Bypass Flashcards
When you hear the testing of the saw
- Re-dose analgesic
- Re-dose paralytics
- Get ready to hold lungs when actually begin sawing
order of clamping/cannulation
aortic side clamped first, then venous.
venous unclamped to fill reservoir
Highest incidence of MI
pre-op and post-op due to anxiety and pain, so treat
Pre-bypass stimulation
variable
Blunting sympathetic responses very important
Pre-bypass sequence
- Room set up
- Pre-op evaluation and patient prep (lines)
- Transport to OR, monitors connected
- Induction
- Foley, TEE, antifibrinolytic, labs, abx
- Saphenous vein harvest
- Sternotomy (lungs down, pain meds)
- LIMA harvesting & repositioning
- Pericardial sutures
- Heparinize & ACT 3 min later
- Cannulation
- Venting the heart
- Partial bypass
- Aortic cross clamping
Bypass sequence
- Full bypass & cardioplegia
- Surgeons connect grafts
- Aortic cross clamp released, re-expand lungs and ventilate
- Give protamine & inotropic support
Post bypass sequence
- Fluid mgmt. after
- Epicardial pacing wire insertion by surgeon
- Chest tube placed by surgeon
- Give cell saver
- Chest closure (hypotension)
- Transfer pt (and hypotension)
- hand of in SICU
Common positioning injury
Brachial plexus - hyperextended arms of chest wall retraction
Brachial and radial artery and nerve compression from screen or chest wall retractor
Heels, sacrum, scalp prone to ischemia from long surgical times
Alopecia
Glucose checks?
Important even in nondiabetic pt as a massive stress response
Baseline ACT and ABGs
obtained while starting antifibrinolytics
When is the highest risk of recall?
Pre-bypass during initial incisions, sternotomy, sternal spread, vessel harvesting
LIMA
Left Internal Mammary Artery has better long term patency
Reduce lung volumes and give faster RR so surgeon can access the vessels
If vessel spasms, may ask to give CCB or NTG low dose
Hypotension managed via Trendelenburg
When the pericardial sac is opened . . .
Retraction sutures are placed
Hypotension
Bradycardia
Heparin dose
300-400 units/kg body weight
Prior to blood being sent into the circuit . . .
THE PATIENT MUST BE ANTICOAGULATED
Confirm ACT 3 minutes after anticoagulation
ACT must be > 400 (450)
HAD2SUE
Heparin ACT Drugs (NMB, amnestic) Drips (turned off) Swan pulled back Urine accounted for Emboli check
SBP before cannulation
btwn 90-100 mmHg or MAP < 70 mmHg
worry about aortic dissection
When is bypass initiated?
When the perfusionist releases the venous clamp to fill the venous reservoir
Hypotension common from hemodilution decreasing SVR
If MAP cannot be raised above 30 mmHg, aortic dissection considered
When reach full flow what will happen to tracings?
Lose PAC and art line
Lungs now being bypassed
Passive lung inflation
200 mL/min is continued
Once on flow - NMB? Anesthetics?
Very important to maintain appropriate anesthetic depth
Infusions on bypass?
All stopped except insulin and antifibrinolytics
Left ventricle is vented . . .
through a left superior pulmonary vein with tip in LV - allows blood to enter the LV
aortic cross-clamp is applied - note the time as this correlates to the start of cardiac arrest
Cardioplegia is given and arrests the heart in diastole
CPB flow
50-60mL/kg/min with a pressure of 50-70mm Hg
Mixed SvO2
is maintained at 70%
Hypertension means?
anesthetic is needed
Deep NMB to prevent shivering is also required
ABGs and ACTs are checked . . .
Q 30 minutes or more
Urine output
goal is 1 mL/kg/hr
Patient’s head and face are monitored for signs of
cannula malposition as indicated by edema and JVD
Rewarming
to 36 degrees
Cardioplegia can induce what?
Hyperkalemia. K levels are monitored
Magnesium is given. Why?
Reduced post-op atrial fib
Coming off bypass - lungs
Gently re-inflated to max 30 cm H2O.
Look over the drape and see them expand
Too aggressive can rupture grafts
Coming off bypass - reperfusion cardioplegia
arrhythmias
ACLS
TEE to assess the heart
Pressors and positive inotropes
Coming off bypass - filling the heart
perfusionist will occlude venous return line to fill the right heart.
CPB is gradually decreased and preload can be added until appropriate status is reached
PAC is re-advanced
CPB can be initiated if emergently needed
IABP can be placed if pharmacologically unable to support the heart
Coming off Pump
Wide Receiver Most Valuable Player
Warm - is the pt and heart warm? Rhythm - NSR? pace? Monitors - turn them back on Ventilation - turn on the ventilator Perfusion - what is the pump flow
Post bypass
heparin reversed
BP is lowered to MAP of 70 or systolic of 90
Venous cannula removed first, arterial cannula second.
Blood left in the reservoir is washed and given back to pt
When can you fast track a pt?
Without low CO syndrome (EFs > 35%)
Bypass machine - flow of blood
Blood is removed from RA via tubing
Drained into a reservoir
Pumped into an oxygenator (adds O2 and removes CO2). Volatile gases can be added here. heat exchanger in conjunction with oxygenator
Filtered back into the aorta to perfuse the body
Electrical arrest
Heart is held in arrest by use of cardioplegia
CI is kept at 2-2.4 L/min and is typically non-pulsatile
The machine can change flow to create a MAP btwn 50-80
Non-endothealized circuit causes
a massive inflammatory response
The Prime
Circuit is primed with electrolyte solution
Air is removed
Meds can be added
Colloids can be added - heparin, mannitol, etc.
Causes dilution anemia that lowers HCT to 22-25%
Cardioplegia mix
Hyperkalemic crystalloid mixed with blood 4:1 blood to crystalloid
First dose (induction dose) is cold with 30 mEq of K, with subsequent doses having 1/2 this K level and are given every 15-20 minutes
The K arrests the heart in diastole
Myocardial protective strategy
Systemic hypothermia
Cardia hypothermia
also provides some cerebral protection
Bypass physiologic effects
Systemic inflammatory response
Large spike in cortisol, catecholamines, vasopressin, angiotensin levels, oxygen free radicals
Bypass physiologic effects
Heart
Myocardial stunning
SIRS can cause injury as well
Bypass physiologic effects
Brain
Type 1 outcomes - death, stroke, coma, TIA
Type 2 outcomes - cognitive defects
*only hypothermia demonstrates efficacy in reducing these complications
Bypass physiologic effects
Lungs
Mild atelectasis Pleural effusions
Hemo/pneumo thorax
Pulmonary emboli
Bypass physiologic effects
Kidneys
AKI
Bypass physiologic effects
GI
splenic hypo-perfusion
Bypass physiologic effects
Coagulation
Platelets and clotting factors are diluted and denatured by mechanical trauma
Protamine too can cause anti-coag effect
Risk factors for CNS injury
poor baseline cognition lower years of education advanced age diabetes CPB time IABP Excessive alcohol intake Hx of CABG Arrhythmia on day of surgery Hx of unstable angina Atheroma of the aorta Presence of carotid disease (repair prior to surgery)
Hypotension and CNS injury
Not risk factor for cognitive decline
Risk of CVA higher - higher pressures perfuse pneumunbric areas better
Hyperthermia post op
common in first 24 hrs
Neuroprotection strategies
- Emboli reduction
- Pulsatile flow
- Hypothermia
- Acid base mgmt
Temp hypothermia of 10 degrees C
Lowers CMRO2 6-7% Blocks metabolism Blocks glutamate Reduces Ca influx Hastens recovery of protein synthesis
Temp over 37 associated with
increased risk of stroke
How does CPB keep CBF autoregulated?
CBF remains autoregulated in non-pulsatile hypothermic pt using alpha stat blood gas mgmt. w/in the range of 50-100 mmHg.
HTN shifts this to 60 mmHg.
Diabetics may require a higher minimum MAP
Glucose mgmt. and CNS
essential
<180
>180 bad for brain
glucose is converted to lactate that increases intracellular acidosis and impairs intracellular homeostasis and metabolism
hemodilution and serum cr
falsely lowers creatinine
Risk factors for AKI
emergent re-do procedures valvular procedures prolonged CPB old age obesity AA HTN anemia atherosclerosis DBM
Renal protection
precedex
glycemic control
Pharmacologic interventions and AKI?
not good for protection or treatment
Anesthesia for Bypass
Pre-meds
Reduce apprehension and provide relief
- benzos - versed
- Alpha agonists (precedex) (note: brady, MAP reduction, CO reduction make these less attractive)
- Continue BB, statins, ASA
- ABX (Cafazolin, Vanco which is re-dosed at end of procedure if 50% of BV is replaced)
Monitoring for Bypass
- ECG leads II and V5
- artline
- Central venous line to monitor RAP and provide pressors
- PAC ? (current guidelines for Cardio shock or NYHA III or IV)
- TEE
- Cerebral oximetry
TEE in bypass
Earliest recognition of ischemia
Allows for aorta assessment where the CPB cannula enters to assess for atheromatous plaques and ensure appropriate cannulation
*Should be used in all cardiac or thoracic aortic surgeries
Anesthesia for Bypass
Induction drugs
- Etomidate is typically preferred
- Propofol in hemodynamically stable pts
- Newer studies show preference for volatile agents over TIVA bc of anesthetic preconditioning - continuous providing greatest benefit
- Ketamine rarely used bc of sympathomimetic effect
- Versed is used bc has minimal hemo effects
Why etomidate?
Lack of inotropic or sympathomimetic effects
Can cause pain on injection
Combine with opioids
Morphine in CABG?
no bc of vasodilation from histamine
did not allow for appropriate amnesia
Fentanyl in CABG
yes but in combo with other anesthetics
max of 20 mcg/kg
Sufena in CABG
More expensive with no benefit over fentanyl
3 mcg/kg
Remifentanil
Good thought, but extreme care must be given to ensure pt control at the end of surgery to prevent an abrupt catecholamine surge
NMB and CABG
Avoid histamine release
Avoid vagolytic effects that cause tachycardia
Vec is hemodynamically stable but repeat doses can accumulate an active metabolite
Roc is hemodynamically stable UNLESS using high doses which can produce mild vagolytic effects
Alpha 2 agonists and CABG
rarely used preoperatively but perhaps in ICU and postop care
Reduce catecholamine levels and provide analgesia
Why is pt ALWAYS heparinized prior to cannulation?
W/o it massive clot formation will occur300-400 units/kg for CPB and given through a central line
ACT is used to measure
ACT values - normal and Bypass
Normal is 80-120 secs
Bypass > 400
Neuraxial anesthesia
Profound sympathectomy
Thoracic epidurals dilate the coronary arteries
Cases can be canceled due to a blood tap during the epidural placement and these pts are on antiplatelet meds
Benefits? reduction in delirium, pneumonia, ARF, myocardial dysfunction, cost savings
Ischemia mgmt
- NTG has blunted response while pt is on CPB due to PVC absorption of the drug, alterations in blood flow and hemodilution
- When coming off pump, NTG is useful to treat residual ischemia, spasm, reduce preload and afterload and is combined with a vasopressor to maintain CA PP. Performs more favorably then using CCB or SNP
- Can use nicardipine or Clevidipine
- BB - esmolol
- Propofol - no benefit/harm
Blood use and Conservation
Antibrinoytics reduce bleeding and chances of needing transfusion Aminocaproic acid and TXA inhibit plasmin Cell saver (lacs coag factors, so dilation coagulopathy can occur) Retrograde autologous priming - reduce the prime solution. arterial system allowed to backprime the CPB machine Ultrafiltration - leaving coag factors and RBCs, raises HCT. Useful in hypervolume pt
Amicar and TXA doses
Amicar - 50 mg/kg bolus over 30 min and then 25 mg/kg/ hr infusion
TXA is given as a 10 mg/kg bolus and a 1-2 mg/kg/ hr
*TXA is 5-10x more potent
Off pump CABG
Involves changing heart geometry which has marked hemodynamic effects
1/3 CABG off pump
Suciton devices are used to pull and suspend the heart during off pump grafting. The heart is lifted to work on posterior vessels.
SV can be reduced by 44%, CO by 32% and MAP by 26% and HR by 26%. Corrected with Trend.
Starfish apical sucion has less hemo effects
Anesthesia technique isn’t different.
BP preferred mgmt. with pressors vs. fluid to avoid aortic cross clamping which reduces embolization risk
Lose temp - no active re-warming
Off pump distal anastomosis
MAP > 80 mmHg
Off pump proximal anastomosis
MAP down to 60 mm Hg
Off pump anticoag
controversial
Some use 100-200 units/kg with target ACTS of 250-300. Others use full dose
MIDCAB
Minimally invasive direct coronary artery bypass
LIMA takedown and anastomosis to the LAD through a small anterior thoracotomy
TECAB
Totally endoscopic coronary revascularization utilizes mall chest wall incisions and thoracospic instruments with robot to perform the surgery
Port Access CABG
uses video assistance for left internal thoracic artery harvesting - CPB is used and anastomoses are sewn
