Hello, my name is Christopher Schott. I'm an associate professor of critical care and emergency medicine at the University of Pittsburgh and VA Pittsburgh Healthcare System. In this session, I'll be discussing whether or not we should apply point-of-care ultrasound to all patients presenting in shock. I have no disclosures related to this presentation. Many providers who routinely use point-of-care ultrasound can provide countless anecdotal stories of how it changed their care for a patient. I easily recall multiple instances of being surprised by what I saw when I put the probe on a patient. I've had patients that were presumed to be in septic shock that turned out to have cardiac tamponade, or patients who presented with acute liver failure that ended up being due to congestive hepatopathy from heart failure not suspected until visualized on a bedside ultrasound exam. In this talk, I will provide the data on when point-of-care ultrasound should be used in patients with shock, as well as when it is sufficient to perform a basic focused exam versus a more complete or advanced exam, with the caveat of having the appropriate training to recognize the limitations of its use. Point-of-care ultrasound was initially established in the 1980s and 90s with a focused assessment with sonography and trauma as a way to determine at the point of care whether or not a patient presenting with blunt abdominal trauma who is hemodynamically unstable has pathology that could be treated intraoperatively. It was subsequently used to reduce the need for invasive procedures such as the diagnostic peritoneal lavage, or DPL, and has shown decreased time to treatment in the OR and decreased mortality in this patient population. Point-of-care ultrasound has since evolved to becoming a focused or goal-directed tool to answer specific questions or guide performance of an invasive procedure. It has subsequently become a core competency for emergency and critical care medicine and expanded to other specialties such as internal medicine, anesthesia, surgery, and many others. Point-of-care ultrasound's use in shock can be divided into diagnostic and procedural applications. It can be used to help identify the etiology of shock during an initial patient evaluation. It can readily help identify cardiogenic, obstructive, and hypovolemic causes of shock. It can be subsequently used to guide resuscitation, looking for evidence of fluid responsiveness and fluid tolerance as ongoing resuscitation occurs. As noted, it can also be used for procedural guidance, particularly for vascular access. Basic point-of-care ultrasound refers to scanning in only B or brightness mode, also known as 2D mode, for qualitative assessments. This is often called a focused or goal-directed exam. Advanced point-of-care ultrasound then refers to incorporation of other imaging modalities such as M-mode, color doppler, and spectral doppler with the addition of quantitative measurements. Over the years, there have been numerous publications of various protocols for point-of-care ultrasound to help determine the etiology of shock. Some of the early and most notable protocols include the FATE, FAST, RUSH, FEEL, and BLUE protocols among many others. In essence, these all look at the pump, tank, and pipes, as described by the RUSH protocol, as ways of determining what the cause of shock is, putting together the findings seen on point-of-care ultrasound. Let's use an example case where we have a patient with relatively normal LV systolic function and what appears to be an enlarged right ventricle in this parasternal long-axis view. Turning to the parasternal short-axis view, we can again see that there is preserved LV systolic function, but that there is evidence of RV impairment and strain as the intraventricular septum is bowing into the LV. These findings, seen here, are referred to as the D-sign. In the apical four-chamber view from this patient, we see that the RV is so enlarged it is now larger than the left ventricle. There is reduced contractility in motion of the RV-free wall, but with preserved contractility at the apex, a constellation of findings known as the McConnell sign. On evaluation of the lungs, we see that there is lung sliding present bilaterally in all fields examined. On assessment of the patient's deep venous system, a non-compressible popliteal vein with echogenic material in the lumen is seen, concerning for a DVT. Putting the findings together, we do not see evidence of a clinically significant pericardial effusion, a normal or preserved LV systolic function, right ventricular strain with increased pressure producing the D-sign, enlarged RV with the McConnell constellation of findings, lung sliding present bilaterally, and a DVT in the right popliteal vein. The summation of these findings would suggest that this patient may be in shock from a massive pulmonary embolism. This is an example of how point-of-care ultrasound can help provide information right at the bedside to determine if or which further testing may be needed, as well as beginning early resuscitation targeting the specific cause of shock in your patient. In this particular case, the diagnosis was suggested with the utilization of basic POCUS, that is, qualitative B-mode images only. Transloresic echocardiography can also be used in the setting of a cardiac arrest. This table is from a paper that looked at the use of POCUS in patients during a cardiac arrest and found that in patients with pulseless electrical activity, or PEA, 38 out of the 51 had what was referred to as pseudo-PEA, where the patient had evidence of cardiac activity, but with poor enough function that there was no palpable pulse during the ACLS pulse rhythm checks. These are due to etiologies such as hypovolemia, severe LV hypokinesis, or obstructive shock due to massive pulmonary embolism or tension pneumothorax. There have been subsequent meta-analyses looking at the use of POCUS during cardiac arrest. There is a trend toward showing that if cardiac activity is seen during the pulse and rhythm checks, there is a highly likelihood for successful return of spontaneous circulation, as opposed to the absence of cardiac activity of an increased likelihood ratio for not obtaining ROSC. However, this is not an absolute and should not be used for definitive prognostication, but rather as another tool to help guide resuscitation, as well as recognize when there may be futility. As I noted before, POCUS can be used to guide resuscitation after the initial diagnosis. In particular, POCUS can specifically answer questions about whether or not your patient can tolerate further IV fluid administration, as well as if you would see benefit from further IV fluid therapy. Here I am demonstrating some of the specific information that may be obtained from POCUS. On the left side of the screen, I have listed ways in which POCUS can help determine whether or not your patient's right heart can tolerate further IV fluids. For example, measurement of the IVC collapsibility in spontaneously breathing patients can provide an estimate of their central venous or right atrial pressure. Looking at the tricuspid annular plane systolic excursion, or TAPC, provides information about your patient's right ventricular systolic function. We can even estimate the patient's pulmonary artery pressures. We can look at the patient's lungs for evidence of pulmonary edema. I have also included ways of determining if the left ventricle can tolerate further fluid administration at the bottom, by using spectral pulse doppler and tissue doppler imaging to calculate their E to E' ratio and the E to A mitral valve inflow as measures of acute diastolic dysfunction from increased afterload. On the right side of the screen are a couple of ways to predict if the patient's cardiac output would benefit from further IV fluid administration. One way is to obtain an apical five-chamber view, where we would put the pulse doppler imaging gate through the left ventricular outflow track and measure the maximum and minimum velocities through the respiratory cycle to calculate stroke volume variation. You can also perform a passive leg raise maneuver in the same way, looking for changes in the velocity time integral when the patient is sitting upright to after they have had an autotransfusion from the passive leg raise maneuver. Let's look at a couple of examples. Imagine you have a 78-year-old patient admitted for septic shock. In obtaining this parasternal long axis view, we do not see a pericardial effusion. We can see that the LV systolic function is normal to hyperdynamic. Looking at the inferior vena cava, we see that it is small in maximum diameter with almost complete collapse during inspiration. Assessment of the lungs bilaterally demonstrate lung sliding throughout and an A profile. Assessment of the right heart in an apical four-chamber view demonstrates a TAPSY measurement that is above the cutoff for normal and may even be hyperdynamic. Performing the passive leg raise in this patient demonstrates a change in the velocity time integral of 13.7%. Putting all of this data together, we have a hyperdynamic EF with no evidence of a pericardial effusion, an IVC that suggests a low CVP or right atrial pressure, dry lungs, a normal TAPSY measurement, and a passive leg raise VTI greater than 12.5%. This data would suggest that the patient is both able to tolerate IV fluids as well as predict that you are likely to see improved cardiac output with further IV fluid administration. Now let's look at the same patient but with a different set of ultrasound findings. Here we see evidence of a decreased LV systolic function in both the parasternal long and short axis with no evidence of any pericardial effusion. Looking at the IVC here, it is plethoric, dilated with minimal changes during respiration. These lungs demonstrate evidence of sliding with B-lines throughout, suggestive of interstitial process, potentially pulmonary edema. This patient's TAPSY measurement is decreased at only 12.6% of change between systole and diastole. When we perform a passive leg raise, we notice a difference of only 6.7%. Putting all of the data together for this patient, we observed a decreased EF with no evidence of pericardial effusion, a plethoric IVC suggestive of elevated central venous pressure, lungs that appear to be wet, decreased right heart systolic function, and decreased responsiveness to an autotransfusion with a passive leg raise maneuver. Therefore, this patient is not likely to tolerate further IV fluids and predict that we are not likely to see increased cardiac output with further IV fluid administration. In this scenario, you may elect to focus therapies more on vasopressor and inotropic support based on the ultrasound findings. A question that frequently comes up is how often do you need to perform a more advanced or complete echo versus a basic or focused point of care exam? A lot of this depends on the specific questions you are trying to answer and the urgency of the situation. For example, in cases where a patient is acutely decompensating, a focused basic exam may be sufficient to recognize big picture pathologies such as a pericardial effusion. However, if a patient has underlying chronic comorbidities, this may affect how we interpret our POCUS findings and require additional Dumonts. Predicting fluid responsiveness may be helpful at the extremes of POCUS findings. However, more often fluid responsiveness is not obvious and the data obtained from our point of care exams may benefit from more advanced measurements and clinical correlation. There is a need for balance. The use of more advanced measurements can add a tremendous amount more data about a patient's hemodynamic profile. However, it may not always be necessary to spend the amount of time needed to perform a more complete echo assessment. You would not want to become paralyzed from making a critical decision while obtaining data that may not be as relevant in that moment. This may be best summarized in the setting of a crashing patient where ultrasound is most useful to determine can't-miss pathologies compared to the more nuanced decision making that may occur during daily rounds. Moreover, it is essential to recognize your limitations as the operator performing a POCUS exam. This may include patients with challenging views as well as not wanting to make interpretations beyond the scope of what you could support by the images and data obtained. This is why the data from a point of care ultrasound exam should always be clinically correlated to the patient in front of you, a true advantage of POCUS. Compared to the studies interpreted by radiologists, cardiologists, and others, POCUS is performed and interpreted by the same provider at the bedside with a more extensive knowledge of a patient's history, comorbidities, physical exam, and clinical course. Let's look at several cases to illustrate this balance. In this case, we are treating a patient during a cardiac arrest. The patient has been unresponsive with no palpable pulse and in PEA on the monitor. During a pulse and rhythm check 10 minutes into the code, we performed a subxiphoid point of care ultrasound assessment with the clip obtained shown on screen. In this case, a basic 2D image was sufficient to recognize that there was no cardiac activity. There is not a need to perform any more advanced measurements. Let's look at another case. In this case, there was a patient in their 40s transferred to the ICU for hypotension and tachycardia. The primary service had obtained a lactate level that was noted to be elevated. The working diagnosis on transfer was that the patient was becoming septic. POCUS was performed on the patient's arrival to the ICU. Here is the parasternal long axis view. Here is the subxiphoid view. Here is a view of the inferior vena cava. In this case, we find that there is evidence of a large pericardial effusion with concerns for cardiac tamponade based on the right atrial and ventricular collapse as well as the pleuric IVC. In this case, qualitative basic POCUS might be sufficient to recognize that this patient is in shock from a pericardial effusion with concerns for tamponade opposed to the previously presumed septic etiology. Here is another case. This one involved a patient in their 60s with a past medical history of diabetes, hypertension, hyperlipidemia, and heart failure. They had been previously intubated. The patient was noted to become acutely hypotensive, so POCUS was performed. Here is the parasternal long axis view. Here is an apical IV chamber view. Here is a subxiphoid view. Here is a view of their IVC. Based on the POCUS findings so far, we note the decreased ejection fraction and the IVC that appears to be enlarged without respiratory variation. If we stopped here, we might be led into thinking that this patient has hypotension from heart failure and that we should not give additional IV fluids. However, let's add some additional views and measurements. Here are views of the patient's lungs. Here was lung sliding, an A-line seen, and all fields examined. Here is a tricuspid and ulnar plane systolic excursion assessment of the right ventricle. A normal value is greater than 20. We then placed the spectral Doppler through the left ventricular outflow tract and slowed down the sweep speed to look for stroke volume variation. It is important to note that this can only be used to determine stroke volume variation in mechanically ventilated patients breathing passively with the ventilator in normal sinus rhythm. Here, the patient was noted to have stroke volume variation of 30.6%. Adding this additional information, we see that there is a reduced EF, but their lungs are dry, the RV function appears to be preserved, and there is a large stroke volume variation. The value of an IVC in the setting of a mechanically ventilated patient may suggest volume responsiveness rather than an estimate of central venous pressure, as it can do in a spontaneously breathing patient. Putting all of this data together, we see that, despite there being a reduced EF, which is chronic in nature for this patient, they appear to be fluid-tolerant and responsive based on the advanced echo measurements. Let's look at one more case. In this, we have a patient in their 50s post-op day 3 following a 4-vessel CABG. A condition C or rapid response was called for this patient being hypotensive. The patient had felt unwell throughout the day and was cool and pale on exam. Our trail line was placed with a map of 55-65 with large pulse pressure variation noted. Based on the data, there is a wide differential for this patient, so point-of-care ultrasound was performed. Here is the peristernal long axis view that was obtained. Looking at this clip, what do you think is the structure labeled with the asterisks? Here are additional views that we obtained. On the left is the best peristernal short axis that we could obtain, and on the right is an apical 4. At this point, we did not feel confident to make a decision based on the quality of the images we obtained. Therefore, we chose to obtain a STAT consultative echo. Here is the peristernal long axis obtained from the consultative echo performed on a device in the echo lab. On this view, what do you think is the structure labeled by the asterisks now? Here is a side-by-side comparison with our point-of-care ultrasound image on the left and the consultative one on the right. Here are the peristernal short axis and apical 4s that were obtained from the consultative echo. From the consultative echo, we were able to see that there was a large anechoic collection posterior to the left atrium impinging it, causing impaired filling and tamponade physiology. The patient was taken emergently to the operating room where 500 cc's of blood clot in the posterior pericardium were evacuated, with immediate improvement in the hemodynamics. This case illustrates the importance of being able to recognize your limitations based on the devices present at the bedside and the quality of the views you can obtain, as well as correlating it to the clinical context of the patient in front of you. When it comes to using point-of-care ultrasound for patients in shock, there are several important pearls and pitfalls to keep in mind. Point-of-care ultrasound is incredibly operator-dependent. It is simply another tool that may be used by the provider at the bedside and not an intervention in and of itself. It requires quality image acquisition before even being able to make an accurate interpretation. The provider needs to not only recognize their own limitations, such as an inability to obtain quality views needed to make their interpretation, as well as recognize the limitations of the measurements themselves. Many of the ones that predict fluid responsiveness were done on patients in normal sinus rhythm that were breathing passively with mechanical ventilation on tidal volumes of 8 cc's per kilogram ideal body weight, and may not be applicable to patients breathing spontaneously. Data may also be inaccurate or skewed if the patient is underlying chronic conditions such as pulmonary hypertension, valvular pathology, atrial fibrillation, or other chronic cardiopulmonary pathologies. Point-of-care ultrasound can more easily rule in findings that are seen rather than ruling out a diagnosis that may simply have not been captured while scanning. It does not replace other data that you have, such as the physical exam, laboratory studies, or other non-invasive and invasive monitoring devices. Therefore, it is always important to correlate the findings and data to the clinical context of the patient in front of you. In summary, point-of-care ultrasound can help demonstrate the diagnostic etiology of shock as well as guide resuscitation. In cardiac arrest, it can help identify reversible causes as well as distinguish true from pseudo-PEA. However, appropriate training to achieve competency in image acquisition and interpretation is critical for point-of-care ultrasound. The use of basic point-of-care ultrasound can be helpful at the extremes during a quick initial assessment, whereas the nuance of advanced POCUS can help differentiate between acute versus chronic conditions as well as nuances in predicting fluid responsiveness. Ultimately, it is a tool to provide additional data at the bedside. Similar to the Swann-Ganz catheter, POCUS is not an intervention. Its utility depends on the operator to correctly obtain and interpret the data appropriately. With the proper training and competency, POCUS is a valuable tool in the contemporary care of patients in shock. Thank you.

point-of-care ultrasound

shock

resuscitation

cardiac tamponade

pulmonary embolism

fluid administration