Indications
Contraindications
As per standard PIV placement:
Risk Factors for Difficult PIV Access
Ultrasound anatomy: What Am I Looking At?
Being familiar with the anatomy and trajectory of the veins will aid in their US localization. Vessels are most easily identified in the transverse axis, providing a cross sectional view. They appear as round or oval anechoic (black) structures (figure 5). Following the vessel along its length with the ultrasound ensures it is patent, straight and free of valves and allows for estimation of trajectory to guide needle approach.
Figure 5: Ultrasound appearance of veins
Veins can be differentiated from arteries, which are also round anechoic structures by assessing their relative wall thickness, compressibility, pulsatility and continuous blood flow. Veins are relatively thin walled compared to arteries and are easily compressed when pressure is applied with the transducer—in fact if you are having a difficult time seeing any veins it is often that the superficial veins are being compressed by the probe—a light touch with a braced hand is best. In addition, when pressure is applied with the probe pulsatility of blood flow being transmitted within the vessel can be seen in arteries but not veins (video 1). Some veins near arteries can appear pulsatile due to transmitted movement so the final step in differentiating the two involves using color mode to assess for continuous flow in veins vs pulsatile flow in the arteries (video 2). Be aware that when a tourniquet is up veins often show no flow.
Video 1: Differentiating between veins and arteries on ultrasound: compression technique
Video 2: Differentiating between veins and arteries on ultrasound: color doppler technique
Many children requiring US-guided IV access will have already had multiple attempts, so it is also important to be able to identify a damaged vessel. Other than trying to avoid sites that are visibly bruised, damaged veins can also be identified on ultrasound. Damaged veins can have clot within the vessel which appears as echogenic material in the vessel lumen (figure 6). A clotted vessel is often not fully compressible as well. Other clues include a hematoma around the vessel which appears as a relatively hyperechoic collection next to or surrounding the vessel (figure 7). If you suspect a damaged vessel choose a section of vein proximal to the area or an alternate site.
Figures 6 & 7: US of damaged vessel with clot and surrounding hematoma
Veins best suited to US-guided catheter placement include those 0.3 to 1.5cm deep, 4mm in diameter with a straight course of at least 1cm in length [12]. Small or superficial veins can be more challenging to identify and cannulate via ultrasound but if successfully placed catheters in small veins have similar longevity to larger ones and those in superficial veins (less that 1.2 cm) have the best longevity and are less prone to dislodgement [12,13]. The relative location to surrounding structures such as arteries, nerves and tendons should also be considered, as they can be injured if in close proximity. It is best to choose a site which is furthest from such key structures.
Anatomy Review: Where Am I Looking?
The veins of the forearm and the saphenous are the primary targets for ultrasound guided peripheral venous access. An ideal site involves choosing a vein that in less than 1.5 cm deep, 4mm in diameter and at least 1 cm in length [12]. The vessels of the distal upper arm are also considerations in those with difficult access, although can be more challenging to cannulate due to surrounding structures and deeper location [12]. If canulating the vessels of the upper arm the cephalic vein is preferred for its superficial location and distance from other structures. The basilic vein of the upper arm is the preferred site for PICC placement and should be avoided. The brachial veins lie very deep and in proximity to arteries and nerves which make access challenging. When using the vessels of the upper arm, consider placing a mid-length catheter as dislodgement of short catheters is more common at these sites.
The cephalic vein begins at the anatomic snuff box and courses laterally along the forearm and upper arm, draining into the axillary vein (figures 1&2). The basilic vein drains the ulnar dorsal veins of the hand and courses medially up the forearm and upper arm, halfway up the forearm the basilic vein penetrates the brachial fascia and continues to run medial to the brachial artery (figures 1&2). Another site in the forearm includes the median antebrachial vein which courses the ventral aspect of the forearm between the cephalic and basilic veins before joining the basilic vein near the elbow (figures 1&2).
Figures 1&2: Upper extremity venous anatomy
The saphenous originates anterior to the medial malleolus and ascends the medial aspect of the leg (figures 3&4).
Figures 3&4: Lower extremity venous anatomy
Introduction
Point of care ultrasound (PoCUS) is the use of portable ultrasonography to answer focused clinical questions or to guide procedures.
Peripheral intravenous (PIV) access is one of the most frequent and essential emergency and inpatient medical procedures. It allows for the timely administration of medications, intravenous fluids and the collection of blood samples. Despite being a high frequency procedure, PIV access is often challenging in children, resulting in multiple attempts and significant distress. Risk factors for difficult PIV placement include young age, history of prematurity, obesity, dehydration, critical illness, chronic illness, IV drug use, difficulty visualizing or palpating veins with a tourniquet and patient anxiety [1,2,3]. The difficult IV access score (DIVA) is externally validated to predict children likely to fail PIV access attempts and includes age, prematurity, and vein characteristics [4]. Difficulty in obtaining PIV access results in diagnostic and treatment delays, as well as increased patient discomfort, anxiety and stress. In this patient population, PoCUS allows for direct visualization of the vasculature and can facilitate access.
Why Ultrasound?
Traditionally, peripheral intravenous (PIV) access is performed blindly using a basic knowledge of human anatomy, surface landmarking, and palpation. Ultrasound allows for the visualization of veins that are not clinically apparent and guides placement through visualization of the catheter and the vein [5].
Studies show the use of ultrasound to guide PIV placement results in increased overall success rates [6]. Importantly, ultrasound use decreases the numbers of attempts and number of needle redirections required; this results in less pain and anxiety for the patient and results in a faster time to successfully obtain IV access [7]. In addition, ultrasound allows access to the larger vessels of the upper arm in the case of difficult access or preference for mid-length catheter placement. Ultrasound guided (USG) PIV access is an easily acquired skill. Following a one-hour course, emergency technicians showed significant improvements in speed, patient satisfaction, number of punctures and complications [8]. A study looking at the competency of emergency nurses trained on ultrasound guided PIV procedure for difficult access patients found an 88% success rate was achieved after 15-26 attempts [9].
These benefits are particularly salient in the pediatric setting where PIV access is inherently challenging and creates significant distress for patients and their caregivers. In one hospital setting where a USG PIV program was established, there was a 20% reduction in referral for PICC placements [10] and a recent randomized controlled trial found for every 3 UG PIVs one missed attempt was prevented [11]. Finally, the use of ultrasound guided PIV access has been endorsed by the Agency for Health Care Research and Quality in the United States.
Point-of-care ultrasound can allow physicians to quickly, safely and accurately determine the presence of free fluid in the peritoneal cavity at the bedside.
In trauma, ultrasound is most useful in identifying intra abdominal hemorrhage in hemodynamically unstable patients and may be used to guide their immediate management and disposition. PoCUS has limitations as a stand-alone test for intra-abdominal injuries in stable patients. Despite its ability to detect small amounts of free fluid, the sensitivity of PoCUS is limited by patients presenting early, late or in those patients with solid organ injuries that are unaccompanied by intraperitoneal bleeding. In addition, hollow viscus and retroperitoneal injuries are not reliably detected using this technique. This limits the utility of PoCUS as a rule out test for intraperitoneal hemorrhage. However, while understanding these limitations, it is clear that PoCUS can be used to improve the quality and efficiency of emergent care in the pediatric trauma patient.
The pelvis is the most dependent area in the supine patient and the most sensitive view to identify free fluid in the abdomen. In this view, the bladder is used as a window to identify free fluid. It is important to view the pelvis in 2 planes to maximize sensitivity.
Figure 7: Pelvic scanning technique (remember to scan in two views: transverse and longitudinal)
When placing the probe in the suprapubic view you are using the bladder as an acoustic window to get transverse and longitudinal cross sections of the patient’s pelvis (figure 8). Fluid often collects in the recto vesicular space in males and in the rectouterine space (pouch of Douglas in females) but a complete investigation involves looking anterior, lateral and posterior to the bladder to ensure that small amounts of free fluid are not missed.
Figure 8: When scanning suprapubic area in the transverse orientation, one is using the bladder as an acoustic window to the bladder, reproductive organs and pelvic brim.
Figure 9: When scanning the suprapubic area in the longitudinal orientation, the bladder is used as an acoustic window to view the reproductive organs and pelvic brim.
Most superficially the bladder is easily identified. Deep to the bladder the reproductive organs are visible: the uterus and cervix in females, and the prostate and seminal vesicles in males. Deep to that lies the rectum and finally the pelvic rim.
Figure 10: Normal suprapubic sonoanatomy, with the bladder highlighted in blue and uterus in green. Areas of interest include the recto vesicular space (1) and posterolateral borders (2) of the bladder and well as the pouch of Douglas in women (3).
Video 6: Pelvis, normal transverse
Video 7: Pelvis, normal transverse
Fluid often collects in the recto vesicular space in males and in the rectouterine space (pouch of Douglas in females) but a complete investigation involves looking anterior, lateral and posterior to the bladder and reproductive organs in all directions to ensure small amounts of free fluid are not missed (video8). The pelvis is the most common area for free fluid to collect in supine pediatric patients [11].
Video 8: Pelvis, free fluid
The left upper quadrant view uses the spleen as a window to identify free fluid within the abdominal cavity.
Figure 4: LUQ scanning technique
When placing the probe in the LUQ you are using the spleen as an acoustic window to get a coronal cross section of the patient’s abdomen (figure 5). Unlike the liver, the spleen is mobile and thus the entire area around the spleen must be investigated for fluid, including: (1) the sub-diaphragmatic space (superiorly), (2) the splenorenal interface and (2) the caudal tip of the spleen.
Figure 5: When scanning the left upper quadrant, one uses the spleen as an acoustic window to get a coronal view of the spleen, right kidney and splenorenal interface.
Superficially, the ribs and chest wall are most easily identified by hypoechoic rib shadows projecting into the abdomen. Deep to the chest wall, the spleen is encountered, followed by the splenorenal interface and left kidney (figure 6, video 4).
Figure 6: Normal LUQ sonoanatomy with the spleen highlighted in blue, left kidney in green, diaphragm in red and vertebral bodies in yellow. Areas of interest include the superior pole of the spleen including the subdiaphragmatic space (1), splenorenal interface (2) and the inferior pole of the spleen (3).
Video 4: LUQ, normal view
Free fluid appears as anechoic stripes or collections around the spleen (video 5).
Video 5: LUQ, free fluid
Pitfalls
Similar to the right upper quadrant, false negative scans are most commonly caused by operator error—due to failing to fully investigate circumferentially around the spleen small amounts of fluid being present or clotted blood. False positives due to perinephric fat and edge artifact also occur in the left upper quadrant. The stomach bubble can also interfere with image interpretation, obscuring free fluid in some cases and mimicking it on others. Differentiating stomach from other structures can be done via anatomic location, appearance of the heterogenous contents and presence of the stomach wall.
The right upper quadrant view uses the liver as an acoustic window to identify free fluid within the abdominal cavity. This is one of the most important views of the abdominal FAST. Free fluid often accumulates in the RUQ as the right paracolic gutter directs fluid from the pelvis to the RUQ and the phrenicocolic ligament and mesentery direct fluid from the LUQ to RUQ.
Figure 1: Scanning technique of the RUQ
When placing the probe in the RUQ you are using the liver as an acoustic window to get a coronal cross section of the patient’s abdomen (figure 2).
Figure 2: When scanning the right upper quadrant, use the liver as an acoustic window to get a coronal view of the liver, right kidney and hepatorenal interface.
Nearest to the probe, the lateral chest wall containing muscle and ribs is easily identified. Often, the hypoechoic rib shadows can be seen projecting into the abdomen. Deep to the chest wall the liver is encountered, followed by the hepatorenal interface and right kidney. The domed diaphragm can be seen cranial to the liver and the vertebral bodies and great vessels can often be identified in the far field deep to the kidney (figure 3, video 1).
Figure 3: Normal RUQ sonoanatomy with the liver highlighted in blue, right kidney in green, diaphragm in red and vertebral bodies in yellow. Your areas of interest include the sub-diaphragmatic space (1), Morrison’s pouch (2) and the liver tip (3).
Video 1: RUQ, normal
When intraperitoneal free fluid is encountered due to infection, ascites or hemorrhage fluid often collects in right paracolic gutter around the caudal edge of the liver and in morrison’s pouch, or the hepatorenal interface (video 2 & 3). Fluid appears as an anechoic stripe or collection in these areas only bounded by the surrounding anatomical structures. In pediatric patients the second most common area for fluid to collect is in the right paracolic gutter adjacent to the caudal liver edge [11].
Video 2: RUQ, free fluid in Morrison’s pouch
Video 3: RUQ, free fluid around the caudal liver tip
PoCUS for abdominal free fluid is not foolproof.
False negative scans are most commonly caused by operator error. Other causes include patients who only have small amounts of fluid in their abdomen, such as trauma patients presenting early or with minimal hemorrhage. In addition, in trauma patients with delayed presentations, blood can clot which can prevent it from collecting in dependent regions or can make it harder to distinguish on ultrasound (due to the variable echogenicity of clotted blood).
False positives can occur as well, most commonly due to perinephric fat or edge artifact. In the case of perinephric fat, free fluid can often be distinguished as anechoic as opposed to hypoechoic, as fat is. In addition, free fluid is bound only by the organs themselves, while perinephric fat is lined by apparent hyperechoic fascial lines giving a “railroad track” or “marbled” appearance. Edge artifact can sometimes be seen projecting from the edge of a curved structure, usually the kidney; it often is less distinct than free fluid, gets larger as it goes deeper and crosses anatomical boundaries—similar to a rib shadow, whereas free fluid tends to be anechoic, well-defined and narrows to dissect planes and respects anatomic boundaries.
To fully evaluate the peritoneal cavity for free fluid, the abdomen must be scanned systematically in three areas. Studies have shown that while the pelvic view is generally the most sensitive, there are several scenarios such as isolated organ trauma in which fluid can be found in one view but not another. We will discuss each view separately.