Prehospital endotracheal intubation: elemental or detrimental?
Modern out-of-hospital emergency medical services (EMS) systems, as we have come to
recognize them today, were established in the 1960s and 1970s when a cadre of intrepid
physicians ventured into the streets and later published their successful experiences
with lifesaving approaches to managing acute coronary syndromes, trauma care, and
cardiopulmonary arrest on-scene 1]-3].
Although physician-staffed ambulance services had been in place in many venues worldwide
for more than a century, the late 20th century evolution of prehospital care was highlighted by documentation of life-saving
outcomes in those first modern EMS programs and their use of invasive ‘advanced life
support’ (ALS) procedures including prehospital endotracheal intubation (ETI) and
intravascular (i.v.) cannulation for drug administration 1]-3]. These life-saving reports helped to propel the widespread adoption of EMS systems
and the concomitant introduction of specially-trained (non-physician) emergency medical
technicians called ‘paramedics’ 1]-5]. Eventually nursing personnel also ventured into the realm of on-scene emergency
response, particularly in the arena of air medical services.
This evolution in out-of-hospital care was especially remarkable in that the formal
training of these non-physician personnel included those advanced care interventions
such as ETI and i.v. drug administration, interventions traditionally provided in
the in-hospital setting by expert physician specialists 1]-9]. Paramedic skill portfolios ranged from basic spinal immobilization and extremity
splinting to the more advanced skills of electrocardiographic (EKG) interpretation,
defibrillation attempts, ETI, i.v. catheter placement and even pericardiocentesis
and tracheotomies in some communities 10].
The skill of ETI had become the definitive airway control for most critically ill
and injured patients, be they in the operating room, in the early phases of an intensive
care unit (ICU) hospitalization, or in the out-of-hospital setting 2]-9],11]. The presumed presence of significant physiological derangements (e.g., hypoxemia,
hypercarbia, hypoperfusion) in cardiopulmonary arrest, head injury and hemorrhagic
states made ETI an intuitive procedure to perform as soon as feasible in the critically
ill and injured 4],5],9],11].
In addition, there were other clinical care imperatives (e.g., airway protection,
ventilatory control, end-tidal carbon monoxide monitoring, drug administration and
airway suctioning) that drove a strong philosophy that EMS personnel should provide
a definitive airway as soon as possible in the out-of-hospital setting for cardiopulmonary
arrest, severe trauma and other life-threatening emergencies 2]-9],11]. Nevertheless, although these invasive skills were now being provided by paramedics
and nurses, for the most part they were still being delegated under the direction
of accountable physician supervisor experts in out-of-hospital care 12]. Early studies conducted in EMS systems with intensive, expert physician supervision,
comprehensive training programs and on-scene supervision of EMS personnel reported
extremely high rates of successful ETI for both children and adults 2]-8],13]-15].
In most of these studies, success was defined not only by accurate anatomic placement
of the endotracheal tube (ETT), but also by absence of significant complications 3]-7]. Moreover, prehospital ETI was soon correlated with positive outcomes particularly
in the most dire of circumstances 7],8],15].
For the most part, prehospital ETI has usually been performed in cardiopulmonary arrest
cases and in the most severely injured trauma patients with significant physiological
impairment (unconscious) and, generally, no gag reflex 5]. As a result, the procedure can be relatively easy to perform by highly-experienced
care providers. However, using unqualified univariate analysis, ETI is typically performed
in those patients with a high-risk of associated morbidity and mortality and thus
can be simplistically correlated with a poor outcome 16]-20]. Paradoxically, in some selected EMS systems, ETI has actually been correlated positively
with survival, particularly in cases of post-traumatic circulatory arrest 7],8]. In turn, this paradoxical finding infers a likely value of ETI in these worst-case
scenarios 7],8],21].
However, despite intuitive biases and impressive inferential studies indicating the
positive effects of prehospital ETI in certain settings, another evolving body of
studies and experiences has unveiled a detrimental effect of prehospital ETI or, at
least, no significant advantage to providing the procedure 17],20],22]-29]. Most notably, a controlled clinical trial conducted in the 1990s in a pediatric
population generated significant concern about prehospital ETI in that vulnerable
population and subsequent studies in adult head injury patients amplified that concern
25],26]. In the pediatric ETI trial, 830 children (age 12Â years or younger) were studied
over a three-year period 26]. Although not statistically significant, survivors with positive neurological outcomes
were slightly more frequent (92 of 104; 23%) in those managed with bag-valve-mask
(BVM) devices (23%), versus 85 of 416 (20%) receiving ETI 26]. In a subsequent case–control study of severely head-injured patients receiving ETI
that was facilitated by rapid sequence induction (RSI), outcomes were worse for patients
receiving the procedure versus those with similar injuries not receiving it 25]. Also, in deference to other studies indicating a survival advantage to ETI in post-traumatic
circulatory arrest 7],8], the on-going univariate association of ETI with mortality in recent studies, though
predictable, has fueled the debate that ETI should no longer be used in the out-of-hospital
setting 16]-18],23].
Adding to this debate has been the concern over interruptions in well-performed chest
compressions during cardiopulmonary resuscitation (CPR), the key factor in restoring
return of spontaneous circulation and eventual survival following cardiac resuscitation.
It is argued that pausing to intubate could, therefore, be detrimental under these
circumstances 30],31]. In turn, ETI has lost priority standing in many venues.
Along with its lowered prioritization in cardiac arrest management, it has been argued
that, overall, there is no strong evidenced-based support for ETI in terms of survival
advantage. So despite the logical value of performing it in critically ill and injured
patients, many have argued that a true value cannot be demonstrated, particularly
in children 20],23],26],31].
Regardless of this evolving sentiment to avoid prehospital ETI altogether and even
consider it as a deleterious procedure, that ‘evidence-based’ position may indeed
be overly simplistic. In the ensuing discussion, it will be delineated how several
under-recognized confounding variables have a major impact on the performance of this
skill and even related outcomes. These variables include non-intuitive factors, such
as how the EMS providers are deployed or how they have been trained to ventilate 32]-44]. These concepts and how they relate to the success of prehospital ETI for the critically
ill and injured will be addressed in the rest of this article. It is hoped that by
being provided these perspectives, one can better delineate the circumstances in which
ETI should be utilized and those in which it should truly be discouraged.
Factors that affect successful prehospital ETI
Unique training challenges
As previously stated, the original EMS programs that first published success with
paramedic-staffed responses generally reported extremely high rates of success with
prehospital ETI placement 2]-10],15]. Also, as stated, others have not demonstrated similar successes 17],20],25],26],28]. In retrospect, when examining the differences in systems that have or have not had
successes in ETI, it appears that several factors are actually strong determinants
of paramedic and nursing proficiency in the skill of ETI. These determinants include:
1) the quality, orientation and types of experiences in the initial training; 2) the
frequency of performance; and 3) on-scene oversight and supervision of ETI performance
3]-6],12],13],29],32]-36].
Proper training for the prehospital environment clearly needs to be somewhat unique.
In contrast to the typical operating room training experience, the skill of ETI performed
in the emergency care setting, and particularly in the out-of-hospital environment,
is wrought with unique challenges 5]. These challenges range from vomit-flooded airways and ground-level patient positions
to ambient lighting and oro-pharyngeal injuries. With full stomachs, relaxed esophageal
sphincters and inadvertent gastric insufflation from BVM or mouth-to-mouth ventilation,
it is commonplace to approach an airway welled-up with vomit in a circumstance with
often less-than-adequate (or delayed) suctioning. In turn, this often requires the
ability to intubate almost instantly without adjuncts.
Unlike the controlled in-hospital environment, in a sunny, bright outdoors setting,
the ambient light causes glare and pupillary constriction for the rescuers. This circumstance
requires that the practitioners are taught and understand the ‘tricks of the trade’,
such as placing a coat or blanket over one’s head (and the head of the patient) in
order to create a makeshift darkened room akin to an old-time photographer’s camera
hood. In contrast, even in the dark of night, heavy rain or awkward confined spaces
may pose their own barriers to easily visualizing vocal cords. Therefore, many of
the classical techniques used by other practitioners in more traditional settings
would not be as effective in the fast-paced, poorly controlled and mobile prehospital
settings where resources and support are limited (Figure 1).
Figure 1. Endotracheal intubation in the out-of-hospital setting. In the early years of out-of-hospital emergency medical services (EMS) systems, advanced
life support personnel were not only trained in the nuances of how to avoid overzealous
ventilation and properly place an endotracheal tube in very challenging circumstances,
but they were also well-supervised on-scene by expert physicians who themselves were
highly-experienced and exceptionally familiar with those challenges as well as methods
to overcome them (photo by Dr. Paul Pepe).
In turn, a key to successful EMS intubation in the out-of-hospital setting is the
street-wise experience of expert highly-experienced medical trainers and EMS medical
directors who not only understand these principles, but also are themselves facile
in such techniques in the out-of-hospital setting 5],6],12].
Frequent skill usage and system staffing configurations
Even if initial training techniques are expert and well-taught, both in the classroom
and on-scene, frequency of performance is a critical factor. For example, studies
have shown the success rates for ETI can be related to the deployment strategy of
the EMS system 2],3],32],33]. In EMS systems using tiered ambulance deployments in which paramedics (ALS providers)
are spared for the most critical calls, many fewer paramedics are needed on the roster
and the individual experience of each paramedic, including frequency of ETI performance,
can be enhanced dramatically 2],32]. Accordingly, this approach has been correlated with improved success rates in terms
of ETI performance 2],32].
This need to enable frequent experience is critical in EMS. While ETI skills may deteriorate
a little with a hiatus from practice, collective experience 2],32] has demonstrated that most prehospital personnel who have performed ETI a hundred
times or more in the out-of-hospital setting may still be able to perform the technique
quite well despite the hiatus. However, the key issue is getting to that threshold
of experience and this prerequisite goal requires high exposure and frequent performance.
Unfortunately, that level of performance is not always achieved in most EMS systems
today. As an example, for a five-year ‘veteran’ paramedic to have achieved a successful
ETI over 100 times, it would mean successful performance of that procedure at least
20 times a year for five years. Most paramedic units are usually staffed by two paramedics,
so if ETI experience were to be shared with a paramedic partner, the implication is
that this particular team would need to face 40 ETI situations a year on their particular
ambulance and shift. In fact, accounting for sick time, vacation time and other factors,
it typically takes 5 to 6 fulltime equivalent paramedics to staff one of those two
positions and thus 10–12 different paramedics will be needed just for that one ambulance
around the clock. Therefore, that particular response unit would need to face approximately
200 to 250 ETI cases a year for each ALS provider to get 20 opportunities to intubate.
Considering that cardiac arrest, respiratory distress and major trauma cases requiring
ETI constitute only 2–3% of all EMS on-scene emergency responses 32], the ambulance in question would need to experience nearly 10,000 EMS incidents a
year overall. In most EMS system configurations, this level of volume would be a logistical-temporal
impossibility for a single ambulance. Unless alternate deployment strategies were
to be utilized, frequent exposure to ETI cases would be clearly limited.
Indeed, alternative deployments are key. Specifically, in some communities, paramedics
(or other types of ALS personnel, such as doctors or nurses) are spared from the majority
of EMS responses. Instead of ALS providers, basic emergency medical technicians (EMTs)
trained to do the non-invasive procedures such as spinal immobilization and splinting
are used for most of the responses 2],3],32],33]. Under such circumstances, overall staffing could, therefore, involve a much smaller
cadre of paramedics. This would permit more frequent exposure to critical illness
and injury for the individual paramedics (ALS providers). The same concept would apply
to nurses or apprentice physicians who staff ambulances and air medical units, particularly
in some European countries 2],32],33]. The fact that air medical units are typically triaged only to the most critical
cases means that those ALS providers staffing the helicopters are part of a deployment
strategy that enhances skill use. Using this so-called ‘tiered’ approach, individual
paramedics (ALS personnel), nurses or doctors each get more chances to perform an
ETI.
While there is great variation from one city to another, on average a city with a
population of 1 million in the U.S. (for example) might be expected to have 100,000
EMS response incidents annually 45]. This volume of cases might predict two or three thousand potential circumstances
for ETI each year. To optimize individual paramedic exposure, it would be best to
limit the number of paramedic (ALS) ambulances to a maximum of 10 ambulances (250
ETI exposures per ambulance per year?×?10 ambulances covers 2 to 3 thousand cases).
In this circumstance, a cadre of 100 to 120 paramedics might be required for the 10
paramedic-staffed units.
In a contrast, in a system experiencing 100,000 EMS responses a year and using all-paramedic
staffing, 35 to 40 ambulances would typically be required minimally and thus 400 to
500 paramedics would be needed 32],33]. This all-ALS provider approach decreases individual exposure to ETI attempts at
least 4 to 5-fold. To make matters worse, in some cities, additional paramedics are
also placed on first-responder vehicles such as responding fire engines 26],28]. In turn, this further compounds the infrequency of exposure for individuals. Moreover,
some ambulances are situated in lower call volume areas than others, creating even
less exposure to ETI opportunities 36].
Fortunately, the great majority (85 to 95%) of EMS incidents do not require an ALS
provider (e.?g., authorized physician, nurse, paramedic) and can be managed by basic
EMTs 32]. In turn, using well-established and well-documented dispatch triage protocols, paramedics
(ALS providers) can be spared and basic EMTs (basic life support [BLS] providers)
are deployed directly to manage the cases 32]. In other situations, after an initial paramedic (ALS) response is made, the basic
EMT ambulance can be called in to transport the less critical patients thus freeing
up paramedics (ALS providers) for the more critical cases.
Not only does this type of system configuration permit the need for fewer ALS personnel,
but it also improves response intervals because paramedics are not tied up transporting
patients and are thus more available. Ironically, by having fewer paramedics, paramedic
response can be improved 32].
Beyond on-scene procedures and moving the patient from the scene, the time to transport,
provide hospital transition, create a record and then return to the primary response
territory is the greatest deterrent to the availability of ambulance crews and thus
a factor in compromised response times. Not surprisingly then, the original EMS systems
reporting excellent paramedic track records with ETI were largely this type of tiered
response system with staffing configurations that utilized basic EMTs for the majority
of responses and spared the much smaller cadre of relatively busy paramedics for the
more critical calls, therefore creating more opportunities for ETI skills usage 2],3],32],44].
Furthermore, the paramedics in these systems rapidly achieved experience seeing many
dozens of cases per year and they eventually became reliably facile. In turn, as they
became exceptionally facile, they deferred ETI attempts to new trainees. As a result,
in these sophisticated EMS systems, the lesser-experienced medics rapidly developed
their own skills even faster. Veterans also maintained their skills by teaching, supervising
and getting to attempt and perform the more difficult intubations when the more novice
personnel could not place the tube.
Unfortunately, today in the U.S. and other countries, the majority of EMS systems
actually utilize all-paramedic (all-ALS) staffing on their ambulances. In addition,
many first-responder crews often supplement ambulance response with additional paramedics
(ALS providers) staffing the first response vehicles as well 26],28],33]. Therefore, it is no surprise that paramedics may not perform ETI as well as their
forerunners 40Â years ago.
Despite the described impact of using an all-paramedic system, one remedy might be
to create a de facto ‘tier’ in those all-ALS systems by creating a team of supervisors,
field training officers, or expert physician responders who routinely respond to critical
calls. Depending upon the geography, vertical (high-rise) challenges, and traffic,
it would be wise to create a small number of senior personnel who can respond across
a designated territory (or even into a fellow senior officer’s territory for back-up)
as a modified approach to ensure high level skills performance. Just as there may
be 10 or so battalion fire chiefs in a city of a million residents spread out over
a large geographical territory, staffing and responding a similar number of senior
EMS personnel into high level cases could be another alternative and one that is now
being adopted by many progressive EMS systems.
Expert on-scene supervision
Finally, even with appropriate, tailored initial training and tiered response systems
with a high frequency of performance for individual paramedics, if the on-scene medics
in training are not properly supervised, they may still develop bad habits in a vacuum.
It is critical to reinforce what constitutes a proper technique (e.?g., sniffing position
in those at low risk of neck injury) and to provide renewed coaching in the actual
patient care setting, especially in terms of confirmation of tube placement and proper
ventilatory techniques. In most EMS systems that provide high rates of ETI success,
in-field medical directors, highly-experienced EMS supervisors and well-coached veteran
paramedics are the norm 2],6],12].
Why successful ETI attempts can even be detrimental
Detrimental effects of ventilatory techniques following intubation
Even if paramedics or other prehospital care providers are expertly trained, highly-skilled,
highly-experienced and highly-supervised performers of intubation for both adults
and children, their ventilatory techniques may still adversely affect outcome 25],37]-39]. The types of patients most likely to need ETI are those with cardiac arrest, chronic
lung disease and severe post-traumatic shock conditions. Yet these patients are also
the most vulnerable to the detrimental cardiovascular effects of the positive pressure
breaths that are being delivered through the ETT 39].
Despite the basic physiological principle that ventilation should match perfusion
(blood flow), over the years, in many venues, EMS personnel have been trained traditionally
to aggressively ventilate patients, usually with the ill-advised rationale that such
an approach was the way to ensure oxygenation and offset metabolic acidosis 37],38]. Even with more judicious training, however, emergency workers can still have the
tendency to over-zealously ventilate such patients in the heat of the emergency 38]. Ironically, while such patients in deep shock actually require infrequent breaths
and a lesser minute ventilation, once the ETT is placed, they may now receive excessive
levels of assisted breathing, not only because of some unsound rote training, but
also because of adrenaline-modulated behaviors 38].
Accordingly, it is now speculated that low national survival rates for out-of-hospital
cardiac arrest and the negative outcomes of several prehospital clinical trials may
have been, in part, the result of uncontrolled ventilatory rates using positive pressure
breaths 39]. For example, in the study of severe traumatic brain injury (TBI) in which RSI-facilitated
ETI was associated with worse outcomes, a key correlation with mortality was the finding
“hyperventilationâ€, defined as an arterial PCO2??24 mmHg 25]. While one might suspect that these negative outcomes may, therefore, be caused by
effects of respiratory alkalosis, such as myocardial depression, cerebral vasoconstriction
and a left shift in the hemoglobin dissociation curve, it is most likely that the
low arterial PCO2 is simply a surrogate variable for overzealous positive pressure ventilation 37]-39].
As Aufderheide and colleagues have shown, despite aggressive, targeted re-training
on respiratory rates and delivery techniques, paramedics still overzealously ventilate
and prolong the duration of positive pressure breaths in the adrenaline-charged environment
of a critical emergency 38]. It is likely that this scenario is exaggerated in children, considering that paramedics
and other emergency care providers are trained to think that pediatric arrests are
mostly the result of hypoxemia and that proscribed respiratory rates are generally
higher than those proscribed for adults 19],26],39]. Also, emotions run even higher in childhood critical emergencies, theoretically
compounding any predisposition to overzealously ventilate. Therefore, clinical trials
that indicated worse outcomes with ETI may have been confounded by unrecognized detrimental
ventilatory techniques 37]-39].
So, paradoxically, in systems where many paramedics are deployed to all prehospital emergency cases with the rationale of improving response times for ALS
procedures (and thus improved survival chances), worse outcomes might actually be
expected, especially with successful ETI. In the EMS system in which the clinical
trial of pediatric intubation was conducted 26], more than 2000 paramedics were trained to perform what resulted in being less than
150 annual pediatric intubations across the system during the study period.
Experience-wise, this type of system configuration issue makes it difficult for the
individual paramedic to get much exposure, even to adult intubations. Clearly, pediatric
intubation situations would be uncommon, or even unlikely over his or her entire career.
This is a set-up for misplaced tubes or significantly delayed ETI. It also means too
frequent and too lengthy pauses in chest compressions if the crews are not facile
at placing the tube. Overall, this scenario provides a clear set-up for under-skilled
attempts at ETI altogether 2],32]. Coupled with high anxiety when dealing with kids, an EMS system that follows typical
protocols for ventilation and/or does not control for overzealous ventilation, may
likely experience even poorer outcomes.
Under these circumstances, one can make a strong argument against using ETI or attempting
ETI, especially in children and other vulnerable groups such as spontaneously-breathing
head injured patients. Nevertheless, it must be kept in mind that there are communities
that can safely enjoy high success rates for ETI and associated good outcomes for
patients, even using certain RSI techniques 3],7],8],21],46]. But, again, these EMS systems are typified by street-wise training, tiered paramedic
ambulance response systems, and patient care protocols involving controlled ventilatory
techniques for critical cases. Places like Houston and Seattle in the 1980s were delivering
only one positive pressure breath every ten seconds to their patients with circulatory
arrest and outcomes were exceptional when compared to other sites 3],7],8],21].
Most importantly, these sites also involved intensive on-scene expert medical oversight
2],12],46]. Therefore, ETI should not be discouraged in such appropriate settings. On the other
hand, as other researchers have implied, ETI and/or RSI should be discouraged in those
EMS systems that are unable to adapt to those appropriate characteristics that facilitate
ETI and its proper use.