Darryl McMillan

Hypertensive extracorporeal limb perfusion (HELP): A new technique for managing critical lower limb ischemia

OBJECTIVE The concept of repeatedly connecting an extracorporeal blood pump to produce pancycle suprasystolic inflow pressures to ischemic limbs is introduced. Balloon catheters allow for limb isolation from the systemic circulation. In the acute phase, it is assumed that pressure is proportion to flow (Poiseuilles Law) and in the chronic phase that collateral growth is related to endothelial shear stress and wall tension. The primary objective was to establish that increased flow could be achieved through collateral circulation in animals and in man with extracorporeal limb hyperperfusion. The second objective was to develop and test an arterial access system capable of intermittent regional hyperperfusion similar in concept to intermittent hemodialysis. Finally, to demonstrate the translocation of these concepts into humans facing major limb amputation where all standard treatment options had been exhausted. METHODS Twelve sheep (6 hyperperfusion and 6 controls) were attached to a cardiac vortex pump and perfused at 200 mm Hg pancycle with the superficial femoral artery doubly ligated and isolated from the systemic circulation with a balloon catheter. Pressure transducers measured carotid and distal femoral pressures and the carotid-femoral index was calculated. To allow hyperperfusion to be repeated transcutaneously, a peripheral access system (PAS [Allvascular, St Leonards, New South Wales, Australia]) was constructed. This device was implanted in the common carotid artery in 8 sheep and opened approximately 3 days a week for continuous arterial access up to 37 days for 67 openings. To demonstrate these principles in humans, 3 patients with critically ischemic limbs were hyperperfused intermittently. Digital thermography compared the other limb as controls and provided objective evidence of the vascular changes. RESULTS The mean carotid-femoral index was 0.6 +/- 0.01 for controls compared with 1.1 +/- 0.28 for the hyperperfusion group (P < .001). The collateral flow was superior to normal flow (ie, with the superficial femoral not occluded). Continuous access to the carotid arterial tree via the access device was 25.3 +/- 8.8 days with 5 of 8 devices open for the entire observational period (maximum 37 days). The human ischemic limbs were hyperperfused at 2-4 times the mean arterial pressure producing 3-6 times an increase in pump flow measurements intermittently for 53 +/- 16 hours. The clinical findings of rest pain, paresthesia, capillary return, and movement showed dramatic improvement as did thermographic emissions. Major amputation was avoided in the cases presented. CONCLUSION Blood flow through collaterals can be very significantly augmented by connection to an extracorporeal pump with isolation from the systemic circulation. The pancycle hyperperfusion can be safely repeated by implantation of an arterial access device. In the longer term, there is evidence of collateral development. When amputation is the only alternative, hypertensive extracorporeal limb perfusion should be considered.

Hypertensive extracorporeal limb perfusion for critical limb ischemia

OBJECTIVE This article reports the early results in humans of hypertensive extracorporeal limb perfusion (HELP) technology in the prevention of major limb amputation due to ischemia. The short-term aim was to dilate pre-existing collateral channels, and the long-term aim was to stimulate remodeling and new collateral development by increasing endothelial shear stress and wall tension. METHODS This study evaluated 20 patients with critical limb ischemia who were treated with HELP. These patients had no other option but major amputation, as determined by at least two vascular surgeons. The arterial circulation to the ischemic limb was isolated from the systemic circulation by the use of an endoluminal balloon catheter in seven patients and by an implantable, inflatable, occlusive cuff in 13. The limbs were hyperperfused through the peripheral access system with an extracorporeal pump, producing a minimally pulsatile waveform at 200% to 300% of the mean arterial pressure. This was performed repeatedly in sessions of 24 to 36 hours, up to a maximum of 74 hours. The primary end point was avoidance of major amputation. The secondary end points were the clinical improvements in rest pain, ulcer healing, and claudication distance. Patients were analyzed and reviewed using infrared thermography and ultrasound imaging parameters of the limb. RESULTS Given adequate arterial access, 39 of 40 connections developed flows four to eight times those supplied to the limb by the normal cardiac output. A progressive decrease was noted in peripheral resistance. All patients developed a pain-free, warm foot or hand while on the pump in the short-term. In the longer term at a mean of 22 months (range, 12-54 months), eight of 20 patients (40%) had avoided major amputation and four more had a delay in amputation of an average of 4 months. The ankle-brachial index changed from 0.04 ± 0.07 (range, 0.00-0.94) to 0.63 ± 0.39 (t-test, P < .05). Bleeding, infection, premature cessation of the treatment, and poor patient selection resulted in the failures. There were two short-term unrelated deaths that occurred at 1 and 3 months follow-up. CONCLUSIONS The collateral circulation of ischemic limbs can be augmented and regulated by a connection to an extracorporeal centrifugal pump, with isolation from the systemic circulation provided by balloons and with an access system providing repeatable pump connections. Major amputation may be avoided in selected cases.