Infra-inguinal bypass

Indications (for patients with TASC C or D disease, and no further endovascular options):

Disabling claudication
- Trial of risk factor modification and exercise is indicated
- Only offer operation is risk/benefit ratio is high and the anatomical considerations are favourable
CLTI

Pre-op workup:

Optimise comorbidities:
- Periop/anaesthetic review
- Rutherford's says just assume they all have coronary artery disease. Only postpone bypass in the presence of frequent or unstable angina, recent MI, poorly controlled CCF, critical AS, or symptomatic/untreated arrhythmia.
- BP control
- Optimise CCF management
Imaging:
- As much information as possible about the PAD and inflow/outflow. CT angio is useful for above-knee arteries. DUS can give a lot of information. Angiography is the best, but not necessarily justified in all cases, especially since it can be done at the start of the bypass itself.

Planning:

Confirm no significant inflow disease present
- Treat anything significant either in advance or on the day
- Iliac lesions of haemodynamic significance should be addressed in nearly all claudicants before proceeding with infra-inguinal bypass. Iliac lesions in patients with CLTI would be acceptable if there is a resting gradient of <10mm Hg and pulse and Doppler waveform at the selected inflow site are normal.
- Easy to miss iliac disease, especially with posterior wall plaque that wasn't picked up on anterior views.
Choose proximal anastomotic site
- Does not need to be CFA. Shorter bypasses from PFA/SFA/POP are just as good in the right patient.
- Short bypasses are especially useful in diabetics with isolated infra-popliteal disease as well as in patients with previous failed bypasses and limited available conduit.
- Note that you need to have backup plans.
Define the target artery
- There is almost always a good option, except in those with multiple failed bypasses
- Bypass all haemodynamically significant disease and insert the bypass into the most proximal limb artery that has at least one continuous runoff artery to the foot. However, isolated popliteal targets with only geniculate branches and no continuity with tibial/peroneal arteries can function surprisingly well if no better conduit is available (but suboptimal in those with frank necrosis/tissue loss in the foot, who probably need pulsatile flow).
- For the above reason, generally prefer to use a tibial target than a peroneal one, because it connects with the foot.
Choose conduit
- Vein mapping. Autogenous is obviously best. Aim for at least 3mm, soft and compressible. Soft and compressible veins 2-3mm are worthy of exploration, but if they do not distend appropriately, find something else.
- For a long bypass, the best options are ipsilateral GSV, contralateral GSV and spliced autogenous vein, in that order.
- For a short bypass, use GSV, arm vein, then SSV.
- If vein is truly unavailable, use Dacron or PTFE for above knee insertion (no difference) and PTFE with distal vein cuff for below-knee insertion.
- Ipsilateral GSV
  - Most readily-available and durable
  - Can be used reversed, non-reversed, and in situ
    - In-situ - better size match between artery and vein, not biologically superior (equivalent results for in situ and reversed)
    - Reversed are more user-friendly and more adaptable
- Contralateral GSV
  - Only 25% of patients will go on to need it on that side, unless the contralateral limb is already ischaemic
- SSV (ipsilateral or contralateral)
  - Suitable for a short bypass
  - Can work for CFA to AK-pop or PFA to BK-pop, if the whole ankle to knee segment is harvested
- Arm veins (cephalic/basilic)
  - Possible to harvest them in one long segment
- Femoro-popliteal deep vein
  - Awkward due to its large size
  - Difficult to harvest
- Prosthetic:
  - Dacron
  - Heparin-bonded Dacron
  - Human umbilical vein
    - Risks of aneurysmal degeneration
    - Thick and cumbersome to handle
  - PTFE
    - Most commonly-used prosthetic conduit for infra-inguinal bypass
    - Not superior to Dacron above-knee
    - 42% 3-year patency rate in a recent randomised trial
    - Can get heparin-bonded PTFE, which is biologically active for 12 weeks, and appears to prevent early graft thrombosis
  - Vein cuffs
    - Confer a significant patency advantage with prosthetic grafts (52% vs 29% at two years)

Procedure:

Assessing inflow site:
- Compare with radial artery pressure - drop of 10mm Hg is significant, as is >15% drop in pressure after administration of intra-arterial papaverine.
- If no good, need to move more proximally or address the inflow problem (endarterectomy vs angioplasty).
Harvesting the vein
- GSV
  - Groin incision over SFJ (plan ahead if also accessing CFA/SFA to use the same incision). Incise along GSV, directly over it.
  - Identify SFJ (easiest in fossa ovalis) then follow GSV down. Skip incisions are preferable.
  - Grasp adventitia, not the vein itself
  - Side branches ligated with 3/0 or 4/0 silk, leaving a short stump so as not to impinge on the conduit
  - Vein spasm can turn a blue vein white and should be treated with local papaverine or lidocaine irrigation
  - Cannulate vein with a 3mm olive tip needle and gently distend with hep saline - it should flow readily, distend smoothly, and be free of fibrotic and non-distensible segments
  - Missed or small avulsed branches should be repaired with longitudinally-oriented 6/0 or 7/0 prolene on a BV-1 or BV-175 needle
  - Small bulldog on proximal end and flush hep saline from the distal end, avoiding overdistension.
  - Place in hep saline bath
- SSV
  - Harvested prone
  - Longitudinal incision on posterior calf
  - Dissect down to vein
  - Careful of sural nerve, which follows SSV
Tunnel conduit
- Tunneller passed from groin incision, beneath sartorius, to the popliteal fossa
- Mark vein to check orientation
- Pull vein through
- Re-check orientation
Proximal anastomosis
- IV heparin 5000 units 5 minutes prior to clamping
- Clamp inflow vessels
- Arteriotomy with an 11 blade, and extend proximally and distally with Potts scissors
- Running 5/0 prolene suture
  - Start with heel and sew halfway along the anastomosis
  - Start with toe and sew back towards the first suture
  - Sew continuously towards each other
- Flush with hep saline
- Release clamps
- Fix obvious problems
- Apply haemostatic agent (FloSeel powder)
- Further repairs
Distal anastomosis
- Check flow through graft
- Check orientation
- Same as above
Closure
- Reapproximate fascia with 3/0 vicryl
- Subcutaneous tissue closed in layers
- Consider drains, especially if concern for lymphatic leak
Completion assessment
- Distal pulse palpation
- Doppler flow assessment
- Arteriography
  - Gold standard, especially in circumstances where run-off is in question
  - Use a 4 or 5 Fr sheath to deliver contrast, preferably for DSA rather than fluoroscopy
- Angioscopy

Post-op

Aspirin
Anticoagulation MAY be beneficial in high-risk grafts, but not routinely given
Perform debridement or formal toe/forefoot amputations 4-10 days after bypass to maximise tissue reperfusion and allow clear demarcation
Frequent neurovascular obs - return to OT if signs of thrombosis
Check for compartment syndrome
Graft surveillance
- Rutherford's recommends ABI and DUS 1/12 post-op, then repeats every three months for a year, then six months for two years, then annually.
- Grafts with focal lesions a/w PSV >300cm/s should have intervention
- Grafts low-flow velocities (<45cm/s throughout), or a drop in ABI exceeding 0.15 in the absence of detectable graft lesions should have angiography to look for inflow/outflow/missed graft lesions.
- Grafts with primary patency on initial surveillance can possibly be discharged after 5 years, but grafts in assisted patency would need surveillance for longer

Complications:

Wound problems
Lymphatic fistula (0.8-6.4%)
- Presents with persistent leakage of yellow or clear fluid from a groin incision
- Lymphoscintigraphy can be useful when the diagnosis is in doubt, or the leakage develops months post-op
- Consider CT to exclude a retroperitoneal lymphocoele or chylous ascites
- Risk of deep wound infection from persistent leakage
- First few days - conservative management (local wound care, antibiotics, bed rest with leg elevation). Most leakages will cease with 7-12 days after initial drainage.
- Persistent high output - closure in OT.
  - Administer blue dye (isosulfan blue) an hour pre-op into the first and third interdigital spaces in the foot, and apply SCDS
  - Find leaking point
  - Oversew or use fibrin glue
  - If no leaking point identified, irrigate and close with interrupted sutures
- VAC therapy may be useful in persistent fistulas
Lymphocoele
- Can usually be easily demonstrated with lymphoscintigraphy
- Consider seroma, haematoma and infection
- Observe small lymphocoeles - will likely reabsorb spontaneously
- Enlarging, symptomatic, or close to a prosthetic graft need exploration
- Explore as above for lymphatic fistula
Bleeding
Graft occlusion/thrombosis (5%)
- Significant problem: at one year post-occlusion of below-knee bypass, >50% of patients will have had an amputation
- Risk factors:
  - Age <60
  - Crural target vessel
  - Dialysis
  - Hypercoagulable state
  - Smoking
  - Missing surveillance appointments
  - Vein graft diameter <3mm
- Assessment
  - Return of ischaemic symptoms
  - Absence of pulse
  - Reduced ABI
  - Finding on DUS surveillance
  - Use Rutherford criteria to decide overall need for and urgency of intervention
- Early: If it occurs early post-operatively, there is probably a cause that needs to be corrected. If no cause identified, the long-term patency rate is poor.
  - Anastomotic defect
  - Local endarterectomy defect
  - Clamp defect
  - Valve defect
  - Poor conduit quality
    - If no other cause found and a marginal conduit was used, consider replacing it
  - Inadequate outflow
    - Difficult to accurately establish!
- Late:
  - Only treat if symptoms are severe enough to warrant intervention. For example, if the original bypass was done for tissue loss, and the ulcer is now healed, may not need intervention.
  - If vein conduit is limited, can attempt thrombolysis or mechanical thrombectomy, and treat the underlying lesion. However, the results are often poor. Up to 85% of patients treated with further endovascular or surgical therapy after the clot is dealt with.
  - Best thing is to do a new bypass with autogenous vein, followed by PTFE with vein patch/cuff
  - When graft stenosis occurs, it's mostly focal and solitary (80%).
    - Factors involved in selecting treatment:
      - Length of lesion
      - Timing (late is >3-6 months)
      - Comorbidities
    - Scenarios:
      - Focal late lesions respond well to PTA
      - Stents should be avoided
      - Circumferentially fibrotic mid-graft lesions are best treated with excision and segmental interposition vein grafts
      - Smaller lesions are amenable to vein patch angioplasty
      - Focal juxta-anastomotic lesions can be treated either by patch angioplasty or short interposition graft or even transposition (for proximal lesions) or vein patching (for distal lesions)
  - Diffuse long-segment stenosis is mostly due to intimal hyperplasia (and wound necessitate replacement of graft).
- Treatment:
  - Decision on intervention as above, based on elaboration of likely cause (inflow, outflow, conduit, operative technique, coagulation factors)
  - Anticoagulation immediately - generally heparin
  - Check for hypercoagulable state
Graft infection
Post-bypass oedema
- Occurs in 50-100% of patients (more common in those with autologous grafts and below-knee bypasses)
- Caused by increased production of interstitial fluid after revascularisation, and lymphatic injury/obstruction during dissection
- Leg swelling first becomes evident with return to ambulation and dependency on day 2 or 3 post-op
  - Consider DVT, infection with cellulitis, and compartment syndrome
- Pitting oedema generally subsides with 2-3 months
- Treat mild oedema with elevation +/- bed rest. Treat CCF.
- Treat moderate-severe oedema with compression wrapping until the incisions have healed, followed by class II compression stockings
Death (2.7%)
MI (4.7%)