Download maintenance and care of patients with ecmo

12 July 2013
No. 23
INTRODUCTION TO ECMO
G. GOVENDER
Commentator: N. Moodley
Moderator: S Goga
DISCIPLINE OF ANAESTHETICS
CONTENTS
INTRODUCTION ................................................................................................... 3
HISTORY OF ECMO............................................................................................. 3
INDICATIONS FOR ECMO ................................................................................... 4
CONTRAINDICATIONS ........................................................................................ 6
TYPES .................................................................................................................. 6
MAINTENANCE AND CARE OF PATIENTS WITH ECMO .................................. 9
SPECIAL CONSIDERATIONS ............................................................................. 9
CRITERIA FOR WEANING OR DISCONTINUING ECMO ................................. 10
COMPLICATIONS .............................................................................................. 10
FUTURE ADVANCEMENTS............................................................................... 11
RESULTS OF RANDOMIZED TRIALS OF EXTRACORPOREAL MEMBRANE
OXYGENATION FOR ACUTE RESPIRATORY DISTRESS SYNDROME ......... 12
CONCLUSION .................................................................................................... 13
REFERENCES.................................................................................................... 14
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INTRODUCTION TO ECMO
INTRODUCTION
Extracorporeal membrane oxygenation (ECMO) is unfamiliar to many of us in
South Africa due to its nonexistent use in the public sector and its limited use in
the private sector.This technology is used primarily in neonates with respiratory
failure, particularly those with Hyaline Membrane Disease. The concept of ECMO
is not to cure disease but rather to allow the lungs to rest which promotes quicker
recovery times. Due to its success with the paediatric sector, this modality is now
more frequently used in adult intensive care units around the world.In recent
years, pivotal progress has been made in the conception and construction of
ECMO circuits. They are now simpler, safer, require less anticoagulation and are
associated with fewer bleeding complications.
The encouraging results of the efficacy and economic assessment of conventional
ventilatory support versus ECMO for severe adult respiratory failure (CESAR) trial
performed in the United Kingdom and the good outcomes of patients who
received ECMO as rescue therapy during the H1N1 influenza pandemic, in which
the latest generation of ECMO technology was used, reignited interest in ECMO
for severe acute respiratory distress syndrome (ARDS).In order for us to mirror
our counterparts internationally in terms of standards of care, we should be
familiarizing ourselves with novel concepts like ECMO, this being the motivation
behind my choice of topic.
HISTORY OF ECMO
As early as 1935 have John Gibbon, Clarence Dennis (1), and others pursued the
development of a mechanical device to take over the function of the heart and
lungs to permit surgical operations on the heart and great vessels. Their
inspiration came from a patient who demised from a pulmonary embolus. Gibbon
was the first to use a roller pump which remains in general practice today. To
substitute the lung, he used direct exposure of blood to oxygen which proved
successful.
Subsequently this technique was modified by Dennis, Morrow, Cross, DeWall,
Rygg (7), and many others, leading to the single-use, disposable, direct gas
interface oxygenators which are widely used today. Gibbon was the first to use the
prosthetic heart/lung machine for a cardiac operation paving the way for success
of extracorporeal circulation for cardiac surgery.However, during the 1950’s, with
more frequent use it became clear that this life supporting device could also be
lethal. Deterioration of organ function occurred in proportion to the amount of time
on cardiopulmonary bypass. It was hypothesized that the direct exposure of blood
to oxygen gas was responsible for this apparent toxicity.
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The development of dimethylpolysiloxane membranes in 1957 was a major
advance. This unique material allows for the transfer of carbon dioxide and
oxygen at rates in excess of ten times that used through other plastics. Using this
silicone rubber, blood oxygenators were constructed which were quite efficient
and successful. Starting with Gibbon, all the studies on extracorporeal circulation
have been conducted with the use of heparin anticoagulation, using a dose
sufficient to produce an infinitely long clotting time (1). In 1971 a San Francisco
Surgeon named Donald Hill (7) l used a modified extracorporeal bypass called
“extracorporeal membrane oxygenation” (ECMO) to treat an adult who was dying
from acute respiratory insufficiency.
The patient was a young man who sustained a ruptured aorta and other injuries in
a motorcycle accident in Santa Barbara, California. This was the first time ECMO
was used on an adult patient. The patient was managed on veno-arterial
extracorporeal support for 3 days and survived. This was a very important
discovery, especially for intensive care units, where acute renal and respiratory
failure was the major concerns in critically ill patients.Similar to the use of
haemodialysis in cases of renal failure, it was hoped that ECMO would offer a
temporary period of life support with extracorporeal circulation that would allow the
damaged lung to recover.
INDICATIONS FOR ECMO
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Respiratory Failure
ECMO support has been proposed for patients with ARDS refractory to
conventional mechanical ventilation, and in other severe conditions such as lung
trauma, severe asthma, pulmonary emboli or patients with chronic lung disease
awaiting lung transplantation.According to the extracorporeal life support
organization (ELSO), ECMO is indicated in the following (2):
 Hypoxemic respiratory failure with a ratio of arterial oxygen tension to fraction
of inspired oxygen (PaO2/FiO2) of <100 mmHg despite optimization of the
ventilator settings, including the Fraction of Inspired Oxygen (FiO2), positive
end-expiratory pressure (PEEP), and inspiratory to expiratory (I:E) ratio
 ECMO should be considered when the risk of mortality is 50% more, and is
indicated when the risk of 80% or greater.
50% mortality risk can be identified by a PaO2/FiO2 < 150 on
FiO2 > 90% and/or Murray score 2-3
 80% mortality risk can be identified by a PaO2/FiO2 < 80 on FiO2
> 90% and Murray score 3-4
The Murray Score is based on the following (2):
 PaO2/FiO2 in mmHg on 100% oxygen for at least 20 minutes.
 Number of quadrants with infiltration seen on chest x-ray.
 PEEP value on the ventilator
 Compliance (ml/cmH2O) which may be calculated as: (Tidal Volume) / (PIPPEEP)
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
Hypercapnic respiratory failure with an arterial pH <7.20, CO2 retention due
to asthma or permissive hypercapnia with a PaCO2 > 80 or inability to
achieve safe inflation pressures (Pplat ≤ 30 cm HO)
Cardiac Failure
 Refractory cardiogenic shock - Inadequate tissue perfusion manifested as
hypotension and low cardiac output despite adequate intravascular volume.
 The persistence of low cardiac output despite volume administration,
inotropes and vasoconstrictors
 Typical causes of refractory cardigenic shock: acute myocardial
infarction, myocarditis, peripartum cardiomyopathy, decompensated
chronic heart failure, post cardiotomy shock.
 Other causes: biventricular failure, refractory malignant arrythmias,
heart failure with severe pulmonary failure
 In some centres, ECMO may be used in septic shock
 Recovery: Acute MI after revascularization, Myocarditis, Postcardiotomy
 Failure to wean from cardiopulmonary bypass after cardiac surgery
Cardiac transplantation
 As a bridge to either cardiac transplantation or placement of a ventricular
assist device
CONTRAINDICATIONS
Most contraindications are relative, balancing the risks of the procedure vs. the
potential benefits.
These include:
 Conditions incompatible with normal life if the patient recovers
 Pre-existing conditions which affect the quality of life (CNS status, end stage
malignancy, risk of systemic bleeding with anticoagulation)
 Age and size of patient
 Futility: patients who are too sick, have been on conventional therapy too
long, or have a fatal diagnosis.
TYPES
There are two common types of ECMO i.e. Veno-atrerial (VA) or Veno-venous
(VV)Peripheral veno-venous ECMO should be the modality of choice for severe
hypoxic respiratory failure wherein no major cardiac dysfunction exists. Therefore,
echocardiography should be performed before veno-venous ECMO placement to
identify severe left ventricular dysfunction, which might necessitate the use of
veno-arterial ECMO.
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Veno- Arterial
 Usually indicated in cardiac failure
 Output canula drains from the venous system and the input canula drains
into the arterial system thereby bypassing the entire cardio-respiratory
system. Pulsatile flow is needed for this modality.
 Venous Canula is placed in the right femoral vein and arterial canula is
placed in the right femoral artery.
 The disadvantage of this method is that pulsatile flow is needed to mimic
cardiac output and large bore cannulation of an artery is needed which can
be associated with complications.
Veno-Venous
 Indication: Isolated Respiratory Failure
 Both input and output cannula is situated in the venous system
 This system extracts the CO2 from the venous system and oxygenates the
venous blood. It still requires a functioning cardiac system to output the
oxygenated blood.
Cannulation for veno-venous ECMO may involve two sites or a single site. In the
two-site approach, blood is typically withdrawn from the inferior vena cava through
a drainage cannula in the femoral vein, and oxygenated blood is reinfused into the
right atrium through a cannula in the internal jugular vein. This approach can
result in recirculation of blood, which occurs when reinfused blood is drawn back
into the circuit in a closed loop. Recirculated blood does not contribute to systemic
oxygenation.
The recent introduction of a bicaval dual-lumen cannula allows single-site
cannulation of the internal jugular vein. Venous blood is withdrawn through one
lumen with ports in both the superior and inferior vena cava. Reinfusion of blood
occurs through the second lumen and is directed across the tricuspid valve. The
advantages of the single-site approach include avoidance of the femoral access
site, improved patient mobility, and considerably reduced recirculation when the
cannula is properly positioned.
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Extracorporeal membrane oxygenation: a clinical update
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MAINTENANCE AND CARE OF PATIENTS WITH ECMO
Peripheral cannulation should be strictly percutaneous by Seldinger technique,
which can be rapidly performed by nonsurgical staff and remotely without the
need for specialized surgical equipment, requires no skin suturing, reduces
bleeding and allows simple decannulation when ECMO has been weaned. The
use of vascular ultrasound before and during the procedure enables immediate
confirmation of venous vessel access, guidewire identification in the right atrium to
exclude coiling in proximal vessels and optimization of cannulae positioning to
reduce recirculation.
Prerequisites
Patients require management in an intensive care unit with a multidisciplinary
team approach:
 Attention should be paid to the following factors:
 Fluid and electrolyte management
 Nutritional Support
 Infection Control
 Pain Relief and sedation if needed
 Anticoagulation
 Psychosocial considerations
Maintenance of the Circuit
 Trained technician
 Medical staff with experience in ECMO use
 Circuit to be checked timorously and regularly
SPECIAL CONSIDERATIONS
 Blood flow
 Maximum flow rates are used during VV ECMO to optimize oxygen
delivery.
 VA ECMO must be high enough to provide adequate perfusion
pressure whilst still being sufficiently low to provide preload so as to
maintain left ventricular output.
 Diuresis
 Ultrafiltration can be added to the ECMO circuit
 Left ventricular monitoring
 Left ventricular output should still be closely monitored during VA
ECMO as Left ventricular function may deteriorate.
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CRITERIA FOR WEANING OR DISCONTINUING ECMO
Patients with respiratory failure
 Radiographic improvement
 Better pulmonary compliance
 Increase in arterial oxyhaemoglobin saturation
Patients with cardiac failure
 Improved Left ventricular output
COMPLICATIONS
Data are from the Extracorporeal Life Support Organization (ELSO)
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Bleeding
 Occurs in more than 40% of patients, can be fatal
 Can be attributed to heparin infusion
 Risk of bleeding can be minimised with frequent monitoring of ACT
according to patient target
Thromboembolism
 More frequent with VA ECMO than VV ECMO because infusion is into the
systemic circulation.
 Heparin infusion required
 Close circuit monitoring for clots is essential
Cannulation-related
 Operator dependant
 Can include arterial dissection, distal ischemia and sepsis
Heparin-induced thrombocytopenia
 When suspected, the heparin infusion is usually replaced by a non-heparin
anticoagulant.
Veno-Arterial specific complications
 Pulmonary haemorrhage
 Cardiac thrombosis
 Stasis of the blood which occurs if left ventricular output is not maintained
can result in thrombosis.
 Coronary or cerebral hypoxia
 Preferential perfusion of the lower extremities due to catheter location
FUTURE ADVANCEMENTS
As mentioned above significant adverse events and potential complications can
occur during extracorporeal life support. These are becoming less common and
less severe with increasing experience and major technological developments,
such as
 Heparin bounded circuits to prevent thromboembolism
 Left ventricular assist devices attached to the ECMO to improve CO2
removal
 Advances in circuit components such as oxygenators and pumps to
improve simplicity of ECMO
 ECMO can also be used on cadavers to increase the viability of organs to
be transplanted
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RESULTS OF RANDOMIZED TRIALS OF EXTRACORPOREAL MEMBRANE
OXYGENATION FOR ACUTE RESPIRATORY DISTRESS SYNDROME
The first multicenter, randomized trial to evaluate ECMO for ARDS was conducted
by the National Institutes of Health in the United States in the 1970s on 90
patients with severe ARDS refractory to conventional ventilation techniques.
Patient survival in that trial was extremely low (<10%) and no improvement with
ECMO was demonstrated. However, that study suffered from major
methodological limitations.In the 1990s, Morris et al. in Utah conducted another
randomized, controlled trial, which was a single-centre study using a device
eliminating CO2.The study was stopped for futility after only 40 patients had been
enrolled, and once again, the results did not advocate the use of this form of
respiratory assistance.
The most recent trial (CESAR) was conducted in the United Kingdom from 2001
to 2006. The patients randomized to receive ECMO support were transferred to a
single centre (Glenfield, Leicester); where as the patients randomized to the
control group were treated conventionally at designated treatment centres.
Mortality or severe disability 6 months after randomization, the primary endpoint,
was lower for the 90 patients randomized to the ECMO group (37 vs. 53%). This
is the first randomized trial showing better outcomes with ECMO for patients with
severe ARDS. However, 22 patients randomized to the ECMO arm did not receive
ECMO (died before or during transport, improved with conventional management
at the referral centre or had a contraindication to heparin).
The other major methodological problem was the absence of a standardized
protocol for mechanical ventilation in the control group. Therefore CESAR is a
good study, but does not convincingly prove ECMO is better than conventional
therapy. What it did show was that transferring adult patients with severe but
potentially reversible respiratory failure to a single centre specialising in the
treatment of severe respiratory failure for consideration of ECMO significantly
increased survival without severe disability. The role and proper use of ECMO for
patients with ARDS have not been definitively established. The continued
evolution of ECMO technology also limits the conclusions that may be drawn from
recent studies.
The role of extracorporeal carbon dioxide removal in ARDS, although potentially
promising, remains to be defined. Although the CESAR trial provides some
guidance for the use of ECMO, it is not clear which patients with ARDS are the
best candidates for this treatment. The most favourable timing for the initiation of
ECMO has not been established. Various strategies to achieve lung rest and their
effects on the inflammatory process have not been compared, nor have any such
strategies been shown to be superior to standard-of-care lung-protective
ventilation during ECMO. The most appropriate strategy for weaning patients with
ARDS from ECMO is also unknown.
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The long-term effects of ECMO, especially potential neuropsychiatric effects,
require further investigation. In short further and better studies are needed to
evaluate ECMO, especially in ARDS.
CONCLUSION
ECMO is at present not available within the public sector and is rarely used in the
private setting in our country. This modality is beneficial with good patient
selection. Most data involves ECMO use within the paediatric population with
promising results. Further studies amongst adult patients are recommended to
guide ECMO use in this group.However, ECMO is costly and labour-intensive. In
the CESAR trial, mean costs per patient in the group that could receive ECMO
were more than twice as high as in the control group, at a mean of £73,979 over a
period of 6 months.Optimal benefit from ECMO requires centralisation of services.
Furthermore adequate staff training including experienced perfusionists, doctors
and ECMO nurses are needed. This may prove difficult in a resource limited
environment.
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