The technology

MIP‑M (Karl Storz, Germany) is a device used to remove kidney stones. MIP‑M is a miniaturised version of percutaneous nephrolithotomy (PCNL) and is suitable for people with kidney stones 12 to 24 mm in diameter in any renal calyx or in the renal pelvis. This device can be used on larger stones but this could increase the operative time and chances of complications. The MIP‑M device comprises a 12 Fr nephroscope, a 16.5/17.5 Fr operating nephrostomy or Amplatz sheath, a single-step dilator and grasping forceps.

The procedure is done by making a small incision, usually in the patient's back, and a needle is inserted into the renal pelvis. The position of the needle is confirmed by X‑ray or ultrasound. A guide wire is placed through the needle into the renal pelvis. It is then withdrawn, leaving the guide wire in place. A single-step dilator is passed over the guide wire to widen the access channel and a 16.5/17.5 Fr sheath is introduced. A miniaturised 12 Fr nephroscope is then passed inside the sheath; it allows the surgeon to see the kidney stones. The nephroscope has a channel through which grasping forceps are introduced to remove small stones. Bigger stones may have to be broken up using ballistic lithotripsy or laser treatments before removal. Ultrasound and laser instruments are also passed through the nephroscope channel.

Irrigation fluid is circulated under controlled pressure to remove stone fragments. This and the design of the sheath help to prevent fluid overload. When removing the instruments under a continuous flow of irrigation fluid, a vortex develops in the lumen of the sheath causing a vacuum effect. This flushes out stone fragments without the need for a stone retrieval basket.

The stone fragmentation equipment must be available and checked to make sure it is compatible with the MIP‑M device before use. MIP‑M may be used with lithotripsy devices as small as 5 Fr in size and ballistic lithotripsy probes up to 2 mm in diameter. The size of the laser fibre used ranges between 200 µm and 600 µm.


The instruments in the MIP‑M system are smaller than standard PNCL devices. This aims to reduce procedural morbidity and complications, including blood loss and infection, in order to reduce the length of hospital stay.

MIP‑M instruments are designed to allow control (inflow and outflow) of irrigation fluid. This can avoid introducing grasping instruments to remove the stone, which in turn can reduce the procedure length.

Current NHS pathway or current care pathway

Small stones may pass out of the kidney into the urine without any treatment. Larger stones and those that cause symptoms may need to be broken up or removed. This is usually done with extracorporeal shock wave lithotripsy (ESWL), flexible ureteroscopy (also known as retrograde intrarenal surgery; RIRS) or PCNL.

  • ESWL is used for stones (up to 20 mm in diameter) that cannot be passed in urine. X‑ray or ultrasound are used to find the stone, which is then broken up using lithotripsy.

  • Flexible ureteroscopy or RIRS is used if the stone is up to 15 to 20 mm in diameter and has moved into the ureter. This is done by inserting a telescope into the urethra, through the bladder and into the ureter. The surgeon can remove the stone using another instrument or try to break it up using a laser so that they can be passed in the urine.

  • PCNL is commonly used for larger stones (larger than 20 mm in diameter). This is done by making a small incision in the patient's back and using a 24 to 30 Fr dilator to open a tract. A 24 to 30 Fr operating sheath is placed over this to allow access for the 18 Fr nephroscope. The stone is either pulled out or broken up using a laser or ultrasound lithotripsy. These fragments are then passed in the urine.

The MIP‑M device would be used as an alternative to standard care for people with kidney stones measuring up to 30 mm in diameter.

Population, setting and intended user

The MIP‑M device would be used in an inpatient surgical setting when patients are under general anaesthetic. The device would most likely be used by urological surgeons. Additional training would be needed for surgeons with no previous experience of doing PCNL surgery. The training is provided by the manufacturer and is included in the cost of the device.


Technology costs

The costs of MIP-M are outlined in table 1.

Table 1 Cost of MIP-M



Additional information

Standard MIP‑M set


Per reusable set, which includes a nephroscope, dilator and sheath, all of which are autoclavable

Foley catheter


Consumable and single use

2 guide wires


Consumable and single use

Ureteric catheter


Consumable and single use

Based on information received from 2 specialist commentators that provided input for this briefing, the estimated cost per procedure is £4,439. This estimate includes costs for staffing, device, consumables, theatre time and an assumed 2‑day stay in hospital. These estimates have not been validated in NHS trusts using MIP-M.

Costs of standard care

The average procedure cost of percutaneous nephrolithotomy is between £4,982 and £5,516 depending on the severity of illness. The average procedure cost of ESWL is £948 and RIRS is between £2,500 and £3,320 depending on severity of illness (NHS reference costs 2015/16). A recent study on the effectiveness of ESWL in removing small renal and ureteric stones in 225 patients found that over 75% of stones were removed after just 1 ESWL session, with a mean of 1.3 sessions needed per patient for complete removal (Al-Marhoon et al. 2013).

Resource consequences

According to clinical experts the estimated cost per procedure of MIP‑M is £4,400 and can be used to remove kidney stones measuring up to 30 mm in diameter. The costs of comparator treatments are estimated at around £1,200 to remove kidney stones measuring up to 20 mm in diameter, based on an average of 1.3 sessions needed per person. Costs of removing kidney stones measuring between 15 mm and 20 mm in diameter are estimated at around £2,900 and the costs of removing kidney stones larger than 20 mm in diameter are estimated to be around £5,200 (NHS reference costs 2016/17). The costs are outlined in table 2.

Table 2 Cost of MIP‑M compared to comparator treatments

NHS reference costs 2016-17

Comparator treatments

Cost of comparator (£)

Cost of MIP-M (£)

Difference in cost per procedure compared to comparator (£)


ESWL used to remove kidney stones up to 20 mm




LB65C, D E

RIRS used to remove kidney stones between 15 mm and 20 mm




LB75A, B

Standard PCNL used to remove kidney stones larger than 20 mm




Using MIP‑M rather than PCNL to remove kidney stones larger than 20 mm in diameter would lead to cost savings. However, savings may also result from using smaller size instruments with MIP‑M procedures compared to those used with comparator treatment options. Using smaller instruments may reduce procedural morbidity and complications including blood loss and infection which may also reduce the length of stay in hospital.

Any training that may be needed for MIP‑M will be included in the cost of the device.

Changes to current care pathway and infrastructure should be minimal as MIP‑M is a smaller version of a current system. At the time of preparing this briefing, there were 17 NHS trusts using this device.