Microsurgery

Question 1

What is the average tissue survival rate for a microvascular free flap?

Answer 1

95% or better

Question 2

What is the reexploration rate for flap compromise?

Answer 2

Approximately 10%.

Question 3

What is the salvage rate for microvascular free flaps that require reexploration for flap ischemia?

Answer 3

50% to 85%.

Question 4

What is the maximum warm ischemia time tolerated by muscle flaps?

Answer 4

Less than 3 hours.

Question 5

What is the maximum warm ischemia time tolerated by bone flaps?

Answer 5

Less than 3 hours.

Question 6

What is the maximum warm ischemia time tolerated by skin and fasciocutaneous flaps?

Answer 6

Approximately 4 to 6 hours.

Question 7

What is the warm ischemia time tolerated by jejunal flaps?

Answer 7

Less than 2 hours.

Question 8

How can the maximum tolerated ischemia time be increased?

Answer 8

Cooling of tissues: up to 12 hours of ischemia tolerated for fasciocutaneous tissues, 8 hours for muscle, and
24 hours for bone.

Question 9

Which results higher flap survival rates, end-to-end or end-to-side anastomoses?

Answer 9

Most studies demonstrate similar patencies.

Question 10

Which type of arteriotomy, slit or circular/oval, is more successful?

Answer 10

Most studies demonstrate similar patencies.

Question 11

Under what circumstances might an end-to-side anastomosis be advantageous?

Answer 11

Vessel size discrepancy (larger donor vessel), only one artery or vein available and needed for distal organ/tissue
perfusion, limited exposure/availability of similar size donor vessels.

Question 12

What anastomotic angles are thought to be the most desirable and result in the greatest amount of blood flow to the recipient vessel in an end-to-side anastomosis?

Answer 12

Based on technical factors and blood flow rates, angles of 45◦ to 90◦ result in greater arterial flow than obtuse angles up to 135◦.

Question 13

What methods relieve vasospasm?

Answer 13

Topical anesthetics (eg, lidocaine), topical papaverine, dilation, adventitial stripping, sympathetic nerve block (eg,
epidural anesthesia for lower extremity reconstruction).

Question 14

What is the reason for adventitial stripping?

Answer 14

To relieve vasospasm and to prevent loose adventitia from being caught in the vessel lumen, a potential trigger for
thrombosis.

Question 15

Which method of adventitial stripping is preferred, blunt or sharp?

Answer 15

Sharp adventitial stripping is associated with less vessel trauma resulting less vasospasm and improved blood flow to
the flap.

Question 16

What are the characteristics of a viable flap?

Answer 16

Warmth, color, softness, capillary refill, and detectable pulse (eg, Doppler).

Question 17

What are signs of inadequate arterial flow?

Answer 17

Pale, cool flap with slow (>2 second) capillary refill and decreased tissue turgor.

Question 18

What are signs of inadequate venous flow?

Answer 18

Cyanotic or dusky flap with fast (<1 second) capillary refill and increased tissue turgor.

Question 19

What are the most reliable methods of free flap monitoring?

Answer 19

Clinical observation, Doppler ultrasound flowmetry, pinprick or scratch testing, pulse oximetry, quantitative
fluorometry, surface temperature probing.

Question 20

How can buried flaps, such as those used for pharyngeal reconstruction, be monitored?

Answer 20

A segment of the flap can be pedicled on separate perforating blood vessels and exteriorized. Alternately, an implantable Doppler can be placed on the vein or artery or both, distal to the anastomosis.

Question 21

How long before a pseudointima forms at the anastomotic site?

Answer 21

Approximately 5 days.

Question 22

How long before a new intima forms at the anastomotic site?

Answer 22

Approximately 1 to 2 weeks.

Question 23

What types of sutures are typically used for microvascular surgery?

Answer 23

Nylon or polypropylene sutures ranging from 8-0 to 12-0.

Question 24

How is the microvascular suture selected?

Answer 24

Thicker sutures with larger needles are indicated for larger vessels. Thinner sutures with finer needles are indicated for smaller vessels. In general, 9-0 sutures are used for vessels of 2 mm or more in diameter and 10-0 sutures are used for vessels of 1 to 2 mm.

Question 25

In an end-to-end anastomosis, what is the maximum size discrepancy between vessels that can be accommodated?

Answer 25

Between 2:1 and 3:1

Question 26

What are some strategies for performing an anastomosis between vessels with a size mismatch?

Answer 26

Other than placing sutures farther apart on the larger vessel, strategies include beveling or spatulating the smaller vessel, partially closing or narrowing the larger vessel lumen with sutures, or using an interposition graft that is intermediate in diameter between the two vessels (see Figure 75-1). When the recipient vessel is larger, an end-to-side anastomosis into the recipient vessel can be performed. Strategiesfordealingwithavesselsizemismatchincludenarrowingthelargervesselwithsutures,bevelingthesmaller vessel, using an interposition graft of intermediate diameter, and performing an end-to-side anastomosis when the recipient vessel is larger.)

Question 27

Under what circumstances can microvascular coupling anastomotic devices generally be used?

Answer 27

Coupling devices are usually used for minimally discrepant, soft, pliable venous microvascular anastomoses.

Question 28

Which has superior patency rates, coupled or hand-sewn anastomoses?

Answer 28

They are similar when used appropriately.

Question 29

Can coupling devices be used on arteries?

Answer 29

Yes, but they generally do not work well on thick-walled or inelastic, atherosclerotic vessels.

Question 30

What is the maximum closing pressure of vascular clips that should be used to minimize damage to vessels?

Answer 30

30 g/mm2.

Question 31

What are some key points when performing an anastomosis for preventing exposure of subendothelium and thereby inducing platelet aggregation?

Answer 31

Use small needles, avoid repeated needle punctures, equal placement of sutures, avoid tying sutures too loose or too tight, avoid use of too many sutures, which can cause endothelial slough.

Question 32

How does heparin prevent coagulation?

Answer 32

Primarily by increasing the action of antithrombin-3, which inactivates thrombin. It also decreases platelet adhesion
and inhibits the conversion of fibrinogen to fibrin.

Question 33

What risks are associated with heparin use?

Answer 33

In addition to bleeding and hematoma formation, heparin can cause thrombocytopenia. Heparin-induced
thrombocytopenia is thought to be caused by antibodies to the complex formed by heparin and platelet factor 4.

Question 34

How does aspirin function to prevent platelet aggregation?

Answer 34

Aspirin blocks the endothelial cyclooxygenase pathway with subsequent blockage of thromboxane A2 preventing
vasoconstriction and thrombus formation.

Question 35

Is high-dose aspirin more effective than low-dose aspirin to prevent platelet aggregation?

Answer 35

No. At low doses, aspirin selectively inhibits thromboxane A2, a platelet aggregator and vasoconstrictor. At high doses, prostaglandin I2, a vasodilator and inhibitor of platelet aggregation are also inhibited. For example, aspirin in doses of 81 and 325 mg has been shown to be more effective in preventing cerebrovascular accidents, myocardial infarction, and death after carotid endarterectomy than doses of 650 and 1300 mg.

Question 36

How does dextran work to prevent clotting?

Answer 36

Dextran is a volume expander that prevents platelet adhesion by increasing the negative electric charge of platelets, erythroctyes, and endothelial cells, resulting in a destabilization of fibrin polymerization. Dextran is also an inactivator of von Willebrand factor, a major contributor to platelet aggregation and adhesion to vessel wall collagen.

Question 37

What are some possible complications associated with the use of low-molecular-weight dextran?

Answer 37

Bleeding, pulmonary edema, and allergic reaction including anaphylaxis.

Question 38

What is the mechanism of the no-reflow phenomenon?

Answer 38

Ischemia results in cellular swelling in the vascular endothelium with subsquent intravascular platelet agregation and leakage of intravascular fluid into the interstitial space.

Question 39

What pharmacologic agents can be used to rescue some free flaps in which anastomotic revision fails to restore flap perfusion or is associated with recurrent thrombosis?

Answer 39

Thrombolytic agents such as streptokinase, urokinase, tissue plasminogen activator.

Question 40

How do thrombolytic agents work?

Answer 40

Thrombolytic agents, such as streptokinase, urokinase, and tissue plasminogen activator, function by directly or indirectly activating plasminogen to form plasmin, which cleaves fibrin in clots as well as fibrinogen and coagulation factors V, VIII, IX, XI, and XII.

Question 41

What are the risks associated with using streptokinase?

Answer 41

In addition to bleeding and hematoma formation, streptokinase is antigenic and can result in an allergic response (6% incidence) with a 0.1% incidence of anaphylactic reaction. Streptokinase can also result in a “lytic state,” causing diffuse bleeding when administered in high doses. Unlike streptokinase, urokinase and tissue plasminogen activator do not appear to be antigenic.

Question 42

What is the mechanism of thrombosis in microvascular anastomosis?

Answer 42

Exposure of subendothelial collagen-containing surfaces to which platelets adhere eventually leading to fibrin
deposition, vasospasm, stenosis, and thrombosis, causing loss of blood flow.

Question 43

What is Virchow’s triad?

Answer 43

Virchow’s triad refers to risk factors for thrombosis and includes stasis, intimal injury, and hypercoagulability

Question 44

Why is bipolar electocautery preferable to monopolar electrocautery in the control of bleeding from or around a recipient or donor blood vessel used in microvascular free tissue transfer?

Answer 44

Bipolar cautery damages tissue, including endothelium and media, over a much more limited distance (approximately 1–2 mm) compared to unipolar cautery.

Question 45

Why is the number of sutures placed in an anastomosis critical?

Answer 45

Too few sutures result in excessive bleeding and thrombus formation; too many result in increased damage to the
endothelium and thrombus formation.

Question 46

Which anastomotic technique demonstrates greater success rates, interrupted suture placement or continuous sutures?

Answer 46

In experienced hands, similar success rates are observed.

Question 47

Does smoking tobacco increase free flap failure rate?

Answer 47

Most retrospective studies demonstrate similar (nondigital) flap survival and thrombosis rates between smokers and nonsmokers, although smokers have a higher incidence of healing complications at the flap interface and at the donor-site wound.

Question 48

What happens to vein grafts when they are used to bridge intra-arterial gaps?

Answer 48

There is ingrowth of smooth muscle cells and creation of a neointima that results in significant thickening of the vein wall. Also, graft length decreases by 26% to 30% when used as an intra-arterial or intravenous graft.

Question 49

In addition to excellent vascular and neural anastomoses what other factor determines the success of functional free skeletal muscle transfer?

Answer 49

Reestablishment of the correct resting tension since very small decreases in resting tension can markedly reduce the power and amplitude of muscle contraction.

Question 50

Name some commonly used donor sites for free osseous and osseocutaneous flaps.

Answer 50

Rib, fibula, iliac crest, second metatarsal, radius, calvarium, scapula.

Question 51

In what ways are vascularized bone transfers superior to nonvascularized bone grafts?

Answer 51

Vascularized bone grafts demonstrate earlier incorporation, bone hypertrophy, mechanical strength to failure,
osseous mass retention, and resistance to local infection.

Question 52

What techniques can be used to prolong ischemia time in limb replantation?

Answer 52

Cooling and AV shunting.

Question 53

What are the major contraindications to replantation?

Answer 53

Concomitant life-threatening injury, multiple segmental injuries to the amputated part, severe crushing or avulsion of the tissues, extreme contamination, inhibiting systemic illness (small vessel disease, diabetes mellitus, etc), prior surgery or trauma to the amputated part precluding replantation.

Question 54

How do leeches function to relieve venous congestion?

Answer 54

By secreting hirudin, a selective thrombin inhibitor that is injected into the hosts tissue as they feed on host blood.

Question 55

What pathogenic bacterium do leeches commonly transmit?

Answer 55

Aeromonas hydrophila.

Question 56

What antibiotics should be used in the prophylaxis or treatment of bacterial infections associated with the use of leeches?

Answer 56

Ciprofloxacin, tetracycline, trimethoprim-sulfamethoxazole, or second- and third-generation cephalosporins.

Question 57

Does the order of anastomosis and microvascular clamp removal affect the survival of free flaps?

Answer 57

There are no significant differences in flap survival based on the order of anastomosis or microvascular clamp removal seen in an animal model, although early, transient venous congestion does develop if the artery is anastomosed first and the clamp on the artery is removed prior to venous anastomosis and clamp removal.

Question 58

Can loupe magnification be safely used for microvascular anastomoses?

Answer 58

High-power loupes have been used for anastomosing vessels greater than 1 mm in diameter with success rates comparable to those achieved using a microscope.

Question 59

Can microvascular surgery be successfully performed in children?

Answer 59

Yes. A success rate of 93% has been observed in children younger than 15 years, despite smaller blood vessel size.

Question 60

Can microvascular surgery be successfully performed in the elderly?

Answer 60

Yes. Age has not been found to be an independent predictor of flap loss in several studies. However, older age is frequently associated with medical comorbidities, including cardiac and peripheral vascular disease, as well as development of other complications related to long surgeries.