A continuous erector spinae catheter added nothing to a single-injection block after PCNL

Design

randomised, triple-masked, placebo-controlled trial with dual primary outcomes

Population

50 adults undergoing outpatient percutaneous nephrolithotomy, all receiving a single-injection erector spinae plane block

Primary outcome

average daily pain intensity and cumulative opioid consumption over postoperative days 1-2

Effect

pain 3.5 against 3.0 (estimated difference 0.25, 95% CI -1.0 to 1.5, P=0.538); oxycodone 10 mg against 15 mg (difference 0, -15 to 5, P=0.358)

Fifty adults having outpatient percutaneous nephrolithotomy all received an ultrasound-guided perineural catheter at the eighth transverse process and the same 20 ml of 0.25% bupivacaine with adrenaline through it. They were then randomised, triple-masked, to automated intermittent boluses of 21 ml of 0.25% bupivacaine or of saline every four hours for about 57 hours through a portable pump. The dual primary outcomes were pain severity and opioid consumption over the first two postoperative days.

Neither separated. Average daily pain was a median 3.5 with the active infusion against 3.0 with placebo (estimated difference 0.25, 95% CI -1.0 to 1.5, P=0.538). Cumulative oxycodone was 10 mg against 15 mg (estimated difference 0, 95% CI -15 to 5, P=0.358). Maximum daily pain, second-night sleep disturbance and pain interference on the Brief Pain Inventory were all the same.

The design deserves credit: everyone got the single-injection block, so the trial asked the question that actually arises in practice - is the catheter worth adding - rather than comparing a catheter against nothing. Fifty patients is small and the confidence intervals are wide enough to leave a modest benefit possible. But a continuous catheter after outpatient surgery carries real costs: the pump, the follow-up, the risk of catheter-related problems at home, and a patient discharged with an infusion. Against a point estimate of zero, that is a poor trade.

• Do not add a continuous erector spinae catheter to a single-injection block for outpatient PCNL as routine
• Keep the single-injection block - it was given to every patient in this trial and was not the thing being tested
• Note that pain was moderate in both groups (median 3.0-3.5, maximum around 7) - there is a real unmet analgesic need here that the catheter did not meet
• Where a catheter is used for other indications, this trial says nothing about those
• Weigh the logistics of discharging a patient with an infusion pump against a benefit this trial could not detect

Why it matters

It tests the increment that matters - catheter on top of block - rather than block against nothing.

Don't overread it

Fifty patients with wide confidence intervals: this excludes a large benefit, not a small one.

The statistics, in plain English

An estimated pain difference of 0.25 points with an interval of -1.0 to 1.5 tells you the true effect is somewhere between slightly worse and mildly better - with 25 patients per arm, a clinically meaningful benefit of around 1 point has not been excluded. This is therefore a null result rather than proof of no effect. What makes it actionable anyway is the direction: the point estimate favoured placebo on pain and the opioid difference was exactly zero, so there is no signal to pursue.

Read the rest in the app

You have read your two free briefings this month. The app carries all 27 specialties, every morning, free — and this finding is waiting in it.

Get Daily Doctor — free

Scan to keep reading on your phone. No account needed to start.