Exam 2 - Topic 3 - Pumps For The ECC Flashcards
1
Q
Methods for moving fluids
A
- Volumetric displacement (mechanically or with other fluids)
Ex. Positive displacement roller pump - mechanical - Centrifugal force (Centrifugal/rotary pump - suck and push)
- Gravity (Drain the Veins)
- Relative vacuum (Drain the Veins)
- Kinetic assist (Ex. Centrifugal pump) (Drain the Veins)
- Mechanical impulse (some old VADs)
2
Q
Kinetic assists method
A
- Example is Centrifugal pump
- Pro: Can create a vacuum for great suction
Safer than roller pumps as it is harder for them to push air - Con: Can make big air bubbles into small micro air bubbles
Can implode reservoir if no vacuum release
3
Q
Heart as a pump
A
- generates blood flow and blood pressure
- blood carried to body via vascular system
- valves of heart ensure one way flow
- controlled by neural innervation, hormones, and volume status
- pumping rate controlled by internal “pacemaker”
4
Q
Arterial pump (vs. Heart as pump)
A
- Also generates blood flow and blood pressure
- Blood carried to body via arterial lines and arterial cannula -> then carried to tissues via vascular system
- Tubing of ECC ensures one way flow (need to clamp when coming off CPB when using centrifugal pump… Otherwise back flow)
- Pump is controlled by perfusionist
- Pumping rate controlled by perfusionist (RPMs and tube diameter)
5
Q
Cardiac output (aka blood flow)
A
- CO = (SV)(HR)
- Determinants:
Preload - venous return / blood volume (amt into heart)
Afterload - Aortic Diastolic pressure / SVR
-> what is it pumping against / size of tubing
Contractility - Starling curve / neural / hormonal
HR - intrinsic / neural / hormonal
6
Q
Starling Curve
A
- Relationship between fill and CO
- > Fill on X axis….CO on Y - Parabolic shape
- increase in fill…increase in CO until max fill reached
- > anything after max fill reduces CO due to over stretching
- > if too overstretched…muscle can never contract back…kills heart
7
Q
Arterial pump CO
A
- What is read on machine if calibrated correctly
- Amount of blood pumped per minute
- PF = (SV)(RPM)
- > SV = pir^2l*2
8
Q
Physiological factors affecting Perfusion flow
A
- Preload: venous return to venous cannula / blood volume / venous return gradient (siphon or augmented)
- Afterload: resistance of tubing, heat exchanger, oxygenator, arterial line filter, and patients SVR
- Contractility: pump type / tubing size / fixed?
- HR: RPMs
9
Q
Characteristics of Ideal Blood Pump
A
- Flow rate of at least 7 L/min against 500mmHg
- Flow independent of afterload and preload
- Controllable SV and pulse rate
- Flow proportional to pulse rate
- Exact and reproducible calibration of pump flow
- Minimal transfer of energy to blood (not damage blood too much)
- Parts in contact w/ blood should be:
- disposable
- smooth
- free of stagnation, turbulence, cavitation
- biocompatible on surface - Have battery / manual backup
10
Q
Positive displacement pump examples
A
- Reciprocating: chamber is alternately filled and emptied
- Roller: most common (what we use)
11
Q
Reciprocating pump
A
- Creates pulsatile flow
- Actuator used to expel bloop from pump chamber
- > either in contact with blood or separated by diaphragm - Needs valves to ensure no back flow
- Used for long term assistance
12
Q
Roller pumps
A
- Output depends on pump speed & volume displaced/rotation
- Has a semi-circular “raceway”
- Volume displaced/rotation based on tubing size & length of raceway
- Can be single, dual, or multiple (dual most common)
- DeBakey a leader in field (stopped tube creeping with new design)
13
Q
Creepage
A
1 - tubing creeping through raceway as roller turns
2 - moving clamp down the tube to compensate for blood pressure
14
Q
Ideal characteristics of boot tubing
A
- transparent
- resilient
- flexible and kink-resistant
- crack proof
- minimal spallation
- biocompatibility
- tolerate temperature extremes (15-42)
15
Q
Types of tubing
A
- Silicone rubber: most biocompatible / most spallation
- Latex: not used in USA
- PVC: most common now / blend of PVC, organic oils, organo-metal soaps
16
Q
Durometer
A
- How hard the tube is
- higher # is higher tubing
- ECC tubing is 65-72 / IV tubing is 80
- Temp affects hardness
- Hardness affects: tubing memory, fatigue life, spallation
17
Q
Spallation
A
- Release of micro particles from inner wall of tubing
- can cause embolic potential
- majority of it happens first 2-4 hours (hence pre-bypass filter)
- What affects spallation
- pump RPMs / tubing durometer / age of tubing
18
Q
Optimal Occlusion
A
- just barely occlusive
- occlusion must be set on all pump heads for every procedure
- > every time
- Always TIGHTEN to occlusion
19
Q
Gold standard of occlusion
A
- raise tubing so meniscus is 30 in above raceway
- meniscus drops 1 cm every 1 min
- not really used
20
Q
Dynamic Occlusion
A
- goal is to get fluid column to stop moving at 200-250 mmHg
- > why? It will match the typical afterload resistance in CPB - clamp distal to outlet
- let pressure settle to 250-300 mmHg
21
Q
Characteristics of Pump Occlusion
A
- Occlusion can vary due to temp and fluid composition
- Over occlusion -> hemolysis, increased tubing wear/stress
- Under occlusion -> back flow / turbulence / inaccurate flow calibration / hemolysis
- Turbulence measured by Reynolds # ( >2000 is bad)
22
Q
Afterload and preload dependence (Roller)
A
- positive displacement pumps are after/preload independent
- doesn’t matter pressure after or before pump….volume displacement is constant at a given RPM
- Consequences: - excessive distal pressure (can blow circuit)
- can generate negative pressure if inlet is clamped
- can pump large volumes of air very fast to patient
23
Q
Roller pump complications
A
- Malocclusion
- Miscalibration
- Fracture / rupture tubing
- “Runaway” pump head
- Loss of power
- Spallation
- Can pump gross volume of air
- Can blow up circuit if arterial line is clamped or occluded
- can pull air out of solution if negative pressure introduced
24
Q
Types of Centrifugal pumps
A
- Axial: Archimedean screw / small prime volume and weak power / most expensive / not used for bypass
- Diagonal: centrifugal / large prime volume / mid power / disposable
- Radial: centrifugal / large prime volume / high power / disposable
25
Q
Rotary / Axial Centrifugal pump
A
- 2.5 - 5L/min
- Very high RPM….can only be used for short time otherwise hemolysis
- placed in Cath lab
26
Q
Diagonal/Radial centrifugal pumps
A
- came about in 1973 by Biomedicus
- requires drive console, disposable pump head, and flow meter
- two types of pump heads: concentric and impellers (fins)
- creates pressure gradient between inlet and outlet via vortex
27
Q
Flow generation formula of Centrifugal pump
A
Blood flow (Q) = (Po - Pi) / R
Po = outlet pressure Pi = inlet pressure R = resistance
28
Q
Centrifugal Force Generation formula
A
F = m*v^2 / r
So….if air gets into pump…force = 0 (air has no mass)…pump will stop
-> have to reprime but it is safer
Also shows us the larger the diameter…the more efficient (more force)
29
Q
Max positive and negative pressures of Cent. Pumps
A
-Maximum positive outlet pressure = 700 - 900 mmHg
>900….BOOM
- Maximum negative inlet pressure = -400 - -500 mmHg
30
Q
Constants for each pump type
A
- Roller - constant flow
- Centrifugal - dependent on inlet/outlet pressure
- Heart - constant pressure
31
Q
Centrifugal pump afterload/preload dependency
A
- They are dependent on them
- Inversely related to afterload
- if afterload pressure>outlet pressure -> no flow - Directly related to preload
- if too low preload…cavitation possible and line chatter - So…flow rate not constant at any given RPM…need flow meter!
32
Q
Complications of Centrifugal pumps
A
- Retrograde flow possible when coming off bypass
- Must clamp when coming off - Pump failure
- Speed surges
33
Q
Safety devices
A
- Low level sensors
- Bubble detectors
- high/low pressure sensors
- one way valves
- battery and flashlight that works
- hand cranks
