in some cases.

Encephalitis

Encephalitis, any infectious disease of the human central nervous system characterized by inflammation of the brain. The typical symptoms are headache, fever, and extreme lethargy, which lead eventually to coma; double vision, delirium, deafness, and facial palsy often occur in the acute stage of the disease. Aftereffects of encephalitis may include deafness, epilepsy, and dementia.

Several types of encephalitis are caused by viral infection of the central nervous system. These types fall into two main groups, primary neurotropic-virus infections (original virus infections in nerve tissues), and secondary infections occurring as complications of a primary virus infection elsewhere in the body.

NEUROTROPIC-VIRUS ENCEPHALITIS

This group comprises several epidemic diseases that primarily affect wild and domestic animals and birds. The disease is transmitted to humans from these animals by insect vectors. St. Louis encephalitis, first recognized in 1933 during an epidemic in St. Louis, Missouri, is transmitted to humans by mosquito bites. Other mosquito-borne types of encephalitis are Japanese B encephalitis, California encephalitis, and equine encephalomyelitis. Ticks are the insect vectors of Russian spring-summer encephalitis.

SECONDARY VIRUS INFECTIONS

This group includes two types, postinfective encephalitis and postvaccinal encephalitis. The first type occurs as an occasional complication of certain viral diseases, including mumps, measles, influenza, and yellow fever. Occasionally infections with the herpes virus involve the brain and cause brain damage or death. The second type may occur, although very infrequently, following the first vaccination with such attenuated-virus vaccines as those against smallpox and yellow fever (see Immune System).

OTHER TYPES

Encephalitis may occur as a result of an infection from a sporozoa called Toxoplasma, which is parasitic in animals, birds, and human beings. It can also be due to infection with the protozoan Trypanosoma cruzi, transmitted by the bite of the tsetse fly (see Trypanosomiasis). In addition, forms of apparently noninfectious encephalitis occur occasionally as a complication in cases of poisoning from contact with heavy metals, particularly lead (see Meningitis).

Meningitis

Meningitis, inflammation of the meninges, the membranes that surround the brain and spinal cord. Meningitis may be caused by a physical injury, a reaction to certain drugs, or more commonly, infection by certain viruses, bacteria, fungi, or parasites. This article focuses on meningitis caused by viral or bacterial infection.

The most common causes of viral meningitis are coxsackie viruses and echoviruses, although herpesviruses, the mumps virus, and many other viruses can also cause the disease. Viral meningitis is rarely fatal, and most patients recover from the disease completely.

Most cases of bacterial meningitis are caused by one of three species of bacteria—Haemophilus influenzae, Streptococcus pneumoniae, and Neisseria meningitidis. Many other bacteria, including Escherichia coli and the bacteria that are responsible for tuberculosis and syphilis, can also cause the disease. Bacterial meningitis can be fatal if not treated promptly. Some children who survive the infection are left with permanent neurological impairments, such as hearing loss or learning disabilities.

SYMPTOMS AND DIAGNOSIS

No matter what the cause, the symptoms of meningitis are always similar and usually develop rapidly, often over the course of a few hours. Nearly all patients with meningitis experience vomiting, high fever, and a stiff neck. Meningitis may also cause severe headache, back pain, muscle aches, sensitivity of the eyes to light, drowsiness, confusion, and even loss of consciousness. Some children have convulsions. In infants, the symptoms of meningitis are often more difficult to detect and may include irritability, lethargy, and loss of appetite. Most patients with meningococcal meningitis develop a rash of red, pinprick spots on the skin. The spots do not turn white when pressed, and they quickly grow to look like purple bruises.

Meningitis is diagnosed by a lumbar puncture, or spinal tap, in which a doctor inserts a needle into the lower back to obtain a sample of CSF. The fluid is then tested for the presence of bacteria and other cells, as well as certain chemical changes that are characteristic of meningitis.

TREATMENT AND PREVENTION

It is imperative to seek immediate medical attention if the symptoms of meningitis develop in order to determine whether the meningitis is viral or bacterial. Any delays in treating bacterial meningitis can lead to stroke, severe brain damage, and even death. Patients with bacterial meningitis are usually hospitalized and given large doses of intravenous antibiotics. The specific antibiotic used depends on the bacterium responsible for the infection. Antibiotic therapy is very effective, and if treatment begins in time, the risk of dying from bacterial meningitis today is less than 15 percent.

No specific treatment is available for viral meningitis. With bed rest, plenty of fluids, and medicine to reduce fever and control headache, most patients recover from viral meningitis within a week or two and suffer no lasting effects.

Good hygiene to prevent the spread of viruses is the only method of preventing viral meningitis. To help prevent the spread of bacterial meningitis, antibiotics are sometimes given to family members and other people who have had close contact with patients who develop the disease. Vaccines are also available against some of the bacteria that can cause meningitis. A vaccine against one strain of Haemophilus influenzae, once the most common cause of bacterial meningitis, was introduced during the 1980s and has been a part of routine childhood immunization.

Death and Dying

Death and Dying, the irreversible cessation of life and the imminent approach of death. Death involves a complete change in the status of a living entity—the loss of its essential characteristics.

PHYSIOLOGY

Death occurs at several levels. Somatic death is the death of the organism as a whole; it usually precedes the death of the individual organs, cells, and parts of cells. Somatic death is marked by cessation of heartbeat, respiration, movement, reflexes, and brain activity. The precise time of somatic death is sometimes difficult to determine, however, because the symptoms of such transient states as coma, faint (see Fainting), and trance closely resemble the signs of death.

After somatic death, several changes occur that are used to determine the time and circumstances of death. Algor mortis, the cooling of the body after death, is primarily influenced by the temperature of the immediate environment. Rigor mortis, the stiffening of the skeletal muscles, begins from five to ten hours after death and disappears after three or four days. Livor mortis, the reddish-blue discoloration that occurs on the underside of the body, results from the settling of the blood. Clotting of the blood begins shortly after death, as does autolysis, the death of the cells. Putrefaction, the decomposition that follows, is caused by the action of enzymes and bacteria.

Organs of the body die at different rates. Although brain cells may survive for no more than 5 minutes after somatic death, those of the heart can survive for about 15 minutes and those of the kidney for about 30 minutes. For this reason, organs can be removed from a recently dead body and transplanted into a living person.

Hemorrhagic Strokes

Hemorrhagic strokes account for the remaining 20 percent of all strokes. They occur when weakened blood vessels within the brain rupture and bleed into the surrounding tissue. The escaped blood can compress or pinch nearby blood vessels, cutting off blood flow and depriving the surrounding tissue of oxygen. Though hemorrhagic strokes occur less frequently than ischemic strokes, they tend to affect larger areas of the brain. Symptoms of a hemorrhagic stroke may be more sudden and more severe, and these strokes carry a greater risk of death than ischemic strokes.

Hemorrhagic strokes can result from an aneurysm, which develops when the wall of a blood vessel weakens and thins, ballooning outward. If left untreated, the aneurysm continues to expand and weaken, increasing the likelihood of rupture. Hemorrhagic strokes can also result from an arteriovenous malformation (AVM), a cluster of enlarged, structurally weak blood vessels that forms during fetal development or possibly at birth. These malformed blood vessels are susceptible to rupture from the normal forces exerted by the flowing blood.