March 2011 sees @EBMedicineʼs Emergency Medicine Practice examine the evidence surrounding the use of Ultrasound in the Emergency Department – Reviewed here by Dr Steve De Luca
Hwang JQ, Kimberly HH, Liteplo AS, Sajed D (2011). An Evidence-Based Approach to Emergency Ultrasound. Emergency Medicine Practice, 13(3). [Abstract and subscription link]
Emergency Ultrasound (EUS) is a rapidly growing branch of the practice of Emergency Medicine. As the utilities for this imaging modality in the ED continue to develop and expand, this monthʼs Emergency Medicine Practice describes the core EUS applications and the various levels of evidence supporting their role in patient assessment and management.
Here are 10 questions which should highlight the important points from this review and describe how Ultrasound can affect your patient.
Q1. What are the 11 core EUS applications?
The 6 initially established modalities include:
- Focused Assessment with Sonography for Trauma (FAST)
- ultrasound for abdominal aortic aneurysm
- emergency echocardiography
- pregnancy ultrasound
- hepatobiliary ultrasound
- renal tract ultrasound
In addition the 5 recently included applications are:
- ultrasound for deep venous thrombosis
- thoracic ultrasound (also incorporated into the E-FAST)
- musculoskeletal ultrasound
- ocular ultrasound
- procedural ultrasound
There are many other patient focused applications ED specialists are deriving from these core 11, including evaluating the patient with an unknown source for sepsis and the undifferentiated hypotensive patient. As technology develops as quickly as skills and knowledge, often the only limitation to utility of EUS is the imagination and technical ability of the clinician.
Q2. Does the FAST scan save lives?
The Cochrane Collaboration investigated this question in 2005, and again in their correction in 2008, in their review of trauma algorithms that include ultrasound. The limited number of RCTʼs on the use of the FAST examination in blunt abdominal trauma failed to demonstrate a signiﬁcant decrease in mortality. However, ultrasound in this setting has been shown to reduce:
- time to recognition of intraabdominal trauma
- time to operative therapy
- hospital costs
- number of CT scans and diagnostic peritoneal lavages performed.
The role of the FAST examination in haemodynamically unstable trauma patients is widely accepted and has been incorporated into the Advanced Trauma Life Support protocol of the American College of Surgeons. The FASTʼs utility in the “stable” patient is less clear but some evidence points towards a positive FAST being a strong predictor of requirement for laparotomy.
Q3. What traumatic pathology is diagnosed on thoracic ultrasound and how does it measure up against chest X-ray?
The Extended-FAST or E-FAST obtains views of both hemithoraces at the levels of the diaphragm-abdominal interface and over bilateral anterior chest walls. With these views pleural effusion / haemothorax and pneumothorax can be identiﬁed.
The sensitivity of ultrasound to diagnose pneumothorax has been quoted as high as 98.1% with a speciﬁcity of 99.2% in the literature. The sensitivity of the supine CXR in the same role varies widely from study to study but has been stated as low as 27.6%, with a speciﬁcity of 100%. In addition ultrasound can detect smaller amounts of pleural ﬂuid, as little as 20mL. Whilst ﬁndings only become apparent on the supine chest X-ray with approximately 175mL of ﬂuid.
In addition, ultrasound was found to be superior to clinical acumen and radiography for detecting rib and sternal fractures.
Q4. How can hydronephrosis be categorised on the basis of renal tract US.
Hydronephrosis on ultrasound is conﬁrmed by the ﬁnding of anechoic areas within the central collecting system indicating dilatation of the calyces and pelvis. Hydronephrosis is graded as:
- mild — prominent calyces and mild splaying of the renal pelvis
- moderate — bear-claw appearance,
- severe — when cortical thinning has occurred
Q5. How does the ultrasound savvy Emergency physician tackle the problem of the early pregnancy patient with abdominal pain?
Ectopic pregnancy has a prevalence of 8% in pregnant patients presenting to the ED and is a major cause of maternal mortality. Multiple studies have demonstrated pelvic ultrasound to be diagnostic of intrauterine pregnancy (IUP) or ectopic pregnancy in over 70% of symptomatic ﬁrst-trimester pregnant patients.
The mainstay of investigating potential ectopic pregnancy is identifying an IUP.
Whilst this doesnʼt entirely exclude ectopic or heterotopic pregnancy, in the patient with no risk factors and a conﬁrmed IUP, their risk is so low that it allows for further out-patient management.
Transabdominal ultrasound can detect an IUP at 6 to 7 weeks gestation and transvaginal ultrasound as early as 5 to 6 weeks.
The ﬁndings consistent with an IUP are a yolk sac, foetal pole, or foetal heart activity within the uterus, surrounded by an 8-mm rim of myometrium.
In the patient with signiﬁcant intraperitoneal free ﬂuid without a deﬁnite IUP, ﬁndings are highly suggestive of ectopic pregnancy and this discovery is potentially life-saving.
Q6. What are the advantages of ultrasound-guided thoracocentesis over blind techniques?
As we now know small effusions can be difﬁcult to diagnose on CXR and lung ﬁeld opaciﬁcation on a CXR can be misleading.
Ultrasound allows for deﬁnite identiﬁcation of ﬂuid and direct visualisation of surrounding structures, including: liver, spleen, diaphragm and consolidated lung parenchyma.
All of which have been accidentally needled during blind technique. The most common major complication of thoracentesis is pneumothorax and ultrasound has been demonstrated to signiﬁcantly reduce this risk.
Ultrasound-guided thoracentesis has the added beneﬁt of real time visualisation to anaesthetise the pleural lining and post procedure evaluation of the thorax to look for pneumothorax and re-expansion pulmonary oedema.
Q7. And what are the beneﬁts of ultrasound guided pericardiocentesis?
Rapid decompensation and cardiac arrest are often the ﬁrst signs noted in the patient with pericardial effusion and subsequent tamponade. Therefore it is an important pathology to detect.
Management following visualisation of pericardial ﬂuid will depend on patient status and may mandate the need for emergent pericardicentesis.
The complications of a subxiphoid blind approach include:
- ventricular puncture
- coronary vascular laceration
- visceral abdominal puncture
- diaphragmatic injury
Complication rates have been reported as high as 50%. Ultrasound guided techniques can reduce this number to 5%. In addition, ultrasound reduced the need for repeat drainage and surgical intervention, with a more reliable catheter placement. It may also be the case that the subxiphoid approach may not be optimal and ultrasound guidance will allow a parasternal or apical approach.
Q8. If youʼre considering aspirating a patientʼs pericardium in an emergent fashion it would be good to know the sonographic features of cardiac tamponade. Other than conﬁrmation of pericardial ﬂuid, what are they?
The ultrasound features of pericardial tamponade are:
- Right ventricular free wall inversion during ventricular diastole (the hallmark ﬁnding).
- Right atrial inversion during ventricular systole (one of the earlier ﬁndings).
- Increased respiratory variation of mitral or aortic inﬂow velocities (inspiratory decrease of more than 25%).
- Dilated IVC with reduction in inspiratory collapse.
Click here for a video showing pericardial tamponade on ultrasound, from HQMEDED.com.
Q9. Do you have to look at the whole lower limb to exclude proximal DVT?
No, is the short answer.
Thrombus is relatively non-compressible and a review of the literature demonstrated that 2 point compression (femoral and popliteal) in combination with D-dimer test is equivalent to whole-leg colour-ﬂow Doppler ultrasound in the management of symptomatic patients with suspected DVT.
These views can be bolstered by looking at colour ﬂow increases in the same areas during augmentation (calf squeeze) and inspiration. Thus excluding thrombosis in the same vessel below and above the respective site visualised.
This quick and easy screen for proximal DVT has implications for cost, length of hospital stay and time required to scan.
Q10. What are the top 4 pearls and pitfalls the budding Emergency Department sonographer should remember?
- Just because you didnʼt visualise pathology doesnʼt mean it isnʼt there.
Know your limitations and level of expertise.
Be focused and speciﬁc. Look for speciﬁc pathology in an attempt to answer a clinical question. Make sure that you, the patient, and other staff understand the purpose and scope of the scan performed.
- Get a system.
Develop, perform and practice your scanning in the same fashion every time to reduce errors, improve consistency and increase efﬁciency.
- Remember the value of repeating a scan, especially an E-FAST scan.
- Make time for ultrasound.
Once trained and practiced EUS can be performed quickly and will become an essential part of your patient assessment process.
To learn how wave your ultrasound wand like a pro, the LITFL team recommends these online resources: