MSM 011 Hocus POCUS- Point of care ultrasound in EM and EMS

Point-of-care ultrasound testing has become an emerging clinical skill in emergency medicine and EMS in recent years. This testing can be used to identify clinical complications related to hypotension, cardiac arrest, and specifically provides direct observation of left ventricular function. This can be useful for EMS providers in the field, especially in the presence of PEA arrest. EMS providers can observe the left ventricle directly and determine what, if any ventricular contractions are present during the arrest. PEA arrests present a special challenge to EM and EMS providers, as it is difficult to know in a pre-hospital setting whether the PEA arrest is due to physiologic cardiac standstill, or if the left ventricle is contracting with such little force that there is no palpable carotid pulse or blood pressure. Obtaining this knowledge may lead to a difference in treatment, specifically if the patient is profoundly hypotensive the treatment algorithm may change to an introduction of sympathomimetic medications and blood pressure augmentation and away from CPR. This is a new and exciting facet of emergency care that is worth exploring in depth.

As research into POCUS expands and evolves, the operational benefits seem obvious. Training paramedics and emergency physicians has not proven to be an intensive task, the use of ultrasound at the bedside may serve to reduce costs and reduce the need for additional diagnostic testing (e.g. x-ray). Despite the each of teaching ultrasound, the is a use and training disparity in hospital systems throughout the United States. Specifically, we see that rural and low volume EDs have lower availability of ultrasonography when compared to urban and high volume EDs. This is relevant, since many patients in the United States do not receive care at academic centers, which tend to be isolated to urban and high volume areas. It has been found that despite this ease of use and training that approximately 47% of EDs use POCUS, and 52% have the availability of POCUS in the ED[1]. These gaps may be due to the cost of the technology that is available to the hospitals, or the time required to teach US to emergency residents. Cost associated with obtaining an ultrasound machine has increased as much as 20% in recent years, driving the cost per unit up to between $25,000 and $116,000[2], though there are machine that are more portable and available for approximately $5000 per unit. The concern of cost naturally leads to the lack of availability in emergency departments and pre-hospital organizations. Thus, before any organization takes the leap into introducing POCUS into their regular practice, they must perform a cost-benefit analysis. We’ve looked at the cost, now let’s look at the benefits.

During the peri-arrest period, POCUS is used to visualize cardiac activity during planned pauses in cardiac arrest. These pauses tend to be built into the arrest during the observational periods after defibrillations and otherwise during standard pulse checks. The US probe is place in the sub-xyphoid or parasternal long axis to obtain a view of the left ventricle and determine cardiac activity, or differentiate cardiac standstill when compared to the observed cardiac rhythm. The process itself allows for a quick view of the myocardium that previously was unavailable, leading providers to assume the movement of the myocardium in relation the cardiac rhythm. In 2016, it was found that the use of POCUS during cardiac arrest increased ROSC by threefold, admission by fourfold, and survival to discharge by six-fold[3]. It is important to note that survival to discharge in this cohort was 3.8 percent, and survival to discharge in the absence of POCUS was 0.6 percent. In this study, there was no other change in ACLS protocols besides the addition of POCUS. During the arrest, providers would observe the left ventricle through transthoracic ultrasound to observe the function of the left ventricle, and would tailor their treatment dependent upon that observation. This study included patients that presented to EMS in cardiac arrest and were transported to the hospital. We have discussed on this site before the risks of transporting patients in cardiac arrest. However, in centers that apply POCUS to their cardiac arrest algorithm, it may be the case that these patients have an increased level of survivability than was previously known. As one might expect, patients with cardiac activity upon ED arrival showed a higher rate of survival than those in PEA, however there was no difference in patients that presented as dynamic arrests with both electrical activity and PEA rhythms. Patients involved in this study that presented in cardiac arrest in hospital showed a higher use of US and a higher rate of survival. This is most likely secondary to the availability of a resuscitation team, and a decreased time of arrest when compared to those that arrested in the pre-hospital setting. These findings are compelling, and begs the question why was there not a higher availability of US in the pre-hospital setting? We know that the available data shows that pre-hospital cardiac arrest is managed well, and it is worth asking the question if the EMS providers were given training on US in the field whether we would have observed a higher survivability rate of cardiac arrest in the field.

In addition to cardiac arrest, POCUS may have a benefit in determining the cause of a patient’s hypotension. Hypotension itself is a predictor of in-hospital mortality with a rate as high as 25%, so it seems apparent that if EMS can determine the cause in the field, it would provide a tangible patient benefit. Transthoracic US, used in a similar fashion as described above can be used to determine the dilation of the inferior vena cava, and can preclude or bypass invasive procedures such as the placement of a central line. As many as 24% of patients who present as hypotensive in a shock state are left with a diagnosis of “undifferentiated hypotension”, a diagnosis that leads to poor treatment algorithms and poor outcomes. A properly trained physician or paramedic can isolate the inferior vena cava with US and determine the filling or collapse of the IVC, and correlate the size of the IVC to central venous pressure. It is important to note that these correlations are just that, and they are not hardline determinants. However, in an emergency setting, they may be a good tool to use. A patient that presents with undifferentiated hypotension in the field can be exposed to IVC US, and depending on the observed diameter of the IVC, treatment can be differentiated between hypovolemic shock (fluids) and non-hypovolemic shock (pressors, inotropes)[4].

Transthoracic ultrasound is largely the standard in emergency care, and especially in the pre-hospital setting due to is ease of use and portability. There is, however emerging data that supports the use of transesophageal ultrasound (TEU) as well. TEU is a procedure that is applied by inserting a probe into the oropharynx in a similar fashion to an OG tube and allowing the probe to enter the esophagus, which offers a posterior view of the myocardium. This procedure so far has proven to be superior to transthoracic US in many ways, and one significant advantage is that the placement of the TEU probe would not interrupt chest compressions in cardiac arrest. The probe can be placed posterior to the ET tube, and guided along the esophagus until a view of the myocardium is obtained, and can offer a continuous view of the heart during the resuscitation. Additionally, the design of the probe, which allows the probe to move 180 degrees, allows for multiple views of the chambers of the heart, as well as allowing views of the heart from different angles depending upon the placement of the probe.

This is a skill that is emerging rapidly in EM and EMS. The skill itself is something that can be taught to resuscitation teams, ED physicians, and paramedics with reliably consistent outcomes. As we move away from standard ACLS algorithms and as more evidence is presented that the medication that are involved in ALCS may not be as effective as we once thought, it is apparent that POCUS may be an important tool to add to the resuscitationist’s toolbox. As centers, organizations, and hospitals analyze the cost-per-unit and the benefits of using US in the field, it should be noted that these interventions very clearly aid in improving outcomes for patients. If we are not in that business, what business are we in?

[1] Sanders, et al. Western J. Emerg. Med Access to and Use of Point-of-Care Ultrasound in the Emergency Department 16:5 747-753 Sept. 2015

[2] http://www.modernhealthcare.com/article/20140701/NEWS/307019945

[3] R. Gaspari et al. Resuscitation 109 (2016) 33–39

[4] Atkinson, Paul & Daly, Cathy My patient has no blood pressure: are they empty or full? Point-of-care ultrasound of the inferior vena cava
in the hypotensive emergency department patient Ultrasound 2011; 19: 169–173. DOI: 10.1258/ult.2011.010053