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Файл:Ординатура / Хирургия / Библиотека им академика М.И. Перельмана / Книга_3781_Библиотеки_им_академика_М_И_Перельмана
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is placed in the proximal IVC, and the return cannula is placed at the IVC/RA junction. It is preferable to place the return outow cannula in the right femoral vein
since the cannula may not reach the RA from the left femoral vein in larger patients.
Finally, a dual lumen bicaval cannula can be introduced from the right IJ, passing
through the RA with the tip positioned in the IVC.Deoxygenated blood is drained
from the drainage ports which are located in the SVC and IVC and oxygenated
blood is returned through the reinjection port which is carefully positioned at the
RA and directed toward the tricuspid valve. The cannula must therefore be placed
under both TEE and uoroscopic guidance to ensure the correct positioning of the
various sideholes and to prevent catastrophic injury to the right heart. The dual
lumen cannula offers various advantages including minimal recirculation, prevention of limb ischemia complications and allows patients to ambulate freely. However,
the cannula is expensive and therefore may be best suited for patients who will
require long-term V-V ECMO therapy and rehabilitation such as those awaiting
lung transplant. Dual lumen cannulation is also more time consuming and therefore
not recommended as rst line for an emergent cannulation.
Common to all forms of cannulation is meticulous avoidance of air in the ECMO
circuit using “wet to wet” connections and robust securing of cannula with multiple
sutures to prevent inadvertent dislodgement. After cannulation, the ECMO circuit is
appropriately connected ensuring no air in the lines. It is recommended that an
“ECMO Initiation Checklist” be performed to ensure appropriate direction of tubing, adequate fresh gas supply, and appropriate levels of oxygen are conrmed.
Support should be initiated slowly to minimize abrupt temperature shifts since rapid
infusion of cold uid can cause the heart to brillate. Cannulation can trigger a
vasodilatory response so vasopressors should be available to support the blood pressure. Conversely, correction of the respiratory acidosis/hypoxia may lead to rapid
improvement in vasomotor tone and cardiac function, so close monitoring is essential. Once ECMO support is established satisfactorily, ventilatory support should be
weaned to lung protective settings to minimize further lung injury.
P. Moonsamy and J. Crowley
V-A ECMO [1, 4]
Cannulation for V-A ECMO can be achieved centrally (in the chest) or peripherally.
Peripheral cannulation is much more expeditious since it does not require a sternotomy and is therefore used in emergencies. Both open and percutaneous peripheral techniques can be used to access the femoral vessels. The open cutdown
technique has the advantage of higher success rate, easier method of ensuring limb
perfusion, and potentially easier removal of the cannulas. Drawbacks include slower
cannulation times, higher rates of bleeding, and infection. We favor ultrasoundguided percutaneous cannulation. In either strategy, the common femoral artery is
accessed below the inguinal ligament but above the bifurcation of the supercial
and deep femoral arteries. A cannula is placed using Seldinger technique. The
venous drainage cannula is placed into the femoral vein below the inguinal ligament
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with the tip located at the IVC/RA junction. The venous cannula can be placed on
the same or contralateral side to the arterial cannula. Cannula size is determined by
the vessel size/patient’s body surface area and by the goal ow. In general, 17Fr
arterial cannulas and 25Fr venous drainage cannulas are used in average sized
patients. When the femoral arterial vessels cannot be accessed, the axillary artery
can be used as an alternate for the arterial return cannula, however this carries higher
rates of bleeding complications. The carotid artery is also commonly used in pediatrics because it can be simply ligated with decannulation. This is not possible
in adults.
Central cannulation is achieved via sternotomy and has the advantages of offer-
ing antegrade arterial ow which is more physiologic and therefore avoids NorthSouth Syndrome (discussed below). The drainage cannula is placed directly into the
right atrium, and the arterial cannula is placed antegrade into the aorta. Central
cannulation carries a higher risk of infection since the patient’s chest must remain
open during the ECMO run, therefore every effort should be made to close the skin
as much as possible after cannulation. Central cannulation also allows support for
higher ows and allows for easy placement of a left ventricular vent in order to
prevent left ventricular dilation (discussed below).
As with V-V ECMO cannulation, the ECMO circuit is appropriately connected
ensuring no air in the lines, an “ECMO Checklist” is performed and support is initiated slowly. Cannulation can trigger a vasodilatory response so vasopressors should
be available to support the blood pressure. Conversely, correction of the low output
state may allow for rapid weaning of vasopressors and close monitoring of blood
pressure is critical.
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Circuit Function andMonitoring While onECMO [8]
The amount of ECMO support delivered to the patient is described by three variables: the ow through the circuit, the percentage of oxygen delivered by the gas in
the oxygenator known as the delivered oxygen fraction (FdO2), and the ow rate of
the gas in the oxygenator known as the sweep ow. The FdO2 is analogous to the
fraction of inspired oxygen (FiO2) on the ventilator and is one of the determinants
of the oxygenation of blood. The sweep ow rate determines the rate of carbon
dioxide removal from the blood and is analogous to the minute ventilation. The ow
through the circuit is determined by several factors: the rotations per minute of the
pump (RPMs), the resistance to drainage through the venous cannula, and the resistance to return through the return cannula. Increasing the RPMs will increase the
ow; however, it is important to remember that the ECMO pump is both preload
dependent and afterload sensitive so the ow may vary at the same RPMs due to
different loading conditions.
Oxygenation of the blood via the ECMO circuit is related to two factors: the
FdO2 and the total ow of the ECMO circuit. Approximately 70% of blood must
participate in efcient gas exchange to maintain an arterial saturation of 90–94%.
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Therefore if 1.0 FdO2 is delivered, then the ECMO circuit ow must be ~70% of the
cardiac output to achieve this goal. This is particularly relevant for V-V ECMO
when deciding the goal ow rates.
Monitoring the ECMO patient includes rstly a full physical exam assessing the
cannulation sites, neurologic status of the patient (stroke is a common complication
especially in anticoagulated patients) and assessing distal extremities especially in
peripherally cannulated patients. The native hemodynamic function of the patient is
also important to continually assess and is indicated by mean arterial pressure, vasopressors, and inotropes. The ventilator settings and the FdO2, sweep gas and ow
(RPMs) delivered by the ECMO circuit should be noted with the intent to continuously wean the patient from the circuit. Frequent laboratory monitoring is also necessary including complete blood count (CBC) to monitor infection (pneumonia is a
common complication), hemoglobin, platelets, and coagulation factors to prevent
bleeding complications. The kidneys do not tolerate long ECMO runs due to relative ischemia, and the patient’s creatinine must be judiciously monitored. CVVH
should be initiated early if the patient’s renal function starts to decline. In addition
to laboratory monitoring, daily chest X-rays and frequent echo are important to
assess cannula location, pulmonary edema, and left ventricular size.
P. Moonsamy and J. Crowley
Weaning ECMO [1]
The patient must have sufcient recovery of native lung function in order to liberate
from the V-V ECMO circuit. This can be detected by improvements in imaging,
lung compliance, and resolution of the underlying disease process. As the patient’s
native lung function improves, the required sweep gas ow and FdO2 will decrease.
Once these are minimal, then the patient can be placed on standard ventilatory settings, and the sweep gas turned to 0LPM.This effectively means the patient is off
ECMO.Flow is maintained in the ECMO circuit in order to prevent thrombosis;
however, no gas exchange is occurring. The patient’s tidal volumes should be
>4–5cc/kg, indicating good lung compliance. The FiO2 delivered by the ventilator
should also be weaned to whatever the clinician is willing to tolerate to come off the
ECMO circuit and just use the ventilator for oxygenation. If the patient tolerates this
“capping trial” for a prescribed period of time (6-24hrs depending on the fragility
of their respiratory status), then they can be decannulated. Decannulation from V-V
ECMO can usually be performed at the bedside with cannula removed and hemostasis obtained with sutures at the skin site and manual pressure. Patients who do not
show signs of lung recovery should be considered for referral to a lung transplant
center that has experience with prolonged ECMO weans and the possibility of lung
transplant if the patient fails to wean.
Weaning from V-A ECMO is more complicated as the sweep ow can never be
reduced to zero because this would create a large shunt with deoxygenated blood
returning to the arterial system. First and foremost, the patient’s underlying problem should have been addressed and treated before weaning and the patient’s
other end organ function should be recovering. The pulsatility of the native heart
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should be assessed with TTE, examination of the arterial line waveform and
should be >20mmHg on low dose inotropes. Once this has been achieved, a “ramp
trial” can be attempted. During this trial, the ECMO ows are slowly decremented
to 2LPM over a period of 12–24h and an echocardiogram is obtained. If this study
is promising, then the patient can be further anticoagulated, and the ows further
reduced until the circuit is clamped and the patient is observed off of ECMO.Caution
must be taken in the setting of right ventricular failure as often the right ventricle
only needs partial unloading and failure to wean may not be apparent immediately. If the wean is successful, the patient can be decannulated from V-A ECMO
which is commonly done via surgical cut down and direct repair of the femoral artery.
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Complications andTroubleshooting [4, 9]
North-South Syndrome
Also known as Harlequin Syndrome, North-South Syndrome (or differential
hypoxia) is a complication specic to peripheral V-A ECMO.The phenomenon is
caused by the retrograde direction of the arterial ow from the cannula up the aorta
toward the heart. The oxygenated “ECMO blood” meets the “native blood” that is
ejected by the heart after it has started to recover and regain pulsatility. If the
patient’s native lung function is severely compromised, then this blood has the
potential to be signicantly hypoxic. This is problematic as the coronaries and the
cerebral circulation are more likely to see native blood and consequently will suffer
hypoxic injury despite adequate performance of the ECMO circuit. Close monitoring for this phenomenon is critical and includes arterial blood gas sampling from the
right upper extremity as this reects the blood entering the cerebral circulation and
will give warning of differential hypoxia.
Troubleshooting depends on the severity of the lung injury. As a rst maneuver,
ventilatory support can be optimized to improve native blood oxygenation. However,
this is not ideal if it results in injurious settings that can potentiate further lung
injury and reduce the likelihood of recovery. Negative inotropes and diuretics can
also be used to depress cardiac function and decrease ejection. If the patient’s cardiac function has recovered signicantly, one could consider also converting to V-V
ECMO.Another option is to create a hybrid circuit, known as veno-arteriovenous
ECMO (V-AV). Here, an additional return cannula is placed in one of the jugular or
subclavian veins and y-connected to the arterial cannula so that some oxygenated
blood is returned to the venous system, “pre-oxygenating” the blood before it passes
into the native lungs and therefore before it is ejected by the heart. In effect, the
patient will then be on both V-V and V-A ECMO.This conguration can be challenging to maintain as it requires higher total drainage to support the ows needed
as well as a partial occluding clamp to adjust the relative venous vs arterial ow. As
a last resort, the patient can be converted to central cannulation (to achieve antegrade arterial ow) or biventricular support can be initiated with separate temporary
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left and right ventricular assist devices and an oxygenator in order to preoxygenate
all the blood going through the right heart.
P. Moonsamy and J. Crowley
Left Ventricular Distension [1]
An additional complication specic to peripheral V-A ECMO is left ventricular
(LV) distension which results from an impaired left ventricle facing the elevated
afterload resulting from retrograde arterial ECMO ow up the aorta. Distension of
the left ventricle will lead to further left ventricular stress in the setting of increased
wall tension as well as the potential for signicant pulmonary edema which will
reduce the likelihood of liberation from ECMO.Frequent echocardiography should
be used to assess for aortic insufciency, LV function, mitral regurgitation, and LV
size. Chest X-rays can also be used to look for pulmonary edema progression, and
consideration of a pulmonary artery catheter to monitor LV lling pressures.
If left untreated, this can lead to irreversible LV injury, pulmonary edema, and
stasis in the LV leading to clot formation. An initial maneuver can be to increase
inotropic support to encourage LV contractility. In addition, ECMO ow can be
increased further to decrease blood returning to the LV.Additional invasive methods
of decompressing the left ventricle can be used such as placement of an intra-aortic
balloon pump, placement of a percutaneous left ventricular assist device (Impella),
atrial septostomy, or placement of a surgical vent via the left ventricular apex or the
left superior pulmonary vein.
Thrombosis
In all forms of ECMO, it is optimal to maintain a reasonable degree of anticoagulation to reduce the risk of thrombosis in the circuit and thrombotic complications in
the patient. The oxygenator and circuit tubing should be monitored closely to check
for clot or brin formation, and the circuit should be switched out if large clots
form. Targeted levels of anticoagulation vary by institution and usually involve targeting a aPTT range, a Xa range, or an activated clotting time. If the risk of bleeding
is too high for a particular patient, just a bolus dose can be used for cannulation
(which carries the highest initial risk of thrombosis due to stasis in the cannula), or
anticoagulation can be avoided all together. Cannulation and running ECMO without anticoagulation have been reported, so in the appropriate patient, this is reasonable acknowledging the likely increased risk of thrombotic complications. Other
strategies to prevent thrombosis include preferentially owing the circuit at higher
rates, having two providers perform cannulation simultaneously to avoid prolonged
periods where a cannula is left clamped with no ow, and ushing of cannulas with
saline to avoid any blood sitting in them while ECMO is being prepared.
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Limb Ischemia
Limb ischemia complications with peripheral V-A ECMO are extremely common,
and frequent physical examination of the distal extremities is very important.
Doppler assessment of distal arterial ow can be challenging given the non-pulsatile
nature of the ECMO circuit. Given that the ECMO cannulas are large and can completely occlude the vessel at the insertion site, patients usually experience ischemia
complications in the limb that was cannulated. We therefore advocate for the routine
placement of a distal perfusion cannula into the supercial femoral artery (SFA) on
the same side that the femoral arterial cannula is placed. A 5–7Fr cannula is placed
antegrade into the SFA under ultrasound guidance. It is easier to place the distal
perfusor before the larger arterial cannula is placed because the SFA can go into
vasospasm after cannulation which makes it difcult to identify.
References
1. Squiers JJ, Lima B, DiMaio JM.Contemporary extracorporeal membrane oxygenation therapy
in adults: fundamental principles and systematic review of the evidence. J Thorac Cardiovasc
Surg. 2016;152(1):20–32.
2. Zapol W. Extracorporeal membrane oxygenation in severe acute respiratory failure.
JAMA. 1979;242(20):2193.
3. Akoumianaki E, Jonkman A, Sklar MC, etal. A rational approach on the use of extracorporeal membrane oxygenation in severe hypoxemia: advanced technology is not a panacea. Ann
Intensive Care. 2021;11:107.
4. Rao P, Khalpey Z, Smith R, etal. Venoarterial extracorporeal membrane oxygenation for cardiogenic shock and cardiac arrest. Circ Heart Fail. 2018;11(9):e004905.
5. https://www.elso.org/registry/internationalsummaryandreports/internationalsummary.aspx.
Accessed 23 Jun 2023.
6. Axtell AL, Funamoto M, Legassey AG, etal. Predictors of neurologic recovery in patients who
undergo extracorporeal membrane oxygenation for refractory cardiac arrest. J Cardiothorac
Vasc Anesth. 2020;34(2):356–62.
7. Osho AA, Moonsamy P, Hibbert KA, et al. Veno-venous extracorporeal membrane oxygenation for respiratory failure in COVID-19 patients: early experience from a major Academic
Medical Center in North America. Ann Surg. 2020;272(2):e75–8.
8. Mazzef MA, Rao VK, Dodd-O J, etal. Intraoperative Management of Adult Patients on
extracorporeal membrane oxygenation: an expert consensus statement from the Society of
Cardiovascular Anesthesiologists-Part I, technical aspects of extracorporeal membrane oxygenation. Anesth Analg. 2021;133(6):1459–77.
9. Sidebotham D.Troubleshooting adult ECMO.J Extra Corpor Technol. 2011;43(1):P27–32.
Chapter 30
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Durable Mechanical Circulatory Support
LynzeFranko andDavidD’Alessandro
Left Ventricular Support
Indications [1–7]
• Initially, left ventricular assist devices (LVADs) were utilized as a temporary
treatment for patients listed for transplant until a heart transplant became available. This was deemed bridge to transplant (BTT).
• Destination therapy (DT) is a term utilized for the treatment of patients with endstage heart failure refractory to optimal medical management who are not candidates for heart transplant. Reasons for these patients not to be a heart transplant
candidate often include age, active substance use such as smoking, insulindependent diabetes with end organ damage, recent cancer history, chronic renal
failure, or other signicant comorbidity. There is current FDA approval for both
BTT and DT indications (now referred to as short term and long term,
respectively).
• Alternative designations for LVAD implementation include bridge to decision
and bridge to candidacy for patients who still have tests or treatments required
before they can ofcially be evaluated or listed for heart transplantation. There is
also bridge to recovery, though this indication is less common. Bridge to recovery patients are often identied after improvement in cardiac function following
L. Franko (*)
Department of Surgery, Massachusetts General Hospital, Boston, MA, USA
e-mail: lfranko@mgb.org
D. D’Alessandro
Division of Cardiac Surgery, Department of Surgery, Massachusetts General Hospital,
Boston, MA, USA
e-mail: dadalessandro@mgh.harvard.edu
Switzerland AG 2024
J. P. Bloom, T. M. Sundt (eds.), Cardiac Surgery Clerkship, Contemporary
Surgical Clerkships, https://doi.org/10.1007/978-3-031-41301-8_30
337© The Author(s), under exclusive license to Springer Nature
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L. Franko and D. D’Alessandro
LVAD implantation. Careful evaluation can identify a small subset of patients in
whom the LVAD can be safely removed.
• Approximately 50% of LVAD utilization is for DT, while 26% is for BTT and
23% is for bridge to candidacy. However, DT or long-term LVAD therapy continues to grow as the primary designation for LVAD treatment.
• Indications for LVAD implantation include:
– New York Heart Association (NYHA) Class IV congestive heart failure symp-
toms refractory to maximal medical therapy and conventional surgical
interventions.
NYHA Stage IV=unable to carry on any physical activity without symptoms of heart failure or having symptoms at rest.
These patients continue to have this level of symptoms despite already being
on maximal medical therapy and having undergone needed surgical interventions, such as coronary artery bypass grafting or valve repair/replacement.
– Ejection fraction <25%.
– Reduced functional capacity with a maximal oxygen consumption (VO2)
<14mg/kg/min or inability to complete the test.
– Dependency on IV inotropes or temporary mechanical circulatory support.
– Estimated mortality over 50% at 1year with medical management.
• Contraindications to LVAD implantation include limited life expectancy due to
malignancy or concomitant end organ failure, pulmonary HTN, signicant right
heart failure, or lack of social support.
• The interagency registry for mechanically assisted circulatory support
(INTERMACS) collects data from government and private organizations regarding the utilization and outcomes of FDA-approved mechanical circulatory support devices. There are also INTERMACS proles or levels that further classify
patients with advanced heart failure (NYHA III–IV) to better assess their need
for mechanical circulatory support and risks related to intervention. INTERMACS
class 1 is identied as critical cardiogenic shock, while class 7 is identied as
advanced NYHA III symptoms.
– Classically, most patients selected for LVADs are INTERMACS class 2–3.
Highest risks of complications and mortality of LVAD implantation are seen
in INTERMACS class 1. Growing evidence shows improved outcomes and
reduction in complications for patients with ambulatory heart failure (class
4–7) prior to signicant decompensation with LVAD implantation. However,
there are concerns that this relatively healthy population can experience devastating complications with LVAD implantation.
• Selection for LVAD therapy is complex as the patient will need to be adherent to
medical therapy, manage the machine/batteries around the clock, and have substantial support systems in place throughout treatment. Further, these patients
can face signicant adverse events and re-hospitalizations. For this reason, selection of patients for LVAD therapy is reviewed by a multi-disciplinary team, who
can help optimize patient selection in order to maximize patient benet.
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339
Devices [3, 5, 8–10]
• Devices can either have pulsatile ow or continuous ow. Initial pulsatile devices
were pneumatic and were associated with high rates of mechanical failure. Given
this, devices were instead focused on continuous ow. In 2016, greater than 95%
of implanted devices were continuous ow. One of the newer devices, HeartMate3
(HM3; Abbott Labs, Chicago, IL), was created with an articial pulse created
with rhythmic pump speed modulation. This is thought to mimic natural blood
ow to theoretically reduce bleeding and thromboembolic events. The HM3 is
currently the only FDA-approved, durable LVAD available in the US.
• Another delineation in devices is between axial ow and centrifugal ow. Axial
ow is created by a propeller within a pipe with blood ow parallel to the axis of
rotation. Centrifugal ow is created by a disk spinning within a cavity with blood
ow perpendicular to the axis of disc rotation. Newer centrifugal pumps also use
magnetic levitation of the disc to reduce friction and hemolysis.
• There are several different LVAD devices. Three commonly utilized LVAD
devices include HeartMate II (HMII; Abbott Labs), HeartWare HVAD
(Medtronic, Minneapolis, MN), and the HM3.
– HeartMate II: FDA approved for BTT 2008 and DT 2010. Axial ow device
with the motor placed within a preperitoneal pocket. The HMII is no longer
being produced and has been replaced by the HM3.
– HVAD: FDA approved for BTT 2012 and DT 2017. Centrifugal ow device
with magnetic levitation. Motor placed within the pericardium. Recently, evidence of increased risk of signicant neurological adverse events was identied in HVAD when compared to HM3. Medtronic has stopped distribution
and sale of the HVAD.
– HeartMate3: FDA approved for BTT 2017 and DT 2018. Centrifugal ow
device with magnetic levitation. Motor placed within the pericardium. This is
currently the most common LVAD device implanted in the US. The
MOMENTUM 3 trial by Mehra etal. (2019) demonstrated survival similar
between HMII and HM3; however, HM 3 had higher rates of survival at
2years free of reoperation and disabling stroke.
REMATCH Clinical Trial [1]
• Randomized Evaluation of Mechanical Assistance for the Treatment of
Congestive Heart Failure (REMATCH) is a randomized multicenter trial evaluating outcomes comparing patients with end-stage heart disease who were not cardiac transplant candidates treated with maximum medical therapy versus
long- term LVAD.
• The study included 129 patients with NYHA stage IV heart failure (68 LVAD vs
61 medical management). The LVAD utilized in this study was the pneumatic
HeartMate VE (Thoratec, Pleasanton, CA). Survival rates were 52% in the LVAD
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group and 25% in the medical management group at 1year. Additionally, at 1
year the LVAD group reported improved quality of life compared to the medical
management group. However, the LVAD group did have 2.35 times more serious
adverse events, including infection, bleeding, and device malfunction. This was
one of the leading studies which indicated survival benet for DT over medical
management.
L. Franko and D. D’Alessandro
Surgical Implantation Technique [11–13]
• Classically, inow of the LVAD is within the apex of the left ventricle (LV). The
most common outow location for LVADs is within the ascending aorta, though
placement within the descending aorta has been utilized with minimally invasive
techniques. The placement of the pump itself is either within the pericardial
pocket (HVAD and HM3) or within a preperitoneal pocket (HMII). The drive
line is tunneled within the abdominal wall, which attaches to a power supply.
• The classic approach for LVAD implantation is through a median sternotomy,
though some less invasive approaches have been developed. These alternative
minimally invasive approaches are particularly benecial in patients with prior
coronary bypass grafts as it can help avoid accidental injury to bypass grafts during redo sternotomies. Further, these approaches can help reduce the formation
of adhesions, which can complicate cardiac transplant in the future. Even with
the classic approach, it is recommended to avoid dissection in areas critical to
cardiac transplantation, like between the aorta and pulmonary artery, in order to
avoid adhesion formation. Cardiopulmonary bypass (CPB) is most often required
with LVAD implantation, though some new techniques do not require this
support.
– Minimally invasive techniques are increasingly utilized. One approach is the
left thoracotomy combined with either mini-sternotomy versus a right minithoracotomy. The inow cannula is implanted via the left thoracotomy. Then,
the outow cannula is most often implanted via a right mini-thoracotomy or
mini-sternotomy. Minimally invasive techniques avoid the need for a complete sternotomy, which has greater morbidity and longer recovery.
• Below is a description of the general surgical technique for a HM3 implantation:
– Cannulate the patient for CPB. Bi-caval cannulation suggested if placing a
temporary RVAD or need for mitral valve repair/replacement.
– Placing the inow cannula in the LV can be performed by two methods: (1)
Sew then cut (described below) or (2) Cut then sew.
The LV apex is elevated to allow for appropriate inow placement. The
inow cannula should point toward the mitral valve. If the inow cannula
is directed toward the septum (placed too laterally), it can create obstruction
of blood ow, which can lead to long-term issues. Transesophageal echo-
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