Sound Waves and Ultrasound Principles
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Questions and Answers

What is the definition of a cycle in a sound wave?

  • One complete positive and negative pressure change (correct)
  • The amplitude of the sound wave
  • The distance traveled during one complete wave
  • The frequency of the sound wave

    • What is the function of piezoelectric crystals in ultrasound transducers?

  • To convert electric current to sound waves (correct)
  • To absorb sound waves
  • To reflect sound waves
  • To convert sound waves to electricity

    • What is the pulse-echo principle in terms of ultrasound transducer function?

  • Measuring the amplitude of sound waves
  • Measuring the frequency of sound waves
  • Converting electric current to sound waves and receiving the reflected waves (correct)
  • Converting sound waves to electricity

    • What is attenuation in sound waves?

    <p>A loss of intensity/amplitude as sound waves travel through a medium</p> Signup and view all the answers

    Which of the following is a factor in sound wave attenuation?

    <p>Refraction</p> Signup and view all the answers

    What is the effect of refraction on sound waves?

    <p>The angle of return of waves becomes different than the angle of transmission</p> Signup and view all the answers

    What is the characteristic of ultrasound transducers?

    <p>They are fixed frequency</p> Signup and view all the answers

    What is the result of absorption in sound wave attenuation?

    <p>Sound waves are converted to heat energy</p> Signup and view all the answers

    What view is used to scan for the cricothyroid membrane?

    <p>Transverse view</p> Signup and view all the answers

    What is the significance of decreased diameter and collapsibility >50% at end inspiration on spontaneous breathing patients?

    <p>Hypovolemia</p> Signup and view all the answers

    What is the benefit of using regional anesthesia in patients?

    <p>Decrease surgical stress response</p> Signup and view all the answers

    What is the characteristic of the endoneurium in peripheral nerves?

    <p>Surrounds individual axon</p> Signup and view all the answers

    What is the sonographic window used to assess the gastric antrum?

    <p>Liver</p> Signup and view all the answers

    What is the characteristic of the epineurium in peripheral nerves?

    <p>Surrounds multiple fascicles</p> Signup and view all the answers

    What is the contraindication of regional anesthesia?

    <p>All of the above</p> Signup and view all the answers

    What is the significance of distension and minimal collapsibility of the IVC?

    <p>Volume overload</p> Signup and view all the answers

    What is the US finding indicative of pneumothorax?

    <p>Lung point</p> Signup and view all the answers

    What is the characteristic of the blood supply in peripheral nerves?

    <p>Microscopic and irregular</p> Signup and view all the answers

    What is the effect of increased lipophilicity on the onset of local anesthetics?

    <p>Slower onset</p> Signup and view all the answers

    Which of the following additives is used to decrease vascular absorption and prolong the block?

    <p>Epinephrine</p> Signup and view all the answers

    What is the mechanism of action of alpha-2 agonists in local anesthesia?

    <p>Inhibiting presynaptic conduction</p> Signup and view all the answers

    What is the advantage of using ultrasound in regional anesthesia?

    <p>Real-time needle guidance</p> Signup and view all the answers

    What is the scanning axis used in ultrasound guided regional anesthesia?

    <p>Short axis</p> Signup and view all the answers

    What is the purpose of the 'heel-toe' maneuver in ultrasound guided regional anesthesia?

    <p>To direct the beam into the needle</p> Signup and view all the answers

    What is the importance of patient assessment in regional anesthesia?

    <p>To discuss the risks and benefits of the procedure</p> Signup and view all the answers

    What is the purpose of the 'RASP' sequence in regional anesthesia?

    <p>To verbalize and document the response to motor stimulation</p> Signup and view all the answers

    What is the effect of increased protein binding on the duration of local anesthetics?

    <p>Increased duration</p> Signup and view all the answers

    What is the purpose of using Exparel in regional anesthesia?

    <p>To prolong the duration of action</p> Signup and view all the answers

    What is the relationship between frequency and penetration in ultrasound transducers?

    <p>Lower frequency probes penetrate deeper into tissue with less resolution</p> Signup and view all the answers

    What is the main difference between color doppler and power doppler modes?

    <p>Color doppler examines direction and velocity, while power doppler examines amplitude</p> Signup and view all the answers

    What is the purpose of POCUS in anesthesiology?

    <p>To improve safety and efficacy of interventions in real-time</p> Signup and view all the answers

    What is the characteristic of an anechoic area on an ultrasound image?

    <p>Complete absence of returning sound waves, appearing black</p> Signup and view all the answers

    What is the definition of acoustic shadowing in ultrasound imaging?

    <p>Caused by a strong reflection or absorption in near US fields</p> Signup and view all the answers

    What is the main purpose of the M-mode in ultrasound imaging?

    <p>To capture returning echoes in one line of a B-mode image and display individual images in sequence over time</p> Signup and view all the answers

    What is the characteristic of a hyperechoic area on an ultrasound image?

    <p>Large amplitude of returning sound waves, appearing bright</p> Signup and view all the answers

    What is the main advantage of using high frequency probes in ultrasound imaging?

    <p>Greater resolution</p> Signup and view all the answers

    What is the purpose of the PLAX view in focused cardiac US assessment?

    <p>To assess the left ventricular function</p> Signup and view all the answers

    What is the characteristic of reverberation artifacts in ultrasound imaging?

    <p>When a sound wave encounters two reflective layers and gets bounced between the two layers before it returns to the transducer</p> Signup and view all the answers

    What is the primary reason for using the antrum as a sono-anatomic indicator of gastric contents?

    <p>It accurately reflects total gastric contents</p> Signup and view all the answers

    What is the significance of a distended IVC with minimal collapsibility?

    <p>Volume/pressure overload</p> Signup and view all the answers

    What is the most diagnostic US finding for pneumothorax?

    <p>Lung point</p> Signup and view all the answers

    What is the characteristic of the perineurium in peripheral nerves?

    <p>Surrounds fascicles and acts as a strength and diffusion barrier</p> Signup and view all the answers

    What is the benefit of using regional anesthesia in patients with OSA?

    <p>All of the above</p> Signup and view all the answers

    What is the characteristic of the mesoneurium in peripheral nerves?

    <p>Surrounds the entire nerve and its associated structures</p> Signup and view all the answers

    What is the most important aspect of patient selection for regional anesthesia?

    <p>Profound comorbidity</p> Signup and view all the answers

    What is the significance of B Lines on ultrasound?

    <p>Indicative of interstitial edema</p> Signup and view all the answers

    What is the importance of patient assessment in regional anesthesia?

    <p>To identify potential complications</p> Signup and view all the answers

    What is the primary difference between a phased array probe and a curvilinear probe?

    <p>Transducer design</p> Signup and view all the answers

    What is the characteristic of the blood supply in peripheral nerves?

    <p>Irregular and microscopic</p> Signup and view all the answers

    What is the primary application of motion 'M-mode' in ultrasound imaging?

    <p>Capturing a single line of a B-mode image over time</p> Signup and view all the answers

    What is the primary difference between an anechoic area and a hypoechoic area on an ultrasound image?

    <p>Anechoic areas have a complete absence of sound waves, while hypoechoic areas have a few sound waves</p> Signup and view all the answers

    What is the primary advantage of using power doppler mode over color doppler mode in ultrasound imaging?

    <p>Power doppler is more sensitive to low-flow states</p> Signup and view all the answers

    What is the primary application of reverberation artifacts in ultrasound imaging?

    <p>Generating a false image of deeper tissue</p> Signup and view all the answers

    What is the primary purpose of POCUS in anesthesiology?

    <p>Guiding regional anesthesia procedures</p> Signup and view all the answers

    What is the primary characteristic of a curvilinear probe?

    <p>Wide field of view</p> Signup and view all the answers

    What is the primary advantage of using high frequency probes in ultrasound imaging?

    <p>Higher resolution of superficial structures</p> Signup and view all the answers

    What is the primary application of the parasternal long axis (PLAX) view in focused cardiac US assessment?

    <p>Assessing left ventricular function</p> Signup and view all the answers

    What is the primary difference between acoustic shadowing and posterior acoustic enhancement artifacts?

    <p>Acoustic shadowing appears as a dark area, while posterior acoustic enhancement appears as a bright area</p> Signup and view all the answers

    What is the primary unit of measurement for frequency in sound waves?

    <p>Hertz (Hz)</p> Signup and view all the answers

    Which of the following is NOT a factor in sound wave attenuation?

    <p>Diffraction</p> Signup and view all the answers

    What is the result of refraction on sound waves in tissue?

    <p>Sound waves change direction</p> Signup and view all the answers

    What is the role of piezoelectric crystals in ultrasound transducers?

    <p>To convert electrical current to sound waves</p> Signup and view all the answers

    What is the relationship between frequency and penetration in ultrasound transducers?

    <p>Higher frequency, shallower penetration</p> Signup and view all the answers

    What is the purpose of the pulse-echo principle in ultrasound transducers?

    <p>To transmit and receive sound waves</p> Signup and view all the answers

    What is the characteristic of ultrasound transducers?

    <p>Fixed frequency</p> Signup and view all the answers

    What is the effect of absorption on sound waves in tissue?

    <p>Sound waves are converted to heat</p> Signup and view all the answers

    What is the result of scatter on sound waves in tissue?

    <p>Sound waves are randomly deflected</p> Signup and view all the answers

    What is the characteristic of the amplitude of a sound wave?

    <p>Represents the intensity of the sound wave</p> Signup and view all the answers

    What is the primary mechanism by which local anesthetics block the sodium channel?

    <p>Blocking the channel in its inactivated state</p> Signup and view all the answers

    What is the effect of increasing the concentration of a local anesthetic on the speed of onset?

    <p>Increased speed of onset</p> Signup and view all the answers

    Which of the following additives is most effective in prolonging the duration of a local anesthetic block?

    <p>Dexamethasone</p> Signup and view all the answers

    What is the primary advantage of using ultrasound in regional anesthesia?

    <p>Real-time needle guidance</p> Signup and view all the answers

    What is the effect of increased lipophilicity on the potency of a local anesthetic?

    <p>Increased potency</p> Signup and view all the answers

    What is the purpose of the 'heel-toe' maneuver in ultrasound guided regional anesthesia?

    <p>To direct the beam into the needle</p> Signup and view all the answers

    What is the effect of increased protein binding on the duration of a local anesthetic block?

    <p>Increased duration</p> Signup and view all the answers

    What is the primary advantage of using Exparel in regional anesthesia?

    <p>Prolonged duration of action</p> Signup and view all the answers

    What is the primary consideration when selecting a local anesthetic for regional anesthesia?

    <p>All of the above</p> Signup and view all the answers

    What is the primary disadvantage of using perineural catheters in regional anesthesia?

    <p>Unreliable management</p> Signup and view all the answers

    Study Notes

    Sound Waves and Ultrasound

    • A sound wave consists of one complete positive and negative pressure change (cycle).
    • The distance traveled during one cycle is the wavelength.
    • Frequency is the number of cycles per second, measured in Hz (Hz).
    • Amplitude is the height of a sound wave, which determines its intensity and can be adjusted by adjusting the gain.

    Pulse-Echo Principle

    • The pulse-echo principle is the basis of ultrasound transducer function.
    • Piezoelectric crystals convert electric current into sound waves.
    • Sound waves travel through a medium (human tissue), hit tissue, and are reflected back to the crystals.
    • The crystals receive the reflected waves and convert them back to electricity as data.
    • The data is converted into pixels on the ultrasound screen.

    Attenuation

    • Attenuation is the loss of intensity or amplitude of sound waves as they travel through a medium.
    • It occurs via absorption, reflection, refraction, and scatter.
    • Four common factors affecting attenuation:
      • Absorption: conversion of acoustic energy to heat in tissue (e.g., bone).
      • Reflection: sound waves bounce back to the transducer while others continue straight through (e.g., air).
      • Refraction: angle of return of waves becomes different than the angle of transmission due to differences in tissue properties.
      • Scatter: sound waves encounter a medium with heterogeneous surface, causing random directions.

    Ultrasound Transducers

    • Ultrasound transducers are fixed frequency and cannot adjust frequency.
    • Amplitude can be adjusted with gain.
    • Different types of transducers have specific frequency ranges:
      • Phased array: 1-5 MHz, high penetration, low resolution.
      • Curvilinear: 5-7 MHz, low frequency.
      • Linear: 6-13 MHz, high frequency, high resolution.
    • Lower frequency probes penetrate deeper into tissue but have lower resolution.
    • Higher frequency probes penetrate shallow tissue but have higher resolution.

    Ultrasound Modes

    • Brightness (B) mode: provides structural information using shades of brightness in a 2D image.
    • Motion (M) mode: captures returning echoes in one line of B-mode image and displays individual images in sequence over time.
    • Doppler modes: examine direction and speed of tissue motion/blood flow, presenting as an audible, color, or spectral display.
    • Types of Doppler modes:
      • Color Doppler: shows blood flow/tissue motion in 2D image, coding direction and velocity in color.
      • Power Doppler: detects movement in low-flow states, examining amplitude of returning frequency shifts.

    Ultrasound Artifacts

    • An ultrasound artifact is a machine-generated image that does not exist in reality.
    • Artifacts can cause misinterpretation or be useful if understood.
    • Types of artifacts:
      • Acoustic shadowing: caused by strong reflection or absorption in near ultrasound fields.
      • Posterior acoustic enhancement: areas deep to echo weak/echo-free structures appear more echogenic.
      • Reverberation: sound waves bounce between two reflective layers, causing an image to appear in deeper tissue.
      • Mirroring: a duplicate image is depicted opposite a reflective layer.

    Point-of-Care Ultrasound (POCUS)

    • POCUS is a diagnostic and therapeutic tool that improves safety and efficacy of interventions in anesthesia.
    • It addresses specific clinical questions to guide evaluation and management.
    • POCUS is complementary to physical examination.
    • Conditions that can be identified using focused cardiac US assessment:
      • Severe LV/RV failure
      • Increased PAPs
      • Pericardial effusions
      • Regional wall motion abnormalities
      • Gross valvular pathology
      • Dynamic assessment of IVC

    Cardiac Ultrasound Views

    • Five common cardiac images:
      • PLAX: probe placed 3/4th ICS L of sternum, indicator towards R shoulder.
      • PSAX: probe placed 3/4th ICS L of sternum, indicator towards L shoulder.
      • Apical 4-chamber: probe placed 4/5th ICS at L nipple/breast, indicator at 2 or 3 o'clock.
      • Subcostal 4-chamber: probe placed subxiphoid with posterior pressure, indicator at 3 or 4 o'clock with overhand grip.
      • Subcostal IVC: probe placed subxiphoid with posterior pressure, indicator at 12 o'clock.
    • Expected sonographic and functional anatomical features in each cardiac view:
      • PLAX: "3 tubes and a hole" (RV/LV/LA/desc aorta/(MV/AV)/pericardium).
      • PSAX: RV/LV/PAP muscles.
      • Apical 4-chamber: LA/LV/RA/RV/MV/TV/septum ("5 chamber" = +AV).
      • Subcostal 4-chamber: LA/LV/RA/RV/pericardium.
      • Subcostal IVC: liver/IVC/RA.

    Antrum Ultrasound Assessment

    • Reasons for using the antrum as a sono-anatomic indicator of gastric contents:
      • It is the area most amenable to US assessment.
      • Liver provides a sonographic window.
      • Limited air.
      • Superficial location.
      • Multiple identifiable tissue layers.
      • Accurate reflection of total gastric contents.
    • Patient and probe position for sonographic assessment of gastric antrum:
      • Probe: Indicator towards patient head; probe Subxiphoid, midline or R of midline.
      • Patient: supine, or right lateral decubitus (superior/final definitive).
    • Gastric antrum images:
      • No contents: no visible content in supine or RLD.
      • Fluid: clear fluid in RLD but none in supine.
      • Early solid: clear fluid in RLD with some debris.
      • Late solid: significant solid content in RLD.

    Regional Anesthesia

    • Benefits of regional anesthesia:
      • Decrease surgical stress response.
      • Decrease systemic analgesic requirements.
      • Decrease opioid-related side effects.
      • Decrease general anesthesia requirements.
      • Potential for chronic pain development.
      • Post-op analgesia.
    • Patient selection:
      • Risk of general vs. regional anesthesia.
      • Primary vs. post-op analgesia.
      • Profound comorbidity.
      • Intolerance to opioids.
      • OSA.
      • PONV.
    • Contraindications:
      • Uncooperative patient.
      • Coagulopathy.
      • Infection at insertion site.
      • Pre-existing neuropathy.
      • Severe pulmonary compromise.

    Neural Anatomy

    • Endoneurium surrounds individual axon.
    • Perineurium surrounds fascicle.
    • Epineurium surrounds multiple fascicles, fat, and vessels.
    • Mesoneurium surrounds functional unit of nerve (+ artery/vein).
    • Axons are dynamic in sheaths.
    • Blood supply is microscopic and irregular.

    Local Anesthetics

    • Mechanism: blocks Na+ channel.
    • Ionized form is the active species at the intracellular binding site on Na+ channels.
    • Higher affinity for open, inactivated state of Na+ channel.
    • Pharmacokinetics/pharmacodynamics:
      • Onset: ↑ concentration/dose = ↑ speed of onset.
      • Duration: ↑ protein binding = ↑ duration.
      • Potency: ↑ lipophilicity = ↑ potency/toxicity.
    • Additives:
      • Epi: decreases vascular absorption, prolongs block.
      • Opioids: prolongs block, neuraxial > PNB.
      • A2 agonists: prolongs block, directly inhibits presynaptic conduction.
      • Dexamethasone: prolongs block, MOA unknown.

    Ultrasound-Guided Regional Anesthesia (USGRA)

    • Advantages:
      • Real-time needle guidance.
      • Decreased LAST risk.
      • Decreased dose/concentration.
    • Disadvantages:
      • Cost.
      • Knowledge requirement.
      • Training requirement.
    • Scanning axis and plane:
      • Short axis/In plane: nerves viewed in short axis, needle advanced in plane.
    • Needle/nerve image acquisition:
      • In plane: look at your hands, tilt to see nerve, slide to see needle.
      • Heel probe to direct beam into needle.
      • To determine how far to insert needle from probe, use pythagorean theorem.

    Regional Anesthesia Preparation

    • Assessment:
      • Comorbidities.
      • Discussion.
      • Informed consent.
      • Eval anatomy.
    • Patient prep:
      • Privacy.
      • Time out.
      • ASA monitors.
      • IV access.
      • O2.
      • Analgesia/anxiolysis.
    • Equipment:
      • (Meh)
    • Block procedure:
      • Maintain meaningful contact with patient.
      • R(esponse), A(spirate), P(ressure), T(otal volume): verbalize and document.

    Sound Waves and Ultrasound

    • A sound wave consists of one complete positive and negative pressure change (cycle).
    • The distance traveled during one cycle is the wavelength.
    • Frequency is the number of cycles per second, measured in Hz (Hz).
    • Amplitude is the height of a sound wave, which determines its intensity and can be adjusted by adjusting the gain.

    Pulse-Echo Principle

    • The pulse-echo principle is the basis of ultrasound transducer function.
    • Piezoelectric crystals convert electric current into sound waves.
    • Sound waves travel through a medium (human tissue), hit tissue, and are reflected back to the crystals.
    • The crystals receive the reflected waves and convert them back to electricity as data.
    • The data is converted into pixels on the ultrasound screen.

    Attenuation

    • Attenuation is the loss of intensity or amplitude of sound waves as they travel through a medium.
    • It occurs via absorption, reflection, refraction, and scatter.
    • Four common factors affecting attenuation:
      • Absorption: conversion of acoustic energy to heat in tissue (e.g., bone).
      • Reflection: sound waves bounce back to the transducer while others continue straight through (e.g., air).
      • Refraction: angle of return of waves becomes different than the angle of transmission due to differences in tissue properties.
      • Scatter: sound waves encounter a medium with heterogeneous surface, causing random directions.

    Ultrasound Transducers

    • Ultrasound transducers are fixed frequency and cannot adjust frequency.
    • Amplitude can be adjusted with gain.
    • Different types of transducers have specific frequency ranges:
      • Phased array: 1-5 MHz, high penetration, low resolution.
      • Curvilinear: 5-7 MHz, low frequency.
      • Linear: 6-13 MHz, high frequency, high resolution.
    • Lower frequency probes penetrate deeper into tissue but have lower resolution.
    • Higher frequency probes penetrate shallow tissue but have higher resolution.

    Ultrasound Modes

    • Brightness (B) mode: provides structural information using shades of brightness in a 2D image.
    • Motion (M) mode: captures returning echoes in one line of B-mode image and displays individual images in sequence over time.
    • Doppler modes: examine direction and speed of tissue motion/blood flow, presenting as an audible, color, or spectral display.
    • Types of Doppler modes:
      • Color Doppler: shows blood flow/tissue motion in 2D image, coding direction and velocity in color.
      • Power Doppler: detects movement in low-flow states, examining amplitude of returning frequency shifts.

    Ultrasound Artifacts

    • An ultrasound artifact is a machine-generated image that does not exist in reality.
    • Artifacts can cause misinterpretation or be useful if understood.
    • Types of artifacts:
      • Acoustic shadowing: caused by strong reflection or absorption in near ultrasound fields.
      • Posterior acoustic enhancement: areas deep to echo weak/echo-free structures appear more echogenic.
      • Reverberation: sound waves bounce between two reflective layers, causing an image to appear in deeper tissue.
      • Mirroring: a duplicate image is depicted opposite a reflective layer.

    Point-of-Care Ultrasound (POCUS)

    • POCUS is a diagnostic and therapeutic tool that improves safety and efficacy of interventions in anesthesia.
    • It addresses specific clinical questions to guide evaluation and management.
    • POCUS is complementary to physical examination.
    • Conditions that can be identified using focused cardiac US assessment:
      • Severe LV/RV failure
      • Increased PAPs
      • Pericardial effusions
      • Regional wall motion abnormalities
      • Gross valvular pathology
      • Dynamic assessment of IVC

    Cardiac Ultrasound Views

    • Five common cardiac images:
      • PLAX: probe placed 3/4th ICS L of sternum, indicator towards R shoulder.
      • PSAX: probe placed 3/4th ICS L of sternum, indicator towards L shoulder.
      • Apical 4-chamber: probe placed 4/5th ICS at L nipple/breast, indicator at 2 or 3 o'clock.
      • Subcostal 4-chamber: probe placed subxiphoid with posterior pressure, indicator at 3 or 4 o'clock with overhand grip.
      • Subcostal IVC: probe placed subxiphoid with posterior pressure, indicator at 12 o'clock.
    • Expected sonographic and functional anatomical features in each cardiac view:
      • PLAX: "3 tubes and a hole" (RV/LV/LA/desc aorta/(MV/AV)/pericardium).
      • PSAX: RV/LV/PAP muscles.
      • Apical 4-chamber: LA/LV/RA/RV/MV/TV/septum ("5 chamber" = +AV).
      • Subcostal 4-chamber: LA/LV/RA/RV/pericardium.
      • Subcostal IVC: liver/IVC/RA.

    Antrum Ultrasound Assessment

    • Reasons for using the antrum as a sono-anatomic indicator of gastric contents:
      • It is the area most amenable to US assessment.
      • Liver provides a sonographic window.
      • Limited air.
      • Superficial location.
      • Multiple identifiable tissue layers.
      • Accurate reflection of total gastric contents.
    • Patient and probe position for sonographic assessment of gastric antrum:
      • Probe: Indicator towards patient head; probe Subxiphoid, midline or R of midline.
      • Patient: supine, or right lateral decubitus (superior/final definitive).
    • Gastric antrum images:
      • No contents: no visible content in supine or RLD.
      • Fluid: clear fluid in RLD but none in supine.
      • Early solid: clear fluid in RLD with some debris.
      • Late solid: significant solid content in RLD.

    Regional Anesthesia

    • Benefits of regional anesthesia:
      • Decrease surgical stress response.
      • Decrease systemic analgesic requirements.
      • Decrease opioid-related side effects.
      • Decrease general anesthesia requirements.
      • Potential for chronic pain development.
      • Post-op analgesia.
    • Patient selection:
      • Risk of general vs. regional anesthesia.
      • Primary vs. post-op analgesia.
      • Profound comorbidity.
      • Intolerance to opioids.
      • OSA.
      • PONV.
    • Contraindications:
      • Uncooperative patient.
      • Coagulopathy.
      • Infection at insertion site.
      • Pre-existing neuropathy.
      • Severe pulmonary compromise.

    Neural Anatomy

    • Endoneurium surrounds individual axon.
    • Perineurium surrounds fascicle.
    • Epineurium surrounds multiple fascicles, fat, and vessels.
    • Mesoneurium surrounds functional unit of nerve (+ artery/vein).
    • Axons are dynamic in sheaths.
    • Blood supply is microscopic and irregular.

    Local Anesthetics

    • Mechanism: blocks Na+ channel.
    • Ionized form is the active species at the intracellular binding site on Na+ channels.
    • Higher affinity for open, inactivated state of Na+ channel.
    • Pharmacokinetics/pharmacodynamics:
      • Onset: ↑ concentration/dose = ↑ speed of onset.
      • Duration: ↑ protein binding = ↑ duration.
      • Potency: ↑ lipophilicity = ↑ potency/toxicity.
    • Additives:
      • Epi: decreases vascular absorption, prolongs block.
      • Opioids: prolongs block, neuraxial > PNB.
      • A2 agonists: prolongs block, directly inhibits presynaptic conduction.
      • Dexamethasone: prolongs block, MOA unknown.

    Ultrasound-Guided Regional Anesthesia (USGRA)

    • Advantages:
      • Real-time needle guidance.
      • Decreased LAST risk.
      • Decreased dose/concentration.
    • Disadvantages:
      • Cost.
      • Knowledge requirement.
      • Training requirement.
    • Scanning axis and plane:
      • Short axis/In plane: nerves viewed in short axis, needle advanced in plane.
    • Needle/nerve image acquisition:
      • In plane: look at your hands, tilt to see nerve, slide to see needle.
      • Heel probe to direct beam into needle.
      • To determine how far to insert needle from probe, use pythagorean theorem.

    Regional Anesthesia Preparation

    • Assessment:
      • Comorbidities.
      • Discussion.
      • Informed consent.
      • Eval anatomy.
    • Patient prep:
      • Privacy.
      • Time out.
      • ASA monitors.
      • IV access.
      • O2.
      • Analgesia/anxiolysis.
    • Equipment:
      • (Meh)
    • Block procedure:
      • Maintain meaningful contact with patient.
      • R(esponse), A(spirate), P(ressure), T(otal volume): verbalize and document.

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    This quiz covers the basics of sound waves, including cycles, wavelengths, frequency, and amplitude. It also explains the pulse-echo principle and the function of ultrasound transducers.

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