Lung Ultrasound in Small Animals: The Vet BLUE SM

Transcription

1 Lung Ultrasound in Small Animals: The Vet BLUE SM Gregory R. Lisciandro, DVM, Dipl. ABVP, Dipl. ACVECC Hill Country Veterinary Specialists & FASTVet.com, San Antonio, Texas USA FASTVet TM and FAST Saves Lives! TM Website Phone Text Focused Ultrasound Techniques for the Small Animal Practitioner, Wiley 2014 Introduction and History: The use of lung ultrasound dates back into the late 1980s, notably with the ultrasound diagnosis in 1987 of pneumothorax (PTX) by a veterinarian, an equine practitioner, Dr Norman Rantanen. Within a year, the ultrasound diagnosis of PTX was similarly described in human medicine. In 1988, Dr Roy Philly dubbed the ultrasound probe the modern stethoscope, a remarkable foresight made unbelievably 27 years ago. More recently, the ultrasound probe has been dubbed the visual stethoscope (Moore 2011) because lung ultrasound artifacts are objectively and clearly discernible independent of patient or ambient noise. Moreover, lung ultrasound has been definitively shown to exceed traditional means of chest auscultation and supine chest radiography in humans with common respiratory conditions (Volpicelli 2012, Lichtenstein 2008). As long ago as 1997, the lung ultrasound finding, then referred to as comet tails, representing forms of interstitial edema was documented in humans by Lichtenstein and colleagues. After that time, it seemed that the focus of lung ultrasound over the next several years changed from the pursuit of lung pathology to further characterization of the ultrasound diagnosis of pneumothorax (PTX). Several comparative studies clearly showed that PTX could be accurately diagnosed, rapidly and point-of-care, by lung ultrasound; and that lung ultrasound exceeded the accuracy, sensitivity and specificity of supine chest radiography. Furthermore, ultrasound-diagnosed PTX was shown to compare quite favorably with computerized tomography (CT), considered the gold standard for the diagnosis of PTX. During this same time, a structured lung ultrasound format was developed called EFAST for extended FAST by Kirkpatrick and colleagues (2004). EFAST was named as such since it was an additional FAST scan that extended from the FAST abdominal views. Because PTX was a real-time finding during B-mode use, other ultrasound modalities were created to document PTX in medical records including the Power Slide using power Doppler (Kirkpatrick) and the seashore sign and stratosphere sign using M-mode (Lichtenstein and colleagues), representing dry lung and PTX, respectively. Again, power Doppler and M-mode were primarily modes for documenting PTX and not diagnosing PTX. The author has found in small animal medicine there often is too much movement to effectively use these documenting modalities. In addition to clearly demonstrating the ultrasound diagnosis of PTX, Lichtenstein and colleagues showed how the search for the lung point, where lung re-contacts the chest wall, not only helped determined the degree of PTX, but also increased the sensitivity of diagnosing PTX using ultrasound (2000). The lung point debunked the myth that the ultrasound diagnosis of PTX was an all or none diagnosis by showing that partial vs. massive PTX could be determined using lung ultrasound. Another off-shoot of the use of lung ultrasound in trauma, was the finding that lung contusions, also referred to as lung blast, could be easily recognized by non-radiologist sonographers (Soldati 2006; Ball 2009). In 2004 Jambrik and colleagues refocused lung sonographers on the pursuit of lung pathology in non-trauma subsets of human patients. In 2006 Volpicelli and colleagues re-enforced a scanning format and additionally showed that the counting of ultrasound lung rockets (also called B-lines) correlated with the degree of lung edema found on computerized tomography. In Chest 2008, Lichtenstein and to FASTVet.com and Gregory Lisciandro, DVM, Dipl. ACVECC at FASTSavesLives@gmail.com. Copyright

2 colleagues published a clinical paper in which they showed that a pattern-based, regional approach, called the BLUE Protocol, could diagnose the most common presenting causes of respiratory disease in human patients with high sensitivity, specificity and accuracy including asthma, COPD, lung edema, PTE, and pneumonia. The BLUE protocol had a remarkable overall accuracy of 90.5%; and the BLUE exam only took minutes helping direct clinical course and diagnostics without the insensitivities of traditional means of physical examination and chest auscultation; and without the delays of waiting for chest radiography and other testing. In another Lichtenstein publication (2009), they found a correlation between pulmonary capillary wedge pressure (invasive) and the presence of lung edema (B-lines or ultrasound lung rockets); and conversely they found that in the absence of lung edema (B-lines or ultrasound lung rockets) that clinically relevant left-sided heart failure could be rapidly ruled out (minutes) with high sensitivity and specificity, point-of-care, and within minutes of patient presentation. A remarkably powerful capability for such a simple, safe, radiation-sparing, point-of-care portable imaging modality, called lung ultrasound. In 2012, an international lung ultrasound consensus statement was made by a group of international lung ultrasound experts. In an evidence-based document, statements were developed regarding the efficacy and clinical utility of lung ultrasound use for various respiratory conditions, re-affirming the positive diagnostic and monitoring potential of lung ultrasound. However, the use of terms such as lung sliding (glide sign in veterinary medicine), and A-lines, and B-lines, C-lines and PLAP continue to thwart the evolution and widespread use of lung ultrasound. These terms are confusing and difficult to grasp in contrast to analogous terms proposed by the author and still appearing in the human literature including glide sign (veterinary term, same as lung sliding in human medicine), A-lines (same, air reverberation artifact), ultrasound lung rockets (B-lines in human medicine), and Shred Sign (Wedge Sign, PTE), Tissue Sign, and Nodule Sign for lung consolidation/infiltration (called C-lines, PLAP, in human literature). These terms (see Proceedings below) have been proposed in the veterinary literature in a clinical review (Lisciandro 2011), textbook available in English and Spanish (and soon in Greek, Japanese, and Chinese) Focused Ultrasound Techniques for the Small Animal Practitioner, Wiley 2014, and in peer-reviewed clinical study by Lisciandro and colleagues (2014). These terms have also appeared in the human literature (Lichtenstein several reviews; Point-of-Care Ultrasound, Soni, Arntfield, Kory Eds. Elsevier 2015). Use of Lung Ultrasound Formats in Small Animals: The reluctance to pro-actively apply lung ultrasound to small animals with respiratory distress is irrational in many respects. The overriding belief that air-filled lung creates insurmountable obstacles, and the continued belief in small animal medicine that imaging lung is difficult to perform leading to mistakes, perpetuate lung ultrasound s delayed use in small animals (dogs and cats). Thoracic FAST called TFAST SM (Lisciandro et al. 2008) was the first standardized abbreviated ultrasound exam of the thorax that included the Chest Tube Site (CTS) for lung surveillance for detection of PTX. Because of the finding of lung pathology found during TFAST SM, the author extended lung surveillance from the TFAST SM CTS with the addition of 6 more lung views. The name of this novel regionally-based lung ultrasound exam is Vet BLUE SM ( Vet for veterinary and BLUE blue for cyanosis and bedside lung ultrasound exam) (Lisciandro et al. 2014). The Vet BLUE regional sites include the caudodorsal lung lobe region (Cd), the perihilar lung lobe region (Ph), the middle lung lobe region (Md), and the cranial lung lobe region (Cr). Each is named as a region because the naming do not directly correlate with anatomical names of lung lobes. This is important to appreciate because 2 parts of a lung lobe or 2 different lung lobes may be coming into view over the same Vet BLUE regional view with as an example dry lung then wet lung then dry lung then wet lung or dry lung and a shred and dry lung then a shred as the patient inspires and expires (this phenomenon in fairly common). The Thoracic FAST SM (TFAST SM ) Exam

3 Reproduced with Permission (left figure) Lisciandro, JVECC 2011;20(2): This material (right figure) is reproduced with permission of John Wiley & Sons, Inc, Focused Ultrasound Techniques for the Small Animal Practitioner, Wiley 2014 Patient Preparation: NO SITES are SHAVED! All images shown by the author are unshaved sites at which the fur is parted and alcohol is applied to the skin and a small amount of acoustic gel to the probe head (most ultrasound manufacturers warn against placing alcohol on the probe head because of alcohol s damaging effects-check with your ultrasound machine manufacturer). No images from cases in this talk were shaved. Patient Positioning: TFAST 3 and Vet BLUE are performed in sternal recumbency or standing in respiratory distressed or compromised small animals. TFAST 3 consists of 5-points as follows: the stationary horizontally probe-positioned left and right Chest Tube Site (CTS) view; the dynamically spotlighted left and right Pericardial Site (PCS) view; and the newer 5 th point DH view (Lisciandro 2011), for the rapid detection of pleural and pericardial effusion and in some instances lung pathology (Lisciandro 2014). The Gator Sign Basic Lung Ultrasound Orientation Reproduced with Permission Lisciandro, JVECC 2011;20(2): for the Small Animal Practitioner, Wiley 2014 Probe Orientation: Lung ultrasound orientation is ALWAYS the same with the visualization of the Gator Sign to properly identify the pulmonary-pleural interface or the Lung Line (the surface of the lung). The probe is held perpendicular to the long-axis of the ribs; Depth is generally set between 4-6 cm; Frequency is generally set between 5-10 MHz; and a microconvex probe is preferred over a linear probe because the probe is acceptable for AFAST 3, TFAST 3 and Vet BLUE (Global FAST 3 ). A phase-array or sector probe is generally not recommended because its focal point is too small. A linear probe may be used; however, it is not ideal for the AFAST 3 and TFAST 3 portions of Global FAST 3 (GFAST 3 ). The rounded rib heads are likened to the eyes, and the pulmonary-pleural (PP-line) interface (also called the lung line) to the bridge of its nose, as a partially submerged gator (alligator) peers at the sonographer. The proximal white line is the focus of ALL lung ultrasound. The major orientation error is looking beyond the PP-line (or lung line ) and mistaking A-line artifacts for the PP-line or lung line or being over the abdomen and mistaking liver, stomach (especially when air-filled), or the gallbladder for lung pathology.

4 Search for the Lung Point The Degree of Pneumothorax Reproduced with Permission Lisciandro, JVECC (2): The Lung Point: The search for the Lung Point is extremely important concept to understand. The Lung Point is the position along the thorax where collapsed lung recontacts the chest wall. The finding of the Lung Point increases the sensitivity of PTX. The Lung Point is determined by finding either a glide sign with A-lines or ultrasound lung rockets or other lung ultrasound findings supporting lung against the thoracic wall. The Lung Pulse has been described in people and its frequency is unknown in veterinary medicine. The Lung Pulse if the finding of lung against the thoracic wall, however, because of severe collapse, the glide sign does not move with inspiration and expiration but rather with the heart beat. A) Thorax in which pneumothorax (PTX) has been excluded. B) PTX has been determined at position 1 and the Lung Point is found at position 2 (PTX is partial). C) PTX has been determined and a Lung Point is nonexistent at any of the 3 probe positions (PTX is massive). Key Point: By dividing the thorax into thirds when searching for the Lung Point a subjective assessment of partial vs. massive PTX may be made. Do not move in small increments when searching for the Lung Point, rather drop the probe down to the middle third then lower third then you re your way back toward the CTS to determine the Lung Point position relative to the CTS. Recording the distance is a way to monitor PTX (worsening, improving, and resolution). Moreover, when PTX is suspected at the CTS view, by locating the Lung Point sensitivity is increased and smaller pneumothoraces may be monitored by using/recording the distance from the CTS to the lung point. Vet BLUE SM Examination for the Small Animal Practitioner, Wiley 2014 and FASTVet.com 2014 The Vet BLUE lung examination is a screening test performed identically as the probe is positioned at the CTS view of TFAST 3. The probe is then moved through regional locations that are bilaterally applied as follows: caudodorsal lung lobe region (Cd - same as the TFAST 3 CTS view, upper third, 8-9 Th intercostal space)), perihilar lung lobe region (Ph 6-7 th intercostal space, middle third),

5 middle lung lobe region (Md 4-5 th intercostal space, lower thrid), and cranial lung lobe region (Cr 2 nd -3 rd intercostal space, lower third). The maximum number of ULRs over the respective single intercostal space at each view is recorded. The counting system is as follows: 1, 2, 3, >3 (when ULRs are still recognized as individuals), and infinity (when the ULRs blend into one another becoming confluent [also called white lung]). Because most typing keyboards do not have an infinity symbol we use the & sign for infinity ULRs. ULRs are counted because they have been shown to correlate with the degree of alveolar-interstitial edema on Computerized Tomography (CT) (Volpicelli, 2006). FASTVet.com Copyright 2015, 2016 Key Point: Best Way to Perform Vet BLUE Accurately is to locate the left TFAST Chest Tube Site directly above the xiphoid in the area of the 8-10 th intercostal space in the upper 1/3 rd of the thorax, cheating cranially to make sure over lung (and not over liver/stomach/abdominal contents). From the left TFAST CTS which is the same as the left Vet BLUE Cd lung point, draw a line (with your alcohol or acoustic coupling gel) to the elbow, halfway to the elbow is the Vet BLUE Ph point, and at the elbow is the Vet BLUE Md point. If the heart is in view at the Vet BLUE Md point, slide above the heart until you see the lung line. The last point is the Vet BLUE Cr which requires pulling the foreleg cranially to get probe be placed in the 2 nd -3 rd intercostal space. Too low at the Cr point, you will see the striations of the pectoral muscles and too high and cranial at the Cr point, you will be in the thoracic inlet (soft tissue and vessels). The Gator Sign and the lung line must be appreciated to know you are in fact over Cr lung. The Vet BLUE points are acquired in the same manner on the right side. Key Point: Perform the Vet BLUE the same way every time. We suggest that you begin on the LEFT and go from dorsal to ventral, move to the right side and do the same, dorsal to ventral. This allows you to think about the pattern in the same manner every time and helps you remember the findings at each site. Also, by completing the Vet BLUE at the right cranial lung lobe region (Cr) region increase your depth, and do your right TFAST pericardial view and proceed with the increased depth to AFAST and Global FAST (GFAST) is finished in < 4-5 minutes by the appropriately trained sonographer! Vet BLUE SM for Respiratory Distress 5 Basic Lung Ultrasound Findings Wet Lung vs. Dry Lung - Basic Lung Ultrasound 101 Shred Sign, Tissue Sign, Nodule Sign - Advanced Lung Ultrasound 202 Wet vs. Dry Lung: Basic easily recognizable lung ultrasound findings are categoriazed into the Wet Lung vs. Dry Lung concept (Lisciandro, JVECC 2011). A Glide Sign with A-lines (reverberation artifact) at the lung line is considered Dry Lung only to be confounded with PTX (A-lines and No Glide Sign). However, many patients in which the probability of PTX is very low, then spending additional time finding the Glide Sign becomes less important and A-lines alone suffice. Ultrasound Lung Rockets (ULRs) are considered Wet Lung and oscillate to and fro with inspiration and expiration and must extend to the far field obliterating A-lines (Lisciandro, JVECC 2011).

6 Shred Sign, Tissue Sign, and Nodule Sign (plus Wedge Sign): These are the 3 more advanced lung ultrasound signs we have created in progressive order of increasing consolidation/infiltration. The Shred Sign is similar to an air bronchogram on TXR (consolidation with aeration of the lung); the Tissue Sign is similar to hepatization of lung (consolidation without aeration); and the Nodule Sign (consolidation/infiltration in discreet nodules). The Wedge Sign is a subset of the Shred Sign and represents micro-pte (infarcts at the lung periphery). for the Small Animal Practitioner, Wiley 2014 and FASTVet.com 2014 Regionally-based Respiratory Pattern Approach Using Vet BLUESM for the Small Animal Practitioner, Wiley 2014 and FASTVet.com 2014 Clinical Cases: Examples of Vet BLUESM regionally-based patterns. A) Dry Lung all fields rules out clinically relevant left-sided heart failure, suggests upper airway obstruction, feline asthma, COPD, PTE and non-respiratory look-a-likes. B) Wet Lung in dorsal, perihilar, and middle lung lobe regions suggests cardiogenic lung edema (left-sided heart failure, volume overload from intravenous fluids). C) Wet Lung in dorsal lung lobe regions suggests forms of non-cardiogenic lung edema. D) Wet Lungs in ventral AFASTSM, TFASTSM, Vet BLUESM, Global FASTSM and Advanced FASTSM are service marks and proprietary to

7 fields with or without signs of consolidation (Shred Sign/Tissue Sign), suggest pneumonia. E) Solitary nodule. F) Multiple nodules suggest metastatic disease or granulomatous disease. Vet BLUE SM Diagnostic Algorithm for Respiratory Distress and Conditions for the Small Animal Practitioner, Wiley 2014 Rule Outs for DRY All Fields on Vet BLUE SM RESPIRATORY Pulmonary Thrombo-embolism (PTE) Upper Airway Conditions (e.g., Collapsing Trachea, Laryngeal Paralysis), Obstruction (e.g., Mass) Chronic Obstructive Pulmonary Disease (COPD), Feline Asthma Centrally located lung pathology away from the lung line (missed by Vet BLUE) CARDIAC Cardiac Tamponade, Cardiac Arrhythmia, Dilated Cardiomyopathy (DCM) UNDIFFERENTIATED HYPOTENSION Anaphylaxis Hemoabdomen, Hemothorax, Hemoretroperitoneum, other cavitary or hemorrhage in a space OTHER NON-RESPIRATORY Pyrexia or High Fever Severe Metabolic Acidosis Severe Anemia NOTE: Dry Lungs ALL Fields is a Rapid (<90 seconds) Highly Sensitive Test Ruling Out Left-sided CHF (Dogs 88%, Cats 96%) - See Reference 1. FASTVet.com Copyright 2015, 2016 Greg Lisciandro, DVM at FASTSavesLives@gmail.com

8 The Use of Vet BLUE in Respiratory Distressed Cats The Tale of 3 Cats The use of thoracic auscultation and breathing patterns for respiratory distress is insensitive and prone to error, coupled with the dangers of transport and restraint in radiology and thoracic radiographic interpretation, making the proactive use of Vet BLUE lung ultrasound incredibly powerful for differentiating respiratory distress in cats. Vet BLUE is a pattern-based approach of using our 5 described basic lung ultrasound findings dry lung (Glide with A-lines), wet lung (Ultrasound Lung Rockets also called B-lines), Shred Sign (Wedge Sign, PTE), Tissue Sign and Nodule Sign (see above). In the Tale of 3 Cats (could make it 4 with pleural effusion), we have Cat #1 with Feline Asthma that is Dry ALL Fields, Cat #2 with Left-sided Congestive Heart Failure that is Wet ALL Fields, and Cat #3 with Metastatic Disease that has the Nodule Sign with various-sized Nodules at nearly every Vet BLUE view. On physical examination, considering auscultation and breathing patterns, all 3 cats look the same with nostril flaring, abdominal breathing, and harsh lung sounds. As described, in seconds, point-of-care, using Vet BLUE the readily learned Vet BLUE patterns are appreciated and not only is shot gun (best guess or empirical) therapy replaced with evidence-based therapy, but also the next best test is better determined. Key Points: 1) Use the presence of wet vs. dry lung to guide diuretic usage (Lisciandro et al. Vet BLUE in Dogs, VRUS 2014 and Cats JVECC accepted 2015; Rademacher et al. Lung Ultrasound in CHF, VRUS 2013) and 2) Look beyond pleural effusion at the Lung Line for the Shred Sign, Tissue Sign, and Nodule Sign. Repeat Vet BLUE a few hours post-thoracocentesis to allow pressure atelectasis to resolve, which often appears as a Shred Sign or Tissue Sign. The Global FASTSM Triad for Volume Status Top Row: The 3 Echo Views of TFAST are the Left Ventricular Short-axis View for Volume and Contractility (shown), the Right Ventricular to Left Ventricular Ratio on the Long-axis 4 Chamber View (not shown), and the LA:AO Ratio on the Short-axis View (not shown). Middle Row: The presence of Dry vs. Wet Lung screens for Left-sided cardiac overload. Bottom Row: The characterization of the Caudal Vena Cava and Hepatic Veins screens for Right-sided cardiac overload. for the Small Animal Practitioner, Wiley 2014 and FASTVet.com 2014 Global FASTSM should be used for rapid evaluation of patient volume status pre-, during, and post- fluid resuscitation by using the GFAST3 Triad (similar to Ferrada et al. 2013). The use of CVP via central lines for fluid resuscitation and its teaching should be abandoned (Marik et al. AFASTSM, TFASTSM, Vet BLUESM, Global FASTSM and Advanced FASTSM are service marks and proprietary to

9 2013). 1) *Top Row Volume and Contractility - the left ventricular short-axis mushroom view (TFAST 3 right PCS view) for volume status [~ preload] and contractility), the Right Ventricular to Left Ventricular Ratio (RV:LV) on the Long-axis 4 Chamber View (not shown) and the LA:Ao Ratio on the Short-axis View (not shown) are also part of TFAST SM 2) Middle Row Left-sided Heart Status/Overload - Dry Lung vs. Wet Lung help determine the absence or presence of clinically relevant non-cardiogenic and cardiogenic pulmonary edema (Lichtenstein and Karakitsos 2012); and numbers of ULRs correlate with degree of interstitialalveolar edema. 3) Bottom Row Right-sided Heart Status/Overload - caudal vena cava at the diaphragm (using the characterization of FAT, flat or bounce) and hepatic vein (HV) distention or tree trunks (TFAST 3 /AFAST 3 DH view for right-sided cardiac status and volume [preload]); normally, the hepatic veins are not readily apparent as the drain into the caudal vena cava (CVC) (Lisciandro 2014). *Not shown, we also teach the LA:Ao ratio short-axis view and the RV:LV ratio 4-chamber long-axis view for additional information regarding left heart and right heart status, respectively. References: 1. Lisciandro GR, et al. Absence of B-lines on Lung Ultrasound (Vet BLUE protocol) to Rule Out Left-sided Congestive Heart Failure in 368 Cats and Dogs. Abstract, J Vet Emerg Crit Care 2016, In Press. 2. Lisciandro GR, et al. Frequency and number of ultrasound lung rockets (B-lines) using a regionally based lung ultrasound examination named vet blue (veterinary bedside lung ultrasound exam) in cats with radiographically normal lung findings. J Vet Emerg Crit Care 2016, In Press. 3. Ward JL, Lisciandro GR, Tou SP, Keene BW, DeFrancesco TC. Evaluation of point-ofcare lung ultrasound (Vet BLUE protocol) for the diagnosis of cardiogenic pulmonary edema in dogs and cats with acute dyspnea. J Am Vet Med Assoc 2015, In Press. 4. Lisciandro GR, et al. Frequency and number of ultrasound lung rockets (B-lines) using a regionally based lung ultrasound examination named vet blue (veterinary bedside lung ultrasound exam) in dogs with radiographically normal lung findings. Vet Radiol and Ultrasound 2014;55(3): Lisciandro GR, et al. Accuracy of Focused Assessment with Sonography for Trauma (FAST) to detect pneumothorax in 145 dogs with blunt and penetrating trauma. J Vet Emerg Crit Care 2008; 18(3): Lisciandro GR. Abdominal (AFAST) and thoracic (TFAST) focused assessment with sonography for trauma, triage, and tracking (monitoring) in small animal emergency and critical care. J Vet Emerg Crit Care 2011; 21(2): Boysen SR, Lisciandro GR. The use of Ultrasound in the Emergency Room (AFAST and TFAST). Vet Clin North Am Small Anim Pract 2013;43(4): Lisciandro GR. Chapter 55: Ultrasound in Animals. In Critical Care Ultrasound (human textbook), Editors Lumb and Karakitsos. Elsevier: St. Louis, MO Lisciandro GR. Chapter 9: The Thoracic (TFAST) Exam; Chapter 10: The Vet BLUE Lung Scan. In Focused Ultrasound for the Small Animal Practitioner, Editor, Lisciandro GR. Wiley Blackwell: Ames IA Lisciandro GR and Armenise A. Chapter 16: Focused or COAST 3 - CPR, Global FAST and FAST ABCDE. In Focused Ultrasound for the Small Animal Practitioner, Editor, Lisciandro GR. Wiley Blackwell: Ames IA 2014.