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Introduction to ultrasound & regional anesthesia

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  • 1. INTRODUCTION TO ULTRASOUND & REGIONAL ANESTHESIA Saad Al-Shamma MBChB DA CABA & IC Department of anesthesia/Al-yarmook Teaching Hospital Baghdad-Iraq
  • 2. Overview • The principle of Ultrasound • rationale for US guidance. • proper techniques of US guidance. • interesting findings seen with US. • specific nerve blocks
  • 3. Image Generation • Ultrasound waves are generated by piezoelectric crystals • the piezoelectric crystals convert the mechanical energy of the returning echoes into an electrical current, which is processed by the machine to produce a two-dimensional grayscale image that is seen on the screen. • Audible sounds spread out in all directions, whereas ultrasound beams are well collimated • The machine spend 100x time to listen to returning echos compared to sent ones.
  • 4. Ultrasound Image Modes • A-mode : the oldest mode(1930), a simple one- dimensional ultrasound image is generated as a series of vertical peaks corresponding to the depth of the structures at which the ultrasound beam encounters different tissues.
  • 5. • B Mode : a two dimensional mode and provide a cross sectional image through the area of interest and is the primary mode currently used in regional anesthesia. • M mode(motion) : one dimensional mode against time mostly used for cardiac imaging.
  • 6. Doppler mode: measures the shift in the frequency between the incident and the reflected wave after hitting a moving object. • Colour -flow: the probe should be slightly tilted to be near the long axis of the vessel blood coming toward the probe appears red and appear blue if it is moving away from the probe , increasing gain improves view for smaller vessels. • Pulsed doppler • Continuous doppler
  • 7. Doppler colour flow mapping
  • 8. Hyperechoic areas have a great amount of energy from returning echoes and are seen as white. Hypoechoic areas have less energy from returning echoes and are seen as gray. Anechoic areas without returning echoes are seen as black. Echogenicity
  • 9. - Ultrasound image of various tissues for regional anesthesia • Veins Anechoic/hypoechoic, non- • pulsatile,compressible • Fat Hypoechoic, compressible • Muscles Heterogeneous (mixture of hyperechoic • lines within a hypoechoic tissue background) • Tendons & Fascia Hyperechoic • Bone Very hyperechoic with acoustic shadowing behind • Nerves Hyperechoic below the • clavicle/hypoechoic above the clavicle • Air bubbles Hyperechoic • Pleura Hyperechoic line • Local anesthetic Hypoechoic, expanding hypoechoic region
  • 10. • reflection occurs at the boundary or interface of different types of tissue. The reflection is inversely related to water content of tissue . • Substances low in water content or high in materials that are poor sound conductors (e.g., air, bone) reflect almost all the sound and appear very bright.
  • 11. Scattered versus specular reflection • In specular reflection incident angle equals the reflected angle & usually the reflection is from smooth surface(e.g. needle ,diaphragm or blood vessels , pleura and peritoneum). • Scattering is the redirection of sound in any direction by rough surfaces or by heterogeneous media.
  • 12. Scattering is the redirection of ultrasound in any direction caused by rough surfaces or by heterogeneous media
  • 13. Attenuation • Attenuation is the loss of mechanical energy of ultrasound. • About 75% of the attenuation is caused by conversion to heat. • The amount of attenuation directly related to: • 1-distance travelled • 2-wavelength used • 3-attenuation coefficient of tissue
  • 14. Anisotropy Anisotropy means that the backscatter echoes from a specimen depend on the directional orientation within the sound field. Anisotropy can be quantified by specifying the transducer frequency and the decibel change in backscatter echoes with perpendicular and parallel orientation of the specimen. Tissues like nerves, tendons, and muscle exhibit anisotropy , but most evident with tendon
  • 15. • The transducer is scanning at a 90 degree angle. The nerve (transverse view) is clearly visible. Arrowhead = median nerve in the forearm •
  • 16. • The transducer is scanning at a 75 degree angle. The nerve is still visible but less clear. Arrowhead = median nerve in the forearm
  • 17. • The transducer is scanning at a 45 degree angle. The nerve is no longer visible. Solution: angle the transducer slowly until the nerve comes into view.
  • 18. resolution • Resolution, the ability to distinguish two close objects as separate • Axial resolution : the minimum separation of above-below planes along the beam axis. It is determined by spatial pulse length: Axial resolution = wavelength (λ) × number of cycle per pulse (n) ÷ 2 • Lateral resolution: is a parameter of sharpness to describe the minimum side-by-side distance between two objects. It is determined by both ultrasound frequency(higher frequency decreases beam width so it improves lateral resolution) .beam width can be determined with focusing the ultrasound beam to the target . • Temporal resolution: depends on frame rate • Two adjacent structures cannot be identified as separate entities on an ultrasound scan if they are less than one wavelength apart.
  • 19. Focusing improves lateral resolution
  • 20. • Types of Ultrasound transducer used in regional anesthesia • 1-linear :high frequency ,higher resolution used for superficial tissues. • 2-curved:low frequency ,lower resolution ,used for deeper tissue
  • 21. 1-Machine Setting • Setting Depth • Setting Gain • Setting Focus • Compound Imaging(sonoCT) 2-transducer handling Transducer movement Transducer orientation 3- nerve and needle localization
  • 22. Ultrasound machine controls • Gain : the wave looses energy and become attenuated deeper in tissue so time gain compensation is required. • Depth • Frequency:8-13 Mhz • For shallow depth<4 cm use frequency>10 MHz • For deeper structures >4cm preferably use frequency <8 Mhz
  • 23. Artefacts • Reverberating artefacts : u/s wave is reflected back between tissue interface so the retuning wave come late in time this will be interpreted by the machine as distant signal. • Mirror artefacts: • Bayonet artefacts : the machine assumes the speed is constant at 1540m/s • Comet tail artefact:usually at the pleural or peritoneal surface • Acoustic enhancement artifacts :(e.g.blood vessels) • Absent blood flow :small b.vessels cant be seen by colored doppler this can be corrected by increasing the gain. • Acoustic shadow: e.g. bone or pleura in supraclavicular block( the area behind the bone is anechoic while hypoechoic in case of pleura).
  • 24. Left : reverberating needle aretefact middle : stone in the bladder with acoustic enhancement behind the bladder & acoustic shadow behind the stone right : mirror image artefact of a haematoma .
  • 25. Factors Reported to Influence Needle Tip Visibility • Angle of insonation • Needle gauge • Bevel orientation • Receiver gain • Needle motion and test injections • Echogenic modifications • Spatial compound imaging • EZ guide (ezono 4000 ):it is based on magnetic identification of the needle during insertion. • Hydro Location Technique(0.5-1 ml) • In animal models: a number of undesired effects, such as fetal weight reduction, postpartum mortality, fetal abnormalities, tissue lesions, hind limb paralysis, blood flow stasis, and tumor regression has been reported.
  • 26. • It is easier to detect a needle with an echogenic tip. The figure shows an example of the echogenic tip needle (Hakko™ Medical Co. LTD Japan) with 3 hyperechoic dots at the needle tip (arrows). •
  • 27. complications of U/s guided n. block • Intravascular injection Minimize it by: 1-careful needle visualization(especially the tip of the needle) 2-aspiration before injection
  • 28. • TREATMENT OF LOCAL ANESTHETIC TOXICITY • 1) Airway, hyperventilation, 100% O2 • 2) Abolish convulsions (Diazepam, Midazolam, Propofol) • 3) Intralipids (1.5 mL/kg over 1 minute (~100mL), then continuous infusion • 0.25 mL/kg/min (~500 mL over 30 minutes) • 4) CPR/ACLS, consider cardiopulmonary bypass
  • 29. Neurologic complications • the incidence of neurologic symptoms following PNB varies depending on the anatomic location, ranging from 0.03% for supraclavicular blocks to 0.3% for femoral blocks to up to 3% for inter-scalene blocks. Fortunately, the vast majority of these neuropathies appear to be temporary rather than permanent neuropathy and resolve over weeks to months.
  • 30. • Suggested etiologies include mechanical trauma from the needle, nerve edema and/or hematoma, pressure effects of the local anesthetic injectate, and neurotoxicity of the injected solutions (both local anesthetics and adjuvants, e.g., epinephrine). (3) Confounding factors that may play a role in nerve injury include preexisting neuropathies (e.g., diabetes mellitus), surgical manipulation, prolonged tourniquet pressure, or compression from postoperative casting.
  • 31. Bioeffect and Safety • ultrasound application could produce a biologic effect can be characterized into two aspects: heating and mechanical. • A modern ultrasound machine displays two standard indices: thermal and mechanical. The thermal index (TI) is defined as the transducer acoustic output power divided by the estimated power required to raise tissue temperature by 1°C. Mechanical index (MI) is equal to the peak rarefactional pressure divided by the square root of the center frequency of the pulse bandwidth. TI and MI indicate the relative likelihood of thermal and mechanical hazard in vivo, respectively. Either TI or MI >1.0 is hazardous. • Biologic effect is directly related to tissue exposure time
  • 32. How to avoid nerve injury • 1-inject LA under direct vision(of the needle tip and the spread of LA after injection) • 2- use a blunted bevel needle(or touhy needle) • 3- don’t inject LA if the pt get severe pain or there is increased resistance. • 4-idealy the pressure of the LA syringe should not exceed 30 psig. • 5-nerve localization by elicitation of parasthesia and nerve stimulation(current 0.3-0.5 mamp) alone is no more recommended.(sometimes current as low as 0.2 ma couldnot guarantee needle contact and on the contrary currnts as high as 1.5 ma could not stimulate nerve when it is in close contact with the nerve, as seen in animal model)
  • 33. • American society of Regional • Anesthesiologists Recommendations • the following are the American society of Regional Anesthesiologists recommendations for performing an • ultrasonography-guided block: • 1. Visualize key landmark structures including muscles, • fascia, blood vessels, and bone. • 2. identify the nerves or plexus on short-axis imaging, • with the depth set 1 cm deep to the target • structures. • 3. Confirm normal anatomy or recognize anatomic • variation(s). • 4. Plan for the safest and most effective needle approach. • 5. Use the aseptic needle insertion technique. • 6. follow the needle under real-time visualization as it is • advanced toward the target. • 7. Consider a secondary confirmation technique, such as • nerve stimulation. • 8. When the needle tip is presumed to be in the correct • position, inject a small volume of a test solution. • 9. Make necessary needle adjustments to obtain optimal • perineural spread of local anesthesia. • 10. Maintain traditional safety guidelines of frequent aspiration, • monitoring, patient response, and assessment • of resistance to injection.
  • 34. Set-up and Monitoring for Regional Blocks • Set-up All supplies located in this area must be readily identifiable and accessible to the anesthesiologist. The area should be of ample size to allow block performance, monitoring, and resuscitation of patients. There should be equipment for oxygen delivery, emergency airway management, and suction, and the area should have sufficient lighting. A practically organized equipment storage cart is desirable and should contain all of the necessary equipment (including equipment required for emergency procedures). A selection of sedatives, hypnotics, and intravenous anesthetics should be immediately available to prepare patients for regional anesthesia. Emergency drugs (atropine, epinephrine, phenylephrine, ephedrine, propofol, thiopental, succinylcholine, amrinone, intralipid) should also be immediately available. Monitoring During the performance of regional anesthesia, it is vital to have skilled personnel monitor the patient at all times(electrocardiography, noninvasive blood pressure, pulse oximetry, and level of consciousness of the patient should be gauged frequently using verbal contact because vasovagal episodes are common with many regional procedures). The patient should be closely observed for systematic toxicity(within 2 minutes for at least 30 minutes after the procedure). Before performing blocks with significant sympathetic effects, a baseline blood pressure reading should be obtained
  • 35. Techniques for Brachial Plexus Blockade • Interscalene Block This block frequently spares the lowest branches of the plexus, the C8 and T1 fibers (which innervate the caudad [ulnar] borderof the forearm). Pneumothorax should be considered if cough or chest pain isproduced while exploring for the nerve (cupola of the lungnear block site). Direct injection into the vertebral artery can rapidly producecentral nervous system toxicity and convulsions. Supraclavicular Block The midpoint of the clavicle is identified. The subclavian arterypulse serves as a reliable landmark in thinner individuals because the plexus lies immediately cephaloposterior to the subclavian artery. Ultrasound imaging and nerve stimulation help avoid puncturing the pleura. There is a risk of pneumothorax because the cupola of the lung lies just medial to the first rib; risk of pneumothoraxis greater on the right side because the cupola of the lung is higher on that side; the risk is also greater in tall, thin patients. Infraclavicular Block This block provides excellent analgesia of the entire arm (blocks the musculocutaneous and axillary nerves more consistently)and allows introduction of continuous catheters to provide prolonged postoperative pain relief. There is a lower risk of blocking the phrenic nerve or stellate ganglion. Vessel puncture is a potential complication. Lateral needle insertion helps avoid the risk of pneumothorax. Axillary Block This block is useful for surgery of the elbow, forearm, and hand(the musculocutaneous nerve may be blocked separately). This block is associated with minimal complications (neuropathy from needle puncture or intraneural injection of local anesthetic) .
  • 36. References • Andrew T. Gray, MD, PhD,ATLAS OF ULTRASOUND-GUI,DED REGIONAL ANESTHESIA 2nd edition,2013 • David L Brown , ATLAS OF REGIONAL ANESTHESIA fourth edition ,2010 • Newyork School of regional anesthesia web site www.nysora.com
  • 37. thank you