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Emergency Ultrasound

Journal Summary

Velocity Time Index
Reviewed by Joshua Guttman, MD

Until prospective data is available, the use of the VTI should not be considered a definitive resuscitation endpoint.

Blanco P, Aguiar FM, Blaivas M. Rapid Ultrasound in Shock (RUSH) Velocity-Time Integral: A Expand the RUSH Protocol. J Ultrasound Med. 2015;34(9):1691-700.

These authors suggest the addition of velocity time integral (VTI) to the RUSH protocol as a surrogate marker for stroke volume. Stroke volume is traditionally measured via the Left Ventricular Outflow Tract (LVOT) VTI. However, since LVOT remains constant, changes in stroke volume during resuscitation must correlate with changes in VTI. Additionally, the LVOT may be difficult to measure, and since it is an area and therefore calculated via πr2, any error in LVOT will be squared. Therefore, using only the VTI is not only faster, but may be a more accurate surrogate for stroke volume. It may be measured serially to assess response to therapy, or it may be used as a measure of fluid responsiveness while performing a passive leg raise test. Normal VTI is 18-22 cm (slightly less in tachycardia and slightly more in bradycardia). It is measured by tracing the pulse wave doppler spectrum at the LVOT in either the apical 5 chamber or apical 3 chamber views. The authors also suggest that if an adequate view of the LVOT cannot be obtained, then inflow at another valve may be used (such as mitral valve inflow). While there are no existing normal values for these areas, increases in VTI can be inferred to suggest improvements in stroke volume.

The strength of this protocol is in the simplicity and feasibility. While performing a LVOT VTI measurement can often be cumbersome and prone to error, measuring VTI can easily be performed as part of the bedside echocardiogram in the critically ill patient as the most accurate measurement of the outcome of our interventions. It can be repeated as often as necessary as the patient’s clinical status changes and can be used to adjust therapeutic strategies. Unfortunately, no prospective studies on outcomes have been performed, and therefore use of the VTI should not be considered a definitive resuscitation endpoint.

FAST & Thoracotomy
Reviewed by Tomislav Jelic, MD

In patients with no evidence of pericardial effusion or cardiac activity, the thoracotomy was essentially futile… more study needed?

Inaba K, Chouliaras K, Zakaluzny S, et al. FAST ultrasound examination as a predictor of outcomes after resuscitative thoracotomy: A prospective evaluation. Ann Surg. 2015;262:512.

Resuscitative thoracotomy is a very resource intensive procedure and potentially dangerous to the providers. This study aimed to answer the question of the ability of a FAST exam to predict outcomes of an ED thoracotomy. The primary focus of the FAST exam was the cardiac view. All FAST examinations were performed by PGY 2 and above EM residents under the supervision of an EM attending. Primary outcomes were survival to discharge or organ donation.

223 patients had an ED thoracotomy performed during the study period. It was a fairly even split between blunt and penetrating pathology. Of the 223 patients, 187 had a FAST performed. A FAST examination with cardiac motion was 100% sensitive and 74% specific for identifying organ donors and survivors. In total, three patients became organ donors (2%) and six patients (3%) survived, two with no functional neurologic activity.

This study suggests that in patients with no evidence of pericardial effusion or cardiac activity, the thoracotomy was essentially futile. A large study, incorporating FAST as a guide to whether a thoracotomy should be performed is needed, thus allowing for this procedure to be done on those with the greatest chance of survival.

DVT
Reviewed by Michael Boniface, MD

Two-point compression ultrasonography may miss 6% of lower extremity DVTs.

Adhikari S, Zeger W, Thom C, et al. Isolated Deep Venous Thrombosis: Implications for 2-Point Compression Ultrasonography of the Lower Extremity. Ann Emerg Med. 2015;66(3):262-6.

“Rule out DVT” is an extremely common complaint for patients presenting to the emergency department. Comprehensive radiology performed ultrasonography of the lower extremity including color flow and spectral Doppler has excellent specificity and sensitivity for evaluation of DVT. Due to ease of use and widespread availability, a clinician performed point-of-care a two point compression protocol (femoral and popliteal) has previously shown similar performance (albeit when combined with a negative serum d dimer or follow-up examination). The assumption in this previously established protocol however is that most DVTs would be visible in the common femoral vein or popliteal vein. This goal of this retrospective chart review of 2,451 patients undergoing formal duplex ultrasonography was to determine the prevalence and distribution of thrombi isolated to veins of the lower extremity other than the common femoral and popliteal veins. Although the majority of thrombi, when present, were detected in the common femoral and popliteal veins, 5.5% of thrombi were isolated to the [superficial] femoral vein and 0.8% isolated to the deep femoral vein. The authors conclude that 6.3% of thrombi would be missed using a standard two-point compression protocol and propose that this data supports the use of an extended point-of-care compression technique to include visualization of the femoral and deep femoral veins. Given the minimal additional effort and time, this is probably worth including in your current exam protocol.

Gallbladder
Reviewed by Michael Boniface, MD

“The Absence of Gallstone on Point-of-Care Ultrasound Rules Out Acute Cholecystitis”…maybe.

Villar J, Summers SM, Menchine MD, et al. The Absence of Gallstones on Point-of-Care Ultrasound Rules Out Acute Cholecystitis. J Emerg Med. 2015;49(4):475-480.

The title of this article makes a very direct and bold claim. Previously adopted protocols for point-of-care evaluation for suspected acute cholecystitis have relied on both presence of gallbladder calculi and secondary findings such as wall thickening, pericholecystic fluid, and sonographic Murphy’s sign. This study was a post-hoc analysis of a previously collected prospective data set with the intention of calculating test characteristics of a simplified definition of a positive test: the presence of gallstones alone. The original study design was excellent including comparison to gold standard of pathology reports from surgical specimens and follow-up attempts for discharged patient. The authors report a 100% sensitivity and negative predictive value for acute cholecystitis based on the gallstones alone. Although these results are impressive, this study has quite a few limitations. The study was not originally designed to answer this question as this represents a re-evaluation of previously collected data. There is a small sample size with only 23 confirmed cases of cholecystitis. The point-of-care operators were also extremely well trained, with half of the supervising emergency physicians being RDMS certified sonographers. At the risk of sounding cliché, a prospective multicenter study may be required to help clarify the true utility of this proposed protocol.

Paracentesis
Reviewed by Michael Boniface, MD

Thrombocytopenia should not prevent us from performing necessary paracenteses.

Kurup AN, Lekah A, Reardon ST, et al. Bleeding Rate for Ultrasound-Guided Paracentesis in Thrombocytopenic Patients. J Ultrasound Med. 2015;34(10):1833-8.

One of medicine’s little ironies is that patients who require paracentesis also tend to have underlying disease that is associated with thrombocytopenia. How nervous should we be before inserting a large needle into a cirrhotic patient with abdominal pain when the platelet count is low? Is platelet transfusion necessary prior to the procedure? This retrospective chart review of 304 ultrasound-guided paracenteses on 205 patients with a mean platelet count of 38,400 identified a 1% incidence of major bleeding complication requiring PRBC transfusion with no patient deaths or need for additional procedure. There was no association between the absolute platelet count and bleeding events. Additional analysis suggests there is not a substantial difference when compared with non-thrombocytopenic patients and no statistically significant increased risk in patients who also have an elevated INR. There is no consensus among professional society guidelines on the need for routine platelet replacement in thrombocytopenic patients prior to undergoing paracentesis, but this data suggests that it may not be necessary and overall is a very safe procedure with low incidence of adverse hemorrhage.

Carotid Flow Time & Blood Loss
Reviewed by Amit Bahl, MD

Mackenzie DC, Khan NA, Blehar D, et al. Carotid Flow Time Changes With Volume Status in Acute Blood Loss. Ann Emerg Med. 2015;66(3):277-282.

So how much fluid should we give to our septic ED patients? For many years now the goal for resuscitation for these patients has been aggressive intravenous fluid therapy to optimize preload with the intention of improving cardiac output. The problem is that not all shock patients respond to volume expansion and in some cases we may be worsening patient outcomes. This is an interesting study that demonstrates the potential value of a non-invasive ultrasound test (carotid flow measurement) coupled with passive leg raise maneuver to assist in identifying patients that are volume responders. Investigators analyzed effect of acute blood loss and passive leg raise maneuver on corrected carotid artery flow time. This was a prospective analysis involving obtaining carotid flow time using doppler before and after blood donation in both the supine position and after passive leg raise maneuver. 70 study subjects participated fully. Donors had a mean blood loss of 452 mL. Mean corrected carotid artery flow time before blood loss was 320 ms (95% confidence interval [CI] 315 to 325 ms); this decreased after blood loss to 299 ms (95% CI 294 to 304 ms). A passive leg raise had little effect on mean corrected carotid artery flow time before blood loss (mean increase 4 ms; 95% CI -1 to 9 ms), but increased mean corrected carotid artery flow time after blood loss (mean increase 23 ms; 95% CI 18 to 28 ms) to predonation levels. In the setting of acute volume depletion, passive leg raise restored corrected carotid flow time to predonation levels.

The main limitation of this study is that it was performed in young, healthy individuals donating blood. It is hard to generalize these results to the elderly patient with numerous comorbidities taking 20 different medications presenting in septic shock. I think this concept has great potential but needs further inquiry in critically ill patients.

 

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