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Understanding the Graphs

PCNL is the removal of stones from the kidney (or upper ureter) using a small puncture incision, into the kidney, in the skin of the affected side. Small instruments are then passed into the kidney (or upper ureter) to break up and remove the stones. PCNL can be performed with the patient lying either face down (prone) or face up (supine).

The headings below represent the three tables in the PCNL dataset.

Number of operations

The number of operations indicates how many PCNL procedures each surgeon has carried out. 

If a patient undergoes more than one PCNL procedure for the same stone, this has been recorded as two procedures.  If a patient has stones in both kidneys, operated on during the same anaesthetic, this has been recorded as two separate procedures.

The number of operations reported may be lower if a surgeon has only worked during part of the relevant time period.

Some surgeons may operate only on smaller, less complex stones, or on patients who are less sick, referring more complex stones and high-risk patients to other surgeons. As a result, the number of procedures that an individual surgeon performs, and their complexity, may be affected by these local referral pathways.

Transfusion rate

This is the proportion of patients (expressed as a percentage) requiring a blood transfusion following surgery.  It is often related to the complexity of the procedure and, separately to the underlying health of the patient.  It may also be an indicator of complications that have arisen following the procedure.

The transfusion rate reported does not take into account the patient’s pre-operative haemoglobin level, which may make the patient more likely to require a transfusion post-operatively. 

The reported rate only identifies whether a patient received a blood transfusion during their admission for PCNL; it does not identify whether the patient was subsequently re-admitted for a blood transfusion.  Patients requiring only a single unit of blood are recorded in the same way as those requiring multiple units of blood (i.e. they either did or did not receive a blood transfusion, with the number of units transfused not being recorded).

The transfusion rate reported may be lower if a surgeon operates only on smaller, less complex stones or on patients who are less sick; equally, it may be higher if the surgeon operates on more complex stones or patients.

Length of stay

The length of stay indicates the number of days a patient stayed in hospital following their procedure.  It is expressed as a median for each surgeon, with a mean and a range.  The length of stay is often related to the complexity of the procedure and, separately, to the underlying health of the patient.  It may also be an indicator of complications which have arisen following the procedure. 

The length of stay reported records only the number of days spent in hospital following the procedure.  It does not record subsequent nights spent if the patient is readmitted to hospital.

The length of stay reported may be shorter if a surgeon operates only on smaller, less complex stones or on patients who are less sick; equally, it may be longer if the surgeon operates on more complex stones or patients.

Average patient risk profile

Some risk factors (e.g. stone complexity, size and other medical problems) can affect the outcome of PCNL in terms of complications, length of stay and the likelihood of requiring a transfusion.

The graphs show what percentage of the hospital or Consultant’s patients has each (potential) risk factor. This can indicate whether the hospital / surgeon operates on high-risk patients or, in fact, specialises in peforming complicated surgery.

N.B. BAUS has included all the data returned in our overall analysis. When presenting individual surgeon/centre results, we have excluded the risk profiles and transfusion rates for those who returned less than five cases per year; this is because statistical analysis of such a low number would be invalid.