Types of venous cannulas
*Single stage
*Two stage (atriocaval/cavoatrial)
(Two stage usually has a wider portion (basket) that sits in the right atrium and a narrower tip with holes that sits in the IVC
Numbers associated with cannulas. What does the higher number mean?
- 36/46
- 34/46
- 29/37
- The higher the number, the larger the cannula
What are 6 ways cannulas are chosen?
- Flow characteristics
- Pressure drop across the cannula
- Size of the patient
- Calculated flows
- Procedure being performed
- Resistance to flow (SVR, vessel diameter)
How does venous blood enter the circuit?
Venous blood enters the circuit by gravity or siphon drainage into the reservoir placed 40-70 cm below the level of the heart.
How is the amount of blood drained in venous drainage determined?
- CVP
- Intravascular volume
- Venous compliance
- Medications
- Anesthesia (depth of anesthesia)
*Resistance in cannulas, tubing, connectors
Characteristics of cannuals
- Wire reinforced to prevent kinking (venous cannula is reinforced)
- Thin walled to permit higher flow
- Straight, angled, low profile designs(low profile design provides clear operative field ideal for minimal incision approaches)
Too much siphon drainage may create ______ pressure in a collapsible atrium.
How is this corrected?
Negative.
(This can lead to collapse of the vessel walls around the cannula causing “chattering” in venous line. So much venous pressure that it is jumping back and forth “chattering”)
*Corrected by adding volume by “retarding the venous return”
The venous line must be ___________ of blood. If there is air in the venous line, it can cause an _______ and the return will cease.
- Full
* Air lock
If a cannula is too small what can happen?
*Will cause blood to flow around the baskets in the cannula, decrease return and fill the heart.
What are 4 measures you can take to reduce obstruction of flow?
- VAVR (vacuum assisted venous return)
- KAVR (kinetic assisted venous return)
- Baskets and fluted tipped venous cannulas
- Raising the table to improve return to the venous reservoir
Pediatric cannula sizes range from ___________
12 to 18 Fr (french)
Adults cannula sizes range from ___________
20-40 Fr (french)
Factors to determine the size of venous cannulae
- Patient requirements (size)
- Anticipated flow rate
- Index of catheter flow indices
What are the different kinds of tips on cannulae?
- Straight or angled
* Made from rigid plastic or metal
Venous cannulae are made out of _________ and may or may not have __________
- Flexible plastic
* wire reinforcement
Caval tapes are placed around the cannulas to isolate venous return to the heart this is _______
Total CPB
Negative pressure risks:
- Aspiration of gross or microscopic air causing cerebral injury
- Hemolysis
- Air aspiration into the blood compartment of membrane oxygenator
- Venous reservoir imploding
Femoral or iliac vein is used in __________
Peripheral venous cannulation
Indications for peripheral venous cannulation include:
- Unstable patients for emergent CPB prior to sternotomy or anesthesia induction
- Reoperations: to provide controlled conditions during sternotomy and exposure of the heart
- Aortic surgery
- Minimally invasive access surgery
- ECMO
Femoral cannulation-lead to ischemia (Presentation-5 P’s)
- Pain/swelling
- Pain with passive stretching
- Pallor
- Pressure measurement
- Pulselessness (may be misleading)
Sites of arterial cannulation
- Proximal aorta
- Innominate artery
- Distal aortic arch
- Femoral
- Axillary
- Subclavian
Choice of site for arterial cannulation is influenced by:
- The planned operation
* The distribution of atherosclerotic plaque
How soon before cannulation is Heparin given?
5 mins before
Activated clotting time must be _______ prior to cannulation
Extended
