The new load & go destination for cardiac arrest?

EMS providers know well the daily tragedies represented by the following three cases, where young or otherwise healthy individuals succumb to sudden and unexpected illness or injury.

Although prehospital personnel make remarkable saves, many previously healthy patients die of medically reversible causes, despite excellent prehospital care, simply because standard resuscitative practice can’t provide sufficient cardiopulmonary support during severe derangements of heart and/or lung function to allow time for recovery or definitive treatment of the immediate cause.

Case I: Witnessed Out-of-Hospital Cardiac Arrest

Your crew responds to the scene of a 55-year-old male who was witnessed to collapse while walking in the park with his wife. Bystanders immediately started chest compressions and called 9-1-1.

On arrival, the patient has been pulseless for nearly 10 minutes. While performing high-quality chest compressions, you place the patient on the monitor and note an initial rhythm of ventricular fibrillation (v fib).

An initial shock of 120 J produces a transient organized rhythm before v fib recurs. Two subsequent shocks are administered along with a bolus dose of amiodarone. The patient then develops a rhythm indicating idioventricular pulseless electrical activity (PEA).

A definitive airway is established by your partner and after 45 minutes of field efforts, the patient is still in PEA. You call online medical control regarding the decision to transport and the physician at the local receiving hospital reviews the care administered so far and says, “We have nothing else to offer this patient,” and authorizes field termination of resuscitation.

Case 2: TCA Overdose

A 31-year-old female is found locked in her bathroom by her mother with an empty bottle of pills and vodka. By the mother’s estimate, the patient has been in the bathroom for approximately 20 minutes before being discovered.

On arrival, you find an unconscious woman with agonal respirations. She has a pulse but is hypotensive with an initial blood pressure of 74/36 mmHg. A 12-lead ECG reveals a wide complex tachycardia at a rate of 104 beats per minute.

Assisted ventilations are given via bag-valve mask, an IV is established and a bolus of crystalloid fluid is started. You perform intubation for airway protection without difficulty as the patient has no gag reflex.

The empty pill bottle reads amitriptyline (Elavil). In consultation with medical control, you initiate treatment for tricyclic antidepressant (TCA) overdose with two 50 mEq doses of sodium bicarbonate.

Transport to the ED is complicated by a tonic-clonic seizure followed by cardiac arrest with an underlying rhythm of polymorphic ventricular tachycardia (v tach). Chest compressions are initiated with repeat dosing of sodium bicarbonate, bolus dose adrenaline and defibrillation.

Care is turned over in the ED and ACLS continues. The physician orders administration of 20% intralipid. After an hour of efforts, the patient is asystolic and resuscitation attempts are abandoned.

Case 3: Pediatric Drowning

Dispatch notifies you of a possible drowning at a nearby city pool.

On arrival, you find a frantic mother who states her 6-year old daughter was in the deep end of the pool and was discovered motionless at the bottom after not being seen for nearly two minutes before being pulled out by lifeguards.

Initial assessment reveals a young female with central cyanosis and frothy sputum while lifeguards perform CPR. You take over and perform excellent PALS care and return of spontaneous circulation (ROSC) is obtained. You take her to the nearby community hospital where she eventually succumbs to severe acute respiratory distress syndrome after two days of mechanical ventilation in the pediatric ICU.

Introducing ECMO

In 1930, John H. Gibbon, Jr., MD, conceived of the use of temporary mechanical cardiopulmonary support while witnessing the hemodynamic collapse and death of a female patient who had developed massive pulmonary embolism following cholecystectomy.

As he watched her vital signs deteriorate, he thought, “If only we could remove the blood from her body by bypassing the lungs, and oxygenate it, then return it to her heart, we could almost certainly save her life.”1

The modern successor to Gibbon’s original idea for a heart lung machine is extracorporeal membrane oxygenation (ECMO). ECMO is best seen as a bridge for a reversible or recoverable insult that’s otherwise refractory to conventional management.

ECMO has been used in neonates and adults across a wide range of illness from meconium aspiration to cardiac arrest. Traditionally, the decision-making process and placement of the patient on ECMO has occurred in hospital ICUs or surgical theaters. But as ECMO devices become cheaper, smaller and more portable, this previously scarce resource is becoming more widely available in nontraditional settings, such as the ED and physician-led EMS services in Europe.

There are two types of EMCO: VV (veno-venous) and VA (veno-arterial), which refer to the source and target of blood flow between the two large-bore catheters and the pump. (See Table 1.) Most often, the cannulas, which resemble very long and large bore IVs, are inserted into the femoral vessels.

In VA, or “heart-lung,” ECMO, deoxygenated venous blood from the right atrium is drained via one cannula and passed through a membrane oxygenator, which serves to oxygenate the blood and remove carbon dioxide, after which the now normally arterialized blood is pumped back into the proximal aorta under pressure via a return cannula to complete the circuit. (See Figure 1)

VA ECMO is required for severe cardiac failure and hemodynamic collapse with or without concomitant respiratory failure. By bypassing the entire cardiopulmonary system, the heart is allowed time to recover from an insult while systemic perfusion and oxygenation to the whole body are maintained. This type of ECMO has been used to support patients with refractory cardiac arrest, as in Case 1 or 2.

VV ECMO, a type of “lung bypass,” is used to treat severe respiratory failure such as the drowning in Case 3. With VV ECMO, no cardiac support is provided as oxygenated blood from the ECMO circuit is directed back into the right side of the heart at the level of the right atrium where it then passes through the normal pulmonary flow cycle without the need to undergo gas exchange in the lungs and on into the systemic circulation. This essentially allows the membrane oxygenator to perform the role of the lungs, while the rest of the patient’s normal circulatory function is maintained.

ECMO in OHCA

A potential role for ECMO in the treatment of out-of-hospital cardiac arrest (OHCA) is especially appealing. Closed chest compressions produce inadequate blood flow to sustain vital organs for an extended period of time, in most cases providing as little as 5.5% of mean aortic blood flow.2

As a method of circulating blood during cardiac arrest, ECMO has now been dubbed “extracorporeal life support (ECLS)” or “extracorporeal cardiopulmonary resuscitation (ECPR)” and can achieve physiologic levels of blood flow while the heart is stopped.

Although progress has been made in the survival of OHCA patients in recent years through attention to high-performance CPR and early defibrillation, many victims with hearts “too young to die” still fail to respond to excellent ALS care. ECPR may extend OHCA survival in the future to these victims.

Through early identification of ECMO candidates and the delivery of excellent prehospital care en route, EMS providers are on the front line of this potential lifesaving intervention.

Although evidence for ECPR is limited to case series, published studies suggest a neurologically intact survival benefit for select patients with OHCA when compared to historical controls.

A systematic review provided a pooled survival rate of 22%, including 13% with good neurologic outcome,3 although defining a matching comparison group of patients who underwent continued resuscitation by conventional methods is likely to be biased due to the nonrandomized nature of the comparison. An estimate of 9% survival for comparable non-ECPR patients has been given in
one study.4

A pilot study in Australia reported on 26 patients (11 of whom experienced OHCA) treated with ECPR, mechanical CPR and intra-arrest therapeutic hypothermia, with a 54% survival to hospital discharge with full neurologic recovery.5

There are several ongoing studies in the United States and around the world, including a recent publication from the University of Minnesota, which show promising results. In the study, three EMS agencies routed 18 refractory
v fib/v tach arrest patients over a three-month period with 83% of the patients being placed on ECMO. Remarkably, 50% survived to hospital discharge with good neurological function.6

Although ECPR seems promising, a critical factor for successful outcomes continues to be early, effective CPR, early selection of qualified cases and rapid placement on the pump.

At the University of Utah Medical Center in Salt Lake City, an interdisciplinary team of prehospital providers from the Salt Lake City Fire Department, emergency physicians, critical care specialists, cardiologists and cardiothoracic surgeons developed an ECPR treatment pathway for select OHCA victims that started in April 2015.

Patients are identified by prehospital providers and the ED is alerted to a potential ECPR candidate prior to arrival. Mechanical CPR devices are used to limit interruptions in blood flow during transport.

On arrival, high-quality mechanical CPR is continued in the ED while the patient is prepped for cannulation using sterile technique. Ultrasound guidance is used as two 6-French angiocatheters are inserted into a femoral artery and femoral vein.

Once access is established and appropriate positioning confirmed by ultrasound, a series of dilators are successively inserted allowing insertion of large bore (15-27 French) cannula that can support the high volume, pressure and flow rates of the ECMO system.

Once the cannula is in place, the machine must be primed and the patient anticoagulated to minimize the risk of clots. When a suitable flow rate has been confirmed, CPR is discontinued.

These patients are then taken emergently to the cardiac catheterization lab for angiography and possible percutaneous intervention (PCI) in the same fashion as victims with ST-elevation myocardial infarction (STEMI). Cooling and rewarming, along with weaning from ECMO and neurologic prognostication occur over the next several days.

See Figure 2 for results to date using ED ECMO alerts for OHCA.

Prehospital Considerations

ECLS seems likely to benefit a select group of patients that require temporary heart/lung support until definitive therapy can be achieved. However, the lack of randomized trials and the heterogeneous nature of case series create uncertainty regarding selection criteria. (See Table 2 for the University of Utah ECLS selection criteria.)

Prehospital protocols should employ criteria broad enough to account for the information-poor environment in which EMS operates, where obtaining a detailed history of the patient’s prearrest health status can be challenging while still avoiding the overtriage and transport of clearly ineligible patients.

Furthermore, protocols requiring the transport of OHCA victims for potential ECLS therapy must carefully consider the risks of transporting victims during arrest, including the considerable potential for interruptions in the continuity and quality of chest compressions and safety risks to the providers.

Therefore, mechanical chest compression devices are probably a necessary component of any field-to-hospital ECPR strategy that aims to optimize outcomes.

Additionally, the time to transition from traditional methods of resuscitation to ECPR is also uncertain. Should crews spend five, 10, 15 or 20 minutes attempting field resuscitation before initiating transport? How far and long should crews travel to reach ECPR-capable facilities?

ECPR programs are likely to be found in tertiary care centers at this time, although the portability of ECPR units may enable a hub-and-spoke type system in the future, extending any benefits outside of what are currently rather local catchment areas. The interfacility transport of patients on a pump is already a reality in some areas.

The Future of ECPR

ECPR is a promising area of advanced resuscitation science that’s enjoying a renaissance in the treatment of OHCA and other, often fatal, conditions. Prehospital providers will play a critical part of the continuum of care, just as in STEMI, stroke and trauma.

Although ECPR is an exciting rescue therapy, outcomes will only be optimal in systems that provide high-quality and minimally interrupted chest compressions in all cases, including those that go on to require ECLS.

References

1. Forrester JS. The heart healers: The misfits, mavericks, and rebels who created the greatest medical breakthrough of our lives. St. Martin’s Press: New York, p 76, 2015.

2. Rubertsson S, Grenvik A, Zemgulis V, et al. Systemic perfusion pressure and blood flow before and after administration of epinephrine during experimental cardiopulmonary resuscitation. Crit Care Med. 1995;23(12):1984-1986.

3. Ortega-Deballon I, Hornby L, Shemie SD, et al. Extracorporeal resuscitation for refractory out-of-hospital cardiac arrest in adults: A systematic review of international practices and outcomes. Resuscitation. 2016;101:12-20.

4. Maekawa K, Tanno K, Hase M, et al. Extracorporeal cardiopulmonary resuscitation for patients with out-of-hospital cardiac arrest of cardiac origin: Propensity-matched study and predictor analysis. Crit Care Med. 2013;41(5):1186-1196.

5. Stub D, Bernard S, Pellegrino V, et al. Refractory cardiac arrest treated with mechanical CPR, hypothermia, ECMO and early reperfusion (the CHEER trial). Resuscitation. 2015;86:88-94.

6. Yannopoulos D, Bartos JA, Martin C, et al. Minnesota Resuscitation Consortium’s advanced perfusion and reperfusion cardiac life support strategy for out-of-hospital refractory ventricular fibrillation. J Am Heart Assoc. 2016;5(6):e003732.