Peripheral Vascular Anesthesia Flashcards
Over 50% of Vasculopaths have this comorbidity.
CAD
Heparin is a naturally occurring anticoagulant produced by ____ and _______.
- Basophils
- Mast Cells
What does heparin bind to?
- Antithrombin III
What happens to AT III when heparin is bound to it?
Enhances 1,000x the ability of AT III to inactivate thrombin and factors XII, XI, IX, X
Heparin will also inhibit thrombin activation of what factors?
- Factor V
- Factor VII
Heparin’s effect on platelet function
Inhibits platelet function
What factor does heparin effect on the extrinsic pathway?
Factor VII
What factor does heparin effect on the common pathway?
Factor V
Lipid solubility of heparin?
Poorly lipid soluble
GI absorption of heparin?
Poorly absorbed in the GI Tract
Does heparin cross the placenta?
No
Heparin’s anticoagulation increases in intensity and duration with increasing ________.
Doses
Heparin’s anticoagulation increases in intensity and duration with decrease ________, _____, and _______.
- Temperature
- Hepatic dysfunction
- Renal dysfunction
CV side effects of heparin
- Relaxation of vascular smooth muscle
- Decreased MAP, Pulmonary arterial pressure, SVR
What is the most common side effect of heparin?
Hemorrhage
What is mild HIT due to?
Platelet aggregation
Plt count for mild HIT?
<100,000
When will mild HIT begin?
Appx 15 days after initiation of heparin therapy
What is the plt count for severe HIT?
< 50,000
When will severe HIT begin?
5-10 days after initiation
What antibody is formed with severe HIT?
IgG
What are the normal functions of IgG?
- Neutralize toxins, viruses, and bacteria
- Opsonize them for phagocytosis
How does IgG react with HIT?
- lgG will bind to receptor on platelet
- Lead to platelet activation
- Activated platelets release pro-thrombotic substances (such as thrombin)
- IgG activates more platelets
Key Takeaway: IgG antibodies in HIT cause the platelets to stick together and form clots
Heparin dose for Vascular Surgery
100 units/ kg
Normal aPTT and Heparinized aPTT
- Normal aPTT: 30-35 seconds
- Heparinized aPTT: 60-70 seconds
Normal ACT
90-120 seconds
When will you draw an ACT during a vascular surgery?
- 3 minutes post heparin injection
- repeat q 30 mins to 1 hour
What is the half life of heparin?
1-2 hours
Reversal for heparin
Protamine
Where can protamine be naturally found?
Salmon Sperm
MOA of Protamine
Protamine is a positively charged alkaline that combines with negatively charged (acidic) heparin
How is heparin naturally cleared in the body?
- Reticuloendothelial system (RES)
- Protamine clears heparin faster
What is the dosage of protamine?
1 mg of protamine / 100 units of heparin
Most common side effect of protamine
Hypotension d/t histamine release
Who might be allergic to protamine?
- Pt on chronic protamine insulin
- Vasectomy
- Fish allergies
What reversal alternative can be used for patients undergoing vascular surgery if they are allergic to protamine?
Platelet factor 4
What is a rare side effect of protamine?
Pulmonary Hypertension which will lead to pulmonary vasoconstriction, pulmonary edema, and hypoxia
Pulmonary HTN from protamine is due to the secretion of ______ and ______.
- Thromboxane
- Serotonin
If a patient is prone to pulmonary hypertension secondary to protamine what can be given as pre-treatment?
Cyclooxygenase Inhibitors (Indomethacin or ASA)
At what GFR will symptoms be noted?
< 25mL/min
What what GFR will a patient be dialysis dependent?
< 10 mL/min
Most ESRD patient have their multisystem side effects controlled with _______.
Renal Replacement Therapy
What are the metabolic abnormalities of ESRD?
- Hyperkalemia
- Hypermagnesemia
- Hypocalcemia
- Hypoalbuminemia
- Water and sodium retention
- Metabolic acidosis
Hgb of ESRD patients
6-8 g/dL
CV complication of ESRD
- Increased cardiac output
- HTN/CHF
- Arrhythmias
What is the increase minute ventilation of ESRD patients due to?
Increased minute ventilation to offset metabolic acidosis
GI complications of ESRD
- Nausea, vomiting, ileus
- Hypersecretion of gastric acid
- Delayed gastric emptying
Neuro complications of ESRD
- Lethargy, confusion
- Peripheral neuropathies
Pros of AV Fistulas
- Best long-term patency
- Lowest rate of infection
- No foreign material used
Cons of AV Fistulas
- Requires a longer “maturation” time (6 weeks or more)
- May require more than one operation to create a functional dialysis fistula
Pros of AV Grafts
- Shorter time required for “maturation”
- Usually requires only one operation
Cons of AV Grafts
- Does not last as long
- More prone to infections…complete removal
- Embolectomies/revisions
Anesthesia Pre-op Considerations for AV Fistulas/ AV Grafts
- Day of surgery dialysis
- Address cardiac/pulmonary issues
- Consider ABG’s
- EKG
- Bleeding time/Coag studies
- BUN, creatinine
- Manage aspiration risk, hyperglycemia, hyperkalemia
Anesthesia Intra-op Considerations for AV Fistulas/ AV Grafts
- Access arm/blood pressure cuff
- Consider invasive monitoring with uncontrolled HTN
- Consider RSI for GA
- Decrease dose of induction agents if hypovolemic/unstable
- Maintain cardiac output
- Adequate ventilation: spontaneous/controlled to prevent hypercarbia
What fluids are usually preferred for ESRD patients?
Isolyte
When would LR be avoided for ESRD patients?
If the patient is hyperkalemic
When will NS will be used for ESRD patients?
If the patient is hypochloremic and alkalotic
What drugs will have an increased effect on ESRD patients due to decreased protein binding?
- Etomidate
- Barbiturates
- BZD
What drugs will have an increased effect on ESRD patients due to elimination concerns?
- Opioid metabolites
- Anticholinergics
- Metoclopromide
- H2 blockers
- Pancuronium
- Neostigmine
- Suggamadex
What fraction of PAD patients are over the age of 75?
two-thirds of PAD population
Clinical indication for revascularization surgery
- Claudication
- Ischemic rest pain
- Gangrene (may be considered emergent d/t potential limb loss)
Anesthesia Pre-op considerations for revascularization surgery.
- History/Physical Assessment (CAD/COPD/CKD/DM)
- Decreases or absent pulses
bruits - Intermittent claudication
- Rest pain
- Hair loss
- Temperature change
- Doppler ultrasound
- Ankle/brachial index
- Angiography
- Consider Type and Cross
Ankle-brachial index formula
SBP at ankle / SBP at arm
Ankle-brachial index for rest pain
0.4
Ankle-brachial index for impending gangrene
0.25
Normal Ankle-brachial index
0.9-1.4
What does an ankle-brachial index > 1.4 indicate?
Calcification/ Vessel Hardening
Ankle-brachial index that indicates severe arterial disease
Less than 0.5
Treatment of PAD
- Stop smoking!!!
- Normalization of blood sugars
- Treatment of hypertension
- Antiplatelet therapy
- Revascularization
What are the types of revascularization procedures?
- Angioplasty
- Stenting
- In-situ bypass
- Synthetic bypas
PAD patients requiring angioplasty and stenting through these arteries have a high success rate.
Iliac arteries
PAD patients requiring angioplasty and stenting through these arteries have a low success rate and are prone to restenosis.
Femoral/popliteal arteries
How long does a revascularization stent last?
10 years
Regions that warrant an in situ bypass
- Femoral-popliteal
- Femoral-tibial
Regions that warrant a synthetic graft bypass
- Aorta-bifemoral
- Axilla-bifemoral
- Femoral-femoral (fem-fem crossover)
Anesthesia Intraop consideration for Femoral-popliteal and Femoral-tibia bypass.
- Few concerns
- Little blood loss
- Sometimes heparin is not reversed
- 45 minute procedure
Anesthesia Intraop consideration for Aorta bi-fem/Axillo bi-fem/fem-fem crossover
- Type and cross
- Large bore IV access
- Central line/SVV monitoring
- Large blood loss may occur
- Heparin often redosed and usually reversed
- 2-4 hour procedure
Anesthesia Post-op Concerns for Revascularization Surgery
- Sudden loss of pulses
- Sudden temperature change
- Complaints of numbness/paresthesia
- Loss of motion/sensation
