Surgery on the great vessels (e.g., aortic coarctation repair, Blalock–Thomas–Taussig shunt creation, closure of patent ductus arteriosus) became common after the turn of the century. However, operations on the heart valves were unknown until, in 1925, Henry Souttar operated successfully on a young woman with mitral valve stenosis. He made an opening in the appendage of the left atrium and inserted a finger in order to palpate and explore the damaged mitral valve. The patient survived for several years, but Souttar's colleagues considered the procedure unjustified, and he could not continue.
Cardiac surgery changed significantly after World War II. In 1947, Thomas Sellors of Middlesex Hospital in London operated on a Tetralogy of Fallot patient with pulmonary stenosis and successfully divided the stenosed pulmonary valve. In 1948, Russell Brock, probably unaware of Sellors's work,
used a specially designed dilator in three cases of pulmonary stenosis.
Later that year, he designed a punch to resect a stenosed infundibulum,
which is often associated with Tetralogy of Fallot. Many thousands of
these "blind" operations were performed until the introduction of cardiopulmonary bypass made direct surgery on valves possible.
Also in 1948, four surgeons carried out successful operations for mitral valve stenosis resulting from rheumatic fever. Horace Smithy of Charlotte used a valvulotome to remove a portion of a patient's mitral valve, while three other doctors—Charles Bailey of Hahnemann University Hospital in Philadelphia; Dwight Harken in Boston; and Russell Brock of Guy's Hospital
in London—adopted Souttar's method. All four men began their work
independently of one another within a period of a few months. This time,
Souttar's technique was widely adopted, with some modifications.
Open-heart
surgery is any kind of surgery in which a surgeon makes a large
incision (cut) in the chest to open the rib cage and operate on the
heart. "Open" refers to the chest, not the heart. Depending on the type
of surgery, the surgeon also may open the heart.
Dr. Wilfred G. Bigelow of the University of Toronto
found that procedures involving opening the patient's heart could be
performed better in a bloodless and motionless environment. Therefore,
during such surgery, the heart is temporarily stopped, and the patient
is placed on cardiopulmonary bypass,
meaning a machine pumps their blood and oxygen. Because the machine
cannot function the same way as the heart, surgeons try to minimize the
time a patient spends on it.
Cardiopulmonary bypass was developed after surgeons realized the limitations of hypothermia
in cardiac surgery: Complex intracardiac repairs take time, and the
patient needs blood flow to the body (particularly to the brain), as
well as heart and lung function. In July 1952, Forest Dodrill
was the first to use a mechanical pump in a human to bypass the left
side of the heart whilst allowing the patient's lungs to oxygenate the
blood, in order to operate on the mitral valve. In 1953, Dr. John Heysham Gibbon of Jefferson Medical School in Philadelphia reported the first successful use of extracorporeal circulation by means of an oxygenator, but he abandoned the method after subsequent failures.
In 1954, Dr. Lillehei performed a series of successful operations with
the controlled cross-circulation technique, in which the patient's
mother or father was used as a "heart-lung machine". Dr. John W. Kirklin at the Mayo Clinic was the first to use a Gibbon-type pump-oxygenator.
Nazih Zuhdi performed the first total intentional hemodilution
open-heart surgery on Terry Gene Nix, age 7, on 25 February 1960 at
Mercy Hospital in Oklahoma City. The operation was a success; however,
Nix died three years later. In March 1961, Zuhdi, Carey, and Greer performed open-heart surgery on a child, aged 3+1⁄2, using the total intentional hemodilution machine.
Modern beating-heart surgery
In the early 1990s, surgeons began to perform off-pump coronary artery bypass,
done without cardiopulmonary bypass. In these operations, the heart
continues beating during surgery, but is stabilized to provide an almost
still work area in which to connect a conduit vessel that bypasses a
blockage. The conduit vessel that is often used is the Saphenous vein.
This vein is harvested using a technique known as endoscopic vessel harvesting (EVH).
Heart transplant
In
1945, the Soviet pathologist Nikolai Sinitsyn successfully transplanted
a heart from one frog to another frog and from one dog to another dog.
Coronary artery bypass grafting,
also called revascularization, is a common surgical procedure to create
an alternative path to deliver blood supply to the heart and body, with
the goal of preventing clot formation. This can be done in many ways, and the arteries used can be taken from several areas of the body.
Arteries are typically harvested from the chest, arm, or wrist and then
attached to a portion of the coronary artery, relieving pressure and
limiting clotting factors in that area of the heart.
The procedure is typically performed because of coronary artery disease
(CAD), in which a plaque-like substance builds up in the coronary
artery, the main pathway carrying oxygen-rich blood to the heart. This
can cause a blockage and/or a rupture, which can lead to a heart attack.
Minimally invasive surgery
As an alternative to open-heart surgery, which involves a five- to eight-inch incision in the chest wall, a surgeon may perform an endoscopic procedure by making very small incisions through which a camera and specialized tools are inserted.
In robot-assisted heart surgery,
a machine controlled by a cardiac surgeon is used to perform a
procedure. The main advantage to this is the size of the incision
required: three small port holes instead of an incision big enough for
the surgeon's hands.
The use of robotics in heart surgery continues to be evaluated, but
early research has shown it to be a safe alternative to traditional
techniques.
Post-surgical procedures
As
with any surgical procedure, cardiac surgery requires postoperative
precautions to avoid complications. Incision care is needed to avoid
infection and minimize scarring. Swelling and loss of appetite are common.
Recovery from open-heart surgery begins with about 48 hours in an intensive care unit, where heart rate, blood pressure,
and oxygen levels are closely monitored. Chest tubes are inserted to
drain blood around the heart and lungs. After discharge from the
hospital, compression socks may be recommended in order to regulate blood flow.
Risks
The
advancement of cardiac surgery and cardiopulmonary bypass techniques has
greatly reduced the mortality rates of these procedures. For instance,
repairs of congenital heart defects are currently estimated to have 4–6%
mortality rates.
A major concern with cardiac surgery is neurological damage. Stroke occurs in 2–3% of all people undergoing cardiac surgery, and the rate is higher in patients with other risk factors for stroke. A more subtle complication attributed to cardiopulmonary bypass is postperfusion syndrome, sometimes called "pumphead". The neurocognitive symptoms of postperfusion syndrome were initially thought to be permanent, but turned out to be transient, with no permanent neurological impairment.
In order to assess the performance of surgical units and individual surgeons, a popular risk model has been created called the EuroSCORE. It takes a number of health factors from a patient and, using precalculated logistic regression coefficients, attempts to quantify the probability that they will survive to discharge. Within the United Kingdom, the EuroSCORE was used to give a breakdown of all cardiothoracic surgery
centres and to indicate whether the units and their individuals
surgeons performed within an acceptable range. The results are available
on the Care Quality Commission website.
Pharmacological and non-pharmacological
prevention approaches may reduce the risk of atrial fibrillation after
an operation and reduce the length of hospital stays, however there is
no evidence that this improves mortality.
Non-pharmacologic approaches
Preoperative physical therapy may reduce postoperative pulmonary complications, such as pneumonia and atelectasis,
in patients undergoing elective cardiac surgery and may decrease the
length of hospital stay by more than three days on average. There is evidence that quitting smoking at least four weeks before surgery may reduce the risk of postoperative complications.
Pharmacological approaches
Beta-blocking
medication is sometimes prescribed during cardiac surgery. There is
some low certainty evidence that this perioperative blockade of
beta-adrenergic receptors may reduce the incidence of atrial fibrillation and ventricular arrhythmias in patients undergoing cardiac surgery.
Vascular surgery is a surgical subspecialty in which vascular diseases involving the arteries, veins, or lymphatic vessels,
are managed by medical therapy, minimally-invasive catheter procedures
and surgical reconstruction. The specialty evolved from general and cardiovascular surgery
where it refined the management of just the vessels, no longer treating
the heart or other organs. Modern vascular surgery includes open
surgery techniques, endovascular (minimally invasive) techniques and
medical management of vascular diseases - unlike the parent
specialities. The vascular surgeon is trained in the diagnosis and
management of diseases affecting all parts of the vascular system
excluding the coronaries and intracranial vasculature. Vascular surgeons
also are called to assist other physicians to carry out surgery near
vessels, or to salvage vascular injuries that include hemorrhage
control, dissection, occlusion or simply for safe exposure of vascular
structures.
History
Early leaders of the field included Russian surgeon Nikolai Korotkov, noted for developing early surgical techniques, American interventional radiologistCharles Theodore Dotter
who is credited with inventing minimally invasive angioplasty (1964),
and Australian Robert Paton, who helped the field achieve recognition as
a specialty. Edwin Wylie of San Francisco was one of the early American
pioneers who developed and fostered advanced training in vascular
surgery and pushed for its recognition as a specialty in the United
States in the 1970s. The most notable historic figure in vascular
surgery is the 1912 Nobel Prize winning surgeon, Alexis Carrel for his techniques used to suture vessels.
Evolution
Medical science has advanced significantly since 1507, when Leonardo da Vinci drew this diagram of the internal organs and vascular systems of a woman.
The specialty continues to be based on operative arterial and venous
surgery but since the early 1990s has evolved greatly. There is now
considerable emphasis on minimally invasive alternatives to surgery. The
field was originally pioneered by interventional radiologists like Dr. Charles Dotter, who invented angioplasty using serial dilatation of vessels.
The surgeon Dr. Thomas J. Fogarty invented a balloon catheter,
designed to remove clots from occluded vessels, which was used as the
eventual model to do endovascular angioplasty. Further development of
the field has occurred via joint efforts between interventional radiology, vascular surgery, and interventional cardiology.
This area of vascular surgery is called Endovascular Surgery or
Interventional Vascular Radiology, a term that some in the specialty
append to their primary qualification as Vascular Surgeon. Endovascular
and endovenous procedures (e.g., EVAR) can now form the bulk of a vascular surgeon's practice.
The treatment of the aorta, the body's largest artery, dates back
to Greek surgeon Antyllus, who first performed surgeries for various
aneurysms in the second century AD. Modern treatment of aortic diseases
stems from development and advancements from Michael DeBakey and Denton Cooley.
In 1955, DeBakey and Cooley performed the first replacement of a
thoracic aneurysm with a homograft. In 1958, they began using the Dacron
graft, resulting in a revolution for surgeons in the repair of aortic
aneurysms. He also was first to perform cardiopulmonary bypass to repair
the ascending aorta, using antegrade perfusion of the brachiocephalic
artery.
Dr. Ted Diethrich, one of Dr. DeBakey's associates, went on to pioneer many of the minimally invasive techniques that later became hallmarks of endovascular surgery. Dietrich later founded the Arizona Heart Hospital
in 1998 and served as its medical director from 1998 to 2010. In 2000,
Diethrich performed the first endovascular aneurysm repair (EVAR) for
ruptured abdominal aortic aneurysm. Dietrich trained several future
leaders in the field of endovascular surgery at the Arizona Heart
Hospital including Venkatesh Ramaiah, MD who served as medical director of the institution following Dietrich's death in 2017.
The development of endovascular surgery has been accompanied by a gradual separation of vascular surgery from its origin in general surgery.
Most vascular surgeons would now confine their practice to vascular
surgery and, similarly, general surgeons would not be trained or
practise the larger vascular surgery operations or most endovascular
procedures. More recently, professional vascular surgery societies and
their training program have formally separated vascular surgery into a
separate specialty with its own training program, meetings and
accreditation. Notable societies are Society for Vascular Surgery
(SVS), USA; Australia and New Zealand Society of Vascular Surgeons
(ANZSVS). Local societies also exist (e.g., New South Wales Vascular and
Melbourne Vascular Surgical Association (MVSA)). Larger societies of
surgery actively separate and encourage specialty surgical societies
under their umbrella (e.g., Royal Australasian College of Surgeons (RACS)).
Currently
Arterial and venous disease treatment by angiography, stenting, and non-operative varicose vein treatment sclerotherapy, endovenous laser treatment
have largely replaced major surgery in many first world countries.
These procedures provide reasonable outcomes that are comparable to
surgery with the advantage of short hospital stay (day or overnight for
most cases) with lower morbidity and mortality rates. Historically
performed by interventional radiologists, vascular surgeons have become
increasingly proficient with endovascular methods.
The durability of endovascular arterial procedures is generally good,
especially when viewed in the context of their common clinical usage
i.e. arterial disease occurring in elderly patients and usually
associated with concurrent significant patient comorbidities especially
ischemic heart disease. The cost savings from shorter hospital stays and
less morbidity are considerable but are somewhat balanced by the high
cost of imaging equipment, construction and staffing of dedicated
procedural suites, and of the implant devices themselves.
The benefits for younger patients and in venous disease are less
persuasive but there are strong trends towards nonoperative treatment
options driven by patient preference, health insurance company costs,
trial demonstrating comparable efficacy at least in the medium term.
A recent trend in the United States is the stand-alone day
angiography facility associated with a private vascular surgery clinic,
thus allowing treatment of most arterial endovascular cases conveniently
and possibly with lesser overall community cost.
Similar non-hospital treatment facilities for non-operative vein
treatment have existed for some years and are now widespread in many
countries.
NHS England
conducted a review of all 70 vascular surgery sites across England in
2018 as part of its Getting It Right First Time programme. The review
specified that vascular hubs should perform at least 60 abdominal aortic
aneurysm procedures and 40 carotid endarterectomies a year. 12 trusts
missed both targets and many more missed one of them. A programme of
concentrating vascular surgery in fewer centres is proceeding.
Infrarenal aortic occlusion imaged with magnetic resonance angiography (MRA).
The management of arterial pathology excluding coronary and
intracranial disease is within the scope of vascular surgeons. Disease
states generally arise from narrowing of the arterial system known as stenosis or abnormal dilation referred to as an aneurysm. There are multiple mechanisms by which the arterial lumen can narrow, the most common of which is atherosclerosis. Symptomatic stenosis may also result from a complication of arterial dissection. Other less common causes of stenosis include fibromuscular dysplasia,
radiation induced fibrosis or cystic adventitial disease. Dilation of
an artery which retains histologic layers is called an aneurysm. An
aneurysms can be fusiform (concentric dilation), saccular (outpouching)
or a combination of the two. Arterial dilation which does not contain
three histologic layers is considered a pseudoaneurysm.
Additionally, there are a number of congenital vascular anomalies which
lead to symptomatic disease that are managed by the vascular surgeon, a
few of which include aberrant subclavian artery, popliteal artery entrapment syndrome or persistent sciatic artery.
Vascular surgeons treat arterial diseases with a range of therapies
including lifestyle modification, medications, endovascular therapy and
surgery.
The aorta is the largest artery in the body and the descending aorta has both a thoracic and an abdominal component. A thoracic aortic aneurysm is located in the chest, and an abdominal aortic aneurysm
is located in the abdomen. Not pictured here are aneurysms which span
both cavities and are referred to as thoracoabdominal aortic aneurysms.
Abdominal
An abdominal aortic aneurysm
(AAA) refers to aneurysmal dilation of the aorta confined to the
abdominal cavity. Most commonly, aneurysms are asymptomatic and located
in the infrarenal position. Often, they are discovered incidentally or
on screening exams in patients with risk factors such as a history of
smoking. Patients with aneurysms which have a diameter less than 5 cm
are at <1% rupture risk per year. When the aneurysm meets size
criteria it can be treated with aortic replacement or EVAR.
Thoracic
Thoracic aortic aneurysms are contained in the chest. Aneurysms of the descending aorta can often be treated with thoracic endovascular aortic repair or TEVAR.
Treating aneurysms which involve the ascending aorta are generally
within the scope of cardiac surgeons, but upcoming endovascular
technology may allow for a more minimally invasive approach in some
patients.
Thoracoabdominal
Thoroacoabdominal aneurysms are those which span the chest and abdominal cavities. The Crawford classification was developed and describes five types of thoracoabdominal aneurysms.
Abdominal aortic aneurysms can be classified as infrarenal, juxtarenal, pararenal or suprarenal as depicted in the illustration.
The Crawford Classification (Extent I-IV) and the Safi modification
(Extent V) for thoracoabdominal aortic aneurysms is pictured above.
Other arterial aneurysms
In addition to treating aneurysms which arise from the aorta, vascular surgeons also treat aneurysms elsewhere in the body.
Indications for repair differ slightly between arteries. For
instance, current guidelines recommend repair of renal and splenic
artery aneurysms greater than 3 cm, and those of any size in women of
childbearing age; whereas celiac and hepatic artery aneurysms are
indicated for repair when their size is greater than 2 cm. This is in
contrast to superior mesenteric artery aneurysms which should be
repaired regardless of size when they are discovered.
Popliteal artery
A popliteal artery aneurysm is an arterial aneurysm localized in the popliteal artery which courses behind the knee. Unlike aneurysms located in the abdomen, popliteal artery aneurysm rarely present with rupture but rather with symptoms of acute limb ischemia
due to embolization of thrombus. Thus, when a patient presents with an
asymptomatic popliteal aneurysm that is greater than 2 cm in diameter a
vascular surgeon are able to offer vascular bypass or endovascular
exclusion depending on several factors.
Early
classification schemes of aortic dissection. Stanford type A are those
which originate in the ascending aorta whereas Stanford type B originate
distal to the left subclavian artery (descending aorta). The Debakey classification describes where the original tear is and the extent of the dissection.
Whereas cardiac surgeons
are usually in charge of managing type A dissections, type B
dissections are typically managed by vascular surgeons. The most common
risk factor for type B aortic dissection is hypertension. The first line treatment for type B aortic dissection is aimed at reducing both heart rate and blood pressure and is referred to as anti-impulse therapy.
A thoracic aortic stent graft, seen on chest X-ray which was placed during a TEVAR procedure.
Should initial medical management fail or there is the involvement of
a major branch of the aorta, vascular surgery may be needed for these
type B dissections. Treatment may include thoracic endovascular aortic
repair (TEVAR) with or without extra-anatomic bypass such as carotid-carotid bypass, carotid-subclavian bypass, or subclavian-carotid transposition.
Visceral artery dissection
Visceral artery dissections are arterial dissections involving the superior mesenteric artery, celiac artery, renal arteries, hepatic artery
and others. When they are an extension of an aortic dissection, this
condition is managed simultaneously with aortic treatment. In isolation,
visceral artery dissections are discovered incidentally in up to a
third of patients and in these cases may be managed medically by a
vascular surgeon. In cases where the dissection results in organ damage
it is generally accepted by vascular surgeons that surgery is necessary.
Surgical management strategies depend on the associated complications,
surgical ability and patient preference.
Mesenteric ischemia
Mesenteric ischemia results from the acute or chronic obstruction of the superior mesenteric artery (SMA). The SMA arises from the abdominal aorta and usually supplies blood from the distal duodenum through two-thirds of the transverse colon and the pancreas.
Chronic mesenteric ischemia
The symptoms of chronic mesenteric ischemia can be classified as abdominal angina
which is abdominal pain which occurs a fixed period of time after
eating. Due to this, patient's may avoid eating, resulting in unintended
weight loss. The first surgical treatment is thought to be performed by
R.S. Shaw and described in the New England Journal of Medicine in 1958. The procedure Shaw described is referred to as mesenteric endarterectomy. Since then, many advances in treatment have been made in minimally invasive, endovascular techniques including angioplasty and stenting.
The
renal arteries supply oxygenated blood to the kidneys. The kidneys
serve to filter the flood and control blood pressure through the
renin-angiotensin system. One cause of resistant hypertension is
atherosclerotic disease in the renal arteries and is generally referred
to as renovascular hypertension.
If renovascular hypertension is diagnosed and maximal medical fails to
control high blood pressure, the vascular surgeon may offer surgical
treatment, either endovascular or open surgical reconstruction.
Cerebrovascular disease
Carotid ultrasound.Carotid endarterectomy.
Vascular surgeons are responsible for treating extracranial
cerebrovascular disease as well as the interpretation of non-invasive
vascular imaging relating to extracranial and intracranial circulation
such as carotid ultrasonography and transcranial doppler. The most common of cerebrovascular conditions treated by vascular surgeons is carotid artery stenosis which is a narrowing of the carotid arteries and may be either clinically symptomatic or asymptomatic (silent). Carotid artery stenosis is caused by atherosclerosis whereby the buildup of atheromatous plaque inside the artery causes narrowing.
Symptoms of carotid artery stenosis can include transient ischemic attack or stroke.
Both symptomatic and asymptomatic carotid stenosis can be diagnosed
with the aid of carotid duplex ultrasound which allows for the
estimation of severity of narrowing as well as characterize the plaque.
Treatment can include medical therapy, carotid endarterectomy or carotid stenting.
Peripheral artery disease PAD is the abnormal narrowing of the arteries which supply the limbs. Patients with this condition can present with intermittent claudication which is pain mainly in the calves and thighs while walking. If there is progression, a patient may also present with chronic limb threatening ischemia
which encompasses pain at rest and non-healing wounds. Vascular
surgeons are experts in the diagnosis, medical management, endovascular
and open surgical treatment of PAD.
Illustration of atherosclerosis causing arterial obstruction which clinically presents at peripheral artery disease.
ABI testing is used by vascular surgeons in the diagnosis of PAD. The blood pressure in the arm and leg are compared as a ratio.
Angioplasty (pictured) and stenting are two endovascular treatments employed by the vascular surgeon.
Management of venous diseases
Chronic venous disease
Chronic venous insufficiency
is the abnormal pooling of blood in the lower extremity venous system
which can lead to reticular veins, varicose veins, chronic edema and
inflammation among other things. Population data suggests that chronic
venous insufficiency affects up to 40% of females and 17% of males. When chronic insufficiency leads to pain, swelling and skin changes it is referred to as chronic venous disease. Chronic venous insufficiency (CVI) is distinguished from post-thrombotic syndrome (PTS) in that CVI is primarily an issue of valvular incompetence of the superficial or deep veins whereas PTS may occur as a long-term complication of deep venous thrombosis.
The vascular surgeon has several modalities to treat lower
extremity venous disease which including medical, interventional and
surgical procedures. For instance, venous ulceration may be treated with
Unna's boots, superficial venous reflux with radiofrequency, laser ablation or vein stripping
if indicated. When indicated, insufficiency in the deep veins may be
treated with reconstruction of the venous valves with internal or
external valvuloplasty.
Varicose veins
A medical illustration of lower extremity varicose veins.
Lower extremity varicose veins is the condition in which the superficial veins become tortuous(snakelike) and dilated (enlarged) to greater than 3mm in the upright position. Incompetent or faulty valves are often present in these veins when investigated with duplex ultrasonography. Vascular treatments can include compression stockings, venous ablation or vein stripping, depending on specific patient presentation, severity of disease, among other things.
Nonthrombotic iliac vein lesions
Nonthrombotic iliac vein lesions (NIVL) include May-Thurner Syndrome
(MTS) whereby there is compression of the left iliac venous outflow
usually by the right iliac artery leading to left leg discomfort, pain,
swelling and varicose veins. NIVL encompasses compression of the iliac
veins on either the right or left side.
Vascular surgeons may offer different treatment modalities depending on
the patient presentation. Minimally invasive diagnostic and therapeutic
options might include intravascular ultrasound, venography and iliac vein stenting whereas surgical management may be offered in refractory cases.
Surgical management strategies involve reconstruction or bypass of the
affected segment such as cross-pubic venous bypass, also known as the
Palma procedure.
Deep vein thrombosis
Deep vein thrombosis (DVT) is the formation of thrombus in a deep vein. DVT is more likely to occur in the lower extremity than the upper extremity or jugular vein. When a DVT involves the pelvic and lower extremity veins it can sometimes be classified as an iliofemoral DVT. Some evidence to suggests that performing an intervention in these cases may be beneficial whereas other evidence does not. Overall, the data shows that there may be a reduction in the incidence in post-thrombotic syndrome in patients who undergo certain procedures for iliofemoral DVT but it is not without risks.
A vascular surgeon may offer venogram, endovascular suction or
mechanical thrombectomy and in some cases pharmacomechanical
thrombectomy. Some lower extremity DVT can be severe enough to cause a condition called phlegmasia cerulea dolens or phlegmasia alba dolens
and can be limb-threatening events. When phlegmasia is present,
intervention is often warranted and may include venous thrombectomy.
Post-thrombotic syndrome
Post-thrombotic syndrome (PTS) is a medical condition that sometimes occurs as a long-term complication of DVT and is characterized by long term edema
and skin changes following DVT. Presenting symptoms may include
itchiness, pain, cramps and paresthesia. It is estimated that between
20% and 50% of patients will experience some degree of PTS. A treatment strategy for PTS may involve the use of compression stockings.
Pulmonary embolism
Surgical management of an acute pulmonary embolism (pulmonary thrombectomy)
is uncommon and has largely been abandoned because of poor long-term
outcomes. However, recently, it has gone through a resurgence with the
revision of the surgical technique and is thought to benefit certain
people. Chronic pulmonary embolism leading to pulmonary hypertension (known as chronic thromboembolic hypertension) is treated with a surgical procedure known as a pulmonary thromboendarterectomy.
Patients with chronic kidney disease may have progression of disease which requires renal replacement therapy to filter their blood. One strategy for this therapy is hemodialysis,
which is a procedure that involves filtering a patient's blood to
remove waste products and returning their blood back to them. One method
which avoids repeated arterial trauma is to create an arteriovenous fistula (AVF). The first procedure described for this purpose is named the Cimino fistula,
after one of the surgeons who first had success with it. Vascular
surgeons may create an AVF for a patient as well as undertake minimally
invasive procedures to ensure the fistula remains patent.
Management of vascular trauma
One
way that vascular trauma may be understood is by categorizing vascular
injury by three criteria: mechanism of injury, anatomical site of injury
and contextual circumstances. Mechanism of injury refers to etiology,
e.g. iatrogenic, blunt, penetrating, blast injury,
etc. Anatomical site functionally refers to whether there is
compressible versus non-compressible hemorrhage, while contextual
circumstances refers to injuries sustained in the civilian or military
realm. Each context can be further broken down: military into combatant
vs. noncombatant and civil into urban vs rural trauma.
This categorization scheme is of both epidemiologic and clinical
significance. For instance, arterial injury in military combatants
currently occurs predominantly in males in their twenties who are
exposed to improvised explosive devices or gunshot wounds; whereas in
the civilian realm, one study conducted in the United States showed the
most common mechanisms to include motor vehicle collisions, firearm
injuries, stab wounds and falls from heights.
Blunt thoracic aortic injury
Advances
in vascular surgery, specifically endovascular technologies, have led
to a dramatic change in the operative approach to blunt thoracic aortic injury (BTAI). BTAI results from a high speed insult to the thorax such as a motor vehicle collision
or a fall from a height. One widely-used classification scheme is based
on the extent of injury to the anatomic layers of the aorta as seen
with computed tomography angiography or intravascular ultrasound.
Grade 1 BTAI are those which tear the aortic intima; grade 2 injuries
refer to intramural hematoma; grade 3 injuries are pseudoaneurysm and
are only contained by adventitial tissue; and grade 4 refer to free
rupture of blood into the chest and surrounding tissue. When indicated, first line intervention involves TEVAR.
A siege engine is a device that is designed to break or circumvent heavy castle doors, thick city walls and other fortifications in siege warfare.
Some are immobile, constructed in place to attack enemy fortifications
from a distance, while others have wheels to enable advancing up to the
enemy fortification. There are many distinct types, such as siege towers that allow foot soldiers to scale walls and attack the defenders, battering rams that damage walls or gates, and large ranged weapons (such as ballistae, catapults/trebuchets and other similar constructions) that attack from a distance by launching projectiles. Some complex siege engines were combinations of these types.
Siege engines are fairly large constructions – from the size of a small house to a large building. From antiquity up to the development of gunpowder,
they were made largely of wood, using rope or leather to help bind
them, possibly with a few pieces of metal at key stress points. They
could launch simple projectiles using natural materials to build up force by tension, torsion, or, in the case of trebuchets, human power or counterweights coupled with mechanical advantage. With the development of gunpowder and improved metallurgy, bombards and later heavy artillery became the primary siege engines.
Siege
engine in Assyrian relief of attack on an enemy town during the reign
of Tiglath-Pileser III 743-720 BC from his palace at Kalhu (Nimrud)
The earliest siege engines appear to be simple movable roofed towers
used for cover to advance to the defenders' walls in conjunction with scaling ladders, depicted during the Middle Kingdom of Egypt. Advanced siege engines including battering rams were used by Assyrians, followed by the catapult in ancient Greece.
In Kush siege towers as well as battering rams were built from the 8th century BC and employed in Kushite siege warfare, such as the siege of Ashmunein in 715 BC.
The Spartans used battering rams in the Siege of Plataea
in 429 BC, but it seems that the Greeks limited their use of siege
engines to assault ladders, though Peloponnesian forces used something
resembling flamethrowers.
The first Mediterranean people to use advanced siege machinery were the Carthaginians, who used siege towers and battering rams against the Greek colonies of Sicily. These engines influenced the ruler of Syracuse, Dionysius I, who developed a catapult in 399 BC.
The first two rulers to make use of siege engines to a large extent were Philip II of Macedonia and Alexander the Great. Their large engines spurred an evolution that led to impressive machines, like the Demetrius Poliorcetes' Helepolis
(or "Taker of Cities") of 304 BC: nine stories high and plated with
iron, it stood 40 m (130 ft) tall and 21 m (69 ft) wide, weighing 180 t
(400,000 lb). The most used engines were simple battering rams, or tortoises,
propelled in several ingenious ways that allowed the attackers to reach
the walls or ditches with a certain degree of safety. For sea sieges or
battles, seesaw-like machines (sambykē or sambuca)
were used. These were giant ladders, hinged and mounted on a base
mechanism and used for transferring marines onto the sea walls of
coastal towns. They were normally mounted on two or more ships tied
together and some sambykē included shields at the top to protect the
climbers from arrows. Other hinged engines were used to catch enemy
equipment or even opposing soldiers with opposable appendices which are
probably ancestors to the Romancorvus. Other weapons dropped heavy weights on opposing soldiers.
Roman siege engines.
The Romans preferred to assault enemy walls by building earthen ramps (agger) or simply scaling the walls, as in the early siege of the Samnite city of Silvium (306 BC). Soldiers working at the ramps were protected by shelters called vineae, that were arranged to form a long corridor. Convex wicker shields were used to form a screen (plutei or plute in English) to protect the front of the corridor during construction of the ramp. Another Roman siege engine
sometimes used resembled the Greek ditch-filling tortoise of Diades,
this galley (unlike the ram-tortoise of Hegetor the Byzantium) called a musculus
("muscle") was simply used as cover for sappers to engineer an
offensive ditch or earthworks. Battering rams were also widespread. The Roman Legions first used siege towers c. 200 BC; in the first century BC, Julius Caesar accomplished a siege at Uxellodunum in Gaul using a ten-story siege tower.
Romans were nearly always successful in besieging a city or fort, due
to their persistence, the strength of their forces, their tactics, and
their siege engines.
The first documented occurrence of ancient siege engine pieces in Europe was the gastraphetes
("belly-bow"), a kind of large crossbow. These were mounted on wooden
frames. Greater machines forced the introduction of pulley system for
loading the projectiles, which had extended to include stones also.
Later torsion siege engines appeared, based on sinew springs. The onager was the main Roman invention in the field.
The earliest documented occurrence of ancient siege-artillery pieces
in China was the levered principled traction catapult and an 8 ft
(2.4 m) high siege crossbow from the Mozi (Mo Jing), a Mohist text written at about the 4th – 3rd century BC by followers of Mozi who founded the Mohist school of thought during the late Spring and Autumn period and the early Warring States period.
Much of what we now know of the siege technology of the time comes from
Books 14 and 15 (Chapters 52 to 71) on Siege Warfare from the Mo Jing.
Recorded and preserved on bamboo strips, much of the text is now
extremely corrupted. However, despite the heavy fragmentation, Mohist
diligence and attention to details which set Mo Jing apart from other
works ensured that the highly descriptive details of the workings of
mechanical devices like Cloud Ladders, Rotating Arcuballistas and
Levered Catapults, records of siege techniques and usage of siege
weaponry can still be found today.
Elephant
Indian, Sri Lankan, Chinese and Southeast Asian kingdoms and empires used war elephants as battering rams.
Medieval designs include a large number of catapults such as the mangonel, onager, the ballista, the traction trebuchet
(first designed in China in the 3rd century BC and brought over to
Europe in the 4th century AD), and the counterweight trebuchet (first
described by Mardi bin Ali al-Tarsusi
in the 12th century, though of unknown origin). These machines used
mechanical energy to fling large projectiles to batter down stone walls.
Also used were the battering ram and the siege tower,
a wooden tower on wheels that allowed attackers to climb up and over
castle walls, while protected somewhat from enemy arrows.
A typical military confrontation in medieval times was for one side to lay siege to an opponent's castle.
When properly defended, they had the choice whether to assault the
castle directly or to starve the people out by blocking food deliveries,
or to employ war machines specifically designed to destroy or
circumvent castle defenses. Defending soldiers also used trebuchets and
catapults as a defensive advantage.
Other tactics included setting fires
against castle walls in an effort to decompose the cement that held
together the individual stones so they could be readily knocked over.
Another indirect means was the practice of mining,
whereby tunnels were dug under the walls to weaken the foundations and
destroy them. A third tactic was the catapulting of diseased animals or
human corpses over the walls in order to promote disease which would
force the defenders to surrender, an early form of biological warfare.
The development of specialized siege artillery, as distinct from field artillery, culminated during World War I and World War II. During the First World War, huge siege guns such as Big Bertha were designed to see use against the modern fortresses of the day. The apex of siege artillery was reached with the German Schwerer Gustav gun, a huge 80 cm (31 in) caliber railway gun, built during early World War II. Schwerer Gustav was initially intended to be used for breaching the French Maginot Line
of fortifications, but was not finished in time and (as a sign of the
times) the Maginot Line was circumvented by rapid mechanized forces
instead of breached in a head-on assault. The long time it took to
deploy and move the modern siege guns made them vulnerable to air attack
and it also made them unsuited to the rapid troop movements of modern warfare.