Lignocaine is a better analgesic than either ethyl chloride or nitrous oxide for peripheral intravenous cannulation

Peripheral intravenous (i.v.) cannulation is a painful, frequently performed ED procedure. It is common practice in other medical settings to offer analgesia prior to cannulation.

The present trial aims to reproduce in the ED studies that found a reduction in the pain of i.v. cannulation after intradermal lignocaine, ethyl chloride topical spray and entonox (50:50 oxygen : nitrous oxide). It also intends to determine which is analgesic most effective and explore the role of entonox for cannulation analgesia.

Three hundred subjects were randomized into four groups: i.v. cannula inserted with (i) no anaesthesia; (ii) entonox; (iii) ethyl chloride; and (iv) 0.1 mL intradermal 1% lignocaine. Pain was recorded on 100 mm visual analogue scales (VAS) after lignocaine injection or ethyl chloride spray and following i.v. cannulation. A clinically significant reduction in VAS pain score was determined to be 13 mm.

Patients cannulated without analgesia reported the most pain. Those cannulated after lignocaine had the least pain (median VAS 20 mm, 95% CI 15-25, vs 1 mm 95% CI 0-6, P < or = 0.001). Ethyl chloride (VAS 11 mm, 95% CI 7-15, P = 0.003) and entonox (VAS 13 mm, 95% CI 8-18, P = 0.047) reduced i.v. cannulation pain but did not reach clinical significance. Neither pain from presenting symptoms (P = 0.3), nor size of cannula (P = 0.8) affected pain scores. VAS scores were independent of sex and age (P = 0.1). Cannulation success was not affected by either the choice of analgesia or cannulation site.

The present trial confirms the findings of Harris and colleagues that lignocaine reduces the pain of cannulation in the ED. Lignocaine reduced the pain of i.v. cannulation more effectively than entonox or ethyl chloride.