The term iatrogenic derives from the Greek words iatros ("physician") and gennan ("to produce"); thus, the term refers to the consequences of medical action. In general, an iatrogenic injury is secondary to a high-risk procedure when a lower-risk option is available; secondary to a lack of medical knowledge, negligence, careless practice, or omission; or secondary to the lack of honesty or medical ethics.
Iatrogenic injuries represent a significant proportion (50%) of the pediatric vascular trauma. The proportion inversely varies with age, with neonates showing the highest percentage (80%), declining to 50% in the 2-year-old to 6-year-old group, followed by older children (33%).
Arterial injuries in infants are rare and in most cases, iatrogenic as a consequence of catheterization, venipuncture, or arterial blood sampling. These lesions require an accurate, noninvasive clinical diagnosis and prompt exploration and reconstruction, using microvascular techniques to restore perfusion and avoid morbidity and even mortality. In this age group, any suspected vascular injury needs immediate clinical and diagnostic assessment in order to avoid potential life-threatening complications. Surgery is mandatory in case of extensive arterial injuries, inadequate distal blood supply or progressive worsening of ischemic clinical findings. 
The widespread use of percutaneous vascular access in children and invasive neonatal resuscitation techniques has led to an increased incidence of vascular complications in the pediatric population. The thrombosis rate in children with vascular access ranges from 1% to 25%. [2, 3]
The risk of iatrogenic vascular injuries secondary to catheterization, cannulation for extracorporeal membrane oxygenation (ECMO), cardiopulmonary bypass, repeated venipuncture, or arterial blood sampling has increased. In particular, transfemoral catheterization, transfemoral arteriography, and umbilical-artery catheterization used for diagnostic and monitoring purposes have been associated with thromboembolism in the lower extremities.
Although the management of these injuries has significantly evolved over time, its treatment in children remains unstandardized. Treatment of these injuries in infants and small children is distinctly different from that in adults. Historically, injured vessels were ligated, or the child was given systemic heparin without repair, however, this expectant therapy resulted in poor limb outcomes, involving high amputation rates and diminished limb growth. Currently, aggressive surgical management has yielded better results, making early diagnosis and definitive repair the current management of choice. 
The children vessels small size, severe arterial vasospasm, and the consequences of diminished blood flow on limb growth must be considered. Also, the need for future growth of blood vessels and long-term duration of the repair must be accounted for.
Trauma is the leading cause of death in children and adolescents aged 1-14 years, and has become a public health problem in many parts of the world. Traumatic vascular lesions, although rare in the pediatric age group, account for 3.3-6.3% of admissions in large trauma centers.
Two thirds of pediatric arterial injuries are iatrogenic. The incidence of iatrogenic arterial injuries is increasing, especially in children younger than 2 years. Rates of arterial injury due to transfemoral cardiac catheterization are in the range of 26-67%.
The incidence of thrombosis after the use of umbilical-artery catheters is unknown. However, several reviews indicate a major complication rate of 17-20%. In one study of 4000 infants with an umbilical-artery catheter, 41 developed a major thromboembolic complication, an incidence of less than 1%.  Arterial complications of umbilical-artery catheters include vasospasm, aortic thrombosis, partial or complete iliac artery thrombosis, or embolism to peripheral and visceral tissues. The position of the umbilical-artery catheters may affect the frequency of thromboembolisms. The tips of umbilical-artery catheters may be positioned high (ie, at the level of T5-T10) or low (ie, at the level of L3-L5). The optimal position to minimize thromboembolisms remains uncertain.
Arteriovenous fistulas secondary to multiple arterial punctures in neonates are rare.
Age and size are important risk factors for arterial injuries. Infants weighting less than 10 kg are at an increased risk of vessel obstruction after cardiac catheterization. One study demonstrated an increased incidence of thromboembolism secondary to transfemoral cardiac catheterization in children younger than 10 years compared with older children. An Italian study of 2898 neonates admitted to the neonatal intensive care unit in 1987-1994 demonstrated a higher risk of iatrogenic vascular injuries in neonates with extremely low or low birth weight (2.6%) when compared to older/heavier neonates (0.3%). 
Different types of catheters used in the pediatric age group have specific associated complications.
Central venous catheters (CVCs) can lead to serious and sometimes life-threatening complications. CVCs are associated with an overall complication rate of 42-80%, including mechanical (5-19%), infectious (5-26%), or thrombotic events (2-26%). The choice of insertion site can influence the incidence and type of complication. The coagulation cascade is activated by the mere presence of a catheter in the vein, which provokes physical and chemical changes in the vascular endothelium, with hemodynamic alterations. These devices are often used in children with hematologic malignancies and hypercoagulable states.
One study revealed fibrin deposits around the catheter in 100% of patients who died while they had a CVC in place.  Complications reported with these vascular devices include infection, incorrect placement, phlebitis, vascular dissection and tears, hemothorax, pneumothorax, thrombosis, migration, pericardial or pleural effusion, chylothorax, peritoneal or retroperitoneal extravasation, cardiac arrhythmias, endocarditis, and pulmonary embolism.
Mechanical complications include arterial puncture or laceration, pneumothorax, hemothorax or mediastinal hematoma, misplacement of the catheter tip, puncture site hematoma or bleeding, and air embolism. About 0.5-1 mL/kg of air is sufficient to produce an air embolism in a child. Most international guidelines for vascular access in pediatric patients currently recommend all insertions to be done under ultrasonographic guidance. This has decreased the number of attempts needed to cannulate the vein as well as the incidence of iatrogenic injury. Placement of central venous access under fluoroscopic guidance allows for correct placement of the catheter and vein dilatation under direct vision.
A randomized controlled trial showed that catheterization of the femoral vein was associated with a significantly increased risk of overall complications compared with catheterization of the subclavian vein, with an increased risk of catheter-related infection and thrombosis.  Risk factors for catheter-related mechanical complications included the following:
Time needed for catheter insertion (number of needle passes): More than 3 attempts were associated with a 6-fold increase in the risk of a mechanical complication.
Insertion during the night (operator fatigue or inexperience): Surgeons who placed over 50 CVCs had a 50% decrease in the rate of complications.
The femoral site has a 5-fold increased incidence of catheter-related infectious complications compared with the subclavian approach. This risk can be reduced with the use of subcutaneous tunneling, antibiotic impregnated catheters, and the use of systemic antibiotics through the catheter.
The femoral approach also has an increased incidence of thrombotic complications (21%) compared with the subclavian catheters (1.9%). Some studies have shown that subclavian catheterization should be preferred over femoral lines whenever possible.
Patients with severe refractory hypoxemia may be at increased risk when the subclavian route is used, whereas patients with morbid obesity may be at higher risk with femoral cannulation.
Cardiac catheterization has a complication rate of 4-8%. Complications include trapping of the angioplasty balloon, vascular tears, lesions of the left pulmonary artery, mitral valve injury, coil migration, embolization, bleeding, and vascular laceration or perforation.
Lin et al (2001) reported on 1674 pediatric cardiac catheterizations performed with a femoral approach.  Iatrogenic inguinal lesions that required surgical repair occurred in 2%, with an overall morbidity rate of 12% and a mortality rate of 3%.
Finally, with advances in interventional catheterization, the use of large catheters and sheaths increase the risk even further.
Catheters are the most common etiologic factor for arterial thromboembolism in children, including those used for transfemoral cardiac catheterization, umbilical-artery catheters, and central or peripheral arterial lines. The mere presence of a catheter in a blood vessel is a risk factor for complications. Pediatric iatrogenic vascular lesions are secondary to arteriography, cardiac catheterism, arterial puncture, repeated blood samples, vascular access, or foreign bodies (eg, fractured or displaced guidewires or catheters). Neonatal thrombosis has been described in association with radial, femoral, pulmonary, and temporal artery lines, as well as with catheters in the femoral and jugular veins. Arterial tears are a rare but potentially lethal complication of CVC placement.
Surgical procedures are also a risk factor for vascular injury. Surgery-related lesions largely result from orthopedic procedures and tumor resections performed by surgical oncologists, who frequently perform large dissections in areas with distorted anatomy where the planes of dissection are usually lost and with large blood vessels involved in the tumor. Furthermore, perivascular tumors preoperatively treated with chemotherapy and/or radiation therapy, experience thinning of the muscular layer of the vessel wall, with fibrosis of the adventitia into the surrounding tumor, thus making them prone to injury during sub-adventitial plane dissection.
The use of partial nephrectomy or nephron-sparing surgery (NSS) has recently gained popularity in patients with renal tumors because the disease-free survival rates are similar between radical nephrectomy and NSS. Pseudoaneurysms, arteriovenous fistulas, and hemorrhage due to vascular lacerations have been reported in these patients. The interventional radiologist plays a key role in the management of such lesions because most can be successfully treated endovascularly.
Appropriate arterial access is needed to manage severe congenital heart malformations. This access should be achieved by following strict protocols, with a limited number of punctures performed by experienced staff and only in large arteries. Residents-in-training should start developing their skills in larger patients who are stable, and must be supervised at all times.
Hypotension during or immediately after a jugular or subclavian puncture should be a warning of a serious event, usually a massive hemothorax. When a vascular lesion occurs in this setting, an endovascular approach is initially preferred because it has been demonstrated to be successful in most instances. If this fails, a surgical approach is required in the shortest time possible.
The usual sequence is arterial puncture, followed by spasm and thrombotic occlusion. The vascular endothelium has a predominant role in blood coagulation and has numerous interactions with perivascular cells and adjacent tissues. Several conditions predispose neonates to thrombotic complications, including congenital heart disease with poor cardiac function, polycythemia, sepsis, maternal diabetes or toxemia, dehydration with low intravascular volume, and low-flow states. Neonates also have lowered concentrations of antithrombin III, proteins C and S, and heparin cofactor II, resulting in a prothrombotic state. Aparently, pediatric vessels are hyperreactive producing severe and persistent vasospasm.
Evidence also suggests that fibrin sleeves form on catheters. Stripping of the sleeve with removal of the catheter may result in subsequent occlusion at the puncture site or distal embolization.
In a 32-month study, investigators monitored 76 children with regard to iatrogenic injury and found that all injuries involved the arteries of the lower extremities.  This finding is consistent with the trend away from puncture of the brachial artery for invasive diagnostic and monitoring procedures. In particular, the arterial injury is often at the level of the common femoral artery secondary to multiple attempts at arterial access in the groin.
In pediatric patients, iatrogenic vascular lesions associated with use of the femoral approach can be divided in ischemic and nonischemic injuries. The former can be further subdivided as acute or chronic. Acute ischemia occurs in 41.2% of patients, whereas chronic ischemia is reported in 20.6%. Nonischemic injuries include pseudoaneurysms, arteriovenous fistulas, hemorrhage, and hematomas.
Umbilical-artery catheters may perforate or tear the vessel, producing bleeding or aortoiliac occlusion due to thrombosis with microembolization and thus occluding a visceral artery.
Pediatric iatrogenic vascular lesions can be either acute or manifest late after the original vascular procedure or trauma.
Usually, signs and symptoms of vascular injuries are immediately apparent. Patients with limb ischemia present with the classic signs of distal hypoperfusion or cold skin plus the "5 Ps:" pulselessness, pallor, paralysis, paresthesia, and pain. Pulses can be difficult to palpate in infants and small children. However, Doppler technology can be used to confirm flow and compare pressures to the contralateral uninvolved limb.
Signs may be transient or may progress quickly to gangrene. Vascular spasm in children is inversely proportional to the size and age of the patient. Simple spasm usually subsides spontaneously within 3 hours. However, lesions suggestive of vascular compromise should not be attributed to spasm. The presence of pulses distal to the lesion does not completely rule out a vascular injury because as many as 25% of patients may have distal pulses even in the presence of a vascular insult. See the images below.
Assessment of pulses and measurement of the ABI is a reliable way to assess arterial injuries. The surgeon shoud consider whether the poor perfusion statebis due to arterial injury, vasospasm, or hypoperfusion from shock. Whereas an ABI ratio of 1 is considered normal in adults and older children, the normal value for ABI index in children younger than 2 years is 0.88. 
Patients with certain vascular injuries have a late presentation. Patients with arteriovenous fistulas, mycotic aneurysms, pseudoaneurysms, renal vascular occlusion with renovascular hypertension, intermittent claudication, or growth retardation of the affected extremity present with subtle signs and symptoms. Particular attention must be paid to poor capillary refill, coolness, diminished pulses, bruits, thrills, blanching, bluish discoloration, lack of movement, and mottling.
Not all patients with thrombosis develop clinical symptoms. On occasion, the vessel is only partially blocked, and collateral blood flow is adequate. This occurs with thromboses associated with umbilical-artery catheters. In a series of 4000 patients, only 1% of patients developed clinical symptoms of thrombosis.  Patients with acute aortic thrombosis secondary to umbilical-artery catheters can present with hypertension or congestive heart failure.
Current practice states that in face of an abnormal clinical examination, if diagnostic test findings are inconclusive, surgical exploration is indicated regardless of patients age, unless the patient is too unstable to undergo surgery.
Hard signs of arterial injury (hemorraghe or expanding hematoma) are absolute indications for surgical exploration. Any child with a nonviable limb should be taken to the operating room for definitive repair. Cases involving vascular injury, a lack of flow on Doppler study, or signs of neurologic deficit should be surgically explored. On the other hand, late repair may be undertaken before the adolescent growth spurt occurs in some children with limb-length discrepancies.
Three approach strategies have been described and are based on the type of injury. Type I refers to life-threatening or limb-threatening lesions (hard signs). Patients with type I injuries require immediate surgical exploration. Type II includes lesions that do not immediately jeopardize limb integrity and that are not life-threatening; however, a vascular injury is evident. If available, Doppler study or preoperative angiography is the best first step. Otherwise, angiography can be performed during surgery. Type III includes the injuries without hard signs. However, because of their location and mechanism of injury, a vascular lesion should be suspected. These are best approached with angiography or CT angiography.
Acute aortic thrombosis is another absolute indication for surgery. Nonoperative therapy is associated with a 100% mortality rate, and several reports describe success with surgery for aortic thrombosis.
Certain anatomical factors contribute to the high rates of iatrogenic vascular injury in children. Kids have small vessels in compact anatomical spaces, and frequently require large catheters. It has been shown that catheters with a diameter over 50% of the arterial diameter result in spasm and low flow rates, making them prone to thrombosis. 
With umbilical-artery catheters, the pathway is through one of the 2 umbilical arteries into the internal iliac artery, the common iliac artery, and then the aorta. With transfemoral catheterization, the injury is at the level of the common femoral artery.
Most neonates and children in the intensive care setting are poor surgical candidates because of their medical illnesses. In this case, the risks of surgery must be weighed against the risk of limb loss and limb growth discrepancy. If surgery is contraindicated, medical therapy (ie, heparin or thrombolytic agents) can be started.