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?

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

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

Refraction Signup and view all the answers

What is the effect of refraction on sound waves?

The angle of return of waves becomes different than the angle of transmission Signup and view all the answers

What is the characteristic of ultrasound transducers?

They are fixed frequency Signup and view all the answers

What is the result of absorption in sound wave attenuation?

Sound waves are converted to heat energy Signup and view all the answers

What view is used to scan for the cricothyroid membrane?

Transverse view Signup and view all the answers

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

Hypovolemia Signup and view all the answers

What is the benefit of using regional anesthesia in patients?

Decrease surgical stress response Signup and view all the answers

What is the characteristic of the endoneurium in peripheral nerves?

Surrounds individual axon Signup and view all the answers

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

Liver Signup and view all the answers

What is the characteristic of the epineurium in peripheral nerves?

Surrounds multiple fascicles Signup and view all the answers

What is the contraindication of regional anesthesia?

All of the above Signup and view all the answers

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

Volume overload Signup and view all the answers

What is the US finding indicative of pneumothorax?

Lung point Signup and view all the answers

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

Microscopic and irregular Signup and view all the answers

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

Slower onset Signup and view all the answers

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

Epinephrine Signup and view all the answers

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

Inhibiting presynaptic conduction Signup and view all the answers

What is the advantage of using ultrasound in regional anesthesia?

Real-time needle guidance Signup and view all the answers

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

Short axis Signup and view all the answers

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

To direct the beam into the needle Signup and view all the answers

What is the importance of patient assessment in regional anesthesia?

To discuss the risks and benefits of the procedure Signup and view all the answers

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

To verbalize and document the response to motor stimulation Signup and view all the answers

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

Increased duration Signup and view all the answers

What is the purpose of using Exparel in regional anesthesia?

To prolong the duration of action Signup and view all the answers

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

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

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

Color doppler examines direction and velocity, while power doppler examines amplitude Signup and view all the answers

What is the purpose of POCUS in anesthesiology?

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

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

Complete absence of returning sound waves, appearing black Signup and view all the answers

What is the definition of acoustic shadowing in ultrasound imaging?

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

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

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

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

Large amplitude of returning sound waves, appearing bright Signup and view all the answers

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

Greater resolution Signup and view all the answers

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

To assess the left ventricular function Signup and view all the answers

What is the characteristic of reverberation artifacts in ultrasound imaging?

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

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

It accurately reflects total gastric contents Signup and view all the answers

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

Volume/pressure overload Signup and view all the answers

What is the most diagnostic US finding for pneumothorax?

Lung point Signup and view all the answers

What is the characteristic of the perineurium in peripheral nerves?

Surrounds fascicles and acts as a strength and diffusion barrier Signup and view all the answers

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

All of the above Signup and view all the answers

What is the characteristic of the mesoneurium in peripheral nerves?

Surrounds the entire nerve and its associated structures Signup and view all the answers

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

Profound comorbidity Signup and view all the answers

What is the significance of B Lines on ultrasound?

Indicative of interstitial edema Signup and view all the answers

What is the importance of patient assessment in regional anesthesia?

To identify potential complications Signup and view all the answers

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

Transducer design Signup and view all the answers

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

Irregular and microscopic Signup and view all the answers

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

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

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

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

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

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

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

Generating a false image of deeper tissue Signup and view all the answers

What is the primary purpose of POCUS in anesthesiology?

Guiding regional anesthesia procedures Signup and view all the answers

What is the primary characteristic of a curvilinear probe?

Wide field of view Signup and view all the answers

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

Higher resolution of superficial structures Signup and view all the answers

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

Assessing left ventricular function Signup and view all the answers

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

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

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

Hertz (Hz) Signup and view all the answers

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

Diffraction Signup and view all the answers

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

Sound waves change direction Signup and view all the answers

What is the role of piezoelectric crystals in ultrasound transducers?

To convert electrical current to sound waves Signup and view all the answers

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

Higher frequency, shallower penetration Signup and view all the answers

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

To transmit and receive sound waves Signup and view all the answers

What is the characteristic of ultrasound transducers?

Fixed frequency Signup and view all the answers

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

Sound waves are converted to heat Signup and view all the answers

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

Sound waves are randomly deflected Signup and view all the answers

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

Represents the intensity of the sound wave Signup and view all the answers

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

Blocking the channel in its inactivated state Signup and view all the answers

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

Increased speed of onset Signup and view all the answers

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

Dexamethasone Signup and view all the answers

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

Real-time needle guidance Signup and view all the answers

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

Increased potency Signup and view all the answers

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

To direct the beam into the needle Signup and view all the answers

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

Increased duration Signup and view all the answers

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

Prolonged duration of action Signup and view all the answers

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

All of the above Signup and view all the answers

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

Unreliable management 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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Description

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.