Ultrafiltration of Low Molecular Proteins

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CPB & Body Water Changes
Seoul National University Hospital
Department of Thoracic & Cardiovascular Surgery
Total Body Water after CPB
* Cardiopulmonary bypass  inflammatory response  Increased
capillary permeability  rise in total body water in extravascular
fluid compartment ( massive edema because of relatively loose
areolar tissue in children )
1. Interstitial edema in the lung
Reduced efficiency of gas transfer
Reduced pulmonary compliance
2. Myocardial edema in heart ; Poor ventricular function
3. Cerebral edema
4. Ascites and prolonged ileus
5. Renal function prejudiced ; Renal immaturity in neonate
Risk Factors for Rise in TBW
1.
2.
3.
4.
5.
Low body weight
Low temperature
Long duration of bypass
Extremes of hemodilution
Tissue ischemia
Pediatric Practice of Hemodilution
1. Background
Hypothermia, Metabolic rate, Flow rate, Blood
2. Level of hematocrit
30%
: recently
20-24%
: majority
less than 15% : accepted in some
3. Low hematocrit
Fall in the delivery of oxygen
Fall in colloid osmotic pressure
Exaggerate any existing capillary leak
Strategies for Fluid Collection
1. Optimize bypass technique
Flow rate for temperature
Perfusion pressure
Even distribution by vasodilation
2.
3.
4.
5.
6.
7.
8.
Minimize circuit volume
Biocompatible circuitry
Appropriate pump prime (albumin, buffers)
Postoperative diuresis
Peritoneal dialysis
Various anti-inflammatory therapies
Ultrafiltration
Third-space Fluid Collection
• After CPB, they may continue to third-space
fluid for 24 to 36 hours in younger patients
• Factors favoring fluid accumulation
1. Elevation of CVP
2. Reduced cardiac output
3. Reduced urine output
4. Need for high ventilatory pressures
Pre-Bypass Management in Young
• Consider any patient who requires CPB in the
first month of life as a high-risk patient
• Premedicate with methylprednisolone 10mg/kg
IV 8 hours and again 2 hours before surgery
• Many centers now administer aprotinin to
neonate and infants at the beginning of
exposure to CPB to reduce inflammatory
response
Modifications of DHCA
• Evidence that continuous, low-flow, hypothermic CPB might
lead to excessive post-bypass edema and diminished pulmonary
function than deep hypothermic circulatory arrest. In part this
may be because of prolonged exposure to CPB.
• Prebypass treatment with steroids and aprotinin, as
well as pre-bypass and pre-DHCA hyperoxygenation
• Adequate duration of cooling(>20min), as well as
higher Hct. during cooling phase
• Use of pH-stat blood gas strategy, for high risk patients
• Limiting the duration of DHCA by intermittent
cerebral perfusion for 1-2 minutes at 15 to 20 minutes
intervals
• Use of modified ultrafiltration
• Attention to postoperative cerebral energetics
Management of Fluid Collection
• Leaving a foramen defect open
• Judicious use of inotropes
• Leaving sternum open to prevent excessive
increases in pulmonary pressures
• Steroids, if given preoperatively and in the
immediate post-CPB period
• Placement of PD catheter
• Short period of ECMO in extremely elevated
CVP & persistent fluid accumulation
Development of Ultrafiltration
* Fluids are passed across porous membranes, and in
which aggregates with a molecular mass less than pore
size are filtered, because of transmembrane gradient.
* In the process of ultrafiltration, no fluid is transfused
back as a replacement for the volume of ultrafiltrate
removed. When the fluid is transfused to compensate
the loss of ultrafiltrate, the process is termed
hemofiltration.
Principles of Ultrafiltration
1. Transmembrane pressure
2.
Blood flow rate
3.
Depth of pores (membrane thickness)
4.
Number of pores (membrane surface area)
5.
Size of pores (membrane composition)
6.
Hematocrit of blood
Construction of Ultrafilters
1. Structure of filter
1) Depth filters
2) Screen filters
2. Type of ultrafilters
1) Paralled plate type
2) Hollow fibers as capillary type
Ultrafiltration During OHS
1. Conventional ultrafiltration
Usually commenced during rewarming phase
of bypass after temperature has reached 28oc.
2. Modified(GOS) ultrafiltration
Rate of blood flow(100-300ml/min)
Suction to the filtrate part(-100, -125cmH2O)
Achieve a hematocrit of 36-42%
Adverse Effects of Ultrafiltration
1. Another source of trauma to the blood
minimal changes in the blood, particularly during
the 1st 15~30 minutes
2. Activate the component casacade, &
leukopenia
3. The ultrafiltrate has been shown to
activate neutrophils.
Ultrafiltration of Low Molecular Proteins
1. Molecular weight proteins upto 50 kilodaltons
are removed.
2. Pressure drop across filter is about 75mmHg.
3. Small molecules or small portion of heparin
& aprotinin are ultrafiltrated & concentrated .
4. Anesthetics, midazolam & alfentanil plasma
level are decreased a bit, but they remain
high enough.
Mechanisms of Beneficial Effects
of MUF
The mechanisms by which use of modified
ultrafiltration (MUF) results in improved
hemodynamics are unknown
• Decreased tissue edema
• Reversal of hemodilution
• Remove systemic inflammatory mediators
& vasoactive substances
Potential Clinical Benefits of MUF
• Improved cardiac function
• Improved pulmonary function &
resulted in a fall in PVR
• Decreased bleeding & blood product
requirements
• Decreased pleural effusions following
Fontan operation
Beneficial Effects of MUF
•
•
•
•
•
Reduce accumulation of total body water
Decrease postoperative blood loss
Decrease postoperative blood products
Increase in arterial blood pressure
Decrease in PVR with unchanged SVR
Factors for Rise in Blood Pressure
1. Increase in viscosity and subsequent increase
in systemic vascular resistance
2. Decrease in myocardial edema
3. Elimination of vasodilators or anesthetic agents
4. Filtration of toxic compounds
(cytokines, myocardial depressant factor, TNF)
Advantages of MUF
1. It ultrafilters the patient.
2. Hemoconcentrates the circuit.
3. Returns nearly all the blood to the patient.
4. Keep the circuit primed at all times.
5. Retains option to ultrafilter during bypass.
6. The perfusionist can devote his attention to
the procedure.
Disadvantages of MUF
1. Delay of approximately 10 minutes
2. Potential for hemodynamic instability
3. Creation of an arteriovenous shunt
4. Intercompartmental fluid shift
5. Entrainment of air from a cannula
6. Obstructive cannula in small aorta
Not Using Modified Ultrafiltration
1. Surgeon’s impatience
2. Some bad experience
3. Increased complexity
4. Doubts about cost-effectiveness
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