Ultrasound-Guided Interventional Procedures in Pain Medicine: A Review of Anatomy, Sonoanatomy, and Procedures: Part I: Nonaxial Structures

Acute pain management of patients with multiple fractured ribs: a focus on regional techniques

PURPOSE OF REVIEW

Thoracic trauma leading to multiple fractured ribs (MFR) remains very common. Good analgesia may help to improve a patient's respiratory mechanics and to avoid intubation of the trachea for ventilatory support and therefore may dramatically alter the course of recovery. We herein review the analgesia options for patients with MFR.

RECENT FINDINGS

For healthy patients with one to two fractured ribs, systemic analgesics may suffice. For more than three to four fractured ribs, studies and experience have reaffirmed the superior analgesia made possible with thoracic epidural, thoracic paravertebral, and intercostal blocks. From experience, interpleural block has significant drawbacks. Catheterization allows the continuation of analgesia for 2 or more days with just one block. Use of the landmark technique is usually satisfactory for accurate block placement but ultrasound and nerve stimulation are showing promise in further improving needle and catheter placement accuracy, especially in the presence of difficult anatomy.

SUMMARY

Thoracic epidural, thoracic paravertebral, and intercostal blocks are the top choices for patients with MFR and they are of equivalent efficacy. Each has unique advantages and disadvantages. Our preference tends to be the thoracic paravertebral approach.

Applied sonoanatomy of the posterior triangle of the neck

The posterior triangle of the neck is an area of the body frequently visited by regional anesthesiologists, acute and chronic pain physicians, surgeons of all disciplines, and diagnosticians. It houses the entire brachial plexus from the roots to the divisions, the scalene muscles, the cervical sympathetic ganglions, the major blood vessels to and from the brain, the neuroforamina and various other structures of more or less importance to these physicians. Ultrasound (US) offers a handy visual tool for these structures to be viewed in real time and, therefore, its popularity and the need to understand it. We will discuss pertinent clinical anatomy of the neck and offer a basic visual explanation of the often-difficult two-dimensional (2-D) images seen with US.

Incidental detection of bowel herniation with ultrasonography and fluoroscopy during a caudal block

BACKGROUND

In contrast to fluoroscopy, ultrasonography allows visualization of structures such as muscles, tendons, vessels, and nerves. We describe a case where ultrasonography in conjunction with fluoroscopy led to the incidental diagnosis of bowel herniation in a patient undergoing a caudal block.

CLINICAL FEATURES

A 71-yr-old woman presented to our chronic pain clinic with a long-standing history of coccydynia for which she had undergone a partial coccygectomy. A trial caudal block was planned. Fluoroscopy of the lower sacral area revealed the presence of a gas bubble inferoposteriorly to the coccygeal remnant. A confirmatory ultrasound scan revealed a hollow structure compatible with bowel. The procedure was abandoned. Subsequently, a non-enhanced computed tomographic scan of the pelvis confirmed the diagnosis of large bowel herniation. The patient was referred to a colorectal surgeon, and she subsequently underwent successful laparoscopic repair of the coccygeal hernia.

CONCLUSION

Ultrasonography can be a valuable adjunct in identifying non-neural pathologies in patients undergoing interventional procedures in chronic pain management. This case report highlights the importance of being vigilant for unanticipated pathologies during ultrasound examinations while performing chronic pain block procedures.

Acoustic Radiation Force Impulse (ARFI) imaging-based needle visualization

Ultrasound-guided needle placement is widely used in the clinical setting, particularly for central venous catheter placement, tissue biopsy and regional anesthesia. Difficulties with ultrasound guidance in these areas often result from steep needle insertion angles and spatial offsets between the imaging plane and the needle. Acoustic Radiation Force Impulse (ARFI) imaging leads to improved needle visualization because it uses a standard diagnostic scanner to perform radiation force based elasticity imaging, creating a displacement map that displays tissue stiffness variations. The needle visualization in ARFI images is independent of needle-insertion angle and also extends needle visibility out of plane. Although ARFI images portray needles well, they often do not contain the usual B-mode landmarks. Therefore, a three-step segmentation algorithm has been developed to identify a needle in an ARFI image and overlay the needle prediction on a coregistered B-mode image. The steps are: (1) contrast enhancement by median filtration and Laplacian operator filtration, (2) noise suppression through displacement estimate correlation coefficient thresholding and (3) smoothing by removal of outliers and best-fit line prediction. The algorithm was applied to data sets from horizontal 18, 21 and 25 gauge needles between 0-4 mm offset in elevation from the transducer imaging plane and to 18G needles on the transducer axis (in plane) between 10 degrees and 35 degrees from the horizontal. Needle tips were visualized within 2 mm of their actual position for both horizontal needle orientations up to 1.5 mm offset in elevation from the transducer imaging plane and on-axis angled needles between 10 degrees-35 degrees above the horizontal orientation. We conclude that segmented ARFI images overlaid on matched B-mode images hold promise for improved needle visibility in many clinical applications.

Ultrasound-guided interventional procedures in pain medicine: a review of anatomy, sonoanatomy, and procedures. Part II: axial structures

There is a growing trend in using ultrasonography in pain medicine as evident by the plethora of published reports. Ultrasound(US) provides direct visualization of various soft tissues and real-time needle advancement and avoids exposing both the health care provider and the patient to the risks of radiation. The US machine is more affordable and transferrable than fluoroscopy, computed tomography scan,or magnetic resonance imaging machine. In a previous review, we discussed the challenges and limitations of US, anatomy, sonoanatomy, and techniques of interventional procedures of peripheral structures. In the present review, we discuss the anatomy, sonoanatomy, and US-guided techniques of interventional pain procedures for axial structures and review the pertinent literature.