There are only 4 indications:

• Sepsis i.e. an infected obstructed system (signs of sepsis or infection)
• Renal impairment not improving with fluid resuscitation
• Pain not controlled with analgesia
• Single functioning kidney or Bilateral obstructing ureteric stones (Anuria)

There are 2 methods for renal decompression

• Retrograde ureteric stent insertion
• Antegrade Nephrostomy insertion

‘Optimal method of urgent decompression of the collecting system for obstruction and infection due to ureteral calculi’ - Maggie Pearle 1998 Journal of Urology

Study Design:

• Single centre randomized control trial

Study Population:

• 42 patient (21/21) with ureteric stones with WCC ≥ 17 and/ or temperature ≥38C
• WCC 17 was chosen as cut-off as patient with ureteric colic can have leucocytosis in the absence of infection

Study Outcomes

• Time to normalization of temperature and WCC

Results

• No significant difference between stent and nephrostomy groups
• Time to normal temperature and time to normal WCC was ~2 days in both

Later studies validated the findings of Pearle et al. (Meta-analysis by Moon et al. 2024)

Therefore the choice of modality for decompression depends on patient and disease factors such as

• Suitability for General Anesthetic
• Availability of Radiology/ Urology service on site
• Feasibility of procedure based on patient characteristics and nature of obstruction and patient preference (if appropriate)
• PCN is preferred in large obstructing stones, extrinsic compression from oncological masses in the abdomen or pelvis or if patient is not safe for a general anesthetic (although not routine but stents can be done in LA)
• Stent is preferred in coagulopathy or patients on blood thinners, if nephrostomy service is not available or if nephrostomy is not practically feasible due to location of kidneys or high BMI or patient is unable to comply with instruction
• Planned subsequent management
• PCN can be preferred who are likely to require PCNL for subsequent stone treatment
• Stent can be preferred in patients who are likely to require ESWL or URS for subsequent stone management
• Pregnancy
• There is increase risk of encrustation during pregnancy (due to hypercalciuria, hyperuricosuria and urinary stasis due to gravid uterus)
• Note that pregnancy has not shown to increase incidence/risk of urolithiasis itself as stone inhibition factors like urinary pH and urinary citrate excretion also increase.
• The exchanges should be done more frequently to avoid difficulties in exchanges due to excessive encrustation(recommended 4-6 weeks)
• PCN is preferred as it avoids a GA for insertion as well as for subsequent changes. Drainage from the PCN can be used as a surrogate marker for the status of the PCN and early exchange can be organized if any concerns are identified. Whereas in case of ureteric stent, the encrustation might remain silent until it becomes severe. However, there are a few small studies that report ureteric stenting to be a safe option in pregnancy as well. (Ngai et al. 2013, Choi et al. 2016)

Rate is more in stone patients less in non-stone patients

El-Faqih et al. 1991 reported their findings in polyurethane stents removed from patients at a single institution (n=~300).

Rate of encrustation as reported by El-Faqih: By 6 weeks: ~10% Between 6-12 weeks: ~50% After 12 weeks: ~75%

Interestingly, 30% stents were reported to have luminal blockage, whereas only 4% patients were reported to develop clinical obstruction. Reinforcing the idea that urine drain around the stent in addition to through it.

Kawahara et al. 2012 later reported similar number in their data from their institute (n=~300) with reported rate of encrustation as, By 6 weeks: ~25% Between 6-12 weeks: ~60% After 12 weeks: ~75%

They also reported that other than the temporal impact, stent calibre also effected the risk of encrustation, with stents >6Fr reported to have a lower risk of encrustations.

Conclusion: A fourth (25%) of patient will develop encrustations within 6 weeks, half (50%) of patients will develop encrustations by 12 weeks, and 3 quarters (75%) of patients will have encrustations after 12 weeks. Larger calibre stents can be used (>6Fr) in an attempt to minimise risk of encrustation in high risk patients. Similarly silicone stents are marketed as having less risk of encrustation with a longer indwelling time of upto a year (Tomer et al. 2021).

Recovery of Renal Function After Ureteral Deligation

Hinman refers to a work by Widen which reported permanent loss of renal function to be directly proportional to the duration of the obstruction in animal experiments on dogs.

Vaughan & Gillenwater described their experiments on dogs in 1970s.

They reported completely recovery after 7 days of obstruction and no recovery after 6 weeks of obstruction. They report 6 months post de-obstruction as the time to maximum recovery.

RENAL IMPAIRMENT AND ITS REVERSlBlLlTY FOLLOWING VARIABLE PERIODS OF COMPLETE URETERIC OBSTRUCTION

A more comprehensive experiment with dogs divided into 7 groups with 5 dogs each. Unilateral ureteric obstruction was produced surgically and corrected after varying durations in the different groups.

Reported on animal studies on rats. Their findings suggested some degree of permanent loss of functioning nephrons (~15%) even with de-obstruction after only 24hrs of unilateral obstruction. However this is compensated by the remaining functional nephrons and therefore GFR is remains comparable to the other healthy kidney.

Animals studies on Rats reported a decline of 50% renal function on DMSA 3 days after complete obstruction. Recovery of renal function was variably depending upon degree of obstruction and the duration of obstruction. Maximum recovery was observed in 7 days after which renal function on DMSA plateaued. In cases of mild partial obstruction, complete recovery was observed in as early as 3 days post release of obstruction.

3 case reports of human patients with ureteric obstruction for 28, 28 and 150 days, having good renal cortex, which showed recovery in renal function after relief of the obstruction.

Reviewed recovery of renal function in patients with HPCR. Their findings suggested recovery to be biphasic with an early recovery phase that happens in first 2 weeks (tubular phase) and a later recovery phase that can take upto 3 months (Glomerular phase)