Introduction:
Most of the procedures performed in the emergency department require regional anesthesia along with sedation. Compared to this, a peripheral nerve block is a safer option and it minimizes the need for post-procedure observation for a prolonged time and hemodynamic monitoring. This has become complicated due to a lack of specialized equipment, inadequate physician training, and physician comfort level. Nerve blocks can cause complications including hematoma, pneumothorax, and localized infection. Hence ultrasound was introduced to overcome these hurdles to enable visualization of the needle tip, target nerve, and anesthetic infusion. Ultrasound-guided nerve blocks (USGBC) will help improve efficacy and reduce post-operative pain and complications. It will help the anesthesiologist visualize the area to be anesthetized and keep the needle pathway precise. Most surgical procedures require regional anesthesia along with sedation to promote patient cooperation and comfort. Ever since it was introduced, a number of advancements like mobile ultrasound platforms, needle recognition software, and higher resolutions have helped the utility of ultrasound by anesthesiologists.
When Were Ultrasound Guided Nerve Blocks Introduced?
Ultrasound-guided nerve blocks were first explored at the University of Vienna during the 1990s by anesthesiologists. Ultrasound-guided brachial plexus and femoral blocks were demonstrated. After ten years, colleagues from the University of Toronto demonstrated the sonoanatomy (anatomy of body structures reflected in the ultrasound) of the brachial plexus. The brachial plexus is a network made up of nerves that carry sensation to the shoulder, hand, and arm from the spinal cord. The first reported use of an ultrasound-guided nerve block was in 1978 for a supraclavicular brachial plexus block.
What Does the Ultrasound Equipment Contain?
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A high-resolution device with pulsatile Doppler (used to detect blood flow by studying the bouncing of high-frequency sound waves, or simply ultrasound) and the color is used.
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Two wideband transducers or three fixed transducers are used. They can be of varying shapes, frequencies, and sizes. Transducers emit ultrasound waves, and when the wave returns to the transducer, an image is produced.
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A gelatinous solution that is sterile is used to reduce the air interface between the transducer and the skin.
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Common needles used in conventional techniques can be used.
What Are the Basics of Ultrasound?
Piezoelectric crystals that contain electric charge are organized to provide acoustic (sound) energy, and they emit sound waves that range between 1 to 18 MHz (megahertz). Objects with a greater difference in impedance will create a hyperechoic or white picture. Objects with slight differences in impedance will create a hypoechoic or gray picture. The areas where there is no return will be black or anechoic. The difference between muscle and fat is small, and it will be gray in color or have a grey border. Injected fluids appear much darker. Various probes are available, but most regional anesthesia uses linear probes. The ultrasound pictures may be optimized by angling, rotating, sliding, tilting, or applying pressure. There are two approaches, in-plane (needle inserted parallel to the probe) and out-of-plane (needle inserted perpendicular to the probe) approaches. The in-plane approach may not be practical because of anatomical restraints, but it allows the needle to be visualized better. This out-of-plane approach helps to visualize the needle that is inserted better.
How Is It Done?
The patient is asked to lie comfortably for the ultrasound-guided nerve block. Before performing the surgery, the anesthetist should identify the painful area and exclude conditions like anesthesia allergies, coagulopathy, and neurologic deficits. Consent should be obtained from the patient after discussing the risks and benefits of the surgery. Neurologic examination should be performed and documented prior to the nerve block. For all kinds of ultrasound-guided nerve blocks, the patient should have intravenous access ready to overcome any adverse event that may occur. A two-person technique should be preferred, one will advance the needle tip, and the other will inject the local anesthesia.
Prior to the procedure, the skin is rubbed with an alcohol solution to make it sterile, and the ultrasound probes are covered with a sterile drape. An ultrasound transducer is selected, a micro convex or low-frequency linear transducer for deep structures, and a linear transducer is used for superficial structures. Following this, the frequency is adjusted on the scanner (10 to 14 MHz for superficial structures and 5 to 9 MHz for deep scanning).
After this, the depth on the scanner is set about one to two centimeters deeper than the calculated nerve depth. This is done because the image may be amplified if the depth setting is optimized. Amplification of the ultrasound is adjusted to improve the image quality and better contrast. The probe is held by the anesthetist in the non-dominant hand, and the probe is slightly rested on the body because compressing the body can obscure the image.
What Is the Local Anesthetic Dose?
Pediatric Ultrasound Guided Nerve Blocks:
Due to the improvement in the accuracy of ultrasound-guided nerve blocks, many pediatric anesthetists are using them. Limb nerve blocks guided by ultrasound have been safe and tolerated well in children. Regional anesthesia using ultrasound has reduced postoperative respiratory complications and metabolic stress response to the surgery and promotes faster gut function and feeding return in pediatric patients. Postoperative opioid consumption has also been significantly reduced due to regional anesthesia techniques.
What Are the Advantages of Using Ultrasound–Guided Nerve Blocks?
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Direct visualization of the nerves is made possible.
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There is a decreased risk of painful muscle contractions.
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The risk of intraneural injection is reduced.
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It is considered a dynamic and safe tool.
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The diffusion of anesthesia can be seen.
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The risk of intravascular injection is diminished.
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The dose of local anesthesia is reduced.
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The quality of the nerve block is better.
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Ultrasound equipment provides high-quality images and comes with greater versatility.
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This technique can be used in unstable patients.
Conclusion
Nerve blocks act as an excellent adjunct for pain management in surgical procedures. Ultrasound-guided nerve blocks help in precise injection and appropriate drug delivery in a particular area without harming the adjacent nerves and soft tissue. It offers many advantages compared to the blind anesthesia technique.
