Download CAUSE: Cardiac arrest ultra-sound exam

Resuscitation (2008) 76, 198—206
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CLINICAL PAPER
C.A.U.S.E.: Cardiac arrest ultra-sound exam—–
A better approach to managing patients in primary
non-arrhythmogenic cardiac arrest!
Caleb Hernandez a, Klaus Shuler a, Hashibul Hannan a, Chionesu Sonyika a,
Antonios Likourezos a,∗, John Marshall a,b
a
b
Department of Emergency Medicine, Maimonides Medical Center, 4802 Tenth Avenue, Brooklyn, NY 11219, United States
Mount Sinai School of Medicine, One Gustave L. Levy Place, New York, NY 10029, United States
Received 23 February 2007; received in revised form 21 June 2007; accepted 25 June 2007
KEYWORDS
Advanced life support
(ALS);
Cardiac arrest;
Cardiac tamponade;
Hypovolemia;
Pulmonary embolism;
Pulseless electrical
activity (PEA);
Tension
pneumothorax;
Ultrasound
Summary Cardiac arrest is a condition frequently encountered by physicians in the hospital
setting including the Emergency Department, Intensive Care Unit and medical/surgical wards.
This paper reviews the current literature involving the use of ultrasound in resuscitation and
proposes an algorithmic approach for the use of ultrasound during cardiac arrest. At present
there is the need for a means of differentiating between various causes of cardiac arrest, which
are not a direct result of a primary ventricular arrhythmia. Identifying the cause of pulseless
electrical activity or asystole is important as the underlying cause is what guides management
in such cases. This approach, incorporating ultrasound to manage cardiac arrest aids in the
diagnosis of the most common and easily reversible causes of cardiac arrest not caused by
primary ventricular arrhythmia, namely; severe hypovolemia, tension pneumothorax, cardiac
tamponade, and massive pulmonary embolus. These four conditions are addressed in this paper
using four accepted emergency ultrasound applications to be performed during resuscitation of
a cardiac arrest patient with the aim of determining the underlying cause of a cardiac arrest.
Identifying the underlying cause of cardiac arrest represents the one of the greatest challenges
of managing patients with asystole or PEA and accurate determination has the potential to
improve management by guiding therapeutic decisions.
We include several clinical images demonstrating examples of cardiac tamponade, massive
pulmonary embolus, and severe hypovolemia secondary to abdominal aortic aneurysm.
In conclusion, this protocol has the potential to reduce the time required to determine the
etiology of a cardiac arrest and thus decrease the time between arrest and appropriate therapy.
© 2007 Elsevier Ireland Ltd. All rights reserved.
! A Spanish translated version of the summary of this article appears as Appendix in the final online version at
10.1016/j.resuscitation.2007.06.033.
∗ Corresponding author. Tel.: +1 718 283 6896; fax: +1 718 635 7274.
E-mail address: [email protected] (A. Likourezos).
0300-9572/$ — see front matter © 2007 Elsevier Ireland Ltd. All rights reserved.
doi:10.1016/j.resuscitation.2007.06.033
C.A.U.S.E. in primary non-arrhythmogenic cardiac arrest
Introduction
Cardiac arrest is a condition frequently encountered by
physicians in the hospital setting including the Emergency Department, Intensive Care Unit and medical/surgical
wards. Since the implementation of preventative health
policy and ACLS, deaths from ventricular fibrillation and
ventricular tachycardia have decreased significantly, however the prevalence of pulseless electrical activity (PEA) and
asystole have increased.1 Unlike ventricular fibrillation and
pulseless ventricular tachycardia where the pattern/rhythm
of electrical activity is the focus of treatment rather than
the underlying cause, PEA and asystole are corrected by
addressing the underlying cause.2 The importance of identifying a reversible underlying cause in these forms of cardiac
arrest is of such importance that almost half of the ACLS
for experienced practitioners manual is dedicated to this
topic and its practical application.2 Hughes et al. provided
a list of the etiologies of PEA in the order of frequency and
ease of reversal.3 He lists the top five conditions as hypoxia,
hypovolemia, tension pneumothorax, pericardial tamponade, and pulmonary emboli. These conditions are potentially
reversible, but the treatment is often invasive and may be
deadly if mistakenly applied to the wrong etiology.4 For this
reason accurate and timely diagnosis of the underlying cause
is crucial. Currently the AHA recommends using physical
signs and the patient’s history to guide the management of
PEA and asystole.2 However, physical examination can be
unreliable and many physicians may withhold therapy for a
fear of causing harm if uncertain of the cause of cardiac
arrest.4
Ultrasound is a diagnostic tool with increasing applications and use in emergency situations.5 Levitt et al. have
observed that emergency physicians had increased confidence in clinical decision-making when presented with
diagnostic ultrasonographic images of medical conditions
versus clinical impression and physical examination alone.6
Ultrasound examination has the potential to bring increased
diagnostic clarity to clinical decision-making and aid in the
identification of a reversible cause for PEA or asystole.
Recently many studies and case reports have examined the
application of emergency ultrasound to cardiac arrest.6—15
Niendorff et al. observed that it was feasible for trained
emergency sonographers to obtain diagnostic images during
resuscitation of cardiac arrest patients and that obtaining
sonographic images did not interfere with the resuscitation process.15 Other investigators have also made this
observation.7,14,15 Many of these investigators have studied
the application of ultrasound to one, or a few, causes of PEA
and cardiac arrest; however a protocol that addresses the
most common cardiac and pulmonary causes of PEA has not
been developed.6—15
There remains a need for an organized and structured
approach to non-arrhythmogenic cardiac arrest with sufficient diagnostic accuracy to justify appropriate aggressive
life-saving therapy. An effective protocol for emergency
ultrasound evaluation in cardiac arrest patients would
address the most likely and reversible causes; severe hypovolemia, tension pneumothorax, cardiac tamponade, and
pulmonary embolus. There is a body of literature supporting the use of ultrasound as an accurate diagnostic aid in
the four above-mentioned conditions. The purpose of this
199
paper is twofold; first, to review the literature involving
ultrasound and resuscitative conditions. Second, to propose
a goal oriented approach to the cardiac arrest patient that
incorporates the use of ultrasound to address the most common reversible causes of non-arrhythmia cardiac arrest. The
name of this new test is C.A.U.S.E., an acronym for cardiac
arrest ultra sound examination, and whose name has the
added benefit of reminding the practitioner that the primary goal of their effort in PEA or asystole should be to
identify and address the underlying cause. The protocol also
serves to organize a process that can at times be chaotic
and disorganized. Past studies have shown that increased
organization during resuscitation increases the likelihood
of survival.16,17 A similar organizational protocol has been
used for the treatment of ventricular arrhythmias using
three-lead electrocardiogram as a diagnostic tool with great
success.1,2
Sonographic applications for cardiac arrest
Ultrasound has been used as an effective diagnostic tool during cardiac arrest and has identified causes of PEA. These
include cardiac tamponade, severe hypovolemia, pulmonary
embolus, tension pneumothorax, and true asystole.
Cardiac tamponade
The use of ultrasound is widely accepted in the diagnosis of
cardiac tamponade in the form of identifying a pericardial
effusion during the FAST screening examination for trauma.
Cardiac tamponade is more accurately identified by visualizing pericardial effusion and right chamber collapse with
either of the parasternal views or the subxyphoid/costal
view.14,15,18
Ultrasound is also highly accurate in diagnosing this
condition. Mandavia et al., demonstrated that emergency
physicians could diagnose the presence of pericardial effusion accurately when compared to a cardiologist with an
overall sensitivity of 96%, specificity of 98% and overall accuracy of 97.5%.18
Currently the AHA recommends identifying neck vein
distention and absence of pulse with CPR as diagnostic criteria for tamponade. However these features are shared
by tension pneumothorax as well. During cardiac arrest situations it could be difficult to differentiate between the
two conditions, as unequal breath sounds are difficult to
appreciate in noisy or chaotic environments (i.e. emergency departments). Regularly using ultrasound to identify
cardiac tamponade would add a greater level of accuracy
to the determination of this cause for cardiac arrest and
may prevent the use of inappropriate therapy. Therapy
for cardiac tamponade is invasive (i.e. pericardiocentesis
or open thoracotomy). Having a test that is available in
real time with greater accuracy than a physical examination would be useful to physicians managing a patient in
cardiac arrest and reduce concerns of making a diagnostic and therapeutic error. Physical examination and history
remain important factors in medical decision-making, and
their importance should not be neglected. There are caveats
that should always be remembered when interpreting sonographic findings. For example patients in chronic renal
200
Figure 1 Subxyphoid emergency ultrasound image of a
patient with cardiac tamponade as a cause of PEA. Notice the
pericardial effusion and right atrial collapse.
C. Hernandez et al.
sound was used to diagnose hypotension as the cause of
PEA.9 He describes a patient with the characteristic signs
of hypovolemia on cardiac sonogram and was found to
have a ruptured abdominal aortic aneurysm. The use of
ultrasound in this case affected the patient’s care significantly.
Ultrasound of the inferior vena cava (IVC) can be a valuable adjunct to cardiac imaging in the setting of cardiac
arrest. IVC is measured in the sub-xiphiod space in the long
axis, using the liver as an acoustic window. There have been
some studies that have linked the IVC diameter to volume
status and right ventricular pressure,20,21 demonstrating a
sensitivity and specificity of 88 and 81%, respectively,20 and
a high degree of correlation between blood loss and IVC
diameter at r = 0.83.21 However, most of these studies were
performed on patients with spontaneous respiration which
is not likely to be the case in the setting of cardiac arrest
where positive pressure ventilation is routine. The authors
recommend that in the setting of cardiac arrest a flat (IVC
diameter <5 mm) or collapsed IVC represents hypovolemia
and should prompt aggressive fluid resuscitation. On the
other hand, a dilated IVC (IVC diameter >20 mm) in the setting of a cardiac arrest would be more consistent with pump
failure from congestive heart failure, cardiac tamponade
or pulmonary embolism or may be as a result of cardiac
arrest itself. In any case echocardiographic findings should
be correlated with clinical impression for a more educated
resuscitative plan.
Ultrasound to diagnose hypovolemia in the presence of
PEA adds increased diagnostic clarity, speed and accuracy,
and may decrease the use of unnecessary, time-wasting
and potentially harmful empiric therapy (i.e. thrombolytics for suspected massive PE in the setting of true aortic
aneurysm rupture). A characteristic emergency ultrasound
image of the heart in hypovolemia may be viewed bellow (Figure 2). There is also an ultrasound of image
demonstrating the cause of this hypovolemia in the same
patient as Picture 2, a ruptured abdominal aortic aneurysm
(Figure 3).
failure may have long standing pericardial effusions that
may be unrelated to the cause of cardiac arrest (i.e.
hyperkalemia), or patients who have trauma to the chest
may have minimal pericardial effusion but demonstrate
clinical signs of tamponade. The characteristic emergency
ultrasound image of cardiac tamponade is depicted above
(Figure 1).
Hypovolemia
Hypovolemia is suggested by flattened right and left ventricles in the subxyphoid or long axis views of the heart,9,15
or by measuring left ventricular end-diastolic area from the
short axis parasternal view.19 Brown et al. reviewed literature on the use of sonography to monitor hemodynamic
status.19 He observed that left ventricular end-diastolic volume correlated extremely well with blood loss (r = 0.96)
and could significantly detect small changes in intravascular volume by as little as 1.75 mL/kg in human subjects
and 5 mL/kg in pigs demonstrating that ultrasounds are
useful as an accurate tool to determine volume status
noninvasively. Hendrickson et al. reports a case where ultra-
Figure 2 Subxyphoid emergency ultrasound image of a
patient with hypovolemia as the cause of PEA. Patient was
actively being resuscitated with two large bore central venous
catheters at time of image acquisition.
C.A.U.S.E. in primary non-arrhythmogenic cardiac arrest
Figure 3 Sonographic evaluation of the aorta in a patient
from Figure 2. This abdominal aortic aneurysm was identified
as the cause of this patient’s hypovolemia and PEA.
Pulmonary embolus
Pulmonary embolus has been observed to be the direct cause
of almost 5% of cardiac arrests, with PEA being the initial
diagnostic rhythm in 63% and asystole in another 32% of
these cases.22 It has also been observed that in patients
presenting with cardiac arrest as a consequence of acute
pulmonary emboli, thrombolytic therapy resulted in a significantly higher return of spontaneous circulation when
compared to similar patients who did not receive thrombolytic therapy, 81% versus 43%, respectively.22 Therefore
having a diagnostic tool with the potential of directing
thrombolytic therapy in patients in cardiac arrest as a consequence of pulmonary emboli has the potential to greatly
impact outcomes in this patient population.
Pulmonary embolus is identified sonographically by the
finding of an engorged right ventricle with a flattened left
ventricle.4,7,15 There are a few reports of the use of cardiac ultrasound in the setting of cardiac arrest. MacCarthy
et al. described a case where a 25-year-old woman experienced cardiac arrest due to massive pulmonary embolus.4
The above findings were recognized on cardiac ultrasound
and the patient was given appropriate management, leading
to the eventual discharge of the patient from the hospital. Similarly Tovar et al. describes a similar case where
transthoracic ultrasound was used to diagnose pulmonary
embolism in a 61-year-old man.7 In this case embolectomy
was performed and the patient was discharged form the
hospital to live a normal life. Both of these case reports
illustrate that sonographic diagnosis of massive pulmonary
emboli allow physicians the confidence to employ aggressive
life-saving therapy that may have not been used or reluctantly used in the face of diagnostic uncertainty, due to the
fear of potential catastrophic negative outcome.
201
The use of transthoracic ultrasound to diagnose pulmonary emboli has been studied as well in patients not
experiencing cardiac arrest. Nazeyrollas et al. performed
a prospective study in 70 patients with suspected acute
pulmonary emboli, he found that right sided enlargement
in this patient population demonstrated a sensitivity of
0.70 and a specificity of 0.86 for diagnosing acute pulmonary emboli when a threshold of 25 mm was used.23
Miniati et al. performed a prospective study in 110 consecutive patients with suspected pulmonary emboli; he found
that echocardiographic criteria for PE demonstrated a sensitivity of 56% and specificity of 90%.24 Similarly Jackson
et al. evaluated patients prospectively with suspected pulmonary emboli and found that ultrasound had a sensitivity
of 0.41 and specificity of 0.91.25 Torbicki and Pruszczyk
reviewed the available literature on the use of ultrasound
to diagnose acute pulmonary emboli and found that cardiac ultrasound has specificity between 81 and 94%, with
a positive predictive value of 71—86%.26 These data all
indicate that ultrasound has poor to moderate sensitivity
as a routine screening test in all patients with suspected
pulmonary emboli. However cardiac ultrasound has demonstrated good to excellent specificity at detecting acute
pulmonary emboli, which may be more important and appropriate in the setting of cardiac arrest, where the need for
specific therapy must be justified.
After reviewing the available literature on the use
of echocardiography in the diagnosis of acute pulmonary
emboli Lebowitz recommended that ultrasound had the
potential to make the greatest clinical impact in patients
with central hemodynamically significant pulmonary emboli
(i.e. those capable of causing cardiac arrest) versus the
majority of patients with small peripheral pulmonary
emboli.27 This recommendation is logical as echocardiographic findings of pulmonary embolus begin to be evident
after acute obstruction of more than 30% of the pulmonary arterial bed.26 Ultrasound therefore appears to be
an excellent bedside test for detecting the presence of large
pulmonary emboli capable of causing cardiac arrest.
A characteristic four-chamber apical view of the heart
of a patient with massive pulmonary embolus is demonstrated below (Figure 4). A CT-scan image of the same
patient demonstrating a large saddle pulmonary embolus is
presented as well (Figure 5).
Tension pneumothorax
Tension pneumothorax is identified sonographically by
absence of ‘‘sliding sign’’ between the visceral and parietal pleura when viewed anteromedially at the level of
the second intercostal interspace and the mid clavicular line. This approach was used by Knudtson et al. in
trauma patients 28 and provides the ability to diagnose
pneumothorax in as little as 30 s with a sensitivity of
92.3%, specificity of 99.6%, and positive predictive value
of 92.3% and accuracy of 99.3%.28 Other studies have
achieved equally impressive accuracies using ultrasound for
the detection of pneumothorax.29,30 This high level of accuracy in both ruling pneumothorax in or out could greatly aid
physicians in managing cardiac arrest. A protocol addressing the pulseless patient should address pneumothorax, as it
202
C. Hernandez et al.
Figure 4 Four-chamber apical view of the heart in patient
with suspected pulmonary embolus. Notice the massive enlargement of both right chambers when compared to the left side of
the heart.
Figure 5 CT angiogram of the chest in a patient from Figure 4,
obtained 1 h after initial ultrasound image. Notice the large
saddle pulmonary embolus. As a result of interventions started
after initial emergency ultrasound patient survived and was discharged from the hospital.
Figure 6 Diagram comparing relative sizes of the cardiac chambers (apical four-chamber view) in cardiac tamponade, pulmonary
embolus, and hypovolemia to that of a normal heart. Please note that this diagram represents images obtained with normal
emergency room probe setting, if using cardiac setting the diagram is flipped to its mirror image. Please see Figure 4 for an
example.
C.A.U.S.E. in primary non-arrhythmogenic cardiac arrest
203
is a common problem and readily reversible. Ultrasound has
been demonstrated to be a highly accurate diagnostic aid for
pneumothorax, and could be of great use in a cardiac arrest
situation where ambient noise may affect the accuracy of
auscultation via stethoscope. Furthermore the high degree
of accuracy afforded by ultrasound assists in differentiating between cardiac tamponade and tension pneumothorax,
both of which present with similar clinical features.
True asystole
Ultrasound has also been useful in distinguishing true asystole from other types of cardiac arrest. Cardiac standstill
or true asystole is identified by complete absence of any
motion in the heart including the valves, atria or ventricles
31
and is often seen in association with severe spontaneous
echo contrast. Blaivas et al. observed that cardiac standstill in the emergency department had a positive predictive
value of 100% for death in the emergency department.13
Salen et al. made similar observations in his study.31 Salen
observed that none of the patients with absence of cardiac kinetic activity on sonogram had spontaneous return of
circulation. However, evidence of kinetic activity on sonographic evaluation of the heart was associated with return
of spontaneous circulation. This knowledge may be useful
for physicians, allowing them to make decisions regarding
the value of continued resuscitative efforts. There appears
to be justification for terminating resuscitative efforts if
no cardiac motion is detected on cardiac ultrasound after
adequate resuscitative efforts were employed.
C.A.U.S.E.
C.A.U.S.E. is a new approach developed by the authors. The
C.A.U.S.E. protocol addresses four leading causes of cardiac
arrest and achieves this by using two sonographic perspectives of the thorax; a four-chamber view of the heart and
pericardium and anteromedial views of the lung and pleura
at the level of the second intercostal space at the midclavicular line bilaterally. The four-chamber view of the heart and
pericardium is attained using either the subcostal, parasternal or apical thoracic windows. This allows the individual
performing the examination to select the most adequate
view depending on the patients’ anatomy. The authors recommend beginning with the subcostal view first as this view
makes it possible for the practitioner to evaluate the heart
without interrupting chest compression.9 If this view is not
possible then the apical or parasternal approaches may be
used during coordinated pulse checks lead by the resuscitation team leader. A four-chamber view is used in this
protocol as it allows for ease of comparison between the
different chambers in the heart, facilitating the diagnosis of
hypovolemia, massive PE, and cardiac tamponade (Figure 6).
Pneumothorax is diagnosed by identifying the lack of sliding sign and comet-tail artifact while looking in the sagital
plane at the second intercostal space of the midclavicular line (Figure 7). For both the cardiac and lung views it
is recommended to use a 2.5—5.0 phased array transducer
probe. This allows the examiner to use the same probe
for both lung, heart and if needed abdominal exam. This
type of probe was used by Knudtson in his study involving
Figure 7 Diagram demonstrating ultrasound findings
observed in pneumothorax and comparing these to findings of
normal lung.
ultrasound for the use of identifying pneumothorax as an
addition to the FAST exam, and it yielded very a high accuracy in detecting pneumothorax,28 yet still remained useful
in identifying the heart and abdominal organs. The protocol is best described in diagram form (Figure 8). Pulseless
patients are treated with standard resuscitative protocol.
After the monitor is attached patients are divided into
two groups: arrhythmogenic (i.e. ventricular fibrillation and
ventricular tachycardia) and non-arrhythmogenic (i.e. massive PE, hypovolemia, tension pneumothorax, etc.) cardiac
arrest. Arrhythmogenic patients are treated with electrical cardioversion, but non-arrhythmogenic patients are then
examined with the C.A.U.S.E. protocol to exclude readily
reversible causes for the cessation of the circulation.
The cardiac view is the first performed as this gives the
potential to diagnose one of the three conditions in a single
view (massive PE, cardiac tamponade, and hypovolemia),
and this view takes the least time, meaning less interference
with resuscitation as possible. If the results of the cardiac
view are inconclusive the pulmonary views are attempted
as these use approximately 30 s per side and diagnose only
one condition, pneumothorax. If these studies are negative
alternate causes of the arrest are considered as described by
204
C. Hernandez et al.
Figure 8
Flow diagram demonstrating use of C.A.U.S.E. protocol in patients with cardiac arrest.
Figure 9 Characteristic image of IVC diameter in a patient
without hypovolemia.
Figure 10 Characteristic image of IVC diameter in a patient
with hypovolemia.
C.A.U.S.E. in primary non-arrhythmogenic cardiac arrest
205
References
Figure 11 High quality subcostal image using newer bedside
ultrasound equipment, demonstrating enlarged right ventricle
and collapsed left ventricle in a patient with confirmed pulmonary embolism. Compare quality of newer machines with
image from Figure 4.
Hughes in order of frequency and ease of reversibility (i.e.
electrolyte and metabolic disturbance, massive hypothermia, massive myocardial infarction, and drugs or toxins).3
If one encounters an abnormal image on examination of the
four chambers of the heart, one may attempt further confirmatory views with the ultrasound to make the diagnosis
more clear (i.e. the finding of collapsed right and left ventricles should be followed by sonographic evaluation of the
IVC and abdominal aorta) (Figures 9 and 10).
Conclusion
Ultrasound is currently the only radiographic modality with
the potential to guide management in real time, at the
bedside, during cardiac arrest without interfering with
resuscitation. This literature review justifies the need for
further study of ultrasound in the setting of cardiac arrest
and also demonstrates that implementation of sonography
into patient-care provides substantial potential benefits to
patients and clinicians alike. As technology and training
improve it will become easier to incorporate ultrasound into
the care of patients in need of resuscitation (Figure 11). The
reviewers included a proposed protocol to add organization
and structure to a clinical scenario that has the potential
for chaos. The protocol is an attempt to incorporate the
most clinically relevant information in the literature on the
applications of ultrasound use for cardiac arrest in an organized manner for clinical application. The hope is that this
protocol will foster future study in the area of sonographic
diagnosis during cardiac arrest, and eventually reduce the
time required for emergency providers to determine the etiology of a cardiac arrest and thus decrease the time between
arrest and appropriate therapy.
Conflict of interest
None.
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