Expected flows & pressures in Isolated Limb Perfusion

Methods to prevent leakage to systemic circulation in Isolated Limb Perfusion

Cannulation sites

Indications for Isolated Limb Perfusion

a) Advanced malignant melanoma of a limb

i) Allows use of a very high dose of cytotoxic drug to be delivered without serious systemic side effects

b) Extensive venous or arterial thrombosis of limb

i) Allows use of thrombolytic drug to be delivered without serious systemic side effects

1. Ideally, blood is circulated only via the major artery & vein of the perfused area

2. Perfusion via the popliteal & axillary vessels

a) Tourniquet is situated proximally around a single bone

b) Complete isolation of limb

3. For perfusion via the femoral or iliac vessels

a) Isolation is compromised

b) Tourniquet encompasses a portion of the pelvic mass & thigh

4. Examples

a) Left common femoral artery (22G) & superficial femoral vein (26G)

b) Left external iliac artery (20G) & left iliac vein (28G)

c) After exposing the appropriate artery & vein, the largest bore reinforced cannulae which the vessels can comfortably accept are inserted & secured

Circuit for isolated limb perfusion

1. Priming volume should be small

a) Minimise excessive haemodilution of limb at initiation of ILP

b) Minimise autologous blood loss at termination of ILP

2. Infant or paediatric oxygenator with integral heat exchanger

3. Low flow pump (50 — 900 ml/min)

4. 1/4” arterial line± arterial filter

5. 1/4” venous line for arm; 3/8” for leg

6. Limb washout line; clamped during perfusion - is used to drain the blood containing the thrombolytic or cytotoxic agents at end of ILP while simultaneously reinfusing a limb washout solution (Dextran ± Hartmans)

Monitoring, ACT & temperature

1. Hct

a) > 15%

b) May require RBC for isolated arm perfusion

2. ACT

a) 5000U heparin in prime

b) Systemic heparinisation is used

i) If local heparinisation used, danger of leak between systemic circulation entering isolated circulation resulting in inadequate heparinisation

c) ??200 -250 sec

d) Note: are hyperthermic/normothermic

e) Reversed at termination with protamine

3. ECG

a) Chemotherapeutic drugs can have an affect on the heart

4. Haemodynamic monitoring

a) Systemic arterial pressures

b) Limb perfusion pressures

5. Temperature monitoring

a) Patients core, limb’s skin, limb’s muscle, circuit blood

b) Hyperthermia used with chemotherapy to potentiate effect of drugs & increase vasodilation

c) Normothermia used with thrombolytic agents

d) Monitor for overheating (>40°C) of limb

6. ABGs

a) Limb is relatively isolated from systemic blood supply; therefor requires oxygenated blood from circuit

b) Hyperthermia increases O₂ consumption of limb

c) pO2 > 400 mmHg has a tumouricidal effect

Expected flows & pressures in Isolated Limb Perfusion

1. Chemotherapy - Flow dependent

a) Blood flow to the limb is the same percentage as the estimated cardiac output of the limb

b) Formula for estimating the pump flow rate in the isolated limb circuit:

i) PQ = ([%LSA/100] ´ CO)

a) PQ = pump flow rate (L/min)

b) %LSA/100 = limb surface area as a function of BSA (Arm: 9%; Leg: 18%)

c) CO = cardiac output (L/min)

c) Once the optimal flow rate has been achieved, there should be no change in the volume of the reservoir assuming vasodilation is not occurring

2. Thrombolytic - Pressure dependent

a) Perfusion of the limb is commenced at a flow rate so that the line pressure will not exceed 250 mmHg

b) As the thrombus lyses, the flow rate can be increased (eg up to 1200ml/min in leg)

Methods to prevent leakage to systemic circulation in Isolated Limb Perfusion

1. To minimise possibility of leak from isolated circuit to systemic circulation

a) Patient’s diastolic BP should be kept higher than the limb perfusion pressure

i) Reduce pump flow rate

a) Easy

b) Increase duration of perfusion

c) May result in compromised blood flows to limb

ii) Increase patient’s SVR

iii) Lower pump resistance

a) Localised phentolamine/SNP

2. Appropriate use of tourniquet

3. Appropriate vessel cannulation

4. Monitoring of leakage

a) Assuming that vasodilation is not occurring, there should be no change in the volume of the reservoir once full flow has been achieved

i) Rise indicates systemic to circuit leakage

ii) Fall indicates circuit to systemic leakage

b) Radioactive tracers/fluoresin — appearance above tourniquet indicates leakage

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