6.Assessing and prompt laparotomy, cannulation of the

6.Assessing
organ’s condition (2,590 words)

 

Post
transplantation, kidneys may function instantly, require a period of recovery
with no function, require a period of recovery with impaired function, or never
work at all. Immediate function depends on the general health of the donor /
kidney characteristics but also on the time of ischaemia plus the additional
harm caused during death and organ retrieval.  
As there is the option of dialysis in order to deal with the initial
graft dysfunction the main focus is to reduce the primary non-function (PNF). 16

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The
perfect kidney derives from a young age donor, without comorbidities prior to
short terminal illness, controlled DCD, with an immediate death when harvesting
is performed and prompt laparotomy, cannulation of the aorta, perfusion and
excellent appearance on retrieval. If the ischaemia time is minimised those
kidneys ought to work instantly without need to undergo special tests on
viability etc.  However, the vast
majority of organs do not belong to the above group. Their viability requires
assessment in order to identify those at greater risk of delayed function or
even potential non-function that would allow better selection and matching for
transplantation.  This would also permit
interventions in order to improve the organ’s condition (reconditioning) – see
relevant chapter.

 

It is estimated that 12 – 18 percent of
kidneys are abandoned because of issues with regards to their functional status
post transplantation. 50 I believe that further optimisation of viability
assessment tools will lead to reduction of above figure and also more accurately
determine which kidneys must be discarded.

 

The research in the field of viability
assessment & evaluation of organs’ condition has focused on;

 

Machine perfusion dynamics;

–         
Machine
perfusion pressures

–         
Machine
perfusion flow rate

–         
Resistance
indices

–         
Machine
perfusate biomarkers

 

Imaging related;

–         
Doppler
ultrasonography and renal scintigraphy

–         
Dynamic
MRI using the Ktrans technique   

 

Biopsy involvement;  

– ‘Pirani’ 

– Banff, and

– CADI (chronic
allograft damage index) scores

– Composite scores
combining donor hypertension and creatinine with histological  

  scoring

 

Other;

–         
Rapid
Sampling Microdialysis for parenchyma assessment

–         
Kidney
perfusate and urine biomarkers

–         
Clinical
donor risk scores

 

One of the key advantages of MP that makes it
attractive to the transplant surgeons is the fact that it permits graft
viability & quality assessment before the transplantation itself.  As mentioned key part of this is the machine
perfusion dynamics such as flow, resistance etc and several well recognised
biomarkers within the perfusate.  It has
been concluded that although these can predict to an extent the subsequent
graft function, so far, they can’t be used alone on decision making on whether
to accept or reject an organ 6.

 

 

Machine perfusion pressures 8

 

When developing machine perfusion as a mode of
organ preservation researchers noticed that when the perfusion pressure was
going up and at the same time the flow rate was decreasing this was a sign that
graft failure is pending 51. However, at the same time low pressures are
responsible for suboptimal perfusion. On the other hand, very high pressures
were demonstrated to cause shear stress an endothelial injury. Porcine kidneys
preserved at higher pressures prior to transplantation they had higher expression
of von Willebrand factor from their endothelial cells. This marker is commonly
present in the endothelial cells of the kidneys of patients suffering from
hypertension or AKI /CKD 52, 53. Lastly kidneys perfused at 25 mmHg compared
to 30 mmHg have greater preservation of their structural integrity and quicker
functional recovery as demonstrated by repeat renal function evaluation post
transplantation 53.  The majority of
research on perfusion pressures has been undertaken on porcine models. The
Newcastle group recommended perfusion pressures of