Machine perfusion

Machine perfusion (MP) is a technique used in organ transplantation as a means of preserving the organs which are to be transplanted. To some degree, it emulates natural perfusion. So far it has mainly been used in kidney transplantation. It is an alternative to cold storage (CS). Its clinical and cost-effectiveness are still subject to research.

Hypothermic perfusion has given the longest storage time for canine kidneys with the best result being 8 day storage. This experimental model used a storage temperature of 8 °C and a Plasma Protein Fraction (PPF) based perfusate. The octanoic acid content of PPF was found to influence the results of preservation in five-day storage. Both octanoic acid and oleic acid stimulated oxygen consumption to a similar degree during hypothermic perfusion suggesting that the detrimental effect of octanoic acid was due to direct metabolic stimulation rather than uncoupling of oxidatative phosphorylation.

An essential preliminary to the development of kidney storage and transplantation was the work of Carrel in developing methods for vascular anastomosis. Carrel went on to describe the first kidney transplants, which were performed in dogs in 1902; Ullman independently described similar experiments in the same year. In these experiments kidneys were transplanted without there being any attempt at storage.

The crucial step in making in vitro storage of kidneys possible, was the demonstration by Fuhrman in 1943, of a reversible effect of hypothermia on the metabolic processes of isolated tissues. Prior to this, kidneys had been stored at normal body temperatures using blood or diluted blood perfusates, but no successful reimplantations had been made. Fuhrman showed that slices of rat kidney cortex and brain withstood cooling to 0.2 °C for one hour at which temperature their oxygen consumption was minimal. When the slices were rewarmed to 37 °C their oxygen consumption recovered to normal.

The beneficial effect of hypothermia on ischaemic intact kidneys was demonstrated by Owens in 1955 when he showed that, if dogs were cooled to 23-26 °C, and their thoracic aortas were occluded for 2 hours, their kidneys showed no apparent damage when the dogs were rewarmed. This protective effect of hypothermia on renal ischaemic damage was confirmed by Bogardus who showed a protective effect from surface cooling of dog kidneys whose renal pedicles were clamped in situ for 2 hours. Moyer demonstrated the applicability of these dog experiments to the human, by showing the same effect on dog and human kidney function from the same periods of hypothermic ischaemia.

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