Design: systematic review with Bayesian random-effects network meta-analysis and meta-regression, synthesising direct and indirect evidence from 17 comparative studies
Population: 3,657 patients with renal calculi ≤2 cm — 1,677 aspiration sheath, 56 direct in-scope suction, 1,924 conventional access sheath
Primary outcome: 30-day stone-free rate, with operative time, fever, sepsis and complications as secondary outcomes
Effect: aspiration sheath stone-free odds ratio 2.5 (95% CrI 2.0–3.1) and sepsis 0.40 (0.12–0.97); direct in-scope suction 3.1 (1.0–8.8); device-level estimates ranged from 5.4 (1.0–29.0) to 1.6 (0.41–6.3)

Suction during flexible ureteroscopy addresses two problems at once: fragments are removed rather than left to settle, and intrarenal pressure stays lower. A Bayesian network meta-analysis pooled 17 comparative studies covering 3,657 patients with renal calculi of 2 cm or less — 1,677 treated with flexible aspiration navigable sheaths (FANS), 56 with direct in-scope suction, and 1,924 with conventional access sheaths — with the 30-day stone-free rate as the primary outcome.

Aspiration sheaths performed substantially better: odds ratio 2.5 for stone-free status (95% credible interval 2.0 to 3.1). Direct in-scope suction pointed the same way but with far less precision (3.1, 1.0 to 8.8), reflecting only 56 patients. Aspiration sheaths also shortened operative time and reduced postoperative fever and complications, and lowered the odds of postoperative sepsis (0.40, 0.12 to 0.97). Device-level analysis showed the effect is not uniform — one system returned an odds ratio of 5.4 (1.0 to 29.0) and another 1.6 (0.41 to 6.3), which did not exclude no effect at all.

Two things follow. First, where an aspiration sheath is available, the default for a sub-2 cm renal stone should be to use it, and the sepsis signal is the reason rather than the stone-free rate — post-ureteroscopy sepsis is the complication that fills intensive care beds, and it is more frequent in Indian practice where infected stones are common. Second, the device-level variation means 'suction' is not one intervention. The evidence supports aspiration sheaths as a class and does not support treating every suction-capable system as equivalent, so a unit choosing equipment should ask which specific device has the data behind it.

Use an aspiration sheath as the default for renal stones of 2 cm or less where one is available.
Ask which specific device a comparative claim rests on; performance varied widely between systems.
Do not treat direct in-scope suction as equivalent — 56 patients is not an evidence base.
Keep infection prophylaxis and preoperative urine culture unchanged; a lower sepsis rate is not a reason to relax either.
Audit your own 30-day stone-free rate and sepsis rate rather than assuming the pooled figures transfer.

Why it matters

The gain that matters here is not the stone-free rate but the sepsis rate, in the complication that turns a day-case procedure into an intensive care admission.

The statistics, in plain English

An odds ratio of 2.5 with a credible interval of 2.0 to 3.1 is a strong and precise result for the sheath class, built on 1,677 treated patients. The sepsis interval (0.12 to 0.97) only just excludes 1.0, which means the direction is probably right but the size is uncertain — sepsis is rare, so few events drive the estimate. The device-specific figures should be read as cautionary rather than as rankings: an interval from 1.0 to 29.0 tells you almost nothing about that device except that it was studied in very few patients. These are pooled comparative studies, not randomised trials, so surgeon experience and case selection travel with the technology.