An aortic aneurysm is an enlargement of the aorta to greater than 1.5 times normal size. They cause no symptoms except when ruptured. There may be abdominal, back, or leg pain, they are most located in the abdominal aorta, but can be located in the thoracic aorta. Aortic aneurysms increase the risk of aortic rupture; when rupture occurs, massive internal bleeding results and, unless treated shock and death can occur. Screening with ultrasound is indicated in those at high risk. Prevention is by decreasing risk factors, such as smoking, treatment is either by open or endovascular surgery. Aortic aneurysms resulted in about 152,000 deaths worldwide in 2013, up from 100,000 in 1990. Aortic aneurysms are classified by their location on the aorta. An aortic root aneurysm of the sinus of Valsalva. Thoracic aortic aneurysms are found within the chest. Abdominal aortic aneurysms, "AAA" or "Triple A", the most common form of aortic aneurysm, involve that segment of the aorta within the abdominal cavity. Thoracoabdominal aortic aneurysms involve both the abdominal aorta.
Most intact aortic aneurysms do not produce symptoms. As they enlarge, symptoms such as abdominal pain and back pain may develop. Compression of nerve roots may cause numbness. Untreated, aneurysms tend to become progressively larger, although the rate of enlargement is unpredictable for any individual. Clotted blood which lines most aortic aneurysms can break off and result in an embolus. Aneurysms can be found on physical examination. Medical imaging is necessary to confirm the diagnosis and to determine the anatomic extent of the aneurysm. In patients presenting with aneurysm of the arch of the aorta, a common sign is a hoarse voice from stretching of the left recurrent laryngeal nerve, a branch of the vagus nerve that winds around the aortic arch to supply the muscles of the larynx. Abdominal aortic aneurysms are more common than their thoracic counterpart. One reason for this is that elastin, the principal load-bearing protein present in the wall of the aorta, is reduced in the abdominal aorta as compared to the thoracic aorta.
Another is that the abdominal aorta does not possess vasa vasorum, the nutrient-supplying blood vessels within the wall of the aorta. Most AAA are true aneurysms; the prevalence of AAAs increases with an average age of 65 -- 70 at the time of diagnosis. AAAs have been attributed to atherosclerosis; the risk of rupture of an AAA is related to its diameter. Rupture risk is related to shape. Before rupture, an AAA may present as a pulsatile mass above the umbilicus. A bruit may be heard from the turbulent flow in the aneurysm. However, rupture may be the first hint of AAA. Once an aneurysm has ruptured, it presents with classic symptoms of abdominal pain, severe and radiating to the back; the diagnosis of an abdominal aortic aneurysm can be confirmed at the bedside by the use of ultrasound. Rupture may be indicated by the presence of free fluid in the abdomen. A contrast-enhanced abdominal CT scan is the best test to diagnose an AAA and guide treatment options. Only 10–25% of patients survive rupture due to large pre- and post-operative mortality.
Annual mortality from ruptured aneurysms in the United States is about 15,000. Most are due to abdominal aneurysms, with thoracic and thoracoabdominal aneurysms making up 1% to 4% of the total. An aortic aneurysm can rupture from wall weakness. Aortic rupture is a surgical emergency, has a high mortality with prompt treatment. Weekend admission for ruptured aortic aneurysm is associated with an increased mortality compared with admission on a weekday, this is due to several factors including a delay in prompt surgical intervention. Coronary artery disease Hypertension Loeys-Dietz Syndrome Hypercholesterolemia Hyperhomocysteinemia Elevated C-reactive protein Tobacco use Peripheral vascular disease Marfan syndrome Ehlers-Danlos type IV Bicuspid Aortic Valve Syphilis IgG4-related disease Pregnancy An aortic aneurysm can occur as a result of trauma, infection, or, most from an intrinsic abnormality in the elastin and collagen components of the aortic wall. While definite genetic abnormalities were identified in true genetic syndromes associated with aortic aneurysms, both thoracic and abdominal aortic aneurysms demonstrate a strong genetic component in their aetiology.
The risk of aneurysm enlargement may be diminished with attention to the patient's blood pressure and cholesterol levels. There have been proposals to introduce ultrasound scans as a screening tool for those most at risk: men over the age of 65; the tetracycline antibiotic doxycycline is being investigated for use as a potential drug in the prevention of aortic aneurysm due to its metalloproteinase inhibitor and collagen stabilizing properties. Anacetrapib is a cholesteryl ester transfer protein inhibitor that raises high-density lipoprotein cholesterol and reduces low-density lipoprotein cholesterol. Anacetrapib reduces progression of atherosclerosis by reducing non-HDL-cholesterol, improves lesion stability and adds to the beneficial effects o
Gastrointestinal bleeding known as gastrointestinal hemorrhage, is all forms of bleeding in the gastrointestinal tract, from the mouth to the rectum. When there is significant blood loss over a short time, symptoms may include vomiting red blood, vomiting black blood, bloody stool, or black stool. Small amounts of bleeding over a long time may cause iron-deficiency anemia resulting in feeling tired or heart-related chest pain. Other symptoms may include shortness of breath, pale skin, or passing out. Sometimes in those with small amounts of bleeding no symptoms may be present. Bleeding is divided into two main types: upper gastrointestinal bleeding and lower gastrointestinal bleeding. Causes of upper GI bleeds include: peptic ulcer disease, esophageal varices due to liver cirrhosis and cancer, among others. Causes of lower GI bleeds include: hemorrhoids and inflammatory bowel disease among others. Diagnosis begins with a medical history and physical examination, along with blood tests. Small amounts of bleeding may be detected by fecal occult blood test.
Endoscopy of the lower and upper gastrointestinal tract may locate the area of bleeding. Medical imaging may be useful in cases. Initial treatment focuses on resuscitation which may include intravenous fluids and blood transfusions. Blood transfusions are not recommended unless the hemoglobin is less than 70 or 80 g/L. Treatment with proton pump inhibitors and antibiotics may be considered in certain cases. If other measures are not effective, an esophageal balloon may be attempted in those with presumed esophageal varices. Endoscopy of the esophagus and duodenum or endoscopy of the large bowel are recommended within 24 hours and may allow treatment as well as diagnosis. An upper GI bleed is more common than lower GI bleed. An upper GI bleed occurs in 50 to 150 per 100,000 adults per year. A lower GI bleed is estimated to occur in 20 to 30 per 100,000 per year, it results in about 300,000 hospital admissions a year in the United States. Risk of death from a GI bleed is between 5% and 30%. Risk of bleeding is more common in increases with age.
Gastrointestinal bleeding can range from small non-visible amounts, which are only detected by laboratory testing, to massive bleeding where bright red blood is passed and shock develops. With bleeding, rapid there may be syncope. Blood, digested may appear black rather than red, resulting in "coffee ground" vomit or tar colored stool called melena. Other signs and symptoms include feeling tired and pale skin color. Gastrointestinal bleeding can be divided into two clinical syndromes: upper gastrointestinal bleeding and lower gastrointestinal bleeding. About 2/3 of all GI bleeds are from 1/3 from lower sources. Common causes of gastrointestinal bleeding include infections, vascular disorders, adverse effects of medications, blood clotting disorders. Obscure gastrointestinal bleeding is. Upper gastrointestinal bleeding is from the ligament of Treitz. An upper source is characterised by hematemesis and melena. About half of cases are due to peptic ulcer disease. Esophageal inflammation and erosive disease are the next most common causes.
In those with liver cirrhosis, 50–60% of bleeding is due to esophageal varices. Half of those with peptic ulcers have an H. pylori infection. Other causes include Mallory-Weiss tears and angiodysplasia. A number of medications are found to cause upper GI bleeds. NSAIDs or COX-2 inhibitors increase the risk about fourfold. SSRIs, anticoagulants may increase the risk; the risk with dabigatran is 30% greater than that with warfarin. Lower gastrointestinal bleeding is from the colon, rectum or anus. Common causes of lower gastrointestinal bleeding include hemorrhoids, angiodysplasia, ulcerative colitis, Crohn's disease, aortoenteric fistula, it may be indicated by the passage of fresh red blood rectally in the absence of bloody vomiting. Isolated melena may originate from anywhere between the proximal colon. A number of foods and medications can turn the stool either black. Bismuth found in many antacids may turn stools black. Blood from the vagina or urinary tract may be confused with blood in the stool.
Diagnosis is based on direct observation of blood in the stool or vomit. This can be confirmed with a fecal occult blood test. Differentiating between upper and lower bleeding in some cases can be difficult; the severity of an upper GI bleed can be judged based on the Blatchford Rockall score. The Rockall score is the more accurate of the two; as of 2008 there is no scoring system useful for lower GI bleeds. Gastric aspiration and or lavage, where a tube is inserted into the stomach via the nose in an attempt to determine if there is blood in the stomach, if negative does not rule out an upper GI bleed but if positive is useful for ruling one in. Clots in the stool indicate a lower GI source. Recommended laboratory blood testing includes: cross-matching blood, hematocrit, coagulation time, electrolytes. If the ratio of blood urea nitrogen to creatinine is greater than 30 the source is more from the upper GI tract. A CT angiography is useful for determining the exact location of the bleeding within the gastrointestinal tract.
Nuclear scintigraphy is a sensitive test for detecting occult gastrointestinal bleeding when direct imaging with upper and lower endoscopies are negative. Direct angiography
The blood vessels are a part of the circulatory system, microcirculation, that transports blood throughout the human body. These vessels are designed to transport nutrients and oxygen to the tissues of the body, they take waste and carbon dioxide and carry them away from the tissues and back to the heart. Blood vessels are needed to sustain life. There are three major types of blood vessels: the arteries, which carry the blood away from the heart; the word vascular, meaning relating to the blood vessels, is derived from the Latin vas, meaning vessel. Some structures -- such as cartilage, the epithelium, the lens and cornea of the eye -- do not contain blood vessels and are labeled avascular; the arteries and veins have three layers. The middle layer is thicker in the arteries than it is in the veins: The inner layer, tunica intima, is the thinnest layer, it is a single layer of flat cells glued by a polysaccharide intercellular matrix, surrounded by a thin layer of subendothelial connective tissue interlaced with a number of circularly arranged elastic bands called the internal elastic lamina.
A thin membrane of elastic fibers in the tunica intima run parallel to the vessel. The middle layer tunica media is the thickest layer in arteries, it consists of circularly arranged elastic fiber, connective tissue, polysaccharide substances, the second and third layer are separated by another thick elastic band called external elastic lamina. The tunica media may be rich in vascular smooth muscle. Veins don't have the external elastic lamina, but only an internal one; the tunica media is thicker in the arteries rather than the veins. The outer layer is the thickest layer in veins, it is made of connective tissue. It contains nerves that supply the vessel as well as nutrient capillaries in the larger blood vessels. Capillaries consist of little more than a layer of endothelium and occasional connective tissue; when blood vessels connect to form a region of diffuse vascular supply it is called an anastomosis. Anastomoses provide critical alternative routes for blood to flow in case of blockages. There is a layer of muscle surrounding the arteries and the veins which help contract and expand the vessels.
This creates enough pressure for blood to be pumped around the body. Blood vessels are part of the circulatory system, together with the blood; the biggest difference in the structure of arteries and veins is the presence of valves. Backflow of blood is prevented in arteries by the heart; however in veins, one-direction valves are used to prevent backflow as a result of a decrease in blood pressure as the blood passes through the circulatory system. There are various kinds of blood vessels: Arteries Elastic arteries Distributing arteries Arterioles Capillaries Venules Veins Large collecting vessels, such as the subclavian vein, the jugular vein, the renal vein and the iliac vein. Venae cavae. Sinusoids Extremely small vessels located within bone marrow, the spleen, the liver, they are grouped as "arterial" and "venous", determined by whether the blood in it is flowing away from or toward the heart. The term "arterial blood" is used to indicate blood high in oxygen, although the pulmonary artery carries "venous blood" and blood flowing in the pulmonary vein is rich in oxygen.
This is because they are carrying the blood to and from the lungs to be oxygenated. Blood vessels function to transport blood. In general and arterioles transport oxygenated blood from the lungs to the body and its organs, veins and venules transport deoxygenated blood from the body to the lungs. Blood vessels circulate blood throughout the circulatory system Oxygen is the most critical nutrient carried by the blood. In all arteries apart from the pulmonary artery, hemoglobin is saturated with oxygen. In all veins apart from the pulmonary vein, the saturation of hemoglobin is about 75%. In addition to carrying oxygen, blood carries hormones, waste products and nutrients for cells of the body. Blood vessels do not engage in the transport of blood. Blood is propelled through arterioles through pressure generated by the heartbeat. Blood vessels transport red blood cells which contain the oxygen necessary for daily activities; the amount of red blood cells present in your vessels has an effect on your health.
Hematocrit tests can be performed to calculate the proportion of red blood cells in your blood. Higher proportions result in conditions such as dehydration or heart disease while lower proportions could lead to anemia and long-term blood loss. Blood vessels transport red blood cells which contain the oxygen necessary for daily activities; the amount of red blood cells present in your vessels has an effect on your health. Hematocrit tests can be performed to calculate the proportion of red blood cells in your blood. Higher proportions result in conditions such as dehydration or heart disease while lower proportions could lead to anemia and long-term blood loss. Permeability of the endothelium is pivotal in the release of nutrients to the tissue, it is increased in inflammation in response to histamine and interleukins, which leads to most of the
Death is the permanent cessation of all biological functions that sustain a living organism. Phenomena which bring about death include aging, malnutrition, suicide, starvation and accidents or major trauma resulting in terminal injury. In most cases, bodies of living organisms begin to decompose shortly after death. Death – the death of humans – has been considered a sad or unpleasant occasion, due to the affection for the being that has died and the termination of social and familial bonds with the deceased. Other concerns include fear of death, anxiety, grief, emotional pain, sympathy, solitude, or saudade. Many cultures and religions have the idea of an afterlife, hold the idea of reward or judgement and punishment for past sin; the word death comes from Old English dēaþ. This comes from the Proto-Indo-European stem *dheu- meaning the "process, condition of dying"; the concept and symptoms of death, varying degrees of delicacy used in discussion in public forums, have generated numerous scientific and acceptable terms or euphemisms for death.
When a person has died, it is said they have passed away, passed on, expired, or are gone, among numerous other accepted, religiously specific and irreverent terms. Bereft of life, the dead person is a corpse, cadaver, a body, a set of remains, when all flesh has rotted away, a skeleton; the terms carrion and carcass can be used, though these more connote the remains of non-human animals. As a polite reference to a dead person, it has become common practice to use the participle form of "decease", as in the deceased; the ashes left after a cremation are sometimes referred to by the neologism cremains, a portmanteau of "cremation" and "remains". Senescence refers to a scenario when a living being is able to survive all calamities, but dies due to causes relating to old age. Animal and plant cells reproduce and function during the whole period of natural existence, but the aging process derives from deterioration of cellular activity and ruination of regular functioning. Aptitude of cells for gradual deterioration and mortality means that cells are sentenced to stable and long-term loss of living capacities despite continuing metabolic reactions and viability.
In the United Kingdom, for example, nine out of ten of all the deaths that occur on a daily basis relates to senescence, while around the world it accounts for two-thirds of 150,000 deaths that take place daily. All animals who survive external hazards to their biological functioning die from biological aging, known in life sciences as "senescence"; some organisms experience negligible senescence exhibiting biological immortality. These include the jellyfish Turritopsis dohrnii, the hydra, the planarian. Unnatural causes of death include homicide. From all causes 150,000 people die around the world each day. Of these, two thirds die directly or indirectly due to senescence, but in industrialized countries – such as the United States, the United Kingdom, Germany – the rate approaches 90%. Physiological death is now seen as a process, more than an event: conditions once considered indicative of death are now reversible. Where in the process a dividing line is drawn between life and death depends on factors beyond the presence or absence of vital signs.
In general, clinical death is neither sufficient for a determination of legal death. A patient with working heart and lungs determined to be brain dead can be pronounced dead without clinical death occurring; as scientific knowledge and medicine advance, formulating a precise medical definition of death becomes more difficult. Signs of death or strong indications that a warm-blooded animal is no longer alive are: Respiratory arrest Cardiac arrest Brain death Pallor mortis, paleness which happens in the 15–120 minutes after death Algor mortis, the reduction in body temperature following death; this is a steady decline until matching ambient temperature Rigor mortis, the limbs of the corpse become stiff and difficult to move or manipulate Livor mortis, a settling of the blood in the lower portion of the body Decomposition, the reduction into simpler forms of matter, accompanied by a strong, unpleasant odor. The concept of death is a key to human understanding of the phenomenon. There are many scientific approaches to the concept.
For example, brain death, as practiced in medical science, defines death as a point in time at which brain activity ceases. One of the challenges in defining death is in distinguishing it from life; as a point in time, death would seem to refer to the moment. Determining when death has occurred is difficult, as cessation of life functions is not simultaneous across organ systems; such determination therefore requires drawing precise conceptual boundaries between death. This is due to there being little consensus on how to define life; this general problem applies to the particular challenge of defining death in the context of medicine. It is possible to define life in terms of consciousness; when consciousness ceases, a living organism can be said to have died. One of the flaws in this approach is that there are many organisms which are alive but not conscious. Another problem is in defining consciousness, which has many different d
Ectopic pregnancy is a complication of pregnancy in which the embryo attaches outside the uterus. Signs and symptoms classically include vaginal bleeding. Fewer than 50 percent of affected women have both of these symptoms; the pain may be described as dull, or crampy. Pain may spread to the shoulder if bleeding into the abdomen has occurred. Severe bleeding may result in fainting, or shock. With rare exceptions the fetus is unable to survive. Risk factors for ectopic pregnancy include: pelvic inflammatory disease due to chlamydia infection, tobacco smoking, prior tubal surgery, a history of infertility, the use of assisted reproductive technology; those who have had an ectopic pregnancy are at much higher risk of having another one. Most ectopic pregnancies occur in the fallopian tube. Implantation can occur on the cervix, ovaries, or within the abdomen. Detection of ectopic pregnancy is by blood tests for human chorionic gonadotropin and ultrasound; this may require testing on more than one occasion.
Ultrasound works best. Other causes of similar symptoms include: miscarriage, ovarian torsion, acute appendicitis. Prevention is by decreasing risk factors such as chlamydia infections through screening and treatment. While some ectopic pregnancies will resolve without treatment, this approach has not been well studied as of 2014; the use of the medication methotrexate works as well as surgery in some cases. It works well when the beta-HCG is low and the size of the ectopic is small. Surgery is still recommended if the tube has ruptured, there is a fetal heartbeat, or the person's vital signs are unstable; the surgery may be laparoscopic or through a larger incision, known as a laparotomy. Outcomes are good with treatment; the rate of ectopic pregnancy is about 1% and 2% that of live births in developed countries, though it may be as high as 4% among those using assisted reproductive technology. It is the most common cause of death among women during the first trimester at 10% of the total. In the developed world outcomes have improved while in the developing world they remain poor.
The risk of death among those in the developed world is between 0.1 and 0.3 percent while in the developing world it is between one and three percent. The first known description of an ectopic pregnancy is by Al-Zahrawi in the 11th century; the word "ectopic" means "out of place". Up to 10% of women with ectopic pregnancy have no symptoms, one third have no medical signs. In many cases the symptoms have low specificity, can be similar to those of other genitourinary and gastrointestinal disorders, such as appendicitis, rupture of a corpus luteum cyst, ovarian torsion or urinary tract infection. Clinical presentation of ectopic pregnancy occurs at a mean of 7.2 weeks after the last normal menstrual period, with a range of four to eight weeks. Presentations are more common in communities deprived of modern diagnostic ability. Signs and symptoms of ectopic pregnancy include increased hCG, vaginal bleeding, sudden lower abdominal pain, pelvic pain, a tender cervix, an adnexal mass, or adnexal tenderness.
In the absence of ultrasound or hCG assessment, heavy vaginal bleeding may lead to a misdiagnosis of miscarriage. Nausea and diarrhea are more rare symptoms of ectopic pregnancy. Rupture of an ectopic pregnancy can lead to symptoms such as abdominal distension, tenderness and hypovolemic shock. A woman with ectopic pregnancy may be excessively mobile with upright posturing, in order to decrease intrapelvic blood flow, which can lead to swelling of the abdominal cavity and cause additional pain; the most common complication is rupture with internal bleeding. Death from rupture is the leading cause of death in the first trimester of the pregnancy. There are a number of risk factors for ectopic pregnancies. However, in as many as one third to one half no risk factors can be identified. Risk factors include: pelvic inflammatory disease, use of an intrauterine device, previous exposure to DES, tubal surgery, intrauterine surgery, previous ectopic pregnancy and tubal ligation. A previous induced abortion does not appear to increase the risk.
Tubal pregnancy is. Hair-like cilia located on the internal surface of the fallopian tubes carry the fertilized egg to the uterus. Fallopian cilia are sometimes seen in reduced numbers subsequent to an ectopic pregnancy, leading to a hypothesis that cilia damage in the fallopian tubes is to lead to an ectopic pregnancy. Women who smoke have a higher chance of an ectopic pregnancy in the fallopian tubes. Smoking leads to risk factors of killing cilia; as cilia degenerate, the amount of time it takes for the fertilized egg to reach the uterus will increase. The fertilized egg, if it doesn't reach the uterus in time, will hatch from the non-adhesive zona pellucida and implant itself inside the fallopian tube, thus causing the pregnancy. Women with pelvic inflammatory disease have a high occurrence of ectopic pregnancy; this results from the build-up of scar tissue in the fallopian tubes. If however both tubes were blocked, so that sperm and egg were physically unable to meet fertilization of the egg would be impossible, neither normal pregnancy nor ectopic pregnancy could occur.
Intrauterine adhesions present in Asherman's syndrome can cause ectopic cervical pregnancy or, if adhesions block access to the tubes via the ostia, ectopic tubal preg
A hemothorax is an accumulation of blood within the pleural cavity. The symptoms of a hemothorax include chest pain and difficulty breathing, while the clinical signs include reduced breath sounds on the affected side and a rapid heart rate. Hemothoraces are caused by an injury but may occur spontaneously: due to cancer invading the pleural cavity, as a result of a blood clotting disorder, as an unusual manifestation of endometriosis, in response to a collapsed lung, or in association with other conditions. Hemothoraces are diagnosed using a chest X-ray, but can be identified using other forms of imaging including ultrasound, a CT scan, or an MRI scan, they can be differentiated from other forms of fluid within the pleural cavity by analysing a sample of the fluid, are defined as having a hematocrit of greater than 50% that of the person's blood. Hemothoraces may be treated by draining the blood using a chest tube, but may require surgery if the bleeding continues. If treated, the prognosis is good.
Complications of a hemothorax include infection within the pleural cavity and the formation of scar tissue. The symptoms of a hemothorax depend on the quantity of blood, lost into the pleural cavity. A small hemothorax causes little in the way of symptoms, while larger hemothoraces cause breathlessness and chest pain, lightheadedness. Other symptoms may occur in association with a hemothorax depending on the underlying cause; the clinical signs of a hemothorax include reduced or absent breath sounds and reduced movement of the chest wall on the affected side. When the affected side is tapped or percussed, a dull sound may be heard in contrast to the usual resonant note. Large hemothoraces that interfere with the ability to transfer oxygen may cause a blue tinge to the lips. In these cases the body may try to compensate for the loss of blood, leading to a rapid heart rate, pale, clammy skin. A hemothorax is caused by an injury, either blunt trauma or wounds that penetrate the chest, these cases are referred to traumatic hemothoraces.
Minor chest injuries can lead to significant hemothoraces. Injuries cause the rupture of small blood vessels such as those found between the ribs. However, if larger blood vessels such as the aorta are damaged, the blood loss can be massive. Hemothorax can occur as a complication of heart and lung surgery, for example the rupture of lung arteries caused by the placement of catheters. Less hemothoraces may occur spontaneously. A hemothorax can complicate some forms of cancer. Tumours responsible for hemothoraces include angiosarcomas, schwannomas and lung cancer. Hemothoraces are more to occur in response to minor trauma when blood is less able to form clots, either as result of medications such as anticoagulants, or because of bleeding disorders such as haemophilia. Hemothoraces can arise due to endometriosis, a condition in which tissue that covers the inside of the uterus forms in unusual locations. Endometrial tissue that implants on the pleural surface can bleed in response to hormonal changes, causing what is known as a catamenial hemothorax.
Those with an abnormal accumulation of air within the pleural space can bleed into the cavity, which occurs in about 5% of cases of spontaneous pneumothorax. The resulting combination of air and blood within the pleural space is known as a hemopneumothorax. Hemothoraces can occur following spontaneous tearing of blood vessels such as in an aortic dissection, although bleeding in these circumstances is into the pericardial space. Spontaneous tearing of blood vessels is more to occur in those with disorders that weaken blood vessels such as some forms of Ehlers-Danlos syndrome, or in those with malformed blood vessels as is seen in Rendu-Osler-Weber syndrome. Other rare causes of hemothorax include neurofibromatosis type 1 and extramedullary haematopoiesis; the thoracic cavity is a chamber within the chest, containing the lungs and numerous major blood vessels. Thin sheets of tissue known as the pleural membranes or pleura line the chest and cover the lungs - the chest wall is lined by the parietal pleura, while the visceral pleura covers the outside of the lungs.
The visceral and parietal pleura are separated by only a thin layer of fluid, forming the pleural cavity. When a hemothorax occurs, blood enters the pleural cavity; the blood loss has several effects. Firstly, as blood builds up within the pleural cavity, it begins to interfere with the normal movement of the lungs, preventing one or both lungs from expanding and thereby interfering with the normal transfer of oxygen and carbon dioxide to and from the blood. Secondly, blood, lost into the pleural cavity can no longer be circulated. Hemothoraces can lead to significant blood loss - each half of the thorax can hold more than 1500 milliliters of blood, representing more than 25% of an average adult's total blood volume; the body may struggle to cope with this blood loss, in order to compensate tries to maintain blood pressure by forcing the heart to pump harder and faster, by squeezing or constricting small blood vessels in the arms and legs. These compensatory mechanisms can be recognised by a rapid resting heart rate and cool fingers and toes.
If the blood within the pleural cavity is not removed, it will clot. This clot tends to stick the parietal and visceral pleura together and has the potential to lead to scarring within the pleura, which if extensive leads to the condition known as a fibrothorax. Following the initial loss of blood, a small hemotho