Cardiac & Resuscitation, Patient Care, Trauma

How to Protect EMS Patients through Better Research & Understanding

Issue 8 and Volume 37.

For the past four decades, the evolving medical discipline of EMS has had its demonstrated successes in many communities worldwide.1–7 Not only has there been a documented lifesaving effect, but many EMS therapies also have been used to diminish morbidity and discomfort for our patients through earlier intervention.8–10

At the same time, in our well-intended attempts to provide prompt and aggressive care for our patients, we have also applied practices that, inadvertently, may have been detrimental for our patients or simply not effective.11–32 In some cases, many interventions that could clearly be lifesaving have been used too zealously or have been provided either too early, or simply too late, leading to a negative effect.13,14,16–18,26

In other cases, we haven’t used the procedure properly. As a result, we were unaware of the resulting ineffectiveness and subsequent loss of a potential lifesaving outcome.12,16,33–39

In many circumstances, based on available data, these detrimental practices were considered standards of care and accepted by the majority of practitioners.17,22,27–31 In other cases, it was a poor understanding of how system configuration can lead to a less-than-optimal result.12,29,30

Fortunately, the ever-evolving EMS focus on “research” and the surrounding emphasis on scientific investigation in the prehospital setting has led to a better understanding of what EMS can and should do for our patients.32,40 The results have saved thousands of lives, raised the stature of the EMS practitioner in the house of medicine and increased the value of EMS in the public eye.31,32, 40–42

Most importantly, in many cases, the research effort itself saved lives. Even when the scientific investigations revealed that seemingly logical practices were actually harmful, the study process itself has generally led to improved survival chances over the pre-study levels—for both study and control groups.31,32

This article will provide historical (and even some current) examples of detrimental EMS practices and how we’ve identified and attempted to retool those practices. It will also attempt to provide future considerations for EMS practices while also providing caveats and cautions regarding the limitations of “gold standard” research and how to temper “evidenced-based medicine” with an ever-watchful eye.

Revisiting the ABCs
Since the origins of EMS practice, airway, breathing and circulation (the so-called “ABCs” of resuscitation) have been heralded as the basics of emergency care. For practitioners, both in the in- and out-of-hospital settings, endotracheal intubation (ETI) is still considered the definitive airway.43 It’s provided not only to better ensure adequate oxygenation and ventilation (carbon dioxide elimination), but also to protect the airway from rapid edema formation (e.g., in burns and inhalation injury) or aspiration of blood or gastric contents.43

In that sense, ETI has traditionally been part of the clinical portfolio for prehospital care personnel.1,2,7,12,43,44 Although it should correlate with a worse outcome (the sickest or most injured patients are the usual recipients), some studies have correlated ETI with good outcomes.7,44–46

However, research initiatives over the past two decades have suggested a detrimental effect or, at the least, no significant advantage, to prehospital ETI, including a controlled clinical trial in a pediatric population.13,15,47–51 Growing sentiment, including standards for cardiac resuscitation, have de-emphasized EMS use of ETI.34,47,52

Nevertheless, the problem may not be the tube, but the way in which it’s used, including prehospital practitioners being facile at placement and their ensuing techniques of providing ventilatory support once ETI has been performed.12–14,16,29,30,48,53–55

The earliest EMS ALS systems were staffed by a core team of skilled physicians or a limited cadre of paramedics whose response deployments were triaged and focused primarily on the relatively smaller group of critically ill patients.1,2,12,29,30 In turn, skill use was frequent and, accordingly, ETI was routinely successful and performed rapidly.2,12,29,30

In the U.S. and many other locales, however, a popular philosophy evolved in the 1970s: More paramedics in a system would provide patients a closer proximity to “advanced” prehospital care. Unfortunately, this deployment strategy also created a dilution of skill use for individual paramedics.29 With a larger pool of advanced providers who must compete for the opportunity to attempt ETI among the relatively small number of patients who require the procedure, skills experience is much less frequent. This dynamic predictably has been associated with less facile, failed intubation attempts in the majority of EMS systems.12,29,50

Nevertheless, even when prehospital practitioner performance of ETI is facile and they can rapidly achieve successful tube placement, the procedure may actually lead to more harm if the practitioners’ ventilatory practices are improper.12–14,16

In many venues, prehospital providers have been demonstrated to overzealously ventilate the patient once an ETI has been placed.13,37 Even relatively controlled ventilation (tidal volume and rate) with positive-pressure breaths can have a profound deleterious effect, especially in the bleeding patient who has experienced significant IV volume loss.13,14,16,37,48,54,55 Even if provided infrequently (i.e., five or six per minute), positive-pressure breaths can maintain adequate oxygenation and ventilation in such fragile patients—and even be correlated with improved outcomes.14,16,44,56 However, even so-called “normal” rates of ventilation can be relatively harmful and are likely to be lethal in extremis conditions.7,13,14,16,54–56

Normal breathing is generated by the diaphragm and other respiratory muscles. The lungs are “pulled open” by creation of a relative vacuum in the thorax. This “negative” intra-thoracic pressure sucks air into the chest and enhances venous return to the heart by also drawing more blood into the chest.16,57 In contrast, providing breaths delivers positive pressure to “push” the lungs open. This creates higher than normal intrathoracic pressure, inhibiting venous blood return back into the heart.12,14,16,54,57

In most normovolemic adults with normal blood pressure and lung function, this intermittent positive pressure, if not given too frequently, is tolerated without observable clinical effect. However, if the patient has a significant degree of relative hypovolemia (e.g., severe hemorrhage, dehydration and sepsis) or obstructive lung disease impairing the outflow of air, the effect of positive pressure can be dramatic and likely detrimental to outcome if breaths are delivered frequently (e.g., greater than five to six per minute).12,14,16,54,57

Also, in general terms, in low-flow states, “ventilation should match perfusion” (impaired blood flow should be matched with constrained ventilation and CPR is certainly a very low-flow state until normal blood pressure is restored.

Therefore, although ETI may often be an appropriate intervention in the prehospital setting, it also can be detrimental if the system isn’t designed to enhance skills for the practitioners and if the EMS providers aren’t controlling the ventilations properly.12,16.29,30,53

For similar reasons, more current consensus guidelines have supported a renewed focus on minimally interrupted chest compressions and de-emphasized rescuer ventilation altogether in sudden-onset (non-traumatic) cardiac arrest cases.34,35,52,57 In addition to inhibition of circulation by
positive-pressure ventilation, there’s another concept of concern.

The key determinant for return of spontaneous circulation (ROSC) is adequate coronary artery perfusion pressure (CPP) without interruption.16,17,34,35,38,39,57 Current studies show that CPP rapidly falls off when hands come off the chest, and it takes many seconds to build up the pressure head again.35,36
Accordingly, if one stops for too long an interval (and too often) to provide rescue breaths, pulse assessments or a shock, the average CPP calculated over a minute (aka, the “minute CPP”) is dramatically diminished and, thus, the resuscitation efforts generally become incompatible with ROSC.35,36,57,58

On the other hand, if compressions are maintained without interruption, a reasonable minute CPP may be maintained, increasing the chances of ROSC and survival with intact neurological status.17,35,36,57,58
In short, the well intentioned and intuitive concept of providing lots of oxygen to a patient who isn’t breathing normally may be more harmful than helpful.16,17,35,37,57,58

At the same time, following our latest mantras with chest compressions, such as “push hard, push fast” and “don’t interrupt,” may also be detrimental if compressions are applied much too fast or if new promising therapies are discovered that require deliberate and controlled CPR interruptions (e.g., stutter re-perfusion concepts) to diminish reperfusion injury.59

Revisiting Trauma Resuscitation
The problems with ETI are more pronounced with certain subpopulations of patients, including those with obstructive lung disease, such as chronic bronchitis, emphysema and asthma, and, as noted above, relative hypovolemia.14,16,52,54,55 Not only does the positive-pressure ventilation have a detrimental effect in terms of inhibiting venous return and cardiac preload, but the relatively slower expulsion of the delivered tidal volume in patients with obstructive lung disease also leads to residual positive-pressure retention at end expiration (i.e., throughout the entire respiratory cycle).52,54,55

The resulting intrinsic positive end-expiratory pressure (PEEP) can impair successful resuscitation, particularly when ROSC would have occurred had ventilations been markedly reduced in frequency.55 Likewise, as previously noted, the effect of even “normal” respiratory rates can be detrimental to those with severe intravascular hypovolemia, such as a hemorrhaging trauma patient.14,16,48

EMS providers have also faced problems with well-intended and intuitively logical attempts to return systemic blood pressure (SBP) to “normal levels” in trauma patients.11,20,22,60–62 Following the publication of improvements in outcomes using experimental hemorrhage models in the 1950s and ’60s, it became standard of care to reverse systemic hypotension, usually through the use of IV isotonic fluid resuscitation and by starting that fluid infusion in the prehospital setting.60,62

Another attractive modality to raise blood pressure in hypotensive injury patients was the use of the so-called military (or medical) anti-shock trousers (MAST), also known as the pneumatic anti-shock garment (PASG)—a device that was adopted from military aviation experience with G-suits.20,22

The PASG resembled a large blood-pressure cuff that surrounded both legs and the abdomen. It was definitively shown to raise SBP and was also touted to provide a tamponade effect to underlying bleeding and stabilization of possible pelvic fractures.20,22 By the 1980s, considering its use as a non-invasive blood-pressure elevating device that basic EMTs could employ, the PASG became required by state law in two-thirds of the U.S. as required EMS equipment.20,22

However, no clinical trials had ever proven its effectiveness in saving lives. Empirically, it made sense to use the PASG, but subsequent prospective controlled trials not only disproved the ability of the PASG to save lives, but also suggested the devices were actually detrimental.

The well-designed studies showed the elevation of SBP, but there was a pronounced trend toward worse outcomes—particularly in patients with distinct vascular injuries.20,22 This later led to a revisiting of the use of IV fluids to raise SBP in trauma patients.23,27,28

The first controlled trials of preoperative administration of isotonic IV fluids for both hypotensive penetrating and blunt trauma patients (with presumed internal hemorrhage) also showed no distinct advantage and a likely detrimental effect, particularly in those with penetrating injuries.20,27,28,62

In retrospect, the original experimental studies that showed a positive effect of fluid infusion and SBP elevation were conducted in models that had a “fixed” hemorrhage.23,60–62 In other words, the severe hemorrhage had been induced but was then controlled (stopped) before the fluid infusion.

In contrast, it’s presumed that internal hemorrhage in trauma patients isn’t yet controlled when fluid infusions are provided in the prehospital setting.20,27,28,62 Based on experimental models of “uncontrolled hemorrhage,” it’s now believed that the provision of IV fluids (or SBP elevation with the PASG) leads to hydraulic worsening of the bleeding, dislodging of early soft blood clots that haven’t yet become fibrinous and perhaps a dilution of residual clotting factors with early fluid administration.23–26 The data suggest that delayed, slower infusions are more optimal, even in head-injured models.26

Well Intentioned but often Disadvantageous
Therefore, based on the most current data, many well-intended interventions that were originally thought to be lifesaving in given situations are actually disadvantageous under those specified conditions.20,22,23,24,27,63 These interventions were the standard of care in EMS and were also zealously pursued as critical therapeutic modalities.20,22,61,62

Sometimes the revelation that the interventions could be harmful came through a better understanding of the physiology. In some cases, however, it was also the circumstances or the timing of the intervention that needed closer scrutiny.26,62,63

In essence, the story is more complicated than a simplified question such as, “Are fluid infusions, the PASG, ventilations or ETI ‘elemental’ or ‘detrimental?’” They’re all double-edged swords that can be tremendously advantageous or even outright lifesaving if used properly or at the right time.
At the same time, certain beneficial interventions can be deleterious if used improperly or in the wrong settings. In addition, their value may not be appreciated if other confounding variables obscure or mask their effectiveness.16,43

For example, some “gold standard” clinical trials haven’t demonstrated a clear lifesaving effect of interventions that work well in experimental settings.18,19,22,32,65,66

At first glance, these studies may be seen as “definitive trials” and the conclusion drawn that the expense of the device or therapeutic modality isn’t indicated, especially after all the time, money and effort that went into their implementation and eventual publication of the studies.19,65,66 However, it has now been suggested that many so-called definitive trials may have been obscured by unrecognized confounding variables.19,32,67

A good example is the original prehospital trial of “high-dose” epinephrine (HDE) conducted in the prehospital setting.19 HDE worked dramatically well in the laboratory. But no overall clear advantage was found in controlled clinical trials. In retrospect, there was no control for ventilation parameters as part of the protocol.16,37
Also, the protocol didn’t follow the timing of drug administration set in the lab because the HDE was given before defibrillation in the laboratory vs. after defibrillation in the trial.18,19

Subsequently, some of the participating EMS agencies were shown to have previously unrecognized excessive ventilation.16,37 Some now speculate that this confounding variable may have overpowered and masked the effect of the HDE.16

Similar concerns have been raised by some when considering the recent trials of the impedance threshold device (ITD) in cardiac arrest.66,67 The ITD wasn’t demonstrated to be effective in one seemingly well-designed, multi-center trial, whereas a parallel study demonstrated a markedly improved outcome when the ITD was used in conjunction with another device.66,67

It’s unclear whether the ITD required use of the other device (e.g., the active compression-decompression pump) to be effective, or whether it simply was a neutral accompanying modality to the pump’s effectiveness.66–68 As alluded to before, however, other unrecognized variables may have obscured the true effect of the ITD and its actual effectiveness including control of the rate and quality of CPR performed.58,64,65,67,68 Again, timing, proper use and other clinical and system factors need to be considered when judging the value of the devices.32,64,65,68

Regardless of the clinical trials’ results, and even the negative outcomes in some studies, it’s clear that the implementation of clinical trials lead to a lifesaving effect for both the tested intervention and control groups—just by implementing the process of scientific investigation.32,40,70 Among numerous factors, prior to the study, experts come together and form an opinion on best practices and provide each other with practical suggestions forming a better protocol for both control and study groups. Then the associated (on-going) educational and quality assurance feedback loops enhance both the practitioners’ renewed focus and a continually improved approach to care delivery for all patients involved. In the end, survival rates go up just by doing the study.32,40,70

The history of many well-intended EMS interventions has provided us with insights about adopting what often seems logical and intuitive at first blush. As we continue to introduce and consider novel interventions, it ‘ paramount that we first do no harm. Part of our mission is to continually “re-search,” rethink, retrain, re-review and reconsider what we’ve been doing.71 Thanks to such a responsible approach, we have already seen dramatic documented improvements in life-saving in many EMS systems and, more importantly, profound improvements in our overall mission of public service. JEMS

Paul E. Pepe, MD, MPH, is professor of surgery, internal medicine, pediatrics, public health and chair of emergency medicine at the University of Texas Southwestern Medical Center and the Parkland Health and Hospital System, as well as the City of Dallas director of Medical Emergency Services for Public Safety, Public Health and Homeland Security.

Sandra M. Schneider, MD, is professor and chair-emeritus of emergency medicine for the University of Rochester in Rochester, N.Y., and immediate past-president of the American College of Emergency Physicians.

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