principles of microsurgery

Question 1

List the general principles of microsurgery

Answer 1

1. CHARACTERIZE THE DEFECT: location, dimensions (diameter, depth, margins), adjacent zone of injury, optimize wound base from infected/necrotic tissue
2. IDENTIFY THE DONOR: like with like, sufficient volume (deadspace) or surface area, pedicle characteristics, donor morbidity
3. IDENTIFY RECIPIENT VESSELS, back-up vessels, consider/anticipate vein graft
4. VESSEL PREPARATION: trim adventitia, leave media/intima undisturbed, examine/irrigate for thrombus/FB, intimal damage, address valves, identify 1’ draining vein
5. MACROSURGERY BEFORE MICROSURGERY: ensure optimal flap and vessel orientation prior to anastomosis
6. MINIMIZE WARM ISCHEMIA
7. TENSION FREE REPAIR following general principles of anastomosis

Question 2

Describe the general principles of microvascular anastomosis

Answer 2

1. Suture is non-absorbable monofilament
2. Repair is end to end, or end to side
3. Technique
   
   1. bites 90’
   2. evenly spaced from each other
   3. bite depth 1-2x thickness arterial; 2-3x thickness vein
   4. tension free
   5. running vs. interrupted
4. Optimize patency
   
   1. choose high flow vessel
   2. anastomosis outside ZOI
   3. perform 2:1 V:A anastomosis if possible
   4. don’t pull up on vessel during suture/tying
   5. reduce warm ischemia time
      5.

Question 3

describe healing of anastomosis

Answer 3

• platelets adhere to exposed endothelius
• re-endothelializes starting at 3-5 days and complete at 1-2 weeks
• balance between # sutures and leakage btwn sutures to limit thrombus formation

Question 4

what anastomotic maneuvers are associated w/ increased thrombogenic potential

Answer 4

• tension on repair
• intimal crush
• large or oblique holes
• untied suture holes
• arteriotimies or tears in vessels

Question 5

what are mechanisms to decrease size discrepancy

Answer 5

• dilation
• oblique cut of ends
• spatulation (smaller vessel in larger; smaller for artery should be OUTFLOW vessel)
• fishmouth incision
• end to side
• vein graft
• different recipient
• vein coupler for size discrepancy in venous anast

Question 6

what are indications for use of vascular grafts in microvascular surgery?

Answer 6

• tension free anast
• allow proper orientation of pedicle
• size discrepancy
• allow anast outside zone of injury

Question 7

what are types of vascular grafts?

Answer 7

• autologous vein
• prosthetic graft
• allograft
• arteriovenous loop

Question 8

define and describe ischemia reperfusion injury?

Answer 8

Definition

• acute inflammatory response and secondary tissue injury when previously ischemia tissue is revascularized

Description

• ischemic tissue will transition to anaerobic metabolism after using all the ATP stores and Na/K+ pumps become ineffective
• With revascularization, oxygen combined by anaerobic by-products releases oxygen free radicals
• also with ischemia is inflammatory marker release (from neutrophils and other substances) of leukotriene and thromboxanes
• OFR, LT, TXA together –> endothelial injury –> vascular permeability + platelet aggregation –> edema + thrombus formation –> eventual pedicle occlusion –> secondary ischemic insult

Manifests as early flap failure, within a few hours of revascularization

Question 9

define and describe the no reflow phenomenon

Answer 9

Definition: failure to reperfuse the flap despite achieving blood flow through the anastomosis

Describe - the ischemia tolerance of the tissue has been exceeded, and irreversible tissue damage has occured:

• early manifestation of ischemia-reperfusion injury
• endothelial swelling, permeability and microthrombi within microvasculature of tissue in flap
• sympathetic dennervation - receptors in flap microvasculature become upregulated and profound vasoconstricution occurs
  *

Question 10

list procoagulant states

Answer 10

• congenital
  
  • factor V leiden (AD & sporadic)
  • prothrombin 20210
  • protein C / protein S deficiency (AD)
  • anti-thrombin III deficiency (AD)
  • dysfirbrinogenemia
• Acquired
  
  • anti-phospholipid antibody syndrome
  • lupus anticoagulant
  • DIC
  • essential thrombocytosis

Question 11

what factors are potential causes of flap failure?

Answer 11

EARLY (#1 is technical failure)

• anast: FB (line, thrombus, valve), intimal damage, back-wall stitch, inversion, traumatic dissection
• flap: no-reflow, ischemia reperfusion, intrinsic vasoconstriction, unrecognized crush/avulsion of tissues
• donor: kink, inside ZOI, low flow

LATE (#1 is related to infection)

• flap: necrotic or infected tissue, supply demand
• Local: anything extrinsic causing compression - kink, hematoma, seroma, drain, limb position
• systemic: hypoxia, hypothermia, hypovolemia, hypotension, hypercoagulable d/o, pain, systemic vasoconstriction

Question 12

discuss your intra-op flap assessment and trouble shooting approach

Answer 12

• assessment
  
  • vessels: away from anast/other vessels the artery is pulsating and the vein is full (but not overdistended)
  • the flap is warm, pale pink, good CR, soft, puntate bleeding from dermal edges or scratch
  • aklund vessel strip test to observe flow
• trouble shooting
  
  • examine modifiable factors external - vessel kink & position, tension, patient temperature, volume status
  • pharmacologic agents for spasm: paparavine, lidocaine
  • revise anastomosis, remove thrombus, irrigate
  • pharmacologic agents after revision of anastomosis or thrombus: intraluminal heperanized saline, systemic IV heparin (5000U), intraluminal thrombolytic through flap (strepo/urokinase, tPA)

Question 13

what is your approach to venous congestion in free tissue transfer for breast reconstruction?

how does this differ to your approach for a replantation

Answer 13

• in free tissue transfer, venous congestion is managed by emergent return to OR for flap salvage attempt, including taking down the flap, taking down and revising the anastomosis, and identify and address the etiology (kink/ compression/ thrombus/ insuffient outflow) , consider 2nd vein, vein graft, intra/post-op pharmatoloci interventions (IV heparin, intraluminal thrombolytic, iv dextran)
• in replantation, often it is known that reoperation will not influence the result, and strategy is to use non-operative interventions to address venous congestion
  
  • anticipation - heparin or dextran drip
  • leeches
  • heparin soaks
  • elevation
  • removal of constricting dressings
  • limiting activity

Question 14

what are the ideal features of a mechanism to minotor free tissue transfer?

Answer 14

o safe and reliable

o continuous, sensitive to early perfusion changes

o distinguishes arterial from venous occlusion

o works on all types of tissue including buried flaps

o non-invasive

o easy to interpret

o inexpensive

Question 15

list techniques / methods to monitor free tissue transfer / revascularization

Answer 15

1. clinical
   
   1. colour, cap refill, external temp, turgor, scratch
2. muscle contractility
3. temperature probe
   
   1. better for digits, ++ unreliable for flaps
4. ultrasound
   
   1. doppler
      
      1. implantable option
   2. laser
5. transcutaneous tissue oxygenation / pulse oximetry
   
   1. penetration < 3mm
6. partial pressure of oxygen _
7. near infrared spectroscopy and oxygen saturation (vioptix)
8. tissue pH - indirect metabolic monitoring; experimental
9. photopleysmography - skin sensor measures blood volume
10. fluorescein
11. SPY indocyanine green fluorescent angiography