The Ultrasound

• Ultrasound machine
• High-frequency linear transducer
• Sterile ultrasound sheath & sterile ultrasound gel

 

The Sterile Field

• Cleaning solution (chlorhexidine, alcohol or betadine)
• Sterile towels & gauze packs
• Marking pen
• Personal protective equipment (gloves, gown, mask and hairnet)

 

The Nerve Block

For the superficial local anesthetic

• One 25G 0.5-inch needle (for superficial local anesthetic injection)
• 1% Lidocaine (2-3 mL in 5mL syringe)

 

For the femoral nerve block

• One echogenic needle (e.g., Pajunk 22G or 21G needle, if available)
• One 22G spinal needle (if echogenic needle unavailable)
• One IV-adaptor (to aid in aspiration/injection)
• Local anesthetic (drawn up in a 20mL syringe)
  • For anesthetic considerations see table
  • Note: maximum anesthetic volume 25mL for all patients

Local Anesthetic (no epi)	Onset	Duration	Recommended Dose	Max Dose	Notes
Lidocaine	5-15mins	2-5hrs	4mg/kg (0.4mL/kg of 1%)	5 mg/kg (0.5mL/kg of 1%)	1%: 10mg/mL 2%: 20mg/ml
Bupivacaine	15-40mins	6-10hrs	1.5 mg/kg (0.6mL/kg of 0.25%)	2.5 mg/kg (1mL/kg of 0.25%)	0.25%: 2.5mg/mL
Ropivacaine	15-40mins	5-9hrs	1.5mg/mg (0.8mL/kg of 0.25%)	3 mg/kg	0.25% 2.5mg/mL

Table 3: Anesthetic Considerations

 

Anatomy of the Inguinal Crease

Prior to placing the ultrasound probe on the patient, it is important to understand the cross-sectional anatomy at the level of the inguinal crease. Most superficially you will find the skin and subcutaneous tissue. Immediately deep to this lies the fibrous membrane of the fascia lata. Deep to the fascia lata, lies the femoral nerve, artery and vein (from lateral to medial).  Of note, medially the femoral artery and vein are surrounded by the thick femoral sheath while laterally the femoral nerve is surrounded by the fascia iliaca. Deep to the neurovascular bundle you will identify the psoas and pectineus muscle, again from lateral to medial (figure 4).

 

Figure 4: Anatomy of the Inguinal Crease

 

Sonographic Anatomy

The ultrasound transducer is first placed along the inguinal crease directly above where the femoral artery is palpated. First, identify the femoral artery and vein. Both will appear as hypoechoic (dark) structures, but the femoral artery will also be non-compressible and pulsatile. Remember, the femoral vein lies medial to the artery and will collapse when pressure is applied with the ultrasound transducer, if you cannot see the vein reduce the pressure you are applying with the transducer until the vein appears medial to the artery (figure 7).

 

Figure 5: Differentiating the femoral artery from the femoral vein.

 

The femoral nerve lies lateral to the femoral sheath which contains the femoral artery, and femoral vein (figure 6) and is covered by the hyperechoic linear plane of the fascia iliaca. The femoral nerve is typically immediately superficial to the hypoechoic iliopsoas muscle (7, 8). The femoral nerve has a hyperechoic appearance on ultrasound and can vary between a circular, triangular and flat appearance (Video 1).

 

Video 1: Sono-anatomy of the inguinal crease

 

In some patients you may see the deep inguinal lymph nodes lying medial to the femoral vein. Lymph nodes appear as slightly hyperechoic circular structures which can easily be confused with the femoral nerve. However, they will be located much more medially than the femoral nerve, and they will disappear from the screen as the ultrasound probe is translated from caudad to cephalad along the skin.

Sometimes the femoral nerve can be difficult to identify, remember it is found lateral to the femoral artery, superficial to the iliopsoas muscle and deep to the fascia iliaca. It has a hyperechoic appearance on ultrasound and can vary between a circular, triangular and flat appearance (figure 6).

 

Figure 6: Localizing the femoral nerve

 

 

With the use of ultrasound, marking surface landmarks has become less important. However, understanding relevant anatomy remains key to interpreting the sonographic anatomy which is crucial to procedural success.

 

Surface Landmarks

First, palpate the pubic tubercle (PT) in the midline and the anterior superior iliac spine (ASIS) which is found laterally over the hip and anterior to the iliac crest. A straight line drawn between the PT and the ASIS represents the inguinal ligament (IL) which serves as the upper border to the area of interest: the femoral triangle. Immediately inferior to the inguinal ligament is the fold of the inguinal crease (IC) where the femoral artery (FA) can be palpated. Medial to the FA lies the femoral vein (FV), and immediately lateral to the FA lies the femoral nerve (FN) (figure 1).

 

Figure 1: Surface Landmarks

PT = Pubic tubercle, ASIS = anterior superior iliac spine., IC = Iliac crest, FA = Femoral artery, FV = Femoral vein, FN = Femoral nerve, IC = inguinal crease

 

The Femoral Triangle

The femoral triangle holds the relevant structures needed to perform a successful femoral nerve block (figure 2). The superior boundary of the femoral triangle is the inguinal ligament, the lateral border is the sartorius muscle; and the medial border is the adductor longus muscle. The floor of the femoral triangle is made up of following muscles: Iliacus, psoas major, pectineus and adductor longus (lateral to medial). The key structures of interest which will need to be identified sonographically (from lateral to medial) include the femoral nerve, femoral artery, and femoral vein.

 

Figure 2: The femoral triangle

 

The Lumbar Plexus & Femoral Nerve

Four major nerves supply the lower extremity; the sciatic, the femoral, the obturator, and the lateral femoral cutaneous nerves. From the regional anesthesia perspective, this is important, in that an isolated femoral nerve block will not provide complete anesthesia for the lower leg. The femoral nerve supplies sensory innervation to the anterior thigh, anteromedial knee, medial lower leg and the medial aspect of the foot and ankle. Importantly, it also innervates the periosteum of the femur. In addition, it supplies motor innervation to the knee extensor muscles, including the quadriceps and sartorius (table 2).

 

Table 2: Distribution of effect of femoral nerve block

After its origin at the lumbar plexus the femoral nerve descends through the posterior third of the psoas major and iliacus muscle. It enters the thigh within the femoral triangle below the inguinal ligament and superior to the iliopsoas muscle (figure 3). Within a few centimeters of the inguinal ligament, the femoral nerve divides into anterior and posterior branches. It is important to place your blockade around the nerve prior to when it diverges, otherwise your block may be incomplete. If you are too distal, you may miss the posterior branch of the femoral nerve which provides motor innervation to the quadriceps muscles–an important consideration in patients with acute femur fractures who are experiencing quadriceps spasm (6).

 

Figure 3: The lumbar plexus

Goal

To provide safe and effective relief of acute pain for the following conditions:

• Femur (neck & shaft) fractures
• Patella injuries/fracture
• Anterior thigh wound care

 

Contraindications

• Patient refusal
• Allergy to local anaesthetic
• Infection over site of injection
• Coagulopathy (relative contraindication, use clinical judgement)

 

Complications

• Intravascular injection causing local anesthetic systemic toxicity (LAST)
• Intra-neuronal injection (can cause temporary or permanent nerve damage)
• Block failure
• Infection

 

The use of landmark-guided femoral nerve blocks for acute pain relief in pediatric patients with femur fractures was first described in 1979 (1). Regional blocks are used widely by anesthetists to manage intra and post-operative pain. However there has been variable uptake into other pediatric specialties, including pediatric emergency medicine.

 

Why Ultrasound?

Traditionally, femoral nerve blocks were performed using anatomic landmarks. However, in the late 1980’s ultrasound began to be used for procedural guidance and by the 2000’s, it’s use was commonplace (2, 3). Today, ultrasound-guidance for femoral nerve blocks is routine and provides several benefits over the traditional approach (table 1). In fact, many now consider it to be standard of care.

 

Table 1: Advantages of ultrasound-guided nerve blocks (4)

 

A retrospective pre- vs. post-implementation cohort study evaluating emergency physician performed femoral nerve blocks for pediatric patients presenting with acute femur fractures found that patients who received ultrasound-guided femoral nerve blocks for femur fracture pain, had longer duration of analgesia, required fewer doses of analgesic medications, and needed fewer nursing interventions than those patients receiving enteral or parenteral analgesic alone (5). When done appropriately, ultrasound-guided femoral nerve blocks are safe, effective and provide optimal pain relief for acute injuries.

Conclusion

Congratulations on taking the first step towards adopting PoCUS as a part of your practice! The key concepts in this chapter can be revisited regularly to help you understand how to generate and interpret different scans. Orienting yourself to a 2D representation of a 3D object will take some time, so take any opportunity you have to reach for an US probe to hone your skills. Image generation is the most difficult skill to obtain with respect to PoCUS but with a systematic approach you will be able to reliably create high-quality scans that can enhance your clinical decision-making.

Documentation

Our documentation recommendations are consistent with those from the Canadian Point of Care Ultrasound Society (CPoCUS). We share the belief that it is important for all physicians completing our modules to use consistent, unambiguous, and easily interpreted language when describing point of care ultrasound studies. It is important to chart using binary wording, and to limit the possible interpretations to those within our scope of practice. With this in mind, we endorse the following documentation recommendations from the Canadian Point of Care Ultrasound Society:

PoCUS for (insert indications here): negative/positive/indeterminate study: No/+ (insert pathology name here)

As an example, in a case of PoCUS for pneumothorax, in which a pneumothorax was found on the patient’s left side one would document the following in the chart:

PoCUS for PTX: positive: + L PTX

In addition to documenting your findings in the chart we strongly encourage users to record their images for QA review and to get ongoing feedback on your scans.

Tips for scanning children

Children, particularly young children can often be fearful of strangers and any medical examination can result in stress, fear and oppositional behavior. The use of a large, unfamiliar machine can add a level of fear and intimidation. There are several things one can do to maximize patient comfort and success of the scan in this challenging population.

Gain the trust of the child by respecting their fear and approaching slowly by first explaining to them what you are going to do in the simplest terms possible. In addition, giving them limited choices about how the scan will proceed (i.e. “Do you want to sit with Mom or Dad when I check your tummy?”) can help them feel more in control.

Normalize the US equipment by having the child handle the probe or having a caregiver hold the probe. Alternatively start by placing the probe on a non-invasive area such as their knee or hand to reassure them that the probe is harmless and engage them with the scan by watching the images on the screen. US gel can feel quite unpleasant when cold so warming the gel prior to use can mitigate this sensation. Having the child play with the gel before administration can prevent them from squirming when you apply it to their body for the scan. The low-frequency probe emits sounds that most children can hear. You can also let them listen to the probe and briefly explain how the machine works.

Use the parents to model the activity so the child is less afraid. You can also use the parents to help hold, comfort or even distract the anxious child.

Anticipate movement of the child either withdrawing from the sensation of the gel or probe or turning to face the screen. To minimize the effects of the child’s movement on the image, one should be sure to anchor one’s hand to the patient, so the probe remains in contact with the patient in the area of interest.

Scanning Modes

B-mode or “brightness mode” is used for the majority of PoCUS scans and was described well throughout this text. It produces a two-dimensional cross-sectional slice of the area where the probe is directed. This modality will be used for the majority of your scans.

M-mode– looks at motion over time in a slice of the ultrasound image on the screen. This is plotted as a waveform with time on the x axis and depth on the y axis. M-mode can be helpful in certain instances when looking at moving structures and will be addressed in individual modules when relevant.

Doppler mode relies on the Doppler shift principle of physics:  waves emitted from a source moving towards the transducer will be higher in frequency compared those emitted from a source moving away from the transducer. This frequency shift can be represented by color (red towards, blue away), or by audible/graphical peaks with spectral Doppler. It is important to keep in mind that the color Doppler modes do not discriminate between arteries and veins but rather the direction of the sound waves source. Therefore, you can have situations where arteries are displayed as blue and veins as red. Doppler will be addressed further in individual modules when relevant.

Understanding images

One of the tougher concepts to grasp is the orientation of the image on the screen in relation to the patient. Since the US probe can be moved and rotated to image patients in varying planes it is important to understand the relation of the image on the screen to the anatomy of the patient. In all cases the image on the top of the screen, or near-field relates to the superficial part of the patient that is touching the probe and the bottom of the screen, or far-field is deepest into the patient. Screen left corresponds to the direction the probe indicator is pointed on the patient, with the right screen being the opposite (Figure 13&14).

Figure 13: Transverse view orientation

 Figure 14: Longitudinal view orientation

It is critical to have a proper reference to know how to interpret what we are seeing. One way to think of it is to imagine the probe is a flashlight looking into the body with the closest structures to the probe at the top of the screen and farthest at the bottom. You aim the flashlight towards the area of interest by manipulating your hand movements. Remind yourself where you are starting by mentally noting the corresponding structures to near-field, far-field, screen right and screen left. This cueing mechanism will become very useful once you start manipulating the probe to optimize images and scan through structures.

Optimizing images

The typical ultrasound machine found in North American hospitals will contain a bevy of buttons. These can be quite intimidating. Fortunately, for the majority of our indications we can focus on the few critical controls and ignore the rest. The most important controls to optimize the image are gain and depth.

Gain controls how bright the image appears on the screen. Adjusting the gain essentially increases or decreases the sensitivity of the machine to ALL ultrasound waves sensed by the transducer. It acts as a “volume control” for the image brightness, turning up the gain makes everything appear brighter on the screen while turning it down makes everything darker.

Figure 15: Gain

Depth controls how deep the ultrasound waves returning to the probe are detected. Increasing depth will allow you to see deeper into the patient, while decreasing help you focus more superficially (Figure 16). There is a numeric scale on the right side of the screen to help orient you to the depth of the image you are viewing. Often it is best to begin imaging an area of interest using the maximum depth and then gradually reduce the depth to optimize the visualization of the area of interest. This helps to landmark surrounding structures and avoid missing anything due to a superficial scan.

Figure 16: Depth