Pediatric Interventional Neuroradiology: “How I Do It” v. I – Diagnostic Angiography

Abstract

Pediatric neurointervention differs from the adult in several important respects. Here we describe a modern approach to readily acquire diagnostic quality images of children. Preparation, access, angiogragraphy and closure have evolved along with new knowledge and technology. This timely “how I do it” series addresses each topic utilizing literature review and our own experience over 35 years.

Our goal is to inform how one readily acquires diagnostic quality images, in well-selected children, without complication. To this end, we integrate personal expertise with the existing literature in a “how I do it” format relevant to both aspiring and experienced practitioners. “Well-selected” simply means angiography will likely change clinical management by answering a specific question the best cross-sectional imaging could not address. Now, on to the “how”: subsequent passages address preparation, access, angiography and closure. While considerations unique to the neonate and infant are discussed, angiography is almost always performed in conjunction with embolisation. Anaesthesia, hydration, temperature, access and dosing challenges tilt risk over benefit for most catheter-based diagnostic studies in this population. ¹

Preparation

The angiography suite is no place for a child, especially a neonate, to linger. Case planning (access site, vessel selection, acquisition modes) and staff communication minimise room time by allowing medicines to be drawn and devices prepped before the patient arrives. Almost all paediatric drugs follow weight-based dosing including heparin and iodinated contrast ² (Table 1). A forced air heating blanket is placed on the table and the room temperature adjusted as needed to prevent hypothermia.

Table 1.

Medications.

Compound	Dose	Notes
Iodinated contrast limit	4–6 mL/kg	Endeavor to remain within this volume, although specific clinical scenarios may require additional contrast
Intravenous heparin	Loading dose: 20–60 units/kg—heparin in vascular access cocktail	If procedure extends beyond second administration of a maintenance dose, consider checking PTT or ACT
	Maintenance dose: 1/5 un-subtracted loading dose q 1 h
Flush bag (1L) heparin	0–14 kg: 2000 units
	15–34 kg: 3000 units
	>34 kg: 5000 units
Vascular access cocktail heparin	36 units/kg max dose 2500 units	Infused into all radial sheaths as well as femoral in small children
Vascular access cocktail nitroglycerin	2.9 mcg/kg max dose 200  mcg
Vascular access cocktail verapamil	0.04 mg/kg max dose 2.5 mg

We affix bubble filters (Pall Medical) to continuous heparinised saline drips to further reduce emboli after manually clearing the lines of air. Saline and contrast are drawn from a manifold and “burped” under vacuum to remove bubbles (Figure 1). Surgical towel fibres represent another source of emboli^3,4 and therefore only non-woven, low-lint varieties are placed onto the operative field. ⁵

Figure 1.

Clearing syringe of bubbles via “burp” technique. Tip capped with non-dominant (left) thumb. Plunger retracted with dominant (right) hand creates a vacuum, drawing sidewall bubbles into solution. Then release the plunger; as it “snaps” back, any remaining bubbles are expelled to the surface of the meniscus. Remove left thumb and expel these bubbles from the tip.

General anaesthesia (GA) ensures a motionless, comfortable child with negligible cardiopulmonary risks compared to adults. Long-term cognitive effects have also been largely excluded.^6,7 Anaesthetic considerations instead focus on blood pressure parameters, availability of protamine and pharmacologic paralysis (avoided in cases where intra-operative monitoring (IOM) is planned, e.g., balloon test occlusion). Balancing total intravenous anaesthesia depth with patient comfort/motion for IOM is challenging before ∼ 6 months of age and generally not feasible in the neonatal period.

Once the patient is draped, complete a final checklist to prevent delays that might prolong sheath or catheter dwell time:

• - ET tube is above the carina

• - Cranium is free of radiopaque lines or monitoring equipment that would impair image quality

• - Rotational angiogram “dry run” performed (if 3DRA is planned)

• - An alternate pulse oximeter is placed in case the accessed extremity loses waveform

• - Forced air blanket is under, not over, the patient to minimise disruption of the operative field

Access

Despite their capacious nominal diameter, ⁸ paediatric arteries are highly vasoactive and readily spasm if repeatedly punctured and haematoma collects adjacent. Care must be taken to achieve first pass cannulation, such as employing US and other techniques described below. Otherwise, let the vessel relax by applying topical nitroglycerin and a warm saline-soaked 4 × 4 and attempt another extremity. A bare catheter will stretch and exert shear stress on the artery, also inducing spasm. Sheaths address the latter irritant and should be uniformly placed (except in the umbilical artery). Prelude Ideal 4 Fr (Merit Medical) is currently the smallest OD sheath at 1.78 mm ⁹ and inserts over an 018″ wire, obviating micropuncture exchange. Vascular “cocktails” (Table 1) may hasten smasmolysis and prevent thrombosis, although the target endothelium tends to be proximal to the (often occlusive) sheath tip and receives no first pass circulation effect. Ideally, sheaths would come coated with the cocktail, akin to drug eluting balloons. Tegaderms placed over the hub and side arm minimise sheath movement, which can further spasm or avulse the artery.

Neonate femoral access should be avoided if possible. Ask ICU colleagues to preserve the umbilical artery with a catheter (UAC) as soon as an intervention is conceived. If the artery has recently closed, staff there may still attempt to recanalise it. Umbilical access involves exchanging the indwelling UAC over a stiff ∼300 cm wire (e.g., Aristotle 14 Zoom) for either a diagnostic (e.g., 4 Fr Glide or 3 Fr Mongoose) or intermediate (e.g., Phenom Plus or DAC 044) catheter. The recurrent course of the artery risks perforation when passing a sheath. A new UAC may be exchanged back into the vessel at the conclusion of the procedure to maintain access. ¹⁰

When umbilical access is untenable, we often involve more experienced Intensivists or Cardiologists (who attain almost daily practice) in the femoral approach. For instance, requesting a femoral “A line” be placed in the ICU, which one can readily exchange for a sheath in the suite, saves time for angiography and intervention. Otherwise, femoral access is facilitated by placing a blood pressure cuff under the buttocks and inflating to protrude the pelvis over the knees. The thighs are spread into a lithotomy position. The superior acetabular rim is marked under X-ray to define the desired skin entry level just inferior. Familiarity with both transverse and longitudinal ultrasound planes is helpful, as one may switch between the two during needle advancement. Briefly activating colour Doppler distinguishes artery from vein in the longitudinal view (Figure 2). It is important to enter the common femoral artery rather than the superficial, as collateral flow to the extremity is much impaired if the latter becomes occluded.

Figure 2.

Femoral access. BP cuff is placed under the buttocks and inflated to raise the pelvis at, or slightly above, the knees. The thighs are abducted to maximise femoral artery exposure. Note: pulse oximeters on both lower extremities; acetabulum is localised with X-ray to define a skin entry zone in the region of the femoral head. The skin is marked for the ultrasound transducer; greyscale and colour Doppler images of the common femoral artery (A) and vein (V) in transverse plane; greyscale and colour Doppler images of the common femoral artery (A) and vein (V) in longitudinal plane; X-ray performed after access obtained to demonstrate needle tip relative to the acetabulum. A high stick can be aborted prior to sheath placement.

Access becomes much easier in infants and young children (<10 years), yet 4 Fr remains a suitable sheath size for diagnostic purposes (and most interventions). The larger arteries of older children (≥10 years) may accommodate 4 Fr radial and 5 Fr femoral access. The latter is compatible with (preferably extravascular) closure devices such as Mynx and Vascade. Closure devices such as Vasoseal have been shown to have higher complications in paediatric patients. ¹¹ On the other hand, external haemostatic patches (Syvek) or balloon dressings (Safeguard) are much more benign. ¹² Radial eliminates post-op bedrest and is preferred for outpatients. Snuffbox arteriotomy preserves the superficial palmar arch ¹³ and is attempted first. A 20 cm + length sheath covers the smaller and more spasm-prone forearm arterial segment, facilitating smooth catheter advancement.

Angiography

Once the sheath is placed, intravenous heparin is administered prior to catheter insertion (Table 1). For cerebral angiography from the femoral approach, an appropriate length 4 Fr angled Glide catheter (Terumo) allows for mostly wireless navigation. Continuous heparinised saline drip at a rate of ∼ 1 drop/2 s prevents blood from accumulating in the lumen without infusing excessive heparin or sodium. Stiffer (e.g., Vert, Mongoose) and recurved (e.g., Simmons) catheters should be advanced over a guidewire. When double-flushing, aspirate only ∼1 mL of blood in neonates and infants to avoid anaemia. Great vessel selection by bony landmarks alone reduces contrast usage. Digital subtraction angiography requires at least 3 fps and a rapid bolus of ∼5 mL 60/40 (contrast to heparinised saline), given children's hyperdynamic cardiovascular state relative to adults. Hand injection 3DRA with a 40 or 50 mL syringe requires less force and contrast than a power injector. Storing and automatically returning to the same table/image detector position for each run lends procedural efficiency.

Radiation dose has received much attention and is particularly germane to spinal angiography, where most radiosensitive organs are exposed. ¹⁴ The cerebrum, by contrast is quite resistant. ¹⁵ Operators should adopt paediatric settings for pulse rate, frame rate, collimation etc. that balance image quality with dose.^16,17 However, no adjustment can offset the significant (>50%) dose reduction provided by modern fluoroscopy units with more efficient photon detectors and advanced image processing software.^18,19

Closure

We employ manual compression to all 4 Fr arteriotomies. The femoral artery is compressed until a dampened or absent waveform appears on the lower extremity pulse oximetry tracing for <2 min. Pressure is then reduced until the waveform returns, yet hemostasis maintained and held so for another ∼10 min. Babies and toddlers receive a padded IV board (Figure 3) under their thigh and buttock, secured in place with ACE wrap or Coban (if no latex allergy), before extubation. Immobilisation reduces bleeding from the access site. Snuffbox closure is faster: a Tip Stop is placed over the arteriotomy and secured with Coban. Manual compression for more than a couple minutes is unusual. In larger children who undergo an intervention necessitating 5 Fr or larger access, we often use extravascular closure devices such as Mynx, but remain conservative regarding manual compression (5–7 min) and bedrest (3–4 h) given their higher failure rate.^20,21 Staff compress the arteriotomy at extubation, as straining and movement are common during this process.

Figure 3.

Immobilisation. A firm plastic “IV” or purpose-built board placed from calf to buttock and secured with Coban or ACE wrap minimises lower extremity movement during extubation and 4 h bedrest.