Differentiating Shock

Imagine you and your partner are dispatched to a low-priority “sick person” call. It sounds like any of a dozen others going on in your city at any given time: an elderly female who “doesn’t feel well” with no priority symptoms. Your communications center advises the call has been pending for about 20 minutes, and you estimate your response will take 10 more.

You arrive at a senior apartment complex and take the elevator to the third floor. You knock on the door, and the patient’s husband greets you with a worried look. “My wife isn’t well,” he says.

Your patient is a female in her 60s who is sitting upright but slumped over in a recliner. She is pale, diaphoretic, and responds only to deep pain.

Recognizing how quickly the situation has escalated, you and your partner immediately take the patient's vital signs and place her on a cardiac monitor. She is in sinus bradycardia at a rate of 46 and has a blood pressure of 64/40, a respiratory rate of 10, and a room-air oxygen saturation of 88%.

The husband is an extremely poor historian and unable to provide much meaningful information about the woman’s medical history.

Undifferentiated Shock

This case is not unlike thousands paramedics respond to across the country every day. Absent a thorough history, what tops the list of your differential diagnoses for this patient? Is she in septic shock? Cardiogenic shock? Does she have a pericardial effusion leading to tamponade? Despite being competent clinicians skilled in the arts of history-taking and the physical exam, it remains difficult for paramedics to truly differentiate many patients’ shock states in the prehospital environment.

In the past the ability of paramedics to differentiate shocked patients was deemed less important than simply rapidly transporting them to a hospital for resuscitation. Today we know that even transient episodes of severe hypotension lead to a significantly increased risk of end-organ damage and resultant morbidity.¹ These patients require and deserve aggressive resuscitation in the field from astute clinician paramedics to optimize their hemodynamics—not just large fluid boluses and a fast ride to a hospital. 

Our ability to provide that level of care requires more than a good history and physical and knowledge of shock physiology. It requires a special set of skills and tools to uncover the underlying cause of the patient’s shock and develop an effective resuscitation plan to address it.

The Role of POCUS

Point-of-care ultrasonography, or POCUS, has evolved over the last 20 years to become a mainstay of emergency department diagnosis and treatment. Whether assessing obstetric patients, visualizing abdominal bleeding, or guiding invasive procedures, the practice of emergency medicine continues to find new, innovative applications for this technology.

A more recent development, however, is the migration of POCUS from the emergency department into the prehospital setting. While as of 2014 North American EMS agencies had an ultrasound adoption rate of only 4%,² there are indications that many progressive EMS agencies are rapidly coming to use POCUS as part of their standard practice. This change has been so rapid that just this year, the nation’s first university-level POCUS course designed specifically for prehospital providers debuted at the Virginia Commonwealth University School of Medicine.³

What makes POCUS such an attractive technology for agencies, and how could it be useful in the hands of paramedics?

What a RUSH

To understand the applications of POCUS in shock, let’s revisit the patient we discussed earlier. This is a patient in undifferentiated shock; she has no obvious trauma, she’s afebrile and has no obvious portal of infection, and the husband doesn’t articulate anything that sounds like a cardiac history. We know she is hemodynamically unstable and near-arrest, but we have no idea why.

While every area and agency has its own set of treatment guidelines and protocols, without a true differentiation of the patient’s shock, most would direct the provider to initially give a sizable fluid challenge and reassess. And while this strategy is safe for many patients, it may cause deleterious effects in many others. The safest way to approach resuscitating the undifferentiated patient is to first correct, or attempt to correct, immediate life threats, then deploy POCUS to guide medical decision-making.

While there are many published techniques and exam protocols to assess critically ill patients, the most prevalent protocol is known as the rapid ultrasound in shock and hypotension, or RUSH exam. This protocol is a quick and relatively easy exam to perform that is designed to help the provider either rule in or reduce their index of suspicion for six emergent causes of shock and allow for more informed clinical decision-making.

The RUSH exam typically consists of six different ultrasound “views.” These views can be easily remembered using the acronym HI-MAP.

Heart—Ultrasound examination of the heart allows for immediate visualization of any large pericardial effusion that may be impacting the patient’s hemodynamics and also allows for a qualitative assessment of the patient’s ventricular function and fluid status. Low cardiac output caused by reduced contractility can indicate cardiogenic shock, while conversely a hyperdynamic left ventricle may indicate a hypovolemic state, two conditions that require very different interventions.

IVC—Considerable controversy surrounds the ability of ultrasound examination of the inferior vena cava to accurately assess a patient’s fluid status. That being said, there is a body of evidence that suggests ultrasonographic examination of IVC diameter in spontaneously breathing patients can provide valuable information about the patient’s fluid and preload status.⁴ This, combined with the overall clinical picture, can help providers assess the appropriateness of fluid resuscitation in hypotensive patients.

Morrison’s pouch—The interface between the liver and the kidney in the right upper quadrant, a space known as Morrison’s pouch, can be examined with ultrasound to detect the presence of free fluid with a high degree of sensitivity and specificity in the setting of trauma.⁵ This translates well for medical causes of intra-abdominal hemorrhage, such as acute pancreatitis or an actively dissecting aortic aneurysm.

Aorta—Patients with abdominal aortic catastrophe can rapidly dissect and decompensate, requiring aggressive management and rapid transport; unfortunately, their symptoms can often mimic those of other conditions, leading providers down a fruitless treatment pathway that quickly spirals out of control. Ultrasound examination of the aorta, however, is extremely sensitive and specific for the detection of AAA, clarifying an otherwise obscure clinical picture for these patients.⁶

Pneumothorax—Perhaps the easiest of all the examinations to perform and interpret with even a minimum of training,⁷ examination of the lung with POCUS can detect pneumothorax with a sensitivity and specificity far better than auscultation of lung sounds or a chest x-ray.⁸

Bringing It All Together

Let’s turn our attention back to the patient one last time. Last year you would have given this patient a rapid fluid bolus to check for fluid responsiveness and only after that considered administering a vasopressor to manage her hemodynamics. But now your agency has provided you with ultrasound.

You take a couple of minutes and quickly perform a RUSH exam. All your findings are normal except for the fact that her left ventricle is barely squeezing. Now that you know her shock is cardiogenic in nature and her preload status is sufficient, you reduce the amount of fluid you administer and instead turn quickly to an inotrope for circulatory support. Her condition stabilizes, and you avoid fluid-overloading her and are able to safely transport her to an area hospital, where she is admitted and treated for heart failure.

Final Thoughts

Ultrasonography, in the hands of competent, confident clinician paramedics, is a powerful tool that has the potential to guide the care of critically ill patients across the spectrum of disease. More than any other emerging prehospital technology, POCUS has the potential to make a greater impact on the diagnosis and treatment of our patients than anything since the introduction of prehospital EKGs. 

This level of practice, however, requires more of a shift in thinking than simply buying a machine and training providers. It requires us to acknowledge that the dichotomy of “stay and play” versus “load and go” is outdated and in some instances potentially harmful to patients. Providers need to be encouraged to effectively resuscitate critically ill patients, rather than providing minimal care and simply driving fast.

Agency managers and medical directors owe it to their providers and the patients they serve to consider incorporating POCUS into their daily practice. The rapidly decreasing cost of equipment, combined with the increasing availability of quality education and training for providers, makes this far more possible than it was even two years ago. We must also encourage EMS providers to be the skilled clinicians they are and reevaluate long-held practices such as using on-scene duration as a measure of performance and demanding short scene times to simply improve system throughput.  

References

1. Van Doorn KJ, Verbrugghe W, Wouters K, et al. The duration of hypotension determines the evolution of bacteremia-induced acute kidney injury in the intensive care unit. PLoS One, 2014 Dec; 9(12).

2. Taylor J, McLaughlin K, McRae A, et al. Use of prehospital ultrasound in North America: A survey of emergency medical services directors. BMC Emerg Med, 2014 Mar 1; 14:6.

3. McNeill B. Ultrasound technology can help paramedics save lives in the field. A groundbreaking new class as VCU is training them how. VCU News, 2018 May 2; https://news.vcu.edu/article/Ultrasound_technology_can_help_paramedics_save_lives_in_the_field.

4. Dipti A, Soucy Z, Surana A, Chandra S. Role of inferior vena cava diameter in assessment of volume status: A meta-analysis. Am J Emerg Med, 2012 Oct; 30(8): 1,414–9.

5. Nishijima DK, Simel DL, Wisner DH, Holmes JF. Does this adult patient have a blunt intra-abdominal injury? JAMA, 2012 Apr 11; 307(14): 1,517–27.

6. Tayal VS, Graf CD, Gibbs MA. Prospective study of accuracy and outcome of emergency ultrasound for abdominal aortic aneurysm over two years. Acad Emerg Med, 2003 Aug; 10(8): 867–71.

7. Lyon M, Walton P. Bhalla V, Shiver SA. Ultrasound detection of the sliding lung sign by prehospital critical care providers. Am J Emerg Med, 2012 Mar; 30(3): 485–8.

8. Lichtenstein DA, Menu Y. A bedside ultrasound sign ruling out pneumothorax in the critically ill. Lung sliding. Chest, 1995 Nov; 108(5): 1,345–8.

Stephanie Louka, MD, AEMT, is an EMS fellow and completed her emergency medicine residency training at VCU Health in Richmond, Va. She is a life member of the Virginia Beach Volunteer Rescue Squad. Her prehospital interests include POCUS and BLS education. She blogs at TeamLouka.com.

Thomas Hudson, NRP, CCP-C, is a paramedic for the VCU Health Department of Emergency Medicine in Richmond, Va. He received both his paramedic and undergraduate science education at VCU and volunteers in his free time with the Richmond Volunteer Rescue Squad.