Acute Pediatric Arterial Occlusion

Iatrogenic Arterial Injury

Children generally suffer acute occlusion of normal arteries where etiological factors include artery wall injury and stasis of blood flow. Arterial cannulation injures the vessel wall and denudes the endothelium exposing prothrombotic subendothelial matrix to flowing blood resulting in platelet adhesion, aggregation and activation of the clotting cascade. The more delicate structure of incompletely developed arteries in younger children likely predisposes them to more severe wall disruption from cannulation. ^{, ,} The relatively small caliber of the femoral and iliac arteries creates a size mismatch with arterial sheaths, catheters and cannulas, often made worse by intense vasospasm. ^{, ,} The result is lumen obstruction with stagnant flow contributing to thrombosis. Other factors suggested to increase risk of catheter-associated thrombosis in young children include inadequate prophylactic anticoagulation, elevated hematocrit common in neonates, and hemoconcentration from sepsis or dehydration ( Fig. 190.1 ).

Femoral artery catheterization carries a 2% risk of an injury requiring operative repair and is the leading cause of acute limb ischemia in children. Femoral cannulation is primarily for invasive blood pressure monitoring in critically ill children, cardiac catheterization, percutaneous treatment of congenital heart and aortic abnormalities, cardiopulmonary bypass, and extracorporeal membrane oxygenation (ECMO). ^{, , ,} Thrombosis was reported in 1.3% of infants less than six months of age undergoing cardiac catheterization in the KID database but this is an underestimation, as much higher rates of occlusion have been reported in prospective clinical trials (8%–9%).

Patient factors correlating with acute femoral occlusion from catheterization include younger age and severe vasospasm. Vasospasm is seen in up to 62% of children during catheterization and is more frequent and severe in neonates. ^{, ,} The combination of catheter size relative to vessel size was found to correlate strongly with degree of vasospasm. Age is a surrogate for smaller vessels with less wall development. In a recent study of children with mean age of 22 ± 8 months of age, the average diameter of the common femoral artery was 3.1 mm. Tadphale et al. recently constructed nomograms for femoral artery diameter vs. age to aid in decisions regarding accessing vessels for diagnostic or interventional procedures ( Fig. 190.2 ). They reported average femoral artery diameter at birth of ∼2 mm, then ∼2.5 mm at 1 year of age, increasing to ∼4 mm by 4 years of age.

In a recent study employing routine use of ultrasound to examine access sites after cardiac catheterization the overall rate of femoral thrombosis was 7.9%, but in the subset of children younger than 6 months of age thrombosis increased to 23.4%. Thrombosis correlated significantly with lower weight, larger sheath size, and longer procedure duration. Others have reported similar associations with increased numbers of catheterizations. These factors reflect the complexity of the intervention, extent of vessel injury, and duration of lumen obstruction/stagnant flow.

Umbilical artery catheters carry a 1%–3% risk of symptomatic arterial thrombosis in neonates. Aortic thrombus can propagate into iliofemoral segments or embolize distally. Risk of thrombosis increases if the patient does not receive adequate heparin prophylaxis while the catheter is in place and varies with catheter positioning. If the catheter tip is positioned above the visceral aortic branches (e.g., above the diaphragm), risk of associated aortic thrombus is significantly reduced compared to tip placement below the diaphragm.

Traumatic Arterial Injury

Vascular trauma is covered extensively in separate chapters that provide comprehensive discussions on the pathogenesis and treatment of blunt and penetrating arterial injuries in adults and children (see Chs. 183 , Vascular Trauma: Extremity and 188 , Vascular Trauma in the Pediatric Population). A recent report from Wang and colleagues studied 1399 pediatric trauma patients and found 23 children who suffered concomitant vascular injuries requiring surgical intervention. As in previous reports, pediatric vascular trauma was more common in the upper extremities than lower extremities (61% vs. 30%) and penetrating injuries were less common than in adults. In a review of the National Trauma Databank, Barmparas and colleagues studied the epidemiology of pediatric vascular injuries in 251,787 traumatized children under age 16. The incidence of vascular injury was 0.6%, nearly threefold lower than for adults. The majority of injuries occurred in males (74%) and most often in the upper extremity (35.7%), abdomen (24.2%) and lower extremity (18.6%). Children with vascular trauma had a much lower mortality than adults (13.2% vs. 23.2%), but mortality among children was highest in infants (18.2%).

Spontaneous Occlusion

Sporadic small case series and case reports have described unprovoked arterial occlusion in association with a variety of inherited and acquired conditions in children ( Table 190.1 ). Spontaneous occlusions are rare and typically associated with conditions causing a hypercoagulable state. These include inherited (e.g., antithrombin and protein C or S deficiency) or acquired thrombophilia (e.g., DIC, nephrotic syndrome, antiphospholipid syndrome), ^, acute inflammation (e.g., sepsis), chronic inflammatory diseases (e.g., Behçet disease), autoimmune disorders (antiphospholipid syndrome), collagen vascular diseases, and heparin-induced thrombocytopenia (HIT). ^, The pattern of unprovoked arterial thrombosis often differs from iatrogenic or traumatic occlusions as more distal arteries are often affected, ^, as in the example of purpura fulminans in the newborn (e.g., from protein C or S deficiency), or in patients with DIC or HIT. Children with a thrombophilia are also more likely to present with concomitant venous thromboses.