Download 6 - Cardiopulmonary arrest

Cardiac arrest
A cardiac arrest, also known as cardiopulmonary arrest or
circulatory arrest, is the abrupt cessation of normal circulation
of the blood due to failure of the heart to contract effectively
during systole.
Characteristics and diagnosis
Cardiac arrest is an abrupt cessation of pump function
(evidenced by absence of a palpable pulse) of the heart that with
prompt intervention could be reversed, but without it will lead to
death.. In certain cases, it is an expected outcome to a serious
illness.
However, due to inadequate cerebral perfusion, the patient will
be unconscious and will have stopped breathing. The main
diagnostic criterion to diagnose a cardiac arrest (as opposed to
respiratory arrest, which shares many of the same features) is
lack of circulation, however there are a number of ways of
determining this.
In many cases, lack of carotid pulse is the gold standard for
diagnosing cardiac arrest, but lack of a pulse (particularly in the
peripheral pulses) may be a result of other conditions (e.g.
shock), .
Causes of cardiac arrest
Cardiac arrest is synonymous with Clinical death. All disease
processes leading to death have a period of (potentially)
reversible cardiac arrest: the causes of arrest are, therefore,
numerous .
Among adults, ischemic heart disease is the predominant cause
of arrest. Other cardiac conditions potentially leading to arrest
include structural abnormalities, arrhythmias and
cardiomyopathies. Non-cardiac causes include infections,
overdoses, trauma and cancer, in addition to many others.
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Reversible causes
Cardiopulmonary resuscitation (CPR), including adjunctive
measures such as defibrillation, intubation and drug
administration, is the standard of care for initial treatment of
cardiac arrest. However, most cardiac arrests occur for a reason,
and unless that reason can be found and overcome, CPR is often
ineffective, or if it does result in a return of spontaneous
circulation, this is short lived. As highlighted above, a variety of
disease processes can lead to a cardiac arrest, however they
usually boil down to one or more of the "Hs and Ts".
Hs
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Hypovolemia - A lack of circulating body fluids,
principally blood volume. This is usually (though not
exclusively) caused by some form of bleeding,
anaphylaxis, or pregnancy with gravid uterus. Peri-arrest
treatment includes giving IV fluids and blood transfusions,
and controlling the source of any bleeding - by direct
pressure for external bleeding, or emergency surgical
techniques such as esophageal banding, gastroesophageal
balloon tamponade (for treatment of massive GI bleeding
such as in esophageal varices),
Hypoxia - A lack of oxygen delivery to the heart, brain
and other vital organs. Rapid assessment of airway patency
and respiratory effort must be performed. If the patient is
mechanically ventilated, the presence of breath sounds and
the proper placement of the endotracheal tube should be
verified. Treatment may include providing oxygen, proper
ventilation, and good CPR technique. In cases of carbon
monoxide poisoning or cyanide poisoning, hyperbaric
oxygen may be employed after the patient is stabilized.
Hydrogen ions (Acidosis) - An abnormal pH in the body
as a result of lactic acidosis which occurs in prolonged
hypoxia and in severe infection, diabetic ketoacidosis,
renal failure causing uremia, or ingestion of toxic agents or
overdose of pharmacological agents, such as aspirin and
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other salicylates, ethanol, ethylene glycol and other
alcohols, tricyclic antidepressants, isoniazid, or iron
sulfate. This can be treated with proper ventilation, good
CPR technique, buffers like sodium bicarbonate, and in
select cases may require emergent hemodialysis.
Hyperkalemia or Hypokalemia - Both excess and
inadequate potassium can be life-threatening. A common
presentation of hyperkalemia is in the patient with endstage renal disease who has missed a dialysis appointment
and presents with weakness, nausea, and broad QRS
complexes on the electrocardiogram . The
electrocardiogram will show tall, peaked T waves (often
larger than the R wave) . Immediate initial therapy is the
administration of calcium, either as calcium gluconate or
calcium chloride. This stabilizes the electrochemical
potential of cardiac myocytes, thereby preventing the
development of fatal arrhythmias. This is, however, only a
temporizing measure. Other temporizing measures may
include nebulized albuterol, intravenous insulin (usually
given in combination with glucose, and sodium
bicarbonate, which all temporarily drive potassium into the
interior of cells. Definitive treatment of hyperkalemia
requires actual excretion of potassium, either through urine
(which can be facilitated by administration of loop
diuretics such as furosemide) or in the stool (which is
accomplished by giving sodium polystyrene sulfonate
enterally, where it will bind potassium in the GI tract.)
Severe cases will require emergent hemodialysis. The
diagnosis of hypokalemia can be suspected when there is
a history of diarrhoea or malnutrition. Loop diuretics may
also contribute. The electrocardiogram may show
flattening of T waves and prominent U waves.
Hypokalemia is an important cause of acquired long QT
syndrome, and may predispose the patient to torsades de
pointes. Digitalis use may increase the risk that
hypokalemia will produce life threatening arrhythmias.
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Hypokalemia is especially dangerous in patients with
ischemic heart disease.
Hypothermia - A low core body temperature, defined
clinically as a temperature of less than 35 degrees Celsius
(95 degrees Fahrenheit). The patient is re-warmed either
by using a cardiac bypass or by irrigation of the body
cavities (such as thorax, peritoneum, bladder) with warm
fluids; or warmed IV fluids. CPR only is given until the
core body temperature reached 30 degrees Celsius, as
defibrillation is ineffective at lower temperatures.
Hypoglycemia or Hyperglycemia - Low blood glucose
from overdose of oral hypoglycemics such as
sulfonylureas, or overdose of insulin. Rare endocrine
disorders can also cause unexpected hypoglycemia.
Generally, hyperglycemia is itself not fatal, however DKA
will cause pH to drop, and nonketotic hyperosmolar coma
leads to a severely hypovolemic state. Hypoglycemia is
corrected rapidly by intravenous administration of
concentrated glucose (typically 25 ml of 50% glucose in
adults, but in children 25% glucose is used, and in
neonates 10% glucose is used.) However, the patient will
often require a continuous intravenous drip until the
causative agent is completely metabolized. In DKA, the
goal is correction of acidosis. In NKH, the goal is adequate
fluid resuscitation.
Ts
Tablets or Toxins - Tricyclic antidepressants, phenothiazines,
beta blockers, calcium channel blockers, cocaine, digoxin,
aspirin, acetominophen. This may be evidenced by items found
on or around the patient, the patient's medical history (i.e. drug
abuse, medication) taken from family and friends, checking the
medical records to make sure no interacting drugs were
prescribed, or sending blood and urine samples to the toxicology
lab for report. Treatment may include specific antidotes, fluids
for volume expansion, vasopressors, sodium bicarbonate (for
tricyclic antidepressants), glucagon or calcium (for calcium
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channel blockers), benzodiazepines (for cocaine), or
cardiopulmonary bypass. Herbal supplements and over-thecounter medications should also be considered.
Cardiac Tamponade - Blood or other fluids building up in the
pericardium can put pressure on the heart so that it is not able to
beat. This is treated in an emergency by inserting a needle into
the pericardium to drain the fluid (pericardiocentesis), or if the
fluid is too thick then a surgical procedure is performed to cut
the pericardium and release the fluid.
Thrombosis (Myocardial infarction) - If the patient can be
successfully resuscitated, there is a chance that the myocardial
infarction can be treated, either with thrombolytic therapy or
percutaneous coronary intervention.
Thromboembolism (Pulmonary embolism) - hemodynamically
significant pulmonary emboli are generally massive and
typically fatal. Administration of thrombolytics can be
attempted, and some specialized centers may perform
thrombolectomy, however, prognosis is generally poor.
Trauma (Hypovolemia) - Reduced blood volume from acute
injury or primary damage to the heart or great vessels. Cardiac
arrest secondary to trauma, particularly blunt trauma, has a very
poor prognosis.
Treatment
Out of hospital arrest
Most out-of-hospital cardiac arrests occur following a
myocardial infarction (heart attack), and present initially with a
heart rhythm of ventricular fibrillation. The patient is therefore
likely to be responsive to defibrillation, and this has become the
focus of pre-hospital interventions. Several organisations
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promote the idea of a "chain of survival", of which defibrillation
is a key step. The links are:
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Early recognition - If possible, recognition of illness
before the patient develops a cardiac arrest will allow the
rescuer to prevent its occurrence. Early recognition that a
cardiac arrest has occurred is key to survival - for every
minute a patient is in cardiac arrest, their chances of
survival drop by roughly 10% [11]
Early CPR - This buys time by keeping vital organs
perfused with oxygen whilst waiting for equipment and
trained personnel to reverse the arrest. In particular, by
keeping the brain supplied with oxygenated blood, chances
of neurological damage are decreased.
Early defibrillation - This is the only effective treatment
for ventricular fibrillation, and also has benefit in
ventricular tachycardia[11] and should be employed in such
cases if the patient has signs of hemodynamic
compromise, or if the patient has pulseless ventricular
tachycardia. If defibrillation is delayed, then the rhythm is
likely to degenerate into asystole, for which outcomes are
markedly worse.
Early advanced care - Early Advanced Cardiac Life
Support is the final link in the chain of survival.
If one or more links in the chain are missing or delayed, then the
chances of survival drop significantly. In particular, bystander
CPR is an important indicator of survival: if it has not been
carried out, then resuscitation is associated with very poor
results. Paramedics in some jurisdictions are authorised to
abandon resuscitation altogether if the early stages of the chain
have not been carried out in a timely fashion prior to their
arrival.
Because of this, considerable effort has been put into educating
the public on the need for CPR. In addition, there is increasing
use of public access defibrillation. This involves placing
automated external defibrillators in public places, and training
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key staff in these areas how to use them. This allows
defibrillation to take place prior to the arrival of emergency
services, and has been shown to lead to increased chances of
survival. In addition, it has been shown that those who suffer
arrests in remote locations have worse outcomes following
cardiac arrest [17]: these areas often have first responder
schemes, whereby members of the community receive training
in resuscitation and are given a defibrillator, and called by the
emergency medical services in the case of a collapse in their
local area.
Hospital treatment
Treatment within a hospital usually follows advanced life
support protocols. In the US, non-traumatic adult resuscitation is
described by ACLS (advanced cardiac life support), pediatric
resuscitation is described by PALS (pediatric advanced life
support), and neonatal resusciation is described by NALS
(neonatal advanced life support.) Depending on the diagnosis,
various treatments are offered, ranging from defibrillation (for
ventricular fibrillation or ventricular tachycardia) to surgery (for
cardiac arrest which can be reversed by surgery - see causes of
arrest, above) to medication (for asystole and PEA). All will
include CPR.
While specific details may vary, all hospitals have protocols as
to how resuscitations should be performed in patients, visitors,
or employees who have arrested unexpectedly in the hospital.
These protocols are often initiated by a Code Blue, which
usually denotes impending or acute onset of cardiac arrest or
respiratory failure, although in practice, Code Blue is often
called in less life-threatening situations that require immediate
attention from a physician.
If not already done, a definitive airway will be establish by the
placement of an endotracheal tube which is then attached to a
mechanical ventilator.
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Cardiac arrest is generally divided into two cases: presence of
disorganized mechanical cardiac activity, or complete absence
of mechanical cardiac activity.
Disorganized mechanical cardiac activity includes ventricular
fibrillation and hemodynamically unstable or pulseless
ventricular tachycardia. This also includes torsade de pointes.
These must all be treated primarily with defibrillation.
Advanced cardiac life support algorithms also detail the
stepwise administration of epinephrine, vasopressin, the
antiarrhythmic agent amiodarone, as well as attempts to correct
possible underlying causes.
Complete absence of mechanical cardiac activity includes
asystole and pulseless electrical activity. This is treated entirely
with pharmacologic agents, specifically epinephrine and
atropine. However, resuscitation is rarely successful without
effective treatment of the underlying cause.
Therapeutic hypothermia
In some cases, doctors may choose to induce hypothermia after
return of spontaneous circulation (ROSC). This procedure is
called therapeutic hypothermia. The first study conducted in
Europe focused on people who were resuscitated 5-15 minutes
after collapse. Patients participating in this study experienced
spontaneous return of circulation (ROSC) after an average of
105 minutes. Subjects were then cooled over a 24 hour period,
with a target temperature of 32-34°C (89.6-93.2°F). 55% of the
137 patients in the hypothermia group experienced favorable
outcomes, compared with only 39% in the group that received
standard care following resuscitation.[18] Death rates in the
hypothermia group were 14% lower, meaning that for every 7
patients treated one life was saved.[18] Notably, complications
between the two groups did not differ substantially. This data
was supported by another similarly run study that took place
simultaneously in Australia. In this study 49% of the patients
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treated with hypothermia following cardiac arrest experienced
good outcomes, compared to only 26% of those who received
standard care.[19]
Peri-arrest period
The period (either before or after) surrounding a cardiac arrest is
known as the peri-arrest period. During this period the patient
is in a highly unstable condition and must be constantly
monitored in order to halt the progression or repeat of a full
cardiac arrest. The preventative treatment used during the periarrest period depends on the causes of the impending arrest and
the likelihood such an event occurring.
Prognosis
The out-of-hospital cardiac arrest (OHCA) has a worse survival
rate (2-8% at discharge and 8-22% on admission), than an inhospital cardiac arrest (15% at discharge). The principal
determining factor is the initially documented rhythm. Patients
with VF/VT have 10-15 times more chance of surviving than
those suffering from pulseless electrical activity or asystole (as
they are sensitive to defibrillation, whereas asystole and PEA
are not).[citation needed]
Since mortality in case of OHCA is high, programs were
developed to improve survival rate. A study by Bunch et al.
showed that, although mortality in case of ventricular fibrillation
is high, rapid intervention with a defibrillator increases survival
rate to that of patients that did not have a cardiac arrest.[13][20]
Survival is mostly related to the cause of the arrest (see above).
In particular, patients who have suffered hypothermia have an
increased survival rate, possibly because the cold protects the
vital organs from the effects of tissue hypoxia. Survival rates
following an arrest induced by toxins is very much dependent on
identifying the toxin and administering an appropriate antidote.
A patient who has suffered a myocardial infarction due to a
blood clot in the left coronary artery has a lower chance of
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survival as it cuts of the blood supply to most of the left
ventricle (the chamber which must pump blood to the whole of
the systemic circulation).
Cobbe et al (1996) conducted a study into survival rates from
out of hospital cardiac arrest. 14.6% of those who had received
resuscitation by ambulance staff survived as far as admission to
an acute hospital ward. Of these, 59.3% died during that
admission, half of these within the first 24 hours. 46.1%
survived to hospital discharge (this is 6.75% of those who had
been resuscitated by ambulance staff), and 89% had normal to
mild neurological disability, 8.5% had moderate impairment,
and 2% suffered major neurological disability. Of those who
were successfully discharged from hospital, 70% were still alive
4 years after their discharge.[21]
Ballew (1997) performed a review of 68 earlier studies into
prognosis following in-hospital cardiac arrest. They found a
survival to discharge rate of 14% (this roughly double the rate
for out of hospital arrest found by Cobbe et al (see above)),
although there was a wide range (0-28%).[22]
Prevention
With positive outcomes following cardiac arrest so unlikely, a
great deal of effort has been spent in finding effective strategies
to prevent cardiac arrest.
As noted above, one of the prime causes of cardiac arrest
outside of hospital is ischemic heart disease. Vast resources
have been put into trying to reduce cardiovascular risks across
much of the developed world. In particular schemes have been
put in place to promote a healthy diet and exercise. For people
considered to be particularly at risk of heart disease, measures
such as blood pressure control, prescription of cholesterol
lowering medications, and other medico-therapeutic
interventions, have been widely used. A magnesium deficiency,
or lower levels of magnesium, can contribute to heart disease
and a healthy diet that contains adequte magnesium may help
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prevent heart disease.[23] Magnesium can be used to enhance
long term treatment, so it may be effective in long term
prevention.
Patients in hospital are far less likely to have a cardiac arrest
caused of primary cardiac origin, and hence present in asystole
or PEA, and have bleak outcomes . Extensive research has
shown that patients in general wards often deteriorate for several
hours or even days before a cardiac arrest occurs[11][24]. This has
been attributed to a lack of knowledge and skill amongst ward
based staff, in particular a failure to carry out measurement of
the respiratory rate, which is often the major predictor of a
deterioration[11] and can often change up to 48 hours prior to a
cardiac arrest. In response to this, many hospitals now have
increased training for ward based staff. A number of "early
warning" systems also exist which aim to quantify the risk
which patients are at of deterioration based on their vital signs
and thus provide a guide to staff. In addition, specialist staff are
being utilised more effectively in order to augment the work
already being done at ward level. These include:
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Crash teams (also known as code teams) - These are
designated staff members who have particular expertise in
resuscitation, who are called to the scene of all arrests
within the hospital.
Medical emergency teams - These teams respond to all
emergencies, with the aim of treating the patient in the
acute phase of their illness in order to prevent a cardiac
arrest.
Critical care outreach - As well as providing the services
of the other two types of team, these teams are also
responsible for educating non-specialist staff. In addition,
they help to facilitate transfers between intensive care/high
dependency units and the general hospital wards. This is
particularly important, as many studies have shown that a
significant percentage of patients discharged from critical
care environments quickly deteriorate and are re-admitted
- the outreach team offers support to ward staff to prevent
this from happening.
Implantable cardioverter defibrillators
A technologically based intervention to prevent further cardiac
arrest episodes is the use of an implantable cardioverterdefibrillator (ICD). This device is implanted in to the patient.
They act as an instant defibrillator in the event of arrhythmia.
Note that standalone ICDs do not have any pacemaker
functions, but they can be combined with a pacemaker, and
modern versions also have advanced features such as antitachycardic pacing as well as synchronized cardioversion. A
recent study by Birnie et al. at the University of Ottawa Heart
Institute has demonstrated that ICDs are underused in both the
United States and Canada.[25] An accompanying editorial by
Simpson explores some of the economic, geographic, social and
political reasons for this.[26] Patients who are most likely to
benefit from the placement of an ICD are those with severe
ischemic cardiomyopathy (with systolic ejection fractions less
than 30%) as demonstrated by the MADIT-II trial.[27]
Ethical issues
Cardiopulmonary resuscitation and advanced cardiac life
support are not always in a person's best interest. This is
particularly true in the case of terminal illnesses when
resuscitation will not alter the outcome of the disease. Properly
performed CPR often fractures the rib cage, especially in older
patients or those suffering from osteoporosis. Defibrillation,
especially repeated several times as called for by ACLS
protocols, may also cause electrical burns.
Some people with a terminal illness choose to avoid such
measures and die peacefully. People with views on the treatment
they wish to receive in the event of a cardiac arrest should
discuss these views with both their doctor and with their family.
A patient may ask their doctor to place a do not resuscitate
(DNR) order in the medical record. Alternatively, in many
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jurisdictions, a person may formally state their wishes in an
advance directive or advance health directive.
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