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The last three decades has seen the evolution of percutaneous nephrolithotomy (PCNL) as the ‘gold standard’ treatment of large renal stones. Initial experience with PCNL was in the prone position  and it was done this way almost exclusively until the last decade. Although prone is still the most widely practised position, the last decade has seen the practise of various different positions for PCNL. These include, prone flexed , lateral , split-leg , supine [5,6] and modified supine positions [7,8].
Prone PCNL has potential disadvantages, as it may cause circulatory and ventilatory compromise, especially in the obese patient. Additional difficulties of prone anaesthesia include direct and indirect pressure effects, e.g. vascular, peripheral nerve and cervical spine injuries, tracheal compression and ocular injury. Simultaneous anterograde and retrograde access is also not feasible in the prone position.
Two recent meta-analyses have shown supine PCNL to be as effective as prone PCNL when comparing stone-free rates, transfusion, complications and it was noted to be significantly quicker than the prone position [9,10]. Today, the debate is not merely whether prone or supine is the best position. There are various supine positions available and we would like to discuss the relative merits of each.
The first described supine position was that of Valdivia  with a 3-L saline bag below the flank. This original position does not allow for easy concurrent retrograde instrumentation and also provides limited space for choosing an access and hence has never been universally popularised. A modification of this was the Galdakao-modified Valdivia position  with again a saline bag below the flank with the legs in lithotomy, the affected side extended with the contralateral leg abducted. This allows access to the entire urinary tract without the need for repositioning and allows simultaneous retrograde access if required.
The Barts modified Valdivia position  offers a large surface area for access with easy manipulation of the nephroscope, as the trunk is placed at 90 ° to the operating table. However, renal access is not always a straightforward and easy endeavour. The position results in rotation of the kidney such that the calyces are viewed end on and also the spine lies in the field of the collecting system. Therefore puncture is difficult to achieve under fluoroscopy alone and often requires ultrasound localisation. Simultaneous retrograde intra-renal surgery (RIRS) is possible although ureteroscopy is performed from a position of relative unfamiliarity due to the rotated position.
With the modified Valdivia position there is not quite the radical rotation of the torso, as with the Barts technique, and therefore puncture under fluoroscopic control is much easier. In this position the kidney is hypermobile. There is therefore the risk that puncture and guidewire manipulation is more difficult. In obese patients especially this leads to longer tracts, which themselves lead to reduced nephroscope mobility. There is therefore a greater torque required to manipulate the scope, which can lead to damage to the renal parenchyma and risk increased bleeding form the tract. The tract is more lateral in the supine position thus there is less radiation exposure for the surgeon and also the surgeon is able to sit during the procedure. The more horizontal access also leads to lower intra-renal pressures and easier washout of fragments. However, there is an inability to distend the pelvi-calyceal system and it is more difficult to employ multiple punctures. Although there is not as much space as the Barts position for multiple punctures this is offset by the relative ease of puncture under fluoroscopy. Ureteroscopy again is performed in a much more familiar and conventional position.
Recently, we have started using a supine position that we have termed ‘the Barts flank-free modified supine position’, involving a 15 ° tilt by using a 3-L saline bag under the ipsilateral rib cage and a small gel pad under the ipsilateral pelvis, with the ipsilateral arm brought across the chest to the contralateral side (Fig. 1). The legs are placed in lithotomy, with the ipsilateral side relatively extended and the contralateral side abducted (Fig. 2). There is no support under the loin thus allowing more space for ideal renal access and the ability to use image-guided access with relative ease. Fluoroscopy is easier and conventional in this supine position, with the surgeon's hands being further from the operative and radiological field. Additionally, the kidney lies in a neutral position as compared with the semi-supine positions, e.g. the modified Valdivia and Barts positions, and therefore it is less likely to displace anteriorly. The kidney is therefore also less mobile and puncture and dilatation are consequently easier. This supine position also offers great flexibility in planning surgery, in that primary ureteroscopy may be embarked upon in this position quite readily and then if percutaneous access is required then no further adjustment is required. However, there is a smaller operative field with the tract being fairly horizontal, even more so than the modified Valdivia, and again this facilitates lower intra-renal pressures and washout of fragments. The more horizontal angle may on occasion make the scope more difficult to manoeuvre due to the low position of the tract with the operating table getting in the way.
Figure 1. ‘The Barts flank-free modified supine position’. Please note gel pad one under the ipsilateral pelvis and gel pad two under the rib cage leaving the flank free, allowing around 15 ° rotation of the patient. The ipsilateral arm is brought across the chest to the contralateral side. The ribs are marked. P.A.L, posterior axillary line; I.C, iliac crest.
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The complete supine position  allows limited space for planning renal access, as the flank is relatively poorly exposed and may result in reduced ability to manoeuvre the nephroscope, especially for anterior calyceal calculi. There is also no readily available retrograde access to the urinary tract and hence combined procedures are not possible.
The traditionally used prone position offers a wide operative field with ease of puncture under image and indeed ultrasound guidance, easy ability to make and dilate multiple tracts but has a significant disadvantage in that simultaneous RIRS in not practical if not impossible. The increased operative time and anaesthetic concerns are well recognised and described in this position. Table 1 shows a comparison of the ease of puncture under image guidance, ability to make and dilate multiple tracts and to carry our simultaneous RIRS between all the mentioned supine together with the prone positions.
Table 1. Comparison of the ease of puncture under image guidance, ability to make and dilate multiple tracts and to carry our simultaneous RIRS between the supine and the prone positions
|Prone||Complete supine||Valdivia||Galdakao modified Valdivia||Barts modified Valdivia||Barts flank-free modified supine|
|Ease of puncture under image guidance||A-P image, puncture routine||A-P image, puncture routine||30° torso rotation makes puncture more difficult||30° torso rotation makes puncture more difficult||Difficult and usually requires ultrasound-guided puncture||15° torso rotation but a 5–10° rotation of c-arm gives an A-P view and hence easy puncture|
|Ease of tract dilatation||Routine with shorter tracts compared with supine positions||Routine, but tract usually longer than with prone position||Kidney more mobile in this position and hence tract dilatation can be more difficult||Kidney more mobile in this position and hence tract dilatation can be more difficult||Kidney more mobile in this position and hence tract dilatation can be more difficult||Kidney less mobile than with the Valdivia and modified Valdivia positions but more mobile than with prone and complete supine|
|Multiple punctures||Large operative field, multiple punctures routine||Difficult due to lack of exposure of flank||More difficult than prone due to support under flank and hence limited exposure||More difficult than prone due to support under flank and hence limited exposure||Routine as flank well exposed||Good exposure as flank is free from support but still less exposure than with prone and Barts modified Valdivia position|
|Combined RIRS||Difficult even in split leg prone position||Difficult as legs not in lithotomy||Difficult as legs not in lithotomy||Routinely performed but trunk rotation makes position of ureteroscopy unfamiliar||Routinely performed but rotation makes position of ureteroscopy unfamiliar||Routinely done and relatively little trunk rotation makes ureteroscopy easier than with Galdakao and Barts modified Valdivia positions|
In summary, all of the supine positions decrease operative duration, as there is no need for re-positioning and allow quick access to the airway for the anaesthetist. However, they vary in the ease of puncture, tract dilatation, ability to make multiple tracts and ability to combine RIRS. There is a lack of high level evidence comparing the various positions used for supine PCNL or indeed any high quality randomised studies comparing the supine with the prone position and this will need to be addressed. Also, there does not appear to be any consensus as to which is the ideal supine position but the modified Valdivia and complete supine positions appear to have been the most widely published. What is important is to say that one supine position does not fit all and the right one must be chosen for the right patient with the right stone burden. It is important for endourologists of today to familiarise themselves with these positions to be able to make these judgements.