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Less Hocus...More POCUS

Morgan Morrow, DNAP, CRNA

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Lecture Objectives

Explain the use of point-of-care ultrasound in anesthesia assessment
Demonstrate where the addition of ultrasonography can improve patient assessment

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How it started…

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How its going now…

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What is POCUS?

Point-of-care ultrasound is real-time ultrasound imaging utilized to answer singular clinical questions

Assessment 🡪 Diagnosis 🡪 Patient specific guided therapy
Frequently answers a “yes” or “no” question

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Does my patient have a full stomach?

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What is my cardiovascular status?

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Where is my cric going to go?

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Date of download: 6/22/2021

Available perioperative point-of-care ultrasound examinations. ETT, endotracheal tube; ICP, intracranial pressure.�

Figure Legend:

From: Perioperative Point-of-Care UltrasoundFrom Concept to Application

Anesthesiology. 2020;132(4):908-916. doi:10.1097/ALN.0000000000003113

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Benefits of POCUS

Portable

Inexpensive

Safe

Easily reproducible

Dynamic

Image quality

POCUS as an assessment tool has a multitude of benefits. Ultrasound at the bedside is extremely portable when compared to other diagnostic imaging modalities. There are a many handheld devices on the market at an affordable price point. Ultrasonography is exceedingly safe, especially compared to imaging that utilizes radiation. Heat to tissues is the largest identifiable risk to the utilization of ultrasonography. Heat increases are seen when changing from B-mode to color doppler and to pulse wave doppler. Best practice is to do these doppler modes for a short of time as possible. Fetal and neonatal tissue are the most sensitive to heat, however, no adverse effects have been confirmed in human patients. The images acquired can be easily reproduced or accessed again. Dynamic imaging can reveal real-time movement of anatomical functions to demonstrate adequate or inadequate movement. This will be of particular interest when we look at gastric contents as well as cardiac function. Finally, the quality of the images an ultrasound can produce are clear in nature and anatomical structures can be identified with ease.

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Quick Review: Physics

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Quick Review: Physics

Electricity is converted to sound vibrations

Waves are emitted by a piezoelectric crystal
Sound is converted to mechanical energy

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Quick Review: Physics

Mechanical sound waves are reflected, refracted, scattered, transmitted, and absorbed by body tissues

Waves reflected to the transducer generate an image

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Quick Review: Physics verbiage

Anechoic

Hyperechoic

Isoechoic

Hypoechoic

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Anechoic: Black (No Echo)

Fluid/liquid (blood vessels, effusions)

Blood vessel

Effusion

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Hyperechoic: Bright white (Big Echo)

Bone, nerve, fascia, rim of bone (bone black because waves cannot penetrate through)

Radial Block Scan

Popliteal Block Scan

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Isoechoic/Hypoechoic: Grey (some reflection of Echo)

Solid organs, soft tissue, muscle

TAP Block Scan

Adductor Block Scan

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Quick Review: Physics

Frequency

HIGH:

IMAGES SUPERFICIALLY

(10-15MHZ)

LOW:

IMAGES DEEP

(2-5 MHZ)

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Frequency: Clinical Correlation

Body habitus:

Larger bodies may require deeper penetration=low frequency

Smaller habitus = higher frequency

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Probes:�Linear Array

High resolution

Rectangular footprint

Good for wide field of view

Common structures of view: musculoskeletal, superficial, vascular, PNBs

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Probes: Curvilinear

High resolution

Deep penetration (low frequency)

Trapezoidal footprint

Common structures of view: deep organs, transabdominal pelvis, neonatal structures

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Probes: Phase Array

Lower frequency

Pie-shaped field of view (small footprint)

Ideal for scanning small spaces (between ribs in cardiac, lungs/pleura)

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Linear array

Curvilinear

Phased array

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Orientations

Transducer Orientation

Body Orientation

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Sagittal Plane-left and right planes

Transverse or Horizontal Plane-upper and lower

Coronal Plane-anterior and posterior

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Image Orientation

Where is the index marker on the probe relative to the position on the patient’s body?

Near field on the image (top of screen) is CLOSEST to the skin

Far field (bottom of screen) is the GREATEST DEPTH

Subcostal 5-chamber view

Ventricle is the first thing the probe “encounters”

It can be easy to get lost in your image or for you to perceive that the image is “backwards.” The best way to confirm that you are scanning in the correct orientation is to note where your probe marker is in relation to the patient’s body. If scanning in the transverse or horizontal plane, if the probe marker is pointing towards the patient’s head, the left side of the screen will reflect images more cephalad and the right side will reflect more caudal images. There are both transducer orientation markers and screen orientation markers and they should be aligned. This will make more sense as you scan live patients and it is simple to align them. When looking at the image, note near and far field and consider the anatomical structures that are initially encountered. In this cardiac image, the heart appears to be upside down. The ventricles are the first anatomic structure encountered by the probe which is why they appear near field, or on the top of the screen compared to the atria.

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“Knobology”

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Depth

Adjusted to bring the target structure in the center of the screen
Too deep? Target structures in near field but appear smaller and have lower resolution
Too shallow? Structures may not be visualized

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Focus

Improves image resolution
The focal zone is the narrowest point of the ultrasound beam to give the best lateral resolution
Focal zone can be set and adjusted to the intended target

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Gain

The further waves travel into a structure, the more their strength is weakened
Machines can compensate for attenuation of waves through time gain compensation
Gain adjust the amount of amplification of the echoes returning to the ultrasound probe
Increasing gain 🡪 Brighter images
Decreasing gain 🡪 Darker images

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Doppler

Utilized to identify flow (blood)

Velocity of flow is depicted by varying intensities of yellow-orange pulsations REGARDLESS of direction of flow

A color box size, location, and angle can be user controlled and only large enough to demonstrate flow

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Scanning tips

Confirm transducer orientation (tap the probe to make sure your marker is oriented to the side of the screen you think it should be on)

In general, when scanning in the transverse plane (ex: PNBs), the probe marker should be pointed to the operators LEFT

When scanning in the coronal or sagittal planes, the marker should be pointed cephalad (to the head)

Slow movements in order to identify anatomical structures

Use only one motion at a time (do not rock and tilt the probe at the same time)

Is the patient position optimal?

Is the patient comfortable?

A few scanning tips to consider if you’re having difficulty with your ultrasound image. To begin, ensure alignment of both orientation markers (both on the probe and on the ultrasound image screen). If you are performing a scan in the transverse plane, likely for a peripheral nerve block, the probe marker should point left and be on the left of the ultrasound screen. If scanning in either the coronal or sagittal planes, the probe marker should be cephalad. Small movements in ultrasound make big changes to imaging. Try and identify structures and slowly scan to identify the targeted object. Also, make only one change at a time to attempt to optimize your image. Finally and most important, ensure that your patient positioning is optimal and that the patient is comfortable in order to tolerate the procedure.

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Tangible utilization for the CRNA

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Cardiac Ultrasound

POCUS used to detect major cardiac pathology

When utilized, POCUS significantly altered anesthetic management in 82% of cases

POCUS cardiac assessment

Ventricular function, pericardial effusion, valvular abnormalities

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Pulmonary Ultrasound

Utilized for a patient with shortness of breath or hypoxia
Thoracic ultrasound

Effusion, pneumothorax, pulmonary edema

Faster than CXR

93% diagnostic accuracy to detect pleural effusion, 97% for alveolar consolidation, 95% for alveolar-interstitial syndrome (versus 47%/75%/72% respectively for CXR)

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Regional anesthesia

Overall improved outcomes, reduced length of stay, decreased complications

Reduces stress, inflammation, complications, improved postoperative pain control, early ambulation

Evidence-based approach to analgesia

Regional anesthesia is an area we are all likely more familiar and comfortable with. However, barriers still exist to the implementation of peripheral nerve blocks to the perioperative patient. USGRA results in longer block durations, faster onset times, improved block success, and an overall reduction in opioid consumption. Currently, available literature states that PNB utilization in surgical procedures remains low and that PNBs are generally underutilized.Increasing utilization of PNBs throughout the perioperative period will likely have a significant impact on the pain management of patients throughout the perioperative period. PNBs are associated with a decreased need for opioid analgesics, lower risk of developing persistent post-surgical pain, overall reduced rates of complications, and lower re-admission rates to the hospital post initial surgical stay discharge. In addition to the vast quantitative data supporting PNB use, qualitative research demonstrates that PNB use improves the overall patient perioperative experience. Patients have reported improved analgesia and satisfaction.

In a pilot study and follow up national survey, I found self-assessed ease with administering peripheral nerve blocks was rated lower. Application of peripheral nerve blocks requires the practitioner to simultaneously obtain an adequate ultrasound image with proper anatomic interpretation, possess the hand-eye coordination required to scan the patient’s anatomy, and concurrent fine motor skill of needle positioning. The placement of peripheral nerve blocks simultaneously occurs while monitoring the patient condition and tolerance to the procedure in real-time in the high-stress perioperative environment. As ultrasound becomes the standard of care and is more frequently utilized, provider comfort will likely increase.

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Hemodynamics

Non-invasive approach to visualize ventricular filling and fluid responsiveness

Inferior vena cava collapsibility and LV end-diastolic pressure can determine overall cardiac filling pressures

Can visualize respiratory variations to pressure changes

Traditionally hemodynamics have been measured through more invasive approaches, such as TEE, and invasive catheters. Through POCUS, both stroke volume and cardiac output can be assessed through a non-invasive approach.

A subcostal view of the inferior vena cava can tell you the status of the right ventricle, as well as the pulmonary and fluid status. The IVC should be measured just proximal to the hepatic veins. Normal measurements are <2.1 cm. The IVC should collapse at least 50% to be considered a normal fluid status. If the IVC collapses without a Valsalva maneuver, the patient is likely volume depleted. If the IVC measures greater than 2.1 cm or does not collapse 50%, they are likely fluid overloaded and or in right heart failure

This measurement can only be done in patients who are spontaneously breathing. We will further explore the applications for this in the cardiac POCUS lecture

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Airway management

Identification of cricothyroid membrane in difficult airway management

ETT positioning

Superior to auscultation-93% sensitivity and 96% specificity compared to 66% and 59% respectively

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Vascular Access

US for CVC identified as a top practice to improve patient safety

Reduces CVC associated infections and complications (pneumo/hemothorax)

“One-stick” standard

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Gastric ultrasound

Quantifying gastric volume and aspiration risk

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Grading system based on qualitative sonographic evaluation

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There are many co-existing conditions which contribute to delayed gastric emptying in the surgical patient, placing them at risk for aspiration. In addition, opting for endotracheal tube over LMA as an airway management strategy in a patient who is perceived to be an increased aspiration risk also comes with the potential for complications. Utilizing gastric scanning, a CRNA can quantify the amount and type of material in the patient’s stomach and determine how to best proceed with the case. In an article in the AANA Journal, utilization of gastric ultrasound was found to be a tool to change the anesthetic management plan in 9% of the patients included. Gastric ultrasound was noted to take about 3 minutes and 35 seconds on average for the providers included. The study noted that treating aspiration would mechanical ventilation costs on average around $47,000 and they determined at the time spent doing POCUS gastric scanning cost around $628 of the provider’s time, which is a large potential cost benefit.

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FAST Assessment

Focused imaging in trauma to detect life-threatening injuries and trauma

Used to detect free fluid intraperitoneal, pleural, or pericardial space

Accuracy described as up to 98% for detecting clinically significant injuries

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ICP Assessment

Non-invasive approach

Can be utilized to determine ocular pressures in patients at risk for post-operative visual loss

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References

Cieslak, J. R., Rice, A. N., Gadsden, J. C., & Vacchiano, C. A. (2020). Does ultrasonographic measurement of gastric content influence airway management decisions? AANA Journal, 88(2), 107-113.
Corl, K. A., George, N. R., Romanoff, J., Levinson, A. T., Chheng, D. B., Merchant, R. C., Levy, M. M., & Napoli, A. M. (2017). Inferior vena cava collapsibility detects fluid responsiveness among spontaneously breathing critically-ill patients. Journal of critical care, 41, 130–137. https://doi.org/10.1016/j.jcrc.2017.05.008
Ihnatsenka, B. & Boezaart, A. P. (2010). Ultrasound: Basic understanding and learning the language. International Journal Shoulder Surgery, 4(3), 55-62.
Novitch, M., Prabhakar, A., Siddaiah, H., Sudbury, A. J., Kaye, R. J., Wilson, K. E., Haroldson, A., Fiza, B., Armstead-Williams, C. M., Cornett, E. M., Urman, R. D., & Kaye, A. D. (2019). Point of care ultrasound for the clinical anesthesiologist. Best practice & research. Clinical anaesthesiology, 33(4), 433–446. https://doi.org/10.1016/j.bpa.2019.06.003
Ramsingh D, Singh S, Canales C, et al. The Evaluation Point-of-Care Ultrasound in the Post-Anesthesia Unit-A Multicenter Prospective Observational Study. J Clin Med. 2021;10(11):2389. Published 2021 May 28. doi:10.3390/jcm10112389
Ramsingh, D. (2019, May 30). Top 10 Perioperative Applications of Point-of-Care Ultrasound for Anesthesiologists. OR Today. https://ortoday.com/top-10-perioperative-applications-of-point-of-care-ultrasound-for-anesthesiologists/
Soni, N.J., Arntfield, R., & Kory, P. (2020). Point of Care Ultrasound. Elsevier.