Vascular Access

Thursday, April 9, 2009

Blood Sampling

Current microtechniques of chemical analysis allow small samples of blood to be taken from children. Capillary tubes can be used for obtaining blood by “heel-stick”. If more blood is needed an antecubital or scalp vein can be used. An assistant will be needed to restrain the child. A 21 or 23 gauge scalp needle (butterfly) with preattached plastic tubing and a small syringe is used to penetrate the skin and enter the vein. Blood will flow immediately and can be aspirated gently by the assistant. Peripheral arterial blood can be sampled in a similar fashion.

Under extreme conditions an experienced physician may use a femoral vein for blood sampling. The child will need to be adequately restrained and the skin prepared with antibacterial solution. The femoral artery is palpated and a small scalp vein needle is inserted just medial to the femoral artery.

Venous Access

Access for infusion therapy can be obtained by percutaneous insertion of steel needles or plastic catheters or by cutdown on peripheral veins. When placing a percutaneous catheter make a small nick in the skin at the insertion site with a separate needle to eliminate skin traction on the plastic catheter and avoid damage to the tip of the catheter. A local anesthetic can be injected to raise a skin wheal at the insertion site. If time allows a topical anesthetic cream can be applied. The needle and plastic catheter are inserted until blood returns. The catheter can then be advanced over the needle into the vein. The catheter is secured by a plastic dressing and tape to allow monitoring of the insertion site and catheter tip site. Phlebitis is the most common complication of peripheral intravenous catheters.

Cutdowns for peripheral venous access are being used less frequently. The cephalic vein at the wrist and the saphenous vein at the ankle are good sites because of their superficial and constant location. Meticulous care should be taken in restraining the extremity and maintaining sterile technique. A vertical incision over the vein provides for greater exposure and the incision can be extended proximally if more length of the vein is needed. A plastic catheter can be placed in the vein by making an oblique venotomy. If the vein is very small the catheter can be passed over a needle. The catheter is secured with absorbable suture and the wound is closed. A sterile dressing is placed and the extremity is immobilized. Peripheral arteries can be cannulated using a similar technique.

Central Venous Access

Central venous access can be obtained by cutdown or percutaneous technique. “PIC” lines or “PCVCs” are small silastic catheters advanced into the central circulation via a peripheral vein. These central lines can be placed with or without ultrasound guidance. These lines cannot be maintained indefinitely but are ideal for several days and up to several weeks. Catheter related sepsis occurs in 2.7-6% of patients with these catheters. Venous thrombosis has been reported in 0.3%.

When short-term, multiple port or large bore access is needed, a percutaneous central line can be placed via the subclavian, external or internal jugular vein. For prolonged parenteral nutrition, blood samplings, or chemotherapy, a tunneled silastic catheter with or without a venous reservoir is preferred. The catheter can be placed with a percutaneous technique or by cutdown utilizing the subclavian, external jugular, internal jugular or saphenous veins. Fluoroscopy should be used during placement of any central line to confirm correct placement. If the subclavian vein has been accessed, a chest x-ray should be obtained to identify an associated pneumothorax or other thoracic complication.

Umbilical Vessel Access

Central venous and arterial access can be obtained through the umbilical cord in a newborn. The distal cord is amputated after the area is prepped with an aseptic solution. The umbilical vein is large and thin-walled and a 5 French plastic catheter can be advanced through the ductus venosus into the right atrium. A 3.5 French soft plastic catheter can be advanced into either of the paired umbilical arteries and positioned in the thoracic or abdominal aorta. The catheter should be positioned above the diaphragm or below the level of the renal arteries. The position of either catheter must be verified by x-ray. Heparin is added to the infusate to prevent thrombosis. Because of the high associated complication rate both of these catheters should be removed as soon as possible.

Intraosseous Access

In emergency situations intravenous access may not be easily or rapidly attainable in an infant or small child. The intraosseous route may be used for infusion of fluid, drugs and blood. Bone marrow needles, short (18-22 gauge) spinal needles or large (14-16 gauge) hypodermic needles can be used. The knee is supported and the tibia prepared with antimicrobial solution. The needle is placed in the midline of the anterior tibia on the flat surface 1-3 cm below the tibial tuberosity. The needle is directed inferiorly at a 60-90% angle and advanced until marrow content is aspirated. The fluid should flow freely into the intramedullary space. The needle is stabilized with a supported dressing to prevent dislodgement. Placement may be checked with a miniature C-arm imaging device.

It is contraindicated to use the intraosseous route in children with diseases of the bone or with ipsilateral extremity fractures. Needle dislodgement with subperiosteal or subcutaneous infiltration of fluid is the most common complication. Compartment syndrome and osteomyelitis have been reported. The infection rate is not higher using this technique. Fears over potential injury to the tibial growth plate have not been substantiated. It is generally advisable to remove an intraosseous needle as soon as possible.



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