Test 6 Flashcards
Venous drainage from superior vena cava
1/3
Venous drainage from inferior vena cava
2/3
-more veins under the heart allowing for more drainage
Types of venous drainage
- achieved by gravity- pressure differential between patient and top of reservoir
- augmented- when gravity alone does not provide adequate drainage requiring a vacuum or kenetic assist (centrifugal)
Siphon Drainage (Gravity)
- Venous reservoir must be below patient
- venous lines must be filled with fluid
- amount of drainage depends on: Central venous pressure, distance from patient to blood level in venous reservoir, and resistance created by cannula, connectors, and venous line
- siphon gradient of 30-40 mmHg is normal
Venous cannula made of/look like
- flexible plastic
- single stage or two stage
- straight or right angled
- wire reinforced to prevent kinking
- tip plastic or metal
Cannula size based on
patient’s weight and BSA
Limiting factor of venous drainage because
narrowest component of CPB venous system
site for venous cannulation
- single cannulation of the right atrium
- bicaval cannulation of the SVC and IVC (mitral valve repair)
- Dual stage cannulation of atrium and IVC (most common)(CABG)
- femoral vein cannulation (reoperations)
two-stage venous cannulation
- single cannula inserted into right atrium through the right atrial appendage
- narrow tip of cannula sits in IVC which drains the vein
- can’t have total pulmonary bypass
- wider portion sits in the RA where it receives blood rom coronary sinus and SVC
Advantages of two-stage cannulation
- simple
- fast
- good right heart decompression
- less traumatic
Disadvantages of two-stage cannulation
- very sensitive to positioning especially when heart is lifted
- leads to poor drainage
process of two-stage cannulation
- Venous cannula placed after insertion of atrial cannula
- purse string sutures in RA appendage
- Cut tip of RA appendage
- insert venous cannula
- tighten purse string
- fill cannula with fluid
- connect cannula to pump lines
- clamp tubing to drapes
bicaval venous cannulation
- separate cannulation of SVC and IVC
- incision through RA or directly in vena cava
- caval tapes often used which forces all venous return of patient to pass to ECC
- caval occlusion is called “total bypass”
Advantages of bicaval venous cannulation
- good caval drainage
- best myocardial protection
- complete right heart exclusion
Disadvantages of bicaval venous cannulation
- slower speed of cannulation
- technically more difficult
- poor right heart decompression when heart lifted
Femoral venous cannulation
- used for emergency CPB
- reoperations
- minimally invasive surgeries
When using femoral cannulation
- want larges cannula as possible
- inserted with the aid of transesopageal echo (TEE)
- most likely need vacuum or kenetic assist
impact of Persistent Left Superior Vena Cava (LSVC)
- .3-.5% of population
- 2-10% of patients with congenital heart disease
Left superior vena cava (LSVC)
- usually drain into the coronary sinus then into RA
- suspected when there is a large coronary sinus
- Sometimes can be seen in echocardiagraphy
Problems associated with LSVC
- complicate passage of PA catheter
- interfere with administration of retrograde cardioplegia because balloon on catheter does not seal then leaks into RA
- if bicaval cannulation used problems with right heart decompression and venous return due to additional system venous blool into RA in which the surgeon can occlude or cannulate LSVC to solve
Complications achieving venous drainage
- atrial dysrhythmias
- laceration of atrium
- bleeding of atrium
- laceration of vena cava
- malposition of cannula tips
- displacement of PA catheter
Causes of low venous return
- reduced venous pressure (hypovolemia or drugs causing venodilation)
- malposition of cannulas
- kinks in venous line
- clamps on venous line
- air lock
- cannulas too small
Venous chatter
- catheter draining too efficiently
- drainage holes become obsructed by RA tissue
- causes sporadic changes in venous flow
- difficult to sew, heart is moving
remedies for venous chatter
- decrease height gradient
- partially occlude venous line
- decrease vacuum
What surgeon wants
- clear, easily visible operative field (exposure)
- small cannula
- no physiological problems from not enough venous return (increased CVP(central venous pressure)/ volume overload
what perfusionists want
- large cannula
- good flow dynamics
- lots of volume draining to the reservoir
- no air
performance of venous cannula depends on
- size
- design
- proper placement
- ability to drain (gravity or vacuum)
