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SAEM Clinical Images Series: Unidentified Intrauterine Object

IUP

A 31-year-old female G3P2 presented to the emergency department with vaginal spotting for one week and worsening lower abdominal cramping. She tested positive on a home pregnancy test one day prior to presentation. On the day of presentation, she passed a small blood clot and bled through one pad. She had not yet seen an OB for this pregnancy. Her last menstrual period was one month and three days prior. The current pregnancy is undesired. She denied fevers, chills, urinary symptoms, lightheadedness, palpitations, shortness of breath, nausea, or vomiting.

 

gestational sac

Vitals: BP 95/55; HR 75; Temp 98.4°F; Resp 16; SpO2 100% on room air

Abdomen: Soft; tender to palpation in the suprapubic region, no guarding or rebound tenderness

GU: Scant blood in the vaginal canal, no clots or tissue; os closed, no adnexal tenderness, no cervical motion tenderness

bHCG: 36,966

Rh Factor: Positive

Hgb: 9.2

Ectopic pregnancy needs to be ruled out. This patient has vaginal bleeding, a positive pregnancy test, and abdominal pain. She has not established care with an OB provider and has not had a confirmed intrauterine pregnancy. Specific ultrasound findings for an ectopic pregnancy include a gestational sac with a yolk sac outside of the uterus. Findings suggestive of an ectopic pregnancy include complex adnexal masses, free fluid with debris (suggestive of rupture), and an empty gestational sac within an adnexal mass.

Yes, this is a viable intrauterine pregnancy (IUP). Confirmation can be done with transabdominal ultrasound but in very early pregnancy may require a transvaginal ultrasound. Findings needed to confirm an IUP include a gestational sac containing a yolk sac within a thickened myometrium. The hyperechoic structure seen on transabdominal and transvaginal ultrasounds for this patient is an intra-uterine device (IUD) that is in place. The risk of pregnancy with an IUD in place is <1%; according to a database of 18 million hospital deliveries, the reports of retained IUD at birth was 12 per 100,000 births. For pregnancies with an IUD in place, the rate of ectopic pregnancy is higher. There is also a higher risk of maternal infection, miscarriage, preterm premature rupture of membranes, preterm birth, and intrauterine fetal demise. For desired pregnancies, if the strings are visible, the IUD is removed as soon as possible and a single dose of azithromycin is given due to increased risk of infection during pregnancy. There is limited evidence to guide management for desired pregnancies when strings are not visible. One option is hysteroscopic removal, although this increases the risk of pregnancy loss. More than 50% of pregnancies with in situ IUDs were found to end in spontaneous abortion.

Take-Home Points

  • A definite IUP requires an intrauterine gestational sac with yolk sac and/or embryo (with or without cardiac activity).
  • Pregnancy with an IUD is extremely rare and increases the risk of ectopic pregnancy, maternal infection, miscarriage, PPROM, preterm birth, and fetal demise.
  • Management for desired pregnancies with IUDs in place when IUD strings are visible consists of early IUD removal with a single dose of prophylactic antibiotics.

  • ACOG Practice Bulletin No. 121: Long-acting reversible contraception: Implants and intrauterine devices. Obstet Gynecol. 2011 Jul;118(1):184-196. doi: 10.1097/ AOG.0b013e318227f05e. PMID: 21691183.
  • Ganer H, Levy A, Ohel I, Sheiner E. Pregnancy outcome in women with an intrauterine contraceptive device. Am J Obstet Gynecol. 2009 Oct;201(4):381.e1-5. doi: 10.1016/j.ajog.2009.06.031. Epub 2009 Aug 29. PMID: 19716537.
  • Roline, C.E., Heegaard, W.G. & Anderson, K.S. Early pregnancy with an intrauterine device in place. Crit Ultrasound J 3, 91–92 (2011). https://doi.org/10.1007/s13089-011-0068-1

Copyright

Images and cases from the Society of Academic Emergency Medicine (SAEM) Clinical Images Exhibit at the 2023 SAEM Annual Meeting | Copyrighted by SAEM 2023 – all rights reserved. View other cases from this Clinical Image Series on ALiEM.

By |2024-09-28T21:27:46-07:00Oct 4, 2024|Ob/Gyn, SAEM Clinical Images, Ultrasound|
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PEM POCUS Series: Soft Tissue Ultrasound

PEM POCUS fascia iliaca block

Read this tutorial on the use of point of care ultrasonography (POCUS) for pediatric soft tissue ultrasonography. Then test your skills on the ALiEMU course page to receive your PEM POCUS badge worth 2 hours of ALiEMU course credit.

Case Goals

  1. List the indications of performing a pediatric soft tissue point-of-care ultrasound (POCUS).
  2. Describe the technique for performing soft tissue POCUS.
  3. Interpret signs of cellulitis, abscess, and soft tissue foreign body on POCUS.
  4. Describe the limitations of soft tissue POCUS.
  5. Differentiate abscess from other soft tissue pathologies such as cysts and lymph nodes.

Case Introduction: Child with abdominal pain

Wendy is a 7-year-old girl who comes into the emergency department with redness, swelling, and pain on her left calf. Her symptoms started 1 week ago as a scratch which progressively got more red and painful. There has been no drainage from the lesion. She has had no fevers, but endorses elevated temperatures of 99 F.

On arrival, her vital signs are:

Vital SignFinding
Temperature100.1 F
Heart Rate95 bpm
Blood Pressure105/68
Respiratory Rate20
Oxygen Saturation (room air)100%

On her exam, you notice a 3 x 3 cm area of erythema and induration on her right calf with questionable fluctuance. The area is tender to palpation. She has no other skin findings noted, and she is able to bear weight. Given your concern for an abscess which may require drainage, a POCUS is performed.

Pediatric Soft Tissue POCUS

Figure 1. Linear ultrasound transducer

Probe

  • Use a linear, high-frequency transducer.

Technique

  • Hold the probe perpendicular to the skin.
  • Scan the area of interest in 2 orthogonal (perpendicular) planes.
  • If there is an abscess:
    • Measure the abscess in 3 dimensions.
    • Use color Doppler to ensure the structure is not vascular.

Pro Tips

  • It is often helpful to ultrasound the unaffected side as a comparison.
  • You cannot see what you didn’t scan. Scan the entirety of the affected area in 2 planes.
  • Be aware of the patient’s comfort throughout the examination.
  • A water bath may be helpful to visualize lesions in extremities such as the hands or feet.
    • The probe sits just below the water’s surface and does not need to contact the skin.
    • The benefits of using a water bath include better visualization of superficial structures and alleviates the need for direct skin contact.
waterbath technique with ultrasound image

Figure 2. Left: Water bath technique; Right: Ultrasound of a toe using a water bath (image courtesy of The Pocus Atlas and Moudi Hubeishy, MD)

soft tissue layers ultrasound

Figure 3. Normal soft tissue layers on ultrasound (image courtesy of The Pocus Atlas)

Normally on a soft tissue ultrasound, you will see layers of defined structures separated by fascial planes.

  1. Epidermis/dermis: This is the topmost layer and has an hyperechoic appearance on ultrasound.
  2. Subcutaneous tissue: This deeper layer will appear slightly more hypoechoic.
  3. Muscular layer: This even deeper layer classically appears striated in the long axis view, while in the short axis view, it will have a speckled appearance.
  4. Bone: This layer appears hyperechoic cortex with posterior shadowing.

Cellulitis has a spectrum of appearances on ultrasound. Early cellulitis may present as skin thickening (Figure 4).

pem pocus cellulitis hazy thickening

Figure 4. Cellulitis with skin thickening

 

As cellulitis progresses, there is effacement of the clearly differentiated structures seen above, and the tissue layers may appear hazy and hyperechoic. More advanced cellulitis may have “cobblestoning” which is the result of edematous fluid separating fat globules in the subcutaneous tissue.

pem pocus cellulitis cobblestoning

Figure 5. Cellulitis with cobblestoning

 

Video 1. Ultrasound showing cellulitis with cobblestoning

Abscesses can have varied appearances. They can be anechoic (black) or filled with debris leading to a heterogeneous appearance of contents. The rim may be echogenic or blend in with surrounding tissue. They may be well-circumscribed or may have irregular borders.

A. Abscess with irregular borders and heterogeneous appearance

B. Well-circumscribed abscess with heterogeneous debris

C. Larger abscess with well-circumscribed borders

D. Abscess with irregular borders and surrounding cellulitis

E. Abscess with irregular borders and more homogenous appearance

F. Superficial abscess with well-circumscribed borders

Table 1. Examples of different appearances of abscesses on ultrasound
Video 2. Ultrasound of a cutaneous abscess

Color Doppler Flow

Placing color Doppler flow on a suspected abscess is helpful to differentiate it from a lymph node or blood vessel (see “Abscess Mimickers” section for lymph node examples). It may also aid in identifying nearby vasculature.

Figure 6. Abscess with color Doppler flow

Video 3. Ultrasound of cutaneous abscess with color Doppler flow

Posterior Acoustic Enhancement

Abscesses may exhibit posterior acoustic enhancement, which results in an enhanced transmission of ultrasound waves through a fluid-filled structure. Sometimes the abscess may not be as obvious and appear less anechoic due to debris. A squish (or swirl) sign may be elicited by putting pressure on the region, which will cause movement of the abscess contents. This finding has also been called “pus-talsis”.

Figure 7. Abscess with posterior acoustic enhancement

Video 4. Ultrasound of cutaneous abscess with squish sign

Size Measurement

Abscesses should be measured in 2 planes. Measure depth in 1 plane and length in 2. An easy way to remember this is to measure a plus sign (+) in one view, and a minus sign (-) in the other.

Figure 8. Measurement of abscess in two planes (images courtesy of Dr. Munaza Rizvi)

Lymph Nodes

Lymph nodes appear as ovid and well-circumscribed structures on ultrasound and may be confused for abscesses. They may be differentiated by their homogenous echotexture, central echogenic hilum. When inflamed, they may exhibit internal vascularity which should not be seen in an abscess.

Figure 9. A lymph node with a hilum (left) and a reactive inguinal lymph node with central vascularity (right)

Cysts

Cysts are fluid-filled, well-circumscribed structures which may be similar to abscesses. A common soft tissue cyst is an epidermoid cyst, which is a subepidermoid nodule filled with keratin. In addition to physical exam clues which may help distinguish cysts from abscess, cysts are typically very well-circumscribed and more homogenous in appearance.

Figure 10. Epidermoid cyst (image courtesy of The Pocus Atlas and Dr. Robert Jones)

Soft tissue foreign bodies are a common pediatric presentation and can be easily identified on ultrasound. X-rays can be used to identify foreign bodies; however, their use is limited to radiopaque objects. On ultrasound, foreign bodies often appear as a hyperechoic defect.

Figure 11. Hyperechoic foreign body (glass) embedded in the soft tissue of a foot with posterior shadowing

Video 5. Ultrasound of soft tissue foreign body

Foreign bodies embedded for a prolonged time may have signs of infection, such as cellulitis or abscess (Figure 12).

Figure 12. Wooden splinter embedded in a patient’s plantar foot with surrounding fluid collection consistent with abscess

A foreign body’s composition can affect how it appears on ultrasound. Different materials can produce characteristic ultrasound artifacts.

Foreign BodyUltrasound FindingsUltrasound Image
WoodHyperechoic with posterior shadowing
GlassHyperechoic with posterior shadowing
May have comet tail artifact

Images courtesy of Dr. Ashkon Shaahinfar

MetalVery hyperechoic
Often has a comet tail or reverberation artifact
Table 2. Foreign body characteristics on ultrasound

Foreign Body Removal

Ultrasound assistance in foreign body removal may be static (used to locate the foreign body’s position) or dynamic (using ultrasound to guide foreign body removal in real-time). Measuring the foreign body and assessing the object’s depth on ultrasound may assist in determining if bedside removal versus surgical removal is indicated.

Limited evidence suggests that there may be some sonographic differences between the papular urticaria of a “skeeter syndrome” and local cellulitis. On ultrasound, both findings will have thickening of dermal and subcutaneous tissues. Angioedema characteristically includes more linear, horizontal, striated bands — in comparison to cobblestoning found in cellulitis [1]. However, additional studies are needed to confirm this.

Figure 13. Ultrasound of angioedema (left) and cellulitis with cobblestoning (right). Angioedema image courtesy of Dr. Laura Malia.

Necrotizing fasciitis is a rare pediatric diagnosis but a rapidly progressive and life-threatening condition if not identified quickly. While necrotizing fasciitis is primarily a clinical diagnosis, imaging may be helpful when the diagnosis is uncertain. Computed tomography (CT) and magnetic resonance imaging (MRI) have good test characteristics; however, these tests are time-consuming and may not be available in all centers. CT also involves ionizing radiation. Point-of-care ultrasound has the benefit of rapid bedside use and lack of ionizing radiation.

On ultrasound, early necrotizing fasciitis presents with thickening of the subcutaneous tissue, similar to cellulitis. Fluid in the fascial layers may also be present, and a thick layer of pre-fascial fluid >4 mm has been associated with necrotizing fasciitis [2]. Subcutaneous air with dirty shadowing (Figure 14) is a characteristic but late finding in necrotizing fasciitis. These findings may be recalled using the “STAFF” mnemonic [3]:

  • Subcutaneous Thickening
  • Air
  • Fascial Fluid

Note: It may be difficult to distinguish early cases of necrotizing fasciitis from cellulitis. Therefore ultrasound should not be used to exclude necrotizing fasciitis. Patients with findings concerning for necrotizing fasciitis require additional work-up and surgical consultation.

Figure 14. Necrotizing fasciitis on POCUS exam showing the presence of air with dirty shadowing within soft tissue (image courtesy of Dr. Di Coneybeare)

For additional reading on ultrasounding necrotizing fasciitis, see these ALiEM articles:

  • As with all ultrasound applications, soft tissue POCUS is operator dependent.
  • The ultrasound can only see what is scanned. You must make sure the lesion is fully imaged.
  • It is difficult to differentiate between various types of fluid on ultrasound. For example, hematomas may resemble abscesses. Therefore clinical context is important.

There have been multiple studies (Table 3) that support the use of soft tissue POCUS for identification of cellulitis or abscess. Soft tissue POCUS has been shown to have good sensitivity and specificity. It has also been shown to be superior to clinical assessment in several pediatric studies.

POCUS can also reduce the length of stay (LOS) for our patients. In one pediatric study including 3,094 children suspected of a soft tissue infection who underwent either POCUS or radiology department ultrasound, POCUS was shown to have a shorter median LOS by 73 minutes (95% CI 52.4-93.6 min) [4].

StudyNMethodsPOCUS Sensitivity (95% CI)POCUS Specificity (95% CI)Conclusions
Gottleib et al., Ann Emerg Med 2020 [5]2,656Systematic review of adult and pediatric studies94.6%

(89.4-97.4%)

85.4%

(78.9-90.2%)

POCUS has good diagnostic accuracy. Led to correct change in management in 10% of cases.
Lam et al., J Emerg Med 2018 [6]327Prospective cohort study of children 6mo-18yrs comparing clinical assessment to POCUS90.3%

(83.4-94.7%)

80%

(70.0-87.4%)

POCUS changed management in 22.9% of cases*
Subramaniam et al., Acad Emerg Med 2016 [7]800Systematic review of adult and pediatric (patients from birth – 21yrs) studies97%

(94-98%)

83%

(75-88%)

POCUS may assist physicians in distinguishing cellulitis versus abscess.
Adams et al., J Pediatr 2015 [8]151Prospective cohort study of patients 3mo-21yrs comparing clinical assessment to POCUS96%

(90-99%)

87%

(74-95%)

POCUS changed management in 27% of cases.** For every 4 ultrasounds performed, 1 correct change in management.
Sivitz et al., J Emerg Med 2009 [9]50Prospective cohort study of children <18yrs comparing clinical assessment to POCUS90%

(77-100%)

83%

(70-97%)

POCUS changed management in 22% of cases.
Table 3. Studies comparing soft tissue POCUS to clinical assessment in the management of soft tissue infections.
* Change in management after POCUS defined by the following:
  • Changed incision location/size
  • Added packing
  • Medical to surgical management
  • Surgical to medical management
  • Consultation of specialist
  • Other
** Change in management defined as when the ultrasound diagnosis was discordant from the physical exam and matched the ultimate lesion classification.

Case Resolution

After reviewing the literature, you decide to perform a POCUS to evaluate for skin abscess. You place a linear, high-frequency transducer over the patient’s affected area and you observe the following:

Video 6. Soft tissue ultrasound showing an abscess with heterogeneous appearance and irregular borders with posterior acoustic enhancement, surrounding soft tissue haziness, cobblestoning

ED Course

The patient underwent successful incision and drainage of the abscess, and she was discharged home with antibiotics.

 

Learn More…

References

  1. Tay ET, Ngai KM, Tsung JW, Sanders JE. Point-of-Care Ultrasound on Management of Cellulitis Versus Local Angioedema in the Pediatric Emergency Department. Pediatr Emerg Care. 2022 Feb 1;38(2):e674-e677. doi: 10.1097/PEC.0000000000002416. PMID: 34398861.
  2. Yen ZS, Wang HP, Ma HM, et al. Ultrasonographic screening of clinically-suspected necrotizing fasciitis. Acad Emerg Med. 2002;9:1448–1451. PMID 12460854.
  3. Castleberg E, Jenson N, Dinh VA. Diagnosis of necrotizing faciitis with bedside ultrasound: the STAFF Exam. West J Emerg Med. 2014 Feb;15(1):111-3. doi: 10.5811/westjem.2013.8.18303. PMID: 24578776; PMCID: PMC3935782.
  4. Lin MJ, Neuman M, Rempell R, Monuteaux M, Levy J. Point-of-Care Ultrasound is Associated With Decreased Length of Stay in Children Presenting to the Emergency Department With Soft Tissue Infection. J Emerg Med. 2018 Jan;54(1):96-101. doi: 10.1016/j.jemermed.2017.09.017. Epub 2017 Oct 27. PMID: 29110982.
  5. Gottlieb M, Avila J, Chottiner M, Peksa GD. Point-of-Care Ultrasonography for the Diagnosis of Skin and Soft Tissue Abscesses: A Systematic Review and Meta-analysis. Ann Emerg Med. 2020 Jul;76(1):67-77. doi: 10.1016/j.annemergmed.2020.01.004. Epub 2020 Feb 17. Erratum in: Ann Emerg Med. 2022 Jan;79(1):90. PMID: 32081383.
  6. Lam SHF, Sivitz A, Alade K, Doniger SJ, Tessaro MO, Rabiner JE, Arroyo A, Castillo EM, Thompson CA, Yang M, Mistry RD. Comparison of Ultrasound Guidance vs. Clinical Assessment Alone for Management of Pediatric Skin and Soft Tissue Infections. J Emerg Med. 2018 Nov;55(5):693-701. doi: 10.1016/j.jemermed.2018.07.010. Epub 2018 Aug 28. PMID: 30170835; PMCID: PMC6369916.
  7. Subramaniam S, Bober J, Chao J, Zehtabchi S. Point-of-care Ultrasound for Diagnosis of Abscess in Skin and Soft Tissue Infections. Acad Emerg Med. 2016 Nov;23(11):1298-1306. doi: 10.1111/acem.13049. Epub 2016 Nov 1. PMID: 27770490.
  8. Adams CM, Neuman MI, Levy JA. Point-of-Care Ultrasonography for the Diagnosis of Pediatric Soft Tissue Infection. J Pediatr. 2016 Feb;169:122-7.e1. doi: 10.1016/j.jpeds.2015.10.026. Epub 2015 Nov 10. PMID: 26563535.
  9. Sivitz AB, Lam SH, Ramirez-Schrempp D, Valente JH, Nagdev AD. Effect of bedside ultrasound on management of pediatric soft-tissue infection. J Emerg Med. 2010 Nov;39(5):637-43. doi: 10.1016/j.jemermed.2009.05.013. Epub 2009 Aug 8. PMID: 19665335.
By |2024-05-12T22:03:30-07:00May 13, 2024|Expert Peer Reviewed (Clinical), Infectious Disease, Pediatrics, PEM POCUS, Ultrasound|
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SAEM Clinical Images Series: An Ultrasonographic Rabbit Hole

hole

An 86-year-old man with a past medical history of coronary artery disease, hypertension, hyperlipidemia, chronic kidney disease, COPD, choledocholithiasis requiring ERCP and sphincterotomy 2 years ago presented with five days of feeling unwell. History was limited due to cognitive impairment. His daughter had reported to staff he had been feeling unwell for five days, intermittently having nausea and generalized abdominal pain, subjective fevers, chest pain, and shortness of breath. His daughter also reported a history of intermittent lower abdominal cramping which was chronic for him. He denied changes to urination or bowel movements.

 

Vitals: BP 106/67, Temp 36.2°C, Pulse 115, Resp 20, SpO2 95%

General: Nontoxic appearing, no distress

Heart: Regular, no murmurs

Lungs: Clear bilaterally, normal work of breathing

Abdomen: Diffusely tender, greatest in left upper quadrant

CBC with differential: WBC 14.1, Neutrophil 12% (high)

Comprehensive metabolic panel (CMP): Total bilirubin 2.7 (high), AlkP 328 (high), AST/ALT normal

Lipase: Normal

Troponin x2: Negative

Chest x-ray: No acute abnormality

This patient has sonographic evidence of perforated gangrenous cholecystitis which was confirmed on subsequent CT scan. Gallbladder perforation is a complication of cholecystitis and has a reported incidence of 5-10%. It has been reported as early as two days after the onset of symptoms to as late as several weeks afterward. The most common site of perforation is the fundus due to relatively poor blood supply. In this case, the culprit perforation was in the proximal body adjacent to the stone which is suspected to have eroded through the wall.

Figure 1 depicts a minimally thickened gallbladder wall measured at 3.5 mm with a large shadowing stone-in-neck and associated perihepatic fluid collection (arrow) with a subtle intraluminal membrane and wall irregularity consistent with gangrenous cholecystitis. Figure 2 doppler images show no flow within the fluid collection and a suspiciously thin gallbladder wall (arrow). Figure 3 again highlights an irregular wall with small “hole sign” (arrow) signifying perforation of the gallbladder into the adjacent fluid collection. This patient was admitted to the hospital’s general surgical service and treated with IV broad-spectrum antibiotics and a percutaneous cholecystostomy tube placed by interventional radiology.

Take-Home Points

  • Look out for “hole signs” with adjacent fluid collection on your gallbladder ultrasounds which would suggest perforation.
  • Intraluminal membranes or wall irregularities suggest gangrenous cholecystitis.
  • Initial treatment includes broad-spectrum antibiotics and cholecystostomy tube decompression.

  • Indiran, V., Prabakaran, N. & Kannan, K. “Hole sign” of the gallbladder. Indian J Gastroenterol 36, 66–67 (2017). https://doi.org/10.1007/s12664-016-0723-3
  • Jeffrey RB, Laing FC, Wong W, Callen PW. Gangrenous cholecystitis: diagnosis by ultrasound. Radiology. 1983 Jul;148(1):219-21. doi: 10.1148/radiology.148.1.6856839. PMID: 6856839.
  • Sood, B.P., Kalra, N., Gupta, S., Sidhu, R., Gulati, M., Khandelwal, N. and Suri, S. (2002), Role of sonography in the diagnosis of gallbladder perforation. J. Clin. Ultrasound, 30: 270-274.

Copyright

Images and cases from the Society of Academic Emergency Medicine (SAEM) Clinical Images Exhibit at the 2023 SAEM Annual Meeting | Copyrighted by SAEM 2023 – all rights reserved. View other cases from this Clinical Image Series on ALiEM.

By |2024-04-01T09:12:28-07:00Feb 16, 2024|Gastrointestinal, SAEM Clinical Images, Ultrasound|
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SAEM Clinical Images Series: Retrobulbar Spot Sign

vision

A 59-year-old male with no known past medical history other than an incidental abdominal aortic aneurysm presented with sudden onset, painless vision loss in his left eye. The patient was watching TV two days prior when he saw a “brightness” in his left eye and then progressive blurriness until his vision faded away, all occurring within the span of a minute. At the time of presentation, he only sees a speck of light from that eye. He denied associated pain, flashes, floaters, jaw claudication, the sensation of a “curtain falling”, prior vision problems, or a history of blood clots.

 

Eyes: Eyelids and lashes normal. Visual acuity: 20/30 OD, Light Perception OS. EOMI. PERRL. OD visual fields intact. Afferent Pupillary Defect OD. Normal conjunctiva. IOP 16 OD, 14 OS. Otherwise CN 3-12 intact.

Complete blood count (CBC): Within normal limits

Basic metabolic panel: Creatine 1.3 (unknown baseline)

ESR: Unmarkable

Central Retinal Artery Occlusion (CRAO) is an ocular emergency that presents as acute painless monocular vision, caused by ischemia and infarction to the retina via thromboembolic disease to the central retinal artery. It requires immediate consultation with ophthalmology as well as neurology as it is considered a stroke equivalent.

The case described above and several previously published case studies highlight the utility of POCUS in identifying CRAO via the retrobulbar spot sign (RBSS) within the optic nerve in a rapid, non-invasive manner that can be done prior to waiting for dilation for a fundoscopy exam. This has the potential to expedite consultations with specialty teams and treatment.

Several studies also reveal the potential of POCUS to predict the etiology of CRAO (arterio-arterial embolization vs cardio-embolic vs vasculitis) and thus to predict the success of thrombolytic treatment in CRAO. In a prospective monocenter study of 46 patients with ophthalmologically confirmed CRAO, embolism from large artery atherosclerosis (LAA, i.e. carotids or aortic arch) was the etiology in 27 patients, cardioembolic in 10 patients, vasculitis in 5 patients, and unknown in 4 patients. Out of the LAA patients, 59% had RBSS compared with only 20% in cardioembolic and 0% in the vasculitis patients. Within the 11 patients that underwent thrombolysis, statistically significant visual improvement occurred in all 4 patients with RBSS negative CRAO, while the 7 patients with RBSS positive CRAO had persistent visual impairment with persistent occlusion of their arteries. This study concludes that their results support the hypothesis that RBSS is seen due to calcium deposits that will not be dissolved with thrombolysis. Another small single-center German study points out the utility of seeing RBSS as 100% specific for an embolic cause of CRA, excluding temporal arteritis from the differential.

Take-Home Points

  • POCUS can guide us in diagnosing a patient with painless vision loss prior to more time-consuming fundoscopy exam.
  • Stroke workup for CRAO is necessary, and don’t forget about secondary prevention/risk stratification which must be part of the management.
  • RBSS may predict poor response to systemic thrombolysis.

  • Ertl M, Altmann M, Torka E, Helbig H, Bogdahn U, Gamulescu A, Schlachetzki F. The retrobulbar “spot sign” as a discriminator between vasculitic and thrombo-embolic affections of the retinal blood supply. Ultraschall Med. 2012 Dec;33(7):E263-E267. doi: 10.1055/s-0032-1312925. Epub 2012 Sep 21. PMID: 23023446.
  • Nedelmann, Matt et al. “Retrobulbar Spot Sign Predicts Thrombolytic Treatment Effects and Etiology in Central Retinal Artery Occlusion” American Heart Association (AHA). Stroke. 2015;46:2322–2324 https://doi.org/10.1161/STROKEAHA.115.009839
  • Smith, Austin T et al. “Using the Retrobulbar Spot Sign to Assist in Diagnosis and Management of Central Retinal Artery Occlusions.” Journal of ultrasound in medicine : official journal of the American Institute of Ultrasound in Medicine vol. 39,1 (2020): 197-202. doi:10.1002/jum.15073

Copyright

Images and cases from the Society of Academic Emergency Medicine (SAEM) Clinical Images Exhibit at the 2023 SAEM Annual Meeting | Copyrighted by SAEM 2023 – all rights reserved. View other cases from this Clinical Image Series on ALiEM.

By |2024-01-28T21:19:20-08:00Jan 29, 2024|Ophthalmology, SAEM Clinical Images, Ultrasound|
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SAEM Clinical Images Series: Utility of Bedside Ultrasonography

fitz-hugh-curtis

A 24-year-old G1P0010 female with a PMHx of ovarian cyst (unknown laterality) and emergency contraceptive use 3 months prior presented with sudden onset abdominal pain (upper > lower) that awoke her from sleep four hours prior to presentation with associated nausea and mild lower back pain. The pain is 10/10, sharp, stabbing, and diffuse. Additionally, she reported trace white vaginal discharge at baseline. No acute increase. She had intermittent vaginal bleeding since contraception use over the past two months, which has now resolved. She denied fever, chills, vomiting, chest pain, shortness of breath, diarrhea, or constipation. No pertinent surgical history.

Constitutional: Uncomfortable. Appearing to be in acute pain.

Cardiovascular: Tachycardia. Regular rhythm and normal heart sounds.

Pulmonary: No respiratory distress. Breath sounds normal.

Abdominal: Diffusely tender abdomen with voluntary guarding, otherwise soft. Normoactive bowel sounds. Negative Murphy’s sign.

Pelvic: Scant white vaginal discharge and CMT. No vaginal bleeding, lacerations, or external lesions.

Neurologic: A&O x 3

WBC: 18.9 k/uL

Hgb: 10.5 g/dL

BMP, lipase, Alk phos/Bili/ALT/AST, PT/PTT, and lactate: Unremarkable

Serum HCG: Negative

Urinalysis (UA): Unremarkable

COVID: Negative

An ideal RUQ ultrasound visualizes the liver, Morrison’s pouch, superior and inferior poles of the right kidney, and diaphragm in the coronal plane. Here, we see a thickened hepatic capsule, septations, and trace ascites.

Fitz-Hugh-Curtis syndrome (FHCS) is characterized by perihepatitis in the setting of pelvic inflammatory disease (PID). It traditionally presents with right upper abdominal pain with associated nausea, vomiting, and fever in women of childbearing age. While overall considered a rare manifestation of PID, the true incidence of FHCS is poorly defined in the literature [1]. The pathophysiology of spread is also poorly understood. It is speculated that bacteria (N. gonorrhoeae, C. trachomatis) travel to the liver via blood, lymphatics or peritoneal fluid, causing perihepatitis [1]. Diagnosing FHCS poses a diagnostic challenge to clinicians. Traditionally, the diagnosis is made via laparoscopic exploration of the abdomen with visualization of the characteristic “violin-string” adhesions, with growing evidence also supporting the use of contrast-enhanced CT [1]. Limited evidence exists to support the use of ultrasonography in diagnosing FHCS. One case report published in 1993 used RUQ abdominal ultrasound to identify septations (violin-string adhesions) and ascites to ultimately diagnose FHCS, later confirmed by serologic and operative evidence [2]. Another case report from 2018 used ultrasonography to identify a thickened hepatic capsule in an 18-year-old female with RUQ pain, later confirming FHCS by CT without the need for laparotomy [3]. While more research is needed, identification of FHCS via bedside ultrasonography in the emergency setting followed by appropriate antibiotic therapy can be an effective approach to FHCS, ideally reserving laparoscopy only for lysis of adhesions in refractory cases.

Take-Home Points

  • RUQ abdominal ultrasound findings of a thickened hepatic capsule, ascites, and septations should raise suspicion for Fitz-Hugh-Curtis syndrome in the emergency setting.

  • Moon, Y.H., Kim, J.H., Jeong W.J., Park, S.Y. Ultrasonographic findings in Fitz-Hugh-Curtis syndrome: a thickened or three-layer hepatic capsule. Yeungnam Univ J Med 35(1), 127-129 (2018).
  • Theofanakis, C.P., Kyriakidis, A.V. Fitz-Hugh–Curtis syndrome. Gynecol Surg 8, 129–134 (2011). https://doi.org/10.1007/s10397-010-0642-8
  • van Dongen PW. Diagnosis of Fitz-Hugh-Curtis syndrome by ultrasound. Eur J Obstet Gynecol Reprod Biol. 1993 Jul;50(2):159-62. doi: 10.1016/0028-2243(93)90181-b. PMID: 8405645.

Copyright

Images and cases from the Society of Academic Emergency Medicine (SAEM) Clinical Images Exhibit at the 2023 SAEM Annual Meeting | Copyrighted by SAEM 2023 – all rights reserved. View other cases from this Clinical Image Series on ALiEM.

By |2023-11-24T21:18:09-08:00Nov 27, 2023|Gastrointestinal, Ob/Gyn, SAEM Clinical Images, Ultrasound|
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PEM POCUS Series: Pediatric Lung Ultrasound

PEM POCUS fascia iliaca block

Read this tutorial on the use of point of care ultrasonography (POCUS) for pediatric lung ultrasound. Then test your skills on the ALiEMU course page to receive your PEM POCUS badge worth 2 hours of ALiEMU course credit.

Module Goals

  1. List indications for performing a pediatric lung point-of-care ultrasound (POCUS).
  2. Describe the technique for performing lung POCUS.
  3. Recognize anatomical landmarks and artifacts related to lung POCUS.
  4. Interpret signs of a consolidation, interstitial fluid, effusion, and pneumothorax on POCUS.
  5. Describe the limitations of lung POCUS.

Child with Cough and Fever: Case Introduction

A 6-year-old boy presents to the emergency department complaining of cough for 3 days and fever for the last day. His fever was 103°F this morning and he received ibuprofen. He has also had abdominal and back pain. He was seen at the emergency department earlier in the day where he had a chest X-ray 6 hours prior that was interpreted as negative for consolidation and bloodwork including a complete blood count and comprehensive metabolic panel that were within normal limits. He presents with persistent cough and fever and now has increased work of breathing.

On arrival, his vital signs are:

Vital SignFinding
Temperature99.7 F
Heart Rate138 bpm
Blood Pressure102/61
Respiratory Rate32
Oxygen Saturation (room air)100%

He is well appearing but has increased work of breathing. His lungs have decreased breath sounds and crackles over the left lung base. No wheezes are appreciated. He has mild subcostal retractions. His abdomen is soft, non-tender, and non-distended. His back is non-tender to palpation. He has normal HEENT, neck, and cardiac examinations, with the exception of tachycardia as above.

Given his presenting signs and symptoms in the setting of a recent chest X-ray that was interpreted as normal, you decide to perform a lung point-of-care ultrasound (POCUS) examination.

Lung POCUS can be performed for a wide range of cardiorespiratory complaints including cough, fever, difficulty breathing, chest pain, hypoxia, and chest trauma. It can also facilitate early diagnosis, allowing for appropriate management. Children are excellent candidates for lung POCUS as they have thinner chest walls and smaller thoracic widths than adults.

Background

The lungs were traditionally considered poorly accessible to ultrasound, as ultrasound waves cannot penetrate air-filled structures; however, lung POCUS relies on the interpretation of patterns of artifacts to evaluate the normal, air-filled lungs.

When there is lung pathology, the consolidation or fluid allows for direct visualization of the pathology with lung POCUS and replaces the air artifacts. Fluid in a consolidation or effusion is easily visualized with ultrasound if the fluid has direct contact with the pleural surface. As lung POCUS will only visualize the lung under the probe, it is essential to completely evaluate the lungs anteriorly, laterally, and posteriorly to avoid missing pathology.

Technique

Positioning and Probe

lung POCUS comfortable positioning child

Figure 1: Younger children can sit in their parent’s lap and give a hug for lateral and posterior lung scanning.

  • The patient should be in a position of comfort: supine, sitting, or in parent’s lap (Figure 1).
    • Warm gel helps with the child’s comfort.
    • Distractions such as a toy, book, or phone/tablet can also help ease anxiety.
  • Use a linear high frequency probe. If increased depth is needed, such as in the evaluation for effusion, a curvilinear or phased array probe may also be used.

 

Scanning Protocols

There are different protocols to scan the lung depending on the purpose of the evaluation. For example, in pneumothorax, we focus on the anterior chest where air rises in a supine patient, and for the extended Focused Assessment with Sonography (eFAST) exam, we focus on more dependent areas where pleural fluid or blood collects. Below we discuss the complete lung exam which is often used in evaluating for pneumonia.

Lung POCUS anatomy 6-zone scan area

Figure 2: The 6-zone lung scanning protocol includes anterior, lateral, and posterior lung fields bilaterally.

  • A 6-zone lung ultrasound protocol is used for a complete lung examination (Figure 2):
    • Anterior lungs bilaterally are scanned in the mid-clavicular line from the apex to the base of the lungs and diaphragm.
    • Lateral lungs bilaterally are scanned in the mid-axillary line from the apex to the base of the lungs and diaphragm.
    • Posterior lungs bilaterally are scanned medial to the scapulae and lateral to the vertebral bodies from the apex to the base of the lungs and diaphragm.
  • Place the probe longitudinally, perpendicular to the ribs, with the probe marker towards the patient’s head. Identify anatomical landmarks on ultrasound (Figure 3, Video 1).
Lung POCUS A lines normal child

Figure 3: Normal lung with A-lines in longitudinal (left) and transverse (right) orientations

 

Video 1: Normal lung POCUS in longitudinal orientation

 

Video 2: Normal lung POCUS in transverse orientation

Normal Lung Findings

  1. Ribs: Hyperechoic, curvilinear structure with posterior acoustic shadowing
  2. Pleural line: Hyperechoic line immediately deep to the ribs
    • Lung sliding sign: Visceral and parietal pleural are juxtaposed and sliding against each other with respirations, giving the pleural line a shimmering or “ants marching on a log” appearance. For additional examples, see the PEM POCUS Endotracheal Intubation Confirmation article, specifically in Section 2 – Indirect Confirmation: Visualize Bilateral Lung Sliding.
  3. Lungs filled with air: Visualized on POCUS as horizontal A-lines, which are a reverberation artifact of the pleural line. The pleural line is reflected as the ultrasound beams bounce back and forth between the probe and the highly reflective pleural line, and therefore the distance between A-lines is the same as the distance between the probe and the pleural line (Figure 4).
Lung POCUS A lines reverberation normal

Figure 4: Reverberation artifact and A-lines. The probe sends out ultrasound waves that bounce back and forth between the highly reflective pleural line and the probe (leftmost 3 arrows). The ultrasound machine then interprets these signals as A-lines equidistant from the pleural line (rightmost 3 arrows).

Lung POCUS pulmonary consolidation

Figure 5: Pneumonia with sonographic hepatization, air bronchograms, and irregular pleural line

 

Video 3: Lung POCUS showing a pneumonia

 

Consolidation will appear as a subpleural, hypoechoic, irregularly shaped area, which will move with respirations. It can have the following findings on lung POCUS:

  • Hepatization refers to the homogenous, soft tissue echotexture due to fluid in the lung.
  • Shred sign refers to the irregular borders of the non-pleural edge of a pneumonia that is not translobar and thus adjacent to normal lung.
  • Pleural line irregularities refer to the hypoechoic or fragmented pleural line at the consolidation.
  • Hyperechoic air bronchograms are air in the bronchioles (white dots or branches) surrounded by hypoechoic (dark), fluid-filled lung (Figure 5 and Video 3).

Lung POCUS B lines waterfall

Figure 6: Lung POCUS showing B-lines (A) and a confluence of B-lines, known as the waterfall sign (B)

Video 4: Lung POCUS showing a confluence of B-lines (waterfall sign)

B-lines represent interstitial fluid and may arise from viral infection, pulmonary edema, or acute respiratory distress syndrome (ARDS).

  • POCUS appearance:
    • Ring-down artifacts that arise from the pleural line and extend to the bottom of the screen (Figure 6A). They move with lung sliding and erase A-lines at their intersection.
    • More than 3 B-lines in an intercostal space has been considered abnormal in the adult population. However it may not always be feasible to accurately count the number of B-lines.
    • The distribution of B-lines may help differentiate etiologies, with focal B-lines in pneumonia or atelectasis, and diffuse B-lines in pulmonary edema or ARDS.
  • Waterfall sign: A confluence of B-lines (Figure 6B and Video 4)

POCUS lung subpleural consolidation

Figure 7: Lung POCUS with subpleural consolidation

Video 5: Lung POCUS with subpleural consolidation

Subpleural consolidations are small hypoechoic or tissue-like structures with pleural line abnormalities and blurred margins (Figure 7 and Video 5). They measure <1 cm and are usually seen with a viral process.

Lung POCUS pleural effusion

Figure 8: Pleural effusion with linear probe (A) and phased array probe for increased depth (B).

Video 6: Lung POCUS with pleural effusion using linear probe

A pleural effusion is visualized as anechoic (black) fluid between the chest wall and lung or between the diaphragm and lung (Figure 8 and Video 6).

  • Scan the lateral chest in the posterior axillary line in the supine patient, as fluid is dependent and will accumulate posteriorly.
  • The pleural effusion can be fluid in an infectious process or blood in the setting of trauma.

Absent Lung Sliding

Video 7: Lung POCUS showing a pneumothorax with absent lung sliding

In pneumothorax, there is air between the visceral and parietal pleural, so there will be no lung sliding visualized on lung POCUS.

  • Scan for a pneumothorax in the anterior chest in the 2nd-4th intercostal space in the mid-clavicular line in a supine patient, as air will rise to the highest point in the chest.
  • The pleural line will appear as a static, hyperechoic line (Video 7).
  • There will be A-lines visualized, but no B-lines.
    • Pro Tip: The presence of B-lines is highly sensitive against the presence of a pneumothorax in that location.

 

Lung Point

Video 8: Lung POCUS with evidence of a lung point

Lung point, when seen, is the edge of the pneumothorax, where regular lung sliding occurs adjacent to absent lung sliding (Video 8).

  • Lung point is 100% specific for pneumothorax, but it may not be visualize d for a large pneumothorax with lung collapse.

 

Motion (M) Mode

Figure 9: Lung POCUS showing a normal lung with the seashore sign (A) and a pneumothorax with the barcode sign (B)

M-mode may also be used to evaluate for pneumothorax.

  • Normal lung: There will be the seashore sign, with a granular pattern representing aerated, moving lung below the pleural line (Figure 9a).
  • Pneumothorax: There will be a barcode or stratosphere sign, with no aeration or movement below the pleural line (Figure 9b).

Additional examples can be found in the PEM POCUS: Endotracheal Tube Confirmation article in Section 2 – Indirect Confirmation: Visualize Bilateral Lung Sliding.

lung abscess

Figure 10: Lung abscess with adjacent lung consolidation and pleural effusion

 

Lung abscess may also be evaluated by lung POCUS and will have a hypoechoic fluid collection (Figure 10).

  • Consolidated lung and pleural effusion are also commonly seen.
  • Lung ultrasound is more accurate than chest X-ray at evaluating lung abscess.

Lung pathology may be missed without a complete lung POCUS scanning protocol, as you will only see pathology located directly under the probe. The lung POCUS is also operator-dependent, and it has a steep learning curve.

False Negative:

  • POCUS can’t visualize a centrally located pneumonia not extending to the pleural surface. A lung consolidation needs to extend to the pleural surface to be visualized on lung POCUS.
  • However, a study in adult patients showed that 99% of lung consolidations extend to the pleura [1]. Thus, in children with smaller lung mass, most consolidations likely will be detected by lung POCUS.

False Positives:

Left Lower Chest

  • Caution is needed at the left lower chest, as the spleen and air in the stomach can be misinterpreted as consolidation (Figure 11).
  • Locate the diaphragm in the left lower chest to be sure you are evaluating lung above the diaphragm.
stomach spleen

Figure 11: The spleen and the stomach with air may be misinterpreted as consolidation.

Thymus

  • In younger children, the thymus may be misinterpreted as a consolidation.
  • The thymus will be adjacent to the heart, have regular echotexture, no air bronchograms, and regular borders (Figure 12).
thymus

Figure 12: Thymus (*) located adjacent to the heart

 

There have been multiple studies of lung POCUS identifying pneumonia in children, and several meta-analyses have been published [2-4]. Table 1 summarizes these studies, showing an overall high accuracy for lung POCUS diagnosis of pneumonia in children.

StudyNSensitivitySpecificityComments
Pereda et al., Pediatrics 20158 studies; 765 patients

96%

93%

Evidence supports lung POCUS as an alternative for diagnosis of pneumonia in children.
Balk et al., Pediatr Pulmonol 201812 studies; 1510 patients

96%

95%

Lung POCUS had significantly better sensitivity than chest X-ray, which had a sensitivity of 87%.
Tsou et al., Acad Emerg Med 201925 studies; 3353 patients

94%

92%

Significant difference in accuracy between novice and advanced sonographers.
Table 1. Meta-analyses of lung POCUS for diagnosis of pneumonia in children

1. Decreased radiation and length of stay

  • A randomized controlled trial comparing lung POCUS to chest X-ray for diagnosis of pneumonia showed a 39% reduction in chest X-ray utilization and a decreased emergency department length of stay from 180 to 132 minutes in the patients receiving only lung POCUS with no cases of missed pneumonia [5].

2. Best view for pneumonia

  • A study looking at lung consolidation locations in children with pneumonia found that 96% of pneumonias were detected by the transverse view, compared to 86% in the longitudinal view.
  • The authors concluded that the transverse orientation detects more pneumonia than the longitudinal view, and that omission of either orientation or any lung zone may miss pneumonia [6].

3. Pneumothorax: POCUS is better

  • A meta-analysis of chest X-ray vs ultrasound for diagnosis of pneumothorax showed that ultrasound had a sensitivity of 88% and specificity of 99% compared to sensitivity of 52% and specificity of 100% for chest X-ray. Furthermore, lung POCUS performed specifically by non-radiologist clinicians had a sensitivity of 89% and specificity of 99% [7].

Case Resolution

The patient’s chest X-ray from earlier in the day was interpreted by the pediatric radiologist as negative for consolidation or other pulmonary pathology. You performed a lung POCUS with a linear, high-frequency probe and observed the following:

Video 9: A lung POCUS of the case patient’s left lower lung (affected side)

Though this child with cough, fever, focal lung findings, and respiratory distress had a negative chest X-ray performed 6 hours earlier, your POCUS evaluation identified a left lower lobe pneumonia which helped you make your diagnosis and start the appropriate treatment.

ED Course

The patient received antibiotics for pneumonia. His work of breathing increased during his emergency department visit, and he was started on high flow nasal cannula at 30 L/min with improvement in his respiratory status. He was admitted to the pediatric intensive care unit. He had a repeat chest X-ray 12 hours later that was interpreted by the pediatric radiologist as having new pleural and parenchymal changes in the left hemithorax with questionable pneumonia. He continued antibiotics, and his repeat X-ray 48 hours later showed a clear left lower lobe consolidation with pleural effusion.

 

Learn More…

References

  1. Lichtenstein DA, Lascols N, Mezière G, Gepner A. Ultrasound diagnosis of alveolar consolidation in the critically ill. Intensive Care Med. 2004 Feb;30(2):276-281. PMID: 14722643
  2. Pereda MA, Chavez MA, Hooper-Miele CC, et al. Lung ultrasound for the diagnosis of pneumonia in children: a meta-analysis. Pediatrics. 2015 Apr;135(4):714-22. PMID: 25780071
  3. Balk DS, Lee C, Schafer J, et al. Lung ultrasound compared to chest X-ray for diagnosis of pediatric pneumonia: A meta-analysis. Pediatr Pulmonol. 2018 Aug;53(8):1130-1139. PMID: 29696826
  4. Tsou PY, Chen KP, Wang YH, et al. Diagnostic Accuracy of Lung Ultrasound Performed by Novice Versus Advanced Sonographers for Pneumonia in Children: A Systematic Review and Meta-analysis. Acad Emerg Med. 2019 Sep;26(9):1074-1088. PMID: 31211896
  5. Jones BP, Tay ET, Elikashvili I, et al. Feasibility and Safety of Substituting Lung Ultrasonography for Chest Radiography When Diagnosing Pneumonia in Children: A Randomized Controlled Trial. Chest. 2016 Jul;150(1):131-8. PMID: 26923626
  6. Milliner BHA, Tsung JW. Lung Consolidation Locations for Optimal Lung Ultrasound Scanning in Diagnosing Pediatric Pneumonia. J Ultrasound Med. 2017 Nov;36(11):2325-2328. PMID: 28586113
  7. Ding W, Shen Y, Yang J, He X, Zhang M. Diagnosis of pneumothorax by radiography and ultrasonography: a meta-analysis. Chest. 2011 Oct;140(4):859-866. PMID: 21546439

Additional Reading

  • Rizvi MB, Rabiner JE. Pediatric Point-of-Care Lung Ultrasonography: A Narrative Review. West J Emerg Med. 2022 Jun 5;23(4):497-504. PMID: 35980421
By |2024-03-04T12:41:15-08:00Aug 9, 2023|Expert Peer Reviewed (Clinical), Pediatrics, PEM POCUS, Radiology, Ultrasound|
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Trick of the Trade: Gel-free ultrasound-guided peripheral IV technique

Ever finally step away from a busy resuscitation and someone stops you for peripheral IV access? You set up everything, have the patient positioned, and then notice there is no sterile ultrasound gel. No gel? No problem. The trick is to eliminate anything of poor acoustic impedance between the ultrasound probe and the patient’s skin.

Trick of the Trade

1. Apply a transparent adhesive dressing with a thin alcohol layer on the probe

Instead of using gel, we squeeze alcohol pads to create a thin alcohol layer and place a transparent adhesive cover, such as Tegaderm ©. The thin alcohol layer serves to eliminate any air bubbles under the adhesive cover as well as minimizes residual adhesive material sticking to the probe when removing the cover. The adhesive cover itself serves as a sterile barrier and a slick surface to improve probe maneuverability. Note that some ultrasound manufacturers do not recommend the use of isopropyl alcohol on their transducers. Therefore check your specific ultrasound’s recommendations before trying [1, 2].

2. Use sterile saline instead of gel on the patient’s skin

Squirt normal saline flush on the patient’s skin to create a coupling medium between the probe and the patient.

Why it works:

Ultrasound procedures use a range of frequencies (1.5-20 MHz) to visualize internal structures and require a medium to replace air, which has a poor acoustic impedance for the ultrasound waves [3]. Acoustic impedance is defined as the resistance of the propagation of ultrasound waves through tissues and is the product of the density and speed of sound in the tissue [4]. Ultrasound gel has an acoustic impedance that is similar to soft tissue and is therefore considered the ideal medium [3]. Because most soft tissue is comprised of water, the acoustic impedance of water, and therefore 0.9% saline, is actually pretty similar [5], as demonstrated by water bath techniques for ultrasounding distal extremity injuries [6].

We find great visual clarity for performing ultrasound-guided peripheral IVs using this trick, as shown in Figure 1.

Peripheral IV ultrasound screen without gel

Figure 1: Peripheral IV ultrasound using alcohol under transparent film dressing and topical saline flush – all without ultrasound gel

Read other Tricks of the Trade articles.

References

  1. Cleaning and Disinfecting FUJIFILM SonoSite Products User Guide [PDF]. Sonosite. 2015. Accessed April 5, 2023.
  2. Disinfectants and Cleaning Solutions for Ultrasound Systems and Transducers [PDF]. Philips. 2021. Accessed April 5, 2023
  3. Afzal S, Zahid M, Rehan ZA, et al. Preparation and Evaluation of Polymer-Based Ultrasound Gel and Its Application in Ultrasonography. Gels. 2022 Jan 6;8(1):42. doi: 10.3390/gels8010042. PMID: 35049577; PMCID: PMC8774352
  4. Suzuko S, Peter G, Philipp L. 20 – Local Anesthetics, Ed(s): Hugh C. Hemmings, Talmage D. Egan, Pharmacology and Physiology for Anesthesia (Second Edition), Elsevier, 2019, Pages 390-411, ISBN 9780323481106. DOI: 10.1016/B978-0-323-48110-6.00020-X
  5. R. Alkins, K. Hynynen, 10.08 – Ultrasound Therapy, Editor(s): Anders Brahme, Comprehensive Biomedical Physics, Elsevier, 2014, Pages 153-168, ISBN 9780444536334. DOI 10.1016/B978-0-444-53632-7.01010-8
  6. LeDonne S, Sengupta D. US Probe: Ultrasound Water Bath for Distal Extremity Evaluation. Alerhand S, Singh M, editors. emDOCs.net – Emergency Medicine Education. 2017.
By |2023-04-06T20:53:38-07:00Apr 12, 2023|Radiology, Tricks of the Trade, Ultrasound|
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