ECMO Basics
ECMO Basics
ECMO Basics
History of ECMO
1930s-1950s: research into bypass for cardiac surgery; invention of roller-pump
1956: Invention of membrane lung
History
1957 cardiopulmonary bypass used in OR 1965-75 ECMO tried in premature infants (universally fatal) 1972 1st human survivor adult patient 1975 1st term neonate survivor 1981- Began use for PPHN By 1986 used in 715 newborns at 18 centers
Basic mechanics
Blood is drained from the right atrium Blood is warmed and oxygenated Excess CO2 is removed Oxygenated blood is returned to the aorta
(or for VV ECMO into the right atrium)
ECMO blood mixes with blood ejected from the left ventricle
Diagram: CNMC ECMO Training Manual, Short BL, Mikesell G, and Muir R (eds), 2004
VA ECMO
Used for respiratory failure Used for cardiac failure Used for both
VA cannulation
VV ECMO
Used primarily for respiratory failure Indirectly improved cardiac function
VV cannulation
Venous drainage
Primarily a passive process Depends on sufficient preload (volume) Lack of venous return results in drop in pressure in the bladder pump stops Improved by height of patient Improved by intravascular volume
Oxygen delivery
Depends on dissolved O2 in plasma and O2 bound to hemoglobin CaO2 = (SaO2 x Hb x 1.36) + (PaO2 x 0.003) On ECMO depends on
Lungs Membrane oxygenator
Ventilation
CO2 removal
Via lungs
May be quite limited Depends on minute ventilation
Membrane oxygenator
Very efficient May be excessive- can put CO2 back into circuit if needed
Indications
Hypoxic respiratory failure not manageable by other means Neonates (Pulmonary hypertension -meconium aspiration, asphyxia, HMD, sepsis, D hernia) Older children (ARDS, pneumonia, status asthmaticus) Cardiac failure not manageable by other means Post cardiac surgery, myocarditis, cardiomyopathy, intractable arrythmias, drug overdose Unlikely to be successful if not off in 5-7 days post bypass Should not be a bridge to cardiac transplant Septic shock not manageable by other means Cardiac arrest ??????????????
Contraindications
Severe Bleeding (Contraindication to anticoagulation)
Neonates-intraventricular hemorrhage > Grade 1 or 2 Major trauma, severe burns??, head injury with bleeds Major coagulopathy
Survival
Neonatal respiratory failure 80% Pediatric respiratory failure 60% Adult respiratory failure 50% Pediatric cardiac 45% Adult cardiac 40%
Univ. of Michigan ECMO website
Pre-cannulation preparation
Neonates:
Head ultrasound- r/o bleed Echocardiogram evaluate for structural heart disease
Labs: Hb, platelets, coags and metabolic panel Lines, tubes, procedures BEFORE bypass
Foley catheter with balloon Nice to have a central line and arterial line Need peripheral access at minimum
Pre-cannulation preparation
Prepare anesthetic
Fentanyl Pancuronium/vecuronium
Resuscitation meds
Epinephrine, CaCl, NaHCO3
Circuit Components
Cannulae:VV ECMO
VV ECMO:
Double lumen right atrial RA femoral; femoral femoral or RA
Available double lumen: 12 31 Fr Usually placed by surgical cutdown in neonates Can be percutaneous in children / adults CXR, sometimes echo, to check position
Venous Reservoir
Also known as bladder On most ECMO circuits, venous return from the patient is completely passive, by gravity Bladder acts as venous resevoir to avoid negative pressure generated by pump, which could cavitate air out of the blood Automatic feedback control to shut off pump when bladder collapses (chirping)
Roller Pump
Reliable use for many years Correct occlusion essential to calculate correct blood flow rate,( flow rate is CALCULATED and NOT MEASUREDrevolutions/min, tubing diameter, occlusion) and avoid hemolysis Hand crank available for power failure
Oxygenator
More accurate name: membrane lung Oxygenation:
FiO2 to oxygenator Blood flow rate Membrane surface area (can add second oxygenator)
CO2 removal
Very efficient removal Affected by gas sweep flow Usually have to add some CO2 back to gas mixture
Heat exchanger
Required Monitoring
Mixed venous sats Pressure monitoring (prepump, postpump, postmembrane) Bubble detector 3 sets of blood gases: post-oxygenator, patient, mixed venous End tidal CO2 very low while on ECMO - low pulmonary blood flows Daily Head U/S in infants
CAVH
Most patients on ECMO develop fluid overload, sometimes anuria, despite diuretics Non-pulsatile flow to kidneys may affect their function Possible to put hemofilter in line with ECMO pump for UF, CAVH or CAVHD Diuretics vs. Ultrafiltration
Heparinization
Heparin bolus (100 units/kg) given just before bypass Activated clotting time at bedside hourly Usual ACT goal: 180-220 Circuit usually needs to be changed every 7-10 days due to clots
Venovenous ECMO
Advantages:
Coronary arteries & lungs receive oxygenated blood Spare carotid Less risk of embolic stroke, air embolus Pulsatile flow to organs
Disadvantages:
No cardiac support- only use for pulmonary indications Lower patient pO2
Complications of ECMO
Hemorrhage (pulmonary, intracranial, GI, surgical site) CNS infarction Seizures (metabolic or CNS cause) Renal failure Hyperbilirubinemia Sepsis
Bleeding
Topical agents Lower ACT goal (180-200, or even 160-180) Set platelet goal higher FFP or fibrinogen/cryoprecipitate Add Amicar Surgical exploration Dont discontinue heparin, give more cryo and platelets Discontinue ECMO
Cardiac Stun
Case: Neonate on VA ECMO x 24 hours, heart rate falls to 20. What do you do? 5-10% of patients on VA ECMO More common in neonates Worsened by hypertension Dont do CPR turn up pump flow
ELSO registry
Founded 1989 145 participating centers worldwide Goal: include All ECMO patients To date:
18,000 newborns 4,000 pediatric patients 1,000 adults
www.elso.med.umich.edu
Summary Points
ECMO is supportive therapy considered for cardiorespiratory failure with reversible cause Consider VA vs VV ECMO depending on underlying pathophysiology Circuit components are complex and require multidisciplinary team effort for effective routine and emergency management